Discharge machining apparatus

Claim 1

SPARK DISCHARGE MACHINING APPARATUS COMPRISING, IN COMBINATION, AN ELECTRODE AND WORKPIECE WHICH FORM A SPARK DISCHARGE GAP THEREBETWEEN, A SERVOMECHANISM RESPONSIVE TO A GAP DISCHARGE CONDITION NORMALLY TO FEED THE ELECTRODE IN RELATION TO THE WORKPIECE FOR NORMALLY MAINTAINING A WORKING GAP DISTANCE THEREBETWEEN AND FOR TEMPORARILY RETRACTING THE ELECTRODE IN RESPONSE TO A SHORTCIRCUIT CONDITION, THEREBY TO INTERRUPT CURRENT FLOW THROUGH THE GAP, AN ENERGY STORAGE CIRCUIT CONNECTED ACROSS THE GAP TO PRODUCE INTERMITTENT SPARK DISCHARGES THEREIN DURING NORMAL MACHINING CONDITIONS, AND MEANS TO DELIVER MACHINING ENERGY TO SAID STORAGE CIRCUIT INCLUDING A RECTIFIER HAVING AN ALTERNATING CURRENT INPUT, AND SATURABLE REACTOR MEANS IN SAID INPUT, INCLUDING A CONTROL COIL AND AN ENERGIZING CIRCUIT FOR SAID COIL CONNECTED TO THE SPARK DISCHARGE GAP FOR MAINTAINING THE REACTOR SUBSTANTIALLY SATURATED IN RESPONSE TO SAID NORMAL MACHINING CONDITIONS, SAID ENERGIZING CIRCUIT INCLUDING MEANS EXPEDITING DEENERIZATION OF SAID CONTROL COIL UPON REMOVAL OF ENERGIZATION THEREOF AS THE ELECTRODE IS BEING RETRACTED, IN RESPONSE TO A SHORT-CIRCUIT CONDITION OF SAID GAP, AND MEANS DELAYING REENERGIZATION OF SAID CONTROL COIL WHILE THE ELECTRODE IS FED BACK TO THE NORMAL WORKING GAP DISTANCE FROM THE WORKPIECE.