Electrically operated reciprocating tool

March 18, 1969 r. _H. doyle 3,434,026

ELECTRICALLY OPERATED RECIPROCATING-TOOL

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United States Patent Office

3,434,026

Patented Mar. 18, 1969

3,434,026

ELECTRICALLY OPERATED RECIPROCATING TOOL

Richard H. Doyle, Mount Prospect, Ill., assignor to Fastener Corporation, Franklin Park, Ill., a corporation of Illinois

Filed Dec. 12, 1966, Ser. No. 600,982

U.S. CI. 318—125 12 Claims

Int. CI. H02k 33/12

The present invention relates to a tool, and more particularly to an improved electrically operated portable tool of the type having a single power stroke.

Portable tools are widely used for many material working operations and it is important that such tools be compact and light enough for easy and convenient manipulation, while being powerful enough to perform the desired operation. It is desirable that such a tool be convenient to use in a variety of locations, and for this reason an electrically operated tool may be preferred. In many applications, a tool with a single power stroke is preferred because of its effectiveness and speed.

One tool which satisfies these diverse requirements is the tool disclosed and claimed in U.S. Patent No. 3,179,866 of Richard H. Doyle, LeRoy N. Hermann and Joseph S. Naber. The tool disclosed in that patent includes a work engaging element having a magnetic portion disposed adjacent an operating winding. A control circuit is disposed in the tool housing and is effective to energize the operating winding during the first complete half cycle of the alternating current potential following actuation of a control circuit by a switch. Energization of the operating winding results in movement of the magnetic portion and work engaging element through a power stroke.

Although the tool shown in the above mentioned patent 35 is highly satisfactory for many material working operations, it would be desirable to provide an even more powerful single stroke tool, without increasing the size and weight of the tool to the point where its portability is impaired. One possibility would be to improve the 40 efficiency of the tool by using an increased amount of magnetic material associated with the work engaging element, but this would increase the weight and size of the tool. Another problem is that the electrical energy available to the tool is limited by the maximum current 45 of 90 amps, or so available in the 110-120 volt lines normally used commercially. The use of energy storage devices, such as capacitors, for providing more power is not feasible because the size of the conductors connected to the tool becomes too large for convenient portability. 50

In many fastener driving operations, a fastener is first sheared from a strip of fasteners, and then is driven, both the shearing and the driving being accomplished by a moving armature accelerated by the operating winding. The force required to shear the staple may be large. 55 For example, approximately 50 pounds of force is required to shear a one and one-half inch, 16 gauge staple. Accordingly, it would be desirable to provide a compact portable tool in which ample momentum is imparted to the armature by acceleration of the armature before shear- θθ ing the staple, without substantially increasing the overall armature stroke and tool size.

Accordingly, it is an object of the present invention to provide an improved electrically operated portable tool.

Another object is to provide an improved portable tool 35 of the single stroke type which is compact in size but which is capable of delivering a large amount of power.

A further object is to provide a tool including an improved winding arrangement and an improved control circuit for increasing the power delivered in the power γθ stroke of the tool.

Another object is to provide an improved electrically operated tool provided with a novel armature assembly for achieving an increased armature displacement or stroke without a substantial increase in the size of the tool, and without the necessity for increasing the displacement or stroke of the work engaging element.

A further object is to provide an improved armature assembly in which the initial inertia to be overcome by the magnetic field produced by the winding is reduced.

Another object is to provide a tool in which the armature attains a sufficient velocity easily to shear a fastener, without increasing the size of the tool.

In accordance with these and many other objects and advantages of the invention, one embodiment of the invention comprises a fastener driving tool including a housing within which is arranged a winding structure and an armature assembly mounted for movement adjacent the winding structure. In order to increase the power or energy imparted to the armature assembly during a single stroke, the winding structure includes a pair of windings disposed along the path of movement of the armature assembly and the control circuit includes means for energizing the windings on succeeding half cycles of the alternating current source in a sequence corresponding to the direction of movement of the armature assembly. Thus the armature assembly is accelerated throughout a full cycle of the alternating current potential source, first by one winding and immediately thereafter by another winding, and powerful single stroke is achieved.

In accordance with a feature of the invention, the control circuit includes means for energizing the first winding during a first half cycle of the alternating current source, and means responsive to energization of the first winding for energizing the second winding during the immediately following half cycle. The control circuit includes a first controlled conduction device in series between the first winding and the potential source, and means for applying a control signal to the first controlled conduction device to energize the first winding during one half cycle. A second controlled conduction device is in series with the second winding and the source. A trigger circuit is provided for applying a control signal to the second controlled conduction device in response to energization of the first winding for energizing the second winding during the following half cycle.

