Canadian Patents Database / Patent 2373247 Summary

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(12) Patent: (11) CA 2373247
(54) English Title: HUMAN POWER AMPLIFIER FOR LIFTING LOAD INCLUDING APPARATUS FOR PREVENTING SLACK IN LIFTING CABLE
(54) French Title: AMPLIFICATEUR DE FORCE HUMAINE POUR LEVAGE DE CHARGES AVEC DISPOSITIF ANTI-MOU POUR L'ELINGUE
(51) International Patent Classification (IPC):
  • B66D 3/18 (2006.01)
  • B66C 1/02 (2006.01)
(72) Inventors :
  • KAZEROONI, HOMAYOON (United States of America)
(73) Owners :
  • KAZEROONI, HOMAYOON (Not Available)
(71) Applicants :
  • KAZEROONI, HOMAYOON (United States of America)
(74) Agent: KIRBY EADES GALE BAKER
(74) Associate agent:
(45) Issued: 2005-05-24
(86) PCT Filing Date: 2000-02-17
(87) Open to Public Inspection: 2000-11-23
Examination requested: 2001-11-06
(30) Availability of licence: N/A
(30) Language of filing: English

(30) Application Priority Data:
Application No. Country/Territory Date
60/134,002 United States of America 1999-05-13
60/146,538 United States of America 1999-07-30
60/146,541 United States of America 1999-07-30
09/443,278 United States of America 1999-11-18

English Abstract




A human power amplifier assist device (10) includes an
end-effector (14) that is grasped by a human operator and applied
to a load (25). The end-effector (14) is suspended, via a line (13),
from a take-up pulley (11), winch or drum that is driven by an
actuator (12) to lift or lower the load (25). The end-effector (14)
includes a force sensor (31) that measures the vertical force imposed
on the end-effector (14) by the operator and delivers a signal to a
controller (20). The controller (20) and actuator (12) are structured
in such a way that a predetermined percentage of the force necessary
to lift or lower the load (25) is applied by the actuator (12), with the
remaining force being supplied by the operator. The load (25) thus
feels lighter to the operator, but the operator does not lose the sense
of lifting against both the gravitation and inertial forces originating
in the load (25).


French Abstract

L'invention concerne un amplificateur de force humaine (10) comprenant un effecteur terminal (14) qui est saisi par un opérateur humain et appliqué à une charge (25). L'effecteur terminal (14) est suspendu par un câble (13) à une poulie, un treuil ou un tambour (11) de tension qui est entraîné par un actionneur (12) pour soulever ou abaisser la charge. L'effecteur terminal (14) comprend un détecteur de force (31) qui mesure la force verticale appliquée à l'effecteur terminal (14) par l'opérateur et fournit un signal à un organe de commande (20) . L'organe de commande (20) et l'actionneur (12) sont conçus de telle façon qu'un pourcentage préétabli de la force nécessaire pour soulever ou abaisser la charge (25) est appliqué par l'actionneur (12), la force restante étant fournie par l'opérateur. L'opérateur trouve la charge (25) ainsi plus légère sans pour autant perdre la sensation de soulever la charge en exerçant un effort contre la pesanteur et les forces d'inertie propres à la charge.


Note: Claims are shown in the official language in which they were submitted.




Claims:

1. ~A human power amplifier assist device, including a pulley with line wound
thereon, an actuator arranged to turn the pulley so as to raise and lower the
line wound
thereon, and an end-effector connected to the line wound on the pulley and
connectable
to a load, the end-effector including a handle to be held by an operator and a
sensor
detecting an operator-applied force on the handle, the assist device
comprising:
a. a controller controlling operation of the actuator, the controller being
responsive to a first signal from the sensor representing operator-applied
force
and a second signal representing tensile force on the line; and
b. the controller being programmed to cause the actuator to turn the pulley so
as to
raise and lower the line, and to halt the actuator so that the line and the
end-
effector connected thereto is maintained in a certain position, as a function
of the
first and second signals.

2. ~The device of claim 1, wherein the controller halts the actuator and
thereby
prevents slack in the line if an operator pushes the end-effector downwardly
while the
end-effector is constrained from moving downwardly.

3. ~The device of claim 1, wherein the pulley stops turning so that no line is
paid out
if an operator pushes the end-effector downwardly while the end-effector is
constrained
from moving downwardly.

4. ~The device of claim 1, wherein the pulley stops turning and prevents line
from
being paid out if an operator pushes the end-effector downwardly when tensile
force on
the line is zero.

5. ~The device of claim 1, wherein if an operator increases or decreases
downward
force on the end-effector a corresponding increase or decrease occurs in
downward speed
of the end-effector for a given load when the end-effector is free to move
downwardly.

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6. ~The device of claim 1, wherein to maintain movement of the end-effector at
a
given speed for an increase or decrease in weight of a load when the end-
effector is free
to move downwardly the operator is required to increase or decrease upward
force.

7. ~The device of claim 1, wherein an increase or decrease in the weight of
the load
causes a decrease or increase, respectively, in an upward speed of the end-
effector for a
given operator force on the end-effector when the end-effector is free to move
downwardly.

8.~The device of claim 1, wherein the actuator includes a brake arranged to
prevent
pulley rotation when the brake is engaged.

9. ~The device of claim 8, wherein the brake becomes engaged when no electric
power is supplied to the actuator so that the pulley is prevented from
rotating during an
electric power failure.

10. ~The device of claim 1, wherein the end-effector includes a dead-man
switch
arranged so that when an operator grasps the end-effector handle the dead-man
switch is
activated and a signal from the dead-man switch prevents a brake from engaging
to
prevent the pulley from rotating.

11. ~The device of claim 1, wherein the end-effector includes a dead-man
switch
arranged so that when an operator removes his/her hand from the end-effector
handle a
signal from the dead-man switch causes a brake to engage to prevent the pulley
from
rotating.

12. ~The device of claim 1, wherein the end-effector includes a dead-man
switch that
causes a signal to be sent to the controller causing the actuator to maintain
its position
when an operator removes his/her hand from the end-effector handle.

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13. ~The device of claim 1, wherein a detector of the second signal includes a
current
sensor that measures electric current supplied to the actuator to estimate
tensile force on
the line.

14. ~The device of claim 1, wherein a detector of the second signal includes a
force
sensor arranged to generate a signal that represents tensile force on the
line.

15. ~The device of claim 1, wherein a detector of the second signal is capable
of
generating a binary signal having one state when line tensile force is zero
and a second
state when line tensile force is not zero.

16. ~The device of claim 1, wherein a detector of the second signal is capable
of
generating a binary signal having one state when the end-effector is
constrained from
moving downwardly and a second state when the end-effector is free to move
downwardly.

17. ~The device of claim 1, wherein a detector of the second signal includes a
switch
that can move to one position when the line is slack and can move to another
position
when the line is other than slack.

18. ~The device of claim 1, wherein a detector of the second signal includes a
force
sensor arranged to generate a signal that represents load force imposed on the
end-
effector by the load.

-39-

Note: Descriptions are shown in the official language in which they were submitted.


CA 02373247 2004-11-12
HUMAN POWER AMPLIFIER FOR LIFTING LOAD INCLUDING
APPARATUS FOR PREVENTING SLACK IN LIFTING CABLE
This application claims the benefit of U.S. Provisional Applications No.
60/134,002, filed on I3 May 1999, No. 60/146,538, filed on 30 July 1999, and
No.
60/I46,541, filed on 30 July 1999.
The present invention relates to material handling devices that Lift end
lower loads as a function of operator-applied force.
The device described here is different from manual material handling
devices currently used by auto-assembly and warehouse workers. Initial
I 5 research generally shows three types of material handing devices are
currently
available on the market.
A class of material handling devices called balancers consists of a
motorized take-up pulley, a line that wraps around the pulley as the pulley
turns, and an end-effector that is attached to the end of the line. The end-
effector has components that connect to the load being lifted. The pulley's
rotation winds or unwinds the line and causes the end-effector to lift or
lower
the load connected to it. In this class of material handling systems, an
actuator generates an upward line force that exactly equals the gravity force
of
the object being lifted so that the tension in the line balances the object's
weight. Therefore, the only force the operator must impose to maneuver the
object is the object's acceleration force. This force can be substantial if
the
object's mass is large. Therefore, a heavy object's acceleration, and
deceleration is limited by the operator s strength.
There are two ways of creating a force in the line so that it exactly equals
the object weight. First, if the system is pneumatically powered, the air
pressure is adjusted so that the lift force equals the load weight. Second, if
the
system is electrically powered, the right amount of voltage is provided to the
amplifier to generate a lift force that equals the load weight. The fixed
preset
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WO 00/69771 PCT/US00/04065
forces of balancers are not easily changed in real time, and therefore these
types of systems are not suited for maneuvering of objects of various weights.
This is true because each object requires a different bias force to cancel its
weight force. This annoying adjustment must be done either manually by the
operator or electronically by measuring the object's weight. For example, the
pneumatic balancers made by Zimmerman International Corporation or
Knight Industries are based on the above principle. The air pressure is set
and
controlled by a valve to maintain a constant load balance. The operator has to
manually reach the actuator and set the system to a particular pressure to
generate a constant tensile force on the line. The LIFTRONIC System
machines made by Scaglia also belong in the family of balancers, but they are
electrically powered. As soon as the system grips the load, the LIFTRONIC
machine creates an upward force in the line which is equal and opposite to
the weight of the object being held. These machines may be considered
superior to the Zimmerman pneumatic balancers because they have an
electronic circuit that balances the load during the initial moments when the
load is grabbed by the system. As a result, the operator does not have to
reach
the actuator on top and adjust the initial force in the line. In this system,
the
load weight is measured first by a force sensor in the system. While this
measurement is being performed, the operator should not touch the load, but
instead should allow the system to find the object's weight. If the operator
does touch the object, the force reading will be incorrect. As a result, the
LIFTRONIC machine then creates an upward line force that is not equal and
opposite to the weight of the object being held. Unlike the assist device of
this
application, balancers do not give the operator a physical sense of the force
required to lift the load. Also, unlike the device of this application,
balancers
can only cancel the object's weight with the line's tension and are not
versatile enough to be used in situations in which load weights vary.
The second class of material handling device is similar to the balancers
3 0 described above, but the operator uses an intermediary device such as a
valve,
posh-button, keyboard, switch, or teach pendent to adjust the lifting and
lowering speed of the object being maneuvered. For example, the more the
operator opens the valve, the greater will be the speed generated to lift the
object. With an intermediary device, the operator is not in physical contact
with the load being lifted, but is busy operating a valve or a switch. The
operator does not have any sense of how much she/he is lifting because
his/her hand is not in contact with the object. Although suitable for lifting
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CA 02373247 2004-11-12
objects of various weights, this type of system is not comfortable for the
operator because the operator has to focus on an intermediary device (i.e.,
valve, push-button, keyboard, or switch). Thus, the operator pays more
attention to operating the intermediary device than to the speed of the
object,
S making the lifting operation rather unnatural.
The third class of material handling device use end-effectors equipped
with force sensors or motion sensors. These devices measure the human
force or motion and based on this measurement vary the speed of the
actuator. An example of such a device is U.S. Patent 4,917,360 to Yasuhiro
Kojima. With this and with similar devices, if the human pushes upward on
the end-effector the pulley turns and lifts the load; and if the human pushes
downward on the end-effector, the pulley turns and lowers the load. A
problem occurs when the operator presses downward on the end-effector to
engage the load with the suction cups, the controller and actuator interpret
this motion as an attempt to lower the load. As a result, the actuator causes
the pulley to release more line than necessary, creating "slack" in the cable.
Hereinafter the term "slack" should be interpreted as meaning an excessive
length of line but should not be construed as including instances where the
line is simply not completely taut. A slack Line may wrap around the
operator's neck or hand. After the slack is produced in the Line by this or
other circumstances, when the operator pushes upwardly on the handle, the
slack line can become tight around the operatoi s neck or hand creating
deadly injuries. Because slack can occur even when suction cups are not used
as the load gripping means, for safe operation it is important to prevent
slack
at all times. During fast maneuvers workers can accidentally hit the Loads
they intend to Lift or their surrounding environment (e.g. conveyor belts)
with the bottom of the end-effector. In palletizing tasks, the workers quite
often use the bottom of the end-effector to fine tune the locations of a box
that
is not will placed. These occurrences will cause slack in the line since the
3 0 operator pushes downwardly on the end-effector handle to situate a box,
while the end-effector is constrained from moving downwardly. In general,
slack in the line can be dangerous for the operator and others in the same
work
environment. The manual material handling device of my invention never
creates slack in the line.
-3-


