Electric Fastener Driving Tool

Abstract

An electric fastener driving tool designed for use with an undulating or alternating current input potential includes a housing with a chamber above a nosepiece structure defining a drive track. A pair of coaxial windings in the chamber slidably receive a magnetic armature connected to a driver blade slidable in the drive track. A plurality of compression springs are interposed between the housing and a plate which rests on a shoulder on the armature and is disposed in a space between the windings. A trigger actuated control circuit energizes the upper winding to retract the armature and compress the springs on the first complete half cycle of properly poled potential occurring after the trigger operation. At the end of this half cycle, the compressed springs drive the armature and driver blade downwardly toward a fastener in the drive track. The control circuit energizes the lower winding on the next following half cycle of input potential to accelerate the downward movement of the fastener driving assembly so that the power available for driving a fastener includes the energy obtained from the compressed springs as well as that obtained from the energization of the lower winding.

Description

This invention relates to an electric fastener driving tool and, more particularly, to a new and improved electric fastener driving tool having increased driving power.

Electric tackers or staplers have been used for a number of years, and a type used successfully in industrial applications is one shown and described in U.S. Pat. No. 3,179,866. In this type of tool, a control circuit trigger actuated at random times relative to the alternating current input potential connects a winding across the input potential for a complete half cycle so that a magnetic armature-driver blade assembly sets the fastener in a single stroke of uniform power. U.S. Pat. No. 3,209,180 discloses a similar tool in which part of the energy from an armature return stroke is resiliently stored for use in the next power stroke. U.S. Pat. No. 3,434,026 discloses a similar tool using an elongated armature and two vertically arranged windings energized on successive half cycles for increasing the energy of the power stroke. However, the energy that can be imparted to the driver blade with these arrangements is, in some applications, inadequate for driving certain types of large fasteners into harder or thicker material.

Accordingly, one subject of the present invention is to provide a new and improved electric fastener driving tool.

Another object is to provide an electric fastener driving tool deriving energy from more than a single half cycle of input potential by using a resilient energy storage means.

A further object is to provide an electric fastener driving tool using two windings, one of which is energized on one half cycle to compress a resilient armature-blade driving means and a second of which is energized on the subsequent half cycle of the input potential to accelerate the resiliently driven armature-blade assembly.

In accordance with these and many other objects, an embodiment of the invention comprises an electric stapler or fastener driving tool designed for use with alternating current potential. The stapler includes a housing having a vertical head portion defining a chamber having secured to its lower end a nosepiece structure defining a drive track to which successive fasteners or staples are supplied by a magazine assembly connected between the nosepiece structure and the lower end of a handle portion of the housing. A pair of vertically spaced windings are disposed within the chamber so that openings therein are axially aligned to receive a magnetic armature, to the lower end of which is connected a driver blade slidable within the drive track. A plate rests on a shoulder formed on the armature in a position disposed between the vertically spaced windings, and this blade is normally held in engagement with an annular stop by a plurality of compression springs interposed between the housing and the plate and peripherally spaced around the upper winding. A return spring is connected to the upper end of the armature to hold the shoulder in engagement with the coupling plate.

A control circuit mounted within the hollow handle is connected to the two windings and is controlled by a trigger or manually actuated switch which is operable at random times relative to the alternating current input potential. When the trigger is actuated, the control circuit energizes the upper winding during the first complete properly poled half cycle of the input potential. When the upper winding is energized, the armature is moved upwardly into the opening in the upper winding and carries with it the coupling plate so that the compression springs are stressed or compressed. During this movement, the driver blade moves upwardly within the drive track to clear the crown of the adjacent staple so that this staple can be fed into the drive track beneath the driver blade. At the end of the first half cycle of the alternating current input potential, the upper winding is no longer energized, and the compression springs operating through the coupling plate drive the armature and connected driver blade downwardly. Coincident with the termination of the energization of the upper winding, the lower winding is energized so that its flux field is coupled to the magnetic armature and drives the armature and driver blade downwardly so that the fastener engaged by the driver blade is driven into a workpiece. In this manner, the energy of the first half cycle of the input potential is used to store energy in the plurality of compression springs, and this energy is added to the energy of the second or next following half cycle which is effective through the lower winding to directly propel the magnetic armature downwardly through its power stroke.

Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a side elevational view in partial section illustrating an electric stapler embodying the present invention;

FIG. 2 is a sectional view taken along line 2--2 in FIG. 1; and

FIG. 3 is a schematic circuit diagram of a power control circuit used with the electric stapler shown in FIG. 1.

Referring now more specifically to FIG. 1 of the drawings, therein is illustrated an electric fastener driving tool or stapler which is indicated generally as 10 and which embodies the present invention. The stapler 10 includes a housing indicated generally as 12 including a vertical head portion 12A defining a chamber 14 and a rearwardly extending hollow handle portion 12B. A nosepiece structure indicated generally as 16 is secured to the lower end of the head portion 12A and defines a drive track 18 to which staples 20 or other suitable fasteners are successively supplied by a magazine assembly indicated generally as 22. The staples 20 are driven by a flat driver blade 24, the lower end of which is slidable within the drive track 18 and the upper end of which is connected to the lower end of a magnetic armature 26. The armature 26 is movable within aligned openings 28 and 30 in a pair of windings 32 and 34, respectively, which are mounted within the chamber 14. A resilient biasing assembly indicated generally as 36 is disposed in the space between the windings 32 and 34.

When the tool 10 is to be operated, a trigger 38 pivotally mounted on the housing 12 operates a control circuit 40 (FIG. 3) mounted within the hollow handle 12B and supplied with an alternating current input potential through a conventional line cord 42 (FIG. 1) to energize the winding 34 on the first complete half cycle following the operation of the trigger 38. Energization of the winding 34 retracts the armature 26 into the coil 34 and stresses the resilient biasing assembly 36 as well as retracts the lower end of the driver blade 24 so that it clears a crown portion 20A of the staple 20 in the magazine assembly 22 next adjacent the drive track 18. This permits this staple 20 to be moved into the drive track 18 below the lower end of the driver blade 24.

At the end of the first half cycle, the control circuit 40 terminates the energization of the winding 34 and permits the resilient biasing assembly 36 to move the armature 26 and the connected driver blade 24 downwardly to engage the staple 20 previously supplied to the drive track 18. On the next following half cycle, the control circuit 40 energizes the winding 32 which is coupled with the moving armature 26, and the flux field of the winding 32 adds further kinetic energy to the armature 26 which is imparted to the staple 20 in the drive track through the driver blade 24. At the end of this half cycle, the control circuit 40 terminates the energization of the winding 32 and disables any further energization of the windings 32 and 34 until such time as the trigger 38 is released and reoperated.

Referring now more specifically to the armature 26, this armature is formed with a lower portion 26A of greater diameter and an upper portion 26B of lesser diameter terminating in a generally conical upper end surface. The upper end of the driver blade 24 is secured as by a drive pin to the large diameter portion 26A of the armature 26. This armature is formed of magnetic material. In the normal position of the tool 10, the greater diameter portion 26A is received within the opening 28 in the lower winding or coil 32 and, more specifically, within a nonmagnetic sleeve 44 which defines the cylindrical opening 28.

The lower winding 32 is provided with a field or pole piece construction 46 of magnetically permeable material. The pole piece construction 46 is generally toroidal in configuration and is disposed within a lower portion of the chamber 14 resting on a circular retaining ring 48. The coil 32 and the pole piece construction 46 are secured in the position shown in FIG. 1 by an annular ring 50 which is interposed between an upper surface of the pole piece construction 46 and the lower surface of a metal ring 52 which rests on a shoulder on the head portion 12A and is secured in position thereon by another circular retaining ring 54.

A slotted metal guide plate 56 is secured to the bottom wall of the head portion 12A to provide means for guiding movement of the driver blade 24. This plate is held in position by a plurality of conventional fasteners, such as machine screws 58. Resting on the upper surface of the guide plate 56 is an annular resilient bumper 60 which cushions the termination of the downward power stroke of the armature 26. This resilient bumper 60 is held in position by an annular retaining plate 62 secured in position by a circular retaining ring 64.

