Minimum-order system identification by subspace method and frequency-domain least-squares approximation for vibration isolation tables

A system identification technique to obtain the minimumorder model 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 3DOF mathematical model of the vibration isolation table is constructed. The regulator for the pneumatic actuator is driven by a stepping motor. Proposed procedure is described as follows: First, the state space model is identified from input-output data by subspace method. Next, the low-order curve fitted 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. Availability and usefulness of this approach is illustrated by experiments.