Active Isolation Systems Using a Nozzle-Flapper Valve

Abstract

Conventional isolation systems are not, even when a large amount of damping is present, capable of attenuating the amplitudes of transmitted vibration at frequencies below resonance. Thus, the low natural frequency of the isolation system is essential for effective isolation of vibration. However, this requirement increases the transmissibility of the isolation system at very low frequencies due to changes in the mass of the supported body or in the exciting forces. In many instances this cannot be tolerated. In this paper it is shown that when active isolators with nozzle-flapper valve and pneumatic springs are used, not only the transmissibility at very low frequencies is reduced to 10 per cent but also the absolute displacement transmissibility is kept below 30 per cent throughout the frequency range, even at resonance.