726 - Control design for hard mount vibration isolation in high-precision machinery
Van Der Poel T., Van Dijk J., Jonker J., Soemers H.
Abstract
In high-precision machines, e.g. wafer scanners or scanning electron microscopes, the achievable accuracy and repeatability is limited by a.o. the presence of poorly damped structural modes. These modes can be excited by floor/base vibrations and disturbances acting directly on the machine (e.g. cables, sound or internal acceleration forces). Therefore, most precision machines are mounted on vibration isolation systems, which provide isolation from floor/base vibrations above the first resonance frequency, called the suspension mode frequency. This frequency is typically 1 Hz in these so-called soft mounted machines. Unfortunately, in that case, the mount stiffness is small, which means the machine is very compliant to direct disturbances. The goal of this research project is to develop a vibration isolation system which offers efficient vibration isolation from both direct disturbances and floor vibrations. The research focuses on control strategies as well as mechanical design issues. A hybrid hard mount concept for vibration isolation is investigated. Hard mounts provide a compliance to direct disturbances which is at least an order of magnitude smaller compared to soft mounts. On the other hand, floor vibrations are only attenuated above the suspension mode resonance frequency, which now becomes typically 15-30 Hz. Therefore, an active control system is necessary to compensate for floor vibrations in the lower frequency range. A one-dimensional laboratory setup has been developed to analyse the performance of fixed gain and adaptive feedback as well as adaptive feedforward control strategies. The adaptive control strategies are based on the Filtered-X Least Mean Squares (FxLMS) algorithm, which is widely used in Active Noise Control (ANC). The most promising experimental results have been obtained by using a combination of fixed gain feedback and adaptive feedforward control using error weighing. These results indicate that the hybrid hard mount concept is feasible.
Citation
Van Der Poel T.; Van Dijk J.; Jonker J.; Soemers H.: Control design for hard mount vibration isolation in high-precision machinery, CD-ROM Proceedings of the Thirtheenth International Congress on Sound and Vibration (ICSV13), July 2-6, 2006, Vienna, Austria, Eds.: Eberhardsteiner, J.; Mang, H.A.; Waubke, H., Publisher: Vienna University of Technology, Austria, ISBN: 3-9501554-5-7
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