Abstract Robot positioning performance is studied in the scope of a robotized X-ray computed tomography application on a ABB IRB4600 robot. The robot has the “absolute accuracy” option, that is, the manufacturer has identified the manufacturing defects and included them in the robot control. Laser-tracker measurement on a 6.5-h long linear trajectory shows thermal drift and backlash issues, affecting the positioning unidirectional repeatability and bidirectional accuracy. A thermo-geometrical model with backlash compensation is developed. Geometrical calibration improves the forwards unidirectional mean accuracy from 1.39 to 0.06 mm between theoretical and optimized geometrical parameters with a stable thermal state. Thermo-geometrical calibration reduces the positioning scattering from a maximum of 0.15 to 0.05 mm (close to the repeatability of the robot). Backlash compensation improves the bidirectional mean accuracy from 1.53 to 0.07 mm.