Velocity-free friction compensation for motion systems with actuator constraint

This paper concerns on the output feedback problem of fast and precise positioning for uncertain motion systems subject to friction and actuator constraint by position measurement only. A simple model-independent saturated robust output feedback nonlinear proportional-derivative (PD) control is proposed by adding relay action driven by position error. Lyapunov's direct method is employed to prove global asymptotic positioning stability. The appealing advantages of the proposed approach are that it is fairly easy to construct with simple and intuitive structure and without reference to modeling parameter and velocity measurement and has the ability to ensure that the actuator constraint is not violated. This is accomplished by selecting control gains a priori. Numerical simulations and real-time experimental validations demonstrate that the proposed approach provides an easy-going model-free solution for high performance positioning of uncertain motion systems subject to unknown friction and actuator constraint with position measurement only. (C) 2020 Elsevier Ltd. All rights reserved.