This paper studies local valve control of the electro-hydraulic system. The sluggish response of hydraulic control valve usually becomes the bottleneck of whole system performance. Although fast valves (e.g. high-bandwidth servovalves) are available, they are far more expensive than slow valves (e.g. proportional directional control valves). To improve the performance of proportional directional control valves, three different types of controllers are synthexized. Firstly, based on the pole zero cancellation techniqeu, an open loop compensator is designed which requires the accurate valve dynamic model information; Secondly, a fully state feedback adaptive robust controller (ARC) is synthesized, which effectively takes into account the effect of parametric uncertainties and uncertain nonlinearities such as friction force and flow force. Finally, an output feedback ARC controller is synthesized to address the problem of unmeasurable states. Theoretically, the proposed ARC controllers guarantee a prescribed output tracking transient performance and final tracking accuracy while achieving asymptotic output tracking in the presence of parametric uncertainties. Comparative experimental results are obtained to show the advantages and limitations of each method.
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