U.S. patent application number 09/365199 was filed with the patent office on 2002-04-11 for apparatus and method for driving objective lens.
Invention is credited to KAWAKAMI, HIROSHI, MURAYAMA, TOMOHIRO, SHINOZUKA, HIROSHI, TATEISHI, TAIZO, WAKABAYASHI, TOMOMI.
Application Number | 20020041563 09/365199 |
Document ID | / |
Family ID | 16772420 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020041563 |
Kind Code |
A1 |
SHINOZUKA, HIROSHI ; et
al. |
April 11, 2002 |
APPARATUS AND METHOD FOR DRIVING OBJECTIVE LENS
Abstract
A method for manufacturing an objective lens driving apparatus
comprising a lens holder which holds an objective lens and is
driven in a focusing direction and a tracking direction with
reference to the optical disk, at least two wires having first ends
secured to the lens holder and controlling posture of the lens
holder, and a wire holder to which second ends of the wires are
fixed, the method comprising the steps of preparing a first
integrally molded member including the lens holder and the wire
holder which are connected together by a holder connecting frame to
be removed after assembly, preparing a second integrally molded
member including the wires which are suspended from a wire holding
frame to be removed after assembly, positioning the second
integrally molded member relative to the first integrally molded
member such that the first ends of the wires are connected to the
lens holder and the second ends of the wires are connected to the
wire holder, and removing the wire holding frame and the holder
connecting frame.
Inventors: |
SHINOZUKA, HIROSHI;
(YOKOHAMA-SHI, JP) ; MURAYAMA, TOMOHIRO;
(YOKOHAMA-SHI, JP) ; WAKABAYASHI, TOMOMI;
(YOKOHAMA-SHI, JP) ; TATEISHI, TAIZO;
(YOKOHAMA-SHI, JP) ; KAWAKAMI, HIROSHI;
(CHIGASAKI-SHI, JP) |
Correspondence
Address: |
PILLSBURY MADISON & SUTRO LLP
INTELLECTUAL PROPERTY GROUP
NINTH FLOOR EAST TOWER
1100 NEW YORK AVENUE N W
WASHINGTON
DC
200053918
|
Family ID: |
16772420 |
Appl. No.: |
09/365199 |
Filed: |
August 2, 1999 |
Current U.S.
Class: |
720/685 ;
369/44.16; G9B/7.083; G9B/7.084; G9B/7.085; G9B/7.138 |
Current CPC
Class: |
G11B 7/0932 20130101;
Y10T 29/49904 20150115; G11B 7/22 20130101; Y10T 29/4998 20150115;
G11B 7/0935 20130101; G11B 7/0933 20130101; Y10T 29/49615
20150115 |
Class at
Publication: |
369/244 ;
369/44.16 |
International
Class: |
G11B 007/00; G11B
017/00; G11B 021/16 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 1998 |
JP |
10-221801 |
Claims
1. A method for manufacturing an objective lens driving apparatus
comprising: a lens holder which holds an objective lens and is
driven in a focusing direction and a tracking direction with
reference to the optical disk; at least two wires having first ends
secured to the lens holder and controlling posture of the lens
holder; and a wire holder to which second ends of the wires are
fixed, said method comprising the steps of: preparing a first
integrally molded member including the lens holder and the wire
holder which are connected together by a holder connecting frame to
be removed after assembly; preparing a second integrally molded
member including the wires which are suspended from a wire holding
frame to be removed after assembly; positioning the second
integrally molded member relative to the first integrally molded
member such that the first ends of the wires are connected to the
lens holder and the second ends of the wires are connected to the
wire holder; and removing the wire holding frame and the holder
connecting frame.
2. A method according to claim 1, wherein said wires, said lens
holder and said wire holder are positioned relative to one another
by bringing the holder connecting frame into contact with the wire
holding frame.
3. An objective lens driving apparatus incorporated in an optical
disk apparatus which is for recording or reproducing information
from an optical disk, comprising: a lens holder which holds an
objective lens and is driven in a focusing direction and a tracking
direction with reference to the optical disk; at least two wires
having first ends secured to the lens holder and controlling
posture of the lens holder; and a wire holder to which second ends
of the wires are fixed, said wires being suspended by a wire
holding frame which is to be removed after assembly, and said wires
being first secured to the lens holder and the wire holder, and
then said wire holding frame being removed.
4. An objective lens driving apparatus according to claim 3,
wherein said lens holder and said wire holder are held in a state
where said lens and wire holders are connected by the holder
connecting frame which is to removed after assembly, and said wires
are first secured to the lens and wire holders, and then the wire
holding frame is removed, thus allowing the lens and wire holders
to move relative to each other.
5. An objective lens driving apparatus according to claim 4,
wherein said wires are positioned with reference to the lens holder
and the wire holder by positioning the wire holding frame with
reference to the holder connecting frame.
6. An objective lens driving apparatus according to claim 3,
wherein: said lens holder is provided with first bosses to which
the first ends of the wires are to be fixed; said first ends of the
wires have first insertion holes, and said first bosses are loosely
inserted into the first insertion holes and then fixed therein by
means of an adhesive; said wire holder is provided with second
bosses to which the second ends of the wires are to be fixed; and
said second ends of the wires have second insertion holes, and said
second bosses are loosely inserted into the second insertion holes
and then fixed therein by means of an adhesive.
7. An objective lens driving apparatus according to claim 3,
wherein: said wire holder includes a main body, and swinging
sections integral with the main body; and said second ends of the
wires are secured to the swinging sections.
8. An objective lens driving apparatus according to claim 7,
wherein: each of the swinging sections has a first end that is
fixed to the main body by means of a thin member, and a second end
that extends to a region close to the main body; and a vibration
suppressing member is interposed between the main body of the wire
holder and the second end of each swinging section.
9. An objective lens driving apparatus according to claim 7,
wherein: said wire holder is provided with a gel reservoir located
at a position corresponding to an intermediate portion of each
wire; and a gel member is sealed in the gel reservoir and serves to
prevent each wire from vibrating.
10. An objective lens driving apparatus according to claim 7,
wherein: said lens holder is provided with a gel reservoir located
at a position corresponding to an intermediate portion of each
wire; and gel for preventing vibration of the lens holder is sealed
in the gel reservoir.
11. An objective lens driving apparatus according to claim 3,
further comprising: a focusing coil, provided for the lens holder,
for driving the lens holder in the focusing direction; a pair of
tracking coils provided for those portions of the lens holder which
are ends, as viewed in the tracking direction; and a pair of
printed wiring boards, provided for those portions of the lens
holder which are ends, as viewed in the tracking direction, and
having wiring connected to the focusing coil and/or the tracking
coil, said printed wiring boards being connected together by means
of a board holding member which is to be removed after assembly,
and said printed wiring boards being first secured to the lens
holder, and then the board holding frame being removed.
12. An objective lens driving apparatus according to claim 3,
further comprising: a focusing coil, provided for the lens holder,
for driving the lens holder in the focusing direction; a pair of
tracking coils provided for those portions of the lens holder which
are ends, as viewed in the tracking direction; and a flexible
printed wiring board, provided for the wire holder and having
external-connection wiring connected to the focusing coil and/or
the tracking coil, said flexible printed wiring board having an
intermediate portion which is intermediate as viewed in the
tracking direction and which is reduced in width.
13. An objective lens driving apparatus according to claim 3,
further comprising: a focusing coil, provided for the lens holder,
for driving the lens holder in the focusing direction; a pair of
tracking coils provided for those portions of the lens holder which
are ends, as viewed in the tracking direction; and a flexible
printed wiring board, provided for the wire holder and having
external-connection wiring connected to the focusing coil and/or
the tracking coil, said flexible printed wiring board having a slit
formed in a portion which is intermediate as viewed in the focusing
direction.