CA 02373247 2004-11-12
The force sensor devices of this class also fail to give an operator a
realistic sense
of the weight of the load being lifted. This can lead to unnatural and
possibly dangerous
load maneuvers.
SUMMARY OF THE INVENTION
The assist device of this application solves the above problems associated
with the
three classes of material handling devices. The hoist of this invention
includes an end-
effector to be held by a human operator; an actuator such as an electric
motor; a computer
or other type of controller for controlling the actuator; and a line, cable,
chain, rope, wire
or other type of line for transmitting a tensile lifting force between the
actuator and the
end-effector. Hereinafter the term "lifting" should be interpreted as
including both upward
and downward movements of a load. The end-effector provides an interface
between the
human operator and an object that is to be lifted. A force transfer mechanism
such as a
pulley, drum or winch is used to apply the force generated by the actuator to
the line that
transmits the lifting force to the end-effector.
In accordance with one aspect of the present invention there is provided a
human
power amplifier assist device, including a pulley with line wound thereon, an
actuator
arranged to turn the pulley so as to raise and lower the line wound thereon,
and an end-
effector connected to the line wound on the pulley and connectable to a load,
the end-
effector including a handle to be held by an operator and a sensor detecting
an operator-
applied force on the handle, the assist device comprising: a. a controller
controlling
operation of the actuator, the controller being responsive to a first signal
from the sensor
representing operator-applied force and a second signal representing tensile
force on the
line; and b. the controller being programmed to cause the actuator to turn the
pulley so as
to raise and lower the line, and to halt the actuator so that the line and the
end-effector
connected thereto is maintained in a certain position, as a function of the
first and second
signals.
A signal representing the vertical force imposed on the end-effector by the
human
operator, as measured by a sensor, is transmitted to the controller that is
associated with
the actuator. In operation, the controller causes the actuator to rotate the
pulley and move
the end-effector appropriately so that the human operator only lifts a pre-
programmed
-4-


CA 02373247 2004-11-12
small proportion of the load force while the remaining force is provided by
the actuator.
Therefore, the actuator assists the operator during lifting movements in
response to the
operator's hand force. Moreover, the tensile force in the line is detected or
estimated, for
example, by detecting the energy or current that is drawn by an actuator. In
addition,
because load force is a dominating factor in establishing the magnitude of
tensile force,
load force can be used to roughly approximate tensile force and vice versa.
Hereinafter, it
should be understood that tensile force can be estimated using load force and
load force
can be estimated using tensile force. A signal representing the load force or
tensile force
on the Line is sent to the controller, and the controller uses the load force
or tensile force
signal to drive the actuator effectively in response to the human input. This,
for example,
can prevent the actuator from releasing line when the load force or tensile
force is zero so
that although the line may become loose (i.e. not taut), slack (as defined
above) will never
be created in the line.
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CA 02373247 2001-11-06
WO 00/69771 PCT/US00/04065
With this load sharing concept, the operator has the sense that he or
she is lifting the load, but with far less force than would ordinarily be
required. The force applied by the actuator takes into account both the
gravitational and inertial forces that are necessary to move the load. Since
the
force applied by the actuator is automatically determined by line force and
the
force applied to the end-effector by the operator, there is no need to set or
adjust the human power amplifier for loads having different weights. There
is no switch, valve, keyboard, teach pendent, or push-button in the human
power amplifier to control the lifting speed of the load. Rather, the contact
force between the human hand and the end-effector handle combined with
line force are used to determine the lifting speed of the load. The human
hand force is measured and used by the controller in combination with line
force to assign the required angular speed of the pulley to either raise or
lower
the line and thus create sufficient mechanical strength to assist the operator
in
the lifting task. In this way, the device follows the human arm motions in a
"natural" way. When the human uses this device to manipulate a load, a
well-defined small portion of the total load force (gravity plus acceleration)
is
lifted by the human operator. This force gives the operator a sense of how
much weight he/she is lifting. Conversely, when the operator does not apply
any vertical force (upward or downward) to the end-effector handle, the
actuator does not rotate the pulley at all, and the load hangs motionless from
the pulley.
Although the existing devices described in earlier paragraphs do lift
loads, they:
do not give the operator a physical sense of the lifting maneuver,
do not compensate for inertia forces,
do not compensate for varying loads,
do not address any key ergonomic concerns, and
do not prevent slack in the line.
3 0 The device of this application does have the above-identified
advantages.
BRIEF DESCRIPTION OF THE DRAWINGS
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CA 02373247 2001-11-06
WO 00/69771 PCT/US00/04065
Fig. 1 illustrates one embodiment of a human power amplifier that
includes an end-effector according to this invention.
Fig. 2 illustrates a cross-sectional view of one embodiment of an end-
effector usable in the invention, showing in particular the structure of the
force sensor that measures operator force.
Fig. 3 illustrates a cross-sectional view of one embodiment of another
end-effector that includes a displacement detector for measuring the force
imposed on the end-effector by an operator.
Fig. 4 illustrates a perspective view of the end-effector of Fig. 3 when
used by an operator to lift a box.
Fig. 5 is a schematic block diagram showing operator and load forces
interacting with elements of the human power amplifier to provide load
movement.
Fig. 6 illustrates the problem of line slack that can occur with prior art
devices that use suction cups to grip a box.
Fig. 7A illustrates a partially cross-sectioned view of one embodiment
of an end-effector that includes a displacement detector for measuring the
force imposed on the end-effector by an operator and a force sensor for
measuring the line tensile force.
Fig. 7B illustrates a partially cross-sectioned view of one embodiment of
an end-effector that includes a displacement detector for measuring the force
imposed on the end-effector by an operator and a force sensor for measuring
the force associated with the weight and acceleration of the load only.
Fig. 8 schematically illustrates how a force sensor can be used to
measure the entire force that the human power amplifier imposes on a
ceiling or on an overhead crane.
Fig. 9 schematically illustrates one embodiment of an actuator that
contains a mechanism and a motion sensor to measure the line tensile force.
Figs. l0A and 10B illustrate partially cross-sectioned views of one
3 0 embodiment of an end-effector that includes a displacement detector for
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CA 02373247 2001-11-06
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measuring the force imposed on the end-effector by an operator and a
mechanism for detecting the line tensile force.
Figs. 11A and 11B illustrate one embodiment of an actuator that
contains a mechanism and a switch to detect the line tensile force.
Figs. 12A and 12B illustrate one embodiment of an end-effector that
includes a displacement detector for measuring the force imposed on the end-
effector by an operator and a switch that transmits a signal when the end-
effector is constrained from moving downwardly.
Fig. 13 illustrates how a clamp-on current sensor can be used to detect
the current drawn by the actuator.
Fig. 14 schematically illustrates operator-applied forces and load forces
interacting with elements of a human power amplifier to move a load while
slack in the line is prevented.
Figs. 15A, 158, 15C, and 15D graphically show values of a control
variable KM as a function of the tensile force in a hoist line.
Fig. 16 illustrates one embodiment of a human power amplifier that
prevents slack in the line even when the end-effector is pushed downwardly
by the operator while the end-effector is constrained from moving
downwardly.
Fig. 17 schematically illustrates both human force and load force used
as feedback signals to provide movement to a load while slack in the cable is
prevented.
Figs. 18A and 18B show flowcharts of software that can be used to drive
a controller practicing the invention.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 illustrates a first embodiment of the invention, showing a
human power amplifier 10. At the top of the device, a take-up pulley 11,
driven by an actuator 12, is attached directly to a ceiling, wall, or overhead
3 0 crane. Encircling pulley 11 is a line 13. Line 13 is capable of lifting or
lowering
a load 25 when the pulley 11 turns. Line 13 can be any type of line, wire,
cable,
belt, rope, wire line, cord, twine, string or other member that can be wound



