Capacitor-type pulse generator for electrical discharge machining, especially for wire-cutting EDM

Abstract

A capacitor-type pulse generator is provided for wire-cutting EDM. The generator includes a capacitor connected on one hand to a DC source in series with a charging switch and on the other hand to the EDM gap in series with a discharging switch. A first sensing circuit turns the discharging switch into conduction when the charging voltage on the capacitor reaches a predetermined level. The charging switch is normally in its conductive state and is turned into its nonconductive state when a second sensing circuit senses that the EDM gap voltage exceeds a preselected value. In a modified generator, parallel-connected discharging switches are triggered in sequence when the capacitor voltage reaches the predetermined level.

What is claimed is: 
     
       1. A capacitor-type pulse generator for wire-cutting EDM, comprising: a capacitor;   a DC source having an output voltage for charging said capacitor;   first switch means connected in series with said capacitor, a wire electrode and a workpiece, said wire electrode and said workpiece defining an EDM gap therebetween;   a first sensing circuit responsive to the charging voltage on said capacitor for turning said first switch means into conduction upon said charging voltage reaching a predetermined level, thereby permitting the charge on said capacitor to be discharged through said EDM gap whereby to form at least one EDM pulse;   second switch means connected in series with said DC source and said capacitor and normally held conductive to permit said capacitor to be charged by said DC source to said predetermined level, said output voltage of said DC source being at least twice said predetermined charging level; and   a second sensing circuit responsive to the EDM gap voltage for turning said second switch means into nonconduction upon the EDM gap voltage exceeding a preselected value.   
     
     
       2. The pulse generator defined in claim 1 wherein said first switch means comprises a plurality of switches connected in parallel with one another and in series with said capacitor and said EDM gap and said first sensing circuit is adapted for triggering said switches successively into the conductive states. 
     
     
       3. The pulse generator defined in claim 1 or claim 2, further comprising an oscillator for providing said second switch means with a train of signal pulses whereby said second switch means is normally switched on and off repetitively to pulsively charge said capacitor with the output voltage of said DC source. .Iadd. 
     
     
       4.  A method of operating a wire-cutting EDM, capacitor-type pulse generator comprising the steps of: (a) charging a capacitor from a DC source, said capacitor being connected in series with a first switch means and a wire EDM gap, and said DC source having an ouptut voltage in excess of a predetermined level to charge said capacitor at an accelerated rate;   (b) generating a signal which is a function of capacitor voltage;   (c) upon said signal reaching said predetermined level, turning said first switch means into conduction to permit the charge on said capacitor to be discharged through said EDM gap; and   (d) upon said signal exceeding a preselected value, turning a second switch means connected in series between said DC source and said capacitor from a conductive state in which said capacitor is charged to a nonconductive state. .Iaddend. .Iadd.5. A method of operating a wire-cutting EDM, capacitor-type pulse generator, comprising the steps of:   (a) charging a capacitor from a DC source, said capacitor being connected in series with a first switch means and a wire EDM gap, and said DC source having an output voltage in excess of a predetermined level to charge said capacitor at an accelerated rate;   (b) generating a first signal which is a function of capacitor voltage;   (c) upon said first signal reaching said predetermined level, turning said first switch means into conduction to permit the charge on said capacitor to be discharged through said EDM gap;   (d) generating a second signal which is a further of wire EDM gap voltage; and   (e) upon said second signal exceeding a preselected value, turning a second switch means connected in series between said DC source and said capacitor from a conductive state in which said capacitor is charged to a nonconductive state. .Iaddend. .Iadd.6. A method of operating a wire-cutting EDM, capacitor-type pulse generator comprising the steps of:   (a) charging a capacitor from a DC source, said capacitor being connected in series with a first switch means and a wire EDM gap, and said DC source having an output voltage in excess of a predetermined level to charge said capacitor at an accelerated rate;   (b) sensing capacitor voltage and generating a signal which is a function of the sensed capacitor voltage;   (c) upon said signal reaching said predetermined level, turning said first switch means into conduction to permit the charge on said capacitor to be discharged through said EDM gap; and   (d) upon said signal exceeding a preselected value, turning a second switch means connected in series between said DC source and said capacitor from a conductive state in which said capacitor is charged to a nonconductive   
     
     
        state. .Iaddend. .Iadd.7.  A method of operating a wire-cutting EDM, capacitor-type pulse generator comprising the steps of: (a) charging a capacitor from a DC source, said capacitor being connected in series with a first switch means and a wire EDM gap, and said DC source having an output voltage in excess of a predetermined level to charge said capacitor at an accelerated rate;   (b) sensing capacitor voltage and generating a first signal which is a function of the sensed capacitor voltage;   (c) upon said first signal reaching said predetermined level, turning said first switch means into conduction to permit the charge on said capacitor to be discharged through said EDM gap;   (d) sensing wire EDM gap voltage and generating a second signal which is a function of the sensed wire EDM gap voltage; and   (e) upon said second signal exceeding a preselected value, turning a second switch means connected in series between said DC source and said capacitor from a conductive state in which said capacitor is charged to a nonconductive state. .Iaddend. .Iadd.8. A method of operating a wire-cutting EDM, capacitor-type pulse generator comprising the steps of:   (a) charging a capacitor from a DC source to impress a voltage across said capacitor, said capacitor being connected on the one hand in series with a first electronic switch means and a wire-EDM gap which together constitute a capacitor discharging circuit and being connected on the other hand in series with said DC source and a second electronic switch means which together constitute a capacitor charging circuit, said DC source having an output voltage in excess of a predetermined capacitor voltage charging level so that said capacitor is charged at an accelerated rate, said second switch means being closed for charging said capacitor;   (b) closing said first switch means when said voltage across said capacitor reaches said predetermined level in step (a) to provide a voltage across said wire-EDM gap; and   (c) opening said second electronic switch means in said capacitor charging circuit when said voltage across said wire-EDM gap in step (b) exceeds a preselected value. .Iaddend. .Iadd.9. The method of operating a wire-cutting EDM, capacitor-type pulse generator set forth in claim 8 wherein said second switch means is repetitively closed and opened by a first electronic timing means whereby said capacitor is pulsively charged.   
     
     
        .Iaddend. .Iadd.10.  The method of operating a wire-cutting EDM, capacitor-type pulse generator set forth in claim 4, 5, 6, 7, or 8 wherein the magnitude of said preselected value is greater than the magnitude of said predetermined level.