U.S. patent application number 09/427825 was filed with the patent office on 2001-11-22 for optical information recording and playback apparatus.
Invention is credited to FUJIKAWA, YASUO, HAYASHI, HIDEKI, HORIBE, RYUSUKE, KADOWAKI, SHIN-ICHI.
Application Number | 20010043523 09/427825 |
Document ID | / |
Family ID | 17938327 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043523 |
Kind Code |
A1 |
HAYASHI, HIDEKI ; et
al. |
November 22, 2001 |
OPTICAL INFORMATION RECORDING AND PLAYBACK APPARATUS
Abstract
An optical information recording and playback apparatus for
recording and playing back an optical information recording medium
having a transparent protective layer comprises a tilt detection
device and an off-track adding device, and includes means for
determining an optimum direction in which the center of a light
spot is to be displaced from the centerline of an information track
on the optical information recording medium to compensate for the
tilting of the optical information recording medium relative to the
light beam, means for setting the amount of displacement as fixed
values, and means for splitting the optical information recording
medium into a number of areas and for activating a tilt detection
function each time switching is made from one area to another
during recording or playback. In this way, by scanning the light
spot on the optical information recording medium with the center of
the light spot displaced from the centerline of the information
track on the optical information recording medium, the degradation
of recording/playback signal quality due to the tilting of the
recording surface of the optical information recording medium can
be reduced.
Inventors: |
HAYASHI, HIDEKI; (NARA-SHI,
JP) ; FUJIKAWA, YASUO; (ONSEN-GUN, JP) ;
KADOWAKI, SHIN-ICHI; (SANDA-SHI, JP) ; HORIBE,
RYUSUKE; (HIRAKATA-SHI, JP) |
Correspondence
Address: |
RATNER & PRESTIA
SUITE 301
ONE WESTLAKES BERWYN
P O BOX 980
VALLEY FORGE
PA
194820980
|
Family ID: |
17938327 |
Appl. No.: |
09/427825 |
Filed: |
October 27, 1999 |
Current U.S.
Class: |
369/44.32 ;
369/53.19; G9B/7.065 |
Current CPC
Class: |
G11B 11/10576 20130101;
G11B 7/094 20130101; G11B 7/0956 20130101 |
Class at
Publication: |
369/44.32 ;
369/53.19 |
International
Class: |
G11B 007/095 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 27, 1998 |
JP |
10-304.874 |
Claims
What is claimed is:
1. An optical information recording and playback apparatus
comprising: a light source; a focusing optical system for focusing
a light beam from said light source into a microscopic spot on a
recording surface of an optical information recording medium having
a transparent protective layer; a light detector for receiving the
light beam reflected or diffracted at the recording surface of said
optical information recording medium, and for converting said
received light beam into an electrical signal; a signal circuit for
converting said electrical signal into a playback information
signal; a signal circuit for generating from said electrical signal
an error signal indicating a positional displacement between an
information track and the light spot on the recording surface of
said optical information recording medium; and driving means for
causing said light spot to follow said information track on said
optical information by using said error signal, said optical
information recording and playback apparatus characterized by the
inclusion of: means for measuring the tilt of said optical
information recording medium relative to said focusing optical
system; and an off-tracking circuit for displacing said light spot
in a direction that reduces jitter of a playback signal obtained by
playing back information recorded on said optical information
recording medium from said information track, by giving an
electrical offset to an error signal indicating a displacement in a
direction parallel to said optical information recording medium and
perpendicular to a scanning direction of said light spot, said
error signal being among the error signals supplied to said driving
means for causing said light spot to follow said information track
on said optical information.
2. An optical information recording and playback apparatus as set
forth in claim 1, comprising a jitter detection device for
detecting the jitter of the playback signal obtained by playing
back information recorded on said optical information recording
medium, and wherein the tilt of said optical information recording
medium relative to said focusing optical system is measured by
using the amount of increase in said playback signal jitter.
3. An optical information recording and playback apparatus as set
forth in claim 1, wherein said means for measuring the tilt of said
optical information recording medium relative to said focusing
optical system is a tilt detection device comprising (1) a tilt
detection light source, (2) a tilt detection focusing optical
system for focusing a light beam from said tilt detection light
source, and (3) a tilt detection light detector for projecting said
tilt detection light beam onto said optical information recording
medium, and for receiving light reflected from said optical
information recording medium for conversion into an electrical
signal.
4. An optical information recording and playback apparatus as set
forth in claim 1, wherein said means for measuring the tilt of said
optical information recording medium relative to said focusing
optical system comprises a focus drive amount detection device for
detecting a focus drive amount representing a drive amount in a
direction perpendicular to said optical information recording
medium, said focus drive amount being among said error signals
supplied to said driving means, and wherein said tilt is measured
based on said focus drive amount and a position currently being
measured on said optical information recording medium.
5. An optical information recording and playback apparatus as set
forth in claim 1, wherein said means for measuring the tilt of said
optical information recording medium relative to said focusing
optical system comprises a focus drive amount detection device for
detecting a focus drive amount representing a drive amount in a
direction perpendicular to said optical information recording
medium, said focus drive amount being among said error signals
supplied to said driving means, and wherein said tilt is measured
based on said focus drive amount.
6. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, comprising a jitter detection
device for detecting the jitter of the playback signal obtained by
playing back recorded information from said optical information
recording medium, and wherein said off-tracking circuit includes
means for varying (1) an off-track direction, the direction in
which said light spot is to be displaced, and (2) an off-track
amount, the amount by which said light spot is to be displaced, in
such a manner as to minimize said playback signal jitter.
7. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, comprising an error rate
detection device for detecting an error rate, the rate at which the
playback signal obtained by playing back recorded information from
said optical information recording medium is in error when
reproduced from an information signal written on said optical
information recording medium, and wherein said off-tracking circuit
includes means for varying (1) an off-track direction, the
direction in which said light spot is to be displaced, and (2) an
off-track amount, the amount by which said light spot is to be
displaced, in such a manner as to minimize said error rate.
8. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, comprising a flag detection
device for detecting a flag that is set when there is a certain
amount of error in a certain amount of information by comparing the
playback signal obtained by playing back recorded information from
said optical information recording medium with an information
signal written on said optical information recording medium, and
wherein said off-tracking circuit includes means for varying (1) an
off-track direction, the direction in which said light spot is to
be displaced, and (2) an off-track amount, the amount by which said
light spot is to be displaced, in such a manner as to minimize the
number of flags in said amount of information.
9. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, comprising an RF signal
detection device for detecting the amplitude of the playback signal
obtained by playing back recorded information from said optical
information recording medium, and wherein said off-tracking circuit
includes means for varying (1) an off-track direction, the
direction in which said light spot is to be displaced, and (2) an
off-track amount, the amount by which said light spot is to be
displaced, in such a manner as to maximize said playback signal
amplitude.
10. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, wherein said off-tracking
circuit includes means for setting the off-track amount, the amount
by which said light spot is to be displaced, as fixed values
providing one value on the inside of said information track and one
value on the outside thereof as viewed in the direction normal to
the scanning direction of said light spot.
11. An optical information recording and playback apparatus as set
forth in any one of claims 2 to 5, wherein said off-tracking
circuit includes means for setting the off-track amount, the amount
by which said light spot is to be displaced, as fixed values
providing more than one value on the inside of said information
track and more than one value on the outside thereof as viewed in
the direction normal to the scanning direction of said light
spot.
