| 摘要 |
<p>PROBLEM TO BE SOLVED: To stably detect minute foreign matter within a glass plate without being affected by multiple reflections or the glass plate thickness.SOLUTION: A first light beam 2 is caused to enter into a glass plate 1 at a prescribed angle, and the light beam I and a reflected light beam II are formed within the glass plate. A second light beam 7 is caused to enter into the glass plate at the same angle as that of the first light beam in the reverse direction, and a light beam I' and a reflected light beam II' are formed within the glass plate. Under the condition that optical paths are caused to cross each other before the light beams enter into the glass plate, the light beams are radiated, the irradiated position is shifted without altering the entering angle of each light beam, a bright spot formed by irradiation of minute foreign matter with the light beams I and I' and another bright spot formed by irradiation with the light beams II and II' are photographed with image pickup means 3 in a direction perpendicular to the glass plate, and the position of the minute foreign matter in the glass plate is determined by the symmetry between the photographed images of the bright spots attributable to the same foreign matter generated by the first light beam and the second light beam.</p> |
