Apparatus and record carrier for optical disc memory with correction pattern and master disc cutting apparatus

• US 4,949,331 A
• Filed: 06/17/1986
• Issued: 08/14/1990
• Est. Priority Date: 06/19/1985
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Maeda, Takeshi, Kaku, Toshimitsu, Shigematsu, Kazuo, Tsunoda, Yoshito
• Primary Examiner(s): Psitos, Aristotelis M.
• Application Number:
  US06/875,442
• Time in Patent Office: 1,519 Days
• Field of Search: 369/43, 369/44, 369/45, 369/93, 369/109, 369/111, 369/275, 369/277, 369/278, 358/342, 358/343
• US Class Current: 369/275.3
• CPC Class Codes: G11B 11/10565 Marks for track change, e.g. prepits, gray codes
• CPC Class Codes: G11B 11/10578 Servo format, e.g. prepits, guide tracks, pilot signals
• CPC Class Codes: G11B 11/10582 Record carriers characterised by the selection of the material or by the structure or form
• CPC Class Codes: G11B 7/0901 for track following only G11B7/0925, G11B7/094, G11B7/0941, G11B7/0943, G11B7/0945, G11B7/0946, G11B7/0948 take precedence
• CPC Class Codes: G11B 7/0938 servo format, e.g. guide tracks, pilot signals
• CPC Class Codes: G11B 7/094 Methods and circuits for servo offset compensation
• CPC Class Codes: G11B 7/24082 Meandering
• CPC Class Codes: G11B 7/261 Preparing a master, e.g. exposing photoresist, electroforming

Abstract

A record carrier having a disc-shaped substrate and a recording layer for optically writing information therein is disclosed which includes a guide groove extended in the rotational direction of the record carrier so that a plurality of revolutions of the guide groove are spaced apart from each other in radial directions of the record carrier, and a pit pattern provided between adjacent guide grooves, at positions arranged at intervals in the above rotational direction, for detecting the deviation of a light spot from the center line between adjacent guide grooves. The recording/reproducing operation for this record carrier is performed in such a manner that the first tracking error signal is detected from diffracted light from the guide groove, the second tracking error signal is detected from the pit pattern, and information is recorded in and reproduced from a land formed between adjacent guide grooves in a state that a tracking operation is performed using the first and second tracking error signals. The second tracking error signal detected from the pit pattern is not affected by the tilting of the record carrier and the movement of the light spot. When a tracking signal obtained by adding the first and second tracking error signals to each other, is used in a closed-loop tracking system, a stable tracking operation can be performed. The polarity of the pit pattern is reversed on every track, and hence a polarity pit having a depth of λ/4 (where λ indicates the wavelength of a reproducing light beam) is provided in the record carrier, to reverse the polarity of the second tracking signal on every track on the basis of a signal from the polarity pit.

Claims

1. A record carrier having a track offset correction pattern comprising a disc-shaped substrate, a recording layer formed on said substrate, first and second regions alternately arranged along the rotational direction of the record carrier, guide grooves disposed in at least said second region and extending in the rotational direction of the record carrier while being spaced apart in the radial direction of the record carrier, a land extending in the rotational direction of the record carrier between adjacent guide grooves, said adjacent guide grooves serving as an optical guide for a light spot which follows on a center line between said adjacent guide grooves, said first region including said correction pattern for correcting track offset, and said correction pattern having at least first elements which are different in optical characteristic from said guide grooves and are provided in said first region while extending on center lines of said guide grooves so that said first elements of said adjacent guide grooves do not overlap each other when viewed in the radial direction of the record carrier, wherein said correction pattern further includes at least one second element which is different in optical characteristic from said guide grooves and is provided on said land in said first region on the center line between said adjacent guide grooves so that said at least one second element overlaps at least a respective one of said first elements of said adjacent guide grooves when viewed in the radial direction of the record carrier.

2. A record carrier according to claim 1, wherein a group formed of one of said first elements and said second element is asymmetric with respect to the center line between said adjacent guide grooves.

