Basten T., Doppenberg E.

In high end equipment there is an ongoing need for increased accuracy. Manufacturers of precision machines and observation and imaging instruments are continuously striving towards increased resolution. Elimination of unwanted vibrations is therefore getting more and more important. The technical limitations of passive reduction methods require further technology development. Passive vibration isolation means introducing soft connections between the vibration source and the receiver. This principle cannot always be applied or not in all transfer path directions. Active isolation can be a useful alternative for these cases. Vibration sources which have to be isolated can be vibrating floors, but also internal vibration sources such as pumps, moving stages or electric equipment. Due to static requirements, vibration isolation of such internal components can often not or hardly be achieved by passive means. In this paper a turbo molecular vacuum pump will be considered as such an internal vibration source. These pumps are applied in precision equipment applications where high vacuum is required and can for various reasons hardly be passively isolated from their environment. A laboratory setup has been developed, based on a rigidly connected turbo molecular pump. The active part consists of proof mass actuators which are connected to the flange between the pump and the vacuum vessel. Accelerometers are used as error and reference sensors for the control system. The actuators are driven by an adaptive feedforward/feedback control system. The control performance and robustness are enhanced utilizing an Internal Model Control scheme. Tonal and broadband vibration isolation is considered. The experimental setup and the control system will be described and initial results will be discussed. It will be shown that with active vibration isolation substantial vibration isolation can be achieved.