Dynamic information storage or retrieval – Dynamic mechanism subsystem – Specified detail of transducer assembly support structure
Reexamination Certificate
2000-10-12
2004-09-07
Davis, David (Department: 2652)
Dynamic information storage or retrieval
Dynamic mechanism subsystem
Specified detail of transducer assembly support structure
Reexamination Certificate
active
06788638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup actuator, and more particularly to an optical pickup actuator suitable for a compact/portable information equipments, such as a notebook computor.
2. Description of the Related Art
Recently, a rapid development of an optical disc has brought a variety of optical pickups for recording information on the optical disc or reproducing information therefrom. The optical pickup is provided with an actuator for tracking control and focusing control, wherein the tracking control is to control a light spot condensed by an objective lens to follow a center of a signal track on the optical disc, and the focusing control is to control the light spot to be focused on a signal track surface. This actuator is driven by a Lorenz force generated in accordance with Fleming's left-hand law by placing a coil within a magnetic field space between a magnet and a magnetic substance.
The optical pickup is tending to be made thinner to keep pace with compact/portable information equipments, such as a notebook computer. The optical pickup actuator can be classified into two types according to a position of the objective lens on a bobbin, i.e. a lens-centering type as shown in
FIG. 1 and a
lens-protruding type as shown in FIG.
4
.
Referring to
FIG. 1
, a conventional lens-centering type actuator is divide into a moving part including an objective lens
2
, a bobbin
4
, tracking coils
10
, focusing coils
12
and wire springs
14
, and a fixed part including permanent magnets
6
and a yoke
8
. In the moving portion, the objective lens
2
serves to condense an incident light beam from a light source on an optical disc. The objective lens
2
is fitted into an annular hole formed in a center portion of the bobbin
4
. The focusing coils
12
are wound around the whole side surfaces of the bobbin
4
, and the tracking coils
10
are adhered to the wound surfaces of the focusing coils
12
. The wire springs
14
are connected between printed circuit boards (not shown) disposed at centers of left/right side surfaces of the bobbin
4
and a frame to support elastically the moving part and to supply a current signal from the frame to the tracking coils
10
and the focusing coils
12
. In the fixed part, the permanent magnets
6
are adhered to the yoke
8
while confronting the tracking coils
10
and the focusing coils
12
to generate a magnetic flux interlinking with the tracking coils
10
and the focusing coils
12
. The yoke
8
is composed of a metallic magnetic substance, outer side portions of which the permanent magnets are adhered to and opposite inner side portions of which are fitted into rectangular holes in the bobbin
4
.
With this lens-centering type actuator, as shown in
FIG. 2
a
, the direction of a focusing drive force is determined by the direction of the magnetic flux generated by the permanent magnets
6
and the direction of electric current applied to the focusing coils
12
. For example, when the direction of the magnetic flux is a direction of x-axis and the direction of electric current flowing in the focusing coils
12
within a magnetic field space is a direction of z-axis (a direction coming from a land surface), the driving force acts in a direction of y-axis in accordance with Fleming's left-hand law. Similarly, when the direction of the magnetic flux is a direction of—x-axis and the direction of electric current is a direction of z-axis, the driving force acts in a direction of—y-axis. This force acting in the vertical direction drives the objective lens
2
in a direction perpendicular to a recording surface of the optical disc.
As shown in
FIG. 2
b
, the direction of tracking drive force is determined by the direction of the magnetic flux generated by the permanent magnets
6
and the direction of electric current applied to the tracking coils
10
. For example, when the direction of the magnetic flux is a direction of z-axis and the direction of electric current is a direction of y-axis, the driving force acts in a direction of x-axis. Similarly, when the direction of the magnetic flux is a direction of z-axis and the direction of electric current is a direction of—y-axis, the driving force acts in a direction of—x-axis. This force acting in the horizontal direction drives the objective lens
2
in a direction horizontal to the recording surface of the optical disc.
However, there is a limitation in making the actuator thin enough in the lens-centering type actuator because a magnetic circuit is constructed on an optical path of the incident light from the light source. In fact, the lens-centering type actuator is accompanied with structural difficulties in constructing the magnetic circuit on the optical path, thus a height H
LCA
from the objective lens
2
to a 45° reflecting mirror
16
becomes high as shown in FIG.
3
.
To solve this problem, a lens-protruding type actuator has been proposed which is constructed as shown in
FIGS. 4 and 5
. Referring to
FIGS. 4 and 5
, the lens-protruding type actuator is divided into a moving part including an objective lens
22
, a bobbin
24
, tracking coils
30
, focusing coils
32
and wire springs
34
, and a fixed part including permanent magnets
26
and a yoke
28
. In the moving part, the bobbin
24
protrudes a semicircle on its one side, and the objective lens
22
is clamped in a center portion of the protruded side of the bobbin
24
. The tracking coils
30
and the focusing coils
32
are disposed within the bobbin
24
while confronting the permanent magnets
26
. The wire springs
34
are connected between printed circuit boards (not shown) positioned at centers of left/right side surfaces of the bobbin
24
and a frame. In the fixed part, the permanent magnets
26
are adhered to the side surfaces of the yoke
28
while confronting the tracking coils
30
and the focusing coils
32
. Both sides of the yoke
28
are fitted into rectangular holes of the bobbin
24
interposing the tracking coils
30
and the focusing coils
32
therebetween.
Since the objective lens
22
protrudes toward a light source, a magnetic circuit of this lens protruding type actuator can be arranged inside the bobbin
24
as to be positioned outside the optical path. Thus, the height H
LPA
from the objective lens
22
to a 45° reflecting mirror
36
becomes low as shown in FIG.
5
.
With this lens-protruding type actuator, the magnetic circuit structure is disposed in a center portion of the bobbin
24
far from the objective lens
22
in order to avoid the optical path, and the moving part has an asymmetric structure with respect to the objective lens
22
. This asymmetric structure of the moving part in the lens-protruding type actuator causes an inconsistency that a center of mass C
mass
does not converge into both centers of tracking/focusing movements TC, FC as shown in FIG.
6
. As a result of this, there is a problem in the conventional lens-protruding type actuator that a vibration mode of the wire springs
34
is found in a driving frequency band making the actuator easily excited.
The moving part of the lens-protruding type actuator is vibrated in a rotational vibration mode due to the inconsistency of the center of gravity with the centers of driving movements of the moving part as shown in
FIGS. 7
a
and
7
b
.
FIG. 7
a
depicts a rolling mode in which the moving part rotates with an angle with respect to a tangential direction (x-axis) of the optical disc.
FIG. 7
b
depicts a pitching mode in which the moving part rotates with an angle with respect to a radial direction (y-axis) of the optical disc.
FIG. 7
c
depicts a yawing mode in which the moving part rotates with an angle with respect to a direction of an optical axis (z-axis) perpendicular to the optical disc. When the moving part is driven along the tracking or focusing direction in these rotational vibration modes, there is a slant movement of the moving part to cause a phase change of the objective lens
22
. That is, the lens-protruding type
Birch & Stewart Kolasch & Birch, LLP
Davis David
LG Electronics Inc.
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