Video disc read back scanner

• US 4,282,598 A
• Filed: 07/14/1978
• Issued: 08/04/1981
• Est. Priority Date: 10/24/1972
• Status: Expired due to Term

• Current Assignee: Discovision Associates (Pioneer Corporation)
• Original Assignee: Discovision Associates (Pioneer Corporation)
• Inventors: Elliott, James E.
• Primary Examiner(s): Faber, Alan
• Application Number:
  US05/924,538
• Time in Patent Office: 1,117 Days
• Field of Search: 358/128, 358/127, 358/130, 358/132, 358/128.5, 179/100.3 V, 179/100.3 H, 179/100.3 M, 179/100.3 E, 179/100.3 D, 179/100.3 L, 179/100.41 L, 179/100.1 G, 360/77, 365/120, 365/121, 250/202, 250/570, 350/285, 350/299, 346/109, 346/108, 346/76 L, 356/399
• US Class Current: 369/44.11
• CPC Class Codes: G11B 7/081 for time base error correction by moving the light beam
• CPC Class Codes: G11B 7/0953 to compensate for eccentricity of the disc or disc tracks

Abstract

A video signal play back device derives video signals from successive tracks formed as a continuous spiral on a video disc using a light source and a lens system, which is carried by a rotatable element at a predetermined spacing from the surface of the disc and which defines a folded optical path. The rotatable element translates the lens system in the radial direction relative to the disc for "coarse" steering of the light beam along the information tracks as the disc is rotated by a turntable. The optical path includes a mirror which is articulated for rotational motion about an axis which shifts the point of impingement of the transmitted light beam upon the disc in the radial direction. The returned beam is directed to a photosensitive pick-up which provides input signals to a circuit which generates a "fine" servo control signal to drive the articulated mirror.

In an alternative embodiment, a second articulated mirror is included for shifting the point of impingement of the light beam in the tangential direction, along the information tracks, for purposes of time base error correction. The radial position of the first articulatd mirror is monitored to control, with a phase shift equal to one-quarter revolution of the disc, tangential movement of the second articulated mirror.

Claims

1. A method of controlling a radiant beam in an apparatus for optically reading information from a plurality of substantially concentric information tracks formed in a rotating disc-shaped information storage medium, said apparatus including radiant beam means for producing a source beam of radiant energy and transducer means for receiving a modulated beam of radiant energy produced by impinging said source beam at a selected location upon said storage medium, said method comprising the steps of:

2. steering said source beam in a radial direction relative to said storage medium to said selected location for following said information tracks;

monitoring the radial location of said source beam relative to said storage medium, and providing a control signal indicative of radial deviations in the location of said source beam from a precisely defined path;

shifting the phase of said control signal by an amount equal to one-quarter revolution of said storage medium; and

moving said source beam in a tangential direction relative to said storage medium to said selected location under the control of said phase-shifted control signal.

3. Apparatus for optically reading information indicia stored in a plurality of substantially concentric information tracks formed in a disc-shaped information storage medium, said apparatus comprising:

radiant beam means for producing a source beam of radiant energy to impinge upon the medium;

means for rotating the medium relative to said source beam to produce a modulated beam of radiant energy representing portions of said source beam reflected from the medium;

transducer means for receiving said modulated beam;

optical means, defining an optical path, for directing said source beam from said radiant beam means to the medium and for directing said modulated beam from the medium to said transducer means, said optical means including means for focusing said source beam to a precise spot substantially the size of the information indicia on the medium, and said optical means further including first and second articulated mirrors disposed in said optical path, said first articulated mirror being arranged to steer said source beam in the radial direction relative to the medium and said second articulated mirror being arranged to steer said source beam in the tangential direction relative to the medium;

translation means for translating the medium and said optical means relative to one another to cause the source beam to move from information track to information track in succession across the medium; and

control means, responsive to said transducer means, for providing an error signal to said first articulated mirror indicative of radial deviations in the location of said source beam from a precisely selected location relative to an information track, said control means further providing an error signal to said second articulated mirror indicative of tangential deviations in the location of said source beam from a precisely selected location relative to an information track, such that said first articulated mirror and said second articulated mirror controllably guide said source beam along a precisely selected path relative to the information tracks on the medium as the medium and the optical means translate relative to one another.

