Eddy current probe subsystem

Claim 1

In a machine for arc welding magnetically permeable work pieces, comprising a tubular torch powered for movement over and along a gap-type joint defined by two laterally spaced work pieces, and a consummable wire electrode feedable axially through the torch for fusion and deposition in the defined joint: the improvement comprising means for generating electric signals representing the position of the torch relative to the gap-type joint, said signal-generating means including a sleeve (88) encircling the torch; said torch and sleeve having meshed threads (at 86) whereby the sleeve is adjustable in the direction of the torch axis; a tube (80) freely encircling said sleeve so that the sleeve can turn on the torch without transmitting a rotary force to the tube; two motor-support arms (74 and 78) affixed to said tube; key means (at 82, 84) for keying the tube to the torch, whereby the tube and associated support arms can be adjusted axially parallel to the torch axis; a barrel (64) freely encircling said tube; a probe mount arm (62) extending from the barrel in the advance path taken by the torch; a probe (44) carried by the mount arm so that a sensor surface of the probe is in a plane slightly spaced from the plane of the work pieces; means for oscillating the probe back and forth across the advance path to be taken by the torch, comprising a first reversible motor (72) mounted on one of the aforementioned support arms, aligned pulleys (70 and 66) carried by the first motor's shaft and barrel (64), and a belt (68) trained around the aligned pulleys; means for adjusting the probe parallel to the torch axis comprising a second motor (76) mounted on the other support arm, aligned pulleys (94 and 90) carried by the second motor's shaft and aforementioned tube (88), and a second belt (92) trained around the last-mentioned pulleys; said probe (44) including a first sensor coil (50) energized by an A.C. source so that an impedance signal of varying intensity is generated in the sensor coil during each oscillatory pass of the probe across the gap between the work pieces, and a second compensator coil (52) located approximately the same distance from the torch as the first coil so that each coil is similarly influenced by magnetic fields generated by the torch arc; said compensator coil being oriented within the probe so that it is substantially further away from the work pieces than the sensor coil.