12. An optical information recording and playback apparatus as set
forth in claim 1, 3, 4, or 5, wherein said off-tracking circuit
includes: means for determining an off-track direction, the
direction in which said light spot is to be displaced, as (1) a
direction moving toward an inner circumference of said optical
information recording medium when said inner circumference of said
optical information recording medium, compared with an outer
circumference thereof, is positioned closer to an incidence side of
said focusing optical system because of the tilting of said optical
information recording medium relative to said focusing optical
system and (2) a direction moving toward said outer circumference
of said optical information recording medium when said outer
circumference, compared with said inner circumference, is
positioned closer to the incidence side of said focusing optical
system because of the tilting of said optical information recording
medium relative to said focusing optical system; and means for
varying an off-track amount, the amount by which said light spot is
to be displaced, in accordance with the degree of the tilting of
said optical information recording medium relative to said focusing
optical system.
13. An optical information recording and playback apparatus as set
forth in claim 1, 3, 4, or 5, wherein said off-tracking circuit
includes: means for determining an off-track direction, the
direction in which said light spot is to be displaced, as (1) a
direction moving toward an inner circumference of said optical
information recording medium when said inner circumference of said
optical information recording medium, compared with an outer
circumference thereof, is positioned closer to an incidence side of
said focusing optical system because of the tilting of said optical
information recording medium relative to said focusing optical
system and (2) a direction moving toward said outer circumference
of said optical information recording medium when said outer
circumference, compared with said inner circumference, is
positioned closer to the incidence side of said focusing optical
system because of the tilting of said optical information recording
medium relative to said focusing optical system; and means for
setting an off-track amount, the amount by which said light spot is
to be displaced, as fixed values providing one value on the inside
of said information track and one value on the outside thereof as
viewed in the direction normal to the scanning direction of said
light spot.
14. An optical information recording and playback apparatus as set
forth in claim 1, 3, 4, or 5, wherein said off-tracking circuit
includes: means for determining an off-track direction, the
direction in which said light spot is to be displaced, as (1) a
direction moving toward an inner circumference of said optical
information recording medium when said inner circumference of said
optical information recording medium, compared with an outer
circumference thereof, is positioned closer to an incidence side of
said focusing optical system because of the tilting of said optical
information recording medium relative to said focusing optical
system and (2) a direction moving toward said outer circumference
of said optical information recording medium when said outer
circumference, compared with said inner circumference, is
positioned closer to the incidence side of said focusing optical
system because of the tilting of said optical information recording
medium relative to said focusing optical system; and means for
setting an off-track amount, the amount by which said light spot is
to be displaced, as fixed values providing more than one value on
the inside of said information track and more than one value on the
outside thereof as viewed in the direction normal to the scanning
direction of said light spot.
15. An optical information recording and playback apparatus as set
forth in any one of claims 1 to 5, comprising means for splitting
said optical information recording medium into a prescribed number
of areas according to the amount of warping contained in said
optical information recording medium, and for measuring the tilt of
said optical information recording medium relative to said focusing
optical system each time switching is made from one area to
another.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical information
recording and playback apparatus which performs recording and
playback using a light beam on an optical information recording
medium having a transparent protective layer.
[0003] 2. Description of the Related Art
[0004] Heretofore, it is known to provide an optical information
recording and playback apparatus which performs recording and
playback using a light beam on an optical information recording
medium having a transparent protective layer, wherein the recording
and playback is performed by scanning a light spot with its center
displaced from the centerline of the information track on the
optical information recording medium. An example of this type of
optical information recording and playback apparatus is disclosed
in Japanese Unexamined Patent Publication with a laid-open No.
8-77583. The configuration and features of this apparatus will be
described below.
[0005] FIG. 7 is a diagram showing the configuration of a
rewritable magneto-optical disk apparatus. In FIG. 7, reference
numeral 41 is a magneto-optical disk, the information recording
medium, formed from a transparent substrate of glass or plastic
material with a magnetic film 42 formed thereon. The
magneto-optical disk 41 is mounted on the rotational shaft of a
spindle motor 43 and rotated at a prescribed speed by the rotation
of the spindle motor 43. Below the optical information recording
medium 41 is disposed an optical head 44, while a bias magnet 53 is
disposed above the medium at a position opposite the optical head
44.
[0006] The optical head 44 contains a semiconductor laser 45 as a
light source for recording and playback; when recording
information, the light beam of the semiconductor laser 45 is
modulated by a laser driving circuit not shown in accordance with
the information signal to be written. The light beam emitted from
the semiconductor laser 45 is first made parallel by a collimator
lens 46, and then passes through a polarization beam splitter 47
and enters an objective lens 48. The incident light beam is
converged by the objective lens 48 and focused as a microscopic
spot onto the magnetic film 42 of the magneto-optical disk 41. In
the meantime, a magnetic field oriented in a particular direction
is applied from the bias magnet 43 to the magneto-optical disk 41,
and a series of information bits is recorded by the application of
this magnetic field and the projection of the modulated light
beam.
[0007] The light beam projected on the magneto-optical disk 41 is
reflected at the medium surface thereof. The reflected light again
passes through the objective lens 48 and enters the polarization
beam splitter 47 at whose polarization plane the light is reflected
toward a beam splitter 49, thus being separated from the light
coming from the semiconductor laser45. The light beam reflected
into the beam splitter 49 is separated into two beams, one of which
is passed through a sensor lens 50 and received by a photosensor
51. The received light signal of the photosensor 51 is fed to an
AT/AF circuit (autotracking, autofocus control circuit) 52 via an
AT offset circuit 59 described later. Based on this signal, the
AT/AF circuit generates a tracking error signal and a focus error
signal. Using the thus generated tracking error signal and focus
error signal, tracking control and focus control are performed by
driving an objective lens actuator 54 and thereby moving the
objective lens 48 in the tracking and focusing directions.
[0008] On the other hand, when playing back information recorded on
the magneto-optical disk 41, the light beam of the semiconductor
laser 45 is set at a reading power not high enough to affect the
recorded information, and this reading light beam is directed to
the intended track to read the recorded information. More
specifically, the reading light beam reflected from the surface of
the optical information recording medium is passed through the
objective lens 48, the polarization beam splitter 47, the beam
splitter 49, and a sensor lens 55, and received by a photosensor
56.
[0009] Next, off-tracking control will be described. Reference
numeral 57 is an amplitude detection circuit for detecting the
amplitude of a playback signal based on the received signal of the
photosensor 56. The amplitude detection circuit 57 detects cross
talk and the amplitude of the playback signal when determining the
off-track direction of the reading light beam, and also when
determining the amount of off-tracking. The detected values are fed
into a CPU 58 via an A/D converter contained therein. The CPU 58 is
a processor circuit for controlling various parts of the apparatus.
When the magneto-optical disk 41 is loaded into the apparatus, the
CPU 58 controls the various parts to control the off-track
direction and off-track amount of the reading light beam. Based on
instructions from the CPU 58, the AT offset adding circuit 59
applies an offset to the AT/AF circuit 52 to displace the reading
light beam off-track in the desired direction by the desired
amount.
[0010] Means for determining the off-track direction will be
described. When the magneto-optical disk 41 is tilted toward its
outer circumference relative to the objective lens 48, as shown in
FIG. 8(a), a crescent-shaped secondary spot 801b is formed on the
disk surface at a position outside the main spot 801a and displaced
toward the outer circumference, resulting in increased cross talk
from the outer track. On the other hand, when the magneto-optical
disk 41 is tilted toward its inner circumference relative to the
objective lens 48, as shown in FIG. 8(b), a crescent-shaped
secondary spot 802b is formed on the disk surface at a position
outside the main spot 802a and displaced toward the inner
circumference, resulting in increased cross talk from the inner
track.
