Electric power supply apparatus for electric discharge machining

Claim 1

ELECTRIC DISCHARGE MACHINING APPARATUS COMPRISING, IN COMBINATION WITH A MACHINING ELECTRODE AND BASE MEANS ADAPTED TO PRESENT A METAL WORKPIECE IN ELECTRIC SPARK DISCHARGE RELATIONSHIP TO SAID ELECTRODE SEPARATED THEREFROM BY A SPARK GAP, A VOLTAGE SOURCE INCLUDING A STORAGE CAPACITANCE CONNECTED BETWEEN SAID ELECTRODE AND WORKPIECE AND MEANS TO CHARGE SAID CAPACITANCE TO PREDETERMINED MACHINING VOLTAGE THROUGH AN IMPEDANCE, THEREBY TO CREATE INTERMITTENT PRIMARY SPARK DISCHARGE IMPULSES BETWEEN THE ELECTRODE AND WORKPIECE, THE TRANSIENT VOLTAGE ACROSS SAID GAP DROPPING BY A SUBSTANTIALLY GREATER AMOUNT WHEN A SHORT CIRCUIT DEVELOPS ACROSS SAID GAP DURING A DISCHARGE IMPULSE THAN DURING OTHER, NORMAL DISCHARGE IMPULSES, AND SEPARATE CIRCUIT MEANS ALSO CONNECTED ACROSS SAID GAP AND SELECTIVELY RESPONSIVE TO SAID GREATER VOLTAGE DROP TO APPLY SECONDARY SPARK DISCHARGE VOLTAGE IMPULSES ACROSS THE ELECTRODE AND WORKPIECE SUBSTANTIALLY ONLY IN RESPONSE TO SUCH GREATER VOLTAGE DROPS, THEREBY TO CLEAR THE SHORT-CIRCUIT CONDITION BY THE ADDED DISCHARGE ENERGY OF SAID SECONDARY IMPULSES WITHOUT ADDING SUCH ENERGY TO NORMAL DISCHARGE IMPULSES.