U.S. patent application number 09/772155 was filed with the patent office on 2002-04-04 for optical storage apparatus.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Ikeda, Toru, Nishida, Masatsugu, Tsukahara, Wataru, Yanagi, Shigenori.
Application Number | 20020039333 09/772155 |
Document ID | / |
Family ID | 18780597 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020039333 |
Kind Code |
A1 |
Tsukahara, Wataru ; et
al. |
April 4, 2002 |
Optical storage apparatus
Abstract
An offset measuring unit receives a servo error signal E1 in
which a change in an offset caused by a change in an amount of
reflection light directly appears and which does not pass through a
filter, and measures an offset amount in the servo error signal
which is caused by a change in the amount of reflection light. A
correction amount calculating unit calculates a correction amount
to cancel out the offset amount and outputs the correction amount
to an offset correcting circuit for an offset generating period so
as to perform correction.
Inventors: |
Tsukahara, Wataru;
(Kawasaki, JP) ; Yanagi, Shigenori; (Kawasaki,
JP) ; Ikeda, Toru; (Kawasaki, JP) ; Nishida,
Masatsugu; (Kawasaki, JP) |
Correspondence
Address: |
GREER, BURNS & CRAIN
300 S WACKER DR
25TH FLOOR
CHICAGO
IL
60606
US
|
Assignee: |
FUJITSU LIMITED
|
Family ID: |
18780597 |
Appl. No.: |
09/772155 |
Filed: |
January 29, 2001 |
Current U.S.
Class: |
369/44.36 ;
G9B/7.089 |
Current CPC
Class: |
G11B 7/094 20130101 |
Class at
Publication: |
369/44.36 |
International
Class: |
G11B 007/095 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 29, 2000 |
JP |
2000-298664 |
Claims
What is claimed is:
1. An optical storage apparatus comprising: an actuator capable of
positioning an objective lens for irradiating a medium with a light
beam from a light source to a target position on the medium; a
servo error signal generating circuit which generate a servo error
signal indicative of a deviation from a target position of the
objective lens on the basis of reflection light from the medium; an
offset correcting circuit which correct an offset by adding an
arbitrary correction amount to the servo error signal outputted
from said servo error signal generating circuit; a filter which
eliminate an unnecessary frequency component from the servo error
signal outputted from said offset correcting circuit; a servo
control unit which position said objective lens to a target
position on the medium on the basis of the servo error signal
outputted from said filter; an offset measuring unit which receive
the servo error signal which does not pass through said filter and
measuring an offset amount in the servo error signal, caused by a
change in an amount of reflection light; and a correction amount
calculating unit which calculate a correction signal to cancel out
said offset amount and outputting the correction signal to perform
correction to said offset correcting circuit for an offset
generating period.
2. An apparatus according to claim 1, wherein said offset measuring
unit receives a light amount change detection signal indicative of
a change in an amount of reflection light from the medium and
measures an offset amount from a difference between a servo error
signal just before a detection start timing of said light amount
change detection signal and a servo error signal just after the
detection start timing, and said correction amount calculating unit
outputs a correction amount calculated on the basis of said offset
amount to said offset correcting circuit for a period of time in
which a light amount change is detected from said light amount
change detection signal.
3. An apparatus according to claim 1, wherein said correction
amount detecting unit inputs a light amount change detection signal
indicative of a change in an amount of reflection light from the
medium and measures an offset amount from a difference between a
servo error signal just before a detection start timing of said
light amount change detection signal and a servo error signal at a
time point after elapse of predetermined time since the detection
start timing, and said correction amount calculating unit outputs a
correction amount calculated on the basis of said offset amount to
said offset correcting circuit for predetermined time since the
detection start timing of said light amount change detection
signal.
4. An apparatus according to claim 2 or 3, wherein said correction
amount calculating unit outputs an auxiliary correction amount
obtained by multiplying a correction amount of last time by a
constant to said offset correcting circuit for a period of time
from the detection start timing of said light amount change
detection signal until a correction amount based on the offset
detection is calculated and outputted.
5. An apparatus according to claim 1, wherein said offset measuring
unit calculates an offset amount on the basis of a plurality of
past detection results.
6. An apparatus according to claim 1, wherein said offset measuring
unit receives a first logical signal indicating whether a light
beam following a track in a medium is in a data area to which data
can be recorded or in an ID area recorded between sectors, and
measures an offset amount in said servo error signal on the basis
of a detection timing of the ID area in said first logical signal,
and said correction amount calculating unit outputs a correction
amount calculated based on said offset amount to said offset
correcting circuit so as to perform correction for a period of
detection of the ID area by said first logical signal.
7. An apparatus according to claim 6, wherein said offset measuring
unit measures an offset amount from a difference between a servo
error signal just before a start timing of detecting the ID area by
said first logical signal and a servo error signal just after the
start timing, and said correction amount calculating unit outputs a
correction amount calculated on the basis of said offset amount to
said offset correcting circuit for predetermined time since the
start timing of detection of the ID area by said first logical
signal.
8. An apparatus according to claim 6, wherein said offset measuring
unit measures an offset amount from a difference between a servo
error signal just before the start timing of the ID area detection
by said first logical signal and a servo error signal at a time
point after elapse of predetermined time since the start timing,
and said correction amount detecting unit outputs a correction
amount calculated on the basis of said offset amount to said offset
correcting circuit for predetermined time since the start timing of
detection of the ID area by said logical signal.
9. An apparatus according to claim 7 or 8, wherein said correction
amount calculating unit outputs an auxiliary correction amount
obtained by multiplying a correction amount of last time by a
constant to said offset correcting circuit for a period of time
since the start timing of detection of the ID area by said first
logical signal until the correction amount based on the offset
detection is calculated and outputted.
10. An apparatus according to claim 6, wherein said offset
measuring unit calculates an offset amount on the basis of a
plurality of past detection results.
11. An apparatus according to claim 1, wherein said offset
measuring unit receives a first logical signal indicating whether a
light beam following a track in a medium is in a data area to which
data can be recorded or an ID area recorded between sectors and a
second logical signal indicating whether the apparatus is recording
data to the medium or erasing data in the medium, and measures an
offset amount in said servo error signal being recorded or erased
on the basis of said first and second logical signals, and said
correction amount calculating unit outputs a correction amount
calculated on the basis of said offset amount to said offset
correcting circuit during said recording or erasing to perform
correction.
12. An apparatus according to claim 7 or 8, wherein said offset
measuring unit measures an offset amount from a difference between
a servo error signal just before a start timing of detection of the
ID area by said first logical signal and a servo error signal just
after start of recording or erasing by said second logical signal
and said correction amount calculating unit outputs a correction
amount calculated on the basis of said offset amount to said offset
correcting circuit during the recording or erasing by said second
logical signal.
13. An apparatus according to claim 6, wherein said offset
measuring unit detects an offset amount from a difference between a
servo error signal just before the start timing of detection of the
ID area by said first logical signal and a servo error signal after
elapse of predetermined time since the start of recording or
erasing by said second logical signal, and said correction amount
calculating unit outputs a correction amount calculated on the
basis of said offset amount to said offset correcting circuit
during the recording or erasing by said second logical signal.
14. An apparatus according to claim 13, wherein said correction
amount calculating unit outputs an auxiliary correction amount
obtained by multiplying a correction amount of last time by a
constant to said offset correcting circuit for a period of time
since the start timing of recording or erasing by said second
logical signal until the correction amount based on the offset
detection is calculated and outputted.
15. An apparatus according to claim 11, wherein said offset
measuring unit calculates an offset amount on the basis of a
plurality of past detection results.
16. An apparatus according to claim 11, wherein in the case of
continuously recording or erasing data to/from a plurality of
sectors, said correction amount calculating unit continuously uses
a correction amount calculated for the first sector for second and
subsequent sectors.
17. An apparatus according to claim 1, wherein said servo error
signal generating circuit is a tracking error signal generating
circuit which generate a tracking error signal indicative of a
deviation from a target position in a medium track center of the
objective lens on the basis of reflection light from the
medium.
18. An apparatus according to claim 1, wherein said servo error
signal generating circuit is a focusing error signal generating
circuit which generate a focusing error signal indicative of a
deviation from a focus position of the objective lens on the medium
on the basis of reflection light from the medium.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an optical storage
apparatus for positioning an objective lens for irradiating a
medium with a light beam from a light source to a target position
on a medium by a tracking control and a focusing control and
performing reproduction, recording, or erasure. More particularly,
the invention relates to an optical storage apparatus for measuring
and correcting an offset in a servo error signal caused by a change
in an amount of reflection light from a medium.
