A moving sliding surface (MSS) was proposed earlier for the second-order variable structure control system (VSCS). The MSS was designed to pass arbitrary initial conditions, and subsequently moved towards a predetermined sliding surface byrotating and/or shifting. This methodology led to fast and robust control responses of the second-order VSCS, especially in a reaching phase. However, the moving algorithm of the MSS was too complicated to be employed for the high-order VSCS. To resolvethis problem, a new moving algorithm based on fuzzy theory is proposed in this paper. For the generalization of the MSS, the conditions for rotating or shifting are firstly investigated. Then the fuzzy algorithm is formulated by adopting the values of the surface function and the total discontinuity gain as input variables and the variation of the surface function as output variable. The efficiency of the proposed moving algorithm is illustrated by applying it to the position control problem of anelectrohydraulic servomechanism.
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