Bremer Institut für Messtechnik, Automatisierung und Qualitätswissenschaft (BIMAQ)
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Item-typ:Veröffentlichung, Geometry Measurement of Submerged Metallic Micro-Parts Using Confocal Fluorescence Microscopy(Springer, 2018-07-10); ; ; The in situ geometry measurement of microstructures in the laser chemical machining (LCM) manufacturing process places high demands on measurement systems because the specimen is submerged in a closed fluid circuit. The steep slopes of the manufactured micro-components and the general lack of accessibility hinder the use of standard techniques such as tactile measurement or conventional confocal microscopy. A technique based on confocal fluorescence microscopy shows promise for increasing the measurability on metallic surfaces with large curvatures. By applying an intensely scattering fluorescent coating to the specimen, the surface position can be determined by the change in fluorescence signal at the boundary between specimen and coating. In contrast to the currently tested thin coatings (<100 μm) the measurements in layers thicker than 1 mm, as required for in situ application at the LCM process, show distinct dependencies on the fluorescent medium in terms of concentration and index of refraction. Hence, a fundamentally different signal evaluation approach based on a physical model of the fluorescence signal is needed to extract the surface position information from the detected fluorescence intensity signal. For the purpose of validation, the measurement of a step geometry is performed under the condition of a thick fluid layer and referenced with a tactile measurement. As a result, the model-based approach is shown to be suitable to detect the geometry parameter step height with an uncertainty of 8.8 μm or a step submerged in a fluid layer with a thickness of 2.3 mm.Wissenschaftlicher ArtikelBand:1Heft:382 71 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Berührungslose Messung von Pitchwinkelabweichungen an Windenergieanlagen aus 150 m Entfernung(De Gruyter Oldenbourg, 2021-08-26); ; ; ; Die Windkraft stellt eine wichtige Energiequelle in Deutschland dar. Form und Lage der Rotorblätter von Windenergieanlagen haben dabei einen großen Einfluss auf die Effizienz und die Lebensdauer der Anlage. Geometrische Merkmale von Rotorblättern werden mit Blattschablonen, photogrammetrischen oder interferometrischen Messverfahren erfasst. Hierzu muss die Anlage jedoch gestoppt und ggf. mit Mustern bzw. Markern versehen werden. Für In-Prozess-Messungen ohne Manipulation der Windenergieanlage bietet sich das Prinzip der Laufzeitmessung an, auf dem sogenannte terrestrische Laserscanner aufbauen. Bisher unbekannt ist jedoch die erreichbare Messunsicherheit bei der Bestimmung von Pitchwinkeln. In diesem Beitrag werden die Messunsicherheiten bei der Erfassung der Rotorblattoberfläche für Distanzen > 100 m experimentell untersucht und zur Bestimmung der Unsicherheit des Pitchwinkels mittels Monte-Carlo Simulation fortgepflanzt. Für die Betrachtung der Pitchwinkelunsicherheit wird unterschieden, ob die Nenngeometrie der Rotorblätter bekannt ist und absolute Aussagen über die Pitchwinkel getroffen werden können, oder ob die Nenngeometrie unbekannt ist und nur relative Pitchwinkelunterschiede zwischen den Rotorblättern ausgewertet werden können.Wissenschaftlicher ArtikelBand:88Heft:11103 80 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The coherence function and its information content for optical metrology(De Gruyter Oldenbourg, 2022-05-24); ; ; ; The coherence function offers new possibilities for optical metrology that are not available with conventional wave field sensing. Its measurement involves a spatio-temporal sampling of the wave fields modulated by the object under investigation. Temporal sampling is well known e. g. by means of White Light Interferometry (WLI) and spatial sampling can e. g. performed by Computational Shear Interferometry (CoSI). The present paper describes an approach that combines both temporal and spatial sampling using a robust common-path setup. While the evaluation of the coherence function is more elaborate than approaches that either sample the temporal or the spatial domain, an information theoretical treatment shows that it also delivers more information about the object under investigation. Our approach is based on the mutual information that represents the reduction of uncertainty about the object as a consequence of the measurements performed. Using a simplified measurement case, we calculate the mutual information for different measurement situations and demonstrate that spatio-temporal sampling of the coherence function results in a higher mutual information as compared to classical approaches. Based on the proposed approach, we identify further open research tasks for an efficient information extraction from the coherence function to surpass current limitations of optical metrology.Wissenschaftlicher ArtikelBand:89Heft:6103 103 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Laser line triangulation for fast 3D measurements on large gearsThe causes of geometrical deviations from the production process and the prediction of application properties, such as noise behavior, wear, or material fatigue, are only possible by having detailed information about the gear geometry. The gold standard for the gear quality inspection