ELECTRICAL DISCHARGE MACHINING POWER SUPPLY WITH PROTECTIVE SYSTEM FOR OUTPUT SWITCH FAILURE

• US 3,805,012 A
• Filed: 03/16/1973
• Issued: 04/16/1974
• Est. Priority Date: 03/16/1973
• Status: Expired due to Term

• Current Assignee: Colt Industries Incorporated
• Original Assignee: Oliver A. Bell Jr, Randall C. Gilleland
• Inventors: Bell, Oliver A. Jr., Gilleland, Randall C.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Jaeger, Hugh D.
• Application Number:
  US05/341,980
• Time in Patent Office: 396 Days
• Field of Search: 219/69C,69P,69S
• US Class Current: 219/69.19
• CPC Class Codes: B23H 1/026 Power supply protection, e.g. detection of power switch breakdown

Abstract

A digitally controlled multivibrator for the power supply is used to supply machining power pulses of predetermined ON and OFF time duration. The pulse output from the digital multivibrator is passed through at least one intermediate drive stage to trigger an electronic output switch, which is operatively connected both to a main DC power source and the gap, to actually provide the machining power pulses thereto. Responsive to a predetermined drop in drive signal being furnished to the output switch, the cut-off of the main machining power source is provided through operation of a field effector transistor switch. In addition, the protective system which would cut off the output switch in its fail-short condition is inhibited for the duration of any gap short circuit condition.

Claims

1. In an electrical discharge machining apparatus including an electronic output switch and a DC power source operatively connected to a machining gap for providing machining power pulses of digitally predetermined ON-OFF time duration thereto, a digital type machining power pulse circuit including separately settable ON-time and OFF-time switches, a counter stage selectively connectible to one of the aforesaid ON and OFF-time switches, a data input selector stage connected intermediate said switches and said counter stage respectively, a bistable means operatively connected to said gap and having a pair of outputs, one of said outputs operably connected to said data input selector stage for connecting the appropriate one of said ON-OFF time switches to the counter stage and the other of said outputs operably connected to the control electrode of said electronic output switch for controlling its ON-OFF operation, and a protective circuit for interrupting power from said power source responsive to failure of said electronic output switch, said system comprising a keying network operatively coupled to the other of said outputs of said bistable means for sensing drive signal level, an electronic switching means having its control electrode coupled to said keying network and a power interruption relay operatively associated with said power source for interrupting it responsive to failure of said drive signal and operation of said switching means.

2. The combination as set forth in claim 1 wherein said second output of said bistable means is connected to the control electrode of said output switch through an intermediate amplifier and waveform shaping drive stage and wherein said keying network is coupled to the output of said drive stage.

3. The combination as set forth in claim 1 wherein said keying network comprises an input capacitor and an attenuating network coupled intErmediate said input capacitor and the control electrode of said electronic switching means.

4. The combination as set forth in claim 3 wherein the output of said attenuating network is connected to a second capacitor, said second capacitor coupled across the control electrode and one of the principal electrodes of said electronic switching means and wherein said second capacitor is discharged responsive to failure of said drive signal thereby triggering said electronic switching means into operation.

5. The combination as set forth in claim 4 wherein a second electronic switching means is included, said second electronic switching means operatively connected to and controlled by said first switching means, said second switching means having one of its principal electrodes connected to said relay.

6. The combination as set forth in claim 5 wherein there is included in said electrical discharge machining apparatus a short circuit cut-off network, said cut-off network further operable to interrupt drive from said drive stage responsive to gap short circuit, and wherein there is included an output from said short circuit cut-off stage for inhibiting the operation of said second electronic switching means for the duration of said short circuit cut-off network operation.

7. The combination as set forth in claim 6 wherein said first electronic switching means comprises a field effect transistor having said second capacitor coupled to its gate and wherein said second electronic switching means comprises a transistor having one of its principal electrodes coupled to the control coil for said relay.

8. The combination as set forth in claim 7 wherein the output from said short circuit cut-off network is coupled to the control electrode for said second electronic switching means through a series resistor-diode network.

9. The combination as set forth in claim 8 wherein a second diode is connected between one of the principal electrodes of said field effect transistor and the junction of said first mentioned diode and the control electrode of said second electronic switching means.

10. The combination as set forth in claim 9 wherein said power interruption relay includes a normally closed contact coupled in series between one terminal of said DC source and one of the power conducting electrodes of said electronic output switch.

11. The combination as set forth in claim 10 wherein said second electronic switching means comprises an NPN transistor held in a normally conductive state and having its power conducting electrodes in series with said relay control coil and a voltage source.

12. In an electrical discharge machining apparatus including an electronic output switch and a DC power source operatively connected to a machining gap for providing machining power pulses of digitally predetermined ON-OFF time duration thereto, a digital type machining power pulse circuit including separately settable ON-time and OFF-time switches, a counter stage selectively connectible to one of the aforesaid ON and OFF-time switches, a data input selector stage connected intermediate said switches and said counter stage respectively, a bistable means operatively connected to said gap and having a pair of outputs, one of said outputs operably connected to said data selector stage for connecting the appropriate one of said ON-OFF time switches to the counter stage and the other of said outputs operably connected to the control electrode of said electronic output switch for controlling its ON-OFF operation, and a protective circuit for interrupting power from said power source responsive to failure of said electronic output switch, said system comprising a keying network operatively coupled to the other of said outputs of said bistable means for sensing drive signal level, an electronic switching means having its control electrode coupled to said keying network and means operatively associated with said power source for interrupting it responsive to failure of said drive sigNal and operation of said switching means.

13. The combination as set forth in claim 12 wherein said second output of said bistable means is connected to the control electrode of said output switch through an intermediate amplifier and waveform shaping drive stage, and wherein said keying network is coupled to the output of said drive stage.

14. The combination as set forth in claim 13 wherein said keying network comprises an input capacitor and an attenuating network coupled intermediate said input capacitor and the control electrode of said electronic switching means.