The use of more than one winding to achieve a longer period of acceleration of the armature gives rise to a necessity for increased armature displacement, since a longer stroke must be used to take advantage of the full period of time during which the windings are energized. In accordance with a feature of the invention, there is provided a novel armature assembly capable of providing a long armature stroke while keeping the tool compact in size, and without the necessity for a long driver blade stroke. Thus the armature assembly includes a work engaging member, including a driver blade, and a magnetic member movable from a rest position to an operating position to drive the work engaging member through a single power stroke. The magnetic member and the work engaging member are coupled together for limited movement with respect to each other, so that upon energization of the winding the magnetic member moves a distance from the rest position before engaging and driving the work engaging member. This construction also assures that the work engaging member has sufficient momentum to shear the fastener from a strip, and does not require a large housing for movement of the artnature.

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

FIG. 1 is a partial sectional view through the head por

3,434,026 tion of a fastener driving tool embodying the present invention;

FIG. 2 is a view similar to FIG. 1 illustrating the fastener driving tool at the end of a power stroke; and

FIG. 3 is a circuit diagram of the control circuit of the tool.

Referring now to the drawing, there are illustrated some portions of an electrically operated fastener driving tool designated by the reference numeral 10. The fastener driving tool 10, preferably of the portable type, includes a housing 12 having a handle portion (not shown) and a vertically extending head portion 14 illustrated in section in FIGS. 1 and 2 of the drawing. Adjacent the lower end of the head portion 14 is disposed an electrical winding structure designated as a whole by the reference numeral 16. An armature assembly 18 is mounted for vertical reciprocating movement adjacent the winding structure 16, and includes a work engaging portion 20 and a magnetic portion 22 coupled to the work engaging portion 20. The tool 10 includes a control circuit generally designated as 24 and illustrated in FIG. 3 of the drawing. Preferably, the control circuit 24 may be contained in the handle of the tool 10. The control circuit 24 serves to energize the winding structure 16 in order to drive the armature assembly 18 downwardly through a single power stroke against a fastener 26 (FIG. 1).

In accordance with a feature of the invention, the electrically operated tool 10 delivers a large amount of power with each single stroke of the armature assembly 18. The winding structure 16 includes a pair of windings 28 and 30, and the control circuit 24 serves to energize the windings in sequence during consecutive half cycles of the alternating current supply voltage. As a result, the armature assembly 18 is accelerated throughout a full cycle of the alternating current potential source, and, as a result, approximately twice as much energy is imparted to the armature assembly as would be the case with a half cycle energization period.

Since the armature assembly is accelerated throughout an entire cycle of the alternating current potential source, the distance through which the armature moves, or the armature stroke, is greater than would be required in a half cycle arrangement. In order to keep the tool 10 compact in size for portable use, and to permit a short driver blade stroke, the work engaging portion 20 and the magnetic portion 22 of the armature assembly 18 are coupled for limited movement relative to each other. As a result, the magnetic portion 22 moves through part of its longer stroke before engaging and driving the work engaging portion through a shorter stroke.

Referring now more specifically to the construction of the tool 10, the two windings 28 and 30 are supported near the lower end of the head portion 14 of the tool on a two-section bobbin 32. The bobbin 32 includes an axially extending opening 34 in which the armature assembly slidingly reciprocates. The windings 28 and 30 are thus disposed along the path of movement of the armature assembly, with the winding 28 being disposed closer to the top of the head portion 14 than the winding 30.

Having reference now to FIG. 3 of the drawings, the control circuit 24 of the tool 10 is illustrated. The control circuit 24 is preferably formed on a suitable support and then encapsulated or “potted” in any of the well known compositions therefor. The circuit 24 may be mounted within the housing 12 of the tool 10, and preferably within the handle which can extend laterally from the illustrated head portion 14 in the manner illustrated in the above mentioned U.S. Patent No. 3,179,866.

The circuit 24 includes a pair of input terminals 36 and 38 adopted for connection to an alternating current potential source as by a flexible conductor, and also includes terminals connected to the windings 28 and 30. The circuit is operated by a trigger actuated or workpiece engaging switch so that when the switch is operated, the armature assembly is accelerated through a single power stroke. More specifically, after operation of the switch, the winding 28 is energized during the first half cycle of the desired polarity occurring after operation of the switch. The winding 30 is operated during the immediately following half cycle by a trigger circuit 40 responsive to energization of the coil 28.