is represented by dimensional measurements with a tactile sensor system. As a result for industrial applications, the slow serial measurement leads to the compromise of a random inspection of the gear geometry. For the purpose of a faster and more extensive surface acquisition, a laser line triangulation sensor is investigated providing 1280 points at a line width of 25 mm with up to 200 lines/s. The results at the tooth of a large cylindrical involute gear with a pitch circle diameter of 922 mm and a face width of 246 mm show the qualification for fast three-dimensional measurements of the convex and reflective surface. The detection of the complete profile line at once is possible. It is shown that the measurement deviation of laser line triangulation can be minimized by increasing the dynamic threshold. The measurement deviations amount to ± 8.2 μm and can be attributed to random and systematic errors. Compared to the standard gear inspection, an acceleration factor of 5700 was attained. An optical scanning of the complete tooth flank provides the prerequisite for an identification of surface defects in the form of breakouts and blemish.Wissenschaftlicher ArtikelBand:100141 155 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, In-situ-Untersuchung von Randschichten während des Gasnitrierens mittels Röntgendiffraktometrie und photothermischer RadiometrieThe aim of most applications of nitriding treatments at steel components is to obtain a compact compound layer and/or a deep diffusion layer. The possibility of a survey of the nitriding treatment by analyzing directly the component´s surface state during the nitriding process is particularly interesting, since it allows a process monitoring and control based on the actual nitriding result. In the present study, two measurement methods were developed and combined with the aim of direct surface state analysis during a nitriding treatment: the in-situ X-ray diffraction method and the photothermal radiometry. An experimental setup including a miniature nitriding furnace was developed in order to allow the combined application of both methods during a nitriding process under controlled atmosphere. In the present work, results of combined in-situ measurements on the steel AISI 4140 regarding the nitride layer formation during nitriding process as well as the nitride layer change during the following denitriding of the layer in nitrogen gas are presented and discussed. The investigations show that the photothermal radiometry is sensitive to the changing surface properties due to growing compound layers and when porous layers are generated. This method has a high potential for implementation in industrial nitriding furnaces, but for this, further development for quantitative evaluations of the measurements will be required.Wissenschaftlicher ArtikelBand:72Heft:396 95 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, In-Process Tool Deflection Measurement in Incremental Sheet Metal FormingIncremental sheet forming is an economical alternative to deep drawing for forming large sheets in small quantities. However, the shape deviations resulting from a process-force-caused tool deflection limits the measuring accuracy. Therefore, an optical multi-sensor system is proposed to enable the contactless in-process measurement of the tool deflection independent of the machine kinematics for the first time. The presented design study of the sensor system aims to meet the requirement of a maximal measurement uncertainty of 15 µm at a measuring distance of up to 2 m. The multi-sensor system consists of a large number of inexpensive angulation sensors, each of which measures an angle to a light source on the tool. Based on the measured angles of all sensors calibrated to each other, the position of the tool in the three-dimensional manufacturing volume can be calculated by multi-angulation. Via experimental characterization of a realized angulation sensor as well as an uncertainty propagation, the measurement uncertainty achievable with the overall system is estimated. As a result, the multi-sensor concept fulfills all requirements for the measurement of the tool deflection in incremental sheet metal forming.Konferenzbeitrag57 80 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, IR thermographic visualization of flow separation in applications with low thermal contrast(Elsevier Science, 2018-01); ; ; A measurement method for IR thermographic visualization of separated flow on rotor blades for wind turbines is demonstrated. Flow separation has a negative influence on the performance of airfoils, e.g., at wind turbine rotors. Thermographic flow visualization is a non-invasive measurement technique to identify different flow regimes, but the visualization of separated flow without explicit additional heating of the measured object has not been possible to date. For this reason, a measurement approach with an enhanced sensitivity is presented, which evaluates temporal temperature fluctuations from a thermographic images series by means of the standard deviation as well as the analysis of selected Fourier coefficients. The approach is validated by wind tunnel experiments with a non-heated circular cylinder as well as a 2D 6 digit NACA-airfoil. The flow and measurement conditions are chosen to be similar to wind turbines in operation. As a result, the flow regimes including the flow separation