Severely damaged historical documents are extremely fragile. In many cases, their secrets remain concealed beneath their cover. Recently, non-invasive digitization approaches based on 3-D scanning have demonstrated the ability to recover single pages or letters without the need to open the manuscripts. This can even be achieved using conventional micro-CTs without the need for synchrotron hardware. However, not all manuscripts may be suited for such techniques due to their material and X-ray properties. In order to recommend which manuscripts and which inks are best suited for such a process, we investigate six inks that were commonly used in ancient times: malachite, three types of iron gall, Tyrian purple, and buckthorn. Image contrast is explored over the complete pipeline, from the X-ray CT scan and page extraction to the virtual flattening of the page image. We demonstrate, that all inks containing metallic particles are visible in the output, a decrease of the X-ray energy enhances the readability, and that the visibility highly depends on the X-ray attenuation of the ink’s metallic ingredients and their concentration. Based on these observations, we give recommendations on how to select the appropriate imaging parameters.

Fringe projection profilometry in combination with other optical measuring technologies has established itself over the last decades as an essential complement to conventional, tactile measuring devices. The non-contact, holistic reconstruction of complex geometries within fractions of a second in conjunction with the lightweight and transportable sensor design open up many fields of application in production metrology. Furthermore, triangulation-based measuring principles feature good scalability, which has led to 3D scanners for various scale ranges. Innovative and modern production processes, such as sheet-bulk metal forming, thus, utilize fringe projection profilometry in many respects to monitor the process, quantify possible wear and improve production technology. Therefore, it is essential to identify the appropriate 3D scanner for each application and to properly evaluate the acquired data. Through precise knowledge of the measurement volume and the relative uncertainty with respect to the specimen and scanner position, adapted measurement strategies and integrated production concepts can be realized. Although there are extensive industrial standards and guidelines for the quantification of sensor performance, evaluation and tolerancing is mainly global and can, therefore, neither provide assistance in the correct, application-specific positioning and alignment of the sensor nor reflect the local characteristics within the measuring volume. Therefore, this article compares fringe projection systems across various scale ranges by positioning and scanning a calibrated sphere in a high resolution grid.

One major advantage of additive manufacturing is the high freedom of design, which supports the fabrication of complex structures. However, geometrical features such as combined massive volumes and cellular structures in such parts can lead to an uneven heat distribution during processing, resulting in different material properties throughout the part. In this study, we demonstrate these effects, using a complex structure consisting of three conic shapes with narrow cylinders in between hindering heat flux. We manufacture the parts via powder bed fusion of Ti6Al4V by applying a laser beam (PBF-LB/M) as well as an electron beam (PBF-EB). We investigate the impact of the different thermal regimes on the part density, microstructure and mechanical properties aided by finite element simulations as well as by thermography and X-ray computed tomography measurements. Both simulations and thermography show an increase in inter-layer temperature with increasing part radius, subsequently leading to heat accumulation along the build direction. While the geometry and thermal history have a minor influence on the relative density of the parts, the microstructure is greatly affected by the thermal history in PBF-LB/M. The acicular martensitic structure in the narrow parts is decomposed into a mix of tempered lath-like martensite and an ultrafine $\alpha$ + $\beta$ microstructure with increasing part radius. The EBM part exhibits a lamellar $\alpha$ + $\beta$ microstructure for both the cylindric and conic structures. The different microstructures directly influence the hardness of the parts. For the PBF-LB part, the hardness ranges between 400 HV${}_{0.5}$ in the narrow sections and a maximum hardness of 450 HV${}_{0.5}$ in the broader sections, while the PBF-EB part exhibits hardness values between 280 and 380 HV${}_{0.5}$.

The development of a virtual metrological CT for numerical measurement uncertainty determination at the Institute of Manufacturing Metrology (Friedrich-Alexander-University Erlangen-Nuremberg (FAU), Germany) using the software aRTist 2 by the BAM German Federal Institute for Materials Research and Testing is described. The virtual metrological CT uses a Monte-Carlo approach for numerical measurement uncertainty determination. Results demonstrating that numerical uncertainty determination according to GUM Supplement 1 and in accordance with uncertainty determination according to guideline VDI/VDE 2630 Part 2.1 is possible for selected measurement tasks are presented.

