DC RESISTANCE WELDING APPARATUS

摘要

A DC resistance welding apparatus having a welding gun for sandwiching workpieces to be welded therebetween. The apparatus has a power supply unit which includes a converter, an inverter, a welding transformer, and a rectifier. The power supply unit supplies a welding current produced from the rectifier to the welding gun. A detector is provided for producing a pulse signal having a leading edge and a trailing edge. The pulse signal corresponds to an output waveform from the inverter. A pulse signal edge detector is provided for detecting and holding current signals corresponding to the leading and trailing edges of the pulse signal. A control is provided for producing a control signal to enable the pulse signal edge detector. A calculator is provided for producing a logarithmic signal from the current signals. The logarithmic signal is indicative of a change in a resistance of the workpieces when the welding current flows therethrough, produced by the pulse signal edge detector and for applying the logarithmic signal to the control. The control is provided to control a flow of current to the welding gun in response to the logarithmic signal. .