Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-03-02
2001-08-21
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044150
Reexamination Certificate
active
06278669
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an objective lens driving apparatus for use in, for example, an optical disk recording and reproduction apparatus for converging light emitted from a light source such as a semiconductor laser or the like to an optical disk, and recording and reproducing information.
2. Description of the Related Art
In general, optical disk recording and reproduction apparatuses such as, for example, laser disk players and compact disk players record signals to and reproduce signals from a recording layer of an optical disk by emitting a light beam such as a laser light beam or the like from an optical head toward the optical disk and receiving the reflected light or transmitted light from the optical disk with the optical head.
An optical head includes an objective lens for inputting and outputting light. The objective lens is disposed to be opposed to the optical disk. A track of the optical disk is traced by moving the objective lens in a radial direction of the optical disk by an actuator.
The objective lens is also moved up and down by an objective lens driving apparatus in accordance with the upward and downward movements of the recording layer of the optical disk caused by a warp of the optical disk. In this manner, the focusing position of the objective lens is adjusted, the tracking shift caused by the decentration of the optical disk is corrected, and a tilt angle of the objective lens with respect to the optical disk is adjusted.
When an optical axis of a light beam emitted from an optical head is tilted with respect to the recording layer of the optical disk, an optical aberration is generated, which may undesirably lower the level of a reproduction signal or cause offset or crosstalk in a focusing servo driving signal for controlling the focus of the optical head or a tracking servo driving signal for controlling the tracking. Specifically in the case of a recording and reproduction apparatus for a high density optical disk such as a digital video disk, which has been recently developed, it is demanded that the angle of the optical axis of the light beam be maintained at the maximum possible precision since even a slight tilt in the optical axis is problematic. Accordingly, an objective lens driving apparatus is also required to control the tilt of the objective lens with high precision.
FIG. 9
is an isometric view of a conventional objective lens driving apparatus
100
, and
FIG. 10
is an isometric view of a lens holder
102
of the objective lens driving apparatus
100
shown in FIG.
9
.
In
FIGS. 9 and 10
, a focusing direction Z (vertical direction) matches a direction perpendicular to a recording layer of an optical disk (not shown), a tracking direction X matches a radial direction of the optical disk, and a tangent direction Y is a tangent direction of the optical disk and perpendicular to the focusing direction Z and the tracking direction X.
As shown in
FIG. 9
, the objective lens driving apparatus
100
includes the lens holder
102
. As shown in
FIGS. 9 and 10
, an objective lens
103
is mounted on a center part of a top surface of the lens holder
102
. A focusing coil
106
is wound around the lens holder
102
, i.e., around the focusing direction Z. In FIG.
10
and the figures described below, parts of the coil
106
on four side surfaces of the lens holder
102
are indicated by reference numerals
106
a
,
106
b
,
106
a
and
106
c
(see
FIG. 11A
for the part
106
c
). A pair of tracking coils
107
are provided in two opposed side surfaces
102
a
of the lens holder
102
and wound around the tracking direction X. The objective lens
103
is positioned between the pair of tracking coils
107
.
As best shown in
FIG. 10
, four elastic supporting members
105
are connected to the lens holder
102
at one end thereof. Referring to
FIG. 9
, the four elastic supporting members
105
each pass through respective holes (not shown) in a supporting holder
104
and are connected to a printed circuit board
111
at the other end thereof.
The supporting holder
104
is secured to a securing base
101
, and the printed circuit board
111
is secured to the supporting holder
104
. Thus, the securing base
101
, the supporting holder
104
, and the printed circuit board
111
are integrated together. As best shown in
FIG. 10
, the four elastic supporting members
105
cantilever the lens holder
102
to the securing base
101
to be movable in the focusing direction Z and the tracking direction X.
Returning to
FIG. 9
, a pair of magnets
108
a
and
108
b
have a magnetization direction in the tangent direction Y. The magnets
108
a
and
108
b
are provided on the securing base
101
so that the same magnetic pole surfaces thereof face each other. The lens holder
102
is positioned between the magnets
108
a
and
108
b
. A pair of magnetic shielding plates
109
each formed of a magnetic material are provided on the securing base
101
so as to interpose the lens holder
102
. The magnetic shielding plates
109
are each arranged perpendicular to the tracking direction X.
With reference to
FIGS. 11A
,
11
B and
1
C, an operation of the conventional objective lens driving apparatus
100
shown in
FIGS. 9 and 10
will be described.
FIGS. 11A
,
11
B and
11
C are schematic plan views of the lens holder
102
shown in FIG.
9
and the vicinity thereof.
Referring to
FIG. 11A
, when an electric current flows in the focusing coil
106
located in the magnetic fields of the magnets
108
a
and
108
b
, a force acts on the focusing coil
106
in the focusing direction Z, thereby moving the lens holder
102
in the focusing direction Z. At this point, as shown in
FIG. 10
, the direction of a force Fa acting on the two opposed parts
106
a
of the focusing coil
106
and the direction of forces Fb and Fc acting on the other two parts
106
b
and
106
c
of the focusing coil
106
are opposite from each other. However, since the parts
106
a
are closer to the magnets
108
a
and
108
b
than the parts
106
b
and
106
c
, the number of magnetic fluxes crossing each of the parts
106
a
is larger than the number of magnetic fluxes crossing each of the parts
106
b
and
106
c
. Accordingly, the force Fa is stronger than the force Fb or Fc. As a result, the lens holder
102
moves in the direction of the force Fa.
Referring to
FIG. 11B
, two opposed parts of each tracking coil
107
are indicated by reference numeral
107
a
, and the other two opposed parts of each tracking coil
107
are indicated by reference numeral
107
b
. When an electric current flows in the tracking coils
107
located in the magnetic fields of the magnets
108
a
and
108
b
, a force acts on the tracking coil
107
in the tracking direction X, thereby moving the lens holder
102
in the tracking direction X. At this point, the direction of a force acting on the two opposed parts
107
a
of the tracking coil
107
and the direction of a force acting on the other two parts
107
b
of the tracking coil
107
are opposite from each other. However, since the parts
107
a
are closer to the magnets
108
a
and
108
b
than the parts
107
b
, the force acting on the parts
107
a
is stronger than the force acting on the parts
107
b
. As a result, the lens holder
102
moves in the direction of the force acting on the parts
107
a.
In the state where the lens holder
102
has not been moved in the tracking direction X as shown in
FIG. 11A
, the force Fb and the force Fc respectively acting on the parts
106
b
and
106
c
of the focusing coil
106
have an equal magnitude. Thus, even when the lens holder
102
is moved in the focusing direction Z, the lens holder
102
does not tilt.
However, in the state where the lens holder
102
has been moved in the tracking direction X as shown in
FIG. 11C
, the angle of magnetic flux Bb crossing the part
106
b
of the focusing coil
106
(enlarged part D) and the angle of magnetic flux Bc crossing the part
106
c
of the focusing coil
106
(enlarged part E) are d
Anzai Joji
Yasuda Akihiro
Edun Muhammad
Kelly Michael K.
Matsushita Electric Industrial Company Ltd.
Snell & Wilmer L.L.P.
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