Gap sensing circuit for electrical discharge machining apparatus

Claim 2

In an electrical discharge machining power supply having an electronic output switch connected to the output of a pulse generator and operatively connected to a DC source and the gap for providing machining power pulses thereto, a gap short circuit protection system comprising: a normally non-conductive electronic switch having its control electrode operatively connected with the gap for triggering into conduction responsive to abnormal gap voltage level and providing an output signal representative of gap short circuit; and a gating means responsive to said signal for passing a series of machining power pulses from said pulse generator during gap short circuit condition, said pulses of said series of the same duty cycle and frequency as the normal machining power pulses supplied to the gap, said gating means further operable to interrupt machining power pulses between each different series for a relatively long interval for the continued duration of the gap short circuit condition.

Claim 3

The combination as set forth in claim 1 wherein said electronic switch for providing said output signal responsive to gap short circuit comprises a field effect transistor having its gate coupled to the gap terminal a series resistor.

Claim 4

In an electrical discharge machining power supply having an electronic output switch connected to the output of a pulse generator and operatively connected to a DC source and the gap for providing machining power pulses thereto, a gap short circuit protection system comprising: a normally non-conductive electronic switch having its control electrode operatively connected with the gap for triggering into conduction responsive to abnormal gap voltage level and providing an output signal representative of gap short circuit; and a gating means responsive to said signal for passing a series of machining power pulses from said pulse generator during gap short circuit condition, said pulses of said series of the same duty cycle and frequency as the normal machining power pulses supplied to the gap, said gating means further operable to interrupt machining power pulses between each different series for a relatively long interval for the continued duration of the gap short circuit condition, said electronic switch for providing said output signal responsive to gap short circuit comprising a field effect transistor having its gate coupled to a gap terminal through a series resistor, said field effect transistor having one of its principal electrodes operatively connected through an inverter to a clear input of a following flip-flop stage intermediate it and said gating means, said flip-flop further having an input connected through a one-shot multivibrator to the pulse generator output for changing the flip-flop state for a predetermined time duration less than the normal machining power pulse on-off time, said field effect transistor operable to provide a clear signal to said flip-flop in the absence of abnormal gap voltage level.

Claim 5

In an electrical discharge machining power supply having an electronic output switch connected to the output of a pulse generator and operatively connected to a DC source and the gap for providing machining power pulses thereto, a gap short circuit protection system comprising: a normally non-conductive electronic switch having its control electrode operatively connected with the gap for triggering into conduction responsive to abnormal gap voltage level and providing an output signal representative of gap short circuit; and a gating means responsive to said signal for passing a series of machining power pulses from said pulse generator during gap short circuit condition, said pulses of said series of the same duty cycle and frequency as the normal machining power pulses supplied to the gap, said gating means further operable to interrupt machining power pulses between each different series for a relatively long interval for the continued duration of the gap short circuit condition, said electronic switch for providing said output signal responsive to gap short circuit comprising a field effect transistor having its gate coupled to a gap terminal through a series resistor, said field effect transistor having one of its principal electrodes operatively connected through an inverter to a clear input of a following flip-flop stage intermediate it and said gating means, said flip-flop further having an input connected through a one-shot multivibrator to the pulse generator output for changing the flip-flop state for a predetermined time duration less than the normal machining power pulse on-off time, said field effect transistor operable to provide a clear signal to said flip-flop in the absence of abnormal gap voltage level.

Claim 6

The combination as set forth in claim 1 wherein the pulse generator is of the free-running type and said gating means is connected intermediate the output of the pulse generator and the control electrode for said electronic output switch.

Claim 7

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto comprising: a gap short circuit protection system for extending pulse off-time responsive to gap short circuit, said system comprising a plurality of gates connected in cascade intermediate the output of said pulse generator and the control electrode of said electronic output switch; and a gap voltage sensing network for providing a signal to said gates, said sensing network enabled in phase with each machining power pulse for a time period of lesser duration than normal pulse on-time.

