Capacitance discharge stud welding apparatus

Claim 1

CAPACITANCE DISCHARGE STUD WELDING APPARATUS COMPRISING, IN COMBINATION, MEANS FOR HOLDING A STUD AND MOUNTING SAID STUD INTO CONTACT WITH A WORKPIECE TO WHICH SAID STUD IS TO BE WELDED; A CAPACITOR CHARGING CIRCUIT, INCLUDING A CAPACITOR, A SOURCE OF DIRECT CURRENT FOR CHARGING SAID CAPACITOR, AND A SWITCH FOR OPENING THE CHARGING CIRCUIT BETWEEN SAID CAPACITOR AND SAID SOURCE OF DIRECT CURRENT; A WELDING CIRCUIT, INCLUDING SAID CAPACITOR CONNECTED BETWEEN THE FIRST-MENTIONED MEANS FOR HODLING SAID STUD AND A GROUND FOR SAID WORKPIECE; AND A CONTROL CIRCUIT FOR CONTROLLING THE CHARGING OF SAID CAPACITOR AND FOR AUTOMATICALLY RENDERING SAID FIRSTMENTIONED MEANS OPERATIVE TO MOVE SAID STUD INTO CONTACT WITH SAID WORKPIECE TO WELD SAID STUD TO SAID WORKPIECE WHEN THE CHARGE ON SAID CAPACITOR REACHES A PREDETERMINED VALUE, SAID CONTROL CIRCUIT COMPRISING, CONNECTED IN SERIES, SAID CAPACITOR, A RELAY OPERATIVE BY CURRENT FROM SAID CAPACITOR TO OPEN SAID SWITCH AND THEN RENDER SAID FIRST-MENTIONED MEANS OPERATIVE, A ZENER DIODE FOR PASSING CURRENT FROM SAID CAPACITOR TO SAID RELAY TO OPERATE THE LATTER WHEN THE VOLTAGE ACROSS SAID DIODE REACHES THE PREDETERMINED CRITICAL VOLTAGE THEREOF, AND A RESISTANCE VARIABLE FOR DETERMINING THE CHARGE ON SAID CAPACITOR AT WHICH SAID ZENER DIODE PASSES CURRENT TO SAID RELAY.