Method of and device for setting reference position for servo spot welding gun

摘要

A method of and device for automatically setting and updating a reference position of a welding tip of a servo spot welding gun to automatically compensate displacement of a distal end of a welding tip by abrasion thereof. A movable welding tip is moved towards a stationary welding tip to press the stationary welding tip until an estimated disturbance load reaches a fist threshold, and then moved in reverse direction away from the stationary welding tip until the disturbance load is reduced to a second threshold. The position of the movable welding tip when the disturbance load is reduced to the second threshold is set and updated as the reference position of an axis of the movable welding tip. The first threshold is set to be greater than a frictional force exerted on the axis of the movable welding tip in the motion towards the stationary welding tip, and the second threshold is set to be equivalent to the frictional force. The above setting and updating of the reference position is performed in cycles of spot welding operations to compensate the abrading of the welding tip. Since the reference position is automatically set and updated to compensate the abraded amount of the welding tip, the distal end of the movable welding tip is constantly positioned to a predetermined position for applying a predetermined pressure to the workpiece.