Dynamic optical information storage or retrieval – Dynamic mechanism optical subsystem – Transducer carriage or actuator
Reexamination Certificate
2001-12-27
2004-11-30
Watko, Julie Anne (Department: 2652)
Dynamic optical information storage or retrieval
Dynamic mechanism optical subsystem
Transducer carriage or actuator
Reexamination Certificate
active
06826769
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a recording and reproducing device, disk cartridge, and optical disk device, which can be used to record and reproduce information in high density, and in particular to a recording and reproducing device, disk cartridge, and optical disk for recording and/or reproducing a data signal with respect to a flexible optical disk.
BACKGROUND OF THE INVENTION
Optical disks, such as a magneto-optical disk, have been widely used conventionally to record and reproduce information using a laser. In recent years, recording density of optical disks has been increasing to accommodate recording of more information. Along with this, optical disks have adopted smaller recording pits.
In order to read out information from such a high-density optical disk, the optical pickup needs to focus a light beam in such a way that the beam spot falls on a small domain of the optical disk where information is recorded. This makes it possible to read out information recorded in such a small domain. The smaller spot size enables recording of more information.
The spot size is proportional to wavelength &lgr; of the light source used, and is inversely proportional to numerical aperture NA of the objective lens. Thus, the spot size of a light beam can be reduced by either reducing the wavelength &lgr; of light from the light source, or by increasing the numerical aperture NA of the objective lens.
However, reducing the spot size by either of these methods causes large comatic aberration on the light beam when the optical disk tilts. The result of this is that the light beam cannot be accurately focused on the optical disk.
One conventional approach to solve this problem is to reduce thickness of the optical disk, and in turn length of optical path in the optical disk, so as to provide a larger margin of error for a tilt of the optical disk substrate.
For example, a CD-ROM has a numerical aperture NA=0.45, wavelength &lgr;=780 nm, and thickness of the optical disk substrate 1.2 mm. In contrast, a DVD-ROM has a numerical aperture NA=0.6, wavelength &lgr;=655 nm, and thickness of the optical disk substrate 0.6 mm. The DVD-ROM thus employs a light source which emits light of a shorter wavelength &lgr;, an objective lens with larger numerical aperture NA, and a thinner optical disk substrate, so as to increase recording capacity and a margin of error for a tilt of the optical disk substrate.
However, rigidity of the optical disk substrate weakens when the thickness of the optical disk substrate is further reduced to provide more margin of error for a tilt of the optical disk substrate. In fact, this only worsens the tilt of the optical disk substrate because weaker rigidity of the optical disk substrate causes the optical disk substrate to flutter. Therefore, there is a limit in reducing wavelength &lgr; of light of the light source and increasing numerical aperture NA of the objective lens.
In light of this problem, Japanese Unexamined Patent Publication No. 308059/1998 (Tokukaihei 10-308059) (published date: Nov. 17, 1998) teaches a recording and reproducing device which stabilizes rotation of an optical disk to allow for use of a thinner optical disk, an objective lens with larger numerical aperture NA, and light of a shorter wavelength &lgr;.
FIG. 52
shows a structure of this recording and reproducing device.
As shown in
FIG. 52
, the recording and reproducing device is adapted to record and reproduce information with respect to an optical disk
401
, by including a spindle
405
for rotating the optical disk
401
, an optical pickup
403
for projecting and focusing a light beam on the optical disk
401
, and an stabilizer
402
for stabilizing rotation of the optical disk
401
. The optical disk
401
is very thin and flexible.
The optical disk
401
has a magnetic center hub
404
which fixes the optical disk
401
on the spindle
405
by magnetic coupling. The optical pickup
403
has focusing means such as a complex objective lens. The stabilizer
402
and the optical pickup
403
are disposed face to face on the both sides of the optical disk
401
.
To record or reproduce information with respect to the optical disk
401
, the optical disk
401
is rotated in the vicinity of the stabilizer
402
. Here, a space of reduced pressure is created between the optical disk
401
and the stabilizer
402
. Thus, the optical disk
401
, being flexible, is drawn toward the stabilizer
402
, and rotates at a constant distance from the stabilizer
402
. As a result, fluttering of the optical disk
401
is suppressed, thereby recording and reproducing information in the recording and reproducing device with the optical pickup
103
having a wavelength of light not more than 650 nm and numerical aperture NA of the complex objective lens not less than 0.7.
Further, the foregoing publication also teaches a recording and reproducing device which uses a disk cartridge
406
integrally provided with the stabilizer
402
, as shown in FIG.
53
. In this case, the optical pickup
403
is inserted into the disk cartridge
406
through an opening (not shown) of the disk cartridge
406
. The provision of the stabilizer
402
with the disk cartridge
406
suppresses fluttering of the optical disk
401
as in the recording and reproducing device of
FIG. 52
, thus realizing recording and reproducing of information with the thin optical disk
401
, the objective lens with large numerical aperture NA, and light of short wavelength &lgr;.
Further, the foregoing publication discloses a structure in which a light beam is focused using a dual objective lens. For example, in a reproducing device shown in
FIG. 54
, a flexible optical disk
501
, fixed on a center hub
503
, is rotated by a spindle
504
, so that the optical disk
501
is drawn toward the stabilizer
502
to stably rotate at a constant distance from the stabilizer
502
.
A light beam
510
from a light source in a light emitting and detecting unit
505
is reflected at a mirror
506
and focused through the dual objective lens composed of a first objective lens
507
and a second objective lens
508
before it strikes the optical disk
501
. The reflected light from the optical disk
501
is detected by a photodetector provided in the light emitting and detecting unit
505
, so as to record or reproduce information with respect to the optical disk
501
.
The dual lens is driven by a biaxial actuator
509
to carry out tracking and focusing. With such a reproducing device, a wavelength of light not more than 650 nm and numerical aperture NA of the dual lens not less than 0.7 can be realized.
However, the foregoing arrangement has the following problems.
Generally, recording and reproducing of information with respect to the optical disk employ a focus control whereby a constant distance is maintained between the optical disk and focusing means to maintain the laser beam in focus, so that the surface of the optical disk carrying the information is always within the depth of focus of the focusing means such as the objective lens.
In this manner, a focus control is carried out to record or reproduce information with respect to the optical disk
401
. The optical pickup
403
approaches the optical disk
401
. In this instance, in the arrangement of the foregoing publication, regardless of whether it is the recording and reproducing device of
FIG. 52
or the recording and reproducing device using the disk cartridge
406
as shown in
FIG. 53
, the surface of the optical pickup
403
provided with the focusing means such as the objective lens is the surface facing the optical disk
401
, which surface has relatively large irregularities. Thus, pressure fluctuates around the focusing means, or around the optical pickup
403
, every time the focusing means is moved during a focus control, which causes fluctuation of air pressure between the optical pickup
403
and the optical disk
401
. That is, the movement of the focusing means causes the optical disk
401
to flutter, which prevents stable f
Hirokane Junji
Iwata Noboru
Conlin David G.
Edwards & Angell LLP
Hartnell, III George W.
Sharp Kabushiki Kaisha
Watko Julie Anne
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