Model-based optimisation of CT imaging parameters for dimensional measurements on multimaterial workpieces

Schmitt, Robert; Buratti, Andrea; Grozmani, Natalia; Voigtmann, Christoph; Peterek, Martin

doi:10.1016/j.cirp.2018.04.003

Cited by 18 publications

(9 citation statements)

References 5 publications

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“…The voltage correlates to the maximum X-ray photon energy and the current to the spectrum intensity [7]. In the best-case scenario, the CT parameters are chosen according to the known geometry and material composition of the sample under investigation [8,9]. Resulting absorption profiles are recorded and stored in the form of projection images.…”

Section: Dmentioning

confidence: 99%

Application of multispectral computed tomography for the characterisation of natural graphite

Krebbers¹,

Grozmani²,

Lottermoser³

et al. 2023

eJNDT

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The established mineralogical and chemical analysis methods for graphite ores require complex sample preparation. Moreover, they do not produce 3D images of the polymineralic rock structure and texture. The lack of 3D information can lead to an erroneous assessment of the quality-determining properties of graphite ores, such as graphite flake size (grain size), graphite flake size distribution, and impurities. Therefore, there is a need to obtain 3D information from graphite ores and concentrates. Industrial computed tomography (CT or single-spectrum CT) is a unique technique that enables the examination of rocks in the 3D regime. The challenge in CT analysis of ores is the different absorption properties of mineral phases present. Low X-ray tube generator voltages lead to pronounced artefacts (volume defects) if highly absorbing gangue phases (e.g. iron sulfides) are present. Therefore, high X-ray tube voltages must be applied. However, graphite and associated gangue minerals, as well as contained cracks and voids in the ore, can exhibit similar absorption properties at higher generator energies (above 120 kV). Multispectral CT (MSP-CT) measurements offer a minimisation of CT artefacts and an increase in grey value contrasts. This work investigates the application of the MSP-CT measurements, significantly improving mineral differentiation.

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Section: Dmentioning

confidence: 99%

Application of multispectral computed tomography for the characterisation of natural graphite

Krebbers¹,

Grozmani²,

Lottermoser³

et al. 2023

eJNDT

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“…ultrasound, focal microscopy) was investigated, although, the focus was not on surface geometry determination [17][18][19][20]. This paper advances the state of the art presented in [4,[8][9][10][11][15][16][17][18][19][20] by:…”

Section: Introductionmentioning

confidence: 99%

“…One difficulty is the a-priori determination of the surface geometry of the measured parts [8]. Due to the physical characteristics of x-rays and limitations of the reconstruction process, inhomogeneities occur in XCT measurements of parts with strongly varying part dimensions or absorption coefficients [9,10]. These appear due to measurement artefacts caused by a combination of varying absorption behaviours of the x-rays (figure 1).…”

Section: Introductionmentioning

confidence: 99%

Adaptive surface geometry determination in multi-material x-ray computed tomography using fringe projection

Großeheide¹,

Geiger²,

Schmidt³

et al. 2022

Meas. Sci. Technol.

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One of the main challenges during digital post-processing of x-ray computed tomographic (XCT) measurement data is the reconstruction of the surface geometry of the measured objects. Conventionally, the surface geometry is defined as an isosurface of identical greyscale values, i.e. the x-ray absorbance of the material, based on a linear interpolation between neighboring voxels. Due to the complex surface geometry and rough surface, XCT measurements of additively manufactured (AM) parts are particularly prone to measurement artefacts caused by various physical effects when the x-rays penetrate the material. The irregular greyscale values at the measured surface geometry render commonly used single threshold greyscale value based isosurfaces as insufficient for representing the external and internal surface of the measured objects. This issue becomes particularly apparent when measuring multi-material objects, such as additively manufactured objects with integrated RFID tags. To address this challenge, this study presents a methodology for reliable surface geometry determination of XCT data based on previously acquired fringe projection (FP) data. For this purpose, the conventionally acquired surfaces geometries from the XCT and FP measurements are extracted, pre-processed and registered to each other before being merged into a single mesh. This merged data set is subsequently used as a starting point or reference for a locally adaptive threshold surface detection algorithm, which is able to capture the surface geometry at a sub-voxel resolution. In order to validate the methodology and confirm the envisaged benefits, selected geometry elements of the resulting surface geometry from measurements samples manufactured by additive manufacturing with integrated RIFD tags are compared to coordinate measurement machine (CMM) reference measurements. The results indicate a more robust surface geometry detection against artifacts especially for multi-material applications.

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“…The energies for this approach must be maximally different but sufficient to radiograph the assembly. Therefore, the best possible assembly orientation cannot be determined based on the minimization of the measurement energy, as has been done in previous studies [10][11][12]. In addition, simple minimization of the penetration length is unsuitable for multi-material assemblies.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the independence of the best assembly orientations with respect to X-ray source parameters in industrial computed tomography

Grozmani¹,

Chupina²,

Schmitt³

2020

eJNDT

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Industrial computed tomography (CT) is a proper tool for extracting both internal and external geometry in one measuring procedure without destroying or rebuilding an assembly. The diversity of assemblies and unique measurement requirements demand an expert user to be able to determine appropriate CT setup parameters. Recent publications have concentrated on the automatic choice of the CT setup parameters or on the determination of features to qualify the chosen setup parameters. Setup parameters consist of X-ray source parameters (i.e., voltage, current, and exposure time), a number of projections, a source-to-object distance (SOD), and an assembly orientation. For multi-material assemblies, it is advantageous to combine two different energies from one or two X-ray sources. Benefits of this combination are a reduction of artifacts, caused by a high absorbing material, and a increased resolution of the CT acquisition (i.e., the combination of high-voltage and low voltage-micro targets). On the basis of previous works, the assembly orientation depends on other CT parameters and requires a correction between measurements with different energies. However, to avoid additional uncertainties due to the fusion of CT volumes, the assembly orientation in the CT system should remain constant for both of the measurements. This study considers the independence of the best assembly orientation tendency and X-ray source parameters. To test the concept, the authors produced CT acquisitions of a multi-material assembly (a polyoxymethylene (POM) cube with two aluminum cylinders) in four different assembly orientations. The choice of assembly orientations was based on the sorted list of minimal required energy. The two sets of X-ray setup parameters that were chosen for the experiment were maximally distant from each other. The concept was validated by statistical analysis of the standard deviations on 48 features of the assembly. The results demonstrated that the group with the best assembly orientations is independent of the X-ray source parameter sets.

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Model-based optimisation of CT imaging parameters for dimensional measurements on multimaterial workpieces

Cited by 18 publications

References 5 publications

Application of multispectral computed tomography for the characterisation of natural graphite

Application of multispectral computed tomography for the characterisation of natural graphite

Adaptive surface geometry determination in multi-material x-ray computed tomography using fringe projection

Investigation of the independence of the best assembly orientations with respect to X-ray source parameters in industrial computed tomography

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