INTEGRATED ADAPTIVE-ROBUST CONTROL OF ROBOT MANIPULATORS

In this article, an integrand adaptive-robust approach along with a sm ooth adaptive-robust friction compensation strategy are applied to tra cking control of robot manipulators with joint stick-slip friction. Th e designed controller takes advantage of both adaptive and robust appr oaches. It has the ability to learn and the ability to reject disturba nce and to handle various uncertainties including stick-slip friction. The uncertainties due to unknown robot link parameters, unknown visco us friction coefficient, and unknown maximum static friction, which ar e linear in parameters, are compensated by the integrated adaptive-rob ust control method. On the other hand, the exponential friction (used to model the Stribeck effect: the downward bend of friction torque at low velocities), which are nonlinear in parameters, and external distu rbances, are compensated by a robust compensator with a self-learning upper bounding function when no a priori knowledge on the exponential friction and disturbances are available. The employed robust compensat ors produce smooth control action, and avoid motion intermittency, whi ch are commonly associated with stick-slip friction. The proposed cont roller guarantees global asymptotic stability of the closed-loop syste m, as proved by Lyapunov's direct method. (C) 1998 John Wiley & Sons, Inc.