Optical pickup actuator

Details Optical pickup actuator Optical pickup actuator

2001-11-02

2004-06-01

Ometz, David (Department: 2653)

Dynamic information storage or retrieval

Dynamic mechanism subsystem

Specified detail of transducer assembly support structure

C369S044160, C359S824000

Reexamination Certificate

active

06744722

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup actuator recording or reproducing information onto an optical disc, and in particular to an optical pickup actuator which is capable of performing a tracking movement with a focusing and a tilt movements.
2. Description of the Conventional Art
Generally, an optical pickup apparatus includes an optical pickup actuator as an object lens focusing an optical spot of an optical beam at the center of a signal track of an optical disc by corresponding to a surface vibration and eccentricity of the optical disc in accordance with rotation of the optical disc.
The optical pickup actuator operates in order to make the object lens perform a focusing and a tracking movements.
Herein, the focusing movement is moving an object lens up and down in order to make an optical spot of an optical beam of the object lens place within a depth of focus on a signal track of an optical disc, and the tracking movement is moving the object lens right and left in order to make the optical spot of the optical beam of the optical lens follow the center of the signal track.
Accordingly, the optical pickup actuator follows the center of the signal track of the optical disc by moving the object lens up and down (focusing servo), right and left (tracking servo) according to a current flowing on a coil and an electromagnetic force between magnets.
FIGS. 1
,
2
,
3
schematically illustrate an optical pickup actuator in accordance with the conventional art.
As depicted in
FIG. 1
illustrating the optical pickup actuator in accordance with the conventional art in the information recording aspect, the optical pickup actuator in accordance with the conventional art includes an object lens
2
focusing an optical beam from a laser diode light source at an information recording surface of an optical disc, a bobbin
4
supporting the object lens
2
, two magnets
6
respectively placed at the front and the rear of the bobbin
4
, a yoke
8
placed at the rear of the magnet
6
and preventing leakage of magnetic flux from the rear of the magnet
5
, a tracking coil
10
placed at the exterior of the bobbin
4
so as to be corresponded to the magnet
6
and a focusing coil
12
wound around the bobbin
4
so as to be at right angles to the tracking coil
10
The optical pickup actuator in accordance with the conventional art performs the focusing movement and the tracking movement by having the tracking coil
10
and the focusing coil
12
within a magnetic space formed with the magnet
6
and the yoke
8
and moving the object lens
2
up-down and right-left by Lorentz force of Fleming's left-hand law.
In more detail, as depicted in
FIG. 2
illustrating the optical pickup actuator in accordance with the conventional art taken along the line A—A of
FIG. 1
, a magnetic circuit of the actuator for performing the focusing movement is constructed with the focusing coil
12
, the magnet
6
magnetized to form a NS and the yoke
8
placed at the rear of the magnet
6
.
Herein, a line of magnetic flux is generated in a horizontal axis direction, and the direction of power N operating the optical pickup actuator works in up and down directions, accordingly the focusing movement is performed.
In addition, as depicted in
FIG. 3
illustrating the optical pickup actuator taken along the line B—B of
FIG. 1
, the magnetic circuit of the optical pickup actuator for the tracking movement is constructed with the magnet
6
magnetized to form N, S polar and the tracking coil
10
placed horizontally at both sides of the magnet
6
on the boundary surface of the magnet
6
.
Herein, the line of magnetic flux is generated in a direction vertical to the ground, and the power N operating the optical pickup actuator works in the right and left directions according to the direction of the current I applied to the tracking coil
10
, accordingly the tracking movement can be performed.
And, as depicted in
FIG. 1
, the pickup actuator further includes a wire spring
14
and a PCB (printed circuit board)
48
mechanically connected to a fixed part (not shown) by having a fixation point at the right and left sides of the bobbin
4
.
As described above, the optical pickup actuator in accordance with the conventional art operated by the magnetic force generated in the magnetic circuit and working in the up-down (focusing) and left-right (tracking) directions performs the focusing movement and the tracking movement by performing the up-down movement and the left-right movement on the basis of the front end portion of the wire spring
14
fixed to the fixed part.
According to the thinness trend of the optical pickup system, in the optical pickup actuator in accordance with the conventional art, it is difficult to form a magnetic circuit on a light path of the laser diode light source.
In the meantime, as described in
FIG. 4
illustrating another optical pickup actuator in accordance with the conventional art, the magnetic circuit is constructed so as to avoid the light path of the light source.
In more detail, as depicted in
FIG. 4
, another optical pickup actuator in accordance with the conventional art includes an object lens
34
focusing a light beam from a light source on an information recording surface of an optical disc, a lens holder
35
supporting the object lens
34
, magnets
38
placed inside the lens holder
36
, yokes
40
placed at the rear of the magnets
38
and preventing leakage of magnetic flux from the rear of the magnets
38
, a tracking coil
42
installed at the lens holder
36
so as to be corresponded to the magnets and a focusing coil
44
wound around the inside diameter of the lens holder
36
so as to be at right angles to the tracking coil
42
.
And, another optical pickup actuator in accordance with the conventional art further includes a wire spring
46
and a PCB
48
(printed circuit board) placed at the right and left sides of the lens holder
36
, supplying a current to the tracking coil
42
and the focusing coil
44
and supporting the lens holder
36
.
Herein, the lens holder
36
has a protrusion portion
36
b
in which the object lens
34
is fixed in order to avoid a light path from the light source, and rectangular holes
36
a
,
36
a′
are formed at the lens holder
36
in order to place the magnets
38
and the yokes
40
at the center portion of the lens holder
36
.
As depicted in
FIG. 4
, in another optical pickup actuator in accordance with the present invention, the up-down movement and the right-left movement of the lens holder
36
according to the tracking movement and the focusing movement are biaxial-operated on the basis of the end portion of the wire spring
46
.
However, in the optical pickup actuator projecting the object lens
34
, because the magnet
38
, the yoke
40
and the tracking coil
42
, etc. for the focusing and the tracking movements are inserted into the holes
36
a
,
36
a′
of the lens holder
36
, a resonance point is lowered in high frequency characteristics. And, because the object lens
34
is installed at the protrusion portion
36
b
, the fixation point of the wire spring
46
becomes far off from the object lens
34
, accordingly unstable movement can occur in a high speed mode.
In addition, in the optical pickup actuator in accordance with the conventional art projecting the object lens
34
, because a separation distance of an excitation force center of the tracking and an excitation force center of the focusing divided into the upper and lower parts is relatively long, a resonance point is lowered and vibration characteristics in the surface direction are bad.
In the meantime, a higher accuracy is required for the optical pickup actuator and a tilt margin of the actuator is gradually lowered in the operation of the actuator, it is impossible to satisfy an optical tilt permissive error by the conventional assembly method.
Accordingly, in the recent optical pickup actuator, besides the focusing and tracking biaxial servo, a triaxial actuato

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