Wire EDM control circuit for rough and finished machining

• US 4,614,854 A
• Filed: 05/22/1984
• Issued: 09/30/1986
• Est. Priority Date: 11/15/1982
• Status: Expired due to Term

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Obara, Haruki, Izumiya, Shunzo
• Primary Examiner(s): Albritton, Clarence L.
• Assistant Examiner(s): Evans, Geoffrey S.
• Application Number:
  US06/618,394
• Time in Patent Office: 861 Days
• Field of Search: 219/69 C, 219/69 S, 219/69 P, 219/69 W
• 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 wire EDM circuit uses a references voltage connected to a short circuit detector for comparing an average voltage with a reference voltage. Whenever the average voltage is below the reference voltage the numeric controller causes the pulse oscillator to stop generating a pulse stream. In order to also finish machine the workpiece a reference voltage switching circuit is used to decrease the reference voltage. There is also provided an internal signal blocking circuit to block an interval signal oscillator to stop generation of the pulse stream when the wire electrode is temporarily in contact with the workpiece or when phenomena similar to a short circuit occurs.

Claims

1. An electric discharge machining control circuit comprising:

a pulse oscillation control circuit means for generating a pulse stream;

an electric discharge machining circuit having a variable circuit constant, operatively connected to said pulse oscillation control circuit means, including a capacitor, a switching means operatively connected to said capacitor which switching means is turned on and off in response to said pulse stream for said pulse oscillation control circuit means for applying a discharge current between a wire electrode and a workpiece in accordance with the variable cicuit constant;

a short-circuit detector means, operatively connected to said electric discharge machining circuit, for comparing a machining voltage between the wire electrode and the workpiece with a reference voltage and for detecting a short circuit between the wire electrode and the workpiece;

gate means, operatively connected to said pulse oscillation control circuit means, for inhibiting generation of said pulse stream in response to said short-circuit detector detecting a short-circuit;

receiving means for receiving a second cut instruction;

average machining voltage switching means, operatively connected to said receiving means, for decreasing an average machining voltage applied between the wire electrode and the workpiece in response to said second cut instruction, by changing a value of said variable circuit constant from that employed during rough machining;

reference voltage switching means, operatively connected to said receiving means, for generating the reference voltage applied to said short-circuit detector means, and for decreasing the reference voltage applied to the short-circuit detector means in response to said second cut instruction from a value applied during rough machining to a lower value such that errors in said detecting of a short circuit are prevented.

2. A circuit according to claim 1, wherein said gate means comprises:

an interval signal oscillator means for generating an interval signal for inhibiting generation of said pulse stream at predetermined intervals in response to said short-circuit detector means detecting one of temporary contact between said wire electrode and the workpiece and a phenomenon similar to a short circuit between said wire electrode and the workpiece occurs; and

an interval signal blocking circuit means for blocking the interval signal oscillator means from inhibiting generation of said pulse stream, in response to the second cut instruction signal.

3. A circuit according to claim 2, wherein said interval signal oscillator means comprises an oscillator.

4. A circuit according to claim 2, wherein said interval signal oscillator means includes counter means for counting output pulses generated by said pulse oscillator and produces said interval signal for every predetermined count.

5. A circuit according to claim 2, wherein said interval signal blocking circuit means blocks an output from said interval signal oscillator means.

6. A circuit according to claim 3, wherein said interval signal blocking circuit means blocks oscillation of said interval signal oscillator means.

7. A circuit according to claim 1, wherein said electric discharge machining circuit includes a resistor operatively connected in parallel with said wire electrode and the workpiece and in series with said switching element, and wherein the value of the variable circuit constant comprises at least one of the capacitance of said capacitor and the resistance of said resistor.

8. A circuit according to claim 4, wherein said interval signal blocking circuit means blocks oscillation of said interval signal oscillator means.

9. An electric discharge machining control circuit for controlling a discharge voltage applied between a wire electrode and a workpiece in a wire-electric discharge machine, said circuit comprising:

discharge machining means, having a variable circuit element with a value, for applying a discharge voltage across a wire electrode and a workpiece in response to a control signal and in accordance with the value of the variable circuit element, and for generating a shunt voltage varying in accordance with the discharge voltage;

short-circuit detector means, operatively connected to receive a reference voltage and a shunt voltage, for detecting a short circuit between the wire electrode and the workpiece and a phenomenon similar to a short circuit, in accordance with said shunt voltage and said reference voltage;

receiving means for receiving a second cut signal;

average machining voltage switching means, operatively connected to the receiving means and to the discharge machining means, for decreasing an average machining voltage applied between the wire electrode and the workpiece in response to the second cut instruction, by changing the value of the variable circuit element from the employed during rough machining;

switching means, operatively connected to the receiving means and to the short-circuit detector means, for generating said reference voltage and for lowering said reference voltage in respnse to said second cut signal to a level such that errors in said detecting circuit are prevented;

pulse stream generator means, operatively connected to the discharge machining means and to the short-circuit detector means, for generating said control signal in accordance with said short circuit detection, said second cut signal and said shunt voltage;

interval signal oscillator means, operatively connected to the discharge machining means, for generating an inhibit signal to inhibit the generation of said control signal in response to said shunt voltage dropping below a predetermined value; and

blocking means, operatively connected to the switching means and to the interval signal oscillator means, for preventing said inhibit signal from inhibiting the generation of said control signal, in response to said second cut instruction.