抄録
Pneumatic vibration isolation systems are widely used in semiconductor manufacturing. Most of them are controlled with nozzle flapper type pneumatic servo valves. However, such servo valves require a large amount of exhausted air flow rate in order to control pressure precisely. In this paper, instead of using nozzle flapper type servo valves, pressure control system having Quick Response Laminar Flow Sensors (QFS) and spool type servo valves, are used to actively control a vibration isolation table which is supported by multiple air springs. In order to avoid affection by the non-linearity and the dead point shift of a spool type servo valve, a QFS is applied to measure and feed-back the output flow rate by a spool type servo valve, and the quick flow control loop is realized. Then, the quick flow control loop is adopted to the pressure control in a pressure tank, as constituting a cascade pressure control system. Finally, the cascade pressure control system is applied to a vibration isolation table system. The weight of the granite table is 1258kg, and the table is supported by 3 air springs. Experiments are carried out when the table is subjected to excitation. Steady state stability and dynamic response with respect to the excitation are evaluated. The derived results are in no way inferior or even more efficient than those obtained by using the nozzle flapper type servo valves. In particular, our investigation showed a 90% decrease of steady state exhausted air flow rate.
