ELECTRIC DISCHARGE MACHINING CIRCUIT FOR ELIMINATING CONCENTRATED DISCHARGES

• US 3,585,340 A
• Filed: 09/16/1968
• Issued: 06/15/1971
• Est. Priority Date: 09/16/1968
• Status: Expired due to Term

• Current Assignee: Terry O. Hockenberry
• Original Assignee: Terry O. Hockenberry
• Inventors: Hockenberry, Terry O.
• Application Number:
  US04/762,259
• Time in Patent Office: 1,002 Days
• US Class Current: 219/69.13
• CPC Class Codes: B23H 1/024 Detection of, and response to, abnormal gap conditions, e.g. short circuits preventing short circuits or other abnormal discharges by altering machining parameters using adaptive control B23H7/16

Abstract

The power supply can be used for electric discharge machining (EDM) apparatus and the like, the power supply includes a circuit for establishing repetitive electric discharges across a discharge gap forming part of EDM apparatus. A voltage detecting circuit in coupled across the EDM gap for developing an output signal when the instantaneous voltage across the gap falls below a predetermined level. A control circuit is coupled to the detecting circuit and to the supply circuit for momentarily lowering gap discharge rate until the lowest instantaneous voltage is at or above said predetermined level.

Claims

1. A power supply for electric discharge machining apparatus and the like, said power supply including circuit means for establishing cycle voltage pulses and electric discharges at a given repetitive rate across a discharge gap forming part of said apparatus, a voltage detecting circuit coupled across said gap for developing an output signal when the instantaneous voltage across said gap falls below a predetermined level above that which exists at short circuit, and a control circuit coupled to said detecting circuit and to said circuit means for lowering said repetitive rate, said control circuit being responsive to said predetermined level to impose a relatively slower voltage rise on at least one of the subsequent voltage pulses.

2. The combination according to claim 1 wherein said circuit means includes a first circuit path for supplying pulses to said gap at said given discharge rate and a second circuit path for supplying pulses to said gap at a slower rate, and said control circuit includes switching means for selectively energizing said circuit paths in response to said signal.

3. The combination according to claim 1 wherein said voltage detecting circuit includes a semiconductive switch, a voltage dividing network coupled across said gap and to said switch, and a source of balancing potential coupled to said switch.

4. The combination according to claim 1 wherein said circuit means includes a pulse-prolonging circuit for prolonging the flow of current across said gap for a predetermined interval following the initiation of each of said discharges.

5. The combination according to claim 2 wherein said circuit paths include capacitance means coupled across said gap for discharging thereacross and are defined by relatively high and low charging resistance means connected in series with said capacitance means and with a source of capacitance charging potential.

6. The combination according to claim 2 wherein said switching means include a first semiconductive switch, said voltage detecting circuit includes a second semiconductive switch, a voltage dividing circuit coupled across said gap and to a control electrode of said second semiconductive switch, and a source of balancing voltage coupled through an emitter-collector circuit of said second semiconductive switch to a control electrode of said first semiconductive switch.

7. The combination according to claim 1 wherein said control circuit additionally is capable of momentarily lowering the repetitive rate until said instantaneous voltage is at or above said predetermined level.

8. The combination according to claim 7 wherein said control circuit is further capable of restoring said given repetitive rate across the discharge gap following return of said instantaneous voltage to values at or above said predetermined level.

9. The combination according to claim 1 wherein said control circuit additionally is responsive to a second and higher predetermined voltage level to impose a relatively steeper voltage rise on each of said voltage pulses.

10. A power supply for electric discharge machining apparatus and the like, said power supply including circuit means for establishing electric discharges at a given repetitive rate across a discharge gap forming part of said apparatus, a voltage detecting circuit coupled across said gap for developing an output signal when the instantaneous voltage across said gap falls below a predetermined level, and a control circuit coupled to said detecting circuit and to said circuit means for momentarily lowering said discharge rate until said instantaneous voltage is at or above said predetermined level said circuit means including a first circuit path for supplying pulses to said gap at said given discharge rate and a second circuit path for supplying pulses to said gap at a slower rate, said control circuit including switching means for selectively energizing said circuit paths in response to said signal, a third circuit path for supplying pulses at a faster rate to said gap, additional switching means coupled in said third circuit path, and a second voltage detecting circuit coupled across said gap and to said additional switching means for closing said additional switching means when the instantaneous gap voltage attains a second predetermined voltage level.

11. The combination according to claim 10 wherein each of said detecting circuits include variable impedance means for variably selecting said first-mentioned and said second voltage levels in correspondence to de-ionization of localized and generalized gap spacings respectively.

12. The combination according to claim 10 wherein said third circuit path includes a pulse-prolonging circuit for prolonging the flow of gap current during a predetermined interval following the initiation of each of said discharges.