Title: Playback apparatus and method, and recording medium
Abstract: At a step S2, a defect period monitoring unit of a defect processing control unit stands by until the defect period monitoring unit detects the start of a defect period. When the defect period monitoring unit detects the start of a defect period, the processing proceeds to a step S3. At the step S3, defect period processing is performed. When the defect period monitoring unit detects the end of the defect period at a step S4, the processing proceeds to a step S5. At the step S5, post-defect period processing is performed.
Patent Number: 6,920,093 Issued on 07/19/2005 to Nishigaki
| Inventors:
|
Nishigaki; Makoto (Saitama, JP)
|
| Assignee:
|
Sony Corporation (Tokyo, JP)
|
| Appl. No.:
|
007276 |
| Filed:
|
November 12, 2001 |
Foreign Application Priority Data
| Nov 14, 2000[JP] | 2000-346677 |
| Current U.S. Class: |
369/44.32; 369/47.14; 369/53.15 |
| Intern'l Class: |
G11B 007/00.5 |
| Field of Search: |
369/4432,471.4,442.7,531.5,443.5
|
References Cited [Referenced By]
U.S. Patent Documents
| 4688202 | Aug., 1987 | Mukai et al.
| |
| 4701603 | Oct., 1987 | Dakin et al.
| |
| 4703468 | Oct., 1987 | Baba et al.
| |
| 4722079 | Jan., 1988 | Matsumoto.
| |
| 4764860 | Aug., 1988 | Takao.
| |
| 5245599 | Sep., 1993 | Ishii et al.
| |
| 5436877 | Jul., 1995 | Ohshima.
| |
| 5481526 | Jan., 1996 | Nagata et al.
| |
| 5623465 | Apr., 1997 | Sasaki et al.
| |
| 5818804 | Oct., 1998 | Obata et al.
| |
| 6510112 | Jan., 2003 | Sakamoto et al.
| |
Primary Examiner: Miller; Brian E.
Assistant Examiner: Battaglia; Michael V.
Attorney, Agent or Firm: Frommer Lawrence & Haug LLP, Frommer; William S., Lee; Samuel S.
Claims
1. A playback apparatus for reproducing data recorded on a disk medium by using
an optical pickup, said playback apparatus comprising:
RF signal generating means for generating an RF signal on the basis of an analog
signal outputted by said optical pickup;
data signal generating means for generating a data signal by binarizing said
RF signal;
defect signal generating means for generating a defect signal for indicating
a defect on said disk medium on the basis of said RF signal;
focus error signal generating means for generating a focus error signal on the
basis of said analog signal outputted by said optical pickup;
focus servo control means for controlling a focus servo of said optical pickup
in response to said focus error signal;
tracking error signal generating means for generating a tracking error signal
on the basis of said analog signal outputted by said optical pickup;
tracking servo control means for controlling a tracking servo of said optical
pickup in response to said tracking error signal;
monitoring means for monitoring said defect signal and thereby detecting a start
and an end of a defect period;
defect period processing control means for controlling said focus servo control
means and said tracking servo control means so that said focus servo control means
and said tracking servo control means perform defect period processing when a result
of the monitoring by said monitoring means indicates said defect period,
wherein the defect period processing includes controlling said focus servo control
means and said tracking servo control means so that at least one of said focus
servo and said tracking servo is not energized; and
post-defect period processing control means for controlling said focus servo
control means and said tracking servo control means so that said focus servo control
means and said tracking servo control means perform post-defect period processing
when a result of the monitoring by said monitoring means indicates the end of said
defect period,
wherein said post-defect period processing control means includes a resetting
means for resetting the length of the post-defect period processing to an initial
value to prevent the post-defect period processing from being ended within less
than a specified time.
2. A playback apparatus as claimed in claim 1,
wherein when said monitoring means detects the start of said defect period during
said post-defect period processing performed under control of said post-defect
period processing control means, said post-defect period processing control means
stops said post-defect period processing, and said defect period processing control
means starts said defect period processing.
3. A playback apparatus as claimed in claim 1, further comprising
a focus error signal previous value hold unit to hold the focus error signal
at a previous value during the defect period processing.
4. A playback apparatus as claimed in claim 1, further comprising
a first post-defect servo control unit to drive the focus servo of the optical
pickup with an increased servo gain.
5. A playback apparatus as claimed in claim 1, further comprising
a tracking error signal previous value hold unit to hold the tracking error signal
at a previous value during the defect period processing.
6. A playback apparatus as claimed in claim 1, further comprising
a second post-defect servo control unit to drive the tracking servo of the optical
pickup with an increased servo gain.
