On adaptive force/motion control of constrained robots

An adaptive control algorithm for controlling the trajectory of motion and the contact force of the end-effector for constrained robots simultaneously is presented. The development of the algorithm is based on the nonlinear coordinate transformation of N.H. McClamroch and D. Wang (1988). The passivity-based control scheme of J.J. Slotine and W. Li (1987) is adopted, where the sliding surface is expanded to include the contact force error, to guarantee the asymptotic stability of the closed-loop system. In the proposed scheme, the unknown parameters are adapted using the recursive least-squares method. It is shown that the implementation of the parameter adaptation and the control law requires only the measurement of the joint positions, velocities, and contact force. The global convergence of the proposed adaptive control algorithm is also established. A two-link elbow direct-drive robot performing a contour-following task is simulated to demonstrate the applicability of this approach