U.S. patent number RE40,928 [Application Number 11/645,328] was granted by the patent office on 2009-10-06 for optical pickup.
This patent grant is currently assigned to TDK Corporation. Invention is credited to Noriyuki Kawano, Mitsuru Kinouchi, Kouichi Ogura, Yoshio Saito.
United States Patent |
RE40,928 |
Kawano , et al. |
October 6, 2009 |
**Please see images for:
( Certificate of Correction ) ** |
Optical pickup
Abstract
An optical pickup comprises an objective-lens driving device
including a movable section provided with an objective lens, a
focusing coil, and tracking coils, and a fixed section provided
with a single magnetic circuit having a magnetic gap, the focusing
coil and the tracking coils being disposed in the magnetic gap. The
point of application of a tracking-driving force, the point of
application of a result force of focusing-driving forces occurring
in and outside the magnetic gap, and the position of the center of
gravity of the movable section are made to substantially coincide
with each other. In addition, the objective lens and the magnetic
circuit are disposed within an area of a window in a lower shell of
a optical disk. Further, a through hole for accommodating a lower
portion of a yoke of the magnetic circuit is provided in a mounting
base on which the objective-lens driving device is mounted. An
inclining fulcrum and a height adjusting means for inclining the
objective-lens driving device about the inclining fulcrum are
provided in the vicinities of the through hole.
Inventors: |
Kawano; Noriyuki (Tokyo,
JP), Ogura; Kouichi (Tokyo, JP), Saito;
Yoshio (Tokyo, JP), Kinouchi; Mitsuru (Tokyo,
JP) |
Assignee: |
TDK Corporation (Tokyo,
JP)
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Family
ID: |
27566782 |
Appl.
No.: |
11/645,328 |
Filed: |
December 26, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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08994560 |
Dec 19, 1997 |
6084834 |
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08888232 |
Jul 3, 1997 |
5877904 |
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08813314 |
Mar 10, 1997 |
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08810340 |
Feb 27, 1997 |
5724337 |
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08330671 |
Oct 28, 1994 |
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Reissue of: |
09576907 |
May 23, 2000 |
06288984 |
Sep 11, 2001 |
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Foreign Application Priority Data
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Oct 29, 1993 [JP] |
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5-271595 |
Dec 1, 1993 [JP] |
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5-301689 |
Dec 22, 1993 [JP] |
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5-346418 |
Nov 22, 1996 [JP] |
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5-292006 |
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Current U.S.
Class: |
369/44.14 |
Current CPC
Class: |
G11B
7/093 (20130101); G11B 7/0932 (20130101); G11B
7/22 (20130101); G11B 7/0935 (20130101); G11B
7/0933 (20130101); G11B 7/0956 (20130101) |
Current International
Class: |
G11B
7/00 (20060101) |
Field of
Search: |
;369/44.14,44.15,44.16,44.22,44.17 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2-16419 |
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Feb 1990 |
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JP |
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2-50819 |
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Apr 1990 |
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JP |
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4-31421 |
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Mar 1992 |
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JP |
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4-137519 |
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Dec 1992 |
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JP |
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5-20703 |
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Jan 1993 |
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JP |
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5-120696 |
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May 1993 |
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JP |
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5-217174 |
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Aug 1993 |
|
JP |
|
7-141671 |
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Jun 1995 |
|
JP |
|
Primary Examiner: Hindi; Nabil Z
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt, L.L.P.
Parent Case Text
This application is a continuation of Ser. No. 08/994,560 filed
Dec. 19, 1997 now U.S. Pat. No. 6,084,834, which is a continuation
of Ser. No. 08/888,232, filed Jul. 3, 1997 now U.S. Pat. No.
5,877,904, which is a division of Ser. No. 08/813,314, filed Mar.
10, 1997 abandoned, and a division of Ser. No. 08/810,340 filed
Feb. 27, 1997 U.S. Pat. No. 5,724,337, which is a continuation of
Ser. No. 08/330,671 filed Oct. 28, 1994 abandoned.
Claims
What is claimed is:
.[.1. An optical pickup device comprising: an objective-lens
driving device for driving an objective lens, which includes a
magnetic circuit; an optical system for transmitting and receiving
light to and from said objective lens; and a base having a through
hole formed therein, on which said objective-lens driving device
and said optical system are mounted, and wherein at least a portion
of said magnetic circuit of said objective-lens driving device is
accommodated in said through hole..].
.[.2. An optical pickup device as claimed in claim 1, further
comprising a movable plate integrally formed with a yoke as said
magnetic circuit, said yoke having a substantially U-shaped
cross-section, on which said objective-lens driving device is
mounted..].
3. An optical pickup device .[.as claimed in claim 2.]. ,
.Iadd.comprising: an objective-lens driving device for driving an
objective lens, which includes a magnetic circuit including a yoke,
and resiliently supporting members for supporting a movable part of
the objective-lens driving device; an optical system for
transmitting and receiving light to and from said objective lens; a
base having a through hole formed therein, on which said
objective-lens driving device and said optical system are mounted,
and wherein at least a portion of said yoke of said magnetic
circuit of said objective-lens driving device is accommodated in
said through hole; and a movable plate integrally formed with said
yoke as said magnetic circuit, said yoke having a substantially
U-shaped cross-section, on which said objective-lens driving device
is mounted,.Iaddend. wherein an inclination of said movable plate
is adjusted relative to said base.
.Iadd.4. An optical pickup device as claimed in claim 3, wherein
said resiliently supporting members are made of wires..Iaddend.
.Iadd.5. An optical pickup device as claimed in claim 3, wherein at
least four resiliently supporting members are
provided..Iaddend.
.Iadd.6. An optical pickup device as claimed in claim 3, wherein
said resiliently supporting members support said movable part of
the objective-lens driving system in a cantilevered
manner..Iaddend.
.Iadd.7. An optical pickup device comprising: an objective-lens
driving device for driving an objective lens, which includes a
magnetic circuit including a yoke, and resiliently supporting
members for supporting a movable part of the objective-lens driving
device; an optical system for transmitting and receiving light to
and from said objective lens; and a base having a through hole
formed therein, on which said objective-lens driving device and
said optical system are mounted, and wherein at least a portion of
said yoke of said magnetic circuit of said objective-lens driving
device is accommodated in said through hole; and wherein said
objective-lens driving device includes coils for generating a
driving force to drive the objective lens, and said resiliently
supporting members serve as paths for supplying electric current to
the coils..Iaddend.
.Iadd.8. An optical pickup device as claimed in claim 7, wherein
said resiliently supporting members are made of wires..Iaddend.
.Iadd.9. An optical pickup device as claimed in claim 7, wherein at
least four resiliently supporting members are
provided..Iaddend.
.Iadd.10. An optical pickup device as claimed in claim 7, wherein
said resiliently supporting members support said movable part of
the objective-lens driving system in a cantilevered
manner..Iaddend.
.Iadd.11. An optical pickup device, comprising: an objective-lens
driving device for driving an objective lens, which includes a
magnetic circuit, and resiliently supporting members for supporting
a movable part of the objective-lens driving device; an optical
system for transmitting and receiving light to and from said
objective lens; a base having a through hole formed therein, on
which said objective-lens driving device and said optical system
are mounted, and wherein at least a portion of said magnetic
circuit of said objective-lens driving device is accommodated in
said through hole; and a movable plate integrally formed with a
yoke as said magnetic circuit, said yoke having a substantially
U-shaped cross-section, on which said objective-lens driving device
is mounted, wherein an inclination of said movable plate is
adjusted relative to said base..Iaddend.
.Iadd.12. An optical pickup device, comprising: an objective-lens
driving device for driving an objective lens, which includes a
magnetic circuit, and resiliently supporting members for supporting
a movable part of the objective-lens driving device; an optical
system for transmitting and receiving light to and from said
objective lens; and a base having a through hole formed therein, on
which said objective-lens driving device and said optical system
are mounted, and wherein at least a portion of said magnetic
circuit of said objective-lens driving device is accommodated in
said through hole; and wherein said objective-lens driving device
includes coils for generating a driving force to drive the
objective lens; and said resiliently supporting members serve as
paths for supplying electric current to the coils..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup for recording
and reproducing information with respect to an optical disk. More
particularly, the present invention relates to an objective-lens
driving device and a mechanism for adjusting the inclination of an
objective lens which are aimed at making the optical pickup compact
and thin and stabilizing the driving of the objective lens in both
a focusing direction and a tracking direction.