14. An objective lens driving apparatus according to claim 3,
further comprising: a chassis to which the wire holder is fixed; an
electromagnetic driving mechanism, arranged between the chassis and
the lens holder, for driving the lens holder; and an actuator cover
formed of a material having high magnetic permeability, coupled to
the chassis and covering movable portions of the wire and the lens
holder.
15. An objective lens driving apparatus according to claim 3,
further comprising: a chassis to which the wire holder is fixed;
and an electromagnetic driving mechanism, arranged between the
chassis and the lens holder, for driving the lens holder, said
chassis having a depression formed in a surface opposite a surface
for which the wire holder is provided.
16. An objective lens driving apparatus incorporated in an optical
disk apparatus which is for recording or reproducing information
from an optical disk, said objective lens driving apparatus
comprising: a lens holder which holds an objective lens and is
driven in a focusing direction and a tracking direction with
reference to the optical disk; at least two wires having first ends
secured to the lens holder and controlling posture of the lens
holder; and a wire holder to which second ends of the wires are
fixed, said wire holder having swinging sections which are integral
therewith and to which the second ends of the wires are fixed.
17. An objective lens driving apparatus according to claim 16,
wherein: said wire holder is provided with a gel reservoir located
at a position corresponding to an intermediate portion of each
wire; and a gel member is sealed in the gel reservoir and serves to
prevent each wire from vibrating.
18. An objective lens driving apparatus according to claim 16,
wherein: each of the swinging sections has a first end that is
fixed to the main body by means of a thin member, and a second end
that extends to a region close to the main body; and a vibration
suppressing member is interposed between the main body of the wire
holder and the second end of each swinging section.
19. An objective lens driving apparatus according to claim 16,
wherein: said lens holder is provided with a gel reservoir located
at a position corresponding to an intermediate portion of each
wire; and gel for preventing vibration of the lens holder is sealed
in the gel reservoir.
20. An objective lens driving apparatus incorporated in an optical
disk apparatus which is for recording or reproducing information
from an optical disk, said objective lens driving apparatus
comprising: a lens holder which holds an objective lens and is
driven in a focusing direction and a tracking direction with
reference to the optical disk; at least two wires having first ends
secured to the lens holder and controlling posture of the lens
holder; and a wire holder to which second ends of the wires are
fixed, said lens holder having first bosses to which the first ends
of the wires are to be fixed, said first ends of the wires having
first insertion holes into which the first bosses are loosely
inserted, and the first bosses and the first insertion holes being
fixed together by means of an adhesive, the wire holder having
second bosses to which the second ends of the wires are fixed, the
second ends of the wires having second insertion holes into which
the second bosses are loosely inserted, and the second insertion
holes and the second bosses being fixed together by means of an
adhesive.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an apparatus and method for
driving an objective lens used to record/reproduce information with
reference to an optical disk, such as a CD (Compact Disk), a CD-RW
(CD-ReWritable), a DVD-ROM (Digital Versatile Disk Read Only
Memory) and a DVD-RAM (DVD-Random Access Memory).
[0002] In recent years, there is an increasing demand for flat-type
optical disk recording/reproducing apparatuses (optical disk
apparatuses). To provide such apparatuses, very strict requirements
are imposed on the design of an objective lens driving apparatus
which is used for recording/reproducing information with reference
to an optical disk.
[0003] For example, in the case of an objective lens driving
apparatus suitable for use in a 1/2-size optical disk having a
height of 12.7 mm, the distance between the surface of the optical
disk and the bottom surface of the objective lens driving apparatus
must be shorter than 7.3 mm. Since the objective lens driving
apparatus is installed in a restricted space, such as the space in
a jacket-size apparatus or the space in a note book-included
apparatus, the size of the objective lens driving apparatus is
restricted in the horizontal direction as well.
[0004] In addition to the above, the objective lens driving
apparatus is required to satisfy the requirements of a DVD disk,
the integration density of which is seven times higher than that of
an CD.
[0005] In the DVD optical system, the objective lens driving
apparatus has to be very small in size and yet it must be provided
with an acceleration generating function so as to ensure reliable
data reproduction even when the disk is rotating fast. The
objective lens driving apparatus must be also provided with such
frequency characteristics as will satisfy wide-band servo
specifications, because the waving and eccentricity of the disk
occur at higher frequencies due to the fast rotation of the
disk.
[0006] A CD system (CD.times.1) and a DVD system (DVD.times.1) will
be compared with each other. (The ".times.1" is a standard transfer
speed for audio CDs.)
[0007] (1) Number of Rotations
[0008] CD.times.1: 3.3 to 8.3 Hz
[0009] DVD.times.1: 9.6 to 23.1 Hz
[0010] (2) Allowable Limit Values in Focusing Direction
[0011] {circle over (1)} Waving Amount (Rotation
Synchronization)
[0012] CD.times.1: .+-.0.5 mm
[0013] DVD.times.1: .+-.0.3 mm
[0014] {circle over (2)} Waving Acceleration
[0015] CD.times.1: 10 m/s.sup.2
[0016] DVD.times.1: 8 m/s.sup.2
[0017] {circle over (3)} Allowable Residual Error
[0018] CD.times.1: .+-.1 .mu.m
[0019] DVD.times.1: .+-.0.23 .mu.m
[0020] (3) Allowable Limit Values in Tracking Direction
[0021] {circle over (1)} Eccentricity (Rotation
Synchronization)
[0022] CD.times.1: .+-.70 .mu.m
[0023] DVD.times.1: .+-.35 .mu.m
[0024] {circle over (2)} Eccentricity Acceleration
[0025] CD.times.1: 0.4 m/s.sup.2
[0026] DVD.times.1: 1.1 m/s.sup.2
[0027] Allowable Residual Error
[0028] CD.times.1: .+-.0.1 .mu.m
[0029] DVD.times.1: .div.0.022 .mu.m
[0030] Allowable Tilt of Objective Lens
[0031] CD.times.1: .+-.5 mrad
[0032] DVD.times.1: .+-.2 mrad
[0033] As can be understood from the above comparison, the
characteristics regarding the waving and eccentricity of the DVD
system are improved; their figures are 0.5-0.6 of those of the CD
system. In spite of this, however, the allowable residual error of
the DVD system is less than 1/4 of that of the CD system. This
means that, due to the use of the servo system adopted, the
accuracy required of the DVD system is twice as high as that of the
CD system. Therefore, the high-frequency characteristic of the
objective lens driving system must be expanded double, and the
oscillation system including a secondary resonating unit and the
electromagnetic driving system must be greatly improved,
accordingly. When the rotating speed of a disk is increased, the
electromagnetic driving system is required to use power with
remarkably high efficiency, since the acceleration increases in
proportion to the square of the number of rotations.
[0034] In the CD system, the allowable tilt of the objective lens
can be realized without imposing severe restrictions on the
manufacture of the CD system. In the DVD system, however, the
allowable tilt of the objective lens cannot be easily realized and
poses a lot of problems in the manufacture of the system,
particularly when mass production of systems is considered. If the
objective lens tilts, the parallelism of the objective lens to the
surface of the optical disk is adversely affected. If this happens,
an RF signal derived from a reflected beam from the disk decreases
in level in accordance with an increase in the tilt angle, so that
the reproduction or recording of data with reference to the optical
disk may not be executed.
