METHOD FOR INSPECTING FOREIGN MATTER IN TRANSPARENT PLATE

PROBLEM TO BE SOLVED: To provide a method for simply inspecting foreign matter in a transparent plate. SOLUTION: In the method for inspecting the foreign matter, light parallel to the surface of the transparent plate is made incident on at least one lateral edge of the transparent plate, such that each total light intensity of the area of one part obtained by equally dividing the lateral edge into ten parts satisfies following relation: 100×(minimum total light intensity in ten parts)/(maximum total light intensity in ten parts)≥60%, and the light is scattered by the foreign matter in the transparent plate and emitted from the surface of the transparent plate as a luminescent spot. The surface of the transparent plate is photographed from a position vertically above the surface of the transparent plate, and image data representing light intensities of respective surface positions of the transparent plate are generated by using an image processing device. A threshold determined additionally based on the light intensity of the luminescent spot due to the foreign matter in the transparent plate and light intensities of luminescent spots due to a foreign matter and a flaw on the surface of the transparent plate, which are identified by visual observations, is used such that the light intensities of respective luminescent spots in the image data are divided into two groups by the threshold. Only the luminescent spot having the light intensity equal to or higher than the threshold is detected and determined as the luminescent spot due to the foreign matter in the transparent plate. COPYRIGHT: (C)2009,JPO&INPIT