[0011] Accordingly, by measuring the amount of cross talk from each
of the adjacent tracks, the tilting direction of the
magneto-optical disk 41 relative to the objective lens 48 can be
identified, and thus the off-track direction of the light spot to
reduce the amount of cross talk can be determined. More
specifically, in the case of FIG. 8(a), the outer circumferential
direction is determined as the off-track direction, and in the case
of FIG. 8(b), the inner circumferential direction is determined as
the off-track direction.
[0012] A prior art example of determining the off-track direction
will be described below. A longest pattern signal is recorded in a
test area provided on a magneto-optical disk. Then, its adjacent
tracks are played back, and the amplitudes of the playback signals
are compared. Based on the result of the comparison, the relative
tilting direction of the optical information recording medium can
be identified, and thus- the off-track direction of the light spot
to reduce the amount of cross talk can be determined.
[0013] Next, means for determining the off-track amount will be
described. While varying the off-track amount, a reading light beam
is projected a predetermined number of times onto the track of the
test area where the longest pattern signal is recorded. The
off-track amount is obtained from the playback signal detected at
this time or from the amount of cross talk leaking from specific
tracks obtained by playing back the adjacent tracks.
[0014] However, the off-track amount that maximizes the amplitude
of the playback signal does not necessarily coincide with the
off-track amount that minimizes the cross talk; therefore, it is
desirable that the off-track amount that maximizes the difference
between the two quantities, as shown in FIG. 9, be determined as
the optimum value.
[0015] Operation will be described when playing back information
recorded on the magneto-optical disk 41 by using the thus
determined off-track direction and off-track amount.
[0016] First, the CPU 58 reads the off-track direction and
off-track amount from its internal memory and, based on the
direction and amount, controls the AT offset adding circuit 59. For
example, when the off-track direction is the inner circumferential
direction, and the off-track amount is a prescribed number of
micrometers, the corresponding control signal is applied from the
CPU 58 to the AT offset adding circuit 59. Upon receiving the
control signal, the AT offset adding circuit 59 applies an offset
corresponding to the off-track direction and off-track amount to
the AT/AF circuit 52. The AT/AF circuit 52 then supplies a driving
signal corresponding to the offset to the objective lens actuator
54, and the objective lens 48 is controlled in accordance with the
driving signal. The reading beam emitted from the semiconductor
laser 45 is thus displaced off-track by the prescribed number of
micrometers in the inner circumferential direction of the optical
information recording medium, and subsequent playback of the
recorded information is performed with the reading light beam thus
displaced off-track.
[0017] The above technique can be applied not only to optical
information recording and playback apparatuses but also to
apparatuses for playing back, for example, read-only recording
media or playback apparatuses for write-once recording media.
[0018] The above-described optical information recording and
playback apparatus requires the provision of a test area where a
prescribed signal is recorded for the measurement of cross talk,
and must be designed to be able to also handle optical information
recording media that do not have such a test area.
[0019] Furthermore, the direction in which the center of the light
spot on the optical information recording medium is displaced from
the centerline of the information track, and which is determined so
as to minimize the cross talk, is not always the direction that
enhances the playback signal quality of the optical information
recording and playback apparatus. There is, therefore, a need for a
method that can more suitably determine the direction and amount to
displace the center of the light spot.
SUMMARY OF THE INVENTION
[0020] In view of the problem associated with the prior art optical
information recording and playback apparatus, it is an object of
the present invention to provide an optical information recording
and playback apparatus that can reduce the degradation of
recording/playback signal quality caused by the tiling of the
optical information recording medium relative to the light
beam.
[0021] It is another object of the present invention to provide an
optical information recording and playback apparatus that can
shorten the time required to determine the optimum position to
which the light spot is to be displaced when reducing the
degradation of recording/playback signal quality caused by the
tiling of the optical information recording medium relative to the
light beam.
[0022] The first invention of the present invention is an optical
information recording and playback apparatus comprising:
[0023] a light source;
[0024] a focusing optical system for focusing a light beam from
said light source into a microscopic spot on a recording surface of
an optical information recording medium having a transparent
protective layer;
[0025] a light detector for receiving the light beam reflected or
diffracted at the recording surface of said optical information
recording medium, and for converting said received light beam into
an electrical signal;
[0026] a signal circuit for converting said electrical signal into
a playback information signal;
[0027] a signal circuit for generating from said electrical signal
an error signal indicating a positional displacement between an
information track and the light spot on the recording surface of
said optical information recording medium; and
[0028] driving means for causing said light spot to follow said
information track on said optical information by using said error
signal,
[0029] said optical information recording and playback apparatus
characterized by the inclusion of:
[0030] means for measuring the tilt of said optical information
recording medium relative to said focusing optical system; and
[0031] an off-tracking circuit for displacing said light spot in a
direction that reduces jitter of a playback signal obtained by
playing back information recorded on said optical information
recording medium from said information track, by giving an
electrical offset to an error signal indicating a displacement in a
direction parallel to said optical information recording medium and
perpendicular to a scanning direction of said light spot, said
error signal being among the error signals supplied to said driving
means for causing said light spot to follow said information track
on said optical information.
[0032] With this configuration, degradation of recording/playback
signal quality due to the tilting of the optical information
recording medium relative to the focusing optical system can be
reduced.
[0033] The second invention of the present invention is an optical
information recording and playback apparatus as set forth in said
the first invention, comprising a jitter detection device for
detecting the jitter of the playback signal obtained by playing
back information recorded on said optical information recording
medium, and wherein
[0034] the tilt of said optical information recording medium
relative to said focusing optical system is measured by using the
amount of increase in said playback signal jitter.
[0035] This configuration achieves the effect of being able to
easily measure the amount of tilting of the optical information
recording medium relative to the focusing optical system, as well
as the effect of reducing the degradation of recording/playback
signal quality caused by the tilting of the optical information
recording medium relative to the focusing optical system.
[0036] The third invention of the present invention is an optical
information recording and playback apparatus as set forth in said
the first invention, wherein said means for measuring the tilt of
said optical information recording medium relative to said focusing
optical system is a tilt detection device comprising (1) a tilt
detection light source, (2) a tilt detection focusing optical
system for focusing a light beam from said tilt detection light
source, and (3) a tilt detection light detector for projecting said
tilt detection light beam onto said optical information recording
medium, and for receiving light reflected from said optical
information recording medium for conversion into an electrical
signal.
[0037] This configuration achieves the effect of measuring the tilt
of the optical information recording medium relative to the
focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the recording surfaced of the optical information
recording medium.
[0038] The fourth invention of the present invention is an optical
information recording and playback apparatus as set forth in said
the first invention, wherein said means for measuring the tilt of
said optical information recording medium relative to said focusing
optical system comprises a focus drive amount detection device for
detecting a focus drive amount representing a drive amount in a
direction perpendicular to said optical information recording
medium, said focus drive amount being among said error signals
supplied to said driving means, and wherein said tilt is measured
based on said focus drive amount and a position currently being
measured on said optical information recording medium.
