U.S. patent application number 09/953194 was filed with the patent office on 2002-03-21 for magneto-optical disk apparatus capable of accurate reproduction of signal by removing magnetic influence by magnet included in optical head and method of detecting intensity of magnetic field applied by magnet.
This patent application is currently assigned to Sanyo Electric Co., Ltd.. Invention is credited to Kajiyama, Seiji, Koyama, Kanichi, Maeda, Mitsuhiko, Shidochi, Masaaki, Takahashi, Seiichiro, Tsuchiya, Yoichi.
Application Number | 20020034128 09/953194 |
Document ID | / |
Family ID | 26600086 |
Filed Date | 2002-03-21 |
United States Patent
Application |
20020034128 |
Kind Code |
A1 |
Shidochi, Masaaki ; et
al. |
March 21, 2002 |
Magneto-optical disk apparatus capable of accurate reproduction of
signal by removing magnetic influence by magnet included in optical
head and method of detecting intensity of magnetic field applied by
magnet
Abstract
A magneto-optical disk apparatus includes a magnetic head in a
position opposed to an objective lens included in an optical head
with a magneto-optical record medium therebetween. The
magneto-optical disk apparatus includes a magnet for cancelling a
first magnetic field emitted toward the magnetic head from a magnet
for focus servo-control or tracking servo-control of the objective
lens. The magnet emits a second magnetic field in a direction
toward the magnetic head. The second magnetic field is opposite in
direction to the first magnetic field, and has the same intensity
as the first magnetic field. Consequently, the signal can be
accurately reproduced from the magneto-optical record medium while
removing a magnetic influence from the magnet included in the
optical head.
Inventors: |
Shidochi, Masaaki;
(Anpachi-gun, JP) ; Koyama, Kanichi; (Fuwa-gun,
JP) ; Tsuchiya, Yoichi; (Hashima-shi, JP) ;
Maeda, Mitsuhiko; (Takatsuki-shi, JP) ; Kajiyama,
Seiji; (Ibi-gun, JP) ; Takahashi, Seiichiro;
(Gifu-shi, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Sanyo Electric Co., Ltd.
Moriguchi-shi
JP
|
Family ID: |
26600086 |
Appl. No.: |
09/953194 |
Filed: |
September 17, 2001 |
Current U.S.
Class: |
369/13.15 ;
G9B/11.029; G9B/11.033; G9B/11.053 |
Current CPC
Class: |
G11B 11/10595 20130101;
G11B 11/10515 20130101; G11B 11/10552 20130101; G11B 11/10543
20130101 |
Class at
Publication: |
369/13.15 |
International
Class: |
G11B 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2000 |
JP |
2000-281211(P) |
Sep 29, 2000 |
JP |
2000-298847(P) |
Claims
What is claimed is:
1. A magneto-optical disk apparatus for recording a signal on a
magneto-optical record medium with a laser beam and a magnetic
field, and reproducing the signal from the magneto-optical record
medium with the laser beam comprising: a magnetic head for applying
a magnetic field to said magneto-optical record medium; a lowering
device for lowering said magnetic head to a position in contact
with said magneto-optical record medium; an optical head disposed
on a side remote from said magnetic head with said magneto-optical
record medium therebetween, and including an objective lens for
converging the laser beam onto said magneto-optical record medium,
a first magnet for performing tracking servo-control of said
objective lens and a second magnet for performing focus
servo-control of said objective lens; and a third magnet for
cancelling a leaked magnetic field produced by at least one of said
first and second magnets and convergently applied toward said
magnetic head.
2. The magneto-optical disk apparatus according to claim 1, wherein
said third magnet emits the magnetic field of an intensity
determined by a magnetic field intensity detecting method using a
DC magnetic field; and said magnetic field intensity detecting
method includes: a first step of irradiating said magneto-optical
record medium with the laser beam, and reproducing the signal from
said magneto-optical record medium by applying a DC magnetic field
in a first direction to a point irradiated with said laser beam
while changing an intensity of the DC magnetic field, a second step
of detecting the number of errors in the signal reproduced in said
first step, a third step of reproducing the signal from said
magneto-optical record medium by applying a DC magnetic field in a
second direction opposite to said first direction onto said
irradiation point, a fourth step of detecting the number of errors
in the signal reproduced in said third step, and a fifth step of
detecting an intensity of the magnetic field applied from said
first or second magnet at said irradiation point based on a
relationship between the error numbers detected in said second and
fourth steps and the intensities of said DC magnetic fields.
3. The magneto-optical disk apparatus according to claim 1, wherein
said third magnet is arranged in the radial direction of said
magneto-optical record medium, and has a length longer than a range
of radial movement of said optical head.
4. The magneto-optical disk apparatus according to claim 1, wherein
said third magnet is arranged on the same side as said optical head
with respect to said magneto-optical record medium.
5. The magneto-optical disk apparatus according to claim 1, wherein
said third magnet is arranged on the same side as said magnetic
head with respect to said magneto-optical record medium.
6. The magneto-optical disk apparatus according to claim 5, wherein
said third magnet has a plate form having first and second planes,
and emits from said first plane the magnetic field for cancelling
said leaked magnetic flux.
7. The magneto-optical disk apparatus according to claim 6, further
comprising: an outer appearance member for covering a loading
portion of said magneto-optical record medium, said third magnet
being arranged on said outer appearance member through said second
plane.
8. The magneto-optical disk apparatus according to claim 6, wherein
said third magnet is arranged on said outer appearance member, and
a magnetic field leakage preventing member for preventing external
leakage of the magnetic field from said second plane is interposed
between said third magnet and said outer appearance member.
9. The magneto-optical disk apparatus according to claim 8, wherein
said magnetic field leakage preventing member is made of metal.
10. A magneto-optical disk apparatus for detecting an intensity of
an influence magnetic field exerted on an irradiation point of a
laser beam by a magnet for servo-control of an objective lens for
irradiating a magneto-optical record medium with the laser beam,
recording a signal on said magneto-optical record medium with the
laser beam and the magnetic field, and/or reproducing the signal
from said magneto-optical record medium with the laser beam,
comprising: a first-magnetic head for applying the magnetic field
to said magneto-optical record medium; a lowering device for
lowering said first-magnetic head to a position in contact with
said magneto-optical record medium; an optical head including an
objective lens arranged on the side remote from said first magnetic
head with said magneto-optical record medium therebetween for
converging the laser beam to said magneto-optical record medium,
and said magnet; a second magnetic head for cancelling said
influence magnetic field; a magnetic head drive circuit for driving
said first or second magnetic head; and a control circuit, wherein
when detecting the intensity of said influence magnetic field, said
control circuit controls said magnetic head drive circuit such that
said first magnetic head applies a DC magnetic field in a first
direction or a DC magnetic field in a second direction opposite to
said first direction to said magneto-optical record medium while
changing the intensity of the DC magnetic field, and determines the
intensity of said influence magnetic field based on the number of
errors in a reproduced signal detected by said optical head under
said DC magnetic field, said magnetic head drive circuit drives
said first magnetic head to apply said DC magnetic field to said
magneto-optical record medium under control by said control
circuit, said optical head detects the signal on said
magneto-optical record medium; and when producing said signal, said
control circuit controls said magnetic head drive circuit to
produce by said second magnetic head the magnetic field of the same
intensity as said determined intensity of the influence magnetic
field, and said magnetic head drive circuit drives said second
magnetic head to produce the magnetic field of the same intensity
as said influence magnetic field under the control by said control
circuit.
11. A method of detecting a magnetic field intensity for detecting
an intensity of a magnetic field applied onto an irradiation point
of a laser beam by a magnet for servo-control of an objective lens
for irradiating a magneto-optical record medium with the laser
beam, comprising: a first step of emitting the laser beam to said
magneto-optical record medium and simultaneously applying a DC
magnetic field in a first direction to said irradiation point while
changing the intensity of said DC magnetic field to reproduce the
signal from said magneto-optical record medium; a second step of
detecting the number of errors in the reproduced signal reproduced
in said first step; a third step of applying a DC magnetic field in
a second direction opposite to said first direction to sad
irradiation point to reproduce the signal from sad magneto-optical
record medium, a fourth step of detecting the number of errors in
the reproduced signal reproduced in said third step; and a fifth
step of detecting an intensity of an influence magnetic field
exerted on said irradiation point by said magnet based on the
relationship between the numbers of errors detected in said second
and fourth steps and the intensities of said DC magnetic
fields.
12. The method of detecting the magnetic field intensity according
to claim 11, wherein in the relationship between the detected
number of said errors and the intensity of said DC magnetic field,
the intensity of said first magnetic field starting increase in
number of said errors during increase in intensity of said DC
magnetic field in said first direction and the intensity of the
second magnetic field starting increase in number of said errors
during increase in intensity of the DC magnetic field in said
second direction are detected, and the average value between the
detected intensities of said first and second magnetic fields is
determined as the intensity of said influence magnetic field.
13. The method of detecting the magnetic field intensity according
to claim 11, wherein a random data pattern recorded on said
magneto-optical record medium is reproduced in said first and third
steps.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magneto-optical disk
apparatus, which can accurately reproduce a signal by removing a
magnetic influence applied from a magnet for servo-control of an
objective lens for converging laser beams onto a magneto-optical
record medium. The invention also relates to a magnetic field
intensity detecting method of detecting an intensity of an
influence magnetic field applied from a magnet for
servo-control.
[0003] 2. Description of the Background Art
[0004] Magneto-optical record mediums have received widespread
attention as record mediums, which are rewritable and have large
storage capacities and high reliability, and are being used as
computer memories and others. Recently, a magneto-optical record
medium having a storage capacity of 6.0 Gbytes is standardized as
AS-MO (Advanced Storage Magneto Optical disk), and practical use
thereof is starting.
