Note: Descriptions are shown in the official language in which they were submitted.
CA 02762156 2011-12-09
SAFETY SYSTEMS FOR POWER EQUIPMENT
Divisional Application
This application is a divisional of application No. 2,660,280, filed March 26,
2009, which is a
divisional of application No. 2,389,596, filed September 29, 2000.
Technical Field
The present disclosure relates to safety systems and more particularly to high-
speed safety
systems for use on power equipment.
Background Art
Beginning with the industrial revolution and continuing to the present,
mechanized equipment
has allowed workers to produce goods with greater speed and less effort than
possible with manually-
powered tools. Unfortunately, the power and high operating speeds of
mechanized equipment creates a
risk for those operating such machinery. Each year thousands of people are
maimed or killed by accidents
involving power equipment.
As might be expected, many systems have been developed to minimize the risk of
injury when
using power equipment. Probably the most common safety feature is a guard that
physically blocks an
operator from making contact with dangerous components of machinery, such as
belts, shafts or blades.
In many cases, guards are effective to reduce the risk of injury, however,
there are many instances where
the nature of the operations to be performed precludes using a guard that
completely blocks access to
hazardous machine parts.
Various systems have been proposed to prevent accidental injury where guards
cannot effectively
be employed. For instance, U.S. Patent Nos. 941,726, 2,978,084, 3,011,610,
3,047,116, 4,195,722 and
4,321,841, all disclose safety systems for use with power presses. These
systems utilize cables attached
to the wrists of the operator that either pull back a user's hands from the
work zone upon operation or
prevent operation until the user's hands are outside the danger zone. U.S.
Patent Nos. 3,953,770,
4,075,961, 4,470,046, 4,532,501 and 5,212,621, disclose radio-frequency safety
systems which utilize
radio-frequency signals to detect the presence of a user's hand in a dangerous
area of the machine and
thereupon prevent or interrupt operation of the machine.
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U.S. Patent Nos. 4,959,909, 5,025,175, 5,122,091, 5,198,702, 5,201,684,
5,272,946, and
5,510,685 disclose safety systems for use with meat-skinning equipment. These
systems interrupt or
reverse power to the motor or disengage a clutch upon contact with a user's
hand by any dangerous
portion of the machine. Typically, contact between the user and the machine is
detected by monitoring
for electrical contact between a fine wire mesh in a glove worn by the user
and some metal component in
the dangerous area of the machine. Although such systems are suitable for use
with meat skinning
machines, they are relatively slow to stop the motion of the cutting element
because they rely on the
operation of solenoids or must overcome the inertia of the motor. However,
because these systems
operate at relatively low speeds, the blade does not need to be stopped
rapidly to prevent serious injury to
the user.
U.S. Patent Nos. 3,785,230 and 4,026,177, disclose a safety system for use on
circular saws to
stop the blade when a user's hand approaches the blade. The system uses the
blade as an antenna in an
electromagnetic proximity detector to detect the approach of a user's hand
prior to actual contact with the
blade. Upon detection of a user's hand, the system engages a brake using a
standard solenoid.
Unfortunately, such a system is prone to false triggers and is relatively slow
acting because of the
solenoid. U.S. Patent No. 4,117,752 discloses a similar braking system for use
with a band saw, where
the brake is triggered by actual contact between the user's hand and the
blade. However, the system
described for detecting blade contact does not appear to be functional to
accurately and reliably detect
contact. Furthermore, the system relies on standard electromagnetic brakes
operating off of line voltage
to stop the blade and pulleys of the band saw. It is believed that such brakes
would take 50ms-ls to stop
the blade. Therefore, the system is too slow to stop the blade quickly enough
to avoid serious injury.
None of these existing systems have operated with sufficient speed and/or
reliability to prevent
serious injury with many types of commonly used power tools. Although
proximity-type sensors can be
used with some equipment to increase the time available to stop the moving
pieces, in many cases the
user's hands must be brought into relatively close proximity to the cutting
element in the normal course
of operation. For example, many types of woodworking equipment require that
the user's hands pass
relatively close to the cutting tools. As a result, existing proximity-type
sensors, which are relatively
imprecise, have not proven effective with this type of equipment. Even where
proximity sensors are
practical, existing brake systems have not operated quickly enough to prevent
serious injury in many
cases.
In equipment where proximity-type detection systems have not proven effective,
the cutting tool
must stop very quickly in the event of user contact to avoid serious injury.
By way of example, a user
may feed a piece of wood through a table saw at a rate of approximately one
foot per second. Assuming
an average reaction time of approximately one-tenth of a second, the hand may
have moved well over an
inch before the user even detects the contact. This distance is more than
sufficient to result in the loss of
several digits, severing of vital vessels and tendons, or even complete
severing of a hand. If a brake is
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triggered immediately upon contact between the user's body and the saw's
blade, the blade must be
stopped within approximately one-hundredth of a second to limit the depth of
injury to about one-eighth
of an inch. Standard solenoids or other electromagnetic devices are generally
not designed to act in this
time scale, particularly where significant force must be generated. For
instance, in the case of solenoids
or electromagnetic brakes that operate on 60hz electrical power, it is
possible that the power line will be
at a phase that has low voltage at the time the. brake is triggered and
several milliseconds may elapse
before the voltage reaches a sufficient level even to begin physical
displacement of the brake, much less
achieve a complete stoppage of the blade or cutting tool.
Brief Disclosure
Safety systems for power equipment are disclosed. The safety systems include a
detection system
adapted to detect a dangerous condition between a person and a working portion
of a machine, such as
accidental contact with the working portion, and a reaction system associated
with the detection system
to cause a predetermined action to take place relative to the working portion
upon detection of the
dangerous condition by the detection system. The detection system may be
adapted to capacitively impart
an electric charge on the working portion and to detect when that charge
drops. The reaction system may
be a brake system to stop the working portion, a retraction system to retract
the working portion, a system
to cover the working portion, or some other system. The safety systems include
other features and
elements, as disclosed.
Machines equipped with safety systems are also disclosed, such as saws,
jointers, and other
woodworking machines. The machines include a working portion, such as a cutter
or blade, a detection
system adapted to detect a dangerous condition between a person and the
working portion, and a reaction
system associated with the detection system to cause a predetermined action to
take place upon detection
of the dangerous condition, such as a brake system to stop the working
portion, a retraction system to
retract the working portion, or a system to cover the working portion. The
machines may include a
control system adapted to control the operability of one or more of the
working portion, the detection
system and the reaction system. The machines include other features and
elements, as disclosed.
Brief Description of Drawings
Fig. 1 is a schematic block diagram of a machine with a fast-acting safety
system.
Fig. 2 is a schematic diagram of an exemplary safety system in the context of
a machine having a
circular blade.
Fig. 3 is a schematic circuit diagram of an electronic subsystem for the
safety system of Fig. 1,
including an excitation system, a contact sense system and a firing system.
Fig. 4 is a schematic circuit diagram of a first alternative electronic
subsystem for the safety
system of Fig. 1, including an excitation system, a contact sense system and a
firing system.
Fig. 5 is a block diagram illustrating the arrangement of a second alternative
electronic
subsystem.
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Fig. 6 is a schematic diagram of an excitation system of the subsystem of Fig.
5.
Fig. 7 shows an exemplary attenuation in signal that occurs when the forger of
a user contacts a
blade.
Fig. 8 is a schematic of a contact sense portion of the subsystem of Fig. 5.
Fig. 9 is a schematic of a power supply of the subsystem of Fig. 5.
Fig. 10 is a schematic of a boost regulator portion and a firing portion of
the subsystem of Fig. S.
Fig. 11 is a schematic of a motor control portion of the subsystem of Fig. S.
Fig. 12 is a schematic of a rotation sensor portion of the subsystem of Fig.
5.
Fig. 13 is a schematic of a user interface portion of the subsystem of Fig. 5.
Fig. 14 is a block diagram of second and third alternative electronic
subsystems.
Fig. 15 is a schematic of an excitation system portion of the subsystems of
Fig. 14.
Fig. 16 is a schematic of a contact sense portion of the second alternative
subsystem of Fig. 14.
Fig. 17 is a schematic of a contact sense portion of the third alternative
subsystem of Fig. 14.
Fig. 18 is a schematic of a power supply and firing system portion of the
subsystems of Fig. 14.
Fig. 19 is a schematic side elevation of an exemplary embodiment, showing the
electrical
isolation of the blade from the arbor and the mounting of the charge plates to
capacitively couple to the
blade. Indicated in dash lines are a bracket for mounting the charge plates,
spacers between the charge
plates and blade, and a brush contact mounted on the arbor block.
Fig. 20 is a magnified cross-sectional view take generally along the line 20-
20 in Fig. 19. For
clarity, the mounting bracket indicated in Fig. 19 is not shown.
Fig. 21 is a schematic cross-sectional view of another exemplary embodiment in
which the arbor
is electrically insulated from the arbor block and the charge plates are
capacitively coupled to the arbor.
Fig. 22 is a top plan view showing the isolation of, and capacitive coupling
to, an arbor on a
contractor style table saw.
Fig. 23 is a cross-sectional view of the embodiment of Fig. 22 taken generally
along the central
elongate axis of the arbor and viewing away from the arbor block.
Fig. 24 is a top plan view showing an alternative assembly for coupling the
charge plates to the
arbor of a contractor style table saw.
Fig. 25 is a cross-sectional view taken generally along the line 25-25 in Fig.
24.
Fig. 26 is a schematic side elevation of a further embodiment in the context
of a band saw.
Fig. 27 is a magnified cross-sectional view taken generally along the line 27-
27 in Fig. 26.
Fig. 28 is a side elevation of another embodiment in which contact with a
guard is detected in the
context of a radial arm saw.
Fig. 29 is a schematic side view of a table saw with a retraction system.
Fig. 30 is a schematic side view of a second side of a table saw with a
retraction system.
Fig. 31 is a schematic side view of a saw with another embodiment of a
retraction system.
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Fig. 32 is a section view of a retraction system using a deformable bushing.
Fig. 33 is a schematic side view of a miter saw with a retraction system.
Fig. 34 is a section view of the miter saw shown in Fig. 33.
Fig. 3 5 shows another embodiment of a miter saw with a retraction system.
Fig. 36 shows a schematic drawing of a retraction system using a spring to
retract a cutting tool.
Fig. 37 is a sectional view of the retraction system shown in Fig. 36.
Fig. 38 also is a sectional view of the retraction system shown in Fig. 36.
Fig. 39 is a schematic view of a band saw with a retraction system.
Fig. 40 is a top view of a roller used in the system shown in Fig. 39.
Fig. 41 is a schematic diagram of the safety system of Fig. 2 including
another spring-biased
brake mechanism.
Fig. 42 is a schematic diagram of the safety system of Fig. 2 including
another spring-biased
brake mechanism.
Fig. 43 is a schematic diagram of the safety system of Fig. 2 including
another spring-biased
brake mechanism.
Fig. 44 is a schematic diagram of the safety system of Fig. 2 including
another spring-biased
brake mechanism.
Fig. 45 is a schematic diagram of the safety system of Fig. 2 including
another spring-biased
brake mechanism.'
Fig. 46 is a fragmentary top plan view of another spring-biased brake
mechanism.
Fig. 47 is a fragmentary top plan view of another spring-biased brake
mechanism.
Fig. 48 is a fragmentary side elevation view of another spring-biased brake
mechanism.
Fig. 49 is a fragmentary side elevation view of another spring-biased brake
mechanism.
Fig. 50 is a fragmentary side elevation view of another spring-biased brake
mechanism.
Fig. 51 is a fragmentary side elevation view of another spring-biased brake
mechanism.
Fig. 52 is a cross-sectional side elevation view of another spring-biased
brake mechanism.
Fig. 53 is an end elevation view of the brake mechanism of Fig. 52.
Fig. 54 is a cross-sectional side elevation view of another spring-biased
brake mechanism.
Fig. 55 is a cross-sectional side elevation view of another spring-biased
brake mechanism.
Fig. 56 is a top plan view of another spring-biased brake mechanism.
Fig. 57 is a side elevation view of another spring-biased brake mechanism.
Fig. 58 is a bottom plan view of the brake mechanism of Fig. 57.
Fig. 59 is a side elevation view of another spring-biased brake mechanism.
Fig. 60 is a side elevation view of a brake mechanism, including a pawl,.
Fig. 61 is a side elevation view of a portion of another brake mechanism.
Fig. 62 is a side elevation view of another pawl.
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Fig. 63 is a side elevation view of another pawl.
Fig. 64 is an isometric view of another pawl.
Fig. 65 is a side elevation view of another pawl.
Fig. 66 is a side elevation view of another pawl.
Fig. 67 is a side elevation view of another pawl.
Fig. 68 is a side elevation view of another pawl.
Fig. 69 is a side elevation view of another pawl.
Fig. 70 is a side elevation view of another pawl.
Fig. 71 is a side elevation view of another pawl.
Fig. 72 is a side elevation view of another pawl.
Fig. 73 is a side elevation view of another pawl.
Fig. 74 is a side elevation view of another brake mechanism.
Fig. 75 is a side elevation view of another brake mechanism.
Fig. 76 is a side elevation view of another brake mechanism.
Fig. 77 is a side elevation view of another brake mechanism.
Fig. 78 is a top plan view of the brake mechanism of Fig. 77.
Fig. 79 is a side elevation view of a brake mechanism with a translational
pawl.
Fig. 80 is a side elevation view of another brake mechanism with a
translational pawl.
Fig. 81 is a side elevation view of another brake mechanism with a
translational pawl.
Fig. 82 is a side elevation view of another brake mechanism with a
translational pawl.
Fig. 83 is a side elevation view of a brake mechanism that includes plural
pawls.
Fig. 84 is a fragmentary side elevation view of another brake mechanism that
includes plural
pawls.
Fig. 85 is a top plan view of another brake mechanism.
Fig. 86 shows a possible configuration of a fusible member.
Fig. 87 shows various embodiments of fusible members.
Fig. 88 shows an embodiment of a firing subsystem used with a machine having a
fast acting
safety system.
Fig. 89 shows another embodiment of a firing subsystem.
Fig. 90 shows still another embodiment of a firing subsystem.
Fig. 91 shows a firing subsystem mounted on a printed circuit board.
Fig. 92 shows a sectional view of electrodes used in a firing subsystem.
Fig. 93 shows a firing subsystem in a cartridge used with a machine having a
fast-acting safety
system.
Fig. 94 shows two electrodes contacting a fusible member.
Fig. 95 shows a graph of data concerning the time to burn a wire under various
conditions.
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Fig. 96 also shows a graph of data concerning the time to burn a wire under
various conditions.
Fig. 97 also shows a graph of data concerning the time to burn a wire under
various conditions.
Fig. 98 shows a graph of data concerning the time to burn a wire under various
conditions.
Fig. 99 shows an explosive charge that can be triggered by a firing subsystem.
Fig. 100 is a fragmentary side elevation view of a safety system having a
replaceable brake
mechanism housed in a cartridge.
Fig. 101 is a side elevation view of the interior of another cartridge.
Fig. 102 is an isometric view of the cartridge of Fig. 101.
Fig. 103 is a side elevation view of the cartridge of Fig. 101 with the pawl
in its blade-engaging
position.
Fig. 104 is a side-elevation view of another cartridge.
Fig. 105 is an isometric view of the interior of another cartridge.
Fig. 106 is an isometric view of a variation of the cartridge of Fig. 105.
Fig. 107 is an isometric view showing the cartridge of Fig. 106 installed in a
machine.
Fig. 108 is a fragmentary side elevation view of another cartridge.
Fig. 109 is a fragmentary side elevation view of another cartridge.
Fig. 110 is a side elevation view of a brake positioning system.
Fig. 111 is a side elevation view of an adjustable brake positioning system.
Fig. 112 is cross-sectional view of a portion of the brake positioning system
of Fig. 111, taken
along line 112-112.
Fig. 113 is a cross-sectional view of a portion of the brake positioning
system of Fig. 111, taken
along line 113-113.
Fig. 114 is a circuit diagram of a blade-to-pawl spacing measurement system.
Fig. 115 is a side elevation view of an alternative brake positioning system.
Fig. 116 is an isometric view of an alternative brake positioning system.
Fig. 117 is a fragmentary side elevation view of an alternative brake
positioning system.
Fig. 118 is a flowchart diagram of an exemplary self-test logic sequence.
Figs. 119A-C are flowchart diagrams of an exemplary self-test and operational
sequence.
Fig. 120 is a schematic block diagram of a logic controller.
Fig. 121 is a schematic diagram of a user interface.
Fig. 122 is a schematic diagram of a firing capacitor charge and test circuit.
Fig. 123 is a schematic block diagram of a logic controller.
Fig. 124 is a schematic diagram of a firing capacitor charge and test circuit.
Fig. 125 is an isometric view of an exemplary pawl adapted for measuring pawl-
to-blade
spacing.
Fig. 126 is a schematic diagram of an exemplary circuit for detecting blade-to-
pawl spacing.
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Fig. 127 is a partial cross-section view of an exemplary magnetic sensor
assembly, where the
arbor is not in cross-sectional view.
Fig. 128 is a schematic diagram of an exemplary circuit for use with a
magnetic sensor assembly.
Fig. 129 is a schematic view of an exemplary EMF sensor assembly.
Fig. 130 is a partial cross-section view of an exemplary optical sensor
assembly, where the arbor
is not in cross-sectional view.
Fig. 131 is a side elevation of an alternative optical sensor assembly.
Fig. 132 is a cross-section view of the alternative optical sensor assembly of
Fig. 131, taken
generally along the line 132-132.
Fig. 133 is a schematic diagram of an exemplary circuit for use with an
optical sensor assembly.
Fig. 134 is a partial cross-section view of an exemplary electrical sensor
assembly, where the
arbor is not in cross-sectional view.
Fig. 135 is a schematic side elevation of an alternative electrical sensor
assembly.
Fig. 136 is a side elevation of a radial arm saw equipped with a safety
system.
Fig. 137 is a side elevation of a miter saw or chop saw equipped with a safety
system.
Fig. 138 is a side elevation of a pneumatic cut-off saw equipped with a safety
system.
Fig. 139 is a side elevation of a pneumatic cut-off saw equipped with an
alternative safety
system.
Fig. 140 is a side elevation of a pneumatic cut-off saw equipped with a second
alternative safety
system.
Fig. 141 is a breakaway side elevation view of a reaction system.
Fig. 142 is a schematic view of an alternative reaction system.
Fig. 143 is a cross-sectional view along lines 143-143 of Fig. 142 of a band
forming part of the
reaction system of Fig. 142.
Fig. 144 is a top elevation view of a hook on the end of the band of Fig 143.
Fig. 145 is a schematic view of an alternative reaction system for obstructing
a blade.
Fig. 146 is a schematic view of an alternative reaction system that breaks the
teeth of a blade.
Fig. 147 is a top view of an alternative reaction system that wraps a cutting
tool.
Fig. 148 shows a covering used in the reaction system of Fig. 147.
Fig. 149 shows a table saw.
Fig. 150 is a schematic side view of one side of a table saw with an improved
safety system.
Fig. 151 is a schematic side view of a second side of the table saw of Fig.
150.
Fig. 152 is a schematic bottom view of the table saw of Fig. 150.
Fig. 153 is a schematic perspective view of the table saw of Fig. 150.
Fig. 154 is a side elevation view of a miter saw with an improved safety
system.
Fig. 155 is a cross-sectional top plan view of the miter saw of Fig. 154.
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Fig. 156 is a side elevation view of another miter saw.
Fig. 157 is a side elevation view of another miter saw.
Fig. 158 is a side elevation view of another miter saw.
Fig. 159 is a side elevation view of another miter saw.
Fig. 160 is a fragmentary cross-sectional view of an electrically isolated
blade.
Fig. 161 is a side elevation of an exemplary implementation of a safety stop
in the context of a
table saw.
Fig. 162 is a side elevation of an exemplary implementation of a safety stop
in the context of a
circular saw.
Fig. 163 is a side elevation of an exemplary implementation of a safety system
in the context of a
band saw.
Fig. 164 is a close-up detail view of the safety system of Fig. 163.
Detailed Description and Best Mode(s) of the Disclosure
A machine embodying a safety system is shown schematically in Fig. 1 and
indicated generally
at 10. Machine 10 may be any of a variety of different machines adapted for
cutting workpieces, such as
wood, plastic, etc., including a table saw, miter saw, chop saw, radial arm
saw, circular saw, band saw,
jointer, planer, etc. Machine 10 includes an operative structure 12 having a
cutting tool 14 and a motor
assembly 16 adapted to drive the cutting tool. Machine 10 also includes a
safety system 18 configured to
minimize the potential of a serious injury to a person using machine 10.
Safety system 18 is adapted to
detect the occurrence of one or more dangerous conditions during use of
machine 10. If such a
dangerous condition is detected, safety system. 18 is adapted to engage
operative structure 12 to limit any
injury to the user caused by the dangerous condition.
Machine 10 also includes a suitable power source 20 to provide power to
operative structure 12
and safety system 18. Power source 20 may be an external power source such as
line current, or an
internal power source such as a battery. Alternatively, power source 20 may
include a combination of
both external and internal power sources. Furthermore, power source 20 may
include two or more
separate power sources, each adapted to power different portions of machine
10.
It will be appreciated that operative structure 12 may take any one of many
different forms,
depending on the type of machine 10. For example, operative structure 12 may
include a stationary
housing configured to support motor assembly 16 in driving engagement with
cutting tool 14.
Alternatively, operative structure 12 may include a movable structure
configured to carry cutting tool 14
between multiple operating positions. As a further alternative, operative
structure 12 may include one or
more transport mechanisms adapted to convey a workpiece toward and/or away
from cutting tool 14.
Motor assembly 16 includes one or more motors adapted to drive cutting tool
14. The motors
may be either directly or indirectly coupled to the cutting tool, and may also
be adapted to drive
workpiece transport mechanisms. Cutting tool 14 typically includes one or more
blades or other suitable
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cutting implements that are adapted to cut or remove portions from the
workpieces. The particular form
of cutting tool 14 will vary depending upon the various embodiments of machine
10. For example, in
table saws, miter saws, circular saws and radial arm saws, cutting tool 14
will typically include one or
more circular rotating blades having a plurality of teeth disposed along the
perimetrical edge of the blade.
For a jointer or planer, the cutting tool typically includes a plurality of
radially spaced-apart blades. For a
band saw, the cutting tool includes an elongate, circuitous tooth-edged band.
Safety system 18 includes a detection subsystem 22, a reaction subsystem 24
and a control
subsystem 26. Control subsystem 26 may be adapted to receive inputs from a
variety of sources including
detection subsystem 22, reaction subsystem 24, operative structure 12 and
motor assembly 16. The
control subsystem may also include one or more sensors adapted to monitor
selected parameters of
machine 10. In addition, control subsystem 26 typically includes one or more
instruments operable by a
user to control the machine. The control subsystem is configured to control
machine 10 in response to the
inputs it receives.
Detection subsystem 22 is configured to detect one or more dangerous, or
triggering, conditions
during use of machine 10. For example, the detection subsystem may be
configured to detect that a
portion of the user's body is dangerously close to, or in contact with, a
portion of cutting tool 14. As
another example, the detection subsystem may be configured to detect the rapid
movement of a
workpiece due to kickback by the cutting tool. In some embodiments, detection
subsystem 22 may
inform control subsystem 26 of the dangerous condition, which then activates
reaction subsystem 24. In
other embodiments, the detection subsystem may be adapted to activate the
reaction subsystem directly.
Once activated in response to a dangerous condition, reaction subsystem 24 is
configured to
engage operative structure 12 quickly to prevent serious injury to the user.
It will be appreciated that the
particular action to be taken by reaction subsystem 24 will vary depending on
the type of machine 10
and/or the dangerous condition that is detected. For example, reaction
subsystem 24 may be configured to
do one or more of the following: stop the movement of cutting tool 14,
disconnect motor assembly 16
from power source 20, place a barrier between the cutting tool and the user,
or retract the cutting tool
from its operating position, etc. The reaction subsystem may be configured to
take any one or
combination of various steps to protect the user from serious injury, as will
be described in more detail
below.
The configuration of reaction subsystem 24 typically will vary depending on
which action(s) are
taken. In the exemplary embodiment depicted in Fig. 1, reaction subsystem 24
is configured to stop the
movement of cutting tool 14 and includes a brake mechanism 28, a biasing
mechanism 30, a restraining
mechanism 32, and a release mechanism 34. Brake mechanism 28 is adapted to
engage operative
structure 12 under the urging of biasing mechanism 30. During normal operation
of machine 10,
restraining mechanism 32 holds the brake mechanism out of engagement with the
operative structure.
However, upon receipt of an activation signal by reaction subsystem 24, the
brake mechanism is released
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from the restraining mechanism by release mechanism 34, whereupon, the brake
mechanism quickly
engages at least a portion of the operative structure to bring the cutting
tool to a stop.
It will be appreciated by those of skill in the art that the exemplary
embodiment depicted in Fig.
1 and described above may be implemented in a variety of ways depending on the
type and configuration
of operative structure 12. Turning attention to Fig. 2, one example of the
many possible implementations
of safety system 18 is shown. System 18 is configured to engage an operative
structure having a cutting
tool in the form of a circular blade 40 mounted on a rotating shaft or arbor
42. Blade 40 includes a
plurality of cutting teeth (not shown) disposed around the outer edge of the
blade. As described in more
detail below, braking mechanism 28 is adapted to engage the teeth of blade 40
and stop the rotation of the
blade. Other systems for stopping the movement of the cutting tool are also
described below. Further,
safety system 18 will be described below in the context of various particular
types of machines 10.
In the exemplary implementation, detection subsystem 22 is adapted to detect
the dangerous
condition of the user coming into contact with blade 40. The detection
subsystem includes a sensor
assembly, such as contact detection plates 44 and 46, capacitively coupled to
blade 40 to detect any
contact between the user's body and the blade. Typically, the blade, or some
larger portion of cutting tool
14 is electrically isolated from the remainder of machine 10. Alternatively,
detection subsystem 22 may
include a different sensor assembly configured to detect contact in other
ways, such as optically,
resistively, etc. In any event, the detection subsystem is adapted to transmit
a signal to control subsystem
26 when contact between the user and the blade is detected. Various exemplary
embodiments and
implementations of detection subsystem 22 are described in more detail below.
Control subsystem includes one or more instruments 48 that are operable by a
user to control the
motion of blade 40. Instruments 48 may include start/stop switches, speed
controls, direction controls,
etc. Control subsystem 26 also includes a logic controller 50 connected to
receive the user's inputs via
instruments 48. Logic controller 50 is also connected to receive a contact
detection signal from detection
subsystem 22. Further, the logic controller may be configured to receive
inputs from other sources such
as blade motion sensors, workpiece sensors, etc. In any event, the logic
controller is configured to control
operative structure 12 in response to the user's inputs through instruments
48. However, upon receipt of a
contact detection signal from detection subsystem 22, the logic controller
overrides the control inputs
from the user and activates reaction subsystem 24 to stop the motion of the
blade. Various exemplary
embodiments and implementations of control subsystem 26 are described in more
detail below.
In the exemplary implementation, brake mechanism 28 includes a pawl 60 mounted
adjacent the
edge of blade 40 and selectively moveable to engage and grip the teeth of the
blade. Pawl 60 may be
constructed of any suitable material adapted to engage and stop the blade. As
one example, the pawl may
be constructed of a relatively high strength thermoplastic material such as
polycarbonate, ultrahigh
molecular weight polyethylene (UHMW) or Acrylonitrile Butadiene Styrene (ABS),
etc., or a metal such
as aluminum, etc. It will be appreciated that the construction of pawl 60 will
vary depending on the
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configuration of blade 40. In any event, the pawl is urged into the blade by a
biasing mechanism in the
form of a spring 66. In the illustrative embodiment shown in Fig. 2, pawl 60
is pivoted into the teeth of
blade 40. It should be understood that sliding or rotary movement of pawl 60
might also be used. The
spring is adapted to urge pawl 60 into the teeth of the blade with sufficient
force to grip the blade and
quickly bring it to a stop.
The pawl is held away from the edge of the blade by a restraining member in
the form of a
fusible member 70. The fusible member is constructed of a suitable material
adapted to restrain the pawl
against the bias of spring 66, and also adapted to melt under a determined
electrical current density.
Examples of suitable materials for fusible member 70 include NiChrome wire,
stainless steel wire, etc.
The fusible member is connected between the pawl and a contact mount 72.
Preferably member 70 holds
the pawl relatively close to the edge of the blade to reduce the distance pawl
60 must travel to engage
blade 40. Positioning the pawl relatively close to the edge of the blade
reduces the time required for the
pawl to engage and stop the blade. Typically, the pawl is held approximately
1/32-inch to '/4-inch from
the edge of the blade by fusible member 70, however other pawl-to-blade
spacings may also be used.
Pawl 60 is released from its unactuated, or cocked, position to engage blade
40 by a release
mechanism in the form of a firing subsystem 76. The firing subsystem is
coupled to contact mount 72,
and is configured to melt fusible member 70 by passing a surge of electrical
current through the fusible
member. Firing subsystem 76 is coupled to logic controller 50 and activated by
a signal from the logic
controller. When the logic controller receives a contact detection signal from
detection subsystem 22, the
logic controller sends an activation signal to firing subsystem 76, which
melts fusible member 70,
thereby releasing the pawl to stop the blade. Various exemplary embodiments
and implementations of
reaction subsystem 24 are described in more detail below.
It will be appreciated that activation of the brake mechanism will require the
replacement of one
or more portions of safety system 18. For example, pawl 60 and fusible member
70 typically must be
replaced before the safety system is ready to be used again. Thus, it may be
desirable to construct one or
more portions of safety system 18 in a cartridge that can be easily replaced.
For example, in the
exemplary implementation depicted in Fig. 2, safety system 18 includes a
replaceable cartridge 80 having
a housing 82. Pawl 60, spring 66, fusible member 70 and contact mount 72 are
all mounted within
housing 82. Alternatively, other portions of safety system 18 may be mounted
within the housing. In any
event, after the reaction system has been activated, the safety system can be
reset by replacing cartridge
80. The portions of safety system 18 not mounted within the cartridge may be
replaced separately or
reused as appropriate. Various exemplary embodiments and implementations of a
safety system using a
replaceable cartridge are described in more detail below.
While a particular implementation of safety system 18 has been described, it
will be appreciated
that many variations and modifications are possible. Several exemplary
embodiments of safety system 18
are described below to partially illustrate the many different configurations,
arrangements, applications,
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CA 02762156 2011-12-09
and combinations of the disclosed safety systems. For clarity, the following
description is arranged into
sections having generally descriptive headings. The sections are:
Section 1: Detection Signal Properties and Circuits
Section 2: Detection of Dangerous Conditions
Section 3: Retraction System
Section 4: Spring-Biased Brake System
Section 5: Brake Mechanism
Section 6: Firing Subsystem
Section 7: Replaceable Brake Cartridge
Section 8: Brake Positioning
Section 9: Logic Control
Section 10: Motion Detection
Section 11: Translation Stop
Section 12: Cutting Tool Disablement
Section 13: Table Saw
Section 14: Miter Saw
Section 15: Circular Saw
It will be understood that the sections and headings are intended merely to
provide organization
to the disclosure and should not be interpreted to limit the disclosure in any
way. For example, while
Section 7 describes various exemplary brake cartridges, Section 7 also
describes other components as
well. Further, several of the other sections will also describe exemplary
embodiments of cartridges.
Section 1: Detection Signal Properties and Circuits
As mentioned above, some embodiments of safety system 18 include a contact
detection
subsystem 22. The contact detection subsystem may take any one of a variety of
different forms. One
exemplary contact detection subsystem includes an electronic subsystem 100, as
shown in Fig. 3.
Electronic subsystem 100 is adapted to work with the two-plate capacitive
coupling system described in
Section 2 below. Electronic subsystem 100 includes an excitation system 101
and a monitoring or contact
sensing system 102. However, it will be appreciated by those of skill in the
electrical arts that the
exemplary configuration of electronic subsystem 100 illustrated in Fig. 3 is
just one of many
configurations which may be used. Thus, it will be understood that any
suitable embodiment or
configuration could be used.
As shown in Fig. 3, excitation system 101 includes an oscillator circuit that
generates a wave
input signal, such as a square wave signal, at a frequency of approximately
200khz and voltage amplitude
of 12 volts. Alternatively, excitation system 101 may be configured to
generate a signal of a different
frequency and/or a different amplitude and/or different waveform. The
oscillator is formed by a pair of
inverters 103, 104 from a CD4040 configured as a bistable oscillator. The
output of inverter 103 is
13
CA 02762156 2011-12-09
connected to a 100pF capacitor 105, which is connected through a 100k)
resistor 106 to the input of
inverter 104. A 10kg resistor 107 is connected between the output of inverter
104 to the junction
between capacitor 105 and resistor 106. The output of inverter 104 is
connected to the input of inverter
103. A 10k12 resistor 108 connects the output of inverter 103 to the input of
another inverter 109, which
serves as an output buffer to drive the input wave signal onto the blade. A
2kSZ series resistor 110
functions to reduce any ringing in the input signal by damping the high
frequency components of the
signal.
It will be appreciated that the particular form of the oscillator signal may
vary and there are. many
suitable waveforms and frequencies that may be utilized. The waveform may be
chosen to maximize the
signal-to-noise ratio, for example, by selecting a frequency at which the
human body has the lowest
resistance or highest capacitance relative to the workpiece being cut. As an
additional variation, the
signal can be made asymmetric to take advantage of potentially larger
distinctions between the electrical
properties human bodies and green wood at high frequency without substantially
increasing the radio-
frequency power radiated. For instance, utilizing a square wave with a 250khz
frequency, but a duty
cycle of five percent, results in a signal with ten times higher frequency
behavior than the base frequency,
without increasing the radio-frequency energy radiation. In addition, there
are many different oscillator
circuits that are well known in the art and which would also be suitable for
generating the excitation
signal.
The input signal generated by the oscillator is fed through a shielded cable
111 onto charge plate
44. Shielded cable 111 functions to insulate the input signal from any
electrical noise present in the
operating environment, insuring that a "clean" input signal is transmitted
onto charge plate 44. Also, the
shielded cable reduces cross talk between the drive signal and the detected
signal that might otherwise
occur should the cables run close together. Alternatively, other methods may
be used to prevent noise in
the input signal. As a further alternative, monitoring system 102 may include
a filter to remove any noise
in the input signal or other electrical noise detected by charge plate 46.
Shielded cable 111 also reduces
radio-frequency emissions relative to an unshielded cable.
As described in more detail below in Section 2, the input signal is coupled
from charge plate 44
to charge plate 46 via blade 40. As shown in Fig. 3, the signal received on
charge plate 46 is then fed via
a shielded cable 112 to monitoring system 102. The monitoring system is
configured to detect a change
in the signal due to contact between the user's body and the blade. It will be
appreciated that monitoring
system 102 may be implemented in any of a wide variety of designs and
configurations. In the exemplary
embodiment depicted in Fig. 3, monitoring system 102 compares the amplitude of
the input signal
received at charge plate 46 to a determined reference voltage. In the event
that the input signal received at
charge plate 46 falls below the reference voltage for a determined time, the
monitoring system produces
an output signal to reaction subsystem 24. The reaction subsystem is
configured to receive the output
signal and immediately act to stop the blade.
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The particular components of monitoring system 102 may vary depending on a
variety of factors
including the application, the desired sensitivity, availability of
components, type of electrical power
available, etc. In the exemplary embodiment, a shielded cable 112 is connected
between charge plate 46
and a voltage divider 113. Voltage divider 113 is formed by two 1M) resistors
114, 115 connected in
series between the supply voltage (typically about 12 volts) and ground. The
voltage divider functions to
bias the output signal from charge plate 46 to an average level of half of the
supply voltage. The biased
signal is fed to the positive input of an op-amp 116. Op-amp 116 may be any
one of many suitable op-
amps that are well known in the art. An example of such an op-amp is a TL082
op-amp. The negative
input of the op-amp is fed by a reference voltage source 117. In the exemplary
embodiment, the reference
voltage source is formed by a 10kS2 potentiometer 118 coupled in series
between two 10kf 2 resistors 119,
120, which are connected to ground and the supply voltage, respectively. A .47
F capacitor 121
stabilizes the output of the reference voltage.
As will be understood by those of skill in the art, op-amp 116 functions as a
comparator of the
input signal and the reference voltage. Typically, the voltage reference is
adjusted so that its value is
slightly less than the maximum input signal voltage from charge plate 46. As a
result, the output of the
op-amp is low when the signal voltage from the charge plate is less than the
reference voltage and high
when the signal voltage from the charge plate is greater than the reference
voltage. Where the input
signal is a periodic signal such as the square wave generated by excitation
system 101, the output of op-
amp 116 will be a similar periodic signal. However, when a user contacts the
blade, the maximum input
signal voltage decreases below the reference voltage and the op-amp output no
longer goes high.
The output of op-amp 116 is coupled to a charging circuit 122. Charging
circuit 122 includes a
240pF capacitor 123 that is connected between the output of op-amp 116 and
ground. A 100k) discharge
resistor 124 is connected in parallel to capacitor 123. When the output of op-
amp 116 is high, capacitor
123 is charged. Conversely, when the output of op-amp 116 is low, the charge
from capacitor 123
discharges through resistor 124 with a time constant of approximately 24 s.
Thus, the voltage on
capacitor 123 will discharge to less than half the supply voltage in
approximately 25-50 s unless the
capacitor is recharged by pulses from the op-amp. A diode 125 prevents the
capacitor from discharging
into op-amp 96. Diode 125 may be any one of many suitable diodes that are well
known in the art, such
as a 1N914 diode. It will be appreciated that the time required for capacitor
123 to discharge may be
adjusted by selecting a different value capacitor or a different value
resistor 124.
As described above, charging circuit 122 will be recharged repeatedly and the
voltage across
capacitor 123 will remain high so long as the detected signal is received
substantially unattenuated from
its reference voltage at op-amp 116. The voltage from capacitor 123 is applied
to the negative input of an
op-amp 126. Op-amp 126 may be any one of many suitable op-amps, which are well
known in the art,
such as a TL082 op-amp. The positive input of op-amp 126 is tied to a
reference voltage, which is
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CA 02762156 2011-12-09
approximately equal to one-half of the supply voltage. In the exemplary
embodiment depicted in Fig. 3,
the reference voltage is provided by reference voltage source 117.
So long as charging circuit 122 is recharged, the output of op-amp 126 will be
low. However, if
the output of op-amp 116 does not go high for a period of 25-50 s, the voltage
across capacitor 123 will
decay to less than the reference voltage, and op-amp 126 will output a high
signal indicating contact
between the user's body and the blade. As described in more detail in Sections
4-6 below, the output
signal from op-amp 126 is coupled to actuate reaction subsystem 24 and stop
the blade. The time
between contact and activation of the reaction system can be adjusted by
selecting the time constant of
capacitor 123 and resistor 124.
It should be noted that, depending on the size, configuration and number of
teeth on the blade
and the position of contact with the operator, the electrical contact between
the operator and blade will
often be intermittent. As a result, it is desirable that the system detect
contact in a period less than or
equal to the time a single tooth would be in contact with a user's fmger or
other body portion. For
example, assuming a 10-inch circular blade rotating at 4000 rpm and a contact
distance of about one-
quarter of an inch (the approximate width of a fingertip), a point on the
surface of the blade, such as the
point of a tooth, will be in contact with the user for approximately 100 s.
After this period of contact,
there will normally be an interval of no contact until the next tooth reaches
the finger. The length of the
contact and non-contact periods will depend on such factors as the number of
teeth on the blade and the
speed of rotation of the blade.
It is preferable, though not necessary, to detect the contact with the first
tooth because the
interval to the second tooth may be substantial with blades that have
relatively few teeth. Furthermore,
any delay in detection increases the depth of cut that the operator will
suffer. Thus, in the exemplary
embodiment, the charging circuit is configured to decay within approximately
25-50 s to ensure that
monitoring system 102 responds to even momentary contact between the user's
body and the blade.
Further, the oscillator is configured to create a 200khz signal with pulses
approximately every 5 s. As a
result, several pulses of the input signal occur during each period of
contact, thereby increasing the
reliability of contact detection. Alternatively, the oscillator and charging
circuit may be configured to
cause the detection system to respond more quickly or more slowly. Generally,
it is desirable to
maximize the reliability of the contact detection, while minimizing the
likelihood of erroneous detections.
