Fast Tomographic Inspection of Cylindrical Objects
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Fast Tomographic Inspection of Cylindrical Objects Wannes Goethals1
· Marjolein Heyndrickx1 · Matthieu Boone1
Received: 18 September 2019 / Accepted: 18 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract This paper presents a method for improved analysis of objects with an axial symmetry using X-ray Computed Tomography (CT). A cylindrical coordinate system about an axis fixed to the object’s center of symmetry forms the most natural base to analyze characteristics of those objects that exhibit axial symmetry, as is often the case for industrial parts. As the sampling grid in the proposed methodology is chosen in reference to the object, down-sampling may be applied in directions where no good resolution is required, to reduce reconstruction time without reducing quality. This is very valuable for in-line applications and fast quality inspection. In combination with algebraic reconstruction algorithms, it permits the use of a pre-computed initial volume perfectly suited to fit a series of scans where same-type objects can have different positions and orientations. Weighted back-projection can also be included when some regions are more likely subject to change, to improve reconstruction stability and defect sensitivity. In this paper, an innovative projection-based pose estimation technique is presented and validated on realistic simulated projections that resemble a setup with high-throughput conditions. Four cylindrical reconstruction strategies are compared to observe the influence of using an initial volume or weighted back-projection on tomographic inspection of medical devices. Finally, the effect of down-sampling the cylindrical reconstruction is analysed on phantoms with varying spatial frequency. Keywords X-rays · Tomography · 3D inspection · In-line · Cylindrical · Pose estimation
1 Introduction Non-destructive evaluation, either in-line or on random test samples, is paramount in a modern production environment to detect internal faults at an early stage. For assembled products, a common fault case is the situation where a component is missing in the final product. These components are often concealed in the assembly, hindering visual inspection. Xray based imaging may offer better insight on manufacturing quality. For in-line inspection, X-ray transmission scanning is usually applied to make 2D projection images. Common examples can be found in defect detection [1–3] or material identification [4]. On the other hand, the more intensive
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Wannes Goethals [email protected] Marjolein Heyndrickx [email protected] Matthieu Boone [email protected]
1
UGCT-Department of Physics and Astronomy, Proeftuinstraat 86, 9000 Ghent, Belgium
3D imaging by X-ray CT is mainly used off-line. The first industrial applications of CT can be found since the 1980s in the field of material analysis, e.g. observing inner structure and processes or locating internal defects. More recently, CT scanners are being used dedicated to metrology for dimensional quality
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