7. A playback method for a playback apparatus to reproduce data recorded on a
disk medium by using an optical pickup, the method comprising:
an RF signal generating step for generating an RF signal on the basis of an analog
signal outputted by said optical pickup;
a data signal generating step for generating a data signal by binarizing said
RF signal;
a defect signal generating step for generating a defect signal for indicating
a defect on said disk medium on the basis of said RF signal;
a focus error signal generating step for generating a focus error signal on the
basis of said analog signal outputted by said optical pickup;
a focus servo control step for controlling a focus servo of said optical pickup
in response to said focus error signal;
a tracking error signal generating step for generating a tracking error signal
on the basis of said analog signal outputted by said optical pickup;
a tracking servo control step for controlling a tracking servo of said optical
pickup in response to said tracking error signal;
a monitoring step for monitoring said defect signal and thereby detecting a start
and an end of a defect period;
a defect period processing control step for controlling processing of said focus
servo control step and processing of said tracking servo control step so that defect
period processing is performed when a result of the monitoring by processing of
said monitoring step indicates said defect period,
wherein the defect period processing includes controlling said focus servo control
step and said tracking servo control step so that at least one of said focus servo
and said tracking servo is not energized; and
a post-defect period processing control step for controlling the processing of
said focus servo control step and the processing of said tracking servo control
step so that post-defect period processing is performed when a result of the monitoring
by the processing of said monitoring step indicates the end of said defect period,
wherein said post-defect period processing control step includes resetting the
length of the post-defect period processing to an initial value to prevent the
post-defect period processing from being ended within less than a specified time.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and a method for playback and a
recording medium, and particularly to an apparatus and a method for playback and
a recording medium suitable for use in preventing a malfunction of a servo of an
optical pickup resulting from a flaw or the like on a disk medium, for example.
FIG. 1 shows a configuration of a conventional optical disk playback apparatus
for reproducing data recorded on an optical disk.
A spindle motor
2 in the conventional optical disk playback apparatus
drives
and rotates an optical disk
1. An optical pickup
3 irradiates the
optical disk
1 with laser light, generates a signal corresponding to the
reflected light, and then outputs the signal to an RF signal generating unit
4,
an FE signal generating unit
5, and a TE signal generating unit
6.
Also, the optical pickup
3 adjusts focus servo operation in response to
a focus drive signal from a focus driver
10, and adjusts tracking servo
operation in response to a tracking drive signal from a tracking driver
12.
The RF signal generating unit
4 generates an RF signal on the basis of
the signal from the optical pickup
3, and then outputs the RF signal to
a binarizing unit
7 and a defect detecting unit
8. The FE signal
generating unit
5 generates a focus error signal (hereinafter described
as an FE signal) on the basis of the signal from the optical pickup
3, and
then outputs the FE signal to a focus servo control unit
9. The TE signal
generating unit
6 generates a tracking error signal (hereinafter described
as a TE signal) on the basis of the signal from the optical pickup
3, and
then outputs the TE signal to a tracking servo control unit
11.
The binarizing unit
7 generates a data signal by binarizing the RF signal
from the RF signal generating unit
4 into
0 or
1. The defect
detecting unit
8 detects a loss of a signal (defect) resulting from a flaw,
a stain or the like present on the optical disk
1 on the basis of the RF
signal from the RF signal generating unit
4, generates a defect signal indicating
a period of a defect detected, and then outputs the defect signal to the focus
servo control unit
9 and the tracking servo control unit
11.
A method for detecting a defect is, for example, to set level of the defect signal
during a period when level of the RF signal is lower than a predetermined threshold
value as High, and to set the defect signal during a period when the level of the
RF signal is higher than the predetermined threshold value as Low. Specifically,
when the RF signal has a level as shown in FIG. 2A, the defect signal has a corresponding
level as shown in FIG.
2B.
During a normal period (period when the level of the defect signal from the
defect detecting unit
8 is Low), the focus servo control unit
9 generates
a focus drive control signal corresponding to the FE signal from the FE signal
generating unit
5, and then outputs the focus drive control signal to the
focus driver
10. When the level of the defect signal is High, the focus
servo control unit
9 holds level of the focus drive control signal at a
predetermined reference value or a value of the focus drive control signal immediately
before the level of the defect signal becomes High, as shown in FIG. 2D, and then
outputs the level of the focus drive control signal to the focus driver
10.
The focus driver
10 generates a focus drive signal corresponding to the
focus drive control signal from the focus servo control unit
9, and then
outputs the focus drive signal to the optical pickup
3.
During a normal period (period when the level of the defect signal from the
defect detecting unit
8 is Low), the tracking servo control unit
11
generates a tracking drive control signal on the basis of the TE signal from the
TE signal generating unit
6, and then outputs the tracking drive control
signal to the tracking driver
12. When the level of the defect signal is
High, the tracking servo control unit
11 holds level of the tracking drive
control signal at a predetermined reference value or a value of the tracking drive
control signal immediately before the level of the defect signal becomes High,
as shown in FIG. 2F, and then outputs the level of the tracking drive control signal
to the tracking driver
12.
The tracking driver
12 generates a tracking drive signal corresponding
to the tracking drive control signal from the tracking servo control unit
11,
and then outputs the tracking drive signal to the optical pickup
3.
