U.S. patent application number 09/752462 was filed with the patent office on 2001-08-23 for information recording/reproducing apparatus and method and information recording medium.
Invention is credited to Maeda, Takeshi, Nakamura, Shigeru, Toda, Tsuyoshi.
Application Number | 20010015945 09/752462 |
Document ID | / |
Family ID | 14177500 |
Filed Date | 2001-08-23 |
United States Patent
Application |
20010015945 |
Kind Code |
A1 |
Toda, Tsuyoshi ; et
al. |
August 23, 2001 |
Information recording/reproducing apparatus and method and
information recording medium
Abstract
An information recording/reproducing apparatus includes a
detector circuit for detecting a state of reflection light from the
recording medium, a control circuit for calculating a radiation
power used for writing the information in the recording medium, in
accordance with the reflection light state, a pulse generator
circuit for generating record pulse information in accordance with
the radiation power, and an optical driver circuit for converting
the record pulse information into optical information in accordance
with the radiation power and driving the optical head to record the
light information into the recording medium. Accordingly, the
apparatus records information by applying light from an optical
head to a record area of a recording medium and changing a state of
the record area and reads the information recorded in the record
area.
Inventors: |
Toda, Tsuyoshi;
(Kodaira-shi, JP) ; Nakamura, Shigeru;
(Tachikawa-shi, JP) ; Maeda, Takeshi;
(Kokubunji-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
14177500 |
Appl. No.: |
09/752462 |
Filed: |
January 3, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09752462 |
Jan 3, 2001 |
|
|
|
09059977 |
Apr 14, 1998 |
|
|
|
Current U.S.
Class: |
369/53.27 ;
G9B/7.014; G9B/7.026; G9B/7.099 |
Current CPC
Class: |
G11B 7/126 20130101;
G11B 7/006 20130101; G11B 7/00454 20130101 |
Class at
Publication: |
369/53.27 |
International
Class: |
G11B 007/125 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 1997 |
JP |
09-096909 |
Claims
What is claimed is:
1. An information recording/reproducing apparatus for recording
information by applying light from an optical head to a record area
of a recording medium and changing a state of the record area and
for reading the information recorded in the record area, the
apparatus comprising: a detector circuit for detecting a state of
reflection light from the recording medium; a control circuit for
calculating a radiation power used for writing the information in
the recording medium, in accordance with the reflection light
state; a pulse generator circuit for generating record pulse
information in accordance with the radiation power; and an optical
driver circuit for converting the record pulse information into
optical information in accordance with the radiation power and
driving the optical head to record the light information into the
recording medium.
2. An information recording/reproducing apparatus according to
claim 1, wherein said control circuit calculates the radiation
power by comparing a reflection light amount in an n-th (n is a
natural number) record area detected with said detector circuit
with a reflection light amount in an (n+1)-th record area detected
with said detector circuit.
3. An information recording/reproducing apparatus according to
claim 1, wherein said control circuit calculates the radiation
power by calculating a second reflection light amount in an
(n+1)-th record area detected with said detector circuit in
accordance with a first reflection light amount in an n-th record
area detected with said detector circuit and by comparing the first
and second reflection light amounts.
4. An information recording/reproducing apparatus according to
claim 1, wherein said control circuit calculates the radiation
power by calculating a difference between a reflection light amount
in an n-th record area detected with said detector circuit and a
reflection light amount in an (n+1)-th record area detected with
said detector circuit, when the difference exceeds a predetermined
range.
5. An information recording/reproducing apparatus according to
claim 2, wherein said control circuit controls said optical driver
circuit so as to apply the calculated radiation power to an area of
the recording medium excepting the record area with information
already recorded.
6. An information recording/reproducing apparatus according to
claim 2, wherein said detector circuit detects the reflection light
state in the record area with information already recorded, and
said control circuit controls said optical driver circuit so as to
record new information in the record area with the information
already recorded.
7. An information recording/reproducing apparatus according to
claim 1, wherein said control circuit comprises: first means for
setting initial values in response to a predetermined power
correction start signal provided for correction of the radiation
power: second means for checking a power correction period in
response to a sample pulse generated in accordance with the
reflection light state of the record area; third means for
measuring the reflection light state during the power correction
period; fourth means for calculating a correction value of the
radiation power in accordance with each measured reflection light
state; and fifth means for converting the record pulse information
into the light information in accordance with the correction
value.
8. An information recording/reproducing method of recording
information by applying light from an optical head to a record area
of a recording medium and changing a state of the record area and
for reading the information recorded in the record area, the method
comprising the steps of: (a) detecting a state of reflection light
from the recording medium; (b) calculating a radiation power used
for writing the information in the recording medium, in accordance
with the reflection light state; (c) generating record pulse
information in accordance with the radiation power; and (d)
converting the record pulse information into optical information in
accordance with the radiation power and driving the optical head to
record the light information into the recording medium.