The upper winding 34 is mounted within the chamber 14 spaced vertically above the lower winding 32 by a field or pole piece construction 66 having an upper plate 66A whose outer periphery rests on a shoulder in the head portion 12A and is secured thereon by a circular retaining ring 68. The upper plate 66A includes a depending portion 66B terminating in a generally conical cavity through which an opening 70 extends. The depending portion 66B limits the degree to which the armature 26 can be retracted into the opening 30 in the upper coil 34.

The resilient biasing assembly 36 includes a one-way coupling to the armature 26 formed by an annular non-magnetic plate 72 whose center opening receives the small diameter portion 26B of the armature 26 so that the plate rests on the shoulder defined by the large diameter portion 26A of the armature 26. The outer periphery of the plate 72 contains a plurality of peripherally spaced openings in which are slidably received a number of guiding pins or posts 74. The lower ends of the posts 74 are received within openings in the ring 52, and the upper ends of these posts or pins 74 are received in openings in the top plate 66A of the pole piece construction 66 for the upper winding 34. A plurality of compression springs 76 encircling the posts 74 are interposed between the lower surface of the top wall 66A and the upper surface of the plate 72. These springs normally resiliently bias the lower surface of the plate 72 into engagement with an annular resilient bumper 78 resting on the upper surface of the ring 52.

To provide means for returning the armature 26 and the connected driver blade 24 to their normal home position following each power stroke of the tool 10, there is provided a flexible cable 80 secured at one end to the upper end of the armature 26. This cable passes out of the top wall 66A through the opening 70 and passes over a pair of pulleys 82 and 84 rotatably mounted between a pair of supports 86 projecting upwardly from the top wall 66A of the pole piece construction 66. The cable 80 then passes downwardly through an elongated tube 88. The upper portion of this tube 88 is secured to the head portion 12A, and the lower portion of this tube projects downwardly beyond the confines of the wall of the head portion 12A. The lower free end of the flexible cable 80 is secured within an opening in a guide ball 90 located within the tube 88. A compression spring 92 extends between the guide ball 90 and a retaining structure at the upper end of the tube 88.

In the normal condition of the tool 10, the compression spring 92 is slightly compressed and exerts an upwardly directed force on the armature 26 so that the large diameter portion 26A of the armature 26 is held against the bottom surface of the plate 72 and the resilient biasing assembly 36. The force provided by the spring 92 is much less than the compressive force of the plurality of springs 76. Thus, the plate 72 serves as a stop establishing the normal position of the armature 26. When the armature 26 is moved upwardly, the spring 92 elongates and moves the ball and connected cable 80 downwardly within the tube 88. Alternatively, when the armature 26 is driven through a power stroke, the spring 92 is compressed, the ball guide 90 moves upwardly within the tube 88, and a portion of the flexible cable 80 passes over the pulleys 82 and 84 to enter the chamber 14. A cover 94 is detachably mounted on the top open end of the head portion 12A to facilitate the assembly of the above-described components.

The magazine assembly 22 can be of any of the types well known in the art and generally comprises a resiliently biased pusher for feeding a strip of staples 20 from right to left (FIG. 1). Since the driver blade 24 in the normal position shown in FIG. 1 occupies the drive track 18 in front of the first staple 20 in the strip, a staple 20 is not normally disposed in the drive track 18. However, when the armature 26 and the connected driver blade 24 are elevated upon energization of the upper winding 34, the lower end of the blade 18 clears the crown 20A of the first staple 20 in the strip, and the magazine assembly 22 feeds the first staple 20 into the drive track 18 below the lower end of the driver blade 24.

As set forth above, the operation of the tool 10 and more specifically the selective energization of the windings 32 and 34 by the alternating current input potential supplied over the line conductors 42 is controlled by the power supply or control circuit 40. This circuit preferably is formed as an encapsulated circuit disposed within the hollow handle 12B. The operation of the control circuit 40 and thus of the tool 10 is controlled by a manually actuated switch indicated generally as 100 (FIG. 3) having an operator portion 100A (FIG. 1) projecting out of the handle portion 12B to normally rest on the trigger 38. The switch 100 is shown in its normal position in FIG. 3 and is operated to its alternative state by actuation of the trigger 38 and elevation of the operator 100A.

