Welding apparatus and control system therefor

Abstract

A resistance-type welder employing a pulsed power supply and a pair of opposed electrodes between which a workpiece may be clamped under pressure, includes a microcomputer based control system for allowing precise selection and control of welding sequences such as the duration during which the workpiece is clamped, the duration during which current is supplied to the electrodes and the duration during which the workpiece remains clamped between the electrodes after current flow is terminated. A plurality of switchable input devices allows data corresponding to a plurality of process variables to be input to a random access memory. A central processor enabled by a manually operable control switch produces control signals for operating a control and firing circuit in accordance with programmed instructions and the data stored in the random access memory in order to control each step in a welding cycle for precise time periods. A sensing circuit detects the level of power supply line voltage and inhibits operation of the central processor when the line voltage falls below a prescribed level. Opto-electrical switches connected to the input devices isolate sensitive logic circuits from spurious input signals. The control circuit also selectively operates a solenoid controlled, hydraulic cylinder for causing the electrodes to clamp the workpiece therebetween.