As described above, the contact between a user's body and the teeth of blade
64 might be
intermittent depending on the size and arrangement of the teeth. Although
monitoring system 102
typically is configured to detect contact periods as short as 25-50 s, once
the first tooth of the blade
passes by the user's body, the contact signal received by the second
electrical circuit may return to
normal until the next tooth contacts the user's body. Thus, while the output
signal at op-amp 126 will go
high as a result of the first contact, the output signal may return low once
the first contact ends. As a
result, the output signal may not remain high long enough to activate the
reaction system. For instance, if
16
CA 02762156 2011-12-09
the output signal does not remain high long enough to actuate firing subsystem
76, fusible member 70,
may not melt. Therefore, monitoring system 102 may include a pulse extender in
the form of charging
circuit 127 on the output of op-amp 126, similar to charging circuit 122. Once
op-amp 126 produces a
high output signal, charging circuit 127 functions to ensure that the output
signal remains high long
enough to sufficiently discharge the charge storage devices to melt the
fusible member. In the exemplary
embodiment, charging circuit 127 includes a 0.47 F capacitor 128 connected
between the output of op-
amp 126 and ground. When the output of op-amp 126 goes high, capacitor 128
charges to the output
signal level. If the output of op-amp 126 returns low, the voltage across
capacitor 128 discharges through
l0k resistor 129 with a time constant of approximately 4.7 ms. A diode 130,
such as an 1N914 diode,
prevents capacitor 128 from discharging through op-amp 126. The pulse extender
insures that even a
short contact with a single tooth will result in activation of the reaction
system.
The above-described system is capable of detecting contact within
approximately 50 s and
activating the reaction system. As described in more detail in Sections 4-6
below, in the context of
reaction system for braking a saw blade, a brake can be released in
approximately less than 100 s and as
little as 20 s. The brake contacts the blade in approximately one to
approximately three milliseconds.
The blade will normally come to rest within not more than 2-l0ms of brake
engagement. As a result,
injury to the operator is minimized in the event of accidental contact with
the cutting tool. With
appropriate selection of components, it may be possible to stop the blade
within 2 ms, or less.
While exemplary embodiments of excitation system 101 and monitoring system 102
have been
described above with specific components having specific values and arranged
in a specific
configuration, it will be appreciated that these systems may be constructed
with many different
configurations, components, and values as necessary or desired for a
particular application. The above
configurations, components, and values are presented only to describe one
particular embodiment that
has proven effective, and should be viewed as illustrating, rather than
limiting, the invention.
Fig. 4 shows alternative embodiments of excitation system 101 and monitoring
system 102, as
well as firing system 76, which is described in Section 6 below. Alternative
excitation system 101 is
configured to generate a square wave signal using only a single comparator 133
such as an LM393
comparator. A 1M resistor 134 is connected between the high input terminal of
comparator 133 and
ground. Another 1M resistor 135 is connected between the high input terminal
of comparator 133 and a
low voltage supply V. A 1M resistor 136 is connected between the high input
terminal of the comparator
and the output of the comparator. A 100 pF capacitor 137 is connected between
the low input terminal of
the comparator and ground. A 27k resistor 138 is connected between the low
input terminal of the
comparator and the output of the comparator. A 3.3k resistor 139 is connected
between the low voltage
supply V and the output of the comparator. The alternative oscillator circuit
illustrated in Fig. 6 produces
a square wave having a frequency of approximately 3-500 khz. A lk resistor 140
is connected between
the output of the comparator and shielded cable 111 to reduce ringing. It will
be appreciated that the
17
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CA 02762156 2011-12-09
values of one or more elements of alternative excitation system 101 may be
varied to produce a signal
having a different frequency, waveform, etc.
As in the exemplary embodiment described above, the signal generated by
alternative excitation
system 101 is fed through shielded cable 111 to charge plate 44. The signal is
capacitively coupled to
charge plate 46 via blade 40. Alternative monitoring system 102 receives the
signal from charge plate 46
via shielded cable 112 and compares the signal to a reference voltage. If the
signal falls below the
reference voltage for approximately 25 s, an output signal is generated
indicating contact between the
blade and the user's body.
Alternative monitoring system 102 includes a voltage divider 113, which is
formed of 22k
resistors 141 and 142. The voltage divider biases the signal received via
cable 112 to half the low voltage
supply V. The lower resistance of resistors 141, 142 relative to resistors
114, 115 serves to reduce 60hz
noise because low-frequency signals are attenuated. The biased signal is fed
to the negative input
terminal of a second comparator 143, such as an LM393 comparator. The positive
terminal of comparator
143 is connected to reference voltage source 144. In the depicted embodiment,
the reference voltage
source is formed by a lOkQ potentiometer 145 coupled in series between two
100k) resistors 146, 147
connected to the low voltage supply V and ground, respectively. A 0.1 F
capacitor 148 stabilizes the
output of the reference voltage. As before, the reference voltage is used to
adjust the trigger point.
The output of second comparator 143 is connected to the base terminal of an
NPN bipolar
junction transistor 149, such as a 2N3904 transistor. The base terminal of
transistor 149 is also connected
to low voltage supply V through a 100k resistor 150, and to ground through a
220pF capacitor 151.
Potentiometer 145 is adjusted so that the voltage at the positive terminal of
comparator 143 is slightly
lower than the high peak of the signal received at the negative terminal of
the second comparator when
there is no contact between the blade and the user's body. Thus, each high
cycle of the signal causes the
second comparator output to go low, discharging capacitor 151. So long as
there is no contact between
the blade and the user's body, the output of the second comparator continues
to go low, preventing
capacitor 151 from charging up through resistor 150 and switching transistor
149 on. However, when the
user's body contacts the blade or other isolated element, the signal received
at the negative terminal of
the second comparator remains below the reference voltage at the positive
terminal and the output of the
second comparator remains high. As a result, capacitor 151 is able to charge
up through resistor 150 and
switch transistor 149 on.
The collector terminal of transistor 149 is connected to low voltage supply V,
while the emitter
terminal is connected to 6800 resistor 152. When transistor 149 is switched
on, it supplies an output
signal through resistor 152 of approximately 40 mA, which is fed to
alternative firing system 76. As
described in more detail below in Section 6, the alternative firing circuit
includes fusible member 70
connected between a high voltage supply HV and an SCR 613, such as an NTE 5552
SCR. The gate
terminal of the SCR is connected to resistor 152. Thus, when transistor 149 is
switched on, the
18
CA 02762156 2011-12-09
approximately 40 mA current through resistor 152 turns on SCR 613, allowing
the high voltage supply
HV to discharge to ground through fusible member 70. Once the SCR is switched
on, it will continue to
conduct as long as the current through fusible member 70 remains above the
holding current of
approximately 40mA, even if the current to the gate terminal is removed. Thus,
the SCR will conduct
current through the fusible member until the fusible member is melted or the
high voltage source is
exhausted or removed. The fact that the SCR stays on once triggered allows it
to respond to even a short
pulse through resistor 152.
Fig. 4 also illustrates an exemplary electrical supply system 154 configured
to provide both low
voltage supply V and high voltage supply ITV from standard 120VAC line
voltage. Electrical supply
system 154 is connected to provide low voltage supply V and high voltage
supply RV to alternative
excitation system 101, alternative monitoring system 102, and alternative
firing system 76. The line
voltage is connected through a 10052 resistor 155 and a diode 156, such as a
1N4002 diode, to a 1000 F
charge storage capacitor 157. The diode passes only the positive portion of
the line voltage, thereby
charging capacitor 157 to approximately 160V relative to ground. The positive
terminal of capacitor 157
serves as the high voltage supply HV connected to fusible link 70. When SCR
613 is switched on upon
detection of contact between the blade and the user's body, the charge stored
in capacitor 157 is
discharged through the fusible link until it melts. It will be appreciated
that the size of capacitor 157 may
be varied as required to supply the necessary current to melt fusible member
70. As described in Section
6, use of a HV capacitor leads to a much higher current surge, and therefore a
faster melting of the fusible
member than is the case with a low voltage system.
The positive terminal of capacitor 157 also provides a transformer-less source
of voltage for low
voltage supply V, which includes a 12k resistor 158 connected between the
positive terminal of capacitor
157 and a reverse 40V Zener diode 159. Diode 159 functions to maintain a
relatively constant 40V
potential at the junction between the diode and resistor 158. It can be seen
that the current through the
12k resistor will be about 10mA. Most of this current is used by the low
voltage circuit, which has a
relatively constant current demand of about 8mA. Note that while resistor 158
and diode 159 discharge
some current from capacitor 157, the line voltage supply continuously
recharges the capacitor to maintain
the HV supply. A 0.1 F capacitor 160 is connected in parallel with diode 159
to buffer the 40V potential
of the diode, which is then connected to the input terminal of an adjustable
voltage regulator 161, such as
an LM317 voltage regulator. The ratio of a lk resistor 144 connected between
the output terminal and
adjustment terminal, and a 22k resistor 163 connected between the adjustment
terminal and ground, set
the output voltage of regulator 161 to approximately 30VDC. A 50 F capacitor
164 is connected to the
output terminal of regulator 161 to buffer sufficient charge to ensure that
low voltage supply V can
provide the brief 40mA pulse necessary to switch on SCR 613. The described low
voltage source is
advantageous because of its low cost and low complexity.
19
CA 02762156 2011-12-09
It should be noted that when high voltage supply HV is discharged through
fusible member 70,
the input voltage to voltage regulator 161 may temporarily drop below 30V,
thereby causing a
corresponding drop in the low voltage supply V. However, since the reaction
system has already been
triggered, it is no longer necessary for the detection system to continue to
function as described and any
drop in low voltage supply V will not impair the functioning of safety system
18.
It will be appreciated by those of skill in the electrical arts that the
alternative embodiments of
excitation system 101, monitoring system 102, firing system 76, and electrical
supply system 154 may be
implemented on a single substrate and/or in a single package. Additionally,
the particular values for the
various electrical circuit elements described above may be varied depending on
the application.
One limitation of the monitoring systems of Figs. 3 and 4 is that they actuate
the reaction system
whenever the incoming amplitude from charge plate 46 drops below a preset
threshold. Under most
circumstances this represents a reliable triggering mechanism. However, when
cutting green wood, a
substantial additional capacitive and resistive load is coupled to the blade.
The moisture in green wood
gives it a very high dielectric constant, and an increased conductivity
relative to dry wood. In fact, when
cutting very green wood, i.e. over 50% moisture content, the amplitude of the
signal on charge plate 46
can drop to a level equivalent to what is seen when a user contacts the blade.
Thus, the systems of Figs. 3
and 4 are limited in their ability to offer protection while processing green
wood.
Another embodiment of an electronic subsystem 100 adapted to accommodate green
wood and
offering certain other benefits is shown in Figs. 5-13. As shown in Fig. 5,
system 100 includes an
excitation system 101 in the form of a class-C amplifier connected to a micro-
controller 171. System 100
also includes a monitoring system 102 in the form of a contact sense circuit
connected to controller 171.
A power supply 173 supplies power to the various elements of system 100. A
motor controller 174 is
adapted to turn a motor off and on based on signals from the controller. A
boost regulator 175 operates to
charge a firing system 176. A rotation sense circuit 177 detects rotation of
the cutting tool. Lastly, a user
interface 178 is provided to allow a user to control operation of the saw and
provide feedback on the
status of the system.
Fig. 6 illustrates the circuitry of the class-C amplifier in more detail. The
amplifier includes a
drive output that is coupled to plate 44 as shown in Fig. 5. The drive output
is sinusoidal at about 500khz
and the amplitude is adjustable between about 3 volts and 25 volts. A 32-volt
input supply line from the
power supply provides power for the amplifier. The base frequency is provided
by a 500khz square wave
input from the controller. The amplitude is controlled by pulse width
modulation from the controller.
The controller is programmed to adjust the drive voltage output from the
amplifier to maintain a
predetermined amplitude at plate 46 under varying capacitive loads. Thus, when
cutting green wood, the
controller ramps up the drive voltage to maintain the desired voltage on plate
46. The controller is
preferably capable of skewing the drive voltage between about 1 and 50% per
millisecond, and more
preferably between 1 and 10%. This allows the system to maintain a constant
output level under the
CA 02762156 2011-12-09
varying load created while sawing green wood, or such as might be created by
placing a conductive
member such a fence near the blade. The controller should preferably not skew
the drive voltage by much
more than 50% per millisecond, or it may counteract the drop in signal created
by a user contact event.
Fig. 7 illustrates the change in signal amplitude seen at plate 46 as the
teeth of a 10-inch, 36-
tooth saw blade spinning at 4000 rpm contacts a user's finger. Each of the
drops in the signal amplitude
is from a single tooth moving through the skin of the finger. It can be seen,
for instance, that the signal
amplitude drops by about 30% over about 50 S as the second tooth strikes the
finger. When cutting very
green wood, the signal attenuation upon contact will be more like 15%, but
will occur over the same
50 S. Therefore, as long as the system can detect a contact event of a 5-25%
or greater drop in less than
100 S, providing a skew rate of around 10% per millisecond should not override
an actual event. It will
be understood that the skew rate and trigger thresholds can be adjusted as
desired. The primary limiting
factor is that the trigger threshold should not be so small that noise creates
false triggers, unless false
triggers are acceptable.
Fig. 8 shows the details of the contact sense circuit. The contact sense
circuit receives input from
plate 46. In this embodiment, the preferred capacitive coupling between the
blade and the plates is about
30pF for the drive plate and about lOpF for plate 46. The larger drive plate
size improved signal transfer
for a given total capacitance of both plates. The actual values are not
critical, and equal values could be
used as well. Generally speaking, the capacitance of the drive plate should be
comparable to the human
body capacitance to be detected, i.e. 10-200pF.
The input from plate 46 is fed through a high-pass filter 179 to attenuate any
low frequency
noise, such as 60hz noise, picked up by plate 46. Filter 179 can also provide
amplification of the signal to
a desired level as necessary. The output of the filter is fed into a set of
comparators 180, 181. Comparator
180 pulses high briefly if the maximum signal amplitude from the filter
exceeds the value at its positive
input set by voltage divider 182. The output pulses from the comparator are
fed to the controller. The
controller samples over a 200 S window and modulates the drive amplitude to
attempt to maintain the
sensed voltage at a level so that 50% of the waveform cycles generate a pulse
through comparator 180. If
less than 50% generate pulses, then the controller raises the drive voltage by
a set amount. Likewise, if
more than 50% generate pulses, the drive voltage is lowered. The system can be
configured to step by
larger or smaller amounts depending on the deviation from 50% observed during
a particular window.
For instance, if 45 pulses are observed, the system may step up the drive
amplitude by 1%. However, if
only 35 pulses are observed, the system may step by 5%. The system will
continually "hunt" to maintain
the proper drive level. By selecting the window duration and adjustment
amount, it is possible to control
the skew rate to the desired level as described above.
Comparator 181 pulses every cycle of the waveform so long as the sensed
voltage exceeds a
lower trigger threshold set by voltage divider 182. Therefore, under normal
circumstances, this is a
500khz pulse. The pulse output from comparator 181 is fed through a divide-by-
four circuit formed by
21
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two D-flip flops to reduce the frequency to 125khz - or an 8 S period. The
output of the divider is fed to
the controller. The controller monitors this line to insure that a pulse
occurs at least every 18 S.
Therefore, if more than about half of the pulse are missing in over an 18 S
period, the controller will
trigger the reaction system. Of course, the particular period can be selected
as desired to maximize
reliability of contact detection and minimize false triggers. A benefit of the
described arrangement is that
a single pulse or even two may be missing, such as due to noise, without
triggering the system. However,
if more pulses are missing, the system will still be triggered reliably. The
particular trigger level for
missing pulses is set by the voltage divider. This level will typically be
between 5 and 40% for the
described system.
Fig. 9 illustrates the circuit of power supply 173. The power supply includes
an unregulated 32-
volt output and regulated 5, 15 and 24-volt outputs. The 24-volt output is
used to power the excitation
signal, which has a relatively large voltage, and the 32-volt output powers a
capacitor charging circuit
described below. The 5-volt output powers the controller and other logic
circuitry, while the 15-volt
output operates most of the analog electronics. A low-voltage output is
monitored by the controller to
insure that adequate voltage is present to operate the system.
Boost regulator 175 and firing system 176 are shown in Fig. 10. Boost
regulator 175 includes a
buck-boost charger 183 that steps up the 32-volt supply input to 180 volts for
charging the firing circuit.
The controller provides a 125khz input to modulate the buck-boost cycle of the
charger. A regulator
circuit 184 monitors the voltage from the firing circuit and turns the charger
on or off as necessary to
maintain the charge near 180 volts. The regulator circuit is constructed with
a predetermined amount of
hysteresis so that the charger will turn on when the firing circuit voltage
falls below 177 volts and turn
off when the voltage reaches 180 volts, as set by the voltage divider inputs
and feedback to comparator
185. The output of comparator 185 is fed to the controller. By monitoring the
charge and discharge time
based on the state of the output of comparator 185, the controller can verify
that the capacitor in the firing
circuit is operating properly and storing adequate charge. An overvoltage
circuit uses a 220V transient
suppressor to signal the controller if the voltage on the capacitor exceeds
about 220V. This testing is
described in more detail in Section 9 below. Additionally, the firing circuit
is described in more detail in
Section 6 below.
Fig. 11 illustrates the circuitry of motor control 174. The motor control
receives a logic level
control signal from the controller to turn the motor on and off based on input
from the user interface,
described in more detail below. The motor control also turns off the motor
when a trigger event occurs.
The logic signal is electrically isolated from the motor voltage by an
optoisolated triac driver. This
isolates the ground of the detection system from the ground of the motor
power. A mechanical relay or
similar device can also be used and will provide the same isolation. When the
optoisolated triac drive
receives a signal from the controller, it turns on Q6040K7 triac to provide
power to the machine.
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The rotation sense circuit is shown in Fig. 12. The purpose of the rotation
sense circuit is to
insure that the contact detection system is not turned off until the cutter or
blade as stopped. The rotation
sense circuit utilizes a hall-effect sensor that is located adjacent a
rotating portion of the machine. A
small magnet is inserted in the rotating portion to signal the hall-effect
sensor. Output of the hall-effect
sensor is fed to the controller. As described in more detail Sections 9 and 10
below, the controller
monitors the output of the hall-effect sensor to determine when the cutter has
coasted to a stop. Once the
cutter stops, any sensed contact will no longer trigger the reaction system.
It should be noted that rotation
of the cutter could be detected by other arrangements as well.
For instance, a small eccentricity can be placed on the cutter or some other
isolated structure that
rotates with the cutter, such as the arbor. This eccentricity can be placed to
pass by sense plate 46 or by a
separate sensing plate. The eccentricity will modulate the detected signal
amplitude so long as the cutter
is rotating. This modulation can be monitored to detect rotation. If the
eccentricity is sensed by sense
plate 46, it should be small enough that the signal modulation generated will
not register as a contact
event. As another alternative, rotation can be sensed by electromagnetic
feedback from the motor. These
and other examples are described in Section 10 below.
Controller may also be designed to monitor line voltage to insure that
adequate voltage is present
to operate the system. For instance, during motor start up, the AC voltage
available to the safety system
may drop nearly in half depending on the cabling to the saw. If the voltage
drops below a safe level, the
controller can shut off the saw motor. Alternatively, the controller may
include a capacitor of sufficient
capacity to operate the system for several seconds without power input while
the saw is starting.
User interface 178 is shown in Fig. 13. The user interface includes start,
stop and bypass buttons
that are used to control the operation of the saw. The bypass button allows
the user to disable the contact
detection system for a single on/off cycle of the saw so as to be able to saw
metal or other materials that
would otherwise trigger the reaction system. The user interface also includes
red and green LED's that
are . used to report the status of the system to a user. More details on the
operation of suitable user
interfaces are described in Section 9 below.
Two additional electronic configurations for detection subsystem 22 are shown
in Figs. 14-18. As
- illustrated in Fig. 15, the alternative detection systems utilize a micro-
controller 171 to manage and
monitor various functions. An excitation system delivers a 350khz sine wave
drive signal through plate
44 to the blade. The circuit for generating the drive signal is illustrated in
Fig. 15. The excitation circuit
uses a 700khz oscillator with an output fed into a double to generate a 1.4Mhz
signal. The output of the
double is fed into a set of S-R flip-flops to extract phase signals at 90-
degree intervals. The phase signals
are used to drive a synchronous detection system that forms on of the two
embodiments of Figs. 14-18
and is shown in more detail in Fig. 17. The 350khz square wave 180-degree
phase signal is fed through
an inverter and a buffer amplifier into a Q=10, 350khz band pass filter.
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The output of the band pass filter is a 350khz sine wave that is fed through
another buffer
amplifier to a sense amplifier 190 shown in Fig. 16. The output of the sense
amplifier is fed to plate 44
and the input from plate 46 is fed back to the negative input. When a user
touches cutter 40, the feedback
on the sense amplifier is reduced, thereby causing the output amplitude to go
up. The result of this
arrangement is that the drive amplitude on the blade is small during normal
use and rises only when a
user touches the blade or green wood is cut. In this embodiment, the preferred
capacitive coupling of the
plates to the blade is about 90pF each, although other values could be used.
The output of the sense amplifier is fed through a buffer and into a 350khz
band pass filter to
filter out any noise that may have been picked up from the blade or plates.
The output of the band pass
filter is fed through a buffer and into a level detector. The level detector
generates a DC output
proportional to the amplitude of the sense amplifier. The output of the level
detector is smoothed by an
RC circuit to reduce ripple and fed into a differentiator. The differentiator
generates an output
proportional to the rate of change of the sense amplifier output amplitude.
As mentioned above, the sense amplifier output only changes when a user
touches the blade or
green wood is cut. The change when cutting green wood is slow relative to what
happens when a user
touches the blade. Therefore, the differentiator is tuned to respond to a user
contact, while generating
minimal response to green wood. The output of the differentiator is then fed
to a comparator that acts as
threshold detector to determine if the output of the differentiator has
reached a predetermined level set by
the a voltage divider network. The output of the threshold detector is fed
through a Schmitt-trigger that
signals the controller that a contact event has occurred. An RC network acts
as a pulse stretcher to insure
that the signal lasts long enough to be detected by the controller.
The output from the level detector is also fed to and analog to digital input
on the controller. It
may be that the under some circumstances, such as while cutting extremely
green wood, the response of
the sense amplifier will be near saturation. If this happens, the amplifier
may no longer be capable of
responding to a contact event. In order to provide a warning of this
situation, the controller monitors this
line to make sure that the detected level is stays low enough to allow a
subsequent contact to be detected.
If an excess impedance load is detected, the controller can shut down the saw
without triggering the
reaction system to provide the user with a warning. If the user wants to
continue, they can initiate the
bypass mode as described above.
The second of the two alternative detection systems of Figs. 14-18 is a
synchronous detector that
uses the phase information generated by the flip-flops in Fig. 15. This system
drives plate 44 through the
ALT DRIVE circuit shown in Fig. 15. This ALT DRIVE circuit and the detection
circuit of Fig. 17 are
substituted for the circuit of Fig 16. As shown in Fig. 17, the signal from
plate 46 is fed through a pair of
buffer/amplifiers into a set of analog switches. The switches are controlled
by the phase information from
the flip-flops. This arrangement generates an output signal that is
proportional to the amplitude of the
signal detected from plate 46 with improved noise immunity because of the
synchronous detection. The
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CA 02762156 2011-12-09
output signal is fed into a differentiator and threshold detector circuit as
previously described. These
circuits send a trigger signal to the controller when the detected signal
amplitude drops at a rate sufficient
for the differentiator to have an output exceeding the threshold level.
Fig. 18 illustrates a power supply and firing system suited for use in these
two alternative
arrangements. The power supply generates plus and minus 15-volt levels, as
well as a 5-volts level. The
capacitor in the firing circuit is charged by a secondary input winding on the
power transformer. This
arrangement provides for isolation of the system ground from the machine
ground and avoids the need to
step up power supply voltage to the capacitor voltage as accomplished by boost
regulator 175. However,
the capacitor charge voltage becomes dependent on the line voltage, which is
somewhat less predictable.
The charging circuit for the capacitor is regulated by an enable line from the
controller. By
deactivating the charging circuit, the controller can monitor the capacitor
voltage through an output to an
A/D line on the controller. When the capacitor is not being charged, it should
discharge at a relatively
know rate through the various paths to ground. By monitoring the discharge
rate, the controller can insure
that the capacitance of the capacitor is sufficient to burn the fusible
member. The trigger control from the
controller is used to fire the SCR to bum the fusible member.
With any of the above electronic subsystems, it is possible to avoid
triggering in the event metal
or metal-foiled materials are cut by looking for the amplitude of the signal,
or the rate of change,
depending on the system, to fall within a window or band rather than simply
exceeding or falling below a
certain threshold. More particularly; when metal is cut, the detected signal
will drop to almost zero, and
will drop within a single cycle. Thus, the controller or threshold detection
circuitry can be configured to
look for amplitude change of somewhat less than 100%, but more than 10% as a
trigger event, to
eliminate triggering on metal or other conductive work pieces which would
normally substantially
completely ground the signal.
It should be noted that, although not essential, all of the described
embodiments operate at a
relatively high frequency - above 100khz. This high frequency is believed to
be advantageous for two
reasons. First, with a high frequency, it is possible to detect contact more
quickly and sample many
cycles of the waveform within a short period of time. This allows the
detection system to look for
multiple missed pulses rather than just one missed pulse, such as might occur
due to noise, to trigger the
reaction system. In addition, the higher frequency is believed to provide a
better signal to noise ratio
when cutting green wood, which has a lower impedance at lower frequencies.
The contact detection subsystem, detection signal properties, circuits,
methods and machines
may be described as set forth in the following numbered paragraphs. These
paragraphs are intended as
illustrative, and are not intended to limit the disclosure or claims in any
way. Changes and modifications
may be made to the following descriptions without departing from the scope of
the disclosure.
1.1 A machine adapted to process a workpiece and including a contact detection
system,
comprising:
CA 02762156 2011-12-09
an electrically conductive sensor position at a potentially dangerous location
in the machine,
where the sensor may contact the workpiece or a user;
a contact detection system connected to the sensor to receive a signal
therefrom, where the
contract detection system is configured to differentiate contact of the senor
with the user from contact of
the sensor with the workpiece based on the rate at which the signal changes
upon contact.
1.2 A woodworking machine, comprising:
a cutter adapted to cut a workpiece;
an excitation system adapted to supply an electrical signal having a first
amplitude and period,
the electrical signal being coupled to the cutter to induce a corresponding
electrical signal of a second
amplitude on the cutter; and
a contact sensing system adapted to sense the electrical signal induced onto
the cutter, where the
contact sensing system is adapted to sense contact between a user and the
cutter based on a change in the
sensed electrical signal over a detection period, where the detection period
is between 5 and 150
microseconds and at least twice the period of the electrical signal.
1.2.1 The machine of paragraph 1.2, wherein the excitation system is adapted
to adjust the first
amplitude based on the sensed electrical signal properties.
1.2.1.1 The machine of paragraph 1.2.1, wherein the excitation system is
adapted to adjust the
first amplitude to maintain a predetermined second amplitude.
1.2.1.2. The machine of paragraph 1.2.1, wherein the adjustment rate of the
first amplitude is less
than 10% per millisecond.
1.3 A woodworking machine, comprising:
a cutter adapted to cut a workpiece;
an excitation system with an electrical output adapted to induce an electrical
signal having a first
amplitude on the cutter, where the excitation system is adapted to adjust the
amplitude of the electrical
output to maintain the first amplitude substantially constant so long as the
electrical load on the cutter
changes within certain boundaries.
1.3.1 The woodworking system of paragraph 1.3, wherein the boundaries include
a maximum
rate of change of the electrical load.
1.4 A contact detection system, comprising:
a sensor;
an excitation system adapted to generate a drive signal, where the drive
signal is coupled to the
sensor to induce a corresponding induced signal on the sensor, where ratio of
the amplitude of the drive
signal to the induced signal varies depending on the objects in proximity to
the sensor; and
a control system adapted to adjust the amplitude of the drive signal to
maintain the induced
signal at a substantially constant amplitude as various objects come into
proximity of the sensor.
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CA 02762156 2011-12-09
Section 2: Detection of Dangerous Conditions
As mentioned above, contact detection plates 44 and 46 are used to detect
contact between the
user's body and cutting tool 14. It will be appreciated that detection
subsystem 22 may employ any one
or more of a wide variety of methods for detecting contact between the blade
and a user's body. In view
of the relatively high response speed of electronic signals and circuits, one
suitable method includes
using electrical circuitry to detect an electronic connection between a user
and the cutting tool. It has
been found that the capacitance of a user's body, as measured through dry
contact with a portion of the
user's body, is approximately 25-200 picofarads. The measured contact
capacitance tends to increase
with increasing body size and with increased coupling between the user's body
and an electrical ground.
As a result of the inherent capacitance of a user's body, when the user
touches cutting tool 14,
the capacitance of the user's body is electrically coupled to the inherent
capacitance of the cutting tool,
thereby creating an effective capacitance that is larger than the inherent
capacitance of the cutting tool
alone. Thus, detection subsystem 22 may be electrically coupled to measure the
capacitance of the cutting
tool, so that any substantial change in the measured capacitance would
indicate contact between the
user's body and the cutting tool.
The exemplary implementation depicted in Fig. 2 illustrates a detection
subsystem 22 that is
configured to detect contact between a user and the cutting tool through a
capacitive coupling between
the blade and plates 44, 46. Detection system 22 includes suitable electrical
circuitry (e.g., such as
described in Section 1 above) to transmit an input signal to plate 44, and to
detect the input signal
through plate 46. Plate 44 is mounted close to, but spaced-apart from, blade
40. Plate 44 is capacitively
coupled to the saw blade by virtue of its size and placement parallel to and
spaced-apart from the saw
blade. Plate 46 is also mounted close to, but spaced-apart from, the saw blade
to establish a second
capacitive coupling. It will be appreciated that the number, size and
placement of charge plates may vary.
The effect of this arrangement is to form two capacitors in series through the
blade, creating a
capacitive shunt at the junction between the capacitors. Plates 44 and 46
function as charge plates of the
capacitors. The input signal is capacitively coupled from charge plate 44 onto
blade 40, and then
capacitively coupled from the blade to charge plate 46. Any change in the
capacitance of the blade
changes the signal coupled to charge plate 46.
When a user touches blade 40, the capacitance of the user's body creates a
capacitive load on the
blade. As a result, the size of the capacitive shunt between the charge plates
and the blade is increased,
thereby reducing the charge that reaches plate 46. Thus, the magnitude of the
input signal passed through
the blade to plate 46 decreases when a user touches the blade. Detection
subsystem 22 is configured to
detect this change in the input signal and transmit a contact detection signal
to logic controller 50.
In some cases, there may be a significant amount of resistance at the contact
point of the user's
dry skin and the blade. This resistance may reduce the capacitive coupling of
the user's body to the blade.
However, when the teeth on the blade penetrate the outer layer of the user's
skin, the moisture inherent in
27
CA 02762156 2011-12-09
the internal tissue of skin will tend to decrease the resistance of the
skin/blade contact, thereby
establishing a solid electrical connection. The sensitivity of detection
subsystem 22 can be adjusted as
desired to recognize even slight changes in the input signal.
Generally speaking, the spacing of the charge plates from the blade is not
critical, and may vary
depending on the charge plate area and the desired capacitive coupling with
the blade. However, it may
be desirable to separate the plates from the blade by a distance selected to
reduce the effect of deflections
in the blade on the capacitance between the blade and the plates. For
instance, if the blade is displaced
1/32 of an inch toward one of the plates by loads created during cutting
operations, the capacitance to that
plate is increased. Since the capacitance is proportional to the area of the
plate divided by the spacing, a
relatively large spacing reduces the relative effect of a given blade
displacement. Distances in the range
of approximately. 1/32 inch and approximately 1/2 inch have proven effective,
although values outside
this range could be used under appropriate circumstances.
It will be appreciated that the charge plates may be positioned at any point
adjacent one or both
sides and/or the perimeter of the blade. In the exemplary embodiment, the
plates are disposed relatively
close to the center of the blade. Since the deflection of the blade typically
is at a minimum near the arbor
upon which it is mounted, placing the charge plates close to the arbor has the
advantage of minimizing
the effect of blade deflection on the capacitive coupling between the plates
and the blade. In various
alternative embodiments, the outer edges of at least one of the charge plates
is radially spaced within
50%, 40%, 30%, 20% or 10% of the blade's radius from the center of the blade.
The charge plates may be mounted within machine 10 in any suitable fashion
known to those of
skill in the art. For example, in the exemplary embodiment depicted in Fig.
19, operative structure 12
includes a pivotal arbor block 250 adapted to support arbor 42. The charge
plates are mounted on a
support member 251 (shown in dashed lines in Fig. 19), which is attached to
arbor block 250. As a result,
charge plates 44 and 46 pivot with the arbor block, thereby maintaining their
position adjacent the blade.
Alternatively, the charge plates may be mounted in a stationary configuration.
In an alternative embodiment, at least one of the charge plates may include
one or more
insulating spacers 252 mounted on the side of the charge plate adjacent the
blade, such as shown in Figs.
19 and 20. Spacers 252 act as physical barriers to prevent the blade from
deflecting too close to the
charge plate. This may be especially useful when the distances between the
charge plates and the blade
are relatively small. The spacers may be constructed of any suitable
electrically insulating material,
including ceramic, glass, plastic, etc. In the exemplary embodiment depicted
in Figs. 19 and 20, spacers
252 cover only a small portion of the area between the charge plates and the
blade. As a result, the
spacers have relatively little effect on the capacitance between the blade and
the plate. Alternatively, the
spacers may cover a substantially larger portion, or even all of the space
between the charge plates and
the blade. In this latter case, the spacer will function, at least partially,
as the dielectric between the
28
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CA 02762156 2011-12-09
conductive surfaces of the charge plates and the blade. Thus, the capacitance
between the blade and the
charge plates will depend on the dielectric constant of the spacer.
In addition to the one or more spacers mounted between the charge plates and
the blade,
opposing spacers (not shown) may be mounted on the side of the blade opposite
the charge plates to
prevent the blade from deflecting too far from the charge plates.
Alternatively, one charge plate may be
mounted on the opposite side of the blade from the other charge plate.
Further, the spacers may be
designed to slide on the surface of the blade as it moves. Additionally, if
the charge plates are mounted
to move into and away from the side of the blade, and resiliently biased
toward the blade, the charge
plates and spacers will move with any deflections of the blade, thereby
maintaining contact between the
spacers and blade even when the blade is deflected. An advantage of this
arrangement is the close
spacing that can be established and maintained, thereby reducing the size of
the plates and maintaining a
constant capacitance between the charge plate and blade.
It will be appreciated that the size of charge plates 44 and 46 may also vary.
Typical plate areas
are between 1 and 10 square inches, although many different sizes may be used,
including sizes outside
of this typical range. In the exemplary embodiment, the charge plate sizes are
selected, in conjunction
with charge plate spacing and dielectric material, to provide a charge plate-
to-blade capacitance that is
comparable (e.g., within an order of magnitude) with the capacitance of the
human body. This
configuration serves to improve the signal-to-noise ratio of the input signal
detected by charge plate 46.
Furthermore, charge plate 44 may be a different size than charge plate 46
and/or be spaced closer or
farther apart from the blade to provide different capacitances. For example,
it may be desirable to size
drive charge plate 44 larger than sense charge plate 46 to increase the
coupling of the drive charge plate.
An example of a suitable charge plate material is copper-plated printed
circuit board, which is
relatively rigid, flat and thin. Other examples include any relatively
electrically conductive material such
as gold, aluminum, copper, steel, brass, etc. The charge plates may take any
shape suitable for the
particular clearances of machine 10. Where there are large grounded metal
structures near the blade, a
larger driving charge plate 44 can be used to partially shield the blade from
capacitive coupling to the
grounded structure. Although the larger plate also will have increased
capacitive coupling to the
grounded structure, this does not interfere with the operation of detection
subsystem 22 because the
detection subsystem is capable of driving much larger capacitance loads than
are created under these
circumstances.
It will be appreciated by those of skill in the art that blade 40 should be
insulated from electrical
ground to allow the input signal to be capacitively coupled from charge plate
44 to charge plate 46. In the
exemplary embodiment depicted in Figs. 19 and 20, blade 40 is electrically
isolated from arbor 42 on
which it rides, thus insulating the blade from ground and the remaining
structure of the machine. There
are a variety of suitable arrangements for providing electrical insulation
between the blade and the arbor,
which may vary depending on the particular configuration of machine 10. For
example, in the case of a
29
CA 02762156 2011-12-09
5/8-inch arbor shaft 42, blade 40 can be formed with a one-inch diameter hole
into which a 3/16-inch
thick cylindrical plastic bushing 253 is fitted, such as shown in Figs. 19 and
20. Insulating washers 254
are disposed on either side of the blade to isolate the blade from the arbor
flange 255 and arbor washer
256. The insulating washers should be thick enough that only negligible
capacitance is created between
the blade and the grounded arbor flange and washer. A typical thickness is
approximately 1/8-inch,
although 1/32-inch or less may be suitable depending on other factors. In
addition, it is possible to
construct some or all of the arbor components from non-conductive materials,
such as ceramic, to reduce
or eliminate the need for electrical isolation from the arbor.
An arbor nut 257 holds the entire blade assembly on arbor 42. Friction
established by tightening
the arbor nut allows torque from the arbor to be transmitted to the saw blade.
It is preferable, although not
essential, that the blade be able to slip slightly on the arbor in the event
of a sudden stop by the brake to
reduce the mass that must be stopped and decrease the chance of damage to the
blade, arbor, and/or other
components in the drive system of the saw. Furthermore, it may be desirable to
construct the bushing
from a material that is soft enough to deform when the blade is stopped
suddenly. For example,
depending on the type of braking system used, a substantial radial impact load
may be transmitted to the
arbor when the brake is actuated. A deformable bushing can be used to absorb
some of this impact and
reduce the chance of damage to the arbor. In addition, proper positioning of
the brake in combination
with a deformable bushing may be employed to cause the blade to move away from
the user upon
activation of the brake, as is discussed in more detail in Section 3 below.
It will be appreciated that the blade insulation assembly described above does
not require special
saw blades such as are described in U.S. Patent No. 4,026,177. Indeed, arbor
42 may be sized to fit
within a plastic bushing 253 received within a standard saw blade 40 having a
5/8-inch diameter hole.
Thus, an operator may use any standard blade on machine 10.
As an alternative to insulating the blade from the arbor, the arbor and/or
part of its supporting
framework may be electrically isolated from ground. One benefit of this
embodiment is that if the blade
is electrically connected to the arbor, then the arbor itself can be used to
capacitively couple the input
signal from charge plate 44 to charge plate 46. As a result, the charge plates
are unlikely to interfere with
installation and removal of the blade, and thus unlikely to be damaged or
removed by a user. While the
particular implementation of this alternative embodiment will vary with the
configuration of the cutting
tool, one exemplary implementation is depicted in Fig. 21.
As shown, blade 40 is mounted directly onto arbor 42. As in Fig. 20, the blade
is secured to the
arbor by arbor flange 255, arbor washer 256 and arbor nut 257. The arbor is
supported for rotational
movement relative to an arbor block 250 by one or more bearings 258 mounted in
the arbor block and
spaced along the elongate axis of the arbor. However, bearings 258 do not
contact the arbor directly.
Instead, electrically insulating sleeves 259 are disposed between the arbor
and the bearings. Arbor block
250 is movable to allow the blade to be raised and lowered, as well as to be
inclined for angled cuts. A
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CA 02762156 2011-12-09
motor (not shown) drives the arbor through a belt 260 that loops over a pulley
261 on the end of the arbor
opposite the blade. The belt typically is non-conducting and thus does not
electrically couple the arbor to
ground.
Sleeves 259 may be constructed of any suitable material that is relatively
durable and non-
conductive, including plastic, ceramic, etc. The sleeves may be configured to
fit over a constant-diameter
arbor as shown, or the arbor may be notched to receive the sleeves so that the
outer diameter of the
sleeves are flush with the outer diameter of the arbor. Furthermore, it will
be appreciated that there are
many other arrangements for electrically insulating the arbor. As just a few
examples, sleeves 259 may
be disposed between bearings 258 and arbor block 250, or at least portions of
the bearings may be
constructed of non-conductive materials. For example, ceramic bearings may be
used. Alternatively,
larger portions of the arbor assembly may be isolated from the rest of the
saw.
In any event, charging plates 44 and 46 are disposed alongside, but slightly
spaced from, the
arbor. The charging plates typically are shaped and arranged relative to the
arbor to ensure adequate
capacitive coupling. For example, the charging plates may be trough-shaped to
conform to the cylindrical
shape of the arbor, as illustrated in Fig. 21. Alternatively, the plates may
be in the form of a ring or tube
to completely surround axially-spaced portions of the arbor. The charging
plates typically are supported
on arbor block 250, such as by mounts 262 extending from the frame. This
arrangement ensures that the
charging plates will move in tandem with the arbor when the position or angle
of the blade is adjusted.
The mounts usually will be configured to electrically insulate the charging
plates from the frame. The
charge plates can be positioned very close to the arbor because it does not
deflect during use like the
blade, thereby allowing smaller charge plates to be utilized.
