In the manufacture of glass containers, a defect that is sometimes found which is difficult to detect comprises a generally horizontal check or mirror-like flaw in the wall of the container. It is essential that such defects or flaws be detected even though they be few in number, with respect to the total number of containers being manufactured.
The prior art has employed various types of inspection devices primarily relying on illuminating the defect and then reading the presence of reflected light emitted by the defect. The following U.S. patents all relate to such devices which are satisfactory to a greater or lesser degree in detecting such defects. The patents are:
U.S. Pat. No. 3,328,000: Rottmann PA1 U.S. Pat. No. 3,349,906: Calhoun et al PA1 U.S. Pat. No. 3,415,370: Husome PA1 U.S. Pat. No. 3,529,167: Calhoun PA1 U.S. Pat. No. 3,601,616: Katsumata PA1 U.S. Pat. No. 3,651,937: Kronseder PA1 U.S. Pat. No. 3,834,429: Schulz PA1 U.S. Pat. No. 3,987,301: O'Conner PA1 U.S. Pat. No. 4,002,823: Van Osterhout PA1 U.S. Pat. No. 4,140,901: Fischer et al PA1 U.S. Pat. No. 4,171,481: Mima et al PA1 U.S. Pat. No. 4,213,042: Beach et al PA1 U.S. Pat. No. 4,221,961: Peyton
All of the aforesaid patents involve methods and apparatus different from, and generally more complex methods and apparatus than the present invention.