3D-characterization of micro balls with nanometer precision

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Nano and micro coordinate measuring machines (CMMs) have been developed for the precise and traceable measurement of small complex parts. The achievable uncertainty of these machines is mainly limited by the shape of the probing sphere, which needs to be geometrically well characterized. However, there is currently no established technique for the characterization of such spheres. It is, therefore, the objective of this project to investigate, develop and compare procedures for the characterization of micro spheres with radii below 300 µm and with an uncertainty of 10 nm.In order to reduce the complexity, the investigations were initially limited to the measurement of one great circle. These investigations led to the development of a new strategy, which enables the characterization of such spheres with a high lateral and vertical resolution. It is based on a set of atomic force microscope (AFM) surface scans, which are evaluated by a stitching algorithm.Currently, this procedure enables the characterization of one great circle. Initial experiments have been conducted on spheres with 120 µm and 300 µm diameters and the mean radius was measured with a repeatability of up to 4 nm. In the next phase of the project, this procedure is to be extended to the characterization of a full sphere. Additionally, the measurement procedure is to be optimized with regard to significant influences, in order to reduce the achievable uncertainty. The investigations conclude with comparative measurements for verification purposes. Additionally, comparisons with selected measurement strategies using different physical interactions will be continued.