Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
This inventlon relates to electricallv operated fas-
tener driving tools and, more particularly, to devices of
this type which are provided with electronic control cir-
cuitry for supplying a predetermined plurality of unidirec-
tional electronic impulses to a solenoid which powers the
fastener driving blade of the device. This results in the
delivery of a like number of driving strokes to a single
fastener for each actuation of the tool. Means is also pro-
vided for preventing the advancement of more than one fas-
tener into the path of the driver blade during the driving
strokes produced in a single actuation of the device.
Electronically operated fastener driving tools are
disclosed in U.SO Patent No. 3,971,969 and in patents cited
therein. The cited patent relates to electrically operated
stapling devices and, in particular, to devices which are
provided with electronic control circuitry for supplying
unidirectional electronic impulses for operating the staple
driving blade of the device. In the cited patent the driving
power is delivered to the blade in two or more pulses corres-
ponding to at least two alternate half-cycles of opposite
polarity from an alternating power source.
An electronic trigger circuit is disclosed in the
General Electric SCR Manual, Fifth Edition, at pp. 202-3
(1972). The GE SCR Manual discloses a one-shot trigger con-
trol circuit which triggers an SCR for one complete half-
cycle only of an AC supply. The SCR Manual teaches that the
disclosed circuit may be utilized for the solenoid drives of
electrically operated tools where load current must flow for
one complete half-cycle only to produce a single stroke of a
solenoid armature regardless of the length of time the trig-
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ger of the device is maintained in the "on" position.
It has been found to be advantageous to operate anelectronic fastener driving tool in such a manner that each
fastener is driven with more than one stroke of the driver
blade. The fastener is thus completely set in the workpiece
and less energy is expended per stroke of the driver blade
rendering the entire operation quieter and resulting in less
wear and tear on the device to therebv extend its useful life.
By providing multiple driving strokes to each fastener, pene-
tration of harder working surfaces than that normally possiblewith single stroke devices is accomplished.
The present invention utilizes circuitrv comprising
only diodes, resistors, capacitors and a sinqle SCR to pro-
vide a predetermined plurality of unidirectional current
pulses to the solenoid during consecutive like-poled half-
cycles of alternating current so that the driver blade will
deliver a predetermined plurality of driving strokes, pre-
ferably two, for a single actuation of the tool. Alternative
mechanical means are also provided, responsive to the acti-
vating mechanism of the tool, to prevent more than one fas-
tener, in a strip of fasteners, for example, from being ad-
vanced into the path of the driver blade during a single
actuation of the tool. In one embodiment, a damper assembly,
also referred to herein as a dashpot assembly, is disclosed
in which the return of the driver blade to its normal rest
position is restrained and the driver blade itself prevents
the travel of the following fasteners into the drive track.
In an alternative embodiment, a clamping assembly responsive
to the actuation of trigger means physically clamps down on
the first following fastener and prevents its movement into
the drive track. By either of these alternative mechanical
means there is prevented the possibility of more than one
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fastener from being driven as a result of the multiple stroke
action of the driver blade.
BRIEF DESCRIPTION OF THE DRArlINGS
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Fig. 1 is a side elevation of the electronic fastener
driving assembly with parts broken away and in section.
Fig. 2 is a fragmentary view of the dashpot seated
against the plunger cap moving upward.
Fig. 3 is a plan view in section through the dashpot
taken along lines 3-3 of Fig. 2.
Fig. 4 is a fragmentary view of the dashpot showing
the parts separated while moving in the downward position.
Fig. 5 is a side view of another embodiment of the
stapler showing the clamping assembly with the clamp in its
raised position.
Fig. 6 is a fragmentary view of the staple clamp
assembly in locked position during operation of the trigger
switch.
Fig. 7 is a vertical section taken substantially along
lines 7-7 of Fig. 6 showing the clamp.
Fig. 8 is an exploded view in perspective showing the
interrelationship of the driver blade, the clamping assembly
and forward portion of the magazine section of the device.
