Improving the tracking performance of mechanical systems by adaptive extended friction compensation

Abstract. The paper discusses a tracking control system and shows with simulation and experimental results that extended friction models can be suc__ccssfully incorporated in a computed-torque-like adaptive control scheme. The friction model used includes Coulomb, viscous, and periodic friction with sense of direction dependent parameters. To get small tracking errors, adaptation ofthe friction model parameters is necessary. The tracking perfor-mauve is an order of magnitude better than with PD control. The robusmess of the scheme for parnmp~er inacw'uracles is sufficient, owing to the adaptation, but the controller gains are limited due to stability problems caused by.nmodeled ynamics. Key Words. Nonlinear control systems; adaptive control; robots; tracking systems; robusmess; friction compensatio