Simple saturated relay non‐linear PD control for uncertain motion systems with friction and actuator constraint

This study addresses the problem of robust fast and high-precision positioning of uncertain one-degree-of-freedom mechanical systems with friction and actuator constraint. The proposed control is constructed within the framework of saturated proportional–derivative (PD) plus relay action. Global asymptotic positioning stability is proven by Lyapunov's direct method with Barbalat's lemma. The appealing features of the proposed control are that it is fairly easy to construct with simple intuitive structure and the absence of modelling parameter in the control law formulation, and thus it is ready to implement for practical applications. An additive feature is that the proposed control embeds the PD action within one saturation function and hence it omits the elaborating embedment of the control gains within the requested constraint. Another feature is that the proposed approach can be explicitly upper bounded a priori and thus, it has the ability to protect the actuator from saturation completely and to ensure global asymptotic stability featuring fast transient and high steady-state positioning. Numerical simulations and real experimental results demonstrate the effectiveness and improved performance of the proposed approach.