Fig. 9 is a horizontal plan view taken generally
along lines 9-9 of Fig. 8 showing the various components as-
sembled.
Fig. 10 is a schematic circuit diagram of an elec-
tronic pulsing circuit constructed in accordance with the
present invention.
DETAILED DESCRIPTION OF ?HE PREFERRED EMBODIMENT
Electronic Circuitry
The electronic fastener is actuated by an electro-
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magnetic triggering circuit with passive crossover detection
and programmable pulse capability powered by an AC source of
energy.
The AC circuit comprises a coil as well as nine com-
ponents. These nine components consist of a reverse blocking
triode thyristor such as a silicon controlled rectifier (SCR)
and eight components including three diodes, three resistors
and two capacitors.
The circuit relies on zero crossing detection for fir-
ing the SCR, but does so without the use of well-known phase
shift or voltaqe comparator techniques. In order to obtain
zero crossing data for the SCR, this circuit uses two passive
RC networks in which the component values are selected so
that their time constants determine that the SCR will be
fired a predetermined number of times, but under all circum-
stances more than once, during repeated like-poled half-cycles
of alternating current. No transistors are used in this
triggering circuit other than the firing SCR.
Bv altering the electrical values of the components in
the two RC networks to alter their time constants it becomes
possible to program this circuit in such a way that it will
deliver a predetermined number of half-cycle pulses. During
each of these half-cycles the SCR is fired and, in turn, the
coil is energized a corresponding number of times. Thus,
when the trigger of the staple gun is activated, this cir-
cuit will deliver a preprogrammed number of pulses and then
shut off regardless of the length of time the trigger is ac-
tivated. In order for the circuit to deliver a subsequent
sequence of pulses the trigger switch has to be released and
reactivated.
Referring to Fig. 10, the operation of the circuit
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after it is connected to a standard 110 volt source of alter-
nating current, is as follows:-
1. With the switch, SWl, in position A (nonactuated)
during the first positive half cycle of the AC source, current
flows through the series path which consists of the solenoid
load L, diode Dl, and the RlCl network. Although the resist-
ance of the solenoid is only approximately 2 ohms, Rl is a
680 ohm resistor, so that there will be very little current
in the loop. Therefore, the current passing through the
solenoid will be much smaller than required to create a suf-
ficient magnetic field to reciprocate its armature, plunger
assembly 26, shown in Figs. 1 and 5. Durina this positive
half cycle, the capacitor of the RlCl network is charged and
it becomes fully charged approximately bv the time the AC
sign wave reaches its maximum amplitude. With the switch
still in its nonactuated position, the R2C2 network is open-
circuited.
2. During the negative half cycle diodes Dl and D3
block the flow of current through the solenoid and the SCR
is not conducting. The R2C2 network continues to be open-
circuited.
3. When the switch is placed in position B (actuation)
by actuation of a trigger which may be either trigger 34,
illustrated in Fig. 1, or trigger 40, illustrated in Fig. 5,
the R2C2 network is connected to the SCR and creates another
loop for the flow of current. If the switch is changed to
position B during the positive half cycle, current will not
flow through the R2C2 network because it is blocked by diode
2.
4. During the negative half cycle of the AC source
after the switch is closed, current can flow through the
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path consisting of resistor R3, the gate of -the SCR, the ca-
thode of the SCR, the R2C2 network and diode D2. This cur-
rent, referred to as gate current, provides a negative cur-
rent pulse to the SCR which allows the SCR to conduct during
the next positive half cycle.
5. During the next positive half cycle, current flows
through the solenoid L, diode Dl, the SCR and diode D2. At
this point, the RlCl network is shunted so that most of the
line voltage appears across the solenoid and, therefore, a
large amount of current is allowed to flow in this loop.
This current is sufficiently large to allow the coil to ac
tuate the solenoid armature to reciprocate the driver blade.
Simultaneously, the RlCl network provides holding current to
the SCR for a sufficient duration to allow the SCR to fire
during the next successive positive half cycle.
