Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-08-25
2002-01-29
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044110, C359S814000
Reexamination Certificate
active
06343053
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an objective lens driving apparatus of an optical disk drive and, more particularly, to an objective lens driving apparatus having an actuator for moving an objective lens in a focusing direction and a tracking direction.
2. Description of the Related Art
FIGS. 1A and 1B
show a first example of a conventional objective lens driving apparatus. In the objective lens driving apparatus shown in
FIGS. 1A and 1B
, an objective lens
1
is supported by an objective lens supporting member
2
that is elastically supported by four wire springs
4
extending from a stationary member
3
. A focusing coil
5
and a tracking coil
6
, which are wound in directions perpendicular to each other, are provided around the objective lens supporting member
2
. An end of each of the wire springs
4
is soldered to a base board
7
at a soldered portion
8
a.
The opposite end of each of the wire springs
4
is soldered to a respective one of the focusing coil
5
and the tracking coil
6
at a soldered portion
8
b.
Accordingly, the wire springs
4
serve as conductive wires to provide an electrical connection to the focusing coil
5
and the tracking coil
6
. Magnets
10
are fixed to yokes
9
so that the objective lens supporting member
2
is interposed between the magnets
10
. A light beam having an optical axis indicated by a chain line
12
is deflected by a prism
11
, and enters the objective lens
1
.
In the above-mentioned structure, the objective lens
1
is moved in a focusing direction indicated by an arrow Z and a tracking direction indicated by an arrow Y by moving the objective lens supporting member
2
by providing control currents to the focusing coil
5
and the tracking coil
6
.
A description will now be given, with reference to
FIG. 2
, of a second example of the conventional objective lens driving apparatus.
FIG. 2
is a perspective view of the second example of the conventional objective lens driving apparatus. In
FIG. 2
, parts that are the same as the parts shown in
FIGS. 1A and 1B
are given the same reference numerals, and descriptions thereof will be omitted.
In the objective lens driving apparatus shown in
FIG. 2
, each of the two magnets
10
is fixed to a respective one of yokes
9
a.
The focusing coil
5
and the tracking coil
6
are situated around the objective lens supporting member
2
. An additional yoke
9
b
is provided near a respective one of the yokes
9
a
so that the focusing coil
5
and the tracking coil
6
are interposed between the yokes
9
a
and
9
b.
Accordingly, a closed magnetic circuit is formed by each of the magnets
10
and a respective pair of the yokes
9
a
and
9
b.
Thus, similar to the first example, the objective lens
1
is movable in a focusing direction indicated by an arrow Z and a tracking direction indicated by an arrow Y by moving the objective lens supporting member
2
by providing control currents to the focusing coil
5
and the tracking coil
6
.
In the above-mentioned first and second examples of the conventional objective lens driving apparatus, the prism
11
must be situated under the objective lens supporting member
2
as shown in
FIG. 1B
since the focusing coil
5
and the tracking coil
6
are present. Thus, there is a problem in that a thickness of the entire apparatus is increased due to the arrangement of the prism
11
.
Additionally, Japanese Laid-Open Patent Application No.9-180207 discloses a third example of the conventional objective lens driving apparatus. In this objective lens driving apparatus, a deflection mirror is provided inside the objective lens supporting member
2
so that the deflection mirror is movable together with the objective lens
1
. Thereby, a light beam is prevented from being offset when the objective lens supporting member
2
is moved in the tracking direction.
It is considered to adopt a structure shown in
FIG. 3
in which structure a driving motor having a closed magnetic circuit similar to the above-mentioned second example is applied to the structure disclosed in Japanese Laid-Open Patent Application No.9-180207. However, in such a case, there is a problem in that the objective lens supporting member
2
is tilted due to a torque generated by an offset between a center of driving force exerted on the focusing coil
5
and the center of gravity of a movable part including the focusing coil
5
as shown in FIG.
4
.
Additionally, since the tracking force is generated by the tracking coil
6
in which a current flows in the focusing direction, there is a problem in that a sufficient drive force cannot be obtained.
Further, the above-mentioned Japanese Laid-Open Patent Application No.9-180207 discloses another embodiment in which an actuator for tracking is formed by a magnetic circuit different from a magnetic circuit of an actuator for focusing. Such a structure has a problem in that an assembling operation is complex and a manufacturing cost is increased.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved and useful objective lens driving apparatus in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an objective lens driving apparatus in which a focusing coil and a tracking coil can be arranged in a parallel relationship with a thin, flat shape so that both the focusing coil and the tracking coil can be moved by a single flat magnet.
Another object of the present invention is to provide an objective lens driving apparatus in which a movable part including a focusing coil is prevented from being tilted.
A further object of the present invention is to provide an objective lens driving apparatus in which drive forces generated by a focusing coil and a tracking coil are increased by forming a closed magnetic circuit.
In order to achieve the above-mentioned objects, there is provided according to the present invention an objective lens driving apparatus for moving an objective lens in a focussing direction and a tracking direction relative to an optical disk, the objective lens driving apparatus comprising:
an objective lens supporting member supporting the objective lens, the objective lens supporting member being movably supported on a stationary member; and
a drive motor provided at least one side of the objective lens supporting member, the drive motor comprising:
a yoke fixed to the stationary member;
a drive magnet mounted to the yoke and having a flat surface parallel to both the focusing direction and the tracking direction, the flat surface having four single-pole areas each of which is magnetized in a direction perpendicular to the flat surface; and
a drive coil assembly mounted on the objective lens supporting member and including a focusing coil and a tracking coil, the drive coil assembly having a flat shape so that the drive coil assembly faces the flat surface of the drive magnet in parallel relationship with a small air gap therebetween.
According to the above-mentioned invention, the drive motor is formed by the combination of the drive magnet having a surface divided into four magnetization areas and the drive coil assembly having a flat shape. The drive magnet generates magnetic fields in different directions in the vicinity of the flat surface. Accordingly, both the focusing coil and the tracking coil can be positioned in the vicinity of the drive magnet and parallel to the flat surface so that both the focusing coil and the tracking coil generate a drive force by being subjected to the magnetic fields in the vicinity of the drive magnet. Thus, the drive motor can be formed in a flat shape. Since the focusing coil does not surround the objective lens supporting member, a light beam can be introduced into an optical system provided within the objective lens supporting member in the tracking direction. Additionally, the entire focusing coil can be subjected to the magnetic field generated by the drive magnet, a focusing force is generated unif
Akanuma Goichi
Koide Hiroshi
Dickstein , Shapiro, Morin & Oshinsky, LLP
Edun Muhammad
Ricoh & Company, Ltd.
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