Welding machine with automatic seam tracking

Claim 1

An automatic tracking welding machine, comprising: (a) an electrical arc generating welding torch (3) movably mounted relative to two objects (5) to be welded together and disposed opposite a weld line gap (10) defined by and between said objects; (b) a pair of magnetic detectors (6a, 6b) for detecting magnetic flux exclusively generated in the objects by the electrical arc current and leaking from said gap; (c) means (7, 40, 13) for rotatably mounting said detectors on a circle coaxial with said welding torch and circumferentially spaced from each other; (d) drive means (15) for rotating said magnetic detectors via said mounting means; (e) a control circuit (100) for producing and applying a drive signal to said driving means in response to output signals from said magnetic detectors to rotate said detectors to a centered position flanking the gap whereat their output signals are equal; (f) a rotary encoder (16) coupled to the drive means for producing an output proportional to the angle of rotation thereof; and (g) means for: (1) determining x and y coordinates of the centered detectors position on the basis of the encoder output and the radial distance between the torch and the detectors, and (2) displacing said welding torch to said determined coordinates such that said welding torch tracks the weld line gap, wherein said control circuit includes a comparator circuit (101) for comparing the output signals of said detectors, and a velocity instruction circuit (102, 103) responsive to the output of said comparator circuit for producing a first drive signal to drive said detectors at a predetermined high velocity in a direction to decrease any detector output difference when said difference exceeds a predetermined value, and a second drive signal to drive said detectors at a lower velocity corresponding to said difference when said difference is smaller than said predetermined value.