U.S. patent application number 11/092937 was filed with the patent office on 2005-11-10 for optical pickup and disc drive device.
This patent application is currently assigned to Sony Corporation. Invention is credited to Hanaoka, Atsuhiro, Horiguchi, Muneyuki, Ohkuma, Hideo.
Application Number | 20050249054 11/092937 |
Document ID | / |
Family ID | 35239308 |
Filed Date | 2005-11-10 |
United States Patent
Application |
20050249054 |
Kind Code |
A1 |
Ohkuma, Hideo ; et
al. |
November 10, 2005 |
Optical pickup and disc drive device
Abstract
An objective lens driving device is to be improved in
sensitivity and reduced in size and thickness. To this end, an
objective lens driving device includes a stationary block arranged
on a stationary plate provided on a movable base, a movable block
holding an objective lens and moved along the focusing direction,
the tracking direction and the tilt direction, support springs for
supporting the movable block with respect to the stationary block,
a first magnetic circuit for causing movement of the movable block
along the focusing direction and along the tracking direction, and
a second magnetic circuit for causing movement of the movable block
along the tilt direction. The second magnetic circuit includes a
pair of tilt magnets, each having two poles so that N poles and S
poles lie along the tangential direction, and a pair of tilt coils
facing the tilt magnets and each having an axis of winding wire
direction along the tangential direction. The tilt magnets and the
tilt coils are mounted to the movable block and the stationary
block, respectively. An objective lens and the second magnetic
circuit are arranged on the opposite sides along the tangential
direction with the first magnetic circuit in-between.
Inventors: |
Ohkuma, Hideo; (Tokyo,
JP) ; Horiguchi, Muneyuki; (Saitama, JP) ;
Hanaoka, Atsuhiro; (Tokyo, JP) |
Correspondence
Address: |
RADER FISHMAN & GRAUER PLLC
LION BUILDING
1233 20TH STREET N.W., SUITE 501
WASHINGTON
DC
20036
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
35239308 |
Appl. No.: |
11/092937 |
Filed: |
March 30, 2005 |
Current U.S.
Class: |
369/44.11 ;
G9B/7.065; G9B/7.084; G9B/7.085 |
Current CPC
Class: |
G11B 7/0933 20130101;
G11B 7/0935 20130101; G11B 7/0956 20130101 |
Class at
Publication: |
369/044.11 |
International
Class: |
A47C 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2004 |
JP |
P2004-117647 |
Claims
1. An optical pickup having a movable base moved along the radial
direction of a disc-shaped recording medium loaded on a disc table;
and an objective lens driving device arranged on said movable base,
wherein the objective lens driving device comprises: a stationary
plate provided on said movable base; a stationary block arranged on
said stationary plate and secured to said movable base; a movable
block holding said objective lens and operated relative to said
stationary block along a focusing direction, which is a direction
towards and away from a recording surface of the disc-shaped
recording medium, along a tracking direction, which is a radial
direction of said disc-shaped recording medium, and along a tilt
direction, which is a direction about an axis extending along the
tangential direction perpendicular to the radial direction of the
disc-shaped recording medium; a plurality of support springs for
movably supporting said movable block relative to said stationary
block; a first magnetic circuit for causing movement of said
movable block along said focusing direction or along said tracking
direction; and a second magnetic circuit for causing movement of
said movable block along said tilt direction; said second magnetic
circuit including a pair of tilt magnets each magnetized to two
poles so that N and S poles are arranged along the focusing
direction, said paired tilt magnets being spaced apart from each
other along said radial direction, and a pair of tilt coils
arranged facing said paired tilt magnets, each of said tilt coils
having an axis of winding wire direction corresponding to the
tangential direction; said paired tilt magnets being provided to
said movable block; said paired tilt coils being provided to said
stationary block; and said objective lens and the second magnetic
circuit being located on both sides of said first magnetic circuit
along the tangential direction.
2. The optical pickup according to claim 1, wherein there is
provided a tilt yoke by bending a portion of said stationary plate
on the opposite side of said tilt magnet along the tangential
direction with said tilt coil in-between.
3. The optical pickup according to claim 1, wherein a back yoke is
provided on the surface of said tilt magnet opposite to the surface
thereof facing said tilt coil.
4. An optical pickup having a movable base moved along the radial
direction of a disc-shaped recording medium loaded on a disc table
and an objective lens driving device arranged on said movable base,
wherein said objective lens driving device comprises: a stationary
block secured to said movable base; a movable block holding said
objective lens and operated relative to said stationary block along
a focusing direction, which is a direction towards and away from a
recording surface of the disc-shaped recording medium, along a
tracking direction, which is a radial direction of said disc-shaped
recording medium, and along a tilt direction, which is a direction
about an axis extending along the tangential direction
perpendicular to the radial direction of the disc-shaped recording
medium; a plurality of support springs for movably supporting said
movable block relative to said stationary block; a first magnetic
circuit for causing movement of said movable block along said
focusing direction or along said tracking direction; and a second
magnetic circuit for causing movement of said movable block along
said tilt direction; said second magnetic circuit including a pair
of tilt magnets each magnetized to two poles so that N and S poles
are arranged along the focusing direction, said paired tilt magnets
being spaced apart from each other along said radial direction, and
a pair of tilt coils arranged facing said paired tilt magnets, each
of said tilt coils having an axis of winding wire direction
corresponding to the tangential direction; said paired tilt magnets
being provided to said movable block; said paired tilt coils being
provided to said stationary block; and a back yoke being arranged
on the surface of said tilt magnet opposite to the surface thereof
facing said tilt coil.
