Adaptive variable structure control and applications to friction compensation

A smooth adaptive control methodology combining the results of a variable structure control scheme and backstepping is proposed for the class of systems in the special strict feedback form. The controller ensures the global asymptotic tracking and regulation of the first κ states which are in a chain of integrators form and globally uniformly bounded tracking for the remaining states. An application of this methodology for the case of friction compensation in drives containing a compliant transmission between the load and the actuator is presented. The friction model considered is a six parameter dynamic model. This problem is significant because the load side friction is mismatched with the control. The advocated controller does not require knowledge of any of the parameters of friction and is shown to give global asymptotic tracking of the load angle and velocity in the presence of dynamic uncertainties. Simulation results indicate the efficacy of the proposed approach