Patent ID: 7868266

Claim:
A spot welding system comprising: a welding gun provided with an electrode pair actuated, to open or close, by a servo-motor as a drive source; a robot carrying either one of said welding gun and a workpiece to be welded, and operating to change relative positions and orientations of said welding gun and said workpiece; and a gun motion controller controlling said servo-motor to actuate said electrode pair of said welding gun to open or close; said gun motion controller comprising: a motion commanding section outputting a motion command to said servo-motor in accordance with a speed set-value designating a closing speed of said electrode pair, so as to allow a pressurizing force exerted by said electrode pair on said workpiece to converge into a previously designated force target-value: and a set-value adjusting section automatically adjusting said speed set-value given to said motion commanding section to an appropriate value; said set-value adjusting section comprising: a force-data obtaining section obtaining force data representing, in a time-series manner, said pressurizing force generated in said electrode pair when said servo-motor actuates said electrode pair to close in accordance with said motion command from said motion commanding section; and an appropriate-value computing section determining said appropriate value of said speed set-value based on pre-convergence transient data in said force data obtained by said force-data obtaining section, wherein said appropriate-value computing section comprises: a representative-value calculating section calculating, from said pre-convergence transient data in said force data obtained by said force-data obtaining section, a representative value of a response pattern of said pre-convergence transient data; a comparing and judging section comparing said representative value calculated by said representative-value calculating section with a representative-value tolerable range previously prepared with reference to said force target-value and judging that, when said representative value is included within said representative-value tolerable range, said speed set-value is said appropriate value and, when said representative value is not included within said representative-value tolerable range, said speed set-value is an inappropriate value; and a regulating section acting, based on a judgment of said comparing and judging section, to terminate, when said speed set-value is judged as said appropriate value, an automatic adjusting process for said speed set-value, and to determine, when said speed set-value is judged as said inappropriate value, a second speed set-value different from said speed set-value judged as said inappropriate value and give said second speed set-value to said motion commanding section.