Force synchronization of multiple robot manipulators with uncertain contact stiffness

With the rapid advancements of robot technology, robots have found more applications in new areas e.g. service and health-care as well as in traditional domains like industry and aerospace. In these situations, it may not be sufficient/feasible to consider robot as mechanism of infinite rigidity and thus solely focus on its motion control. More and more research efforts have been devoted to the force interaction of robot with its working environment or object under manipulation. Compared to the topic of motion synchronization of multi-robot system which has proved to be efficient in industrial production processes and found its applications in various areas such as formation control of mobile robots etc, force synchronization of multiple robot system was not explored in literature until the recent work [1] where constant force synchronization of robot manipulators is addressed. In this study, we further explore the more challenging issue of force synchronization with time-varying desired force command trajectory. The main difficulty lies in the unknown contact stiffness during the interaction task, and adaptive design technique has been resorted to for tackling this problem. Both force tracking error of single manipulator and mutual coupling errors between each pair of the whole robotic system are guaranteed to converge through Lyapunov analysis. Simulation studies confirm the efficiency of the developed control strategy with uncertain contact stiffness.