9. A method according to claim 8, wherein said step (b) calculates
the radiation power by comparing a reflection light amount in an
n-th (n is a natural number) record area with a reflection light
amount in an (n+1)-th record area.
10. A method according to claim 8, wherein said step (b) calculates
the radiation power by calculating a second reflection light amount
in an (n+1)-th record area in accordance with a first reflection
light amount in an n-th record area and by comparing the first and
second reflection light amounts.
11. A method according to claim 8, wherein said step (b) calculates
the radiation power by calculating a difference between a
reflection light amount in an n-th record area and a reflection
light amount in an (n+1)-th record area, when the difference
exceeds a predetermined range.
12. A method according to claim 8, wherein said step (d) applies
the calculated radiation power to an area of the recording medium
excepting the record area with information already recorded.
13. A method according to claim 8, wherein said step (a) detects
the reflection light state in the record area with information
already recorded, and said step (d) records new information in the
record area with the information already recorded.
14. A method according to claim 8, wherein said step (b) comprises
the steps of: (b1) setting initial values in response to a
predetermined power correction start signal provided for correction
of the radiation power: (b2) checking a power correction period in
response to a sample pulse generated in accordance with the
reflection light state of the record area; (b3) measuring the
reflection light state during the power correction period; (b4)
calculating a correction value of the radiation power in accordance
with each measured reflection light state; and (b5) converting the
record pulse information into the light information in accordance
with the correction value.
15. A method according to claim 14, wherein said step (b1)
calculates the initial values of a ratio of a voltage measured at a
predetermined record area to a predicted voltage at another record
area, a corrected power of the radiation power, and a predetermined
reference power.
16. A method according to claim 14, wherein said step (b4)
calculates the correction values of: a voltage ratio Ks of a
predetermined erase power .DELTA.Pe for erasing information
recorded in the record area, to a predicted voltage Vs for an i-th
record area; an (i+1)-th predicted voltage (Vs).sub.i+1 based on
the voltage ratio Ks and the erase power .DELTA.Pe for the i-th
record area, and a voltage ratio (Km).sub.i+1 of an (i+1)-th
measured voltage (Vm).sub.i+1 to the (i+1)-th predicted voltage
(Vs).sub.i+1; correction powers .delta.Pe, .delta.Pw1 and
.delta.Pw2 for the (i+1)-th record area based on the voltage ratio
(Km).sub.i+1, the erase power .DELTA.Pe, and predetermined
reference powers .DELTA.Pw1 and .DELTA.Pw2; and corrected powers
.DELTA.Pe.sub.i+1, .DELTA.Pw1.sub.i+1 and .DELTA.Pw2.sub.i+1 for
the (i+1)-th record area through addition of the correction powers
.delta.Pe, .delta.Pw1 and .delta.Pw2 to the erase power .DELTA.Pe
and the predetermined reference powers .DELTA.Pw1 and .DELTA.Pw2,
respectively.
17. A method according to claim 14, wherein the correction powers
.delta.Pe, .delta.Pw1 and .delta.Pw2 are obtained by multiplying
the erase power .DELTA.Pe, and predetermined reference powers
.DELTA.Pw1 and .DELTA.Pw2 by a ratio of a measured voltage Ve for
the record area without information to a measured voltage Vw for
the record area with information.
18. A storage medium storing a program to be read and executed by a
control circuit including at least a memory unit and a processor
unit, the program comprising: a setting program for setting initial
values in response to a predetermined power correction start signal
provided for correction of the radiation power: a checking program
for checking a power correction period in response to a sample
pulse generated in accordance with the reflection light state of
the record area; and a correction value calculation program for
measuring the reflection light state during the power correction
period, and calculating a correction value of the radiation power
in accordance with each measured reflection light state.
19. A storage medium according to claim 18, wherein said correction
value calculation program calculates the correction values of: a
voltage ratio Ks of a predetermined erase power .DELTA.Pe for
erasing information recorded in the record area, to a predicted
voltage Vs for an i-th record area; an (i+1)-th predicted voltage
(Vs).sub.i+1 based on the voltage ratio Ks and the erase power
.DELTA.Pe for the i-th record area, and a voltage ratio
(Km).sub.i+1 of an (i+1)-th measured voltage (Vm).sub.i+1 to the
(i+1)-th predicted voltage (Vs).sub.i+1; correction powers
.delta.Pe, .delta.Pw1 and .delta.Pw2 for the (i+1)-th record area
based on the voltage ratio (Km).sub.i+1, the erase power .DELTA.Pe,
and predetermined reference powers .DELTA.Pw1 and .DELTA.Pw2; and
corrected powers .DELTA.Pe.sub.i+1, .DELTA.Pw1.sub.i+1 and
.DELTA.Pw2.sub.i+1 for the (i+1)-th record area through addition of
the correction powers .delta.Pe, .delta.Pw1 and .delta.Pw2 to the
erase power .DELTA.Pe and the predetermined reference powers
.DELTA.Pw1 and .DELTA.Pw2, respectively.
