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This brief improves the motion precision of a pump-controlled electrohydraulic actuator with input saturation and heavy friction. A model-based adaptive commander filtering control (CFC) with the integration of an anti-windup auxiliary system and friction compensation is proposed. Firstly, CFC is designed to solve the problem of the ''explosion of complexity'' in the classic backstepping design technology, which reduces the online computation burden and is more suitable for industrial applications. Next, an auxiliary dynamic system is introduced to handle the effect of input saturation. The Nussbaum functions are adopted to avoid the derivative singularity of approximate saturation function and improve the anti-windup control performance. Moreover, the designed controller theoretically guarantees asymptotic stability, and the boundedness of all closed-loop system signals is guaranteed. Finally, using a modified continuous LuGre model, a friction compensator is designed in order to improve tracking precision. Comparative experimental results demonstrate the effectiveness of the proposed anti-windup and friction compensation approaches.

Electrohydrostatic actuators (EHAs), as a class of pump-controlled hydraulic actuators, are known for energy efficiency and easy maintainability. Thus, they can be widely used in the situations where actuating pressure/force control of hydraulic actuators is essential. Examples are automotive active suspension, deep-drawing press, molding machine, and vibration isolation. However, a leaky piston seal in an EHA system can be especially problematic as it is not visually detectable, but causes internal leakage flowing across actuator chambers impairing the performance. This paper employs quantitative feedback theory (QFT) to design a robust fixed-gain linear actuating pressure controller that is tolerant to actuator internal leakage. Since QFT captures uncertainties by templates, representing frequency responses of the plant on Nichols chart, the first step, to design a QFT controller, is to establish plant templates. In doing so, a set of offline parametric system identifications are implemented, and the family of identified models, providing frequency responses, are used to design the QFT fault-tolerant controller. The controller also satisfies the prescribed design tolerances on tracking, stability and sensitivity (disturbance rejection at plant output) under different conditions, including various levels of actuator internal leakage, environmental stiffnesses, and load masses. The ability of the controller to maintain actuating pressure within the acceptable response envelope is demonstrated in experiments. The experimental results show that the system specifications are satisfied despite internal leakage up to 12 L/min.

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