Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2002-02-15
2002-12-03
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S275300
Reexamination Certificate
active
06490233
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to information recording media, and particularly to a high-density information recording medium and a high-density optical recording medium of which the track width is smaller than a beam spot or a detecting means such as a magnetic head.
Japanese laid-open patent publication No. 6-176404, for example, describes an example of a high-density (narrow track) recording medium. This example uses as a recording medium an optical recording medium in which groove portions and land portions are formed on a substrate and information recording areas are formed on both of the groove portions and the land portions. Prepits are formed on a virtual prolonged line of a boundary portion between the groove portion and the land portion as identification information of a recording unit (sector), whereby recording information is recorded on both of the groove portions and the land portions and identification (address) information indicative of a recording area is handled by the prepits. Also, one prepit commonly uses address information for a pair of groove portion and land portion. According to this system, when the recording medium of this system is applied to a phase change type recording medium and a magneto-optical recording medium, information from the adjacent land portion or groove portion can be prevented from being mixed into the groove portion and the land portion owing to an interference effect caused within the beam spot (i.e. crosstalk can be cancelled out), and hence the tracks of the recording medium can be narrowed, thereby making a high-density recording become possible.
However, in the example according to the related art, inasmuch as information indicative of the position on the information recording medium is concentrated in the prepit portions and the prepit portions located in a discrete fashion, position information cannot be obtained from portions other than the prepit portions. As a consequence, it is difficult to control a rotational speed of a disk precisely with a high reliability. There is then presented the problem from a reliability standpoint that the recording medium according to the relate art is not persistent to, in particular, defects or the like.
SUMMARY OF THE INVENTION
A first object of the present invention is to provide an information recording medium in which the aforementioned problems can be solved and which can be made high in recording density and highly reliable by assigning position information to other portions than prepit portions.
A second object of the present invention is to provide an information recording and/or reproducing method in which the aforementioned problems can be solved and in which information can be recorded and/or reproduced with a high recording density and with a high reliability by using an information recording medium in which position information is assigned to other portions than prepits.
In order to attain the above-mentioned first object, the present invention used the means which follow:
(1) In an information recording medium having almost spiral-like or concentric tracks comprising both of groove portions and a land portion between the groove portions, the recording medium is divided into groups of a plurality of areas in the radius direction, each track is divided at circular arc recording units having the same central angle arranged to be radial in the radius direction within each group, identification information indicative of the recording unit is provided in the track at every recording unit, the each track is divided into groups such that a length of a circular arc-shaped recording unit becomes almost constant between the groups, and the groove portion and the land portion are wobbled in the radius direction of the information recording medium.
Thus, position information can be reliably obtained in the recording portions because the identification information is provided at every recording unit, and the groove portions and the land portions, which are the recording portions, are wobbled. In other words, recorded information can be accessed reliably and recording information can be positioned with a high accuracy. Further, since the recording units are arranged to be positioned in the radius direction of the information recording medium, the tracks can be accessed with ease, and a crosstalk caused between position information of each recording unit can be suppressed to the minimum. Since the tracks are disposed in such a manner that the lengths of the circular arc-shaped portions which are the recording units become almost the same, the recording density becomes approximately uniform. Thus, it becomes possible to efficiently use the whole surface of the disk. Furthermore, it is possible to correct the displacement of tracking with a high accuracy.
Japanese laid-open patent publication No. 6-243468 describes a technology in which grooves are wobbled and a linear velocity of a disk is calculated by a wobble cycle detecting circuit, thereby rotating the disk at a constant linear velocity (CLV).
(2) Wobble cycles and phases of the groove portion and the land portion are uniformly arranged to be radial with respect to the adjacent tracks within each group, whereby the wobbling between the adjacent tracks can be reliably reproduced without interference. Also, since the widths of the respective tracks become constant, the recording characteristics can be prevented from being affected.
(3) A constant integral multiple of the cycle at which the groove portion and the land portion are wobbled is made coincident with the length of the circular arc-shaped recording unit. Thus, the starting point and the ending point of the recording unit can be detected reliably, and it becomes possible to detect an accurate position in the recording unit. Moreover, since the length of the recording unit and the wobble cycle in which the groove portion and the land portion are wobbled are synchronized with each other, it is possible to automatically and constantly keep the relative speed of the recording medium constant by making the frequency of the wobbling become constant.
(4) The maximum values of the amplitudes of wobbling in which the groove portion and the land portion are wobbled were selected to be smaller than one-tenth of the track width. Thus, the influence that is exerted upon the recording and reproducing characteristics by the above-mentioned wobbling could be suppressed to be less than 1−cos (180/10)=−26 dB, and the influence which affects an S/N (signal-to-noise ratio)(~20 dB) necessary for the normal recording and/or reproduction can be suppressed to be negligibly small.
(5) Identification information was formed by prepits which were very small concave portions and convex portions disposed in the spacing between the groove portion and the land portion. Thus, it becomes easy to mass-produce an information recording medium with identification information previously provided therein by a simple manufacturing process such as an injection molding. Therefore, a productivity with which an information recording medium is mass-produced can be raised.
(6) Identification information was disposed in an intermediate portion formed between a track and a track adjoining to the former track. Thus, since one identification information can be used by both of the two tracks, identification information assigned to one information area is doubled, and hence a reliability of the identification information can be improved. The information tracks in which identification information is disposed can be discriminated from each other by effectively utilizing a difference between the positions of the directions along the track. Moreover, since a relationship between the identification information of the adjacent track and the identification information of the track falls within a constant range, it becomes possible to discriminate the track from the identification information of the adjacent track.
(7) The track of the groove portion and the track of the land portion were dis
Fushimi Tetsuya
Minemura Hiroyuki
Miyamoto Harukazu
Sugiyama Hisataka
Suzuki Motoyuki
Antonelli Terry Stout & Kraus LLP
Hindi Nabil
Hitachi , Ltd.
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