5. A disc drive device comprising a disc table for loading a
disc-shaped recording medium thereon and an optical pickup for
radiating laser light via an objective lens to the disc-shaped
recording medium loaded on said disc table, said optical pickup
including a movable base moved along the radial direction of a
disc-shaped recording medium loaded on a disc table, and an
objective lens driving device arranged on said movable base,
wherein said objective lens driving device comprises: a stationary
plate provided on said movable base; a stationary block arranged on
said stationary plate and secured to said movable base; a movable
block for holding said objective lens and operated relative to said
stationary block along a focusing direction, which is a direction
towards and away from a recording surface of the disc-shaped
recording medium, along a tracking direction, which is a radial
direction of said disc-shaped recording medium, and along a tilt
direction, which is a direction about an axis extending along the
tangential direction perpendicular to the radial direction of the
disc-shaped recording medium; a plurality of support springs for
movably supporting said movable block relative to said stationary
block; a first magnetic circuit for causing movement of said
movable block along said focusing direction or along said tracking
direction; and a second magnetic circuit for causing movement of
said movable block along said tilt direction; said second magnetic
circuit including a pair of tilt magnets each magnetized to two
poles so that N and S poles are arranged along the focusing
direction, said paired tilt magnets being spaced apart from each
other along said radial direction, and a pair of tilt coils
arranged facing said paired tilt magnets, each of said tilt coils
having an axis of winding wire direction corresponding to the
tangential direction; said paired tilt magnets being provided to
said movable block; said paired tilt coils being provided to said
stationary block; and said objective lens and the second magnetic
circuit being located on both sides of said first magnetic circuit
along the tangential direction.
6. The disc drive device according to claim 4, wherein there is
provided a tilt yoke by bending a portion of said stationary plate
on the opposite side of said tilt magnet along the tangential
direction with said tilt coil in-between.
7. The disc drive device according to claim 4, wherein a back yoke
is provided on the surface of said tilt magnet opposite to the
surface thereof facing said tilt coil.
8. A disc drive device comprising a disc table for loading a
disc-shaped recording medium thereon and an optical pickup for
radiating laser light via an objective lens to the disc-shaped
recording medium loaded on said disc table, said optical pickup
including a movable base moved along the radial direction of a
disc-shaped recording medium loaded on a disc table and an
objective lens driving device arranged on said movable base wherein
said objective lens driving device comprises: a stationary block
secured to said movable base; a movable block holding said
objective lens and operated relative to said stationary block along
a focusing direction, which is a direction towards and away from a
recording surface of the disc-shaped recording medium, along a
tracking direction, which is a radial direction of said disc-shaped
recording medium, and along a tilt direction, which is a direction
about an axis extending along the tangential direction
perpendicular to the radial direction of the disc-shaped recording
medium; a plurality of support springs for movably supporting said
movable block relative to said stationary block; a first magnetic
circuit for causing movement of said movable block along said
focusing direction or along said tracking direction; and a second
magnetic circuit for causing movement of said movable block along
said tilt direction; said second magnetic circuit including a pair
of tilt magnets each magnetized to two poles so that N and S poles
are arranged along the focusing direction, said paired tilt magnets
being spaced apart from each other along said radial direction, and
a pair of tilt coils arranged facing said paired tilt magnets, each
of said tilt coils having an axis of winding wire direction
corresponding to the tangential direction; said paired tilt magnets
being provided to said movable block; said paired tilt coils being
provided to said stationary block; and a back yoke being provided
on the surface of said tilt magnet opposite to the surface thereof
facing said tilt coil.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2004-117647 filed in the Japanese
Patent Office on Apr. 13, 2004, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an optical pickup and a disc drive
device. More particularly, it relates to an optical pickup having a
driving device for an objective lens in which a movable block is
moved in the three directions of focusing, tracking and tilt with
respect to a stationary block and to a disc drive device having the
optical pickup.
[0004] 2. Description of Related Art
[0005] The disc drive device records and/or reproduces information
signals for a disc-shaped recording medium, such as an optical
disc. This disc drive device is provided with an optical pickup
that is moved radially of the disc-shaped recording medium for
illuminating laser light thereon.
[0006] The optical pickup is provided with an objective lens
driving device, and by this objective lens driving device, the
objective lens held by the movable block is moved along the
focusing direction or is moved along the tracking direction, in
order to condense the spot of the laser light illuminated via the
objective lens on the disc-shaped recording medium on a recoding
track thereof. The focusing direction is the direction along which
the objective lens held by the movable block of the objective lens
driving device is moved towards and away from the recording surface
of the disc-shaped recording medium by way of a focusing
adjustment, and the tracking direction is substantially the radial
direction of the disc-shaped recording medium along which the
objective lens is moved for tracking adjustment.
[0007] The practice in the optical pickup has been to effect
focusing adjustment and tracking adjustment by the objective lens
driving device. Recently, there has been developed an objective
lens driving device, also called a tri-axial actuator, which
enables an adjustment for surface plane deviation of the rotating
disc-shaped recording medium by allowing a movable block to be
tilted relative to the recording surface of the disc-shaped
recording medium in addition to a biaxial adjustment of a focusing
adjustment and a tracking adjustment, for improving the follow-up
characteristics of the laser light spot with respect to the
recording track. Thus, with the objective lens driving device,
called a tri-axial actuator, the movable block is moved along the
focusing direction, the tracking direction and a tilt direction
which is a direction about an axis extending along the tangential
direction perpendicular to the radial direction of the disc-shaped
recording medium.
[0008] As the objective lens driving device, called the tri-axial
actuator, the following type devices have been developed so
far.
[0009] For example, a movable block holding an objective lens is
movably carried on a stationary block via a support spring, a tilt
coil for tilting the movable block relative to the stationary block
is provided to the movable block, and a tilt magnet positioned
facing the tilt coil is provided to the stationary block. The
device type in which the tilt coil is provided to the movable block
is termed a moving-coil-type device.
