US 4,541,082 AGranted

Device for optically tracking information

AssigneeHitachi, Ltd.

InventorsTatsuo Horikoshi, Seiji Yonezawa, Toshiaki Tsuyoshi, Hiroshi Tooyama, Masatoshi Otake

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Abstract

A device for optically tracking information recorded on an optical disc wherein a photodetector is disposed on the optical axis of an optical system for guiding diffracted waves to the photodetector. The origin of a fictitious X-Y coordinate system at the photodetector is placed on the above-mentioned optical axis, X- and Y-axes of the coordinate system are made parallel to and perpendicular to an information track having the information pits on the rotating recording medium, and the photodetector is divided into four equal parts. A first summation signal indicating the sum of output signals from the four parts of the photodetector is converted into a binary signal, and a difference signal between second summation signals each indicating the sum of output signals from a pair of photodetector parts facing each other with the origin of the coordinate system therebetween is converted into another binary signal. A signal indicating a direction in which the light beam deviates from the information track, is formed on the basis of the above-mentioned binary signals, and a tracking signal indicating the deviation of the light beam from the information track is formed by full-wave rectifying the difference signal and modifying the rectified signal with the above-mentioned direction indicating signal.

Claims10

Dependent claims

A device for optically tracking information suitable for use in an information reproducing device including a laser light source, a rotating recording medium in which predetermined information is recorded in the form of a track so that said information can be optically reproduced, an optical system disposed between said laser light source and said rotating recording medium for irradiating said track with a light beam from said laser light source, and a photodetector for sensing diffracted waves from information pits on said track, to reproduce said information by an electric signal from said photodetector, said device for optically tracking information comprising:

first means for detecting a first summation signal indicating the sum of output signals from four parts of said photodetector, said photodetector being disposed on the optical axis of said optical system, a fictitious X-Y coordinate system at said photodetector having the origin thereof on said optical axis, an X-axis of said coordinate system being made parallel to the direction of said track, a Y-axis of said coordinate system being made perpendicular to the direction of said track, each of said four parts of said photodetector being disposed one by one in four quadrants of said coordinate system;
second means for detecting a difference signal between second summation signals, each of said second summation signals indicating the sum of output signals from a pair of parts of said photodetector, said pair of parts facing each other with said origin of said coordinate system therebetween;
third means for converting said difference signal into a binary signal, said binary signal having one of high and low levels in accordance with a change in amplitude of said first summation signal, an output from said third means indicating a direction in which said light beam deviates from said track;
and
fourth means for detecting peak values of said difference signal, an output of said fourth means indicating the magnitude of deviation of said light beam from said track.

2 more elements

Dependencies are inferred from the claim text.