6. During the negative half cycle between the two
firing positive half cycles, no current flows through the
solenoid because of diodes Dl and D3. During this interme-
diate negative half cycle, the biasing spring of the stapler
attempts to restore the solenoid armature to its retracted
position. By the time the third positive half cycle occurs
after the switch is placed in its actuating position, the
time constant of the RlCl network will have sufficientlv
decayed to no longer provide the necessary holding current
to fire the SCR a third time. Consequently, to get the SCR
to fire again, the switch will have to be released to allow `
the RlCl network to once again recharge and then the switch
must be reactivated.
7. Note, that the R2C2 network need provide a signal
to the gate only once regardless of the number of times that
it is desired to fire the SCR because once this SCR is acti-
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vated by a pulse of current it will continue to conduc-t dur-
ing successive positive half-cycles as long as there is suf-
ficient holding current supplied.
It can be seen from the above that the number of half-
cycle repeated firings of the SCR is a function of the SCR
holding current and gate current. The necessary holding cur-
rent of the SCR varies with different SCRs and their para-
meters are provided by the manufacturer. The time constant
of the holding current is determined by the passive network
comprising Rl and Cl. The gate current of the SCR is also a
specification which varies with different SCRs and forms a
portion of the manufacturer's specifications. The time con-
stants of the gate current are determined by the passive net-
work comprising R2 and C2. Consequently, by varving the
electrical values of the components of these RC networks it
becomes possible to program this circuit to fire a predeter-
mined number of times.
It has been found that more advantageous operation of
the driver blade of the electronic fastener may be accomp--
lished by using a multiple predetermined number of pulses asthe driving energy source. In the preferred embodiment a
predetermined number of unidirectional pulses, preferably
two, are derived from a like number of successive cycles of
the alternating current source.
When the values of the four critical components are
selected as shown in Table 1 hereinbelow, the RlCl network
and the R2C2 network function so as to fire the SCR two
successive times during two successive cycles of alternating
current each time the trigger switch is activated. The
values for the components presented in Table 1 and the values
which are cited in this and the following two paragraphs are
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meant to be illustrative rather than exclusive, although this
comhination of values has been found to be a desirable set
in terms of both reliability and cost efficiency. Moreover,
the values of the components may be selected so as to produce
a number of driving strokes greater than two for each actua-
tion of the device.
Table 1
Component Value
Rl 680 Q
Cl 10 ~f
R2 1,000
C2
Additionally, the circuit in Fig. 10 utilizes resis-
tor R3 whose resistance is 100 ohms. Resistors Rl, R2 and
R3 are all 1/4 watt (although 1/2 watt may be used) deposi-
ted carbon film resistors having axial leads and maximum
working voltages of 250 volts.
Diodes D1 and D3 are both 3 amp silicon diodes, where-
as diode D2 is a 750 milliamp silicon diode. All three di-
odes are rated 200 volts Peak Inverse Volta~e.
The SCR used in this application is a plastic silicon
controlled rectifier, 200 volts PIV which is capable of han-
dling forward currents between 8 and 12 amps. The peak for-
ward surge current for one half-cycle (8.3 milliseconds) must
be able to handle at least 100 amps. The gate trigger cur-
rent is in the range of 5 milliamps to 30 milliamps at 35 C `
and the holding current window is in the range of 12 milli-
amps to 30 milliamps at 25 C. Any of the following devices
is satisfactory: Motorola 2N4443, Motorola 2N6396, Unitrode
R08037580.