BRIEF SUMMARY OF THE INVENTION
[0035] As described above, the transition to the DVD system
requires an objective lens driving apparatus which is highly
sensitive, covers a wide frequency range and hardly tilts, and
which can be provided in a very restricted space. However, such an
objective lens driving apparatus cannot be easily designed by
utilizing the structure of the conventional CD system or the
conventional manufacturing system. In other words, the conventional
technology regarding the CD system is not very useful in producing
the required objective lens driving apparatus.
[0036] Accordingly, an object of the present invention is to
provide an objective lens driving apparatus which is highly
sensitive, covers a wide frequency range and hardly tilts, which
can be provided in a very restricted space and which has such a
structure as enables further enhancement in performance. Another
object of the present invention is to provide a method for
manufacturing the objective lens driving apparatus.
[0037] [I] According to the first aspect of the present invention,
there is provided a method for manufacturing an objective lens
driving apparatus comprising: a lens holder which holds an
objective lens and is driven in a focusing direction and a tracking
direction with reference to the optical disk; at least two wires
having first ends secured to the lens holder and controlling
posture of the lens holder; and a wire holder to which second ends
of the wires are fixed, the method comprising the steps of:
preparing a first integrally molded member including the lens
holder and the wire holder which are connected together by a holder
connecting frame to be removed after assembly; preparing second
integrally molded member each including the wires which are
suspended from a wire holding frame to be removed after assembly;
positioning the second integrally molded members relative to the
first integrally molded member such that the first ends of the
wires are connected to the lens holder and the second ends of the
wires are connected to the wire holder; and removing the wire
holding frame and the holder connecting frame.
[0038] With this structure, since the lens holder and the wire
holder are prepared as one integrally molded member, the wires can
be attached to them in such a manner that the positional
relationships which they have immediately after they are molded are
maintained. Moreover, since the wires suspended by the wire holding
frame are prepared as integrally molded members, the wires, even
though they are thin, can be easily assembled without damage.
[0039] According to one embodiment, the wires, the lens holder and
the wire holder are positioned relative to one another by bringing
the holder connecting frame into contact with the wire holding
frame.
[0040] [II] According to the second aspect of the present
invention, there is provided an objective lens driving apparatus
incorporated in an optical disk apparatus which is for recording or
reproducing information from an optical disk, the objective lens
driving apparatus comprising: a lens holder which holds an
objective lens and is driven in a focusing direction and a tracking
direction with reference to the optical disk; at least two wires
having first ends secured to the lens holder and controlling
posture of the lens holder; and a wire holder to which second ends
of the wires are fixed, the wires being suspended by a wire holding
frame which is to be removed after assembly, and the wires being
first secured to the lens holder and the wire holder and then the
wire holding frame being removed.
[0041] With this structure, since the wires suspended by the wire
holding frame are prepared as integrally molded members, the wires,
even though they are thin, can be easily assembled without
damage.
[0042] According to one embodiment, the lens holder and the wire
holder are held in such a manner that they are connected by the
holder connecting frame which is to removed after assembly. After
the wires are secured to the two holders, the wire holding frame is
removed, thus allowing the two holders to move relative to each
other. The wires are positioned with reference to the lens holder
and the wire holder by positioning the wire holding frame with
reference to the holder connecting frame.
[0043] With this structure, since the lens holder and the wire
holder are prepared as one integrally molded member, the wires can
be attached to them in such a manner that the positional
relationships which they have immediately after they are molded are
maintained.
[0044] According to one embodiment, the lens holder is provided
with first bosses to which the first ends of the wires are to be
fixed. The first ends of the wires have first insertion holes.
After being loosely inserted into the first insertion holes, the
first bosses are fixed therein by means of an adhesive. The wire
holder is provided with second bosses to which the second ends of
the wires are to be fixed. The second ends of the wires have second
insertion holes. After being loosely inserted into the second
insertion holes, the second bosses are fixed therein by means of an
adhesive.
[0045] With this structure, the wires can be reliably bonded to the
lens holder or the wire holder, with no need for direct adhesion
between them.
[0046] According to one embodiment, the wire holder comprises a
main body, and swinging sections integral with the main body. The
second ends of the wires are secured to the swinging sections. One
end of each swinging section is fixed to the main body by means of
thin members, while the other end thereof extends to the region in
the vicinity of the main body. It is preferable that a vibration
suppressing member be interposed between the main body and the
other end of each swinging section.
[0047] With this structure, since the swinging sections used for
holding the second ends of the wires are integral with the wire
holder, the wires can be assembled with high accuracy, which
corresponds to the accuracy at which they are molded. Since this
structure is effective in suppressing the resonance of the wires,
excellent servo characteristics are ensured at high-frequency
regions.
[0048] It is preferable that the above-mentioned swinging section
be provided for each of the wires. However, if it is provided for
one of the wires, resonance can be significantly suppressed.
[0049] According to one embodiment, the wire holder is provided
with a gel reservoir located at a position corresponding to an
intermediate portion of the wire. A gel member is sealed in the gel
reservoir and serves to prevent the wire from vibrating.
[0050] The structure described above is effective in preventing the
wires from buckling. In many cases, the vibration due to high-order
resonant frequencies is transmitted in the direction in which the
wires extend, and this vibration is likely to cause buckling of
wires. According to the present invention, the gel described above
serves to suppress the vibration at the middle point of each the
wire, and the vibration can therefore be suppressed.
[0051] According to one embodiment, the lens holder is provided
with a gel reservoir located at a position corresponding to an
intermediate portion of the wire. A gel member for preventing
vibration of the lens holder is sealed in the gel reservoir.
[0052] The structure described above is effective in preventing the
lens holder from vibrating at high-order resonant frequencies.
[0053] According to one embodiment, the objective lens driving
apparatus further comprises: a focusing coil, provided for the lens
holder, for driving the lens holder in the focusing direction; a
pair of tracking coils provided for those portions of the lens
holder which are ends, as viewed in the tracking direction; and a
pair of printed wiring boards, provided for those portions of the
lens holder which are ends, as viewed in the tracking direction,
and having wiring connected to the focusing coil and/or the
tracking coils, the printed wiring boards being connected together
by means of a board holding member which is to be removed after
assembly, and the printed wiring boards being first secured to the
lens holder and then the board holding frame being removed.
[0054] With this structure, since the printed wiring boards need
not be positioned relative to each other, they can be easily
assembled. In addition, since the board holding member is removed
after assembly of the printed wiring boards, movement of the lens
driving apparatus need not be affected thereby.
[0055] According to one embodiment, the objective lens driving
apparatus further comprises: a focusing coil, provided for the lens
holder, for driving the lens holder in the focusing direction; a
pair of tracking coils provided for those portions of the lens
holder which are ends, as viewed in the tracking direction; and a
flexible printed wiring board, provided for the wire holder and
having external-connection wiring connected to the focusing coil
and/or the tracking coils, the flexible printed wiring board having
an intermediate portion which is intermediate as viewed in the
tracking direction and which is reduced in width.
[0056] Since the intermediate portion of the flexible printed
wiring board has a reduced width, the wire holder (which serves as
a swinging section) is not prevented from moving.
[0057] According to one embodiment, the objective lens driving
apparatus further comprises: a focusing coil, provided for the lens
holder, for driving the lens holder in the focusing direction; a
pair of tracking coils provided for those portions of the lens
holder which are ends, as viewed in the tracking direction; and a
flexible printed wiring board, provided for the wire holder and
having external-connection wiring connected to the focusing coil
and/or the tracking coils, the flexible printed wiring board having
a slit formed in a portion which is intermediate as viewed in the
focusing direction.
[0058] Since the intermediate portion of the flexible printed
wiring board has a slit, the wire holder (which serves as a
swinging section) is not prevented from moving.