[0010] With the moving-coil-type objective lens driving device, two
support springs each are needed for supplying driving currents to
the focusing coils for focusing adjustment, the tracking coils for
tracking adjustment and the tilt coil for tilt adjustment provided
to the movable block side, such that the movable block is carried
by the stationary block with a sum total of six support
springs.
[0011] On the other hand, with a tri-axial actuator, which is of
the type different from the moving-coil-type device, the movable
block holding the objective lens is movably supported by the
stationary block via support springs, while a tilt coil for tilting
the movable block relative to the stationary block is provided to
the stationary block, and a tilt magnet positioned facing the tilt
coil is provided to the movable block (see, for example, the Patent
Publication 1 (Japanese Laid-Open Patent Publication 2000-222755)).
The device type in which the tilt magnet is provided to the movable
block is called a moving-magnet-type device.
[0012] With the moving-magnet-type objective lens driving device,
in which the tilt magnet is provided to the movable block, the
weight of the movable block becomes larger than that of the
moving-coil-type device. However, the moving-magnet-type device
does not need a support spring for supplying the driving current to
the tilt coil and hence is meritorious when compared to the
moving-coil-type device, in that the number of component parts may
be reduced and in that the assembly operation can be
facilitated.
SUMMARY OF THE INVENTION
[0013] Problems to be Solved by the Invention
[0014] With the objective lens driving device described in patent
Publication 1, the tilt magnet provided to the movable block has a
single N pole and a single S pole, while the tilt coil provided to
the stationary block has the winding core direction corresponding
to the focusing direction, and hence the movable block is moved
along the tilt direction under cooperation between the driving
current flowing in about one-fourth part of the tilt coil wound in
the from of a square tube and the magnetic flux of the magnet.
Consequently, the portion of the tilt coil used for tilt adjustment
is small, and hence the device may be lowered in sensitivity.
[0015] For combating the decrease in sensitivity, it becomes
necessary to use a magnet of a high magnetic force or to supply a
large driving current to the tilt coil. However, this raises the
manufacturing cost or power consumption of the objective lens
driving device.
[0016] Moreover, should the tilt coil be arranged so that the
winding core direction corresponds to the focusing direction, the
space in which to mount the tilt coil along the tangential
direction is correspondingly increased and the objective lens
driving device is increased in size along the tangential direction
in a manner deterrent to size reduction. In addition, the
supporting state of the movable block tends to be unstable.
[0017] With the objective lens driving device, the laser light
radiated from a light source is conducted to the objective lens via
an uplift mirror arranged on the opposite side of the disc-shaped
recording medium with the movable block in-between. If in such case
a magnetic circuit formed by, for example, a coil or a magnet is
arranged about the objective lens, the optical path of the laser
light radiated from the light source so as to be incident on the
uplift mirror needs to be provided below the magnetic circuit, with
the result that the objective lens driving device is increased in
thickness, contrary to the demand for reducing its thickness. In
particular, in an optical pickup provided to a device for a mobile
phone, in which there is raised a high demand for a reduction in
thickness, deterrence of the reduction in thickness is a major
problem.
[0018] To overcome the above problem, it is desirable to provide an
objective lens driving device that may be improved in sensitivity
and reduced in size and thickness.
[0019] Means to Solve the Problem
[0020] For accomplishing the above problem, the present invention
provides an optical pickup and a disc drive device in which an
objective lens driving device includes a stationary plate provided
on the movable base; a stationary block arranged on the stationary
plate and secured to the movable base; a movable block for holding
the objective lens and operated relative to the stationary block
along a focusing direction, which is a direction towards and away
from a recording surface of the disc-shaped recording medium, along
a tracking direction, which is a radial direction of the
disc-shaped recording medium, and along a tilt direction which is a
direction about an axis extending along the tangential direction
perpendicular to the radial direction of the disc-shaped recording
medium; a plurality of support springs for movably supporting the
movable block relative to the stationary block; a first magnetic
circuit for causing movement of the movable block along the
focusing direction or along the tracking direction; and a second
magnetic circuit for causing movement of the movable block along
the tilt direction. The second magnetic circuit includes a pair of
tilt magnets each magnetized to two poles so that N and S poles are
arranged along the focusing direction. The paired tilt magnets are
spaced apart from each other along the radial direction. The second
magnetic circuit also includes a pair of tilt coils arranged facing
the paired tilt magnets, with each of the tilt coils having an axis
of the winding wire direction corresponding to the tangential
direction. The paired tilt magnets are provided to the movable
block, the paired tilt coils are provided to the stationary block,
while the objective lens and the second magnetic circuit are
located on both sides of the first magnetic circuit along the
tangential direction.
[0021] Hence, with the optical pickup and the disc drive device,
according to the present invention, the portion of the tilt coil
usable for tilt adjustment may be increased.
[0022] The present invention also provides an optical pickup
including a movable base moved along the radial direction of a
disc-shaped recording medium loaded on a disc table and an
objective lens driving device arranged on the movable base. The
objective lens driving device comprises a stationary plate provided
on the movable base; a stationary block arranged on the stationary
plate and secured to the movable base; a movable block for holding
the objective lens operated relative to the stationary block along
a focusing direction, which is a direction towards and away from a
recording surface of the disc-shaped recording medium, along a
tracking direction, which is a radial direction of the disc-shaped
recording medium, and along a tilt direction, which is a direction
about an axis extending along the tangential direction
perpendicular to the radial direction of the disc-shaped recording
medium; a plurality of support springs for movably supporting the
movable block relative to the stationary block; a first magnetic
circuit for causing movement of the movable block along the
focusing direction or along the tracking direction; and a second
magnetic circuit for causing movement of the movable block along
the tilt direction. The second magnetic circuit includes a pair of
tilt magnets each magnetized to two poles so that N and S poles are
arranged along the focusing direction. The paired tilt magnets are
spaced apart from each other along the radial direction. The second
magnetic circuit also includes a pair of tilt coils arranged facing
the paired tilt magnets and each having an axis of the winding wire
direction corresponding to the tangential direction. The paired
tilt magnets are provided to the movable block, while the paired
tilt coils are provided to the stationary block. The objective lens
and the second magnetic circuit are located on both sides of the
first magnetic circuit along the tangential direction.