Turning attention to Figs. 22 and 23, an alternative arrangement for
capacitively coupling charge
plates 44 and 46 to arbor 40 is shown. This arrangement has proven suitable
for use with contractor style
table saws which are available from a variety of manufacturers. Arbor block
250 includes two spaced-
apart, and generally parallel support members 263 adapted to receive bearings
258 within central recesses
264. Electrically-insulating bushings 265 are disposed in the bearings and
adapted to receive arbor 42.
Each bushing 265 includes an outer lip or flange 266 which abuts the outer
edges of the bearing. The
bushings may be constructed of ERTYLITETM (PET-P), or any other electrically-
insulating material
adapted to support the arbor within the bearings.
Arbor flange 255 is integrally formed with arbor 42 and abuts against the
flange of one of
bushings 265. The opposite end of arbor 42 is threaded to receive one or more
locking nuts 267, which
tighten against the flange of the other bushing 265 to retain arbor 42 within
bearings 258. Pulley 261 is
mounted on the arbor adjacent locking nuts 267.
As shown in Fig. 23, bushings 265 completely insulate the arbor from the
bearings and the arbor
block. Alternatively, the bushings could be configured to fit between bearings
258 and support members
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263. In any event, the arbor remains securely and symmetrically positioned to
rotate freely within the
bearings.
Charge plates 44 and 46 take the form of electrically-conductive tubes having
inner diameters
larger that the diameter of arbor 42. Tubes 44, 46 may be constructed of any
suitable material such as
brass tube, copper pipe, etc. It will be appreciated that the size of charge
tubes 44 and 46 may be selected
to provide a desired capacitance with the arbor. Indeed, the size of the
charge. tubes may be different to
provide different capacitances. For example, in the embodiment depicted in
Figs. 22 and 23, charge tube
44 is longer than charge tube 46, thereby providing a higher capacitance
between charge tube 44 and the
arbor, than between charge tube 46 and the arbor. Alternatively, or
additionally, the inside diameters of
the charge tubes may be different to provide different capacitances due to
different blade-to-charge plate
spacings.
Charge tubes 44 and 46 are received in an electrically-insulating support
housing or tube 268,
having an inner diameter adapted to receive charge tubes 44 and 46. Insulating
tube 268 may be formed
of any suitable electrically-insulating material such as polycarbonate, nylon,
PVC, etc. The insulating
tube serves to prevent the charge tubes from being grounded by the arbor
block, bearings, etc. Insulating
tube 268 is positioned around arbor 42 and received into inner apertures 269
in support members 263.
Inner apertures 269 are axially colinear with arbor 42. Thus, where charge
tubes 44 and 46 are centrally
positioned within the insulating tube, the inner diameters of the charge tubes
are automatically positioned
by the insulating tube to be axially colinear or symmetrical with the arbor.
It will be appreciated that while the charge tubes and insulating tube in the
exemplary
embodiment are cylindrical, other shapes may also be used. For example,
insulating tube 268 may have a
rectangular outer cross-section while maintaining its circular inner cross-
section. Likewise, charge tubes
44 and 46 may have any suitable outer cross-sectional shape to match the inner
shape of the insulating
tube. In any event, mounting the charge tubes to support members 263 ensures
that the support tubes
maintain the correct position about the arbor regardless of the movement of
arbor block 250.
In addition to electrically insulating and automatically positioning the
charge tubes, insulating
tube 268 also serves to enclose and protect the charge tubes from damage and
debris. In the exemplary
embodiment, insulating tube 268 defines a hole 270 positioned between charge
tube 44 and charge tube
46 to allow electrical cables (not shown) to be soldered or otherwise
connected to the charge tubes to
carry the signals to and from the detection circuitry of detector subsystem
22. Alternatively, two holes
may be used, each positioned over one of the charge tubes.
Since the charge tubes should not come into contact with each other, the fit
between the charge
tubes and insulating tube is typically tight enough to frictionally prevent
movement of the charge tubes
along the axis of the insulating tube. Alternatively, a bump or ring may be
formed or positioned on the
inner diameter of the insulating tube between the charge tubes to prevent the
charge tubes from coming
into contact. As a further alternative, hole 270 may be used to apply a caulk,
glue, epoxy, or similar
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material between the charge tubes and insulating tube to prevent the charge
tubes from moving. As
another alternative, one or more set-screws may be threaded through the
insulating tube to bear against
the charge tubes.
Turning attention now to Figs. 24 and 25, an alternative embodiment of the
insulating tube and
charge tubes for use with a contractor style saw is depicted. Insulating tube
268 includes a hollow bore
with outwardly beveled ends to receive charge tubes 44 and 46. Each charge
tube has an inner narrowed
rim portion 271 to which an electrical cable (not shown) may be attached
(e.g., by solder, etc.). The
narrowness of rims 271 allow the cables to be attached before the charge tubes
are inserted into the
insulating tube. Typically, the cables are fed through hole 270.
Insulating tube 268 also includes a recessed region 272 adapted to receive a
Hall Effect or similar
sensor assembly 1000 for detecting blade/arbor rotation. Sensor 1000 is
described in more detail below in
Section 10. The sensor is aligned over a hole 273 in charge tube 44 to sense
the passage of a magnet
disposed on the arbor (not shown). Alternatively, the sensor may be aligned
over a hole 273 in charge
plate 46. In some cases, such as where charge plates 44 and 46 are identical,
it may be desirable to place
hole 273 in both charge plates to reduce the number of different parts for
manufacture.
While a few exemplary arrangements for capacitively coupling the charge plates
to the arbor
have been described, it will be understood that there are many suitable
arrangements and that the
invention is not limited to any particular one. For example, if there is
insufficient room between the
bearings for the charge plates, one or both of the charge plates may be
positioned between the bearings
and the pulley, or on the side of the pulley opposite the bearings.
It will appreciated that one or both of the charge plates may be capacitively
coupled to other
portions of operative structure 12 rather than blade 40 or arbor 42. For
example, charge plates 44 and 46
may be coupled to an arbor block 250 which is electrically insulated from the
remainder of the operative
structure and machine 10. In such a configuration, the blade should be
electrically coupled to the arbor
block. Therefore, insulating bushings between the blade and arbor, or between
the arbor and arbor block,
should be omitted. As additional examples, the charge plates may be coupled to
the bearings, pulley, etc.
It also will be appreciated that charge plates 44 and 46 may be capacitively
coupled to other
types of cutting tools, including those with a non-circular blade or cutter.
For example, Figs. 26 and 27
depict an exemplary embodiment in which the charge plates are capacitively
coupled to the blade of a
band saw 275. Typically, band saw 275 includes a main housing 276 enclosing a
pair of vertically
spaced-apart wheels 277. The perimeter of each wheel 277 is coated or covered
in a high-friction material
such as rubber, etc. A relatively thin, continuous loop blade 40 tightly
encircles both wheels. A
workpiece is cut by passing it toward blade 40 in a cutting zone 278 between
wheels 277. An upper
blade-guide assembly 279 and a lower blade-guide assembly 280 maintain the
revolving blade in a stable
path within cutting zone 278. The workpiece is passed toward the blade on a
table 281, which forms the
bottom of the cutting zone.
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The blade should be electrically insulated from the main housing, which
usually is grounded.
Thus, blade-guide assemblies 279 and 280, which may include ball-bearing
guides and/or friction pads,
etc., are constructed to electrically insulate the blade from the main
housing. In addition, the high-friction
coating on wheels 277 electrically insulates the blade from the wheels.
Alternatively, the wheels may be
constructed of electrically non-conductive material.
Charge plates 44 and 46 may be arranged in a variety of ways depending on the
application and
the space constraints within the main housing. Two possible arrangements are
illustrated in Fig. 26. In
the first arrangement, charge plates 44 and 46 are disposed closely adjacent
the blade as it rides along one
of the wheels 277. The charge plates may be formed in an are to match the
perimeter of the wheel and
maintain a constant spacing with the blade. This arrangement has the advantage
of easily maintaining a
constant blade-to-charge plate spacing since the blade is held in a constant
path against the perimeter of
the wheel. The charge plates may be connected to the main housing via a non-
conductive mount to
maintain electrical insulation from the housing.
Another of the many possible arrangements for the charge plates includes a
charge plate block
282 which is configured to extend along the blade as it travels between wheels
277. As can best be seen
in the detail view of Fig. 27, the charge plate block includes charge plates
44 and 46. In the depicted
implementation, the charge plate block has a substantially C-shaped cross-
section sized to fit around the
sides and back edge (i.e., non-toothed edge) of the blade. The charge plate
block is mounted on main
housing 276 and resiliently biased, such as by one or more springs 283, toward
the moving blade. Since
blade 40 may tend to move or deflect slightly in its path, springs 283 ensure
that the charge plate block is
able to move along with blade. Charge plate block 282 typically is made of a
durable, electrically non-
conductive material such as ceramic, plastic, etc. Charge'plates 44 and 46 are
disposed on or within the
charge plate block. Although the charge plates are illustrated as being
disposed on opposite sides of blade
40, the charge plates may alternatively be on the same side of the blade. The
self-aligning configuration
of the charge plate block ensures that the blade-to-charge plate spacing is
substantially constant despite
the motion of the blade.
In addition to band saws, the charge plates may be capacitively coupled to
machines such as
jointers, planers, etc., which have cylindrical cutter heads. The cutter heads
typically are mounted to
rotate about an arbor. Thus, charge plates 44 and 46 may be capacitively
coupled to the arbor as
described above, or to a flat end of the cutter head, etc.
While one exemplary system and method for detecting contact between the user's
body and the
blade is described herein, many other systems and methods may be used. For
example, the detection
system may sense the resistance of the human body upon contact between the
user's body and the blade.
As shown in Fig. 19, the sensor assembly of detection subsystem 22 may include
a brush contact 284 or
similar sensor to make direct electrical contact with the blade. Brush contact
284 may be mounted, for
example, on arbor block 250. Typically, the blade and brush contact are
electrically isolated from the
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arbor block. Alternatively, the brush contact may be configured to directly
couple to the arbor or another
portion of operative structure 12 as described above in connection with charge
plates 44 and 46. In any
event, contact between the user's body and blade would function as a switch to
form a conductive path
detectable by suitable circuitry in detection subsystem 22 and/or control
subsystem 26. As a further
alternative, brush contact 284 may be used to detect a capacitive rather than
conductive load upon the
blade. As further alternative, the detection subsystem sensor assembly may be
configured to detect
contact by optical, magnetic, or other non-electrical means.
As an alternative to detecting contact between the user and the blade,
detection subsystem 22
may be configured to detect proximity of the user's body to the blade by
detecting contact between the
user's body and a guard adjacent the blade. If the guard is positioned so that
the user's body must contact
the guard before contacting the blade, then the blade may be stopped before
the user comes into contact
with the blade. It will be appreciated that this alternative detection
subsystem may be implemented in a
variety of different configurations and for any type of machine 10. As one
example, Fig. 28 shows an
exemplary embodiment for use on a radial arm saw 286.
Typically, radial arm saw 286 includes a horizontal base 287, a vertical
support column 288
extending upward from base 287, and a guide arm 289 which extends from column
288 vertically spaced
above base 287. A carriage 290 is slidably coupled to the underside of guide
arm 289. The bottom end of
carriage 290 is connected to a saw housing 291 and motor assembly 16, allowing
blade 40 to be pulled
across the base to cut workpieces (not shown) supported on the base. A guard
member 292, such as those
known in the art, is positioned on at least one side of blade 40. Guard member
292 is disposed relative to
the blade so that any portion of the user's body approaching the blade will
first strike against the guard
member. Typically, guard member 292 is movably coupled to housing 291 to
maintain its blade-shielding
position as the blade passes over the workpiece.
The guard member is electrically insulated from housing 291 but electrically
coupled to the
detection subsystem (not shown). Thus, any contact between the user's body and
the guard member is
detected. The detection subsystem may be conductively coupled to the guard
member by any suitable
means (not shown) such as electrical cable, etc. Alternatively, the detection
subsystem may be
capacitively coupled to the guard member by one or more charge plates disposed
adjacent the guard
member such as described above.
The systems, methods and machines to detect dangerous conditions may be
described as set forth
in the following numbered paragraphs. These paragraphs are intended as
illustrative, and are not intended
to limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
2.1 A woodworking machine comprising:
a conductive cutter;
an excitation system adapted to adapted to induce an electrical signal on the
cutter;
CA 02762156 2011-12-09
a first capacitive coupling adapted to electrically connect the excitation
system to the cutter;
a contact sense system adapted to monitor the electrical signal induced on the
cutter; and
a second capacitive coupling adapted to electrically connect the contact sense
system to the
cutter.
2.2 A woodworking machine, comprising:
a motor;
an electrically isolated rotatable arbor configured to be driven by the motor;
a circular saw blade;
an excitation system adapted to generate an electrical signal; and
a capacitive coupling adapted to capacitively couple the excitation system to
the arbor to transfer
a portion of the electrical signal to the blade.
2.3 A woodworking machine, comprising:
a conductive cutter;
an excitation system adapted to generate an electrical signal;
a capacitive coupling linking the excitation system to the cutter, where the
capacitive coupling
has a capacitance of at least 10 picofarads.
Section 3: Retraction System
As briefly mentioned above, reaction subsystem 24 can be configured with a
retraction system to
retract or move a cutting tool away from the point of accidental contact with
a user. Moving away from
the point of accidental contact reduces the time the cutting tool is in
contact with the user, thereby
minimizing any injury to the user. Moving the cutting tool away from the point
of accidental contact also
prevents the cutting tool from moving toward the user, which could increase
any injury to the user. For
example, a spinning blade in a miter saw has substantial angular momentum, and
that angular momentum
could cause the blade to move downward toward a user when a brake pawl hits
the blade. The spinning
blade in a table saw also has substantial angular momentum that could cause
the blade to move upward
toward a user when a brake pawl hits the blade, depending on the position of
the brake, the weight of the
blade and the amount of play in the structure supporting the blade. Preventing
any such movement
lessens the potential injury to the user. A retraction system may be used in
addition to or instead of other
safety mechanisms.
Figures 29 and 30 show sectional views of a table saw configured with both a
retraction system
and a braking mechanism. A blade 300 is mounted on an arbor 301 to spin in the
direction of arrow 302.
A table 303 (not shown in Fig. 30), which defines the work surface for the
table saw, is adjacent the blade
and the blade extends above the table. A support structure 304 may support
blade 300 and arbor 301 in
any known way, or as described in more detail in Section 13 below.
Blade 300 is configured to pivot up and down so that a user can position the
blade to extend
above the table as needed. The blade pivots around a pin 305. A user may pivot
the blade to adjust its
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position by turning a shaft 306 on which a worm gear 307 is mounted. The worm
gear is mounted on the
shaft so that it turns with the shaft, but so that it may slide on the shaft
when necessary, as explained
below. Worm gear 307 is mounted on shaft 306 like a collar, with the shaft
extending through a
longitudinal hole in the worm gear. The worm gear is held in place during
normal operation of the saw by
a spring clip 308, which is positioned in a groove or channel 309 on the worm
gear and which also
engages a detent or shoulder on shaft 306 to hold the worm gear in place. The
worm gear engages an
arcuate rack 310 that supports an arbor block 311, which in turn supports
arbor 301 and blade 300. Thus,
when a user turns shaft 306, such as by turning a knob attached to the shaft
(not shown), worm gear 307
moves arbor block 311 and the blade up or down, depending on the direction
that the worm gear is
turned.
A brake cartridge 312 is mounted in the saw adjacent blade 300. The brake
cartridge includes a
pawl 314 biased toward blade 300 by a spring 316. The pawl is held away from
blade 300 by a release
mechanism 318, as described generally above and as described in more detail in
Sections 4-5 and 7-8
below. The cartridge is configured so that the release mechanism releases the
pawl into the blade upon
the receipt of a detection signal, as described in Section 6 below.
Brake cartridge 312 is positioned on the blade's pivot axis so that pawl 314
can move around pin
305. Thus, when pawl 314 hits the blade, the angular momentum of the blade is
transferred to the arbor
block, and the blade, arbor block, rack and cartridge try to retract or move
down in the direction of arrow
320. Alternatively, the cartridge may be positioned on a pin different from
pin 305, but that still pivots
with the blade.
The blade will move down to the extent permitted by the contact between rack
310 and worm
gear 307. If the worm gear is fixed in place, the downward movement of the
blade may strip teeth on the
rack and/or worm gear, and may prevent the blade from moving down as far as
desired. In the
embodiment shown in Figs. 29 and 30, the worm gear is adapted to snap free and
move on shaft 306
when the pawl hits the blade.
When the pawl hits the blade, the resultant angular momentum impulse causes
spring clip 308 to
snap loose, allowing the worm gear to slide down the shaft toward an end 322
of the shaft. The spring
clip snaps loose because the rack moves down when the blade is stopped, and
the rack contacts the worm
gear and forces the worm gear to move. The force of the rack against the worm
gear causes the spring
clip to snap loose. The worm gear is put back in place by moving it back along
shaft 306 until the spring
clip snaps into place on the shaft.
The table saw shown in Figs. 29 and 30 also includes a support 326 configured
with a seat or
region 328 in which is placed an impact-absorbing material 330. The support is
positioned under the
arbor and arbor block so that when the blade retracts, the arbor block strikes
impact-absorbing material
330. Support 326 and impact absorbing material 330 act as a barrier to stop
the downward movement of
the blade. The support is positioned so that blade 300 may retract a
sufficient distance. The impact-
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CA 02762156 2011-12-09
absorbing material can be any one of a number of cushioning materials, such as
rubber, dense foam,
plastic, etc. One material found to be suitable is available under the part
number C-1002-06 from
AearoEAR, of Indianapolis, Indiana. Alternatively, impact-absorbing material
330 may be attached to the
undersurface of the arbor block instead of on support 326. Additionally,
support 326 may take many
forms. In fact, shaft 306 may be configured and positioned so that it provides
a surface to stop the
downward movement of the blade.
Figure 30 also shows a splitter 335 that extends above table 303 behind blade
300 to prevent
kickback. A blade guard may also substantially enclose blade 300. Figure 30
further shows a housing 337
for electronic components relating to the safety system, and a motor mount
339, which are not shown in
Fig. 29.
In the construction described above, the angular momentum of the blade causes
the blade, arbor
block and cartridge to all pivot down when the pawl strikes the blade. Thus,
the angular momentum of
the blade causes the retraction. Blade 300 is permitted to move downward a
sufficient distant so that the
blade is completely retracted. The ability of the blade to retract minimizes
any injury from accidental
contact with the blade.
Figure 31 shows another embodiment of a retraction system used with a brake
pawl. A saw 331
includes a blade 300 and a brake cartridge 312 housing a brake pawl 314. The
cartridge and pawl are
mounted to the frame of the saw by a pin 332. The pin is mounted to the saw in
such a way that it may
not pivot up and down with the blade. When the blade hits the pawl, the blade
climbs down the pawl, or
in other words, moves generally around the point of contact with the pawl. The
pawl and blade do not
pivot downward together, as in the embodiment shown in Figs. 29 and 30,
because the pawl is fixed to
the frame of the saw. In this embodiment, the blade retracts by "climbing"
down the pawl.
Another embodiment of a retraction system comprises a compressible bushing.
Typically, a blade
300 in a table saw, miter saw or other machine is mounted to an arbor over a
bushing 333, as shown in
Fig. 32. A locking nut, washers and an arbor flange are used to secure the
blade to the arbor. Bushing 333
may be constructed from a material that is soft enough to deform when the
blade is stopped suddenly. For
example, depending on the type of braking system used, a substantial radial
impact load may be
transmitted to the arbor when the brake is actuated. A deformable bushing can
be used to absorb some of
this impact and reduce the chance of damage to the arbor. In addition, proper
positioning of the brake in
combination with a deformable bushing may be employed to cause the blade to
move away from the user
upon activation of the brake. Where a plastic bushing is placed between the
blade and the arbor, the
substantial force created by stopping the blade almost instantly may cause the
bushing to deform.
Typically, the edge of the mounting hole of the blade will bite into the
bushing as the blade attempts to
rotate about the pawl. Therefore, if the pawl is mounted at the back of the
blade, then the blade will tend
to move downward into the bushing and away from the user when the pawl engages
the blade.
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Figures 33 and 34 show a miter saw equipped with both a brake and a retraction
system. The
miter saw is configured with a pivotal motor assembly to allow the blade to
move upward into the
housing upon engagement with a brake pawl 348. Motor assembly 350 is connected
to housing 352 via
pivot bolt 354, allowing the motor assembly to pivot about bolt 354 in the
direction of blade rotation. A
spring 356 is compressed between the housing and an anchor 358 to bias the
motor assembly against the
direction of blade rotation. The motor assembly may include a lip 360, which
slides against a flange 362
on the housing to hold the end of the motor assembly opposite the pivot bolt
against the housing.
When the saw is in use, spring 356 holds the motor assembly in a normal
position rotated fully
counter to the direction of blade rotation. However, once the pawl is released
to engage the blade, the
motor assembly and blade pivot upward against the bias of the spring. In this
embodiment, the pawl is
positioned at the front of the blade so that the pivot bolt 354 is between the
pawl and the arbor. This
arrangement encourages the blade to move upward into the housing when stopped.
The spring is selected
to be sufficiently strong to hold the motor assembly down when cutting through
a workpiece, but
sufficiently compressible to allow the blade and motor assembly to move upward
when the blade is
stopped. Of course, the blade and motor assembly may be configured in any of a
variety of ways to at
least partially absorb the angular momentum of the blade.
Figure 35 shows an alternative configuration of a miter saw adapted to move
away from an
accidental contact with a user by absorbing the angular momentum of the blade.
In this configuration, the
miter saw includes two swing arms 370 and 372. One end 374 of each swing arm
370, 372 is connected
to base 376, and the opposite end 378 of each swing arm is connected to
housing 380, the blade, and/or
the motor assembly (not shown). The position of the swing arms relative to
each other may vary
depending on the swing arm motion desired. In Fig. 34, swing arm 370 is
connected to base 376
somewhat below and forward of swing arm 372. Typically, the motor assembly is
rigidly attached to end
378 of swing arm 370, while housing 380 is connected to rotate about end 378
of swing arm 370. End
378 of swing arm 372 is connected only to the housing. Alternatively, the
motor assembly may be
connected to rotate about end 378 of swing arm 370 along with the housing.
The geometry of the configuration shown in Fig. 35 causes the housing and/or
motor assembly to
rotate as the swing arms pivot. Significantly, when the swing arms move
upward, the housing and/or
motor assembly rotate in the same direction in which the blade rotates during
cutting. As a result, when a
brake pawl engages the blade and transfers the angular momentum of the blade
to the housing and/or
motor assembly, the housing and/or motor assemblies tend to rotate in the same
direction as the blade.
This causes the swing anus to pivot upward, drawing the blade away from the
workpiece and the user's
body. Thus, the miter saw configuration illustrated in Fig. 35 is adapted to
absorb the angular momentum
of the blade and translate that angular momentum into an upward force on the
swing arms.
In any of the systems described above, a spring or other force can be used to
push the blade away
from the point of contact with the user. The spring could be released by a
mechanism similar to the
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mechanism that releases the pawl to strike the blade. Figures 36-38 show how a
spring may be used to
retract a blade in a table saw. Figure 36 is a top view and Figs. 37 and 38
are side views of an arbor block
381 holding an arbor 382 used to drive a blade (not shown). Arbor block 381 is
pivotally mounted to pin
383 so that the arbor block and blade may pivot up and down to adjust the
position of the blade in the
saw.
A segment gear 384, like rack 310 described above in connection with Figs. 29
and 30, is also
mounted on pin 383, and is connected to arbor block 381 in the manner
described below, to raise and
lower the arbor. Segment gear 384 includes a side portion 385 positioned
substantially perpendicularly to
the plane of arbor block 381, and a top portion 386 positioned over arbor
block 381. The side portion 385
includes gear teeth 387 to engage a worm gear to raise and lower the arbor
block. Side portion 385 and
top portion 386 are connected to each other and move together. Top portion 386
extends over the top of
the entire arbor block, as shown. The arbor block is constructed with a region
to accommodate top
portion 386 so that top portion 386 does not extend substantially above the
arbor block, which could limit
the ability of the arbor block and blade to pivot upward when desired, such as
by contacting the underside
of a table in a table saw.
A pocket 388 is formed in arbor block 381 to house a spring 389. In the
position shown in Fig.
37, spring 389 is compressed between top portion 386 of segment gear 384 and
arbor block 381 because
the segment gear and arbor block are coupled together.
The segment gear and arbor block are coupled by a compound linkage having, as
shown in Fig.
38, a first arm 390 attached at one end to the arbor block and at its other
end to a second arm 391. The
second arm, in turn, is attached to top portion 386 of segment gear 384, as
shown. First and second arms
390 and 391 are hingedly connected to each other, and to the arbor block and
segment gear. The arms are
configured so that the force of the spring pushing apart the arbor block and
the top portion of the segment
gear biases the first and second arms in such a way that the arms want to
move. A fusible member 392,
which may take the form of a wire as described above, restrains the arms from
movement. Of course,
numerous different linkages may be used, and numerous types and configurations
of fusible members or
other release mechanisms may be used. The linkage may be selected to provide a
sufficient mechanical
advantage so that the arbor block and top portion of the segment gear may be
held together with as thin a
fusible member as possible, so that the fusible member may be burned as easily
as possible. Various
analogous compound linkages are described in Section 4 below. The fusible
member may be burned by a
system as described above, or as described in more detail in Section 6 below.
The compound linkage and
the fusible member are preferably configured so that they accommodate spring
forces of 100 to 500
pounds or more.
When the fusible member is burned, the compound linkage is free to move, and
the spring pushes
arbor block 381 down, away from top portion 386 of the segment gear, as shown
by the dashed lines in
Fig. 37, thereby retracting the blade. The stronger the spring, the faster the
blade will be retracted. The
CA 02762156 2011-12-09
segment gear does not move because it is coupled through teeth 387 to a worm
gear or some other
structure.
Retracting a blade by a spring or some other force may be thought of as direct
retraction. A
spring or other force may be used with some other retraction system to
increase the speed that a cutting
tool retracts, or a spring or other force may be used as the sole means of
retraction. The systems for direct
retraction described above may be used on various pieces of equipment,
including table saws, miter saws
and band saws.
Figure 39 is a schematic diagram of a system to retract the blade of a band
saw. Typically, a band
saw includes a main housing enclosing a pair of vertically spaced-apart
wheels. The perimeter of each
wheel is coated or covered in a high-friction material such as rubber, etc. A
relatively thin, continuous
loop blade tightly encircles both wheels. A workpiece is cut by passing it
toward blade in a cutting zone
between the wheels. The workpiece is passed toward the blade on a table, which
forms the bottom of the
cutting zone.
The band saw shown in Fig. 39 includes roller 393 positioned adjacent the
blade. The roller is
configured to contact the blade and push the blade away from the point of
accidental contact with a user.
In addition, the roller may be configured to push the blade off the wheels,
thereby stopping the motion of
the blade. A top view of the roller is shown in Fig. 40 pushing against a
blade in the direction of the
arrow. The roller may be part of a cartridge, and may be released into the
blade just as the pawls
described above are released. The roller should have a diameter large enough
so that the roller can roll
over the teeth of the blade.
The systems for direct retraction of a cutting tool may also be implemented on
hand-held circular
saws. Such saws typically include a base plate that contacts a workpiece
during sawing. The base plate
supports the saw on the workpiece. The base plate may be configured so that it
is pushed down when the
blade contacts a user. The result of that action is to effectively retract the
blade because the base plate
would push the user away from the blade.
The retraction systems, methods and machines may be described as set forth in
the following
numbered paragraphs. These paragraphs are intended as illustrative, and are
not intended to limit the
disclosure or claims in any way. Changes and modifications may be made to the
following descriptions
without departing from the scope of the disclosure.
3.1 A woodworking machine comprising:
a working portion;
a detection system adapted to detect a dangerous condition between a person
and the working
portion; and
a retraction system associated with the detection system to cause the working
portion to retract
upon detection of the dangerous condition.
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3.1.1 The woodworking machine of paragraph 3.1 where the working portion is a
spinning
blade having angular momentum, and where the retraction system is adapted to
retract the blade by using,
at least partially, the angular momentum of the blade.
3.2 A table saw comprising:
a worksurface; and
a rotatable blade adapted to raise and lower relative to the worksurface
around a pivot point,
where the rotation of the blade defines a feed direction for a workpiece to be
fed into the saw, and where
the pivot point is downstream of the blade relative to the feed direction.
3.3 A table saw comprising:
a worksurface;
a rotatable blade adapted to raise and lower relative to the worksurface
around a pivot point;
a gear system adapted to raise and lower the blade;
a release in the gear system adapted to allow the blade to drop down relative
to the worksurface
upon the occurrence of a specified event.
3.3.1 The table saw of paragraph 3.3 where the specified event is braking the
blade.
3.3.2 The table saw of paragraph 3.3 further comprising a stop to limit the
dropping down of
the blade.
3.4 A saw comprising:
a rotatable blade adapted to raise and lower around a pivot point, where the
blade is mounted on
an arbor;
an arbor block adapted to hold the arbor, and further adapted to retract the
arbor and blade upon
the occurrence of a specified event.
3.4.1 The saw of paragraph 3.4 where the arbor block comprises first and
second pieces held
together until the occurrence of the specified event, and further comprising
stored mechanical energy that
is released to move the first and second pieces apart upon the occurrence of
the specified event.
3.5 A miter saw comprising:
a base having a cutting region;
a blade;
a brake system adapted to brake the blade; and
a linkage between the blade and base, where the linkage is configured to cause
the blade to move
away from the cutting region when the brake system brakes the blade.
3.5.1 The miter saw of paragraph 3.5 where the linkage is configured so that
the angular
momentum of the blade causes the blade to move away from the cutting region
when the brake system
brakes the blade.
3.6 A miter saw comprising:
a base;
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a housing pivotally connected to the base;
a blade;
a mounting system holding the blade in the housing; and
a brake system adapted to brake the blade;
where the mounting system is configured so that the blade pivots into the
housing when the brake
system brakes the blade.
3.7 A band saw comprising:
a worksurface having a cutting zone;
a blade adjacent the cutting zone;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a retraction system associated with the detection system to push the blade
away from the cutting
zone upon detection of the dangerous condition.
Section 4: Spring-Biased Brake System
As discussed above, safety system 18 includes a brake mechanism 28 that is
adapted to stop the
cutting tool, thereby preventing or reducing injury to the user. As also
discussed previously, brake
mechanism may include at least one pawl 60 adapted to engage the cutting tool
to stop the rotation
thereof. Illustrative examples of suitable pawls are described in Section 5
below. For purposes of the
following discussion, cutting tool 14 will be described in the context of a
blade 40, such as on a table
saw, miter saw, circular saw or the like. It should be understood that blade
40 may include single blades,
such as plywood or carbide-tipped blades, or an assembly of several blades,
such as a dado blade.
As further discussed, pawl 60 is urged from its cocked, or restrained,
position toward blade 40 or
other cutting tool by biasing mechanism 30. In Fig. 2, biasing mechanism 30
includes a spring 66. From
its compressed position shown in Fig. 2, spring 66 biases the pawl to move
into engagement with blade
40. In Fig. 2, a restraining mechanism 32 is shown restraining pawl 60 from
moving toward the blade
under the biasing force exerted by spring 66. However, upon release of
restraining mechanism 32, the
pawl is no longer retained in its cocked position. As such, the pawl moves
quickly into engagement with
the blade under the force exerted by spring 66, such as shown in Fig. 41. An
example of how restraining
mechanism 32 may release the pawl is when a sufficiently high current is
passed through fusible member
70. Other suitable release and restraining mechanisms are described in more
detail below in Section 6.
In Fig. 2, the particular embodiment of spring 66 shown is a coiled
compression spring. As used
herein, spring 66 will be used to refer to any suitable spring generally, such
as any of the particular types
of springs discussed herein or other suitable spring mechanisms known in the
art. Particular types of
springs are referred to herein with particular reference numbers, such as
coiled compression spring 402.
In Fig. 2, as well as in Figs. 41-59, various embodiments of spring-biased
brake mechanisms are shown
and described and include various elements, subelements and possible
variations. It should be
understood that spring-biased brake mechanisms may include any one or more of
these elements,
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subelements and variations, regardless of whether those elements, subelements
are variations are shown
in the same or different figures or descriptions.
The speed at which the pawl will engage and stop the blade is dependent upon
the force exerted
upon pawl 60 by the spring. Therefore, the more force the spring exerts upon
the pawl, the faster the
pawl will travel the distance from its restrained position to the blade. In
experiments, springs that exert
forces in the range of 10 pounds to 500 pounds upon the pawl have proven
effective, with springs that
exert forces in the range of 50 and 200 pounds being preferred, and a- 100-
pound force proving
particularly effective. However, it should be remembered that the restraining
mechanism not only must
counteract the force exerted by the spring, but also must be able to quickly
release the pawl from its
cocked position. Therefore, there may be a tradeoff between increasing the
spring force and increasing
the complexity, strength and cost of the restraining mechanism to be able to
restrain the increase in spring
force. Also, any mechanical advantage from the placement and associated
structure, if any, coupling the
spring to the pawl should be taken into account.
Brake mechanisms 28 utilizing other springs 66 are shown in Figs. 42-44. In
Fig. 42, spring 66
takes the form of a leaf spring 404, which has base portion 406 and a pawl-
engaging portion 408 adapted
to engage and urge pawl 60 toward blade 40. Base portion 406 is secured to a
suitable mounting
assembly 410. Mounting assembly 410 may be any suitable structure that
supports the base portion of
the leaf spring to bias the pawl-engaging portion 408 toward the pawl. As
shown, leaf spring 404 is a
cantilevered leaf spring. Another example of a suitable mounting assembly 410
is shown in Fig. 43, in
which the mounting assembly includes a plurality of spaced-apart supports 411.
In Fig. 44, a torsion spring 412 is utilized to bias pawl 60 into engagement
with blade 40. Spring
412 includes a fixed end 414, a biasing end 416 adapted to engage pawl 60, and
a coiled portion 418
intermediate the ends. As shown, torsion spring 412 is mounted on the same pin
or axle 420 that pawl 60
is mounted upon. It will be appreciated that spring 412 may be interposed
between the axle and the pawl,
mounted on the axle adjacent or spaced-apart from the pawl, or mounted on
structure other than axle 420.
In Fig. 45, an extension spring 422 is shown. Unlike a compression spring that
resists
compressive forces, extension spring 422 resists being elongated from its
resting, or zero load, position.
Therefore, instead of pushing or urging pawl 60 toward the blade by pushing
upon the pawl, extension
spring 422 pulls the pawl toward the blade or other cutting tool. As shown,
extension spring 422
includes a biasing end portion 424 coupled to the pawl and a fixed end portion
426 coupled to a suitable
mounting assembly 410 generally toward the blade relative to the biasing end
portion. The mounting
assembly to which fixed end portion 426 is coupled may include a linkage, or
mount, 428 that couples
the end portion to the mounting assembly. Similarly, biased end portion 426
may be coupled to the pawl
or other structure that moves with the pawl by a linkage or mount 430.
Mounting assembly 410 may
include any suitable structure able to support fixed end portion 426 without
interfering with the operation
of operative structure 12. For example, it may be mounted adjacent blade 40,
coupled to the blade's
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arbor, mounted on structure that moves with the blade as the blade is tilted,
raised or lowered, etc.
Alternatively, extension spring 422 may act upon a portion of the pawl, or
linkage coupled thereto, that is
on the other end of the pawl's pivot axis than the blade-engaging portion of
the pawl. This configuration
is illustrated in dashed lines in Fig. 45. This configuration may be preferred
because mounting assembly
410 is spaced further away from the blade, and may be more easily positioned.
Although a single spring 66 is shown in Figs. 2 and 41-45, it should be
understood that brake
mechanism 28 may include more than one spring. For example, in the
illustrative embodiment shown in
Fig. 45, a pair of extension springs 422 may be used, such as shown in Fig.
46. When two or more
springs are used, they may be of similar or different types and strengths.
In Figs. 2 and 41-46, springs 66 are shown directly engaging pawls 60. It
should be understood
that the springs may alternatively engage other structure in communication
with pawl 60. For example,
springs 66 may engage one or more linkages through which the spring's biasing
force is passed to the
pawl. In such a configuration, restraining mechanism 32 may restrain any
suitable portion of the biasing
mechanism and pawl assembly to prevent the pawl from being moved into
engagement with the blade or
other cutting tool. For example, in the context of a restraining mechanism
that includes a fusible member
70, the fusible member may be coupled to pawl 60, spring 66, or the one or
more linkages
interconnecting the spring and pawl.
An example of a brake mechanism 28 in which spring 66 directly engages a
linkage instead of
pawl 60 is shown in Fig. 47 in the context of a brake mechanism having a pair
of pawls 60 adapted to
engage a blade 40. As shown, pawls 60 include blade-engaging portions 434
adapted to engage blade 40.
Pawls 60 are pivotal about axles or pins 436 and include distal portions 438
to which linkages 440 are
coupled. Linkages 440 are further coupled to a spring-engaging linkage 442,
which as shown, includes
an end 444 adapted to be moved toward blade 40, thereby drawing the blade-
engaging portions of the
pawls into contact with the blade. In Fig. 47, a compression spring 402 is
shown engaging linkage 442,
however, any of the springs described herein could be used.
Springs 66 may also exert a biasing force upon an engagement mechanism instead
of pawl 60. In
such an embodiment, the force of the spring is not applied to the pawl unless
restraining mechanism 32
releases the engagement mechanism or biasing mechanism to urge the pawl into
engagement the blade or
cutting tool of machine 10. An advantage of such a brake mechanism is that the
biasing mechanism is
not exerting force upon the pawl until the pawl is urged into contact with
blade 40. This may, but does
not necessarily, enable pawl 60 to be selectively removed and replaced from
the brake mechanism
without disabling biasing mechanism 30.
Additionally, or alternatively, biasing mechanism 30 may be self-contained as
a module or
cartridge that can be selectively removed and replaced from the rest of the
brake mechanism when the
fusible member or other portion of restraining mechanism 32 that counteracts
the force of spring 66 is
secured between portions of this module.
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An example of a brake mechanism with an engagement mechanism 446 is shown in
Fig. 48. As
shown, spring 66 acts upon engagement mechanism 446, which is depicted to
include a pivotal plate 450.
Plate 450 selectively prevents the spring's biasing force from being exerted
upon pawl 60. As shown,
restraining mechanism 32, such as fusible member 70, prevents plate 450 from
pivoting about its axle
452 under the biasing force of spring 66. As a result, the pawl is not urged
toward the blade. Module or
cartridge 448 is shown schematically in dashed lines, and is a possible rather
than necessary element of
brake mechanism 28. Module 448 typically will be mounted upon a suitable
support or receiver in the
machine, and may also include a connection with a suitable mechanism for
releasing restraining
mechanism 32. For example, contact mount 72 may be electrically connected to a
portion of the release
mechanism that does not form part of the replaceable module.
A variation of this brake mechanism is shown in Fig. 49, in which engagement
mechanism 446
takes the form of a slidable member 454 that is adapted to translate, or
slide, along tracks 456 toward and
away from blade 40. As shown, fusible member 70 restrains the slidable member
454 from moving
toward the blade, thereby preventing the spring from urging pawl 60 into
contact with blade 40. Also
shown in Fig. 49, is a variation of this brake mechanism, in which fusible
member 70 extends across the
travel path of slidable member 454 to prevent member 454 from moving under the
force exerted by
spring 66. In fact, fusible member 70 may itself form engagement mechanism
446, such as shown in
Fig. 50, where the fusible member extends across the path of spring 66,
thereby preventing the spring
from urging pawl 60 into the blade or other cutting tool.
The brake mechanisms shown in Figs. 47-49 may also be understood as including
biasing
mechanisms 30 with compound release mechanisms because there is more than one
step for the brake
mechanism to be actuated and pawl 60 to engage the blade or other cutting
tool. Unlike the brake
mechanisms shown in Figs. 41-46, in which the release of restraining mechanism
32 was all that was
required for spring 66 to urge pawl 60 into the blade or other cutting tool,
the brake mechanisms shown
in Figs. 47-49 utilize a compound release to engage blade 40 with pawl 60. For
example, the release of
restraining mechanism 32 may free a portion of biasing mechanism 30 to move,
such as to engage
engagement mechanism 446 or a linkage, which in turn transfers this force to
pawl 60.
In Fig. 51, another example of a brake mechanism 28 with a compound release,
or compound
release mechanism, is shown. In Fig. 51, an illustrative embodiment of a self-
contained actuator
assembly is shown. As shown, spring 66 is housed in a shell 458 with an open
end 460 through which
the spring, or a suitable linkage coupled to the spring, may extend upon
release of restraining mechanism
32. In the illustrative embodiment shown in Fig. 51, end 460 is at least
partially covered by a spanning
member 462 positioned between the spring and pawl 60. Member 462 does not need
to completely close
end 460, however, it should prevent spring 60 from passing through end 460 and
engaging pawl 60.
