Independent force and position control for cooperating manipulators handling an unknown object and interacting with an unknown environment

This paper presents a unified framework for system design and control in cooperative robotic systems. It introduces a highly generalized cooperative system configuration that involves any number of manipulators grasping a rigid object in contact with a deformable working surface whose real physical parameters are unknown. The dynamics of the closed chain mechanism are expressed based on the object׳s center of mass (CoM), and different robust controllers are designed for position and force control subspaces. The position controller is composed of a sliding mode control term, and it involves the position and velocity feedback of an end-effector, while the force controller is developed based on the highest derivative in feedback methodology. The force controller does not use any derivation of the force signal or internal force controller induced in the system, and it appears to be suitable for practical implementation. Using a Lyapunov stability approach, the controller is proven to be robust with varying system dynamics. The position/orientation and the force errors are also demonstrated to asymptotically converge to zero under such conditions. The simulation results for two-joint arms moving a rigid object are presented to validate the theoretical results.