Power source arrangement for electric discharge machining

• US 4,431,895 A
• Filed: 04/08/1981
• Issued: 02/14/1984
• Est. Priority Date: 04/16/1980
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Obara, Haruki
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US06/252,215
• Time in Patent Office: 1,042 Days
• Field of Search: 219/69 M, 219/69 C, 219/69 G, 219/69 P, 219/69 S, 219/69 R, 219/68
• US Class Current: 219/69.18
• 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 power source arrangement for electric discharge machining in which a power source and a switching element are connected in parallel to an electrode and a workpiece and the switching element is driven by a pulse signal of a predetermined period to perform electric discharge machining of the workpiece, there being also provided a pulse signal generator for generating a pulse signal in which the ratio of the OFF interval to the ON interval gradually increases with the lapse of time and a detector for detecting the occurrence of an arc or short in the spark gap. Upon detection of arcing or shorting in the spark gap by the detector, the pulse signal generator is activated so that the pulse signal of the predetermined period to be applied to the switching element is gated by the output pulse signal from the pulse signal generator until the arc or short is removed.

Claims

1. A power source arrangement for electric discharge machining, in which a power source and a switching element are connected in series to an elongated electrode and a workpiece electrode separated from the elongated electrode by a gap and the switching element is driven by a pulse signal to perform electric discharge machining of the workpiece, comprising:

detector means for comparing a reference voltage and the gap voltage in the gap between the electrode and the workpiece to generate a detector signal when arcs and shorts form in the gap between the electrode and the workpiece;

oscillator means for continuously producing a pulse signal having a predetermined period;

pulse signal generator means responsive to the detector signal for generating an additional pulse signal having ON and OFF intervals, the ratio of the OFF interval to the ON interval of the additional pulse signal gradually increasing with the lapse of time, said pulse signal generator means including first means responsive to the detector means for generating a first digital signal for a first predetermined period of time following the detection of an arc or short, a second gate having a first input responsive to the first means and a second input, and means connected between the output of the detector means and the second input of the second gate for allowing the pulse signal of predetermined period to pass through the first gate when the detector means detects neither an arc nor a short; and

gate means responsive to the additional pulse signal and to the pulse signal of a predetermined period for driving the switching element until the arc or short is removed following the detection of its occurrence by the detector means, said gate means including a first gate having a first input for receiving the additional pulse signal and a second input for receiving the pulse signal of predetermined period, the output of the first gate driving the switching element;

wherein the first means comprises a first timer connected to the detector and a first oscillator connected to the first timer, wherein the second gate comprises an OR gate, and wherein the means connected between the detector means and the second input of the second gate comprises an inverter.

2. A power source arrangement for electric discharge machining, in which a power source and a switching element are connected in series to an elongated electrode and a workpiece electrode separated from the elongated electrode by a gap and the switching element is driven by a pulse signal to perform electric discharge machining of the workpiece, comprising:

detector means for comparing a reference voltage and the gap voltage in the gap between the electrode and the workpiece to generate a detector signal when arcs and shorts form in the gap between the electrode and the workpiece;

oscillator means for continuously producing a pulse signal having a predetermined period;

pulse signal generator means responsive to the detector signal for generating an additional pulse signal having ON and OFF intervals, the ratio of the OFF interval to the ON interval of the additional pulse signal gradually increasing with the lapse of time, said pulse signal generator means including first means responsive to the detector means for generating a first digital signal for a first predetermined period of time following the detection of an arc or short, a second gate having a first input responsive to the first means and a second input, and means connected between the output of the detector means and the second input of the second gate for allowing the pulse signal of predetermined period to pass through the first gate when the detector means detects neither an arc nor a short; and

gate means responsive to the additional pulse signal and to the pulse signal of a predetermined period for driving the switching element until the arc or short is removed following the detection of its occurrence by the detector means, said gate means including a first gate having a first input for receiving the additional pulse signal and a second input for receiving the pulse signal of predetermined period, the output of the first gate driving the switching element;

wherein the pulse signal generator means additionally comprises second means for generating a second digital signal for a second predetermined period of time following the expiration of the first period of time, the ratio of the OFF interval to the ON interval of the second digital signal being greater than the ratio of the OFF interval to the ON interval of the first digital signal, wherein the second gate has a third input responsive to the second means, and wherein the second means comprises a second timer connected to the detector and a second oscillator connected to the second timer.

3. A power source arrangement for electric discharge machining, in which a power source and a switching element are connected in series to an elongated electrode and a workpiece electrode separated from the elongated electrode by a gap and the switching element is driven by a pulse signal to perform electric discharge machining of the workpiece, comprising:

detector means for comparing a reference voltage and the gap voltage in the gap between the electrode and the workpiece to generate a detector signal when arcs and shorts form in the gap between the electrode and the workpiece;

oscillator means for continuously producing a pulse signal having a predetermined period;

pulse signal generator means responsive to the detector signal for generating an additional pulse signal having ON and OFF intervals, the ratio of the OFF interval to the ON interval of the additional pulse signal gradually increasing with the lapse of time, said pulse signal generator means including first digital signal for a first predetermined period of time following the detection of an arc or short, a second gate having a first input responsive to the first means and a second input, and means connected between the output of the detector means and the second input of the second gate for allowing the pulse signal of predetermined period to pass through the first gate when the detector means detects neither an arc nor a short; and

gate means responsive to the additional pulse signal and to the pulse signal of a predetermined period for driving the switching element until the arc or short is removed following the detection of its occurrence by the detector means, said gate means including a first gate having a first input for receiving the additional pulse signal and a second input for receiving the pulse signal of predetermined period, the output of the first gate driving the switching element;

wherein the pulse signal generator means additionally comprises second means for generating a second digital signal for a second predetermined period of time following the expiration of the first period of time, the ratio of the OFF interval to the ON interval of the second digital signal being greater than the ratio of the OFF interval to the ON interval of the first digital signal, wherein the second gate has a third input responsive to the second means, wherein the pulse signal generator means additionally comprises third means for generating a third digital signal for a third predetermined period of time following the expiration of the second period of time, the ratio of the OFF interval to the ON interval of the third digital signal being greater than the ratio of the OFF interval to the ON interval of the second digital signal, and wherein the second gate has a third input responsive to the third means.

4. The arrangement of claim 3, wherein the third means comprises a third timer connected to the detector and a third oscillator connected to the third timer.