For the Spherical Surface Defects Evaluation System (SSDES), lens centering is essential to obtain the precise scanning trace and defect features without mismatch. Based on a combination of auto-collimating microscopy and Computer-Aided Alignment (CAA), an auto-centering system that can measure the deviation of large spherical center with respect to a reference rotation axis rapidly and accurately is established in this paper. The auto-centering system allows the closedloop feedback control of spherical center according to the different images of the crosshair reticle on CCD. Image entropy algorithm is employed to evaluate image clarity determined by the auto-focus experiment of 50μm step-length. Subsequently, an improved algorithm that can search the crosshair center automatically is proposed to make the trajectory of crosshair images and the position of rotation axis more reliable based on original circle fitting algorithm by the least square method (LSM). The comparison results indicates to show the high accuracy and efficiency of the proposed fitting method with LSM.

Date Published: 27 September 2016
PDF: 8 pages
Proc. SPIE 9684, 8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test, Measurement Technology, and Equipment, 96841N (27 September 2016); doi: 10.1117/12.2243299

Published in SPIE Proceedings Vol. 9684:
8th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optical Test, Measurement Technology, and Equipment
Yudong Zhang; Fan Wu; Ming Xu; Sandy To, Editor(s)