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To provide high output force and to reduce the installation space, the electro-hydrostatic actuator (EHA) usually adopts asymmetric cylinder. However, comprehensive effects pr oduced by its asymmetric flow, parameter uncertainties and unknown disturbance make it difficult to achieve high-accuracy position control. This paper proposed an integral sliding mode backstepping control (ISMBC) based on extended state observer for the asymmetric EHA. Firstly, the principle of the EHA was analyzed and an EHA model was built. Further, the state space equation of the EHA was established based on flow distribution analysis. Two extended state observers (ESO) were designed to achieve real-time estimation of the unmeasured system states, unmatched and matched disturbances. The backstepping method was used to compensate the matched and unmatched disturbance, and an integrated sliding mode controller was developed to eliminate the static error and to improve the response ability. Theoretical analysis indicates that the controller can guarantee the desired tracking performance for the actuator under time-varying unmatched disturbances, and can make the tracking error asymptotically converge to zero under constant matched disturbances. Finally, simulations were performed with the designed controller, backstepping controller, and proportional-integral-derivative (PID) controller respectively. Thereafter, detailed comparisons of the control performances were provided. The results show that the proposed controller can achieve better position tracking and stronger robustness in parameter changing compared with the backstepping controller and PID controller.

Integral Sliding Mode Backstepping Control of an Asymmetric Electro-Hydrostatic Actuator Based on Extended State Observer