Impedance control of cooperative manipulators

The goal of this paper is the application of a geometrically consistent impedance concept to control a multi-arm system. It is assumed that a common rigid object is rigidly grasped by the manipulators in the system. In order to avoid large internal forces, a six-DOF impedance is imposed at each end-effector. Moreover, a six-DOF impedance behaviour is enforced at the object level to confer a compliant behavior when interaction with the external environment occurs. Geometric consistency is ensured thanks to the use of the unit quaternion to describe object frame orientation. The overall control scheme is derived according to an inverse dynamics strategy with adoption of an inner motion loop for each manipulator, providing robustness to unmodeled dynamics and disturbances. Simulation results are presented to show the applicability of the technique to cooperative manipulation tasks involving interaction with environment.