[0039] This configuration achieves the effect of being able to
easily measure the tilt of the optical information recording medium
relative to the focusing optical system, as well as the effect of
reducing the degradation of recording/playback signal quality
caused by the tilting of the optical information recording medium
relative to the focusing optical system.
[0040] The fifth invention of the present invention is an optical
information recording and playback apparatus as set forth in said
the first invention, wherein said means for measuring the tilt of
said optical information recording medium relative to said focusing
optical system comprises a focus drive amount detection device for
detecting a focus drive amount representing a drive amount in a
direction perpendicular to said optical information recording
medium, said focus drive amount being among said error signals
supplied to said driving means, and wherein said tilt is measured
based on said focus drive amount.
[0041] This configuration achieves the effect of being able to
easily measure the tilt of the optical information recording medium
relative to the focusing optical system, as well as the effect of
reducing the degradation of recording/playback signal quality
caused by the tilting of the optical information recording medium
relative to the focusing optical system.
[0042] The sixth invention of the present invention is an optical
information recording and playback apparatus as set forth in any
one of said the first to fifth inventions, comprising a jitter
detection device for detecting the jitter of the playback signal
obtained by playing back recorded information from said optical
information recording medium, and wherein
[0043] said off-tracking circuit includes means for varying (1) an
off-track direction, the direction in which said light spot is to
be displaced, and (2) an off-track amount, the amount by which said
light spot is to be displaced, in such a manner as to minimize said
playback signal jitter.
[0044] This configuration achieves the effect of determining the
optimum off-track position and the effect of measuring the tilt of
the optical information recording medium relative to the focusing
optical system, as well as the effect of reducing the degradation
of recording/playback signal quality caused by the tilting of the
optical information recording medium relative to the focusing
optical system.
[0045] The seventh invention of the present invention is an optical
information recording and playback apparatus as set forth in any
one of said the first to fifth inventions, comprising an error rate
detection device for detecting an error rate, the rate at which the
playback signal obtained by playing back recorded information from
said optical information recording medium is in error when
reproduced from an information signal written on said optical
information recording medium, and wherein
[0046] said off-tracking circuit includes means for varying (1) an
off-track direction, the direction in which said light spot is to
be displaced, and (2) an off-track amount, the amount by which said
light spot is to be displaced, in such a manner as to minimize said
error rate.
[0047] This configuration achieves the effect of determining the
optimum off-track position and the effect of measuring the tilt of
the optical information recording medium relative to the focusing
optical system, as well as the effect of reducing the degradation
of recording/playback signal quality caused by the tilting of the
optical information recording medium relative to the focusing
optical system.
[0048] The eighth invention of the present invention is an optical
information recording and playback apparatus as set forth in any
one of said the first to fifth inventions, comprising a flag
detection device for detecting a flag that is set when there is a
certain amount of error in a certain amount of information by
comparing the playback signal obtained by playing back recorded
information from said optical information recording medium with an
information signal written on said optical information recording
medium, and wherein said off-tracking circuit includes means for
varying (1) an off-track direction, the direction in which said
light spot is to be displaced, and (2) an off-track amount, the
amount by which said light spot is to be displaced, in such a
manner as to minimize the number of flags in said amount of
information.
[0049] This configuration achieves the effect of determining the
optimum off-track position and the effect of measuring the tilt of
the optical information recording medium relative to the focusing
optical system, as well as the effect of reducing the degradation
of recording/playback signal quality caused by the tilting of the
optical information recording medium relative to the focusing
optical system.
[0050] The ninth invention of the present invention is an optical
information recording and playback apparatus as set forth in any
one of said the first to fifth inventions, comprising an RF signal
detection device for detecting the amplitude of the playback signal
obtained by playing back recorded information from said optical
information recording medium, and wherein
[0051] said off-tracking circuit includes means for varying (1) an
off-track direction, the direction in which said light spot is to
be displaced, and (2) an off-track amount, the amount by which said
light spot is to be displaced, in such a manner as to maximize said
playback signal amplitude.
[0052] This configuration achieves the effect of determining the
optimum off-track position and the effect of measuring the tilt of
the optical information recording medium relative to the focusing
optical system, as well as the effect of reducing the degradation
of recording/playback signal quality caused by the tilting of the
optical information recording medium relative to the focusing
optical system.
[0053] The tenth invention of the present invention is an optical
information recording and playback apparatus as set forth in any
one of said the first to ninth inventions, wherein said
off-tracking circuit includes means for setting the off-track
amount, the amount by which said light spot is to be displaced, as
fixed values providing one value on the inside of said information
track and one value on the outside thereof as viewed in the
direction normal to the scanning direction of said light spot.
[0054] This configuration achieves the effect of reducing the time
required to determine the off-track amount, the effect of
determining the off-track position, and the effect of measuring the
tilt of the optical information recording medium relative to the
focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0055] The eleventh invention of the present invention is an
optical information recording and playback apparatus as set forth
in any one of said the second to ninth inventions, wherein said
off-tracking circuit includes means for setting the off-track
amount, the amount by which said light spot is to be displaced, as
fixed values providing more than one value on the inside of said
information track and more than one value on the outside thereof as
viewed in the direction normal to the scanning direction of said
light spot.
[0056] This configuration achieves the effect of reducing the time
required to determine the off-track amount, the effect of
determining the off-track position, and the effect of measuring the
tilt of the optical information recording medium relative to the
focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0057] The twelfth invention of the present invention is an optical
information recording and playback apparatus as set forth in said
the first, third, fourth, or fifth invention wherein said
off-tracking circuit includes:
[0058] means for determining an off-track direction, the direction
in which said light spot is to be displaced, as (1) a direction
moving toward an inner circumference of said optical information
recording medium when said inner circumference of said optical
information recording medium, compared with an outer circumference
thereof, is positioned closer to an incidence side of said focusing
optical system because of the tilting of said optical information
recording medium relative to said focusing optical system and (2) a
direction moving toward said outer circumference of said optical
information recording medium when said outer circumference,
compared with said inner circumference, is positioned closer to the
incidence side of said focusing optical system because of the
tilting of said optical information recording medium relative to
said focusing optical system; and
[0059] means for varying an off-track amount, the amount by which
said light spot is to be displaced, in accordance with the degree
of the tilting of said optical information recording medium
relative to said focusing optical system.
[0060] This configuration achieves the effect of reducing the time
required to determine the off-track direction, the effect of
determining the off-track position, and the effect of measuring the
tilt of the optical information recording medium relative to the
focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0061] The thirteenth invention of the present invention is an
optical information recording and playback apparatus as set forth
in said the first, third, fourth, or fifth invention wherein said
off-tracking circuit includes:
[0062] means for determining an off-track direction, the direction
in which said light spot is to be displaced, as (1) a direction
moving toward an inner circumference of said optical information
recording medium when said inner circumference of said optical
information recording medium, compared with an outer circumference
thereof, is positioned closer to an incidence side of said focusing
optical system because of the tilting of said optical information
recording medium relative to said focusing optical system and (2) a
direction moving toward said outer circumference of said optical
information recording medium when said outer circumference,
compared with said inner circumference, is positioned closer to the
incidence side of said focusing optical system because of the
tilting of said optical information recording medium relative to
said focusing optical system; and
[0063] means for setting an off-track amount, the amount by which
said light spot is to be displaced, as fixed values providing one
value on the inside of said information track and one value on the
outside thereof as viewed in the direction normal to the scanning
direction of said light spot.