Fusible member 70, or another suitable embodiment of restraining mechanism 32,
is coupled to member
462 and prevents spring 66 from urging the spanning member into contact with
pawl 60. As shown,
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member 70 passes through shell 458, and in the illustrated embodiment, spring
66. It should be
understood that shell 458 may be used with embodiments of brake mechanism 28
that do not include a
compound release, in which case pawl 60 would typically abut the open end of
the shell.
Other exemplary embodiments of self-contained actuator assemblies are shown in
Figs. 52 and
53, where restraining mechanism 32 is releasably coupled to a lever arm 464
that in turn is coupled to an
end portion 466 of a carrier 468. Lever, or pivot, arm 464 pivots about a
pivot axis defined by a
projecting portion 465 on shell 458. It should be remembered that arm 464,
carrier 468 and shell 458
(including portion 465) must be sufficiently strong to withstand the force of
spring 66. End portion 466
of carrier 468 should be mounted on arm 464 so that it will release relatively
immediately upon release of
restraining mechanism 32 and initial pivoting of arm 464 about portion 465.
Alternatively, arm 464
should be able to pivot without obstruction until pawl 60 is fully engaged
with blade 40 so that the pivot
arm does not impede the motion of pawl 60, and thereby increase the time
required to stop blade 40. In
such a configuration where arm 464 pivots without restricting the motion of
the pawl, arm 464 does not
need to release from carrier 468, and instead these portions may remain
coupled together.
Carrier 468 includes an elongate support 470 that extends through shell 458
and further includes
a pawl-receiving portion 472 that is adapted to releasably receive pawl 60,
thereby allowing the pawl to
be selectively removed and replaced without dismantling or otherwise
disassembling the rest of brake
mechanism 28. As shown, pawl-receiving portion 472 also forms a spanning
member in that it prevents
the spring from urging the pawl into engagement with blade 40. In Figs. 52 and
53, portion 472 and pawl
60 are shown having complimentary configurations so that the pawl may be
coupled to the pawl-
receiving portion without requiring additional securing mechanisms. In the
embodiment shown, the pawl
may be either slid onto portion 472 from an end, or alternatively by briefly
deflecting portion 472
outwardly as the pawl is inserted into its mounted position. It will be
appreciated, however, that
additional securing mechanisms may be used, such as screws, pins, and other
releasable fasteners.
Because neither spring 66 nor fusible member 70 act directly upon the pawl or
pawl-receiving portion,
the coupling between these portions does not have to be strong. As a further
variation, pawl 60 may be
fixedly secured to, or even integrally formed with, carrier 468, or at least
the pawl-engaging portion
thereof.
A variation of a self-contained actuator is shown in Fig. 54, in which the
length of carrier 468 is
selectively adjustable, thereby allowing the relative positioning of the pawl
relative to blade 40 to also be
adjustable. As shown, support 470 includes a threaded portion 474 that is
threadingly received into pawl-
receiving portion 472. The length of carrier 468 may be adjusted by rotating
support 470, such as via a
user-manipulable portion 476, to increase or decrease the extent to which
portion 474 is received into
pawl-receiving portion 472. In Fig. 54, pawl-receiving portion 472 is also
shown including key structure
478 that prevents pawl 60 from being installed into the pawl-receiving portion
other than in a position
defined by key structure 478.
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Another embodiment of a spring-biased brake mechanism is shown in Fig. 55. As
shown, lever
arm 464 includes an end portion 480 that couples to shell 458 proximate open
end 460. In the
embodiment shown, end portion 480 is received into a notch 481 in the shell,
and includes a shoulder 482
about which the arm pivots upon release of restraining mechanism 32.
Alternatively, shell 458 may
include a ledge or projection upon which arm 464 is seated. Preferably, at
least an end region 483 of
elongate support 470 generally conforms to the inner diameter of spring 66 to
resist shifting or tilting of
the carrier when in the restrained position shown in Fig. 55. -
As shown, support 470 includes an edge 471 that extends generally parallel and
against spring
66, with a generally opposed edge 473 tapering from pawl-receiving portion 472
toward end portion 466.
Also shown in Fig. 55 is another example of a pawl-engaging portion 472 with a
key structure 478. Edge
471 is on the side of support 470 distal pivot arm 464 to stabilize the
carrier during installation and while
in the restrained position. Edge 473 is on the side of support 470 distal the
lever arm 464 to allow the
support to tilt as it is urged from shell 458 upon release of restraining
mechanism 32. This configuration
of carrier is an example of a carrier that may be integrally formed, or
monolithic, with pawl 60.
In the brake mechanisms shown in Figs. 52-55, the portion of fusible member 70
not coupled to
pivot arm 464 may be secured to any suitable supporting structure to allow the
fusible member to
counteract, the force of spring 66. This supporting structure may form part of
the brake mechanism
shown in Figs. 52-55, such as securing the fusible member to shell 458 or pawl-
receiving portion 472. In
such a configuration, the portions of the brake, biasing and restraining
mechanisms shown in Figs. 52-55
form a self-contained module or self-contained actuator.
In Fig. 56, an embodiment of a shell and pivot arm assembly is shown in which
the distance
between the pivot axis 484 of arm 464 and the region upon which arm 464
supports carrier 468 is
reduced from the embodiments shown in Figs. 42-54. As shown, arm 464 is
pivotally coupled to shell
458 by a pair of mounts 485 and includes a carrier-receiving portion 486. In
the embodiment shown in
Fig. 56, arm 464 may have a generally planar configuration that allows the arm
to extend against a
portion of the shell's end 487. Upon release of the restraining mechanism, arm
464 pivots relative to
shell 458 and portion 486 pivots into the shell and releases the carrier to
move under the force of spring
66. As shown, end 487 of shell 484 is sufficiently open to permit portion 486
to pivot into the shell and
release carrier 468. As shown, end 487 is also sufficiently obstructed to
prevent spring 66 from passing
therethrough. Also illustrated in Fig. 56 is an embodiment of support 470 that
generally conforms to the
inner dimension of spring 66, thereby supporting carrier 468 against axial
tilting within the shell as the
carrier passes through the shell. Another suitable configuration for support
470 is shown in dashed lines
in Fig. 56.
In Figs. 57 and 58, another example of a spring-biased brake mechanism with a
lever arm 464
that releases from open end 460 of shell 458 is shown. As shown, arm 464 is
pivotally coupled to shell
458 by pins 488 and includes a pair of catches 489 that engage a spanning
member 462. As shown,
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CA 02762156 2011-12-09
spanning member 462 includes a cover 490 that covers open end 460 of shell 458
and includes
projections 491 that are engaged by catches 489. Alternatively, spanning
member 462 may include any
other suitable configuration sufficient to prevent spring 66 from passing
through, or urging- another
member through, end 460 prior to release of restraining mechanism 32.
Preferably, catches 489 are
shaped to release spanning member 462 as arm 464 begins to pivot upon release
of restraining
mechanism 32.
In Fig. 59, another example of a spring-biased brake mechanism is shown. As
shown, lever arm
464 and shell 458 are adapted to facilitate more uniform positioning of
carrier 468, and thereby pawl 60,
as arm 464 is secured in a cocked, or restrained, position by restraining
mechanism 32, such as fusible
member 70. Prior to attachment of fusible member 70, lever arm 464 is pivoted
about edge 492 of shell
458 as the arm is pivoted to the position shown in solid lines in Fig. 59. In
this interval, there is a
mechanical advantage achieved because the distance 493 between edge 492 and
the proximate edge 494
of carrier 468 is much less than the distance 495 between edge 492 and fusible
member 70. However, to
continue pivoting arm 464 downward, this mechanical advantage is lost because
the fulcrum about which
the arm is pivoted changes, as reflected by distances 493' and 495'. As shown,
arm 464 now pivots
about the edge 496 of extension 498. The corresponding amount of force
required to pivot arm 464 may
be used as an indicator of when arm 464 is positioned properly, at which point
fusible member may be
attached. Of course, if fusible member is a preformed member of fixed length,
then precise positioning
of the lever arm 464 and pawl 60 are achieved simply by the attachment of the
fusible member.
It will be appreciated that the spring-biased brake mechanism described above
may be
implemented with many variations. For example, the spring-biased mechanisms
disclosed herein may be
used to drive the retraction of blade 40 on a table saw, miter saw or other
machine, such as described in
Section 3 above and Sections 13 and 14 below.
The brake systems and methods may be described as set forth in the following
numbered
paragraphs. These paragraphs are intended as illustrative, and are not
intended to limit the disclosure or
claims in any way. Changes and modifications may be made to the following
descriptions without
departing from the scope of the disclosure.
4.1 A woodworking machine comprising:
a working portion;
a detection system adapted to detect a dangerous condition between a person
and the working
portion; and
a reaction system associated with the detection system to cause a
predetermined action to take
place relative to the working portion upon detection of the dangerous
condition, where the reaction
system includes stored mechanical energy to cause the predetermined action to
take place.
4.1.1 The woodworking machine of paragraph 4.1 where the reaction system
includes a spring
as the repository of the stored mechanical energy.
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4.1.2 The woodworking machine of paragraph 4.1 where the reaction system
includes a brake
and a spring to cause the brake to engage the working portion.
4.2 A woodworking machine comprising:
a cutter;
a detection system adapted to detect contact between a person and the cutter;
a brake pawl to stop the cutter upon the detection by the detection system of
contact between the
person and the cutter; and
stored mechanical energy to cause the brake pawl to engage the cutter.
4.2.1 The woodworking machine of paragraph 4.2 where the stored mechanical
energy is a
spring.
4.2.2 The woodworking machine of paragraph 4.2.1 where the spring pushes the
brake pawl
into contact with the cutter.
4.2.3 The woodworking machine of paragraph 4.2 where stored mechanical energy
is in a self-
contained cartridge.
4.3 A woodworking machine comprising:
a working portion;
a detection system adapted to detect a dangerous condition between a person
and the working
portion; and
a brake system adapted to engage and brake the working portion upon detection
by the detection
system of the dangerous condition, where the brake system includes a brake
pawl and a spring module
adapted to move the brake pawl into engagement with the working portion.
4.4 A brake cartridge for a woodworking machine, the cartridge comprising:
a housing;
a brake pawl in the housing; and
a spring module in the housing adapted selectively to move the brake pawl,
where the biasing
module is self-contained.
4.4.1 The brake cartridge of paragraph 4.4 where the spring module includes a
coil spring held
in compression by a mechanism.
Section 5: Brake Mechanism
As described above, safety system 18 includes a brake mechanism 28 that is
adapted to stop the
cutting tool, thereby preventing or reducing injury to the user. As also
discussed previously, brake
mechanism may include at least one pawl 60 adapted to engage the cutting tool
to stop the rotation
thereof. For purposes of the following discussion, cutting tool 14 will be
described in the context of a
blade 40, such as on a table saw, miter saw, circular saw or the like. It
should be understood that blade
40 may include single blades, such as plywood or carbide-tipped blades, or an
assembly of several
blades, such as a dado blade.
CA 02762156 2011-12-09
As discussed, pawl 60 may be made of any suitable material that is capable of
quickly stopping
the blade or other cutting tool within the desired time increment, such as
less than 5 milliseconds, and
preferably, 3 milliseconds or less. The above examples of thermoplastic and
metallic materials have
proven effective, although other materials may be used so long as they are
able to stop the blade within
the desired time increment. Preferably, the pawl is formed of a material that
does not damage the
machine, and even more preferably, the pawl is formed of a material that does
not damage the cutting
tool. The pawl may be formed by any suitable method, such as by cutting sheets
of the desired material
to size or by molding. Similarly, the pawls may be annealed to increase their
strength.
It should be understood that the heavier the pawl, the more force it will take
to urge the pawl into
contact with the blade or other cutting tool within the selected time
increment and the more restraining
force that restraining mechanism 32 will need to exert to counteract the
biasing mechanism. On the other
hand, the pawl must have sufficient mass and strength to withstand the forces
exerted upon the pawl by
the blade. It should also be understood that the longer it takes for pawl 60
to engage the blade after
detection of a dangerous, or triggering, condition by detection subsystem 22,
the longer the blade will
. rotate and potentially cut the user's hand or other body part. Therefore, it
is preferred that this time be
minimized, such as by decreasing the distance pawl 60 must travel to engage
the blade and increasing the
speed at which the pawl moves to travel this distance. The speed at which the
pawl travels is largely
dependent upon the weight of the pawl, the force with which biasing mechanism
30 urges the pawl
toward the blade upon release of restraining mechanism 32, and any friction in
the mechanism.
There is not a specific pawl size, geometry or weight that is required to be
suitable for use to stop
the blade or other cutting tool. Instead, the size, geometry and weight may
vary, depending upon such
factors as the particular type of machine and cutting mechanism with which the
pawl is used, the pawl
material or combinations of materials, the corresponding structure of biasing
mechanism 30 and
restraining mechanism 32, etc. As such, the following discussion of materials,
sizes and geometries are
meant to provide illustrative examples of some suitable materials, geometries
and sizes. Similarly, pawls
may be formed with any combination of one or more of the subsequently
discussed elements,
subelements and possible variations, regardless of whether the elements,
subelements and possible
variations are shown together in the same figure.
The thickness of pawl 60 may vary. Thicknesses in the range of approximately
1/2 inch and
approximately 1 inch have proven effective, although thicknesses outside of
this range may be used so
long as the pawl may reliably stop the blade. When thicker blades, such as
dado blades are used, the
pawl is more likely to have a thickness greater than 1 inch.
Pawl 60 engages the blade to quickly stop the rotation of the blade. Pawl 60
may engage the
blade in several different configurations, such as engaging the side of the
blade or the teeth of the blade.
As shown in Fig. 60, pawl 60 is pivotally mounted on an axle 502 that extends
through a bore 504 in the
pawl, and pawl 60 is adapted to pivot into the teeth 506 of blade 40 under the
influence of biasing
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mechanism 30, such as spring 66. It will be appreciated that the pivotal pawls
described herein may
alternatively pivot with an axle upon which the pawl is secured, as opposed to
pivoting about the axle.
Other suitable biasing mechanisms are described above in Section 4.
Preferably, pawl 60 is adapted to be
self-locking, i.e., drawn into tighter engagement with the teeth of blade 40
due to the relative geometry of
the blade and pawl as they are drawn together. For example, when blade 40 is
spinning in the indicated
direction in Fig. 60, the blade will draw the pawl into tighter engagement
with the blade when the blade
contacts the pawl.
The spacing from pawl 60 to blade 40 when the pawl is in its restrained, or
cocked, position may
vary. For example, this spacing may vary depending on the configuration of the
particular cutting tool,
the detection system, and/or the brake system. Preferably, this distance is
minimized to reduce the time
required for the pawl to travel across this distance and engage the blade. It
has been found that a space of
approximately 1/32-inch to '/4-inch between the pawl and blade provides
suitable results. A spacing of
approximately 1/8-inch has proven particularly effective, although larger and
smaller distances may be
used. Because many cutting tools such as saw blades do not have precisely
uniform dimensions, it may
be necessary to position the pawl sufficiently away from the blade to account
for variations or
irregularities in a particular blade, such as described in Section 8 below.
Also it may be necessary to
adjust the position of the pawl whenever a blade is replaced to account for
variations between particular
blades. For example, for circular saw blades having a nominal diameters of 10-
inches and nominal
thicknesses of 0.125-inch, actual blades from various manufacturers or for
different applications may
have diameters that range between 9.5-inches and 10.5-inches and thicknesses
that range between 0.075-
inch and 0.15-inch.
In the illustrative embodiment of pawl 60 shown in Fig. 60, it can be seen
that pawl 60 includes a
body 508 with a contact surface 510 that is adapted to engage blade 40. Pawl
60 also includes an
engagement member 512 that is adapted to be engaged by biasing mechanism 30.
As shown engagement
member 512 forms part of the face 514 of the pawl that faces generally away
from the cutting tool.
Engagement member 512 may also include a recess into or protrusion from the
body of the pawl. In the
mounting position shown in Fig. 60, pawl 60 pivots into the blade upon release
of restraining mechanism
32, such as when the safety system sends a current through fusible member 70.
When the pawl contacts
the blade, the contact surface extends generally tangential to the blade, and
the teeth of the blade embed
into the pawl.
Another illustrative example of pawl 60 is shown in Fig. 61. As shown, the
pawl is somewhat
smaller than the pawl shown in Fig. 60. An advantage of a smaller pawl is that
it will be lighter than a
larger pawl constructed from the same material, and therefore it will not
require as great of spring force
to urge the pawl into the blade in a selected time interval as a heavier pawl.
On the other hand, a smaller
pawl will tend to, but not necessarily, have a smaller contact surface 510. In
Fig. 61, the pawl includes a
blade-engaging shoulder 514 that is adapted to engage the blade before the
contact surface, or at least a
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substantial portion of the contact surface, engages the blade. Shoulder 514
may include a protrusion 516
that extends from the surface 518 of the pawl generally facing the blade.
Shoulder 514 and/or protrusion
516 engage the blade prior to the contact surface of the pawl, and this
contact quickly pivots the contact
surface of the pawl into engagement with the blade. In essence, the shoulder
or protrusion reduce the
time and/or spring force required to quickly move the pawl into a position to
stop the blade by using the
blade momentum, transferred by contact with the shoulder, to draw the pawl
into the blade. Also shown
in Fig. 61 is another embodiment of engagement member 512, which as shown
includes a collar 520
extending from surface 514 and into which a portion of spring is received.
Collar 520 has an inner
diameter that is greater than the diameter of the portion of the spring
received therein. Collar 520
facilitates the positioning of the spring during assembly, or cocking, of the
brake mechanism.
Another illustrative example of a suitable pawl 60 is shown in Fig. 62. As
shown, the pawl is
somewhat larger than the previously illustrated pawls and includes a contact
surface 510 that generally
conforms to the outer diameter of the blade. Also shown in Fig. 62 is a
mounting assembly 522 for
restraining mechanism 32. As shown, mounting assembly 522 includes an aperture
524 through which a
portion of the restraining mechanism, such as a portion of fusible member 70,
extends. Fusible member
70 may also be described as extending around a portion 526 of the pawl. Other
suitable fusible members
and restraining mechanisms are described in more detail below in Section 6.
To increase the gripping action of the pawls on the blade, the contact surface
510 of the pawls
may be coated with a performance-enhancing material 527, such as shown in Fig.
63. An example of a
performance-enhancing material is a relatively high-friction material such as
rubber or a material that
"tangles," or snares, in the teeth of the blade or other cutting tool, such as
Kevlar cloth or metal mesh.
Alternatively, the pawls may be constructed of a harder material than the
blade and have a ridged surface
to "bite" into the blade. Alternatively, or additionally, the pawl may be
configured with grip structure
529 such as coatings of high-friction material, grooves, notches, holes,
protuberances, etc., to further
increase the gripping action of the pawls.
Pawl 60 may include one or more removed regions. These regions may take any
suitable form,
such as depressions that extend partially through the pawl or bores or other
apertures that extend
completely through the pawl. An example of a pawl showing plural removed
regions 528 in the form of
depressions 530 is shown in Fig. 64. The removed regions reduce the overall
weight of the pawl, thereby
decreasing the relative force that biasing mechanism 30 needs to exert on the
pawl to move the pawl into
contact with the blade within a selected time interval, as compared to a
similar pawl of greater weight.
Depressions, or recesses, 530 may also improve the grip of the pawl on the
teeth of the blade by allowing
the teeth to bite more deeply into the pawl.
An example of another embodiment of engagement member 514 is also shown in
Fig. 64 in the
form of a depression 532 that extends into the body 508 of the pawl and into
which a portion of spring 66
extends. Depression 532 may be laterally open, or may include sidewalls 534,
such as indicated in
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dashed lines. Also shown in Fig. 64 is a mount 535 adapted to be coupled to
biasing mechanism 30. As
shown, mount 535 takes the form of a projection around which a portion of a
coil spring (such as spring
66 shown in Fig. 61) extends. It should be understood that mount 535 may be
used independent of
depression 532 and/or side walls 534. The pawl shown in Fig. 64 also shows
another suitable
embodiment of a mounting assembly 522 for restraining mechanism 32. As shown,
the mounting
assembly includes a mount 536 for a linkage 538, which is coupled to a fusible
member that is not
physically in contact with pawl 60.
The pawl shown in Fig. 64 may also be described as having a body 508 with a
blade-engaging
portion 540 and at least one region of reduced thickness compared to the blade-
engaging portion. For
example, the previously described depressions 530 have a reduced thickness
compared to blade-engaging
portion 540. The increased thickness of the blade-engaging portion provides
additional strength to that
portion of the pawl, while the reduced-thickness portions reduce the overall
mass of the pawl. Pawl 60
may also be described as including one or more ribs, or supports. 542
extending generally between bore
504 and blade engaging portion 540 to strengthen the pawl.
An example of a pawl having plural removed regions 522 in the form of
apertures 544 is shown
in Fig. 65. Apertures 544 reduce the comparative weight of the pawl compared
to a similar pawl that
does not include apertures or other removed regions. Apertures 544 also
provide regions into which the
material forming pawl 60 may deform, or flow, into as the blade or other
cutting tool strikes the pawl.
Having these deformation regions reduces the stress to the pawl as it engages
the blade. It should be
understood that the size and positioning of the removed regions 522 discussed
herein are for purposes of
illustration and that these regions may be positioned in any suitable location
on the pawl in a variety of
shapes, sizes and configurations.
A variation of the pawl of Fig. 65 is shown in Fig. 66, in which the apertures
544 have been filled
with another material 546. It should be understood that some or all of the
apertures may be partially or
completely filled with material 546. For example, the body of pawl 60 may be
formed from one of the
previously described materials, with the apertures filled with another of the
previously described
materials or a material other than those described above. As a particular
example, the body of the pawl
may be formed from polycarbonate or ABS, with apertures 544 filled with
aluminum or another suitable
metal.
Another variation of the pawl of Fig. 65 is shown in Fig. 67. In Fig. 67, pawl
60 includes a
plurality of apertures 544 through which one or more wires 548 are passed. As
shown, a single wire 548
is looped through the apertures and also extends across a portion of contact
surface 510. Although
illustrated schematically with the number of wires or wire strands shown in
Fig. 67, there may preferably
be many strands of wire, such as in the range of approximately 20 and
approximately 500 strands. It
should be understood that a "strand" of wire is meant to refer to a length of
wire extending across the
pawl, such as transverse to the plane of the blade or other cutting tool,
regardless of whether the strand is
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connected to other strands or formed from the same unitary length of wire as
other strands. Alternatively,
the wire or wires could be threaded through one or more of the apertures
without extending across the
contact surface. An example of a suitable material for wire 546 is high
tensile strength stainless steel,
which is available in a variety of diameters. In experiments, diameters of
0.01 inch have proven
effective, but larger or smaller diameter wires 548, as well as wires formed
of other materials may be
used.
Other forms of composite pawls include pawls formed from two or more regions
of different
materials. An example of such a composite pawl 60 is shown in Fig. 68, in
which the body 508 of the
pawl includes a region 550 of material that is a different material than the
rest of the body and which
forms at least a portion of blade-engaging portion 540. It should be
understood that the region 550 may
have a variety of shapes, including layers of generally uniform thickness,
such as shown in solid lines in
Fig. 68, or less uniform shapes, such as layer 550' shown in dashed lines in
Fig. 68.
Pawl 60 may also be formed as composites of materials, such as by layers of
different materials
or by impregnating or embedding a particular material of construction with
another material to add or
enhance a desired property. For example, a thermoplastic material may include
a framework or
dispersion of fibers or other materials. An example of a pawl constructed of
such a composite is shown
in Fig. 69, in which the body of the pawl is formed of a core material 552
into which a filler material 554
is added. Filler material 554 may take the form of particulates, fibers, woven
fibers, pellets and the like.
Pawl 60 may also include a removable blade-engaging portion 540. This allows
the pawl to be
recharged for reuse after the pawl is used to stop blade 60 and the blade-
engaging portion is damaged by
the blade. It should be understood that "removable" means that the blade-
engaging portion may be
selectively removed and reattached to the rest of the pawl. An example of such
a pawl is shown in
Fig. 70, in which the pawl includes body 508 and removable blade-engaging
portion 540'. Portion 540'
may be formed of the same or a different material or combination of materials
as body 508. Blade-
engaging portion 540' may be attached to body 508 by any suitable attachment
mechanism 556, which is
only schematically illustrated in Fig. 70. Examples of suitable attachment
mechanisms 556 include
interlocking portions on the body and blade-engaging portion and/or mechanical
linkages coupled
between the body and blade-engaging portion.
In Fig. 71, pawl 60 includes a sheath, or cover, 558 that overlies at least
the blade-engaging
portion of the pawl. Sheath 558 is formed of a material that enhances the
pawl's ability to stop blade 40,
preferably without damaging the blade. For example, sheath 558 may be formed
of Kevlar cloth.
Similarly, such a material may be embedded into the thermoplastic or other
material forming pawl 60,
such as schematically illustrated in Fig. 69. Sheath 558 may extend completely
or partially around the
pawl, or alternatively may be partially embedded in the pawl, such as shown in
Fig. 72. Furthermore,
Kevlar cloth, or pieces thereof may be embedded into the thermoplastic or
other material forming the
CA 02762156 2011-12-09
pawl, such as discussed previously with respect to Fig. 69, regardless of
whether this material extends
across the blade-engaging portion of the pawl.
A variation of a pawl that includes sheath 558 is shown in Fig. 73. In Fig.
73, the body of the
pawl defines a frame 560 that includes spaced-apart side walls 562 defining a
channel 564 therebetween.
Sheath 558 extends across the channel and is positioned to engage and stop the
blade as the pawl is urged
into the blade.
When pawl 60 is mounted to pivot into engagement with a blade or other cutting
tool, the pawl
may include more than one pivot axis. An example of such a pawl is shown in
Figs. 74-76, in which the
pawl is mounted on a pair of pivot arms 566. As shown, pawl 60 has an elongate
contact surface 510 that
engages a large portion of the blade. Arms 566 may have the same or different
lengths, and can be
mounted to pivot anchors (not shown) positioned outside or inside the
perimeter of the blade. An
advantage of a pawl with an elongate contact surface is that the force exerted
by the pawl is distributed
across a larger portion of the blade, thereby allowing the blade to be stopped
more quickly. The longer
contact surface can also be used to reduce the chance of damage to the blade
because the braking force is
spread over more teeth.
In Fig. 74, arms 566 are mounted to suitable portions of machine 10 distal the
blade relative to
pawl 60, while in Fig. 75, the arms are mounted proximate the blade relative
to pawl 60. In Fig. 76, one
of the pivot arms extends distal the blade, while the other extends proximate
the blade relative to the
pawl. An advantage of pivot arms that extend toward, or proximately, the blade
relative to the pawl is
that the pawl cannot be pivoted to a point after which the pawl will pivot
away from the blade rather than
toward the blade. In the embodiment of pawl 60 shown in Fig. 75, for example,
the pawl will always be
drawn into tighter engagement with the blade when the blade is rotating in the
direction shown and
strikes the pawl.
It should be understood that the previously described axle 502 or other
structure to which the
pawls are mounted may be fixed relative to the housing of the machine. In
embodiments of the machine
in which the position of the blade is adjustable, the pawl is preferably
mounted to move with the blade as
the blade's position is adjusted. This latter arrangement ensures that the
pawl is maintained in a
predetermined position relative to the blade.
Alternatively, the pawl may be mounted on a portion of the machine that does
not adjust with the
blade, but in a mounting orientation suitable for use with the blade
regardless of the blade's mounting
position. An illustrative example of such a "stationary" pawl is shown in
Figs. 77 and 78. By
"stationary," it is meant that the position of the pawl does not move with the
blade as the relative position
of the saw is moved. However, upon actuation of the reaction subsystem, pawl
60 will still move into
engagement with the blade. Alternatively, with machines in which the blade may
raise and lower as well
as tilt, the pawl may be adapted to move with one adjustment, such as tilting
with the blade, but remain
fixed with the other, such as when the blade is raised or lowered.
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As shown in Figs. 77 and 78, pawl 60 is elongate and sized and shaped to
extend along the outer
perimeter 568 of blade 40 as the blade is adjusted vertically. Similarly the
width of pawl 200 is sized to
extend the breadth of the incline of blade 40. As shown in Figs. 77 and 78,
pawl 60 is mounted generally
parallel with the vertical axis of travel of the blade, and generally normal
to the axis of incline of the
blade. As a result, the spacing between the blade and contact surface 510
remains constant regardless of
the position or orientation of the blade.
The upper end portion of pawl 60 is pivotally attached to upper pivot arms 570
by pivot pins 572
that pass through one end of arms 570 into the sides of the pawl. The other
ends of pivot arms 570 are
pivotally attached to one or more mounts (not shown), by pivot pins 574. The
lower end portion of pawl
60 is pivotally attached to lower pivot arms 576 by pivot pins 578 that pass
through one end of arms 576
into the sides of the pawl. The lower pivot arms are pivotally attached to
mounts (not shown) by pivot
pins 580. Biasing mechanism 30, such as one or more springs 66, is attached to
the lower pivot arms on
the side of pivot pins 580 opposite pivot pins 577. Thus, pawl 60 is
configured to pivot toward or away
from blade 40. Upon release of restraining mechanism 32, such as fusible
member 70, the biasing
mechanism urges the upper ends of pivot arm 576 downward, thereby drawing the
lower end of the pivot
arms and the corresponding end portion of pawl 60 into engagement with the
blade.
Pivot arms 570 and 576 are sized and arranged such that pawl 60 cannot pivot
up past the blade
without striking the edge of the blade. When the pawl strikes the blade while
the blade is rotating, the
movement of the blade causes the pawl to continue pivoting upward until the
pawl is firmly wedged
between the blade and pivot arms, thereby stopping the blade. The contact
surface 510 of the pawl may
be textured, coated, etc., to enhance the gripping action between the pawl and
the blade.
Pawl 60 is biased upward to pivot toward the blade by biasing mechanism 30,
which for example
includes one or more springs 66 that are anchored to the saw frame or other
suitable mounting structure.
Thus, when the pawl is free to pivot, springs 66 drive the pawl quickly toward
the blade. Similar to the
exemplary embodiment described above, fusible member 70 is connected to the
pawl to hold it away
from the blade. The fusible member is sized to hold the pawl spaced slightly
away from the edge of the
blade. However, when a sufficient current is passed through the fusible member
the fusible member will
melt, causing the pawl to pivot toward the blade under the bias of mechanism
30.
It will be appreciated that many variations to the exemplary embodiment
depicted in Figs. 77 and
78 are possible. For example, the pawl may be configured to pivot toward the
blade solely due to
gravity. Alternatively, springs 66 may be compression springs which normally
hold the pawl away from
the blade until it is pivoted upward under the force of another spring, an
explosive charge, a solenoid, gas
pressure, etc. Further, the pawl may be mounted on the other side of the blade
to pivot downward into
the blade under the force of a spring, an explosive charge, a solenoid, gas
pressure, etc.
Another example of a suitable pawl 60 is shown in Fig. 79. As shown, pawl 60
includes a
rearward portion 582 facing generally away from contact surface 510. Portion
582 includes a plurality of
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race portions 584 that in cooperation with a corresponding plurality of race
portions 586 on a suitable
mounting structure 588 forming part of machine 12, define races 590 within
which rollers 592 are
housed. Toothed rollers 592 are rotatable within races 590 and direct the
translational movement of pawl
60 toward blade 40 when the blade strikes pawl 60. The rollers also reduce the
friction of moving the
pawl under braking load relative to a sliding surface. Preferably, pawl 60
includes guide pins 593 that
travel within tracks (not shown), which define the range of translational
positions of pawl 60 while
maintaining the rollers in contact with the races.
In Fig. 80, another illustrative embodiment of a brake mechanism 28 that
includes a pawl 60 that
moves via translation into engagement with the blade or other cutting tool is
shown. Pawl 60 includes a
contact surface that preferably, but does not necessarily, conform to the
outer diameter of blade 40. Pawl
60 is retained in its cocked, or restrained, position by restraining mechanism
32, which as shown,
includes one or more fusible members 70. Preferably, brake mechanism includes
guide structure 501 that
defines a track 503 along which the pawl travels as it is urged toward the
blade or other cutting tool by
biasing mechanism 30. An example of such a guide structure is shown in Fig.
80, in which the guide
structure includes a housing 505 into which the pawl is at least partially
received in its cocked, or
restrained, position, and from which the pawl at least partially projects upon
release of restraining
mechanism 32. Much like a piston moving within a cylinder, pawl 60 travels in
a translational path
defined by the inner dimensions of housing 505 under the urging of biasing
mechanism 30.
Other illustrative examples of brake mechanisms 28 with translational pawls
are shown in
Figs. 81 and 82. In Fig. 81, guide structure 501 includes two or more guide-
engaging members 507 that
project from pawl 60 to engage a corresponding number of guides 509. Guides
509 are spaced apart
from the pawl and define the translational path of the pawl. In Fig. 82, pawl
60 includes internal guide-
engaging members 507, such as one or more internal bores 511 extending
parallel to the translational
path of the pawl. A corresponding number of guides 509 extend at least
partially within the bores to
define the travel path of the pawl. In Figs. 80-82, pawls 60 are urged along a
translational path directly
into blade 40. It should be understood that the pawls and/or the guide
structure may be inclined at an
angle relative to the blade, such as to counteract the angular momentum of the
blade or to utilize the
braking force to draw the pawl more tightly against the blade.
Although the exemplary embodiments are described above in the context of a
single brake pawl
that engages the teeth of a blade, the brake system may incorporate a brake
mechanism with two or more
pawls that engage two or more locations on the perimeter of the blade to
decrease the stopping time
and/or spread the stopping forces. An example of such a brake mechanism is
shown in Fig. 83, in which
brake mechanism 28 includes two spaced-apart pawls 60 adapted to engage the
perimeter of blade 40.
Pawls 60 are only schematically illustrated in Fig. 83 and could include any
of the previously described
pawl or pawls incorporating one or more of the features, elements, subelements
and variations described
above. The pawls may be released from their cocked, or restrained, positions
by a common release
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mechanism, or each pawl may have its own release mechanism. When brake
mechanism 28 includes
plural pawls, it may be desirable to position the pawls on opposite sides of
the arbor about which the
blade rotates to reduce the load on the arbor when brake mechanism 28 is
actuated and pawls 60 engage
the blade.
When brake mechanism 28 includes plural pawls, the pawls may also be
constrained or
interconnected to act together. An example of such a brake mechanism is shown
in Fig. 84, in which the
brake mechanism includes a plurality of interconnected pawls 60. As shown,
each pawl 60 includes one
or more toothed regions 513 having a plurality of teeth 515. Regions 513 of
adjacent pawls 60 are
interconnected by toothed gears, or linkages, 517 that communicate the
rotation of one pawl to the other
pawls so that the pawls move as a unit. It should be understood that one or
more of the pawls or gears
are coupled to a suitable biasing mechanism and restraining mechanism to bias
the pawls into contact
with blade 40 and to selectively restrain the movement of the pawls until
safety system 18 actuates the
reaction subsystem. In a variation of the brake mechanism shown in Fig. 84,
gears 517 may be omitted,
in favor of links interconnecting the pawls.
As discussed, the pawl or pawls of brake mechanism 28 may contact any suitable
portion of
blade 40 or other cutting tool 14. In the illustrative embodiments shown in
Figs. 2 and 60-84, the pawls
were mounted to engage the teeth or outer perimeter of the blade. An example
of another suitable contact
portion of the blade is the side of the blade. Specifically, brake mechanism
28 may include two or more
pawls adapted to engage opposed sides of the blade. An example of such a brake
mechanism is
illustrated in Fig. 85. As shown, pawls 60 are pivotally mounted on either
side of blade 40. Each pawl
includes a blade-engaging portion 540 adjacent the blade, and a distal portion
519. The pawls are
pivotally mounted on pins 521 that pass through pivot apertures 523 in the
pawls intermediate the blade-
engaging portion and the distal portion. Lever arms 525 are coupled to distal
portions 519. Thus, when
the lever arms of each pawl are pivoted upward (as shown in Fig. 85), the
blade-engaging portions close
together. The pawls are mounted relative to the blade so that the contact
surfaces pivot toward the blade
in the direction of blade travel. Once the pawls contact and grip the blade,
they continue to pivot inward
pulled by the downward motion (as shown in Fig. 85) of the blade. As a result,
the blade is pinched more
and more tightly between the contact surfaces 510 of the pawls until the pawls
can close no further, at
which point the blade is stopped between the pawls.
To ensure that both pawls close together on the blade, a linkage 527 is
attached, at either end, to
lever arms 525. Linkage 527 is coupled to a biasing mechanism, not shown,
which urges the pawls into
contact with the blade, through force exerted through linkage 527 and lever
arms 525.
It will be appreciated that the dual-pawl system described above may be
implemented with many
variations. For example, the linkage may be driven upward by any of the other
actuating means described
above, including an explosive charge, solenoid, compressed gas, etc. As
another example, one or more
pawls may be positioned to contact only one side of the blade. Additionally,
the linkage may be omitted,
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and each pawl actuated by a separate spring, explosive charge, solenoid, etc.
Similarly, although a
circular blade 40 was used to illustrate one type of cutting tool for which
the brake system may be used, it
may also be used with other shapes of blades, such as blades used in jointers,
shapers and band saws.
For example, an alternative embodiment of brake mechanism 28 in the context of
a band saw 594
is depicted in Figs. 163 and 164. In this embodiment, brake mechanism 28
severs the blade upon receipt
of a contact detection signal. By severing the blade, the tension fit of the
blade around wheels 595 is
released, allowing the blade to be stopped or moved without stopping the
wheels.
As can best be seen in the detail view of Fig. 164, alternative brake
mechanism 28 includes an
explosive cable-or bolt-cutting device 596 positionable adjacent blade 40 to
sever the blade upon receipt
of a detection signal. Suitable cable cutting devices 596 are available from a
variety of sources, including
Cartridge Actuated Devices, Inc., of Fairfield, New Jersey. The size and
configuration of device 596 may
vary depending on such factors as the size and width of blade 40, the blade
material, blade speed, etc.
Typically, cutting device 596 will be positioned closely adjacent the
underside of the band saw table to
block the continued downward movement of the blade after it is severed. An
electronics unit 597 similar
to those described above is operatively coupled to device 596 to transmit an
activation signal to the
device once contact between the user's body and the blade is detected by the
electronics unit. Device 596
then severs the blade virtually instantaneously, thereby releasing the tension
fit of the blade around
wheels 595. Once severed, the blade substantially stops moving even though the
wheels continue to turn.
As described above, the safety stop may optionally be configured to shut off
the motor to band saw 594
as well as to sever the blade. Additionally, one or more pawls (not show) may
be configured to engage
and stop the blade at the same time device 596 severs the blade, thereby
ensuring the blade does not
continue to move after being severed.
The brake systems, components and methods may be described as set forth in the
following
numbered paragraphs. These paragraphs are intended as illustrative, and are
not intended to limit the
disclosure or claims in any way. Changes and modifications may be made to the
following descriptions
without departing from the scope of the disclosure.
5.1 A woodworking machine comprising:
a cutter adapted to cut a workpiece and including at least two cutting
surfaces;
a brake system adapted to stop the cutter, where the brake system includes a
thermoplastic pawl
adapted to engage the cutting surfaces on the cutter.
5.1.1 The brake system of paragraph 5.1, wherein the pawl is self locking
against the cutter
upon contact with the cutting surfaces.
5.1.2 The brake system of paragraph 5.1, wherein the pawl is pivotally mounted
to the
machine.
5.2 A brake system adapted to stop a circular saw blade with plural teeth
disposed around a
perimeter, comprising:
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a first brake pawl adapted to contact the teeth of the blade at a first
location on its perimeter;
a second brake pawl adapted to contact the teeth of the blade at a second
location on its perimeter
different from the first location; and
an actuation mechanism adapted to urge both pawls into the teeth of the blade
simultaneously.
5.3 A brake system adapted to stop a circular saw blade, comprising:
a brake pawl with a blade contacting region shaped to simultaneously engage a
region of the
circular saw blade including at least 30 degrees of the perimeter of the
blade; and
an actuation system adapted to selectively drive the brake pawl into the
blade.
5.4 A woodworking machine comprising:
a cutter adapted to cut a workpiece and including at least two cutting
surfaces;
a brake system adapted to stop the cutter, where the brake system includes a
pawl adapted to
engage the cutting surfaces on the cutter and constructed of two different
materials having different
physical properties.
5.4.1 The machine of paragraph 5.4, wherein at least one of the materials is a
thermoplastic.
5.4.2 The machine of paragraph 5.4, wherein at least one of the materials is a
metal.
5.5 A woodworking machine comprising:
a cutter adapted to cut a workpiece and including at least two cutting
surfaces;
a brake system adapted to stop the cutter, where the brake system includes a
metal pawl adapted
to engage the cutting surfaces on the cutter.
