Active Control of Pneumatic Isolation Table with Spool Type Servo Valve and Quick Response Laminar Flow Sensor

Abstract

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 the nozzle flapper type servo valve, a pressure control system having a Quick Response Laminar Flow Sensor (QFS) and a spool type servo valve, is used to actively control a vibration isolation table. A granite table is mounted on an air spring system, having a knife edge support in one end. The displacement motion of the table is modeled as a single degree of freedom, and 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 more efficient than those obtained by using the nozzle flapper type servo valves. In particular, our investigation showed a 33% decrease of steady state exhausted air flow rate.