[0064] This configuration achieves the effect of reducing the time
required to determine the off-track amount, the effect of reducing
the time required to determine the off-track direction, the effect
of determining the off-track position, and the effect of measuring
the tilt of the optical information recording medium relative to
the focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0065] The fourteenth invention of the present invention is an
optical information recording and playback apparatus as set forth
in said the first , third, fourth, or fifth invention wherein said
off-tracking circuit includes:
[0066] means for determining an off-track direction, the direction
in which said light spot is to be displaced, as (1) a direction
moving toward an inner circumference of said optical information
recording medium when said inner circumference of said optical
information recording medium, compared with an outer circumference
thereof, is positioned closer to an incidence side of said focusing
optical system because of the tilting of said optical information
recording medium relative to said focusing optical system and (2) a
direction moving toward said outer circumference of said optical
information recording medium when said outer circumference,
compared with said inner circumference, is positioned closer to the
incidence side of said focusing optical system because of the
tilting of said optical information recording medium relative to
said focusing optical system; and
[0067] means for setting an off-track amount, the amount by which
said light spot is to be displaced, as fixed values providing more
than one value on the inside of said information track and more
than one value on the outside thereof as viewed in the direction
normal to the scanning direction of said light spot.
[0068] This configuration achieves the effect of reducing the time
required to determine the off-track amount, the effect of reducing
the time required to determine the off-track direction, the effect
of determining the off-track position, and the effect of measuring
the tilt of the optical information recording medium relative to
the focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0069] The fifteenth invention of the present invention is an
optical information recording and playback apparatus as set forth
in any one of said the first to thirteenth inventions, comprising
means for splitting said optical information recording medium into
a prescribed number of areas according to the amount of warping
contained in said optical information recording medium, and for
measuring the tilt of said optical information recording medium
relative to said focusing optical system each time switching is
made from one area to another.
[0070] This configuration achieves the effect of reducing the time
required to determine the off-track amount, the effect of reducing
the time required to determine the off-track direction, the effect
of determining the off-track position, and the effect of measuring
the tilt of the optical information recording medium relative to
the focusing optical system, as well as the effect of reducing the
degradation of recording/playback signal quality caused by the
tilting of the optical information recording medium relative to the
focusing optical system.
[0071] As described above, provisions are made in the present
invention to determine the direction of displacement and the amount
of displacement, for example, when scanning a light spot on the
optical information recording medium by displacing the center of
the light spot from the centerline of the information track to
reduce jitter of the playback signal. The apparatus thus configured
can also handle optical recording media that do not have a test
area. Furthermore, the direction in which the center of the light
spot is displaced and the amount of displacement can be limited,
achieving the effect of reducing the time required to determine the
optimum position to which the light spot is displaced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0072] FIG. 1 is a block diagram of an optical information
recording and playback apparatus according to a first embodiment of
the present invention, which includes a jitter detection device and
off-track adding device;
[0073] FIG. 2 is a block diagram of an optical information
recording and playback apparatus according to a second embodiment
of the present invention, which includes a tilt detection device
and off-track adding device;
[0074] FIG. 3 is a block diagram of an optical information
recording and playback apparatus according to a third embodiment of
the present invention, which includes a focus drive amount
detection device and off-track adding device;
[0075] FIG. 4(a) is a diagram showing the intensity distribution of
a light spot when, due to R tilt (radial tilt), an optical disk
recording medium is tilted with the inner circumference of the disk
lying closer to the incidence side of a light beam than the outer
circumference thereof;
[0076] FIG. 4(b) is a diagram showing the intensity distribution of
the light spot when, due to R tilt, the optical disk recording
medium is tilted with the inner circumference of the disk lying
closer to the incidence side of the light beam than the outer
circumference thereof;
[0077] FIG. 5 is a diagram showing the relationship between a phase
difference TE signal and the amount of displacement of the light
spot in the presence of R tilt;
[0078] FIG. 6 is a diagram showing the relationship between
playback signal jitter and the amount of displacement of the light
spot in the presence of R tilt;
[0079] FIG. 7 is a block diagram showing the configuration of a
rewritable magneto-optical disk apparatus according to the prior
art;
[0080] FIG. 8(a) is a diagram showing how a spot is formed on the
disk surface when the recording medium is tilted toward its outer
circumference relative to an objective lens in the prior art
apparatus;
[0081] FIG. 8(b) is a diagram showing how a spot is formed on the
disk surface when the recording medium is tilted toward its inner
circumference relative to an objective lens in the prior art
apparatus; and
[0082] FIG. 9 is a diagram showing the results of measurements when
cross talk and playback signal amplitude are measured while varying
a reading light beam.
DESCRIPTION OF THE REFERENCE NUMERALS
[0083] 1. OPTICAL INFORMATION RECORDING MEDIUM
[0084] 2. TRANSPARENT PROTECTIVE LAYER
[0085] 3. SPINDLE MOTOR
[0086] 4. OPTICAL HEAD
[0087] 5. SEMICONDUCTOR LASER
[0088] 6. POLARIZATION BEAM SPLITTER
[0089] 7. QUARTER-WAVE PLATE
[0090] 9. PHOTOSENSOR
[0091] 10. JITTER DETECTION DEVICE
[0092] 11. CPU
[0093] 12. OFF-TRACK ADDING CIRCUIT
[0094] 13. FOCUS/TRACKING SERVO CIRCUIT
[0095] 14. OBJECTIVE LENS ACTUATOR
[0096] 15. TILT DETECTION DEVICE
[0097] 16. FOCUS DRIVE AMOUNT DETECTION DEVICE
[0098] 41. MAGNETO-OPTICAL DISK
[0099] 42. MAGNETIC FILM
[0100] 43. SPINDLE MOTOR
[0101] 44. OPTICAL HEAD
[0102] 45. SEMICONDUCTOR LASER
[0103] 46. COLLIMATOR LENS
[0104] 47. POLARIZATION BEAM SPLITTER
[0105] 48. OBJECTIVE LENS
[0106] 49. BEAM SPLITTER
[0107] 50. SENSOR LENS
[0108] 51. PHOTOSENSOR
[0109] 52. AT/AF CIRCUIT
[0110] 53. BIAS MAGNET
[0111] 54. OBJECTIVE LENS ACTUATOR
[0112] 55. SENSOR LENS
[0113] 56. PHOTOSENSOR
[0114] 57. AMPLITUDE DETECTION CIRCUIT
[0115] 58. CPU
[0116] 59. AT OFFSET APPLICATION CIRCUIT
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0117] Embodiments of the optical information recording and
playback apparatus of the present invention will be described below
with reference to the accompanying drawings.
[0118] (Embodiment 1)
[0119] FIG. 1 is a diagram showing the configuration of an optical
information recording and playback apparatus according to a first
embodiment of the present invention.
[0120] The configuration of this embodiment will be described below
with reference to FIG. 1. The configuration shown in the figure
differs from the prior art optical information recording and
playback apparatus by the inclusion of a jitter detection device 10
and off-track adding device 12.
[0121] In FIG. 1, the jitter detection device 10 performs the
function of detecting jitter of a playback signal, while the
off-track adding device 12 performs the function of displacing the
center of a light spot from the centerline of an information track
on an optical information recording medium.
[0122] This embodiment concerns one embodiment of the present
invention described in claims 1, 2, 6, 7, 8, 9, 10, 11, and 15 of
the invention.
[0123] In this embodiment, an optical disk recording medium is used
as the optical information recording medium. In this specification,
the term R tilt (radial tilt) refers to the tilt of the optical
disk recording medium relative to focusing optics in a direction
normal to the scanning direction of the light spot on the optical
disk recording medium.