3. A record carrier according to claim 2, wherein each revolution of said land is divided into a plurality of sectors, each sector includes a header field in which a header signal including address information for identifying a respective sector is formed in advanced with pits of a phase structure, and a recording field which follows said header field, and wherein said first region is provided in said header field.

4. A recording carrier according to claim 2, wherein a mark for identifying said correction pattern is provided together with said correction pattern, on every other revolution of said land.

5. A record carrier having a track offset correction pattern comprising a disc-shaped substrate, a recording layer formed on said substrate, first and second regions alternatively arranged along the rotational direction of the record carrier, guide grooves disposed in at least said second region and extending in the rotational direction of the record carrier while being spaced apart in the radial direction of the record carrier, a land extending in the rotational direction of the record carrier between adjacent guide grooves, said adjacent guide grooves serving as an optical guide for a light spot which follows on a center line between said adjacent guide grooves, and first elements different in optical characteristic from said guide grooves and being provided in said first region while extending on center lines of said guide grooves so that said first elements of adjacent guide grooves do not overlap each other when viewed in the radial direction of the record carrier, said first elements of said adjacent guide grooves form said correction pattern for correcting track offset, wherein each revolution of said land is divided into a plurality of sectors, each sector including a header field in which a head signal including address information for identifying a respective sector is formed in advance with pits of a phase structure, and a recording field which follows said header field, and wherein said first region is provided in said header field, wherein said correction pattern further includes at least one second element which is different in optical characteristic from said guide grooves and is provided on said land in said first region on the center line between adjacent guide grooves so that said at least one second element overlaps at least a respective one of said first elements of adjacent guide grooves when viewed in the radial direction of record carrier.

6. A record carrier according to claim 5, wherein a group formed of one of said first elements and said at least one second element is asymmetric with respect to the center line between said adjacent guide grooves.

7. A record carrier according to claim 6, wherein said correction pattern further includes third elements which are different in optical characteristic from said guide grooves and are provided in said first region on respective center lines of said adjacent guide grooves so that each of said third elements overlaps said at least one second element so as to form said asymmetric group when viewed in the radial direction of the record carrier.

8. A record carrier according to claim 5, wherein a mark for identifying said correction pattern is provided together with said correction pattern, on every other revolution of said land.

9. A record carrier having a track offset correction pattern comprising a disc-shaped substrate, a recording layer formed on said substrate, first and second regions alternately arranged along the rotational direction of the record carrier, guide grooves disposed in at least said second region and extending in the rotational direction of the record carrier while being spaced apart in the radial direction of the record carrier, a land extending in the rotational direction of the record carrier between adjacent guide grooves, said adjacent guide grooves serving as an optical guide for a light spot which follows on a center line between the adjacent guide grooves, first elements different in optical characteristic from said guide grooves and being provided in said first region while extending on center lines of said guide grooves so that said first elements of said adjacent guide grooves do not overlap each other when viewed in the radial direction of the record carrier, at least one second element different in optical characteristic from said guide grooves and being provided in said first region while extending on the center line between adjacent guide grooves so that said at least one second element overlaps at least a respective one of said first elements of the adjacent guide grooves when viewed in the radial direction of the record carrier, and said first elements of said adjacent guide grooves and said at least one second element between said adjacent guide grooves form said correction pattern for correcting track offset.

10. A record carrier according to claim 9, wherein a group formed of one of said first elements and said second elements is asymmetric with respect to the center line between said adjacent guide grooves.

11. A record carrier according to claim 9, wherein each revolution of said land is divided into a plurality of sectors, each sector including a header field in which a header signal including address information for identifying a respective sector is formed in advance with pits of a phase structure, and a recording field which follows said header field, and wherein said first region is provided in said header field.

12. A record carrier according to claim 11, wherein a group formed of one of said first elements and said at least one second element is asymmetric with respect to the center line between said adjacent guide grooves.

13. A record carrier according to claim 12, wherein a mark for identifying said correction pattern is provided together with said correction pattern, on every other revolution of said land.