[0023] Since the tilt coils are arranged with the winding core
direction extending along the tangential direction, the portion of
the tilt coils usable for generating the force of thrust in the
movable block along the tilt direction may be increased to improve
the sensitivity of the movable block at the time of tilt
adjustment.
[0024] Moreover, since the movable block may be improved in
sensitivity, it is unnecessary to use the magnet with a stronger
magnetic force, while the driving current supplied to the tilt
coils may be smaller, with the result that the power consumption as
well as the manufacture costs of the objective lens driving device
may be lowered.
[0025] Additionally, since the winding core direction of the tilt
coils is not the focusing direction, the tilt coil mounting space
along the tangential direction may be smaller, and hence the size
of the objective lens driving device along the tangential direction
may be reduced.
[0026] Since the objective lens and the second magnetic circuit are
arranged on opposite sides along the tangential direction with the
first magnetic circuit in-between, the uplift mirror may be
provided at the same height level as the first magnetic circuit,
and hence the objective lens driving device may be correspondingly
reduced in thickness. This reduction in thickness is particularly
desirable in an optical pickup used for mobile equipment.
[0027] Furthermore, since the tilt magnets and the tilt coils are
provided to the movable block and to the stationary block,
respectively, the support springs for supplying the current to the
tilt coils may be dispensed with, thereby reducing the number of
component parts and simplifying the assembling performance of the
objective lens driving device.
[0028] Since there is provided a tilt yoke by bending a portion of
the stationary plate on the opposite side of the tilt magnet along
the tangential direction with the tilt coil in-between, there is no
need to provide dedicated separate tilt yokes, while the portion
for securing the stationary block and the tilt yokes may be used in
common, thus reducing the number of component parts. Since a back
yoke is provided on the surface of the tilt magnet opposite to the
surface thereof facing the tilt coil, it is possible to improve the
sensitivity of the movable block at the time of tilt
adjustment.
[0029] Additionally, the stray magnetic flux from the tilt magnets
may be reduced, and the second magnetic circuit does not tend to be
affected by the first magnetic circuit, while the movable block may
be prevented from being tilted relative to the stationary block
under the effect of the stray magnetic flux.
[0030] The present invention also provides a disc drive device
comprising a disc table for loading a disc-shaped recording medium
thereon and an optical pickup for radiating laser light via an
objective lens to the disc-shaped recording medium loaded on the
disc table. The optical pickup includes a movable base, moved along
the radial direction of a disc-shaped recording medium, and loaded
on a disc table, and an objective lens driving device arranged on
the movable base. The objective lens driving device includes a
stationary plate provided on the movable base; a stationary block
arranged on the stationary plate and secured to the movable base;
and a movable block for holding the objective lens and operated
relative to the stationary block along a focusing direction, which
is a direction towards and away from a recording surface of the
disc-shaped recording medium, along a tracking direction, which is
a radial direction of the disc-shaped recording medium, and along a
tilt direction, which is a direction about an axis extending along
the tangential direction perpendicular to the radial direction of
the disc-shaped recording medium. The objective lens driving device
includes a plurality of support springs for movably supporting the
movable block relative to the stationary block, a first magnetic
circuit for causing movement of the movable block along the
focusing direction or along the tracking direction, and a second
magnetic circuit for causing movement of the movable block along
the tilt direction. The second magnetic circuit includes a pair of
tilt magnets each magnetized to two poles so that N and S poles are
arranged along the focusing direction, with the paired tilt magnets
being spaced apart from each other along the radial direction. The
second magnetic circuit also includes a pair of tilt coils arranged
facing the paired tilt magnets, each of the tilt coils having an
axis of the winding wire direction corresponding to the tangential
direction. The paired tilt magnets are provided to the movable
block, and the paired tilt coils are provided to the stationary
block. The objective lens and the second magnetic circuit are
located on both sides of the first magnetic circuit along the
tangential direction.
[0031] Since the tilt coils are arranged with the winding core
direction corresponding to the tangential direction, the portion of
the tilt coils usable for generating the force of thrust in the
movable block along the tilt direction is larger, thus improving
the sensitivity of the movable block at the time of tilt
adjustment.
[0032] Moreover, since the movable block may be improved in
sensitivity, it is unnecessary to use the magnet with a stronger
magnetic force, while the driving current supplied to the tilt
coils may be reduced, with the result that the power consumption as
well as the manufacturing costs of the objective lens driving
device may be lowered.
[0033] Additionally, since the winding core direction of the tilt
coils is not the focusing direction, the tilt coil mounting space
along the tangential direction may be smaller, and hence the size
of the objective lens driving device along the tangential direction
may be reduced.
[0034] Since the objective lens and the second magnetic circuit are
arranged on opposite sides along the tangential direction with the
first magnetic circuit in-between, the uplift mirror may be
provided at the same height level as the first magnetic circuit,
and hence the objective lens driving device may be correspondingly
reduced in thickness. This reduction in thickness is particularly
desirable in an optical pickup used for mobile equipment.
[0035] In addition, since the tilt magnets and the tilt coils are
provided to the movable block and the stationary block,
respectively, the support springs for supplying the current to the
tilt coils may be dispensed with, thereby reducing the number of
component parts and simplifying the assembling performance of the
objective lens driving device.
[0036] Since a tilt yoke is provided by bending a portion of the
stationary plate on the opposite side of the tilt magnet along the
tangential direction with the tilt coil in-between, there is no
need to provide dedicated separate tilt yokes, while the portion
for securing the stationary block and the tilt yokes may be used in
common, thus reducing the number of component parts.
