Robust control of a novel active pneumatic vibration isolator through floor vibration observer

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(infinity) 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.