GB771263A - Improved timing apparatus particularly for electric welding machines - Google Patents

Abstract

771,263. Control systems for resistance welders. GENERAL ELECTRIC CO. June 14, 1955 [June 14, 1954], No. 17134/55. Class 38 (4). Timing apparatus for controlling the " weld " and " cool " periods in resistance welding comprises a valve 40 having connected to its grid a " weld" " timing circuit 52, 53, 56 which is charged up over rectifiers 84-86 when a valve 60 is rendered conducting by operation of an initiating switch 67. The voltage of condenser 53 now allows valve 40 to conduct, thereby energizing firing transformer 18 for ignitron 9, which conducts to initiate flow of welding current. Valve 41 is arranged to trail 40 and, through firing transformer 28, causes the other welding ignitron 10 to conduct. Conduction of valve 40 also energizes a transformer 73 which, in association with rectifiers 72, 82, 83 charges condensers 68, 69 of a " cool time circuit 68-70, the voltage on condenser 68 being then applied as negative bias to valve 60 which, consequently, becomes non-conducting and terminates charging of the " weld " time circuit. The condensers 52, 53 then discharge into one other at a rate determined by resistor 56 and eventually the voltage across 53 falls to the cut-off value of valve 40, which extinguishes and terminates flow of welding current. Timing circuit 68-70 now commences to time out, progressively reducing the bias on valve 60, which (provided switch 67 is maintained closed) eventually conducts to initiate another welding cycle. During the " weld " period the condensers 68, 69 of the " cool timing circuit receive charge at about only half full voltage due to the inclusion of a resistor 78 in the supply circuit to the charging transformer 73. The condensers are, however, changed to full voltage when valve 40 times out by a previously non-conducting valve 74 then becoming conducting and providing an alternative energization circuit for transformer 73. By this means the instant of initiation of the " cool " period is rendered independent of supply circuit voltage fluctuations. Specification 659,996 is referred to.