John Hagen - Rochester MN,
Daniel Neseth - Mantorville MN,
INTERNATIONAL BUSINESS MACHINES CORPORATION - ARMONK NY
A glass disk is illuminated through an edge and an image of a segment of the disk edge is captured by a CCD camera. If internally reflected light is refracted and diffused by an anomaly in a disk edge, the anomaly will appear as a brilliant light spot on the image. Brilliant spots on a disk edge are detected as bright pixels; and within inspection zones, rows of pixels or areas of pixels are compared with a threshold value. Pixel strings having illumination intensity greater than the threshold are counted; and whenever the resulting count is larger than a predetermined number, the disk is rejected as having an anomaly of a size warranting rejection. In inspection area zones, pixel counts of intensities greater than a threshold value warrant rejection.