GAP SHORT CIRCUIT PROTECTIVE SYSTEM FOR ELECTRICAL DISCHARGE MACHINING

• US 3,627,968 A
• Filed: 08/21/1969
• Issued: 12/14/1971
• Est. Priority Date: 08/21/1969
• Status: Expired due to Term

• Current Assignee: Colt Industries Incorporated
• Original Assignee: Kurt H. Sennowitz
• Inventors: Sennowitz, Kurt H.
• Primary Examiner(s): Staubly, R. F.
• Application Number:
  US04/851,952
• Time in Patent Office: 845 Days
• Field of Search: 219/69C,69F,69G,69P,69S
• 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

A circuit is provided to sense gap condition for impending or actual short circuit condition. Responsive to such condition, a portion of the drive voltage for the gap output switch is fed back, stored, amplified and applied to control the circuit pulser to narrow pulse on-time. Additionally, a means is provided for varying the cutoff reference voltage conjointly with change in frequency being made to the pulser.

Claims

1. In an apparatus for machining a conductive workpiece by passing machining power pulses across a dielectric coolant filled gap between a tool electrode and the workpiece, an electronic output switch operatively connected in series with a power supply across said gap, a pulsing means of variable on-off time for turning said switch on and off to pRovide said machining power pulses, at least one drive stage operatively connected between said pulsing means and said switch, an electronic cutoff switch operatively connected between said gap and said pulsing means for controlling its on-off time, means for sensing a gap short circuit condition operatively connected between said gap and said cutoff switch for enabling it responsive to said condition, said sensing means comprising a peak voltage storing network, and a feedback network operatively connected between said drive stage and said cutoff switch to operate said cutoff switch and reduce said on-time of said pulsing means responsive to said condition.

2. The combination as set forth in claim 1 wherein said feedback network comprises a variable time constant RC network, said RC network being diode coupled between the output of said drive stage and the control network of said cutoff switch.

3. In an apparatus for machining a conductive workpiece by passing machining power pulses across a dielectric coolant filled gap between a tool electrode and the workpiece, an electronic output switch operatively connected in series with a power supply across said gap, a pulsing means of variable on-off time for turning said switch on and off to provide said machining power pulses, at least one drive stage operatively connected between said pulsing means and said switch, an electronic cutoff switch operatively connected between said gap and said pulsing means for controlling its on-off time, means for sensing a gap short circuit condition operatively connected between said gap and said cutoff switch for enabling it responsive to said condition. Said sensing means comprising a diode-capacitor network for storing peak gap voltages and including a variable time constant RC network for delay adjustment, and a feedback network operatively connected between said drive stage and said cutoff switch to operate said cutoff switch and reduce said on-time of said pulsing means responsive to said condition.

4. In an apparatus for machining a conductive workpiece by passing machining power pulses across a dielectric coolant filled gap between a tool electrode and the workpiece, an electronic output switch operatively connected with a power supply across said gap, a pulsing means of variable on-off time for turning said switch on and off to provide said machining power pulses, at least one intermediate drive stage operatively connected between said pulsing means and said switch, an electronic cutoff switch operatively connected between said gap and said pulsing means for reducing its on-time, said cutoff switch having a pair of power electrodes and a control electrode, one of said power electrodes operatively connected to and controlling said pulsing means, a feedback network including a controllable delay stage connected between said drive stage and the other of said power electrodes of said cutoff switch for operating it, and a gap short circuit sensing network comprising a peak voltage storage network including a unidirectional current conducting device and a capacitor, said sensing network operatively connected between said gap and said control electrode of said cutoff switch for enabling it responsive to said condition.

5. In an apparatus for machining a conductive workpiece by passing machining power pulses between a tool electrode and said workpiece across a dielectric coolant filled gap, a power supply, an electronic output switch having a control electrode and a pair of power electrodes, said power electrodes operatively connected between said power supply and said gap for providing machining power pulses thereto, a multivibrator comprising a pair of switches biased and coupled for alternate operation, a drive stage coupled between the output of said multivibrator and the control electrode of said switch for operating it with predetermined on-off time, a feedback circuit connected between the output signal of said drive stage for providing a control signal to the appropriate one of said multivibrator switches to reduce the on-time of said pulses, and a gap short circuit sensing network comprising a gap peak voltage storage network operatively connected between said gap and said feedback circuit for operating it responsive to gap short circuit condition.

6. In an electrical discharge machining apparatus including an electronic switch operatively connected with a power supply across a machining gap, a pulsing means of variable frequency and variable on-off time operatively connected to said switch for operating it to provide machining power pulses across said gap, the improvement comprising a cutoff means including a preset reference voltage operatively connected between said gap and said pulsing means for reducing the on-time of said pulses responsive to gap short circuit condition, a drive stage operatively connected between said pulsing means and said switch for amplifying and resquaring said pulses from said pulsing means, said cutoff means operatively connected to the output of said drive stage for operation responsive to said condition, and a peak voltage sensing network coupled between said gap and said cutoff means for providing a signal thereto responsive to said condition.

7. The combination as set forth in claim 6 wherein a delay stage is included in said cutoff means, said delay period adjustable to provide maximum delay during relatively long on-time, low-frequency rough machining and to provide minimum delay during relatively short on-time, high-frequency finish machining.