5.5.1 The machine of paragraph 5.5, wherein the pawl is formed primarily of
aluminum.
Section 6: Firing Subsystem
In many embodiments of safety system 18, a fusible member, such as member 70
shown in Fig.
2, will be used to restrain some element or action, such as to hold a brake or
pawl away from a blade, as
explained above. Such a fusible member may take different forms, but typically
is a wire that will melt
when a given amount of electrical current is passed through the wire, also as
explained above. Once the
wire melts, the brake or pawl is released to stop the blade.
When a pawl is used as a brake, the fusible member may be attached between the
pawl and an
anchor or mount, such as contact mount 72 shown in Fig. 2, to prevent the pawl
from moving into the
blade. In that embodiment, the pawl is biased by a spring toward the blade, so
the pawl constantly pulls
against the fusible member. Therefore, the fusible member should have a high
tensile strength to bear the
constant pull of the pawl and to prevent the fusible member from accidentally
breaking. Additionally, the
fusible member should have a high tensile strength so that the strength is
maximized relative to the heat
that is required to melt the member. Fusible members with high resistance are
also preferred because of
the more rapid heat build up for a given current. It will be appreciated that
the size of the fusible member
will depend, at least partially on the force required to restrain the spring.
In general, greater spring forces
are desirable to increase the speed and force with which the pawl contacts the
blade. Where more
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pressure is required, a larger diameter fusible member may be needed, thereby
requiring a larger amount
of current to melt the fusible member. A greater amount of current, in turn,
may require a firing system
with more expensive electronic components. Thus, a safety system using a
fusible member to release a
brake or pawl must consider factors such as the amount of force applied to the
fusible member and the
size of the fusible member.
In the arrangement of a pawl and a fusible member shown in Fig. 2 and
discussed above, spring
66 biases pawl 60 toward blade 40 with a specified force, and fusible member
70 is wire that has a tensile
strength sufficient hold the pawl against the force of the spring. For
example, the fusible member may be
a 0.010-inch nichrome wire or a steel strand, and the spring may have a spring
force of between
approximately 5 and 25 pounds.
In Fig. 2, the fusible member is generally less than about 1 to 3 inches in
length, and is wrapped
around contact mount 72. Contact mount 72 is often generally circular in cross-
section so that it does not
present any edges that would concentrate stress to a specific section of the
fusible member. Alternatively,
a contact mount may include an edge to focus stress at a desired section of
the fusible member. The
contact mount may take many forms. It may be a stud or projection around which
a fusible member is
wrapped, it may be a screw with a radial hole through which the fusible member
is threaded so that the
screw can be turned to wrap the fusible member around the screw, it may be
clamps, or it may be some
other structure.
In Fig. 2, mount 72 includes a break region or gap of about 0.010 to 0.5-inch
(or less) between
halves of the mount. Current flows from one half of the mount, through the
fusible member, to the other
half of the mount and then to ground. The short break region is beneficial to
focus the power to a small
region to help melt the fusible member. The two halves of the mount may be
thought of as two closely
spaced electrodes, where the electrodes also serve as mounts for the fusible
member. When electrodes
also act as mounts, they must be strong enough to support the load of the
fusible member.
Mounts to anchor the fusible member, alternatively, can be separate from the
electrodes, and the
electrodes may simply contact the fusible member. For example, in Fig. 2,
contact mount 72 may be an
anchor, and electrodes may be positioned against fusible member 70 between
mount 72 and pawl 60.
It will be appreciated that the fusible member can be arranged in many
alternative ways. As one
example, one loop of wire can be attached to a contact stud and the opposite
loop attached to a grounded
stud. If the middle of the wire is placed over the end of the spring adjacent
the pawl, the spring will be
released when the wire is melted. In this arrangement, the current to melt the
fusible member travels only
from the contact stud, through the fusible member and into the grounded stud.
In other embodiments, a wire with a relatively low tensile strength may be
used to hold a pawl
against a large spring force by looping the wire so that different portions of
the wire work together to
hold the pawl. For example, a wire may be looped in the configuration of the
letter "M" or "W", as
shown in Fig. 86. In this arrangement, fusible member 70 is fastened at one
end to anchor 600. From
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there the fusible member wraps around a first post 601 on one side of pawl 60,
then around mount 602,
then around a second post 603 on the opposite side of the pawl, after which
the fusible member is
fastened to second anchor 604. In this manner, the sections of the fusible
member between anchor 600
and post 601, between post 601 and mount 602, between mount 602 and post 603,
and between post 603
and anchor 604 act like four separate strands that together hold the pawl away
from the blade. Thus, a
fusible member with tensile load strength of 30 pounds may hold a pawl biased
toward the blade with a
force of up to 120 pounds. In Fig. 86, mount 602 is configured to pass a surge
of electrical current
through a portion of the fusible member to melt the member. The fusible member
then breaks apart at
mount 602 and releases the pawl. This embodiment allows for the use of a
fusible member with a
relatively small diameter that may be melted with less current.
In some embodiments a fusible member will be used to hold a two-stage linkage,
trap or
compound release. The linkage or compound release, in turn, would restrain
some action or hold some
element such as a pawl. By holding the linkage or compound release, the
fusible member effectively
restrains an action or holds an element. Using a linkage or a compound release
provides a mechanical
advantage that allows the system to use a fusible member with a smaller
diameter and lesser tensile
strength to hold forces up to hundreds of pounds or more. This may allow use
of a smaller fusible wire
that can be melted more quickly and/or with a smaller current surge. Various
linkages and compound
releases are described in more detail in Section 4 above.
The fusible member also may be formed from a wire overmolded with end caps or
crimp blocks
to establish a given length. Overmolding the ends of a wire with caps or crimp
blocks provides an
effective way to grip and hold the wire. Figure 87 shows three such fusible
members. First, a wire 605 is
doubled back, and both ends of the wire are secured in loop 606. Loop 606 is a
molded plastic element,
and wire 605 is crimped or kinked at its ends 607 to keep the wire from
breaking free of the loop. Loop
606 would typically be molded or pressed over the ends of the wire. Wire 605
may extend around
electrodes, and loop 606 may extend over a pin on a pawl or a pin in a
compound release.
The second fusible member shown in Fig. 87 is similar to the one just
described, except that it
has two loops, one at each end of the wire. As mentioned, the ends of the wire
are crimped or kinked to
secure the wire to the loops and to prevent the wire from being pulled away
from loops.
Another wire 608 is also shown in Fig. 87, having caps 609 molded over the
ends of the wire.
The caps may be used to secure the wire in some embodiments.
Fusible members like those shown in Fig. 87 would be advantageous in a system
employing
cartridge 82 because the cartridge could simply be reloaded with a new fusible
member after firing, and
the fusible member would fit in the cartridge because it is of a given length
and construction.
Of course, it will be understood by one of skill in the art that fusible
members may be configured
in numerous ways to hold a pawl or brake, and that the specific embodiments
described simply illustrate
possible ways. The fusible members themselves also may take different forms,
such as a wire or a foil
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sheet. In some embodiments, it may be desirable to form the fusible member
from a larger wire, sheet or
strip with a reduced waist section of small size/width to achieve a higher
current density at in the waist
section for more focused heating.
As explained above, the fusible member is connected to a firing system 76 that
produces a
sudden current surge to melt the fusible member in response to an output
signal from the contact
detection system. For the exemplary fusible member described above in
connection with Fig. 2,
approximately 20-100 Amps are required to ensure complete and rapid melting.
As will be appreciated
by those of skill in the art, there are many circuits suitable for supplying
this current surge.
One embodiment of firing system 76 is illustrated in Fig. 88. That exemplary
embodiment
includes one or more charge storage devices that are discharged through the
fusible member in response
to an output signal from the control subsystem. (The output signal from the
control subsystem is
dependant on detection of contact between the user and a blade, as explained
above.) The use of charge
storage devices obviates the need for a large current supply to melt the
fusible member. It will be
appreciated, however, that a current supply may be used instead of charge
storage devices. Alternatively,
other devices may be used to supply the necessary current, including a silicon-
controlled rectifier or triac
connected to a power supply line.
The firing system shown in Fig. 88 includes a pair of relatively high-current
transistors 610
coupled to pass the current stored in the storage devices to fusible member
70. Transistors 610 are
switched on by the output signal from control subsystem 26. As illustrated in
Fig. 88, the output signal
from control subsystem 26 is connected to the gates of transistors 610. Any
suitable transistors may be
used, such as IRFZ40 MOSFET transistors, which are well known in the art. The
transistors are
connected in parallel between charge storage devices 611 and fusible member
70. In the exemplary
embodiment, charge storage devices 611 are in the form of a 75,000 F
capacitor bank. A 100-ohm
resistor 612 connected to a 24-volt supply voltage establishes and maintains
the charge on the capacitor
bank. When the output of control subsystem 26 goes high, transistors 610 allow
the charge stored in the
capacitor bank to pass through the fusible member. The sudden release of the
charge stored in the
capacitor bank heats the fusible member to its melting point in approximately
1 to 5 ms. Alternatively,
one or more of the transistors may be replaced by other switching devices such
as SCR's. One advantage
of using stored charge to fuse the fusible member is that the firing system
does not rely on the capacity of
line power or the phase of the line voltage.
Fig. 89 shows an alternative embodiment of firing system 76. The alternative
firing circuit
includes fusible member 70 connected between a high voltage supply HV and an
SCR 613, such as an
NTE 5552 SCR. The gate terminal of the SCR is connected to control subsystem
26. Control subsystem
26 turns on SCR 613 by supplying approximately 40 mA of current, thereby
allowing the high voltage
supply HV to discharge to ground through fusible member 70. Once the SCR is
switched on, it will
continue to conduct as long as the current through fusible member 70 remains
above the holding current
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of approximately 40mA, even if the current to the gate terminal is removed.
Thus, the SCR will conduct
current through the fusible member until the fusible member is melted or the
high voltage source is
removed. The fact that the SCR stays on once triggered allows it to respond to
even a short pulse from
control system 26. It should be noted that a high voltage (HV) capacitor might
supply the high voltage
pulse. Use of a HV capacitor leads to a much higher current surge, and
therefore a faster melting of the
fusible member than is the case with a low voltage system. It will be
appreciated that the size of the HV
capacitor may be varied as required to supply the necessary current to melt
fusible member 70.
Figure 90 shows yet another embodiment of firing system 76. This embodiment
includes a
fusible member 70 connected between a 390 F capacitor, identified by reference
number 620, and a
TYN410 SCR, identified by reference number 621. In embodiments like the one
shown in Fig. 90, the
capacitor 620 may range in value from approximately 100 F to 5000 F. Capacitor
620 is connected
between a high voltage charging line 622 (from a buck-boost charger, for
example), which charges the
capacitor to approximately 180-200 volts, and ground. The gate terminal of the
SCR is connected to the
control subsystem at 623. A signal from the control subsystem at 623 turns on
SCR 621, allowing the
capacitor to discharge to ground through fusible member 70. In this
embodiment, the capacitor is
believed to provide a pulse of approximately 1000 to 1500 amps. As explained
above, once the SCR is
switched on, it will continue to conduct as long as the current through
fusible member 70 remains above
the holding current, so the SCR will conduct current through the fusible
member until the fusible member
is melted or the high voltage source is removed. Firing system 76 also
includes a lk resistor 624
connected between the gate of the SCR and ground to hold the signal at 623 to
ground until a signal from
the control subsystem draws it up so that the firing system is not triggered
by noise. A sense line 625 is
connected between SCR 621 and fusible member 70 so that the control system can
monitor the charge on
capacitor 620 to insure that the capacitor is charged and functioning.
Connecting sense line 625
downstream from fusible member 70 relative to capacitor 620 allows the control
system to check the
capacitor through the fusible member, which means that the control system also
checks that fusible
member 70 is intact and functioning. It should be noted that the sense line
could also be used to charge
the capacitor.
It will be appreciated by those of skill in the electrical arts that the
exemplary embodiments of
the firing system discussed above are just several of many configurations that
may be used. Thus, it will
be understood that any suitable embodiment or configuration could be used. The
control systems, power
supplies, sense lines and other items related to or used with firing systems
are discussed in more detail in
Sections 1 and 2 above, and Section 9 below.
Figure 91 shows a firing system 76 assembled on a printed circuit board 630.
The firing system is
similar to the circuit shown in Fig. 90, and includes capacitor 620 and SCR
621. A socket 631 is
associated with the printed circuit board so that the circuit can be connected
to the control system, sensor
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line and power supply. A contact mount 632, made from spaced apart electrodes
634 and 636, is mounted
on the printed circuit board. A fusible member extends around the contact
mount in use.
A top, sectional view of contact mount 632 and electrodes 634 and 636 is shown
in Fig. 92, and
fusible member 70 is wrapped over the electrodes. The electrodes are
constructed with a small gap 640,
as described above, and it is at that gap that the fusible member breaks or
burns when current passes from
one electrode to the other through the fusible member. Contact mount 632 is
configured to fit over a
supporting plug, and flanges 642 help hold the mount on the plug.
Figure 93 shows printed circuit board 630, including capacitor 620 and SCR
621, mounted in
cartridge 82. The cartridge houses pawl 60, spring 66, and fusible member 70.
Fusible member 70
restrains pawl 60 from moving outwardly by restraining the motion of compound
linkage 650. Fusible
member 70 extends around contact mount 632. Contact mount 632 fits over a
supporting plug that is part
of the cartridge housing. Fusible member 70 bums when firing system 76 on
printed circuit board 630
sends a surge of current through the fusible member. Compound linkage 650 and
pawl 60 are then free to
move, and spring 66 quickly forces pawl 60 outwardly. Cartridge 82 can be
configured to fit into various
types of power equipment, such as table saws, jointers, etc. Additionally,
cartridge 82 can be "re-loaded,"
or replenished with a new pawl and fusible member, and reused after the firing
system has fired.
Figure 94 shows an embodiment in which a fusible member 70 is mounted between
an anchor
652 and a pawl 60. Two electrodes 653 and 654 contact the fusible member
between the anchor and
pawl, but do not support the fusible member. Electrodes 653 and 654 may take
the form of conductive
traces on a printed circuit board 656. The conductive traces are formed on the
surface of the printed
circuit board and extend slightly above that surface, so that fusible member
70 can contact them by
extending across them. The printed circuit board can be positioned so that
electrodes 653 and 654 apply
some pressure against fusible member 70 to insure contact with the fusible
member. Electrodes 653 and
654 are connected to a firing subsystem, as described. Of course, the
configuration and orientation of
electrodes 653 and 654 can vary.
Figures 95 through 98 show data concerning the time it takes for a firing
subsystem to burn a
wire given varying factors, such as the firing system, the wire size, the load
on the fusible member, etc.
Figure 94 shows the approximate time it takes to burn a wire as the load on
the wire varies. The wire
tested was stainless steel, ASTM 302/304, spring tempered, with a diameter of
.010 inches and was
wrapped over brass electrodes with a 0.044 inch gap. The firing system used a
390 F capacitor charged
to 163 volts to bum the wire. The wire burned in approximately the following
times for the specified
loads: 231 is with a 5 pound load, 98 is with a 10 pound load, 68 s with a 15
pound load, 48 s with a
20 pound load, 39 p.s with a 25 pound load, 33 s with a 30 pound load, 22 p
with a 35 pound load, and
18 is with a 40 pound load. This data shows that the time to bum a fusible
member decreases as the load
on the member increases.
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Figure 96 shows the approximate time it takes to bum a wire as the spacing
between electrodes
varies. The wire tested was stainless steel, ASTM 302/304, spring tempered,
with a diameter of 0.010-
inches and was wrapped over brass electrodes. The firing system used a 390 F
capacitor charged to 163
volts to bum the wire. The wire had a load of 20 pounds. The wire burned in
approximately the following
times for the specified gaps: 70 s with a 0.1 inch gap, 47 s with a 0.044
inch gap, and 37 s with a
0.013 inch gap. This data shows that the time to burn a fusible member
decreases as the gap between
electrodes decreases.
Figure 97 shows the approximate time it takes to burn a wire as the voltage on
the capacitor in
the firing system varies. The wire tested was stainless steel, ASTM 302/304,
spring tempered, with a
diameter of. 0 10 inches and was wrapped over brass electrodes with a .044
inch gap. The firing system
used a 390 pF capacitor. The wire burned in approximately the following times
for the specified
voltages: 296 s with 123 volts, 103 s with 133 volts, 81 [Ls with 143 volts,
57 s with 153 volts, 47 s
with 163 volts, 40 s with 173 volts, and 39 s with 183 volts. The wire did
not burn with voltages of
only 103 or 113 volts. This data shows that the time to burn a fusible member
decreases as the voltage
increases.
Figure 98 shows the approximate time it takes to burn wires of varying sizes.
The wires tested
were all stainless steel, ASTM 302/304, spring tempered, wires. The wires were
wrapped over brass
electrodes with a .044 inch gap. The firing system used a 390 F capacitor
with 163 volts. The wire had a
load of 40 pounds. The wire burned in approximately the following times for
the specified diameter sizes:
18 s with a .010 inch diameter, 39 p.s with a .011 inch diameter, and 81 s
with a .012 inch diameter. A
wire with a .013 inch diameter did not burn. This data shows that the time to
burn a wire decreases as the
diameter of the wire decreases.
This data shows that a system as described above can apply a load of 25 to 200
pounds to move a
pawl toward a blade in less than 200 s, and preferably in less than 50 s.
Stainless steel is a good
material for fusible members because it has high resistance, high strength and
good corrosion resistance.
Firing system 76 may also be used to trigger some action other than burning a
fusible member.
For example, firing system 76 can fire a small explosive charge to move a
pawl. Figure 99 shows a
relatively small, self-contained explosive charge 660 in the form of a squib
or detonator that can be used
to drive pawl 60 against a blade. An example of a suitable explosive charge is
an M-100 detonator
available, for example, from Stresau Laboratory, Inc., of Spooner, Wisconsin.
The self-contained charge
or squib focuses the force of the explosion along the direction of movement of
the pawl. A trigger line
662 extends from the charge, at it may be connected to firing system 76 to
trigger detonation.
Explosive charge 660 can be used to move pawl 60 by inserting the charge
between the pawl and
a stationary block 664 adjacent the charge. When the charge detonates, the
pawl is pushed away from the
block. A compression spring 66 is placed between the block and pawl to ensure
the pawl does not bounce
back from the blade when the charge is detonated. Prior to detonation, the
pawl is held away from the
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blade by the friction-fit of the charge in both the block and pawl. However,
the force created upon
detonation of the charge is more than sufficient to overcome the friction fit.
Alternatively, the pawl may
be held away from the blade by other mechanisms such as a frangible member,
gravity, a spring between
the pawl and block, etc.
Firing system 76 may also trigger a DC solenoid, which can be over-driven with
a current surge
to create a rapid displacement, a pressurized air or gas cylinder to supply
the pressure in place of the
spring or charge, or an electromagnet to either repel the pawl against the
blade or to release a spring-
loaded pawl toward the blade.
The firing and release systems and methods may be described as set forth in
the following
numbered paragraphs. These paragraphs are intended as illustrative, and are
not intended to limit the
disclosure or claims in any way. Changes and modifications may be made to the
following descriptions
without departing from the scope of the disclosure.
6.1 A mechanical release comprising:
an electrode system including first and second electrodes electrically
connected to a current
source;
a fusible member electrically interconnecting the electrodes;
a electrical gate system interposed between at least one of the electrodes and
the current source to
selectively control flow of current from the current source to the at least
one electrode, where the fusible
member carries a tensile load of at least 10,000 psi between the electrodes.
6.1.1 The mechanical release of paragraph 6.1, wherein the fusible member has
a tensile
strength of at least 100,000 psi.
6.1.2 The mechanical release of paragraph 6.1, wherein the fusible member is
formed from a
material chosen from the group consisting of stainless steel and nichrome.
6.1.3 The mechanical release of paragraph 6.1, wherein the fusible member is
spring tempered.
6.2 A woodworking machine, comprising:
a cutter;
a brake adapted to stop the cutter, where the brake has an idle position and a
braking position;
a biasing system adapted to urge the brake from the idle position to the
braking position; and
a release mechanism adapted to selectively hold the brake in the idle position
against the bias of
the biasing mechanism.
6.2.1 The machine of paragraph 6.2, wherein the release mechanism is a single
use device.
6.2.1.1 The machine of paragraph 6.2.1, wherein the release mechanism includes
a fusible
member.
6.2.1.1.1 The machine of paragraph 6.2.1.1, wherein the release mechanism
includes first
and second electrodes connected to a current source and the fusible member
electrically interconnects the
electrodes.
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6.2.2 The machine of paragraph 6.2, wherein the release mechanism includes an
electromagnet.
6.3 A woodworking machine, comprising:
a cutter;
a brake adapted to stop the cutter, where the brake has an idle position and a
braking position;
and
an actuation system adapted to selectively move the brake from the idle
position to the braking
position, where at least a portion of the actuation system must be replaced
after moving the brake from
the idle position to the braking position.
6.3.1 The machine of paragraph 6.3, wherein the actuation system includes an
explosive
device.
6.3.2 The machine of paragraph 6.3, wherein the actuation system includes a
fusible member
that is melted to allow the brake to move from the idle position to the
braking position.
6.3.3 The machine of paragraph 6.3, wherein the brake and at least part of the
actuation system
are housing in a replaceable cartridge.
Section 7: Replaceable Brake Cartridge
As described above and depicted in Fig. 2, a portion of safety system 18 may
be contained in a
replaceable cartridge 80. In Figs. 100-109, various embodiments of cartridges
80 are shown having
various elements, subelements and possible variations. It should be understood
that cartridges may
include any one or more of these elements, subelements and variations,
regardless of whether those
elements, subelements are variations are shown in the same or different
figures or descriptions.
Examples of suitable brake and biasing mechanism 28 and 30, including suitable
pawls 60 that
may be used with the cartridges described herein are described above in
Sections 4 and 5.
Cartridge 80 should include or be in communication with the operative portions
of release
mechanism 34 required to cause restraining mechanism 32 to release pawl 60 to
engage the blade or other
cutting tool of the machine. For example, in Fig. 2, it can be seen the mounts
72 are in electrical
communication with firing subsystem 76. Upon activation of detection subsystem
22, such as upon
detection of a dangerous or triggering condition, firing subsystem 76 actuates
release mechanism 32,
such as by melting fusible member 70 with a surge of current stored by
subsystem 76. Examples of
suitable restraining mechanisms 32 and firing subsystems 76 for use in
cartridges 80 are described above
in Section 6.
The communication between the firing subsystem and mounts 72 may be by any
suitable
electrical linkage. Preferably, the electrical connection between mounts 72
and subsystem 76 is
automatically established when cartridge 80 is installed within machine 10.
For example, housing 82
may include contacts that engage corresponding contacts associated with the
firing subsystem when the
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cartridge is installed in its mounting position with the machine.
Alternatively, a plug and socket
assembly may be used to electrically interconnect the mounts 72 and firing
subsystem 76.
Cartridge 80 is removably installed in machine 10 so that brake mechanism 28,
and more
particularly pawl 60, is positioned near the blade or other cutting tool of
the machine. Cartridge 80 may
include a brake positioning system or other suitable mechanism for selectively
adjusting the position of
the pawl and/or cartridge relative to blade 40. For example, the position of
the cartridge relative to the
blade or other cutting tool may be adjustable such as by pivoting or sliding
the cartridge relative to one or
more of the mounting bolts. In which case, pawl-to-blade spacing may be
determined indirectly by
measuring the blade-to-cartridge spacing if desired. Alternatively, the
cartridge may be stationary and
the pawl may be adjustable within the cartridge. As a further alternative,
both the cartridge and pawl are
adjustable. Similarly, the position of the mounting bracket may be adjustable
relative to the blade.
Examples of suitable brake positioning systems are described below in Section
8.
As shown in Fig. 100, machine 10 includes a support structure 702 adapted to
receive cartridge
80 and operatively position the cartridge for use in safety system 18. Support
structure 702 may extend
from or be mounted on any suitable structure forming part of machine 10. When
blade 40 is adjustable, it
may be preferable for cartridge 80 and/or support structure 702 to move with
the blade so that the desired
positioning of pawl 60 to blade 40 is maintained. Alternatively the cartridge
may include a pawl 60 sized
to accommodate adjustments to the position of the blade without requiring
corresponding adjustments to
the cartridge and/or mounting structure.
Examples of suitable support structures include one or more mounting brackets
704 to which the
cartridge is attached by any suitable releasable fastening mechanism, such as
bolts, pins or screws.
Support structure 702 may additionally, or alternatively, include one or more
axles 706 upon which the
cartridge is mounted. For example, pawl 60 is shown in Fig. 100 pivotally
mounted on an axle 706 that
passes through pawl 60 and at least a portion of cartridge 80. Also shown in
Fig. 100, is mounting
bracket 704 that supports and positions cartridge 80 relative to blade 40.
Another example of a suitable
support structure is a socket or other receiver within machine 10. Typically,
cartridge 80 will be
supported in sufficient directions and/or positions to retain the cartridge in
its intended mounting position
and orientation. Cartridge 80 and support structure 702 preferably include key
structure 703 that
prevents the cartridge from being installed within machine 10 other than in
its intended mounting
position. An example of a suitable key structure 703 is shown in Fig. 100, in
which housing 82 of
cartridge 80 includes a bevel 705 that mates with mounting bracket 704. It
should be understood that key
structure 703 may include any suitable mechanism, including the relative size,
shape and positioning of
cartridge 80 and support structure 702, that prevents the cartridge from being
installed in a position other
than its intended mounting position.
Another cartridge is shown in Fig. 101. Similar to the cartridge shown in
Figs. 2 and 100,
cartridge 80 includes a housing 82, a brake mechanism 28 having a pawl 60, a
biasing mechanism 30
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such as spring 66, and a restraining mechanism 32 such as fusible member 70.
Also shown is another
example of a suitable key structure 703, namely, the irregular shape of
housing 82 and mounting bracket
704 against which the housing is supported.
As shown, pawl 60 includes an aperture, or bore, 708 through which an axle or
pin 706 may
extend to support the pawl and cartridge within machine 10. Also shown is an
aperture 710 in one or
more of the cartridge's side walls 712 through which axle 706 extends.
Alternatively, cartridge 80 may
be supported by a support structure 702 that does not directly support pawl
60. For example, pawl 60
may pivot about an axle forming part of cartridge 80, which in turn is
supported by support structure 702,
such as pins, mounting brackets or the like. However, it may be preferable to
support pawl 60 with at
least one of support structures 702 to increase the supporting force provided
other than by cartridge 80.
Similarly, this reduces the strength required for cartridge 80 because support
structures 702 absorb much
of the force imparted on pawl 60 as the pawl engages the blade or other
cutting tool of the machine.
Pawl 60 should be retained in its mounting position within cartridge 80 when
the cartridge is not
installed within the machine. An example of a suitable coupling 714 between
the pawl and cartridge is
shown in Fig. 102, in which the aperture 710 through cartridge 80 is larger
than the corresponding
aperture 708 through pawl 60. Pawl 60 includes an outwardly extending bushing,
or carrier, 716 that
extends at least partially through the sidewalls of the cartridge to position
the pawl relative to the
cartridge. It should be understood that it that this configuration could be
reversed, with pawl 60 having a
larger aperture than cartridge 80 and with the cartridge having an inwardly
extending bushing or carrier
that passes at least partially through the aperture in pawl 60.
Also shown in more detail in Fig. 102 is the cartridge's opening 718 through
which at least a
portion of pawl 60 projects upon release of restraining mechanism 32. Although
pawl 60 is shown
completely within housing 82 in Fig. 102, it should be understood that at
least a portion of pawl 60 may
project from housing 82 when the pawl is in its cocked, or restrained,
position. Opening 718 may include
a cover 720 that seals the opening and thereby prevents contaminants such as
dust, particulate, water,
grease and the like from entering the cartridge and possibly interfering with
the operation thereof.
Although only a portion of cover 720 is shown in Fig. 102, it should be
understood that the cover
preferably covers the entire opening 718. Cover 720 may be formed of any
suitable material to prevent
contaminants from entering the cartridge through opening 718, while not
interfering with the operation of
brake mechanism 28. Examples of suitable materials for cover 720 include tape
and thin metal, paper or
plastic films. When a cover 720 is used that completely closes opening 718,
the entire cartridge is
preferably, but not necessarily, sealed against the entry of contaminants.
Cover 720 may be attached to
cartridge 80 through any suitable mechanism, such as with an adhesive 722. In
embodiments of the
cartridge in which the pawl is not prevented from pivoting or otherwise moving
by restraining
mechanism 32, cover 720 may also function as a pawl-restraining mechanism that
prevents the pawl from
extending through opening 718 until release of biasing mechanism 30 by the
restraining mechanism.
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Returning briefly to Fig. 101, it can be seen that biasing mechanism 30
includes spring 66, which
is compressed between a spring-receiving portion 724 of the pawl and a support
726 forming part of
cartridge 80. As shown, support 726 extends from the housing of the cartridge,
although any suitable
support may be used, including the end wall 728 of the cartridge, a support
that extends from the end
wall, and a support that extends from at least one of the cartridge's side
walls 712.
In the embodiment of pawl 60 shown in Fig. 101, the pawl includes a blade-
engaging surface 730
and a distal portion 732 that is coupled to linkages 734 and 736. Linkage 734
is pivotally coupled to
housing 82, and linkage 736 interconnects distal portion 732 of pawl 60 to
linkage 734. As shown, both
linkages are in compression when pawl 60 is in its cocked, or restrained,
position. It should be
understood, however, that any suitable number and type of linkage may be used.
Alternatively,
restraining mechanism 32 may retain the pawl directly, such as shown in Figs.
2 and 100. As a further
alternative, restraining mechanism 32 may restrain a support positioned
intermediate spring 66 and pawl
60 and upon which biasing mechanism 32 acts, thereby leaving pawl completely
or relatively free from
the bias of spring 66 until the release of restraining mechanism 32.
Fusible member 70 extends around contact mount 72 and at least a portion of
one of the linkages
to prevent pawl 60 from pivoting under the force of biasing mechanism 32. As
shown, the ends of
fusible member 70 are coupled to the linkages. Upon release of restraining
mechanism 32, such as when
a sufficient current is passed through fusible member 70 via contact mount 72,
the fusible member no
longer retains the linkages and pawl in the position shown, and the pawl
pivots to its blade-engaging
position, which is shown in Fig. 103.
Firing subsystem 76 may alternatively be located within housing 80, such as
schematically
illustrated in Fig. 104. An advantage of locating firing subsystem 76 within
cartridge 80 is that the firing
subsystem may be replaced with the rest of the cartridge. It also enables the
capacitor or other current-
storing or current-generating device 742 used to release fusible member 70 to
be housed near contact
mounts 72 and connected thereto by a direct linkage 744, instead of by wires.
Also shown in Fig. 104 is
plug 746 that extends through a port 748 in housing 82 and which is adapted to
electrically connect firing
subsystem 76 with controller 50 or another suitable portion of control
subsystem 26. Alternatively,
contacts 750 are shown extending from or forming a portion of housing 82.
Another exemplary cartridge is shown in Fig. 105. As shown, cartridge 80
includes firing
subsystem 76 of release mechanism 34. Also shown in Fig. 105 is another
version of linkages 734 and
736, in which linkage 734 is in tension instead of compression. The linkage
assemblies shown in
Figs. 101 and 105 may both be referred to as over-center linkages. In Fig.
105, fusible member 70 is
shown having a fixed length defined by end portions 752 that are adapted to be
coupled to contact mount
72 and linkages 734 and 736, respectively. An advantage of a fixed length
fusible member is that it
facilitates easier assembly of cartridges with uniform pawl positions.
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Unlike support 726, which is shown in Fig. 101 supporting the end of spring 66
distal pawl 60, in
Fig. 105, cartridge 80 includes a removable support 754. Support 754 may be
selectively removed from
cartridge 80 to release, or at least substantially reduce, the biasing force
exerted by spring 66 upon pawl
60. For example, support 754 may be removed after actuation of brake mechanism
28 to remove the
spring force so that it is easier to remove and replace the cartridge. An
example of a suitable support 754
is a clip 756 that extends through at least one of the cartridge's side walls
712. Clip 756 may be
supported between both of the cartridges side walls. Alternatively, cartridge
80 may include an internal -
support 758 adapted to support the ends 760 of clip 756, such as shown in Fig.
106, in which the pawl is
shown in its blade-engaging position. Preferably clip 756 or other support 754
may be removed from the
cartridge without having to first remove the cartridge from machine 10. For
example, clip 756 may
include a portion 762 that extends external cartridge 80 and which may be
grasped by a tool to withdraw
the clip from the cartridge, such as shown in Fig. 107. A benefit of the
embodiment shown in Fig. 106 is
that pulling clip 756 releases spring 66, which in turn breaks fusible member
70. The safety system's
controller may be configured to detect this break in fusible member 70, and
respond accordingly to the
fault in the system.
In Figs. 104-06, firing subsystem 76 is shown housed within cartridge 80. It
should be
understood that other components of the safety system's electronics may also
be housed within cartridge
80. For example, the cartridge may include a sensing assembly to determine if
the cartridge is properly
installed within machine 10, with operation of the machine being prevented
until the safety system
receives a signal that the cartridge is properly installed.
Placing most of safety stop 30 in the cartridge allows manufacturers to
develop improved
electronics, additional functions, etc., without requiring significant, if
any, changes to the machine. As a
further alternative, safety system 18 may include a plurality of cartridges,
including at least one cartridge
that contains pawl 60 and at least one cartridge that contains electronics,
such as firing subsystem 76
and/or other electronic portions of the safety system. An example of such a
cartridge assembly is shown
in Fig. 108. As shown, a pair of cartridges 80 are shown and indicated
generally at 80' and 80".
Cartridges 80' and 80" may also be described as subcartridges or modules that
are united to form
cartridge 80. Cartridge 80' includes an electronics unit 764, such as firing
subsystem 76 or control
subsystem 26, and an electrical connector 766 configured to operably engage
plug 768, attached to cable
770. The cable includes conductors for supplying electrical power to the
electronic unit. The cable may
also conduct output signals from the electronics unit, such as a cutoff signal
to stop motor assembly 16,
or a signal to control subsystem 26, depending upon the particular electronics
housed in cartridge 80'.
Although plug 768 and cable 770 are shown as being freely movable, it will be
appreciated that plug 768
may be rigidly mounted to the support surface upon which cartridge 80 is
mounted. Further, plug 768
may be rigidly positioned to ensure that the cartridge is properly aligned and
oriented when the connector
is engaged with the plug. Cartridge 80", on the other hand, includes pawl 60
and the biasing and
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restraining mechanisms, which are collectively indicated as module 772 to
indicate that the biasing and
restraining mechanisms may also form a cartridge or module that may be
selectively removed and
replaced. Preferably, the cartridges are in communication with each other,
such as to release the
restraining mechanism responsive to a signal from electronics unit 764.
Optionally, cartridge 80", or any of the previously described cartridges, may
be provided in
different sizes or configurations to accommodate different blade sizes. For
example, a longer version of
the cartridge, such as shown in Fig. 109, may be used for a smaller diameter
blade 40. Furthermore,
different cartridges may be provided for different applications that use
different types of blades (e.g.,
dado, cross-cutting, ripping, plywood, etc.). For example, a first cartridge
having a first type pawl may
be provided for a first type blade, while a second cartridge having a second,
different pawl may be
provided for a second, different blade. Alternatively, the electronics of one
cartridge may be different
from those of another cartridge to allow for different applications (e.g.,
cutting plastic rather than wood).
Additionally, plural cartridges may be used simultaneously to ensure the
safety stop responds optimally
for each material.
The brake cartridges and related machines and methods may be described as set
forth in the
following numbered paragraphs. These paragraphs are intended as illustrative,
and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
7.1 A woodworking machine comprising:
a working portion;
a detection system adapted to detect a dangerous condition between a person
and the working
portion; and
a brake system to brake the working portion upon the detection by the
detection system of the
dangerous condition, where the brake system is housed in a cartridge.
7.1.1 The woodworking machine of paragraph 7.1 where the cartridge is
configured to be
replaced after the brake system has braked the working portion.
7.1.2 The woodworking machine of paragraph 7.1 where cartridge houses a brake
pawl
adapted to contact the working portion, a biasing mechanism adapted to move
the brake pawl into contact
with the working portion, and a release system adapted to release the biasing
mechanism.
7.1.2.1 The woodworking machine of paragraph 7.1.2 where the biasing mechanism
includes a
spring.
7.1.2.2 The woodworking machine of paragraph 7.1.2 where the biasing mechanism
includes a
spring and a mechanical linkage restraining the brake pawl against the spring.
7.1.2.3 The woodworking machine of paragraph 7.1.2 where the release system
includes a
fusible member.
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7.1.2.4 The woodworking machine of paragraph 7.1.2 where the release system
includes a
fusible member and a firing circuit to melt the fusible member.
7.1.2.5 The woodworking machine of paragraph 7.1.2 where the cartridge is
sealed.
7.1.2.6 The woodworking machine of paragraph 7.1.2 where the cartridge is made
of plastic,
where the cartridge includes an opening through which the brake pawl may move,
and where the opening
is covered until the brake pawl moves through the opening.
7.1.3 The woodworking machine of paragraph 7.1 further comprising a
worksurface adjacent
the working portion, where the working portion is a blade, where the blade is
configured to raise and
lower relative to the worksurface, and where the cartridge is mounted to raise
and lower with the blade.
7.1.4 The woodworking machine of paragraph 7.1 where the cartridge mounts on a
shaft in the
machine.
7.2 A brake cartridge for a woodworking machine, the cartridge comprising:
a housing;
a brake pawl in the housing; and
a mechanism to move the brake pawl.
Section 8: Brake Positioning
Brake mechanisms, such as described above, may be positioned relative to the
blade in a variety
of ways. For example, one exemplary brake positioning system is shown
generally at 800 in Fig. 110.
Cartridge 80 and brake pawl 60 are typically pivotally mounted on a large axle
or pin 802. The cartridge
and pawl are fixed together until the brake is fired, at which time the brake
pawl is shoved rapidly into
the blade. The motion of the blade and geometry of the pawl then cause the
blade to drive deeply into the
pawl creating tremendous deceleration. Pin 802 is sufficiently large,
typically 0.75 inches, to absorb the
impact of deceleration without damage. The large diameter of pin 802 also
reduces the chance that it will
fracture brake pawl 60 during braking. The pivotal mounting of the cartridge
on the pin permits the
spacing between the blade and the face of the brake pawl to be adjusted by
rotating the cartridge around
the pin. The brake position system serves to establish and maintain the proper
spacing between the face
of the pawl and the perimeter of blade 40.
In its simplest form, brake positioning system 800 incorporates a fixed pin
804 to position
cartridge 80, and thereby brake pawl 60. This arrangement is generally
sufficient where the size of the
blade is known and sufficiently fixed for all blades that might be used. Pin
804 is arranged parallel to pin
802 to allow cartridge 80 to be slid onto both pins simultaneously. A flexible
snap clip 806 snaps over the
edge of cartridge 80 to retain it on the pins. When the cartridge is to be
removed, the clip is lifted away
from the cartridge, and the cartridge is slipped off of the pins. A clearance
pin 808 is preferably mounted
at a fixed radius from the arbor axis, 5 1/16th inches for instance, to insure
that no larger blade than will
clear the pawl will fit on the saw. The clearance pin is preferably located at
a just slightly smaller radial
position from the arbor than the nearest portion of the pawl so that the blade
will contact the pin prior to
CA 02762156 2011-12-09
contacting the pawl. Alternatively, the pin may take the form of a curved are
that is sufficiently large to
insure that at least one tooth of the blade will engage it.
An adjustable brake positioning system 800 is shown in Figs. 111-113. Brake
positioning system
800 includes a plurality of positioning teeth 812 formed on the back of
cartridge 80. A corresponding
plurality of positioning teeth 814 are formed on a cartridge mounting surface
816. The teeth preferably
have a pitch of approximately 1/32nd to 1/4`h of an inch. The teeth are spaced
so that relatively small
adjustments can be made by selecting where to engage the teeth. A curved wall
818 is formed along part
of the inside front edge of the cartridge. The curved wall is positioned to
engage the perimeter of the
blade just prior to the positioning teeth engaging each other as the cartridge
is slipped onto pin 802. This
insures that the pawl will be spaced back from the blade by at least the
distance the wall projects forward
from the pawl - typically 1/16th to 1/8th inch. Once the positioning teeth are
engaged, the rotational
position of the cartridge is fixed. The cartridge is then slid the rest of the
way onto the pin. Snap clip 806
retains the cartridge against the mounting surface and in proper position. A
tab 820 formed on the edge of
the cartridge extends over the blade. The tab blocks the blade from being
removed unless the cartridge is
partially disengaged and rotated back away from the blade. Thus, the tab
insures that the blade cannot be
removed and replaced with a new blade without resetting the position of the
cartridge. It can be seen that
by making the cartridge pivotal on pin 802, adjustable positioning of the
brake pawl relative to the blade
is simplified.