CA 02373247 2001-11-06
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around a pulley and can provide a lifting force to a load. Attached to line 13
is
an end-effector 14, that includes a human interface subsystem 15 (including a
handle 16) and a load interface subsystem 17, which in this embodiment
includes a pair of suction cups 18. Also, shown is an air hose 19 for
supplying
suction cups 18 with low-pressure air.
In the preferred embodiment, actuator 12 is an electric motor with a
transmission, but alternatively it can be an electrically-powered motor
without a transmission. Furthermore, actuator 12 can also be powered using
other types of energy including pneumatic, hydraulic, and other alternative
forms of energy. As used herein, transmissions are mechanical devices such
as gears, pulleys and lines that increase or decrease the tensile force in the
line. Pulley 11 can be replaced by a drum or a winch or any mechanism that
can convert the motion provided by actuator 12 to vertical motion that lifts
and lowers line 13. Although in this embodiment actuator 12 directly powers
the take-up pulley 11, one can mount actuator 12 at another location and
transfer power to take-up pulley 11 via another transmission system such as
an assembly of chains and sprockets. Actuator 12 is driven by an electronic
controller 20, that receives signals from end-effector 14 over a signal cable
21.
Because there are several ways to transmit electrical signals, signal cable 21
can
be replaced by other alternative signal transmitting means (e.g. RF, optical,
etc.). In a preferred embodiment controller 20 essentially contains three
major components:
1. An analog circuit, a digital circuit, or a computer with input
output capability and standard peripherals. The responsibility of this portion
of the controller is to process the information that is received from various
sensors and switches and to generate command signals for the actuator.
2. A power amplifier that sends power to the actuator based on a
command from the computer discussed above. In general, the power
amplifier receives electric power from a power supply and delivers the proper
3 0 amount of power to the actuator. The amount of electric power supplied by
the power amplifier to actuator 12 is determined by the command signal
computed within the computer.
3. A logic circuit, composed of electromechanical or solid state
relays, to start and stop the system depending on a sequence of possible
3 5 events. For example, the relays are used to start and stop the entire
system
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CA 02373247 2001-11-06
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operation using two push buttons installed either on the controller or on the
end-effector. The relays also engage the friction brake in the presence of
power failure or when the operator leaves the system. In general, depending
on the application, one can design many architectures for logic circuit.
Human interface subsystem 15 is designed to be gripped by a human
hand and measures the human force, i.e., the force applied by the human
operator against human interface subsystem 15. Load interface subsystem 17
is designed to interface with a load and contains various holding devices. The
design of the load interface subsystem depends on the geometry of the load
and other factors related to the lifting operation. In addition to the suction
cup 18 shown in Fig. 1, hooks and grippers are examples of other means that
connect to load interface subsystems. For lifting heavy objects, the load
interface subsystem can contain more than two suction cups.
The human interface subsystem 15 of end-effector 14 contains a sensor
(described below) that measures the magnitude of the vertical force exerted by
the human operator. If the operator's hand pushes upward on the handle 16,
the take-up pulley 11 moves the end-effector 14 upward. If the operator s
hand pushes downward on the handle 16, the take-up pulley moves the end-
effector 14 downward. The measurements of the forces from the operator's
hand are transmitted to the controller 20 over signal cable 21 (or alternative
signal transmission means). Furthermore, while the preferred embodiment
of my system includes a sensor positioned in proximity to the end-effector 14,
other operator-applied force estimating elements can be used to estimate
operator-input that are not in proximity to the end-effector 14.
Using these measurements, the controller 20 assigns the necessary
pulley speed to either raise or lower the line 13 to create enough mechanical
strength to assist the operator in the lifting task as required. Controller 20
then powers actuator 12, via power cable 23, to cause pulley 11 to rotate. All
of
this happens so quickly that the operator's lifting efforts and the device's
3 0 lifting efforts are for all purposes synchronized perfectly. The
operator's
physical movements are thus translated into a physical assist from the
machine, and the machine's strength is directly and simultaneously
controlled by the human operator. In summary, the load moves vertically
because of the vertical movements of both the operator and the pulley. One
3 5 of the most important properties of the device of this invention is that
the
actuator and pulley turn causing the end-effector to follow the operator's
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hand motion upwardly and downwardly yet the line does not become slack if
the end-effector is physically constrained from moving downwardly and the
end-effector is pushed downwardly by the operator.
A dead-man switch with a lever 26 on handle 16 (described below)
sends a signal to controller 20 via a signal cable 22 (or other alternative
signal
transmission means). When the operator holds onto handle 16, the dead-
man switch sends a logic signal to the controller 20 causing the end-effector
to
follow the operator's hand. When the operator releases handle 16, the dead-
man switch sends a different logic signal to the controller 20 causing the end-

