Verifying the measurement accuracy for X-ray cone-beam CT scans of objects smaller than 5 mm diameter

Dimensional metrology has become an important and well-established application of industrial X-ray computed tomography (CT). Currently there is an increasing need to use CT-based metrology for objects scanned at very high resolution (< 1 μm voxel size). In order to validate the measurement accuracy of a CT scanner, calibrated length standards are required that match the range of field-of-view (FOV) sizes offered by the scanner. While there are now many lengths standards available for FOV diameters of 50 mm and above [1], so far there are few or no standards that are suitable for a small FOV diameter, and at the same time meet the requirements of guideline VDI/VDE 2617/2630 [2], dealing with CT-based metrology. In order to fit a FOV diameter of less than 5 mm, a length standard was designed in accordance with that guideline, manufactured from a support material and ruby spheres, and tactile measurements were performed with a ZEISS F25 coordinate measurement machine. CT metrology was performed using a ZEISS METROTOM 800, and the results are compared.