Fast Tomographic Inspection of Cylindrical Objects

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.