Parallel force/position control with stiffness adaptation

In the framework of parallel force/position control for a robot manipulator in contact with a compliant environment, a new scheme is proposed which is aimed at controlling the end-effector force in the face of uncertainty on the surface stiffness. The controller is of inverse dynamics type with a force feedforward action. Adaptation to unknown stiffness is achieved by resorting to a suitable estimate update law driven by the force error. Tracking of both position along the unconstrained directions and force along the constrained direction is ensured. Experimental results on an industrial robot with open control architecture are presented.