[0059] According to one embodiment, the objective lens driving
apparatus further comprises: a chassis to which the wire holder is
fixed; an electromagnetic driving mechanism, arranged between the
chassis and the lens holder, for driving the lens holder; and an
actuator cover formed of a material having high magnetic
permeability, coupled to the chassis and covering movable portions
of the wire and the lens holder.
[0060] It is preferable that the chassis and the actuator cover be
held at least four positions. For example, the cover and the yoke
provided for the chassis are preferably kept in contact with each
other in such a manner that the yoke holds the actuator cover.
[0061] Since this structure enables the cover to be adsorbed by the
chassis, the vibration of the cover is prevented. Since the
vibration of the cover is prevented, the fluxes between the
magnetic poles are prevented from varying.
[0062] According to one embodiment, the objective lens driving
apparatus further comprises: a chassis to which the wire holder is
fixed; and an electromagnetic driving mechanism, arranged between
the chassis and the lens holder, for driving the lens holder, the
chassis having a depression formed in a surface opposite a surface
for which the wire holder is provided,
[0063] Where this structure is used for adjusting the tilt angle in
the tangential direction of the lens, the wire holder is provided
with a stepped portion at a position away from the objective lens.
Such a stepped portion enables the adjustment to be made with a
high degree of freedom.
[0064] The structure described above is also advantageous in that
the lens holder is allowed to move in a wide range with no need to
employ a thick objective lens driving apparatus.
[0065] According to one embodiment, the lens holder and the wire
holder are preferably suspended by reduced-width, thin suspension
members. The suspension members are preferably designed such that
they can be easily cut off or removed. For example, they are half
cut. To provide half-cut structures, pressing or etching may be
utilized. If the suspension members are made of plates having a
thickness of 80 .mu.m, the half-cut portions may be 30 .mu.m or so.
When pressing is utilized, the half-cut portions are provided by
forming V-shaped grooves. When etching is utilized, they are
provided by forming a U-shaped groove.
[0066] It is preferable that the suspension members extend in the
same direction as the wires. Where this structure is employed, the
wire holding frame can be removed without subjecting the wires to
an external force.
[0067] The suspension members are preferably located at positions
corresponding to weld lines with reference to the position where
the mold resin is injected from the mold. When this structure is
adopted, the resin flows toward the suspension members after
reaching the weld lines. Since the weld lines are deformed and set
in the fitted state, the mechanical strength of the weld-line
portions is improved, and that of the entire holder is also
improved.
[0068] [III] According to the third aspect of the present
invention, there is provided an objective lens driving apparatus
incorporated in an optical disk apparatus which is for recording or
reproducing information from an optical disk, the objective lens
driving apparatus comprising: a lens holder which holds an
objective lens and is driven in a focusing direction and a tracking
direction with reference to the optical disk; at least two wires
having first ends secured to the lens holder and controlling
posture of the lens holder; and a wire holder to which second ends
of the wires are fixed, the wire holder having swinging sections
which are integral therewith and to which the second ends of the
wires are fixed.
[0069] According to this structure, the swinging sections, which
hold the second ends of the wires, are integral with the wire
holder. Accordingly, the wires can be assembled with such high
accuracy as corresponds to the accuracy at which they are molded.
This structure is effective in suppressing the resonance of the
wires, so that excellent servo characteristics are ensured at
high-frequency regions.
[0070] [IV] According to the fourth aspect of the present
invention, there is provided an objective lens driving apparatus
incorporated in an optical disk apparatus which is for recording or
reproducing information from an optical disk, the objective lens
driving apparatus comprising: a lens holder which holds an
objective lens and is driven in a focusing direction and a tracking
direction with reference to the optical disk; at least two wires
having first ends secured to the lens holder and controlling
posture of the lens holder; and a wire holder to which second ends
of the wires are fixed, the lens holder having first bosses to
which the first ends of the wires are to be fixed, the first ends
of the wires having first insertion holes into which the first
bosses are loosely inserted, the first bosses and the first
insertion holes being fixed together by means of an adhesive, the
wire holder having second bosses to which the second ends of the
wires are fixed, the second ends of the wires having second
insertion holes into which the second bosses are loosely inserted,
and the second insertion holes and the second bosses being fixed
together by means of an adhesive.
[0071] With this structure, the wires can be reliably bonded to the
lens holder or the wire holder, with no need for direct adhesion
between them.
[0072] [V] According to the fifth aspect of the present invention,
there is provided an optical head apparatus comprising the
objective lens driving apparatus according to one of the second to
fourth aspects. There is also provided an optical disk apparatus
comprising the optical head apparatus.
[0073] The structure of the fifth aspect is effective in
suppressing the tilt phenomenon, and the optical disk apparatus
comprising this optical head apparatus suppresses read and write
errors to the maximal degree.
[0074] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0075] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0076] FIG. 1 is a perspective view of an objective lens driving
apparatus according to one embodiment of the present invention.
[0077] FIG. 2 is a plan view showing the positional relationships
between a lens holder, a wire holder, and wires.
[0078] FIG. 3 is a schematic diagram illustrating an allowable
precision error when the lens holder, the wire holder ad the wires
are assembled together.
[0079] FIG. 4 is a plan view showing how the objective lens driving
apparatus is manufactured.
[0080] FIG. 5 is a perspective view showing how the objective lens
driving apparatus is manufactured.
[0081] FIG. 6 is a perspective view showing how the objective lens
driving apparatus is manufactured.
[0082] FIG. 7 is a plan view showing how the objective lens driving
apparatus is manufactured.
[0083] FIG. 8 is a perspective view showing how the objective lens
driving apparatus is manufactured.
[0084] FIG. 9 is a perspective view of a chassis having a yoke.
[0085] FIG. 10 is a perspective view showing the perspective view
showing how the objective lens driving apparatus is
manufactured.
[0086] FIG. 11 is a perspective view showing the bottom face of the
objective lens driving apparatus.
[0087] FIG. 12 is a perspective view showing a state where a
flexible printed wiring board is attached to the rear end face of
an objective lens driving apparatus.
[0088] FIG. 13 is a plan view showing an optical head apparatus
incorporating an objective lens driving system.
[0089] FIG. 14 is a block diagram showing an optical disk apparatus
incorporating an optical head apparatus.
DETAILED DESCRIPTION OF THE INVENTION
[0090] An embodiment of the present invention will now be described
with reference to the accompanying drawings.
[0091] FIG. 1 is a perspective view showing an objective lens
driving apparatus 1 according to the present invention.
[0092] (Basic Structure)
[0093] The objective lens driving apparatus is a so-called
four-wire system. A lens holder 3 for supporting an objective lens
2 and a wire holder shown in FIG. 4 are connected together by means
of four elastic wires 6 in such a manner that the lens holder 3
(i.e., the objective lens 2) can be moved in both the focusing
direction (F) and the tracking direction (T).
[0094] The lens holder 3 is provided with a center rib 8. The
center rib 8 has a lens holder section 9 located at the distal end
and adapted to hold the objective lens 2. Stays 10 extend in the
tracking direction From the intermediate portion of the center rib
8.
[0095] A focus-direction driving coil 12 (hereinafter referred to
as a focus coil) and a pair of tracking-direction driving coils 13
(hereinafter referred to as tracking coils) are fixed to the rear
end of the center rib 8.
