Collaboration of multiple mobile manipulators with compliance based Leader/Follower approach

Cooperative robotic manipulation is a promising industrial technology that has been attracting much research attention. However most existing control methods for this goal require either online force sensing or the exact parameters of the robot, which is usually difficult and expensive. In this paper, two mobile manipulators are utilised to verify a simple cooperative manipulation control scheme. The mobile platforms track offline designed trajectories in order to maintain a formation, while the robotic arms holding a rigid object on top convey compliant behaviours so that the internal force likely to be caused by the motion error of the platforms is suppressed. The dual-arm control is in a Leader-Follower structure and the compliance feature is achieved with a classic PD controller with gravity compensation, easy to implement in industrial application. The effectiveness of the control system is exhibited in experiments.