Study on calibration method of rotary axis based on vision measurement

For the purpose of inspecting the film cooling holes on high-pressure turbine blade in a rapid and accurate manner, a non-contact four-axis vision coordinate measuring system was designed and established in the paper. With regard to the determination difficulty of the spatial location of the rotary axis, a calibration method based on vision measurement was proposed in the paper, which fully considered the imaging characteristics of industrial CCD used in the system. In the calibrating procedure, a specially designed cuboid mental block was applied as the target. Through the coordination between the turntable and the coordinate measuring machine, the industrial CCD focused on the block surface and then captured the sharp edges of the block. And then, the spatial orientation of the rotary axis in the machine coordinate system could be determined by edge extraction, pixel distance calculation, physical distance conversion and algebraic operation etc. Finally, a gauge block was selected to be inspected by the measuring system to verify the calibration method and results, whose nominal size was 80 mm. As the experimental results showed, the measuring errors were all smaller than ±0.01 mm. Therefore, the calibration method of rotary axis proposed in the paper showed higher calibration precision and repeatability, which could meet the inspecting requirements of the shape and position parameters of film cooling holes.