[0096] The focusing coil 12 is shaped as a rectangular tube, the
cavity of which extends in the focusing direction (i.e., the
vertical direction). The central portion of the focusing coil 12,
as viewed in the tracking direction, is fixed to the reverse side
of the center rib 8. The paired tracking coils 13 are in the
regions between the stays 10 and the ends portions of the focusing
coil 12, as viewed in the tracking direction. The regions in which
the tracking coils 13 are located are filled with an adhesive (such
as an epoxy resin). With this structure, the tracking coils 13 are
firmly secured to the lens holder 3 not only through the focusing
coil 12 but also directly.
[0097] Magnets, indicated by numerals 15 and 16 are arranged to
face each other, with the focusing coil 12 and the tracking coils
13 being located therebetween. The magnets 15 and 16 are fixed to
the surfaces of a pair of yokes 18 and 19 (FIG. 9), and these yokes
stand upright on the chassis 17 to which the wire holder 4 is
fixed. The magnets 18 and 19 are arranged to form magnetic
paths.
[0098] With this structure, either the focusing coil 12 or the
tracking coils 13 located between the magnets 15 and 16 is
energized. As a result, the lens holder 3 is moved by a driving
force acting in either the focusing direction or tracking
direction. Since two pairs of magnets are employed, an intense
magnetic field is generated. Even though the apparatus is small as
a whole, a desirable servo driving effect is obtained.
[0099] The posture of the lens holder 3 is controlled by the four
wires 6 connected thereto, and the objective lens is prevented from
tilting.
[0100] FIG. 2 is a plan view showing the positional relationships
between the lens holder 3, the wire holder 4, and the wires 6. The
structure of the wire holder 4 will be described, referring to that
Figure. The wire holder 4 comprises a main body 20 having arms 20a
extending in the tracking direction (F). The wire holder 4 also
comprises a pair of swinging sections 22 which are swingably
coupled to both sides of the main body 20 by means of flexible thin
members 21.
[0101] A gel reservoir 24 is provided in the distal end portion of
each arm 20a. It is located at a position corresponding to an
intermediate portion of the corresponding wire 6. Gel 25 is sealed
in the gel reservoir 24, and the intermediate portion of the wire 6
is held by the gel 25, thus preventing vibration of the wire. Each
arm 20a is provided with a reference hole 26 used for positioning
the objective lens 2.
[0102] The swinging sections 22 hold the ends of the wires 6. The
swinging sections 22 are designed to have such a natural frequency
(several hundred kHz) as enables the absorption of displacement,
which may occur in the bucking direction of the wires 6 when the
objective lens apparatus is used within a predetermined servo band.
One end of each swinging section 22 is coupled to the corresponding
thin member 21, while the other end is located close to the main
body 20. Gel 27 serving as a damper for the swinging section 22 is
inserted between each swinging section 22 and the main body 20. The
Gel 27 may be replaced with any kind of material as long as this
material has a vibration-preventing effect. For example, a viscous
material or an elastic material may be used.
[0103] The wire holder 4 and the lens holder 3 are formed of a hard
synthetic resin, such as a liquid crystal polymer.
[0104] The wires 6 are formed of a material having moderate
elasticity and conductivity. For example, they are formed of BeCu
or another copper-based material with the required property. Flat
fixing pads 6a and 6b are located at the ends of each wire 6. The
fixing pads 6a and 6b are adhered to the wire holder 4 and the lens
holder 3.
[0105] In FIGS. 1 and 2, numerals 30 and 31 indicate adhesion holes
formed in the fixing pads 6a and 6b. Bosses 32 and 33 projected
from the lens holder 3 and the wire holder 4 are loosely inserted
in the adhesion holes 30 and 31, and the gaps between the bosses
32, 33 and the holders 3 and 4 are filled with an adhesive, thereby
obtaining reliable bonding strength.
[0106] The wires 6 are arranged in such a manner that one pair of
them extend in the tracking direction and another pair of them
extend in the focusing direction.
[0107] With this structure, the posture of the lens holder 3 is
controlled by the four wires 6, as described above, and the lens
holder 3 can be driven in both the focus and tracking directions.
Hence, the position of the optical spot formed by the objective
lens 2 can be moved along a track of the optical disk.
[0108] (Problems of DVD-systems and CD-systems of High Transfer
Rates)
[0109] The objective lens driving apparatus of the embodiment is
designed for use in optical disk drives, particularly a DVD system
and a CD-ROM system with a high transfer rate. When this type of
objective lens driving apparatus is designed, the control of a tilt
angle and the performance in a high-frequency servo band have to be
taken into due consideration.
[0110] FIG. 3 is a schematic diagram showing the positional
relationships between the lens holder, the wire holder and the
wires. In a DVD-system, the allowable tilt angle error should be,
for example, 2 mrad in the focusing-direction movable range, as
described above. Let us assume that the distance "L" between the
support points of one wire is 11 mm and the distance "t" between
two wires is 2.5 mm, as shown in FIG. 3. In this case, the
allowable relative errors for "L" and "t" should be 0.015 mm so as
to attain the allowable tilt angle 2 mrad.
[0111] Although the wires, the wire holder and the lens holder has
to be positioned accurately relative to each other, ordinary jigs
cannot be employed for this positioning. This is because the jigs
are required to have precision which is about one tenth of the
allowable relative error. Such a requirement cannot be easily
satisfied in practice with an ordinary mechanical assembly
technique since the jigs are mass-produced.
[0112] The lens holder and the wire holder are molded components.
If they are formed by use of different molds, it is necessary to
consider the dimensional errors between the molds. If a large
number of components are manufactured by use of the same mold,
model numbers must be assigned to them for management.
[0113] In the case of a small-sized objective lens driving
apparatus, the wires employed in them are very thin and easily
deformed. At the time of positioning or assembly, it may happen
that the wires will be deformed, resulting in an dimensional
error.
[0114] In the case where the objective lens driving apparatus of
the present invention is incorporated in a DVD system, the servo
band will be a band of very high frequencies in comparison with the
case where the same apparatus is incorporated in a CD system. For
example, the servo band will be 1.3 to 2.3 kHz in the focusing
direction, and will be 3 to 3.8 kHz in the tracking direction. It
is therefore important to prevent resonance of the wires. In
particular, buckling vibration must be prevented since such
vibration will cause the secondary resonance in the neighborhood of
the upper limit of the servo band to exceed the allowable limit
value. In addition, the tilt angle must not greatly exceed the
allowable limit in spite of the lateral-direction inertia force
produced when the optical head apparatus is performing a seek
operation at high speed.
[0115] In one type of conventional apparatuses, the wires are held
at one end by a flexible board attached to a wire holder. This
structure, however, inevitably requires a large number of parts. In
addition, the assembling accuracy between the flexible board and
the wire holder is greatly dependent on the positions where the
wires are attached.
[0116] According to the present invention, the problems at the time
of assembly are solved by adopting the manufacturing method
described below.
[0117] According to the present invention, the swinging sections 22
are integrally provided for the wire holder 4, and the wires 6 are
attached to the swinging sections 22. To suppress the buckling
vibration of the wires 6, the gel reservoir 24 of the wire holder
main body 20 is filled with gel 25, and the intermediate portion of
each wire 6 is held by the gel 25 of the gel reservoir 24. In this
manner, the problem regarding the high-frequency band is solved.
According to the embodiment, another gel reservoir 8a is formed at
the position indicated by "8a" in FIG. 5, and this gel reservoir 8a
is also filled with gel 28. With this structure, the lens holder is
prevented from vibrating at a frequency within the high-frequency
band. According to the present embodiment, moreover, the space
between the swinging section 2 and the wire holder 30 is filed with
gel 27, so as to suppress the vibration of the swinging
section.
[0118] (Manufacturing Method of Objective Lens Driving
Apparatus)
[0119] FIGS. 4-11 are plan and perspective views showing how the
objective lens driving apparatus according to the present invention
is manufactured.