[0124] Referring now to FIGS. 4(a) and 4(b), a description will be
given of why jitter of the playback signal increases if there is an
R tilt between the optical disk recording medium and the focusing
optics.
[0125] FIGS. 4(a) and 4(b) illustrate the intensity distribution of
the light spot when there is an R tilt.
[0126] FIG. 4(a) is a diagram showing the intensity distribution of
the light spot when, because of the R tilt, the optical disk
recording medium is tilted with the inner circumference of the disk
lying closer to the incidence side of the light beam than the outer
circumference thereof.
[0127] In the absence of R tilt, the center 401a of the main beam
is substantially aligned with the theoretical center obtained from
the phase difference TE signal, as shown at reference numeral 401
in the figure. However, in the presence of R tilt, the center 402a
of the main beam shifts toward the outer circumference, as shown at
reference numeral 402 in the figure.
[0128] This is the first factor contributing to increased
jitter.
[0129] Further, as shown in the figure, coma occurs because of the
presence of R tilt and the protective layer of the optical disk
recording medium. This is the second factor contributing to
increased jitter.
[0130] FIG. 4(b) is a diagram showing the intensity distribution of
the light spot when, because of the R tilt, the optical disk
recording medium is tilted with the outer circumference of the disk
lying closer to the incidence side of the light beam than the inner
circumference thereof. Here also, the same factors as given in FIG.
4(a) contribute to increased jitter, the only difference being
that, in FIG. 4(b), the main beam shifts in the opposite direction
and the coma is produced on the opposite side across the optical
axis.
[0131] To address the first jitter increase due to the main beam
shift, in the case of FIG. 4(a), playback is performed by
displacing the light spot in the direction of the inner
circumference of the optical disk recording medium (as indicated at
reference numeral 403 in the figure), while in the case of FIG.
4(b), playback is performed by displacing the light spot in the
direction of the outer circumference of the optical disk recording
medium (as indicated at reference numeral 404 in the figure), thus
bringing the center of the main beam closer to the theoretical
center obtained from the phase difference TE signal. This is the
method of the present invention for suppressing the jitter increase
due to the R tilt.
[0132] Though the jitter due to coma cannot be eliminated, this
method offers an enormous effect in suppressing the jitter increase
due to the R tilt.
[0133] FIG. 5 shows the relationship between the phase difference
TE (tracking error) signal and the amount of displacement of the
light spot in the presence of R tilt.
[0134] As shown in FIG. 5, the zero cross point of the phase
difference TE signal, that is, the theoretical center obtained from
the phase difference TE signal, always indicates about the center
of the information track on the optical disk recording medium,
regardless of the presence or absence of Rtilt. Further, the
relationship between the phase error TE signal and the amount of
displacement of the light spot is not affected by the presence or
absence of R tilt.
[0135] From the above, it can be seen that the phase difference TE
signal, which is independent of the variation of the R tilt, is
suitable as the TE signal for accurately displacing the light spot.
Accordingly, the phase difference TE signal is used as the TE
signal in the optical information recording and playback apparatus
of the present embodiment.
[0136] Referring again to FIG. 1, the configuration for playing
back the optical disk recording medium according to the first
embodiment will be described below.
[0137] Reference numeral 1 is the optical disk recording medium
which is provided with a transparent protective layer 2. The
optical disk recording medium is mounted on the rotational shaft of
a spindle motor 3 and rotated at a prescribed speed by the rotation
of the spindle motor 3. An optical head 4 is disposed below the
optical disk recording medium 1.
[0138] The optical head 4 contains a semiconductor laser 5 which
emits light by being driven by a laser driving circuit not shown.
The emitted light beam passes through a polarization beam splitter
6 and enters an objective lens 8. The light beam is then focused
onto the recording surface of the optical disk recording
medium.
[0139] The reflected light again passes through the objective lens
8 and enters the polarization beam splitter 6. Since the
polarization state of the light has been changed on the way by a
quarter-wave plate 7, the light is reflected at the polarization
plane of the polarization beam splitter 6 and received by a
photosensor 9.
[0140] The received light is used to derive a playback signal and a
servo control signal. A CPU 11 takes in the servo control signal
and issues an instruction to a focus/tracking servo circuit 13 to
make the light spot follow the information track on the optical
disk recording medium.
[0141] As a result, the focus/tracking servo circuit 13 applies a
driving current to an objective lens-actuator 14; the light spot is
thus made to follow the information track on the optical disk
recording medium, and the playback signal is obtained.
[0142] Next, a description will be given of the configuration of a
means for detecting the amount of R tilt based on the amount of
increase in playback signal jitter.
[0143] While the light spot is being maintained on the information
track on the optical disk recording medium by the focus/tracking
servo circuit 13, the jitter detection device 10 detects jitter
based on the playback signal fed from the photosensor 9.
[0144] The CPU 11 takes in the detected jitter value, and compares
this jitter value with a jitter reference value obtained by adding
an allowable jitter increase amount to the value of jitter detected
at start-up at the innermost portion of the optical disk recording
medium where the R tilt is the smallest.
[0145] If the detected jitter value of the playback signal is worse
than the jitter reference value, it is determined that the amount
of the tilt is such a degree that requires an off-tracking
operation.
[0146] The configuration for performing the off-tracking operation
will be described below.
[0147] The off-tracking here means displacing the light spot in a
direction normal to the scanning direction of the light spot.
[0148] When the CPU 11 judges that the detected jitter value is
worse than the reference value, control is performed to displace
the light spot.
[0149] The off-track adding device 12 applies an electrical offset
to a tracking servo section of the focus/tracking servo circuit 13
in accordance with the instruction from the CPU 11. Then, a driving
current corresponding to the offset is supplied to the objective
lens actuator 14. As a result, the light spot is displaced off
center. The configuration for performing the off-tracking operation
will be referred to as the off-tracking circuit.
[0150] The following four configurations are examples of the means
used to determine the optimum off-track position. Any of the
following configuration examples can be used in the present
embodiment.
[0151] The first configuration is a means wherein jitter is
detected using the jitter detection device 10 and the off-tracking
operation is repeated until the jitter is minimized.
[0152] The second configuration is a means wherein an error rate
detection device not shown detects an error rate, the rate at which
the playback signal obtained by playing back recorded information
from the optical disk recording medium is in error when reproduced
from an information signal written on the optical disk recording
medium, and the off-tracking operation is repeated until the error
rate is minimized.
[0153] The third configuration is a means wherein a C1 flag
detection device not shown detects the number of C1 flags that are
set when there is a certain amount of error in (a certain amount
of) information by comparing the playback signal obtained by
playing back recorded information from the optical disk recording
medium with the information signal written on the optical disk
recording medium, and the off-tracking operation is repeated until
the number of detected C1 flags is minimized.
[0154] The fourth configuration is a means wherein an RF signal
detection device not shown detects the amplitude of the playback
signal and the off-tracking operation is repeated until the
amplitude of the playback signal is maximized.
[0155] Further, the optimum off-track position determining means
can be simplified.
[0156] This will be explained below. FIG. 6 shows the relationship
between the amount of displacement of the light spot and the jitter
of the playback signal in the presence of R tilt.