[0005] A signal is recorded on the magneto-optical record medium in
such a manner that a magnetic head is initially in contact with a
surface of a side of the magneto-optical record medium provided
with a magnetic layer, and a magnetic field modulated with the
record signal (i.e., signal to be recorded) is applied to the
magnetic layer of the magneto-optical record medium while floating
the magnetic head by rotating the magneto-optical record medium at
a predetermined rotation speed. Laser beams are emitted to a side
remote from the magnetic head for heating a predetermined region of
the magnetic layer of the magneto-optical record medium to or above
a predetermined temperature. Thereby, magnetic domains, which are
magnetized in different directions in response to the record
signal, are formed on the record layer of the magnetic layer to
record the signal.
[0006] For reproducing the signal from the magneto-optical record
medium, the magnetic domains on the regions, which are heated to or
above the predetermined temperature by laser beam irradiation, are
transferred onto the reproduction layer, and the magnetic domains
thus transferred are detected as a rotation angle of a plane of
polarization of the laser beams. Thereby, the signals are
reproduced from the magneto-optical record medium. In this case,
the magnetic head is disposed on the side opposite to the side
irradiated with the laser beams. When reproducing the signal, the
magnetic head is not in contact with the magneto-optical record
medium, and is spaced from the magneto-optical record medium.
[0007] When the signal recorded on the magneto-optical record
medium is to be reproduced, such a manner is employed for quick
reproduction of the signal that the magnetic head is kept in
contact with the magneto-optical record medium, and the side
opposite to the magnetic head is irradiated with the laser beams
for reproducing the signal.
[0008] When the signal is reproduced from the magneto-optical
record medium while keeping the magnetic head in contact with the
magneto-optical record medium, a magnetic force applied from a
magnet, which is used for focus servo-control or tracking
servo-control of an objective lens for converging the laser beams
onto the magneto-optical record medium, concentrates on a core
(made of a magnetic material such as ferrite) of the magnetic head,
and thus exerts an adverse effect on the reproduced signal.
SUMMARY OF THE INVENTION
[0009] Accordingly, an object of the invention is to provide a
magneto-optical disk apparatus, which can reproduce signals from a
magneto-optical record medium while removing an influence of a
magnetic field, which is concentratedly applied to a core of a
magnetic head from a magnet performing focus servo-control or
tracking servo-control of an object lens.
[0010] Another object of the invention is to provide a magnetic
field intensity detecting method of detecting an intensity of a
magnetic field, which is concentratedly applied to a core of a
magnetic head from a magnet performing focus servo-control or
tracking servo-control of an object lens.
[0011] The invention provides a magneto-optical disk apparatus for
recording a signal on a magneto-optical record medium with a laser
beam and a magnetic field, and reproducing the signal from the
magneto-optical record medium with the laser beam, including a
magnetic head for applying a magnetic field to the magneto-optical
record medium; a lowering device for lowering the magnetic head to
a position in contact with the magneto-optical record medium; an
optical head disposed on a side remote from the magnetic head with
the magneto-optical record medium therebetween, and including an
objective lens for converging the laser beam onto the
magneto-optical record medium, a first magnet for performing
tracking servo-control of the objective lens and a second magnet
for performing focus servo-control of the objective lens; and a
third magnet for cancelling a leaked magnetic field produced by at
least one of the first and second magnets and convergently applied
toward the magnetic head.
[0012] In the above magneto-optical disk apparatus according to the
invention, the magnetic head is lowered by the lowering-device, and
comes into contact with the magneto-optical record medium. When the
magneto-optical record medium turns, the magnetic head floats from
the magneto-optical record medium. The third magnet cancels the
magnetic influence, which may be exerted on the magneto-optical
record medium by the first or second magnets included in the
optical head for performing the tracking servo-control of the
objective lens or the focus servo-control thereof. While floating
the magnetic head from the magneto-optical record medium, recording
and/or reproducing of the signal on the magneto-optical record
medium are performed. According to the invention, therefore, the
recording and/or reproducing of the signal on the magneto-optical
record medium can be accurately performed while keeping the
magnetic head in contact-with the magneto-optical record
medium.
[0013] Preferably, the third magnet emits the magnetic field of an
intensity determined by a magnetic field intensity detecting method
using a DC magnetic field, and the magnetic field intensity
detecting method includes a first step of irradiating the
magneto-optic record medium with the laser beam, and reproducing
the signal from the magneto-optical record medium by applying a DC
magnetic field in a first direction to a point irradiated with the
laser beam while changing an intensity of the DC magnetic field, a
second step of detecting the number of errors in the signal
reproduced in the first step, a third step of reproducing the
signal from the magneto-optical record medium by applying a DC
magnetic field in a second direction opposite to the first
direction onto the irradiation point, a fourth step of detecting
the number of errors in the signal reproduced in the third step,
and a fifth step of detecting an intensity of the magnetic field
applied from the first or second magnet at the irradiation point
based on a relationship between the error numbers detected in the
second and fourth steps and the intensities of the DC magnetic
fields.
[0014] The magnetic head is lowered by the lowering device to make
contact with the magneto-optical record medium. When the
magneto-optical record medium turns, the magnetic head floats from
the magneto-optical record medium. The third magnet cancels the
magnetic influence, which is applied to the magneto-optical record
medium by the first magnet for tracking servo-control of the
objective lens included in the optical head or the second magnet
for the focus servo-control of the objective lens. While keeping
the magnetic head in a position floated from the magneto-optical
record medium, recording and/or reproducing of the signal on the
magneto-optical record medium are performed. The intensity of the
magnetic field emitted from the third magnet is determined to be
equal to the magnetic field intensity , which is detected based on
the relationship between the number of errors in the signal
reproduced by applying the DC magnetic field to the magneto-optical
record medium and the intensity of the DC magnetic field. According
to the invention, therefore, the recording and/or reproducing of
the signal on the magneto-optical record medium can be accurately
performed while keeping the magnetic head in contact with the
magneto-optical record mediums
[0015] Preferably, the third magnet of the magneto-optical disk
apparatus is arranged in the radial direction of the
magneto-optical record medium, and has a length longer than a range
of radial movement of the optical head.
[0016] When the optical head moves in the radial direction of the
magneto-optical record medium in a seek operation or the like, the
first and second magnets included in the optical head change their
positions. Even in this case, the third magnet removes the magnetic
influence exerted by the first or second magnet. According to the
invention, therefore, the signal can be accurately reproduced while
removing the magnetic influence exerted from the magnet, which is
included in the optical head, even when the optical head moves in
the radial direction of the magneto-optical record medium.
[0017] Preferably, the third magnet of the magneto-optical disk
apparatus is arranged on the same side as the optical head with
respect to the magneto-optical record medium.
[0018] A magnetic flux coming from the first or second magnet
included in the optical head enters the third magnet arranged on
the same side as the optical head with respect to the
magneto-optical record medium. According to the invention,
therefore, it is possible to eliminate the magnetic influence by
the magnet included in the optical head even if the third magnet is
arranged on the same side as the optical head with respect to the
magneto-optical record medium.
[0019] Preferably, the third magnet of the magneto-optical disk
apparatus is arranged on the same side as the magnetic head with
respect to the magneto-optical record medium.
[0020] The magnetic flux coming from the first or second magnet
included in the optical head is cancelled by the magnetic flux
coming from the third magnet arranged on the side opposite to the
optical head with respect to the magneto-optical record medium.
According to the invention, therefore, it is possible to eliminate
the magnetic influence by the magnet included in the optical head
even if the third magnet is arranged, on the side opposite to the
optical head with respect to the magneto-optical record medium.
[0021] Preferably, the third magnet of the magneto-optical disk
apparatus has a plate form having first and second planes, and
emits from the first plane the magnetic field for cancelling the
leaked magnetic flux caused by the first or second magnet.
[0022] The third magnet for eliminating the magnetic influence by
the first or second magnet included in the optical head has a plate
form, and emits the magnetic flux from the plane of the plate form.
According to the invention, therefore, the third magnet for
removing the magnetic influence by the first or; second magnet
included in the optical head can be easily attached.
[0023] Preferably, the magneto-optical disk apparatus further
includes an outer appearance member for covering a loading portion
of the magneto-optical record medium, and the third magnet is
arranged on the outer appearance member through the second
plane.
[0024] Once the position of the third magnet for removing the
magnetic influence by the first or second magnet included in the
optical head is adjusted, the third magnet will remove the magnetic
influence by the first or second magnet. According to the
invention, therefore, the magnetic influence by the first or second
magnet can be stably removed.
[0025] Preferably, the -third magnet of the magneto-optical disk
apparatus is arranged on the outer appearance member, and a
magnetic field leakage preventing member for preventing external
leakage of the magnetic field from the second plane is interposed
between the third magnet and the outer appearance member.
[0026] The magnetic field leak preventing member prevents the
external leakage of the magnetic field through the outer appearance
member. According to the invention, therefore, the signal is not
erased even when the magneto-optical record medium or the like is
located near the magneto-optical disk apparatus.
[0027] Preferably, the magnetic field leakage preventing member is
made of metal.
[0028] The magnetic field leakage preventing member prevents the
external leakage of the magnetic field through the outer appearance
member, and further removes the magnetic influence caused by the
first or second magnet included in the optical head so that it
enhances the magnetic flux emitted from the third magnet. According
to the invention, therefore, a magnet of a small magnetic flux
density can be used for removing the magnetic influence by the
first or second magnet included in the optical head.
