| 摘要 |
PROBLEM TO BE SOLVED: To distinguish a faulty disk from a normal disk, with reference to the height or depth of a recessed and protruded defect. SOLUTION: The light-receiving surface of a regularly reflected light-receiving means for receiving the regularly reflected light of a light of a light beam and a disk surface are moved relative to each other, and the classification of a disk is determined on the basis of the distance of light reception between the light receiving surface of the regularly reflected light receiving means and the disk surface. A fine moving means is operated, so as to lengthen and shorten the distance of light reception. The quantity of light to be received by the reflected regularly light-receiving means is changed, according the height or depth of a recessed and protruded defect with the operation of the finely moving means. Here, the classification of the disk is determined by a control means on the basis of the distance of light reception. In other words, the height or depth of the recessed and protruded defect is detected from the distance of light reception, at which the quantity of light becomes maximum to precisely distinguish a faulty disk, in which a recessed and protruded defect of a height or depth equal to a predetermined value or more on the disk surface from a normal disk in which no recessed and protruded defect of the height or the depth equal to the prescribed value or more on the disk surface.
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