Protection circuit for electrical discharge machining power supply apparatus

Claim 2

Apparatus for machining a conductive worKpiece by electrical discharges across a dielectric coolant filled gap between a tool electrode and a workpiece including a source of machining power, an electronic output switch having a control electrode and a pair of power electrodes, said power electrodes operably connected between said power source and said gap for providing machining pulses thereto, a drive signal means connected to said control electrode of said switch for rendering it alternately conductive and non-conductive, and a cut-off means operatively connected to said source, wherein the improvement comprises: a detecting network connected to the output of said drive signal means; a voltage divider coupled to said network; a field effect transistor having its principal electrodes connected in series with a positive voltage source and a reference voltage source; a signal diode connected between said divider and the gate electrode of said field effect transistor; and an electronic switching means having its control electrode connected to a principal electrode of said field effect transistor and a principal electrode connected to said cut-off means for actuating it and providing interruption of said power source responsive to a predetermined magnitude voltage change from said drive signal means representative of failure of said output switch.

Claim 3

The combination as set forth in claim 1 wherein said apparatus includes a multiple machining gap set-up, each of said gaps having connected to it a different electronic output switch and a different drive signal source, and wherein said detecting network comprises a separate network operably connected to each of said drive signal sources, and wherein a plurality of field effect transistors having their principal electrodes connected in parallel are coupled between said positive voltage source and said reference voltage source for actuating said cut-off means responsive to the operation of any one of said field effect transistors.

Claim 4

The combination as set forth in claim 1 wherein said cut-off means comprises a relay and wherein said source of machining power includes a set of normally closed contacts in series therewith, said relay operable to open said contacts and interrupt said machining power source responsive to said drive signal voltage change.

Claim 5

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric filled gap including a multiple gap set-up wherein there is provided a source of machining power, an electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive signal means operatively connected to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive signal means, wherein the improvement comprises: a plurality of field effect transistors, each having their principal electrodes connected in parallel one to the other; a source of reference potential connected to one of said principal electrode terminals; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; and an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode of both said field effect transistors for receiving a cut-off signal therefrom representative of output switch failure and thereby actuating said cut-off means to interrupt said machining power source.

Claim 6

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric filled gap including a multiple gap set-up wherein there is provided a source of machining power, an electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive signal means operatively connected to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive signal means, wherein the improvement comprises: a plurality of field effect transistors, each having their principal electrodes connected in parallel one to the other; a source of reference potential connected to one of said principal electrode terminals; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; and an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode of both said field effect transistors for receiving a cut-off signal therefrom representative of output switch failure and thereby actuating said cut-off means to interrupt said machining power source.

Claim 7

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric coolant filled gap in a plural gap machining set-up wherein there is provided a source of machining power, a separate electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive means operatively connecteD to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive means, wherein the improvement comprises: a plurality of field effect transistors corresponding to the number of gaps, said field effect transistors having their principal electrodes connected in parallel one to the other; a reference voltage source connected to a common principal electrode terminal of said transistors; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; and an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode terminal of said field effect transistors for receiving a cut-off signal therefrom and thereby actuating said cut-off means responsive to output switch failure.

Claim 8

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric coolant filled gap in a plural gap machining set-up wherein there is provided a source of machining power, a separate electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive means operatively connecteD to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive means, wherein the improvement comprises: a plurality of field effect transistors corresponding to the number of gaps, said field effect transistors having their principal electrodes connected in parallel one to the other; a reference voltage source connected to a common principal electrode terminal of said transistors; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; and an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode terminal of said field effect transistors for receiving a cut-off signal therefrom and thereby actuating said cut-off means responsive to output switch failure.

Claim 9

The combination as set forth in claim 5 wherein a capacitor is connected to the control electrode, said cut-off switch for storing a voltage and rendering it operable responsive to voltage level during normal output switch on-time.

Claim 10

The combination as set forth in claim 5 wherein said cut-off means comprises a relay having its contacts connected in series with said source of machining power for interrupting it responsive to failure of any one of said electronic output switches.

Claim 11

The combination as set forth in claim 5 wherein said gate control circuit comprises a coupling capacitor, a voltage divider and a signal diode, said diode connected in series with the gate electrode of one of said field effect transistors.

Claim 12

The combination as set forth in claim 5 wherein said drive signal means includes a drive transistor stage including a PNP transistor having its emitter coupled to the control electrode of said electronic output switch and wherein said detecting means is further connected to said drive transistor emitter.

Claim 13

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric coolant filled gap in a plural gap machining set-up wherein there is provided a source of machining power, a separate electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive means operatively connected to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive means, comprising: a plurality of field effect transistors corresponding to the number of gaps, said field effect transistors having their principal electrodes connected in parallel one to the other; a reference voltage source connected to a common principal electrode terminal of said transistors; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode terminal of said field effect transistors for receiving a cut-off signal therefrom and thereby actuating said cut-off means responsive to output switch failure; said drive means including a drive transistor stage having a PNP transistor having its emitter coupled to the control electrode of said electronic output switch; said detecting means further connected to said drive transistor emitter; a pulse generator comprising an astable multivibrator having its output connected to said drive transistors for operating them; and a separate cut-off means responsive to gap short circuit operatively connected to said multivibrator for reducing its on-time responsive to said condition, said last mentioned cut-off means further connected to the control electrodes of said field effect transistors for holding them inoperable during saId condition.

Claim 14

Apparatus for machining a conductive workpiece by means of electrical discharges across a dielectric coolant filled gap in a plural gap machining set-up wherein there is provided a source of machining power, a separate electronic output switch having a control electrode and a pair of power electrodes associated with each of said gaps and said source, a drive means operatively connected to the control electrode of each of said output switches for turning them on and off in unison, a cut-off means operatively connected to said machining power source and a detecting means operatively connected to said drive means, comprising: a plurality of field effect transistors corresponding to the number of gaps, said field effect transistors having their principal electrodes connected in parallel one to the other; a reference voltage source connected to a common principal electrode terminal of said transistors; a separate gate control circuit coupled between the gate of each of said field effect transistors and said detecting means; an electronic cut-off switch, said switch having its control electrode diode coupled to a like principal electrode terminal of said field effect transistors for receiving a cut-off signal therefrom and thereby actuating said cut-off means responsive to output switch failure; said drive means including a drive transistor stage having a PNP transistor having its emitter coupled to the control electrode of said electronic output switch; said detecting means further connected to said drive transistor emitter; a pulse generator comprising an astable multivibrator having its output connected to said drive transistors for operating them; and a separate cut-off means responsive to gap short circuit operatively connected to said multivibrator for reducing its on-time responsive to said condition, said last mentioned cut-off means further connected to the control electrodes of said field effect transistors for holding them inoperable during saId condition.