Computed tomography helical scanning for dimensional metrology: Evaluation of measurement errors

In industrial X-ray computed tomography, it is frequently necessary to scan long objects that exceed the dimensions of the detector, while meeting dimensional accuracy requirements (for example, in automotive and aerospace fields). Conventional scans using circular trajectories face limits when dealing with internal and complex features on elongated work pieces. To this extent helical scanning is a valuable solution that also enables obtaining a strong improvement on image quality, eliminating the cone beam artifacts that characterize conventional scans. To use helical scanning for dimensional quality control, the assessment of metrological performances is needed. In this work, metrological performances for helical scanning are investigated and compared with those of conventional circular scans. Repeated helical scans are performed to investigate the influence of main helical scans parameters when performing dimensional measurements. Experimental results show that helical scanning, with appropriate scan parameters, performs better than traditional circular scans with a strong improvement on image quality.