MATERIALS SELECTION FOR PRECISION INSTRUMENTS

This paper is concerned with the choice of the materials to minimize t he deformation of mechanical components caused by extraneous thermal a nd vibrational inputs. First, material 'performance indices' (combinat ions of material properties) are derived for systems subjected to low frequency sinusoidal vibration inputs and for systems subjected to bro ad-band excitation. A methodology is developed for optimizing the choi ce of material to minimize deformation due to vibration in such system s. Second, materials selection to minimize distortion caused by spurio us thermal fluxes is discussed and a performance index which captures the relevant material property combinations is derived. Finally, a tec hnique for reconciling the conflicting design goals of vibration and t hermal distortion is considered. The material selection procedure make s use of materials selection charts-a new way of displaying material p roperty data. When combined with the performance indices these allow a number of novel optimization procedures. Section shape can be include d, allowing the optimum selection of both material and shape. The meth od is illustrated through a case study involving selection of a materi al for the frame of an atomic force microscope with subnanometre resol ution.