effector to remain stationary. In a preferred embodiment of this invention, a
friction brake 24 has been installed on the actuator 12. The friction brake
engages whenever the operator releases the dead-man switch or at any time
there is a power failure. One can use an end-effector with two handles, only
one of which needs to be instrumented with a sensor to measure operator-
applied force. For lifting heavy objects, one can use two human power
amplifiers similar to the human power amplifier 10 shown in Fig. 1, one for
the left and one for the right hand.
I first describe, in detail, the architecture of two classes of end-effectors
that allow for measurement of the operator force. I will then explain the
control algorithm that allows for the operation of the system and prevention
of the slack in the line. A flow chart is also given to explain the
implementation of the control algorithm.
Two families of the end-effectors are described here. Fig. 2 shows a
version of end-effector 30 that measures the vertical human force via a force
sensor. A force sensor 31 is installed between a handle 32 and a bracket 33
and
is connected to controller 20 via signal cable 21. Force sensor 31 has a
threaded
part 34 that screws into an inside bore within handle 32, which is grasped by
the operator. The other side of the force sensor 31 is connected to bracket 33
via a cylinder 35. The outside diameter of cylinder 35 is slightly smaller
than
3 0 the inside diameter of handle 32. This clearance allows a sliding motion
between handle 32 and cylinder 35, guaranteeing that the forces from the
operator that are in the vertical direction pass through force sensor 31
without
any resistance and that the forces from the operator that are not in the
vertical
direction are transferred to bracket 33 and not to force sensor 31. If these
non-
3 5 vertical forces were to pass through force sensor 31, they could either
introduce false readings in the sensor or damage the force sensor assembly.
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CA 02373247 2004-11-12
The force sensor used in embodiments of this invention can be selected
from a variety of force sensors that are available in the market, including
piezoelectric based force sensors, metallic strain gage force sensors,
semiconductor strain gage force sensors, Wheatstone bridge-deposited strain
gage force sensors, and force sensing resistors. Regardless of the particular
type of force sensor chosen and its installation procedure, the design should
be such that the force sensor 32 measures only the operator force against the
end-effector 30. Bracket 33 is connected to cylinder 35 rigidly and it
includes
hook 36 to interface the load and eyelet 37 to be connected to the line 13.
In a second group of embodiments, the force imposed by the operator
against the end-effector is measured by the displacement of the handle rather
than a force sensor of the kind described above. The lower cost and ease of
use of displacement measurement systems can make this type of end-effector
more attractive in some situations. A partially cross-sectioned view of one
1 S embodiment of an end-effector of the second group is shown in Fig. 3. Fig.
4
shows a perspective view of the end-effector of Fig. 3 when used by an
operator to lift load 25 (e.g. a box). Similar to the end-effector described
above, end-
effector 40 includes a human interface subsystem 41 and a load interface
subsystem 42. Human interface subsystem includes a handle 16 that is grasped
by the operator and thus measures the human force, not the load force. Load
interface subsystem 42 includes a bracket 44 that bolts to a hook 45 or a
suction
cup or any other type of device that can be used to hold an object. An eyelet
46
is mounted in bracket 47 for connecting bracket 47 to a line 13.
A handle 16 is held by the operator and connected rigidly to the ball-nut
portion 49 of the ball spline shaft mechanism securely. Balls 50 located in
grooves of spline shaft 51 allow for linear motion of ball-nut 49 and handle
16
freely along a spline shaft 51, with no rotation relative to spline shaft 51.
The
spline shaft 51 is secured to bracket 47 which is connected to line 13 via an
eyelet 46.
In this embodiment, the spline shaft 51 is press fitted into bracket 47.
Member 44 holding a hook 45 is connected to bracket 47 via bolts 52. Member
44 has hole patterns that allow for connection of a suction cup mechanism, a
hook, or any device to hold the object. A coil spring 53 is positioned around
spline shaft 51 between the ball-nut portion 49 of the ball-spline shaft
3 S mechanism and a stop 54 and urges handle 16 upward. Note that stop 54 can
be a clamp ring that is secured to spline shaft 51 rigidly.
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In this embodiment, a linear encoder measures the motion of the
handle 16 relative to bracket 47. The encoder system has a sensor 48 that
produces an electric signal on signal cable 21. The encoder also has a
reflective
strip 55 mounted on handle 16 by adhesive. The reflective strip has dark
horizontal stripes. As the handle moves linearly relative to bracket 47, the
sensor 48 detects the light and dark regions of the strip 55 and sends
appropriate pulses via signal cable 21 as it observes the light (or dark)
regions
of the strip 55. The leading and trailing edges of pulse signals will then be
counted in the controller 20. Fig. 3 shows the end-effector when handle 16 is
pushed upwardly to its upper limit (the bull-nut 49 is pushed against the
bracket 47). Rather than gluing a reflective strip with dark stripes on handle
16, one can laser mark the handle 16 itself. The controller assumes zero
position for the handle 16 at this location and calculates the handle
displacement by counting the pulses carried over the signal cable 21. The
handle displacement and the spring stiffness, taken together, yield a value
for
the human force. The linear motion detector used in this embodiment can be
a magnetic linear encoder, a linear potentiometer, a LVDT (linear variable
differential transformer), a capacitive displacement sensor, an eddy current
proximity sensor or a variable-inductance proximity sensor.
Alternatively, the ball spline shaft mechanism shown in Fig. 3 can be
replaced by a linear bushing mechanism, wherein a bushing (slider) and a
shaft slide relative to one another with no balls. There should be little
friction between the bushing (slider) and the shaft.
A dead-man switch 56 is installed on handle 16 sends a signal to
controller 20 via signal cable 22 (or by alternative signal transmission
means).
A lever 26, pivoting around hinge 58, is installed on the handle 16 and pushes
against the switch 56 when the operator holds onto handle 16. In a preferred
embodiment of this invention, a friction brake 24 has been installed on the
actuator 12. This friction brake engages when the operator releases the dead-
3 0 man switch and any time there is a power failure. In addition, as an
optional
feature, the assist device controller can be designed so that when the
operator
leaves the handle 16, the controller transfers the actuator to position
control
mode. In position control mode, the controller tries to keep the actuator (and
consequently the end-effector) at the position where the operator left the
3 5 device. As soon as the operator returns and grasps the handle 16, the
actuator
moves out of position control mode. In a preferred embodiment, the position
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control mode includes a standard feedback system that uses the encoder on
the actuator as a feedback signal and maintains the position of the actuator
where the operator left the device. Although this optional feature holds the
actuator and the end-effector stationary when the operator leaves the handle,
I do not recommend that practitioners substitute this feature for the friction
brake discussed above. The position control feature will not work if there is
a
sensor, computer or power failure.
The sole purpose of the spring installed in the end-effector is to bring
the handle back to an equilibrium position when no force is imposed on the
handle by the operator. Fig. 3 shows the end-effector using compression
springs. One can use other kinds of springs, such as cantilever beam springs,
tension springs or belleville springs in the end-effector. Basically, any
resilient element capable of bringing the handle back to its equilibrium
position will be sufficient. For example, one can use a bellow not only to
protect the end-effector from dust and moisture, but also to bring back the
handle to its equilibrium position. The structural damping in the resilient
element (e.g. springs) or the friction in the moving elements of the end-
effectors (e.g. bearings) provide sufficient damping in the system to provide
stability. As shown in Fig. 3, only one spring is used to push the handle
upwardly. However, one can also use two springs to keep the handle at a
middle position. The second spring can be positioned around spline shaft 51
between the ball-nut portion 49 of the ball-spline shaft mechanism and
bracket 47 and urges handle 16 downwardly. As shown in Fig. 4 an optional
brace 59 can be connected to handle 16 to create stability and comfort for
operators. This brace 59 has a hinge 57 and allows for a rotational motion
along arrow 43. Because brace 59 transfers all forces imposed on the
operator's
hand to the operator's lower arm, by-passing the operator's wrist, some
operators may find that brace 59 makes operation more comfortable.
As explained above, other types of operator-input estimating elements
can be used in place of the specific embodiments described above. Examples of
alternative operator-input estimating elements may include sensors that
evaluate energy consumed by the actuator during lifting or sensors that are
not in proximity to the end-effector that can estimate load force or tensile
force to estimate operator-applied force.
3 5 The block diagram of Fig. 5 shows the basic control technique of the
device. As described above, in a preferred embodiment, the force or
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displacement sensor in the end-effector delivers a signal to controller 20
that
is used to control actuator 12 and to apply an appropriate torque to pulley
11.
If (e) is the input command to actuator 12 then, in the absence of any other
external torque on the actuator, the linear velocity of the outermost point of
S the pulley or the velocity of the end-effector (v) can be represented by:
v = G a (1)
where (G) is the actuator transfer function. A positive value for (v)
means downward speed of the end-effector. In addition to the input
command (e) from the controller, the line tensile force, (fR) will also affect
the
end-effector velocity. The input command (e) and the line tensile force, (fR),
contribute to the end-effector velocity such that:
v=Ge+SfR (2)
where (S) is the actuator sensitivity transfer function which relates the
line tensile force (fR) to the end-effector velocity (v). If a closed loop
velocity
controller is designed for the actuator such that (S) is small, the actuator
has
only a small response to the line tensile force. A high-gain controller in the
closed-loop velocity system results in a small (S) and consequently a small
change in velocity, (v), in response to the line tensile force. Also note that
non-back-driveable speed reducers (usually high transmission ratios) produce
2 0 a small (S) for the system.
The line tensile force, (fR), can be represented by equation 3:
fR = f + p (3)
where (f) is the operator-applied force on the end-effector and force (p)
is imposed by the load and the end-effector, referred to herein as the "load
force" on the line. Positive values for (f) and (p) represent downward forces.
Note that (p) is force imposed on the line and is equal to the weight and
inertia force of the load and end-effector taken together:
p=W- ~ d v
where W is the weight of the end-effector and load taken together as a
whole and d v is the end-effector acceleration. If the end-effector and load
C dt ~
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do not have any acceleration or deceleration, then (p) is exactly equal to the
weight of the end-effector and load, (W). Also note that inspection of Fig. 5
and equation 4 reveals that variable (E) in the block diagram of Fig. 5
presents
dt in equation 4, therefore p = W - E v .
The human force, (f), is measured and passed to the controller 20 that
delivers the output signal (e). A positive number (fup), in the computer, is
subtracted from the measurement of the human force, (f). The role of (fup)
will be explained below. If the transfer function of the controller is
represented by (K), then the output of the controller (e) is:
a = K(f - f"p ) (5)
Substituting for (fR) and (e) from equations (3) and (5) into equation (2)
results in the following equation for the end-effector velocity (v):
v = GK(f - f"p ) + S(f + p) (6)
Measuring an upward human force on the end-effector is only possible
when the line is under tension caused by the weight of the end-effector. If
the
end-effector is light, then the full range of human upward forces may not be
measured by the sensor in the end-effector. To overcome this problem, a
positive number, (fup), is introduced in equation (5). As equation (6) shows,
in the absence of (f) and (p), (fup) will cause the end-effector to move
upwardly. Suppose the maximum downward force imposed by the operator
is fmax. Then (fup) is preferably set approximately at the half of fmaX.
Substituting for (fup), equation (7) represents the load velocity:
v = GK(f - f 2 ) + S(f + p)
If the operator pushes downwardly such that f= fmax, then the
maximum downward velocity of the end-effector is:
v~H,r, = GK( f 2 X ) + S(fmax + p)
If the operator does not push at all, then the maximum upward
velocity of the end-effector is:
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vUP = -GK( f 2x ) + S(p) (9)
Therefore, by the introduction of (fup) in equation (5), one does not
have to worry about the measurement of the upward human force. If S=0,
the upward and downward maximum speeds are identical in magnitude.
However in the presence of non-zero S, for a given load and under equal
conditions, the magnitude of the maximum upward speed is smaller than the
magnitude of the maximum downward speed. This is very natural and
intuitive for the operator.
Going back to equation (6), it can be observed that the more force an
operator imposes on the end-effector, the larger the velocity of the load will
be. Using the measurement of the operator force, the controller assigns the
pulley speed properly to create enough mechanical strength to assist the
operator in the lifting task. In this way, the end-effector follows the human
arm motions in a "natural" way. In other words the pulley, the line, and the
end-effector mimic the lifting/lowering movements of the human operator,
and the operator is able to manipulate heavy objects more easily without the
use of any intermediary device.
I now describe some important characteristics of this device via three
experiments. Substituting for p in equation 6 and rearranging its terms
results
2 0 in equation 10:
(1 + SE) v = (GK + S)f - GK(fUP ) + S(W) (10)
Equation (11) shows that any change in the load weight, (0W), and any
change in the force imposed by the operator on the end-effector, (Of), will
result in a variation of the end-effector speed, (0v), such that:
(1+SE)Ov=(GK+S) (~f)+S(OW) (11)
Experiment 1
If Ov = 0 for two different objects being maneuvered (i.e. the operator
maintains similar operational speeds), then:
0 = (GK + S) (Of) + SCOW) (12)
Rearranging the terms of equation (12) results in equation (13):
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GS +1=- ~W (13)
Equation (13) indicates that an increase or a decrease in the load weight
(OW) will lead to an increase or a decrease in the upward human force, if
operational speed is expected to remain unchanged. In other words, if the
load weight is increased, the operator needs to increase his/her upward hand
force or decrease his/her downward force to maintain the same operational
