METHOD AND DEVICE FOR DETECTING MICRO FOREIGN MATTER WITHIN TRANSPARENT PLATE BODY

PROBLEM TO BE SOLVED: To stably detect a light-blocking micro foreign matter inside plate glass separately from a foreign matter on the surface of the plate glass, and acquire information on the depth of the micro foreign matter.SOLUTION: A detection device includes image processing means that discriminates a micro foreign matter inside plate glass from a foreign matter on the surface of the plate glass on the basis of an image captured by imaging means, to determine a position of the micro foreign matter inside the plate glass. A light irradiation position on the plate glass is changed without changing incident angles of first and second light beams. The imaging means images a bright point generated when the same foreign matter is irradiated with internal light beams I and I' and a bright point generated when it is irradiated with internal light beams II and II'. The image processing means discriminates a foreign matter on the surface of the plate glass on the basis of the image captured by the imaging means and image symmetry of the bright points formed by the same foreign matter generated by the first and second light beams, to determine a position of the micro foreign matter inside the plate glass.