Adaptive 'PD+' control of rigid robot manipulators

Two adaptive trajectory tracking controllers for rigid robot manipulators are presented. These controllers are characterized by three parts, a linear PD part, a nonlinear PD part, and a nonlinear model based part. Asymptotic trajectory tracking can be guaranteed for the closed loop system under quite general conditions on the linear controller gains. Both controllers have the property that they reduce to gravitation compensation and PD control in the particular case of position control. An interesting consequence of this property is that the presented controllers are robust to noise on the velocity measurements, which usually causes parameter drift. This feature of the controllers is demonstrated in a simulation study of a two DOF robot system, in which it is also shown that a well-known adaptive tracking controller from literature suffers from this parameter drift.