Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2003-03-17
2004-06-08
Young, W. R. (Department: 2652)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
Reexamination Certificate
active
06747921
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for driving an objective lens used in an optical head for optically recording information onto an optical disk and optically reading information therefrom, and particularly to an apparatus for driving an objective lens for inputting and outputting light with respect to the optical head.
2. Description of the Related Art
In an optical head for recording and reproducing information with respect to an optical disk such as a compact disk, an objective lens for inputting and outputting light is disposed so as to be opposed to an optical disk, and the objective lens is moved in a radius direction of the optical disk by an actuator, whereby a track on the optical disk is traced.
Furthermore, in order to regulate a focus position of the objective lens by moving the objective lens upward and downward in accordance with the up and down movement of the optical disk surface caused by warpage thereof, to correct a tracking shift of the objective lens caused by eccentricity of the optical disk, and to regulate a relative tilt angle between the optical disk and the objective lens, the objective lens is moved by an apparatus for driving an objective lens.
In the apparatus for driving an objective lens, the objective lens is moved in three directions: a vertical direction (focusing direction) of the optical disk, a radius direction (tracking direction) of the optical disk, and a tangent direction of the optical disk, thereby enabling the optical head to exactly trace a track on the optical disk.
A conventional apparatus for driving an objective lens is described in, for example, Japanese Laid-Open Publication No. 4-319537.
FIG. 12
is a schematic view thereof. In this figure, an objective lens
101
is held by a lens holder
102
, and the lens holder
102
is connected to an elastic supporting plate
103
via four wires
104
. The lens holder
102
is elastically supported by the elastic supporting plate
103
by using each wire
104
, so that the lens holder
102
can be moved in any of a focusing direction F, a tracking direction T, and a tangent direction K of an optical disk with respect to the elastic supporting plate
103
.
A pair of electromagnetic coils
106
a
and
106
b
are provided on a base
105
. The elastic supporting plate
103
is fixed to the base
105
, and the lens holder
102
is disposed between the electromagnetic coils
106
a
and
106
b
. By appropriately regulating an electromagnetic force of the electromagnetic coils
106
a
and
106
b
, the lens holder
102
is moved in the focusing direction F, the tracking direction T, and the tangent direction K of an optical disk.
A pair of slits
103
a
are formed in the elastic supporting plate
103
, thereby providing a pair of supporting portions
103
b
. Resonance of each wire
104
is suppressed by an elastic force of the supporting portions
103
b.
In recent years, there has been a demand for a thinner apparatus for driving an objective lens of the above-mentioned type, capable of stably positioning an objective lens with high precision. In order to satisfy such a demand, an apparatus for driving an objective lens has been variously modified and developed. The process thereof will be described below.
As shown in
FIG. 13
, a basic structure of an apparatus
200
for driving an objective lens of the above-mentioned type includes a lens holder
202
for holding an objective lens
201
, a base
203
, and a plurality of wires
204
connecting the lens holder
202
to the base
203
. A light beam
205
passes through the objective lens
201
and is reflected by a prism
206
to be input and output between an optical head (not shown) and an optical disk (not shown). In this structure, the height of the apparatus
200
for driving an objective lens is added to the height of the prism
206
, so that the optical head becomes bulky, which is not preferable.
Therefore, in an apparatus
300
for driving an objective lens shown in
FIG. 14
, considering that the height of a lens holder
302
is larger than a distance between the respective wires
304
at a connected portion between the lens holder
302
and each wire
304
, an objective lens
301
is disposed away from the connected portion so as to make the lens holder
302
thinner at a portion of the objective lens
301
, and a prism
306
is disposed at a portion where the lens holder
302
is thinner. Thus, the optical head is made thinner.
In the structure shown in
FIG. 14
, the objective lens
301
is disposed away from the connected portion between the lens holder
302
and each wire
304
. Therefore, when resonance occurs in each wire
304
, a vibration amplitude of the objective lens
301
which is disposed away from the connected portion becomes large, degrading displacement frequency characteristics of the apparatus for driving an objective lens. Furthermore, resonance around an axis in the tracking direction T (i.e., resonance in a direction represented by an arrow A) occurs in the vicinity of a cutoff frequency of a gain of a servo driving system which moves the objective lens
301
in the focusing direction F. This makes focus control by the servo driving system unstable.
Furthermore, in the case where the objective lens
301
is moved in a radial tilt direction which is a direction around an axis in the tangent direction K of an optical disk, as well as the focusing direction F and the tracking direction T, each wire
304
is greatly twisted. Therefore, unnecessary resonance is likely to occur, further degrading the displacement frequency characteristics of the objective lens
301
. Furthermore, a diameter, a length, and the like of each wire
304
are not determined so as to suppress unnecessary resonance of each wire
304
, but determined by a lower order resonance frequency of an apparatus for driving an objective lens. Therefore, an unnecessary resonance frequency of each wire
304
cannot be shifted by changing the diameter, length, and the like of each wire
304
.
Thus, in an apparatus
400
for driving an objective lens shown in
FIG. 15
, an elastic supporting portion
406
is provided on a base
403
, and one end of each wire
404
is fixed to the elastic supporting portion
406
, whereby vibration of the elastic supporting portion
406
is further suppressed by a damping member (not shown). In this structure, a resonance frequency of each wire
404
is shifted by the elastic supporting portion
406
, whereby a resonance amplitude of each wire
404
is decreased. Because of this, the displacement frequency characteristics of an objective lens
401
are enhanced. Furthermore, a resonance frequency of each wire
404
can be removed from the vicinity of a cutoff frequency of a gain of a servo driving system which moves the objective lens
401
in the focusing direction F, without affecting a lower order resonance frequency of the apparatus
400
for driving an objective lens, whereby focus control by the servo driving system can be made stable.
However, in the apparatus
400
for driving an objective lens shown in
FIG. 15
, a printed substrate made of synthetic resin is used for the elastic supporting portion
406
in order to improve the ease of assembly. The printed substrate's characteristics (e.g., coefficient of elasticity) change remarkably depending upon temperature and time. Therefore, a resonance frequency, a resonance amplitude, and the like of each wire
404
cannot be made stable.
Furthermore, in the case where a distance between the respective wires
404
is decreased in the focusing direction F so as to make the apparatus
400
for driving an objective lens thinner, a tilt of an optical axis of the objective lens
401
when the objective lens
401
is moved is increased for the following reason. When a distance between the respective wires
404
is decreased in the focusing direction F, a radius of a path of the objective lens
401
when the objective lens
401
is moved in the focusing direction F becomes smaller, as a result of which a til
Fujii Hitoshi
Kojima Takayuki
Kubota Daisaburo
Mohri Masanari
Urairi Kenichiro
Matsushita Electric - Industrial Co., Ltd.
Snell & Wilmer LLP
Young W. R.
LandOfFree
Apparatus for driving an objective lens utilizing flexible... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for driving an objective lens utilizing flexible..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for driving an objective lens utilizing flexible... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3350602