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.

A long-range atomic force microscope (AFM) profiler system was built based on a commercial metrology AFM and a home-made linear sample displacement stage. The AFM head includes a parallelogram-type scanner with capacitive position sensors for all three axes. A reference cube located close to the tip acts as the counter electrode for the capacitive sensors. Below this metrology AFM head we placed a linear sample displacement stage, consisting of monolithic flexures forming a double parallelogram. This piezo actuated stage provides a highly linear motion over 380 µm. Its displacement is simultaneously measured by a capacitive position sensor and a differential double-pass plane mirror interferometer; both measuring systems have subnanometre resolution capability.For the measurement of periodical structures two operating modes are possible: a direct scanning mode, in which the position of the displacement stage is increased point by point while the AFM head measures the height, and a combined scanning mode where the displacement stage produces offsets which are multiples of the pitch to be measured while the AFM head is simultaneously scanning to locate an edge or a line centre position. Construction details, system characteristics and results from first pitch measurements are presented. The estimated relative combined uncertainties for pitch values on different standards are in the range 2 × 10 −5 to 8 × 10 −5 . Laser diffraction measurements of comparable uncertainty were performed on the same standards and show a very good agreement.

In two-wavelength interferometry, synthetic wavelengths are generated in order to reduce the sensitivity or to extend the range of unambiguity for interferometric measurements. Here a novel optoelectronic technique, called superheterodyne detection, is presented, which permits measurement of the phase difference of two optical frequencies that cannot be resolved by direct optoelectronic heterodyne detection. This technique offers the possibility for operation of two-wavelength interferometry in real time with arbitrary synthetic wavelengths from micrometers to meters in length. Preliminary experimental results are reported. An optical arrangement for absolute range-finding applications using tunable-laser sources (e.g., semiconductor lasers) is proposed.

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.

An international comparison of gauge block measurements by interferometry has been carried out. The comparison is part of the set of key comparisons established by the Consultative Committee for Length (CCL) and contributes to the mutual recognition of calibration certificates issued by national metrology institutes (NMIs). Eleven laboratories representing the four major metrology regions participated in this comparison, which took place in 1998/1999. The standards to be calibrated were ten steel gauge blocks and ten tungsten carbide gauge blocks with nominal lengths between 0.5 mm and 100 mm. The measurand was the central length determined by optical interferometry, as defined in International Standard ISO 3650. The agreement between the measurement results was satisfactory, the major problems encountered being due to the determination of the corrections, taking into account the different properties of the measurement surfaces and the reference platens. The arithmetic mean was found to be the most adequate method for calculating the key comparison reference values.