METHOD OF STABLY DETECTING MINUTE FOREIGN MATTER WITHIN GLASS PLATE, AND APPARATUS FOR IMPLEMENTING THE SAME

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. 【課題】多重反射やガラス板厚に影響されずに、ガラス板内部の微小異物を安定的に検出する。【解決手段】第１の光ビーム２を所定角度でガラス板１内部に進入させ、光ビームＩと反射した光ビームIIとをガラス板内部に形成する。第２の光ビーム７を前記第１の光ビームの角度と同じ角度で反対方向からガラス板内部に進入させ、光ビームＩ'と反射した光ビームII'とをガラス板内部に形成する。光ビームがガラス板進入前に光路を交差させる条件で、光ビームを照射し、各光ビームの進入角度を変えることなく照射位置を移動させ、異物が前記光ビームＩとＩ'により照射されて生じた輝点と前記光ビームIIとII'により照射されて生じた輝点とをガラス板に対して垂直方向より撮像手段３により撮像し、前記第１の光ビームと第２の光ビームとによって生じた同一異物による輝点の画像の対称性によって前記微小異物のガラス板中における位置を判定する。【選択図】図４