[0029] The invention also provides a magneto-optical disk apparatus
for detecting an intensity of an influence magnetic field, which is
exerted on an irradiation point of a laser beam by a magnet
employed for servo-control of an objective lens for irradiating a
magneto-optical record medium with the laser beam, recording a
signal on the magneto-optical record medium with the laser beam and
the magnetic field, and/or reproducing the signal from the
magneto-optical record medium with the laser beam. The
magneto-optical disk apparatus includes a first magnetic head for
applying the magnetic field to the magneto-optical record medium; a
lowering device for lowering the first magnetic head to a position
in contact with the magneto-optical record medium; an optical head
including an objective lens arranged on the side remote from the
first magnetic head with the magneto-optical record medium
therebetween for converging the laser beam to the magneto-optical
record medium, and the magnet; a second magnetic head for
cancelling the influence magnetic field; a magnetic head drive
circuit for driving said first or second magnetic head; and a
control circuit. When detecting the intensity of the influence
magnetic field) the control circuit controls the magnetic head
drive circuit such that the first magnetic head applies a DC
magnetic field in a first direction or a DC magnetic field in a
second direction opposite to said first direction to said
magneto-optical record medium while changing the intensity of the
DC magnetic field. The control circuit determines the intensity of
the influence magnetic field based on the number of errors in a
reproduced signal detected by the optical head under the DC
magnetic field. The magnetic head dive circuit drives the first
magnetic head to apply the DC magnetic field to the magneto-optical
record medium under control by the control circuit. The optical
head detects the signal on the magneto-optical record medium. When
producing the signal, the control circuit controls the magnetic
head drive circuit to produce by the second magnetic head the
magnetic field of the same intensity as the determined intensity of
the influence magnetic field. The magnetic head drive circuit
drives the second magnetic head to produce the magnetic field of
the same intensity as the influence magnetic field under the
control by the control circuit.
[0030] According to the above magneto-optical disk apparatus of the
invention, when the intensity of the influence magnetic field,
which is applied from the magnet for servo-control of the objective
lens, is to be detected, the control circuit controls the magnetic
head drive circuit to produce the DC magnetic field of a changed
intensity from the first magnetic head. The optical head reproduces
the signal from the magneto-optical record medium under the DC
magnetic field, and the number of errors in the reproduced signal
is detected. The above operation is performed for the DC magnetic
fields in the two directions. The control circuit receives the
detected number of errors, and obtains the relationship between the
number of errors and the intensity of the DC-magnetic field. The
control circuit obtains the magnetic field intensity exhibiting a
lateral symmetry, and determines the intensity of the influence
magnetic field.
[0031] When reproducing the signal, the control circuit controls
the magnetic head drive circuit to produce by the second magnetic
head the magnetic field of the same intensity as the determined
influence magnetic field intensity, and the magnetic head drive
circuit drives the second magnetic head under the control by the
control circuit so that the second magnetic head, produces the
magnetic field of the game intensity as the influence magnetic
field. According to the invention, therefore, the magnetic field
for cancelling the influence magnetic field can be produced based
on the measured intensity of the influence magnetic field. As a
result, the recording and/or reproducing of the signal on the
magneto-optical record medium can be accurately performed.
[0032] The invention provides a method of detecting a magnetic
field intensity for detecting an intensity of a magnetic field
applied onto an irradiation point of a laser beam by a magnet
employed for servo-control of an objective lens for irradiating a
magneto-optical record medium with the laser beam. The method
includes a first step of emitting the laser beam to the
magneto-optical record medium and simultaneously applying a DC
magnetic field in a first direction to the irradiation point while
changing the intensity of the DC magnetic field to reproduce the
signal from the magneto-optical record medium; a second step of
detecting the number of errors in the reproduced signal reproduced
in the first step; a third step of applying a DC magnetic field in
a second direction opposite to the first direction to the
irradiation point to reproduce the signal from the magneto-optical
record medium a fourth step of detecting the number of errors in
the reproduced signal reproduced in the third step; and a fifth
step of detecting an intensity of an influence magnetic field
exerted on the irradiation point by the magnet based on the
relationship between the numbers of errors detected in the second
and fourth steps and the intensities of the DC magnetic fields.
[0033] According to the above method of detecting the magnetic
field intensity of the invention, the laser beam is emitted to the
magneto-optical record medium, and the DC magnetic field is applied
while changing the intensity on the irradiation point of the laser
beam. The number of errors in the reproduced signal is detected.
This detection of the number of errors is performed for the cases
of applying the DC magnetic fields in the two directions,
respectively, and the intensity of the influence magnetic field is
determined from the relationship between the numbers of errors in
the reproduced signal and the intensities of the DC magnetic
fields. According to the invention, therefore, the DC magnetic
field is applied to the magneto-optical record medium to detect the
number of errors in the reproduced signal, whereby the intensity of
the influence magnetic field applied from the magnet for
servo-control of the objective lens can be easily detected.
[0034] Preferably, in the relationship between the detected number
of the errors and the intensity of the DC magnetic field, the
intensity of the first magnetic field starting increase in number
of the errors during increase in intensity of the DC magnetic field
in the first direction and the intensity of the second magnetic
field starting increase in number of the errors during increase in
intensity of the DC magnetic field in the second direction are
detected, and the average value between the detected intensities of
the first and second magnetic fields is determined as the intensity
of the influence magnetic field.
[0035] In the relationship between the number of errors in the
reproduced signal and the intensity of the DC magnetic field, rapid
increase in number of the errors occurs at two values of the DC
magnetic field intensity. The two values of the DC magnetic field
intensity are detected, and the average value between them is
calculated to determine the intensity of the influence magnetic
field. According to the invention, therefore, the intensity of the
influence magnetic field can be easily and accurately
determined.
[0036] Preferably, a random data pattern recorded on the
magneto-optical record medium is reproduced in the first and third
steps.
[0037] Since the random data pattern recorded on the
magneto-optical record medium is reproduced, and the intensity of
the influence magnetic field is determined based on the number of
errors in the signal thus reproduced. According to the invention,
therefore, it is not necessary to record and reproduce data of a
specific pattern used for detecting the intensity of the influence
magnetic field on and from the magneto-optical record medium so
that the intensity of the influence magnetic field can be easily
determined.
[0038] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] FIG. 1 shows a data format of a magneto-optical record
medium to be used for recording and reproducing data by a
magneto-optical disk apparatus;
[0040] FIG. 2 shows a segment structure of the magneto-optical
record medium shown in FIG. 1;
[0041] FIG. 3 shows a manner of detecting an intensity of an
influence magnetic field from magnets for servo-control of an
objective lens;
[0042] FIG. 4 shows a relationship between the number of errors in
a reproduced signal and an intensity of a DC magnetic field;
[0043] FIG. 5 is a flowchart showing an operation of detecting the
intensity of the influence magnetic field applied from the magnets
for servo-control of the objective lens according to the
invention;
[0044] FIG. 6 is a perspective view showing a portion of the
magneto-optical disk apparatus including a magnetic head and an
optical head according to an embodiment of the invention;
[0045] FIG. 7 is a cross section viewed in a direction A in FIG.
6;
[0046] FIG. 8 is a perspective view of the objective lens included
in an optical head of the magneto-optical disk apparatus shown in
FIG. 6 as well as an architecture performing focus servo-control
and tracking servo-control of the objective lens;
[0047] FIG. 9 is a perspective view showing a magnet of the
magneto-optical disk apparatus shown in FIG. 6;
[0048] FIG. 10 is a perspective view showing a state where a cover
member in FIG. 6 is closed;
[0049] FIG. 11 is a plan viewed from a magnetic head side in FIG.
10;
[0050] FIG. 12 is a cross section viewed from a semiconductor laser
side in FIG. 10;
[0051] FIG. 13 is a perspective view showing a magnetic field
leakage preventing material for preventing external leakage of a
magnetic field;
[0052] FIG. 14 is a cross section viewed in the direction A in
FIGS. 6 and 10;
[0053] FIG. 15 is a cross section showing positions of magnets
arranged in the magneto-optical disk apparatus shown in FIG. 6;
[0054] FIG. 16 shows an effect of the magnets in the
magneto-optical disk apparatus shown in FIG. 6, and particularly
shows a relationship between the number of errors and an MH
current;
[0055] FIG. 17 is a cross section showing another example of the
position of the magnet in the magneto-optical disk apparatus shown
in FIG. 6;
[0056] FIG. 19 is a cross section showing still another example of
the position of the magnet in the magneto-optical disk apparatus
shown in FIG. 6;
[0057] FIG. 19 is a cross section showing yet another example of
the position of the magnet in the magneto-optical disk apparatus
shown in FIG. 6;
[0058] FIG. 20 is a schematic block diagram of a magneto-optical
disk apparatus of a first embodiment; and
[0059] FIG. 21 is a schematic block diagram of a magneto-optical
disk apparatus of a second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0060] Embodiments of the invention will now be described with
reference to the drawings. The same or corresponding portions bear
the same reference numbers, and description thereof is not
repeated.
[0061] (First Embodiment)
[0062] Referring to FIGS. 1 and 2, description will now be given on
a magneto-optical record medium, on which recording and/or
reproducing of signals are to be performed.
[0063] Referring to FIG. 1, a magneto-optical record medium 10 is
provided with frames (Frame), which are equally spaced from each
other and form record units, respectively. Each frame is formed of
39 segments (Segment) S0, S1, S2, . . . and S38.