20. A storage medium according to claim 19, wherein the correction
powers .delta.Pe, .delta.Pw1 and .delta.Pw2 are obtained by
multiplying the erase power .DELTA.Pe, and predetermined reference
powers .DELTA.Pw1 and .DELTA.Pw2 by a ratio of a measured voltage
Ve for the record area without information to a measured voltage Vw
for the record area with information.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to information
recording/reproducing techniques for recording/reproducing
information to/from an information recording medium, and more
particularly to information recording/ reproducing techniques
capable of optimizing light radiation power to be used for
recording information on the information recording medium, in
accordance with the state of the recording medium.
[0003] 2. Description of the Related Art
[0004] Optical disks and the like have already used practically for
recording/reproducing information by using laser beams. One example
of rewritable optical disks is a phase change type optical disk
which utilizes a reversible phase change between a crystalline
state and an amorphous state. In order to obtain the amorphous
state, an optical disk is heated to a melting point or higher by
applying a high power (record power) and thereafter it is rapidly
cooled, and in order to obtain the crystalline state, the optical
disk is heated to a crystallization temperature by applying a
middle power (erase power) between the high power and a read power
and thereafter it is rapidly cooled. By changing the laser power in
the above manner, information can be overwritten with a single
laser beam. A method of setting an optimum record power when
information is written upon radiation of a laser beam, is described
in JP-A-7-73466 as a trial write recording control method. With
this method, an optimum combination of the record power (high
level) and erase power (middle power) for overwrite is decided in
the following manner. Information is recorded with a record power
having a constant ratio to an erase power, and by lowering the
record power, the power level at which an erroneous operation
during reproduction starts is detected. By changing the ratio to an
erase power, the above operation is repeated. The smallest ratio of
the record power to the erase power is obtained, and an operation
margin is multiplied by the smallest ratio to determined the
optimum record power.
SUMMARY OF THE INVENTION
[0005] It is a first object of the present invention to provide an
information recording/reproducing method, an information
recording/reproducing apparatus and an information recording medium
capable of high density recording wherein a laser power is changed
by detecting reflection light from a recording medium to suppress
as much as possible the shape of each record mark from being
deformed, to form a high precise record mark and to improve the
reliability of data.
[0006] It is a second object of the present invention to provide an
information recording/reproducing method, an information
recording/reproducing apparatus and an information recording
medium, capable of increasing a record data transfer speed during
high precision overwrite, by switching between preset optimum
powers in the record area and in the non-record area.
[0007] In order to achieve the first object of the invention, in
recording data by changing the state of a record area of a
recording medium by applying light, the state of the record area is
detected, and in accordance with the detected state, light
radiation is controlled.
[0008] In this case, the state of the record area is detected from
reflection light from the recording medium, and light radiation is
controlled in accordance with the n-th (n is a natural number)
detected reflection light amount and the (n+1)-th detected
reflection light amount. Light radiation is preferably controlled
by calculating the (n+1)-th light amount from the n-th light
reflection amount and comparing both the amounts.
[0009] The above operation is performed periodically or any time as
desired. It is therefore possible to suppress as much as possible
the shape of each record mark from being deformed, to form a high
precise record mark and to improve the reliability of data.
[0010] In order to achieve the second object of the invention,
prior to recording data, light radiation powers suitable for the
states of record and non-record areas are calculated and the
calculated radiation powers are selectively used in accordance with
the state of each area. In this case, prior to recording data, a
record mark and a space are formed in an area excepting the data
field of a recording medium, and the light reflection amounts of
the record area and non-record area are detected by using the erase
power. In accordance with this detection results, at least one of
the record and erase powers is preset to control the light
radiation.
[0011] In this case, as different from the approach to achieve the
first object, the preset power levels are switched between the
record area and non-record area to perform overwrite. Therefore, it
is not necessary to calculate a change ratio of the reflection
light amount from the record area to that from the non-record area.
Accordingly, the power level can be changed at high speed, the high
precision overwrite becomes possible, and the record data transfer
rate can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram showing the circuit of an
information recording/reproducing apparatus according to the
invention.
[0013] FIGS. 2A to 2C show waveforms illustrating the operation of
the information recording/reproducing apparatus.
