GAP CONDITION DETECTOR CIRCUIT

• US 3,843,864 A
• Filed: 03/21/1973
• Issued: 10/22/1974
• Est. Priority Date: 03/21/1973
• Status: Expired due to Term

• Current Assignee: Leonard M. Wohlabaugh
• Original Assignee: Leonard M. Wohlabaugh
• Inventors: Wohlabaugh, Leonard M.
• Primary Examiner(s): Goldberg, E. A.
• Assistant Examiner(s): Jaeger, Hugh D.
• Application Number:
  US05/343,484
• Time in Patent Office: 580 Days
• Field of Search: 219/69C,69P,69D,69G,69S 315/186 318/650
• US Class Current: 219/69.13
• CPC Class Codes: B23H 1/02 Electric circuits specially adapted therefor, e.g. power supply, control, preventing short circuits or other abnormal discharges

Abstract

A device for detecting the gap condition of electric discharge machining operations and effecting retraction of the work electrode, flushing of the workpiece, and interruption of the current pulses to the electrode when a preselected current is exceeded. The device includes means for adjusting the sensitivity, as well as the time of electrode retraction. In addition, the operating current range may be selected through a group of current limiting resistors each providing an input signal and isolated from the other resistors by way of a diode matrix.

Claims

1. In an electrical discharge machining apparatus, a power supply connected across the gap between a workpiece and an electrode by a power switch conducting current pulses to the electrode, means for interrupting said current pulses in response to excessive current flow through the gap, comprising current limiting means connected in series to the gap and the power switch, means for monitoring the volt drop across the current limiting means, reference voltage means for establishing a reference voltage, comparison means connected to said reference voltage means and the monitoring means for detecting a volt drop exceeding said reference voltage to produce an operating signal, and means connected to the comparison means and the power supply switch for disabling the power supply in response to said operating signal.

2. The combination of claim 1 wherein said current limiting means includes a plurality of resistors connected in series between the power switch and the gap, and a plurality of isolation diodes interconnecting the resistors in parallel to the monitoring means.

3. The combination of claim 2 wherein said power switch includes a plurality of power transistors respectively connected in series with said resistors.

4. The combination set forth in claim 3 wherein said electric discharge machine includes switch means for selectively disconnecting each of said resistors from said power supply whereby the total current required for a particular application may be selectively adjusted.

5. In an electrical discharge machining apparatus, a power supply connected across the gap between a workpiece and an electrode by a power switch conducting current pulses to the electrode under control of a timing control assembly, means for interrupting said current pulses in response to excessive current flow through the gap, comprising selective current limiting means connected in series between the gap and the power switch, means for monitoring the volt drop across the current limiting means, reference voltage means for establishing a preselected reference voltage, comparison means connected to said reference voltage means and the monitoring means for detecting a volt drop exceeding said preselected reference voltage to produce an operating signal, signal transmitting means connecting the comparison means to the timing control assembly for disabling the same in response to said operating signal, and adjustable means connected to the signal transmitting means for maintaining the timing control assembly disabled for a retract period of preselected duration.