[0003] 2. Description of the Related Arts
[0004] Attention is paid to an optical disk as a removable storage
medium as a core of multimedia which has rapidly been developing in
recent years, and a magnetooptic disk (MO), a phase change optical
disk (PD), and the like exist. An optical disk drive using such an
optical disk as a storage medium has an objective lens for
irradiating a medium with a light beam from a laser light source,
which is mounted on an actuator movable in the radial direction of
the medium, and performs a servo control of positioning the light
beam to a target track position on the medium and positioning the
objective lens so as to achieve focus on the medium by moving the
objective lens in an optical axis direction. Such a servo control
is performed by generating a servo error signal (a tracking error
signal and a focusing error signal) indicative of a deviation from
the target position of the objective lens on the basis of
reflection light from the medium and positioning the objective lens
to the target position on the basis of the servo error signal
(tracking control and focusing control). Since the servo error
signal used for the servo control is generated by receiving the
reflection light from the medium by a photodetector, an amount of
light received by the photodetector changes according to an amount
of the reflection light from the medium and a light emitting power
itself of the laser light source. Consequently, an offset component
is generated in the servo error signal, and the servo stability
deteriorates. The phenomenon of occurrence of an offset in the
servo error signal due to a change in the amount of reflection
light received by the photodetector will be described as follows.
Although the phenomenon will be described with respect to a track
system here, the phenomenon with respect to the focusing system is
similar.
[0005] FIG. 1 shows a construction of a tracking error signal
generating circuit. Specifically, the tracking error signal
generating circuit includes: a photodetecting unit 300 having a
pair of photodetectors 302 and 304 for receiving reflection light
from a medium and performing a photoelectric conversion;
current-to-voltage converters 306 and 308 for converting currents
ia and ib from the photodetectors 302 and 304 to voltages Va and
Vb, respectively; a subtractor 310 for obtaining a difference
(Va-Vb) of the two voltage signals Va and Vb derived by the
conversion by the current-to-voltage converters 306 and 308; an
adder 312 for obtaining a sum (Va+Vb); and a divider 314 for
performing division between outputs of the subtractor 310 and the
adder 312 and outputting the result as a tracking error signal E10.
Although there is a case that the output of the subtractor 310 is
used as a tracking error signal, generally, in order to suppress
variations in amplitude according to the reflection light amount,
the output of the subtractor 310 is divided by the total amount of
reflection light calculated by the adder 312, thereby making the
amplitude of the tracking error signal constant. Consequently, an
ideal output of the tracking error signal E10 is obtained as
follows.
E10=(Va-Vb)/(Va+Vb)
[0006] When individual differences in the current-to-voltage
converters 306 and 308 are considered and it is assumed that a
small offset Vofs exists on the output Va side, the track error
signal E10 is obtained as follows.
E10={(Va+Vofs)-Vb}/{(Va+Vofs)+Vb}
[0007] The offset Vofs is a small offset voltage which is always
constant irrespective of currents supplied to the
current-to-voltage converters 306 and 308. When the outputs Va and
Vb of the current-to-voltage converters 306 and 308 have
sufficiently large values, an influence of the offset Vofs is small
and an influence on the tracking error signal E10 is also a little.
When the difference between each of the outputs Va and Vb and the
offset Vofs is too small to ignore the relation between the outputs
Va and Vb and the offset Vofs, a change amount of the offset with
respect to the amplitude of the tracking error signal E10 becomes
too large. Conventionally, to deal with the offset change in the
tracking error signal due to variations in the amount of the
reflection light from the medium, an offset correction is performed
in such a manner that a tracking error signal is fetched by an A/D
converter in a DSP (Digital Signal Processor), when a change in the
reflection light amount is detected, an offset amount is measured,
a correction amount is calculated from the offset amount and, after
that, the correction amount is added to the tracking error signal
in the DSP (JP11328696a and U.S. patent application Ser. No.
09/196,098).
[0008] FIG. 2 shows a conventional tracking servo control unit. The
tracking error signal E10 generated in FIG. 1 is supplied to an
adding circuit 200 for correcting an offset, and an arbitrary
correction amount from a DSP 205 is added to the tracking error
signal E10 to thereby correct the offset. Unnecessary frequency
band components in an offset-corrected tracking error signal E11
are eliminated by a notching circuit 202 and a low pass filter 204
and, after that, the resultant signal is fetched as a tracking
error signal E12 by an A/D converter 206 in the DSP 205. The DSP
205 supplies the tracking error signal fetched by the A/D converter
206 to a correction amount detecting unit 224. An offset amount
caused by a change in the amount of the reflection light in a
sector ID area at the time of reproduction or in a data area at the
time of recording or reproduction is measured, a correction amount
to cancel out the offset amount is calculated and added to the
output of the A/D converter 206 at an addition point 222, and an
offset-corrected tracking error signal E13 is outputted. The
correction amount detecting unit 224 uses an MOXID signal E14 and a
write gate signal E15 supplied as signals for detecting a change in
the reflection light to an edge port 232. As shown in FIG. 3A, the
MOXID signal is a logical signal which becomes at the H level in
the data area in a medium sector and becomes at the L level in an
ID area between sectors. Since the amount of reflection light
decreases in the ID area, by using the MOXID signal, an offset is
measured in the ID area and corrected. FIG. 3B shows the tracking
error signal E10 inputted to the adding circuit 200, and an offset
occurs in the ID area where the MOXID signal E14 becomes at the L
level. FIG. 3C shows sampling timings of the A/D converter 206, the
tracking error signal E12 in FIG. 3D which has passed the notching
filter 202 and the low pass filter 204 is sampled at timings of
arrows to be converted to digital data, and the digital data is
fetched. The correction amount detecting unit 224 measures an
offset amount from a difference between sample values before and
after the detection start timing in the ID area, calculates a
correction amount having an amplitude of FIG. 3E from the measured
offset amount, outputs the correction amount for a predetermined
time, and adds the correction amount at the addition point 222,
thereby obtaining the offset-corrected tracking error signal E13 as
shown in FIG. 3F. The track error signal E13 in which the offset
caused by a change in the reflection light amount has been
corrected passes through an input gain multiplying unit 208, a PID
computing unit 210, an output gain multiplying unit 212, and a D/A
converter 214 and is outputted from the DSP 205. By the output, a
driving current is passed from a power amplifier 215 as a driver to
a tracking coil 216 to thereby position an objective lens 220
mounted on an actuator 218 to the track center of a target track.
The DSP 205 is also provided with a D/A converter 230 of an offset
eliminating unit 226. A correction amount to cancel out an offset
brought about by a cause other than the change in the reflection
light amount is fixedly added to the adding circuit 200, thereby
correcting the offset. At the time of recording or erasing, by
using the MOXID signal E14 and the write gate signal E15, an offset
associated with an increase in the reflection light in the data
area subsequent to the ID area is measured and corrected.
[0009] In such a conventional tracking servo control unit, however,
since the tracking error signal E12 read by the DSP 205 via the A/D
converter 206 is derived by passing the tracking error signal E10
generated by the tracking error signal generating circuit of FIG. 1
to the filters such as the notching filter 202 and the low pass
filter 204, as obvious from a comparison between the signal
waveform of FIG. 3B before passing through the filters and that of
FIG. 3D after passing through the filters, a delay occurs also in
an offset in the tracking error signal in the ID area and the
waveform becomes dull. Conventionally, the tracking error signal
E12 having such a delay and a dull waveform is fetched by the A/D
converter 206 into the DSP 205 and is subjected to the offset
correction. It is consequently difficult to, for example, determine
the timing of measuring the offset amount from the MOXID signal
E14. Particularly, in the case of the recording process, an offset
(decrease in the reflection light amount) is caused also by the ID
area just before a recording process, and an offset (increase in
the reflection light amount) is caused also by the recording
operation performed in the data area. There is a limitation in the
offset correction, so that a problem that the offset cannot be
sufficiently cancelled out occurs. In recent years, the rotational
speed of an optical disk tends to be increasing, so that
reliability of the calculation of the correction amount based on
the measurement of the offset amount and promptness of the
correction effect of cancelling out the offset are required. From
this viewpoint as well, the correcting process using the tracking
error signal which has passed the filters is limited.
SUMMARY OF THE INVENTION
[0010] According to the invention, there is provided an optical
storage apparatus in which a servo control at the time of
reproduction, recording, and erasing is stabilized and stability of
a whole drive is improved by accurately detecting and correcting an
offset amount in a servo error signal caused in association with a
change in an amount of reflection light.
[0011] The invention is directed to an optical storage apparatus
having: an actuator capable of positioning an objective lens for
irradiating a medium with a light beam from a light source to a
target position on the medium; a servo error signal generating
circuit which generate a servo error signal indicative of a
deviation from a target position of the objective lens on the basis
of reflection light from the medium; an offset correcting circuit
(adding circuit) for correcting an offset by adding an arbitrary
correction amount to a servo error signal outputted from the
tracking error signal generating circuit; a filter which eliminate
an unnecessary frequency component from the servo error signal
outputted from the offset correcting circuit; and a servo control
unit which position the objective lens to a target position on the
medium on the basis of the servo error signal outputted from the
filter.