[0120] As shown in FIG. 4, the lens holder 3 and the wire holder 4
are prepared as one integrally molded member 36 in the state where
the two holders are suspended by a U-shaped holder connecting frame
35. FIG. 4 is a view of the upper side of the member 36.
[0121] As shown in FIG. 5, the wires 6 are prepared as integrally
molded sheet-like metal member 39s in the state where they are
suspended by a rectangular wire holding frame 38.
[0122] A detailed description will now be given of the integrally
molded member 36 including the lens holder 3 and the wire holder 4,
and of the integrally molded members 39 including the wires 6.
[0123] The integrally molded member 36 including the lens holder 3
and the wire holder 4 is shown in FIG. 4. As shown in FIG. 4, the
holder connecting frame 35 and the lens holder 3 are suspended by
two narrow and thin suspension members 40. Likewise, the frame 35
and the wire holder 4 are suspended by two narrow and thin
suspension members 41. As will be described later, the wires 6 are
first assembled and secured to the lens holder 3 and the wire
holder 4, and then the suspension members 40 and 41 are bent and
cut off for the removal of the holder connecting frame 35.
[0124] To enable the suspension members to be easily bent or cut
off, it is preferable that the suspension members 40 and 41 have
half-cut portions. These half-cut portions are provided by pressing
or etching. Where the suspension members are made of plates having
a thickness of 80 .mu.m, the half-cut portions may be 30 .mu.m or
so. When pressing is utilized, the half-cut portions are provided
by forming V-shaped grooves. When etching is utilized, they are
provided by forming a U-shaped groove.
[0125] To prevent the wires 6 from being applied with a force, the
half-cut portions of the suspension members 40 and 41 extend in the
same direction as the wires 6. With this structure, the wires 6 are
prevented from being undesirably bent in the step of bending and
cutting off the suspension members 40 and 41.
[0126] The suspension members 40 and 41 are preferably located at
positions corresponding to weld lines with reference to the
position where mold resin is injected from the mold. The term "weld
lines" used herein is intended to mean lines along which resins
injected into the mold collide with each other inside the mold.
Where the suspension members 40 and 41 are provided at the
positions corresponding to the weld lines, the resin that has
reached the weld lines flows toward runner sections used for
forming the suspension members. In this case, the weld lines are
distorted and have complicated shapes. In a microscopic aspect, the
weld-line portions have a large number of fitted-state shapes, the
mechanical strength of the weld-line portions is improved, and the
rigidity of the entire holder is also improved. Accordingly, the
occurrence of a complicated resonant mode is suppressed.
[0127] The holder connecting frame 35 holds the lens holder 3 and
the wire holder 4 in such a manner that those faces of the holders
3 and 4 to which the fixing pads 6a and 6b of the wires 6 are at
the same level. The holder connecting frame 35 has two side
portions between which the holders 3 and 4 are sandwiched. One of
the side portions is provided with a stepped section 43 engageable
with the edge of the wire holding frame 38, and the other side
portion is provided with a projection 44 for positioning. The
projection 44 is tapered; its diameter gradually decreases toward
the tip end. This structure enables smooth and easy engagement with
reference to the wire holding frame 38.
[0128] As shown in FIG. 5, each integrally molded member 39 holds
its two wires 6 by means of four suspension members 46. Since the
structure shown in FIG. 5 employs two integrally molded members 39
of wires, the total number of suspension members 46 is eight. The
coupling portions between the suspension members 46 and the wires 6
have the narrowest width, so that the suspension members 46 and the
wires 6 can be easily separated from each other by cutting off the
coupling portions.
[0129] As shown in FIG. 6, the rectangular wire holding frame 38
for holding the wires 6 is so designed as to enable the wires 6 to
be positioned when the wire holding frame 38 is brought into
contact with the stepped section 43 and projection 44 (FIG. 4) of
the holder connecting frame 35. The state of positioning is shown
in FIG. 7 in two dimensions.
[0130] The manufacturing steps will be described in the order in
which they are carried out.
[0131] (1) The integrally molded member 36 including the lens
holder 3 and the wire holder 4 which are connected together by the
holder connecting frame 35, is prepared, as shown in FIG. 5. Then,
the tracking coils 13 and the focusing coil 12 are fixed to the
lens holder 3 of the integrally molded member 36 by use of an
adhesive (e.g., a UV-setting resin, an epoxy resin, or the
like).
[0132] The tracking coils 13 are secured by the adhesive introduced
into the space between the focusing coil 12 and the stays 10 of the
lens holder 3. Accordingly, the focusing coil 12 is secured to the
lens holder 3 not only through the tracking coils 13 but also
directly. With this structure, a driving force can be efficiently
transmitted from the coils 12 and 13 to the lens holder 3, with the
result that the high-frequency characteristics of the movable
portions are improved.
[0133] Of the four side portions of the focusing coil 12, the side
portion that is closest to the objective lens 2 is coupled directly
to the center rib 8 of the lens holder 3 by use of an adhesive. The
side portion that is closest to the wire holder 4 and the
corresponding portion of the center rib 8 are coated with
silicone-based gel (in place of which, a soft adhesive that does
not become hard may be used), so that the gel-coated portion can
function as a damper. In this manner, there are two fixing portions
that are away from each other in the direction in which the wires
extend, and different fixing materials are used between them. With
this structure, natural vibration of the lens holder 3 (center rib
8) is suppressed, and the secondary resonance of the objective lens
2 is prevented.
[0134] Thereafter, a pair of flexible wiring boards 48, used for
electrical connection between the coils 12, 13 and the wires 6, are
adhered to the front face of the lens holder 3. The flexible wiring
boards sandwich the objective lens and are located at those
portions of the lens holder which are ends as viewed in the tracing
direction. The flexible wiring boards 48 are prepared as an
integrally molded member in the state where they are connected by a
board holding member 49. This board holding member 49 is removed
after the integrally molded member including the flexible wiring
boards is assembly with reference to the lens holder 3. Due to this
process, the flexible wiring boards 48, which are fine members, are
very easy to handle. In addition, since the board holding member 49
is removed after the adhesion step, the movable portions can be
light in weight, thus enabling high-speed driving. Terminals (not
shown) of the coils 12 and 13 are soldered to the flexible wiring
boards 48.
[0135] A protective sheet, which is indicated by "50" in the
drawings, is adhered to the center rib 8 of the lens holder 3. As
shown in FIG. 1, the protective sheet 50 is located close to the
lens holder section 9. In the case of a thin lens driving
apparatus, such as that of the present embodiment, the range in
which the objective lens 2 is allowed to move in the focusing
direction is narrow. If the servo circuit fails to perform control
due to an external shock applied thereto, it may happen that the
disk will collide with the objective lens 2. To prevent damage to
the disk, the protective sheet 50 is employed. The protective sheet
50 is projected more than the objective lens 2 and is thus closer
to the disk. The protective sheet 50 is fitted in a recess 51
formed in the center rib 8 of the lens holder 3, and is adhered to
the wall of the recess 51 so that it does not separate from the
center rib in spite of the friction caused by the disk rotating at
high speed.
[0136] (2) Next, two integrally molded members 39 including the
wires 6 are prepared. As shown in FIG. 5, they are positioned with
reference to the integrally molded member 36 that includes the lens
holder 3 and the wire holder 4, with one of them being orientated
from above and the other being orientated from below.