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PREFERRED MECHANICAL MODES OF THE INVENTION
Dashpot Assembly
The electronic fastener driving tool of this invention
is a multiple stroke device in which a fastener, for example,
a staple, receives a predetermined plurality of blows from the
driver blade to set it in a workpiece. In a preferred embodi-
ment of the device (dual pulse) each fastener is struck twice
by the driver blade. Since it is common practice to continu-
ously urge fasteners into position for being driven, the tool
must be provided with means to prevent a second fastener from
moving into the driving position while the driver blade is
applying a second stroke to the first fastener. Means are
provided for accomplishing this by the use of a dashpot assem-
bly which restricts the upward or return movement of the .
driver blade during the dwell time between its first and
second strokes. As a result, the driver blade does not fully
retract between the first and second strokes and physically
blocks the second fastener, and all others in a following
strip of fasteners, from the drive track until the first fas-
tener has been struck twice and is fully set in the workpiece.
The dashpot assembly 10, as shown in Fig. 1, is con-
nected to the armature or plunger assembly 12 of the fastener
tool 8 and moves vertically within the body cavitv 14 of the
head portion thereof together with and in response to the
movement of the armature assembly 12 which is upwardly biased
by resilient means such as tension spring 16. The dashpot
assembl~ comprises a cup-shaped device 18, shown in detail
in Fig. 2, which is preferably made of a plastic material
such as low density polyethylene. There is provided a plur-
ality of holes 20 at the bottom surface of the cup, shown inFig. 3, to provide for the flow of air therethrough during
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movement of the device in response to actuation of the tool.
The dashpot cup is loosely connected by tubular shoulder ri-
vets 22 to a plunger cap 24 which, in turn, is connected to
the plunger 26 of the armature assembly. The plunger cap
serves both to retain the spring 16 which upwardly biases
the armature assembly and to close the holes 20 during up-
ward movement of the armature. In operation, the plunger is
drawn into the solenoid 30 upon activation of the device by
actuation of trigger 34. The dashpot cup 18 is designed to
fit snugly but slidably within the circumferential wall of a
cylindrically-shaped interior enclosure 28 which fits within
the body cavity 14 and rests on the upper end of solenoid 30.
Upward or return movement of the dashpot cup 18 within the
interior enclosure 28, or similar enclosure, whether integ-
rally formed with the body of the tool or separately enclosed
as in the present embodiment, causes frictional and air
pressure resistance that retards its upward travel and, con-
sequently, the upward movement of the plunger assembly to
which it is connected, Full retraction of the driver blade
32 which is connected to the plunger 26 is thereby prevented
during the dwell time between the first and second strokes
applied to a fastener in a dual pulse embodiment of the de-
vice. As a result, the lower portion of the driver blade 32
physically blocks the following fastener from moving into
the driving position beneath the driver blade until the
first fastener such as staple Sl has been completely set in
a workpiece.
In operation, the dashpot works as follows: during
the first pulse of the solenoid which is initiated by actu-
ation of the trigger 34, the plunger moves down into sole-
noids 30 and the dashpot, due to friction and inertia, hesi-
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tates through approximately 0.055 inches provided by the
shoulder rivets which connect the dashpot to the plunger cap
as shown in Fig. 4. This provides a gap between the plunger
cap 24 and the bottom of dashpot 18 which allows air to rush
through the holes 20 in the bottom of the dashpot cup so that
the plunger is unrestricted on its downward stroke. During
the dwell between pulses, the return spring moves the plunger
cap 24 up against the dashpot cup, closing the holes 20 and
compressing the air in the body cavity 14. The air pressure
in the body cavity works against the return spring and slows
the return of the plunger assembly so that the second pulse
to the solenoid occurs before the driver blade has reached
the top of the next staple S2 in line. Dotted line 33 of
Fig. 1 illustrates the approximate return position of the
driver blade 32 between strokes in a multiple pulse operation.
The driver blade thus physically prevents staple S2 from mov-
ing into the drive track. In order that the plunger might
return to its initial rest position to drive the following
staple S2 after staple Sl has been completely set in a work-
piece, the top of the body cavitv cylinder is provided witha bleed hole 36 which regulates the rate of upward movement
of the dashpot assembly and allows the spring 16 to return
the plunger 26 to its initial, upward biased position. The
fastener is then ready for the next staple S2 to be driven
upon further activation of the device by reactuation of the
trigger 34.