speed. The term (GK/S +1) in equation (13) is the force amplification factor.
The larger (K) is chosen to be, the greater the force amplification in the
system
will be. Consequently, if the force amplification is large, the operator
"feels"
only a small percentage of the change of the load weight. Essentially, the
operator still retains a sensation of the dynamic characteristics of the free
mass, yet the load essentially "feels" lighter. This method or toad sharing
gives the operator a sense of how much he/she is lifting. Inspection of
equation (13) shows that, variations in load weight, (~W), results in a small
variation in the operator force, (Of), if (S) is a small quantity. In other
words,
the operator will have little feeling of the variation in the load weight if
(S) is
a small quantity. I will explain later how to cure this problem and give a
more pronounced feeling of the load variation to the operator when (S) is a
small quantity. Also, note that at very low frequencies (rather slow and
smooth maneuvers), the left side of equation 13 approaches a large number.
This indicates that an increase or decrease in the load weight (~W) will lead
to
a very small increase or a decrease in the upward human force (almost
unnoticeable), if operational speed is expected to remain unchanged.
However, at higher frequencies (rather fast and harsh maneuvers), the
2 5 operator will have a more pronounced feeling of the load weight variation.
In other words, if the operator is performing a relatively slow lifting
movement, the additional force necessary to maintain operational speed of a
heavier load versus a lighter load may be unnoticeable. But if the operator is
performing a rapid lifting movement, the additional force necessary to
3 0 maintain operational speed of a heavier load versus a lighter load may be
more noticeable.
Experiment 2
If Of = 0, (i.e. operator decides to maintain similar forces on the end-
effector for two different load weights), then equation (11) reduces to:
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CA 02373247 2004-11-12
(1 + SE)w = SCOW) (14)
This means that an increase in load weight, (0W), will lead to an
increase of downward speed, if the operator maintains a constant hand force.
Moreover an increase or decrease in the weight of the load, (~W), will cause a
decrease or increase, respectively, in the upward end-effector speed for a
given
operator force on the end-effector. Essentially, the Ioad falls faster and
goes up
slower if there is an increase in the load weight for a given operator form.
From equations (I3) and (14), it can be deduced that for an increase of load
weight, the operator needs either to increase his/her upward force to
maintain similar operational speed or to decrease his/her upward operational
speed to maintain similar force on his/her hand. This dynamic behavior is
very comforting and natural for the workers.
Finally, if ~W = 0, (i.e. the load weight is constant), then:
(1 + SE)Av = (GK + S)Af (15)
This means that an increase or a decrease in the operator downward
force (Af) will lead to an increase or a decrease, respectively, in the
downward
operational speed, if the load weight is unchanged. One can also interpret
equation (15) differently: for a given load weight, an increase in operational
2 0 speed requires more operator force. In general, the larger (K) is chosen
to be,
the Iess the operator force will be.
As Fig. S indicates, (K) may not be arbitrarily large. Rather, the choice of
(K) must guarantee the closed-loop stability of the system shown in Fig. 5.
The human force (f) is a function of human arm impedance (H), whereas the
load force (p) is a function of load dynamics (E), i.e. the weight and
inertial
forces generated by the load. One can find many methods to design the
controller transfer function (K). An article entitled "A Case Study on
Dynamics of Haptic Devices: Human Induced Instability in Powered Hand
Controllers," by Kazerooni and Snyder, published in AIAA Journal of
Guidance, Control, and Dynamics, Vol. 18, No. 1,1995, pp. 108-113
describes the conditions for the closed loop stability of the
system. Practitioners are not confined to one choice of
controller; a simple low pass filter as a controller, in many cases, is
adequate to
stabilize the system of Fig. 5. Some choices of linear or non-linear
controllers
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CA 02373247 2004-11-12
may lead to a better overall performance (large force amplification and high
speed of operation) in the presence of variation of human arm impedance (I-~
and load dynamics (E).
The choice of (K) also depends on the available computational power,
elaborate control algorithms to stabilize the closed system of Fig. 5 while
yielding a large force amplification with high speed of maneuvers might
require a fast computer and a large memory. An article entitled "Human
Extenders," by H. Kazerooni and J. Guo, published in ASME Journal of
Dynamic Systems, Measurements, and Control, Vol. 115, No. 2{B), June 1993,
pp. 281-289 describes stability of the closed loop system and a method of
designing (K).
loop system and a method of designing (K).
One can arrive at the theoretical values of (G) and (S) using standard
modeling techniques. There are many experimental frequency domain and
time domain methods for measuring {S) and (G), which yield superior results.
I rernmmend the use of a frequency domain technique in identifying (G) and
(S). For example the book titled "Feedback Control of Dynamic Systems," by
G. Franklin, D. Powell, and A. Emami-Naeini, Addison Wesley, 1991,
describes in detail the frequency-domain and time-domain methods for
identifying various transfer functions.
Note that linear system theory was used here to model the dynamic
behavior of the elements of the system. This allows me to disclose the system
properties in their simplest and most commonly used form. Since most
practitioners are familiar with Linear system theory, they will be able to
understand the underlying principles of this invention using mathematical
tools of linear system theory (i.e. transfer functions). However, one can also
use nonlinear models and follow the mathematical procedure described
above to describe the system dynamic behavior.
A special problem can occur in the device when the operator pushes
downward on the end-effector but the end-effector is prevented from moving
downward. This situation can be explained with the help of the following
example using suction cups as the load gripping means. As shown by the
end-effector 14 in Fig. 6, if the operator pushes the handle 16 downward to
ensure firm engagement of the suction cups 18 with the box 25, the actuator
(not shown in Fig. 6) will unwind the line 13. This occurs because the
3 5 controller, reacting to the downward human force on the end-effector 14,
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concludes incorrectly that the operator wants to lower the end-effector and
sends a command signal to the actuator which causes the actuator to unwind
the line 13. In some instances the unwound "slack" portion of line 13 can
amount to a few feet. After the engagement of the suction cups 18 with the
box 25, when the operator pushes the handle 16 upward to lift the box, the
actuator and pulley must take up the slack in line 13 before the box 25 is
lifted.
This impedes the operator since he has to wait while the actuator winds the
slack in line 13. Moreover, the sudden change in the line tensile force from
zero (i.e. when the line is slack) to a non-zero value (i.e. when the line is
not
slack), will jerk the end-effector 14. This sudden jerk can cause the box to
be
dropped. In summary, the operator's motion during the lifting operation is
impeded due to unnecessary slack in the line 13; and the box may be dropped
due to the sudden change in the line's condition from slack to tight.
The slack in the line can have far more serious consequences than
slowing down the workers at their jobs; the slack line may wrap around the
operator's neck or hand. As stated earlier, after the slack is produced in the
line, when the operator pushes upwardly on the handle, the slack line may
become tight around the operator's neck or hand creating serious or even
deadly injuries. It is therefore important to ensure that the line 13 will
never
2 0 become slack.
In accordance with another aspect of this invention, when the operator
pushes the end-effector handle 16 downward to ensure tight engagement
between the suction cups 18 and the box 25, the actuator does not unwind the
line 13. In other words, the device described here has the "intelligence" to
recognize that the operator is simply pushing downwardly to engage the box
with the suction cups 18 and he does not intend to move his hand further
downward. On the other hand, if the operator pushes against the end-effector
handle 16 downwardly when there is no box to resist the motion of the end-
effector, the actuator of this invention will unwind the line 13 to ensure
that
3 0 the downward operator motion is not impeded. The assist device described
here is able to differentiate between these two cases; in the first case the
actuator does not unwind the line 13, while in the second case the actuator
does unwind the line 13.
In order to prevent the slack in the line 13, one needs to detect the line
3 5 tensile force (fR). Then, with the knowledge of the line tensile force,
one
needs to adjust the pulley speed so rope is not unwound unnecessarily, and
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therefore slack is prevented in the line. In its simplest form, to prevent
slack
in the line, when (fR) becomes zero the actuator and pulley must be stopped.
In a more sophisticated form, to prevent slack in the line, smoothly, as the
tensile force in the line, (fR), approaches zero, the pulley rotational speed
must
be forced to approach zero and in the limit when a zero tensile force is
registered in the controller for the line, the pulley rotational speed must be
forced to zero. In other words the slack in the line is prevented by
appropriately reducing the pulley speed to zero when tensile force is zero.
Previously, I stated that the pulley speed depends on the signal
representing the operator force only. However for the device that will not
create slack in the line, the pulley speed depends on the signal representing
the line tensile force in addition to the signal representing the operator
force
on the end-effector handle. Two methods are preferred for detecting the rope
tensile force. The first method involves the direct detection of the rope
tensile force while the second method estimates the rope tensile force based
on measurement of the power consumed by the actuator or the electric
current used in actuator. Knowledge of line tensile force can then be used to
force the actuator and pulley to have zero speed so slack is prevented in the
line.
In direct detection of the line tensile force, a force sensor can be used to
directly measure the line tensile force. Fig. 7A shows an end-effector 60
having a force sensor 61 installed on the end-effector between the end-
effector
60 and line 13. Screw 62 is used to install the force sensor 61 to bracket 47
of
the end-effector. A set of screws 63 are used to connect bracket 64 to force
sensor 61. Eyelet 46 is screwed to bracket 64 and provides an interface to
line
13. The force between line 13 and the end-effector 60 passes through the force
sensor 61 and therefore the force sensor 61 always measures the line tensile
force. Signal cable 65 carries a signal representing the line tensile force to
the
controller 20.
Alternatively, a force sensor can be installed on the end-effector to
measure the force associated with the load only as shown in Fig. 7B. Force
sensor 61 is connected to part 44 via screw 62. A set of screws 63 are used to
connect bracket 64 to force sensor 61. Suction cups 18 are connected to
bracket
64 and provide an interface to box 25. In this case force sensor 61 always
3 S measures a force that is equal to the weight and inertia force due to
acceleration of the load only. Signal cable 65 carries a signal representing
this
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force to the controller 20 and therefore the force representing the weight and
inertia force of the load (labeled as p~) will be identified in the
controller.
Measurement of pLand f in conjunction with calculation (or direct
measurement) of end-effector acceleration leads to calculation of the line
tensile force, ( fR), according to equation (16):
fR=pL+f+WE 1-gdtv (16)
where WE is the weight of the end-effector itself and is known in
advance. For maneuvers with low acceleration, the force measured by the
sensor is always a tensile force (e.g. a positive value) as long as the line
is not
slack. The moment the load and the end-effector encounter an obstruction
blocking downward movement, the sensor shows a compressive force (e.g. a
negative value). This change of sign during the measurement of p~ flags the
existence of zero line tensile force. Also note that since the load force (p~)
is
typically greater than operator-applied force (f), one can roughly estimate
tensile force (fR) by ignoring f in equation 16. Finally for maneuvers with
low
acceleration, the line tensile force is approximately equal to the sum of the
weight of the end-effector and the weight of the load. Here I recommend that
practitioners make sure equation 16 is truly satisfied in using any signal in
flagging the zero line tensile force.
A force sensor suitable for use in this invention can be selected from a
variety of force sensors that are available in the market, including
piezoelectric based force sensors, metallic strain gage force sensors,
semiconductor strain gage force sensors, Wheatstone bridge-deposited strain
gage force sensors, and force sensing resistors. Regardless of the particular
type of force sensor chosen and its installation procedure, the design should
be such that the force sensor allows an estimation of load force or line
tensile
force with reasonable accuracy.
Alternatively, one can install a force sensor directly between the
actuator 12 and the rail or trolley as shown in the human power amplifier 70
3 0 of Fig. 8. Force sensor 71 measures the entire force being imposed on the
rail
72 by the lifting device. A signal representing the measured force is sent to
the controller 20 via a signal cable 73. When the line tensile force is zero,
then the force sensor output signal represents the weight of the actuator,
pulley, brake and all the components connected to the rail 72. This value can
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be measured and saved in the controller memory in advance. When the line
tensile force is not zero, the force sensor output signal increases to include
the
line tensile force. Therefore, by subtracting a constant value (saved value in
the memory) from the force sensor output signal, one can detect the line
tensile force.
Fig. 9 shows how a motion sensor or estimator can be used to measure
the line tensile force. Rope 13 is wound on pulley 11, and actuator 12 is
connected to trolley 81 via bolts 82. Bar 83 is free to rotate around point 84
on
the actuator body and holds an idler pulley 85 on one end and connects to a
tensile spring 86 on its other end. The tensile spring 86 is anchored to the
actuator body at point 87. The idler pulley 85 is pushed against line 13 via
the
force of spring 86. The rotation of bar 83 is measured by angular motion
sensor 88. One can use variety of motion sensors such as optical encoder,
resolver, or a potentiometer to measure the rotation of bar 83 relative to the
actuator body. The larger the line tensile force is, the more bar 83 turns in
the
anti-clockwise direction. For small values of the line tensile force, the bar
83
turns in the clock wise direction due to force of the tensile spring 86.
Signal
cable 89 carries the motion sensor output to the controller. One can calibrate
the output signal of the motion sensor 88 to measure or estimate the value of
the line tensile force. Instead of transforming the tensile force to
rotational