[0037] Since a back yoke is provided on the surface of the tilt
magnet opposite to the surface thereof facing the tilt coil, it is
possible to improve the sensitivity of the movable block at the
time of tilt adjustment.
[0038] Additonally, the stray magnetic flux from the tilt magnets
may be reduced, and the second magnetic circuit is not liable to be
affected by the first magnetic circuit, while the movable block may
be prevented from being tilted relative to the stationary block
under the effect of the stray magnetic flux.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 shows, in conjunction with FIGS. 2 and 12, the best
mode of carrying out the present invention and, specifically, is a
schematic cross-sectional view of a disc drive device of the
present invention.
[0040] FIG. 2 is a partially-exploded, enlarged perspective view
showing a portion of an objective lens driving device.
[0041] FIG. 3 is an enlarged perspective view of the objective lens
driving device.
[0042] FIG. 4 is an enlarged perspective view showing the objective
lens driving device from which a power feed base plate has been
detached.
[0043] FIG. 5 is an enlarged perspective view showing the objective
lens driving device, as viewed from a direction different from the
viewing direction of FIG. 3.
[0044] FIG. 6 is an enlarged exploded perspective view showing a
stationary block.
[0045] FIG. 7 is an enlarged perspective view showing the objective
lens driving device, as viewed from a direction different from the
viewing directions of FIGS. 3 and 5, with a portion thereof being
removed.
[0046] FIG. 8 is an enlarged perspective view showing a first
magnetic circuit and a second magnetic circuit.
[0047] FIG. 9 is a schematic enlarged side view showing an
objective lens driving device.
[0048] FIG. 10 is a schematic view showing the direction of the
magnetic force in the case where there is provided no back
yoke.
[0049] FIG. 11 is a schematic view for illustrating the operation
which may occur in the case where there is provided no back
yoke.
[0050] FIG. 12 is a schematic view showing the direction of the
magnetic force in the case where there is provided a back yoke.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] The best mode of an optical pickup and a disc drive device
according to the present invention is now explained with reference
to the drawings.
[0052] The disc drive device 1 includes respective components and
units in an outer casing 2, as shown in FIG. 1. In the outer casing
is formed a disc entrance opening, not shown. Within the outer
casing 2, there is mounted a chassis, not shown. A disc table 3 is
secured to a motor shaft of a spindle motor mounted on the
chassis.
[0053] On the chassis, there are mounted guide shafts 4, 4 for
extending parallel to each other and a lead screw 5 rotated by a
feed screw, not shown.
[0054] An optical pickup 6 includes a movable base 7, optical
components provided on the movable base 7, and an objective lens
driving device 8 arranged on the movable base 7. The ends of the
movable base 7 are fitted with bearings 7a, 7b, which are slidably
supported by the guide shafts 4, 4.
[0055] A nut member, not shown, is provided on the movable base 7.
When the lead screw 5 is rotated by a feed motor, the nut member is
fed in a direction consistent with the direction of rotation of the
lead screw 5, such that the optical pickup 6 is moved along the
radial direction of a disc-shaped recording medium 100 that is to
be loaded on the disc table 3.
[0056] The objective lens driving device 8 includes a base member
9, a stationary plate 10, a stationary block 11 and a movable block
12 operated relative to the stationary block 11 (see FIGS. 2 and
3).
[0057] The base member 9 is formed of, for example, SPCC (cold
rolled stainless steel sheet) or a silicon steel sheet and, as
shown in FIG. 2, made up by a base part 9a secured to the movable
base 7 and yoke parts 9b, 9b bent from the base part 9a
perpendicularly thereto. The yoke parts 9b, 9b are provided spaced
apart from each other in the fore-and-aft direction, that is, in
the tangential direction (TA) of the disc-shaped recording medium
100.
[0058] The surfaces of the yokes 9b, 9b facing each other are
fitted with magnets 13, 13.
[0059] The stationary plate 10 is provided spaced apart along the
tangential direction (towards rear) with respect to the base member
9 and secured to the movable base 7. The stationary plate 10 is
formed by a sheet of a magnetic metal material, for example, SPCC
(cold rolled stainless steel) or a silicon steel and made up by a
plate base 10a secured to the movable base 7 and tilt yokes 10b,
10c, bent from a forward end part of the base plate 10a and spaced
apart from each other along the radial direction (RAD) of the
disc-shaped recording medium 100.
[0060] The stationary block 11 is secured to the plate base 10a of
the stationary plate 10. On the left and right ends of the back
surface of the stationary block 11, there are provided a sum total
of four terminals 11a, 11a, . . . in a vertically-spaced apart
relation relative to each other, as shown in FIGS. 4 and 5.
[0061] The lower end of the stationary block 11 is provided with
terminal pins 11b, 11b protruded towards the rear from the back
surface thereof (see FIG. 4). These terminal pins 11b, 11b are
located spaced apart in the left and right directions.
[0062] On the forward surface of the stationary block 11, there are
formed forwardly protruded positioning lugs 11c, 11c spaced apart
from each other in the left and right directions (see FIG. 6).
[0063] On the rear surface of the stationary block 11 is mounted a
relay substrate 14 (see FIG. 4). The relay substrate 14 is made up
by a basic part 14a and four connecting parts 14b, 14b, . . .
protruded in the left and right directions from the basic part 14a.
The foremost parts of the connecting parts 14b, 14b, . . . of the
relay substrate 14 are connected with, for example, solders 15, 15,
. . . to the terminals 11a, 11a, . . . respectively.
