Experimental study of contact transition control incorporating joint acceleration feedback

Joint acceleration and velocity feedbacks are incorporated into a classical internal force control of a robot in contact with the environment. This is intended to achieve a robust contact transition and force tracking perform ance for varying unknown environments, without any need of adjusting the co ntroller parameters, A unified control structure is proposed for free motio n, contact transition, and constrained motion in view of the consumption of the initial kinetic energy generated by a nonzero impact velocity. The inf luence of the velocity and acceleration feedbacks, which are introduced esp ecially for suppressing the transition oscillation, on the postcontact trac king performance is discussed. Extensive experiments are conducted on the t hird joint of a three-link direct-drive robot to verify the proposed scheme for environments of various stiffnesses, including elastic (sponge), less elastic (cardboard), and hard (steel plate) surfaces. Results are compared with those obtained by the transition control scheme without the accelerati on feedback. The ability of the proposed control scheme in resisting the fo rce disturbance during the postcontact period is also experimentally invest igated.