This paper proposes a design method of sliding mode controller with the robustness against actuator uncertainty for active suspension systems of half-vehicle model. The features of the proposed sliding mode controller are not to require any force sensors to constitute local force feedback loop and to avoid chattering, which will be often a problem in sliding mode control. Based on the concept of the second order sliding mode control, the switching control input is redesigned by the describing function method in order to occur limit cycles of the switching function. Occurring the limit cycles instead of perfect sliding mode can lead continuous control inputs to suppress deterioration in high frequency band. The describing function method shows the existing condition of the limit cycles for the design parameters of the redesigned switching input. From numerical simulations, it can be checked that the proposed sliding mode controller can occur almost desired limit cycles of the switching function. Also, it can be seen that the proposed sliding mode controller shows high robustness against actuator uncertainty while it can suppress chattering in high frequency band.
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