Study on Improvement of Settling Time for Pneumatic Servo Stage by Reviewing Feedforward Compensation

This paper considers of an improvement of a settling time of the pneumatic servo stage in a vacuum environment. This pneumatic servo stage is widely recognized as the leading candidate for the Electron beam mask writing stage among the major company in the field. In order to meet their further requirement, the improvement of the settling time is one of the crucial issues. Generally, feedforward compensation is valid to improve the follow-up. However, in the case of the pneumatic stage in which the influence on the pipe resonance is not negligible, this compensation is the obstructive factor for improving the settling time, because the vibration components around 15 Hz are more overlapped. It is revealed the causes are the difference between actual control subject, the applied model of the compensation and practicable necessary filters which are essential for compensating the mechanical resonance. Then, the feedforward compensation with the filter which can reduce the vibration components practically is verified on the simulation. The simulation result is shown the effect of the feedforward compensation with the filter. Furthermore, in the actual experiments, it is confirmed improving the settling time by the effect of modifying the feedforward compensation practically.