Control of moment and orientation for a robot manipulator in contact with a compliant environment

This work is aimed at studying the problem of controlling the moment and the orientation of a robot manipulator whose end effector is in contact with a compliant environment. Differently from classical operational space formulations, a geometrical approach is pursued where orientation displacements are described in terms of unit quaternions. Regulation to a constant desired moment and tracking of a time-varying desired orientation trajectory is achieved, and the convergence of the closed-loop system is analyzed. Simulation results for a six-joint industrial robot are developed and an experimental test is carried out to demonstrate the effectiveness of the proposed approach in a practical contact task.