2. Description of the Related Art
In general, an optical pickup is comprised of an objective-lens
driving device having an objective lens and an optical system block
for transmitting and receiving light with respect to the objective
lens, and is structured such that the objective-lens driving device
is mounted on a mounting base of the optical system block.
To accurately effect the recording and reproduction of information
with respect to an optical disk, it is necessary to accurately set
the optical axis of the objective lens perpendicular to the disk
surface.
For this reason, a mechanism for adjusting the inclination of an
objective lens is conventionally known (e.g., Unexamined Japanese
Patent Application (Kokai) No. 62-287443) which is arranged as
follows: As shown in FIG. 1, a spherically convex mounting surface
103 is made to project from a bottom surface 102a of an
objective-lens driving device 102 having an objective lens 101. In
addition, as shown in FIG. 2, a spherically concave mounting
surface 106 is formed in a mounting base 105 of an optical system
block 104, the spherically convex mounting surface 103 is fitted in
the spherically concave mounting surface 106, and the inclination
of the objective lens 101 is made adjustable with respect to the
center (fulcrum) 107 of a sphere formed by the spherically convex
mounting surface 103 and the spherically concave mounting surface
106 by means of height adjusting screws 108.
However, since the spherically convex mounting surface 103, the
spherically concave mounting surface 106, and the height-adjusting
screws 108 are disposed between the objective-lens driving device
102 and the mounting base 105 of the optical system block 104, the
thicknesswise dimension becomes large, thereby constituting a
hindrance to the attempt to make the optical pickup thin.
In addition, to accurately effect the recording and reproduction of
information with respect to an optical disk, it is necessary to
prevent the occurrence of unwanted resonance. To prevent the
occurrence of such unwanted resonance, in a conventional
objective-lens driving device 201A shown in the perspective view in
FIG. 3, the position of the center of gravity of a movable section
204, which has an objective lens 202, a focusing coil 203A for a
focusing direction Z, and a pair of tracking coils 203B for a
tracking direction Y, is aligned with an optical axis 205, and the
central axes of the focusing coil 203A and the tracking coils 203B
are aligned with the optical axis 205 (e.g., Unexamined Japanese
Patent Application (Kokai) No. 2-230522).
The optical pickup having this arrangement is capable of preventing
the occurrence of unwanted resonance, but it is necessary to
dispose a light source, a reflecting mirror, a light-receiving
element, and the like below the objective-lens driving device to
effect the recording and reproduction of information. Hence, it has
been difficult to make the optical pickup compact and thin.
To make the objective-lens driving device compact and thin, in a
conventional objective-lens driving device 201B shown in the
exploded perspective view in FIG. 4, the central axes of a focusing
coil 208A and a pair of tracking coils 208B are not aligned with
the optical axis 205, and the focusing coil 208A and the tracking
coils 208B are disposed in a magnetic gap 207 provided in a single
magnetic circuit 206 (e.g., Unexamined Japanese Patent Application
(Kokai) Nos. 4-102235 and 4-103038).
In addition, in the objective-lens driving device disclosed in
Unexamined Japanese Patent Application (Kokai) 4-103038, to
accurately drive the movable section in the direction of the
optical axis (focusing direction), a focusing-driving force which
is provided outside the magnetic gap is minimized, so as to prevent
an unnecessary force, such as moment, from acting in the movable
section. It has been thought that this focusing-driving force
occurring outside the magnetic gap, i.e., the leakage flux density,
should be suppressed to as low a level as possible partly for
preventing interference with metallic parts such as a motor
disposed in the vicinity of the objective-lens driving device.
In addition, although the conventional objective-lens driving
device 201B shown in FIG. 4 is capable of making the optical pickup
compact and thin, there is a drawback in that, if an attempt is
made to adjust the position of the center of gravity to either one
of the driving points, the other driving point is offset from the
position of the center of gravity, so that unwanted resonance
occurs on the offset side.
FIG. 5A shows a schematic arrangement of an optical disk apparatus
portion in a magneto-optic recording/reproducing system, in which
an optical disk 301 is provided with an optical pickup 304 having a
magnetic head 302 on one side and an objective lens 303 on the
other side. The magnetic head 302 and the optical pickup 304 are
driven in the radial direction of the optical disk 301 by a head
driving device 305 and a feed motor 306, respectively, and the
optical disk 301 is rotated by a spindle motor 307. Among such
optical disk apparatuses, those of a type in which the optical disk
301 is covered with a cartridge 308 for the purpose of protecting
the optical disk 301 have come to be marketed in recent years. This
cartridge-type optical disk is arranged as follows: As shown in
FIG. 5B, the optical disk 301 is rotatably accommodated in a space
formed between an upper shell 308a and a lower shell 308b, and the
shells 308a and 308b are provided with windows 308c and 308d,
respectively. When the optical disk 301 is not in use, the windows
308c and 308d are closed by a shutter 308e, and, during recording
or reproduction, the shutter 308e is moved laterally to open the
windows 308c and 308d and insert the magnetic head 302 and the
objective lens 303 into the windows.
In the conventional optical pickup 304, as described in, for
example, Unexamined Japanese Patent Application (Kokai) 61-139945,
a circuit for driving the objective lens 303 in the focusing
direction and the tracking direction is disposed at a position
other than that below the objective lens 303, whereby a free space
is formed below the objective lens 303, and a reflecting mirror is
disposed at that position, thereby making the overall optical
pickup 304 thin.
With such a conventional apparatus, as shown in FIG. 6A, the
optical disk 301 and the objective lens 303 are opposed to each
other with an interval L.sub.33 therebetween so that the optical
axis of the objective lens 303 aligns with a central portion, as
viewed in the rotating direction of the disk, of the window 308d of
the lower shell 308b. In this arrangement, however, since a
magnetic circuit 309 for effecting the positional adjustment of the
objective lens 303 in the focusing and tracking directions is
disposed outside the window 308d, there arises a need to provide a
gap L.sub.31 between a lower surface of the lower shell 308b and an
upper surface of a yoke 310 constituting the magnetic circuit 309.
As a result, the distance L.sub.32 between the lower surface of the
lower shell 308b and the lower surface of the magnetic circuit 309
becomes large, thereby constituting a hindrance to making the
optical pickup 304 thin and compact.
FIG. 7 shows an exploded perspective view of a conventional
objective-lens driving device (Unexamined Japanese Patent
Application (Kokai) No. 3-212826).
A conventional objective-lens driving device 401 shown in the
drawing is arranged as follows: A lens holder 403 with an objective
lens 402 affixed thereto is cantilevered by being soldered onto a
printed circuit board 409 in which four wires 404 inserted in an
intermediate member 405 are secured to the intermediate member 405.
The intermediate member 405 is mounted on a yoke base 406.
Incidentally, the printed circuit board 409 and the four wires 404
are electrically connected to each other. Electric current is
allowed to flow across a focusing coil 407A and a pair of tracking
coils 407B, which are arranged in the holder 403, via these four
wires 404, to thereby drive the objective lens 402 in the focusing
direction Z and the tracking direction Y.
To accurately effect the recording and reproduction of information
with respect to the optical disk, it is necessary to prevent the
occurrence of unwanted resonance.
For this reason, as shown in FIG. 8, a damping-member accommodating
portion 405a is formed in the intermediate member 405, and a gel
damping member 408 is filled in the accommodating portion 405a.
However, as for the conventional objective-lens driving device 401,
since the intermediate member 405 is attached to the yoke base 406,
and a printed circuit board 409 is secured to the intermediate
member 405 by means of screws or the like, the number of component
parts used is large. Hence, there has been a problem in that if the
respective component parts are fixed by means of an adhesive, the
number of assembling steps increases, so that the fabrication is
not facilitated.
In addition, if the printed circuit board 409 is secured to the
intermediate member 405 by means of screws, there have been cases
where both ends of the printed circuit board 409 at portions remote
from the wires 404 become lifted off due to changes in temperature
and aged deterioration, as shown in FIG. 9. Hence, the four wires
404 are respectively deflected or conversely pulled, and the
supporting balance becomes deteriorated, thereby resulting in
changes in the angle of the optical axis of the objective lens 402
and unwanted resonance. Further, in cases where the yoke base 406
and the intermediate member 405, and the intermediate member 405
and the printed circuit board 409 are secured separately, if the
bottom surface of the yoke base 406 is set as an assembling
reference plane A, as shown in FIG. 10, there has been a problem in
that it is difficult to set a B surface of the printed circuit
board 409 perpendicular to the reference plane A, thereby making it
impossible to drive the objective lens 402 with high accuracy.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the
above-described circumstances, and it is an object of the present
invention to provide a mechanism for adjusting the inclination of
an objective lens which makes it possible to make an optical pickup
thin.
