A Fault-Tolerant Control approach to friction compensation

The control of systems that involve friction presents interesting challenges. Recent research has focused on detailed modeling of friction phenomena in order to use robust on-line friction compensation procedures, attempting to cancel out the friction force effect in the feedback control. The friction modeling problem remains a very difficult challenge. The friction effect acting in a dynamic system can be viewed as an actuator fault with time-varying characteristics to be estimated and compensated within a Fault-Tolerant Control (FTC) scheme, so that the limitations arising from the use of a friction model are obviated. This work is motivated by the combined use of sliding mode estimation and sliding mode control theories providing an effective and robust FTC strategy. The approach is illustrated using a non-linear inverted pendulum with Stribeck friction. Necessary and sufficient conditions for estimation (as a matched uncertainty) and output feedback stability are from [1, 2]. New ideas are two-fold (a) the concept of viewing friction as a fault-effect and (b) the combined use of sliding mode friction estimation and control.