The control circuit 24 includes an operating circuit generally designated as 42 for energizing the winding 28 during the properly polarized half cycle following operation of the control switch, which switch includes a set of normally closed switch contacts 44α and a set of normally open switch contacts 446. The opening circuit 42 may be of any suitable type, and may comprise a circuit similar in some respects to the control circuit shown in the pending application of Richard H. Doyle, LeRoy N. Hermann and Joseph S. Naber, Ser. No. 257,677, filed Feb. 11, 1963, which application is assigned to the same assignee as the present invention.

The operating circuit 42 includes a gated unidirectional controlled conduction device 46, such as a silicon controlled rectifier, having an anode connected to one terminal of the winding 28 and a cathode connected to the supply terminal 36. When a positive potential is supplied to the anode of the gated rectifier 46 and a trigger signal is applied to the control or gate electrode thereof, the winding 28 is directly connected across the supply terminals 36 and 38 to develop a magnetic field for actuating the aramture assembly 18.

The gate electrode of the gated rectifier 46 is provided with an operating control signal under the control of a second controlled conduction device 48, such as a silicon controlled switch. The cathode of the switch 48 is connected to the supply terminal 36 through a resistance element 50 and is coupled to the control electrode of the gated rectifier 46 through a blocking diode 52. The anode of the switch 48 is connected to the pair of normally open contacts 446 of the operating switch. The operating switch is actuated to close the normally open contacts 446 and to open the normally closed contacts 44α when it is desired to operate the tool 10.

The normally closed contacts 44α connect an energy storing means or storage capacitor 54 to a charging circuit including a capacitor 56 that is shunted by a resistance element 58. Positive-going half cycles of the alternating current potential from the supply terminals 36 and 38 are continuously supplied through a diode 60 to charge the capacitors 54 and 56. When the tool 10 is to be operated, the contacts 44α are opened and the contacts 446 are closed whereupon the storage capacitor 54 is disconnected from its charging circuit and is connected to the anode of the controlled switch 48 so as to provide an operating potential therefor. The energy stored in the capacitor 5 4is such as to maintain the controlled switch 48 in a conductive condition for a period of time no longer than a full cycle of the alternating current potential source.

In order to synchronize the periods of conduction of the controlled conduction devices 46 and 48 with the potential supplied by the source 14 so as to insure that the potential applied across the rectifier 46 is of a proper polarity, and to insure that the rectifier 46 is fired at the beginning of the half cycle, the control electrode of the silicon controlled switch 48 is connected to a differentiating network including a capacitor 62 and a pair of resistance elements 64 and 66. The positive-going alternations in the alternating current potential source provide positive-going pulses or spikes at the gate electrode of the silicon controlled switch 48.

These positive-going pulses are continuously applied to the switch 48 so long as the circuit 24 is connected to an alternating current potential source. However, the device 48 is normally not placed in a conductive condition due to the absence of an operating potential across the anode and cathode of the device. However, during the

3,434,026 first properly poled half cycle following the time at which the contacts 44Z> are closed, the positive-going pulse supplied to the control electrode of the switch 48 places this device in a conductive state so that the storage capacitor 54 is discharged through the resistance element 50. This provides a positive-going pulse that is forwarded through ⁵the diode 52 to the gate electrode of the silicon controlled rectifier 46. Since the trigger pulse for the device 48 occurs only during positive-going alternations in the potential supplied through the supply terminals, the anode . θ of the device 46 is also at a positive potential with respect to its cathode, and the trigger pulse supplied through the diode 52 places the silicon controlled rectifier 46 in a conductive condition to connect the winding 28 directly across the potential source 14 during the entire half cycle j_gof the proper polarity.

In order to insure stable operation of the rectifier 46 and switch 48, the resistance element 64 is coupled between the gate electrodes of the devices 46 and 48. This resistance element provides a feedback signal from the ₂θ device 46 to the device 48 in order to hold the device 48 in its conductive condition, thereby insuring that the enabling signal to the device 46 is maintained and that the capacitor 54 is fully discharged to prevent multiple firing of the tool 10. 25

B+ regulation is provided by means of a Zener diode 68 connected between the supply terminal 36 and the anode of the diode 60. In addition, a capacitor 70 and resistance element 72 are provided for shifting the phase of the alternating current potential applied to the diode 60 ₃θ as compared to the phase of the potential supplied by the source.

