Arc gap current monitor circuit

Claim 2

In an electrical discharge machining apparatus wherein workpiece material is removed by periodic machining power pulses transferred between a tool electrode and a conductive workpiece across an arc gap, including an output first electronic control device operatively connected between a main power supply and said arc gap for providing periodic machining power pulses to said arc gap at predetermined ON-OFF times and frequencies, wherein the improvement comprises: an arc gap current monitor circuit having phase inverter stage means operatively connected between said main power supply and said arc gap; said phase inverter stage means including a second electronic control device having a control electrode and a pair of power electrodes; a first impedance component operatively connected in series circuit between said arc gap and said control electrode of said second electronic control device; a second impedance component operatively connected in series circuit between a first terminal of said main power supply and one of said power electrodes of said second electronic control device; and a third impedance component operatively connected in series circuit between said arc gap and the other power electrode of said second electronic control device; whereby the occurrence of a shorting condition in said arc gap will render said second electronic control device nonconductive.

Claim 3

The combination according to claim 1, including an electrical component operatively connected between said control electrode of said second electronic control device and said other power electrode of said second electronic control device, said electrical component having a substantially low impedance to the flow of electrons in a predetermined direction and having a substantially greater impedance to the flow of electrons in a direction opposite to that of said predetermined direction.

Claim 4

The combination according to claim 1, including: a third electronic control device operatively connected to said second electronic control device, and a fourth electronic control device operatively connected to said third electronic control device, whereby the occurrence of a shorting condition in said arc gap will render said second and third electronic control devices non-conductive and will render said fourth electronic control device conductive.

Claim 5

In an electrical discharge machining apparatus wherein workpiece material is removed by periodic machining power pulses transferred between a tool electrode and a conductive workpiece across an arc gap, including an output first electronic control device operatively connected between a main power supply and said arc gap for providing periodic machining power pulses to said arc gap at predetermined ON-OFF times and frequencies, wherein the improvement comprises: an arc gap current monitor circuit having phase inverter stage means operatively connected between said main power supply and said arc gap; said phase inverter stage means including a second electronic control device having a control electrode and a pair of power electrodes; a first impedance component operatively connected between said arc gap and said control electrodes of said second electronic control device; a second impedance component operatively connected between a first terminal of said main power supply and one of said power electrodes of said second electronic control device; a third impedance component operatively connected between said arc gap and the other power electrode of said second electronic control device; a third electronic control device operatively connected to said second electronic control device; a fourth electronic control device operatively connected to said third electronic control device; whereby the occurrence of a shorting condition in said arc gap will render said second and third electronic control devices non-conductive and will render said fourth electronic control device conductive; drive means operatively connected to the control electrode of said output first electronic control device for rendering said output first electronic control device alternately conductive and non-conductive; pulse means operatively connected to said drive means for operating said drive means with pulses of predetermined ON-OFF times; and coupling means operatively connected between said fourth electronic control device and said pulse means for coupling a predetermined voltage from said fourth electronic control device to said pulse means, when said fourth electronic control device has been rendered conductive, to cause said pulse means to have a substantially long OFF time.

Claim 6

In an electrical discharge machining apparatus wherein workpiece material is removed by periodic machining power pulses transferred between a tool electrode and a conductive workpiece across an arc gap, including an output first electronic control device operatively connected between a main power supply and said arc gap for providing periodic machining power pulses to said arc gap at predetermined ON-OFF times and frequencies, wherein the improvement comprises: an arc gap current monitor circuit having phase inverter stage means operatively connected between said main power supply and said arc gap; said phase inverter stage means including a second electronic control device having a control electrode and a pair of power electrodes; a first impedance component operatively connected between said arc gap and said control electrodes of said second electronic control device; a second impedance component operatively connected between a first terminal of said main power supply and one of said power electrodes of said second electronic control device; a third impedance component operatively connected between said arc gap and the other power electrode of said second electronic control device; a third electronic control device operatively connected to said second electronic control device; a fourth electronic control device operatively connected to said third electronic control device; whereby the occurrence of a shorting condition in said arc gap will render said second and third electronic control devices non-conductive and will render said fourth electronic control device conductive; drive means operatively connected to the control electrode of said output first electronic control device for rendering said output first electronic control device alternately conductive and non-conductive; pulse means operatively connected to said drive means for operating said drive means with pulses of predetermined ON-OFF times; and coupling means operatively connected between said fourth electronic control device and said pulse means for coupling a predetermined voltage from said fourth electronic control device to said pulse means, when said fourth electronic control device has been rendered conductive, to cause said pulse means to have a substantially long OFF time.