The construction of the control circuit 40 (FIG. 3) is well known. More specifically, substantially identical circuitry for selectively energizing the winding 34 is shown and described in detail in U.S. Pat. No. 3,662,190, and a circuitry 102 for selectively energizing the lower winding 32 is shown and described in U.S. Pat. No. 3,434,026. In general, the control circuit 40 is so arranged that when a switch 100 is actuated to its alternate setting from the one shown in FIG. 3 to initiate a cycle of operation of the tool 10, the winding 34 is energized for the first complete positive-going half cycle of the input potential applied to the lines 42. This energization of the upper winding 34 automatically triggers the energization of the lower winding 32 on the next following and oppositely poled half cycle of the alternating current input potential.

In view of the detailed description of the circuit for controlling the winding 34 in the above-identified patent, only a brief summary of this circuit is set forth therein, and reference is made to the above-identified patent for a detailed description.

When an alternating current potential is applied to the lines 42, a trigger capacitor 104 charges up so that the end of the capacitor 104 adjacent the switch 100 is negatively charged. When it is desired to energize the winding 34, the switch 100 is operated into the opposite position from that shown in FIG. 3 by operating the trigger 38. This connects the negative end of the trigger capacitor 104 to the lower line 42. The next time the upper head 42 goes positive with respect to the lower lead 42, a positive pulse is generated at the anode of a silicon controlled rectifier (SCR) 106. This positive pulse causes current to flow through a resistor 108, and this current causes a transistor 110 to conduct. The transistor 110 connects a diode 112 to the positive side of the trigger capacitor 104. A positive current now flows through the diode 112 and into the control gate of an SCR 114. The SCR 114 now conducts and connects the winding 34 directly across the supply lines 42 for the remainder of the positive half cycle.

At the end of the positive half cycle, the SCR 114 turns off and stops the flow of current to the winding 34. The switch 100 still connects the trigger capacitor 104 to the line 42, but now the trigger capacitor 104 is discharged, and it holds the collector of the transistor 110 at roughly the potential of the lower line 42. Thus, no current flows from the trigger capacitor 104 into the control gate of the rectifier 114. Since it would take at least two volts to overcome the junction potentials of the transistor 110, the diode 112, and the SCR 114, a margin of insurance is provided which insures that the SCR does not fire a second time. Ultimately, when the switch 100 is returned to the position shown in FIG. 3, a charging path is re-established for the trigger capacitor 104, and the capacitor 104 is recharged.

When the winding 34 is energized by rendering the SCR 114 conductive, the field of the energized winding 34 retracts the small diameter portion 26B of the armature 26 into the opening 30 with the cable 80 being taken up by extension of the compression spring 92 within the tube 88. The insertion of the armature 26B into the opening 30 is limited by engagement with the depending portion 66B on the top plate 66A. As the armature 26 moves upwardly, the lower end of the driver blade 20 clears the crown 20A of the first staple 20 and permits this staple to be advanced into the drive track 18 beneath the lower end of the driver blade 24. Further, during this upward movement of the armature 26, the plate 72 resting on the shoulder provided by the large diameter portion 26A is elevated against the compressive force of the plurality of springs 76. Thus, these springs are all compressed to store energy subsequently to be imparted to the armature 26 and its connected driver blade 24.

When the control circuit 40 terminates conduction through the SCR 114 and the upper coil or winding 34 is no longer energized, the compression springs 76 acting on the plate 72 drive the armature 26 and the driver blade 24 downwardly so that the driver blade 24 engages the staple 20 in the drive track 18 and starts driving or setting of this fastener. When the plate 72 strikes the cushion 78, further movement of the plate 72 is arrested, and this plate is uncoupled from the armature 26 so that it moves downwardly into the opening 28 with the force of inertia imparted by release of the energy stored in the previously compressed springs 76. During this movement of the armature 26, the cable 80 moves into the opening 30 by compressing the spring 92 within the tube 88.

