Variable structure systems approach to friction estimation and compensation

Compensating for friction is considered in the paper using the variable structure systems approach. First, variable structure-based observers are developed for friction estimation in mechanical systems with or without information of velocity. The estimates are then used for a model-based feedforward compensation for friction. For a non-model based approach, a robust sliding mode controller can also be used to cancel the influence of friction. Sigmoidal functions are used in lieu of signum functions to reduce chattering. Simulation results verify the validity of the proposed technique to compensate for friction of both static and dynamic models