[0064] Magneto-optical record medium 10 has a planar structure
having grooves 1 and lands 2, which are arranged radially
alternately to each other, and are formed in spiral or concentric
forms. Each segment has a length of 532 DCBs (Data Channel Bits),
and is provided at its leading end with a fine clock mark (FCM:
Fine Clock Mark) 3 indicating phase information of a clock used for
recording and reproducing data. Fine clock marks 3 are formed by
providing lands each hazing a constant length on groove 1 at
constant intervals, and providing grooves each having a constant
length on land 2 it constant intervals. Segment S0 forming the
leading end of the frame bears address information (Address)
following fine clock mark 3 for representing an address on
magneto-optical record medium 10. The address information (Address)
is preformatted with wobbles 4-9 at the time of production of
magneto-optical record medium 10.
[0065] Wobbles 4 and 5 are formed on the opposite walls of groove
1, respectively. Likewise, wobbles 6 and 7, and wobbles 8 and 9 are
formed on the opposite walls of the same grooves 1, respectively.
These wobbles 4 and 5 store the same address information; and
wobbles 6 and 7, and 8 and 9 store the same address information.
This manner of address information recording is referred to as a
one-side stagger manner. By employing the one-side stagger manner;
the address information can be accurately detected even when-the
laser beam shifts from the center of groove 1 or land 2 due to tilt
or the like of magneto-optical record medium 10.
[0066] The region bearing the address information and the region
provided with fine clock marks 3 are not used for recording user
data. Segment Sn is formed of fine clock mark 3 and user data (User
Data n-1).
[0067] Referring to FIG. 2, description will now be given on the
specific structures of the segments. Among segments S0, S1, S2, . .
. and S38 forming the frame, segment S0 is an address segment
preformatted on magneto-optical record medium 10 and segments
S1-S38 are data segments, which are reserved as regions for
recording the user data. Segment S0 is formed of a fine clock mark
region FCM of 12 DCBs and address Address of 520 DCBs. Segment S1
is formed of fine clock mark region FCM of 12 DCBs, Pre-Write of 4
DCBs, Data of 512 DCBs and Post-Write of 4 DCBs.
[0068] Pre-Write represents the start of data writing, and is
formed of, e.g., a predetermined pattern "0011". Post-Write
represents the end of data, and is formed of, e.g., a predetermined
pattern "1100".
[0069] The user data region in segment S1 includes a header
(Header), which is a fixed pattern, e.g., for determining a
position of data in the reproducing operation, compensating a
position of reproduction clock and adjusting a laser power. The
fixed pattern recorded in the header is a pattern, in which DC
components are suppressed and, for example, a predetermined number
of domains each having a length of 2T and spaced by 2T from each
other as well as a predetermined number of domains each having a
length of 8T and spaced by 8T from each other are recorded.
[0070] Phase compensation is performed by performing adjustment
such that timing of sampling of an analog signal; which is obtained
by reproducing the domains of 2T, may match with the phase of the
clock used for recording and reproducing the data. The domains of
2T and 8T are reproduced. The laser power is adjusted such that the
intensity of the signal obtained by reproducing the domains of 2T
may exhibit a ratio of 50% or more with respect to the intensity of
the signal obtained by reproducing the domains of 8T. The position
determination of the data is performed in the reproducing operation
by reproducing the domains of 8T and determining whether the
position of a digital signal produced by converting the reproduced
signal matches with the predicted position of the digital signal of
the domains of 8T or not. Each of the patterns of Pre-Write,
Post-Write and Header is recorded continuously to the user data
when recording the user data.
[0071] Referring to FIGS. 3-5, description will now be given on a
method of detecting the magnetic field intensity according to the
invention. Referring to FIG. 3, a magnetic head 30 is formed of a
core 301 and a coil 302 wound around core 301. A current in a
constant direction is supplied through coil 302 so that core 301
applies DC magnetic fields DC1 and DC2 to a reproduction layer 101
of magneto-optical record medium 10. In this case, the direction
and value of the current flowing through coil 302 are changed so
that DC magnetic fields DC1 and DC2 of different magnitudes are
applied to reproduction layer 101. From the side opposite to that,
from which DC magnetic fields DC1 and DC2 are applied, an optical
head 20 emits laser beams LB to detect the reproduced signal. In
FIG. 3, reproduction layer 101 and laser beams LB are depicted in
large sizes as compared with core 301 of magnetic head 30 for easy
understanding.
[0072] Magnetic domains magnetized in different directions are
formed at the record layer (not shown) of magneto-optical record
medium 107 and thereby a predetermined signal is recorded in
advance This signal is formed of a random data pattern, e.g., of
"10101010 . . . ". In this case, a current in a constant direction
is supplied through coil 302 so that a DC magnetic field in a
constant direction is applied to reproduction layer 101 of
magneto-optical record medium 10. If the direction of the DC
magnetic field is the same as the direction of the magnetic domains
transferred onto the reproduction layer, the magnetic domain
transferred onto the reproduction layer can be detected without an
influence by the DC magnetic field. In the case where the domains
magnetized in the direction opposite to the direction of the DC
magnetic field is transferred from the record layer, the magnetic
domains are detected without an influence by the DC magnetic field
as long as the intensity of the DC magnetic field is in such a weak
range that does not invert the magnetization of the reproduction
layer. In the case where the applied DC magnetic field is strong to
invert the magnetization of the reproduction layer, the magnetic
domains of the direction different from that transferred to the
reproduction layer is detected. Accordingly, even in the case where
a random data pattern of, e.g., "10101010 . . . " is recorded, it
is possible to determine the magnetic field intensity, which starts
inversion of the magnetization transferred onto reproduction layer
101, by applying the DC magnetic field in the constant direction to
reproduction layer 101 of magneto-optical record medium 10.
[0073] By changing the value of current supplied through coil 302,
the intensities of DC magnetic fields DC1 and DC2 are changed.
[0074] When reproducing the magnetic domain having magnetization
102, the magnetic domain having magnetization 102 is transferred
from the record layer onto reproduction layer 101. A current, which
applies DC magnetic field DC1 onto reproduction layer 101, is
supplied through coil 302. While changing the value of
current-flowing through coil 302, the magnetic domain transferred
onto reproduction layer 101 by laser beams LB is detected, and the
number of errors in the reproduced signal is measured for each
current value. When reproducing the magnetic domain having a
magnetization 103, a current is similarly supplied through coil
302. Thus the current, which applies DC magnetic field DC2 onto
reproduction layer 101, is supplied through coil 302. While
changing the value of current flowing through coil 302, the
magnetic domain transferred onto reproduction layer 101 by laser
beams LB is detected, and the number of errors in the reproduced
signal is measured for each current value.
[0075] Referring to FIG. 4, description will now be given on the
relationship between the magnetic field intensity and the number of
errors where are measured in the foregoing method. A curve k1
represents a result of measurement from grooves 1 of
magneto-optical record medium 10, and a curve k2 represents a
result of measurement from lands 2 of magneto-optical record medium
10. In both grooves 1 and lands 2, the relationship between the
number of errors and the magnetic field intensity exhibits a
symmetry with respect to a certain intensity. More specifically, in
grooves 1 and lands 2, the magnetic field intensity of 20 mA forms
a center. In the course of decreasing the magnetic field intensity
from 20 mA and applying the DC magnetic field in the opposite
direction, or in the course of increasing the magnetic field
intensity from 20 mA, the number of errors starts to increase
rapidly when the intensity is shifted by about 50 mA from 20
mA.
[0076] If no influence were exerted from the magnets for
servo-control of the objective lens, the center of the magnetic
field intensity would be equal to 0 mA in accordance with the
measuring principle already described with reference to FIG. 3.
However, the center of the magnetic field intensity is equal to 20
mA according to the actual measurement. Therefore, it can be
considered that the magnet for the servo-control of objective lens
22 exerts the magnetic-field corresponding to 20 mA to the
irradiation point of the laser beams. Accordingly, in the
relationship shown in FIG. 4, the amount of shift from 20 mA of the
magnetic field intensity; which exhibits the symmetry, is equal to
the intensity of magnetic field, which is exerted from the magnet
for servo-control of objective lens 22 to the irradiation point of
laser beams.
[0077] Referring to FIG. 5, description will now be given on the
flowchart of the method of detecting the intensity of magnetic
field, which is exerted to the irradiation point of the laser beams
from the magnets for servo-control of objective lens 22. When the
detecting operation starts, optical head 20 emits the laser beams
to magneto-optical record medium 10 (step S1). Magnetic head 30
applies the DC magnetic field in the constant direction having
changed intensity to magneto-optical record medium 10 (step S2),
and the signal is reproduced from magneto-optical record medium 10
(step S3). Based on the reproduced signal, the number of errors is
detected (step S4). Thereby, the number of errors in the reproduced
signal is detected for each intensity of the DC magnetic field.
Thereafter, it is determined-whether the direction of the DC
magnetic field is to be changed or not (step S5). When the
direction of the DC magnetic field is to be changed, the steps
S2-S4 are repeated, and the number of errors in the reproduced
signal is detected for the different direction of the DC magnetic
field. When the numbers of errors in the reproduced signal for the
magnetic field are detected in the two directions of the DC
magnetic field, "No" is selected in step S5. From the relationship
between the magnetic field intensity, and the number of errors in
reproduced signal, the intensity of magnetic field, which is
exerted to the irradiation point of laser beam from the magnets
for, servo-control of objective lens 22, is determined (step S6).
Thereby, the operation of detecting the magnetic field intensity
ends.
[0078] By using the method of detecting the magnetic field
intensity according to the invention, as described above, it is
possible to detect easily the intensity of the influence magnetic
field exerted from the magnets for servo-control of objective lens
22.
[0079] Description will now be given on a magneto-optical disk
apparatus, which can record and/or reproduce signals on
magneto-optical record medium 10 while removing the influence by
the magnetic field, which is determined by the method of detecting
the magnetic field intensity according to the invention.
