Improving tracking accuracy of a MIMO state feedback controller for elastic joint robots

In this paper a control scheme is addressed to improve the tracking accuracy of flexible joint robots without replacing the structure of a MIMO state feedback controller which is used effectually with the DLR medical robots. By using the desired position, the new desired link torque, as well as their derivatives the effects of nonlinear dynamics are compensated and the tracking accuracy is thereby increased. Hereby, the new desired link torque takes the whole rigid body dynamics into account, not only the friction and gravitation compensation terms. A stability analysis based on the Lyapunov theory and Barbalat´s lemma is given for this new MIMO state feedback control scheme. Experimental results validate the practical efficiency of the approach.