Clamping Assembly
An alternative mechanism for preventing a second fas-
tener from entering the path of the driver blade 32 before
a first fastener such as staple Sl has been completelv set
in a workpiece is the clamping assembly 38 which is shown in
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Figs. 5-9. The clamping assembly operates mechanically in
conjunction with the movement of trigger switch 40 so that
when the trigger is squeezed clamp 48 presses down against
the next following staple S2 in the magazine 42, pressing it
against the staple rail 66 as shown in Figs. 6 and 7. Staple
S2 and those following it in the magazine 42 are thus res-
trained from forward movement until the trigger switch 40 is
released. Upon release of the trigger switch 40, clamp 48
moves upward into the rest position as shown in Fig. 5 and
staple S2 is urged forward into the path of the driver blade
by a spring (not shown) in the magazine 42.
Clamping assembly 38, shown in detail in Fig. 6,
comprises a clamp 48 and a pivotable lever member 44 which
is connected to and rotates about pivot 46. Pivotable lever
member 44 has two elongated end portions including a forward
projecting tang 52 and a rearward projecting arm 58. Tang
52 of pivotable lever member 44 projects through hole 50
which is located generally centrally in clamp 48. As shown
in Figs. 5 and 6, the rearward projecting arm 58 of the pi-
votable lever member 44 is resiliently connected to a block-
ing member 54 by resilient means such as spring 56. The
blocking member 54 is attached for movement with trigger
switch 40. Thus, when trigger switch 40 is s~ueezed, it is
raised from its rest or unactuated position (see Fig. 6,
dashed line 40) to its actuated position and blocking member
54 is also raised. Simultaneously, rearward projecting mem-
ber 58 of said pivotable lever member is caused by spring 56
to be raised and to rotate in a counterclockwise direction
about pivot 46. At the same time, tang 52 is rotated in a
counterclockwise direction and, because it communicates with
clamp 48 through hole 50, moves clamp 48 downward so that it
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presses staple S2 against staple rail 66. Staple S2 is thus
prevented from moving into the path of the driver blade.
As shown in Fig. 7, clamp 48 is provided at its bottom
edge with two tangs 60 which are positioned to press against
the top of a staple as it rests on the staple rail 66. The
tangs 60 are preferably canted forward as shown in Fig. 8.
The bottom edge of the tangs 60 are constructed so as to have
a horizontal edge which rests flush against the top of the
staple. This construction concentrates the pressure of the
clamp 48 on the staple pressing it firmly against the tracks
of the staple rail.
The interrelationship of the various parts of the
clamping assembly and the forward portion of the magazine
assembly are shown in an exploded view in perspective in Fig.
8. As illustrated therein, sheath 68 is designed for attach-
ment to the side plates 70 of magazine 42 and defines a por-
tion of the drive path for driver blade 32. The sheath 68
and the side plates 70 are connected by pivot 46 which extends
through aligned openings 80 and by a rivet (not shown) which
extends through aligned openings 82. Openings 80 and 82 of
side plates 70 may, if desired, be provided with inwardly
projecting bearing collars.
Enclosed within the sheath 68 are a driver backing
plate 62 which is provided with an elongated generally cen-
trally located hole 72, clamp 48 and tang 52 of the pivotable
lever member which extends through both hole 50 of clamp 48
and elongated hole 72 of backing plate 62. The elongated
hole 72 of the driver backing plate 62 has a width approxi-
mating the width of hole 50 but is of a greater length to
accommodate rotational movement of tang 52. This permits
the driver backing plate 62 to remain stationary while the ~,
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clamp 48 is moved up and down b~ tang 52 during operation of
the device. 3acking plate 62 is also prevented from move-
ment by elongated portions 76 which fit within and engage
notches 78 of the side plates 70. Tabs 74 which project in-
ward from side plates 70 prevent rearward movement of the
clamp 48. A number of the various elements shown in Fig. 8
and referred to above are shown assembled in Fig. 9 which
illustrates the interrelationship of these parts.
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