Patent GB-658272-A (GB)
Title: Improvements in or relating to apparatus for controlling the energisation of a number of electro-responsive windings
IPC: B23K11/24
Filed: 1948-04-19
Abstract: 658,272. Switching systems for resistance welding. IGRANIC ELECTRIC CO., Ltd. April 19, 1948, No. 10764. Convention date, April 19, 1947. [Class 38 (iv)] A sequence of timed operations, such as are necessary in resistance-welding systems, is controlled by the timed sequential energization from an A.C. source of a plurality of electromagnetic switches, the windings of which are individually in series with a corresponding number of normally non-conducting discharge tubes across the source, each tube having a separate and adjustable timing circuit associated with its control grid and means being provided to initiate timing action in the several circuits in the desired sequence, whereby the switch windings are energized by conduction of the tubes in that sequence as the circuits time out. Each timing circuit comprises means for applying an alternating "turn on" voltage to the tube which is normally overcome by a D.C. hold-off " voltage obtained from a condenser shunted by a timing resistor and charged from the A.C. source through a rectifier, timed conduction of the associated tube being initiated by opening the charging circuit, whereupon the " hold-off " voltage eventually falls to an ineffective value at a rate determined by the time constant of the resistor-condenser combination. In the resistance welding system shown, closure of push-button 57 energizes relays 50a, 55a, thereby energizing (over contact 55d) a valveactuating coil 15b of a fluid-pressure system to cause electrode 12 to move into contact with the work and also energizing (over contact 50b and from a transformer 21) the anode circuits of timing tubes 27-29. The grid circuits of these tubes and of a further tube 26 receive A.C. bias from potentiometer 30-33 and negative hold-off bias from condensers 34-37 charged over rectifiers 51-54, so that the tubes are non-conducting. Upon energization of relay 50a, however, the charging circuit for condenser 34 is opened at contact 50c and the holdoff bias for tube 26 leaks away through resistor 42; relay 46a in the anode circuit of this tube thereupon responds, provided contacts 16b of a switch 16a responsive to pressure in the electrode-actuating cylinder 10 have closed. Contacts 46b actuate and close the ignition circuit of ignitrons 17, 18 in the primary circuit of the welding transformer 13 which becomes energized and remains so until the ignition circuit is opened at contacts 47b by response of a relay 47a in the anode circuit of tube 27, the associated timing condenser 35 discharging during this period through resistor 43 due to its charging circuit now being open at contacts 46c. In a similar manner relays 48a, 49a sequentially respond, the former terminating (at contacts 48b) an "after weld" period initiated by relay 47a and the latter deenergizing relays 50a, 55a over contact 49b to terminate the cycle of operations. If the pushbutton remains closed, so that relays 50a, 55a do not de-energize, the open contacts 48b prevent energization of 15b and a repetition of the cycle. The latter may be obtained by moving a change-over switch 56 to its other position to remove the short-circuit about contacts 49b.