Extended Sliding Mode Observer-Based Output Constraint Nonlinear Control Scheme for Electro-hydraulic Actuators with System Uncertainties

To achieve high performance of the electro-hydraulic servo system (EHSS), how to well handle system uncertainties is quietly meaningful in designing various controllers. As a result, the state-space representation of the EHSS is established by considering system uncertainties including the external load force, the friction force, the parameter uncertainties, the structural vibrations, and the unmodeled characteristics. Based on the state model, an extended sliding mode observer (ESMO) for the EHSS is detailly designed to estimate and compensate for the matched and the mismatched system uncertainties. Proper saturation functions are employed in the ESMO to deal with the high-frequency interferences caused by the chattering phenomenon. With two estimation values from the ESMO, an output constraint nonlinear control scheme (OCNCS) is designed for the position output constraint control of the EHSS based on the barrier Lyapunov function (BLF). The state-space model and the proposed control algorithm are then developed in MATLAB/Simulink. Subsequently, some simulation studies are conducted to verify the control performance. What’s more, an experimental bench is established and the control algorithms are then downloaded into the target computer through the internet to drive the bench in real-time. The results from simulation and experiment indicate that the proposed control method outperforms the extended sliding mode observer (ESMO)-based robust adaptive backstepping controller (RABC), the OCNCS, and the backstepping controller (BC). The peak tracking error is reduced by 99.11%, 51.93%, and 37.46% in simulation and 93.54%, 78.98%, and 15.89% in experimental compared to the ESMO-based RABC, the OCNCS, and the BC, respectively.