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

Precision Engineering

Division 5

Anni Röse from PTB was featured as DPG Physicist of the week in April, 2021. She studied physics in Göttingen, Germany and received her M.S. degree from the Georg-August University in 2018. Since 2019 she has been pursuing a Ph.D. degree in mechanical engineering at the Ilmenau University of Technology and is a part of the working group 5.42 “Multiwavelength interferometry for geodetic lengths” at PTB.

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In June 2020 the EMPIR network project "Support for a European Metrology Network on Advanced Manufacturing" was started. This project targets at the strengthening of European manufacturing industry through innovative metrology. For the first time, a coordination at the European level will be realised, which enables an infrastructure for sharing of metrological knowledge. Moreover, a research agenda will be developed in a dialogue with stakeholders from different industry sectors, which will support and accelerate the development and integration of metrology for advanced manufacturing.

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High-speed roughness measurements with piezoresistive silicon microprobes require good dynamic properties of the probe. For this purpose, tip flight tests were carried out with these microprobes on rectangular structures, in which the flight distance of the microprobe tips in the rectangular grooves was measured as a function of the probing force and the traverse speed. For the investigated probing forces of 2 µN to 12 µN and the investigated traverse speeds of 20 µm/s to 10 mm/s, no tip flight was observed for the investigated 5 mm long microprobes; they therefore show excellent dynamic behavior.

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A novel 3D measuring method based on scanning electron microscopy and the "shape from shading" reconstruction approach was tested to characterize the shape of silicon-microprobe-tips. It could be shown that there is an optimal working distance, that tilting of up to 2 ° is tolerable, that the rotation of the sample is not critical for flat samples, but that there are edge deviations in the image for topographic structures. The system is suitable for the evaluation of microprobe tips and their morphology in the topmost tip area and allows high-resolution 3D-reconstructions within a few seconds.

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The eccentric nanoindentation of silicon micropillars has been investigated. It could be shown that 10 % deviation of the measured indentation modulus occurs when the location of indentation is deviating by up to 40 % of the radius of the pillar from the pillar’s centre. During these measurements the measured indentation hardness remains almost constant, while the measured indentation modulus follows a parabolic dependence on the eccentricity. Further factors which need to be taken into account are the elastic compression and a bending or buckling effect during the experiments.

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The novel picoindenter from PTB, which uses the tip of an atomic force microscope (AFM) as an indenter to characterize nanomaterials dimensionally and mechanically, has now been decisively extended: In the "Laboratory for Emerging Nanometrology" (LENA) at TU-BS, pyramid-like Berkovich tips were produced on AFM cantilevers using a focused ion beam (FIB). These tips can also be used in the picoindenter. Compared to the conventional, conically shaped AFM tips, such indenters are mechanically more stable and enable fast dynamic measurements. Due to their high conductivity, electrical measurements are also possible for the first time.

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Sinusoidal chirp standards with surface wavelengths from 3.2 µm to 12 µm with three different amplitudes (0,4 µm, 0,7 µm, 1 µm) have been used to determine the topographic spatial resolution of optical microscopes applied for the measurement of structures with different aspect ratios. First results measured by an optical microscope operated in white light interference mode and confocal mode indicate a sensitivity of the spatial resolution depending on the aspect ratio of the structures to be measured.

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Areal roughness measurements particularly with optical techniques play an increasing role for many applications in industry. This poses the question how factors influencing the roughness measurement can be identified reliably. To tackle this issue, the properties especially of confocal microscopy are systematically investigated by comparison to the spatially higher resolving atomic force microscopy. For this purpose different novel roughness standards with marked reference fields have been developed for areal measurements so that different instruments and methods can be compared directly.

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Within the framework of the EURAMET project 1242 ‘Measurement of areal roughness by optical microscopes’, coordinated by PTB, comparative measurements of areal roughness with different optical microscopes were carried out for the first time at 6 national metrology institutes. The comparison results revealed a large deviation up to 60 % from the reference roughness parameters, depending on the measuring principle, the spatial frequency spectrum and the flank angles of the texture. By closely linking experiment and modeling, a better understanding of the influencing variables is expected to be achieved together with other research partners in the future. The aim is to develop good practice guides for the safe and traceable measurement of...

