Patent GB-752193-A (GB)
Title: Improvements in sequencing system for welding machines
IPC: B23K11/24
Filed: 1954-01-28
Abstract: 752,193. Control systems for resistance welding. WELDING RESEARCH, Inc. Jan. 28, 1954 [Feb. 18, 1953], No. 2587/54. Class 38 (4). A sequence timer for timing a series of operations, such as occur in resistance welding, comprises a plurality of commutating circuits, such as 10, 20 and 24, 32, energized in parallel and each timing one operation, the arrangement being such that only one circuit is in operation at a time and upon timing out puts into operation the following circuit. Each circuit comprises a switching valve, which allows energization of a resistor-capacitor timing circuit, and a discharge valve by which the capacitor-upon attainment of given voltage-is discharged through a transformer into the firing circuit of the next switching valve to initiate charging of the condenser of the following timing circuit. In the arrangement shown in Fig. 1, assuming the switching valve 10 to be conducting and the switching valve 24 to be non-conducting, closure of switch 42 allows condenser 44 to charge, at a rate dependent upon the setting of the potentiometer top 41 and the magnitude of resistor 46. When the condenser acquires sufficient voltage to break down valve 34 it discharges through transformer 31, the voltage pulse in the secondary winding 30 of which causes valve 24 to become conducting. Valve 10 is extinguished by a pulse passed by commutating condenser 55. Timing circuit 70, 72 now becomes effective and when the associated discharge valve 56 fires transformer 18 is pulsed to refire valve 10. The firing of valves 34, 56 may be synchronized with the mains voltage cycle by transformers 50, 66 connected in the grid circuits of these valves. Fig. 2 shows a complete timer for a resistance welder. Movement of a two-position manual switch to its first position closes relay X1 to effect energization of a relay 152 which causes the electrodes to engage the work, further movement of the switch to its second position then causing closure of relay contacts Y1, Y2. Valve 76 is conducting, in readiness to commence timing of the " squeeze " period when contacts A1 are closed in response to the pressure on the electrodes attaining a predetermined value. This timing period is terminated by conduction of the discharge valve 87 which, through transformer 95, triggers valves 97, 108 to cause energization of a " weld period " timing panel 112. Commutating condenser 99 extinguishes valve 76. The timing panel controls a circuit comprising cold cathode tubes 172-194 for accurately counting the number of current pulses supplied to the weld and which at the end of a preselected count delivers a firing pulse to valve 115 which extinguishes valves 97, 108 and which, in association with discharge valve 123, times the " hold " period. Conduction of 123 at the end of this period fires valve 131 to effect extinction of valves 115, 150, the latter causing the electrodes to disengage the work. If, however, switch 140, or foot-controlled contactor X2, is closed, valve 141 and its associated transformer 86 cause the timing cycle to repeat. The timing panel 112, when energized over valve 108, generates a square voltage wave which is differentiated by the circuit 160, 165 and applied to the trigger line 170 for the counting tubes 172-194 over rectifier 171 which removes the negative pulses. According to the number of current impulses required for the weld, a positive voltage, sufficient to fire the tube, is applied to a selected one of the counting tubes, so that there is a voltage drop across a resistor in its cathode lead, say the resistor 178. This voltage appears as positive bias on the grid of the next tube and prepares the tube for triggering by the next pulse on the line 170. The remainder of the tubes are similarly triggered in turn, the last providing an output pulse over transformer 201 for firing valve 115.