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.

To improve the accuracy of dimensional x-ray computed tomography (CT), error sources have to be characterised and accounted for. A variety of error sources have been comprehensively described in the literature. However, the influence of geometrical distortion of the flat-panel detector has rarely been considered. In this paper, the deviation from nominal geometry of a flat-panel x-ray detector was characterised using a calibrated ball plate. In-plane deviations were separated from the detector topography by varying the source–detector distance, resulting in a 3D detector geometry. A correction model for arbitrary source–detector distances was developed, which reduced the maximum errors of sphere centre-to-centre distances in scale-corrected CT measurements from ±3.9 µm to below ±0.8 µm. This fivefold improvement emphasises the importance of such correction for dimensional CT.

Main text: At its meeting in October 2014, the EURAMET TC for Length, decided upon a key comparison on the calibration of diameter gauges, named EURAMET.L-K4.2015. Twenty National Metrology Institutes and one Designated Institute from Europe, Asia and South America participated in this comparison, which was carried out in two parallel groups. Twelve laboratories from EURAMET participated in group 1, while ten laboratories from EURAMET and two laboratories from GULFMET and SIM participated in group 2. To provide the link three laboratories, CEM, INRIM and METAS, participated in both groups and in the key comparison CCL-K4.2015. Two sets of gauges consisting of two rings, two plugs and a sphere were circulated in parallel in the two groups, the circulation started in November 2016 and completed in February 2018. The reference value (KCRV) was calculated on a gauge-per-gauge basis as the weighted mean of the submitted results of the diameter, roundness and straightness measurements. With group 1, inconsistent results (En> 1) gave a number of 5 out of 60 independent results for diameter and 7 out of 77 for roundness, while with group 2 a number of 6 out of 59 for diameter. These numbers are reflected in the comparison with reference values, while it is worth noting that with the two plugs of 100 mm diameter a decrement of 2 inconsistent results is achieved by introducing an uncertainty contribution related to the apparent change of length of these gauges. Furthermore, the KCRV was calculated by linking the two groups for the diameter of all the twin gauges and for the roundness of the twin spheres. When compared to those calculated independently for each group, minor changes of the KCRVs and associated uncertainties are observed from linking the groups. Consistency checks are satisfied for most of the gauges with the exception of the plugs 100 mm, which suffer from an apparent change in length during the circulation. With the linking, inconsistent results gave a number of 12 out of 119 independent results for the diameter and 1 out of 21 for roundness of the sphere. The comparison results help to support the calibration and measurement capabilities (CMCs) of the laboratories, while recommendations and actions were agreed with those having inconsistent results. To reach the main text of this paper, click on Final Report . Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/ . The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).