In some cases, the conventional optical disk playback apparatus supplies the
defect
signal generated by the defect detecting unit
8 to the FE signal generating
unit
5 and the TE signal generating unit
6.
In such cases, during a normal period (period when the level of the defect signal
from the defect detecting unit
8 is Low), the FE signal generating unit
5 supplied with the defect signal generates the FE signal on the basis of
the signal from the optical pickup
3, and then outputs the FE signal to
the focus servo control unit
9. When the level of the defect signal is High,
the FE signal generating unit
5 holds level of the FE signal at a predetermined
reference value or a value of the FE signal immediately before the level of the
defect signal becomes High, as shown in FIG. 2C, and then outputs the level of
the FE signal to the focus servo control unit
9. The focus servo control
unit
9 outputs a focus drive signal as shown in FIG. 2D corresponding to
the FE signal whose level is being held constant.
During a normal period (period when the level of the defect signal from the
defect detecting unit
8 is Low), the TE signal generating unit
6
supplied with the defect signal generates the TE signal on the basis of the signal
from the optical pickup
3, and then outputs the TE signal to the tracking
servo control unit
11. When the level of the defect signal is High, the
TE signal generating unit
6 holds level of the TE signal at a predetermined
reference value or a value of the TE signal immediately before the level of the
defect signal becomes High, as shown in FIG. 2E, and then outputs the level of
the TE signal to the tracking servo control unit
11. The tracking servo
control unit
11 outputs a tracking drive signal as shown in FIG. 2F corresponding
to the TE signal having a fixed value.
Thus, even if normal reflected light is not obtained because of the presence
of a flaw or the like on the optical disk
1, the conventional optical disk
playback apparatus thus formed holds the level of the focus drive signal and the
tracking drive signal while the level of the defect signal is High. Therefore,
a malfunction of a focus servo and a tracking servo of the optical pickup
3
is prevented.
However, in the case of a long High-level period of the defect signal or
depending on an error in the output of the held focus drive signal and tracking
drive signal, the optical pickup
3 is displaced substantially from an original
servo control position when the level of the defect signal returns to Low.
Japanese Patent Laid-Open No. Sho 59-203276, for example, discloses a method
for preventing such displacement which, directing attention to characteristics
of the TE signal such as periodicity, generates a pseudo error signal approximating
an original TE signal by calculation using a tracking error and a track period,
and uses the calculated pseudo error signal instead of the original TE signal while
the level of the defect signal is High.
Also, Japanese Patent Laid-Open No. Sho 64-39638 discloses a method which changes
focus offset adjusting voltage to a predetermined value to thereby prevent displacement
of a focus coil while the level of the defect signal is High, and thus minimizes
the error when the level of the defect signal returns to Low.
The conventional techniques described above are all principally aimed to reduce
a range of the control error while the level of the defect signal is High and after
the level of the defect signal returns to Low, and give no consideration to reduction
of a period from the return to Low of the level of the defect signal to the return
to a normal control state of the servo.
In general, as the High-level period of the defect signal becomes longer, the
control error tends to be increased. Hence, in case where the control error is
large if not departing from a normal servo control range when the level of the
defect signal returns to Low, for example, as shown in FIGS. 3A,
3B,
3C,
3D, and
3E, the servo continues to be unstable and requires considerable
time before the servo returns to a normal control state.
In order to return the servo quickly to the normal control state, there is known
a method which maintains a servo loop gain at a higher-than-normal level immediately
after a track jump or the like. However, when the servo loop gain is high, the
servo is generally too sensitive to a defect such as a flaw on the optical disk.
Therefore, the method of increasing the servo loop gain cannot be used to improve
defect passage characteristics.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above, and it is accordingly
an object of the present invention to reduce time required for the servo to return
to the normal control state after the level of the defect signal returns to Low.
According to the present invention, there is provided a playback apparatus
comprising: RF signal generating means for generating an RF signal on the basis
of an analog signal outputted by an optical pickup; data signal generating means
for generating a data signal by binarizing the RF signal; defect signal generating
means for generating a defect signal for indicating a defect on a disk medium on
the basis of the RF signal; focus error signal generating means for generating
a focus error signal on the basis of the analog signal outputted by the optical
pickup; a focus servo control means for controlling a focus servo of the optical
pickup in response to the focus error signal; tracking error signal generating
means for generating a tracking error signal on the basis of the analog signal
outputted by the optical pickup; tracking servo control means for controlling a
tracking servo of the optical pickup in response to the tracking error signal;
monitoring means for monitoring the defect signal and thereby detecting a start
and an end of a defect period; defect period processing control means for controlling
the focus servo control means and the tracking servo control means so that the
focus servo control means and the tracking servo control means perform defect period
processing when a result of the monitoring by the monitoring means indicates the
defect period; and post-defect period processing control means for controlling
the focus servo control means and the tracking servo control means so that the
focus servo control means and the tracking servo control means perform post-defect
period processing when a result of the monitoring by the monitoring means indicates
the end of the defect period.
