Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2001-04-25
2003-09-23
Edun, Muhammad (Department: 2653)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044150, C369S030850, C369S030850
Reexamination Certificate
active
06625091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup for recording and/or reproducing signals on and from discs, such as CDs (compact discs), MD (minidiscs), and DVD (digital versatile discs), and more particularly, to an optical pickup which is suitably reduced in size.
2. Description of the Related Art
A typical type of optical pickup generally comprises an optical chassis in which a light-emitting element and a light-receiving element are mounted, an actuator held on the optical chassis so as to mount thereon a lens holder having an objective lens, and a cover for enclosing the actuator with the objective lens exposed therefrom. The actuator is provided with an electromagnetic driving section for driving the lens holder in the focusing and tracking directions of a disc. Such an optical pickup is incorporated in optical disc players, such as CD players. A light beam emitted from the light-emitting element, such as a semiconductor laser, is collected by the objective lens, and the feedback light beam from the disc is passed through the objective lens and is received by the light-receiving element.
FIG. 9
is an exploded perspective view of an example of this type of optical pickup,
FIG. 10
is a plan view of an actuator used in the optical pickup, and
FIG. 11
is a cross-sectional view of the actuator. The optical pickup shown in these figures generally comprises an optical chassis
1
made of a metal material, such as aluminum, an actuator
4
held on the optical chassis
1
so as to mount thereon a lens holder
3
having an objective lens
2
, and a cover
5
for enclosing the actuator
4
with the objective lens
2
exposed therefrom.
The optical chassis
1
is driven in the radial direction of a disc D along a guide shaft G (see FIGS.
7
and
8
). An upright portion
6
vertically standing on a bottom plate
1
d
has a large-diameter mounting hole
7
and a small-diameter through hole (not shown) connected thereto. A light emitting and receiving device (hologram unit)
8
composed of a combination of a semiconductor laser (light-emitting element) and a photodetector (light-receiving element) is held inside the mounting hole
7
. The light emitting and receiving device
8
is covered with a support plate
9
which is screwed to the outer side face of the upright portion
6
of the optical chassis
1
. The light emitting and receiving device
8
is connected to a signal processing circuit (not shown) via a flexible printed circuit board
10
a
. A reflecting mirror
11
is fixed at a mounting angle of 45° at about the center of the bottom plate
1
d
of the optical chassis
1
. A light beam emitted from the light emitting and receiving device
8
passes through the through hole, is reflected in the vertical direction (upward in
FIG. 9
) by the reflecting mirror
11
, and travels toward the disc D. The feedback light beam reflected by the disc D is reflected in the horizontal direction by the reflecting mirror
11
, passes through the through hole, and is received by the light emitting and receiving device
8
.
The actuator
4
comprises a lens holder
3
having an objective lens
2
and a focusing coil FC and a plurality of tracking coils TC wound thereon, a holder supporting portion
13
for elastically supporting the lens holder
3
via a plurality of wires
12
(supporting members), a magnet holder
15
having a stopper face
15
a
and stopper walls
15
b
for regulating the allowable amount of movement of the lens holder
3
, and a pair of magnets
14
mounted thereon, and a base member
16
for fixedly mounting the magnet holder
15
and the holder supporting portion
13
thereon.
The base member
16
also functions as a magnetic yoke. An electromagnetic driving section constituted by the base member
16
, the magnets
14
, the focusing coil FC, and the tracking coils TC drives the lens holder
3
in the focusing direction (upward and downward direction in
FIGS. 9 and 11
) and in the tracking direction (upward and downward direction in
FIG. 10
) of the disc D. These components of the actuator
4
are covered with a dustproof cover
5
which is attached to the holder supporting portion
13
or the base member
16
by snap fitting or by other means. Since the upper surface of the cover
5
has an opening
5
a
for exposing the objective lens
2
therefrom, it will not interfere with the passage of light beams. A flexible printed circuit board
10
b
mounted on the holder supporting portion
13
is electrically connected to the coils FC and TC via the wires
12
.
The actuator
4
is placed on the bottom plate
1
d
of the optical chassis
1
, a mounting screw
18
passed through a coil spring
17
is inserted into a hole formed in the base member
16
from above and is screwed into the optical chassis
1
, and two adjusting screws
19
are passed through holes formed in the optical chassis
1
from below and are screwed into the base member
16
, thereby fixing the base member
16
to the optical chassis
1
in a state in which the optical axis of the objective lens
2
is adjusted. The optical axis of the objective lens
2
positioned directly above the reflecting mirror
11
must be perpendicular to the recording surface of the disc D in order to precisely record/reproduce signals on and from the recording surface. Since the lens holder
3
is supported on the base member
16
via the wires
12
and the holder supporting portion
13
, the lens holder
3
and the base member
16
are inevitably placed in a slightly twisted positional relationship (a relationship in which the bottom surface of the lens holder
3
and the bottom surface of the base member
16
are not in parallel with each other) in the step of assembling the actuator
4
. For this reason, the optical axis of the objective lens
2
must be adjusted when mounting the actuator
4
on the optical chassis
1
. An operation of adjusting the optical axis will be described specifically. An annular spherical face
20
centered on the optical axis of the objective lens
2
is formed at the bottom of the base member
16
, as shown in
FIG. 11
, and an annular bearing face
1
e
is formed on the bottom plate
1
d
of the optical chassis
1
. By rotating the two adjusting screws
19
, the base member
16
is rocked on the optical chassis
1
with the spherical face
20
and the bearing face
1
e
used as sliding faces, and the mounting attitude (inclination) of the actuator
4
is adjusted so that the optical axis of the objective lens
2
is perpendicular to the recording surface of the disc D.
When the lens holder
3
elastically supported by a plurality of wires
12
is moved excessively, the resilient force of the wires
12
may be reduced. Therefore, the magnet holder
15
as a component of the actuator
4
is provided with a stopper face
15
a
for regulating the allowable amount of movement of the lens holder
3
toward the side opposite from the disc (apart from the disc D) in the focusing direction, and a pair of stopper walls
15
b
for regulating the allowable amount of movement of the lens holder
3
in the tracking direction. When the lens holder
3
is moved to the lowermost point of the allowable moving range in the focusing direction, the bottom surface thereof abuts against the stopper face
15
a
, and further movement of the lens holder
3
is limited. When the lens holder
3
is moved to the limit of the allowable moving range in the tracking direction, the side face thereof abuts against the stopper wall
15
b
, and further movement of the lens holder
3
is limited. When the lens holder
3
is moved to the uppermost point of the allowable moving range in the focusing direction, the upper surface thereof abuts against the rim of the opening
5
a
of the cover
5
, and further movement of the lens holder
3
is limited.
Recently, there has been a strong demand for further reducing the thickness of this type of optical pickup. In the above-described conventional optical pickup, the magnet holder
15
, the base member
16
, and the optical chas
Alpine Electronics Inc.
Edun Muhammad
LandOfFree
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