[0012] (Fundamental Construction)
[0013] According to the invention, the optical storage apparatus is
characterized by including: an offset measuring unit which receive
the servo error signal E1 which does not pass through the filter
and measuring an offset amount in the servo error signal, caused by
a change in an amount of reflection light; and a correction amount
calculating unit which calculate a correction signal to cancel out
the offset amount and outputting the correction signal to perform
correction to the offset correcting circuit for an offset
generating period. According to the invention as described above,
the tracking error signal before being passed to the filter is
received, an offset is measured, and the correction amount is
calculated from the measured offset and used for correction.
Consequently, a change in the offset due to a change in the amount
of reflection light directly appears in the tracking error signal
before being passed to the filter. As a result, the offset amount
can be detected with high precision, and time for applying the
correction amount is relatively easily determined. In addition, the
offset-corrected servo error signal is passed through the filters
and fetched by a servo control unit by a DSP. Consequently, there
is also an advantage that, even if the timing of the offset
correction is deviated more or less and an offset remains, the
offset is filtered by the filter after that, so that an influence
of a slight deviation in the correction timing can be eliminated.
As a result, tracking in the ID area at the time of reproduction
and tracking in the data area at the time of recording or erasing
becomes stable, and the stability of the entire drive is improved.
Since all of the changes from the conventional technique can be
dealt in the DSP, the invention can be realized without increasing
the cost by adding a new circuit part or the like.
[0014] The offset measuring unit receives a light amount change
detection signal indicative of a change in an amount of reflection
light from the medium and measures an offset amount from a
difference between a servo error signal just before a detection
start timing of the light amount change detection signal and a
servo error signal just after the detection start timing. In this
case, the correction amount calculating unit outputs a correction
amount calculated on the basis of the offset amount to the offset
correcting circuit for a period of time in which a light amount
change is detected from the light amount change detection signal.
The offset measuring unit may receive a light amount change
detection signal indicative of a change in an amount of reflection
light from the medium and measures an offset amount from a
difference between a servo error signal just before a detection
start timing of the light amount change detection signal and a
servo error signal at a time point after elapse of predetermined
time T1 since the detection start timing. Consequently, the servo
error signal in which an offset appears can be measured with
reliability in a state where the tracking is in the ID area, so
that accuracy and reliability of measurement of an offset are
increased. The correction amount calculating unit may output a
correction amount calculated on the basis of the offset amount to
the offset correcting circuit for predetermined time T1 since the
detection start timing of the light amount change detection signal.
The correction amount calculating unit outputs an auxiliary
correction amount obtained by multiplying a correction amount of
last time by a constant smaller than 1 to the offset correcting
circuit for a period of time from the detection start timing of the
light amount change detection signal until a correction amount
based on the offset detection is calculated and outputted.
Consequently, even when there is a time delay between the
appearance of the offset in the servo error signal and the start of
the correction, by correcting the offset by using the auxiliary
correction amount obtained by multiplying the correction amount of
last time by a coefficient ranging, for example, 0.5 to 0.75, the
effect of cancelling out the offset can be further increased. The
offset measuring unit calculates an offset amount on the basis of a
plurality of past detection results. Therefore, an adverse
influence on the offset correction in the case where a change which
is not purely due to the reflection light amount, such as a medium
defect, appears in the servo error signal can be reduced.
[0015] (Offset Correction in ID Area)
[0016] The invention is constructed as follows to correct an offset
in the ID area necessary at the time of reproduction. First, the
offset measuring unit receives a first logical signal (MOXID
signal) indicating whether a light beam following a track in a
medium is in a data area to which data can be recorded or in an ID
area recorded between sectors, and measures an offset amount in the
servo error signal on the basis of a detection timing of the ID
area in the first logical signal. The correction amount calculating
unit outputs a correction amount calculated based on the offset
amount to the offset correcting circuit so as to perform correction
for a period of detection of the ID area by the first logical
signal. Specifically, the offset measuring unit measures an offset
amount from a difference between a servo error signal just before a
start timing of detecting the ID area by the first logical signal
and a servo error signal just after the start timing. The
correction amount calculating unit outputs a correction amount
calculated on the basis of the offset amount to the offset
correcting circuit for predetermined time T1 since the start timing
of detection of the ID area by the first logical signal. The offset
measuring unit measures an offset amount from a difference between
a servo error signal just before the start timing of the ID area
detection by the first logical signal and a servo error signal at a
time point after elapse of predetermined time T2 since the start
timing. At this time, the correction amount detecting unit outputs
a correction amount calculated on the basis of the offset amount to
the offset correcting circuit for predetermined time T1 since the
start timing of detection of the ID area by the first logical
signal. The correction amount calculating unit outputs an auxiliary
correction amount obtained by multiplying a correction amount of
last time by a constant to the offset correcting circuit for a
period of time since the start timing of detection of the ID area
by the first logical signal until the correction amount based on
the offset detection is calculated and outputted. Further, the
offset measuring unit calculates an offset amount on the basis of a
plurality of past detection results.
[0017] (Offset Correction During Recording or Erasing)
[0018] The offset measuring unit receives a first logical signal
(MOXID signal) indicating whether a light beam following a track in
a medium is in a data area to which data can be recorded or an ID
area recorded between sectors and a second logical signal (write
gate signal) indicating whether the apparatus is recording data to
the medium or erasing data in the medium, and measures an offset
amount in the servo error signal being recorded or erased on the
basis of a first logical signal and a second logical signal. In
this case, the correction amount calculating unit outputs a
correction amount calculated on the basis of the offset amount
measured during the recording or erasing to perform correction to
the offset correcting circuit. As described above, offsets caused
by light amount changes which are different in the ID area and the
data area subsequent to the ID area occur during recording or
erasing. By using two kinds of logical signals corresponding to the
different light amount changes, the offset can be accurately
measured and corrected. Specifically, the offset measuring unit
measures an offset amount from a difference between a servo error
signal just before a start timing of detection of the ID area by
the first logical signal and a servo error signal just after start
of recording or erasing by the second logical signal. The
correction amount calculating unit outputs a correction amount
calculated on the basis of the offset amount during the recording
or erasing by the second logical signal to the offset correcting
circuit. The offset measuring unit detects an offset amount from a
difference between a servo error signal just before the start
timing of detection of the ID area by the first logical signal and
a servo error signal after elapse of predetermined time T3 since
the start of recording or erasing by the second logical signal.
Consequently, the servo error signal can be measured at the timing
when the offset appears due to a change in the reflection light
amount by the start of recording or erasing. In this case, the
correction amount calculating unit outputs a correction amount
calculated on the basis of the offset amount during the recording
or erasing by the second logical signal to the offset correcting
circuit. The correction amount calculating unit outputs an
auxiliary correction amount obtained by multiplying a correction
amount of last time by a constant to the offset correcting circuit
for a period of time since the start timing of recording or erasing
by the second logical signal until the correction amount based on
the offset detection is calculated and outputted. The correction
amount calculating unit cancels out the offset also in the period
until the correction amount is outputted. The offset measuring unit
calculates an offset amount on the basis of a plurality of past
detection results, thereby suppressing an adverse influence due to
a medium defect or the like. In the case of continuously recording
or erasing data to/from a plurality of sectors, the correction
amount calculating unit continuously uses a correction amount
calculated for the first sector for second and subsequent sectors.
Further, the servo error signal generating circuit is a tracking
error signal generating circuit which generate a tracking error
signal indicative of a deviation from a target position in a medium
track center of the objective lens on the basis of reflection light
from the medium. The servo error signal generating circuit also
includes a focusing error signal generating circuit which generate
a focusing error signal indicative of a deviation from a focus
position of the objective lens on the medium on the basis of
reflection light from the medium.
