Precision Engineering

The scientific journal “Surface Topography: Metrology and Properties (STMP)” has awarded the research results described in the publication “Bottom-up approach for traceable calibration of tip geometry of stylus profilometer” as “Paper of the Year 2022”.

Rough surfaces lead to systematically smaller indentation modules in nanoindentation. This influence has now been systematically examined for the first time on rough crystalline Si surfaces and a correction method has been developed with which it will be possible in the future to reduce the corresponding uncertainty contribution to less than 1 %.

An important milestone was reached with the successful assembly and the first tests of the metrological UHV-STM. The instrument will enable to get valuable insights about crystalline surfaces and pave the way towards the use of novel materials in metrology.

As part of the QI-Digital initiative, the potential of digitization for new ways of making the quality infrastructure more effective and efficient is to be examined and demonstrated. Using the example of additive manufacturing, the necessary steps for an optimal interaction of the QI components and data management have now been analyzed and implemented using an additively manufactured demonstrator (replacement) component.

The development of a controller for atomic force microscopes (AFM) based on artificial intelligence (AI) has been started. The aim of the research is to develop a strategy for the safe realisation of an AI-based controller for sensitive devices such as atomic force microscopes as well as the development of the controller itself. Results so far indicate a great potential of the AI controller, but also show the difficulties in its realisation.

The TeleYAG-II absolute interferometer, developed within the European EMPIR research project 18SIB01 GeoMetre, has been used in several locations in Europe where high accuracy measurement of large distances is important: the world's best reference baseline for high accuracy distance measurement in Finland, at the geodetic fundamental stations of Metsähovi, Finland and Wettzell, Germany, and at a new 200 m reference baseline at Warsaw Polytechnic University.

The knowledge about specific geometric features of devices and parts are of significant importance for explosion protection. To support an international key comparison led by the working group 3.54, 100 test samples developed and produced by the Scientific Instrumentation (department 5.5) were calibrated by working group 5.32. The calibrations establish the reference for the reliable judgment of measurement results provided by all 85 participating international laboratories.

A fast and easy-to-use method and a test object were developed for the measurement and correction of beam-hardening in computed tomographic (CT) images. The method consists of measuring the attenuation curve, i.e., the grey values of a radiographic image of a new developed test object in relation to the material penetration length. The cone-like object was designed so that in the radiographic image all central radial profiles feature a linear increase of the material length. A look-up table can be extracted from the measurements for the correction of the so-called beam hardening artefact.

In working group 2.51 "Magnetic Measurements", a 3D coil system was to be built for the TransMeT project "Traceable calibration device for vector magnetometers". For this purpose, a coil former had to be designed and manufactured that accommodates 4 coil windings in each of 3 spatial directions and enables the positioning of different magnetometers to be calibrated within the magnetic field.

Tape measures are classic and widely used length measuring devices. They are tested and calibrated in many places - worldwide in national metrology institutes such as PTB, but in Germany also in federal state calibration authorities or accredited laboratories. To ensure the comparability of this work, PTB leads two interlaboratory comparisons: the international EURAMET.L-S27 as well as a national interlaboratory comparison within the framework of the German Calibration Service DKD.

In a research project funded by the Central Innovation Programme for SMEs (ZIM) of the BMWK, the measurement deviations of the tactile-optical 3D micro probe (3D fibre probe) were improved in cooperation with Werth Messtechnik GmbH. For this purpose, a new type of sensor for the probe deflection in the z-direction was realised. This reduced the probing errors to values < 150 nm.

A pico-force MEMS-Indenter with a maximum indentation depth up to 10 µm has been developed to measure the mechanical properties of compliant materials. First quasi-static measurements of soft PDMS samples using a clamped spherical AFM probe as the indenter have been obtained. Data analysis indicates that this pico-force indenter with a noise floor of 0.2 nN is capable of measuring soft materials with elastic moduli down to 100 kPa.

Microforce standards based on silicon bending beams are well suited for in-situ measurement of the probing force of various contact stylus profilometers. However, the measurement uncertainty is limited, to a large extent, by the unknown zero-load bending of the bending beam. A rapid method using a large aperture Fizeau interferometer has now been successfully used for the first time to determine the zero-load deflection of microforce standards.

The standards for profile roughness measurements have been revised and brought together in the new three-part standards series ISO 21920. Calculation rules have been adapted to technical progress and made more precise in many places. Parameters are now predominantly calculated directly for the entire evaluation length and no longer for individual section lengths first, and some of the filtering according to the ISO 16610 series has been newly regulated, which sometimes results in differences in the old-new parameters.

Within the scope of a bachelor thesis, a fundamental modernisation of the gauge block measuring station 1 m comparator for mechanical comparison measurements is being addressed. The alternative to interferometric calibrations thus offered to customers of calibration services is particularly in demand because of the economic efficiency due to shorter measuring time with only slightly greater measurement uncertainty at the same time. The modernisation is aimed at fail-safety and further development possibilities.

A new method for traceable calibration of size and form of microspheres was realised by stitching a series of atomic force microscopic (AFM) images measured at different orientations of microspheres. The stitching algorithm is achieved using an Iterative Closest Point (ICP) point-to-plane algorithm. As the AFM tip geometry is one of the most significant error sources for the developed method, it was traceably calibrated to the lattice constant of crystal silicon. The standard deviation of measured radius values of four repeated measurements reaches 5 nm.

A universal automated approach to calibrate Rockwell hardness reference blocks has been developed within a TransMeT-project and validated through interlaboratory comparison. The developed method allows to perform calibrations much more efficiently, simplifies the compliance with the standard and eliminates the need for an expert user.

If rotary tables are used for measurement with coordinate measuring machines (CMM), the resulting geometry deviations must be determined in all 6 degrees of freedom using suitable calibration procedures. With the aid of a ball plate, the measurement of the deviations can be performed directly on the CMM in a self-calibrating manner. With the new procedure of PTB, the measurement effort required for this purpose can be significantly minimized compared to the previous method with the aid of an unregularly populated ball plate.