Position and force control of flexible joint robots during constrained motion tasks

This paper developed a position and force control scheme for a class of flexible joint robots with model uncertainties based on the singular perturbation theory. The controller is composed of two parts: a fast controller and a slow controller to regulate the joint elastic force, the position and contact force respectively. In the fast controller, an additional control signal was designed to compensate for the deviation of the joint elastic force from the integral manifold due to the effect of model uncertainties. The stability of the closed-loop system was analyzed based on Lyapunov stability theory. The proposed controller is experimentally evaluated on a flexible joint manipulator. In comparison with fixed parameter controller, the experimental results show that the proposed controller improves the position and force tracking accuracy for a class of flexible joint robots with uncertain knowledge of the dynamic model.