| 摘要 |
Defect detection apparatus provides a moving light beam which illuminates the surface of a rotating grooved disc with a light spot spanning a plurality of convolutions of the groove. The beam is translated to rapidly scan the grooved surfaces in a radial pattern. The structure of the groove convolutions, absent any defects, diffracts the incident beam producing a plurality of reflected beams. A first lens, provided in the path of the reflected beams, provides, in a focal plane thereof, a Fourier transformation of the light amplitude data of the respective reflected beams. A second lens, provided in the diffracted beam path downstream of the first lens, provides at the surface of a photodetector, an inverse Fourier transformation which is an image of the scanning spot. Blocking means, placed in the focal plane of the first lens intercept the reflected beams when defect-free groove regions are illuminated, to prevent the conversion of light energy to electric energy by the photodetector. When a defect exists in the illuminated region of the groove, portions of the reflected beams bypass the blocking means to produce in the photodetector electrical signals indicative of the presence of a defect. Writing apparatus, for mapping 1:1 polar plots of disc record defect locations on disc-shaped photosensitive paper supported on a turntable, accepts electrical signals representing defect occurrences after compensation for the presence of dust in the illuminated region. These signals activate a gate that permits passage of a recording beam of light to the surface of the turntable. Relative motion is established between the turntable and the recording beam in a manner causing markings resulting from gate activations to be located on the photosensitive paper with radial and circumferential positions corresponding to the locations of the defects appearing on the grooved disc.
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