Claim 7

The combination according to claim 4, wherein said coupling means includes a variable potentiometer.

Claim 8

The combination according to claim 5, wherein said main power supply is a variable power supply, and including a low voltage switch operatively connected between a predetermined point on said variable potentiometer and one of the power electrodes of said fourth electronic control device, whereby during low voltage operation of said main power supply said power electrode of said fourth electronic control device is connected to said predetermined point of said variable potentiometer, and during high voltage operation of said main power supply said power electrode of said fourth electronic control device is automatically switched to the high voltage end of said variable potentiometer.

Claim 9

The combination according to claim 4, wherein said pulse meaNs comprises a multivibrator having a pair or electronic control devices biased for alternate operation, and a pair of resistance-capacitance networks each operatively connected to a control electrode of one of said pair of electronic control devices, respectively; a diode element operatively connected in the resistance portion of one of said resistance-capacitance networks; and said coupling means being operatively connected to one terminal of said diode element to feed a predetermined voltage to said multivibrator through said fourth electronic control device when said fourth electronic control device has been rendered conductive in response to a shorting condition between said tool electrode and said conductive workpiece.

Claim 10

The combination according to claim 7, wherein said first, second and third impedance components are each a resistance element, and wherein the trigger signal for said arc gap current monitor circuit is not taken directly from said arc gap, and no resistance-capacitance or diode coupled signal is discharged into said arc gap, and including a substantially high resistance element connected to the other terminal of said diode element, which high resistance element in conjunction with the capacitance of said one resistance-capacitance network provides a long time constant to give said multivibrator a long OFF time.

Claim 11

The combination according to claim 1 including: drive means operatively connected to the control electrode of said output first electronic control device for rendering said output first electronic control device alternately conductive and non-conductive; a multivibrator operatively connected to said drive means for supplying said drive means with a series of substantially rectangular wave pulses; said multivibrator having a pair of electronic control devices biased for alternate operation; a pair or resistance-capacitance networks each operatively connected to a control electrode of one of said pair of electronic control devices, respectively; and means operatively connected to said multivibrator for independently varying the interpulse period and the pulse width of said series of substantially rectangular wave pulses generated by said multivibrator.

Claim 12

In an electrical discharge machining apparatus wherein workpiece material is removed by periodic machining power pulses transferred between a tool electrode and a conductive workpiece across an arc gap, including an output first electronic control device operatively connected between a main power supply and said arc gap for providing periodic machining power pulses to said arc gap at predetermined ON-OFF times and frequencies, wherein the improvement comprises: an arc gap current monitor circuit having phase inverter stage means operatively connected between said main power supply and said arc gap; said phase inverter stage means including a second electronic control device having a control electrode and a pair of power electrodes; a first impedance component operatively connected between said arc gap and said control electrodes of said second electronic control device; a second impedance component operatively connected between a first terminal of said main power supply and one of said power electrodes of said second electronic control device; a third impedance component operatively connected between said arc gap and the other power electrode of said second electronic control device; and wherein said second and third impedance components are resistance elements having substantially equal values of resistance.

Claim 13

In an electrical discharge machining apparatus wherein workpiece material is removed by periodic machining power pulses transferred between a tool electrode and a conductive workpiece across an arc gap, including an output first electronic control device operatively connected between a main power supply and said arc gap for providing periodic machining power pulses to said arc gap at predetermined ON-OFF times and frequencies, wherein the improvement comprises: an arc gap current monitor circuit having phase inverter stage means operatively connected between said main power supply and said arc gap; said phase inverter stage means including a second electronic control device having a control electrode and a pair of power electrodes; a first impedance component operatively connected between said arc gap and said control electrodes of said second electronic control device; a second impedance component operatively connected between a first terminal of said main power supply and one of said power electrodes of said second electronic control device; a third impedance component operatively connected between said arc gap and the other power electrode of said second electronic control device; and wherein said second and third impedance components are resistance elements having substantially equal values of resistance.