Claim 8

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto comprising: a gap short circuit protection system for extending pulse off-time responsive to gap short circuit, said system comprising a plurality of gates connected in cascade intermediate the output of said pulse generator and the control electrode of said electronic output switch; and a gap voltage sensing network for providing a signal to said gates, said sensing network enabled in phase with each machining power pulse for a time period of lesser duration than normal pulse on-time.

Claim 9

The combination as set forth in claim 5 wherein said gates are connected intermediate the output of said free-running pulse generator and an intermediate drive stage, said drive stage having its output connected to the control electrode of said electronic switch.

Claim 10

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto, comprising: a gap short circuit protection system for extending machining power pulse off-time responsive to gap short circuit condition; a sensing means including an electronic switch having its control electrode operably connected to the gap for providing an output signal responsive to abnormal gap voltage swing; and electronic-output a gating means coupled intermediate said pulse generator and the electronic output switch, said gating means connected to said electRonic switch output signal and operable to interrupt a predetermined number of pulses from said pulse generator responsive to said signal.

Claim 11

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto, comprising: a gap short circuit protection system for extending machining power pulse off-time responsive to gap short circuit condition; a sensing means including an electronic switch having its control electrode operably connected to the gap for providing an output signal responsive to abnormal gap voltage swing; and electronic-output a gating means coupled intermediate said pulse generator and the electronic output switch, said gating means connected to said electRonic switch output signal and operable to interrupt a predetermined number of pulses from said pulse generator responsive to said signal.

Claim 12

The combination as set forth in claim 7 wherein said sensing means including an electronic switch comprising an FET transistor having its gate coupled to the negative terminal of the gap through a series resistor, said FET transistor operable to provide said output signal in the event the return to normal negative voltage level of said terminal does not occur within a period less than the normal machining power pulse on-time.

Claim 13

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto, comprising: a gap short circuit protection system for extending machining power pulse off-time responsive to gap short circuit condition; a sensing means including an electronic switch having its control electrode operably connected to the gap for providing an output signal responsive to abnormal gap voltage swing; a gating means coupled intermediate said pulse generator and the electronic output switch, said gating means connected to said electronic switch output signal and operable to interrupt a predetermined number of pulses from said pulse generator responsive to said signal; said sensing means including an electronic switch comprising an FET transistor having its gate coupled to the negative terminal of the gap through a series resistor, said FET transistor operable to provide said output signal in the event the return to normal negative voltage level of said terminal does not occur within a period less than the normal machining power pulse on-time; and an inverter and a flip-flop connected intermediate the output of said FET and said gating means, said FET transistor further having its output connected to the clear input of said flip-flop, said flip-flop enabled in phase with each machining power pulse through one-shot multivibrator connected intermediate said flip-flop and the output of said free-running pulse generator.

Claim 14

In an electrical discharge machining power supply having a free-running pulse generator and an electronic output switch coupled to the output of said pulse generator and connected to the gap for providing machining power pulses of preset frequency and on-off time thereto, comprising: a gap short circuit protection system for extending machining power pulse off-time responsive to gap short circuit condition; a sensing means including an electronic switch having its control electrode operably connected to the gap for providing an output signal responsive to abnormal gap voltage swing; a gating means coupled intermediate said pulse generator and the electronic output switch, said gating means connected to said electronic switch output signal and operable to interrupt a predetermined number of pulses from said pulse generator responsive to said signal; said sensing means including an electronic switch comprising an FET transistor having its gate coupled to the negative terminal of the gap through a series resistor, said FET transistor operable to provide said output signal in the event the return to normal negative voltage level of said terminal does not occur within a period less than the normal machining power pulse on-time; and an inverter and a flip-flop connected intermediate the output of said FET and said gating means, said FET transistor further having its output connected to the clear input of said flip-flop, said flip-flop enabled in phase with each machining power pulse through one-shot multivibrator connected intermediate said flip-flop and the output of said free-running pulse generator.