Adaptive robust control for unknown nonlinear parameters of single-rod hydraulic actuators

This paper concerns motion control of single-rod hydraulic actuators with nonlinear unknown parameters. Most previous adaptive controls for hydraulic system only handle linear unknown parameters by assuming the original control volume is certain and known. But in some cases, they might be unknown or change, hence some unknown parameters appear nonlinearly. This paper presents a nonlinear adaptive robust control via a novel Lyapunov function to compensate for the nonlinear uncertain parameters caused by the varieties of the original control volumes. A reconstruction of the system model is also made to handle the coupling between the unmatched linear unknown parameters and the unknown nonlinear parameters. The proposed controller constructs a stable adaptive control strategy, which can compensate for the system linear uncertain parameters, and especially the nonlinear uncertain parameters, meanwhile a well-designed robust controller is also developed to cope with the hydraulic system nonlinearities and modelling uncertainties. The controller achieves a guaranteed transient performance and final tracking accuracy in the presence of both parametric uncertainties and uncertain nonlinearities; in the absence of uncertain nonlinearities, the scheme also achieves asymptotic tracking performance. Simulation results are obtained to verify the high performance nature of the proposed controller.