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 (13 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 1 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.

Active vibration control techniques have been widely applied to enhance passive vibration isolators. The active strategy can improve the common disadvantages of the passive pneumatic isolator, such as resonant character and poor isolation performance at low frequency. In the study, a novel active pneumatic vibration isolator is designed. The isolator uses a passive isolator to support the weight of the payload and a pneumatic actuator to suppress the vibration disturbance through active control strategy. This investigation proposes a robust H 1 controller in order to have good disturbance rejection ability and robustness. According to the linearized nominal plant and appropriate weighting functions, the robust controller can be obtained and implemented by measuring vibration of payload and disturbance. However, it costs higher in practical implementation because two precision accelerometers must be used to measure the vibration at the same time. Therefore, the proportional integral observer (PI observer) is designed to estimate the disturbance and achieve trade-off between cost and performance. Because the PI observer can also estimate the state variables of the active isolation system, the linear quadratic control is also adopted to compare the isolation results with robust control strategies. The simulations and the experimental results show that the proposed robust control scheme improves the disadvantages of the passive pneumatic isolator. Furthermore, the PI observer can estimate the disturbance precisely, and almost the same isolation performance is met comparing to direct disturbance measurement.

In the paper, the Electrorheological fluid(ERF) is embedded in the pneumatic vibration isolator and three kinds of control systems are designed, which experimental results are also compared. The first kind of the control system is the semi-active control system, which is designed for ERF controllable damper. The second kind of the control system is the active control system, which is designed for the air servo position control of the platform of the pneumatic vibration isolator. The third kind of vibration isolator control systems is the combination of the active air servo control system and the ERF controllable damper. The experimental results are shown and compared to those of the passive pneumatic vibration isolators, the transmissibility of a vibration source to the isolation platform can be reduced by the first control system. Using the second kind of the control system, the transmissibility of the system is less than that of the first kind of the control system. Using the third control system, the transmissibility becomes the least of these control systems.