motion one can transform the line tensile force into linear motion. This can
be accomplished by installing the idler pulley on a bar that has translational
movement. Then a linear potentiometer, a linear encoder or an LVDT can be
used to detect this linear motion.
Rather than generating a signal representing the line tensile force
magnitude, one might be interested in a detection device that generates a
binary signal; one signal when the line tensile force is zero and another
signal
when the line tensile force is not zero. These devices have lower cost since
they give limited information about the rope tensile force. Figs. l0A and Fig.
lOB show an end-effector 90 having a tensile force detector comprising a
momentary switch 91, mounted on bracket 47, for generating a binary signal.
Rope 13 is firmly connected to bracket 47, plate 92 is able to rotate along
hinge
93. Tensile spring 94 is connected between plate 92 and bracket 47 causing
plate 92 to rotate along the direction of arrow 95. Plate 92 also has a hole
that
allows the rope 13 to pass through. A signal cable 96 carries the momentary
switch output to the controller. Stop 97, preferably a plastic sphere is
rigidly
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connected to rope 13. Stop 97 does not allow plate 92 to rotate along the
arrow
direction 95 when the line tensile force is non-zero (Fig. 10A). In fact in
the
presence of a non-zero tensile force in the line 13, stop 97 causes plate 92
to be
at the position shown in Fig. l0A not pressing against switch 91. When the
S line tensile force is zero (as shown in Fig. lOB), plate 92 pushes against
switch
91 by the force of a spring 94. Therefore this limited force detecting device
detects that tensile force exists in the rope, but is not able to measure the
magnitude of the rope tensile force. Basically, this method uses the tensile
force in the line to create a binary electric signal, representing the
presence or
absence of line tensile force for the controller; one signal when the line
tensile
force is non-zero and another signal when the line tensile force is zero.
Alternatively, one might be interested in employing the rope tensile
force at another location on the rope to detect the presence of line tensile
force. This is shown in Fig. 11A and Fig. 11B where Iine tensile force, at the
top of the device near the actuator 12, is employed to generate a binary
signal
for the controller. Line 13 is wound on pulley 11, and actuator 12 is
connected
to trolley 81 via bolts 82. Bar 83 is free to rotate along point 84 on the
actuator
body and holds an idler 85 on one arm and connects to a tensile spring 86 on
its other arm. The tensile spring 86 is anchored to the actuator body at point
87. The idler 85 is pushed against rope 13 via the force of spring 86. When
the
rope tensile force is not zero as shown in Fig. 11A, the rope tensile force
overcomes the spring force and causes bar 83 to be separated from switch 98.
When the rope tensile force is zero as shown in Fig. 11B, the idler 85 is
pushed toward left by the force of the tensile spring 86. This causes switch
98
2 S to be activated by bar 83. Therefore, a signal is generated by the switch
when
the Iine tensile force is zero. Signal cable 99 carries the momentary switch
output to the controller. Instead of transforming the tensile force to
rotational movement as shown in Figs. 11A and Fig. 11B, one can transform
the line tensile force into linear motion. This can be accomplished by
installing the idler pulley 85 on a bar that has translational movement and is
supported on a linear bearing. The idler pulley is in contact with the line 13
and the tensile force in the line causes transnational movement for the bar.
The movement of the bar, in return, causes a switch 98 to be activated.
Another preferred method of detecting the status of the line tensile
3 5 force involves instrumentation of the end-effector 79 with a switch as
shown
in Fig. 12A and Fig. 12B. Switch 74 is preferably installed on a horizontal
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section of bracket 44. Bracket 75 holding two suction cups 18 is free to slide
in
the vertical direction relative to part 44. Slots 76 are provided in part 44
as
bearing surfaces for sliding motion of part 75 relative to part 44. Fig. 12A
shows the end-effector 79 where the end-effector is not constrained by any
object from moving downwardly and switch 74 is not pressed. Optional
compression springs 78 are installed between bracket 75 and part 44 to
maintain a distance between part 44 and bracket 75. When the end-effector is
lowered (Fig. 12B), and part 75 is prevented from going downwardly by box 25,
this causes switch 74 to be pressed by part 75 generating an electric signal.
At
this moment, the entire force associated with the weight and inertia of the
end-effector, and the operator force (shown by the right hand side of equation
16) are supported by box 25 and not by the line 13. This indicates that the
line
tensile force (the left side of equation 16) is zero. Therefore, the signal
generated by switch 74 determines not only the existence of the obstruction,
but also the existence of zero tensile force on the line. Therefore, the
sensory
system of Figs. 12A and 12B is not only an obstacle detector, but also a
tensile
force detector. This signal is carried to the controller 20 by the signal
cable 77
and can be used to declare the zero tensile force in the line. When there is
no
object to prevent the downward motion of the end-effector, then part 75 is
lowered either by its own weight or by the force of compression springs 78
releasing switch 74. Therefore, this end-effector is able to create a binary
signal, one when the force in the line is zero and another one when the force
in the line is not zero.
A second preferred method estimates the line tensile force based on the
current or energy consumed by the actuator to support the end-effector and
any load connected to it on the line. The energy consumed by the system to
support the end-effector and a load connected to it can include many different
types of energy including electric, pneumatic, hydraulic, and other
alternative
types of energy. If pneumatic or hydraulic actuators are used in the system,
3 0 then the load pressure in the actuator can be used to estimate line
tensile
force. In a specific preferred embodiment line tensile force can be determined
by measuring the current in the electric actuator, since the current in the
electric actuator is related to the tensile force in the line. Moreover,
measuring the current used in the electric actuator is a cost-effective
approach
in estimating the line tensile force since measurement of electric current is
usually available in many of the electronic amplifiers that drive the electric
actuators. Even if the current measurement is unavailable in the electronic
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amplifier for the motor, one can use a clamp-on current sensor to measure
the current that is used by the motor. The clamp-on current sensor can be
installed on any part of the cable that powers the electric actuator 12. The
clamp-on current sensor is essentially a Hall effect sensor that detects the
S magnetic field strength around a wire, which is proportional to the electric
current flow. In a preferred embodiment of this invention, the amplifier that
powers the electric motor has a built-in sensor to measure the current drawn
by the electric motor of the actuator 12 and thereby estimates line tensile
force.
Fig. 13 shows the inventive assist device with a clamp-on current
sensor 100 used to detect the current used in the actuator. The current from
the power supply in controller 20 to actuator 12 is carried by a cable 23 and
the
signal representing the measure of the electric current used by the motor is
sent to the controller via signal cable 101. I will explain later how the
current
measurement can be used to detect or estimate the line tensile force, but I
will
first explain how the knowledge about the rope tensile can be used to prevent
slack in the line.
Once the tensile force in the line is measured or estimated via the
methods described above, the actuator speed must be modified according to
the measured or estimated line tensile force. If the line tensile force is
zero,
then the input to the actuator should be modified to generate zero speed in
the actuator so no extra line is unwounded. This can be done by introducing
variable KM into the control block diagram, as shown in Fig. 14. If the
transfer
function of the controller is represented by (K), then the output of the
controller (e) is:
e=KM K(f-fup) (17)
Inspection of Fig. 14 shows that the line velocity can be represented by
equation (18):
v = G KM K(f - f"p) + S(fR) (18)
where KM is a variable such that KM = 1 when the line tensile force, (fR)
is non-zero. Substituting KM = 1 in equation (18) results in equation 19 when
the line tensile force is non-zero:
v = G K(f - f"p)+S(fR) (19)
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Equation 19 is similar to equation 6, and therefore it states that the
behavior described previously by three experiments are still valid. When the
rope tensile force (fR), is detected to be zero via any of the methods
described
above, (KM) must be changed to a zero value. Substituting zero for (fR) and
(KM) in equation (18) results in a zero value for line speed (v). This means
that no line will be unwound and slack in the line will be prevented when
(fR) is detected to be zero. For instance, when an operator is moving the end-
effector downwardly, either with or without a load connected to it, tensile
force on the line will be a non-zero value. If the operator brings the end-
effector into contact with an obstruction that results in the weight of the
end-
effector (and any load connected to it) being supported by that load or
obstruction, tensile force on the line will go to zero. While operator-applied
force may be detected and may cause line to be paid out momentarily, the
instant the line is no longer taut (i.e. tensile force is zero), the operator-
applied force (f) no longer contributes to line motion and slack is prevented.
Although I prefer to program the system to prevent slack by evaluating
tensile force, there are other ways to prevent slack in the line. An
alternative
method in detecting the slack in the line during quasi static operation (low
accelerations and decelerations maneuvers) involves simultaneous
evaluation of operator-applied force (f) and tensile force (fR) to detect
whether
or not the end-effector is supported by the line. The first step is to
calibrate
the system before operation to evaluate the tensile force on the line derived
solely from the weight of the end-effector (WE). During operation, the value
of operator-applied force (f) on the end-effector and the tensile force (fR)
on
the line are simultaneously evaluated. Then, by subtracting the value of the
operator-applied force (f) from tensile force (fR), the controller can isolate
load
force (p) using equation (3). Finally, by comparing the value of (p) to the
stored value (WE) the controller can determine whether or not the end-
effector is being supported by the line. As long as the load force (p) is
approximately equivalent to the weight of the end-effector (WE), the system
will know that the end-effector is neither engaged with a load nor supported
by an obstruction and that it is safe to pay out line. If at any moment the
load
force (p) is not at least equal to the weight of the end-effector (WE), the
system
will know that the end-effector is supported by some obstruction and will
adjust actuator speed to zero to prevent slack in the line.
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The variation of (KM) as a function of (fR) is shown graphically in Fig.
15A where (KM) changes from one to zero when the rope tensile force changes
from a non-zero value to zero. When zero tensile force in the line has been
detected, the actuator speed will become zero and the actuator will not
unwind the line. It is important to make sure that the system can come out of
the slack control when the operator initiates an upward motion on the end-
effector. However, since KM = 0, the upward motion of the operator will not
create any tensile force on the line to end the slack control mode if Fig. 15A
is
used to model (KM) at all times. This implies that the use of plot 15A forces
the system to prevent slack, but the system cannot come out of the slack
control.
To cure this problem, we use the plot of Fig. 15B when the signal
representing the operator force indicates upward motion and plot of Fig. 15A
when the signal representing the operator force indicates downward motion.
The plot of Fig. 15B has a non-zero value of C1 for (KM) when the Iine tensile
force is zero. The non-zero value of (KM) results in a non-zero, but small
value for the actuator speed when the upward motion is initiated by the
operator. This causes the system to come out of slack control and results in
the end-effector being lifted when the operator initiates an upward motion.
One can use a variety of functions to create a smooth transition between the
values of (KM).
If a force detection device gives a complete measurement of the line
tensile force (e.g. Fig. 7A, Fig. 7B, Fig. 8, Fig. 9, and Fig. 13), then Fig.
15C can be
used to represent variation of (KM) as a function of line tensile force when
the
signal representing the operator force on the end-effector indicates a
downward motion. The smooth transition between the two values of (KM ) as
a function of rope tensile force leads to less jerky motion for the device.
Fig.
15D shows the variation of (KM) as a function of line tensile force when the
signal representing the operator force on the end-effector indicates an upward
motion. Note that the non-zero value of Cl for (KM) when the line tensile
force is zero ensures that the system will come out of slack control when the
signal representing the operator force on the end-effector indicates an upward
motion. One can use a variety of mathematical functions to represent the
plot of Figs. 15C and 15D. For example, equation (20) is a good candidate to
3 5 mathematically present the plot of Figs. 15C and 15D:
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f~ z
KM -1 _ (1 _ Ci )e cZ (20)
where Cl is a non-zero value, but smaller than unity, when the signal
representing the operator force on the end-effector indicates an upward
motion. Equation (20) results in the plot of Fig. 15C if C1 is chosen to be
zero.
C2 can be chosen to yield an appropriate slope for the plot. Large values for
C2
result in a larger slope for the plot of equation (20). In one embodiment Cl
and CZ were chosen to be 0.4 and 600, respectively. The variation of (KM), as
shown in Figs. 15A, 15B, 15C, and 15D, can be programmed in controller 20.
One can also use a look-up table to generate numerical values of (KM).
Slack prevention upon detection of zero line tension can be used to
prevent only pay out or unreeling of line without effecting reeling in of
line.
Then an upward force signal from an operator can be acted on by winding
line upward even though line force is zero when the upward signal occurs.
Fig. 16 illustrates an embodiment of the invention that offers slack
prevention and can be used for depalletizing. As can be seen in Fig. 16, the
line does not become slack if the end-effector is pushed downwardly by the
operator while the end-effector is constrained from moving downwardly.
End-effector 14 is connected to electric actuator 12 mounted on the ceiling or
on an overhead crane. As the shaft rotates the pulley, the pulley's rotation
winds or unwinds the line 13 and causes the line 13 to lift or lower the end-
effector 14 and box 25. Two suction cups 18 are used to engage the box 25 to
the end-effector 14. The actuator 12 is controlled by the electronic
controller
20. The computer located in controller 20 receives two signals: one signal
from end-effector 14 over signal cable 21, representing the operator force,
and
a second signal from a current sensor, representing electric current drawn by