Referring back to the control circuit 40, when the SCR 114 is placed in conduction, the circuit 102 effects the energization of the lower coil or winding 32 on the next following or negative-going half cycle of the alternating current potential input. More specifically, when the SCR 114 is placed in conduction, a capacitor 116 is charged through a diode 118. At the termination of the period of conduction of the SCR 114, the upper line 42 begins to go negative relative to the lower line 42, and an SCR 120 is properly biased for conduction. The diode 118 is now back biased, and the capacitor 116 discharges through a resistance element 122 to provide gate current for the SCR 120. This places the SCR 120 in conduction so that the coil 32 is connected directly across the input lines 42. At the termination of the negative-going half cycle, conduction through the SCR 120 is terminated.

The armature 26 is disposed closely enough adjacent the lower winding 32 to be within its effective field when the SCR 120 is placed in conduction to energize this winding. This positioning of the armature 26 relative to the winding 32 at the time energizing the winding 32 is controlled or determined by the biasing force applied to the armature 26 by the biasing assembly 36, the position into which the armature 26 was retracted within the upper winding 34, the mass of the armature 26 and its connected blade 24, and the spacing of the windings 32 and 34. These factors are adjusted to insure the desired position of the armature 26 relative to the field of the winding 32 as this winding is energized.

Thus, the field of the energized winding 32 adds additional energy to the moving armature 26 which is imparted to the driver blade 24 for driving the fastener 20 disposed within the drive track 18. When the energization of the winding 32 is terminated, as described above, the compressed tension spring 92 moves the ball guide 90 downwardly within the tube 88 and retracts the flexible cable 80 so that the armature 26 is retracted to the normal position shown in FIG. 1 determined by engagement of the shoulder formed on the large diameter portion 26A with the apertured plate 72. The tool 10 remains in this condition even though the trigger 38 remains depressed because an additional cycle of operation of the control circuit 40 cannot be initiated until such time as the switch 100 is released to recharge the trigger capacitor 104. When the trigger 38 is released, the switch operator 100A returns to its normal position, the switch 100 is restored to its normal position, and the control circuit 40 is prepared for an additional cycle of operation.

The use of the winding or coil 34 to retract the armature 26 against the bias of the assembly 36 provides an additional advantage of reducing the recoil of the tool 10 away from a workpiece. More specifically, this retraction of the armature 26 in a direction away from the workpiece results in a reaction on the tool 10 tending to force the nosepiece structure 16 downwardly toward the workpiece. With the mass of the tool 10 thus moving toward the workpiece, the recoil resulting from the subsequent downward movement of the armature 26 and the blade 24 during the driving of a fastener or staple 20 is damped or reduced. This recoil reduction is of particular advantage in tools wherein the terminal velocity of the moving system, i.e., the armature 26 and the blade 24, is low. As an example, the movable drive components in an electric tacker attain a lower maximum terminal velocity than the comparable piston and driver blade in a pneumatic stapler.

Although the present invention has been described with reference to a single illustrative embodiment thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention.

Claims

What is claimed and desired to be secured by Letters Patent of the United States is:

1. An electric tool for driving fasteners into a workpiece using an electric potential comprising

a housing with a nosepiece structure defining a drive track,

a magazine assembly for feeding successive fasteners into the drive track at a given position therein,

fastener driving means including a driver movable in the drive track and an armature for actuating the driver, said driver normally occupying at least a portion of said given position in the drive track to prevent a fastener from entering the drive track,

resilient operating means coupled to the fastener driving means for imparting movement to the driver by resilient force,

winding means magnetically coupled to said armature for stressing the resilient operating means,

and a control circuit coupled to the winding means and energized by the potential for energizing the winding means for a period of time to stress the resilient operating means and then deenergizing the winding means to release the resilient operating means and to momentarily withdraw the driver from said given position in the drive track so that the magazine assembly can feed a fastener into the drive track beneath the driver.

2. An electric tool for driving fasteners comprising

a housing including a nosepiece defining a drive track,

a pair of spaced winding means having aligned openings therein,

fastener driving means including a driver slidable in the drive track and armature means coupled to the driver and including magnetic means movable in said aligned openings,

resilient means coupled to the fastener driving means and arranged to bias the driver into the drive track,

and a control circuit coupled to the pair of winding means for controlling the sequential energization thereof, said control circuit including first means to energize one of the winding means to move the driver away from the drive track and stress the resilient means and second means to energize the other one of the winding means after said one of the winding means so that the resilient means and said other winding means jointly move the driver toward the drive track.