[0014] FIGS. 3A to 3C are diagrams illustrating the relationship
between record waveforms and record marks.
[0015] FIG. 4 is a circuit diagram of an example of a laser driver
used by the information recording/reproducing apparatus according
to the invention.
[0016] FIGS. 5A to 5C are diagrams illustrating the state of record
marks after overwrite.
[0017] FIGS. 6A to 6F show waveforms illustrating an example of a
power correction method according to the invention.
[0018] FIG. 7 is a block diagram showing an example of a record
level detector used by the information recording/reproducing
apparatus according to the invention.
[0019] FIG. 8 is a flow chart illustrating the operation of a power
correction method used by the information recording/reproducing
apparatus according to the invention.
[0020] FIGS. 9A and 9H show waveforms illustrating another example
of the power correction method according to the invention.
[0021] FIG. 10 is a block diagram showing another example of the
record level detector used by the information recording/reproducing
apparatus according to the invention.
[0022] FIG. 11 is a circuit diagram showing another example of the
laser driver used by the information recording/reproducing
apparatus according to the invention.
[0023] FIGS. 12A to 12C show waveforms illustrating another example
of the power correction method according to the invention.
[0024] FIGS. 13A to 13C illustrate the relationship between the
sector format of a recording medium, a data record start signal and
a power correction start signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] Embodiments of the invention will be described. FIG. 1 shows
the structure of an information recording/reproducing apparatus
according to an embodiment of the invention. Reference numeral 1
represents a laser, 2 and 4 represent a lens, 5 represents a
recording medium, 7 and 7a represent a photo detector, 9 represents
a reproducing circuit, 12 represents a record level detector, 14
represents a laser driver, 15 represents a record pulse generator,
17 represents a power monitor, and 19 represents a controller.
[0026] The information recording/reproducing apparatus is
constituted of an optical system including the laser 1, lens 4 and
the like, a record processing system including the record pulse
generator 15 as its main part, and a reproducing system including
the reproducing circuit as its main part for converting a signal
reproduced from an optical head into a data signal. The recording
medium 5 is made of a record film and a substrate for supporting
the record film.
[0027] Upon reception of an instruction or record data supplied
from a higher level host, the controller 19 analyzes the
instruction, or modulates the record data to obtain a code train
corresponding to a modulation scheme. A synthesizer 16 is an
oscillator for generating a main clock of the apparatus. If a
record method called ZCAV (Zoned Constant Angular Velocity) is
incorporated in which a different main clock is used for each zone
to make the record densities at the inner and outer circumferences
generally equal and to increase the capacity of the recording
medium, the oscillation frequency of the synthesizer 16 is required
to be varied with each zone.
[0028] For servo control of the position of a light spot during
information recording/reproducing, a focus error signal and a track
error signal are obtained by using the photo detector 7 and a
cylindrical lens (not shown) disposed in front of the photo
detector 7. The error signals are input to the controller 19 which
in turn supplies a servo signal to a servo driver 18 to drive an
actuator 6 and control the position of the light spot.
[0029] For information recording, a code train modulated with
record data and supplied from the controller 19 and the main clock
supplied from the synthesizer 16 are input to the record pulse
generator 15 which generates a record pulse train for controlling
the length and width of each record mark.
[0030] The record pulse train is input to the laser driver 14 which
supplies a record current to the laser 1 to generate a light beam
with a high output power. The light beam from the laser 1 is made
parallel by the lens 2, transmits through a prism 3, and is
converged on the recording medium 5 by the lens 4 to thereby record
marks corresponding to the code train. During recording, light
reflected from the recording medium 5 becomes incident upon the
photo detector 7 whose output is supplied via a pre-amplifier 8 to
the record level detector 12.
[0031] Sample pulses of the record pulse train are input to the
record level detector 12 which detects a change in the reflection
light during recording and outputs it to the controller 19. In
accordance with this detected change, the controller 19 calculates
an optimum record power so that the laser driver 14 can operate to
apply a laser beam with the optimum record power to the recording
medium 5. In such a manner, since an optimum power is always set,
record marks can be recorded with high precision.
[0032] A high frequency superposing circuit 13 is provided in order
to reduce noises to be caused by the laser 1. From the viewpoint of
a life time of the laser, high frequency superposition may be
stopped during record/erase operation.
[0033] For reproduction, the laser 1 oscillates at an output power
lower than that during recording, and the laser beam is applied to
the recording medium 5. Light reflected from the recording medium 5
is guided to a separate optical path by the prism 3 and becomes
incident upon the photo detector 7 which photoelectrically converts
the reflection light. The signal output from the photo detector 7
is then amplified by the pre-amplifier 8 and input to the
reproducing circuit 9 constituted of a wave equalizer, an automatic
gain controller, a binarizing circuit and the like, which circuit 9
changes an input reproduction signal to a binarized signal.