the actuator 12. The signal representing the current drawn by the actuator 12
is not shown in Fig. 16 since in this embodiment of the invention the
available current sensor is in the power amplifier (located in controller 20)
that powers the electric actuator 12. The computer in controller 20 sets the
speed that pulley 11 has to turn, based on two signals representing the
operator force on the end-effector 14 and the tensile force in line 13. The
controller 20 powers the actuator 12 via cable 23. The resulting motion of
actuator 12 and pulley 11 is enough to either raise or lower the line 13 the
correct distance that creates enough mechanical strength to assist the
operator
3 5 in the lifting or lowering the task as required. If the operator's hand
pushes
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upward on handle 16, the pulley 11 rotates so as to pull line 13 upward,
lifting
box 25. If the operator's hand pushes downward on the handle 16, the pulley
rotates so as to move line 13 downward, lowering box 25. However, as shown
in Fig. 16, the line does not become slack if the end-effector is pushed
downwardly by the operator while the end-effector is constrained from
moving downwardly.
Here, I now explain how the measurement of current drawn by the
actuator can be used to estimate the line tensile force if an electric
actuator is
used in the system. The magnitude of the torque generated by actuator 12 to
turn the pulley 11 and lift the load is proportional to the current that is
used
in the actuator 12. This is presented by equation (21):
TT = KrI (21)
where (TT)is the total torque generated by actuator 12, (I) is the current
used in actuator 12, and (KT) is a proportionality constant. The value of (KT)
is
usually supplied by the actuator manufacturer. (KT)can also be measured
experimentally by measuring current drawn by the actuator for some known
loads on the actuator. Although equation (21) is widely reported as the true
relationship between the torque generated by the actuator and electric current
drawn by the actuator, depending on the quality of the power amplifier that
powers the actuator, there might be some residual current measurement
when no torque is generated. The power amplifier must be calibrated to take
into account this residual biased current measurement. The amount of
torque available to lift the load and end-effector, TL, is equal to the
difference
between the total torque generated by actuator 12 and the torque required to
rotate pulley 11 and all rotating components of the actuator. This is
presented
in equation (22):
T~ = Tr - Tr (22)
where TP is the torque required to turn pulley 11 and all rotating
components of actuator 12. The torque TP is calculated in equation (23):
3 0 TP = Ira + BPco + To (23)
where:
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IP = moment of inertia of all rotating components of the actuator
(motor and transmission) and pulley as reflected on the motor shaft
BP = coefficient of friction of the same components above
a = angular acceleration of the electric motor shaft
cu = angular velocity of the electric motor shaft
To = constant torque due to coulomb friction in the system
Both (a) and (~) (the angular acceleration and angular velocity of the
motor shaft) can be estimated by measuring the motor shaft angle using many
standard estimation techniques.
(IP) and (BP)are two parameters associated with the actuator and can be
measured experimentally. (BP) represents the proportionality of the torque
with the motor speed during steady state behavior (i.e. constant actuator
speed). Practitioners must measure the required torque to turn the motor
shaft at constant speeds. (BP)is a proportionality constant between the motor
steady state speed and the required torque. (IP) represents the
proportionality
of the torque with the motor acceleration during high acceleration
maneuvers. There are many ways of measuring (IP) and (BP) using standard
parameter estimation techniques. For example, the Extended Kalman Filter is
a well-known approach in parameter estimation and can be found in the
control sciences literature. "Adaptive Control," by Shankar Sastry and Marc
Bodson, Prentice Hall, 1989, and "Time Series Analysis," by George Box and
Gwilym Jenkins, Hgolden-Day, 1976, are two good references in model
estimation. Two simple experiments can measure BP and h.
One can measure (IP) by driving the actuator with a high frequency
sinusoidal input torque. At high frequencies, the torque to overcome the
frictional torque is rather small in comparison with the inertial torque due
to
acceleration, and (IP) is proportionally constant between the motor
acceleration and the motor torque. By measuring the motor shaft acceleration
and torque, one can arrive at a value for (IP). To measure (BP), one can drive
3 0 the actuator with constant speed. At constant speeds the torque associated
with the inertial torque due to acceleration is zero and (BP) is
proportionally
constant between the motor speed and the motor torque. By measuring the
motor shaft speed and torque, one can arrive at a value for (BP).
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(To) is a small constant torque due to dry friction in the actuator (in
particular in the transmission part of the electric actuator.) For high
performance and well-lubricated electric actuators with little friction, (To)
is a
small quantity and can be neglected, otherwise it can be measured
experimentally.
Substituting for (TP) from equation (23) and (TT)from equation (21) into
equation (22) yields an equation for the torque required to lift the load:
TL =K,.I-(IPa+BPm+To) (24)
By measuring the current in actuator 12 and the velocity and
acceleration of the actuator shaft, one can calculate (TL) from equation (24).
The tensile force in the wire line, (fR), is:
fR = [K,.I - (IPa + BPw + To )]/R (25)
where R is the radius of pulley 11. For actuators that have gear heads
with very large transmission ratios (non-back-driveable systems), the motor
torque that supports the line tensile force is usually small in comparison
with
the motor torque that accelerates (or decelerates) the rotating parts of the
actuator. In other words the current used to provide torque to maintain the
line tensile force only constitutes a small portion of the current drawn by
the
electric motor if high transmission ratios are used. Moreover, actuators
having low transmission ratios will yield a larger range for the current
reading due to tensile force variation than of the actuators with high
transmission ratios.
Note that equation (23) shows the basic and linear form of the
dynamics of the actuator. If the actuator is designed properly and is well
lubricated, equation (23) governs the dynamics of the system well. In
instances requiring more precision, one might use equation (26) below, which
is similar to equation (25) with the friction force modeled by a non-linear
relation, g(ca):
fR - ~KTI _ (Ira + g(co) + To )~~R (26)
3 0 The structure of g(w) can be estimated experimentally using standard
system identification techniques. Again, the Extended Kalman Filter is a well-
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known approach in parameter estimation and can be found in the control
sciences literature.
The slack control methods described here were motivated based on an
application of the device using the suction cups. Even if the human power
amplifier device is not employed for use with the suction cups, the slack
control described above is preferably implemented in the device. There are
many situations when the operator can inadvertently push the load interface
subsection onto various surrounding objects including the objects to be
maneuvered. The downward residual force of the operator will cause slack in
the line if the end-effector is prevented from moving downward. Therefore,
it is important to prevent slack in the line at all times.
Inspection of equation (13) shows that variations in load weight, (0W),
results in a small variation in the operator force, (Of), if (S) is a small
quantity.
In other words, the operator will have little feeling about the variation in
the
load weight if (S) is a small quantity. If the line tensile force, (fR), is
measured
or estimated for slack prevention as discussed above, then using (fR), one can
further improve the system performance by creating more pronounced
feeling for the operator if the load weight changes. Here I explain how this
improvement can be accomplished. Once the line tensile force (fR) is known,
one can calculate the load force (p) from equation (3). The load force (p) can
then be used as a feedback signal:
e=KMK(f_fuP)+Qp (27)
where (Q) is a controller transfer function operating on the load force
(p). Throughout this application (Q) might also be referred to as a force
feedback transfer function since it feeds the load force back to the
controller.
A comparison of equation 17 with equation 27 indicates how both operator
force and load forces are used as feedback signals in equation 27, but only
operator force is used in equation 17. Fig. 17 shows the implementation of
equation 27. Substituting (e) from equation (27) into equation (2) and
3 0 following the same mathematical process described previously results in
equation (28) for the line velocity (v):
v = GK(f - fuP) + GQp + (S)(f + p) (28)
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Equation (29) shows that any change in load weight (OW) and any
change in the force imposed by the operator on the end-effector (Of) will
result
in a variation of the end-effector speed (Ov) such that:
(1 + SE + GQE) Ov = (GK + S)~f + (S + GQ)(OW ) (29)
The load force feedback transfer function, (Q), effectively increases the
system overall sensitivity to load from (S) to (S+GQ). If we define the
apparent sensitivity to load, S', as:
S' = S + GQ (30)
then equation (29) can be re-written as:
(1 + SE + GQE) w = (GK + S)Of + (S' )OW (31)
Equation (31) is similar to equation (11), but the system sensitivity to
load force is increased from (S) to (S'). Moreover all characteristics
previously
described in the three experiments are still valid. For example, the effect of
this optional load feedback in Experiment 1. Equation (13), when the load
feedback transfer function (Q) is used can be rewritten as equation (32):
GK + S _ _ 4W (32)
S' 0f
Comparing equations (13) and (32) demonstrates that, since (S') is larger
than (S), if the operational speed is expected to remain unchanged, any
increase in the load weight will lead to a greater increase in the required
upward human force if the load force feedback (Q) is used. In other words, for
a given increase in load weight, the operator feels more force when the load
force feedback is used. The choice of load force feedback is optional. If (S)
is
sufficiently large to give a reasonable sensation for the variation of the
load
force to the operator, then one does not need to implement the load force
feedback; if (S) is small, then implementation of load force feedback will
improve system performance in a sense that the operator will have a more
pronounced sensation of the variation of the load force.
Here I explain two simple variations of equation 27. Since operator
force (f) is usually small in comparison with load force (p), then (p) in
equation (27) can be replaced by (fR):
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a = KM K(f - fuP ) + QfR (33)
Also, rather than using load force as feedback, one can use p~ (the force
due to the weight and inertia of the load only) if (pL) is readily available
as
shown in the example of Fig. 7B:
e=KMK(f-f~P)+QpL (34)
Figs. 18A and 18B show a flowchart of a computer program that can be
used in controller 20. The control program initializes all input and output
hardware in the system first. This includes analog-to-digital, digital-to-
analog
and quadrature counters in addition to any other peripherals in the
controller. After calculation of all constants needed in the controller, the
controller disengages the frictional brake on the actuator and will energize a
green light on the controller indicating that the system is ready to be
operated.
The controller then enters the main control loop; it reads the actuator
position, human force, current in the actuator, and the dead-man switch. The
software then implements the transfer function (K) on the signal representing
the human force. The transfer function (K) should be chosen to guarantee the
closed-loop system stability. Using the value of the actuator position, the
controller will estimate the line tensile force using equation (17) above.
Using
the value of the human force, the software will determine if the human force
2 0 is downward (+) or upward (-). Depending on the direction of the human
force, the software calculates a value for KM using plots similar to Figs. 15B
and Fig. 15C. Since the value of KM is obtained from the plot of either Fig.
15B
or Fig. 15C, there will be a discontinuity in calculation of magnitude of KM.
The jump among the various values of KM can be smoothed by using a digital
filter. Therefore a digital filter is designed to filter high frequency
components associated with KM. In this embodiment, a digital low-pass filter
was written in the software to smooth the value of KM.
The software then checks to see if the dead-man switch is pressed or
not. If the dead-man switch is pressed, then the software sends the modified
3 0 value of (e) to the actuator. If the dead-man switch is not pressed the
software
keeps the actuator in its current position using a position controller and
engages the friction brake. This friction brake engages and prevents the
actuator from rotating when the dead-man switch is released. This friction
brake adds more rigidity to the system when the operator is not attending the
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CA 02373247 2001-11-06
WO 00/69771 PCT/US00/04065
device. As an additional safety feature, I prefer to have the friction brake
engage any time there is a power failure.
There are many hoists that use an intermediary device such as a valve,
push-button, keyboard, switch, or teach pendent to adjust the lifting and
lowering speed of the object being maneuvered. For example, in a valve-
controlled hoist, the more the operator opens the valve, the greater the
lifting
speed of the object becomes. With an intermediary device, the operator does
not have any sense of how much she/he is lifting because her/his hand is not
in contact with the object but is busy operating a valve or a switch. However,
it is possible for the operator to activate the intermediary device (e.g. DOWN
push-button) to bring a load down while the load is constrained from moving
downwardly. The method of preventing slack described above can be used
with these hoists without lack of generality. In other words, the switches and
sensors described here (e.g. Figs. 9, 10A, lOB, 11A, 11B) can be used with
these
devices to send the controller information about the line tensile force (e.g.
the
magnitude of the line tensile force or lack of line tensile force). Moreover,
if
these devices are powered electrically, then the line tensile force can also
be
estimated from current measurement as described above.
Although particular embodiments of the invention are illustrated in
the accompanying drawings and described in the foregoing detailed
description, it is understood that the invention is not limited to the
embodiments disclosed, but is intended to embrace any alternatives,
equivalents, modifications and/or arrangements of elements falling within
the scope of the invention as defined by the following claims. For example,
while many of the embodiments described above use operator-applied force as
the input to the system, the advantages that my system provides, particularly
load weight sensitivity and slack prevention, can also benefit hoists that use
valves or up-down switches to lift loads. Moreover, although specific
equations have been set forth to describe system operation there are
alternative ways to program the system to achieve specific performance
objectives. The following claims are intended to cover all such modifications
and alternatives.
-36-

