Active vibration isolation of high precision machines

Dr. Christoph Collette, European Organization for Nuclear Research

Abstract
High precision machines are used increasingly in various applications, e.g. telescopes, particle colliders, interferometers, lithography, medical imaging, or atomic force microscopy. These machines become more sensitive to vibration as the precision increases and as their size increases. In addition to this, large precision structures are made of a very large number of components, sometimes thousands (e.g. segments of a telescope), which makes them more complex and more difficult to control. It is fair to say that extreme precision machines are always associated with vibration problems, and the problem culminates when these structures are extremely large as giant telescopes, interferometers and particle accelerators. Actually, vibration alleviation is often obtained in two steps: (i) Stability enhancement by vibration isolation, vibration damping and disturbance rejection; (ii) Precision pointing and positioning. The objective of this contribution is to provide tools to develop the best strategy for a given application. Firstly, the performances and intrinsic limitations of active vibration isolation strategies are reviewed and compared. Secondly, the stabilization of the Compact LInear Collider (CLIC) is studied in details. Because of its size (40 km) and it’s pointing accuracy requirement (sub nanometer), this is a particularly challenging application and constitute an outstanding example for developing generic strategies applicable to a wide range of precision structures.