[0080] Referring to FIG. 6, a magneto-optical disk apparatus 100
includes optical head 20, magnetic head 30 and a magnet 41. Optical
head 20 includes a semiconductor laser 21, which emits laser beams
converged by an objective lens (not shown in FIG. 6) onto
magneto-optical record medium 10. Optical head 20 is movable along
rails 1A and 1B in the radial direction DR1 of magneto-optical
record medium 10.
[0081] Magnetic head 30 is arranged on the side remote from optical
head 20 with magneto-optical record medium 10 therebetween.
Magnetic head 30 applies a magnetic field, which is modulated with
a record signal, to magneto-optical record medium 10 when recording
the signal on magneto-optical record medium 10. The magnetic head
30 is attached to a slider 31. Slider 31 is fixed to a support
member 33 by an arm 32 made of a plate spring. Support member 33 is
fixed to a support member 34 by a screw 35. A support member 36 has
an end fixed to optical head 20. Support member 36 is provided at
the other end with an opening 37. Columnar members 38A end 38B are
located on the opposite sides of opening 37, and are fitted with a
shaft 39 extending therethrough. Support member 34 has an opening
38 at the side remote from the end fixed to support member 33.
Support member 34 is provided at the opposite ends of opening 38
with columnar members 34A and 34B, which are located inside
columnar members 38A and 38B of support member 36, respectively.
Columnar members 34A and 34B are coupled to columnar members 38A
and 38B by shaft 39. A spring 42 is arranged inside columnar
members 34A and 34B, and is fitted around shaft 39.
[0082] FIG. 7 is a cross section viewed in a direction A in FIG. 6.
Spring 42 pushes support member 34 toward magneto-optical record
medium 10 in a normal direction DR2 of magneto-optical record
medium 10. Thereby, support member 33, arm 32 and slider 31 receive
a force toward magneto-optical record medium 10, and magnetic head
30 is pushed against magneto-optical record medium 10. Since arm 32
is formed of the plate spring, magnetic head 30 is elastically
pushed against magneto-optical record medium 10.
[0083] A screw 43 extends through support member 34, and has an end
in contact with a member 44, which is fixed to support member 36.
By turning screw 43 clockwise, screw 43 moves toward member 44 to
increase the distance between support members 34 and member 44.
This reduces a pushing force, by which magnetic head 30 is pushed
against magneto-optical record medium 10. By turning screw 43
counterclockwise screw 43 moves away from member 44 to reduce the
distance between support member 34 and member 44. This increases
the pushing force, by which magnetic head 30 is pushed against
magneto-optical record medium 10. Thus, screw 43 controls the
pushing force for pushing magnetic head 30 against magneto-optical
record medium 10.
[0084] By moving a lever 45 in a direction of an arrow 46, magnetic
bead 30 is spaced from magneto-optical record medium 10. Loading
and unloading of magneto-optical record medium 10 are performed in
this spaced state.
[0085] In this invention, screw 43, member 44, spring 42, support
members 34 and 33, and arm 32 form a lowering mechanism for lowing
magnetic head 30 to a position in contact with magneto-optical
record medium 10.
[0086] Since magnetic head 30 is connected to optical head 20 via
slider 31, arm 32, support members 33 and 34, and support member
36, magnetic head 30 moves in, radial direction DR1 of
magneto-optical record medium 10 in accordance with movement of
optical head 20 in radial direction DR1 of magneto-optical record
medium 10. Accordingly, once the optical axis of laser beams
emitted from optical head 20 was positioned concentrically with the
magnetic field applied from magnetic head 30, the optical axis of
laser beam emitted from optical head 20 matches with the center of
magnetic field even when optical head 20 moves in the radial
direction of a magneto-optical record medium 10 in the seek
operation.
[0087] As shown in FIG. 7, magnetic head 30 is in contact with
magneto-optical record medium 10 before turning magneto-optical
record medium 10. In this state, magneto-optical record medium 10
turns in a direction of an arrow 48A (see FIG. 6) at a
predetermined rotation speed, whereby air flows into a space
between magnetic head 30 and magneto-optical record medium 10, and
magnetic head 30 floats from magneto-optical record medium 10. In
this case, a distance of about 5 .mu.m is formed between magnetic
head 30 and magneto-optical record medium 10.
[0088] Accordingly, when recording the signal on magneto-optical
record medium 10, magnetic head 30 is floated by turning
magneto-optical record medium 10 at a predetermined rotation speed,
and the magnetic field modulated with the record signal is applied
to magneto-optical record medium 10. When reproducing the signal
from magneto-optical record medium 10, optical head 20 emits the
laser beam to magneto-optical record medium 10 while floating
magnetic head 30 by rotating magneto-optical record medium 10 at a
predetermined speed. Thus, lever 45 is not used to space-magnetic
head 30 from magneto-optical record medium 10 when reproducing the
signal from magneto-optical record medium 10.
[0089] Referring to FIG. 8, description will now be given on focus
servo-control and tracking servo-control of objective lens 22. A
magnet 24 is arranged on one of the surfaces of support member 23,
and a coil 25 is arranged around support member 23 and magnet 24. A
magnet 26 is arranged on one of the surfaces of support member 28,
and a coil 27 is opposed to magnet 26. Although not shown, a coil
having the same structure as coil 27 is arranged beside coil 27.
Objective lens 22 is disposed on the surface of support member 28
opposite to the surface carrying magnet 26. By energizing coil 25,
coil 25 receives a Lorentz force in normal direction DR2 (which may
also he referred to as a "focus direction") of magneto-optical
record medium 10 from magnet 24, and moves in focus direction DR2.
Thereby, objective lens 22 can move in focus direction DR2. Coil 27
and the coil (not shown) are energized to receive a Lorentz force
in radial direction DR1 (which may also be referred to as a
"tracking direction") of magneto-optical record medium 10 from
magnet 26 so that objective lens 22 can move in tracking direction
DR1 of magneto-optical record medium 10.
[0090] Optical head 20 shown in FIGS. 6 and 7 includes magnets 24
and 26, and coils 25 and 27. Focus servo-control and tracking
servo-control of objective lens 22 are performed by energizing
coils 25 and 27. In the operation of reproducing the signal with
laser beams while keeping magnetic head 30 in contact with
magneto-optical record medium 10 as described above, a magnetic
flux coming from magnets 24 and 26 is concentrated on the core
(made of magnetic material such as ferrite) of magnetic head 30,
and the magnetic flux thus concentrated on the core of magnetic
head 30 affects the magnetic layer of magneto-optical record medium
10 opposed to magnetic head 30. As a result, in the operation of
transferring the magnetic domain from the record layer forming the
magnetic layer of magneto-optical record medium 10 to the
reproduction layer through a non-magnetic layer, the transferred
domain on the reproduction layer is affected by the magnetic flux
concentrated on the core of magnetic head 30. As a result, the
plane of polarization of laser beams is rotated by magnetization,
which is different from the magnetization to be originally held by
the magnetic domain transferred onto the reproduction layer, and it
is difficult to detect the rotation of the plane of polarization of
the laser beam to be caused originally.
[0091] Referring to FIG. 6 again magnet 41 is attached to a lid
member 40. FIG. 6 is a perspective view showing lid member 40 in
the open state.
[0092] Referring to FIG. 9, magnet 41 has a plate form having a
flat surface 410, from which a magnetic flux is emitted, and a flat
plane 411 receiving an incoming magnetic flux. Thus, magnetic flux
.phi.1 is emitted from flat surface 410, and enters flat surface
411.
[0093] FIG. 10 is a perspective view showing a state, in which lid
member 40 shown in FIG. 6 is moved in a direction of an arrow 48B
(see FIG. 6) to a closed position. Lid member 40 is not shown in
FIG. 10 for clearly showing a position of magnet 41 with respect to
optical head 20 and magnetic head 30. Magnet 41 is on the same as
magnetic head 30 with respect to magneto-optical record medium 10,
and is arranged such that the longitudinal direction thereof is
parallel to radial direction DR1 of magneto-optical record medium
10. Magnetic flux .phi.1 emitted from flat surface 410 of magnet 41
cancels the magnetic flux caused by magnets 24 and 26 included in
optical head 20 so that the magnetic flux caused by magnets 24 and
26 may not exert a magnetic influence on the magnetic layer of
magneto-optical record medium 10.
[0094] FIG. 11 is a plan viewed from the same side as magnetic head
30 and magnet 41 in FIG. 10. Magnet 41 is not disposed immediately
above magnetic head 30, but is disposed in a position shifted
toward rail 1A from the position of magnetic head 30. The reason
for this will be described later.
[0095] FIG. 12 is a cross section viewed from the same side as rail
1A in FIG. 10, magneto-optical record medium 10 is laid on a turn
table 111. A spindle motor 110 rotates turn table 111 at a
predetermined speed, and thereby rotates-magneto-optical record
medium 10 at the predetermined speed. Objective lens 22 is disposed
at a position opposed to magnetic head 30 with magneto-optical
record medium 10 therebetween. Magnet 41 has a longitudinal length
longer than a record region 10R of magneto-optical record medium
10. This is for the purpose of cancelling a magnetic influence,
which may be exerted by magnets 24 and 26 on the magnetic layer of
magneto-optical record medium 10 when magnetic head 20 performs the
seek along rails 1A and 1B, and thus in radial direction DR1 of
magneto-optical record medium 10, and thereby magnets 24 and 26
included in optical head 20 as well as magnetic head 30 move in
radial direction DR1, of magneto-optical record medium 10. Thereby,
the signal can be reproduced while cancelling the magnetic
influence exerted by magnets 24 and 26 on the magnetic layer of
magneto-optical record medium 10 wherever magnets 24 and 26 as well
as magnetic head 30 move in record region 10R of magneto-optical
record medium 10.
[0096] A steel plate 47 is attached to flat surface 411 of magnet
41. Steel plate 47 is arranged on lid member 40. Thereby, steel
plate 47 in contact with flat surface 411 of magnet 41 has
magnetism. Assuming that flat surfaces 410 and 411 of magnet 41
provide N- and S-poles, respectively, as shown in FIG. 13, a flat
surface 471 of steel plate 47, which is in contact with flat
surface 411 of magnet 41, provides an N-pole, and flat surface 472
provides an S-pole. Assuming that flat surface 471 emits a magnetic
flux .phi.2, magnetic flux .phi.2 is added to magnetic flux .phi.1
emitted from plat surface 410 of magnet 41. As a result, magnet 41
emits magnetic fluxes .phi.1+.phi.2. Magnet fluxes, .phi.1+.phi.2
are used for cancelling the magnetic flux coming from magnets 24
and 26 included in optical head 20.
[0097] Steel plate 47 receives magnetic flux .phi.2 through flat
surface 472. Therefore, if steel plate 47 is not interposed between
magnet 41 and lid member 40, magnetic flux .phi.1 would pass
through lid member 40 into magnet 41. Thereby, magneto-optical
record medium 10 located near lid member 40 would be magnetically
affected, and the recorded signal might be erased. Accordingly,
magnet 41 is attached to lid member 40 with steel plate 47
therebetween for the purpose of reducing the magnetic flux passing
through lid member 40 into magnet 41.
[0098] Steel plate 47 is made of a material, which is selected to
provide such a relationship that a flux density of magnetic flux
.phi.2 is smaller than a flux density of magnetic flux .phi.1.
Thereby, a magnetic influence, which may be externally exerted, can
be smaller than that in the case where magnet 41 is directly
attached to lid member 40. Since steel plate 47 emits magnetic flux
.phi.2 from flat surface 471 toward magnetic head 30 as already
described, the density of magnetic flux to be provided by magnet 41
can be smaller than that in the case where steel plate 47 is not
employed.
[0099] More specifically, if steel plate 47 is not employed, magnet
41 must provide the flux density from 5250 to 5650 gauss for
cancelling the magnetic flux coming from magnets 24 and 26 included
in optical head 20. By employing steel plate 47, the required flux
density of magnet 41 is equal to about 2600 gauss, and thus can be
half. The leaked magnetic field caused by magnet 41, which is
measured outside lid member 40, is equal to about 360 gauss if
steel plate 47 is not employed. By employing steel plate 47, it
decreases to about 50 gauss or less, and thus to 1/6-{fraction
(1/7)}.
[0100] As described above, magnet 41 is disposed on lid member 40
with steel plate 47 therebetween. Thereby, it is possible to reduce
the flux density of magnet 41, which is required for cancelling the
influence by the magnetic flux coming from magnets 24 and 26. It is
also possible to reduce the externally leaked magnetic flux of
magnet 41. Steel iron 47 is made of a tinplate of 0.2 mm in
thickness.
[0101] FIG. 14 is a cross section viewed in a direction A in FIGS.
6 and 10. Magnets 41 and 47 are arranged in positions shifted from
magnetic head 30 toward rail 1A. The reason for this will now be
described with reference to FIG. 15. A magnetic field Hex1 directed
from magnets 24 and 26 toward magnetic head 30 is present between
magnets 24 and 26 included in optical head 20 and magnetic head 30.
Magnetic field Hex1 does not enter magnetic head 30 in the normal
direction, but enters magnetic head 30 from magnets 24 and 26 at an
angle .theta. with respect to the normal direction of magnetic head
30. Accordingly, for cancelling magnetic field Hex1 with a magnetic
field Hex2 emitted from magnet 41, magnetic field Hex2 must enter
magnetic head 30 at angle .theta. with respect to the normal
direction of magnetic head 30. For the above reason magnet 41 is
not located immediately above magnetic head 30, but is located at
the position shifted from magnetic head 30 toward rail 1A. Magnetic
field Hex2 has the same magnitude as magnetic field Hex1, but the
directions thereof are opposite to each other.
[0102] A distance L1 between magnet 41 and magneto-optical record
medium 10 is 6.38 mm, and a distance L2 between magnet 41 and the
center of magnetic head 30 is 6.7 mm. As a result, magnetic field
Hex2 coming from magnet 41 enters magnetic head 30 at angle .theta.
of 53.9 degrees.
[0103] Referring to FIG. 16, an effect by magnet 41 will now be
described. FIG. 16 shows a relationship between the number of
errors and the DC magnetic field intensity, which is measured in
the magnetic field intensity detecting method according to the
invention. The abscissa gives an MH current corresponding to the
intensity of the DC magnetic field. The ordinate gives the number
of errors in reproduced signal, which are detected from the
magneto-optical record medium 10.
[0104] A curve k3 represents the case where magnet 41 is not
arranged, and a curve k4 represents a case where magnet 41 is
arranged. It is assumed that, by flowing the MH current in the
positive direction through coil 302, a DC magnetic field DC1 is
applied to reproduction layer 101. It is also assumed that, by
flowing the MH current in the negative direction through coil 302,
a DC magnetic field DC2 is applied to reproduction layer 101.
[0105] First, description is given on the case where magnet 41 is
not employed. A magnetic domain having magnetization 102 is
transferred onto reproduction layer 101, and DC magnetic field DC1
having a changed intensity is applied to reproduction layer 101.
When the MH current is in a range from 0 to 40 mA, the number of
errors hardly changes. The number of errors starts to increase with
the MH current of 50 mA, and rapidly increases when the MH current
exceeds 50 mA. Also, a domain having magnetization 103 is
transferred onto reproduction layer 101, and DC magnetic field DC2
having a changed intensity is applied to reproduction layer 101. In
this case, the number of errors hardly changes when the MH current
is in a ranged from -10 to 0 mA. When the MH current lowers to or
below -10 mA, and thus increases in absolute value to or above 10
mA, the number of errors rapidly increases. The number of errors
rapidly increases in accordance with certain increase in
intensities of DC magnetic fields DC1 and DC2 because DC magnetic
fields DC1 and DC2 invert the magnetic domain transferred onto
reproduction layer 101 to the direction of magnetization.
[0106] As a result, in the structure not provided with magnet 41,
the number of errors and the MH current exhibit the relationship
represent by curve k3, and the MH current exhibit a curve, which is
symmetrical with respect to a value of +20 mA. In principle, if no
magnet field other than DC magnetic fields DC1 and DC2 is applied
to the region on reproduction layer 101 bearing the transferred
domain, the MH current should exhibit a curve symmetrical with
respect to 0 mA. However, the value of center, which was actually
measured, is shifted negatively by 20 mA. In view of this fact, it
is considered that a magnetic field in the same direction as
magnetization 102 was applied to the region on reproduction layer
101 bearing the transferred domain. Thus, it can be determined that
the magnetic field produced by magnets 24 and 26 included in
optical head 20 was applied to the region on reproduction layer 101
bearing the transferred magnetic domains.
[0107] However, in the case where magnet 41 is employed, the MH
current exhibits curve k4, which is symmetrical with respect to 0
mA. Thus, the magnetic domain having magnetization 102 is
transferred onto reproduction layer 101 and DC magnet field DC1
hang the changed intensity is applied to reproduction layer 101.
Thereby the number of errors hardly changes when the MH current is
in a range from 0 to 20 mA. The number of errors rapidly increases
when the MH current exceeds 20 mA. The magnetic domain having
magnetization 103 is transferred onto reproduction layer 101, and
DC magnetic field DC2 having the changed intensity is applied to
reproduction layer 101. Thereby, the number of errors hardly
changes when the MH current is in a range from -20 to 0 mA. The
number of errors rapidly increases wherein the MH current is lower
than -20 mA, and thus is larger in absolute value than 20 mA. The
number of errors increases with increase in intensities of DC
magnetic fields DC1 and DC2 for the reason already described.
[0108] As a result, the curve k4 is obtained, which is symmetrical
with respect to the MH current of 0 mA. Accordingly, provision of
magnet 41 can remove the influence exerted by the magnetic fields
of magnets 24 and 26 included in optical head 20.
[0109] In the above description, the magnet, which produces
magnetic field Hex2 for cancelling magnetic field Hex1 applied from
magnets 24 and 26 included in optical head 20 toward magnetic head
30, is disposed on the same side as magnetic head 30 with respect
to magneto-optical record medium 10. However, the invention is not
restricted to this, and the magnet for producing magnetic field
Hex2 cancelling magnetic field Hex1 may be disposed on the same
side as optical head 20 with respect to magneto-optical record
medium 10.
[0110] FIG. 17 is a cross section of a structure, in which the
magnet for producing magnetic field Hex2 cancelling magnetic field
Hex1 is disposed on the same side as optical head 20 with respect
to magneto-optical record medium 10, and corresponds to FIG. 7. A
magnet 41A is disposed under optical head 20. Magnet 41A has a
longitudinal length longer than record region 10R in
magneto-optical record medium 10. Magnet 41A is disposed such that
the longitudinal direction thereof is parallel to radial direction
DR1 of magneto-optical record medium 10. Thereby, even when magnets
24 and 26 included in optical head 20 and magnetic head 30 move in
radial direction DR1 of magneto-optical record medium 10 for the
seek operation of optical head 20, magnet 41A can cancel magnetic
field Hex1 applied from magnets 24 and 26 to magnetic head 30.
[0111] Referring to FIG. 18, magnet 41A is disposed under optical
head 20. Even in this case, magnet 41A is not disposed immediately
under magnetic head 30, but is disposed in the position shifted
toward rail 113 from magnetic head 30. In FIG. 18, radial direction
DR1 of magneto-optical record medium 10 is perpendicular to the
sheet of the drawing.
[0112] Referring to FIG. 19, description will now be given on such
disposition that magnet 41A is shifted toward rail 1B with respect
to magnetic head 30. As already described, magnetic field Hex1
directed from magnets 24 and 26 included in optical head 20 toward
magnetic head 30 is present between magnets 24 and 26 and magnetic
head 30. Magnetic field Hex1 applied form magnets 24 and 26 enters
magnetic head 30 at angle .theta. with respect to the normal
direction of magnetic head 30. For cancelling magnetic field Hex1
with magnetic field Hex2 emitted from magnet 41A, therefore,
magnetic field Hex2 directed from magnetic head 30 toward magnet
41A must enter magnet 41A at angle .theta. with respect to the
normal direction of magnet 41A. For this reason, magnet 41A is not
disposed immediately under magnetic head 30, but is shifted toward
rail 1B from the position of magnetic head 30.
[0113] Referring to FIG. 20, magneto-optical disk apparatus 100
includes spindle motor 110, optical head 20, magnetic head 30,
magnet 41, a fine clock mark detecting circuit (FCM detecting
circuit) 120, a PLL circuit 130, an address detecting circuit 140,
a BPF 150, an A/D converter 160, a waveform equalizing circuit 170,
a Viterbi demodulating circuit 180, an unformat circuit 190, a data
demodulating circuit 200, a BCH decoder 210, a header detecting
circuit 220, a controller 230, a timing generating circuit 240, a
BCH encoder 250, a data modulating circuit 260, a format circuit
270, a magnetic head drive circuit 280 and a laser drive circuit
290.
[0114] Magnet 41 prevents the concentration of the magnetic field,
which is emitted from magnets 24 and 26 included in optical head
20, on magnetic head 30. Spindle motor 110 rotates magneto-optical
record medium 10 at a predetermined rotation speed. Optical head 20
emits the laser beams onto magneto-optical record medium 10, and
detects the reflected beams. FCM detecting circuit 120 detects a
fine clock mark detection signal indicating the position of fine
clock mark 3 on magneto-optical record medium 10, and outputs the
fine clock mark detection signal thus detected to PLL circuit 130
and timing generating circuit 240.
[0115] PLL circuit, 130 produces a clock based on the fine clock
mark detection signal sent from FCM detecting circuit 120, and
sends the clock thus produced to address detecting circuit 140, A/D
converter circuit 160, waveform equaling circuit 170, Viterbi
demodulating circuit 180, unformat circuit 190, data demodulating
circuit 200, controller 230, timing generating circuit 240, data
modulating circuit 260 and format circuit 270.
[0116] Address detecting circuit 140 receives an address signal,
which is detected by optical head 20 from segment S0 on
magneto-optical record medium 10 in a tangential push-pull method,
detects the address information in synchronization with the clock
supplied from PLL circuit 130 and produces the address detection
signal, which indicates the fact that the address information is
detected, at the final position of the address signal. Address
detecting circuit 140 sends the address information thus detected
to controller 230, and sends the address detection signal thus
produced to header detecting circuit 230 and timing generating
circuit 240.
[0117] BPF 150 cuts off high and low ranges of the reproduced
signal reproduced from magneto-optical record medium 10. A/D
converter 160 converts the reproduced signal from an analog signal
to a digital signal in synchronization with the clock sent from PLL
circuit 130.
[0118] Waveform equalizing circuit 170 effects PR (1, 1) waveform
equalization and others on the reproduced signal, which is
converted into the digital signal in synchronization with the clock
sent from PLL circuit 130. This equalization is performed to cause
one-to-one waveform interference between the data before and after
the detection signal.
[0119] Viterbi demodulating circuit 180 converts the reproduced
signal in the multilevel form into the binary form in
synchronization with the clock sent from PLL circuit 130, and
outputs the reproduced signal thus converted to unformat circuit
190 and header detecting circuit 220.
[0120] Unformat circuit 190 removes pre-write (Pre-Write),
post-write (Post-Write) and header (header), which are recorded in
a user data region on magneto-optical record medium 10, based on
the timing signal supplied from header detecting circuit 220.
[0121] Data demodulating circuit 200 receives the reproduced
signal, which is unformatted, in synchronization with the clock
sent from PLL circuit 130, and performs the demodulation for the
digital modulation effected at the time of recording.
[0122] BCH decoder 210 performs the error correction on the
reproduced signal thus demodulated to output the signal as
reproduced data. Header detecting circuit 220 detects the position
of the header included in the reproduced signal based on the
address information sent from controller 230 and the address
detection signal sent from address detecting circuit 140, and
produces the timing signals for the pre-write (Pre-Write) and
header (Header) from the reproduced signal in synchronization with
the clock sent from PLL circuit 130. The timing signs thus produced
for the header (Header) is output to unformat circuit 190 and data
demodulation circuit 200.
[0123] Controller 230 receives the address information detected by
address detecting circuit 140, and controls the servo-mechanism
(not shown) based on the address information to access the intended
position by optical head 20. Controller 230 outputs the address
information to header detecting circuit 220 in synchronization with
the clock sent from PLL circuit 130, and controls timing generating
circuit 240.
[0124] Timing generating circuit 240 controlled by controller 230
produces timing signal in synchronization with the clock supplied
from PLL circuit 130 based on the fine clock mark detection signal
supplied from FCM detecting circuit 120 and the address end
position supplied from address detecting circuit 140, and outputs
the timing signal thus produced to format circuit 270, magnetic
head drive circuit 280 and laser drive circuit 290.
[0125] BCH encoder 250 adds an error correction code to the record
data. Data modulating circuit 260 modulates the record data into a
predetermined format. Format circuit 270 operates in
synchronization with the clock sent from PLL circuit 130 and based
on the timing signal sent from timing generating circuit 240 to add
pre-write (Pre-Write), header (Header) and post-write (Post-Write)
to the record data for formatting the record data to match with the
user data region. Format circuit 270 outputs the data thus
formatted to magnetic head drive circuit 280.
[0126] Magnetic head drive circuit 280 drives magnetic head 30 in
synchronization with the timing of timing signal sent from timing
generating circuit 240 and based on the output of format circuit
270.
[0127] Laser drive circuit 290 drives semiconductor laser 21
included in optical head 20 based on the timing signal sent from
ting generating circuit 240.
[0128] Magnetic head 30 is driven by magnetic head drive circuit
280, and adds the magnetic field, which is subjected to
magnetic-field modulation with the record pattern or data pattern,
to magneto-optical record medium 10.
[0129] Description will now be given on the operation of recording
data on magneto-optical record medium 10 by magneto-optical disk
apparatus 100. When magneto-optical record medium 10 is loaded on
magneto-optical disk apparatus 100, controller 230 controls the
servo-mechanism (not shown) to drive spindle motor 110 at a
predetermined rotation speed, and also controls laser drive circuit
290 via timing generating circuit 240 to emit the laser beams with
a predetermined intensity from optical head 20.
[0130] Thereby, servo-mechanism (not shown) drives spindle motor
110 at the predetermined rotation speed, and spindle motor 110
turns magneto-optical record medium 10 at the predetermined speed.
Before magneto-optical record medium 10 turns at the predetermined
rotation speed, magnetic head 30 is in contact with magneto-optical
record medium 10. In accordance with rotation of magneto-optical
record medium 10 at the predetermined speed, magnetic head 30
floats. Optical head 20 emits the laser beams of a predetermined
intensity, which are converged by objective lens 22 onto
magneto-optical record medium 10, and detects the beams reflected
thereby. Optical head 20 outputs the focus error signal and
tracking error signal to the servo-mechanism (not shown), which
turns on the focus servo-control and tracking servo-control of
objective lens 22 of optical head 20 based on the focus error
signal and tracking error signal, respectively.
[0131] Thereafter, optical head 20 detects the optical signal in
the radial push-pull method from magneto-optical record medium 10,
and outputs the detected optical signal to FCM-detecting circuit
120. FCM detecting circuit 120 detects the fine clock mark
detection signal from the received optical signal, and outputs the
detected fine clock mark detection signal to PLL circuit 130 and
timing generating circuit 240. PLL circuit 130 produces the clock
based on the fine clock mark detection signal, and outputs the
clock thus produced to address detecting circuit 140, A/D converter
160, waveform equalizing circuit 170, Viterbi demodulating circuit
180, unformat-circuit 190, data demodulating circuit 200,
controller 230, timing generating circuit 240, data modulating
circuit 260 and format circuit 270.
[0132] Address detecting circuit, 140 receives the address signal,
which is detected from segment S0 of magneto-optical record medium
10 by optical head 20 in the tangential push-pull method, and
detects the address signal in synchronization with the clock
supplied from PLL circuit 130. Also, address detecting circuit 140
produces the address detection signal, which indicates the fact
that the address information is detected, at the end position of
address information. The detected address information is output to
controller 230, and the produced address detection signal is output
to header detecting circuit 220 and timing generating circuit
240.
[0133] BCH encoder 250 adds an error correction code to the record
data. Data modulating circuit 260 modulates the record data, which
is sent from BCH encoder 250, into a predetermined format in
synchronization with the clock sent from PLL circuit 130. Data
modulation circuit 260 outputs the modulated record data to format
circuit 270.
[0134] Controller 230 controls timing generating circuit 240 to
generate the timing signal for generating the record signal
suitable to the format of the data region when the address signal
sent from address detecting circuit 140 designates the address of
data region on magneto-optical record medium 10. Timing generating
circuit 240 generates the timing signal synchronized with the clock
based on the fine clock mark detection signal and address signal
supplied thereto, and outputs the generated timing signal to format
circuit 270, magnetic head drive circuit 280 and laser drive
circuit 290.