Another object of the present invention is to provide an
objective-lens driving device which makes it possible to make an
optical pickup compact and thin and drive the objective lens stably
in both the focusing direction and the tracking direction.
Still another object of the present invention is to provide a
cartridge-type optical disk apparatus having a structure which
makes it possible to make the optical disk apparatus thin and
compact.
A further object of the present invention is to provide an
objective-lens driving device which is easy to manufacture and is
capable of driving the objective lens with high accuracy.
In accordance with a first aspect of the present invention, there
is provided a mechanism for adjusting the inclination of an
objective lens for use in an optical pickup including an
objective-lens driving device, having an objective lens, and an
optical system block for transmitting and receiving light with
respect to the objective lens, the objective-lens driving device
being mounted on a mounting base of the optical system block. In
the adjusting mechanism, a recessed portion or a through hole
portion is formed in the mounting base of the optical system block,
a projecting portion of a bottom of the objective-lens driving
device is accommodated in the recessed portion or the through hole
portion, and an inclining fulcrum for inclining the objective lens
and height adjusting means for inclining the objective-lens driving
device about the inclining fulcrum are provided in vicinities of
the recessed portion or the through hole portion of the mounting
base.
In accordance with a second aspect of the present invention, there
is provided a mechanism for adjusting the inclination of an
objective lens for use in an optical pickup including an
objective-lens driving device, having an objective lens and a yoke,
and an optical system block for transmitting and receiving light
with respect to the objective lens, the objective-lens driving
device being mounted on a mounting base of the optical system
block. In the adjusting mechanism, a movable plate with a
substantially U-shaped cross section which is formed integrally
with the yoke is provided, a recessed portion or a through hole
portion is formed in the mounting base of the optical system block,
a lower portion of the yoke formed integrally with the movable
plate is accommodated in the recessed portion or the through hole
portion, and an inclining fulcrum for inclining the objective lens
and height adjusting means for inclining the objective-lens driving
device about the inclining fulcrum are provided in vicinities of
the recessed portion or the through hole portion of the mounting
base.
In accordance with a third aspect of the present invention, in the
mechanism for adjusting the inclination of an objective lens
according to the second aspect of the invention, the height
adjusting means includes an urging member for upwardly urging the
objective-lens driving device from the mounting base of the optical
system block, and a screw for tightening the objective-lens driving
device against the mounting base of the optical system block.
In accordance with a fourth aspect of the present invention, there
is provided an optical disk apparatus in which a magnetic circuit
of the objective-lens driving device is disposed within a window
area of a lower shell of the optical disk. In a case where such a
structure is adopted, to prevent the demagnetization of the optical
disk, it is preferred that optical disk-side opposite ends of a
yoke constituting the magnetic circuit of the driving device for
driving an objective lens be magnetically short-circuited by a
magnetic member.
In accordance with a fifth aspect of the present invention, there
is provided an optical disk apparatus in which opposite end
portions, as viewed in a tracking direction, of an objective lens
holder which are opposed to the disk are formed into inclined
surfaces, so as to prevent the lens holder from colliding against
an edge on the innermost peripheral side or outermost peripheral
side of the window in the lower shell, and to prevent an increase
in the vertical dimension of the lens holder. In addition, in the
optical disk apparatus in which such inclined surfaces are formed
at the opposite end portions, as viewed in the tracking direction,
of the objective lens holder which are opposed to the disk, the
magnetic circuit of the objective-lens driving device is preferably
disposed within the window area of the lower shell of the optical
disk, and a portion of the objective lens holder which opposes a
side edge of the window in the lower shell is preferably formed
into an inclined surface.
In accordance with a sixth aspect of the present invention, there
is provided an objective-lens driving device comprising: a movable
section including an objective lens, a focusing coil, and a
tracking coil; and a fixed section which includes a single magnetic
circuit having a magnetic gap and in which the focusing coil and
the tracking coil are both disposed in the magnetic gap, wherein a
point of application of a resultant force of a focusing-driving
force generated by a magnetic flux in the magnetic gap and a
reversely-oriented focusing-driving force generated outside the
magnetic gap by a magnetic flux leaking from the magnetic gap is
brought close to a point of application of a tracking-driving force
by controlling an amount of leakage magnetic flux.
Furthermore, the weight of the movable section is distributed such
that a position of a center of gravity of the movable section is
located between the point of application of the tracking-driving
force and the point of application of the resultant force of the
focusing-driving forces.
In accordance with a seventh aspect of the present invention, there
is provided an objective-lens driving device comprising: a movable
section including an objective lens, a focusing coil, and a
tracking coil; and a fixed section which including a single
magnetic circuit having a magnetic gap, both of the coils being
disposed in the magnetic gap, wherein a point of application of a
tracking-driving force, a point of application of a resultant force
of focusing-driving forces respectively occurring in and outside
the magnetic gap, and a position of a center of gravity of the
movable section are made to substantially coincide with each
other.
In accordance with an eighth aspect of the present invention, there
is provided an objective-lens driving device comprising: a movable
section including an objective lens and a coil for generating a
driving force in a predetermined direction; a resiliently
supporting member serving as a path for supplying electric current
to the coil and supporting the movable section in a cantilevered
manner or on both sides thereof; a printed circuit board
electrically connected to at least one fixed end side of the
resiliently supporting member; and a base having a yoke for
generating the driving force; and an intermediate member for fixing
the printed circuit board and the base by molding in a state in
which the printed circuit board and the base are positioned
relative to each other.
In accordance with a ninth aspect of the present invention, in the
objective-lens driving device according to the eighth aspect of the
invention, the intermediate member has a guide hole for inserting
the resiliently supporting member there-through to connect the
fixed end side of the resiliently supporting member, and a
damping-member accommodating portion for accommodating a damping
member for damping unwanted resonance of the movable section is
formed in a vicinity of the guide hole.
In accordance with the mechanism for adjusting the inclination of
an objective lens according to the first aspect of the invention,
the fulcrum for inclining the objective lens and the height
adjusting means are provided in the vicinities of the recessed
portion or the through hole portion formed in the mounting base of
the optical system block, and it is thereby possible to make the
optical pickup thin.
In accordance with the mechanism for adjusting the inclination of
an objective lens according to the second aspect of the invention,
since the yoke and the movable plate are formed integrally, the
optical pickup can be made thin, and since the yoke and the movable
plate are formed integrally, the fabrication is facilitated.
In accordance with the mechanism for adjusting the inclination of
an objective lens according to the third aspect of the invention,
the objective-lens driving device can be inclined about the fulcrum
for inclining the objective lens in accordance with the degree of
tightening of the screw, thereby inclining the objective lens.
In accordance with the objective-lens driving device according to
the fourth aspect of the invention, since the magnetic circuit is
disposed within the window in the lower shell, the dimension
between the lower surface of the magnetic circuit of the driving
device and the lower surface of the lower shell can be reduced,
thereby making it possible to obtain a thin device. In addition,
according to the fifth aspect of the invention, since the radially
opposite end portions of the objective lens holder, which are
opposed to the disk, are formed into inclined surfaces, it is
possible to make the lens holder thin.
In accordance with the objective-lens driving device according to
the sixth aspect of the invention, since the point of application
of the resultant force of focusing-driving forces respectively
occurring in and outside the magnetic gap is brought close to the
point of application of the tracking-driving force, their distances
with respect to the position of the center of gravity of the
movable section can both be reduced. Therefore, it is possible to
easily prevent the occurrence of unwanted resonance in both the
focusing direction and the tracking direction. Furthermore, since
the position of the center of gravity of the movable section can be
located between the point of application of the tracking-driving
force and the point of application of the resultant force of the
focusing-driving forces respectively occurring in and outside the
magnetic gap, the distances between the position of the center of
gravity of the movable section and the point of application of the
resultant force and between the position of the center of gravity
of the movable section and the point of application of the
tracking-driving force are both made short. Therefore, it is
possible to prevent the occurrence of unwanted resonance in both
the focusing direction and the tracking direction.
In accordance with the objective-lens driving device according to
the seventh aspect of the invention, the focusing coil and the
tracking coils are disposed in the magnetic gap, so that the
objective-lens driving device can be made compact and thin. In
addition, since the point of application of the tracking-driving
force and the position of the center of gravity of the movable
section are made to substantially coincide with each other, it is
possible to make the device compact and thin. Hence, it is possible
to realize a stable servomechanism in which unwanted resonance does
not occur in both the focusing direction and the tracking
direction.