[0157] The optical disk recording medium used here is a
single-layer DVD disk having a transparent protective layer
thickness of 0.6 mm, a track pitch of 0.74 .mu.m, and a minimum pit
length of 0.40 .mu.m. The results show that the amount by which the
light spot is displaced according to the R tilt to achieve the best
jitter result for the playback signal is 0.08 .mu.m for an R tilt
of 0.35 deg. and 0.11 .mu.m for an R tilt of 0.7 deg., the values
thus clustering around 0.1 .mu.m.
[0158] From these results, it can be seen that the amount of
displacement of the light spot can be fixed at a predetermined
value. Means using fixed values can be accomplished either by a
means that sets the amount of displacement as fixed values
providing one value on the inner circumferential side and one value
on the outer circumferential side as viewed in the direction normal
to the scanning direction of the light spot, or by a means that
sets the amount of displacement as fixed values providing more than
one value on the inner circumferential side and more than one value
on the outer circumferential side as viewed in the direction normal
to the scanning direction of the light spot.
[0159] From the results of FIG. 6 it has been found that an effect
equivalent to that obtained with the means that displaces the light
spot to the optimum off-track position can be achieved using the
means that sets one fixed value on the inner circumferential side
and one fixed value on the outer circumferential side as viewed in
the direction normal to the scanning direction of the light spot.
Accordingly, the means using such fixed values is advantageous
since it can reduce the time required to determine the amount of
displacement of the light spot.
[0160] In the present embodiment, the single-layer DVD disk was
played back under the following conditions.
[0161] First, the reference value stored in the CPU was set at 14%,
i.e., 6.8% representing the jitter between data clocks at the
innermost portion plus 7.2% which is the allowable jitter increase
amount. The predetermined amount by which the light spot was
displaced was set at 0.1 .mu.m, which corresponds to 1/6 of the
track pitch.
[0162] As a result, when the R tilt was 0.7 deg., the jitter
between data clocks was improved nearly 4% by displacing the center
of the light spot from the centerline of the information track.
[0163] Further, if the optical disk recording medium is split into
a number of areas in the radial direction, with provisions made to
measure the jitter of the playback signal each time the playback
area changes from one area to the next, the time spent in the
process of detecting jitter and performing control according to the
detected jitter can be reduced compared with the above-described
configuration which constantly measures the jitter of the playback
signal.
[0164] (Embodiment 2)
[0165] FIG. 2 is a diagram showing the configuration of an optical
information recording and playback apparatus according to a second
embodiment of the present invention.
[0166] The configuration of this embodiment will be described below
with reference to FIG. 2. The configuration shown in the figure
differs from the prior art optical information recording and
playback apparatus by the inclusion of a tilt detection device 15
and off-track adding device 12.
[0167] In FIG. 2, the tilt detection device 15 performs the
function of detecting the tilt of the optical information recording
medium relative to the focusing optics, while the off-track adding
device 12 performs the function of displacing the center of the
light spot from the centerline of the information track on the
optical information recording medium.
[0168] This embodiment concerns one embodiment of the present
invention described in claims 1, 3, 6, 7, 8, 9, 10, 11, 12, 13, 14,
and 15 of the invention.
[0169] In this embodiment, in the optical disk recording medium
playback configuration the same elements as those in the first
embodiment are designated by the same reference numerals, and
descriptions of such elements will not be repeated here.
[0170] In the second embodiment, a description will be given of the
configuration of the means for detecting the amount of R tilt and
the direction of the R tilt by using the tilt detection device
15.
[0171] The tilt detection device 15 comprises a light source,
focusing optics, and a light detector.
[0172] The light beam emitted from the tilt detection device 15 is
projected onto the optical disk recording medium 1, and the
reflected light is detected by the light detector in the tilt
detection device 15. The amount of R tilt is detected from the
variation of the reflected light.
[0173] The detected tilt amount is compared with a tilt reference
value obtained by adding an allowable tilt amount to the value of
the R tilt detected at start-up at the innermost portion of the
optical disk recording medium where the Rtilt is the smallest. If
the detected tilt amount is larger than the tilt reference value,
it is determined that the tilt amount is such a degree that
requires an off-tracking operation.
[0174] The configuration for performing the off-tracking operation
will be described below.
[0175] As in the first embodiment, the off-tracking operation is
performed using the off-tracking circuit.
[0176] To determine the optimum off-track position, the
off-tracking operation is repeated using one of the four measures,
i.e., the jitter of the playback signal, the error rate, the C1
flag, or the RF signal, as in the first embodiment.
[0177] Furthermore, as in the first embodiment, the off-track
position determining means can be simplified by setting the
off-track amount as fixed values, i.e., one fixed value or more
than one fixed value on each of the inner and outer circumferential
sides as viewed in the direction normal to the scanning
direction.
[0178] In the second embodiment, the off-track direction
determining means can also be simplified since the direction of the
R tilt is known because of the provision of the tilt detection
device.
[0179] It is also seen that the off-track direction that reduces
the playback signal jitter is the same as the direction in which
the inner circumference or the outer circumference of the optical
disk recording medium is tilted toward the incidence side of the
light beam, as previously shown in FIGS. 4(a) and 4(b). That is, in
the case of FIG. 4(a), playback is performed by displacing the
light spot in the direction of the inner circumference of the
optical disk recording medium (as indicated at reference numeral
403 in the figure), while in the case of FIG. 4(b), playback is
performed by displacing the light spot in the direction of the
outer circumference of the optical disk recording medium (as
indicated at reference numeral 404 in the figure).
[0180] Therefore, the CPU 11 controls the off-track direction in
accordance with the direction of the R tilt.
[0181] The off-track amount determining means here can be
accomplished by a means that obtains the optimum off-track position
using one of the four measures, i.e., the jitter of the playback
signal, the error rate, the C1 flag, or the RF signal, as in the
first embodiment, a means that varies the off-track amount
according to the amount of change of the R tilt, a means that
provides one fixed value on each of the outer and inner
circumferential sides as viewed in the direction normal to the
scanning direction, or a means that provides more than one fixed
value on each of the outer and inner circumferential sides as
viewed in the direction normal to the scanning direction.
[0182] Next, detailed setting conditions and experimental results
according to the present embodiment will be described.
[0183] The optical disk recording medium used here is a
single-layer DVD disk having a transparent protective layer
thickness of 0.6 mm, a track pitch of 0.74 .mu.m, and a minimum pit
length of 0.40 .mu.m.
[0184] The reference value for the amount of R tilt was set at 0.5
deg. and the amount of displacement at 1/6 of the track pitch.
[0185] The direction of displacement was set the same as the
direction in which the inner circumference or the outer
circumference of the optical disk recording medium is tilted toward
the incidence side of the light beam, as shown in FIGS. 4(a) and
4(b).
[0186] As a result, when an R tilt of 0.7 deg. was detected, the
jitter between data clocks was improved nearly 4% by displacing the
center of the light spot from the centerline of the information
track.
[0187] Further, by splitting the optical disk recording medium into
a number of areas in the radial direction, and making provisions to
measure the R tilt each time the playback area changes from one
area to the next, the time spent in the process of detecting the R
tilt and performing control according to the detected R tilt can be
reduced.
[0188] The tilt detection device is not limited to the
above-described method, but the present invention can also be
carried out by using, for example, a method that samples the light
reflected from the specular surface of the disk and detects the R
tilt using the tracking signal at that time.
[0189] (Embodiment 3)
[0190] FIG. 3 is a diagram showing the configuration of an optical
information recording and playback apparatus according to a third
embodiment of the present invention.
