Spot welding system and method of controlling pressing force of spot welding gun

Abstract

A spot welding system using a spot welding gun having a servomotor for driving welding tips capable of suppressing variation of pressing force due to influence of heat generated by welding current to obtain an uniform pressing force. A difference between the temperature T detected by a temperature sensor and an initial temperature T0 is multiplied by a coefficient A to obtain a pressing force compensation amount α. A pressing force d estimated by an observer is subtracted from the compensated command pressing force p′ and an obtained difference is multiplied by a constant K2 to obtain a torque command (current command) τ for driving the servomotor to press the objects by the welding tips. Since the commanded pressing force is compensated in accordance with the temperature, a constant and stable pressing force is produced without influence of the temperature variation.

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