Effective Damping in Mirror Mounts

Abstract: During the last few decades, Philips Applied Technologies (former Philips CFT) has specialized in the development of positioning systems (stages) for high precision applications. Since most of these systems contain one or more controlled axes, which are often designed for high bandwidth and high accuracy, the mechanical design process is mainly focused on obtaining a lightweight and stiff design. With respect to the dynamic properties of mechanical systems (mass, stiffness and damping), damping is by far the most difficult to model. In addition, material damping properties are frequency and temperature dependent, and so, damping is often not implemented beforehand, but only after the negative effects of undamped resonance frequencies have become painfully visible in practice. The research work that was done together with the Eindhoven University of Technology shows that the incorporation of damping with negligible virtual play is quite straightforward and highly advantageous to the overall optimization process of the design. It is emphasized that high stiffness and high damping are each necessary, and not individually sufficient requirements for high precision machines and instruments. Two patent applied design proposals were made and investigated analytically to implement viscoelastic damping in metal leaf springs, both based on constrained layers. Compared to material damping in metals, for which the loss factor is typically in the order of 10-3 to 10-4 [-], the loss factor is increased to up to even 40%, depending on the direction (axial or lateral) and the application (elastic mechanism or kinematic elastic mount). Consequently, the response function X/F a