G - Physics – 11 – B
Patent
G - Physics
11
B
352/32.2
G11B 7/00 (2006.01) G11B 7/09 (2006.01) G11B 21/10 (2006.01)
Patent
CA 1143062
ABSTRACT OF THE DISCLOSURE A servo control apparatus for maintaining a scanning device, such as a beam of radiation, aligned with an information recording track on a moving record- ing medium, such as a record disc. The apparatus is especially adapted for use in correcting for tracking deviations brought about by temperature-induced expan- sion and contraction of the disc, which causes the recording track being scanned to move radially out- wardly or inwardly relative to the beam of radiation. In the preferred embodiment, the apparatus includes a movable mirror for oscillating the beam in a radial direction, in accordance with a periodic dither signal. This causes a corresponding variation in the intensity of the beam reflected by the disc, with the amplitude and phase angle of this intensity variation, relative to that of the dither signal, indicating the direction and magnitude of the deviation of the beam from the track centerline. Whenever the magnitude exceeds a prescribed level, a step forward or step reverse pulse signal is coupled to a stepper motor, to increment the beam in the appropriate radial direction, whereby the beam is maintained substantially aligned with the centerline of the recording track.
346652
Discovision Associates
Gowling Lafleur Henderson Llp
LandOfFree
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