[0019] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
detailed description with reference to the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a circuit block diagram of a conventional tracking
error signal generating circuit;
[0021] FIG. 2 is a block diagram of a conventional tracking servo
control unit;
[0022] FIGS. 3A to 3F are time charts of waveforms of respective
parts in an offset correcting process in FIG. 2;
[0023] FIGS. 4A and 4B are block diagrams of an optical disk drive
to which the present invention is applied;
[0024] FIGS. 5A and 5B are block diagrams of a tracking servo
control unit which perform an offset correcting process of the
present invention;
[0025] FIG. 6 is a flowchart of a first embodiment of correcting an
offset in an ID area according to the present invention;
[0026] FIGS. 7A to 7F are time charts of signals of respective
parts in the first embodiment of FIG. 6;
[0027] FIGS. 8A and 8B are flowcharts of a second embodiment of
correcting an offset in an ID area according to the present
invention;
[0028] FIGS. 9A to 9G are time charts of signals of respective
parts in the second embodiment of FIG. 6;
[0029] FIGS. 10A and 10B are a flowchart of a third embodiment of
correcting an offset in an ID area according to the present
invention;
[0030] FIGS. 11A to 11F are time charts of signals of respective
parts in the third embodiment of FIGS. 10A and 10B;
[0031] FIGS. 12A and 12B are flowcharts of a fourth embodiment of
correcting an offset in an ID area according to the present
invention;
[0032] FIG. 13 is a flowchart of an integration filter process in
FIG. 12B;
[0033] FIGS. 14A to 14F are time charts of signals of respective
parts in the fourth embodiment of FIGS. 12A and 12B;
[0034] FIG. 15 is a flowchart of a fifth embodiment of correcting
an offset at the time of recording/erasing according to the present
invention;
[0035] FIGS. 16A to 16F are time charts of signals of respective
parts in the fifth embodiment of FIG. 15;
[0036] FIGS. 17A and 17B are flowcharts of a sixth embodiment of
correcting an offset at the time of recording/erasing according to
the present invention;
[0037] FIGS. 18A to 18G are time charts of signals of respective
parts in the sixth embodiment of FIGS. 17A and 17B;
[0038] FIGS. 19A and 19B are flowcharts of a seventh embodiment of
correcting an offset at the time of recording/erasing according to
the invention;
[0039] FIGS. 20A to 20G are time charts of signals of respective
parts in the seventh embodiment of FIGS. 19A and 19B;
[0040] FIGS. 21A and 21B are flowcharts of an eighth embodiment of
correcting an offset at the time of recording/erasing according to
the invention;
[0041] FIGS. 22A to 22G are time charts of signals of respective
parts in the eighth embodiment of FIGS. 21A and 21B;
[0042] FIGS. 23A, 23B and 23C are flowcharts of a ninth embodiment
of correcting an offset at the time of recording/erasing according
to the invention;
[0043] FIGS. 24A to 24E are time charts of signals of respective
parts in the ninth embodiment of FIGS. 23A, 23B and 23C;
[0044] FIGS. 25A to 25C are flowcharts of a tenth embodiment of
correcting an offset in an ID area and at the time of
recording/erasing according to the present invention; and
[0045] FIGS. 26A to 26I are time charts of signals of respective
parts in the tenth embodiment of FIGS. 25A to 25C.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] FIGS. 4A and 4B are block diagrams of an optical disk drive
as an optical storage apparatus to which an offset correcting
process of the invention is applied. As an example of a storage
medium, a magnetooptic disk (MO) cartridge is used. The optical
disk drive is constructed by a controller 10 and an enclosure 12.
The controller 10 has an MPU 14 to perform an overall control, an
interface controller 16 to transmit/receive data to/from a host, an
optical disk controller (ODC) 18 having a formatter and an ECC
function necessary to read/write data from/to a medium, and a
buffer memory 20. For the optical disk controller 18, an encoder
22, a laser diode control circuit 24, and a laser diode unit 30 are
provided as a write system. As a read system for the optical disk
controller 18, a detector 32, a head amplifier 34, a read LSI
circuit 28, and a decoder 26 are provided. The detector 32 detects
return light from a magnetooptic disk and outputs an ID signal and
an MO signal via the head amplifier 34 to the read LSI circuit 28.
The read LSI circuit 28 generates a read clock and read data from
the received ID signal and MO signal and outputs the read clock and
read data to the decoder 26. An environment temperature in the
apparatus detected by a temperature sensor 36 is supplied to the
MPU 14, and a light emitting power in the laser diode unit 30 is
optimized on the basis of the environment temperature. Further, the
MPU 14 controls a spindle motor 40 via a driver 38 and also
controls an electromagnet 44 via a driver 42. The electromagnet 44
supplies an external magnetic field at the time of recording and
erasing when the MO cartridge is used. In the case of a
super-resolution magnetooptic medium (MSL medium) in a 1.3 GBMO
cartridge, the electromagnet 44 supplies an external magnetic field
also at the time of reproduction. A DSP 15 has a function of a
servo control unit 62 for positioning an objective lens mounted on
a head actuator to a target position in a magnetooptic disk on the
basis of a servo error signal. The servo control unit 62 has two
functions of a tracking control of positioning the objective lens
to a target track position in a medium and a focusing control of
controlling the objective lens so as to achieve focus on the
medium. In correspondence with the servo control unit 62, a
photodetector 46, a focusing error signal generating circuit 48, a
tracking error signal generating circuit 50, and a track zero cross
(TZC) detecting circuit 52 are provided. Each of the photodetector
46 and the tracking error signal generating circuit 50 has the same
circuit construction as that in FIG. 1. For example, in the case of
adopting a knife edge method as a focusing optical system, the
focusing error signal generating circuit 48 can generate a focusing
error signal by the same circuit construction as that of the
tracking error signal generating circuit in FIG. 1. A tracking
error signal E0 from the tracking error signal generating circuit
50 is input into the adding circuit 100. The offset correcting
signal E3 from DSP 15 is input into the other side of the adding
circuit 100. The tracking error signal E1 from the adding circuit
100 is input into the track zero cross detecting circuit 52, as
well as into the notching circuit 102, and further is given into
DSP15 through the low pass filter 104 as a tracking error signal
E2. The tracking error signal E1 from the adding circuit 100 is
given to DSP 15 directly. Functions of a circuit part on the low
pass filter 104 from the adding circuit 100 will be explained in
the following description. With respect to the focusing control,
the servo control unit 62 in the DSP 15 drives a focusing actuator
56 by a driver 54 to position the objective lens to a focus
position in the optical axis direction. With respect to the
tracking control, the servo control unit 62 drives a head actuator
60 using a VCM via a driver 58 to position the objective lens to
the target track center on the medium.
[0047] FIGS. 5A and 5B are block diagrams showing functions of the
offset correcting process in the present invention in the case
where the servo control unit 62 of FIG. 4A and 4B serves as a
tracking servo control unit as an example. A tracking error signal
E0 outputted from the tracking error signal generating circuit 50
in FIG. 4B is supplied to one of inputs of an adding circuit 100
operating as an offset correcting circuit, and a tracking error
signal E1 from the adding circuit 100 is directly fetched by an A/D
converter 122 in the DSP 15 so as to be used for an offset
correcting process. An offset correcting signal E3 outputted from a
D/A converter 130 in the DSP 15 is supplied to the other input of
the adding circuit 100, so that a standing offset amount of the
tracking error signal E0 can be cancelled out by setting a
correction amount from an offset eliminating unit 127. For this
purpose, the A/D converter 122 converts the offset-cancelled
tracking error signal E1 outputted from the adding circuit 100 by
sampling of the A/D converter 122 to digital data, fetches the
digital data, and supplies the digital data to a correction amount
detecting unit 124. The correction amount detecting unit 124 has an
offset measuring unit 125 and a correction amount calculating unit
126. The offset measuring unit 125 measures an offset included in
the tracking error signal E0 by a change in the amount of the
reflection light from the medium. On the basis of the measured
offset amount, the correction amount calculating unit 126
calculates a correction amount to be added to the tracking error
signal E0 by the adding circuit 100 to thereby cancel out the
offset. The standing offset correction amount calculated by the
offset eliminating unit 127 is added to a signal indicative of the
correction amount sent from the correction amount detecting unit
124 at an addition point 128. A resultant signal is converted by
the D/A converter 130 to the analog offset correction signal E3. By
adding the offset correction signal E3 to the tracking error signal
E0 in the adding circuit 100, the offset amount in the tracking
error signal E0 is cancelled out. The tracking error signal E1
outputted from the adding circuit 100 is also passed through a
notching circuit 102 and an uncharing low pass filter (LPF) 104
where unnecessary frequency band components (components of
frequencies twice as high as the sampling frequency or higher) are
eliminated. A resultant signal as a tracking error signal E2 is
sampled by an A/D converter 106 in the DSP 15 to thereby obtain
digital data and the digital data is fetched. The tracking error
signal E1 outputted from the adding circuit 100 is also inputted to
the TZC circuit 52 in FIG. 4B. The tracking error signal E2 fetched
by the A/D converter 106 into the DSP 15 is multiplied by an input
gain by an input gain multiplying unit 108. The input gain is used
to absorb variations in input sensitivities by a circuit constant
and signal sensitivity. For low pass compensation and phase
advance, the tracking error signal data normalized by the input
gain multiplying unit 108 is passed to a PID filter 110, multiplied
by an output gain obtained when the tracking servo loop is closed
by an output gain multiplying unit 112, and resultant data is
outputted as a control instruction value (current instruction
value) via a D/A converter 114. The output gain in the output gain
multiplying unit 112 is to absorb variations in sensitivity of the
output system such as driving sensitivity of the driver and
acceleration of the actuator. The control instruction signal
outputted from the D/A converter 114 drives a tracking coil 116 via
the driver 58 using a power amplifier. By driving the tracking coil
116, the tracking servo control of moving an objective lens 120
mounted on a head moving mechanism unit 118 of the head actuator in
the radial direction of the medium so as to be positioned in a
target position is performed. An MOXID signal E4 and a write gate
signal E5 are inputted to an edge port 132 of the DSP 15. The MOXID
signal E4 is a logical signal (first logical signal) indicating
whether the current tracking position is in the data area or ID
area in the medium sector. When the current tracking position is in
the data area, the MOXID signal E4 is at the H level. When the
current tracking position is in the ID area, the MOXID signal E4 is
at the L level. Consequently, by monitoring the MOXID signal E4
connected to the edge port 132, the DSP 15 can determine whether
the tracking position is in the data area or ID area during
tracking. The result of determination of the MOXID signal E4 on the
basis of the monitoring of the state of the edge port 132 is used
for the offset correction performed by measuring an offset and
calculating a correction amount in the correction amount detecting
unit 124. On the other hand, the write gate signal E5 is a logical
signal (second logical signal) which goes down from the H level to
the L level when the apparatus starts a write control (recording
control) or an erasing control and, on completion of the write or
erase control, which goes up from the L level to the H level.
