Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-07-17
2002-10-08
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06463019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup for recording and reproducing information with respect to an optical disk. More particularly, the present invention relates to an objective-lens driving device and a mechanism for adjusting the inclination of an objective lens which are aimed at making the optical pickup compact and thin and stabilizing the driving of the objective lens in both a focusing direction and a tracking direction.
2. Description of the Related Art
In general, an optical pickup is comprised of an objective-lens driving device having an objective lens and an optical system block for transmitting and receiving light with respect to the objective lens, and is structured such that the objective-lens driving device is mounted on a mounting base of the optical system block.
To accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to accurately set the optical axis of the objective lens perpendicular to the disk surface.
For this reason, a mechanism for adjusting the inclination of an objective lens is conventionally known (e.g., Unexamined Japanese Patent Application (Kokai) No. 62-287443) which is arranged as follows: As shown in
FIG. 1
, a spherically convex mounting surface
103
is made to project from a bottom surface
102
a
of an objective-lens driving device
102
having an objective lens
101
. In addition, as shown in
FIG. 2
, a spherically concave mounting surface
106
is formed in a mounting base
105
of an optical system block
104
, the spherically convex mounting surface
103
is fitted in the spherically concave mounting surface
106
, and the inclination of the objective lens
101
is made adjustable with respect to the center (fulcrum)
107
of a sphere formed by the spherically convex mounting surface
103
and the spherically concave mounting surface
106
by means of height adjusting screws
108
.
However, since the spherically convex mounting surface
103
, the spherically concave mounting surface
106
, and the height-adjusting screws
108
are disposed between the objective-lens driving device
102
and the mounting base
105
of the optical system block
104
, the thicknesswise dimension becomes large, thereby constituting a hindrance to the attempt to make the optical pickup thin.
In addition, to accurately effect the recording and reproduction of information with respect to an optical disk, it is necessary to prevent the occurrence of unwanted resonance. To prevent the occurrence of such unwanted resonance, in a conventional objective-lens driving device
201
A shown in the perspective view in
FIG. 3
, the position of the center of gravity of a movable section
204
, which has an objective lens
202
, a focusing coil
203
A for a focusing direction Z, and a pair of tracking coils
203
B for a tracking direction Y, is aligned with an optical axis
205
, and the central axes of the focusing coil
203
A and the tracking coils
203
B are aligned with the optical axis
205
(e.g., Unexamined Japanese Patent Application (Kokai) No. 2-230522).
The optical pickup having this arrangement is capable of preventing the occurrence of unwanted resonance, but it is necessary to dispose a light source, a reflecting mirror, a light-receiving element, and the like below the objective-lens driving device to effect the recording and reproduction of information. Hence, it has been difficult to make the optical pickup compact and thin.
To make the objective-lens driving device compact and thin, in a conventional objective-lens driving device
201
B shown in the exploded perspective view in
FIG. 4
, the central axes of a focusing coil
208
A and a pair of tracking coils
208
B are not aligned with the optical axis
205
, and the focusing coil
208
A and the tracking coils
208
B are disposed in a magnetic gap
207
provided in a single magnetic circuit
206
(e.g., Unexamined Japanese Patent Application (Kokai) Nos. 4-102235 and 4-103038).
In addition, in the objective-lens driving device disclosed in Unexamined Japanese Patent Application (Kokai) 4-103038, to accurately drive the movable section in the direction of the optical axis (focusing direction), a focusing-driving force which is provided outside the magnetic gap is minimized, so as to prevent an unnecessary force, such as moment, from acting in the movable section. It has been thought that this focusing-driving force occurring outside the magnetic gap, i.e., the leakage flux density, should be suppressed to as low a level as possible partly for preventing interference with metallic parts such as a motor disposed in the vicinity of the objective-lens driving device.
In addition, although the conventional objective-lens driving device
201
B shown in
FIG. 4
is capable of making the optical pickup compact and thin, there is a drawback in that, if an attempt is made to adjust the position of the center of gravity to either one of the driving points, the other driving point is offset from the position of the center of gravity, so that unwanted resonance occurs on the offset side.
FIG. 5A
shows a schematic arrangement of an optical disk apparatus portion in a magneto-optic recording/reproducing system, in which an optical disk
301
is provided with an optical pickup
304
having a magnetic head
302
on one side and an objective lens
303
on the other side. The magnetic head
302
and the optical pickup
304
are driven in the radial direction of the optical disk
301
by a head driving device
305
and a feed motor
306
, respectively, and the optical disk
301
is rotated by a spindle motor
307
. Among such optical disk apparatuses, those of a type in which the optical disk
301
is covered with a cartridge
308
for the purpose of protecting the optical disk
301
have come to be marketed in recent years. This cartridge-type optical disk is arranged as follows: As shown in
FIG. 5B
, the optical disk
301
is rotatably accommodated in a space formed between an upper shell
308
a
and a lower shell
308
b,
and the shells
308
a
and
308
b
are provided with windows
308
c
and
308
d,
respectively. When the optical disk
301
is not in use, the windows
308
c
and
308
d
are closed by a shutter
308
e,
and, during recording or reproduction, the shutter
308
e
is moved laterally to open the windows
308
c
and
308
d
and insert the magnetic head
302
and the objective lens
303
into the windows.
In the conventional optical pickup
304
, as described in, for example, Unexamined Japanese Patent Application (Kokai) 61-139945, a circuit for driving the objective lens
303
in the focusing direction and the tracking direction is disposed at a position other than that below the objective lens
303
, whereby a free space is formed below the objective lens
303
, and a reflecting mirror is disposed at that position, thereby making the overall optical pickup
304
thin.
With such a conventional apparatus, as shown in
FIG. 6A
, the optical disk
301
and the objective lens
303
are opposed to each other with an interval L
33
therebetween so that the optical axis of the objective lens
303
aligns with a central portion, as viewed in the rotating direction of the disk, of the window
308
d
of the lower shell
308
b.
In this arrangement, however, since a magnetic circuit
309
for effecting the positional adjustment of the objective lens
303
in the focusing and tracking directions is disposed outside the window
308
d,
there arises a need to provide a gap L
31
between a lower surface of the lower shell
308
b
and an upper surface of a yoke
310
constituting the magnetic circuit
309
. As a result, the distance L
32
between the lower surface of the lower shell
308
b
and the lower surface of the magnetic circuit
309
becomes large, thereby constituting a hindrance to making the optical pickup
304
thin and compact.
FIG. 7
shows an exploded perspective view of a conventional objective-lens driving device (Unexamined Japanese Patent Application (Kokai) No. 3-212826)
Kawano Noriyuki
Kinouchi Mitsuru
Matsuura Hiroyuki
Ogura Kouichi
Saito Yoshio
Hindi Nabil
TDK Corporation
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