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Abstract

An automatic optical inspection of a moving web of glass for defects is provided by transversely scanning a moving web of glass with a light source which is internally reflected within the glass and travels towards the edge of the glass when the scanning light source strikes defects within the web. The light leaving the edges of the glass as a result of internal reflection is captured on opposite edges of the glass web. The captured light is detected and converted to electrical signals which are utilized to determine whether defects are present in the glass web in accordance with the characteristics of the electrical signals so generated. An apparatus is provided for the inspection method which includes edge detectors having a mouthlike construction fitting over the edges of the glass web and collecting internally reflected radiation from the edges of the web and applying it to photomultiplier tubes which are cooled. The mouthlike structure is made completely light tight by having brushes mounted thereon which do not scratch or alter the glass product surface. The edge detectors are enslaved mechanically so as to follow the movements of the glass web so that the system will not disturb the manufacturing process. Since internal reflection is the detection mechanism, and dirt on the surface does not scatter light internally, this method differentiates between dirt, the detection of which is not desired, and defects in optical contact with and under the surface of the glass which are desired to be detected.

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First Claim