The defect period processing control means can control the focus servo control
means and the tracking servo control means so that the focus error signal or the
tracking error signal of the optical pickup is held at a predetermined value.
The post-defect period processing control means can control the focus servo control
means and the tracking servo control means so that servo operation of the optical
pickup is sped up.
When the monitoring means detects the start of the defect period during the
post-defect period processing performed under control of the post-defect period
processing control means, the post-defect period processing control means can stop
the post-defect period processing, and the defect period processing control means
can start the defect period processing.
According to the present invention, there is provided a playback method
comprising: an RF signal generating step for generating an RF signal on the basis
of an analog signal outputted by an optical pickup; a data signal generating step
for generating a data signal by binarizing the RF signal; a defect signal generating
step for generating a defect signal for indicating a defect on a disk medium on
the basis of the RF signal; a focus error signal generating step for generating
a focus error signal on the basis of the analog signal outputted by the optical
pickup; a focus servo control step for controlling a focus servo of the optical
pickup in response to the focus error signal; a tracking error signal generating
step for generating a tracking error signal on the basis of the analog signal outputted
by the optical pickup; a tracking servo control step for controlling a tracking
servo of the optical pickup in response to the tracking error signal; a monitoring
step for monitoring the defect signal and thereby detecting a start and an end
of a defect period; a defect period processing control step for controlling processing
of the focus servo control step and processing of the tracking servo control step
so that defect period processing is performed when a result of the monitoring by
processing of the monitoring step indicates the defect period; and a post-defect
period processing control step for controlling the processing of the focus servo
control step and the processing of the tracking servo control step so that post-defect
period processing is performed when a result of the monitoring by the processing
of the monitoring step indicates the end of the defect period.
According to the present invention, there is provided a program on a recording
medium, comprising: an RF signal generating step for generating an RF signal on
the basis of an analog signal outputted by an optical pickup; a data signal generating
step for generating a data signal by binarizing the RF signal; a defect signal
generating step for generating a defect signal for indicating a defect on a disk
medium on the basis of the RF signal; a focus error signal generating step for
generating a focus error signal on the basis of the analog signal outputted by
the optical pickup; a focus servo control step for controlling a focus servo of
the optical pickup in response to the focus error signal; a tracking error signal
generating step for generating a tracking error signal on the basis of the analog
signal outputted by the optical pickup; a tracking servo control step for controlling
a tracking servo of the optical pickup in response to the tracking error signal;
a monitoring step for monitoring the defect signal and thereby detecting a start
and an end of a defect period; a defect period processing control step for controlling
processing of the focus servo control step and processing of the tracking servo
control step so that defect period processing is performed when a result of the
monitoring by processing of the monitoring step indicates the defect period; and
a post-defect period processing control step for controlling the processing of
the focus servo control step and the processing of the tracking servo control step
so that post-defect period processing is performed when a result of the monitoring
by the processing of the monitoring step indicates the end of the defect period.
The playback apparatus and method and the program on a recording medium according
to the present invention generate an RF signal on the basis of an analog signal
outputted by an optical pickup, generate a data signal by binarizing the RF signal,
and generate a defect signal for indicating a defect on a disk medium on the basis
of the RF signal. Also, the playback apparatus and method and the program on a
recording medium according to the present invention generate a focus error signal
on the basis of the analog signal outputted by the optical pickup, and control
a focus servo of the optical pickup in response to the focus error signal. In addition,
the playback apparatus and method and the program on a recording medium according
to the present invention generate a tracking error signal on the basis of the analog
signal outputted by the optical pickup, and control a tracking servo of the optical
pickup in response to the tracking error signal. Furthermore, the playback apparatus
and method and the program on a recording medium according to the present invention
detect a start and an end of a defect period by monitoring the defect signal, perform
defect period processing when a result of the monitoring indicates the defect period,
and perform post-defect period processing when a result of the monitoring indicates
the end of the defect period.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a configuration of a conventional optical
disk playback apparatus;
FIGS. 2A, 2B, 2C, 2D, 2E, and 2F are diagrams
of assistance in explaining conventional processing for handling a defect;
FIGS. 3A, 3B, 3C, 3D, and 3E are diagrams of assistance
in explaining conventional processing for handling a defect;
FIG. 4 is a block diagram showing a configuration of an optical disk playback
apparatus according to an embodiment of the present invention;
FIG. 5 is a flowchart of assistance in explaining defect handling processing
by the optical disk playback apparatus;
FIGS. 6A, 6B, 6C, 6D, and 6E are diagrams of assistance
in explaining defect handling processing by the optical disk playback apparatus;
FIGS. 7A, 7B, 7C, 7D, and 7E are diagrams of assistance
in explaining defect handling processing by the optical disk playback apparatus;
FIGS. 8A, 8B, 8C, 8D, and 8E are diagrams of assistance
in explaining defect handling processing by the optical disk playback apparatus;
FIGS. 9A, 9B, 9C, 9D, and 9E are diagrams of assistance
in explaining defect handling processing by the optical disk playback apparatus;
FIGS. 10A, 10B, 10C, 10D, and 10E are diagrams
of assistance in explaining defect handling processing by the optical disk playback
apparatus; and
FIGS. 11A, 11B, 11C, 11D, and 11E are diagrams
of assistance in explaining defect handling processing by the optical disk playback apparatus.
DETAILED DESCRIPTION OF THE PREFFERED EMBODIMENTS
An example of configuration of an optical disk playback apparatus to which the
present invention is applied will be described with reference to FIG.
4.
A spindle motor
22 forming the optical disk playback apparatus
20
drives and rotates an optical disk
21. An optical pickup
23 irradiates
the optical disk
21 with laser light, generates a signal corresponding to
the reflected light, and then outputs the signal to an RF signal generating unit
24, an FE signal generating unit
25, and a TE signal generating unit
26. Also, the optical pickup
23 adjusts focus servo operation in
response to a focus drive signal from a focus driver
39, and adjusts tracking
servo operation in response to a tracking drive signal from a tracking driver
46.
The RF signal generating unit
24 generates an RF signal corresponding
to the signal from the optical pickup
23, and then outputs the RF signal
to a binarizing unit
27 and a defect processing control unit
28.
The FE signal generating unit
25 generates an FE signal on the basis of
the signal from the optical pickup
23, and then outputs the FE signal to
a focus servo control unit
33. The TE signal generating unit
26 generates
a TE signal on the basis of the signal from the optical pickup
23, and then
outputs the TE signal to a tracking servo control unit
40.
The binarizing unit
27 converts the RF signal from the RF signal generating
unit
24 into digital data of
0 or
1, thus generating a data signal.
A defect detecting unit
29 forming the defect processing control unit
28
detects a loss of a signal (defect) resulting from a flaw, a stain or the like
present on the optical disk
21 on the basis of a result of comparison between
level of the RF signal from the RF signal generating unit
24 and a predetermined
threshold value, for example. The defect detecting unit
29 generates a defect
signal that has a Low level during a normal period (not a period of a defect) and
has a High level during a defect period. The defect detecting unit
29 outputs
the defect signal to a defect period monitoring unit
30.
The defect period monitoring unit
30 monitors the defect signal from the
defect detecting unit
29. During a period in which the defect signal has
a High level, the defect period monitoring unit
30 generates a defect period
signal indicating the High level of the defect signal, and then outputs the defect
period signal to a defect period processing control unit
31. When the level
of the defect signal has returned from High to Low, the defect period monitoring
unit
30 generates a defect period end signal indicating that the level of
the defect signal has returned from High to Low, and then outputs the defect period
end signal to a post-defect period processing control unit
32.
In response to the defect period signal from the defect period monitoring unit
30, the defect period processing control unit
31 controls a pre-stage
switch
34 and an FE signal previous value hold unit
37 of the focus
servo control unit
33, as well as a pre-stage switch
41 and a TE
signal previous value hold unit
44 of the tracking servo control unit
40.
In response to the defect period end signal from the defect period monitoring
unit
30, the post-defect period processing control unit
32 controls
a post-stage switch
36 of the focus servo control unit
33, as well
as a post-stage switch
43 of the tracking servo control unit
40.
In the focus servo control unit
33, the FE signal from the FE signal generating
unit
25 is supplied to the pre-stage switch
34, the FE signal previous
value hold unit
37, and a post-defect servo control unit
38.
The pre-stage switch
34 performs switching under control of the defect
period processing control unit
31. When the pre-stage switch
34 is
turned to a terminal (a) side, the FE signal from the FE signal generating unit
25 is outputted to a normal servo loop filter unit
35. On the other
hand, when the pre-stage switch
34 is turned to a terminal (b) side, an
FE signal held by the FE signal previous value hold unit
37 is outputted
to the normal servo loop filter unit
35. Normally, the pre-stage switch
34 is turned to the terminal (a) side.
The normal servo loop filter unit
35 generates a focus drive control signal
by subjecting the FE signal inputted thereto via the pre-stage switch
34
to low-frequency boost processing, phase compensation processing, low-pass filter
processing and the like. The normal servo loop filter unit
35 then outputs
the focus drive control signal to a terminal (b) side of the post-stage switch
36.
The post-stage switch
36 performs switching under control of the post-defect
period processing control unit
32. When the post-stage switch
36
is turned to a terminal (a) side, a focus drive control signal from the post-defect
servo control unit
38 is outputted to the focus driver
39. On the
other hand, when the post-stage switch
36 is turned to a terminal (b) side,
the focus drive control signal from the normal servo loop filter unit
35
is outputted to the focus driver
39. Normally, the post-stage switch
36
is turned to the terminal (b) side.
Under control of the defect period processing control unit
31, the FE
signal previous value hold unit
37 holds the level of the FE signal from
the FE signal generating unit
25, and then outputs the level of the FE signal
to the terminal (b) side of the pre-stage switch
34.
The post-defect servo control unit
38 generates a focus drive control
signal by subjecting the FE signal from the FE signal generating unit
25
to gain increase processing in addition to the processing of the normal servo loop
filter unit
35. The post-defect servo control unit
38 then outputs
the focus drive control signal to the terminal (a) side of the post-stage switch
36.
The focus driver
39 generates a focus drive signal on the basis of the
focus drive control signal from the post-stage switch
36, and then outputs
the focus drive signal to the optical pickup
23.
In the tracking servo control unit
40, the TE signal from the TE signal
generating unit
26 is supplied to the pre-stage switch
41, the TE
signal previous value hold unit
44, and a post-defect servo control unit
45.
The pre-stage switch
41 performs switching under control of the defect
period processing control unit
31. When the pre-stage switch
41 is
turned to a terminal (a) side, the TE signal from the TE signal generating unit
26 is outputted to a normal servo loop filter unit
42. On the other
hand, when the pre-stage switch
41 is turned to a terminal (b) side, a TE
signal held by the TE signal previous value hold unit
44 is outputted to
the normal servo loop filter unit
42. Normally, the pre-stage switch
41
is turned to the terminal (a) side.
The normal servo loop filter unit
42 generates a tracking drive control
signal by subjecting the TE signal inputted thereto via the pre-stage switch
41
to low-frequency boost processing, phase compensation processing, low-pass filter
processing and the like. The normal servo loop filter unit
42 then outputs
the tracking drive control signal to a terminal (b) side of the post-stage switch
43.
The post-stage switch
43 performs switching under control of the post-defect
period processing control unit
32. When the post-stage switch
43
is turned to a terminal (a) side, a tracking drive control signal from the post-defect
servo control unit
45 is outputted to the tracking driver
46. On
the other hand, when the post-stage switch
43 is turned to a terminal (b)
side, the tracking drive control signal from the normal servo loop filter unit
42 is outputted to the tracking driver
46. Normally, the post-stage
switch
43 is turned to the terminal (b) side.
Under control of the defect period processing control unit
31, the TE
signal previous value hold unit
44 holds the level of the TE signal from
the TE signal generating unit
26, and then outputs the level of the TE signal
to the terminal (b) side of the pre-stage switch
41.
The post-defect servo control unit
45 generates a tracking drive control
signal by subjecting the TE signal from the TE signal generating unit
26
to gain increase processing in addition to the processing of the normal servo loop
filter unit
42. The post-defect servo control unit
45 then outputs
the tracking drive control signal to the terminal (a) side of the post-stage switch
43.
The tracking driver
46 generates a tracking drive signal on the basis
of the tracking drive control signal from the post-stage switch
43, and
then outputs the tracking drive signal to the optical pickup
23.
A control unit
50 controls a drive
51 to read a control program
stored
on a magnetic disk
52, an optical disk
53, a magneto-optical disk
54, or a semiconductor memory
55, and then controls the whole of
the optical disk playback apparatus
20 on the basis of the read control program.
Defect handling processing by the optical disk playback apparatus
20
will next be described with reference to a flowchart of FIG.
5 and FIGS.
6A,
6B,
6C,
6D, and
6E. The defect handling processing
is intended to handle a loss of a signal (defect) resulting from a flaw, a stain
or the like present on the optical disk
21, and is started simultaneously
with a start of processing of reproducing data from the optical disk
21.
At a step S
1, the defect period processing control unit
31 of the
defect processing control unit
28 effects control to turn the pre-stage
switch
34 of the focus servo control unit
33 and the pre-stage switch
41 of the tracking servo control unit
40 to the terminal (a) side,
which is a normal position.
At a step S
2, the defect period monitoring unit
30 of the defect
processing control unit
28 monitors the defect signal from the defect detecting
unit
29 and stands by until the defect period monitoring unit
30
detects the start of a defect period, that is, the defect period monitoring unit
30 detects a change in the level of the defect signal from Low to High,
as shown in FIG.
6A. When the defect period monitoring unit
30 detects
the start of a defect period (Td in FIG.
6A), the processing proceeds to
a step S
3.
At the step S
3, the defect period monitoring unit
30 generates a
defect period signal, and then outputs the defect period signal to the defect period
processing control unit
31. In response to the defect period signal from
the defect period monitoring unit
30, the defect period processing control
unit
31 controls the pre-stage switch
34 and the FE signal previous
value hold unit
37 of the focus servo control unit
33, as well as
the pre-stage switch
41 and the TE signal previous value hold unit
44
of the tracking servo control unit
40, as processing during a defect period.
Under control of the defect period processing control unit
31, the FE
signal previous value hold unit
37 holds the level of an FE signal inputted
from the FE signal generating unit
25 immediately before the defect period
Td, as shown in FIG. 6B, and then outputs the level of the FE signal to the terminal
(b) side of the pre-stage switch
34. The TE signal previous value hold unit
44 holds the level of a TE signal inputted from the TE signal generating
unit
26 immediately before the defect period Td, as shown in FIG. 6D, and
then outputs the level of the TE signal to the terminal (b) side of the pre-stage
switch
41. The pre-stage switches
34 and
41 are turned to
the terminal (b) side.
At a step S
4, the defect period monitoring unit
30 monitors the
defect signal from the defect detecting unit
29 and stands by until the
defect period monitoring unit
30 detects the end of the defect period, that
is, the defect period monitoring unit
30 detects a change in the level of
the defect signal from High to Low, as shown in FIG.
6A.
Thus, during the defect period Td, the FE signal held by the FE signal previous
value hold unit
37 is supplied to the normal servo loop filter unit
35,
while the TE signal held by the TE signal previous value hold unit
44 is
supplied to the normal servo loop filter unit
42.
Hence, during the defect period Td, the focus drive control signal generated
by the normal servo loop filter unit
35 on the basis of the FE signal is
also held constant, and accordingly the focus drive signal generated by the focus
driver
39 on the basis of the focus drive control signal is also held constant,
as shown in FIG.
6C. In addition, the tracking drive control signal generated
by the normal servo loop filter unit
42 on the basis of the TE signal is
also held constant, and accordingly the tracking drive signal generated by the
tracking driver
46 on the basis of the tracking drive control signal is
also held constant, as shown in FIG.
6E.
Thus, during the defect period Td, a focus coil and a tracking coil within
the optical pickup
23 are held at a position immediately before the defect
period Td.
When the defect period monitoring unit
30 detects the end of the defect
period (Td in the figure) at the step S
4, the processing proceeds to a step S
5.
At the step S
5, the defect period monitoring unit
30 generates a
defect period end signal and then outputs the defect period end signal to the post-defect
period processing control unit
32. In response to the defect period end
signal from the defect period monitoring unit
30, the post-defect period
processing control unit
32 controls the post-stage switch
36 of the
focus servo control unit
33, as well as the post-stage switch
43
of the tracking servo control unit
40, as processing after the defect period.
Ta in FIGS. 6A,
6B,
6C,
6D, and
6E denotes a period
during which the post-defect period processing is performed.
Under control of the post-defect period processing control unit
32,
the post-stage switches
36 and
43 are turned to the terminal (a)
side. Thus, immediately after the defect period Td, a focus drive control signal
with an increased servo gain from the post-defect servo control unit
38
is supplied to the focus driver
39, while a tracking drive control signal
with an increased servo gain from the post-defect servo control unit
45
is supplied to the tracking driver
46.
At a step S
6, the defect period monitoring unit
30 determines whether
the defect signal is brought into a defect state again. When the defect period
monitoring unit
30 determines that the defect signal is brought into a defect
state again, the post-defect period processing is stopped immediately, and the
processing returns to the step S
3 to repeat the processes from the step
S
3 on down. When the defect period monitoring unit
30 determines
at the step S
6 that the defect signal is not brought into a defect state
again, the processing proceeds to a step S
7.
At the step S
7, whether the post-defect period processing is to be ended
or not is determined on the basis of whether a predetermined condition (to be described
later) is satisfied. The processing at the steps S
6 and S
7 is repeated
until it is determined that the post-defect period processing is to be ended. When
it is determined at the step S
7 that the post-defect period processing is
to be ended, the post-stage switches
36 and
43 are turned to the
terminal (b) side. Then, the processing returns to the step S
2 to repeat
the processes from the step S
2 on down.
The conditions for turning the post-stage switches
36 and
43 to
the terminal (b) side, that is, the conditions for timing of ending the period
Ta are: passage of a predetermined time after turning the post-stage switches
36
and
43 to the terminal (a) side; the passing of a reference level by the
FE signal and the TE signal; and reoccurrence of a defect state. The post-stage
switches
36 and
43 are turned to the terminal (b) side when one of
the conditions is satisfied.
As described above, according to the defect handling processing by the optical
disk playback apparatus
20, the post-defect period processing, in which
an action for correcting servo displacement is produced more strongly than during
a normal period (a period of no defect), is started immediately after detection
of the end of the defect period Td. Therefore, servo displacement can be corrected
quickly as compared with a case (FIGS. 3A,
3B,
3C,
3D, and
3E) where the post-defect period processing is not performed.
Incidentally, the turning of the pre-stage switches
34 and
41
while the post-defect period processing is performed at the step S
5 is not
determined uniquely because the turning of the pre-stage switches
34 and
41 is changed depending on the method of the post-defect period processing
and a situation in which a defect state occurs again.
The above-described operation of the post-defect servo control unit
38
of the focus servo control unit
33 and the post-defect servo control unit
45 of the tracking servo control unit
40 will hereinafter be described
as first operation.
The post-defect servo control unit
38 of the focus servo control unit
33 may detect a difference between the level of the FE signal immediately
after the end of the defect period and a reference level and output a pulse voltage
acting to reduce the difference to the terminal (a) of the post-stage switch
36
as a focus drive control signal.
Similarly, the post-defect servo control unit
45 of the tracking
servo control unit
40 may detect a difference between the level of the TE
signal immediately after the end of the defect period and a reference level and
output a pulse voltage acting to reduce the difference to the terminal (a) of the
post-stage switch
43 as a tracking drive control signal. Such operation
of the post-defect servo control units
38 and
45 will hereinafter
be described as second operation.
When the post-defect servo control units
38 and
45 perform the
second operation, the condition for timing of returning the post-stage switches
36 and
43 to the terminal (b) side, that is, the condition for timing
of ending the period Ta for performing the post-defect period processing is the
passing of a reference level by the FE signal and the TE signal.
FIGS. 7A,
7B,
7C,
7D, and
7E show a result of defect
handling processing when the post-defect servo control units
38 and
45
perform the second operation.
FIGS. 8A,
8B,
8C,
8D, and
8E show a result of processing
when a relatively short defect occurs three times during the performance of the
post-defect period processing in which the post-defect servo control units
38
and
45 perform the first operation.
FIGS. 9A,
9B,
9C,
9D, and
9E show a result of processing
when a relatively short defect occurs three times during the performance of the
post-defect period processing in which the post-defect servo control units
38
and
45 perform the second operation.
Since the servo is in a more unstable state during the post-defect period processing
than during normal operation, the level of the focus drive signal and the tracking
drive signal held immediately after reoccurrence of a defect state may not necessarily
be appropriate.
Therefore, when a defect state occurs, output voltage of the focus drive
signal and the tracking drive signal may be fixed at a reference level (for example
zero potential) so that voltage is not applied to the focus coil and the tracking coil.
In such a case, by resetting the length of the period Ta to an initial value,
it is possible to prevent the post-defect period processing from being ended within
less than a specified time. It is also possible to deal with a case where a defect
state continually occurs in a short time.
FIGS. 10A,
10B,
10C,
10D, and
10E show a result
of processing where the output voltage of the focus drive signal and the tracking
drive signal is set to be fixed at a reference level when a defect state occurs,
and a relatively short defect occurs three times during the performance of the
post-defect period processing in which the post-defect servo control units
38
and
45 perform the first operation.
FIGS. 11A,
11B,
11C,
11D, and
11E show a result
of processing where the output voltage of the focus drive signal and the tracking
drive signal is set to be fixed at a reference level when a defect state occurs,
and a relatively short defect occurs three times during the performance of the
post-defect period processing in which the post-defect servo control units
38
and
45 perform the second operation.
As described above, the optical disk playback apparatus
20 to which the
present invention is applied monitors reoccurrence of a defect, and when a defect
occurs, the optical disk playback apparatus
20 stops the post-defect period
processing to perform defect processing again. Therefore, it is possible to solve
the problem of the servo becoming too sensitive to a defect such as a flaw when
the loop gain of the servo is increased, and it is thereby possible to make the
servo less affected by a defect even when the servo loop gain is high.
It is to be noted that the present invention can be applied not only to playback
apparatus such as the present embodiment for playing back an optical disk such
as a CD (Compact Disc) but also to playback apparatus for playing back a DVD (Digital
Versatile Disc), an MD (Mini Disc), a magneto-optical disk and the like.
The series of processing steps described above may be carried out not only by
hardware but also by software. When the series of processing steps is to be carried
out by software, a program is installed from a recording medium onto a computer
where programs forming the software are incorporated in dedicated hardware, or
a general-purpose personal computer that can perform various functions by installing
various programs thereon, for example.
Examples of the recording medium include not only program-recorded package
media distributed to users to provide the program separately from computers, such
as the magnetic disks
52 (including a floppy disk), the optical disks
53
(including CD-ROM (Compact Disk-Read Only Memory) and DVD (Digital Versatile Disk)),
the magneto-optical disks
54 (including MD (Mini Disk)), or the semiconductor
memories
55, as shown in FIG. 4, but also a ROM and a hard disk storing
the program and supplied to a user in a state of being preincorporated in a computer.
It is to be noted that in the present specification, the steps describing the
program recorded on a recording medium include not only processing steps carried
out in time series in the described order but also processing steps carried out
in parallel or individually and not necessarily in time series.
As described above, the playback apparatus and method and the program on a recording
medium according to the present invention detect the start and the end of a defect
period by monitoring a defect signal, perform defect period processing when a result
of the monitoring indicates a defect period, and perform post-defect period processing
when a result of the monitoring indicates the end of the defect period. Therefore,
it is possible to reduce time required for the servo of an optical pickup to return
to a normal control state after the end of a defect period.
*