[0191] The configuration of this embodiment will be described below
with reference to FIG. 3. The configuration shown in the figure
differs from the prior art optical information recording and
playback apparatus by the inclusion of a focus drive amount
detection device 16 and off-track adding device 12.
[0192] In FIG. 3, the focus drive amount detection device 16
performs the function of measuring the focus drive amount on the
optical information recording medium, while the off-track adding
device 12 performs the function of displacing the center of the
light spot from the centerline of the information track on the
optical information recording medium.
[0193] This embodiment concerns one embodiment of the present
invention described in claims 1, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, and 15 of the invention.
[0194] In this embodiment, in the optical disk recording medium
playback configuration the same elements as those in the first
embodiment are designated by the same reference numerals, and
descriptions of such elements will not be repeated here.
[0195] In the third embodiment, a description will be given of the
configuration of the means for detecting the amount of R tilt and
the direction of the R tilt by using the focus drive amount
detection device 16.
[0196] First, the operation for measuring the R tilt of the optical
disk recording medium using the focus drive amount and playback
radial position will be described.
[0197] In FIG. 3, an average focus drive value per revolution of
the optical disk recording medium is detected using the focus drive
amount detection device 16. In this specification, this value will
be called the focus drive amount.
[0198] The detected focus drive amount varies substantially
proportionally to the amount of displacement from the neutral
position of the objective lens actuator 14.
[0199] Accordingly, by detecting this drive amount, the amount of
surface wobbling of the optical disk recording medium can be easily
determined. Further, if the amount of surface wobbling and the
radial position currently being played back are known, the R tilt
can be determined.
[0200] Since the optical disk recording medium has the
characteristic that its R tilt is small at the inner
circumferential portion and increases toward the outer
circumference, the R tilt at the inner circumferential portion can
be taken as the reference.
[0201] Therefore, the focus drive amount at the innermost portion
is stored in the CPU 11 at start-up, and the focus drive amount is
detected during playback and compared with the first stored focus
drive amount; that is, the R tilt of the optical disk recording
medium is calculated based on the difference between the two focus
drive amounts and on the radial position currently being played
back.
[0202] Further, the tilt detection method can be simplified to such
an extent that only the amount of change of the focus drive amount
can be detected.
[0203] The reason is that since the R tilt that increases the
jitter of the optical disk recording medium is predominantly in the
outer circumferential area, the amount of change at the playback
radial position can be generally represented by a value obtained at
or near the outermost area.
[0204] This is advantageous because it can eliminate the time
required to convert the amount of change of the focus drive amount
between the innermost area and the current playback area into the R
tilt.
[0205] The focus drive amount detected at or near the outermost
area is compared with the reference value of the focus drive amount
obtained by adding an allowable focus drive amount to the focus
drive amount detected at start-up at the innermost area of the
optical disk recording medium where the R tilt is the smallest. If
the detected focus drive amount is larger than the reference value,
it is determined that the tilt amount is such a degree that
requires an off-tracking operation.
[0206] The detection of the focus drive amount at or near the
outermost area is performed at start-up together with the detection
of the focus drive amount at the innermost area.
[0207] The configuration for performing the off-tracking operation
will be described next.
[0208] As in the first embodiment, the off-tracking operation is
performed using the off-tracking circuit. To determine the optimum
off-track position, the off-tracking operation is repeated using
one of the four measures, i.e., the jitter of the playback signal,
the error rate, the C1 flag, or the RF signal, as in the first
embodiment. Furthermore, as in the first embodiment, the off-track
position determining means can also be simplified by setting the
off-track amount as fixed values, i.e., one fixed value or more
than one fixed value on each of the inner and outer circumferential
sides as viewed in the direction normal to the scanning
direction.
[0209] Further, in the third embodiment, the off-track direction
determining means can be simplified because the direction of the R
tilt is known from the polarity of the focus drive amount obtained
by the focus drive amount detection device.
[0210] It is also seen that the off-track direction that reduces
the playback signal jitter is the same as the direction in which
the inner circumference or the outer circumference of the optical
disk recording medium is tilted toward the incidence side of the
light beam, as previously shown in FIGS. 4(a) and 4(b).
[0211] The CPU 11 controls the off-track direction in accordance
with the direction of the R tilt.
[0212] The off-track amount determining means here can be
accomplished by a means that obtains the optimum off-track position
using one of the four measures, i.e., the jitter of the playback
signal, the error rate, the C1 flag, or the RF signal, as in the
first embodiment, a means that varies the off-track amount
according to the amount of change of the focus drive amount, a
means that provides one fixed value on each of the outer and inner
circumferential sides as viewed in the direction normal to the
scanning direction, or a means that provides more than one fixed
value on each of the outer and inner circumferential sides as
viewed in the direction normal to the scanning direction.
[0213] Next, detailed setting conditions and experimental results
according to the present embodiment will be described.
[0214] The optical disk recording medium used here is a
single-layer DVD disk having a transparent protective layer
thickness of 0.6 mm, a track pitch of 0.74 .mu.m, and a minimum pit
length of 0.40 .mu.m. The reference value for the focus drive
amount was set at a value corresponding to 0.5 deg. in terms of the
R tilt, and the amount of displacement was set at 1/6 of the track
pitch.
[0215] The direction of displacement was set the same as the
direction in which the inner circumference or the outer
circumference of the optical disk recording medium is tilted toward
the incidence side of the light beam, as shown in FIGS. 4(a) and
4(b).
[0216] As a result, when a focus drive amount corresponding to an R
tilt of 0.7 deg. was detected, the jitter between data clocks was
improved nearly 4% by displacing the center of the light spot from
the centerline of the information track.
[0217] Further, by splitting the optical disk recording medium into
a number of areas in the radial direction, and making provisions to
measure the amount of change of the focus drive amount each time
the playback area changes from one area to the next, the time spent
in the process of detecting the drive amount and performing control
based on the detected drive amount can be reduced.
[0218] The playback signal used in each of the above-described
embodiments can be derived from a signal recorded on the optical
information recording medium by a recording operation of the
optical information recording and playback apparatus, or
alternatively, an address signal or other information prerecorded
on the optical information recording medium can be used to derive
the playback signal.
[0219] Accordingly, though the above-described embodiments have
dealt mainly with an optical information recording and playback
apparatus, the present invention can be equally applied to an
optical information playback apparatus, in which case also the same
effects as described thus far can be achieved.
[0220] Each of the above-described embodiments has been described
by taking an optical disk recording medium as an example of the
optical information recording medium, but the application is not
limited to this specific example; for example, the invention is
also applicable to other types of optical information recording
media such as card type media.
[0221] In the case of such a recording apparatus, the invention can
also reduce the quality degradation of the recorded signal by
performing the above-described operations.
[0222] In any of the above-described embodiments, a program
recording medium, such as an optical disk or a magnetic disk, may
be created that holds a program for having a computer implement all
or part of the functions of all or part of the means of the
apparatus so that the program can be run on the computer to carry
out the above-described operations. In this case also, the same
effects as described above can be achieved.
[0223] As described above, according to the present invention, in
an optical information recording and playback apparatus that
performs recording and playback using a light beam on an optical
information recording medium having a transparent protective layer,
an advantageous effect can be obtained that reduces the quality
degradation of the recording/playback signal caused by the tilting
of the optical information recording medium relative to the light
beam. The invention also offers an advantageous effect that reduces
the time required to determine the optimum position to which the
light spot is to be displaced.
* * * * *