5. Apparatus as set forth in claim 3, wherein said optical means includes beam separating means disposed in said common portion of said optical path for separating said modulated beam from the path of said source beam and for directing said modulated beam along a path to said transducer means.

7. Apparatus as set forth in claim 5, wherein said beam splitting prism is angularly oriented in said optical path such that portions of said source beam reflected by said beam splitting prism are directed along a path other than the path leading to said transducer means.

4. Apparatus for optically reading information indicia stored in a plurality of substantially concentric information tracks formed in a disc-shaped information storage medium, said apparatus comprising:

radiant beam means for producing a source beam of radiant energy to impinge upon the medium;

means for rotating the medium relative to said source beam to produce a modulated beam of radiant energy representing portions of said source beam reflected from the medium;

transducer means for receiving said modulated beam;

optical means, defining an optical path, for directing said source beam from said radiant beam means to the medium and for directing said modulated beam from the medium to said transducer means, said modulated beam and said source beam having at least a portion of said optical path in common, said optical means including means for focusing said source beam to a precise spot substantially the size of the information indicia on the medium, and said optical means further including first and second articulated mirrors disposed in said common portion of said optical path, said first articulated mirror being arranged to steer said source beam in the radial direction relative to the medium and said second articulated mirror being arranged to steer said source beam in the tangential direction relative to the medium;

translation means for translating the medium and said optical means relative to one another to cause the source beam to move from information track to information track in succession across the medium; and

control means, responsive to said transducer means, for providing an error signal to said first articulated mirror indicative of radial deviations in the location of said source beam from a precisely selected location relative to an information track, said control means further providing an error signal to said second articulated means indicative of tangential deviations in the location of said source beam from a precisely selected location relative to an information track, such that said first articulated mirror and said second articulated mirror controllably guide said source beam along a precisely selected path relative to the information tracks on the medium as the medium and the optical means translate relative to one another.

6. Apparatus as set forth in claim 4, wherein said beam separating means comprises a beam splitting prism and a quarter wave plate disposed between said prism and the medium.

8. Apparatus for optically reading information indicia stored in a plurality of substantially concentric information tracks formed in a disc-shaped information storage medium, said apparatus comprising:

radiant beam means for producing a source beam of radiant energy to impinge upon the medium;

means for rotating the medium relative to said source beam to produce a modulated beam of radiant energy representing portions of said source beam reflected from the medium;

transducer means for receiving said modulated beam;

optical means, defining an optical path, for directing said source beam from said radiant beam means to the medium and for directing said modulated beam from the medium to said transducer means, said optical means including means for focusing said source beam to a precise spot substantially the size of the information indicia on the medium and means for steering the source beam along a precisely defined path relative to the information tracks on the medium, said modulated beam and said source beam having at least a portion of said optical path in common, and said optical means further having beam separating means, including a beam splitting prism and a quarter wave plate disposed between said beam splitting prism and the medium, for separating said modulated beam from the path of said source beam and for directing said modulated beam along a path to said transducer means, said beam splitting prism being angularly oriented in said optical path such that portions of said source beam reflected by said beam splitting prism are directed along a path other than the path leading to said transducer means;

translation means for translating the medium and said optical means relative to one another to cause the source beam to move from information track to information track in succession across the medium; and

control means, responsive to said transducer means, for providing an error signal to said steering means indicative of deviations in the location of said source beam from said precisely defined path, such that said steering means controllably guides said source beam along said precisely defined path relative to the information tracks on the medium as the medium and the optical means translate relative to one another.