Dynamic information storage or retrieval – Information location or remote operator actuated control – Selective addressing of storage medium
Patent
1979-04-06
1981-06-02
Wolff, John H.
Dynamic information storage or retrieval
Information location or remote operator actuated control
Selective addressing of storage medium
369 33, 346 76L, 346108, 369 44, G11B 700
Patent
active
042713340
ABSTRACT:
A servo control apparatus for maintaining a scanning device, such as a beam of radiation, aligned with an information recording track on a moving recording medium, such as a record disc. The apparatus is especially adapted for use in correcting for tracking deviations brought about by temperature-induced expansion and contraction of the disc, which causes the recording track being scanned to move radially outwardly 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.
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Broadbent, "A Review of the MCA Disco-Vision System", Journal of the SMPTE, Jul. 1974, vol. 83, pp. 554-559.
Clark Ronald J.
Discovision Associates
McElheny Jr. Donald
Wolff John H.
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