Abstract: A capacitor type welding power unit incorporates a constant-current charging control circuit which serves to control a charging current being supplied to a capacitor so as to be substantially constant during the charging. By such a control circuit, which typically performs a thyristor firing control, the charging voltage of the capacitor is made to follow a reference signal, which is preferably set to change linearly with time, and it reaches a preset target value in a predetermined time regardless of fluctuations in the supply voltage. Furthermore, such a control circuit enables the capacitor to be directly connected to the output terminals of a rectifier circuit with no charging resistor being provided so as to reduce resistance heating and so as to lower power consumption in charging the capacitor.

Abstract: Disclosed is an invertor type DC welding machine incorporating constant-voltage control to assure a high and reliable quality of weld. The pulse width of the high-frequency output of the invertor circuit is controlled at the invertor switching rate by the constant-voltage control on a feedback loop basis in which a DC weld voltage applied to the workpieces to be welded between electrodes is detected and is compared with the value of a reference weld voltage to produce an error signal for controlling the operation of the invertor circuit, so that the DC weld voltage is maintained constant regardless of variations in the resistance of the portion to be welded during a welding operation. A timing system is further provided which momentarily monitors the change in the resistance between electrodes to terminate the welding operation at an optimum time after a nugget is produced in the porton to be welded.

Abstract: Disclosed is an inverter type DC welding machine incorporating constant-power control to assure a high and reliable quality of weld. The pulse width of the high-frequency output of the inverter circuit is controlled at the inverter switching rate by the constant-power control on a feedback loop basis in which the value of a weld power actually supplied to the portion to be welded between electrodes is computed and the computed value is compared with the value of a reference weld power to produce an error signal for controlling the operation of the inverter circuit, so that the actual weld power is maintained constant regardless of variations in the resistance of the portion to be welded during a welding operation.

Abstract: Disclosed is an user interface with a resistance welding control which provides a visual presentation of character data unlikely to lead misinterpretation on user's part on a frame-by-frame basis using a menu and conversation system and can handle as many welding schedules as there are with a single unit. Memory means stores character data so as to form different frames for predetermined item. In respone to certain user's request, any one of the frame is immediately called upon display means to that the user may enter necessary data of welding conditions associated with the selected item. While being visually presented on the screen, the entered data will be written into the memory means as part of the selected item.