Proportional control for guidance system

Abstract

A guidance system for seeking, following, and maintaining the position of a welding apparatus with respect to a seam or joint to be welded by sensing changes in the surfaces, hereinafter called reference surfaces, at or adjacent to the seam. The system includes a probe adapted to detect and follow the reference surface(s) and to detect changes and deviations in the vertical and/or horizontal components of these surfaces, respectively. The torch of the welding apparatus is mounted upon and positioned by a motor-driven cross-slide providing both horizontal and vertical movement. The probe is mounted on the torch or on its own slide, which may be either on the torch or separate therefrom. Within the probe are two variable resistors, the resistance of each of which is changed by a displacement, horizontal or vertical as the case may be, of a probe shaft which engages and tracks upon the reference surfaces, either one or more angular surfaces having horizontal and vertical components (as in a V-joint) or a vertical and a horizontal surface (as in a lap joint). A voltage impressed upon each variable resistor is detected and applied, through an amplifier, to a trigger pulse generator, which generates pulses supplied to a silicon-controlled rectifier network through which power is supplied to the corresponding slide positioning motor. Variations in resistance in the respective resistor within the probe housing change the time of the pulses generated with respect to a reference phase of the applied voltage to supply a voltage to the positioning motor corresponding in magnitude and polarity to the deviation or change in the direction of the path being followed by the probe and welding apparatus. The motors are thereby enabled to cooperate to correct the position of the probe and torch, for both vertical and/or horizontal deviations and changes simultaneously and at speeds proportional to the respective rates of change of the path, both horizontally and/or vertically, and to apply necessary braking action for each correction for each direction in proportion to speed of correction. The invention also includes a circuit for disabling (deactivating, disconnecting or turning off) the motors, respectively, when the respective cross-slides reach the limits of their travel, respectively. The disabling circuit is unaffected in operation by electromagnetic radiation, noise, transients and other pulses in the circuit of which it is a part. The disabling circuit incorporates optical transistors controlled by optical diodes to which normally closed limit switches are connected. Opening of the limit switch, at the respective ends of travel of the respective cross-slides, permits current to flow through the optical diode to activate the transistor and disable the circuit and brake the corresponding positioning motors.