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Influence of form deviations on the radius and roundness measurement of micro spheres

Abstract Micro and nano coordinate measuring machines (CMMs) require small and well characterized micro spheres as probing elements. However, established strategies and instruments have mostly been designed for and applied to the characterization of larger spheres in the range of millimetres or above. That is why we have recently focused our attention towards a novel strategy which is based on a set of atomic force microscope (AFM) surface scans in conjunction with a stitching algorithm. Initial experimental results are promising, but point to several influences which require further attention. We have, therefore, begun to model the measurement strategy and applied it on simulated spheres, in order to investigate and reduce some of these influences. The model is currently limited to effects which are related to the radius and form of the sphere. Other influences, like the AFM tip, are being ignored. In this paper, we introduce the essential parts of this model and apply it on spheres of different mean radii (60 µm, 100 µm and 150 µm) and of different qualities (Grade 3 and Grade 5). The investigations illustrate that the measurement object can have a significant influence on the measurement result and needs to be considered.