Electrical discharge machining power supply circuit with phase control for gap short circuit protection

Claim 2

In an electrical discharge machining power supply circuit including a power supply and a periodically operated electronic switch coupled between said power supply and the machining gap, said power supply including a plural phase AC power source, a gap short circuit protective system wherein the improvement comprises a like plurality of electronic triggering devices with their principal electrodes coupled between said source and said gap, a control circuit coupled across a like principal electrode and the control electrode of all of said devices for firing them in controllable succession, a sensing network coupled to said gap for providing an output signal responsive to gap short circuit, and means coupled between said network and said control circuit for interrupting the firing of said devices responsive to said signal.

Claim 3

The combination as set forth in claim 1 wherein said control circuit includes a firing voltage source for said devices and wherein said last mentioned means comprises an electronic switch having its control electrode coupled to said sensing network and its principal electrodes connected across said firing voltage source for shunting it for the duration of said signal.

Claim 4

The combination as set forth in claim 1 wherein said sensing network comprises a resistor and a capacitor coupled across said gap for providing an output signal representative of average gap voltage.

Claim 5

The combination as set forth in claim 2 wherein said electronic triggering devices comprise semiconductor controlled rectifiers and said electronic switch comprises a transistor having its base operatively connected to said sensing network and its emitter and collector operatively coupled across said firing voltage source.

Claim 6

In an electrical discharge machining power supply circuit including a power supply and a periodically operated electronic switch coupled between said power supply and the machining gap, said power supply including at least one phase of alternating current potential, a gap short circuit protective system wherein the improvement comprises an electronic triggering device having a control electrode and having its principal electrodes connected between said phase of alternating current potential and said gap, a control circuit including a firing voltage source cOnnected across said control electrode and one of said principal electrodes for rendering it conductive for controllable time durations, a sensing network connected to said gap for providing an output signal responsive to gap short circuit condition, and control means connected between said network and said control circuit for interrupting the firing of said device responsive to said signal.

Claim 7

In an electrical discharge machining power supply circuit including a power supply and a periodically operated electronic switch coupled between said power supply and the machining gap, said power supply including at least one phase of alternating current potential, a gap short circuit protective system wherein the improvement comprises an electronic triggering device having a control electrode and having its principal electrodes connected between said phase of alternating current potential and said gap, a control circuit including a firing voltage source cOnnected across said control electrode and one of said principal electrodes for rendering it conductive for controllable time durations, a sensing network connected to said gap for providing an output signal responsive to gap short circuit condition, and control means connected between said network and said control circuit for interrupting the firing of said device responsive to said signal.

Claim 8

The combination as set forth in claim 5 wherein said device comprises a semiconductor controlled rectifier having its anode and cathode connected between said phase and said gap, wherein said control circuit includes a firing voltage source for said controlled rectifier and wherein said control means comprises an electronic switch having its control electrode connected to said sensing network and its principal electrodes connected across said firing voltage source for shunting it responsive to said signal.

Claim 9

The combination as set forth in claim 5 wherein said control means comprises an electronic switch having its control electrode coupled to the output of said sensing network and its principal electrodes operatively connected to said firing circuit for preventing firing of said semiconductor controlled rectifier for the duration of said signal.

Claim 10

The combination as set forth in claim 7 wherein a pulser is operatively coupled to said electronic switch to periodically turn it on and off during continuance of said signal.

Claim 11

The combination as set forth in claim 5 wherein said firing circuit includes a unijunction transistor oscillator circuit operable at selectable frequencies.