Electric discharge machining control apparatus

• US 4,833,289 A
• Filed: 01/15/1988
• Issued: 05/23/1989
• Est. Priority Date: 06/18/1986
• Status: Expired due to Fees

• Current Assignee: Fanuc Corporation
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Obara, Haruki
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): Evans, Geoffrey S.
• Application Number:
  US07/148,651
• Time in Patent Office: 494 Days
• Field of Search: 219/69 P, 219/69 C, 219/69 G, 219/69 S
• US Class Current: 219/69.18
• CPC Class Codes: B23H 7/04 Apparatus for supplying current to working gap; Electric circuits specially adapted therefor

Abstract

An electric discharge machining control apparatus which controls an electric discharge machining power source of a wire electric discharge machine in accordance with a leakage current flowing between a wire electrode (2) and a workpiece (3). This permits stable electric discharge and satisfactory surface roughening. The control apparatus described above, the peak value of a machining voltage applied between the wire electrode (2) and the workpiece (3) is detected by means of a peak voltage detecting circuit (D4, R8, R9, C2). When the leakage current increases so that a detection value is reduced, the on and off times of switching elements (Tr1, Tr2), interposed between a DC power source (1) and the wire electrode and between the DC power source and the workpiece, are changed from a value smaller than the time constant (R1.C1) of a charge and discharge circuit to a value larger than the time constant. Thus, the machining voltage increases. When the leakage current is reduced again the on and off times are changed to the value smaller than the time constant. Thus, the effective machining voltage is kept at a proper value.

Claims

1. An electric discharge machining control apparatus for intermittently applying a machining voltage between a wire electrode and a workpiece, said machining control apparatus being used with a capacitor electric discharge power source with switching element control for electrically charging and discharging a capacitor by means of a switching element which is turned on and off by an oscillator, said machining control apparatus comprising:

a peak voltage detecting circuit for detecting a peak value of said machining voltage which changes with a change in a leakage current flowing between said wire electrode and said workpiece; and

control means having a comparator for comparing the peak voltage value detected by said peak voltage detecting circuit with a reference voltage value, said control means being operable to change, in accordance with an output of said comparator, an oscillation frequency of said oscillator so as to change a ratio of an on time period of said switching element to an off time period thereof, whereby a fluctuation in said leakage current is compensated so that said machining voltage is controlled in a manner stabilizing electric discharge machining.

2. An electric discharge machining control apparatus according to claim 1, wherein said machining control apparatus is used with an electric discharge machine which performs rough machining and finish machining each including straight machining and corner machining, said control means being operable to maintain said machining voltage at a small value enough to prevent deteriorated surface roughness of a machined surface of said workpiece when the straight machining of the finish machining is performed, said control means being operable to increase the machining voltage up to a value at which electric discharge machining is performed in a stabilized manner when the corner machining of the finish machining, where said leakage current increases, is performed.

4. An electric discharge machining control apparatus for intermittently applying a machining voltage between a wire electrode and a workpiece, said machining control apparatus being used with a capacitor electric discharge power source with switching element control for electrically charging and discharging a capacitor by means of a switching element, said machining control apparatus, comprising:

a peak voltage detecting circuit for detecting a peak value of said machining voltage;

a differential amplifier for receiving the peak voltage detected by said peak voltage detecting circuit;

a V-f converter for converting the output voltage of said differential amplifier into a frequency; and

control means for turning on and off said switching element in accordance with an output of said V-f converter so as to change a ratio of an on time period of said switching element to an off time period thereof, whereby a fluctuation in said leakage current is compensated so that said machining voltage is controlled in a manner stabilizing electric discharge machining.

3. An electric discharge machining control apparatus according to claim 4, wherein said capacitor electric discharge power source with switching element control includes a bipolar electric discharge power source for applying positive and negative voltages between the wire electrode and the workpiece, said electric discharge machining control apparatus comprises an absolute value detecting circuit for detecting the absolute value of the voltage between said wire electrode and said workpiece, and said peak voltage detecting circuit receives the output of said absolute value detecting circuit.

5. An electric discharge machining control apparatus according to claim 4, wherein said machining control apparatus is used with an electric discharge machine which performs rough machining and finish machining each including straight machining and corner machining, said control means being operable to maintain said machining voltage at a small value enough to prevent deteriorated surface roughness of a machined surface of said workpiece when the straight machining of the finish machining is performed, said control means being operable to increase the machining voltage up to a value at which electric discharge machining is performed in a stabilized manner when the corner machining of the finish machining, where said leakage current increases, is performed.

6. An electric discharge machining control apparatus according to claim 4, wherein said capacitor electric discharge power source wit switching element control includes a bipolar electric discharge power source for applying positive and negative voltages between the wire electrode and the workpiece, said electric discharge machining control apparatus comprises an absolute value detecting circuit for detecting the absolute value of the voltage between said wire electrode and said workpiece, and said peak voltage detecting circuit receives the output of said absolute value detecting circuit.

7. An electric discharge machining control apparatus for use with an electric discharge power source for applying a voltage from a DC power source, as a machining voltage, between the wire electrode and the workpiece, through a current limiting resistor circuit with a variable resistance value and a switching element, comprising:

a peak voltage detecting circuit for detecting a peak value of said machining voltage; and

control means having a comparator for comparing the peak voltage value detected by said peak voltage detecting circuit with a reference voltage value, said control means being operable to change, a resistance value of said current control resistor circuit in accordance with an output of said comparator, whereby a fluctuation in said leakage current is compensated so that said machining voltage is controlled in a manner stabilizing electric discharge machining.

8. An electric discharge machining control apparatus according to claim 7, wherein said machining control apparatus is used with an electric discharge machine which performs rough machining and finish machining each including straight machining and corner machining, said control means being operable to maintain said machining voltage at a small value enough to prevent deteriorated surface roughness of a machined surface of said workpiece when the straight machining of the finish machining is performed, said control means being operable to increase the machining voltage up to a value at which electric discharge machining is performed in a stabilized manner when the corner machining of the finish machining, where said leakage current increases, is performed.

9. An electric discharge machining control apparatus for use with a capacitor electric discharge power source for applying a voltage from a DC power source to a parallel circuit including a capacitor connected between the wire electrode and the workpiece and in parallel therewith, through a current limiting resistor circuit with a variable resistance value, said machining control apparatus, comprising:

a peak voltage detecting circuit for detecting a peak value of a machining voltage; and

control means having a comparator for comparing the peak voltage value detected by said peak voltage detecting circuit with a reference voltage value, said control means being operable to change a resistance value of said current limiting resistor circuit in accordance with an output of said comparator, whereby a fluctuation in said leakage current is compensated so that said machining voltage is controlled in a manner stabilizing electric discharge machining.

10. An electric discharge machining control apparatus according to claim 9, wherein said machining control apparatus is used with an electric discharge machine which performs rough machining and finish machining each including straight machining and corner machining, said control means being operable to maintain said machining voltage at a small value enough to prevent deteriorated surface roughness of a machined surface of said workpiece when the straight machining of the finish machining is performed, said control means being operable to increase the machining voltage up to a value at which electric discharge machining is performed in a stabilized manner when the corner machining of the finish machining, where said leakage current increases, is performed.