GB2176734A - Electromagnetically driven stapler with a rebound absorbing device - Google Patents

Abstract

A stapler includes multiple coils 41, 42, sequentially energised to progressively accelerate a firing base 10 to drive an impact rod 12 to drive fasteners. A hollowed compartment 102 of the bar of the firing base 10 is partly filled with metallic particles 101 to absorb recoil momentum of the firing base. A control circuit for sequentially driving a stapler having two coils 41/42 energised via two TRIACS includes a first TRIAC being activated by a trigger pulse synchronised with an AC supply by means of an SCR and a second TRIAC being activated by the back emf generated on switching off the first coil. The stapler is useful as a hand held power tool with minimum recoil. <IMAGE>

Description

SPECIFICATION Electromagnetically driven stapler with a rebound absorbing device This invention relates to an improved stapler for heavy-duty use with a more powerfully driven impact rod and an absorbing device which can absorb most of the impact force of the rebounded impact rod.

According to the present invention a stapler includes a reciprocatable firing base comprising an impact rod for driving staples, the rod being reciprocatable within and in coaxial relationship with a plurality of electromagnetic coils which are spaced axially along the travel of the rod and are sequentially energised in use by a firing circuit to provide progressive acceleration of the firing base.

Preferably the firing base includes an axially elongate compartment partially filled with particles for absorbing the recoil momentum of the firing base and advantageously the particles are metallic.

In a preferred embodiment the stapler has two coils and the control circuit includes a first and second TRIAC, being arranged for energising first and second coils respectively, the circuit being powered by an AC supply from which, when triggered, the first TRIAC passes current through the first coil during at least part of a single half cycle and the second TRIAC passes current through the second coil during the following half cycle.

Preferably the first TRIAC is turned on by a trigger pulse which is shaped by means of an SCR such that the shaped pulse turns off the first TRIAC at the end of the half cycle of the AC supply ie. when the voltage changes from positive to negative.

Conveniently the second TRIAC is turned on by means of the back emf generated in the first coil when the shaped trigger pulse turns off the first TRIAC.

A particular embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings of which: Figure 1 is a perspective and sectional view of the assembled stapler, Figure 2 is a diagram of the electric circuit of the stapler of Figure 1, Figure 3 is a sectional view of the chamber of the stapler of Figure 1, and Figure 4 is a sectional view of part of the chamber of Figure 3 showing two coil compartments.

Referring to Figure 1 and Figure 4, the stapler has a chamber 20 in which there is a firing base 10 comprising a round hollowed bar with a circular flange 11 at one end and at its other end a slender flat impact rod 12 with a head 22 for driving staples. An elongate compartment 102 of the hollowed bar 10 is partly filled with small heavy metal particles 101.

At the front of the chamber 20 there are two annular compartments housing coils 41 and 42 and at the rear of the chamber a return spring 13 is located between the circular flange 11 and the wall of the rear coil housing compartment to give a retracting force for the firing base.

The two electromagnetic coils 41 and 42 are placed in the two adjoining annular compartments around a tubular channel such that the firing base 10 and the impact rod 12 can be accelerated by the two-stage coils 41, 42 consecutively so as to move along the channel to strike the preset staples into the target object (not shown).

The stapler has a handle 30 containing a circuit board 40 with electrical connections to a plug seat 33 and to the coils 41, 42 the circuit being such as to energise coils 41, 42 in response to depression of a trigger 31 to establish magnetic forces accelerating the firing base 10 and the impact rod 12.

On firing, the firing base 10 moves from right to left as shown in Figures 1 and 3 and the particles 101 are accelerated by this movement. On impact with a target, the rod 12 and base 10 rebound from left to right and particles 101 impact internally against the front end of the firing base 10 which has the effect of arresting the recoil movement. The spring 13 then retains the firing base in the retracted position until firing is repeated.

Referring to Figure 2, the electric circuit consists primarily of a SCR (Silicon Controlled Rectifier), TRIACs 1, 2 connecting in parallel or series with load resistors (R), capacitors (C), diodes (D) and, Zener diodes (D2). After one of the alternative power supplies of 110V, 60HZ or 220V, 60HZ is connected to the plug seat 33, with the trigger 31 contacting point "a", the voltage of the power supply is dropped through load resistors R1?r R2.

The rectified electric current through Diode D1 begins to charge Capacitor C1, and the charging process will cease after a pre-set period of time; on the other hand, an approximately rectangular signal wave is transmitted between the Resistor R3 and Zener Diode D2, and this signal through the RC network, comprising Resistor R4 and Capacitor C2, creating a pulse signal across Resistor R4 which turns the SCR on and off at the frequency of the AC supply eg. 60HZ. On pressing down the trigger to connect another circuit at point "b", the capacitor C1 discharges forming a trigger pulse which is shaped by the SCR to become synchronised with the AC supply thereby producing a shaped trigger pulse across R5 which makes TRIAC 1 function allowing only positive half wave current passing TRIAC 1.This current gives effect to a magnetic field in coil 41 which is responsible for the first-stage acceleration of the firing base 10 including the impact rod 12.

