Vision based diameter estimation for continuous float-zone silicon crystal growth production

Diameter measurement of cylinder with vision system is of great importance for diameter control in the float-zone silicon crystal growth. Targeted for float-zone silicon crystal growth, a vision-based diameter measurement with estimated expanded uncertainty for large diameter scope, is presented. The method is developed over two steps: camera calibration, diameter measurement and correction. Firstly, camera calibration identifies intrinsic and extrinsic properties of camera. Intrinsic parameters of camera model are obtained from the pattern of a checkerboard in advance. Then extrinsic parameters are inferred by tracking corner points of checkboard while rotating the checkerboard around cylinder axis. Finally, with estimated intrinsic and extrinsic parameters, pseudo diameter can be determined from the image points and corrected into actual diameter by trigonometric principle. The effectiveness of the proposed method was experimentally verified by measuring cylindrical gauges with diameter ranging from 5 mm to 150 mm.