Patent ID: 7600435

Claim:
A method of determining deterioration of pressurizing performance of a spot welding gun which has a movable side electrode tip moved by driving force of a servo motor and a fixed side electrode tip in opposition to said movable side electrode tip and which carries out welding of a work piece under pressurized state between said movable side electrode tip and said fixed side electrode tip, said method comprising: obtaining reference data that reflect a dynamic state of said servo motor when said movable side electrode tip is moved in a straight line in a predetermined operational mode without bringing said movable side electrode tip into contact with said work piece in the case where said movable side electrode tip is operated normally and said work piece is pressurized by a specified pressurizing force; performing data processing on said reference data to extract a reference characteristic value to be referenced when determining deterioration of pressurizing performance of said spot welding gun; obtaining diagnostic data that reflect a dynamic state of said servo motor when said movable side electrode tip is moved in said operational mode without bringing said movable side electrode tip into contact with said work piece in the case where a operational state of said movable side electrode tip changes and said work piece is no longer pressurized by said specified pressurizing force, in the same way as in the case where said movable side electrode tip is operated normally; performing data processing on said diagnostic data to extract a diagnostic characteristic value to be provided in order to determine deterioration of pressurizing performance of said spot welding gun; and, determining deterioration of pressurizing performance of said spot welding gun based on said reference characteristic value and said diagnostic characteristic value.