[0064] A pair of tilt coils 16, 16 are mounted to the front surface
of the stationary block 11 on the left and right sides thereof,
that is, the tilt coils are spaced apart along the radial direction
of the disc-shaped recording medium 100 (see FIGS. 3 and 6). These
tilt coils 16, 16 are mounted to the stationary block 11 by being
fitted on positioning lugs 11c, 11c provided on the front surface
of the stationary block 11. Thus, by providing the positioning lugs
11c, 11c to the stationary block 11, the tilt coils 16, 16 may
readily be mounted in position to the stationary block 11.
[0065] The tilt coils 16, 16 are formed substantially to a square
tubular shape with a thin wall thickness and mounted to the
stationary block 11 so that the direction of winding cores thereof
coincides with the fore-and-aft direction, that is, with the
aforementioned tangential direction. The tilt coils 16, 16 are
provided with upper and lower portions 16a, 16a, . . . operating
for generating the force of thrust in the movable block 12 along
the tilt direction. Meanwhile, the tilt direction is the direction
of deviation of the plane of the disc-shaped recording medium 100
from its intended plane (direction indicated by R in FIG. 3), that
is, the direction of rotation of the disc-shaped recording medium
about an axis extending along the tangential direction.
[0066] One end of the tilt coils 16, 16 is mounted by being coiled
about the terminal pins 11b, 11b provided to the back surface of
the stationary block 11 (see FIG. 4).
[0067] To the relay substrate 14 mounted to the back surface of the
stationary block 11, there is fixedly connected a substrate for
power supply 17, connected in turn to a power supply circuit, not
shown (see FIGS. 4 and 5). The substrate for power supply 17 is,
for example, a flexible printed circuit board and includes four
connecting parts (lines) 17a, 17a, . . . and two connecting parts
(lines) 17b, 17b. The connecting lines 17a, 17a, . . . are
connected by, for example, solders 18, 18, . . . to the connecting
lines 14b, 14b, . . . of the relay substrate 14, respectively,
while the connecting lines 17b, 17b are connected by, for example,
solders 19, 19 to one end of the tilt coils 16, 16 mounted to the
terminal pins 11b, 11b. Thus, the driving current for tilt
adjustment is supplied to the tilt coils 16, 16 from a power supply
circuit via connecting lines 17b, 17b of the substrate for power
supply 17.
[0068] In this manner, one end of the tilt coils 16, 16 is coiled
around the terminal pins 11b, 11b, and the one end of the tilt
coils 16, 16 is secured to the connecting lines 17b, 17b by the
solders 19, 19, and hence the substrate for power supply 17 can be
secured to the tilt coils 16, 16 extremely readily, thus
simplifying the operation of connecting the substrate for power
supply 17 to the tilt coils 16, 16 and improving the connection
reliability.
[0069] Towards the forward end of the stationary block 11 are
formed vertically-extending openings for yokes 11d, 11d (see FIGS.
6 and 7) within which are arranged tilt yokes 10b, 10b of the
stationary plate 10 introduced from below. The tilt yokes 10b, 10b
are arranged directly in rear of the tilt coils 16, 16.
[0070] To the terminals 11a, 11a, . . . of the stationary block 11
are attached the rear ends of support springs 20, 20, . . . (see
FIGS. 3 and 4). These support springs 20, 20, . . . are connected
via terminals 11a, 11a, . . . and connecting parts 14b, 14b, . . .
of the relay substrate 14 to the connecting lines 17a, 17a, . . .
of the substrate for power supply 17. The support springs 20, 20, .
. . are protruded forward from the stationary block 11.
[0071] The movable block 12 includes a movable holder 21 and an
objective lens 22 held thereby (see FIGS. 3 to 5).
[0072] The movable holder 21 is formed as one with a lens mounting
unit 23 and a coil holder 24 mounted to the rear side of the lens
mounting unit 23.
[0073] The lens mounting unit 23 is formed with a vertically
extending through-opening 23a (see FIG. 7), and the objective lens
22 is mounted overlying the through-opening 23a.
[0074] The coil holder 24 is formed as a vertically perforated
substantially rectangular frame, and a focusing coil 25 and a pair
of tracking coils 26, 26 are held in the inside of the coil holder
24 formed on perforation.
[0075] The focusing coil 25 is used for causing movement of the
movable block 12 along the focusing direction, that is, in the
direction towards and away from the disc-shaped recording medium
100 (direction F in FIG. 3). The tracking coils 26, 26 are used for
causing movement of the movable block 12 along the tracking
direction, that is, in the direction substantially along the radius
of the disc-shaped recording medium 100 (direction T in FIG.
3).
[0076] The focusing coil 25 and the tracking coils 26, 26 are each
in the form of a substantially square-shaped tube, with the
focusing coil 25 having a winding core extending in the up-and-down
direction (focusing direction), and with the tracking coils 26, 26
having winding cores extending in the fore-and-aft direction
(tangential direction). The tracking coils 26, 26 are provided
spaced apart from each other on the front side of the focusing coil
25.
[0077] The ends of the focusing coil 25 and the tracking coils 26,
26 are connected to connection terminals 21a, 21a, . . . provided
on both lateral sides of the movable holder 21. To the connection
terminals 21a, 21a, . . . are connected forward ends of the support
springs 20, 20, . . . . Hence, the movable block 12 is connected by
the support springs 20, 20, . . . and maintained in the hollow
state.
[0078] If, in the objective lens driving device 8, the movable
block 12 is maintained in the hollow state relative to the
stationary block 11 by the support springs 20, 20, . . . , as
described above, and the movable block 12 is moved in a direction
in which the focusing direction is the up-and-down direction, the
movable block 12 is moved downwards under its own gravity and the
support springs 20, 20, . . . become flexed such that the forward
ends of the support springs 20, 20, . . . are at a lower position
than the rear ends thereof. With the objective lens driving device
8, the position thereof in which the movable block 12 is moved
downwards under its own weight is set as a neutral position along
the focusing direction of the movable block 12. Thus, in the
neutral position along the focusing direction, the center in the
up-and-down direction of tilt magnets 29, 29, that is, the neutral
line M1 between the magnetic poles, coincides with the center M2 in
the up-and-down direction of the tilt coils 16, 16.
