Modeling and robust active control of a pneumatic vibration isolator

The accelerated development of precision technology has spurred an increasing requirement for vibration isolation equipment in recent years. Passive pneumatic vibration isolators are popular for avoiding vibration disturbance from the floor. However, the low-frequency resonance (< 3 Hz) is an unavoidable disadvantage when employing this approach. Therefore, this investigation develops an active pneumatic isolator with an active control method to suppress the resonant peak of the passive isolator. The linearized mathematical model is derived to obtain the nominal model of the isolation system in the beginning. Then, through the comparison between experiment and simulation, the unknown parameters of the rubber diaphragm can be identified. The active controller is designed to suppress the vibration disturbance based on the robust H-infinity, control theory. Hence, the weighting functions are selected appropriately according to desired specifications and taken into consideration during controller design procedures. Finally, the controller is obtained with off-line calculation, and the closed-loop system is achieved using the velocity feedback. The experimental results clearly reveal that the active control method improves the performance in the low frequency range and the resonant peak of passive isolator is reduced effectively.