Dynamic information storage or retrieval – Storage medium structure – Specified center hole or locating structure
Reexamination Certificate
1997-12-17
2002-06-25
Dinh, Tan (Department: 2653)
Dynamic information storage or retrieval
Storage medium structure
Specified center hole or locating structure
C369S290100
Reexamination Certificate
active
06411594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc such as an optical disc and a magneto-optical disc onto/from which data is written or read out by an optical disc recording/reproduction apparatus.
2. Description of the Prior Art
An optical disc including a magneto-optical disc has been suggested for saving audio, video, or computer data. This optical disc, for example, has a recording section on a transparent substrate and data is recorded on this recording section.
For example, as shown in
FIG. 1
, a magneto-optical disc having a signal recording plane only on one side is formed from a disc-shaped transparent resin such as polycarbonate includes: a substrate
102
having a thickness of, for example, about 1.2 mm; a recording layer
103
formed on the substrate
102
; and a protection layer
104
formed on the recording layer
103
. This magneto-optical disc
101
is an optical disk normalized by the International Standard Organization (ISO) such as ISO/IEC 10089 and 13549 and enables data writing by forming the recording layer
103
from a magnetized film. The magneto-optical disc
101
has a clamp portion
105
at the center portion.
Moreover, an optical disc recording and/or reproduction apparatus enabled to write or read data onto/from the magneto-optical disc
101
includes: a clamp
106
for holding a hub (not depicted) provided in the clamp portion
105
of the mounted magneto-optical disk
101
and for rotating the magneto-optical disc
101
; and an objective lens
107
for focusing a laser beam emitted from a light source (not depicted) on the recording layer
103
. The objective lens
107
and the clamp
106
are arranged at positions matching the configuration of the magneto-optical disc mounted on the optical disc recording and/or reproduction apparatus.
For example, the objective lens
107
is supported in such a manner that it can move within a predetermined stroke for focus servo. The objective lens
107
is positioned at a neutral position (position X
1
in
FIG. 1
) of the focus servo for the magneto-optical disc
101
.
The optical disc recording and/or reproduction apparatus is configured for writing or reading onto/from the magneto-optical disc
101
.
Here, the magneto-optical disc
101
can have increase data recording density by decreasing the thickness of the substrate as shown in FIG.
2
. It should be noted that FIG.
1
and
FIG. 2
show a single-sided type magneto-optical disc, but a double-sided magneto-optical disc can have further increased data recording density.
It has been desired to provide an optical disc recording and/or reproduction apparatus capable of recording or reproducing data onto from both of the magneto-optical disc
101
having a conventional substrate thickness of about 1.2 mm. and a magneto-optical disc
109
which is said to enable a higher recording density by reducing a substrate thickness. That is, an apparatus compatible for both of the discs is desired.
In this case, it is considered to design a compatible optical disc recording and/or reproducing apparatus to match with, for example, the conventional magneto-optical disc
101
. For example, if the objective lens
107
is subjected to a focus servo when a magneto-optical disc is mounted, data can be recorded or reproduced onto/from both of the magneto-optical discs
101
and
109
.
However, if it is impossible to obtain a stroke (a distance between X
1
and X
2
in
FIG. 2
) required for carrying out a focus servo to the magneto-optical disc
109
, the optical disc recording and/or reproduction apparatus cannot carry out focusing.
Furthermore, if focus is obtained at a shift limit position of the objective lens
107
during a focus servo, a focus characteristic is deteriorated because the objective lens
107
is not positioned at a neutral position for carrying out an appropriate focusing.
Moreover, in order to provide a greater shift stroke for the objective lens
107
, the optical disc recording and/or reproduction apparatus should have an additional function.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disc onto which focusing can be obtained with the same objective lens even if the substrate thickness varies.
The optical disc according to the present invention includes: a transparent substrate; a recording layer formed on the transparent substrate; and a clamp portion provided at a center portion of the transparent substrate; the clamp portion and the transparent substrate having surfaces different in height so that the recording layer plane is positioned in the vicinity of a focus position of the objective lens which is at a neutral position.
According to another aspect of the invention, the optical disc has a higher recording density than a normalized optical disc, and includes: a transparent substrate having a smaller thickness than the normalized optical disc; a recording layer formed on the transparent substrate; and a clamp portion which has a thickness identical to that of the normalized optical disc and is rotatably supported by a clamper provided in an optical disc recording and/or reproduction apparatus.
The optical disc having the aforementioned configuration is enabled to minimize the stroke of the objective lens provided in the optical disc recording and/or reproduction apparatus.
REFERENCES:
patent: 4634617 (1987-01-01), Ohta et al.
patent: 4926410 (1990-05-01), Suzuki et al.
patent: 5072438 (1991-12-01), Suzuki et al.
patent: 5085910 (1992-02-01), Matsushima et al.
patent: 5151310 (1992-09-01), Yanagisawa et al.
patent: 5438564 (1995-08-01), Takahashi
patent: 5448547 (1995-09-01), Minoda et al.
patent: 5560880 (1996-10-01), Takahashi et al.
Dinh Tan
Sony Corporation
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