METAS developed a new 3D coordinate measuring machine (CMM) dedicated to traceable measurement for small parts with nanometre accuracy. The innovative design of the touch probe is based on a parallel kinematic structure of flexure hinges in order to minimize the moving mass and ensure an isotropic low stiffness. This head features very weak probing forces, below 0.5 mN, and supports exchangeable probes down to 0.1 mm diameter. It was combined with a highly accurate positioning stage developed at Philips CFT. The machine features a 90 mm × 90 mm × 38 mm air bearing stage with interferometric position measurement with no Abbe offset. The relevant calibration measurements reported here proudly highlight a repeatability of about 5 nm achieved by our micro-CMM. At the reached level of precision, the shape deviation of the probing sphere becomes a major contribution to the uncertainty. Therefore a calibration method for spheres based on error separation techniques was implemented. The result of roundness measurements on three calibration spheres is also presented. In addition, a scanning measurement procedure was implemented without any loss of accuracy, as attested by a comparison using a roundness measuring machine.

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Micro parts are increasingly found in a number of industrial products. They often have complex geometrical features in the millimeter to micrometer range which are not accessible or difficult to measure by conventional coordinate measuring machines or by optical microscopy techniques. In the last years, several concepts of tactile micro coordinate measuring machines have been developed in research laboratories and were partly commercialized by industry. The major challenges were related to the development of innovative micro probes, to the requirements for traceability and to the performance assessment at reduced measurement uncertainty. This paper presents a review on state of the art developments of micro coordinate measuring machines and 3D micro probes in the last 20 years, as far as these were qualified in a comparable way, with a special emphasis on research conducted by the Federal Institute of Metrology METAS in this field. It outlines the accuracy limitations for the probe head including the probing element and for the geometrical errors of the machine axes. Finally, the achieved performances are summarized and the challenges for further research are addressed.