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A novel type of material measure for characterising two-dimensional (2D) instrument transfer functions (ITF) of optical areal surface topography measuring instruments has been developed. After being calibrated by the metrological large range atomic force microscope of PTB, the calibrated material measure has been successfully applied both in research and industry, showing its advantages like excellent flexibility, ease of use, high measurement repeatability and robustness.

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In a novel approach, instead of a single, high-resolution measurement image, which is strongly influenced by drift, multiple low-resolution measurement images are recorded. These show less drift distortions each and can be used to reconstruct the temporal course of the drift. The low-resolution measurement images can be corrected using the reconstructed drift and combined to a high-resolution, almost completely drift-free data set using data fusion.

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After the failure of a central electronic component of the measurement data acquisition of the primary angle comparator WMT 220, a complete renovation of the control and data acquisition of the angle table was carried out with substantial support from the company Dr. Johannes Heidenhain GmbH. In this context, the software for controlling the drives and reading out the new counter and phase measurement electronics also had to be recreated under Windows. First measurements with the new electronics were carried out. The now significantly higher data acquisition rate offers new possibilities for data analysis.

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By means of Monte Carlo simulation of image formation in the electron microscope, the research group is able to generate large training data sets of high quality, which are of central importance for machine learning. On this basis, machine learning is being used within the framework of two European projects for the detection of particles and for the morphological characterization of soot, respectively.

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State of the art three-dimensional atomic force microscopes (3D-AFM) cannot measure three spatial directions independently from each other. The 3D-Nanoprobe, a novel design based on a structured cantilever, is optimized to separate them. The detection method is based on two optical levers or one optical lever and an interferometer.

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As part of a project with industrial cooperation a measurement standard for the traceability of roughness measurements on involute gear flanks is developed. Algorithms enable the extraction of the deviations of the curved profiles and the calculation of the common roughness parameters. The software is applicable to both data from profilometers and coordinate measuring machines.

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A novel 3D test body for coordinate measuring machines was developed by the industrial partner in a ZIM project and investigated at PTB. The test body made of industrial ceramics has dimensions of 0.8 m x 0.8 m x 0.3 m and embodies a multitude of 3D- and 2D-sphere distances. With the test body, coordinate measuring machines should be measured and corrected in a limited volume in future. The goal is a significant reduction of the measurement uncertainty of calibration services.

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For traceable coordinate measurements, manufacturers and users of industrial CT scanners need a feasible method as well as standards to calibrate the geometric magnification. To determine the magnification with high precision, a time-effective method has therefore been developed using low-cost 2D metal grid foils. In this way, the accuracy of the geometric magnification’s traceability reached 2 × 10-5. This method is currently being tested within the scope of the EMPIR project titled AdvanCT with the aim of subsequently achieving widespread dissemination.

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The EMPIR research project 19ENG07 "Metrology for enhanced reliability and efficiency of wind energy systems - Met4Wind" was launched in September 2020. The aim is to improve industry-oriented production metrology for mechanical components of wind energy systems such as gears, shafts and bearings as well as rotor blades in order to be able to evaluate production processes more reliably and thus ultimately increase the service life and efficiency of such systems.

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Often, beams from multiple light sources have to be spatially superposed for sensor systems so that they propagate along the same direction. Waveguide architectures for beams that are vastly spectrally separated were compared to each other in a systematic study. The results can be used for the development of novel standards in length metrology with reduced measurement uncertainties.

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The absolute length of a single crystal silicon gauge block was measured in the temperature range between 285 K and 320 K and at air pressures from atmospheric pressure down to 10-5 hPa. The method was based on imaging interferometry and achieved measurement uncertainties of relative length changes of better than 10-9. The result on thermal expansion could confirm the previously recommended reference data of CODATA with a smaller measurement uncertainty than was previously valid.

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“Structure from Motion” is a photogrammetric technique for capturing three-dimensional objects, that is well suited for the contactless measurement of roundwood on vehicles. In cooperation with Dralle A/S (Hørsholm/Denmark), the Physikalisch-Technische Bundesanstalt (PTB) has evaluated the metrological performance of a system newly developed for the measurement of roundwood stacks on vehicles. The evaluation employed logs, whose lengths and diameters were measured using a fringe projection system, which the PTB provides as reference measurement system in legal metrology.

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