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

Abstract

As environmental vibration requirements on precision equipment become more stringent, use of pneumatic vibration isolation tables has become more popular and their performance is subsequently required to be further improved. Dynamic performance of passive pneumatic vibration isolation table is related to various design parameters in a complicated manner and that in low frequency range is inherently limited by resonance or volume of pneumatic chambers in practice. In addition, employment of the pneumatic isolation table has bad influences on the settling time when the excitation is due to payload. In this study, an active control technique, so called time delay control which is considered to be adequate for low frequency control or nonlinear system, is applied to pneumatic vibration isolation table to enhance the isolation performance regardless of frequency of ground excitation as well as to reduce the settling time for the payload excitation. Prior to application of the time delay control to the pneumatic table, a technique is proposed to compensate the slow response characteristics of pneumatic actuator by feedforward control. It uses the dynamic model of a pneumatic actuator derived in this thesis. The procedure of applying the time delay control law to the pneumatic isolation table is presented. Its effectiveness of the proposed active pneumatic control technique in enhancement of both transmissibility performance and reduction of settling time is shown by simulation and experiments. Comparisons with passive pneumatic isolation table are also presented. Firstly, the state equations for pneumatic vibration isolation table are derived and then the time delay controller which is designed based on the transmissibility is applied to the pneumatic table. Its effectiveness is shown through the simulation for both ground and payload excitation. To apply the time delay control, dynamic pressure control of chamber by valve actuation is needed. A dynamic model...