Optical: systems and elements – Lens – With support
Reexamination Certificate
2001-03-28
2003-05-27
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S814000, C359S824000, C369S044150
Reexamination Certificate
active
06570720
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an objective lens drive device of an optical pickup constituting optical disk apparatus that can radiate an optical spot on a recording medium on a disk to optically read information therefrom.
(Related Art 1)
An optical pickup constituting optical disk apparatus is generally composed of an object lens drive device equipped with an objective lens and an optical system for transmitting/receiving light to/from the objective lens, the object lens drive device is arranged on a stand for mounting an optical system block. The object lens drive device is composed of a movable part equipped with an objective lens, a focus coil and tracking coils, and a fixed part equipped with a magnetic circuit. The movable part is supported by the fixed part via four wires partially enclosed/held with an elastic damper material such as a viscoelastic material.
(Related Art 2)
In a first related art, the movable part is not inclined when it is moved in the focusing direction, because the position of center of gravity of the movable section coincides with the center of drive device in the focusing direction. Next, when the movable part is moved in the tracking direction, the position of center of gravity in the movable part moves the same amount as the tracking moving amount. However, the position of center of drive device in the focusing direction can be assumed as the center of the magnetic circuit in the fixed part so that moving in the focusing direction while moving in the tracking direction causes dislocation between the position of center of drive and the position of center of gravity in the movable part in the focusing direction thereby generating an angular moment around the center of gravity. This generates an inclination of the movable part in the tracking direction.
As a means for solving these problems, an optical pickup is known wherein a movable part including an objective lens is simultaneously driven in the focusing direction and tracking direction, and, in case the center of drive of focusing is dislocated from the center of gravity of the movable part, the rotation moment generated on the movable part is made symmetrical about the center of gravity (for example, Japanese Patent Publication No. Hei. 8-50727).
As shown in
FIG. 19
, the optical pick up is equipped with magnet holding pieces
208
a,
208
b,
and facing yokes
209
a
through
209
d
provided inside the magnet holding pieces and split in the tracking direction so that these pieces face each other, on a base
202
as a fixed base. Via this configuration, as shown in
FIGS. 20A and 20B
, the magnetic flux density distribution of the magnetic circuit for the focusing drive coil
210
is shaped in twin peaks. This maintains the balance of the rotation moment even in case the movable part including the objective lens
203
is dislocated in the tracking direction and focusing direction, thus preventing inclination of the optical axis of the objective lens
203
.
In
FIGS. 19 and 20
,
201
a
and
201
b
represent magnets,
204
represents a lens holder,
205
represents a tracking drive coil,
206
a
trough
206
d
represent support members,
207
represents a fixed member, X represents a tracking direction, Y represents a direction perpendicular to a focusing direction and the tracking direction, and Z represents the focusing direction.
(Related Art 3)
In the objective lens drive device according to the first related art, a single magnetic circuit is used and tracking coils are glued on the focus coil and arranged in a magnetic gap in order to downsize and making more low-profile the drive. However, the objective lens drive device according to the related art had a problem that the center of a drive force via a focus coil in the focusing direction was dislocated from the center of a drive force via tracking coils in the tracking direction and making the center of gravity of the movable part coincide with the center of one driving force dislocates the other, and a moment is generated according to the dislocation amount, thus causing unwanted resonance.
As a means for solving these problems, an optical pickup is known wherein a focus coil is arranged to pinch a tracking coil or a tracking coil is arranged to pinch a focus coil in order to cause the center of each drive force to coincide with each other (for example, Japanese Patent Publication No. Hei. 6-124467).
As shown in
FIG. 21
, the focus coil
310
is fixed to the top and bottom sections of a bobbin
312
via adhesion and the a tracking coil
311
is fixed to the center of the bobbin
312
via adhesion in a position it is pinched by the focus coil
310
. As shown in
FIG. 22
, the focus coil
310
is fixed to the center of the bobbin
312
via adhesion and the tracking coil
311
is fixed to the focus coil
310
via adhesion in a position it pinches the focus coil
310
from top and bottom, the respective coils placed in a yoke
309
that fixes a permanent magnet
309
via adhesion. The optical pickup allows the center of a drive force in the focusing direction (arrow A) and in the tracking direction (arrow B) to coincide with the center of gravity of the movable part by feeding a current across both coils
310
,
311
.
(Related Art 4)
In the objective lens drive according to the first related art, it is required to raise a high-order resonance frequency in order to support high-speed optical disk apparatus. As a means for solving this problem, an objective lens drive device is known wherein the objective lens attachment section of the lens holder is formed to gradually get thinner toward the free end so that a high-order resonance frequency may be raised (for example, Japanese Patent Publication No. Hei. 8-194962).
As shown in
FIG. 23
, the lens holder
411
is formed with its bottom face tapered so that the objective lens attaching section
411
c
may become thinner toward the free end (on the left in the figure) of the lens holder
411
and that the objective lens attaching section
411
c
becomes thicker toward the fixed part (on the right in the figure). The objective lens attaching section
411
c
has a thickness b at the front edge and a thickness c at the rear edge.
In the objective lens drive device according to the second related art, a problem arises that a magnetic circuit must have a complicated shape in order to provide twin-peak magnetic flux distribution of the magnetic circuit for the focusing drive coil
21
. Even in such a configuration, it is difficult to sufficiently downsize the moment. This leads to a problem that moving the movable part in the tracking direction causes the inclination of the movable part and generates coma aberration, thus worsening the read signal jitter.
Further, in the objective lens drive device according to the third related art, a problem arises that a side facing the side arranged in the magnetic gap of the focus coil
310
is arranged outside the magnetic gap thus influenced by a leak magnetic flux from the magnetic circuit and generating a drive force and a moment in the opposite direction, resulting in that it is difficult to make the center of gravity of the magnetic circuit coincide with the center of the actual driving force.
In the objective lens drive device according to the fourth related art, a problem arises that, since the fixed part of the objective lens attaching section
411
c
of the lens holder
411
is formed to gradually become thicker, a mirror (right angle prism) arranged beneath the objective lens
411
b
must be lowered as the fixed part of the objective lens attaching section
411
c
is made thicker, thus preventing a low-profile optical pickup.
SUMMARY OF THE INVENTION
The invention aims at solving the above problems in the related art.
Means for solving the problems will be explained using
FIG. 1
corresponding to an example of the invention. According to the invention, a coil unit on which a focus coil
3
f
and tracking coils
3
t
are formed is arranged in a magnetic gap
5
g
of a magnetic circuit containing at least one magnet
5
Epps Georgia
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
TDK Corporation
Thompson Timothy
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