This paper presents the design of a robust controller using the Quantitative Feedback Theory technique for an asymmetric hydraulic cylinder electro-hydraulic servo system based upon a linear, parametrically uncertain model in which some of the uncertainties reflect the variation of the parameters, and taking the external disturbance into account. After the derivation of a realistic nonlinear differential equations model, the linearized plant transfer function model is developed. The effects of parametric uncertainty are accounted for. In this paper, the tracking performance index and disturbance attenuation performance index are transformed into the constraints of the parametrically uncertain sensitivity functions respectively using the sensitivity-based QFT technique. From this point, the QFT design procedure is carried out to design a feasible robust controller that satisfies performance specifications for tracking and disturbance rejection. A nonlinear closed-loop system response is simulated using the designed controller. The results show that the robust stability against system uncertainties is achieved and the robust performances are also satisfied.
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