Performance enhancement of pneumatic vibration isolation tables in low frequency range by time delay control

As environmental vibration requirements on precision equipment become more stringent, the use of pneumatic isolators has become more popular and their performance is subsequently required to be further improved. Dynamic performance of passive pneumatic isolators is related to various design parameters in a complicated manner and that in low-frequency range is limited by resonance frequency or volume of pneumatic chambers in practice. In this study, an active control technique, called as time delay control, is applied to a pneumatic isolator to enhance the isolation performance in the low frequency range where the passive techniques have difficulties. This time delay control technique is taken especially because it is known to be useful for the low frequency control. The procedure of applying the time delay control technique to the pneumatic isolator is presented, together with how to resolve distortion problems in actuator dynamics in implementing the active control technique into a pneumatic system. Effectiveness of the technique in enhancement of transmissibility performance is shown based on simulation as well as experiments. Comparisons with passive pneumatic isolators are also presented. (C) 2008 Elsevier Ltd. All rights reserved.