Performance evaluation of an image-based measurement method used to determine the geometric errors of cone-beam CT instruments

Today, 3D X-ray microscopes (XRMs) have the unique ability to achieve higher resolution, non-destructive imaging, within larger parts than traditional X-ray micro computed tomography (CT) systems. Such unique capability is, more and more, of interest to industrial quality control entities as they grapple with small features in precision manufactured parts for various industries such as automotive, electronics, aerospace, medical devices, and additive manufacturing, to name a few examples.

Section: Measurement Performancementioning

confidence: 99%

Improving the dimensional accuracy of computed tomography data obtained with high-resolution 3D X-ray microscopes

Villarraga-Gómez¹,

Kotwal²,

Parwani³

et al. 2022

“…Baldo et al [17] described the experimental investigation of the geometric errors of a cone-beam CT system using an imagebased measurement method to map them. Special attention was given to the evaluation of the effectiveness of the measurement method itself to detect the geometric errors, by properly designing the experiments and using statistical techniques such as the analysis of means and analysis of ranges, which combine the graphic power of average and range chart with the sensitivity of the analysis of variance.…”

Section: Outcomes Of Other Collaborative Projectsmentioning

confidence: 99%

CT-based dimensional metrology developments in Brazil: Current status and outlook

Baldo¹,

Fernandes²

2023

Since the 1980s Computed Tomography (CT) has been used in many industrial sectors for non-destructive inspection, including flaw detection, failure analysis, and assembly analysis. Back to the 2000s CT has become a metrology tool for dimensioning and tolerancing analysis as well, in which some topics have gained attention of researchers, such as the traceability of a measurement result and the evaluation of the measurement uncertainty. In Brazil, the first two CT systems for dimensional applications were installed about a decade ago in two research centers. For years these two CT infrastructures for dimensional metrology allowed companies of different segments to benefit from the technique and made it possible for researchers to be involved in the field of CT for dimensional metrology. More recently, those promising initiatives have been drastically reduced for reasons such as the obsolescence of those CT infrastructures, despite the significant research efforts that have been observed in other venues. To reverse this negative outlook associated with the field of CT dimensional metrology in Brazil, this paper outlines an integrative framework for collaborative research and development in the subject, which encourages measures, e.g., to fund basic and applied researches, to train and educate people, and to support industries through measurement services and bespoke solutions.

“…The underlying concept is to minimize the reprojection error, which is a measure for the difference between the measured 2D coordinates of the projected sphere midpoints in the detector image and the calculated ones setting up an analytical formula for the forward projection. Investigations that are based on this methodology can be found in [3][4][5][6]. Geometry calibration based on spherical markers is also relevant for CT systems that have a high degree of geometric freedom and thus are able to perform 3D scan trajectories.…”

Section: Introductionmentioning

confidence: 99%

“…While the Deng correction according to (1) was applied e.g. in [3,4], it was not used in [5] as no clear improvements were observed. One problem of equation ( 1) is that it is quite sensitive to errors from the ellipse detection, especially for small values of c. Lüthi et al [6] and Kang et al [7] used equation ( 2) that is more stable but needs the sphere radius and the axial distance from the source x 0 as additional input.…”

Section: Introductionmentioning

confidence: 99%

CT scan trajectory calibration based on projected metal spheres: When and how should errors from elliptical distortion be corrected?

Butzhammer¹,

Braun²,

Hausotte³

2023

The majority of geometry calibration procedures for industrial X-ray Computed Tomography (CT) are based on determining projected sphere centres in X-ray projections. The centres are typically derived from the elliptical contours that arise for cone beam setups. However, the ellipse centre is not identical with the projected sphere centre. A correction method (also known as Deng correction) exists, but is only used in some instances in literature. To this extent, it is an open question for which cases the correction leads to a significant improvement. For specific cases, it can even lead to larger errors. In this contribution, we therefore analyse the parameter range for which the correction is suitable. This is done by means of a simulation parameter study. Additionally, we propose an adapted correction formula that can be used for 3D scan trajectory calibration where the source-detector-distance is known. It is further proposed to keep the ellipse orientation in the ellipse fitting routine fixed. The results from simulation are selectively compared with experimental findings. Overall, the adapted correction leads to superior results compared with the original Deng correction. Whether a correction leads to an improvement at all strongly depends on the ratio between the axial source-object-distance and the sphere radius and on the position of the projected sphere centre on the detector. A theoretically derived decision criterion was largely confirmed. The presented results therefore can give a guidance for potential users who want to decide whether a correction is advantageous for a given sphere radius and CT system geometry.