US Patent 10576576 Spot welding system

To provide a spot welding system capable of shortening a cycle time of spot welding. A robot controller measures a time between a transmission time of a welding command signal to a welding machine and a reception time of a welding completion signal, after determining completion of pressuring by a spot welding robot, and subtracts a predetermined welding time from the measured time, thereby calculating a communication delay time between the robot controller and the welding machine. A spot welding system advances transmission timing of the welding command signal and the welding completion signal by the calculated communication delay time.