Geometric qualification for robot CT with flexible trajectories

Kang, Risheng; Probst, Gabriel; Vlaeyen, Michiel; Fei, Guanghai; Guerrero, Patricio; Haitjema, Han; Slaets, Peter; Dewulf, Wim

doi:10.58286/26589

Cited by 4 publications

(3 citation statements)

References 14 publications

(17 reference statements)

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“…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. In [7], a method and a phantom that is suitable for a twin robotic CT system was presented. In our own work [8], we implemented multi-sphere based scan trajectory calibration for a CT device with a hexapod as additional object manipulator on top of the rotary table.…”

Section: Introductionmentioning

confidence: 99%

“…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. They determine x 0 using an iterative procedure, which can imply additional effort.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Butzhammer¹,

Braun²,

Hausotte³

2023

eJNDT

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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.

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Section: Introductionmentioning

confidence: 99%

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

eJNDT

View full text Add to dashboard Cite

show abstract

“…This typically requires increased efforts regarding the image processing. Kang et al [13] addressed this problem by using uniquely identifiable collinear markers.…”

Section: Introductionmentioning

confidence: 99%

Calibration of 3D scan trajectories for an industrial computed tomography setup with 6-DOF object manipulator system using a single sphere

Butzhammer

Müller²,

Hausotte³

2022

Meas. Sci. Technol.

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In industrial X-ray computed tomography (CT), the application of more complex scan paths in comparison to the typical circular trajectory (360° rotation of the measurement object) can extend the potential of CT. One way to enable such 3D scan trajectories is to use a 6-degrees-of-freedom object manipulator system. In our case, a hexapod is mounted on top of the rotary table of a commercial CT scanner. This allows for adaptive tilting of the measurement object during the scan. For high accuracy, the geometry calibration of such setups is typically done using the X-ray projections of a calibrated multi-sphere object. Contrary to this, here, we demonstrate a procedure that is based on only a single sphere and can therefore experimentally be implemented with low effort. Using the intrinsic geometry parameters of the CT device as prior information, the hexapod coordinate system with respect to the CT machine coordinate system is determined by means of a one-step optimization approach. The resulting parameters are used to calculate projection matrices that enable the volume reconstruction for 3D scan trajectories. The method is validated using simulated X-ray images and experimental investigations including dimensional measurements. For the used setup, geometric measurement results for 3D scan trajectories that are calibrated with the presented method show in sum increased errors compared to the circular scans. A limited pose accuracy of the manipulator system is discussed as a potential cause. The results nevertheless indicate that the presented method is generally feasible for dimensional CT measurements provided that the pose accuracy is sufficient. The calibration procedure can therefore be a low-cost and easier to implement alternative compared to trajectory calibration methods based on multi-sphere objects, but with a tendency towards lower measurement accuracy. The methodology can in principle be transferred to different setups with 6-DOF manipulator systems, e.g. C-arm CT devices with a robot arm.

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Challenges in non-destructive X-ray CT testing of riveted joints in the automotive industry

Schromm,

Beckmann,

Moosmann

et al. 2024

Discov Appl Sci

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Despite recent advancements, contemporary laboratory-based industrial computed tomography (CT) technology has not yet achieved the status of an efficient and economically viable in situ non-destructive method for examining riveted joints that are commonly used in the automotive industry. 2D X-ray or 3D CT systems can only reliably assess a rivet joint’s condition in rare, and favorable circumstances. Moreover, a comprehensive analysis to identify the obstacles preventing CT from efficiently capturing high-resolution, and contrast-rich scans of riveted joints in general is lacking. This work delves into the challenges and limitations of the technology that prevent operators from reaching the desired precision required for rigorous quality control. The study specifically addresses questions concerning in situ reachability and positioning of the sample structure, radiodensity and beam hardening, the relationship between spot size and power, and economic feasibility—all within the context of analyzing riveted joints in the automotive industry. Additionally, we provide an abstracted overview of the current industrial X-ray tube market, which informs our discussion on these specific aspects. Through a combination of experimental findings, analytical insights, and deductions, we shed light on the persistent difficulties in achieving resolutions comparable to macro-sectioning and microscopy, which are currently considered the gold standard in examining riveted joints. Our investigation further explores the potential of a photon-counting detector paired with a conventional, laboratory-based X-ray source. Furthermore, we investigate the use of a synchrotron beamline as an X-ray source in conjunction with a custom-designed detector optimized for such beam geometries. This detector employs scintillators coupled with optical magnification, functioning similarly to an X-ray microscope. Our findings and data collection conclusively reveal that commercially available CT systems still fail to meet the requirements for efficient testing, underscoring the urgent need for further research and development to enable widespread implementation.

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Geometric qualification for robot CT with flexible trajectories

Cited by 4 publications

References 14 publications

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

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

Calibration of 3D scan trajectories for an industrial computed tomography setup with 6-DOF object manipulator system using a single sphere

Challenges in non-destructive X-ray CT testing of riveted joints in the automotive industry

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