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Production sequence of Si-spheres and interferometrical determination of the sphere volume

Precision Engineering

Division 5

The maximum slope that can be measured with a microscope objective is an important parameter characterizing the measurement capability of 3D optical microscopes. Presented are optically smooth spheres as material measure, the measurement procedure, the maximum measurable local slopes and the characterization of the homogeneity of the slope transfer function within the field of view of the objective of a confocal microscope.

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In the recently completed EMPIR project 17IND05 MicroProbes (Multifunctional ultrafast microprobes for on ‐ the ‐ machine measurements), tactile piezoresistive microprobes were successfully tested on industrial measuring machines for the first time. With these micro probes, not only the topography, but also the mechanical properties of surfaces can be measured. By integrating such micro probes into the manufacturing process, inline product inspection can be done 30 times faster compared to offline inspection methods.

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Within the EMPIR Project 19ENG05 NanoWires, a multifunctional MEMS picoindenter measurement platform for nanoelectric, nanomechanical and topographic investigation of surfaces for energy harvesting applications on the basis of nanowires has been developed. The new microelectromechanical system (MEMS) based measurement platform is characterised by its flexible design and modular software framework.

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As part of the DFG project KO1483/5-1, the influence of surface form and local differences in the surface potential (patch potentials) on capacitive displacement sensors was systematically investigated. Using cylindrical thin-film electrodes specially manufactured at PTB, it was shown that the waviness has a measurable influence on the electric field, but the roughness is negligible in practical applications. Furthermore, it was demonstrated for the first time that patch potentials influence the linearity in such a way that they must be taken into account in the uncertainty budget.

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According to the new mise en pratique, the lattice spacing of silicon can be used as a secondary realization of the meter in nanometrology. To this end, a reliable and robust workflow has been established using transmission electron microscopy (TEM). Cross-sectional specimens of Si of various thicknesses were successfully prepared using a focused ion beam (FIB). The {220} lattice spacings of Si were measured by double aberration corrected TEM with a spatial resolution of 60 pm. Thereby, unavoidable drifts were effectively minimized. Finally, the standard deviation of the measured {220} d-spacings of Si reached 1 pm.

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Standards with calibration structures in three dimensions are an important tool for the traceable calibration of high-resolution 3D microscopes. A process has been developed for the fabrication of such standards that enables large-scale production and therefore low unit costs. The first prototypes have been manufactured and presented.

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A large gear measurement standard has been calibrated for a European industrial company that manufactures gearboxes for wind turbines, among other things, in order to monitor its production process. The calibration was carried out on the coordinate measuring machine in the Competence Center Wind. In addition to the gear measurements, the diameter, form and straightness of 3D geometric elements were also calibrated.

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In cooperation with industrial partners, a software test module was developed, which enables manufacturers of coordinate measuring machines and developers of evaluation algorithms for gears to test their software against independent reference data generated by the PTB. The test covers the widest possible range of common gear geometries, including the most important flank modifications. The new software test module will be integrated into PTB's existing TraCIM system (https://tracim.ptb.de).

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To determine the metrological structural resolution (MSR), two known methods that use different measurands were compared with each other, the "curved-edge based" (CEB) and the "profile-based spectral" (PBS) method. For the first time, it was possible to establish an analytical relationship between the results of the two methods and to successfully confirm this relationship through experiments and simulations. This analytical relationship will allow a standardised definition of MSR in industrial X-ray CT in the future.

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As part of the EMPIR project TracOptic, a ray-optical model of a chromatic confocal distance sensor was developed using PTB's Matlab library SimOptDevice. Incorporating techniques from computer graphics, this model considers the scattering characteristics of measurement objects by utilizing Bidirectional Reflection Distribution Functions (BRDF). Through simulated measurements, it becomes possible to correct systematic measurement errors or to incorporate them into the estimation of measurement uncertainty.

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As part of the QI-Digital initiative, industrial computed tomography (CT) is used for quality assurance in the "additive manufacturing" use case. The digitalization of the quality infrastructure requires a reduction in the high storage requirements of CT measurement data. To this end, compression algorithms were analyzed, and the measurement deviations caused by compression were quantified. To reduce these measurement deviations, neural networks were tested.

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In the BMWK-funded lighthouse project GEMiMEG-II, digital calibration certificates for standards frequently used in coordinate metrology have been developed for the first time. The DCC structures for reference spheres, ring gauges as well as ball and hole plates correspond to the latest DCC schema and are now being tested for use in fully digitized processes.

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As part of the EMPIR project 19ENG07 Met4Wind, optical areal measurements were carried out for the first time on the large gear standard with a diameter of 2 meters. Two objectives have been achieved: the characterisation of the optical sensor, which was developed for fast industrial applications, and the confirmation of the applicability of the holistic evaluation algorithm for optically measured gear surfaces.

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Adhesives are often used to join optical components such as mirrors or lenses in high-accuracy applications. Since the requirements for the temporal stability of these connections are very high, the question arises as to suitable methods with which changes in the adhesive gap thickness can be measured at sub-nm level. Of particular interest here is the fact that adhesives effectively absorb moisture in air or release it again in a vacuum, accompanied by expansion or shrinkage. Based on measurements of the absolute length of test specimens enclosing an adhesive gap of approx. 0.1 mm, the drying-induced shrinkage of the adhesive gaps could be followed sub-nm accurately over several years in a vacuum.

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A thickness sensor for metal strips between five and several hundred micrometres thickness in production in the cold rolling mill was developed together with a small medium-sized German company within the technology transfer program TransMET. The sensor is based on a combination of optical triangulation and multi-wavelength interferometry. In addition, a detailed measurement uncertainty budget for thickness measurement under these difficult measurement conditions could be established.

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PTB paves the way for a new method of measuring in sawmills with successful type examinations in the field of round timber measurement. With the so-called “variable caliper”, the replica of a measuring caliper rotating around the individual log finds its way into the practice of legal metrology.

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As part of the QI-Digital project, a computer tomograph from Werth Messtechnik GmbH was put into operation in 2022. The range of tasks includes additively and conventionally manufactured components made of plastic and metal as well as combinations of several materials. The evaluations include dimensional accuracy tests and analyses inside the object.

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