[0079] By setting the position of the movable block 12, which has
taken its own gravity into account, as the neutral position thereof
along the focusing direction, variations in tilt characteristics of
the movable block 12 attendant on the focusing movements become
symmetrical in the up-and-down direction, thereby assuring
reliability in the tilt movements of the objective lens driving
device 8.
[0080] Meanwhile, in case the objective lens driving device 8 is
used in a state in which the focusing direction is not the
up-and-down direction, it is sufficient if the position of the
movable block 12 when the driving current supplied to the focusing
coil 25 as the focusing servo is applied to the movable block 12 is
zero is set as the neutral position of the movable block 12 along
the focusing direction.
[0081] The support springs 20, 20, . . . are supplied from a power
supply circuit with driving currents for focusing adjustment or for
tracking adjustment via connecting lines 17a, 17a, . . . of the
substrate for power supply 17 and via connecting parts 14b, 14b, .
. . of the relay substrate 14. Thus, two each of the support
springs 20, 20, . . . operate as power supply members for supplying
power to the focusing coil 25 and the tracking coils 26, 26.
[0082] The forward sides of the focusing coil 25 and both the
forward and rear sides of the tracking coils 26, 26 are associated
with a pair of magnets 13, 13, secured to the yoke parts 9b, 9b
(see FIG. 8). By arranging the magnets 13, 13 in this manner, a
first magnetic circuit 27 for causing movement of the movable block
12 in the focusing direction or in the tracking direction is formed
by the magnets 13, 13, yoke parts 9b, 9b, focusing coil 25 and the
tracking coils 26, 26.
[0083] On the rear side upper surface of the coil holder 24 of the
movable holder 21, there are mounted back yokes 28, 28 and the tilt
magnets 29, 29 in vertically stacked states, with the back yokes
being spaced apart from the magnets in the left and right direction
(see FIGS. 2 and 3). The tilt magnets 29, 29 are magnetized to N
poles 29a, 29a and S poles 29b, 29b separated from the N poles
along the focusing direction, as shown in FIG. 2.
[0084] The tilt magnets 29, 29 are positioned facing the tilt coils
16, 16 mounted on the forward surface of the stationary block 11
(see FIG. 8). With the tilt magnets 29, 29 positioned facing the
tilt coils 16, 16 in this manner, a second magnetic circuit 30 for
causing movement of the movable block 12 along the tilt direction
is formed by the tilt magnets 29, 29, back yokes 28, 28, tilt coils
16, 16 and the tilt yokes 10b, 10b.
[0085] When the driving current is supplied to the focusing coil 25
or to the tracking coils 26, 26 from the power supply circuit
through the substrate for power supply 17, the relay substrate 14
and the support springs 20, 20, . . . , the movable block 12 is
moved in the focusing direction (direction F in FIG. 3) or in the
tracking direction (direction T in FIG. 3), depending on the
relationship between the direction of the driving current and the
direction of the magnetic flux generated in the magnets 13, 13 and
the yoke parts 9b, 9b.
[0086] Moreover, when the driving current is supplied from the
power supply circuit through the substrate for power supply 17 to
the tilt coils 16, 16, the movable block 12 is moved in the tilt
direction (direction R in FIG. 3) by the relationship between the
direction of the driving current and the direction of the magnetic
flux generated in the back yokes 28, 28 and the tilt magnets 29, 29
and the tilt yokes 10b, 10b. It is noted that tilt adjustment is
effected by the movable block 12 being moved along the tilt
direction by the force of thrust generated in opposite directions
(up-and-down direction) on the left and right sides of the movable
block in case the driving current is supplied to the tilt coils 16,
16.
[0087] When the movable block 12 is moved in the focusing
direction, the tracking direction or in the tilt direction, the
support springs 20, 20 are elastically deformed.
[0088] An uplift mirror 31 is arranged below the objective lens 22
mounted to the movable holder 21 (see FIG. 9).
[0089] In the above-described disc drive device 1, if the disc
table 3 is run in rotation with the rotation of a spindle motor,
not shown, the disc-shaped recording medium 100, mounted on the
disc table 3 is run in rotation at the same time as the optical
pickup 6 is moved along the radius of the disc-shaped recording
medium 100, by way of recording and/or reproducing the disc-shaped
recording medium 100.
[0090] If, during this recording and/or reproducing operation, the
driving current is supplied to the focusing coil 25, the movable
block 12 of the objective lens driving device 8 is moved along the
focusing direction F-F in FIG. 3 relative to the stationary block
11, so that the light spot of laser light radiated from a light
source, not shown, and illuminated via objective lens 22 is
condensed substantially vertically, in order to cope with the
warping of the disc-shaped recording medium 100, by way of
performing the focusing adjustment.
[0091] When the driving current is supplied to the tracking coils
26, 26, the movable block 12 of the objective lens driving device 8
is moved along the tracking direction T-T, shown in FIG. 3,
relative to the stationary block 11, so that the light spot of
laser light radiated from the light source and illuminated via the
objective lens 22 is condensed on a recording track of the
disc-shaped recording medium 100, by way of performing the tracking
adjustment.
[0092] When the driving current is supplied to the tilt coils 16,
16, the movable block 12 of the objective lens driving device 8 is
moved along the tilt direction R-R, shown in FIG. 3, with respect
to the stationary block 11, such that the spot of the laser light
radiated from the light source and illuminated via objective lens
22 is condensed on the recording track of the disc-shaped recording
medium 100, by way of performing tilt adjustment.