In accordance with the objective-lens driving device according to
the eighth aspect of the invention, since the printed circuit board
and the base are secured to each other by being positioned relative
to each other when the intermediate member is formed by molding, a
bonding process and a screw-tightening process can be omitted in
assembling the printed circuit board, the base, and the
intermediate member. Hence, the relative positional accuracy
between the printed circuit board and the base can be improved.
In accordance with the objective-lens driving device according to
the ninth aspect of the invention, since the damping member is
accommodated in the damping-member accommodating portion, the
damping member suppresses the vibration of the resiliently
supporting member, thereby damping the unwanted resonance of the
movable section.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an objective-lens driving device
for describing a conventional mechanism for adjusting the
inclination of an objective lens;
FIG. 2 is a cross-sectional view of the conventional mechanism for
adjusting the inclination of an objective lens;
FIG. 3 is a perspective view of another conventional mechanism for
adjusting the inclination of an objective lens;
FIG. 4 is a perspective view of still another conventional
mechanism for adjusting the inclination of an objective lens;
FIG. 5A is a schematic diagram illustrating an optical disk
apparatus of a cartridge type;
FIG. 5B is an exploded perspective view illustrating a schematic
arrangement of an optical disk and a cartridge;
FIGS. 6A and 6B are diagrams of dimensional relationships among
various parts in a conventional example and in this embodiment,
respectively, in which the optical disk apparatuses are viewed in a
tracking direction;
FIG. 7 is a is a perspective view of a conventional objective-lens
driving device;
FIG. 8 is a side view illustrating a mechanism for preventing
unwanted resonance;
FIG. 9 is a cross-sectional view illustrating a conventional
problem;
FIG. 10 is a cross-sectional view illustrating another conventional
problem;
FIG. 11 is a cross-sectional view of an optical pickup in
accordance with a first embodiment of the present invention, and
illustrates one example of a mechanism for adjusting the
inclination of an objective lens;
FIG. 12 is an exploded perspective view of the mechanism for
adjusting the inclination of an objective lens;
FIG. 13 is a perspective view illustrating another example of a
movable plate shown in FIG. 12;
FIG. 14 is a vertical cross-sectional view illustrating an optical
disk apparatus in accordance with a second embodiment of the
present invention;
FIG. 15 is a perspective view of the optical disk apparatus shown
in FIG. 14;
FIG. 16 is a perspective view illustrating a magnetic circuit of an
objective-lens driving device in accordance with the second
embodiment;
FIGS. 17A and 17B are diagrams of dimensional relationships among
various parts on the outer peripheral side or inner peripheral side
of the disk in a conventional example and a comparative example,
respectively;
FIG. 18 is a diagram of dimensional relationships among various
parts in accordance with the second embodiment;
FIG. 19 is a perspective view of an essential portion of an
objective-lens driving device in accordance with a third embodiment
of the present invention;
FIG. 20 is a vertical cross-sectional view of FIG. 20;
FIG. 21 is a horizontal cross-sectional view of FIG. 20;
FIG. 22 is a diagram illustrating the relationships between various
driving forces and the position of the center of gravity;
FIG. 23 is a graph illustrating the relationship between the
thickness of an upper yoke on the one hand, and a in-gap magnetic
flux density and a leakage magnetic flux density, on the other;
FIG. 24 is a graph illustrating the effect of the thickness of a
U-shaped yoke with respect to pitching resonance in accordance with
the third embodiment;
FIG. 25 is a diagram illustrating the positional relationships
among respective points of application;
FIG. 26 is a diagram of a transmission characteristic in accordance
with the third embodiment;
FIG. 27 is a diagram of a transmission characteristic in another
example;
FIG. 28 is a diagram of a transmission characteristic in still
another example;
FIG. 29 is a side view of an objective-lens driving device in
accordance with a fourth embodiment of the present invention;
FIG. 30 is a perspective view of a yoke in accordance with the
fourth embodiment;
FIG. 31 is a side view illustrating a method of fabrication in
accordance with the fourth embodiment;
FIG. 32 is another side view illustrating the method of fabrication
in accordance with the fourth embodiment;
FIG. 33 is a plan view illustrating the method of fabrication in
accordance with the fourth embodiment; and
FIG. 34 is a cross-sectional view taken along the line C--C in FIG.
33.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the accompanying drawings, a description will be
given of the preferred embodiments of the present invention.
First Embodiment
FIG. 11 is a cross-sectional view of an optical pickup in
accordance with a first embodiment of the present invention, and
illustrates one example of a mechanism for adjusting the
inclination of an objective lens. FIG. 12 is an exploded
perspective view thereof.
First, a description will be given of an optical pickup to which a
mechanism 130 for adjusting the inclination of an objective lens in
accordance with this embodiment is applied.
As shown in FIG. 11, this optical pickup is comprised of an
objective-lens driving device 110 having an objective lens 111 and
an optical system block 120 for transmitting and receiving light to
and from the objective lens 111, in addition to the mechanism 130
for adjusting the inclination of an objective lens. The
objective-lens driving device 110 is disposed on a mounting base
121 of the optical system block 120.
The objective-lens driving device 110 has a lens holder 112 for
holding the objective lens 111, an unillustrated driving coil for
driving the lens holder 112 in the focusing direction and the
tracking direction, a yoke 114 which constitutes a magnetic circuit
together with a permanent magnet 113, and projects from the bottom
side of the objective-lens driving device 110, and a supporting
base 116 which also serves as a path for supplying electric current
to the driving coil and supports the lens holder 112 side via a
bundling member 115.
The optical system block 120 is provided with the mounting base 121
on which the objective-lens driving device 110 is disposed, and is
further provided with an optical system which includes a light-beam
generating source, such as a semiconductor laser, and optical
elements, such as a beam splitter, as well as a light detecting
element for receiving a reflected light beam. In this optical
system block 120, a light beam is made incident upon the objective
lens 111 from the light-beam generating source via the optical
system, and a light spot is formed on the optical disk by the
objective lens 111. The light beam reflected from the optical disk
is received by the light detecting element via the optical system,
and a light detection signal corresponding to the intensity of the
reflected light beam thus received is outputted.
Next, a description will be given of the mechanism 130 for
adjusting the inclination of an objective lens in accordance with
this embodiment, which is used in the above-described optical
pickup.
This mechanism 130 for adjusting the inclination of an objective
lens has a movable plate 131 for fixedly disposing the
objective-lens driving device 110, and a through hole portion 132
is formed in the mounting base 121 of the optical system block 120.
A lower portion of the yoke 114 projecting from the bottom side of
the objective-lens driving device 110 is accommodated in the
through hole portion 132, and an inclining fulcrum 133 for
inclining the objective lens 111 and a height adjusting means 134
for inclining the objective-lens driving device 110 about the
inclining fulcrum 133 are provided in the vicinities of the through
hole portion 132 of the mounting base 121.
The height adjusting means 134 is provided with an urging member
135, such as a leaf spring, for upwardly urging the objective-lens
driving device 110 from the mounting base 121 side of the optical
system block 120, as well as two height adjusting screws 136 for
tightening the objective-lens driving device 110 toward the
mounting base 121 side of the optical system block 120.
The movable plate 131 has a substantially U-shaped cross section
for connecting collars 131a on both sides thereof and a bottom
131b. The supporting base 116 of the objective-lens driving device
110 is fixedly disposed on this movable plate 131. In addition, a
notch 131c is formed in the bottom 131b of the movable plate 131 so
that the yoke 114 of the objective-lens driving device 110 can
enter the lower side. As a result, the thickness of the movable
plate 131 and the thickness of the inclination adjusting mechanism
130 are not affected by the thickness of the optical pickup,
thereby making it possible to reduce the thicknesswise dimension.
In addition, one collar 131a of the movable plate 131 has a
spherical-portion receiving hole 131d, and the other collar 131a
has two female screws 131e for threadedly engaging with the height
adjusting screws 136, respectively.
The spherical-portion receiving hole 131d, which is formed in the
movable plate 131 and has a smaller diameter than a spherically
convex portion 137, is received on the spherically convex portion
137 formed on the mounting base 121 of the optical system block
120. A lower edge of the spherical-member receiving hole 131d is
made to abut against the surface of the spherically convex portion
137, thereby forming the inclining fulcrum 133.
Next, a description will be given of a method of adjusting the
inclination in accordance with this embodiment.
First, after the objective-lens driving device 110 is assembled,
the objective-lens driving device 110 is fixedly disposed on the
movable plate 131. The yoke 114 of the objective-lens driving
device 110 enters the lower side through the notch 131c formed in
the movable plate 131 without interfering with the movable plate
131. The movable plate 131 is placed on the mounting base 121 of
the optical system block 120. The bottom 131b of the movable plate
131 enters the lower side without interfering with the mounting
plate 121 through the opening 132 formed in the mounting plate 121
of the optical system block 120. The lower edge of the
spherical-member receiving hole 131d and the surface of the
spherically convex portion 137 abut against each other, with the
result that the fulcrum 133 for inclining the objective lens 111 is
formed. Then, the height adjusting the objective lens 111 is
formed. Then, the height adjusting screws 136 are inserted through
insertion holes 121d provided in the mounting base 121, and are
made to threadedly engage with the female screws 131e of the
movable plate 131. The movable plate 131 is set in a state in which
it is pushed upwardly about the inclining fulcrum 133 by the urging
member 135.
Here, as the degree of tightening of one or both of the two height
adjusting screws 136 is adjusted, as required, the objective-lens
driving device 110 is inclined about the inclining fulcrum 133 in
accordance with the degree of tightening. Thus, it is possible to
adjust the inclination of the objective lens 111 in the direction
of the X-axis (jitter direction) and the direction of the Y-axis
(tracking direction).
In accordance with this embodiment arranged as described above,
since the inclining fulcrum 133 and the height adjusting means 134
are provided in the vicinities of the through hole portion 132
formed in the mounting base 121 of the optical system block 120, it
is possible to make the optical pickup thin. Also, since the
objective-lens driving device 110 is inclined about the inclining
fulcrum 133 in accordance with the degree of tightening of the
height adjusting screws 136, the adjustment of the inclination of
the objective lens 111 can be effected easily. In addition, since
the lower portion of the yoke 114 projecting from the bottom of the
objective-lens driving device 110 is accommodated in the opening
132 formed in the mounting base 121 of the optical system block
120, the optical pickup can be made thin substantially by the
portion of the thickness of the mounting base 121 of the optical
system block 120. Further, since the arrangement provided is such
that the inclination can be adjusted by one inclining fulcrum 133
and the two adjusting points, and the urging member 135 is disposed
outside one side 138a, opposing the inclining fulcrum 133, of a
triangle 138 formed by the three points, it is possible to
appropriately pressurize the spherically convex portion 137 and
realize the inclination of the optical axis in the X-axis direction
and the Y-axis direction smoothly in a saved page. Moreover, since
the spherically convex portion 137 projects from the mounting base
121 of the optical system block 120, the spherically convex portion
137 can be formed integrally through die casting or injection
molding, and the inclination of the optical axis in the X-axis
direction and the Y-axis direction can be realized with a small
number of component parts.
It should be noted that the present invention is not confined to
the above-described embodiment, and various modifications are
possible. For example, an arrangement may be provided such that, as
shown in FIG. 13, the yoke (114) is formed by uprightly raising
portions 131f of the bottom 131b of a movable plate 131', and the
movable plate and the yoke are formed integrally by a metal-pressed
component. In this case, the heightwise positions of the bottoms of
the yoke (114) and the movable plate 131' can be set at the same
level, so that the optical pickup can be made thinner and
fabrication is facilitated. In addition, an arrangement may be
alternatively provided such that a concave portion is formed in the
mounting base 121, while a spherically convex portion is formed on
the movable plate 131 or 131' so as to form the fulcrum for
inclining the objective lens 111.
In accordance with the first embodiment detailed above, since the
fulcrum for inclining the objective lens and the height adjusting
means are provided in the vicinities of the recessed portion or the
through hole portion formed in the mounting base of the optical
system block, it is possible to make the optical pickup thin.
In addition, since the yoke and the movable plate are formed
integrally, the optical pickup can be made thin, and the
fabrication is facilitated.
Further, since the urging member and the screws are used, the
objective-lens driving device can be inclined about the fulcrum for
inclining the objective lens, so that the adjustment of the
inclination of the objective lens can be effected easily.
Furthermore, since two or more adjustment screws are provided,
adjustment in the jitter direction and the tracking direction
becomes possible.
Also, the spherically convex portion constituting the inclining
fulcrum is formed integrally with the mounting base, the
fabrication of the mounting base is facilitated.
Second Embodiment
Next, a description will be given of a second embodiment.
FIG. 14 is a vertical cross-sectional view illustrating an optical
disk apparatus in accordance with a second embodiment of the
present invention. FIG. 15 is a perspective view thereof. In FIGS.
14 and 15, reference numeral 311 denotes a base formed of a resin
or the like, and a U-shaped yoke 310 constituting a magnetic
circuit for driving the objective lens 303 as well as a reflecting
mirror 320 are fixed on the base 311. Permanent magnets 312 are
fixed on opposing surfaces of the yoke 310, respectively, and are
magnetized in the left-and-right direction, as shown in FIG. 14. A
support 315 formed of a resin is fixed at one end of the base 311
by means of screws 316, and the support 315 and a lens holder 313
are connected to each other by means of four wire springs 314.
These wire springs 314 have their root portions penetrating the
support 315. Proximal ends of the springs 314 are secured by
soldering 317 to a printed circuit board 315a which is fixed to the
support 315 by bonding or the like, while distal ends of the
springs 314 are fixed by soldering 317 to a pair of printed circuit
boards 313e which are respectively fixed to both sides of the lens
holder 313 by bonding or the like. The lens holder 313 is arranged
such that the objective lens 303 is attached to one end thereof and
a remaining portion is formed as a frame 313a. The yoke 310 to
which the permanent magnets are fixed is inserted in the frame 313a
in such a manner as to be relatively movable. That is, as shown in
the perspective view of FIG. 16, a focusing coil 318 is formed in a
rectangular shape, a pair of tracking coils 319 is fixed on one
surface thereof, and the focusing coil 318 is inserted and fixed in
the frame 313a such that the focusing coil 318 surrounds one of the
permanent magnets 312 and one column portion 310a to which it is
fixed, with a predetermined distance. As shown in FIG. 16, the
portion of the focusing coil 318 to which the tracking coils 319
are fixed is inserted between the pair of permanent magnets
312.
With respect to a magnetic circuit 309 of the device for driving
the objective lens 303, if the current is allowed to flow across
the focusing coil 318 in the direction of arrow i1, as shown in
FIG. 16, a magnetic flux .phi. generated between the pair or
permanent magnets 312 crosses the coil through which this current
flows. As a result, the focusing coil 318, i.e., the lens holder
313, is urged in a direction in which it approaches an optical disk
301, as indicated by the arrow F.sub.31, and the lens holder 313
becomes stationary where it balances with the resiliency of the
wire springs 314. If the direction of the current is reversed, the
lens holder 313 is urged in a direction in which it moves away from
the optical disk 301. Meanwhile, if a current i2 is allowed to flow
across vertically oriented portions a of the pair of tracking coils
319, the lens holder 313 is subjected to a force acting in the
direction of the arrow F.sub.32 (the tracking direction=the radial
direction of the optical disk), and if the direction of the current
is reversed, the direction of the acting force is also reversed. It
should be noted that the tracking coils 319 are arranged in an area
outside the area between the opposing portions of the pair of
permanent magnets 312 so that the amount of the magnetic flux
crossing at portions b on both sides of the tracking coils 319 is
reduced.
In the present invention, the magnetic circuit 309 of the device
for driving the objective lens 303, together with the objective
lens 303, is disposed within a window 308d of a lower shell 308b,
as shown in FIG. 14. Since the magnetic circuit 309 is disposed
within the area of the window 308d, as shown in FIG. 6B, it is
possible to reduce the dimension L.sub.310 from the lower surface
of the lower shell 308b to the lower surface of the magnetic
circuit 309, thereby making it possible to make the apparatus thin
and compact. In this case, distal ends of the yoke 310 are
magnetically short-circuited by a short-circuiting member 321
having high permeability, such as iron, so that the magnetically
recorded surface of the optical disk 301 will not be demagnetized
by the magnetic field generated by the permanent magnets 312.
In addition, as shown in FIG. 15, opposite end portions 313b, as
viewed in the tracking direction, of the lens holder 313 are formed
into inclined surfaces, thereby making it possible to reduce the
thickness of the lens holder 313. A description will be given of
this point with reference to FIGS. 17A, 17B, and 18. As shown in
FIG. 17A, the lens holder 313 requires the width L.sub.35 of the
magnetic circuit 309 (yoke 310) so as to drive the lens holder 313
in the focusing direction and the tracking direction. In addition,
the lens holder requires mechanical leeway for moving in the
tracking direction, i.e., an arbitrary dimension is required as the
gap (L.sub.36-L.sub.35) between the width inside the frame 313a and
the yoke 310. Furthermore, it is necessary to secure the width of
the frame 313a of the lens holder 313. Consequently, a width
L.sub.37 which is substantially larger than the diameter of the
objective lens 303 is required as a whole. In the lens holder 313
which requires such a width L.sub.37, if the opposite end portions
of the lens holder 313 as viewed in the radial direction of the
optical disk are formed into square shapes in the conventional
manner, in a case where the objective lens 303 is driven in the
focusing direction in a state in which the objective lens 303 has
been moved to the innermost peripheral side or outermost peripheral
side of the optical disk 301, the lens holder 313 does not enter
inside the window 308d, and collides against the lower surface of
the lower shell 308b. This occurs due to the fact that the distance
L.sub.34 between the upper portion of the lens holder 313 and the
lower shell 308b is smaller than the amount of movement in the
upward direction for focusing, as shown in FIG. 17A. However, if
this distance is made greater as indicated by L.sub.38 in FIG. 17B,
the distance L.sub.39 between the lower surface of the lower shell
308b to the lower surface of the magnetic circuit 309 would become
greater (if the working distance of the objective lens 303 is
fixed).
In contrast, in this embodiment, as shown in FIG. 18, since the
side surfaces 313b of the lens holder 313 are inclined, it is
possible to reduce the thickness of the lens holder 313 without
undermining the strength of the lens holder 313 while the vertical
distance between the lens holder 313 and an edge d on the innermost
peripheral side or outermost peripheral side of the window 308d is
kept at the large distance L.sub.38 in the same way as in FIG. 17B.
As a result, it is possible to reduce the overall thickness
L.sub.310 from the lower surface of the lower shell 308b to the
lower surface of the magnetic circuit 309.
As shown in FIGS. 14 and 6B, if a portion 313c of the lens holder
313 which opposes a side edge e of the window 308d in the lower
shell 308b is formed into an inclined surface for a similar reason,
it is possible to make the apparatus thin and compact for the same
reason.
It should be noted that the arrangement of the magnetic circuit
309, the structure for supporting the lens holder 313, and the like
in the above-described embodiment are only illustrative, and it
goes without saying that various modifications are possible.
In accordance with the above-described second embodiment, in the
cartridge-type optical disk apparatus, since the magnetic circuit
of the objective-lens driving device is disposed inside the window
area of the lower shell, it is possible to make the optical pickup
thin and compact.
In addition, since the optical disk-side opposite ends of the yoke
of the magnetic circuit of the objective-lens driving device are
magnetically short-circuited by a magnetic member, the magnetically
recorded surface of the optical disk is prevented from being
demagnetized despite the fact that the magnetic circuit is brought
into close proximity to the optical disk.
In addition, since the opposite end portions, as viewed in the
tracking direction, of the objective lens holder which are opposed
to the disk are formed into inclined surfaces, it is possible to
make the apparatus thin and compact while securing the strength of
the lens holder and mechanical leeway during movement in the
focusing direction and the tracking direction.
Moreover, since the magnetic circuit of the objective-lens driving
device is disposed within the window area of the lower shell of the
optical disk, and a portion of the objective lens holder which
opposes a side edge of the window in the lower shell is formed into
an inclined surface, the apparatus can be made further thin and
compact.
Third Embodiment
Hereafter, a description will be given of a third embodiment of the
present invention with reference to the drawings.
FIG. 19 is a perspective view of an essential portion illustrating
an example of the objective-lens driving device in accordance with
the third embodiment of the present invention. FIG. 20 is a
vertical cross-sectional view thereof, and FIG. 21 is a horizontal
cross-sectional view thereof.
An objective-lens driving device 210 in the third embodiment is
comprised of a movable section 213 including an unillustrated
objective lens, an unillustrated lens holder for holding the
objective lens, a focusing coil 211 secured to the lens holder, a
pair of tracking coils 212, and the like; and a fixed section 217
which has a magnetic circuit constituted by a U-shaped yoke 214, an
upper yoke 215, and a pair of magnets 216a and 216b, and supports
the movable section 213 by means of unillustrated spring members
serving as paths for supplying current to the respective coils 211
and 212 of the movable section 213.
The U-shaped yoke 214 of the fixed section 217 is formed with a
U-shaped cross section such that a pair of a first leg 214a and a
second leg 214b are opposed to each other. The upper yoke 215 is
secured to distal end faces of the first and second legs 214a and
214b of the U-shaped yoke 214. The pair of magnets 216a and 216b
are disposed on the respectively inner sides of the first and
second legs 214a and 214b of the U-shaped yoke 214 so that
different poles, i.e., the S pole and the N pole, are opposed to
each other. A magnetic gap 218 is formed between the pair of
magnets 216a and 216b.
The focusing coil 211 of the movable section 213 is formed by
winding a coil member around its central axis such that its cross
section becomes a hollow rectangle. The focus coil 211 is disposed
around the first leg 214a of the U-shaped yoke 214 with a gap
therebetween such that its central axis becomes parallel to an
optical axis 219, and a portion of the focus coil 211 passes the
magnetic gap 218. Consequently, if current is supplied to the
focusing coil 211, the unillustrated lens holder moves in the
focusing direction (in the direction of the optical axis) Z. In
addition, each of the tracking coils 212 is wound in such a manner
as to allow the current to flow in the focusing direction Z, and is
secured on the magnetic gap 218 side of the focusing coil 211. As a
result, if current is supplied to the tracking coils 212, the
unillustrated lens holder moves in the perpendicular direction Y
with respect to the optical axis 219.
In the objective-lens driving device 210 of this embodiment,
various parts are so designed that, as shown in FIG. 22, a point of
application 212t of a tracking-driving force generated by the
tracking coils 212, a point of application 212f of a resultant
force (F.sub.21+F.sub.22) of an in-gap focusing-driving force
F.sub.21 occurring within the magnetic gap 218 and an outside-gap
focusing-driving force F.sub.22 occurring outside the magnetic gap
218 (on the outer side of the first leg 214a), and the position
213a of the center of gravity of the overall movable section 213
including the objective lens and the lens holder, substantially
coincide with each other at a given point in a direction X
tangential to the track (in a direction perpendicular to the
focusing direction Z and the tracking direction Y).
Specifically, various parts are designed in accordance with the
following technique. Namely, if it is assumed that the distance in
the direction X tangential to the track between the position of the
center of gravity 213a of the movable section 213 and a point of
application 211a of the focusing-driving force F.sub.21 occurring
within the magnetic gap is L.sub.0, that the distance between the
point of application 212t of the tracking-driving force and the
point of application 211a of the focusing-driving force F.sub.21
occurring within the magnetic gap 218 is L.sub.21, that the
distance between the point of application 211a of the
focusing-driving force F.sub.21 occurring within the magnetic gap
218 and the resultant force (F.sub.21+F.sub.22) of the in-gap
focusing-driving force F.sub.21 and the outside-gap
focusing-driving force F.sub.22 is L.sub.22, that the distance
between the point of application 211a of the in-gap
focusing-driving force F.sub.21 and a point of application 211b of
the outside-gap focusing-driving force F.sub.22 is L.sub.23, that
the in-gap magnetic flux density occurring within the magnetic gap
218 is B.sub.1, and that the outside-gap magnetic flux density
(hereafter referred to leakage magnetic flux density) occurring in
a portion where the outside-gap focusing-driving force F.sub.22
acts is B.sub.2, the following relationships hold:
L.sub.22=F.sub.22L.sub.23/(F.sub.21-F.sub.22)=B.sub.2L.sub.23/(B.sub.1-B.-
sub.2) (1)
The reason for this is that if the effective width L and the
current I are assumed to be fixed, the driving force F is in a
proportional relationship with the magnetic flux density B.
Accordingly, the values of L.sub.0, L.sub.21, L.sub.22, L.sub.23,
B.sub.1, and B.sub.2 are selected in such a way that L.sub.22 on
the one hand, and L.sub.21 and L.sub.0 on the other, become
substantially equal.
Consequently, since the point of application 212f of the resultant
force (F.sub.21+F.sub.22), the point of application 212t of the
tracking-driving force generated by the tracking coils 212, and the
position 213a of the center of gravity of the overall movable
section 213 substantially coincide with each other at a given point
in the X direction, it is possible to prevent the occurrence of
unwanted resonance.
Referring also to FIGS. 23 and 24, a description will be given of
the effects of the embodiment arranged as described above.
FIG. 23 is a graph illustrating the relationship between the
thickness of the upper yoke 215 on the one hand, and the in-gap
magnetic flux density B.sub.1, and the leakage magnetic flux
density (outside-gap magnetic flux density) B.sub.2, on the other.
FIG. 24 is a graph illustrating the effect of the thickness of the
U-shaped yoke 214 with respect to the pitching resonance, and is a
graph which illustrates the phase and the magnitude (gain) of
resonance (pitching resonance) in a mode of rotation about the
Y-axis.
According to this embodiment, since the focusing coil 211 and the
tracking coils 212 are disposed within one magnetic gap 218, it is
possible to make the device compact and thin. Also, as is apparent
from FIG. 23, the in-gap magnetic flux density B.sub.1, and the
leakage movable plate B.sub.2 change with the thickness of the
upper yoke 215, and the greater the thickness of the upper yoke
215, the greater the in-gap magnetic flux density B.sub.1, becomes
and the smaller the leakage magnetic flux density B.sub.2 becomes.
Accordingly, at an arbitrary distance L.sub.23, the greater the
thickness of the upper yoke 215, the smaller L.sub.22 becomes, and
the point of application 212f of the resultant force
(F.sub.21+F.sub.22) approaches the point of application 211a of the
in-gap focusing-driving force F.sub.21. Therefore, in a case where
L.sub.21 and L.sub.23 are fixed as dimensions, if the thickness of
the upper yoke 215 is set to an appropriate value so that the
values of B.sub.1, and B.sub.2 become such that L.sub.21=L.sub.22,
the point of application 212t of the tracking-driving force, the
point of application 212f of the resultant force (F.sub.21+F.sub.2)
of the in-gap focusing-driving force F.sub.21, and the outside-gap
focusing-driving force F.sub.22, and the position 213a of the
center of gravity of the overall movable section 213 substantially
coincide with each other at a given point in the X direction. Since
the point of application 212t of the tracking-driving force and the
position 213a of the center of gravity of the overall movable
section 213 substantially coincide with each other, it is possible
to prevent the occurrence of resonance about the Z-axis with the
position 213a of the center of gravity set as the center. Since the
point of application 212f of the resultant force
(F.sub.21+F.sub.22) and the position 213a of the center of gravity
of the movable section 213 substantially coincide with each other,
it is possible to prevent the occurrence of resonance about the
Y-axis with the position 213a of the center of gravity set as the
center. Thus, by making active use of the outside-gap
focusing-driving force F.sub.22, which has conventionally been
considered as being needed to be minimized, it becomes possible to
prevent the occurrence of unwanted resonance in both the tracking
direction Y and the focusing direction Z.
In addition, as is apparent from FIG. 24, if the thickness of the
upper yoke 215 is set to an appropriate value, it is possible to
prevent the occurrence of pitching resonance.
Also, although a measure against the focusing side is adopted in
the objective-lens driving device disclosed in Unexamined Japanese
Patent Application (Kokai) 4-102235 in the known example, this
embodiment has an advantage in that it is capable of coping with
the tracking side as well.
FIG. 25 is a diagram illustrating the positional relationships
among the respective points of application 211a, 212f, and 212t and
the position 213a of the center of gravity in the direction X
tangential to the track in accordance with a modification of the
objective-lens driving device of the present invention. This
modification differs from the above-described embodiment in the
relationships among the respective points of application 211a,
212f, and 212t and the position 213a of the center of gravity, and
the other aspects are similar to those of the above-described
embodiment.
In this embodiment, various parts are arranged such that
|L.sub.21-L.sub.22|<|L.sub.21|, and L.sub.0 is determined such
that L.sub.21.gtoreq.L.sub.0.gtoreq.L.sub.22 (when
L.sub.21.gtoreq.L.sub.22) or
L.sub.21.ltoreq.L.sub.0.ltoreq.L.sub.22 (when
L.sub.21.ltoreq.L.sub.22).
Referring to FIGS. 26 to 28 as well, a description will be given of
the effects of this modification.
FIG. 26 is a diagram of a transmission characteristic of an
actuator in the focusing direction Z when settings were provided
such that L.sub.0=200 .mu.m, L.sub.21=400 .mu.m, and L.sub.22=150
.mu.m, and S.sub.2=50 .mu.m, and S.sub.1=200 .mu.m. FIG. 27 is a
diagram of a transmission characteristic of the actuator when the
position 213a of the center of gravity and the position of the
point of application 212f were arranged reversely, and the value of
S.sub.2 was similarly set to 50 .mu.m. FIG. 28 is a diagram of a
transmission characteristic of the actuator in the tracking
direction Y when settings were provided such that L.sub.0=200
.mu.m, L.sub.21=400 .mu.m, and L.sub.22=250 .mu.m, and S.sub.2=50
.mu.m, and S.sub.1=200 .mu.m. Additionally, portions indicated by
dotted-dash-line circles in FIGS. 26 to 28 show points of
resonance.
As is apparent from FIG. 26, resonance of the frequency of rotation
about the Y-axis with the position 213a of the center of gravity
set as the center appeared in the portion indicated by the
dotted-dash-line circle, but the resonance was sufficiently small.
Accordingly, as shown in FIG. 25, if the distance S between the
point of application 212t of the tracking-driving force and the
point of application 212f of the resultant force
(F.sub.21+F.sub.22), i.e., an actual focusing-driving force, is
made short, and the position 213a of the center of gravity of the
overall movable section 213 is disposed within that distance (S),
it is possible to reduce both the distance S.sub.1 between the
position 213a of the center of gravity and the point of application
212t and the distance S.sub.2 between the position 213a of the
center of gravity and the point of application 212f as compared
with conventional examples, thereby making it possible to
sufficiently reduce the occurrence of unwanted resonance in the two
directions.
As is apparent from FIG. 27, resonance of the frequency of rotation
about the Y-axis with the position 213a of the center of gravity
set as the center appeared in the portion indicated by the
dotted-dash-line circle. If a comparison is made with FIG. 26,
although the phase was reversed, the value of resonance was
sufficiently small. As is apparent from FIG. 28, resonance of the
frequency of rotation about the Z-axis with the position 213a of
the center of gravity set as the center appeared in the portion
indicated by the dotted-dash-line circle, but the resonance was
sufficiently small. Accordingly, even if the position 213a of the
center of gravity of the overall section 213 is not disposed
between the point of application 212t of the tracking-driving force
and the point of application 212t of the actual focusing-driving
force (resultant force), insofar as S.sub.1 and S.sub.2 are
sufficiently small, it is possible to reduce the occurrence of
unwanted resonance to a sufficiently small level. Thus, if S.sub.1
and S.sub.2 are made small, the unwanted resonance can be made
sufficiently small by making S small, without adopting the
above-described arrangement.
It should be noted that the present invention is not limited to the
above-described embodiment, and may be implemented by adopting
various modifications. For example, in order to control the values
of the in-gap magnetic flux density B.sub.1, and the leakage
magnetic flux density B.sub.2, the thickness, the shape and the
like of one leg 214a of the yoke 214 may be devised, and various
values including L.sub.21 and L.sub.23 may be determined such that
L.sub.21=L.sub.22.
In accordance with the third embodiment of the present invention
detailed above, the following advantages are obtained.
Since the point of application of the resultant force of
focusing-driving forces respectively occurring in and outside the
magnetic gap is brought close to the point of application of the
tracking-driving force, their distances with respect to the
position of the center of gravity of the overall movable section
can both be reduced. Therefore, it is possible to easily prevent
the occurrence of unwanted resonance in both the focusing direction
and the tracking direction.
Further, since the position of the center of gravity of the overall
movable section is located between the point of application of the
tracking-driving force and the point of application of the
resultant force of the focusing-driving forces respectively
occurring in and outside the magnetic gap, the distances between
the position of the center of gravity of the overall movable
section and the point of application of the resultant force and
between the position of the center of gravity of the overall
movable section and the point of application of the
tracking-driving force are both made short. Therefore, it is
possible to prevent the occurrence of unwanted resonance in both
the focusing direction and the tracking direction.
Additionally, since various parts are arranged in such a manner as
to satisfy the formulae: |L.sub.0-L.sub.22|.ltoreq.50 .mu.m and
|L.sub.0-L.sub.21.ltoreq.200 .mu.m, it is possible to reduce
unwanted resonance.
Furthermore, since the arrangement provided is such that the
focusing coil and the tracking coils are disposed in a single
magnetic circuit, and the point of application of the resultant
force of focusing-driving forces respectively occurring in and
outside the magnetic gap, and the position of the center of gravity
of the movable section are made to substantially coincide with each
other, it is possible to make the device compact and thin. Hence,
it is possible to realize a stable servomechanism in which unwanted
resonance does not occur in both the focusing direction and the
tracking direction.
Moreover, since the arrangement provided is such that the focusing
coil and the tracking coils are disposed in a single magnetic
circuit, the point of application of the tracking-driving force,
the point of application of the resultant force of focusing-driving
forces respectively occurring in and outside the magnetic gap, and
the position of the center of gravity of the movable section are
made to substantially coincide with each other by selecting the
values of L.sub.0, L.sub.21, L.sub.22, L.sub.23, B.sub.1, and
B.sub.2 in such a manner as to satisfy the aforementioned formula,
it is possible to make the device compact and thin. Hence, it is
possible to realize a stable servomechanism in which unwanted
resonance does not occur in both the focusing direction and the
tracking direction. In addition, since the values of L.sub.0,
L.sub.21, L.sub.22, L.sub.23, B.sub.1, and B.sub.2 can be selected
as required, design of a high degree of freedom is possible. Also,
since the present invention can be arranged on the basis of
magnetic flux density which is easier to measure than the driving
force, the design of various parts is facilitated.
Furthermore, as shown in FIG. 4, in the case that the
objective-lens driving device is made thin by arranging the
magnetic circuit of the driving device within the window area of
the lower shell of the optical disk, the magnetic circuit is
required to be minimized. If the symmetry of the magnetic circuit
is unbalanced, undesired resonance may occur. According to the
invention, this undesired resonance is prevented.
Fourth Embodiment
Hereafter, a description will be given of a fourth embodiment of
the present invention with reference to the drawings.
FIG. 29 is a side view illustrating another example of the
objective-lens driving device in accordance with the fourth
embodiment of the present invention.
As shown in the drawing, an objective-lens driving device 410 in
this embodiment is comprised of a movable section 412 including an
objective lens 411 and unillustrated coils for generating driving
forces in predetermined directions Y and Z; a plurality of (in this
embodiment, four) wires 414 serving as resiliently supporting
members for supporting the movable section 412 in a cantilevered
manner and also serving as paths for supplying electric current to
the coils; a printed circuit board 413 electrically connected to
fixed ends of the wires 414; a yoke base 415 for producing the
driving forces; and an intermediate member 416 for fixing the
printed circuit board 413 and the yoke base 415 by molding in a
state in which the printed circuit board 413 and the yoke base 415
are positioned relative to each other.
The movable section 412 has an unillustrated lens holder to which
an objective lens 402 is secured, and a focusing coil and tracking
coils (not shown) for driving the objective lens 402 in the
focusing direction Z and the tracking direction Y are arranged in
the lens holder.
As shown in the perspective view in FIG. 30, the yoke base 415 is
formed as a substantially U-shaped yoke portion 415a and a
substantially Z-shaped placing portion 415b for placing the printed
circuit board 413 thereon are formed integrally by press-working a
metal plate. The placing portion 415b is provided with through
holes 415c for strengthening a joining force with respect to the
intermediate member 416.
As shown in FIG. 29, the printed circuit board 413 has four through
holes 413a, which also serve as through holes for the wires 414, so
as to strengthen the joining force between the printed circuit
board 413 and the intermediate member 416. On an outer surface 413b
of the printed circuit board 413, soldered land portions which are
provided with plating are respectively formed around the through
holes 413a for connecting external connecting cables.
The intermediate member 416 is formed of an injection molding
member such as a plastic resin. When this intermediate member 416
is formed by injection molding, the printed circuit board 413 and
the yoke base 415 are secured to each other. In addition, when the
intermediate member 416 is formed, guide holes 416a for the
insertion of the wires 414, as well as a damping-member
accommodating portion 416b for filling a damping member 418 such as
silicone in the vicinities of the guide holes 416a, are also
formed.
Next, also referring to FIGS. 31 to 34, a description will be given
of a method of manufacturing the objective-lens driving device 410
in this embodiment.
First, as shown in FIG. 31, the printed circuit board 415 and the
yoke base 415 formed by press working are disposed in a
predetermined position in an unillustrated mold for injection
molding, and are positioned. Through this positioning, the printed
circuit board 413 is placed on the placing portion 415b of the yoke
base 415, and the printed circuit board 413 is held in an upright
position by using a bottom 415d of the yoke base 415 as a reference
plane by means of the unillustrated mold.
In this state, the intermediate member 416 is molded by injection
molding, as shown in FIG. 32. Since the injection molding member
for the intermediate member 416 passes through the through holes
415c provided in the yoke base 415 and the through holes 413a
provided in the printed circuit board 413, and flows around to the
opposite side, the printed circuit board 413 and the yoke base 415
are secured firmly to the intermediate member 416. In addition,
when the intermediate member 416 is formed by injection molding,
the guide holes 416a and the damping-member accommodating portion
416b are also formed. A plan view in this state is shown in FIG.
33, and a cross-sectional view taken along the line C--C in FIG. 33
is shown in FIG. 34.
Next, the four wires 414 are passed through the guide holes 416a
formed in the intermediate member 416, and are connected to the
soldered land portions formed on the outer surface 413b of the
printed circuit board 413 by means of solder 417. The movable
section 412 including the objective lens 411 and the unillustrated
coils is secured to the distal ends of the wires 414 by means of
soldering.
Subsequently, the damping member 418 is filled in the
damping-member accommodating portion 416b formed in the
intermediate member 416.
The yoke base 415, the intermediate member 416, and the printed
circuit board 413 are assembled in the above-described manner.
According to this embodiment, since the yoke base 415 and the
printed circuit board 413 are simultaneously secured when the
intermediate member 416 is formed by injection molding, instead of
securing the yoke base 415 and the intermediate member 416 as well
as the intermediate member 416 and the printed circuit board 413 by
means of an adhesive, screws, or the like, there is an advantage in
that the number of component parts and auxiliary materials used
decreases, and the number of assembling steps can also be
reduced.
In addition, since the yoke base 415 and the printed circuit board
413 are positioned in the mold and are integrally formed by using
the intermediate member 416, the relative positional accuracy
becomes high.
Also, since the molding is effected by causing the intermediate
member 416 to enter the through holes 413a of the printed circuit
board 413, there is no lifting off of the printed circuit board 413
at the boundary between the intermediate member 416 and the through
holes 413a in the printed circuit board 413 due to temperature
changes, aged deterioration and the like. Hence, there is an
advantage in that it is possible to prevent a change in the angle
of the optical axis of the objective lens 411 and the occurrence of
unwanted resonance due to the deterioration of the supporting
balance.
Further, if the intermediate member 416 is formed by a color which
easily reflects light, when the wires on the printed circuit board
413 are soldered by a noncontact soldering apparatus using a light
beam, the light can be focused on the soldering land portions
around them without being concentrated on the through holes 413a in
the printed circuit board 413. Hence, there is an advantage in that
wire soldering can be provided effectively.
Furthermore, since the vibration of the wires 414 is suppressed by
the damping member 418 to dampen the unwanted resonance of the
movable section 412, it becomes possible to drive the objective
lens 411 more accurately.
It should be noted that the present invention is not limited to the
above-described embodiment, and various modifications are possible.
For instance, the printed circuit board 413 and the yoke base 415
many not contact each other insofar as relative positional accuracy
can be ensured. Also, the damping member 418 may be provided on the
distal end side of the wires 414 to suppress the vibration. In
addition, the movable section may be supported on both sides by
means of wires. In this case, it suffices if the printed circuit
board is disposed on at least one fixed end side of the wires.
In accordance with the fourth embodiment of the present invention
detailed above, the following advantages are obtained.
Since the bonding process and the screw-tightening process can be
omitted in assembling the printed circuit board, the base, and the
intermediate member, and the relative positional accuracy between
the printed circuit board and the base can be improved, it is
possible to provide an objective-lens driving device which
facilitates fabrication, and in which the objective lens can be
driven with high accuracy.
Since part of the intermediate member enters the through holes at
the time of molding the intermediate member, the joining force
between the printed circuit board and the base is strengthened,
thereby improving the reliability.
Since the printed circuit board can be prevented from becoming
lifted off in the vicinities of the fixed ends of the resiliently
supporting members, it is possible to prevent changes in the angle
of the optical axis of the objective lens and the occurrence of
unwanted resonance due to the deterioration of the supporting
balance.
Since the unwanted resonance of the movable section is dampened by
suppressing the vibration of the resiliently supporting members by
means of the damping member, the objective lens can be driven with
greater accuracy.
Since the base is formed integrally with the yoke, the base can be
fabricated easily.
* * * * *