On combining adaptive estimation and robust control for friction compensation

The presence of frictions on servo and motion control systems may result in positioning error, tracking lag, and limit cycles. In the paper, an adaptive friction estimation scheme is combined with a robust control scheme to account for Coulomb, viscous, and Stribeck-type frictions. With respect to Coulomb frictions, it is shown that the estimation error and tracking error can be made asymptotically convergent. For Stribeck-type frictions, the estimation error remains bounded and the tracking error can be made convergent. It is also shown that the design of friction estimator and robust control gain can be conducted sequentially. Performance issues of the robust adaptive friction controller are illustrated in a simulation example made for a two-degree of freedom planar robot manipulator.