[0093] With the optical pickup 6, described above, in which there
are provided the tilt magnets 29, 29 having N poles 29a, 29a and S
poles 29b, 29b separated from the N poles along the focusing
direction, and in which the direction of the winding cores of the
tilt coils 16, 16 is the tangential direction, about one-half
portions 16a, 16a, . . . of the entire tilt coils 16, 16 may be
used as portions responsible for producing the force of thrust
along the tilt direction in the movable block 12, thereby improving
the sensitivity of the movable block 12 at the time of tilt
adjustment.
[0094] Since the movable block 12 may be improved in sensitivity,
there is no need to use magnets with correspondingly strong
magnetic force, while there is also no necessity for supplying high
driving current to the tilt coils 16, 16, thereby reducing
manufacturing costs of the objective lens driving device 8 and
power consumption.
[0095] Additionally, since the direction of the winding cores of
the tilt coils 16, 16 is not the focusing direction, a small
mounting space for the tilt coils 16, 16 along the tangential
direction suffices, with the result that the size of the objective
lens driving device along the tangential direction may be
reduced.
[0096] Moreover, with the objective lens driving device 8, in which
the objective lens 22 and the second magnetic circuit 30 for tilt
adjustment are arranged on opposite sides along the tangential
direction of the first magnetic circuit 27 responsible for focusing
adjustment and tracking adjustment, the uplift mirror 31 may be of
the same height level as the first magnetic circuit 27, and hence
the objective lens driving device 8 may correspondingly be reduced
in thickness. This reduction in thickness is particularly suitable
for an optical pickup used for a portable apparatus.
[0097] With the objective lens driving device 8 in which the tilt
magnets 29, 29 are provided to the movable block 12 and the tilt
coils 16, 16 are provided to the stationary block 11, there is no
necessity for providing a support spring for supplying the power to
the tilt coils 16, 16, with the result that the number of component
parts may correspondingly be reduced to simplify the assembly
process for the objective lens driving device 8.
[0098] In addition, with the objective lens driving device 8 in
which the stationary plate 10 for securing the stationary block 11
is bent to form the tilt yokes 10b, 10b there is no need to provide
dedicated tilt yokes, and the plate base 10a and the tilt yokes
10b, 10b, as components for securing the stationary block 11, may
be used in common, with the consequence that the number of
component parts may be reduced further.
[0099] With the objective lens driving device 8, the back yokes 28,
28 are provided on the surfaces of the tilt magnets 29, 29 opposite
to the surfaces thereof facing the tilt coils 16, 16.
[0100] The result is that the movable block 12 may be improved in
sensitivity at the time of tilt adjustment.
[0101] Except where the back yokes 28, 28 are provided, the upper
portions of the tilt magnets 29, 29 are attracted towards the first
magnetic circuit 27, while the lower portions thereof are repulsed
by the first magnetic circuit 27, given the relationship of the
directions of the magnetic force produced in relevant parts, as
shown in FIG. 10. Hence, the tilt magnets 29, 29 are subjected to
the force of downward movement P, with the result that the movable
block 12 is moved downwards to affect the focusing operation.
[0102] The objective lens driving device 8 is provided with paired
tilt magnets 29, 29 and paired tilt coils 16, 16 spaced apart from
the paired tilt magnets along the tracking direction (direction T
shown in FIG. 11) such that, when the movable block 12 has been
moved along the tracking direction by the tracking operation, the
positional relationships between the tilt magnets 29, 29 and the
first magnetic circuit 27 are changed, so that, should the tilt
magnets 29, 29 be affected by the first magnetic circuit 27, the
force of movement acting on the tilt magnets 29, 29 on the left
side differs from that on the right side. In such a case, there is
the fear that the movable block 12 is tilted in the direction
indicated by R shown in FIG. 11 to tilt the optical axis of the
laser light illuminated via objective lens 22 on the disc-shaped
recording medium 100.
[0103] Moreover, if in the objective lens driving device 8, the
spring force of the support springs 20, 20 differs on the left and
right sides due to manufacturing tolerances, the position of the
base member 9 along the tracking direction is adjusted in general
so that the tilt in the R-direction of the movable block 12 during
the focusing movement will be optimum (zero). In this case, the
positional relationships between the tilt magnets 29, 29 and the
first magnetic circuit 27 may again be changed, as above, such that
the force of movement acting on the tilt magnets 29, 29 on the left
side differs from that on the right side, and hence the movable
block 12 may be tilted in the R-direction shown in FIG. 11.
[0104] However, with the objective lens driving device 8 in which
the back yokes 28, 28 are provided on the surfaces of the tilt
magnets 29, 29 opposite to the surfaces thereof facing the tilt
coils 16, 16, as described above, the stray magnetic flux from the
tilt magnets 29, 29 is decreased, as shown in FIG. 12, so that the
second magnetic circuit 30 is not liable to be affected by the
first magnetic circuit 27, and hence it is possible to prevent the
movable block 12 from being tilted in the R-direction.
[0105] The objective lens driving device 8 does not necessarily
need to be provided with the back yokes 28, 28. In such a case, the
objective lens 22 may be maintained spaced apart from the
disc-shaped recording medium 100 by taking advantage of the force
of movement generated in the tilt magnets 29, 29 in a direction
towards the base member 9 (towards below), in the non-use state in
which no driving current is supplied to the focusing coil 25,
without a dependency upon the posture during use of the movable
block 12, so that the disc-shaped recording medium 100 may be
prevented from contacting with the objective lens 22.
[0106] In the foregoing, the focusing and tracking directions are
assumed to be the up-and-down direction and the left and right
direction, respectively. This is merely for the sake of
illustration so that the present invention is not limited to these
specific directions.
[0107] It should be noted that the particular shape as well as the
structure of respective parts shown in the best mode for carrying
out the invention is merely exemplary, so that the technical scope
of the invention is not to be limited by the merely exemplary shape
or structure.
[0108] That is, it should be understood by those skilled in the art
that various modifications, combinations subcombinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *