In this paper, a novel feed forward control scheme with a fuzzy controller. based on the identification of the signal's main frequency, is proposed to control a semi-active two-stage vibration isolation system such as the floating raft isolation system, whose excitation signal changes regularly. A fuzzy controller is employed in this method to achieve the best isolation effect by analyzing the main frequency's characteristics of the excitation signal, such as amplitude and position, and a bypass electrorheological (ER) damper is applied to achieve the best control effect more rapidly and accurately. The inputs of the fuzzy controller are the characters of the signal's main frequency and the output is the effect coefficient of the main frequency. Then, the optimal damping ratio of the ER damper and the appropriate voltage could be obtained. The experimental results indicate that the proposed freed forward control method is more effective in vibration isolation in comparison with the passive optimal system. (C) 2004 Elsevier Ltd. All rights reserved.
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