Similarly, the write gate signal E5 is recognized by the DSP 15 via
the edge port 132. On the basis of the write gate signal E5, the
correction amount detecting unit 124 performs the offset correction
in the data area at the time of the write control and erase
control.
[0048] FIG. 6 is a flowchart of the first embodiment of the offset
correction in the ID area according to the present invention. The
ID area in a magnetooptic disk is positioned at the head of each
sector and information of tracks of a sector and sectors and the
like is recorded in the form of pits on a land. Since the ID area
has a pit structure in such a manner, the amount of reflection
light of the light beam arriving at the ID area is reduced by
diffraction. The reason why an offset occurs in the tracking error
signal due to the reduction in the reflection light in the ID area
is as described above in the explanation of the tracking error
signal generating circuit in FIG. 1. The DSP 15 can detect the ID
area start timing during tracking, that is, a change in the
reflection light amount by the MOXID signal connected to the edge
port 132. Consequently, by executing processes according to the
flowchart of FIG. 6, an offset component included in the tracking
error signal when the light beam arrives at the ID area can be
measured and corrected.
[0049] The flowchart of FIG. 6 shows only a portion related to the
offset correction based on offset measurement and calculation of a
correction amount of the present invention in sampling processes
performed every sampling frequency to realize the offset correction
in the ID area. First, in step S1, the DSP 15 fetches the tracking
error signal E1 outputted from the adding circuit 100 via the A/D
converter 122 before the tracking error signal E1 is passed to the
notching circuit 102 and the low pass filter 104. In step S2,
whether the trailing edge of the MOXID signal is detected or not is
checked. When the trailing edge is not detected, the program
advances to step S3 where tracking error data fetched by sampling
is stored. When the trailing edge of the MOXID signal is detected,
the process of measuring the offset amount and calculating the
correction amount is performed. Specifically, the tracking error
data stored in step S4 by the sampling of last time is called.
Subtraction is executed between the tracking error data and
tracking error data sampled this time in step S5, thereby
calculating an offset amount. After calculating the offset amount,
the correction amount to correct the offset amount is calculated
and outputted from the D/A converter 130. At this time, a gain
amount in the adding circuit 100 has to be considered. In step S6,
the offset amount is divided by a circuit gain constant to obtain
the correction amount. In step S7, the calculated correction amount
is outputted from the D/A converter 130 to the adding circuit 100
and is added to the tracking error signal E0, thereby cancelling
out the offset. Such an offset correcting process is performed in
the entire ID area. A process of clearing the correction amount
added at the end position of the ID area is also necessary.
Although the timing of clearing the correction amount can be
determined by a method of monitoring the rising edge of the MOXID
signal E4, in the first embodiment, a clearing timing is set after
elapse of specific time T1 since the trailing edge of the MOXID
signal in step S8. More specifically, in the sampling process after
calculating the correction amount, the elapse of the specific time
T1 since the trailing edge of the MOXID signal E4 is monitored in
step S8. Before the elapse, the process of clearing the correction
amount is not performed and the program continues to the subsequent
processes. When the elapse of the specific time T1 is determined,
the correction amount is cleared in step S9.
[0050] FIGS. 7A to 7F are time charts of waveforms of respective
parts in the offset correcting processes in FIG. 6 and show the
MOXID signal E4, the tracking error signal E1 used for the offset
correction, sampling timings, the specific time T1 after which the
correction amount is cleared, the correction amount outputted from
the D/A converter 130, and the tracking error signal E2 passed
through the notching circuit 102 and the low pass filter 104 and to
be fetched by the DSP 15 for the tracking servo control,
respectively. As obvious from the time charts, when the MOXID
signal E4 goes down to the L level at time t1, an offset amount is
calculated as a difference between the tracking error data at a
sampling point SP1 of last time in the tracking error signal E1 and
tracking error data at a first sampling point SP2 after time t1,
and a correction amount based on the offset amount is outputted for
the specific time T1 since the time t1. The specific time T1 is set
to be slightly shorter than the elapse time of the ID area from the
time t1 to time t3.
[0051] FIGS. 8A and 8B are flowcharts of a second embodiment of
offset correction in the ID area. FIGS. 9A to 9G are time charts of
signal waveforms of respective parts. In the first embodiment of
FIG. 6 and FIGS. 7A to 7F, at the time when the trailing edge of
the MOXID signal E4 is recognized, the offset amount is detected by
the difference between the tracking error data at the first
sampling point SP2 and the tracking error data at the immediately
preceding sampling point SP1. When the tracking error data fetched
at the first sampling immediately after the trailing of the MOXID
signal E4 is used for the calculation of the offset amount,
however, there is a case that the tracking error data at the
sampling point SP2 before the offset appears in the tracking error
signal is sampled and used for the calculation. In the second
embodiment of FIGS. 8A and 8B, therefore, the tracking error data
is sampled at a timing after the MOXID signal goes down and an
offset certainly occurs in the tracking error signal, so that the
offset amount can be calculated accurately.
[0052] In the flowchart of FIGS. 8A and 8B, in order to realize
processes for calculating the offset amount with reliability,
underlined processes in steps S2, S4, and S6 are added to the
flowchart of the first embodiment of FIG. 6. In the processes for
calculating the offset amount with reliability, time is monitored
also after the detection of the trailing edge of the MOXID signal
E4. A flag indicative of detection of the trailing edge is
therefore necessary. When the trailing edge of the MOXID signal E4
is detected in step S1, a trailing edge detection flag is set in
step S2. That is, when the trailing edge of the MOXID signal is
detected in step S1, an MOXID signal trailing edge detection flag
is set in step S2. Before the MOXID signal goes down, the program
advances from step S1 to step S3 where the tracking error signal E1
is fetched by the A/D converter 122, and whether the MOXID signal
trailing edge detection flag is set or not is checked in step S4.
When the flag is not set, the tracking error data fetched is stored
in step S5. In the case where the trailing edge detection flag is
set in step S4, whether specific time T2 has elapsed since the
trailing edge or not is checked in step S6. When the specific time
T2 has elapsed, in a manner similar to steps S4 to S7 in FIG. 6,
the offset amount and the correction amount are calculated and,
further, a correction is performed by outputting the correction
amount in steps S7 to S10. The trailing edge detection flag is
cleared in step S11. In a manner similar to the first embodiment of
FIG. 6, the correction amount is cleared in steps S12 and S13 when
the specific time T1 has elapsed since the trailing edge of the
MOXID signal. In the second embodiment, as obvious from the time
charts of FIGS. 9A to 9G, the tracking error data at the sample
point SP2 is fetched at the first sampling timing after the elapse
of the specific time T2 since the time t1 at which the MOXID signal
E4 goes down, and the offset amount can be calculated as the
difference between the fetched tracking error data and the tracking
error data at the sample point SP1 just before the time t1.
Consequently, the offset amount can be accurately measured at a
timing at which the offset amount has certainly already appeared in
the tracking error signal in the ID area.
[0053] FIGS. 10A and 10B are flowcharts of a third embodiment of
the offset correcting process in the ID area according to the
invention. FIGS. 11A to 11G show time charts of signal waveforms of
respective parts. In the second embodiment of FIGS. 10A and 10B,
calculation of the offset amount, calculation of the correction
amount and, further, correction of the offset after elapse of the
specific time T2 since the trailing edge of the MOXID signal are
performed with the intention of performing the processes certainly
after the offset occurs. As a result, the timing of the offset
correction is naturally delayed. In the case of intentionally
delaying the timing of the offset correction as described above,
during a period from the calculation of the correction amount to
the cancellation of the offset from the tracking error signal, the
offset is left as it is in the tracking error signal. Although the
signal is passed through the filters, if the influence of the
offset is exerted also on the tracking error signal E2, the
correction effect is reduced in half.
[0054] In a third embodiment of FIGS. 10A and 10B, during the
period from the trailing edge of the MOXID signal to the start of
the offset correction, a value obtained by multiplying the
correction amount of the offset calculated in the preceding ID area
by a constant smaller than 1 is used as an auxiliary correction
amount and is added to the tracking error signal E0 to perform
correction. The correction amount of last time is multiplied by a
constant in consideration of a change in waveform until the offset
occurs fully. It is empirically considered that about 0.5 to 0.75
is proper as the constant used to calculate the auxiliary
correction amount. In the flowchart of FIGS. 10A and 10B, in order
to realize the process of adding the auxiliary correction amount,
underlined processes in steps S7, S8, S9, and S13 are added to the
flowchart of the second embodiment of FIGS. 8A and 8B.
Consequently, until the specific time T2 is elapsed since the
trailing edge of the MOXID signal instep S6, the correction amount
of last time is read in step S7, the correction amount of last time
is multiplied by a constant which lies in the range from about 0.5
to 0.75 to thereby calculate the auxiliary correction amount in
step S8, and the auxiliary correction amount is outputted from the
D/A converter 130 to the adding circuit 100 and added to the
tracking error signal E0 in step S9, thereby correcting the offset
by using the auxiliary correction amount. In the case where the
specific time T2 has elapsed since the trailing edge of the MOXID
signal in step S6, the calculation of the offset amount,
calculation of the correction amount, and output of the correction
amount are performed in steps S10 to S12. Subsequently, in step
S13, in association with the process of adding the auxiliary
correction amount, the calculation result of the correction amount
is stored for the calculation of the auxiliary correction amount in
the next ID area. In the processes of the third embodiment of FIGS.
10A and 10B, the auxiliary correction amount is calculated in step
S8 at every sampling until elapse of the specific time T2 since the
detection of the trailing edge of the MOXID signal. It is also
possible not to calculate the auxiliary correction amount every
time but to add a branching process so as to calculate the amount
only once in the beginning. Alternately, it is also possible to
perform a process of calculating and storing the auxiliary
correction amount in the next ID area at the time of calculating
the correction amount and unconditionally outputting the already
calculated auxiliary correction amount at the time of next
detection of the trailing edge of the MOXID signal.
[0055] In the time charts of the third embodiment of FIGS. 11A to
11G, for the specific time T2 since the time t1 at which the MOXID
signal E4 goes down, an auxiliary correction amount 130 calculated
from the correction amount of last time is outputted. As a result,
even when the offset correcting process is started at the first
sampling timing after elapse of the specific time T2, it can be
prevented that the offset caused by the time delay remains and
exerts an influence on the servo control unit. The tracking error
data at the sample point SP2 of the first sampling timing after the
elapse of the specific time T2 is a signal from which the offset
has been eliminated by using the auxiliary correction amount 130.
The difference between the tracking error data at the sample point
SP2 and that at the sample point SP1 just before the ID area is
reduced by the amount corresponding to the eliminated offset. A
value obtained by adding a correction amount calculated by
measuring the offset to the auxiliary correction amount 130 is used
as a correction amount used after that.
[0056] FIGS. 12A and 12B show a flowchart of a fourth embodiment of
an offset process in the ID area according to the invention. FIG.
13 shows a flowchart of an integration filter process in the fourth
embodiment. Further, FIGS. 14A to 14G show time charts of signal
waveforms of respective parts in the fourth embodiment. In the
foregoing first to third embodiments, only an offset amount
obtained in the ID area for the offset correction is used as an
input for calculating the correction amount. When a change which is
not purely due to the reflection light amount but is caused by, for
example, a medium defect in the ID area appears in the tracking
error signal, the correction amount different from a correction
amount to be inherently added is added to the tracking error
signal, and the offset correction is not therefore accurately
performed. In the case of using the auxiliary correction amount as
in the third embodiment, there is the possibility that an adverse
influence is exerted on the offset correction value obtained by
using the auxiliary correction amount in the ID area. In the fourth
embodiment of FIGS. 12A and 12B, therefore, by using a plurality of
past offset amounts as inputs to calculate the correction amount,
the tracking servo control system can be prevented from being made
unstable by a sporadic offset calculation result due to a change in
the tracking error signal which is not caused by the reflection
light amount but is caused by a medium defect or the like. In the
fourth embodiment, specifically, calculated offset amounts are
averaged by being passed to the integration filter, and the
correction amount is obtained by using the averaged offset amount.
Obviously, the averaging process can be performed not only by the
method of using the integration filter but also by a method of
calculating an average of a plurality of past offset amounts.
Similar effects are produced.
[0057] In the flowchart of FIGS. 12A and 12B, an underlined process
in step S12 is added to the third embodiment of FIGS. 8A and 8B to
realize the calculation of the correction amount for averaging the
offset amounts by using the integration filter. All of the
processes except for the process in step S12 added to average the
offset amounts by using the integration filter are not always
necessary. For example, in the case of adding a process of
averaging offset amounts by using the integration filter in step
S13 in the fourth embodiment to the flowchart of the first
embodiment of FIG. 6 or the flowchart of the second embodiment of
FIGS. 8A and 8B, a similar function can be also realized. In the
fourth embodiment, after calculating an offset amount as a result
of substraction performed between data sampled this time in step
S11 and data sampled last time in step S11, the offset amounts are
averaged by being passed to the integration filter in the newly
added step S12. The integration filter outputs a value obtained by
adding the result derived by multiplying the output value of last
time by a constant and an input value of this time, and the output
value is expressed by the following equation.
integration filter output value=[(integration filter output value
of last time).times.(integration constant)+(offset amount of this
time)]/(integration filter gain)
[0058] FIG. 13 specifically shows the integration filter process in
step S12 in FIG. 12B as a subroutine. In the integration filter
process, in step S1, an output value of the integration filter of
last time is read and, in step S2, the integration filter output
value of last time is multiplied by an integration constant equal
to or smaller than 1. In step S3, the result of multiplication and
the offset amount are added. In step S4, the result of addition is
divided by the gain of the integration filter, and the derived
value is used as an integration filter output value of this time.
In step S5, the integration filter output value is stored for
calculation of the integration filter of the next time. The
integration constant used for the calculation of the integration
filter output value is one or smaller as a condition. Empirically,
a value around 0.8 to 0.9 is appropriate. The integration filter
output value calculated in such a manner is used as an integrated
correction amount 140 generated subsequent to the auxiliary
correction amount 130 in FIG. 14F for correcting the offset in the
tracking error signal.
[0059] FIG. 15 is a flowchart showing a fifth embodiment of an
offset correcting process at the time of recording or erasing
according to the invention. FIGS. 16A to 16F show signal waveforms
of respective parts. In an optical disk drive of the present
invention, at the time of erasing information recorded in the data
area in the medium or recording information to the data area, the
light beam changes to have a stronger intensity as compared with
that at the time of reproduction. By the increase in the light
emitting amount of the light beam, the amount of reflection light
from the medium naturally increases. At the time of recording or
erasing, therefore, due to an increase in the amount of reflection
light, an offset occurs in the tracking error signal. As shown in
FIGS. 5A and 5B, the write gate signal E5 is connected via the edge
port 132 to the DSP 15, which is a logical signal going down to the
L level after confirming the target ID area at the time of
recording or erasing information to/from the medium. By confirming
the trailing edge of the write gate signal E5, the DSP 15 can
detect timings of recording and erasing. The rising edge to the H
level of the write gate signal E5 is the timing at which the
recording or erasing is finished. By the rising edges, the DSP 15
can detect the ending timings of recording and erasing. In a state
where the MOXID signal E4 is also connected to the edge port 132 in
a manner similar to the write gate signal E5, also by monitoring
the MOXID signal E4 which goes down to the L level in the ID area
in the sector after the recording or erasing, timings of recording
and erasing can be detected. At the start timing of recording or
erasing obtained by the trailing edge of the write gate signal E5
as described above, the correction amount detecting unit 124
provided in the DSP 15 measures the offset amount in the tracking
error signal at the time of recording or erasing by the offset
measuring unit 125, and calculates the correction amount to cancel
out the measured offset amount, and can apply the correction amount
to the adding circuit 100.
[0060] The processes in the flowchart of FIG. 15 are necessary to
realize the correction of the offset in the tracking error signal
at the time of recording or erasing. The processes only in a part
related to the offset correcting process at the time of recording
or erasing are extracted from the sampling processes performed
every sampling frequency of the A/D converter 122. The process of
correcting an offset in the tracking error signal at the time of
recording as an example will be described as follows. In step S1,
the DSP 15 fetches the tracking error signal E1 to the inside via
the A/D converter 122. In step S2, whether the MOXID signal E4 is
at the L level or not, that is, whether an offset occurs in the
tracking error signal in the ID area or not is checked. When the
MOXID signal is not at the L level, that is, when the tracking
position is not in the ID area, whether the write gate signal is at
the L level indicative of a recording operation or not is checked
in step S3. When the write gate signal is not at the L level as
well, the program advances to step S4 where the tracking error data
fetched by the sampling at this time is stored. When the MOXID
signal goes down to the L level in the ID area in step S2, the
program advances from step S2 to step S10 and the tracking error
data fetched in step S5 is not stored. When the trailing to the L
level of the write gate signal is detected in step S3 in a sampling
process after that, the program advances to step S6 where the
tracking error data stored in the preceding sampling process just
before the ID area is called. In step S7, a subtraction operation
is performed between the called tracking error data and the
tracking error data sampled this time, thereby calculating an
offset amount. After the offset amount is calculated, in step S8,
the correction amount is calculated by a dividing operation using
the circuit gain constant. In step S9, the calculated correction
amount is outputted from the D/A converter 130 to the adding
circuit 100 and is added to the tracking error signal E0, thereby
correcting the offset. After the offset correction of adding the
correction amount to the tracking error signal is started, a
process of clearing the correction amount at the timing of an end
of recording is required. In the fifth embodiment, in the method of
clearing the correction amount at the ending timing of recording or
erasing, the trailing timing to the L level of the MOXID signal
indicative of the start of the ID area in the next sector is used.
Specifically, the detection of the trailing edge of the MOXID
signal is confirmed in step S10. When the detection of the trailing
edge is confirmed, the process of clearing the correction amount is
performed in step S11.
[0061] By the offset correcting process at the time of recording or
erasing in the fifth embodiment as shown in FIG. 15, as the signal
waveforms of respective parts in FIGS. 16A to 16F, the difference
between the tracking error data at the sample point SP1 which is
the sampling timing just before the time t1 at which the MOXID
signal E4 goes down to the L level and the tracking error data at
the first sample point SP2 after the write gate signal E5 goes down
to the L level is calculated as an offset amount, and the
correction amount based on the offset amount is outputted up to the
trailing edge of the MOXID signal E4 to the L level indicative of
the start of the ID area in the next sector.
[0062] FIGS. 17A and 17B are flowcharts of a sixth embodiment of
the invention for performing the offset correction at the time of
recording or erasing. FIGS. 18A to 18G show signal waveforms of
respective parts in the sixth embodiment. In the fifth embodiment,
at the time when the trailing edge of the write gate signal is
recognized, the difference between the sampled tracking error data
and the tracking error data fetched at the sampling before the ID
area just before the sampled tracking error data is calculated and
used as an offset amount. In a manner similar to the offset amount
in the ID area in the second embodiment of FIGS. 8A and 8B,
however, if the tracking error data is fetched at the first sample
timing immediately after the trailing edge of the write gate signal
and the offset amount is calculated, there is a case such that the
offset amount is calculated before the offset fully changes in the
tracking error signal due to an increase in the reflection light
amount. In a sixth embodiment of FIGS. 17A and 17B and FIGS. 18A to
18G, by using the time point after elapse of specific time T3 since
the detection of the trailing edge of the write gate signal as a
timing of detecting the offset amount, the offset amount is
calculated on the basis of the tracking error data in which an
offset has fully changed. The flowchart of the sixth embodiment is
a flowchart obtained by adding processes necessary to improve the
accuracy of the timing of calculating the offset amount to the
flowchart of the fifth embodiment of FIG. 15. Underlined processes
of steps S1, S2, and S8 are added. Specifically, a process such
that when the trailing edge of the write gate signal is detected in
step S1, a detection flag is set in step S2 is added. The process
of setting the detection flag is necessary to monitor the elapsed
time T3 since the trailing edge also after the recognition of the
trailing edge of the write gate signal. When the detection flag is
set by the trailing edge of the write gate signal in step S5, the
program advances to step S8 where the elapse of the specific time
T3 since the trailing edge of the write gate signal is monitored.
When it is before the elapse of the specific time T3, steps S9 to
S13 are skipped and the processes are not performed. After elapse
of the specific time T3, by the processes of steps S9 to S13, the
offset correcting process is performed by the calculation of the
offset amount, calculation of the correction amount, and addition
of the correction amount. The point of using the tracking error
data sampled this time and the tracking error data sampled just
before the ID area at the time of calculating the offset amount is
the same as that of the fifth embodiment.
[0063] As a result of the offset correcting process in the sixth
embodiment of FIGS. 17A and 17B, as shown in signal waveforms in
respective parts in FIGS. 18A to 18G, the offset amount is
calculated as a difference between the tracking error data fetched
at the sample point SP1 as a sampling timing just before the time
t1 at which the MOXID signal E4 goes down and the tracking error
data at the sample point SP2 as a first sampling timing after
elapse of the specific time T3 since the time t3 at which the write
gate signal E5 goes down. A correction amount calculated based on
the offset amount is outputted until the MOXID signal E4 in the
next ID area goes down.
[0064] FIGS. 19A and 19B show a flowchart of a seventh embodiment
of the invention of calculating an auxiliary correction amount and
performing a correcting process until the offset correction is
performed since a start timing of recording or erasing. FIGS. 20A
to 20G show signal waveforms of respective parts. In a manner
similar to the third embodiment of correcting an offset in the ID
area in FIGS. 10A and 10B and FIGS. 11A to 11F, as in the sixth
embodiment of FIGS. 17A and 17B and FIGS. 18A to 18G, when the
offset is corrected by calculating the offset amount, calculating
the correction amount, and adding the correction amount after the
specific time T3 since the trailing edge of the write gate signal,
the timing of starting the offset correction is naturally delayed.
In this case, the time in which the offset change appearing on the
tracking error signal is left until the start of the offset
correction becomes long. Consequently, although the tracking error
signal E2 is passed through the filters such as the notching
circuit 102 and the low pass filter 104 for the servo control, if
the influence of the offset is exerted on the tracking error signal
E2, the effect of the offset correction is reduced in half. In the
seventh embodiment of FIGS. 19A and 19B, therefore, during the
period from the start timing of recording or erasing to the start
of the offset correction, an auxiliary correction value obtained by
multiplying the correction amount calculated at the time of
immediately preceding recording or erasing by a predetermined
constant smaller than 1 is calculated and added to the tracking
error signal to thereby perform an auxiliary offset correction. The
correction amount is multiplied by the constant smaller than 1 in
consideration of variations in waveforms until the offset fully
occurs. It is empirically considered that a value about 0.6 to 0.9
is appropriate as the constant. In the flowchart of FIGS. 19A and
19B, in order to realize the offset correction using such an
auxiliary correction amount, processes necessary for the offset
correction by using the auxiliary correction amount are added to
the flowchart of the sixth embodiment of FIGS. 17A and 17B. That
is, underlined processes in steps S9 to S11 and step Sl5 are added.
In the offset correcting process of the seventh embodiment, until
the specific time T3 is elapsed since the trailing edge of the
write gate signal in step S8, the stored correction amount of the
last recording or erasing time is read in step S9, the correction
amount of last time is multiplied by a constant which lies in the
range from about 0.6 to 0.9 to thereby calculate the auxiliary
correction amount in step S10, and the auxiliary correction amount
is outputted from the D/A converter 130 to the adding circuit 100
in step S10 and is used to correct the offset. After the specific
time T3 has elapsed in step S8, in a manner similar to the sixth
embodiment of FIGS. 17A and 17B, the correction amount is
calculated, and the output of the D/A converter 130 is switched
from the auxiliary correction amount to the calculated correction
amount. The above processes are the processes in steps S12 to S17.
In step S15, the calculated correction amount is stored for the
calculation of the auxiliary correction amount used at the time of
the next recording or erasing. In the processes of FIGS. 19A and
19B, the auxiliary correction amount is calculated and outputted in
steps S9 to S11 every sampling until the specific time T3 is
elapsed since the trailing edge of the write gate signal. It is
also possible to add a determination branch so as to calculate the
auxiliary correction amount only once in the beginning.
Alternately, a process of calculating and storing an auxiliary
correction amount to be used at the time of next recording or
erasing upon calculation of a correction amount and unconditionally
outputting the stored auxiliary correction amount at the time of
next detection of the trailing edge of the write gate signal may be
used. As a result of the offset correcting process of the seventh
embodiment, as shown in signal waveforms of FIGS. 20A to 20G,
during the period in which the track error data at the sample point
SP2 is fetched at the first sampling timing after the elapse of the
specific time T3 since the write gate signal E5 goes down at time
t3 and the calculation of the offset amount, calculation of the
correction amount, and output of the correction amount are
performed, the auxiliary correction amount 150 obtained by
multiplying the correction amount of last time by a constant is
outputted.
[0065] FIGS. 21A and 21B show a flowchart of an eighth embodiment
of the invention for averaging the offset amounts at the time of
recording or erasing. FIGS. 22A to 22G show signal waveforms of
respective parts. In the fifth to seventh embodiments of the offset
correction at the time of recording or erasing, only the offset
amount at the time of recording or erasing used for the offset
correction is used as an input of the calculation of the correction
amount. When a change which is not purely caused by the reflection
light amount but is caused by, for example, a defect in a medium
appears in the tracking error signal, the correction amount
different from that to be inherently added is added to the tracking
error signal. In the case of using the auxiliary correction amount
as in the seventh embodiment, there is the possibility that an
adverse influence is exerted on the offset correction at the time
of next recording or erasing. In the eighth embodiment of FIGS. 21A
and 21B, therefore, by using a plurality of past offset amounts as
inputs to calculate the correction amount, the tracking servo
control system can be prevented from being made unstable by a
calculation result which is sporadically changed due to a medium
defect or the like while suppressing an adverse influence on the
result of calculation of the correction amount. In the eighth
embodiment, calculated offset amounts are averaged by being passed
to the integration filter, and the correction amount is calculated
by using the averaged offset amount. The averaging process can be
performed not necessarily by using the integration filter, but by a
method of simply calculating an average of a plurality of past
offset amounts. In the flowchart of the eighth embodiment, to
realize the calculation of the correction amount by averaging
offset amounts by using the integration filter, an underlined
process of step S14 is added. The details of the averaging process
by using the integration filter in step S14 are similar to the
integration filter process in the offset correction in the ID area
shown in FIG. 13. The following point is also the same. An output
result of the integration filter is divided by a circuit gain
constant in step S15 to thereby calculate the correction amount and
is stored for the next calculation of the auxiliary correction
amount in step S16. The integration constant used for the
calculation by the integration filter is one or smaller as a
condition. Empirically, a value around 0.8 to 0.9 is appropriate.
As processes of averaging the offset amounts in FIGS. 21A and 21B
by using the integration filter, all of the processes except for
the integration filter process in step S14 are not always
necessary. For example, by adding the process of averaging the
integration filter process in step S14 to the fifth embodiment of
FIG. 15 or the sixth embodiment of FIGS. 17A and 17B, similarly,
the function of the correction calculation by averaging the offset
amounts can be realized.
[0066] FIGS. 23A, 23B and 23C show flowcharts of a ninth embodiment
of offset correction according to the present invention at the time
of recording or erasing successive sectors. FIGS. 24A to 24E show
signal waveforms of respective parts. In the case where information
is continuously recorded or erased to/from successive sectors in a
medium in an optical disk drive of the present invention, a change
in the amount of reflection light from the medium becomes
significant. To be specific, an offset due to reduction in the
amount of reflection light occurs in the ID area, an offset occurs
due to an increase in the light emitting power at the time of
recording and erasing, and the offset repeatedly occurs every
continuous sectors. At the time of continuous recording or erasing,
tracking error data which is not influenced by the offset cannot be
fetched. On the other hand, the time for tracking the data area in
which recording or erasing is performed is much longer than that
for the ID area. Consequently, the accuracy of the correction
amount added for the offset correction is very important. In the
ninth embodiment of FIGS. 23A, 23B and 23C when the continuous
recording or erasing is performed, the correction amount used for
recording or erasing in the first sector is held and is
continuously used as an offset amount during the recording or
erasing of the second or subsequent sectors, thereby enabling
stable offset correction to be realized. The flowchart of FIGS.
23A, 23B and 23C are derived by adding the function of continuously
using the correction amount calculated in the first sector during
the continuous recording or continuous erasing to the flowchart of
the eighth embodiment of FIGS. 21A and 21B. That is, underlined
processes in steps S8, S13, S14, S15, and S22 are added. By
similarly adding the correcting process added for the continuously
recording or erasing to each of the fifth embodiment of FIG. 15,
the second embodiment of FIGS. 17A and 17B, and the seventh
embodiment of FIGS. 19, an offset correcting process at the time of
continuous recording or erasing can be properly performed. In the
offset correcting process in the ninth embodiment, for the first
sector, the offset correction by the calculation of the offset
amount, calculation of the correction amount, and outputting of the
correction amount, which is the same as that in the eighth
embodiment of FIGS. 21A and 21B, is performed. In step S22, a
continuous write flag is set. Consequently, for the second and
subsequent sectors, when it is confirmed instep S13 that the
continuous write flag is set, the correction amount of last time is
read in step S14 and is outputted from the A/D converter 130 to the
adding circuit 100 to perform the offset correction in step S15.
When the offset correction is finished in such a manner with
respect to the final sector by the continuous recording or erasing,
the write gate signal rises to the H level in step S5 and the
trailing edge is not detected. It is confirmed that the write gate
signal is not at the L level in step S6. After that, the program
advances from step S7 to step S8 where the continuous write flag is
cleared and the series of continuous write or erasing offset
correcting processes are finished. As shown in signal waveforms of
FIGS. 24A to 24E, with respect to the offset correction of
continuous recording or erasing in the ninth embodiment, the
correction amount calculated for the first sector at time t1 is
outputted as it is for the second and subsequent sectors. In this
case, the auxiliary correction amount and the calculated inherent
correction amount are repeatedly outputted.
[0067] FIGS. 25A to 25C show a flowchart of a tenth embodiment of
performing the offset correction at the time of reproduction in the
ID area and the offset correction at the time of recording or
erasing in the data area, achieved by including all of the
processes in the foregoing first to ninth embodiments. FIGS. 26A to
26I show signal waveforms of respective parts. As shown in the
flowchart, for performing the correction of cancelling out the
offset in the tracking error signal caused by a change in the
amount of reflection light from the medium, by providing the
process function of both the offset correcting process in the ID
area and the offset correcting process at the time of recording or
erasing in the first to ninth embodiments of FIGS. 6 to 24E, the
most effective offset correction can be realized.
[0068] Specifically, the flowchart of the tenth embodiment of FIGS.
25A to 25C includes all of the processes in the offset correction
in the ID area of FIGS. 11A to 13 and the offset correcting process
of continuous recording or erasing in FIGS. 23A, 23B and 23C.
[0069] According to the present invention as described above,
although the servo error signal used for the servo control is
passed to the filters, in the offset correction of the present
invention, the offset correction of receiving the servo error
signal before being passed to the filters, for example, the
tracking error signal, measuring an offset, calculating the
correction amount from the measured offset, and cancelling out the
offset included in the tracking error signal is performed. A change
in the offset due to a change in the amount of reflection light
directly appears in the tracking error signal before being passed
to the filter. As a result, calculation by measuring the offset
amount can be realized with high precision, the accurate offset
amount is obtained, and the correction amount used for the offset
correction becomes accurate as well. Thus, the offset correction
with higher precision can be realized. The offset-corrected servo
error signal is passed through the filters and fetched by the servo
control unit by the DSP. Consequently, there is also an advantage
that, even if the timing of the offset correction is deviated more
or less and an offset remains, by passing the signal through the
filter after that, an influence of a slight deviation in the
correction timing can be eliminated. As a result, at the time of
reproduction when an offset occurs in the ID area and at the time
of recording or reproduction when an offset occurs in the data
area, tracking becomes stable and the stability of the entire
apparatus is improved. Since all of the changes in the invention in
the conventional offset correction based on the filtered tracking
error signal are dealt in the DSP, the invention can be realized
without increasing the cost by adding a new circuit part or the
like.
[0070] Although the optical disk drive using a magnetooptic disk as
an optical medium has been described as an example in the foregoing
embodiments, the offset correction of the present invention can be
also applied as it is to other appropriate removable optical disks
such as a phase change optical disk, and a DVD.
[0071] In the above-described embodiments, the offset correction
has been described by using the tracking servo control as an
example in the servo controls in the optical disk drive. The offset
correction can be also similarly performed with respect to the
focusing servo control.
[0072] The present invention is not limited to the embodiments,
includes appropriate modifications which do not deteriorate the
object and advantages of the invention, and is not limited by the
numerical values presented in the embodiments.
* * * * *