Abstract: A method, controller and control system for controlling a robot that is used in concert with at least one other robot to perform an operation on one or more work objects. Each robot controller checks whether a common reference value is not acceptable, and if so, provides a signal for the robot to wait before proceeding to the next task. Each robot controller also checks whether the target object is in the correct position or not; and also checks whether or not another robot has stopped. If either another robot has stopped and/or if the work object is not in the right position, the robot waits.