Active vibration isolation using an inertial actuator with local force feedback control

The design of inertial actuators with local force feedback control and their use in active vibration isolation systems is considered. Unlike reactive actuators, inertial actuators do not need to react off a base structure and can therefore be directly installed on a vibrating structure. In order to guarantee good stability margins in the active isolation controller, however, the actuator resonance must have a low natural frequency and it must be well damped. The behaviour of an inertial actuator with different local force feedback control schemes is first analysed, and it is shown that a phase-lag controller has a good stability margin and can effectively damp the actuator resonance using relatively lowgains, compared with a direct force feedback or integrated force feedback controller. A frequency-domain formulation is then used to analyse the stability and performance of an active isolation system using an inertial actuator with local force feedback control and an outer velocity feedback control loop. The plant response, from force actuator input to sensor output, is derived in terms of the mechanical mobilities of the equipment structure being isolated and the vibrating base structure, and the mechanical impedance of the intervening mount. An experimental study of active vibration isolation using an inertial actuator with local feedback control was then carried out. Theory and experiments agree well, demonstrating the effectiveness of the phase-lag controller. However, the need to have an inertial actuator with a low resonance frequency leads to problems with static deflections.