3. The electric tool set forth in claim 2 including

a magazine assembly for feeding fasteners into the drive track at a given location therein,

and stop means for the fastener driving means normally positioning the driver in the drive track in said given location to prevent a fastener entering the drive track until the driver has been moved by the energization of said one winding means.

4. An electric tool for driving fasteners into a workpiece comprising

a housing including a nosepiece structure defining a drive track, the end of the nosepiece being adapted to be placed adjacent the workpiece,

a pair of spaced first and second winding means in the housing, at least the first winding means including an opening,

fastener driving means including a driver slidable in the drive track and armature means for actuating the driver, the armature means including a magnetic portion movable in the opening of the first winding means,

stop means,

resilient means coupled to the armature means and biasing the armature means and driver toward the nosepiece structure, said resilient means normally engaging the stop means,

coupling means coupling the resilient means to the second winding means and being movable away from the stop means in a direction away from the nosepiece structure to stress the resilient means when the second winding means is energized,

and a control circuit coupled to the first and second winding means for energizing the second winding means followed by the first winding means whereby the resilient means is stressed and released to supply kinetic energy to the fastener driving means followed by acceleration of the armature means as the first winding means is energized.

5. The electric tool set forth in claim 4 in which

the coupling means includes an opening in the second winding means and an extending portion to the armature means movable within the opening in the second winding means.

6. The electric tool set forth in claim 4 in which

the resilient means includes an apertured member separably coupled to the armature means and a plurality of spaced compression springs disposed between the apertured member and the housing.

7. An electric tool for driving fasteners into a workpiece comprising

a housing having a chamber and a nosepiece structure defining a drive track,

vertically spaced first and second windings in the chamber having aligned openings therein,

fastener driving means including a driver movable in the drive track and an armature means with a magnetic portion movable in the openings,

a coupling means movably mounted between the first and second windings and coupled to the armature means for movement with the armature means in a direction toward the first winding and away from the nosepiece structure, said coupling means permitting movement of the armature means free of the coupling means when the armature moves toward the second winding and the nosepiece structure,

resilient means interposed between the coupling means and the housing to be stressed by movement of the coupling means and armature away from the nosepiece structure,

and control means coupled to the first winding for momentarily energizing the first winding to move the armature means toward the first winding to stress the resilient means and for then energizing the second winding to move the armature means toward the nosepiece structure and away from the coupling means.

8. The electric tool set forth in claim 7 in which

the resilient means are coaxially mounted relative to the openings in the first and second windings.

9. The electric tool set forth in claim 7 in which

the coupling means includes a shouldered portion on the armature means and a movable plate resting on the shouldered portion,

and the resilient means includes a plurality of spaced compression springs interposed between the housing and the plate.

10. An electric tool for driving fasteners into a workpiece using a potential with successive undulations comprising

a housing with a nosepiece structure defining a drive track,

fastener driving means including a driver movable in the drive track and an armature for actuating the driver,

resilient operating means coupled to the fastener driving means for imparting movement to the driver by resilient force and including a first winding means for stressing the resilient operating means,

a second winding for imparting motion to the driver and including an opening in which the armature is movable,

and a control circuit coupled to the first and second winding means and energized by the potential for energizing the first winding on a given undulation in the potential and for energizing the second winding on a following undulation.

11. An electric tool for driving fasteners into a workpiece using an electric potential comprising

a housing with a nosepiece structure defining a drive track,

a magazine assembly for feeding successive fasteners into the drive track at a given position therein,

fastener driving means including a driver movable in the drive track and an armature for actuating the driver,

resilient operating means coupled to the fastener driving means for imparting movement to the driver by resilient force.

a winding means for stressing the resilient operating means by moving at least the armature in a direction away from the nosepiece structure and against the bias of the resilient operating means,

and a control circuit coupled to the winding means and energized by the potential for energizing the winding means for a brief period of time to accelerate the armature in a direction away from the nosepiece structure and produce a reaction force acting on the tool and tending to force the nosepiece structure against the workpiece, the control circuit thereafter terminating the energization of the winding means to release the resilient operating means for actuating the fastener driving means to drive a fastener.