Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1999-09-14
2001-05-01
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064200, C428S064400, C428S913000, C430S270110, C430S495100, C430S945000, C369S275300, C369S275400, C369S277000
Reexamination Certificate
active
06224959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc and an optical disc stamper for manufacturing such an optical disc.
2. Description of the Related Art
As an example of the related art, explanations are hereinafter given about how address information is recorded in prepits on a DVD-RAM, a rewritable optical disc with 2.6 GB recording capacity on one side thereof, by referring to
FIGS. 5
,
6
, and
7
.
The recording side of a DVD-RAM (2.6 GB) is divided into a plurality of cocentric areas which are called bands
501
. Each band has tracks formed therein spirally, and a plurality of land tracks and groove tracks are disposed alternately per round and in succession. Each track is composed of a plurality of sectors which are data recording/playback units and each sector starts at the same position circumferentially as that of adjacent track sectors within the same band. At the top of each sector, a header which indicates synchronizing signals, address information and the like in the form of arranged prepits, and header areas
500
in a long strip shape in a radial direction are observed in appearance. An enlarged view of the header areas
500
is shown in FIG.
5
. Recording areas of groove tracks
600
or prepits
603
, when viewed through a base of the disc, are usually convex. Recording areas of the land tracks
601
are formed adjacent to the recording areas of the groove tracks
600
.
When data is recorded/played back in the DVD-RAM drive, tracking servo is applied in a manner such that an optical spot follows a groove track center line
604
or a land track center line
605
, and then a recording mark is written in the recording areas
600
and
601
, and the data is read. A sector header is composed of arrays of the prepits
603
, which are arranged on the border lines of the land tracks and the groove tracks. The header portion is divided into an ID
1
-
2
area and an ID
3
-
4
area, and each of them is arranged on the border lines of both sides.
In detecting these prepits using the DVD-RAM drive, a beam is converged at an objective lens
701
, is transmitted through a base
701
a
1
, and is then made to focus on a recording layer
703
a
1
, and is further caused to track on the groove track center line
604
or the land track center line
605
. The quantity of light of a reflection beam
700
is detected by using two-piece sensors
704
and
705
which are divided parallel to the track center line
605
and a header playback signal
707
a
2
is obtained by finding a difference between the outputs from the two sensors. When the light spot is located at the edge of a prepit
706
, the luminous intensity distribution in the x axis direction of the reflection beam
700
will be as shown in distribution
707
a
1
, and the output of the two-piece sensor
704
increases and becomes the state of point
708
a
3
of a header playback signal
710
a
3
. On the other hand, when the light spot is not located at the edge of the prepit, the luminous intensity distribution in the x axis direction of the reflection beam
700
will be as shown in distribution
707
a
2
and, therefore, the outputs of the two-piece sensors
704
and
705
become the same and become the state of point
709
a
3
of the header playback signal
707
a
3
.
With this conventional prepit arrangement in the DVD-RAM header area and by this detecting method, when the disc has a tilt in its radial direction or when a track offset is caused for some reason, the reading rate of the header playback signals suddenly decreases, and a tilt margin or an off-track margin becomes narrow. The reason for this is explained by using FIG.
7
.
When there is no disc tilt as shown with regard to the header playback signal
710
a
3
, an output signal is at 0 level in the state of
709
a
3
if the light spot is not located at a prepit, and high signal amplitude can be obtained.
When there is a disc tilt, however, the luminous intensity distribution of a reflection beam when the light spot is located at the edge of a prepit
706
b
1
is as shown in distribution
707
b
1
, the peak of luminous intensity further shifting toward a negative direction compared to the distribution
707
a
1
and, therefore, a differential signal of the two-piece sensors
704
and
705
becomes the state of point
708
b
3
of the header playback signal
710
b
3
, and remains at a lower level than that of point
708
a
3
. When the light spot is not located at the edge of a prepit, the peak of the luminous intensity in the luminous intensity distribution of the reflection beam also shifts to a negative direction as shown in distribution
707
b
2
, a differential signal of the two-piece sensors
704
and
705
becomes the state of point
709
b
3
of the header playback signal
710
b
3
and does not become a 0 level. Consequently, the playback signal amplitude decreases and the SN ratio (signal-to-noise ratio) lowers, thereby lowering the reading rate of the header signal and narrowing the margin for the disc tilt.
Likewise, when a track offset occurs, the signal amplitude decreases, thereby lowering the reading rate of the header signal and narrowing the margin for the track offset.
Therefore, it is an object of the present invention to enhance the reading rate of the header signal, and to provide an optical disc which can have a sufficient margin for the disc tilt or track offset.
SUMMARY OF THE INVENTION
(1) An optical disc of the present invention has substantially ring-shaped groove tracks and land tracks disposed alternately every round on the recording side thereof, and the optical disc is capable of rewriting information to both of these tracks. The optical disc is characterized in that prepits representing address information of sectors are disposed on the center lines of the groove tracks or land tracks.
(2) The optical disc of the present invention as described in paragraph (1) above is characterized in that a total length of the prepits on the groove tracks within a single sector is always longer than that on the land tracks.
(3) The optical disc of the present invention as described in paragraph (1) above is characterized in that the prepits on the groove tracks are recorded in space position modulation, and the prepits on the land tracks are recorded in pit position modulation.
(4) The optical disc of the present invention as described in paragraph (3) above is characterized in that the prepit data modulation mode is 2-7 modulation.
REFERENCES:
patent: 1-181134 U (1989-12-01), None
patent: 7-192288 (1995-07-01), None
patent: 9-81965 (1997-03-01), None
Miyamae Akira
Nagasaka Kimio
Evans Elizabeth
Oliff & Berridg,e PLC
Seiko Epson Corporation
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