[0034] The binarized signal of the reproducing circuit 9 is input
to a PLL (Phase Locked Loop) circuit 10 for self-blocking which
means that the basic frequency of binarized signal or data is used
for a clock signal. A reproduction clock synchronized with the
binarized signal obtained by the PLL circuit 10 is input to a
discriminating circuit 11 for data discrimination. A data
discrimination signal obtained by the discriminating circuit 11 is
input to the controller 19 to demodulate data from the
discrimination signal.
[0035] Next, a method of recording information on a recording
medium according to an embodiment will be described with reference
to FIGS. 2A to 2C. In this embodiment, a modulation method using
(1, 7) RLL codes is incorporated. FIGS. 2A and 2B show record code
trains modulated in accordance with the main clock supplied from
the synthesizer 16 and the record data supplied from the controller
19, respectively shown in FIG. 1. These record cord trains include
seven trains 2Tw to 8Tw in the case of (1, 7) RLL codes, each being
a NRZI (Non Return To Zero Inverse) signal which reverses its
polarity at the modulation code "1" for mark length recording. Tw
is a detection window width which is equal to the period Tw of the
main clock supplied from the synthesizer 16.
[0036] The record pulse generator 15 generates a record pulse train
(FIG. 2C) corresponding to the high level of the record code shown
in FIG. 2B. The pulse width of the start pulse of the record pulse
train shown in FIG. 2C is different from those of the second and
following pulses, in order to prevent the width of a record mark
from being varied with heat of laser radiation. The start pulse has
a pulse width of 3/2 Tw shorter by 1/2 Tw than the pulse width 2Tw
of the (1, 7) RLL code. The record pulse trains having the pulse
width of 3Tw or longer shown in FIG. 2C have a pulse width
corresponding to the first pulse 3/2 Tw and a combination of the
second and following pulses 1/2 Tw and spaces 1/2 Tw (same as the
main clock waveform). These pulses are generated synchronously with
the main clock shown in FIG. 2A so that the precision of the pulse
width and interval can be improved. The pulse width of each record
pulse train shown in FIG. 2C can be set to a desired value which is
an integer multiple of the period 1/2 Tw of the main clock.
[0037] FIGS. 3A to 3C show the relationship between a record
waveform (FIG. 3A), control signals (FIG. 3B) and record marks
(FIG. 3C). The record waveform shown in FIG. 3A is constituted of
the record pulse train and gaps as shown in FIG. 2C. As shown in
FIG. 3B, at the ends of the record pulse trains A and B, the record
pulse train C provides a suspension or gap period having a width of
Tw. Since the record pulse train C provides the gap having a
certain time width (in this example, Tw) after the final end (final
trailing edge of a mark forming portion) of the record pulse train
A or B, heat from the final end of the record pulse train A or B
can be prevented from changing the temperature at the leading edge
of the next pulse train. The control signals shown in FIG. 3B are
generated by the record pulse generator 15 and supplied to the
laser driver 14. FIG. 3C shows record marks formed by applying the
laser pulse train having the record waveform shown in FIG. 3A.
[0038] The laser power is set to five levels. As shown in FIG. 3A,
the laser power has five levels, including: a reproduction power
Pr; a power Pb lower than the reproduction power by an amount
corresponding to a suspension of high frequency superposition
during recording; an erase power Pe set by the record pulse train
C; and record powers Pw1 and Pw2 set by the record pulse trains A
and B. During reproduction, the power monitor 17 monitors a change
in the reproduction power, and feeds back this change to the laser
1 to maintain the reproduction power Pr constant. As shown in FIG.
3A, the record waveform has a power of the start pulse 3/2 Tw set
lower by .DELTA.Pw2 than the power of the succeeding pulse 1/2 Tw.
In this manner, the width of the record mark formed by the
preceding record pulse train is made equal to that of the record
mark formed by the succeeding record pulse train, and at the same
time, the record mark lengths can be controlled with high
precision. In other words, the temperature at the recording medium
set by the preceding record pulse train is made equal to the that
set by the succeeding record pulse train so that the record mark
width can be made constant. Therefore, the amplitude of a
reproduction signal obtained from the recording medium becomes
constant. A binarized signal can be formed by slicing the
reproduction signal at the center of its amplitude or at a certain
level.