The trigger being released returns to its original position in contact with point "a" by means of a spring and capacitor C1 is recharged. On the point of the shift of the alternate electric voltage at R5 from positive to negative, the TRIAC 1 immediately ceases funtioning and a back emf is induced on coil 41 at the same time which establishes a forward bias voltage for the actuation of TRIAC 2. The actuated TRIAC 2 drives coil 42 to provide the second stage magnetic force for the next stage of accelerating the firing base and impact rod to magnify the momentum of the firing base for a more powerful and effective strike on the target (the striking position being as indicated in Figure 4 marked by the dotted line).

The Diode D4 and Resistor R6 are responsible for dissipating all the electric charges in the circuit consisting of D4, R6 and TRIAC 1 immediately on the starting of TRIAC 1 to completely discharge the capacitor C1, and in this way the SCR can be blocked to take electric charges from next positive half pulse of alternate voltage so as to prevent the TRIAC 1 from being actuated by not offering adequate electric potential across R5. This step can stop a magnetic in coil 41, owing the the alternate voltage, not to slow down the accelerated firing base at second stage. The magnetic force in coil 41 could slow down the firing base by dragging the rear half of the base with its mass center passing through the geometric center of the coil 41, so that it is necessary to stop the establising of the magnetic field at this time.The magnetic field can also be stopped on the alternate voltage shifting from negative to positive pulse leading to TRIAC 2 being turned off. According to the theory used above, the stapler can gain more powerful momentum by adopting more coils.

Referring to Figure 3, the firing base 10 accelerated by coils 41, 42 moves forward to hit an object and in the meantime compresses a return spring 13 by means of its rear flange 21. The compressed spring 13 tends to retract the firing base to its original position after impact. Before the impact rod hits the target, the metal particles 101 confined in the interior compartment of the firing base move along with the base, but a proportion of the particles lag behind the base, so a rebounded base will move against those particles 101 still moving forward and in this manner a considerable momentum will be taken away to prevent a bouncing-back movement of the firing base.

All the above said motions take place within a time interval of the order of 1/360 second.

The rebounded base can be so decelerated by the heavy-weight metal particles that it will not repeatedly bounce back and forth which causes imperfect striking on objects. So the present invention is particularly characterized by its methods of increasing momentum of the firing base and the momentum-absorbing device which makes the stapler more effective than conventional ones.

Claims (10)

1. A stapler having a reciprocatable firing base comprising an impact rod for driving staples, the rod being reciprocatable within and in coaxial relationship with a plurality of electromagnetic coils which are spaced axially along the travel of the rod and are sequentially energised in use by a firing circuit to provide progressive acceleration of the firing base.

2. A stapler as claimed in Claim 1 wherein the firing base includes an axially elongate compartment partially filled with particles for absorbing the recoil momentum of the firing base.

3. A stapler as claimed in Claim 2 wherein the particles are metallic.

4. A stapler as claimed in any of Claims 1 to 3 having two coils.

5. A stapler as claimed in Claim 4 wherein the control circuit includes a first and second TRIAC, being arranged for energising first and second coils respectively, the circuit being powered by an AC supply from which, when triggered, the first TRIAC passes current through the first coil during at least part of a single half cycle and the second TRIAC passes current through the second coil during the following half cycle.

6. A stapler as claimed in Claim 5 wherein the first TRIAC is turned on by a trigger pulse which is shaped by means of an SCR such that the pulse turns off the first TRIAC at the end of the halfcycle of the AC supply.

7. A stapler as claimed in Claim 6 wherein the second TRIAC is turned on by means of the back emf generated in the first coil when the shaped trigger pulse turns off the first TRIAC.

8. An improved stapler with powerful magnetic coils to increase the momentum of firing base for better hitting capability and with a device to absorb rebounded momentum of firing base consists of two or more electromagnetic coils which are lined up consecutively externally aound firing base. Those coils are connected to circuit board at one end and controlled by the loop on the board to produce magnetic field on current circling in coil, in such way firing base can be accelerated continuously to obtain a maximum hitting momentum at the end.

A firing base located inside the stapler, consists of a hollow round bar with one end flanged and a flat impact rod connecting as a whole to the front of the base. Those heavyweight metal particles of definite amount, confined in the interior of the round bar, are moved forward because of the physical character of inertial but just lag a little in time behind the firing base, so the rebounded firing base will reversely move against those particle moving forward, and the collisions will absorb most of the residual momentum and naturally slow down the base to avoid a back-and-forth collision.

9. A stapler as claimed in Claim 8 with a control loop on the circuit board which consists primarily of one SCR (Silicon Controlled Rectifier) and two TRIACS electrically in series or parallel with Resistors, Diodes, Zener Diodes. The two triacs are actuated by SCR, when the trigger is pressed and released, to allow current instantly passing for the purpose of creating magnetic field on coils to accelerate firing base.

10. A stapler as hereinbefore described with reference to and as shown in the accompanying drawings.