Because of the importance of establishing correct pawl-to-blade spacing, it
may be desirable to
incorporate a spacing detection system to insure correct spacing. One example
of such a system is shown
at 824 in Fig. 114. System 824 includes an electrode 826 located on the face
of the pawl adjacent the
blade. As described in Sections 1 and 2 above, in one contact detection system
suitable for use with the
present invention, an electrical signal is applied to the blade via a drive
electrode. This signal can be
picked up by electrode 826 and monitored to ensure that it has an amplitude in
a predetermined range. In
particular, the amplitude detected by electrode 826 will fall off rapidly with
distance from the blade.
Therefore, by monitoring the detected amplitude, proper spacing can be
verified. The system preferably
deactivates or prevents initial actuation of the machine if the detected
spacing is outside normal range.
The user is then signaled to make appropriate adjustment.
An alternative brake positioning system 800 is shown in Fig. 115. The position
system of Fig.
115 utilizes a snap catch 830 with a rib 832 facing the cartridge. The catch
is mounted to cartridge
support surface 816 and is biased to push against the cartridge. The end face
of the cartridge includes a
groove 834 adapted to receive rib 832. In use, the cartridge is slipped over
pin 802 while rotated back
from the blade. Once the cartridge is fully installed on the pin, it is
rotated forward until rib 832 snaps
into groove 834. A small ledge 836 projects over the edge of cartridge 80 when
the rib is engaged in the
groove to prevent the cartridge from vibrating off along the axis of the pin.
Once the cartridge is fired, the
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user can lift tab 838 to disengage the rib and allow the cartridge to rotate
back. The backward rotation
can be used to release any remaining pressure from the actuation spring in the
cartridge.
Fig. 116 shows another brake positioning system 800. In the system of Fig.
116, cartridge 80
includes a recess 850 formed on one side. A spring latch 852 is positioned to
engage recess 850 as
cartridge 80 is rotated back away from the blade. The latch is positioned to
locate the face of the pawl
approximately 1/8t' of an inch away from the perimeter of the blade, although
different spacing could of
course be used. The user can remove the cartridge by lifting the latch,
rotating the cartridge forward until
it clears the latch and then sliding the cartridge off pin 802. As described
in more detail in Section 7
above, when the cartridge is fired, the pawl will normally be somewhat
embedded on the blade and
biased toward the blade by a spring 66. A release pin 756 is removable to
release the back of the spring
and remove the biasing pressure. This allows the pawl to be loosened from the
blade more easily and
eliminates the pressure on the blade that would otherwise make removal of the
blade more difficult.
Fig. 117 shows a further brake positioning system 800. In this embodiment,
pawl 60 and brake
cartridge 80 are mounted on a support assembly 860 that is selectively movable
to adjust the position of
the pawl and/or cartridge. It will be appreciated that support assembly 860
may be configured in a variety
of different ways. In the exemplary embodiment depicted in Fig. 117, assembly
860 includes a plurality
of gears 862 having toothed perimeters. Each gear includes a support post 864
extending outward
therefrom. Cartridge 80 is mounted on assembly 860 so that a first one of the
posts passes through the
brake pawl 60 and cartridge, while the second post passes only through the
cartridge. The pawl is adapted
to pivot about the first post, which supports the pawl and absorbs the energy
of the blade when during
braking. The second post functions to angularly position the pawl relative to
the blade and prevent the
cartridge from rotating about the first post.
When the cartridge and pawl are mounted on the first and second posts, the
pawl may correctly
positioned relative to the blade by rotating gears 862. Assembly 860 also
includes a worm screw 866 or
other suitable mechanism to rotate the gears. A handle or similar device may
be mounted on the worm
screw to facilitate turning. In the exemplary embodiment, worm screw 866 is
adapted to simultaneously
engage both gears so that the gears turn in tandem. As a result, cartridge 80
and brake pawl 60 maintain a
constant angular position relative to the blade as the gears are turned.
However, as shown in Fig. 177, the
cartridge and pawl move toward and away from the blade when the worm screw is
turned. This allows
the brake to be correctly positioned for different sized blades. Further, this
embodiment alleviates the
need for different sized pawls and/or cartridges for different sized blades.
In alternative embodiments, gears 862 may be different sizes so as to rotate
different amounts
when the worm screw is turned. This may be useful where it is desirable to
change the angular position of
the pawl relative to the blade when the pawl is moved toward and away from the
blade.
In the embodiment depicted in Fig. 117, the pivot point of the pawl is
translated as the pawl is
moved toward and away from the blade. In a further alternative embodiment, the
position of the pawl
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may be adjusted by simply pivoting the pawl about its pivot post. In such an
embodiment, it may be
desirable to have a relatively long pawl to accommodate blades of
substantially different sizes.
The brake positioning systems, methods and related machines may be described
as set forth in
the following numbered paragraphs. These paragraphs are intended as
illustrative, and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
8.1 A woodworking machine, comprising:
a cutter;
a brake cartridge including a brake pawl adapted to selectively engage and
stop the cutter; and
a brake positioning system adapted to receive and adjustably position the
brake cartridge relative
to the cutter.
8.1.1 The machine of paragraph 8.1, wherein the brake positioning system
allows the cartridge
to be adjusted to accommodate different sized cutters.
8.1.2 The machine of paragraph 8.1, wherein the brake positioning system
includes a pivot on
which the cartridge is mounted and the position of the brake cartridge
relative to the cutter is adjusted by
rotating the cartridge on the pivot.
8.2 A woodworking machine, comprising:
a cutter;
a motor adapted to drive the cutter;
a brake adjustably positionable adjacent the cutter;
a sensor system adapted to sense the spacing between the cutter and the brake;
and
a control system configured to control the operation of the motor and to
receive a signal from the
sensor system representative of the spacing between the cutter and the brake,
where the control system is
further configured to selectively prevent operation of the motor dependent on
the signal received from the
sensor.
8.2.1 The machine of paragraph 8.2, wherein the sensor system includes an
electrode mounted
on the brake pawl proximal to the cutter and the signal is dependant on the
electrical coupling of the
electrode and the cutter.
Section 9: Logic Control
Considering logic controller 50 now in more detail, it will be appreciated
that the logic controller
may be configured to perform a variety of functions depending on the
particular type of machine 10
and/or the application. For example, logic controller 50 may be configured to
conduct various self-test
safety checks when the machine is switched on or off and during use, to ensure
that detection subsystem
22 is operating properly and to prevent inadvertent triggering of reaction
subsystem 24. Additionally, the
logic controller may be configured to control one or more display devices to
inform a user of the status of
machine 10 and safety system 18. Furthermore, logic controller 50 may be
implemented in a variety of
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ways including using one or more custom application specific integrated
circuits (ASICs),
microprocessors, micro-controllers, digital logic circuits, and/or analog
circuits, etc.
In one exemplary embodiment, logic controller 50 is configured to perform the
self-check logic
sequence shown in Fig. 118. The exemplary sequence begins when the user
initially supplies power to
the system, indicated at 901. The logic system first checks to determine
whether the spacing between the
blade and pawl is correct, as indicated at 902. The blade-to-pawl spacing may
be measured by any
suitable mechanism such as described in more detail below. If the spacing is
outside acceptable limits,
the system responds with an error signal, indicated at 903. The error signal
may be an audible and/or
visible signal, etc. In one embodiment described in more detail below, control
subsystem includes a user
interface adapted to indicate the status of the machine and annunciate any
error conditions. Preferably,
the logic system remains in the error state and prevents further operation of
the machine until the correct
blade-to-pawl spacing is detected.
If the blade-to-pawl spacing is acceptable, the logic system determines
whether the input signal
produced on charge plate 44 by detection subsystem 22 is being detected at a
sufficient amplitude on
charge plate 46, as indicated at 904. This step ensures that the reaction
subsystem will not be triggered
accidentally upon start-up due to a fault in the detection subsystem, a
grounded blade, incorrectly placed
charge plates, etc. If the proper input signal is not detected, logic
controller 50 responds with an error
signal 903. It will be appreciated that either the same or a different error
signal may be produced for each
fault condition.
If the proper input signal is detected, the logic controller proceeds to
determine whether a fusible
member is present, as indicated at step 905. The presence of a fusible member
may be determined by any
suitable means such as described in more detail below. If no fusible member is
present, logic controller
50 returns an error signal 903. If a fusible member is detected, the logic
controller then checks the
electrical charge stored by firing subsystem 76, as indicated at 906. This
step ensures that sufficient
charge is present to melt the fusible member if the dangerous condition is
detected. Exemplary circuitry
for detecting sufficient charge is described in more detail below. If
sufficient charge is not detected
within a determined time period, the logic controller responds with an error
signal 903.
In the sequence depicted in Fig. 118, after the predetermined checks are
completed, logic
controller 50 allows power to be sent to motor assembly 16, as indicated at
907. It will be appreciated
that the electrical sequence described above typically is completed within no
more than a few seconds if
no faults are detected. In addition to an initial power-up sequence, logic
controller 50 may be configured
to perform any of a variety of checks during operation. For example, the
rotation of the blade may be
monitored by known mechanisms and the firing system may be disabled when the
blade is not moving.
This would allow the user to touch the blade when it is stopped without
engaging brake mechanism 28.
Various exemplary embodiments and implementations of a blade motion detection
system are described
in Section 10 below.
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It will appreciated that many variations on the logic sequence described above
may be
implemented. For example, some embodiments of logic controller 50 may include
a battery, a capacitor
or other charge storage device to ensure the detection and reaction subsystems
will continue to function
at least temporarily after power to the machine is turned off. As another
example, power to the motor
assembly may be shut off if an error occurs other than contact detection such
as incorrect blade-to-charge
plate spacing, insufficient charge on the charge storage devices, etc. Thus,
logic controller 50 may be
implemented to provide any of a variety of safety and/or operational functions
as desired.
Additionally, since reaction subsystem 24 is configured to stop cutting tool
14 upon contact with
a user's body, it may also be desirable to stop motor assembly 16, or at least
the portion of the motor
assembly adapted to drive the cutting tool, to prevent damage to the motor as
it tries to drive the stalled
cutting tool. However, since machine 10 typically is designed with the
expectation that the cutting tool
may stop due to binding, etc., it will usually be sufficient to turn off the
motor assembly within a few
seconds. This can be accomplished simply by cutting power to the motor. For
example, when machine 10
includes a magnetic contactor switch 48, the logic controller may be adapted
to interrupt the circuit
holding the magnetic contactor closed so that power to the motor is
interrupted. It should be understood
that this step is optional, in that interrupting power to the machine's motor
assembly is neither necessary
nor sufficient to prevent serious injury to the user when the user touches the
machine's cutting tool.
Therefore, the principal benefit of this step is to reduce the likelihood of
damaging the motor assembly or
drive system while the brake. system is preventing rotation or other movement
of the cutting tool. It will
be appreciated that there are many other suitable ways of stopping motor
assembly 12. As one example,
power to the motor assembly may be controlled directly by safety stop 30
(e.g., through solid state on/off
switches, etc.). This embodiment is described in more detail in Section 1
above. Also, it is possible to
simply allow existing overload circuitry to trip in and turn off the stalled
motor.
Since the contact detection subsystem described above relies on certain
electrical properties of
the human body, the use of safety system 18 while cutting some materials, such
as foil-coated insulation,
may cause the detection circuitry to falsely register contact with a user. In
addition, as described above in
Section 1, extremely green wood may cause false triggers in some types of
detection subsystems due to
the relatively high dielectric constant of green wood. Therefore, it may be
desirable to provide a manual
bypass or override control that prevents the brake from operating for a
particular cutting operation. A
suitable override control may include a mechanical switch between fusible
member 70 and firing system
76. Alternatively, the switch may be a single-use switch configured to reset
itself after each use. As a
further alternative, safety system 18 may include sensors adjacent the
workpiece to detect the presence of
foil, green wood, etc., and disable the reaction subsystem automatically. This
latter alternative relieves
the user of having to remember to disable and re-enable the brake system.
In any event, the override control may be configured in a variety of ways
depending on the
application and the level of safety desired. For example, the override control
may be configured to time-
CA 02762156 2011-12-09
out (i.e., turn off) if the user does not switch the machine on within a
predetermined time (e.g., 3, 5 or 10
seconds, etc.). This would prevent the user from actuating the override
control and then becoming
distracted before proceeding to cut the workpiece and forgetting the safety
system had been disabled. In
some embodiments, it may be desirable to allow a user to override the error
caused by a failed self-test
(e.g., no fusible member, insufficient stored charged, missing or incorrectly
installed cartridge 80, etc.).
In other embodiments, logic controller 50 may be configured to require that
the detection and reaction
subsystems are operational before allowing the user to engage the override.
Typically, the override control is configured to reduce the likelihood that it
will be actuated
accidentally by the user. For example, the override control switch may be
located away from the
remaining operator switches and away from an area on machine 10 where the user
is likely to
accidentally bump against while using the machine. Alternatively or
additionally, override control switch
48 may include a cover or similar barrier which the user must remove or
overcome before the switch can
be actuated. Such covered switches are known to those of skill in the art. As
an additional safety measure,
logic controller 50 may be configured to produce a visual and/or audible alarm
or warning when the
override is actuated. Furthermore, where logic controller 50 is adapted to
control.the supply of power to
motor assembly 16, the logic controller may be configured to "pulse" the motor
one or more times to
alert the user that the blade is about to begin moving with the safety system
disabled. This would alert a
user, who accidentally actuated the override while in contact with the blade,
to quickly move away from
the blade.
In view of the above considerations, an alternative embodiment of logic
controller 50 may be
configured to perform the self-test and detection logic shown schematically in
Figs. 119A-C. The main
logic sequence, indicated generally at 910 in Fig. 119A, begins when machine
10 is first connected to
power source 20, as indicated at 911. Logic controller 50 begins sequence 910
by performing a system
integrity check, as indicated at 912. The system integrity check may include
any one or more of a variety
of checks which typically will vary depending on the particular type and
configuration of machine 10. In
the exemplary embodiment, system integrity check 912 includes testing the
sufficiency of power source
20 (here, standard line current) by any suitable means which are known to
those of skill in the art. The
system integrity check may also include driving the detection signal onto
charge plate 44 and attempting
to detect the signal at charge plate 46. Failure to detect the detection
signal at charge plate 46 may
indicate a number of problems such as an electronic failure in detection
subsystem 22, a mis-positioned
or grounded charge plate, grounded blade, etc. Exemplary system integrity
check 912 also includes a
pawl-to-blade spacing test to ensure that pawl 60 is properly positioned
adjacent blade 40 so that the pawl
will engage and stop the blade if released. Exemplary mechanisms for detecting
correct blade-to-pawl
spacing are described in more detail below. If any of the tests performed
during system integrity check
912 is negative, logic controller turns motor assembly 16 off (if on), as
indicated at 913, and outputs an
error signal to the user, as indicated at 914. Once the user corrects the
error and resets the logic controller
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(e.g., by disconnecting and then reconnecting the power to machine 10), the
system integrity check is
repeated.
If system integrity check 912 is successful, logic controller 50 proceeds to
check fusible member
70 as well as the stored charge in firing subsystem 76, as indicated at 915.
If either the fusible member
test or the stored charge test is negative, the logic controller turns off the
motor assembly, indicated at
913, and then outputs an error signal, indicated at 914. It may be desirable
to repeat step 915 one or more
times, or provide a delay between steps 912 and 915 to ensure that firing
subsystem 76 has sufficient
time to build up the electrical charge.
If both the fusible member and firing subsystem tests are successful, the
logic controller then
proceeds to one of two operational loops depending on whether the user-
operable override switch has
been activated, as indicated at 916. It will be appreciated that testing for a
user override signal after
performing the fusible member/charge storage test prevents a user from
overriding safety system 18
unless the safety system is functional. Thus, for example, if a contact
detection occurs and the brake is
triggered, the user cannot proceed to operate the system until the fusible
member, and/or pawl, and/or
firing subsystem, etc., is replaced (typically by replacing cartridge 80).
Alternatively, step 915 may be
eliminated from the main operational loop. This would allow machine 10 to be
operated regardless of
whether safety system 18 was completely functional by engaging the override.
In any event, if the override has been actuated, logic controller 50 proceeds
to operate in an
override loop, as indicated at 917 and detailed in Fig. 119B. Typically, logic
controller 50 first outputs a
warning signal, as indicated at 918 and described above. Next, at step 919,
the logic controller checks the
status of START switch 48, which is operable by a user to-turn on motor
assembly 16. As described
above, logic controller may be configured to read START switch 48 as being
"on" only if it is actuated
within a predetermined period after the override is enabled. If the START
switch is "off," logic controller
50 turns off the motor assembly (if on), as indicated at 920, and exits the
override loop as indicated at
921. As shown in Fig. 119A, the logic controller returns to the system
integrity check at the end of the
override loop. Thus, the logic controller will continue to perform the system
integrity check and the
fusible member/stored charge tests until the START switch is actuated. This
ensures that if a user
engages the override and then delays actuating the START switch, the system
will not turn on the motor
assembly if a failure occurs between the time the override is enabled and the
time the START switch is
actuated.
If, at step 919, the START switch is on, logic controller proceeds to turn on
motor assembly 16,
as indicated at 922. The motor assembly remains on until STOP switch 48 is
actuated by the user, as
indicated at 923. Once the STOP switch is actuated, logic controller 50 turns
off the motor assembly, as
indicated at 920, and exits the override loop at 921. As mentioned above, the
logic controller returns to
step 912 after exiting the override loop.
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If, at step 916, the override has not been engaged by the user, logic
controller 50 proceeds to the
detection loop 925, which is shown in detail in Fig. 119C. In the exemplary
embodiment, detection loop
925 is depicted with two logic paths which are executed simultaneously. In a
first path 926 the logic
controller monitors detection subsystem 22, while in a second path 927 the
logic controller continually
rechecks the fusible member and stored charge in firing subsystem 76. This
dual-path operation ensures
that machine 10 will be shut down if a failure occurs while the blade is in
motion. It will be appreciated
by those of skill in the art that the dual-path operation may be implemented
in a variety of ways including
the use of interrupts, state machines, etc. Alternatively, the two paths may
be implemented in a single
sequential loop. However, since testing of the stored charge consumes several
milliseconds or even
several seconds in some embodiments, it is typically desirable, in those
embodiments, to execute both
paths simultaneously so that several milliseconds or more do not pass between
successive contact
detection measurements.
Path 927 includes testing fusible member 70 and the charge stored by firing
subsystem 76, as
indicated at 928. This test is continuously repeated unless and until either
the fusible member test or the
stored charge test fails, at which point logic controller 50 turns the motor
assembly off, as indicated at
929, and outputs an error message, as indicated at 930. The logic controller
also stops executing test 928
when it exits the detection loop or when an error in path 926 occurs, as
described below. The tests of
fusible member 70 and firing subsystem 76 at step 928 may be the same as, or
different than, the tests
that are used in the main loop at step 915. In any event, the logic controller
must be reset from step 930,
as described above.
Path 926 is the contact detection path and includes testing for excessive
impedance loading on
the blade, as indicated at 931. Step 931 ensures that power will not be
supplied to the motor assembly if
the capacitive load on the blade is so high that the detection subsystem might
not be able to detect a
contact between the blade and the user. This might occur for a variety of
reasons. For example, if the
blade is cutting highly dielectric materials (e.g., green wood), the
capacitive load on the blade will
increase. This issue is described in more detail in Section 1 above.
As another example, the user might accidentally actuate the START switch while
in contact with
the blade. Since some exemplary detection subsystems rely on a sudden change
(rather than an absolute
level) in the signal detected at charge plate 46, step 931 ensures that the
safety system will not allow the
blade to begin rotating if the user is touching the blade when the START
switch is actuated. In this
embodiment, the logic controller is configured to set the value for excessive
capacitive loading at
approximately at least that amount of loading caused when a user contacts the
blade. However, it will be
appreciated that logic controller 50 may be configured to recognize any
desired amount of capacitive
loading as being excessive.
If the capacitive load on the blade is too high, logic controller 50 outputs
an error signal, at 932,
and turns off motor assembly 16 (if on), as indicated at step 933. The logic
controller then exits the
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detection loop, at 934, and returns to system integrity check 912 in the main
operational loop shown in
Fig. 119A. It will be appreciated that safety system 18 will not be enabled
during the several seconds it
takes the blade to spin down. This is because the capacitive loading is too
high to accurately detect
contact with the user, and is likely to trigger even though no contact has
occurred. In alternative
embodiments, the logic controller may continue to monitor for contact
detection while the blade is
rotating and actuate the firing system if contact is detected. Alternatively,
the logic controller may be
configured to actuate the firing system if the loading becomes too high.
Once the logic controller returns to the main loop after detecting a high
capacitive loading error,
the user may nevertheless operate machine 10 by engaging the override. If the
user does not actuate the
override, safety system 18 will not supply power to motor assembly 16 until
the capacitive loading
problem is corrected.
If, at step 931, the capacitive loading on the blade is within defined limits,
the logic controller
proceeds to test the contact detection signal from detection subsystem 22, as
indicated at 935. If contact is
detected, the logic controller determines whether the blade is rotating, as
indicated at 936. If the blade is
rotating, the logic controller actuates the firing subsystem, at 937, turns
off motor assembly 16, at 929,
and outputs an error, at 930. The logic controller must then be reset as
described above.
However, if the blade is not rotating at step 936, then the logic controller
outputs an error signal,
at step 932, turns off the motor assembly (if on), at 933, and exits the
detection loop, at 934. Thus, if a
user touches the blade when it is not rotating, the safety system will detect
the contact but will not actuate
the firing subsystem. This allows a user to change or adjust the blade without
actuating the brake.
However, the user would typically remove power from machine 10 before
adjusting or replacing the
blade, in which case, neither safety system 18 nor motor assembly 16 would be
operable.
If no contact is detected at step 935, logic controller 50 checks the status
of STOP switch 48, as
indicated at 938. If the STOP switch is actuated, the logic controller turns
off the motor assembly (if on),
as indicated at 939, and checks for blade rotation, as indicated at 940. If
the blade is rotating, the logic
controller loops back to step 931 so that the contact detection is active as
long as the blade continues to
rotate. Thus, if a user actuates the STOP switch and then contacts the blade
before it spins down, safety
system 18 will react to stop the blade. Once the blade ceases to rotate, the
logic controller exits the
detection loop, as indicated at 934.
If the STOP switch has not been actuated at step 938, the logic controller
checks the status of
START switch 48, as indicated at 941. If the START switch has been actuated,
the logic controller turns
the motor assembly on (if off), and loops back to repeat the contact
detection, as indicated at 942. If the
START switch has not been actuated, the logic controller turns off the motor
assembly (if on), as
indicated at 939, and checks for blade rotation, at 940. The logic controller
continues to execute the
detection loop until the blade stops, at which point the logic controller
exits the detection loop, as
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CA 02762156 2011-12-09
indicated at 934. Thus, the logic controller is configured to continuously
monitor for contact detection
whenever the blade is rotating and the user has not engaged the override.
Those of skill in the art will appreciate that control subsystem 26 and logic
controller 50 may be
implemented using many different components and many different configurations.
Therefore, while two
exemplary implementations are described below, it should be understood that
any other suitable
implementation may be used.
A first exemplary implementation is illustrated schematically in Fig. 120.
Logic controller 50
takes the form of a PIC16C63A-20/SO controller available from Microchip
Technology, Inc., of
Chandler, Arizona. The logic controller is coupled to power source 20, contact
detection subsystem 22,
and a user interface 178. The user interface may include any suitable
mechanism adapted to display
signals to a user and to allow a user to input signals to the logic
controller. Examples of suitable user
interface mechanisms which are known to those of skill in the art include
lights, display screens, buzzers,
sirens, switches, buttons, knobs, etc. In one exemplary embodiment depicted in
Fig. 121, user interface
178 includes START, STOP, and OVERRIDE switches to allow the user to input
control commands, and
a pair of LED lights which indicate the system status. The LED lights may
indicate system status in a
variety of ways such as color, blinking, etc.
The logic controller is also connected to control motor assembly 16 via a
suitable motor control
circuit 174, such as is described in more detail in Section 1 above, and to
firing subsystem 76. When the
logic controller receives a signal from detection subsystem 22 that contact
between the user and blade has
occurred, the logic controller actuates firing subsystem 76 and stops motor
assembly 16. The operation
and testing sequences are implemented by software instructions stored within,
and executable by, the
logic controller. It will be appreciated that the software instructions may
take a variety of forms.
The logic controller of the exemplary implementation depicted in Fig. 120 is
configured to
conduct a variety of self.-tests before enabling power to motor control 174,
as well as whenever the blade
is moving. For example, the logic controller is configured to evaluate the
line voltage supplied by power
source 20, and to shut off the motor if the voltage drops below a minimum
value sufficient to operate the
safety system. The logic controller is also adapted to test the contact sense
signal received from the
detection subsystem to ensure the charge plates are correctly positioned, that
the detection signal is
properly coupled across the blade, and that the capacitive load on the blade
is within defined limits.
Further, the logic controller is also coupled to a blade rotation sense
component 177. Examples of
suitable mechanisms for detecting blade rotation are described below in
Section 10.
In addition, logic controller 50 is also adapted to detect whether firing
subsystem 76 has
sufficient stored charge to melt fusible member 70. It will be appreciated
that detection of sufficient
stored charge in the firing subsystem may be carried out in a variety of ways
depending on the
configuration of the firing system. In each of the exemplary implementations
described herein, firing
subsystem 76 includes a single 390 F firing capacitor 620 configured to
discharge through fusible
CA 02762156 2011-12-09
member 70 via a suitable SCR 621 connected to ground. Exemplary firing
subsystems 76 are described
in greater detail in Section 6 above.
In the implementation depicted in Fig. 120, the firing capacitor is both
charged and tested by a
buck-boost regulator 175, which is shown in greater detail in Fig. 122. Buck-
boost regulator 175 includes
a buck-boost charger 183 that steps up an 32-volt supply input to 180 volts
for charging the firing
capacitor. Logic controller 50 provides a 125khz input to control the buck-
boost cycle of the charger. A
regulator circuit 184 monitors the voltage on the firing capacitor and turns
charger 183 on or off as
necessary to maintain the charge near 180 volts. Regulator circuit 184 is
constructed with a
predetermined amount of hysteresis so that the charger will go on when the
firing circuit voltage falls
below 175 volts and turn off when the voltage reaches 180 volts, as set by the
voltage divider inputs and
feedback to comparator 185.
The output of comparator 185 is fed to logic controller 50. The logic
controller monitors both the
time required to charge and to discharge the firing capacitor based on the
state of the output of
comparator 185. Thus, the controller can verify that the firing capacitor is
operating properly and storing
adequate charge. If the firing capacitor cannot reach 180 volts quickly enough
or discharges too rapidly,
the logic controller determines that the firing capacitor or charging system
has failed and takes
appropriate action based on its programming.
It should be noted that regulator circuit 184 measures the voltage across the
firing capacitor
through fusible member 70. As a result, the regulator circuit is also testing
the integrity of the fusible
member since a missing or failed fusible member would prevent the regulator
circuit from detecting the
voltage on the firing capacitor. While testing both the firing capacitor
charge and. fusible member with a
single mechanism or test provides obvious savings of both processor cycle time
and component costs, the
fusible member may alternatively be tested separately from the firing
capacitor charge.
A second exemplary implementation of logic controller 50 is illustrated
schematically in Fig.
123. Logic controller 50 is implemented by a 87C752 controller available from
Philips Semiconductor of
Sunnyvale, California. As in the first exemplary implementation described
above, the logic controller of
the second implementation is coupled to power source 20, contact detection
subsystem 22, firing
subsystem 76, user interface 178, motor control 174, and blade rotation sense
177. Suitable examples of
power source 20, contact detection subsystem 22, and motor control 174 are
described in more detail in
Section 1 above. Exemplary firing subsystems 76 are described in Section 6
above. Exemplary circuitry
and mechanisms for sensing blade rotations are described in Section 10 below.
As shown in Fig. 124, the firing capacitor charging circuit for the second
implementation is
regulated by an enable line from logic controller 50. By deactivating the
charging circuit, the logic
controller can monitor the capacitor voltage through an output to an analog-to-
digital converter (A/D)
line on the logic controller. When the capacitor is not being charged, it will
normally discharge at a
relatively known rate through the various paths to ground. By monitoring the
discharge rate, the
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CA 02762156 2011-12-09
controller can insure that the capacitance of the capacitor is sufficient to
burn the fusible member.
Optionally, the logic controller may be configured to measure the voltage on
the firing capacitor at a
plurality of discharge intervals to evaluate the integrity of the capacitor.
In one embodiment, the logic
controller measures the capacitor voltage at three defined intervals during a
discharge cycle, which
should correspond to 3%, 5% and 7% of the full charge voltage. The logic
controller may be configured
to interpret a low voltage at any of the discharge intervals as a failure, or
may require a low voltage at
two or more discharge intervals to indicate a failure.
As with the first exemplary implementation described above, the logic
controller is configured to
test the firing capacitor through fusible member 70, thereby simultaneously
testing the fusible member.
Alternatively or additionally, the logic controller may test the fusible
member independently of the
capacitor by monitoring the capacitor voltage during charging.
As mentioned above, logic controller 50 may also be configured to monitor the
pawl-to-blade
spacing. It is well known in the art that many cutting tools such as saw
blades do not have precisely
uniform dimensions. As a result, when a new blade is installed on a saw, the
pawl may no longer be
correctly spaced from the blade. An incorrectly positioned pawl may slow the
stopping speed of the pawl
or prevent the pawl from stopping the blade. Therefore, to ensure the blade is
stopped with uniform
braking speed, it may be necessary to adjust the position of the pawl whenever
a blade is replaced.
Exemplary mechanisms and methods for automatically positioning the pawl are
described in Section 8
above. However, regardless of whether the pawl is automatically positioned,
configuring logic controller
50 to detect incorrect blade-to-pawl spacing provides an additional level of
assurance that a user is
protected against accidental contact with the blade.
It will be appreciated that there are many ways in which incorrect spacing
between blade 40 and
pawl 60 may be detected. As one example, Fig. 125 illustrates a pawl 945
having a capacitive system for
detecting correct pawl spacing. Similar to pawl 40 shown in Fig. 2, pawl 945
may include a portion 946
that is beveled or otherwise shaped to quickly and completely engage the teeth
of a cutting tool. In
addition, pawl 945 includes a pair of generally parallel, spaced-apart arms
947 which extend beyond
portion 946. Arms 947 are disposed to extend on either side of the blade,
without touching the blade,
when the pawl is in place adjacent the blade. Each arm includes a capacitor
plate 826 disposed on the
inside surface of the arm adjacent the blade. Conductive leads 949 run from
each capacitor plate 826 to
suitable blade detector circuitry (not shown).
Capacitor plates 826 are positioned on arms 947 such that, when the pawl
spacing is within a
desired range, the blade extends between the two capacitor plates. It will be
appreciated that the
capacitance across plates 826 will vary depending on whether the blade is
positioned between the plates.
The blade detector circuitry is configured to drive an electrical signal
through conductive leads 949 and
detect changes in the capacitance across the plates.
87
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Suitable circuitry that may be used with pawl 945 is well known to those of
skill in the art. One
exemplary pawl-to-blade spacing detection circuit is indicated generally at
824 in Fig. 126. As described
above in Sections 1 and 2, one exemplary contact detection system suitable for
use with the present
invention applies an electrical signal to the blade via a drive plate (not
shown). This signal can be picked
up by either or both of plates 826 and monitored to insure that it has an
amplitude in a predetermined
range. In particular, the amplitude detected by plates 826 will fall off
rapidly with distance from the
blade. Therefore, by monitoring the detected amplitude, proper spacing can be
verified. If the proper
signal is not detected, circuit 824 conveys an error signal to logic
controller 50, which prevents operation
of machine 10 until proper pawl-to-blade spacing is detected. Other examples
include circuits similar to
the exemplary contact detection circuits described in Section 1.
Capacitor plates 826 can optionally be shaped to detect when the pawl is too
close to the blade as
well as not close enough. Alternatively, two pairs of capacitor plates may be
positioned on the pawl: one
pair to detect if the pawl is too close to the blade, and the other pair to
detect if the pawl is too far from
the blade. In any event, the detector circuitry is configured to transmit an
error signal to logic controller
50, which then takes appropriate action.
While one exemplary automatic pawl spacing detection system has been described
above, it will
be appreciated that there are many possible variations. For example, both
capacitor plates may be
positioned on the same side of the blade rather than on opposite sides. The
capacitor plates and/or blade
detection circuitry may be separate from the pawl. In the latter case, for
example, the capacitor plates and
detection circuitry may be mounted on a separate electronics board associated
with the pawl.
Alternatively, the capacitor plates may be replaced with one or more light-
emitting diodes and detectors
such that, when the pawl is properly positioned, the blade obstructs the
optical path between the diodes
and detectors. Other methods of detecting the proximity of the blade to the
pawl are also possible. As a
further option, capacitor plates 826 may function as charge plates 44, 46 as
well as pawl-spacing
detectors.. In addition, a detection plate may be mounted on beveled face 946
of the pawl. This plate can
be used to detect the drive input signal used for contact detection. The
amplitude of the signal detected at
the plate will be inversely proportional to the space between the plate and
the teeth of the blade. If this
signal does not have an amplitude over a given threshold, the system would
interpret this as indicating
that the pawl face is not close enough to the blade.
In embodiments where portions of safety system 18 are mounted in a replaceable
cartridge 80,
logic controller may also be configured to detect whether the cartridge is
properly connected to the
remainder of the safety system. One exemplary method of testing for an
operable connection with the
cartridge is by testing a component mounted in the cartridge (e.g., the
fusible link, charge stored by
firing system, etc.). Alternatively, a cable (not shown) connecting cartridge
80 to logic controller 50 may
include a separate signal line which is grounded or otherwise biased when the
cartridge is connected. In
addition to detecting an operable connection to the cartridge, the correct
blade-to-pawl spacing may be
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CA 02762156 2011-12-09
detected by measuring the blade-to-cartridge spacing. For example, capacitor
plates 826 may be placed
on cartridge housing 82 rather than on the pawl itself. Furthermore, failure
of the blade-to-cartridge
spacing test could also be used to detect an inoperable connection to the
cartridge.
The control systems, methods and related machines may be described as set
forth in the
following numbered paragraphs. These paragraphs are intended as illustrative,
and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
9.1 A woodworking machine comprising:
a working portion;
a detection system adapted to detect a dangerous condition between a person
and the working
portion;
a reaction system associated with the detection system to cause a
predetermined action to take
place upon detection of the dangerous condition; and
a control system adapted to control the operability of one or more of the
working portion, the
detection system and the reaction system.
9.1.1 The woodworking machine of paragraph 9.1 where the control system is
adapted to
control the operability of one or more of the working portion, the detection
system and the reaction
system by processing data received from one or more of the working portion,
the detection system and
the reaction system.
9.1.2 The woodworking machine of paragraph 9.1 where the control system is
adapted to
perform self tests on the machine.
9.1.3 The woodworking machine of paragraph 9.1 where the control system is
adapted to
determine whether the'detection system is functioning.
9.1.4 The woodworking machine of paragraph 9.1 where the control system is
adapted to
determine whether the reaction system is functioning.
9.1.5 The woodworking machine of paragraph 9.1 where the reaction system
includes a
capacitor, and where the control system is adapted to perform a self test to
determine whether the
capacitor is functioning.
9.1.6 The woodworking machine of paragraph 9.1 where the reaction system
includes a fusible
member, and where the control system is adapted to perform a self test to
determine whether the fusible
member is in place.
9.1.7 The woodworking machine of paragraph 9.1 where the detection system
imparts an
electric signal to the working portion, and where the control system is
adapted to effectively monitor that
electric signal.
9.1.8 The woodworking machine of paragraph 9.1 where the control system is
adapted to
prevent inadvertent triggering of the reaction system.
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9.1.9 The woodworking machine of paragraph 9.1 where the control system is
adapted to
control display devices relating to the functioning of the machine.
9.1.10 The woodworking machine of paragraph 9.1 where the working portion is
driven by a
motor, and where the control system is adapted to control the motor.
9.1.11 The woodworking machine of paragraph 9.1 where the working portion
includes a blade,
where the reaction system includes a brake pawl positioned adjacent the blade
and adapted to contact the
blade, and where the control system is adapted to monitor the position of the
brake pawl relative to the
blade.
9.1.12 The woodworking machine of paragraph 9.1 further comprising a frame
supporting the
working portion, where the working portion includes an electrically conductive
cutter electrically isolated
from the frame, where the detection system imparts an electrical signal on the
electrically conductive
cutter, and where the control system is adapted to monitor whether the
electrical signal has been imparted
to the electrically conductive cutter.
9.1.13 The woodworking machine of paragraph 9.1 where the reaction system
includes a firing
subsystem to trigger the predetermined action, where the firing subsystem
includes a fusible member, and
where the control system checks whether the fusible member is in place.
9.1.14 The woodworking machine of paragraph 9.1 where the reaction system
includes a firing
subsystem to trigger the predetermined action, where the firing subsystem is
adapted to hold a charge,
and where the control system checks whether the firing subsystem is holding
the charge.
9.1.15 The woodworking machine of paragraph 9.1 where the control system
repeatedly checks
the operability of one or more of the working portion, the detection system
and the reaction system while
the machine is running.
9.1.16 The woodworking machine of paragraph 9.1 where the control system
includes a
microprocessor.
9.1.17 The woodworking machine of paragraph 9.1 where the control system
allows a user to
bypass the reaction system.
9.1.18 The woodworking machine of paragraph 9.1 further comprising a frame
supporting the
working portion, where the working portion includes an electrically conductive
cutter electrically isolated
from the frame, where the detection system imparts an electrical signal on the
electrically conductive
cutter, and where the control system is adapted to monitor whether the
imparted electrical signal
produces a detection signal within a predetermined range.
9.2 A saw comprising:
a blade;
a detection system adapted to detect a dangerous condition between a person
and the blade;
a reaction system associated with the detection system to cause a
predetermined action to take
place upon detection of the dangerous condition; and
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a control system adapted to monitor and control the functioning of the
detection and reaction
systems.
9.3 A method of controlling a saw, where the saw includes a blade driven by a
motor, a
detection system adapted to detect a dangerous condition between a person and
the blade, and a reaction
system associated with the detection system to cause a predetermined action to
take place upon detection
of the dangerous condition, the method comprising:
checking to see whether the detection system is functioning;
checking to see whether the reaction system is functioning; and
powering the motor to drive the blade if the detection and reaction systems
are functioning.
Section 10: Motion Detection
As mentioned above, safety system 18 may include a sensor or sensor assembly
for detecting
motion of the blade or cutting tool. The sensor assembly typically is coupled
to send a signal to logic
controller 50 indicating whether the blade is in motion. The logic controller
may be configured to
respond differently to the detection of a dangerous condition based on whether
the blade is moving. For
example, it is often necessary for a user of machine 10 to touch blade 40 when
preparing the machine for
use, and when installing or removing the blade. Usually, the user would
disconnect all power from
machine 10 while performing such operations. However, in the event that the
user neglects to disconnect
the machine from power source 20 before touching the blade, logic controller
50 would receive a contact
detection signal from detection subsystem 22. If safety system 18 includes a
blade motion sensor, then
logic controller 50 may be configured not to actuate firing subsystem 76 when
the blade is not moving.
Instead, the logic controller may be configured to take one or more other
actions such as disabling motor
assembly 16, sounding an alarm, displaying an error, etc. Alternatively, the
logic controller may be
configured to take no action if contact is detected while the blade is not
moving.
In addition to detecting whether the blade is moving, safety system 18 may
also be configured to
determine the speed at which the blade is moving. This allows the logic
controller to distinguish between
rapid blade movement which could cause injury to the user, and slow blade
movement which generally
would not cause injury to the user. Thus, for example, a user could move the
blade by hand without
actuating firing subsystem 76. In some embodiments, the blade motion sensor
may be configured to
determine relative blade speed. In alternative embodiments, logic controller
50 may be configured to
analyze the signal from the blade motion sensor to determine relative blade
speed.
It will be appreciated that the speed at which a blade is considered likely to
cause injury will vary
depending on the type of machine 10 and blade 40. For example, a 14-inch
carbide tooth blade on a table
saw will cause serious injury at a lower speed than a 5 3/8-inch plywood blade
on a cordless trim saw.
Thus, an embodiment of safety system 18 for use on the table saw may be
configured to actuate the firing
subsystem only at blade speeds above approximately 10, 25, 60, or 90 rpm,
while an alternative
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embodiment of safety system 18 for use on the trim saw may be configured to
actuate the firing
subsystem only at blade speeds above approximately 40, 100, or 240 rpm.
