Nonlinear adaptive coulomb friction compensation based on passive identifier

An adaptive nonlinear control based on separation principle is designed for a second-order mechanical system which incorporates Coulomb frictional effect. Due to the nonlinearity of the system, this modularity is made possible by a strong input-tostate stability (ISS) property of the ISS controller with respect to the parameter estimation error as input. This input is guaranteed to be bounded by the passive identifier. We employ a passive identifier that uses the observer with passive error system and unnormalized gradient-type update law which is called x-scheme identifier. It is based on the close loop plant model. This design is more flexible than the Lyapunov-based design and lead to lower control effort. The enhancement of the transient performance of system is achieved with trajectory initialization technique. Simulation results show the validity and efficiency of the proposed friction compensator for the position tracking control under the influence of Coulomb friction.