[0039] FIG. 4 shows the laser driver 14 for generating record marks
according to an embodiment of the invention. The record pulse
trains A, B and C shown in FIG. 3B are input via inverters 41 to
current switches 42 which drive the pulse trains at high speed. The
amount of current of each current switch 42 is controlled by the
controller via each D/A converter 43. Each current amount is
determined by the current/power characteristics (I-L
characteristics) of the laser 1, and FIG. 3A shows the laser powers
(.DELTA.Pw1, .DELTA.Pw2 and .DELTA.Pe) applied to the recording
medium 5. In response to the on/off of each recording pulse train
A, B, C, current flows through the laser 1 and the record waveform
shown in FIG. 3A can be obtained. An APC (Auto Power Controller)
circuit 44 controls a current to be supplied to the laser 1 in
accordance with an instruction from the power monitor 17.
[0040] For comparison with the present invention, the shapes of
record marks formed by a conventional technique will be described
with reference to FIGS. 5A to 5C. FIG. 5A shows the shapes of
record marks recorded on a recording area of a recording medium,
FIG. 5B shows the amount of light reflected from the recording
medium during overwrite, and FIG. 5C shows the shapes of record
marks overwritten on the recording medium with the record marks
shown in FIG. 5A. In a phase change type optical disk, generally
the crystalline state corresponds to a non-record or erase state
and the amorphous state corresponds to a record state. The length
and width of each record mark shown in FIG. 5A are highly precise.
Light absorption is large in the amorphous region (mark) and small
in the crystalline region (space), so that the amount of reflection
light reduces in the mark region as indicated by a solid line in
FIG. 5B. The broken line indicates the amount of reflection light
if the mark is not recorded and the region is in a non-record or
erase state. Therefore, as new record marks are overwritten, the
length of the mark becomes long by .alpha. and the width becomes
wide by .gamma., as shown in FIG. 5C, lowering the reliability of
data.
[0041] FIGS. 6A to 6F illustrate power correction for record marks
to be overwritten, In the example shown in FIGS. 6A to 6F, the
power correction is performed by using the erase power Pe. A new
record pattern (a mark length 3Tw, a space length 5Tw, and a mark
length 3Tw) is overwritten on a recording medium with the record
pattern (a mark length 4Tw, a space length 2Tw, and a mark length
2Tw) already written. FIG. 6A shows a data record start signal.
When this signal rises, new data is recorded. FIG. 6B shows a power
correction start signal used immediately before data record for
generating a corrected erase power.
[0042] The timing when the power correction start signal is
generated will be described with reference to FIGS. 13A to 13C. The
recording medium 5 is written with data in the sector format such
as shown in FIG. 13A. An address field 20 is an area for storing a
physical address of the pre-recorded sector of the disk, and a data
field 22 is an area for storing data. A gap field 21 is provided
between the address field 20 and data field 22, as a switching area
to the record operation after the record sector is confirmed by the
address field 20. A buffer field 23 is an area for absorbing a
shift in the data field to be caused by a rotation variation of the
recording medium 5 during recording.
[0043] FIG. 13B shows the data record start signal (corresponding
to FIG. 6A) in response to which the data record in the data field
starts. FIG. 13C shows the power correction start signal
(corresponding to FIG. 6B) which is generated at the start of the
gap field 21 before the data field 22 and terminated at the end of
the data field 22.
[0044] The reason why the power correction start signal is set up
before the data record start signal is as follows. Since the gap
field 21 is not written with data, it is always in a non-record
state. Therefore, even if the erase power is applied to this field,
a reflection factor in the non-record state (crystalline state) can
be obtained always.
[0045] Returning back to the description of FIGS. 6A to 6F, FIG. 6C
shows sample pulses used for detecting light (FIG. 6D) reflected
from the recording medium. These sample pulses can be generated
easily by using the main clock and record pulse trains generated by
the record pulse generator 15.
[0046] The sample pulses shown in FIG. 6C is generated from the
main clock shown in FIG. 2A and the record pulse trains A and C of
the control signals shown in FIG. 3B. Specifically, the sample
signals shown in FIG. 6C are generated by the record pulse
generator 15 shown in FIG. 1 as logical products of inverted
signals of the main clock shown in FIG. 2A and a logical product of
the record pulse trains A and C. The pulse width of the sample
pulse can be set as desired.
[0047] In this embodiment, the sample pulses are used for detecting
a level of the erase power Pe shown in FIG. 3A. Sample pulses for
detecting the record power level can also be formed easily from the
main clock and record pulse trains driving the laser driver 14.
Sample pulses for detecting levels of the record powers Pw1 and Pw2
can be formed in a similar manner from the main clock and record
pulse trains A and B.
[0048] As above, by using sample pulses generated from the main
clock (FIG. 2A) and record pulse trains (FIG. 3B), the levels of
the erase and record powers can be easily detected.
[0049] FIG. 6D shows the amount of reflection light during
overwrite. The reflection light in a conventional method is
indicated by a solid line, whereas the erase level after power
correction is indicated by a broken line. FIG. 6E shows the
corrected erase power level during overwrite, and FIG. 6F shows the
shapes of record marks with power correction.
