Method and apparatus for information retrieval from an optically readable storage medium

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG.
1 of the drawings for purposes of illustration, there is shown a new and improved system for information retrieval embodying features of the present invention.
In the drawings, the same numeral will be used in the several views to represent the same element.
In FIG.
1, a generalized video disc player is shown for purposes of illustrating the pinciples of the invention and includes a spindle on which a video disc 10 is mounted for rotation by a spindle motor 12 at a preselected angular rate.
Information is recorded on the video disc 10 in a frequency modulated format as successive light reflective and non-reflective regions along tracks that are formed either as a continuous spiral or in discrete concentric rings.
The video disc player also includes an optical system 14 which produces a laser read beam 16 and directs it through an optical read head 18 having an objective lens for focusing the read beam to a precise spot on the video disc 10.
A reflected beam 20, modulated by the information recorded in the tracks, is gathered by the read head 18 and returned through the optical system 14 to a signal recovery subsystem 22.
The spindle motor 12 is mounted on a carriage 24 for translation of the video disc 10 in the direction indicated by a double-headed arrow 26 by means of a carriage motor 28.
Coarse steering of the read beam 16 along the information tracks is accomplished by translating the carriage 24 either at a uniform rate equal to the pitch of spirally-formed tracks or stepwise if the tracks are formed as discrete concentric rings.
A tracking subsystem 30 is included in the video disc player to enable the read beam to follow eccentricities that are inherent in the information tracks with present technology.
Also, since the description that follows will assume that the information tracks are formed in a spiral manner, wherein one complete revolution of the video disc comprises one information track, a stop motion subsystem 32 is shown in FIG