Industrial x-ray computed tomography (CT) represents an established measurement technique in the field of nondestructive testing and dimensional metrology. However, the measurement accuracy is sometimes limited by measurement artifacts that cannot be avoided using a standard circular scan trajectory. This problem can be addressed with the aid of flexible 3D trajectories, but up to date, the application of these is mainly restricted to special CT devices using robot arms. In this paper, we present results using a hexapod as an additional positioning system in a commercial industrial CT scanner. In addition to the 360^∘rotation, task-specific tilting of the part during the scan is possible in this way. We used and adapted geometry calibration procedures based on a multi-sphere reference object to enable reconstruction with high accuracy. Using a demonstrator test fixture with high absorbing elements, we show that severe metal and truncation artifacts can be avoided for a region-of-interest scan. Furthermore, cone-beam artifacts, which are inherent to circular scan trajectories, can be reduced significantly. Using measurement objects that can be measured well with a circular trajectory, we found that applying a 3D trajectory leads to dimensional measurement deviations in the same range or even lower than those of a circular trajectory. This suggests that the pose repeatability of the hexapod is sufficient to perform complex scan paths without general loss of accuracy. The obtained results could be relevant for end users of conventional CT scanners, as upgrading existing devices is in principle possible. The presented investigations form the basis for the application of trajectory optimization algorithms.

Zusammenfassung: Koordinatenmesssysteme sind vielseitig einsetzbar zur Prüfung geometrischer Merkmale an komplexen, dreidimensionalen Werkstücken. Eine wirkungsvolle Qualitätssicherung ist allerdings nur dann möglich, wenn ihre Eignung für die konkrete Messaufgabe nachgewiesen ist. Die DIN EN ISO 14253 DIN EN ISO 14253-1:2013-12 (2013). Geometrische Produktspezifikationen (GPS) – Prüfung von Werkstücken und Messgeräten durch Messen – Teil 1: Entscheidungsregeln für den Nachweis von Konformität oder Nichtkonformität mit Spezifikationen. fordert daher, dass die Messunsicherheit bekannt und mit der Toleranz vereinbar ist (siehe auch Imkamp und Kistner Imkamp, D. und Kistner, T. (2016). Neue ISO 9001 Revision – und ihre Bedeutung für die Messtechnik in der Produktion. In 18. GMA/ITG-Fachtagung Sensoren und Messsysteme 2016, Seiten 488–492. AMA Service GmbH. ). Die Herausforderung liegt in der Bestimmung der Messunsicherheit. Diese kann für Koordinatenmesssysteme sehr aufwendig und komplex sein, da sich Unsicherheitsbeiträge u. a. aus dem Messgerät, dem Werkstück und der Umgebung in verschiedener Weise überlagern und sich für die individuellen Merkmale zu sehr unterschiedlichen Messunsicherheiten addieren. Es existieren unterschiedliche Ansätze, diese merkmalspezifischen Messunsicherheiten zu ermitteln. Der vorliegende Beitrag beschreibt ein auf numerischer Simulation basierendes Verfahren und stellt neue Entwicklungen vor. Diese beinhalten unter anderem die Unterstützung von Messungen mittels taktiler Scanningtechnologie und die Berücksichtigung des Unsicherheitseinflusses, der durch unvollständige Erfassung (Unterabtastung) der Prüfmerkmale verursacht wird. Die Eingangsgrößen und deren Ermittlung werden beschrieben. Neben der präzisen Erfassung der Eingangsgrößen wird auch eine vereinfachte Methode vorgestellt, die es Anwendern ermöglicht, die zu erwartende Messunsicherheit grob abzuschätzen, ohne eine aufwendige messtechnische Erfassung aller Einflussgrößen durchzuführen.