Alternatively or additionally, the logic controller may be configured to
interpret blade motion as
being dangerous only when detected during or soon after motor assembly 16 was
in operation. In other
words, the blade motion detection would only be active while the blade was
being moved by the motor
assembly and during a relatively brief period afterward while the blade was
coasting to a stop. Any blade
motion detected at other times would be ignored.
Safety system 18 may include any of a wide variety of sensor assemblies to
detect blade
movement. Furthermore, each sensor assembly may be adapted as necessary
depending on the particular
type of blade 40 and/or the configuration of machine 10. While several
exemplary sensor assemblies are
described herein, it will be understood that a variety of other methods and
mechanisms may be suitable
for automatically detecting the motion of a blade.
One exemplary embodiment of -safety system 18 includes a magnetic sensor
assembly 1000
configured to detect movement of the blade. It will be appreciated that the
blade movement may be
detected by monitoring the blade or any other portion of the safety system
that moves with the blade,
including the arbor, bearings, motor assembly, arbor pulley, etc. In the
exemplary implementation
depicted in Fig. 127, magnetic sensor assembly 1000 includes a Hall effect
sensor 1001 and one or more
magnets 1002. A coil could also be used to detect magnetic field fluctuations
from rotation. The magnets
are mounted on arbor 42. Sensor 1001 is mounted and configured to detect blade
motion by detecting the
movement of the magnets on the arbor. Sensor 1001 may be any suitable Hall
effect sensor such as, for
example, the sensor available from Micronas Intermetall of San Jose,
California, under the part no.
HAL114.
Hall effect sensor 1001 may be mounted adjacent the arbor by any suitable
method. In the
exemplary implementation, the sensor is mounted in a recessed region 272 of an
insulating tube 268. The
insulating tube also supports charge plates 44 and 46, as is described in more
detail above in Section 2.
The recessed region is disposed over a hole 273 in charge plate 44.
Alternatively the recessed region may
be disposed over a hole 273 in charge plate 46. In any event, magnet 1002 is
disposed on arbor 42 to pass
beneath or adjacent hole 273 as the arbor rotates within the insulating tube.
Hole 273 allows sensor 1001
to detect the field created by magnet 1002 as it passes. Sensor 1001 includes
one or more connector leads
1003 connectable to receive power from, and transmit signals to, logic
controller 50.
Magnets 1002 may be mounted on the arbor in any suitable fashion. Typically,
the magnets are
mounted so as not to extend above the surface of the arbor. For example, the
magnets may be press-fit
and/or glued in a recess formed on the arbor. Alternatively, one or more of
the magnets may be mounted
to extend above the surface of the arbor. The size and number of magnets 1002
may be varied to control
the signal produced by sensor 1001. In alternative embodiments, magnets 1002
may be mounted at other
locations such as adjacent an end of arbor 42, or on blade 40, etc.
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Sensor 1001 may be connected to send signals to logic controller 50 via any
suitable circuitry.
For example, Fig. 128 illustrates one exemplary rotation sense circuit 177
adapted to couple the signals
from sensor 1001 to logic controller 50. Those of skill in the art will
appreciate that circuit 177 may be
modified as needed for a particular application.
Another example of a suitable method for detecting blade motion is through
electromagnetic
field (EMF) measurements. As is known to those of skill in the art, when power
to an electric motor is
shut off, the motor will produce EMF pulses on the input power cables as the
motor spins down. Thus,
where blade 40 is driven by an electric motor assembly 16, the blade may be
assumed to be in motion
whenever an EMF pulse is detected on the power supply cables, as well as
whenever power is being
supplied to the motor assembly.
Thus, in another exemplary embodiment depicted in Fig. 129, safety system 18
includes an EMF
sensor assembly 1005 configured to detect motion of blade. Sensor assembly
1005 includes an EMF
detection circuit 1006 disposed in the power supply path between motor
assembly 16 and power source
20. Circuit 1006 is adapted to monitor power cables 1007 which extend between
the power source and
the motor assembly, and to detect the presence of EMF pulses on the cables.
Alternatively, circuit 1006
may be disposed at any other location suitable for detecting EMF pulses from
motor assembly 16. Circuit
1006 may be any circuit or mechanism adapted to detect EMF pulses, such as are
known to those of skill
in the art. Circuit 1006 is also coupled to logic controller 50, and adapted
to convey a signal to the logic
controller indicating the presence and/or absence of EMF pulses on cables
1007. Optionally, circuit 1006
and/or logic controller 50 may be adapted to analyze the detected EMF
emissions, and evaluate the speed
of blade 40. In such case, the logic controller may be configured not to
actuate firing subsystem 76 when
the speed of the blade is not likely to cause serious injury to the user.
In another exemplary embodiment, safety system 18 includes an optical sensor
assembly adapted
to optically detect movement of blade 40. Safety system 18 may be configured
to optically detect blade
motion in a variety of ways. For example, a rotary optical encoder may be
coupled to the arbor to detect
rotation of the arbor. Any rotary encoder may be used, such as those available
from Omron Electronics
Inc., of Schaumburg, Illinois. Alternatively, other optical sensor assemblies
may be used as described
below.
Typically, the optical sensor assembly will be at least partially enclosed to
prevent saw dust or
other debris from interfering with the detection. One exemplary implementation
of an optical sensor
assembly is indicated generally at 1010 in Fig. 130. Sensor assembly 1010
includes an optical detector
1011 adapted to detect light from an optical source 1012. Alternatively,
plural optical sources and/or
plural optical detectors may be used. It will be appreciated that any of a
variety of different optical
sources may be used which are known to those of skill in the art, including an
incandescent or fluorescent
bulb, light emitting diode (LED), laser diode, etc. Similarly, any of a
variety of different optical detectors
may be used which are known to those of skill in the art, including a
photodiode, phototransistor, etc.
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In any event, the optical source is arranged so that the signal received at
the optical detector
when the blade is moving is different than the signal received when the blade
is stationary. For example,
the source and detector may be arranged so that a signal is received only when
the blade is moving, or
only when the blade is stationary. Alternatively, source 1012 and detector
1011 may be arranged so that
the amount of emitted light that reaches the detector varies when the blade is
in motion.
The implementation depicted in Fig. 130 uses this latter arrangement. Sensor
assembly 1010
includes an LED 1012 mounted in insulating tube 268 to emit light through hole
273 in charge plate 44
or 46. The light reflects off arbor 42 and is detected by a photodiode 1011
which is also mounted in
insulating tube 268 adjacent hole 273. The arbor includes one or more reduced-
reflection regions 1013
adapted to reduce the amount of light reflected to photodiode 1011. Regions
1013 may be formed by
coating the arbor with a light-absorbing coating, roughening the arbor to
cause random scattering of the
light, etc. In any event, the reduced reflecting regions create a varying
signal at the photodiode when the
arbor is rotating. In contrast, a constant signal is produced at the
photodiode when the arbor is stationary.
The minimal clearance between arbor 42 and charge plates 44, 46 tends to
maintain the space
between the arbor and the photodiode/LED relatively free of debris which could
block the signal.
Alternatively, the insulating tube assembly may be sealed in a protective
housing (not shown).
In another alternative implementation depicted in Figs. 131 and 132, optical
sensor assembly
1010 includes a barrier member 1014 mounted on the arbor and disposed between
photodiode 1011 and
LED 1012. Alternatively, the barrier member may be mounted on any other
portion of cutting tool 14 or
motor assembly 16 adapted to move with the blade. Barrier member 1014 includes
one or more light-
transmitting regions or holes 1015, which may take any desired shape or size.
The photodiode and LED
are mounted in a support member 1016 attached to an arbor block 250, and
disposed on either side of
barrier member 1014. The photodiode is aligned so that emitted light will pass
through holes 1015.
Likewise, the LED is aligned to detect the light which passes through the
holes. Thus, as arbor 42 rotates,
light from-the LED is alternately blocked and transmitted by the barrier
member, thereby creating a
varying signal at the photodiode.
Photodiode 1011 and LED 1012 may be connected to any suitable driving
circuitry such as are
known to those of skill in the art. Fig. 133 shows one exemplary circuitry for
producing an optical signal
at LED 1012 and detecting the signal at photodiode 1011. The particular values
of the circuit components
and voltage supplies may be selected as desired for a specific application. In
any event, the photodiode is
coupled to transmit a signal to logic controller 50 to indicate whether blade
40 is moving.
In another exemplary embodiment, safety system 18 includes an electrical
sensor assembly
adapted to electrically detect movement of blade 40. There are numerous
methods and mechanisms for
electrically detecting blade movement. The particular method and/or mechanism
selected will typically
depend on the specific type and configuration of machine 10. For example,
where charge plate 46 is
configured to capacitively detect a signal induced in the blade, any
incidental eccentricity in the blade or
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the blade rotation will cause the capacitance between the blade and charge
plate 46 to vary as the blade
rotates. As a result, charge plate 46 will detect a varying signal amplitude
when the blade is rotating.
Thus, a single sensor may be configured to detect both contact with the user
and rotation of the blade.
Preferably, the incidental variation is insufficient in magnitude and/or rate
of change to trigger reaction
subsystem 24.
Rather than rely on incidental eccentricities, safety system 18 may include an
exemplary
electrical sensor assembly adapted to detect a signal variation caused by a
designed eccentricity or non-
uniformity in the blade. Alternatively, the sensor assembly may be adapted to
detect the signal from an
eccentricity in some portion of cutting tool 14 that moves with the blade and
is electrically coupled to the
blade. One exemplary implementation of such a sensor assembly is indicated
generally at 1020 in Fig.
134. Sensor assembly 1020 includes a detection electrode 1021 capacitively
coupled to detect an
electrical signal on arbor 42. Electrode 1021 may be mounted in any suitable
fashion to provide electrical
insulation from arbor 42 as well as the remainder of cutting tool 14 and
machine 10. In the exemplary
implementation, electrode 1021 is mounted in insulating tube 268 and arranged
to extend to a point
closely adjacent the arbor between charge plates 44 and 46. Sensor assembly
1020 also includes one or
more eccentricities 1022 disposed on the arbor and substantially aligned with
electrode 1021 so as to pass
by the electrode as the arbor rotates.
It will be appreciated that eccentricities 1022 may be configured in any
desired quantity, size,
shape or form adapted to cause a variation in the capacitance between the
arbor and the electrode as the
arbor rotates. In the exemplary implementation, eccentricities 1022 take the
form of beveled regions
formed on the surface of arbor 42. Thus, the space between the electrode and
the arbor is greater (and
therefore the capacitance is less) when an eccentricity is positioned beneath
the electrode than when an
eccentricity is not positioned beneath the electrode. Alternatively,
eccentricities 1022 may take other
forms adapted to vary the capacitance between the arbor and electrode,
including raised regions,
dielectric pads, etc. In any event, if an electrical signal is induced in the
arbor (e.g., by charge plate 44 of
contact detection subsystem 22), then electrode 1021 will detect variations in
that signal if the arbor is
rotating. Conversely, the electrode will detect no variations in the signal if
the arbor is stationary.
Turning attention now to Fig. 135, another exemplary implementation of
electrical sensor
assembly 1020 is shown in which electrode 1021 is disposed adjacent the teeth
1023 of blade 40.
Electrode 1021 may be mounted on arbor block 250 or any other suitable portion
of machine 10.
Additionally, the electrode may be positioned at the side of the blade (as
shown in Fig. 134) or at the
perimeter of the blade facing in toward the arbor. The size, shape and
position of the electrode may vary
depending on the position and size of teeth 1023. In any event, as teeth 1023
pass by electrode 1021, the
capacitance between the blade and the electrode varies, thereby by varying the
amplitude of the signal
detected by the electrode. Alternatively, a plurality of electrodes may be
positioned at various points
adjacent the teeth so that blade motion would be detected by modulations in
the relative signal
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amplitudes at the electrodes. Such an alternative detection mechanism may also
be used with other
implementations of sensor assembly 1020.
While a few exemplary magnetic, EMF, optical and electrical sensor assemblies
have been
described for detecting blade motion, it will be appreciated that many
modifications and variations to
such sensor assemblies are possible. Furthermore, safety system 18 may include
other types of motion
detection sensors such as mechanical sensors, sonic and ultra-sonic sensors,
etc. In any event, the
invention provides effective and reliable means for discriminating between
conditions which are, and are
not, likely to cause injury to a user of power machinery.
The motion detection systems, methods and related machines may be described as
set forth in the
.10 following numbered paragraphs. These paragraphs are intended as
illustrative, and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
10.1 A woodworking machine comprising:
a working portion adapted to work when moving;
a detection system adapted to detect a dangerous condition between a person
and the working
portion;
a reaction system associated with the detection system to cause a
predetermined action to take
place relative to the working portion upon detection of the dangerous
condition; and
a motion detection system adapted to detect motion of the working portion and
to disable the
reaction system when the working portion is not moving.
10.1.1 The woodworking machine of paragraph 10.1 where the working portion is
a spinning
blade and where the motion detection system detects whether the blade is
spinning.
10.1.2 The woodworking machine of paragraph 10.1 where the motion detection
system detects
the speed of the motion and considers the working portion to be not moving if
the working portion is
moving below a threshold speed.
10.1.3 The woodworking machine of any of paragraphs 10.1 where the motion
detection system
includes a sensor.
10.1.3.1 The woodworking machine of paragraph 10.1.3 where the sensor is a
Hall effect sensor.
10.1.3.2The woodworking machine of paragraph 10.1.3 where the sensor is an
electromagnetic
field sensor.
10.1.3.3The woodworking machine of paragraph 10.1.3 where the sensor is an
optical sensor.
10.1.3.4The woodworking machine of paragraph 10.1.3 where the sensor is an
electrical sensor.
10.2 A woodworking machine comprising:
a working portion adapted to work when moving;
a motor to drive the working portion
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a detection system adapted to detect a dangerous condition between a person
and the working
portion; and
a reaction system associated with the detection system to cause a
predetermined action to take
place relative to the working portion upon detection of the dangerous
condition, where the reaction
system causes the predetermined action only when the motor is running or
during a defined period of
time after the motor has been running.
Section 11: Translation Stop
In the case of miter saws, chop saws, radial arm saws, and other power
equipment in which a
cutting tool moves down onto or across a workpiece to cut the workpiece,
reaction subsystem 24 can
include a system to stop the cutting tool from continuing to move down onto or
across the workpiece.
Stopping the translational motion of the cutting tool can minimize any injury
from accidental contact
between a user and the cutting tool.
Fig. 136 illustrates an exemplary implementation of a system to stop the
translational motion of a
cutting tool in the context of a radial arm saw 1100. Typically, radial arm
saw 1100 includes a horizontal
base 1102, a vertical support column 1104 extending upward from base 1102, and
a guide arm 1106 that
extends from column 1104 vertically spaced above base 1102. A carriage 1108 is
slidably coupled to the
underside of guide arm 1106. The bottom end of carriage 1108 is connected to a
saw housing 1110 and to
a motor assembly 1112, allowing a blade 1114 to be pulled across the base to
cut workpieces (not shown)
supported on the base. Radial arm saw 1106 is preferably equipped with a
system as described above to
stop the spinning of the blade, which includes a brake pawl 60 in a cartridge
82.
In use, a user grasps a handle 1116 on the saw and pulls the saw and blade
across a workpiece on
base 1102. In so doing, a user may accidentally pull the saw into contact with
a misplaced finger or some
other part of his body. Upon contact, brake pawl 60 works to stop the blade
from spinning, but since the
user may be pulling the saw toward his or her body when contact is detected,
the saw may continue to
move toward the user even after pawl 60 has stopped the blade. This continued
movement may cause the
stopped blade to be driven over a portion of the user's body (e.g., the user's
hand), causing further injury.
A system to stop the movement of the carriage and saw along the guide arm once
contact is detected
between the blade and the user's body addresses this issue.
It will be appreciated that there are a wide variety of ways to stop the
sliding movement of
bracket 1108 along arm 1106. Fig. 136 illustrates two examples. One example
includes a pivoting wedge
assembly 1118. Assembly 1118 includes a wedge or pawl 1120 pivotally coupled
to guide bracket 1108.
An actuator 1122 mounted on bracket 1108 is operatively coupled to the control
and detection
subsystems associated with brake pawl 60 and cartridge 82 so that when pawl 62
is released, actuator
1122 engages pawl 1 1 20. During normal operation, actuator 1122 maintains the
wedge spaced-apart from
guide arm 1106. However, once contact between the blade and the user's body is
detected, the detection
system sends an actuation signal to actuator 1122. The signal sent to actuator
1122 may be the same
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signal that triggers the release of brake pawl 60, or it may be a different
signal. In any event, upon receipt
of the actuation signal, the actuator drives against wedge 1120, causing it to
pivot into the guide arm,
preventing further movement of the guide bracket forward along the guide arm.
The wedge may be
constructed or coated with a high friction material such as rubber, and/or may
be configured with teeth,
etc., to increase its braking action.
The other exemplary braking configuration illustrated in Fig. 136 includes a
lockable spool
assembly 1124. Assembly 1124 may be used in place of, or in addition to, wedge
assembly 1118. In any
event, the lockable spool assembly includes a spring-loaded spool 1126 mounted
on support column
1104. One end of a tether or cable 1128 is attached to guide bracket 1108,
while the other end is wound
around spool 1126. As the user pulls the saw across the base, the spool
unwinds, allowing the tether to
extend. The spring-loading of the spool ensures that the spool maintains a
slight tension on the tether and
retracts the tether around the spool when the user pushes the saw back toward
the support column.
Assembly 1124 also includes a spool brake, such as pawl 1130, operatively
coupled to the control and
detection systems associated with brake pawl 60. Thus, when contact between
the blade and the user's
body is detected, an actuation signal is sent to the spool brake, causing the
spool to lock. Once the spool
locks, the tether prevents further movement of the saw away from support
column 1104. In an alternative
implementation of spool assembly 1124 not shown in Fig. 136, the lockable
spool may be contained in,
or placed adjacent to, cartridge 82, in which case the tether would run from
the spool backward to
support column 1104.
It will be appreciated that there are many alternative methods, devices, and
configurations for
stopping the travel of the guide bracket and the saw along the guide arm. Any
one or more of these
alternatives may be used in place of, or in addition to, the braking
configurations illustrated in Fig. 136
and described above.
Fig. 137 illustrates an exemplary implementation of a system to stop the
translational motion of a
cutting tool in the context of a miter saw or chop saw 1150. It will be
understood that miter saw 1150
may be any type of miter saw including a simple miter saw, compound miter saw,
sliding compound
miter saw, etc. Typically, miter saw 1150 includes a base or stand 1152
adapted to hold the workpiece to
be cut. A swing arm 1154 is pivotally coupled to base 1152 to allow the arm to
pivot downward toward
the base. Attached to arm 1154 is a housing 1156 adapted to at least partially
enclose a circular blade
1158. A motor assembly 1112 is coupled to the housing, and includes a rotating
arbor 1160 on which the
blade is mounted. Motor assembly 1112 includes a handle 1162 with a trigger
(not shown) operable to
run the saw. An optional blade guard (not shown) may extend from the bottom of
housing 1156 to cover
any portion of the blade exposed from the housing. A person uses miter saw
1150 by lifting the saw up,
placing a workpiece on base 1152, and then bringing the saw down onto the
workpiece to cut the
workpiece.
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Miter saw 1150 also preferably includes a brake pawl 60 in a cartridge 82
configured to stop the
spinning of the blade, as described above. A saw blade spinning at several
thousand revolutions per
minute has substantial angular momentum. Thus, when the brake pawl engages and
stops the blade, the
angular momentum must be transferred to the brake. Because the swing arm of
the miter saw is free to
pivot in the direction of blade rotation, the angular momentum of the blade
may be transferred to the
swing arm when the blade is suddenly stopped, causing the swing arm to swing
downward. This sudden
and forceful downward movement of the swing arm may cause injury to the user
if a portion of the user's
body is beneath the blade.
There are many suitable means for preventing the sudden downward movement of
the swing
arm. For example, the pivotal connection between the swing arm and the base of
the miter saw may be
electrically lockable, for example using an electromagnetic leaf brake, to
prevent the arm from pivoting.
The signal to lock the connection may be provided by the detection system.
Alternatively, a shock
absorber, such as a gas discharge cylinder, may be connected between the swing
arm and the base to limit
the speed with which the swing arm can pivot relative to the base, as shown at
1180 in Fig. 137. This
arrangement also serves to limit how far the blade moves between the time
contact between the blade and
user is detected, and the time the blade is stopped by the pawl. While there
are many other ways of
connecting the swing arm to the base to prevent sudden movement of the arm
toward the base, most such
arrangements transfer the angular momentum to the swing arm/base assembly.
Depending on the weight
and balance of the saw, the angular momentum may be sufficient to cause the
entire saw to overturn.
Therefore, it may be desirable to secure the base to a stable surface with
clamps, bolts, etc.
Figure 137 shows one way to prevent the sudden downward movement of swing arm
1154.
Swing arm 1154 includes a cam portion 1170 having a cam surface 1172. Cam
portion 1170 may be
integral with the swing arm and housing 1156. A stopping pawl 1174 is mounted
to vertical support 1104
adjacent cam surface 1172, and an actuator 1176 is positioned adjacent pawl
1174. The actuator 1176 is
operatively coupled to the control and detection subsystems associated with
brake pawl 60 and cartridge
82 so that when pawl 62 is released, actuator 1176 engages pawl 1174. During
normal operation, actuator
1176 maintains the pawl spaced-apart from cam surface 1172. However, once
contact between the blade
and the user's body is detected, the detection system sends an actuation
signal to actuator 1176, which
may be the same or a different signal that triggers the release of brake pawl
60. In any event, upon receipt
of the actuation signal, the actuator drives against pawl 1174, causing it to
pivot into cam surface 1172,
preventing further movement of the swing arm. Pawl 1174 may be constructed or
coated with a high
friction material such as rubber, and/or may be configured with teeth, etc.,
to increase its braking action.
Cam portion 1170 may be modified so that it extends as far as possible from
the point around which it
pivots, in order to provide as great a moment arm as possible to help stop the
downward motion of the
swing arm.
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The miter saw in Fig. 137 also includes a piston/cylinder 1180 connected
between swing arm
1154 and base 1152. That piston/cylinder limits the speed with which the swing
arm can pivot relative to
the base, and can also serve to stop or limit the downward motion of the blade
when accidental contact
with the blade is detected.
There are many alternative methods, devices, and configurations for stopping
the swing arm from
moving down. Any one or more of these alternatives may be used in place of, or
in addition to, the pawl
and cam configuration illustrated in Fig. 137 and described above. What is
important is to provide a
mechanical stop to halt the downward motion of the swing arm when the blade
contacts a user.
Fig. 138 illustrates an alternative translation stop mechanism implemented in
the context of a
pneumatic up-cut chop saw 1181. Chop saw 1181 includes a blade 40 mounted to a
pivotal arbor block
1182. The blade and/or some associated portion of the saw, are electrically
isolated and coupled to a
detection system as described in Sections 1 and 2 above. This arrangement
allows detection of contact of
the blade with a user as described in those cases.
The arbor block is pivoted to the upward position shown in the dashed lines by
a pneumatic
cylinder 1183. The cylinder may be actuated by the user, such as by stepping
on a foot switch, or may be
operated by an electronic controller. In either case, a solenoid valve (not
shown) is normally provided to
control the delivery of air to the cylinder. A blade guard 1184 is provided to
cover the blade as it emerges
through the top of the table. In many cases the blade guard moves down upon
actuation of the saw to
serve as a hold down on the material being cut. A metal strip 1885 along the
bottom of the blade guard
can therefore be electrically isolated and used as an electrode to also detect
contact with a user as
described above. Because the blade guard is not spinning, it may not be
necessary to use a capacitive
coupling to detect contact, and any suitable system can be utilized. In any
case, the detection system then
monitors for contact between the bottom of the blade guard and a user.
Although not essential, it is
preferable that the control subsystem only treat a detected contact as a
dangerous condition and trigger
the reaction system during actual actuation of the saw. Otherwise, inadvertent
contact when the user is
positioning stock to be cut may result in false triggers where no danger was
present. However, if the
bottom of the guard is touching the user at any time during the actuation
cycle of the saw, the reaction
system should be triggered. Because the user's hand may be covered by a glove
or may be positioned
under the board, in most cases it is not sufficient just to use the blade
guard for contact detection. Rather,
contact between the user and the blade (as the blade passes through the glove)
can also be monitored and
trigger the reaction system. Alternatively, the glove can be constructed of,
or incorporate, electrically
conductive material.
As an alternative or in addition to monitoring for contact with the blade
guard, a region of the
table of the saw around the blade opening can be isolated and monitored for
user contact, just as with the
blade guard. For instance a metal strip 2cm wide with a slot for the blade to
pass through can be installed
in an insulating material into the portion to the table through which the
blade projects. This strip can then
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serve as a contact detection electrode. Therefore, if a user's hand contacts
the electrode on the table, i.e.
is on the table within 1cm of the blade, when the saw is actuated, the
reaction system can be triggered.
Similar systems can of course be used on many other types of woodworking
machinery, such as on the
infeed section of a planer, to detect dangerous conditions.
Saw 1181 includes a reaction system 24 configured to interrupt the upward
motion of the saw if
contact with a user is detected at the guard/table or by the blade. Reaction
system 24 includes a first link
1186a extending between arbor block 1182 and an end of a lever link 1186b. The
lever link pivots about
a pivot point 1187 and is connected at the opposite end to a second link
1186c. The pivot point is
positioned so that the second link travels substantially farther than the
first link during actuation of the
saw. A spring 1188 is connected to the free end of the second link to tension
the entire linkage
mechanism against upward motion of the saw. This tension, although not
essential, is beneficial to insure
that any slop in the linkage is already taken up when the brake is actuated,
as described below, to thereby
minimize upward travel after actuation.
The reaction system also includes a brake mechanism 28 in the form of a pawl
1189. The pawl is
mounted on a pivot 1190 and biased toward the second link by a biasing
mechanism 30 in the form of a
stack 1191 of belleville springs. The springs are preferably positioned to
push the pawl against the pivot
in a direction to minimize any slop or play in uptake when the face of the
pawl contacts the second link.
Again, this reduces the upward movement of the blade after triggering of the
brake. A restraining
mechanism in the form of an electromagnet 1192 is magnetically connected to
the upper side of the pawl
to hold the pawl against the biasing mechanism. Typically, the pawl is
constructed from a hard, magnetic
metal and is provided with serrations on the front surface to grip or bite
into the link when engaged. The
pawl can also be provided with a magnetic plate attached to the top to engage
the electromagnet. A slide
surface 1193 is provided opposite the pawl to guide the second link and
provide a support for the second
link when the pawl pushes against the linkage. A retainer 1194 holds the
second link against the slide
surface so no play is present when the pawl is actuated and to insure that the
link does not accidentally
contact the pawl prior to release. The face of the pawl is preferably
positioned so that it rides very close -
preferably between 0.1 mm and 2mm - to minimize the time required for
engagement with the link.
Under normal conditions, a current is driven through the electromagnet to hold
the pawl. Upon
actuation of the reaction system, the electrical current is interrupted, and
preferably a current of the
opposite polarity is applied for a short period of time, to quickly release
the pawl to be pushed over into
contact with the second linkage by the spring. The pawl then immediately binds
against the second
linkage to prevent further upward motion of the blade. Simultaneously, the
pneumatic cylinder is
reversed to begin retraction of the blade. Simple reversing of the cylinder by
a standard solenoid valve,
by itself, is not fast enough to stop upward motion quickly enough to prevent
serious injury. Braking by
the pawl, however, can stop upward motion in 1-5 milliseconds and restrain the
pneumatic cylinder until
the solenoid valve can be reversed to retract the blade. Preferably, the
retraction begins in substantially
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less than 100 milliseconds so that the user does not have time to react and
jerk their hand across the still
spinning blade, thereby causing more serious injury.
After the brake pawl is released, a shoulder 1195 located on the second link
is positioned to reset
the pawl against the electromagnet when the blade is fully lowered. When the
blade is lowered, the
shoulder pushes against the underside of the pawl to lift the pawl back into
contact with the
electromagnet. This resets the system so that it is ready for repeated use. It
should be understood that the
electromagnetic release can be used interchangeably with the fusible member
release previously
described. The fusible member is generally cheaper to implement, but has the
disadvantage of being
suitable for only a single use.
An alternative reaction system configuration to stop translational movement
similar to the system
of Fig. 138 is shown in Fig. 139. The system of Fig. 139 includes only a
single link 1186 connected to an
extension arm 1199 connected to arbor block 1182. The extension arm provides
some mechanical
advantage, similar to the lever link of Fig. 138. When the reaction system is
actuated, pawl 1189 grips
link 1186 as previously described to stop upward movement of the blade. As
before, spring 1188
maintains a tension on the link to take up any play that may be present or
develop in the mechanism. It
should be understood that the system of Figs. 138 and 139 could be used
together to create additional
mechanical advantage in the translation stopping mechanism.
Fig. 140 illustrates another reaction system similar to those of Figs. 138 and
139. In the reaction
system of Fig. 140, the brake is mounted on a carriage 1196, which slides
along link 1186 on bushing
1197. The carriage is mounted to a brace 1198 that is coupled to arbor block
1182 to pivot therewith. As
the arbor block pivots upwardly, the carriage is driven along the link. When
contact is detected, the pawl
is released to catch against the surface of the link and stop the upward
travel of the blade. As described
above, springs 1188 and 1191 are positioned to eliminate any play in the
translation stop mechanism. It
should be noted that different cut-off saws have different mechanisms, such as
cams, eccentrics, etc., to
raise and lower the blade and the above-described translation stops and
variations thereof can be applied
to such different mechanisms as well.
The translation stops described above can also be used in connection with
various braking or
blade retraction systems to obtain combined benefit. For instance, the blade
may be braked at the same
time as the translation stop is engaged to further minimize the chance of
serious injury. Alternatively or
in addition, a retraction mechanism may be provided to quickly retract the
blade.
The systems and methods to stop translational motion, and related machines,
may be described as
set forth in the following numbered paragraphs. These paragraphs are intended
as illustrative, and are not
intended to limit the disclosure or claims in any way. Changes and
modifications may be made to the
following descriptions without departing from the scope of the disclosure.
11.1 A woodworking machine comprising:
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a cutting portion, where the cutting portion is adapted to move
translationally relative to a
workpiece to be cut;
a detection system adapted to detect a dangerous condition between a person
and a determined
portion of the machine; and
5. a reaction system adapted to interrupt the translational movement of the
cutting portion upon the
detection by the detection system of the dangerous condition between the
person and the portion of the
machine.
11.1.1 The woodworking machine of paragraph 11.1 where the determined portion
of the
machine is the cutting portion.
11.1.2 The woodworking machine of paragraph 11.1 where the determined portion
of the
machine is a guard.
11.1.3 The woodworking machine of paragraph 11.1 where the reaction system is
adapted to
interrupt the translational movement of the cutting portion by stopping that
movement.
11.1.4 The woodworking machine of paragraph 11.1 where the reaction system is
adapted to
interrupt the translational movement of the cutting portion by reversing that
movement.
11.1.5 The woodworking machine of paragraph 11.1 further comprising a brake
system to stop
the motion of the cutting portion upon the detection by the detection system
of the dangerous condition.
11.1.6 The woodworking machine of paragraph 11.1 where the determined portion
is the cutting
portion, and where the dangerous condition is contact between the person and
the cutting portion.
11.1.7 The woodworking machine of paragraph 11.1 where the determined portion
is the cutting
portion, and where the dangerous condition is proximity between the person and
the cutting portion.
11.2 A radial arm saw comprising:
a guide arm;
a blade mounted to slide along the guide arm;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system adapted to interrupt the sliding movement of the blade upon
the detection by
the detection system of the dangerous condition between the person and the
blade.
11.2.1 The saw of paragraph 11.2 where the reaction system includes a member
configured to
contact and wedge against the guide arm.
11.2.1.1 The saw of paragraph 11.2.1 where the member is a pawl.
11.2.2 The saw of paragraph 11.2 where the blade is mounted to slide along the
guide arm on a
support structure, where the reaction system includes a tether between the
support structure and an
anchor, and where the tether is adapted to stop the sliding of the blade on
the guide arm upon detection of
the dangerous condition.
11.2.2.1 The saw of paragraph 11.2.2 where the tether is adapted to play out
as the blade slides
along the guide arm.
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11.2.2.2The saw of paragraph 11.2.2 where the tether is would around a spool,
and where the
spool is locked to prevent the tether from playing out upon detection of the
dangerous condition.
11.3 A miter saw comprising:
a base;
a swing arm supported by the base and adapted to pivot toward a workpiece to
be cut;
a blade mounted to move with the swing arm to contact the workpiece when the
pivot arm pivots
toward the workpiece;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system adapted to interrupt the movement of the blade and swing arm
upon the
detection by the detection system of the dangerous condition between the
person and the blade.
11.3.1 The miter saw of paragraph 11.3 where the reaction system includes an
electric lock
configured to prevent the swing arm from pivoting.
11.3.2 The miter saw of paragraph 11.3 further comprising a piston/cylinder to
limit the speed
with which the swing arm can pivot.
11.3.3 The miter saw of paragraph 11.3 where the swing arm includes a cam
portion, and
further comprising a pawl adapted to engage the cam portion to stop the
pivoting of the swing arm upon
the detection of the dangerous condition.
11.4 A safety system for machines, the safety system comprising:
a detection system adapted to detect a dangerous condition between a person
and a working
portion of a machine, where the working portion has a motion; and
a reaction system associated with the detection system to interrupt the motion
of the working
portion upon detection of the dangerous condition between the person and the
working portion by the
detection system.
11.4.1 The safety system of paragraph 11.4 where the dangerous condition is
contact between the
person and the working portion of the machine, and where the detection system
is adapted to capacitively
impart an electric charge on the working portion and to detect when that
charge drops.
11.4.2 The safety system of paragraph 11.4 where the motion of the working
portion is
translational, and where the reaction system stops that translational motion.
11.4.3 The safety system of paragraph 11.4 where the relation system
interrupts the motion of
the working portion within 25 milliseconds after detection of the dangerous
condition.
11.5 A chop saw comprising:
a blade mounted on a pivotal arbor block and adapted to pivot into contact
with a workpiece to
cut the workpiece;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system adapted to interrupt the movement of the blade and pivotal
arbor block upon
the detection by the detection system of the dangerous condition between the
person and the blade.
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11.5.1 The chop saw of paragraph 11.5 further comprising a pneumatic cylinder
to pivot the
blade and pivotal arbor block.
11.5.2 The chop saw of paragraph 11.5 where the detection system detects
contact between the
person and the blade.
11.5.3 The chop saw of paragraph 11.5 further comprising a blade guard, and
where the
detection system detects contact between the person and the blade guard.
11.5.4 The chop saw of paragraph 11.5 further comprising a worksurface through
which the
blade extends to cut the workpiece, and where the detection system detects
contact between the person
and at least a portion of the worksurface.
11.5.5 The chop saw of paragraph 11.5 where the reaction system comprises a
brake
mechanism and a linkage between the pivotal arbor block and an anchor, where
the linkage includes at
least a portion that moves when the pivotal arbor block pivots, and where the
brake mechanism is
adapted to restrict the movement of the linkage to stop the motion of the
pivotal arbor block.
11.5.6 The chop saw of paragraph 11.5 where the reaction system comprises:
a linkage having a lever link adapted to pivot around a pivot point, the lever
link having two ends
and the pivot point being closer to one end than the other end, a first link
connected between the pivotal
arbor block and the end of the lever link closest to the pivot point, and a
second link connected to the
other end of the lever link, where movement of the pivotal arbor block causes
the first link to move,
which in turn causes the lever link to pivot around the pivot point, which in
turn causes the second link to
move; and
a brake mechanism adapted to stop the movement of the second link, which in
turn stops the
movement of the pivotal arbor block.
11.5.6.1The chop saw of paragraph 11.5.6 where the reaction system further
comprises a spring
connecting the second link to a predetermined point.
11.5.7 The chop saw of paragraph 11.5 where the reaction system comprises:
a member fixed to and extending from the pivotal arbor block and moving with
the pivotal arbor
block;
a link attached at one end to the member, where the link moves with the
member; and
a brake mechanism adapted to stop the movement of the link, which in turn
stops the movement
of the pivotal arbor block.
11.5.7.1The chop saw of paragraph 11.5.7 where the reaction system further
comprises a spring
connecting the link to a predetermined point.
11.5.8 The chop saw of paragraph 11.5 where the reaction system comprises:
a brace mounted to the pivotal arbor block and adapted to move with the
pivotal arbor block;
a link associated with the brace;
a carriage fixed to the brace and adapted to slide on the link as the brace
moves; and
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a brake mechanism adapted to stop the movement of the carriage, which in turn
stops the
movement of the brace and pivotal arbor block.
11.5.8.1The chop saw of paragraph 11.5.8 where the reaction system further
comprises a spring
connecting the link to a predetermined point.
11.5.9 The chop saw of paragraph 11.5 where the reaction system comprises a
brake
mechanism and a linkage between the pivotal arbor block and an anchor, where
the linkage includes at
least a portion that moves when the pivotal arbor block pivots, where the
brake mechanism is adapted to
restrict the movement of the linkage to stop the motion of the pivotal arbor
block, where the brake
mechanism includes a brake pawl, and where the brake mechanism includes an
electromagnet adapted to
hold the brake pawl in a non-braking position until detection of the dangerous
condition.
11.5.9.1 The chop saw of paragraph 11.5.9 further comprising a member
configured to engage the
brake pawl and move the brake pawl into contact with the electromagnet to
thereby set the brake in a
non-braking position.
Section 12: Cutting Tool Disablement
In many of the embodiments described above, reaction subsystem 24 is
configured to stop and/or
retract a blade. However, alternative embodiments of reaction subsystem 24 may
be configured to
prevent serious injury to a user in other ways. For example, Fig. 141
illustrates one embodiment of a
reaction system adapted to disable the dangerous portions of a cutting tool.
In the embodiment of Fig.
141, the cutting tool is a generally cylindrical cutting head having one or
more elongate blades mounted
on the outer surface of the cutting head. Such cutters are used in jointers,
such as jointer 1200, and
planers. In operation, the cutting head is rotated about its cylindrical axis.
When a workpiece is passed
across the cutting head, the blades make wide cuts into the adjacent surface
of the workpiece. As with
machines using circular blades described above, machines using cylindrical
cutting heads may also cause
severe injury if the blades come into contact with the user's body during
operation. The reaction
subsystem of Fig. 141, indicated at 24, is designed to prevent or minimize
such injury. For clarity, many
of the components of safety system 18 are not shown in Fig. 141 since they are
similar to the components
described above in the context of other cutting machines.
Jointer 1200 includes a generally cylindrical cutterhead 1202 mounted to
rotate on an arbor 1204.
The arbor typically is mounted in one or more bearing assemblies (not shown)
and rotationally driven by
a motor assembly (not shown), which is coupled to the arbor either directly or
by a belt-and-pulley
system. The cutterhead is mounted in a. main frame assembly 1206 to extend
upward in the space
between infeed table 1208 and outfeed table 1210. A workpiece is cut by
sliding it along infeed table
1208, past the cutterhead and onto outfeed table 1210. Typically, the vertical
positions of the infeed and
outfeed tables are independently adjustable to control the depth of cut into a
workpiece and alignment
with the upper surface of the cutterhead.
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The cutterhead is usually constructed of metal, such as steel, and typically
includes three knife
blades 1212 mounted to extend above the surface of the cutterhead. It will be
appreciated that fewer or
more knife blades may be used and that the utility of safety system 18 is not
limited by the number of
blades on cutterhead 1202. One or more electrically non-conductive bushings
1214 are placed between
the cutterhead and arbor to insulate the cutterhead and blades from frame
1206. Charge plates 44 and 46
may be placed adjacent the cutterhead to couple the signal generated by the
detection subsystem across
the cutterhead. In Fig. 141, the charge plates (shown in dashed lines) are
mounted adjacent one flat end of
the cutterhead. Alternatively, the arbor may be insulated from the frame and
the charge plates may be
positioned around the arbor as described above in Section 2.
Due to the relatively few blades, first contact between the user's body and
the cutterhead may be
on one of the blades or on the surface of the cutterhead itself. However, the
blades and cutterhead are
electrically coupled so that any contact with the user's body is detected
regardless of whether or not it
occurs on the blades. Once contact is detected, the reaction system is
actuated to quickly stop the rotation
of cutterhead 1202 and/or disable the blades.
In the embodiment depicted in Fig. 141, safety system 18 includes a reaction
system 24
configured to cover the blades to prevent them from causing injury to the
user. Specifically, the reaction
system of Fig. 141 includes a flexible sheet 1220 such as plastic, rubber,
metal foil, metal sheet, metal
mesh, fabric, etc., configured to cover the blades. A particularly preferred
material is stainless steel sheet
0.005-0.050 inches thick. Sheet 1220 includes a hook 1222 disposed at one end
to engage any of the
blades 1212. The hook is preferably formed integrally with the sheet in the
form of a short fold shaped to
catch on a blade. Alternatively, the hook may be separate and joined to the
sheet. When hook 1222 is
pushed against cutterhead 1202, the next passing blade catches the hook,
causing sheet 1220 to wrap
around the cutterhead as it rotates. Thus, the blades are covered by sheet
1220, which protects the user
from serious injury. Typically, the outer surface of hook 1222 is rounded or
beveled to prevent injury to
the user when the hook is pulled around the cutterhead.
