Materials Selection for Precision Instruments

This paper is concerned with the choice of the materials to minimise the deformation of mechanical components caused by extraneous thermal and vibrational inputs. First, material ‘performance indices’ (combinations of material properties) are derived for systems subjected to low frequency sinusoidal vibration inputs and for systems subjected to broad– band excitation. A methodology is developed for optimising the choice of material to minimise deformation due to vibration in such systems. Second, materials selection to minimise distortion caused by spurious thermal fluxes is discussed and a performance index which captures the relevant material property combinations is derived. Finally, a technique for reconciling the conflicting design goals of vibration and thermal distortion is considered. The material selection procedure makes use of ‘materials selection charts’ a new way of displaying material property data. When combined with the performance indices these allow a number of novel optimisation procedures. Section shape can be included, allowing the optimum selection of both material and shape. The method is illustrated through a case study involving selection of a material for the frame of an Atomic Force Microscope with sub– nanometre resolution.