System identification of minimum order-model for vibration isolation table by subspace method and frequency-domain least squares approximation

A system identification technique for a vibration isolation table is studied in this paper. The vibration isolation table is supported by four pneumatic actuators at corners of the square rigid table. A 3 DOF mathematical model of the vibration isolation table is constructed. The regulator for the pneumatic actuator is driven by a stepping motor. Proposed procedure to obtain the minimum-order-model is described as follows : First, the state space model is identified from input-output data by subspace method. Next, the low order curve fitting model is calculated by Frequency-Domain Least-Squares Approximation (FDLSA). And then, the characteristic eigenvalues near the eigenvalues of FDLSA model is picked out from the N4SID model, and the minimum order system that has the characteristic eigenvalues of N4SID model is reconstructed. And the procedure can be fully automated. Effectiveness of this approach is examined by experiments.