A single figure which represents the drawing illustrating the invention.

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Admin Status

Title Date
Forecasted Issue Date 2005-05-24
(86) PCT Filing Date 2000-02-17
(87) PCT Publication Date 2000-11-23
(85) National Entry 2001-11-06
Examination Requested 2001-11-06
(45) Issued 2005-05-24
Expired 2020-02-17

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Request for Examination $400.00 2001-11-06
Filing $300.00 2001-11-06
Maintenance Fee - Application - New Act 2 2002-02-18 $100.00 2001-11-06
Maintenance Fee - Application - New Act 3 2003-02-17 $100.00 2003-02-10
Maintenance Fee - Application - New Act 4 2004-02-17 $100.00 2004-02-04
Maintenance Fee - Application - New Act 5 2005-02-17 $200.00 2005-02-04
Final Fee $300.00 2005-03-09
Maintenance Fee - Patent - New Act 6 2006-02-17 $200.00 2006-01-30
Maintenance Fee - Patent - New Act 7 2007-02-19 $200.00 2007-01-30
Maintenance Fee - Patent - New Act 8 2008-02-18 $200.00 2008-01-30
Maintenance Fee - Patent - New Act 9 2009-02-17 $200.00 2009-01-30
Maintenance Fee - Patent - New Act 10 2010-02-17 $250.00 2010-02-02
Maintenance Fee - Patent - New Act 11 2011-02-17 $250.00 2011-01-31
Maintenance Fee - Patent - New Act 12 2012-02-17 $450.00 2012-04-30
Maintenance Fee - Patent - New Act 13 2013-02-18 $250.00 2013-01-30
Maintenance Fee - Patent - New Act 14 2014-02-17 $250.00 2014-02-10
Maintenance Fee - Patent - New Act 15 2015-02-17 $450.00 2015-02-16
Maintenance Fee - Patent - New Act 16 2016-02-17 $450.00 2016-02-15
Maintenance Fee - Patent - New Act 17 2017-02-17 $450.00 2017-02-13
Maintenance Fee - Patent - New Act 18 2018-02-19 $450.00 2018-02-12
Maintenance Fee - Patent - New Act 19 2019-02-18 $450.00 2019-02-11
Current owners on record shown in alphabetical order.
Current Owners on Record
KAZEROONI, HOMAYOON
Past owners on record shown in alphabetical order.
Past Owners on Record
None
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.

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Description
Date
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Cover Page 2002-04-30 2 49
Representative Drawing 2002-04-29 1 8
Description 2001-11-06 36 2,030
Abstract 2001-11-06 1 59
Claims 2001-11-06 15 646
Drawings 2001-11-06 20 363
Claims 2004-11-12 3 99
Description 2004-11-12 37 2,034
Cover Page 2005-04-22 1 46
PCT 2001-11-06 6 184
Assignment 2001-11-06 4 124
PCT 2001-11-07 7 219
Correspondence 2002-05-07 1 38
Correspondence 2002-05-23 1 19
PCT 2001-11-07 7 228
Assignment 2002-06-18 1 33
Correspondence 2002-07-12 1 10
Correspondence 2002-08-13 4 145
Prosecution-Amendment 2004-05-12 4 143
Prosecution-Amendment 2004-11-12 17 726
Correspondence 2005-03-09 1 30