Method and apparatus for tracking an optically readable information track

Tracking apparatus for use in a system for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular and concentrically arranged tracks, each track formed by a succession of light-reflecting and light-scattering regions, and wherein the portions of the successive light-scattering regions forming one side of each track are adapted to scatter radiation incident thereon in a first direction, and the portions of the successive light-scattering regions forming the other side of each track are adapted to scatter radiation incident thereon in a second direction, said tracking apparatus operating to controllably position an incident beam of radiation in a prescribed relationship relative to a selected one of the tracks, said tracking apparatus comprising:

• an objective lens for focusing the incident beam of radiation onto the information storage disc, as the disc is rotated relative thereto, said incident beam of radiation being reflected by the disc in accordance with the stored information;
• said objective lens further operating to collect the reflected beam of radiation and to direct it to information recovery means for detecting the modulated intensity thereof;
• means, separate from the information recovery means, for detecting radiation scattered by the sides of the selected track and for producing an error signal indicative of the position of the incident beam of radiation relative to the centerline of the track, said means including
• a first photodetector for detecting radiation scattered in said first direction, and
• a second photodetector for detecting radiation scattered in said second direction;
• and
• means responsive to the error signal for controllably positioning the incident beam of radiation in the prescribed relationship relative to the selected track.

Apparatus for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular and concentrically arranged tracks, each track formed by a succession of light-reflecting and light-scattering regions representative of the information stored thereon, and wherein the portions of the successive light-scattering regions forming one side of each track are adapted to scatter radiation incident thereon in a first direction and the portions of the successive light-scattering regions forming the other side of each track are adapted to scatter radiation incident thereon in a second direction, said apparatus comprising:

• means for rotating the disc at a prescribed angular velocity;
• optical means for directing an incident beam of radiation onto the disc, said incident beam being reflected by the disc in accordance with the stored information;
• said optical means further operating to collect the reflected radiation and thereby produce a reflected beam of radiation;
• information recovery means for detecting the modulated intensity of the reflected beam of radiation;
• and
• tracking means for controllably positioning the incident beam of radiation in a prescribed relationship relative to a selected one of the tracks, whereby the radiation reflected from the disc and detected by said information recovery means is representative of the information stored on the track, said tracking means including
• means, separate from said information recovery means, for detecting radiation scattered by the sides of the selected track and for producing an error signal indicative of the position of the incident beam of radiation relative to the centerline of the track, and
• means for adjusting the relative position of the incident beam of radiation in accordance with the error signal.

Tracking apparatus for use in a system for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular tracks arranged in a spiral pattern, each track formed by a succession of planar light-reflecting regions and light-scattering bumps, and wherein the portions of the successive light-scattering bumps forming the inboard side of each track are adapted to scatter radiation incident thereon in a radially inward direction, and the portions of the successive light-scattering bumps forming the outboard side of each track are adapted to scatter radiation incident thereon in a radially outward direction, said tracking apparatus operating to controllably position an incident beam of radiation in substantial alignment with the centerline of a selected one of the tracks, said tracking apparatus comprising:

• a microscope objective lens for focusing the incident beam of radiation onto the disc, said incident beam being reflected by the disc in accordance with the stored information;
• said microscope objective lens further operating to collect the reflected beam of radiation and to direct it to information recovery means for detecting the modulated intensity thereof;
• an inboard photodetector for receiving radiation scattered radially inwardly by the disc and for producing an inboard signal proportional to the magnitude of such radiation;
• an outboard photodetector for receiving radiation scattered radially outwardly by the disc and for producing an outboard signal proportional to the magnitude of such radiation, wherein said inboard and outboard photodetectors are elongated in shape and positioned intermediate the objective lens and the disc, on opposite sides of the objective lens, the longitudinal axes of the photodetectors, being substantially parallel to that of the selected track;
• a differential amplifier circuit for producing an error signal proportional to the difference between said inboard signal and said outboard signal, said error signal thereby indicative of the deviation of the incident beam of radiation relative to the centerline of the selected track;
• an angularly movable radial tracking mirror for adjusting the radial position of the incident beam of radiation relative to the disc;
• and
• a radial tracking mirror transducer, responsive to the error signal, for controllably moving the radial tracking mirror to position the incident beam of radiation in substantial alignment with the centerline of the selected track.

