Optical pickup actuator performable tilting operation

Details Optical pickup actuator performable tilting operation Optical pickup actuator performable tilting operation

2001-07-13

2004-10-05

Huber, Paul W. (Department: 2653)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044160

Reexamination Certificate

active

06801483

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup apparatus recording information on an optical disc or reproducing information recorded on an optical disc.
2. Description of the Prior Art
Recently, according to rapid development of disc mediums in relation to the optics, various optical pickup apparatus for recording/reproducing information onto/recorded on an optical disc are being developed.
Generally, an optical pickup apparatus includes an optical pickup actuator operating an objective lens in order to make an optical spot of an optical beam of the objective lens follow the center of signal tracks of an optical disc against a surface vibration and an eccentricity, etc. due to rotation of the optical disc.
The optical pickup actuator controls the objective lens so as to perform a focusing operation and a tracking operation.
Herein, the focusing operation means operating the objective lens up and down in order to make an optical spot of an optical beam of the objective lens place within a depth of focus, and the tracking operation means operating the objective lens right and left in order to make an optical spot of an optical beam of the objective lens follow the center of signal tracks of an optical disc.
In more detail, corresponding to an optical pickup, a position of a disc track can be varied relatively by an error and deformation in a manufacture process, a vibration due to rotation of the optical disc and an error of the optical pickup itself, etc., in order to compensate the variation of the position of the disc track an object lens is operated by an optical pickup actuator with electric signals
The optical pickup actuator operates the object lens by an electromagnetic force generating between a current of a coil and a magnet by using the coil and the magnet.
FIG. 1A
is a plan view illustrating an optical pickup actuator in accordance with the prior art, and
FIG. 1B
is a front view illustrating the optical pickup actuator in accordance with the prior art.
The optical pickup actuator in accordance with the prior art includes an objective lens
101
at the center portion, a lens holder
102
having coils
105
,
106
on a circumference for tracking and focusing operations, a plurality of magnets
103
and a plurality of yokes
104
separately installed at both sides of the lens holder
102
in order to construct a magnetic circuit, a plurality of suspension wires
107
separately fixed to a plurality of protrusion portions
108
of the lens holder
102
in order to support the lens holder
102
, and a damper holder
109
fixed to a base
100
and fixing the other end of each of the plurality of suspension wires
107
.
Herein, a focusing coil
105
is wound on the circumference of the lens holder
102
in order to perform the focusing operation, and a tracking coil
106
is wound on each corner portion.
Each of the plurality of yokes
104
made with a ferromagnetic material and projected from the base
100
is placed on the right side or the left side of the lens holder
102
, each of the plurality of magnets
103
is fixed inside each yoke
104
.
The plurality of protrusion portions
108
are formed at the center portion of the front and the rear surfaces of the lens holder
102
, an end of each suspension wire
107
having a two-stage structure is brazed on each protrusion portion
108
, the other end of each suspension wire
107
is connected to a PCB
120
through the damper holder
109
.
Herein, a damper (not shown) is placed inside the damper holder
109
in order to give an attenuation characteristic to the suspension wires
107
having a stiffness, the PCB
120
is coupled to the rear of damper holder
109
, and the other end of each suspension wire
107
is brazed and fixed to the PCB
120
.
The plurality of suspension wires
107
support the lens holder
102
so as to be in a lifting state and transmit an operating signal from the PCB
120
to the focusing coil
105
, the tracking
106
.
The operation of the optical pickup actuator in accordance with the prior art will now be described.
Because the tracking coil
106
is wound on the lens holder
102
in a certain direction, it generates a magnetic flux in a designated direction when a current flows, the magnetic flux generates an attractive force and a repulsive force by the fixed magnets
103
and an electromagnetic force generated between the tracking coil
106
and the magnets
103
.
Herein, as depicted in
FIG. 1A
, a tracking servo for compensating a tracking error is operated by moving the lens holder
102
back and forth by the attractive force and the repulsive force.
And, being different from the tracking coil
105
, because the focusing coil
106
is wound in a vertical direction, a magnetic flux of the focusing coil
106
is generated in up and down directions and generates a power in a vertical direction by electric-magnetically working with a magnetic flux of each magnet
103
, accordingly the lens holder
102
moves up and down as the focusing direction, and the focusing servo operates in order to compensate it.
In a moving coil method, the focusing coil
105
and the tracking coil
06
are installed at the circumference of the lens holder
102
and move to a tracking and a focusing directions according to the lens holder
102
. On the contrary, in a moving magnet method, a magnet is installed at the circumference of a lens holder and moves according to the lens holder. Herein, both methods use a Lorentz power of Fleming's left-hand rule.
In the meantime, in a high density disc, because data to be recorded by a unit length of a track increases and the number of tracks increases, a control for reading and writing information on a high density disc can not be performed sufficiently in the conventional actuator as depicted in FIG.
1
.
In more detail, as depicted in (a) and (b) of
FIG. 2
, under the circumstances of a width of a track formed at a disc
110
and a distance from a present track to a next track in accordance with the conventional recording density, it is possible to access data sequentially with movement of a pickup and the lens holder
102
of an actuator.
However, as depicted in (c) and (d) of
FIG. 2
, in a disc
110
′ having a high density format, the conventional optical pickup actuator can not access data accurately.
In order to solve above-mentioned problem, as depicted in
FIG. 3
, if the lens holder
102
of the actuator performs a tilt operation in a tangential direction and a radial direction on the disc
110
′ having the high density format, data can be accessed more accurately.
As depicted in
FIG. 4
, a tilt component has to be compensated in order to get a laser beam reflected through a reflector
111
be incident on a plane of reflection of the optical disc
110
by an objective lens
101
.
However, in order to compensate the tilt component by an operation method of the lens holder, the actuator has to perform not only a translational motion in a tracking direction and a focusing direction but also a tilting motion in a radial direction (X axis rotation mode) and a tangential direction (Y axis rotation mode), it is impossible to perform the tilt motion in the conventional actuator.
Although the lens holder can perform the tilting motion by changing the magnetic field structure (depicted in FIG.
1
), a degree of freedom of each of the two-stage suspension wires installed at both sides of the lens holder lowers.
For example, when the actuator operates as a pitching mode as depicted in
FIG. 5
, it has a resonance frequency (f0) of 2~5 KHz as depicted in
FIG. 6
, there is a problem to get an operating sensitivity.
In more detail, because a resonance frequency of a pitching mode as a rotation mode in a tangential direction is not less than 2 Khz due to a big spring constant of the suspension wire for performing the tilting motion in the tangential direction, it is impossible to perform the tilting motion in the tangential direction and get the operating sensitivity.
Herein, as depicted in
FIG.

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