The sheet preferably extends across the entire width of the cutterhead and is
preferably longer
than two-thirds of the circumference of the cutterhead to allow it to cover
all three blades simultaneously.
More preferably, the sheet should be longer than the circumference of the
cutterhead to wrap more than
once around the head. The sheet is typically formed with an inward curl. The
curl reduces the tendency of
the sheet to spring away from the cutterhead. The free end of the sheet is
stored around a spool 1224. The
spool may include a torsion spring or other device to limit the number of
rotations the spool can undergo,
thereby pulling the cutterhead to a stop. Alternatively, the end of material
1220 opposite the hook may be
anchored to stop the cutterhead before it makes a full rotation. Additionally
or alternatively, the jointer
motor assembly may be shut off to stop rotation of the cutterhead.
The hook is moved into contact with the cutterhead by being mounted to the
front of a drive plate
1226 or other high speed actuator assembly. The hook may be spot welded or
adhesively attached to the
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plate, secured thereto with soft rivets, or may be provided with several holes
through which protrusions
on the plate can be pushed. The attachment needs to hold the hook securely
during normal use, while
allowing it to split away when caught by a blade. The drive plate is
preferably substantially as wide as
the hook to provide sufficient rigidity to insure that the entire hook engages
a blade simultaneously.
Figs. 142-144 illustrate an alternative blade covering system for a machine
using a circular blade.
The reaction system of Fig. 142 includes a band 1230 of flexible material that
is used to wrap around the
teeth of blade 40. Band 1230 includes a loop 1232 formed at the leading end.
The loop is hooked around
a pair of torsion springs 1234 and held in place by a guide structure (not
shown) secured to the frame of
the saw. The springs are held in a cocked position by a fast-acting release
system (not shown), such as
described above in Sections 4 and 6. When the springs are released, they pull
loop 1232 down into a
gullet 1236 of blade 40. The gullet captures the leading edge of the loop and
pulls the loop off of the
springs and drags the band forward as illustrated by the dashed lines in Fig.
142. The width of the loop
forms a shock absorbing structure to absorb some of the impact of the gullet
catching the loop. It is also
possible to provide a compressible material at the leading end of the loop as
a shock absorbing system to
reduce impact loading.
The trailing section of the band is shaped to fold over the teeth of the
blade, as shown in Fig. 143.
The trailing section of the band is stored on a spool 123 8. The C-shape of
the band flattens out when the
band is wound on the spool. The band is preferably formed of a spring-temper
material to return to an
unbiased C-shape when curved to match the perimeter of the blade, such as
spring temper stainless steel
of 0.005 to 0.050 thickness.
The leading end of the band is preferably positioned as close as possible to
the location where the
blade emerges from the guard or housing on the saw. This insures that the band
will reach the location of
the user as soon as possible to minimize injury. The motor of the saw will
preferably be disengaged as
soon as the reaction system is actuated. In addition, the reaction system of
Figs. 142-144 is also
preferably used in connection with translation stopping systems such as
described above in Section 11, or
retraction systems such as disclosed above in Section 3, to further minimize
injury.
Fig. 145 illustrates another alternative reaction system in which the cutter
is obstructed upon
actuation of the reaction system. In particular, a pawl 1240 is pushed into
contact with the teeth of blade
40 upon actuation of the reaction system. The pawl is preferably formed from a
plastic material, such as
polycarbonate, that forms curls 1242 in gullets 1236 between the teeth upon
being cut by the teeth. The
curls block the sharp edges of the teeth to prevent the teeth from cutting
into a user. The pawl may also
be constructed from material softer than polycarbonate, such as ultra-high
molecular weight polyethylene
(UHMWPE) to reduce the braking effect on the blade as the curls are formed.
The blade should
preferably have gullets that are shaped with relatively parallel sides to
minimize the tendency of the curls
to slip out. As with the band system described above, it is preferable that
the pawl be located as close as
possible to where the blade emerges from the guard or housing to minimize the
number of unblocked
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teeth to which the user is exposed. Of course, the same principle can be
applied to other cutters, such as a
jointer or shaper, with appropriate modification.
Fig. 146 illustrates another alternative reaction system in which the teeth on
the cutter are broken
or shifted. A pawl 1244 is provided to selectively engage the teeth of blade
40. The pawl is formed of a
material hard enough to dislodge or break the carbide inserts 1246 on the
teeth upon contact. Suitable
materials would include carbide and hardened steel. The pawl is actuated by
the mechanism described
above for brake pawl 60. When actuated, the pawl shifts into the path of the
teeth of the blade, as
illustrated in Fig. 146. The pawl shifts into contact with a brace structure
1248 adapted and positioned to
support the pawl against the teeth. Brace structure may be in any suitable
form including a pin, post,
bracket, etc. In any event, the carbide inserts are shattered by the impact
from striking the pawl. This
reaction system is preferably used in conjunction with translation stopping
systems or retraction systems,
and serves primarily to generate sufficient user-to-blade clearance to give
the translation or retraction
system more time to operate.
Figs. 147 and 148 illustrate another embodiment of a reaction system in which
a cutting tool is
wrapped with a covering. A shaper is shown at 1260 with a work surface 1262, a
fence 1264 and a
cutting head 1266. A workpiece is slid on the work surface and along the fence
past the cutting tool. The
cutting tool shapes the workpiece at is moves past. The safety system on
shaper 1260 includes a pair of
vertically spaced shafts 1268 that pivot around pin 1270. Shafts 1268 are
biased toward cutting head
1266 by spring 66, as explained above in connection with other embodiments. A
fusible member 70
restrains shafts 1268 from pivoting toward the cutting head. The safety system
also includes a covering
1272, which takes the form of a sheet of material mounted between the two
shafts as shown in Fig. 148.
The covering is mounted to the shafts by pockets 1274 and 1276 formed in the
material. The shafts are
slipped into the pockets so that the covering spans the area between the
shafts. The pockets extend along
the upper and lower edges of the covering on the end of the covering adjacent
the shafts. The covering
extends away from the shafts and is wound on a spool 1278. When the system
detects accidental contact
with cutting head 1266, as described above in connection with other
embodiments, fusible member 70 is
burned and shafts 1268 are released to pivot toward the cutting head because
of spring 66.. When shafts
1268 move toward the cutting head, the covering contacts the cutting head and
the cutting head catches
on or bites into the covering and pulls the covering off of shafts 1268 and
off of spindle 1278 until the
covering has wrapped the cutting head. The covering can be any material
sufficiently strong to absorb the
sudden acceleration when caught on the cutting head, and sufficiently pliable
to catch on the cutting head
and wrap around it. Possible materials include Kevlar fabric, stainless steel
mesh, natural or synthetic
fabrics, etc. The covering may be used in connection with an internal brake to
more rapidly slow the
cutting head or the power to the motor may be disengaged to stop the cutting
head.
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The various ' embodiments described above for covering, blocking or disabling
the cutter are
particularly suitable for use on relatively light machinery, such as portable
circular saws and miter saws,
or on machinery with relatively heavy cutters such as jointers, shapers and
planers.
The systems and methods for cutting tool disablement and safety, and related
machines, may be
described as set forth in the following numbered paragraphs. These paragraphs
are intended as
illustrative, and are not intended to limit the disclosure or claims in any
way. Changes and modifications
may be made to the following descriptions without departing from the scope of
the disclosure.
12.1 A machine, comprising
a cutting element;
a motor adapted to drive the cutting element;
a detection system adapted to detect a dangerous condition; and
a reaction system adapted to at least partially shield the cutting element in
respond to detection of
a dangerous condition.
12.1.1 The machine of paragraph 12.1, wherein the cutting element is circular
with cutting
edges disposed around a perimeter and the reaction system includes a strip of
material adapted to wrap
around the perimeter of the cutting element.
12.2 A machine comprising:
a cutting element with one or more cutting edges;
a motor adapted to drive the cutting element;
a detection system adapted to detect a dangerous condition; and
a reaction system adapted to disable the cutting edges upon detection of a
dangerous condition by
the detection system.
12.2.1 The machine of paragraph 12.2, wherein the reaction system separates
the cutting edges
from the cutting element.
12.3 A machine comprising:
a cutting element having one or more cutting edges;
a motor adapted to drive the cutting element;
a detection system adapted to detect a dangerous condition related to the
cutting element; and
a reaction system adapted to block the cutting edges in response to detection
of the dangerous
condition.
Section 13: Table Saw
It will be appreciated that safety system 18 may be configured for use on
table saws in a variety
of ways. Figure 149 shows one type of a table saw 1400, often called a
contractor's saw. It includes a
table 1401 through which a blade 1402 extends from beneath the table. The
table and blade are supported
by a housing 1403 and legs 1404. Housing 1403 encloses the mechanics that
support, position and drive
the blade. A motor to drive the blade can be positioned in or outside of the
housing. A switch 1405 turns
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the saw on and off, causing blade 1402 to spin. Handles, such as handle 1406,
are used to adjust the
position of the blade relative to the table, for example, how far the blade
extends above the table or how
the blade tilts relative to the top of the table. Of course, table saws take
many different configurations,
from large saws sized for industrial use to small saws that can be placed on a
bench top or counter, and
table saws come with various types of tables and housings. Essentially, a
table saw is a saw with a flat
workspace or "table" and a cutting blade projecting up through the table. A
user places a workpiece on
the table and slides it into the blade to cut the workpiece.
Figures 150 and 151 show side elevation views of the internal mechanism one
type of table saw
configured with a safety system as described above. Figure 152 shows a bottom
view of the same saw,
and Fig. 153 shows a perspective view.
In the saw, blade 1402 is mounted on an arbor 1407 by a nut (not shown). The
arbor spins the
blade in the direction of arrow 1409. Table 1401 (not shown in Fig. 151),
which defines the work surface
for the table saw, is adjacent the blade and the blade extends above the
table.
An arbor block 1410 supports arbor 1407 and holds the arbor in bearings to
allow the arbor to
rotate. The arbor is connected to a motor (not shown), such as by a belt
extending around a pulley on the
arbor and a pulley on the motor's drive shaft, and the motor drives or spins
the arbor, as is known in the
art. The motor may be mounted on motor plate 1411 shown in Fig. 150.
Arbor block 1410 is also mounted on a pin 1412 and may pivot around that pin.
Pin 1412, in
turn, is mounted to a support member 1413 that, along with another support
member 1414, comprise at
least part of the supporting frame from the table saw. The supporting frame is
connected to the housing,
legs, and/or table.
Blade 1402 is configured to pivot up and down so that a user can position the
blade to extend
above the table as needed. The blade pivots around pin 1412. A user may pivot
the blade to adjust its
position by turning a shaft 1415 on which a worm gear 1416 is mounted. The
worm gear is mounted on
the shaft so that it turns with the shaft, but so that it may slide on the
shaft when necessary, as explained
below. Worm gear 1416 is mounted on shaft 1415 like a collar, with the shaft
extending through a
longitudinal hole in the worm gear. The worm gear is held in place during
normal operation of the saw by
a spring clip 1417, which is positioned in a notch or channel on the worm gear
and which also engages a
detent or groove on shaft 1415 to hold the worm gear in place. The worm gear
engages a rack or segment
gear 1418 that is connected to or part of arbor block 1410. Thus, when a user
turns shaft 1415, such as by
turning a knob or handle attached to the shaft, like handle 1406 in Fig. 149,
worm gear 1416 moves rack
1418 and the blade up and down, depending on the direction that the worm gear
is turned.
Most table saws are also configured to allow blade 1402 to tilt from side to
side relative to table
1401. That is accomplished by a system similar to shaft 1415, worm gear 1416,
and rack 1418, but
oriented generally perpendicularly to the plane of the blade. Support members
1413 and 1414 may be
used as part of that system; for example, support member 1414 may comprise a
segment gear or rack like
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rack 1418. The support members include arcuate projections 1440 that fit into
arcuate grooves or slides in
mounting blocks (not shown) to allow the support members to pivot. The
mounting blocks are secured to
the table of the saw.
A brake cartridge 1419 is mounted in the saw adjacent blade 1402. (The
cartridge is shown open
in Figs. 150 and 152, and shown with a cover in Fig. 153.) The cartridge may
be configured as described
above in Sections 7 and 8. The brake cartridge includes a pawl 1420 biased
toward blade 1402 by a
spring 1421. Various pawls are described in more detail in Section 5 above.
The pawl is held away from
blade 1402 by a release mechanism 1422, as described in Section 4 above. The
cartridge is configured so
that the release mechanism releases the pawl into the blade upon the receipt
of a detection signal, as
explained in more detail in Section 6 above. The detection signal that causes
the release of the pawl, and
the system or systems to generate that signal, are explained in more detail in
Sections 1 and 2 above.
Electronics that form at least part of the system to detect contact between a
user and the blade, and then
to signal the release of the brake pawl, are enclosed in housing 1423 mounted
on arbor block 1410. The
housing should be closed to prevent sawdust and other particles from entering
the housing and potentially
15. damaging the electronics housed therein.
When the pawl is released, the pawl quickly hits the teeth of the blade. The
teeth bite into the
pawl, stopping the blade. The saw described above can stop the blade in 2-10
milliseconds, thereby
reducing the extent of injury caused by accidental contact with the blade.
Brake cartridge 1419 is positioned on the blade's pivot axis so that pawl 1420
can move around
pin 1412. Thus, when pawl 1420 hits the blade, the angular momentum of the
blade is transferred to the
arbor, and the blade, arbor, rack and cartridge tend to retract or move down
in the direction of arrow
1424. The blade will move down to the extent permitted by the contact between
rack 1418 and worm
gear 1416. If the worm gear is fixed in place, the downward movement of the
blade may strip teeth on the
rack and/or worm gear, and may prevent the blade from moving down as far as
desired. In the
embodiment shown in Figs. 150 and 151, the worm gear is adapted to snap free
and move on shaft 1415
when the blade hits the pawl.
When the blade hits the pawl, the force of the impact causes spring clip 1417
to snap loose,
allowing the worm gear to slide down the shaft toward an end 1425 of the
shaft. The spring clip snaps
loose because the rack is urged down when the blade is stopped, and the rack
contacts the worm gear and
forces the worm gear to move. The force of the rack against the worm gear
causes the spring clip to snap
loose. The worm gear then moves into a receptacle 1426 formed around the end
of the shaft. The worm
gear is put back in place by simply lifting up on the arbor to pivot the blade
up, which causes the rack to
move up and the worm gear to slide back along shaft 1415 until the spring clip
snaps into place on the
shaft.
The table saw shown in Figs. 150 and 151 also includes a support 1427
configured with a seat or
region 1428 in which is placed an impact-absorbing material 1429 (shown in
Figs. 150 and 151, but not
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in Fig. 153). The support is positioned under the arbor and arbor block so
that when the blade retracts, the
arbor block strikes impact-absorbing material 1429. Support 1427 and impact-
absorbing material 1429
act as a barrier to stop the downward movement of the blade. The support is
positioned so that blade
1402 may retract a sufficient distance. The impact-absorbing material can be
any one of a number of
cushioning materials, such as rubber, dense foam, plastic, etc. One material
found to be suitable is
available under the part number C-1002-06 from AearoEAR, of Indianapolis,
Indiana. Alternatively,
impact-absorbing material 1429 may be attached to the undersurface of the
arbor block instead of on
support 1427. Additionally, support 1427 may take many forms. In fact, shaft
1415 may be configured
and positioned so that it provides a surface to stop the downward movement of
the blade.
In the construction described above, the angular momentum of the blade causes
the blade, rack
and cartridge to all pivot down when the pawl strikes the blade. Thus, the
angular momentum of the
blade causes the retraction. Blade 1402 is permitted to move downward a
sufficient distant so that the
blade is completely retracted. The ability of the blade to retract minimizes
any injury from accidental
contact with the blade and works simultaneously with the braking system
described above. The ability of
the blade to retract is in part because the point around which the blade
pivots relative to the direction that
the blade spins may be described as on what could be thought of as the "back
side" of existing table saws.
The brake cartridge is also mounted on this "back side," and may be mounted to
pivot with the blade as
described above, or may be fixedly mounted to the frame of the saw so it does
not pivot with the blade
and so that the blade climbs down the pawl when the pawl engages the blade.
Other configurations to
cause the blade to retract, which can be used alone or in conjunction with the
embodiment described
herein, are described in Section 3 above.
Figure 151 also shows a splitter 1430 that extends above table 1401 behind
blade 1402 to prevent
kickback. A blade guard may also substantially enclose blade 1402 and prevent
accidental contact with
the blade.
Table saws like those described above can include logic controls to test that
the saw and its safety
system are functioning properly. For example, the logic controls can verify
that the brake pawl is in place
adjacent the blade, and that the firing system is ready to release the pawl
into the blade upon the detection
of accidental contact between the blade and a user. The saws also may include
various signals, lights,
etc., to inform a user of the status of the saw and the features in operation.
Self tests, logic controls and
user interfaces are described in Sections 9 and 10 above.
Fig. 161 shows another embodiment of a safety system in the context of a
typical table saw. Saw
blade 40 is mounted to rotate on arbor 42. The arbor extends outward (as
viewed in Fig. 161) from a
swing arm 1432, which pivots about an axle 1434 to raise and lower the blade.
A worm gear 1436
engages an arcuate rack on the swing arm to pivot the swing arm about the
axle. Safety system 18
includes a bracket 1438 that attaches to swing arm 1432, for example, by one
or more bolts 1440
extending through the bracket. Disposed on mounting bracket 1438 are charging
plates 44 and 46. The
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charging plates are positioned parallel to, and slightly spaced from, blade 40
to create the capacitive
shunt between the plates. The mounting bracket may be constructed of an
electrically insulating material
or include electrical insulation between the bracket and the charging plates.
Mounting bracket 1438 extends from the end of swing arm 1432 beyond the edge
of blade 40. A
pawl 60 is pivotally mounted on a bolt 1442 extending from the bracket. The
free end of the pawl is
biased toward the edge of the blade by a compression spring 66. The spring is
held in compression
between the pawl and a spring block 1444, which extends from the bracket. A
fusible member 70 is
anchored to a pair of contact studs 1446. The fusible member is coupled to the
pawl and holds it away
from the edge of the blade against the spring bias.
An electronics unit 1448 contains a contact detector such as detection
subsystem 22 described
above. Shielded cables extend from the electronics unit to charging plates 44
and 46, respectively.
Electronics unit 1448 also includes a current generator, such as firing
subsystem 76 described above,
which is connected to contact studs 1446. A power cable 1450 extends from
electronics unit 1448 to a
suitable power source (not shown). When the contact detector detects contact
between the user's body
and the blade, the firing circuit melts the fusible member, thereby releasing
the pawl, which engages and
abruptly stops the blade.
It should be noted that by placing the pawl and the charging plates on bracket
1438 which is
attached to the swing arm, the pawl and charging plates move with the blade
when it is adjusted. This
eliminates the need to reposition the pawl and/or the charging plates whenever
the blade is moved.
Furthermore, the embodiment of safety system 18 depicted in Fig. 161 is
suitable for easy installation or
retrofit of existing table saws which do not currently have a safety stop. The
only requirement to retrofit
an existing saw is to tap one or more holes into the end of the swing arm to
receive bolts 1440. The exact
positioning of bracket 1438 can be adjusted as necessary, for example to
extend downward, to fit within
the particular saw housing.
The table saws described above are configured to absorb the impact of a brake
pawl stopping a
blade. However, on some table saws, small saws for example, it may be
desirable to construct the saw
knowing that if the brake pawl stops the blade, the saw would be damaged,
perhaps by bending the arbor
or other support structure. In fact, the saw may be constructed specifically
to absorb the energy of
stopping the blade by destroying or damaging part of the saw. Such saws may be
thought of as disposable
to the extent they are intended to be used only until an accident occurs
requiring the brake pawl to stop
the blade. A disposable saw may be less expensive to manufacture, and reduced
injury to a user in the
event of an accident would more than justify the entire cost of the saw.
Table saws equipped with the disclosed systems and methods may be described as
set forth in the
following numbered paragraphs. These paragraphs are intended as illustrative,
and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
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13.1 A table saw comprising:
a worksurface;
a rotatable blade adapted to extend up through the worksurface;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a brake system adapted to stop the rotation of the blade upon detection of the
dangerous
condition by the detection system.
13.1.1 The table saw of paragraph 13.1 where the blade is electrically
isolated from the rest of
the saw, and where the detection system is adapted to capacitively impart an
electric signal on the blade
and to detect the occurrence of a determined change in the signal.
13.1.2 The table saw of paragraph 13.1 where the blade is mounted on an arbor
and where the
blade and arbor are electrically isolated from the rest of the saw, and where
the detection system is
adapted to capacitively impart an electric signal on the blade and arbor and
to detect the occurrence of a
determined change in the signal.
13.1.3 The table saw of paragraph 13.1 where the dangerous condition is
contact between the
person and the blade.
13.1.4 The table saw of paragraph 13.1 where the dangerous condition is
proximity between the
person and the blade.
13.1.5 The table saw of any one of paragraphs 13.1 where the brake system
includes a brake
pawl adapted to engage the blade.
13.1.5.1 The table saw of paragraph 13.1.5 where the brake pawl is part of a
replaceable
cartridge.
13.1.5.2The table saw of paragraph 13.1.5 where the brake pawl is biased
toward the blade by a
spring.
13.1.5.3 The table saw of paragraph 13.1.5 where the brake pawl is restrained
from engaging the
blade by a fusible member.
13.1.5.3.1 The table saw of paragraph 13.1.5.3 where the brake system includes
a linkage
between the brake pawl and the fusible member.
13.1.6 The table saw of any one of paragraphs 13.1 further comprising a firing
system to trigger
the brake system upon detection of the dangerous condition.
13.1.6.1The table saw of paragraph 13.1.6 where the firing system includes a
capacitor.
13.1.7 The table saw of paragraph 13.1 further comprising a frame supporting
the blade, where
the blade is adapted to be raised and lowered relative to the frame, and where
the brake system is
configured to raise and lower with the blade.
13.1.8 The table saw of paragraph 13.1 further comprising a frame supporting
the blade, where
the blade is adapted tot be tilted relative to the frame, and where the brake
system is configured to tilt with
the blade.
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13.2 A table saw comprising:
a worksurface;
a rotatable blade adapted to extend up through the worksurface;
a detection system adapted to detect a dangerous condition between a person
and the blade;
a brake system adapted to stop the rotation of the blade; and
a firing system adapted to trigger the brake system upon detection of the
dangerous condition by
the detection system.
13.2.1 The table saw of paragraph 13.2 where the brake system includes a brake
pawl biased
toward the blade, where the firing system includes a fusible member
restraining the brake pawl from
contacting the blade, and where the firing system melts the fusible member to
release the brake pawl into
the blade.
13.2.2 The table saw of paragraph 13.2 further comprising a test system to
test the operability of
the firing system.
13.3 A safety system for table saws, where a table saw includes a rotatable
blade, the safety
system comprising:
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a brake system adapted to stop the rotation of the blade upon detection of the
dangerous
condition by the detection system.
Section 14: Miter Saw
Turning now to Figs. 154 and 155, an exemplary embodiment of machine 10 is
shown in the
context of a miter saw 1510, which is also commonly referred to as a chop saw.
It will be understood that
miter saw 1510 may be any type of miter saw including a simple miter saw,
compound miter saw, sliding
compound miter saw, etc. Typically, miter saw 1510 includes a base or stand
1512 adapted to hold the
workpiece to be cut. A swing arm 1514 is pivotally coupled to base 1512 to
allow the arm to pivot
downward toward the base. Attached to arm 1514 is a housing 1516 adapted to at
least partially enclose a
circular blade 40. A motor assembly 16 is coupled to the housing, and includes
a rotating arbor 42 on
which the blade is mounted.- Motor assembly 16 includes a handle 1518 with a
trigger 1520 operable to
run the saw. Blade 40 rotates downward toward base 1512. An optional blade
guard (not shown) may
extend from the bottom of housing 1516 to cover any portion.of the blade
exposed from the housing. A
person uses miter saw 1510 by placing workpiece on base 1512 beneath the
upraised blade and then
bringing the blade down via swing arm 1514 to cut the workpiece. It should be
understood that various
embodiments of miter saws with improved safety systems are disclosed herein
and include various
elements, subelements, features and variations. Miter saws may include any one
or more of the elements,
subelements, features and variations disclosed herein, regardless of whether
or not the particular
elements, subelements, features and/or variations are described together or
shown together in the figures.
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The portion of saw 1510 from which sensors 44 and 46 detect contact with a
user should be
electrically isolated from ground and the remaining portion of saw 1510 to
allow an input signal to be.
capacitively coupled from one plate to the other. For example, blade 40 may be
electrically isolated from
the rest of the saw via a plastic or other nonconductive bushing, such as
shown in Fig. 160 at 1570.
Alternatively, the blade and arbor assembly may be electrically isolated. Also
shown in Fig. 160 are
insulating washers 1572 and 1574 that isolate blade 40 from arbor flange 1576
and arbor washer 1578.
The insulating -washers should be sufficiently thick that only negligible
capacitance is created between
the blade and the grounded arbor flange and washer. A typical thickness is
approximately 1/8-inch,
although thicker or thinner washers may be used. In addition, some or all of
the arbor components may
be formed from non-conductive materials, such as ceramics, to reduce or
eliminate the need for bushing
1570.
An arbor nut 1580 holds the entire blade assembly on arbor 42. Friction
established by tightening
the arbor nut allows torque from the arbor to be transmitted to the saw blade.
It is preferable, although not
essential, that the blade be able to slip slightly on the arbor in the event
of a sudden stop by the brake to
reduce the mass that must be stopped and decrease the chance of damage to the
blade, arbor, and/or other
components in the drive system of the saw. Alternatively, a threaded arbor
bolt may be used in place of
nut 1580. The arbor bolt has a threaded shaft that is received into arbor 40,
and a head that retains the
blade assembly on the arbor.
Furthermore, it may be desirable to construct the bushing from a material that
is soft enough to
deform when the blade is stopped suddenly. For example, depending on the type
of braking system used,
a substantial radial impact load may be transmitted to the arbor when the
brake is actuated. A deformable
bushing can be used to absorb some of this impact and reduce the chance of
damage to the arbor. In
addition, proper positioning of the brake in combination with a deformable
bushing may be employed to
cause the blade to move away from the user upon activation of the brake, as
will be discussed in further
detail below.
In an alternative embodiment, the arbor and/or part of its supporting
framework is electrically
isolated from ground instead of isolating the blade from the arbor. One
benefit of this embodiment is that
if the blade is electrically connected to the arbor, then the arbor itself can
be used to capacitively couple
the input signal from charge plate 44 to charge plate 46. An example of such a
configuration is described
above in Section 2.
Any of the various configurations and arrangements of safety system 18
described above may be
implemented in miter saw 1510. In the exemplary embodiment depicted in Figs.
154 and 155, safety
system 18 is a cartridge-type system. With the exception of charging plates 44
and 46, both brake
mechanism 28 and detection subsystem 22 are contained within cartridge 80.
Examples of suitable
cartridges 80 are described in Sections 7 and 8 above. The cartridge is
configured to be mounted on the
front inside surface of housing 1516 by any suitable fastening mechanism 1522,
such as by one or more
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bolts 1524. The housing may include a movable panel or door 1526 to allow
access to the cartridge.
Alternatively, cartridge 80 may be inserted into a port or opening in the
housing. A pawl 60 is mounted
in the cartridge and is positionable in front of the blade. Examples of
suitable pawls and brake
mechanisms incorporating the same are described in Sections 4 and 5. It should
be understood that
cartridge 80 is not essential to all embodiments of the miter saw disclosed
herein and that miter saw 1510
may be implemented without requiring a cartridge. Instead, the brake mechanism
of the safety system
may be mounted in any suitable operative position relative to blade 40 without
being housed in a
cartridge.
Charge plates 44 and 46 are attached to the inside wall of housing 1516 by one
or more mounts
1528. The mounts are attached to the housing by any suitable fastening
mechanism 1522, such as by
bolts 1532, and are configured to position the charge plates parallel to, and
closely adjacent, blade 40. As
shown in Fig. 155, the spacing between the charge plates and the blade is
preferably much less than the
spacing between the charge plates and the housing to minimize any parasitic
capacitance between the
charge plates and the housing. Alternatively, the housing may be constructed
from an electrically non-
conductive material.
Cables 1534 and 1536 connect the charge plates to safety system's electronics
unit, which may
be housed in the cartridge or elsewhere on the miter saw. Electrical power for
safety system 18 is
provided by any suitable source, such as a cable extending from motor assembly
16. In addition to
actuating the engagement of the pawl with the blade, the electronics unit
within cartridge 80 is also
configured to interrupt the power to motor assembly 16 when contact between
the user's body and the
blade is detected.
A circular blade spinning at several thousand revolutions per minute possesses
a substantial
amount of angular momentum. Thus, when the pawl engages a circular blade such
as is found on miter
saw 1510 and stops the blade within a few milliseconds, the angular momentum
must be transferred to
the brake mechanism, including pawl 60. Because the swing arm of the miter saw
is free to pivot in the
direction of blade rotation, the angular momentum of the blade may be
transferred to the swing arm when
the blade is suddenly stopped, causing the swing arm to swing downward. This
sudden and forceful
downward movement of the swing arm may cause injury to the user if a portion
of the user's body is
beneath the blade. Therefore, an alternative embodiment of miter saw 1510
includes means for
preventing the swing arm from moving downward when the blade is stopped. In
addition, the pawl
typically is mounted at the front of the miter saw to urge the blade to climb
upward away from the user
(i.e., deforming the plastic bushing) when engaged by the pawl.
It will be appreciated that there are many suitable means for preventing
sudden downward
movement of the swing arm. For example, the pivotal connection between the
swing arm and the base of
the miter saw may be electrically lockable, for example using an
electromagnetic leaf brake, to prevent
the arm from pivoting. The signal to lock the connection may be provided by
the detection system. An
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example of a miter saw with a lockable swing arm is shown in Fig. 156, in
which an electromagnetic leaf
brake is schematically illustrated at 1537. Alternatively, or additionally, a
shock absorber may be
connected between the swing arm and the base to limit the speed with which the
swing arm can pivot
relative to the base. This arrangement also serves to limit how far the blade
moves between the time
contact between the blade and user is detected, and the time the blade is
stopped by the pawl. An
example of a miter saw with a shock absorber 1539 is shown in Fig. 157
extending between the base and
swing arm of the miter saw. While there are many other ways of connecting the
swing arm to the base to
prevent sudden movement of the arm toward the base, most such arrangements
transfer the angular
momentum to the swing arm/base assembly. Depending on the weight and balance
of the saw, the
angular momentum may be sufficient to cause the entire saw to overturn.
Therefore, it may be desirable
to secure the base to a stable surface with clamps, bolts, etc.
Alternatively, the miter saw can be configured to absorb any angular momentum
without
allowing the swing arm to move downward. For example, the exemplary embodiment
depicted in
Figs. 154 and 155 is configured with a pivotal motor assembly to allow the
blade to move upward into
the housing upon engagement with the pawl. Motor assembly 16 is connected to
housing 1516 via pivot
bolt, or axle, 1540, allowing the motor assembly to pivot about bolt 1540 in
the direction of blade
rotation. A spring 1542 is compressed between the housing and an anchor 1544
to bias the motor
assembly against the direction of blade rotation. The motor assembly may
include a lip 1546, which
slides against a flange 1548 on the housing to hold the end of the motor
assembly opposite the pivot bolt
against the housing.
When the saw is in use, spring 1542 holds the motor assembly in a normal
position rotated fully
counter to the direction of blade rotation. However, once the pawl is released
to engage the blade, the
motor assembly and blade pivot upward against the bias of the spring. In this
embodiment, the pawl is
positioned at the front of the blade so that the pivot bolt 1540 is between
the pawl and the arbor. This
arrangement encourages the blade to move upward into the housing when stopped.
The spring is selected
to be sufficiently strong to hold the motor assembly down when cutting through
a workpiece, but
sufficiently compressible to allow the blade and motor assembly to move upward
when the blade is
stopped.
While one exemplary implementation of safety system 18 in the context of a
miter saw has been
described, the invention should not be seen as limited to any particular
implementation as the
configuration and arrangement of safety system 18 may vary among miter saws
and applications. For
example, the pivoting motor assembly configuration may also be combined with
one or more of the other
systems described above which prevent the swing arm from pivoting suddenly
toward the base. Further,
it will be appreciated that the blade and motor assembly may be configured in
any of a variety of ways to
at least partially absorb the angular momentum of the blade.
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Fig. 158 shows an alternative configuration of miter saw 1510 adapted to
absorb the angular
momentum of the blade. In this configuration, the miter saw includes two swing
arms 1550 and 1552.
One end 1554 of each swing arm is connected to base 1512, and the opposite end
1556 of each swing arm
is connected to housing 1516, blade 40, and/or the motor assembly (not shown).
The position of the
swing arms relative to each other may vary depending on the swing arm motion
desired. In Fig. 158,
swing arm 1550 is connected to base 1512 somewhat below and forward of swing
arm 1552. Typically,
the motor assembly is rigidly attached to end 1556 of swing arm 1550, while
housing 1516 is connected
to rotate about end 1556 of swing arm 1550. End 1556 of swing arm 1552 is
connected only to the
housing. This arrangement replicates the motion of the motor assembly and
trigger found on many
conventional miter saws. Alternatively, the motor assembly may be connected to
rotate about end 1556 of
swing arm 1550 along with the housing.
The configuration shown in Fig. 158 causes the housing and/or motor assembly
to rotate as the
swing arms pivot. Significantly, when the swing arms move upward, the housing
and/or motor assembly
rotate in the same direction in which the blade rotates during cutting. As a
result, when the pawl engages
the blade and transfers the angular momentum of the blade to the housing
and/or motor assembly, the
housing and/or motor assembly tend to rotate in the same direction as the
blade. This causes the swing
arms to pivot upward, drawing the blade away from the workpiece and the user's
body. Thus, as
described above, the miter saw configuration illustrated in Fig. 158 is
adapted to absorb the angular
momentum of the blade and translate that angular momentum into an upward force
on the swing arm.
The configuration shown in Fig. 158 and described above illustrates a further
alternative
embodiment of a miter saw with safety system 18. Specifically, the safety
system may be configured to
move the blade of the cutting tool rapidly away from the user when contact
with the user's body is
detected in addition to, or instead of, stopping the blade. This alternative
embodiment may be
implemented in the context of any of the cutting tools described herein. For
example, a table saw
implemented with safety system 18 may include a swing arm adapted to pivot
downward to pull the
blade beneath the upper surface of the saw when a dangerous, or triggering,
condition is detected, such as
contact between the user and the blade while the blade is rotating. A spring
(not shown) may be coupled
to the swing arm to increase the speed with which it drops downward. It will
be appreciated that similar
implementations may be configured in the context of all the saws described
herein. In the case of the
miter saw, a electromagnetic leaf brake can be used to stop the movement of
the arm upon contact with a
user. In addition, the restraining mechanism can be used to release a spring
to push the arm upward upon
contact of the blade and user. With such systems, it may not be necessary to
abruptly stop the blade to
avoid injury.
Another example of a miter saw 1510 is shown in Fig. 159. As shown, saw 1510
illustrates
another suitable mechanism for stopping the sudden downward movement of swing
arm 1514 when
safety system 18 is actuated and pawl 60 engages blade 40. Swing arm 1514
includes a cam portion
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1560 having a cam surface 1562. Cam portion 1560 may be integral with the
swing arm and housing
1516. A stopping pawl 1564 is mounted to vertical support 1566 adjacent cam
surface 1562, and an
actuator 1568 is positioned adjacent pawl 1564. The actuator is operatively
coupled to the control and
detection subsystems associated with brake pawl 60 and cartridge 80 so that
when pawl brake pawl 60 is
released, actuator 1568 engages stopping pawl 1564. During normal operation,
actuator 1568 maintains
the pawl spaced-apart from cam surface 1562. However, once contact between the
blade and the user's
body is detected, the detection system sends an actuation signal to actuator
1568, which may be the same
or a different signal that triggers the release of brake pawl 60. In any
event, upon receipt of the actuation
signal, the actuator drives against stopping pawl 1564, causing it to pivot
into cam surface 1562,
preventing further movement of the swing arm. Stopping pawl 1564 may be
constructed or coated with a
high friction material such as rubber, and/or may be configured with teeth,
etc., to increase its braking
action. Cam portion 1560 may be modified so that it extends as far as possible
from the point around
which it pivots, in order to provide as great a moment arm as possible to help
stop the downward motion
of the swing arm.
Safety system 22 may also protect the user from injury by wrapping the blade
with a protective
surface upon detection of a dangerous, or triggering, condition.
Alternatively, or additionally, system 22
may protect the user by disabling the teeth of the blade. Examples of these
embodiments of safety
system 22 are described in Section 12 above.
Miter saws equipped with the disclosed systems and methods may be described as
set forth in the
following numbered paragraphs. These paragraphs are intended as illustrative,
and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
14.1 A miter saw comprising:
a base;
a blade supported by the base;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system associated with the detection system to cause a
predetermined action to take
place upon detection of the dangerous condition.
14.1.1 The miter saw of paragraph 14.1 where the reaction system includes a
brake system to
brake the blade.
14.1.2 The miter saw of paragraph 14.1 where the reaction system includes a
mechanism to
retract the blade.
14.1.3 The miter saw of paragraph 14.1 where the reaction system includes a
mechanism to
cover the blade.
14.2 A miter saw comprising:
a base;
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a swing arm supported by the base and adapted to move toward a workpiece to be
cut;
a blade mounted to move with the swing arm to contact the workpiece when the
pivot arm moves
toward the workpiece;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system adapted to interrupt the movement of the blade and swing arm
upon the
detection by the detection system of the dangerous condition between the
person and the blade.
Section 15: Circular Saw
Fig. 162 illustrates safety system 18 implemented in the context of a hand-
held circular saw
1500. Typically, circular saw 1500 includes a housing 1502 that contains a
motor assembly (not shown),
a guide plate 1504, and a retractable blade guard 1506. Blade 40 is coupled to
the motor assembly by
arbor 42. Safety system 18 may be implemented on saw 1500 according to any of
the embodiments and
configurations described above. In the exemplary implementation depicted in
Fig. 162, the safety system
is illustrated as a cartridge-based system. Cartridge 1508 includes a pawl 60,
and is attachable to housing
1502 so that the pawl may engage the blade. Charge plates (not shown) may be
mounted to an inner
surface of the housing adjacent the blade or any other location suitable to
capacitively couple the input
signal across the blade and detect contact. The cartridge and pawl are shown
as mounted adjacent the
front of the blade to avoid interference with blade guard 1506. Alternatively,
the pawl and cartridge may
be mounted adjacent any other portion of the blade.
As described above, safety system 18 may be implemented on a circular saw with
a brake pawl
that engages and stops the blade. Alternatively, or additionally, safety
system 18 may be configured to
take other action to prevent serious injury to the user. As one example,
safety system 18 may include a
fast-acting actuator, such as a spring, adapted to push guide plate 1504 down
quickly. This would serve
to push the user's hand or body away from the blade by retracting the blade
above the guide plate.
Circular saws equipped with the disclosed systems and methods may be described
as set forth in
the following numbered paragraphs. These paragraphs are intended as
illustrative, and are not intended to
limit the disclosure or claims in any way. Changes and modifications may be
made to the following
descriptions without departing from the scope of the disclosure.
15.1 A circular saw comprising:
a blade supported in a housing;
a detection system adapted to detect a dangerous condition between a person
and the blade; and
a reaction system associated with the detection system to cause a
predetermined action to take
place upon detection of the dangerous condition.
15.1.1 The circular saw of paragraph 15.1 where the reaction system includes a
brake system to
brake the blade.
15.1.2 The circular saw of paragraph 15.1 where the reaction system includes a
mechanism to
retract the blade.
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15.1.3 The circular saw of paragraph 15.1 where the reaction system includes a
mechanism to
cover the blade.
Industrial Applicability
The present invention is applicable to power equipment, and specifically to
woodworking
equipment such as table saws, miter saws, chop saws, band saws, circular saws,
jointers, etc.
It is believed that the disclosure set forth above encompasses multiple
distinct inventions with
independent utility. While each of these inventions has been disclosed in its
preferred form, the specific
embodiments thereof as disclosed and illustrated herein are not to be
considered in a limiting sense as
numerous variations are possible. The subject matter of the inventions
includes all novel and non-obvious
combinations and subcombinations of the various elements, features, functions
and/or properties
disclosed herein. No single feature, function, element or property of the
disclosed embodiments is
essential to all of the disclosed inventions.
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