A track centering method for use with a system for recovering information from an optically readable record medium, wherein the information is stored in a track having sides adapted to scatter in a predetermined direction any radiation impinging thereon, said tracking method functioning to controllably position an incident beam of radiation in a prescribed relationship relative to the track, said method comprising the steps of:

• directing the incident beam of radiation onto the record medium as the medium is moved with respect thereto, said beam of radiation being reflected by the medium in accordance with the stored information;
• directing the reflected beam of radiation to information recovery means for detecting the modulated intensity thereof;
• detecting radiation scattered by the sides of the track, and producing an error signal indicative of the position of the incident beam of radiation relative to the centerline of the track;
• and
• controllably positioning the incident beam of radiation in the prescribed relationship relative to the track, in accordance with the error signal.

Tracking apparatus for use in a system for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular and concentrically arranged tracks, each track formed by a succession of light-reflecting and light-scattering regions, and wherein the portions of the successive light-scattering regions forming one side of each track are adapted to scatter radiation incident thereon in a first direction, and the portions of the successive light-scattering regions forming the other side of each track are adapted to scatter radiation incident thereon in a second direction, said information recovery system including an objective lens for focusing an incident beam of radiation onto the disc and information recovery means for detecting radiation reflected from the disc, said tracking apparatus operating to controllably position the beam of radiation in a prescribed relationship relative to a selected one of the tracks, said tracking apparatus comprising:

• means for detecting radiation scattered by the sides of the selected track and for producing an error signal indicative of the position of the beam of radiation relative to the centerline of the track, said means including
• a first photodetector for detecting radiation scattered in said first direction, and
• a second photodetector for detecting radiation scattered in said second direction;
• and
• means for adjusting the relative radial position of the beam of radiation in accordance with the error signal;
• wherein radiation reflected by the disc is directed back through the objective lens to the information recovery means;
• wherein the objective lens includes two axially aligned lenses arranged in spaced relationship with respect to each other;
• and wherein said first and second photodetectors are elongated in shape and positioned intermediate the two axially aligned lenses in the objective lens, on opposite sides of the optical axis os the objective lens, the longitudinal axes of the photodetectors being substantially parallel to that of the selected track.

Tracking apparatus for use in a system for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular and concentrically arranged tracks, each track formed by a succession of light-reflecting and light-scattering regions, and wherein the portions of the successive light-scattering regions forming one side of each track are adapted to scatter radiation incident thereon in a first direction, and the portions of the successive light-scattering regions forming the other side of each track are adapted to scatter radiation incident thereon in a second direction, said information recovery system including an objective lens for focusing an incident beam of radiation onto the disc and information recovery means for detecting radiation reflected from the disc, said tracking apparatus operating to controllably position the beam of radiation in a prescribed relationship relative to a selected one of the tracks, said tracking apparatus comprising:

• means for detecting radiation scattered by the sides of the selected track and for producing an error signal indicative of the position of the beam of radiation relative to the centerline of the track, said means including
• a first photodetector for detecting radiation scattered in said first direction, and
• a second photodetector for detecting radiation scattered in said second direction;
• and
• means for adjusting the relative radial position of the beam of radiation in accordance with the error signal;
• wherein radiation scattered by the disc is directed back through the objective lens to said first and second photodetectors;
• and wherein said first and second photodetectors are elongated in shape and positioned on opposite sides of the optical axis of the objective lens to receive scattered radiation transmitted by the objective lens, the longitudinal axes of the photodetectors being substantially parallel to that of the selected track.

Tracking apparatus for use in a system for recovering information from a rotatable information storage disc, wherein the information is stored in a plurality of substantially circular and concentrically arranged tracks, each track formed by a succession of light-reflecting and light-scattering regions, and wherein the portions of the successive light-scattering regions forming one side of each track are adapted to scatter radiation incident thereon in a first direction, and the portions of the successive light-scattering regions forming the other side of the each track are adapted to scatter radiation incident thereon in a second direction, said information recovery system including an objective lens for focusing an incident beam of radiation onto the disc and information recovery means for detecting radiation reflected from the disc, said tracking apparatus operating to controllably position the beam of radiation in a prescribed relationship relative to a selected one of the tracks, said tracking apparatus comprising:

• means for detecting radiation scattered by the sides of the selected track and for producing an error signal indicative of the position of the beam of radiation relative to the centerline of the track, said means including
• a first photodetector,
• a first transparent block positioned to receive radiation scattered in said first direction and to transmit such radiation to said first photodetector,
• a second photodetector, and
• a second transparent block positioned to receive radiation scattered in said second direction and to transmit such radiation to said second photodetector;
• and
• means for adjusting the relative radial position of the beam of radiation in accordance with the error signal.