[0050] The power correction operation will be described. In
response to the power correction start signal shown in FIG. 6B,
only the erase power Pe shown in FIG. 3A is applied to the
recording medium 5. By using the first sample pulse shown in FIG.
6C, the reflection light level is detected in the non-record or
erase state to obtain the relationship between the radiated power
and the reflection light level (voltage from the pre-amplifier 8)
to predict the reflection light level to be detected by the next
sample pulse shown in FIG. 6C. The predicted reflection light level
is compared with that measured by using the next sample pulse. The
power is changed in accordance with a change ratio of the measured
value to the predicted value. The above operations are repeated for
each sample pulse shown in FIG. 6C. Namely, the (n+1)-th predicted
value calculated from the n-th measured value is compared with the
(n+1)-th measured value, and the power is changed in accordance
with its change ratio. In this manner, even if there are marks
already recorded, the shape of a new mark becomes generally the
same as that of a mark recorded in a non-record area.
[0051] FIG. 7 shows the record level detector 12 according to an
embodiment of the invention. The record level detector 12 is
constituted of a sample/hold circuit 70 and an A/D converter 71. A
voltage converted from reflection light by the photo detector 7 is
amplified by the pre-amplifier 8 to have a predetermined level and
input to the sample/hold circuit 70. This voltage held by the
sample/hold circuit 70 in response to the sample pulse (FIG. 6C) is
supplied to the A/D converter 71. The converted digital voltage is
supplied to the controller 19.
[0052] FIG. 8 is a flow chart illustrating the operation of a
program for a power correction method. This power correction
program is executed by the controller 19. In response to the power
correction start signal (FIG. 6B), initial values are set at step
81. This step corresponds to a setting program of the power
correction program. The initial values include the i-th (first)
measured voltage (Vm).sub.i, a ratio (Km).sub.i=1 to a predicted
voltage (Vs).sub.1, correction powers .delta.Pe, .delta.Pw1 and
.delta.Pw2 (=0), and reference powers .DELTA.Pe, .DELTA.Pw1 and
.DELTA.Pw2. The reference powers are optimum record powers set by
the controller 19. Next, it is checked at step 82 whether the power
correction period continues. If in the power correction period, the
power correction method continues, whereas if not, it is terminated
at step 83. These steps correspond to a check program of the power
correction program. During the power correction period, the
controller 19 fetches the measured voltage Vm (reflection light
level) at each sample pulse (FIG. 6C) at step 84 to perform the
following processes 1 to 5 at step 85. This step corresponds to a
correction value calculation program of the power correction
program.
[0053] Process 1: a ratio Ks of the erase power .DELTA.Pe to a
reference voltage Vs is calculated.
Ks=Vs/.DELTA.Pe,
if i=1, Vs=(Vs).sub.i=(Vm).sub.i
[0054] (this calculation is performed only for the first sample
pulse, or before the data record start)
[0055] Process 2: a ratio (Km).sub.i+1 of a measured voltage
(Vm).sub.i+1 to a predicted voltage (Vs).sub.i+1 is calculated.
[0056] (for (i+1)-th sample pulse)
(Vs).sub.i+1=Ks.times.(.DELTA.Pe).sub.i
(Km).sub.i+1=(Vm).sub.i+1/(Vs).sub.i+1
If i=1, (Vs).sub.i=Vs and (.DELTA.Pe).sub.i=.DELTA.Pe
[0057] Process 3: correction powers (.delta.Pe).sub.i+1,
(.delta.Pw1).sub.i+1 and (.delta.Pw2).sub.i+1 are calculated.
(.delta.Pe).sub.i+1=((Km).sub.i+1-1).DELTA.Pe
if i=1, (.delta.Pe).sub.i=0
(.delta.Pw1).sub.i+1=((Km).sub.i+1-1).DELTA.Pw1
if i=1, (.delta.Pw1).sub.i=0
(.delta.Pw2).sub.i+1=((Km).sub.i+1-1).DELTA.Pw2
if i=1, (.delta.Pw2).sub.i=0
[0058] Process 4: corrected powers (.DELTA.Pe).sub.i+1,
(.DELTA.Pw1).sub.i+1 and (.DELTA.Pw2).sub.i+1 are calculated.
(.DELTA.Pe).sub.i+1=.DELTA.Pe+(.delta.Pe).sub.i+1
if i=1, (.DELTA.Pe).sub.i=.DELTA.Pe
(.DELTA.Pw1).sub.i+1=.DELTA.Pw1+(.delta.Pw1).sub.i+1
if i=1, (.DELTA.Pw1).sub.i=.DELTA.Pw1
(.DELTA.Pw2).sub.i+1=.DELTA.Pw2+(.delta.Pw2).sub.i+1
if i=1, (.DELTA.Pw2).sub.i=.DELTA.Pw2
[0059] Process 5: the powers are set again.