[0137] FIGS. 6 and 7 show how the integrally molded members 39
including the wires 6 are positioned with reference to the
integrally molded member 36 including the lens holder 3 and the
wire holder 4. As described above, the wires 6 are positioned with
reference to the lens holder 3 and the wire holder 4 by bringing
the holder connecting frame 35 and the wire holding frame 38 into
engagement with each other. To be more specific, the edge of the
wire holding frame 38 is fitted in the stepped section 43 of the
holder connecting frame 35 and by bringing the projection 44 of the
holder connecting frame into engagement with the wire holding frame
38.
[0138] By following these procedures, the holders 3 and 4 and the
wires 6 can be positioned with reference to one another, with no
need to touch them. In addition, since a structure for positioning
the holders 3 and 4 and the wires 6 is not needed, the apparatus
can be small in size.
[0139] To adhere the wires 6 to the holders 3 and 4, the bosses 32
and 33 projected from the holders 3 and 4 are first inserted
loosely in the adhesion holes 30 and 31 of the pads 6a and 6b of
the wires 6. Then, the gaps between the bosses 32, 33 and the
holders 3 and 4 are filled with an adhesive. In this manner, the
wires 6 and the holders 3 and 4 are adhered to each other by means
of the bosses 32 and 33, and no adhesive is used between the fixing
pads 6a and 6b and the upper surfaces of the holders 3 and 4. Owing
to this feature, the wires 6 do not move with reference to the
holders 3 and 4, and a reliable bonding strength is ensured.
[0140] The above-described connection between the holders 3 and 4
and the wires 6 has not been attained until the present invention.
According to the present invention, the holders 3 and 4 and the
wires 6 are not directly positioned relative to each other, so that
it is not necessary to bring them into direct engagement with each
other.
[0141] (3) Next, projection pieces (indicated with numerals "52" in
FIG. 7), which are extended from the pads 6a located on the lens
holder side, are soldered to the flexible wiring boards 48. With
this structure, the coils 12 and 13 and the wires 6 are
electrically connected to each other.
[0142] (4) Next, the wire holding frame 38 is removed. The wire
holding frame 38 is removed by first taking away portions A and B
and then taking away portions C and D (portions A-D are shown in
FIG. 7). At the boundaries between portions A-D, half-cut portions
54 (e.g., V-shaped notches) are formed beforehand, so as to enable
easy removal of each portion of the wire holding frame 38.
[0143] As shown in FIG. 7, the half-cut portions 54 are extended in
such a direction that the coupling positions (breaking-off
positions) between the suspension members 46 and the wires 6 are on
extension lines between the half-cut portions 54. With this
structure, both the half-cut portions 54 and the coupling portions
of the suspension members 46 can be broken off simultaneously.
Hence, the pads 6a and 6b of the wires 6 are prevented from being
applied with a force acting in the direction in which the pads 6a
and 6b are separated.
[0144] FIG. 8 is a perspective view showing a state in which the
wire holding frame 38 has been removed.
[0145] (5) After the process described above, the resultant
structure is placed on a jig, and the holder connecting frame 35 is
removed. The lens holder 3 and the wire holder 4 are suspended by
the holder connecting frame 35 by means of the suspension members
40 and 41. Since these suspension members are thin and narrow in
width and formed of a glass fiber-reinforced LCP or the like, they
can be removed very easily.
[0146] FIG. 2 is a plan view showing a state in which the holder
connecting frame 35 has been removed.
[0147] The lens holder 3, the wire holder 4 and the wires 6, which
are assembled in the manner described above, are hardly deformed,
are assembled with high precision, and provide a stable
structure.
[0148] The tilt angle characteristics are dependent greatly on the
initial precision of those portions of the lens and wire holders 3
and 4 to which the wires 6 are fixed and on the assembling
accuracy. Although these factors were problems in the mass
production of apparatuses, a solution to the problems has been
provided by the present invention. According to the present
invention, the lens holder 3 and the wire holder 4 are prepared as
parts of an integrally molded member. If a large number of lens
holders and a large number of wire holders are prepared
independently of each other, the differences in the holders of each
type and the combinations between the two types of holders have to
be taken into account at the time of assembly. For this purpose,
the holders of each type must be managed by attaching a model
number to each of them. In addition, the molds must be maintained
by parting grinding (particle grinding), and articles produced by
them inevitably vary in precision before and after the maintenance.
Further, articles or members to be assembled cannot be always set
on a jig with the same precision. These problems can be solved by
the present invention. According to the present invention, the
wires 6 are employed in pairs, and the wires of each pair are
prepared as parts of an integrally molded member 39 in the state
where the wires 6 are suspended by the wire holding frame 38. Owing
to this structure, damage to the wires or other members is
prevented, and the problems at the time of positioning can be
solved.
[0149] (6) A description will now be given as to how yokes 18 and
19 and magnets 15 and 16 are assembled.
[0150] As shown in FIG. 9, the yokes 18 and 19 are formed by
bending parts of the chassis 17. Magnets 15 and 16 are pasted on
the surfaces of the yokes 15 and 16, beforehand.
[0151] The chassis 17, having the yokes and magnets described
above, is placed at the predetermined position on a jig (not
shown). This jig has a pair of guide poles for positioning the wire
holder 4. The chassis 17 is carefully positioned by inserting the
guide poles into the reference holes 26 (FIG. 1) of the wire holder
4. To make the unnecessary play minimal, the guide poles and the
reference holes 16 are formed in such a manner that they can be set
in a so-called "transitional-fit state."
[0152] According to this embodiment, the wire holder 4 and the lens
holder 3 are positioned at the accuracy determined by the mold.
Therefore, the lens holder 3, the yokes 18 and 19, and the magnets
15 and 16 are positioned at the predetermined accuracy by merely
positioning the wire holder 4 with reference to the chassis 17.
After being positioned, the wire holder 4 is firmly fixed to the
chassis 17 at least two positions by use of UV-setting
adhesive.
[0153] (7) After the objective lens driving apparatus is assembled
with reference to the chassis 17 in the manner described above, an
actuator cover 58 is attached to the resultant structure, as shown
in FIG. 10. As can be seen from FIG. 10, the actuator cover 58
covers those portions of the objective lens driving apparatus 1
which are opposed to the optical disk. The actuator cover 58 serves
to protect the objective lens driving apparatus 1 from the wind
pressure or dust caused by the rotation of the optical disk.
[0154] The actuator cover 58 is attached to the chassis 17 by
engagement between stopper holes 59 formed in the actuator cover 58
and stopper projections 60 formed on the side walls of the chassis
17.
[0155] The actuator cover 58 is a light-in-weight magnetic member.
It is attracted and firmly coupled to the chassis 17 by the
attraction force of the magnets 15 and 16. To be more specific, the
actuator cover 58 is in contact with the top faces of the four
yokes 18 and 19 and is held on the top faces in the magnetically
attracted state. Since the magnets 15 and 16 are not projected from
the top faces of the yokes 18 and 19, they do not collide with the
actuator cover 58.
[0156] With the above structure, the actuator cover 58 can be held
at four positions, and vibration due to the resonance of the servo
system can be suppressed. In addition, since the actuator cover is
made of a magnetic member, it enables formation of a closed
magnetic path. Accordingly, a powerful magnetic force can be
utilized for driving the lens holder.
[0157] In the engaged state between the stopper holes 59 and the
stopper projections 60, there is a slight gap in the focusing
direction. The actuator cover 58 is provided with
disengagement-preventing sections 61, by which the actuator cover
58 is prevented from disengaging from the chassis 17.
[0158] (8) Before the actuator cover 58 is attached to the chassis
17, the objective lens 2 and a dichroic filter 56 (which is
indicated by "63" in FIG. 11) are provided. The dichroic filter 56
includes a transmission filter that has waveband-selection
characteristics for DVD/CD systems. By means of the dichroic filter
56, a laser beam is shaped so that a suitable beam spot is formed
on a CD.
