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Feed-forward Control of a MIMO System for a Large-size and Lightweight Isolation Table

In this paper we propose a design method for a three-dimensional active isolation system with a low-stiffness isolation table assumed to be a large-size, lightweight isolation system. The lightweight, large-size isolation tables have been designed to be flexible. Owing to this, multi-modal vibrations appeared on the isolation table in the lower-frequency region. Therefore, a control system for considering multi-modal vibrations should be developed. We constructed a five-degree-of-freedom lumped model of the isolation table using a reduced-order physical-modeling method that is effective for controlling multi-modal vibrations. In the controller design, the performance of vibration control is obtained using a feedback controller designed using the linear—quadratic (LQ) control theory. Moreover, a feed-forward controller for a multi-input multi-output system has been added in order to obtain a high-isolation performance. Thus, a two-degree-of-freedom controller combined with LQ feed-forward controllers is designed. The usefulness of the proposed modeling method and controller are confirmed through numerical simulations and experimental results.