Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-10-25
2004-01-27
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044150, C359S814000
Reexamination Certificate
active
06683831
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an objective lens actuator used in an optical disk device for recording and reproducing information on/from an optical disk such as a magneto-optical disk, for displacing an objective lens in a focus direction and in a track direction so as to perform focus servo and tracking servo to the optical disk.
BACKGROUND OF THE INVENTION
FIGS.
9
(
a
) through
9
(
c
) show a schematic structure of a magneto-optical disk device
51
, one of optical disk devices. The magneto-optical disk device
51
is made up of a mechanical chassis
52
, a spindle motor
53
fixed to the mechanical chassis
52
, an optical pick-up
54
provided with an objective lens
59
, a magnetic head unit
55
fixed to the optical pick-up
54
, a feeder
57
and guide axes
58
for moving the optical pick-up
54
in a direction of a radius of a magneto-optical disk
56
chucked by the spindle motor
53
.
The optical pick-up
54
focuses a light beam emitted from a laser light source (not shown) onto the magneto-optical disk
56
by the objective lens
59
. The objective lens
59
is driven in a focus direction and in a tracking direction by an actuator
60
which will be mentioned later [see FIGS.
10
(
a
) and
10
(
b
)], so as to follow the surface vibration of a disk and the decentering of a track.
The magnetic head unit
55
is made up of a suspension
55
a
and a slider section
55
b
. The suspension
55
a
presses the slider section
55
b
with an appropriate force by elastic deformation, so as to prevent the slider section
55
b
from detaching from the magneto-optical disk
56
when the surface vibration of the disk occurs.
FIGS.
10
(
a
) and
10
(
b
) show a detailed structure of the objective lens actuator
60
. The objective lens
59
is held by an objective lens holder
61
. The objective lens holder
61
is fixed to an actuator base
63
via four support wires
62
which are located in parallel to one another. More specifically, the objective lens holder
61
is fixed via the support wires
62
to a rising section
63
b
of the actuator base
63
, which is formed by raising one end of a horizontal section
63
a
of the actuator base
63
in a lengthwise direction, vertically with respect to the horizontal section
63
a.
On a side of the objective lens holder
61
opposite to a side facing the rising section
63
b
, a focus coil
64
and a tracking coil
65
are fixed. A magnetic flux is generated in a cavity in a magnetic circuit
66
made up of permanent magnets
66
a
and a yoke
66
b
, and the magnetic flux and a current flowing the foregoing coils react one another, permitting the objective lens
59
to be displaced freely in the focus direction and the tracking direction.
When a light beam is spot-emitted on the magneto-optical disk
56
by the objective lens
59
of the optical pick-up
54
, as shown in
FIG. 11
, the temperature of a section subjected to the spot emission in a recording medium
56
b
formed on a disk substrate
56
a
of the magneto-optical disk
56
is increased, and the coercive force of a magnetic substance of the recording medium
56
b
in the section is decreased. Here, if a magnetic field is given to the section subjected to the spot emission by a magnetic head
55
c
of the slider section
55
b
, the section is easily magnetized, and information is recorded on the magneto-optical disk
56
.
Incidentally, in the magneto-optical disk device
51
structured as mentioned above, when trying to displace the objective lens holder
61
in the focus direction [in a direction of an arrow A in FIG.
10
(
b
)] so as to perform focus servo, a reaction force [a force acting in a direction of an arrow B in FIG.
10
(
b
)] is applied to the magnetic circuit
66
and the actuator base
63
which directly supports the magnetic circuit
66
, vibrating the whole optical pick-up
54
. The vibration is transmitted to the magneto-optical disk
56
via the guide axes
58
and the spindle motor
53
. As a result, the magneto-optical disk
56
is vibrated, which makes it difficult to perform stable focus servo.
Thus, for example, Japanese Unexamined Patent Publication No. 7-105550 (Tokukaihei 7-105550, published on Apr. 21, 1995) (U.S. Pat. No. 5,719,834) discloses a structure for elastically supporting the magnetic circuit
66
with flexibility in a focus direction, using two parallel leaf springs
67
, as shown in FIGS.
12
(
a
) and
12
(
b
). More specifically, the magnetic circuit
66
is fixed, via the parallel leaf springs
67
located parallel to the horizontal section
63
a
of the actuator base
63
, to a rising section
63
c
of the actuator base
63
, which is formed by raising the other end of the horizontal section
63
a
in a lengthwise direction (on a side opposite to the rising section
63
b
in the lengthwise direction), vertically with respect to the horizontal section
63
a
. Therefore, in this structure, a slight vanity is formed between the magnetic circuit
66
and the horizontal section
63
a.
In this structure, when the objective lens holder
61
is moved in the focus direction, the magnetic circuit
66
is moved in a direction opposite to the moving direction of the objective lens holder
61
, by a reaction force applied to the magnetic circuit
66
. At this time, the parallel leaf springs
67
supporting the magnetic circuit
66
flex, and eventually, the vibration of the magnetic circuit
66
caused by the reaction force is absorbed by the flexure of the parallel leaf springs
67
. Therefore, this structure can prevent the actuator base
63
and the optical pick-up
54
from being vibrated by the displacement of the magnetic circuit
66
in accordance with the displacement of the objective lens holder
61
in the focus direction, achieving stable focus servo.
However, in the structure disclosed in the foregoing publication which supports the magnetic circuit
66
using the parallel leaf springs
67
, there is a problem that it is difficult to downsize the actuator
60
.
That is, in the structure disclosed in the foregoing publication, since the parallel leaf springs
67
are provided between the magnetic circuit
66
and the rising section
63
c
, a length a of the horizontal section
63
a
in the lengthwise direction, is increased compared with the case where the parallel leaf springs
67
are not provided, resulting in an increase in the size of the actuator
60
.
Here, it can be considered, for example, to adopt a technique for downsizing the actuator
60
by decreasing the length of the parallel leaf springs
67
in the lengthwise direction without changing a spring constant, using a material with a low Young's modulus to form the parallel leaf springs
67
. In this case, however, the parallel leaf springs
67
flex more, compared with the case where longer parallel leaf springs
67
having the identical spring constant are formed using a material with a higher Young's modulus, and the parallel leaf springs
67
are likely to be subjected to plastic deformation. This structure causes a problem in the displacement of the magnetic circuit
66
in accordance with the displacement of the objective lens holder
61
in the focus direction.
Incidentally, in order to prevent plastic deformation, it can also be considered, for example, to provide a stopper for limiting the displacement of the parallel leaf springs
67
. In this case, however, if the length of the parallel leaf springs
67
is short, the positioning accuracy of the stopper should be enhanced, increasing design load.
SUMMARY OF THE INVENTION
The present invention is made to solve the foregoing problems, and its object is to provide an objective lens actuator which is capable of performing stable focus servo even if a reaction force of a force acting on an objective lens holder is generated, and being downsized with a simple structure.
To achieve the foregoing object, an objective lens actuator in accordance with the present invention is structured so as to include:
an objective lens holding element for holding
Nagatome Seiichi
Tanaka Toshiyuki
Conlin David G.
Edun Muhammad
Edwards & Angell LLP
Hartnell, III George H.
Sharp Kabushiki Kaisha
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