[0159] As shown in FIG. 12, a flexible printed wiring board 64 for
connection to an external circuit is secured to the rear end faces
of the swinging sections 22 of the wire holder 4. The flexible
printed wiring board 64 is arranged such that it bridges the region
between the swinging sections 22. In order to allow the swinging
sections 22 to operate independently of each other, the board's
middle portion as viewed in the tracking direction (i.e., the
portion located between the two swinging sections 22) has a reduced
width. To allow the wire holder 4 to move without restrictions, a
slit 66 is formed in the board's middle portion as viewed in the
focusing direction. Four projection pieces 67 (FIG. 1) extended
from the pads at the rear ends of the wires 6 are soldered to the
hands of the flexible printed wiring board 64.
[0160] (9) By following the steps described above, the objective
lens driving apparatus according to one embodiment of the present
invention is completed.
[0161] As shown in FIG. 9, a stepped section 17a is formed in the
reverse side of the chassis 17, in such a manner that the chassis
17 is lower in level in the portion where the wire holder 4 is
arranged than in the portion where the lens holder 3 is
arranged.
[0162] With this structure, the wire holder 4 located away from the
objective lens 2 can be arranged in the depressed portion of the
chassis 17. Owing to this, the tilt angle of the objective lens 2
can be adjusted in the tangential direction with a high degree of
freedom.
[0163] The structure described in the preceding paragraph is
advantageous in that the movable range of the lens holder can be as
wide as possible, and this advantage can be obtained without an
increase in the thickness of the objective lens driving
apparatus.
[0164] (Structure of the Entire Optical Head Apparatus)
[0165] FIG. 13 shows part of an optical head apparatus (which
includes an objective lens driving apparatus) and an optical disk
apparatus.
[0166] Referring to FIG. 13, numeral 70 denotes a base. on this
base 70, a first optical module 71 and a second optical module 72
are mounted. The first optical module 71 is a module for a compact
disk (CD), while the second optical module 72 is a module for a
digital video disk (DVD).
[0167] The optical modules 71 and 72 emit a laser beam in
accordance with signals supplied thereto from a controller 73. The
laser beam travels by way of a first prism 74 (i.e., a
waveband-selection reflecting means) and a second prism 75 and
enters the objective lens 2 of the objective lens driving
apparatus. The laser beam emerging from the objective lens 2 forms
a beam spot on an optical disk (not shown).
[0168] The laser beam reflected by the optical disk travels back to
the optical modules 71 and 72 along the same routes of the emitted
beam but in the opposite direction. In accordance with the
intensity level of the reflected laser beam, the optical modules 71
and 72 output an electric signal. The base 70 is provided with a
feed mechanism 78. By this feed mechanism 7I, the base 70 is
advanced or retreated in the radial direction of the optical
disk.
[0169] According to the present embodiment, the second optical
module 72 for DVD is arranged slantwise with reference to the
radial direction of the optical disk. To be more specific, the
first optical module 71 for CD (wherein the optical path is
comparatively short) is arranged at right angles to the feed
direction of the feed mechanism 78. The second optical module 72
for DVD, which is considerably large in comparison with the first
optical module 71, is arranged in the back region in such a manner
that optical axis of the light beam emitted from the second optical
module 72 is parallel to the inner wall of the casing of the
optical disk apparatus (not shown). With this structure, the
apparatus as a whole is compact in size.
[0170] FIG. 14 illustrates an optical disk apparatus incorporating
an optical head apparatus and used for recording/reproducing video
data and sound data with reference an optical disk. Referring to
FIG. 14, numeral 133 denotes an optical disk. The optical disk 133
is rotated by a disk motor 134.
[0171] An optical head apparatus 135, the structure of which was
described above, is opposed to the signal-recorded side of the
optical disk 133. From the optical head apparatus 135, a laser beam
is radiated to the signal-recorded side of the optical disk 133, so
as to write data in the optical disk 133 or read data therefrom.
The optical head apparatus 135 is supported in such a manner as to
be movable in the radial direction of the optical disk 133.
[0172] First, a description will be given of the reproducing
operation. Data that are read from the optical disk 133 by the
optical head apparatus 135 are supplied to a
modulation/demodulation/error correction section 136. This section
136 performs both demodulation processing and error correction
processing with respect to the data supplied from optical head
apparatus 135, by use of a track buffer memory 137.
[0173] Of the data output from the modulation/ demodulation/error
correction section 136, video data is supplied to an MPEG (Moving
Picture Image Coding Experts Group) encoder/decoder 138. This MPEG
encoder/decoder 138 performs MPEG decode processing with respect to
the video data supplied from the modulation/demodulation/error
correction section 136, by use of a frame memory 139.
[0174] The video data output from the MPEG encoder/ decoder 138 is
supplied to a video encoder/decoder 140, for video decode
processing. The video data subjected to the video decode processing
is produced from output terminal 141. Sound data, included in the
data output from the modulation/demodulation/error correction
section 136, are supplied to an audio encoder/decoder 142. After
being subjected to audio decode processing, the sound data are
produced from output terminal 143.
[0175] Next, a description will be given of the recording
operation. Video data supplied to input terminal 144 are first
supplied to the video encoder/decoder 140. After being subjected to
video encode processing, the video data are supplied to the MPEG
encoder/decoder 138. This MPEG encoder/decoder 138 performs MPEG
encode processing with respect to the video data supplied from the
video encoder/decoder 140, by use of the frame memory 139.
[0176] Sound data supplied to input terminal 145 are first supplied
to the audio encoder/decoder 142, for audio encode processing. The
video data output from the MPEG encoder/decoder 138 and the sound
data output from the audio encoder/decoder 14 are supplied to the
modulation/demodulation/- error correction section 136.
[0177] The modulation/demodulation/error correction section 136
performs modulation processing and error code attaching processing
with respect to the supplied image data and the sound data, by use
of the track buffer memory 137. The data output from the
modulation/demodulation/error correction section 136 are recorded
in the optical disk 133 by the optical head 135.
[0178] The disk motor 134, the modulation/demodulation/ error
correction section 136 and the MPEG encoder 142 are controlled by
an MPU (Micro Processing Unit) 146.
[0179] Although one embodiment of the present invention has been
described above, the present invention is in no way limited to that
embodiment and can be modified in a variety of manners, without
departing from the spirit and scope of the present invention.
[0180] For example, in the above embodiment, two swinging sections
22 are provided for the wire holder 4. In place of this structure,
a single swinging section 22 may be provided on one side of the
wire holder 4. Since, in this case, the wire holder 4 is secured on
the side where the swinging section is not provided, improvements
on the tilt angle characteristics can be expected.
[0181] In the above embodiment, the holders 3 and 4 are prepared as
parts of an integrally molded member, and the wires 6 are also
prepared in the same way. However, the present invention covers the
case where only the wires 6 are prepared as parts of integrally
molded members.
[0182] In the above embodiment, the swinging sections 22 are held
by thin members 21 that are integrally formed with the wire holder
4. The thin members 21 may be replaced with metallic leaf spring
members.
[0183] In the above embodiment, the actuator cover 58 is held by
means of the yokes 18 and 19. This holding structure may be
replaced with any type of structure as long as the actuator cover
58 is supported at four positions or more. In addition, the
actuator cover 58 need not be a magnetic member. Even if it is made
of a nonmagnetic member, the intended function can be attained as
long as the surface opposed to the optical disk is held at four
positions or more.
[0184] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *