Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-03-28
2003-12-16
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C359S823000
Reexamination Certificate
active
06665238
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an optical pickup used in an optical player/recorder that performs reproduction from and recording onto an optical recording medium such as an optical disc, a lens driving device that is a principal part of the optical pickup, and a production method for the lens driving device.
(2) Description of the Related Art
A lens driving device is used in an optical pickup contained in an optical player/recorder that reproduces data from and records data onto an optical recording medium, such as an optical disc including a CD (Compact Disc) and a DVD (digital versatile disc). This lens driving device performs focusing control to focus a laser beam on a recording surface of an optical recording medium, and tracking control to follow a track on the recording surface.
For instance, a CD loaded in a CD player/recorder rotates at a high speed (200 to 500 rotations per second), and therefore an object lens is moved frequently at short time intervals through the focusing/tracking control. Due to this driving of the objective lens, a variety of resonance frequencies inherent in the CD player/recorder are produced over a wide frequency range, which has a negative effect on a read from the optical recording medium.
A lens driving device is therefore required to have a mechanism for suppressing such resonance occurring to the objective lens over a wide frequency band including low to high frequencies.
An example of a conventional lens driving device that suppresses such resonance is disclosed in Japanese Laid-Open Patent Application No. 7-105551.
FIG. 1A
is a diagrammatic view of this lens driving device
500
as the first conventional example. For ease of explanation, a fixed member
507
alone is shown in sectional view.
As shown in the figure, for the lens driving device
500
, a movable member
502
carrying an objective lens
501
is supported in a cantilevered state by a fixed member
507
via four fine elastic supporting members
503
-
506
, of which supporting members
504
and
506
are hidden by supporting members
503
and
505
.
The fixed member
507
is filled with a damping material, which encloses a base portion of each of the elastic supporting members
503
-
506
. A part of the enclosed base portion of each of the elastic supporting members
503
-
506
is slightly bent upward, which is considered to increase the damping material's effect of suppressing vibrations occurring to the supporting members
503
-
506
, especially small quick vibrations in a high frequency range.
Another example of a conventional lens driving device is disclosed in Japanese Laid-Open Patent Application No. 9-7203.
FIG. 1B
shows an external appearance of the second conventional lens driving device
600
in perspective view.
As shown in the figure, for the lens driving device
600
, a movable member
602
carrying an objective lens
601
is supported in a cantilevered state by a fixed member
607
via four fine elastic supporting members
603
-
606
. An end of the supporting member
603
is shaped into a form similar to a letter “U” to form a bent part
603
a
. Other supporting members
604
-
606
are also shaped into this form.
The supporting members
603
-
606
are not parallel to one another. When viewed from a direction “A”, the supporting members
603
-
606
are slanted relative to a direction perpendicular to a longitudinal direction of the supporting members
603
-
606
, and connect the movable member
602
with the fixed member
607
.
When a principal plane of each of the supporting members
603
-
606
is slanted as stated above, a displacement of each supporting member caused by vibrations in the focusing (vertical) direction and the tracking (horizontal) direction becomes large. By applying a damping material (not shown in the figure) to bent parts like the bent part
603
a
, resonance of the supporting members
603
-
606
is considered to be effectively suppressed.
The lens driving devices
500
and
600
of the first and second conventional technology, however, have the following problems.
The lens driving device
500
is capable of effectively suppressing resonance in the focusing direction and the longitudinal direction of the supporting members
503
-
506
. This driving device
500
, however, cannot effectively suppress a vibration in the tracking direction perpendicular to the above two directions.
With the lens driving device
500
, end parts of the supporting members
503
-
506
are attached one by one to the movable member
502
and the fixed member
507
, with the supporting members
503
-
508
being slightly and uniformly curved. Giving a uniform curve to all the supporting members
503
-
506
, however, is very difficult. When the supporting members
503
-
506
having a different extent of the curving are used to connect the movable member
502
with the fixed member
507
, the fixed member
507
supports the movable member
502
in a state of the movable member
502
being tilted relative to the fixed member
507
. Such variations in the curving can actually exist between different lens driving devices, which is not desirable for obtaining correct optical information. To suppress such variations, the plurality of supporting members
503
-
506
need to be attached one by one while the extent of the curving of each supporting member is precisely adjusted. Such production process, however, extremely decreases the productivity.
The insert molding is considered to overcome this problem. The insert molding is performed in a manner that embeds end parts of each elastic supporting member in the movable member
502
and the fixed member
507
. This production process may provide almost uniform extent of the curving to all the supporting members
503
-
506
although the problem of vibrations in the tracking direction still remains.
With the second conventional technology, on the other hand, a bent part is provided to each of the elastic supporting members
603
-
606
, which are slanted in the stated manner and connect the movable member with the fixed member. This construction appears to be capable of suppressing vibrations in the tracking direction as well as the focusing direction. However, when the plurality of the supporting members
603
-
606
are attached one by one in the production process, a total number of production processes increases, and variations in properties of supporting members
603
-
606
may be caused by deformations in the supporting members
603
-
606
during the production process.
To reduce these variations, the elastic supporting members
603
-
606
may be integrally molded with the movable member and the fixed member by the insert molding as stated above. However, it is impossible to perform the insert molding using simple molds composed of a top mold, a bottom mold, and side molds since principal planes of the supporting members
603
-
606
are not parallel to one another. Accordingly, producing the lens driving unit
600
by the insert molding requires more pieces of molds, which makes production processes more complex.
SUMMARY OF THE INVENTION
The present invention is made in view of the above problems, and aims, as the first object, to provide a lens driving device that is capable of effectively suppressing resonance over high and low frequency bands, which is caused by the high-speed driving of the objective lens, and that can be produced with high productivity. As the second object, the present invention aims to provide a production method for such lens driving device. As the third object, the present invention aims to provide an optical pickup including the lens driving device.
The first object is achieved by a lens driving device, including: an objective lens; a first member that holds the objective lens; a second member; a plurality of supporting members that are elastic and that each include a first connected part and a second connected part that are connected respectively to the first member and the second member, so that the second member supports the first memb
Ijima Shin'ichi
Nakanishi Hideyuki
Onozawa Kazutoshi
Yamanaka Kazuhiko
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