In order to energize the winding 30 on the half cycle of the alternating current potential source immediately following the energization of the winding 28, the trigger _3gcircuit 40 includes a diode 74 and a capacitor 76 connected in shunt with the winding 28. During the period of time in which the winding 28 is energized, the capacitor 76 becomes charged and a positive gate signal is applied through a resistance element 78 to a second gated 40 unidirectional conduction device 80, such as a silicon controlled rectifier. The resistance 78 serves to limit the current flowing to the gate electrode and to prolong the gating signal. During the half cycle of the alternating current potential source immediately following energiza- _4gtion of the winding 28, the controlled conduction device 80 is placed in a conductive condition by the gate signal applied by the triggering circuit 40. Accordingly, for the duration of this half cycle the winding 30 is effectively connected across the input terminals 36 and 38. ₅θ

Since the energy stored in the storage capacitor 54 is sufficient to maintain the controlled conduction device 48 in a conductive condition for no longer than one full cycle of the potential supplied to the circuit, and since the silicon controlled rectifier 46 is placed in a _ggnon-conductive condition as soon as the potential on its anode swings negative relative to its cathode, the windings 28 and 30 are energized only once in response to each actuation of the switch 24. When the switch is returned to its normal position, the contacts 44b open θθ and the contacts 44a close. Thus the storage capacitor is disconnected from the anode of the silicon controlled switch 48 and is reconnected to its charging circuit. A high value resistance 82 is connected across the contacts of the switch 44 in order to keep the anode of the _6gsilicon controlled switch 48 from floating when the switch is in its illustrated normal condition.

From the above it can be seen that each time the tool 10 is operated, the windings 28 and 30 are sequentially energized during successive half cycles of the alternating γθ current potential source and as a result a substantial amount of energy is imparted to the armature assembly 18 as it moves downwardly to drive a fastener 26. In order to take advantage of this longer period of energization, it is necessary that the armature displacement, or 75 stroke, be made longer than the armature stroke in a half cycle tool such as that disclosed in the above identified U.S. Patent No. 3,179,866. However, in order to maintain the head portion 14 of the tool 10 of a compact size suitable for use in a portable tool, and in order to avoid the necessity of a long stroke for the work engaging member 20, the work engaging member 20 and the magnetic member 22 of the armature assembly 18 are coupled for relative movement with respect to one another. As a result, the stroke of the work engaging member 20 is shorter than the stroke of the magnetic member 22, and it is not necessary to provide structure for guiding the work engaging portion through a long stroke. In addition, the height of the head portion 14 is less than would be required if the magnetic portion 22 and work engaging portion 20 were fixed to one another. A further advantage is that when the winding structure is energized, the magnetic member 22 is accelerated independently of the work engaging member, and the initial inertia is reduced.

More specifically, referring now to FIGS. 1 and 2, the magnetic member 22 is formed entirely of magnetic material and includes an upper, generally cup-shaped portion 84 threaded onto a lower portion 86. The upper portion 84 includes an axial recess 88, and the lower portion includes a smaller axial recess 90. A spring 92 is held in compression between the bobbin 32 and a flange 84α on the upper portion 84 for urging the entire armature assembly 18 toward its rest position, illustrated in FIG. 1.

In order to allow limited movement between the magnetic portion 22 and the work engaging portion 20, the work engaging portion includes a shank member 94 slidably received in the axial recess 90. The member 94 includes an enlarged head 94a held captive in the larger recess 88 of the upper portion 84 of the magnetic member 22, and a lost motion connection is produced between the two parts of the armature assembly 18. The relative movement between these parts is limited by the travel of the head 94α within the recess 88.

The work engaging portion also includes a fastener driving blade 96 attached by a pin 98 to the shank member 94. Suitable cushion members 100, 102 and 104 are provided for cushioning impacts between the housing, the magnetic member 22 and the work engaging member 20. A pin 106 extends downwardly from the top of the housing 12 for holding the work engaging portion 20 in its rest position.

When the coils 28 and 30 are energized, as described above, to drive the armature assembly 18 through a power stroke, the magnetic member 22 is accelerated through an initial part of its stroke without being hindered by the work engaging member 20. The inertia to be overcome is less than if these two members were fixed together. The work engaging member 20 may be made of magnetic material, and if so, it also begins to move downwardly and may engage the fastener 26. After the magnetic member 22 has moved through part of its stroke, it reaches or overtakes the work engaging member 20, and forces it through a short fastener driving stroke, during which the fastener is first sheared, then driven. In FIG. 2 the armature assembly 18 is shown at the end of the power stroke.

After completion of the power stroke, the spring 92 returns the armature assembly 18 to its rest position. Advantageously, the magnetic portion 22 is lifted independently of the work engaging portion at the beginning of the return stroke. Accordingly, the magnetic portion attains ample velocity before the driver blade 96 is lifted. In addition, rebound of the magnetic portion 22 from the top of the housing Id is not transferred to the driver blade 96. Such rebound, if permitted, could partially drive the next fastener, and could result in a jam of two fasteners during the next power stroke.

Although the present invention has been described with reference to a single illustrative embodiment thereof, it should be understood that numerous other modifications

3,434,026 and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of this invention.