[0135] Format circuit 270 formats the record signal sent from data
modulating circuit 260 based on the timing signal to match with the
format of the data region, and outputs the formatted record signal
to magnetic head dive circuit 280. Magnetic head drive circuit 280
drives magnetic head 30 to produce the magnetic field, which is
modulated with the record signal, in synchronization with the
timing signal. Laser drive circuit 290 drives semiconductor laser
21 included in optical head 20 in synchronization with the timing
signal, and optical head 20 irradiates magneto-optical record
medium 10 with the laser beams converged by objective lens 22.
Magnetic head 30 applies the magnetic field, which is modulated
with the record signal, to magneto-optical record medium 10.
Thereby, the record data is recorded on magneto-optical record
medium 10.
[0136] Then, description will now be given on the operation of
reproducing the signal from magneto-optical record medium 10 by
magneto-optical disk apparatus 100. After magneto-optical record
medium 10 is loaded on magneto-optical disk apparatus 100, magnetic
head 30 floats, and the focus servo-control and tracking
servo-control of objective lens 22 are performed. These operations
are performed in the same manner as those for the signal
recording.
[0137] Thereafter, optical head 20 detects the optical signal from
magneto-optical record medium 10 in the radial push-pull method,
and outputs the detected optical signal to FCM detecting circuit
120. FCM detecting circuit 120 detects the fine clock mark
detection signal from the optical signal supplied thereto, and
outputs the fine clock mark detection signal thus detected to PLL
circuit 130 and timing generating circuit 240. PLL circuit 130
produces the clock based on the fine clock mark detection signal,
and outputs the clock thus produced to address detecting circuit
140, A/D converter 160, waveform equaling circuit 170, Viterbi
demodulating circuit 180, unformat circuit 190, data demodulating
circuit 200, controller 230, timing generating circuit 240, data
modulating circuit 260 and format circuit 270.
[0138] Address detecting circuit 140 receives the address signal,
which is detected from segment S0 of magneto-optical record medium
10 by optical head 20 in the tangential push-pull method, and
detects the address signal in synchronization with the clock
supplied from PLL circuit 130. Also, address detecting circuit 140
produces the address detection signal, which indicates the fact
that the address information is detected, at the end position of
address information. The detected address signal is output to
controller 230, and the produced address detection signal is output
to header detecting circuit 220 and timing generating circuit
240.
[0139] Header detecting circuit 220 detects the position of the
header included in the reproduced signal based on the address
information sent from controller 230 and the address detection
signal sent from address detecting circuit 140, and produces the
timing signals for the pre-write (Pre-Write) and header (Header)
from the reproduced signal in synchronization with the clock sent
from PLL circuit 130. The timing signal thus produced for the
header (Header) is output to unformat circuit 190 and data
demodulation circuit 200.
[0140] Optical head 20 outputs the reproduced signal thus detected
to BPF 150, which cuts off the high and low ranges of the
reproduced signal. A/D converter 160 converts the reproduced analog
signal, which is output from BPF 150, from the analog signal into
the digital signal in synchronization with the clock sent from PLL
circuit 130.
[0141] Waveform equalizing circuit 170 effects PR (1, 1) waveform
equalization on the reproduced signal, which is converted into the
digital signal, in synchronization with the clock sent from PLL
circuit 130. This equalization is performed to cause one-to-one
waveform interference between the data before and after the
detection signal.
[0142] Thereafter, Viterbi demodulating circuit 180 converts the
reproduced signal, which was subjected to the waveform equalization
and is in the multilevel form, into the binary form in
synchronization with the clock sent from PLL circuit 130, and
outputs the reproduced signal thus converted to unformat circuit
190 and header detecting circuit 220.
[0143] Thereby, header detecting circuit 220 detects the position
of the header included in the reproduced signal based on the
address information sent from controller 230 and the address
detection signal sent from address detecting circuit 140, and
produces the timing signals for the pre-write (Pre-Write) and
header (Header) from the reproduction signal in synchronization
with the clock sent from PLL circuit 130. The produced timing
signal for header (Header) is sent to unformat circuit 190 and data
demodulating circuit 200.
[0144] Unformat circuit 190 removes the pre-write (Pre-Write),
post-write (Post-Write) and header (header), which are recorded in
the user data region on magneto-optical record medium 10, based on
the timing signal supplied from header detecting circuit 220.
[0145] Data demodulating circuit 200 receives the reproduced
signal, which is unformatted, in synchronization with the clock
sent from PLL circuit 130, and performs the demodulation for the
digital modulation effected at the time of recording. BCH decoder
210 performs the error correction on the reproduced signal thus
demodulated to output the signal as reproduced data. Thereby, the
operation of reproducing the signal from magneto-optical record
medium 10 is completed. When reproducing the signal, magnetic head
30 is kept in the floating state with respect to magneto-optical
record medium 10. If magnet 41 were not employed, magnets 24 and 26
included in optical head 20 would magnetically affect the magnetic
layer of magneto-optical record medium 10 to impede accurate
reproduction of the signal. However, magnet 41 can cancel the
magnetic influence by magnets 24 and 26 so that the signal can be
reproduced accurately.
[0146] According to the first embodiment of the invention, the DC
magnetic fields, which have changed intensities in the directions
of the two DC magnetic fields, are applied to the reproduction
layer of the magneto-optical record medium to detect the numbers of
errors in the reproduced signal, and the relationship is determined
between the numbers of errors thus detected and the intensities of
the DC magnetic fields. Therefore, it is possible to measure the
actual intensity of the influence magnetic field exerted from the
magnets performing the servo-control of the objective lens.
Further, the intensity of the influence magnetic field, which is
exerted from the magnets for servo-control of the objective lens,
is actually measured, and the signal is reproduced from the
magneto-optical record medium while using the magnet for removing
the influence by the influence magnetic field. Therefore, it is
possible to prevent lowering of the characteristics of the
reproduced signal, which may be caused by the magnets for
servo-control of the objective lens.
[0147] [Second Embodiment]
[0148] In a second embodiment, the same manner as the detection
manner in the first embodiment can be employed for detecting the
intensity of the influence magnetic field exerted from the magnets
for servo-control of objective lens 22.
[0149] Referring to FIG. 21, a magneto-optical disk apparatus 400
of the second embodiment includes the same structures as those of
magneto-optical disk apparatus 100 shown in FIG. 20, and
additionally includes a magnetic head 300. Further, BCH decoder 210
in the second embodiment is configured to output an error rate of
the reproduced signal, i.e., the number of errors to controller
230. Structures other then the above are the same as those of
magneto-optical disk apparatus 100.
[0150] Magnetic head 300 is driven by magnetic head drive circuit
280. Magneto-optical disk apparatus 400 actually measures the
intensity of the influence magnetic field exerted from the magnets
for servo-control of the objective lens, and can perform recording
and/or reproducing of the signal while removing the influence by
the magnetic field, of which intensity is actually measured. The
intensity of the influence magnetic field exerted from the magnets
for servo-control of the objective lens 22 is detected in the same
detecting manner as the first embodiment.
[0151] Controller 230 controls the magnetic head drive circuit 280
through timing generating circuit 240 such that magnetic head 30
may apply the DC magnetic field having the changed intensity to
magneto-optical record medium 10. Controller 230 also controls
laser drive circuit 290 so that optical head 20 may emit the laser
beams of a predetermined intensity to magneto-optical record medium
10. Magnetic head drive circuit 280 drives magnetic head 30 to emit
the DC magnetic field, of which intensity is changed under control
by controller 230, and magnetic head 30 applies the DC magnetic
field having the changed intensity to magneto-optical record medium
10. Laser beam drive circuit 290 drives semiconductor laser 21 in
optical head 20, and optical head 20 emits the laser beam of the
predetermined intensity to magneto-optical record medium 10. The
magneto-optical signals detected for the respective intensities of
DC magnetic field are subjected to the reproducing processing by
BPF 150, A/D converter 160, waveform equalizing circuit 170,
Viterbi demodulating circuit 180, unformat circuit 190, data
demodulating circuit 200 and BCH decoder 210, as already described
in connection with the first embodiment. BCH decoder 210 outputs
the error rate of reproduced signal, i.e., the number of errors to
controller 230.
[0152] Thereby, controller 230 determines the intensity at the
center of the symmetrical distribution of the magnetic field
intensity based on the relationship between the intensity of the DC
magnet field and the number of errors in the reproduced signal,
which is determined based on the number of errors supplied from BCH
decoder 210. Thereby, controller 230 determines the intensity of
the influence magnetic field. Based on the intensity of the
influence magnetic field thus determined, controller 230 controls
the magnetic head drive circuit 280 via timing generating circuit
240 to produce the magnetic field for cancelling the influence
magnetic field. Magnetic head drive circuit 280 drives magnetic
head 300 under control by controller 230, and magnetic head 300
produces the magnetic field for cancelling the influence magnetic
field.
[0153] Magneto-optical disk apparatus 400 records and/or reproduces
the signals on magneto-optical record medium 10 while removing the
influence magnetic field, which may be exerted by the magnets for
servo-control of objective lens 22, by magnetic head 300.
[0154] Magneto-optical disk apparatus 400 performs the operations
of recording the signal on magneto-optical record medium 10 and
reproducing the signal from magneto-optical record medium 10 in the
same manners as those in the first embodiment.
[0155] According to the second embodiment, the magneto-optical disk
apparatus actually measures the intensity of the influence magnetic
field applied from the magnets for servo-control of the objective
lends, and produces the magnetic field for removing the influence
magnetic field based on the result of the actual measurement.
Therefore, recording and/or reproducing of the signal on the
magneto-optical record medium can be performed accurately.
[0156] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *