U.S. patent application number 11/826958 was filed with the patent office on 2008-01-24 for method for measuring a tilt control value of a pickup head in an optical disk drive.
This patent application is currently assigned to MEDIATEK INC.. Invention is credited to Hsu-Feng Ho, Chih-Hsien Kao, Shih-Hao Ke, Jia-Hao Lin.
Application Number | 20080019236 11/826958 |
Document ID | / |
Family ID | 34132807 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080019236 |
Kind Code |
A1 |
Lin; Jia-Hao ; et
al. |
January 24, 2008 |
Method for measuring a tilt control value of a pickup head in an
optical disk drive
Abstract
A method for measuring a tilt angle of a pickup head. The method
includes the steps of: moving the pickup head to a track to be
measured; radiating a laser beam with a constant power; defining a
proper range of tilt control values; controlling the tilt angle of
the pickup head according to the range of tilt control values,
acquiring a RF signal corresponding to each tilt control value, and
storing an associated value of a associated signal; detecting the
maximum among the stored associated values; selecting and storing
the tilt control value corresponding to the maximum as the optimum
tilt control value for the track if there is a maximum; and
modifying the range of tilt control values and executing the
previous steps if there is no maximum. The so-called associated
signal includes a tracking error signal, a reading/writing RF
signal, an S-curve signal, or the RF signal.
Inventors: |
Lin; Jia-Hao; (Tai Chung
County, TW) ; Kao; Chih-Hsien; (Hsin Chu City,
TW) ; Ho; Hsu-Feng; (Taipei City, TW) ; Ke;
Shih-Hao; (Tai Chung County, TW) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
MEDIATEK INC.
Hsin-Chu City
TW
|
Family ID: |
34132807 |
Appl. No.: |
11/826958 |
Filed: |
July 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10914097 |
Aug 10, 2004 |
7263041 |
|
|
11826958 |
Jul 19, 2007 |
|
|
|
Current U.S.
Class: |
369/44.32 ;
369/53.19; G9B/7.065 |
Current CPC
Class: |
G11B 7/0956
20130101 |
Class at
Publication: |
369/044.32 ;
369/053.19 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 11, 2003 |
TW |
092122032 |
Claims
1. A method for measuring a tilt control value of a pickup head in
an optical disk drive, the pickup head having an object lens, the
method comprising the steps of: radiating a laser beam with a
constant power; defining a set of tilt control values; controlling
the tilt angle of the object lens of the pickup head according to
the set of tilt control values, acquiring an associated signal
corresponding to each tilt control value, and storing each
associated value of the associated signal for each tilt control
value; detecting a maximum value among the stored associated
values; and selecting the tilt control value corresponding to the
maximum value as the optimum tilt control value for the track and
storing the optimum tilt control value.
2. The method according to claim 1, further comprising a step of
performing a focus control.
3. The method according to claim 1, wherein the associated signal
is a tracking error signal and the associated value is the level of
the tracking error signal.
4. The method according to claim 1, wherein the associated signal
is a reading/writing RF signal and the associated value is the
amplitude of the reproducing/writing RF signal.
5. The method according to claim 1, wherein the associated signal
is a S-curve signal and the associated value is the level of the
S-curve signal.
6. The method according to claim 1, wherein the associated signal
is an RF signal and the associated value is the level of the RF
signal.
7. The method according to claim 1, wherein the step of detecting
the maximum value comprises the step of filtering the stored
associated value so as to filter out noises.
Description
[0001] This application is a Continuation of co-pending application
Ser. No. 10/914,097, filed on Aug. 10, 2004, for which priority is
claimed under 35 U.S.C. .sctn. 120 and claims the benefit of the
filing date of Taiwan Application Ser. No. 092122032, filed on Aug.
11, 2003, under 35 U.S.C. .sctn. 119(a)-(d), the entire contents of
which are hereby incorporated by reference.
BACKGROUND
[0002] The invention relates to a method for measuring a tilt
control value of a pickup head in an optical disk drive, and more
particularly to a method for measuring a tilt control value of a
pickup head by using signals, such as a tracking error (TE) signal,
a radio frequency ripple (RF ripple, RFRP) signal, a S-curve
signal, or an RF signal, which are derived from the reproduction
signal of the pickup head.
[0003] A pickup head (Optical Pickup Head) in an optical recording
and reproducing device needs one actuator to adjust the positions
and angles of the object lens of the pickup head to enable the
optical device to read or write information, such as EFM (Eight to
Fourteen Modulation) signal, in a robuster manner. The actuator can
precisely move the object lens to the desired position (angle).
However, when the to-be-read or to-be-written optical disk is
curved, or the tilt angle of the pickup head is incorrect, the read
or written information may be deteriorated. In order to compensate
for this information deterioration, the relative tilt angle between
the pickup head and the optical disk has to be measured and the
tilt angle of the pickup head has to be adjusted timely.
[0004] FIG. 1 shows the architecture of a typical tilt measuring
device. As shown in this drawing, the typical tilt measuring device
includes a pickup head 10, a tilt detector 13, and an object lens
16. The pickup head 10 is pivoted upon a rotating shaft 18 and
rotated under the control of an actuator (not shown). The tilt
detector 13 utilizes a light emitter 12 to emit light rays and
utilizes optical receivers 14a and 14b to receive the reflected
light rays. Thus, the tilt value may be measured according to the
signals of the optical receivers 14a and 14b and the actuator is
controlled according to the tilt value. This method directly
utilizes the relative tilt angle between the pickup head and the
optical disk to adjust the tilt angle of the pickup head.
[0005] FIG. 2 shows a method for measuring the tilt angle of the
pickup head without using a displacement detector. As shown in this
drawing, the tilt control module 20 includes a reproduction signal
generator 22, a jitter detector 23, a tilt control unit 24, a tilt
actuator 25, and a memory 26. The reproduction signal generator 22
is used for converting the RF signal generated by the pickup head
into the EFM (Eight to Fourteen Modulation) signal. The
reproduction signal generator 22 may be a slicer to slice the RF
signal into the signal with level 0 or 1. The jitter detector 23
receives the EFM signal and detects the jitter amount of the EFM
signal. The typical jitter amount is obtained by calculating the
wandering level of the EFM signal. The tilt control unit 24 outputs
different tilt values corresponding to different pickup head's tilt
values, records the corresponding jitter amounts, and selects the
tilt value with minimum jitter amount or the tilt value with jitter
amount smaller than a threshold, as the optimum tilt control value
for the track. The tilt actuator 25 outputs a drive signal to the
optical module 21 to adjust the pickup head's tilt angle according
to the tilt control value of the tilt control unit 24. The tilt
control value may be a digital signal and stored in the memory 26.
In addition, the tilt control value is converted by a
digital/analog converter (DAC) and then outputted to the tilt
actuator 25. The tilt actuator 25 converts the signal, such as the
voltage signal ranging from 0 to 4V, corresponding to the tilt
control value into the drive signal for driving the pickup head to
rotate.
[0006] The above method can adjust the pickup head's tilt angle to
the preferred position without using a displacement detector.
However, only the optical disk with data can be utilized to
calculate the jitter amount of the EFM signal, so as to adjust the
pickup head's tilt angle. Thus, the tilt control value for the
blank optical disk cannot be adjusted because the EFM signal cannot
be obtained.
SUMMARY
[0007] In view of the above-mentioned problems, an object of the
invention is to provide a method for measuring a tilt control value
of a pickup head without using a displacement detector, wherein the
method is adapted to both the blank optical disk and the disk with
data.
[0008] To achieve the above-mentioned object, the invention
provides a method for measuring a tilt control value of a pickup
head. The method includes the steps of: moving the pickup head to a
track to be measured; radiating a laser beam with a constant power;
defining a set of tilt values; controlling the tilt angle of the
pickup head according to the set of tilt values, acquiring an RF
signal corresponding to each tilt value, and storing an associated
value of an associated signal for each tilt value according to the
RF signal; detecting the maximum value among the stored associated
values; storing the tilt control value corresponding to the maximum
as the tilt control value for the track if there is a maximum
value; and modifying the set of the tilt values and executing the
previous steps if there is no maximum value.
[0009] The so-called associated signal includes the tracking error
signal, the reading/writing RF signal, the S-curve, or the RF
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 shows the architecture of a typical tilt measuring
device.
[0011] FIG. 2 shows the architecture of an optical device for
measuring the tilt angle of the pickup head.
[0012] FIG. 3 shows the relationship between the tilt control value
and the level of tracking error signal, wherein the horizontal axis
represents the tilt control value and the vertical axis represents
the level of tracking error signal.
[0013] FIG. 4 shows the relationship between the tilt control value
and the amplitude of the writing/reading RF signal, wherein the
horizontal axis represents the tilt control value and the vertical
axis represents the amplitude of the writing/reading RF signal.
[0014] FIG. 5 shows the relationship between the tilt control value
and the level of the S-curve signal, wherein the horizontal axis
represents the tilt control value and the vertical axis represents
the level of the S-curve signal.
[0015] FIG. 6 shows the relationship between the tilt control value
and the level of the RF signal, wherein the horizontal axis
represents the tilt control value and the vertical axis represents
the level of the RF signal.
[0016] FIG. 7 shows a flow chart of the method for measuring the
tilt angle of the pickup head of the invention.
DETAILED DESCRIPTION
[0017] The method for measuring the tilt angle of the pickup head
of the present invention will be described with reference to the
accompanying drawings. In general, when the power of the laser beam
is constant, if there is no tilt angle between the pickup head and
the optical disk (i.e., the angle therebetween is 90 degrees), the
RF signal reproduced from the optical disk has a maximum value
because the reflective amount of the laser beam is the maximum. The
associated signal derived from the RF signal is also the maximum.
The invention measures the tilt control value of the pickup head
according to this property. The associated signals include, without
limitation to, a tracking error signal, a reading/writing RF
signal, an S-curve signal, and a RF signal.
[0018] FIG. 3 shows the relationship between the tilt control value
and the level of a tracking error signal, wherein the horizontal
axis represents the tilt control value and the vertical axis
represents the level of the tracking error signal. The tilt control
value is typically a digital signal. For example, the range of the
tilt control value of FIG. 3 is from -16 to 16. A DAC (not shown)
converts the tilt control value into an analog signal, which is
then provided to a tilt actuator (not shown) to control the tilt
angle of the pickup head. As shown in FIG. 3, under the same
environment, for example, when the power of the laser beam is
constant, the level of tracking error signal is changed with the
change of the tilt control value. When the level of tracking error
signal is the maximum, it represents that the tilt control value at
this time causes no tilt angle between the pickup head and the
optical disk. Consequently, as long as a proper range of the tilt
control value is defined and the corresponding level of the
tracking error signal within this range of tilt control value is
obtained, the tilt control value corresponding to the maximum level
of the tracking error signal is selected as the optimum tilt
control value for this track.
[0019] FIG. 4 shows the relationship between the tilt control value
and the amplitude of writing/reading RF (W/RRF) signal, wherein the
horizontal axis represents the tilt control value and the vertical
axis represents the amplitude of the W/RRF signal. The tilt control
value is typically a digital signal. For example, the range of the
tilt control value of FIG. 4 is from -22 to 16. A DAC (not shown)
converts the tilt control value into an analog signal, which is
then provided to a tilt actuator (not shown) to control the pickup
head's tilt angle. As shown in FIG. 4, under the same environment,
for example, when the power of the laser beam is constant, the
amplitude of the W/RRF signal is changed with the change of the
tilt control value. When the amplitude of the W/RRF signal is the
maximum, it represents that the tilt control value at this time
causes no tilt angle between the pickup head and the optical disk.
Consequently, as long as the range of the tilt control value is
defined and the corresponding amplitude of the W/RRF signal within
this range of the tilt control value is obtained, the tilt control
value corresponding to the maximum amplitude of the W/RRF signal is
selected as the optimum tilt control value for this track.
[0020] FIG. 5 shows the relationship between the tilt control value
and the level of the S-curve signal, wherein the horizontal axis
represents the tilt control value and the vertical axis represents
the level of the S-curve signal. The tilt control value is
typically a digital signal. For example, the range of the tilt
control value of FIG. 5 is from -16 to 16. A DAC converts the tilt
control value into an analog signal, which is then provided to a
tilt actuator (not shown) to control the tilt angle of the pickup
head. As shown in FIG. 5, under the same environment, for example,
when the power of the laser beam is constant, the level of the
S-curve signal is changed with the change of the tilt control
value. When the level of the S-curve signal is the maximum, it
represents that the tilt control value at this time causes no tilt
angle between the pickup head and the optical disk. Consequently,
as long as the proper range of the tilt control value is defined
and the corresponding level of the S-curve signal within this range
of the tilt control value is obtained, the tilt control value
corresponding to the maximum S-curve level is selected as the
optimum tilt control value for this track.
[0021] FIG. 6 shows the relationship between the tilt control value
and the level of the RF signal, wherein the horizontal axis
represents the tilt control value and the vertical axis represents
the level of the RF signal. The tilt control value is typically a
digital signal. For example, the range of the tilt control value of
FIG. 6 is from -16 to 16. A DAC converts the tilt control value
into an analog signal, which is then provided to a tilt actuator
(not shown) to control the tilt angle of the pickup head. As shown
in FIG. 6, under the same environment, for example, when the power
of the laser beam is constant, the level of RF signal is changed
with the change of the tilt control value. When the level of the RF
signal is the maximum, it represents that the tilt control value at
this time causes no tilt angle between the pickup head and the
optical disk. Consequently, as long as the proper range of the tilt
control value is defined and the corresponding level of the RF
signal within this range of the tilt control value is obtained, the
tilt control value corresponding to the maximum level of the RF
signal is selected as the optimum tilt control value for this
track.
[0022] FIG. 7 shows a flow chart of the method for measuring the
tilt angle of the pickup head of the invention. As shown in this
drawing, the method for measuring the tilt angle of the pickup head
of the invention includes the following steps.
[0023] Step S702: Move the pickup head to the position of a track
to be adjusted. For example, when the optical disk is just put into
the optical disk drive, the pickup head may be moved to the inner
track and the outer track and the tilt control value may be
measured and stored, respectively.
[0024] Step S704: Radiate a laser beam with a constant power and
perform a focus control. During the measuring procedure, the power
of the laser beam is held constant.
[0025] Step S706: Define a proper range of tilt control value. The
proper range of the tilt control value may be selected to the
optimum range according to the experiences so that the measuring
time may be shortened.
[0026] Step S708: Control the tilt angle of the pickup head
sequentially according to the range of the tilt control value,
acquire the RF signal corresponding to each tilt control value, and
calculate and store the associated value of a associated signal for
each tilt control value according to the RF signal. The so-called
associated value may include the level of the tracking error
signal, the amplitude of the W/RRF signal, the level of the S-curve
signal, and the level of the RF signal. These signals are already
provided by the optical disk drive units and are generated by the
combination of the main beam and the sub beam. So, detailed
descriptions thereof will be omitted.
[0027] Step S712: Detect the maximum among the stored associated
values. If there is no maximum, the range of the tilt control value
may be too small, and the process jumps to step S714. If there is a
maximum, the process jumps to step S716.
[0028] Step S714: Enlarge the proper range of the tilt control
value and jump back to step S708.
[0029] Step S716: Select and store the tilt control value
corresponding to the maximum associated value as the optimum tilt
control value for the track.
[0030] In step S708, if the associated signal is the tracking error
signal, the tracking error signal amplitude is recorded. If the
associated signal is the S-curve signal, amplitude of the S-curve
signal is recorded, and the S-curve signal may be observed by
moving the lens upwards and downwards. If the associated signal is
the RFRP or W/RRF signal, the maximum peak value of the RFRP or
W/RRF signal is sought. If the associated signal is the RF signal,
the maximum level of the RF signal is sought.
[0031] In step S712, before detecting the maximum among the
associated values, it is possible to filter the stored associated
values so as to filter out the noises and thus to smooth the curve
corresponding to the stored associated values. Consequently, the
maximum will not be influenced by the noises.
[0032] Thus, the method for measuring the tilt angle of the pickup
head of the invention can correctly measure the optimum tilt
control value of the pickup head without using a displacement
detector, so that the error rates of data reproducing and writing
may be reduced.
[0033] While certain exemplary embodiments have been described and
shown in the accompanying drawings, it is to be understood that
such embodiments are merely illustrative of and not restrictive on
the broad invention, and that this invention not be limited to the
specific construction and arrangement shown and described, since
various other modifications may occur to those ordinarily skilled
in the art.
* * * * *