are resolved and are in agreement with reference measurements, while the sensitivity of standard thermographic flow visualization was too low. In addition, the Fourier analyses method results in an improvement of the contrast to noise ratio between turbulent and separated flow by 11.6 % compared to the evaluation of the temperature standard deviation. Further improvements are expected in future when taking the complete spatiotemporal temperature fluctuations into account.Wissenschaftlicher ArtikelBand:88125 149 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Systematische Ursachenforschung von Erosionsschäden an Windenergieanlagen mittels Computertomographie (XRM) als Basis zur Schadensminimierung und Serviceoptimierung (SUrfErCut) : Schlussbericht vom 30.09.2022(2022-09-30); ; ; ; Im Projekt wurde erstmalig das µ-CT und XRM-Verfahren zur zerstörungsfreien Charakterisierung mehrfach zyklisch belasteter Probekörper angewandt und das an realgroßen Probekörper mit Auflösungen bis zu einem Mikrometer. Die bildbasierte Prüfmethode ermöglicht die Identifizierung, Verortung und Charakterisierung der prozessbedingten- und künstlichen Fehlstellen. Die Anwendung der Röntgenverfahren auf die mehrfach zyklisch belasteten Probekörper ermöglicht die Identifizierung und Bewertung von initial Schädigungen “Efects of defects” und in Abhängigkeit von Position, Fehlergröße auf das Bauteilversagen. Am Ende der Untersuchungen steht ein Katalog von aufzufinden Fehler, die in der Produktion zu vermeiden sind und nach der Produktion sowie in der Anwendung der WEA aufgefunden werden müssen. Ein wesentlicher Aspekt war die Entwicklung von automatisierte Auswerteverfahren der µ-CT und XRM-Bilddaten. Im Projekt wurden Methoden der Künstliche Intelligenz (KI) in Form von „machine learning“ und „deep learning“ erprobt und angewandt. Dazu wurden Verfahren wie das „Random Forest Classification“ (machine Learning) zur Erzeugung von annotierten Datensätzen zum Training von neuronalen Netzen angewandt sowie Untersuchung möglicher und relevanter Architekturen und Formen von neuronalen Netzen (z.B. U-Net und Sensor 3D) durchgeführt. An ausgewählten Proben wurden Vergleiche zwischen dem U-Net und Sensor 3D hinsichtlich Fehlstellenerkennung durchgeführt wobei sich das Sensor 3D als das geeignetere zeigte. Auch wurden Verfahren zur Visualisierung der Entwicklung der Fehlstelle nach zyklischer Erosionsbelastung entwickelt und angewandt. Im Projekt wurde erstmalig aktive Thermografie zur Defektdetektion an rotorblattähnlichen, mehrfach zyklisch mit Regen belasteten Probekörpern erfolgreich angewandt. Es wurde gezeigt, dass aktive Thermografie, insbesondere Langpuls-Thermografie auch ohne besonders starke und komplizierte Datenverarbeitung ein mächtiges Tool bei der Defektdetektion an thermisch trägen Materialien darstellt, speziell bei der Qualitätssicherung Wartung von Rotorblättern an Windenergieanlagen.Bericht357 200 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Tooth flank approximation with root point iteration – potentials and limits in gear metrologyGear production demands high-precision metrology, for which a holistic evaluation approach of the geometric data is proposed to overcome current restrictions. The holistic approximation with integrated partitioning and iterative root point calculation can cope even with modified flanks and is validated for gear parameter estimation with systematic deviations <0.2 µm. Apart from low signal-to-noise-ratio cases, where the approximation suffers from the multidimensionality of the optimization, the accuracy of standard evaluation procedures is achieved. Furthermore, holistic approximation is able to perform the required mathematical separation of the integral geometric elements of a tooth flank automatically when determining unknown gear parameters.Wissenschaftlicher ArtikelBand:70Heft:195 90 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Particle image velocimetry in refractive index fields of combustion flowsOptical measurements inside reacting flows are often disturbed by refractive index fields, e.g., due to the strong density gradients in flames. Although occurring measurement errors due to light refraction are a known problem for certain particle image velocimetry (PIV) applications, only a qualitative analysis of the resulting measurement uncertainty inside flame flows has been carried out to date. As an important step forward, a measurement approach is proposed, which enables a quantification of the resulting measurement uncertainties due to light refraction. As an example, the measurement approach is applied to a premixed propane flame. The uncertainty analysis is based on the determination of occurring particle position errors due to light refraction inside the flame. For three different measurement planes, the velocity field is measured with PIV and the particle position errors are experimentally measured and verified by ray-tracing simulation based on the measured refractive index field, which is determined by the background-oriented Schlieren method. In the examined flow, maximal position errors amount up to 14 μm and yield significant systematic velocity errors of up to 4% and random velocity errors of up to 6%. In contrast to the systematic velocity error, the random velocity error varies significantly for the analyzed measurement planes inside the flame flow.Wissenschaftlicher ArtikelBand:60109 73