Geometric errors of CT scanners and their estimation by imaging a reference object

Abstract

Computed Tomography (CT) has been included in the routine of the dimensional quality loop of manufactured products over the past two decades. Characterized by a complex measurement chain, many influence factors may affect the accuracy of CT measurements. Misalignments stemming from imperfections of the components of the CT metrology instrument exemplify an influence factor over which the user may have no control. In this regard, this paper describes the experimental study of the geometric errors of a CT instrument using an image-based method to map them. The experiments were designed with the purposes of understanding the time-related variation pattern of the geometric errors and assessing the actual measurement capability of the image-based method itself to discriminate the geometric errors. The experimental findings can contribute to an optimized use of the CT technology for dimensional measurements, for example, by assisting the proper actions to be taken by the user for error correction.

Photothermal effect in X-ray images for computed tomography of metallic parts: Stainless steel spheres

“…Because the workpiece is rotating around a fixed axis within the programmed four tomographies in a row, every two images for the same view-point at the same rotation angle can be compared. The angular precision at the rotation stage of NIKON’s CT system XT H 225 can be reviewed at [ 32 ]. The proposed radiography difference (RD) method estimates dimensional fluctuations of the object of interest caused by the projection image acquisition itself, independent of the choice of 3D image reconstruction and further data processing.…”

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

“…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. The measurement method was further investigated by the same research team [18] and the utilization of process behavior charts to operate the CT measurement process up to its full potential was presented as well in a separate conference paper [19].…”