A test object for calibration and accuracy assessment in X-ray CT metrology

While Computer Tomography (CT) has since long been used for medical applications and material inspecti on, its application field has recently been broadened to in clude dimensional metrology in industry. However, the acc ura y of CT-based measurements remains yet largely uncert ain. Not only are the measurements influenced by a numbe r of factors and parameters like e.g. workpiece orientat ion, magnification, edge detection... but also the calibra t on method matters greatly. This paper investigates the influence of these factors and parameters and the c alibration method (rescaling and correction) on accuracy and repeatability of the measurements, using a test obj ect with parallel grooves. The test object is also used to i llustrate how more accurate CMM measurements can be used to calibrate CT measurements and to compare different calibration and compensation strategies.