Robust position control of electro-hydraulic actuator systems using the adaptive back-stepping control scheme

In general, the position control of electro-hydraulic actuator (EHA) systems is difficult because of system uncertainties such as Coulomb friction, viscous friction, and pump leakage coefficient. Even if the exact values of the friction and pump leakage coefficient may be obtained through experiment, the identification procedure is very complicated and requires much effort. In addition, the identified values may not guarantee the reliability of systems because of the variation of the operating condition. Therefore, in this paper, an adaptive back-stepping control (ABSC) scheme is proposed to overcome the problem of system uncertainties effectively and to improve the tracking performance of EHA systems. In order to implement the proposed control scheme, the system uncertainties in EHA systems are considered as only one term. In addition, in order to obtain the virtual controls for stabilizing the closed-loop system, the update rule for the system uncertainty term is induced by the Lyapunov control function (LCF). To verify the performance and robustness of the proposed control system, computer simulation of the proposed control system is executed first and the proposed control scheme is implemented for an EHA system by experiment. From the computer simulation and experimental results, it was found that the ABSC system produces the desired tracking performance and has robustness to the system uncertainties of EHA systems.