| 摘要 |
1435922 Detecting record deviations PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 8 May 1973 [11 May 1972 19 April 1973] 21902/73 Heading G1A [Also in Division G5] Optical apparatus for reading a reflective record carrier includes means for detecting shifts in the plane of the carrier by using at least one auxiliary beam reflected from the carrier to at least two radiation detectors which provide a difference signal indicative of such shifts. In the embodiment shown, the two detectors 68, 69 define a slit 67 illuminated by an off-axis beam 66 derived from a main laser read-out beam 61 by a splitter 63. The image of the slit after reflection from the carrier 1 in its desired plane d falls on the slit itself, but otherwise illuminates one of the detectors. To maximize the difference signal at small deviations, the detectors, which are preferably photodiodes, have light-insensitive margins adjacent the slit 67 which are as narrow as possible, or may have subsidiary light-sensitive areas thereat, Fig. 12 (not shown). In a second embodiment, Fig. 3 (not shown), the image of a slit (30) is normally focused at the edge of a radiation-absorbing screen (34) so that the detectors (35', 35") behind the screen receive equal illumination. The difference signal may control focusing of a lens (33). The position of a half-silvered screen (32) is adjusted in response to differences in the output of additional detectors (37', 37") outside the screen (34) in order to maintain alignment. In a third embodiment, Fig. 4 (not shown), detectors (D n ) are arranged in an inclined row and separated by illuminated slits (S n ). One only of the slits is imaged sharply on itself after reflection at the carrier 1, so that adjacent detectors receive no radiation therefrom; the detector outputs thus indicate the position of the carrier. In a fourth embodiment, Fig. 5 (not shown), auxiliary beam (51b), which may be the first-order reflection from a diffraction grating (54), strikes the carrier at an acute angle and is reflected to the detectors (56', 56"). The other first-order beam (51c) is reflected to additional detectors (57', 57") providing a difference signal to control the position of a half-silvered mirror (52), in order to maintain alignment. |