[0060] In the above processes 1 to 5, the process 1 is performed
immediately after the power correction starts to calculate the
ratio Ks of the power to the reference voltage for calculation of
the predicted voltage Vs. The ratio Ks of the power to the voltage
is a ratio in the non-record state (crystalline state) wherein the
erase power is applied to the non-record area before the data
record starts, this area being always in the non-record state
(crystalline state). It is therefore always possible to calculate
the ratio Ks in the non-record state (crystalline state).
[0061] In the processes 2 to 5, data obtained by the (i+1)-th
sample pulse is used together with data obtained by the i-th sample
pulse at the process 1. At the process 2, the (i+1)-th predicted
voltage (Vs) is calculated as a product of the i-th .DELTA.Pe and
the ratio Ks to calculate the ratio (Km).sub.i+1 of the measured
voltage (Vm).sub.i+1 to the predicted voltage (Vs).sub.i+1. In this
case, the measured voltage is lower than the predicted voltage if
light is applied to the area with the record mark, because of a
different light absorption. Therefore, the change ratio is
reflected upon the record and erase powers to lower the powers and
eliminate a different light absorption. If the area has no record
mark, the measured voltage and predicted voltage are equal so that
the power is not necessary to be changed. This operation is
performed at the processes 3 and 4, and the new power set at the
process 5 is supplied to the laser driver 14.
[0062] Why it is necessary to calculate the predicted voltage will
be described. The measured voltage becomes lower than the predicted
voltage not only by the presence of a record mark but also by a
corrected power set upon detection of the record mark. Therefore,
if there is a record mark which extends over a plurality of sample
pulses (FIG. 6C), the power is lowered at each sample pulse by the
power correction method, so that an optimum power cannot be
calculated. However, since the ratio Km of the measured voltage to
the predicted value is used, this problem can be solved.
Specifically, if the record mark is already present, the ratio Km
smaller than "1" is used to lower the corrected power than the
initial power, whereas if there is no record mark, i.e., the
non-record state (crystalline state), the ratio Km=1 is used so
that the correction power becomes zero and the initially set
reference power is used as the corrected power. In this manner, by
incorporating the predicted voltage, it becomes possible to
discriminate between the record state and non-record state and set
an optimum power.
[0063] After the data record starts, the above processes 2 to 5 are
repeated so that a record mark can be formed with high precision.
In the above description, the power is corrected by detecting a
change in the reflection light amount by using the erase power. It
is also possible to correct the power by detecting a change in the
reflection light amount by using the record power level Pw1, Pw2.
In this case, the sample pulses can be generated from the main
clock and the record pulse train A, and the predicted voltage can
be calculated as a product of the ratio Ks calculated at the
process 1 and a reference power .DELTA.Pw1, .DELTA.Pw2. Also in
this case, although there is a different light absorption factor,
the processes similar to the above are performed to obtain an
optimum record power.
[0064] If the frequency of the main clock is set higher (e.g., an
integer multiple of the main clock), the period of the sample
pulses can be shortened so that the power can be corrected more
precisely. In this embodiment, the reflection light amount is
detected and the power is corrected at each sample pulse. Instead
of sample pulses, the voltage may be monitored at all times in an
analog manner to correct the power in accordance with the voltage
change. In this case, it is obvious that marks can be formed more
precisely.
[0065] Next, the power correction method according to another
embodiment of the invention will be described. In the embodiment
shown in FIGS. 6A to 6F and FIG. 8, the controller 19 is used for
realizing a high precision power correction. In this embodiment,
power can be corrected with a more simplified circuit structure,
assuming that the light absorption factor of an area with a record
mark is known in advance.
[0066] The signals shown in FIGS. 9A and 9B are the same as those
shown in FIGS. 6A and 6B. In this embodiment, two types of sample
pulses A and B are used as shown in FIGS. 9C and 9D to detect a
light absorption difference between the mark and space. At each
sample pulse A, the reflection light amount is detected by using a
newly set erase power, and at each sample pulse B, the reflection
light amount is detected by using an erase power set before its
newly set erase power. Immediately before data is recorded (from
the power correction start signal to the data record start signal),
the sample pulses A and B may be generated at the same timings. The
reflection light level detected by using the sample pulse A is used
as a reference level. In order to detect a light absorption
difference between the mark and space, positive and negative levels
smaller in absolute value than the level change to be caused by a
light absorption difference are added to the reference level to
obtain two levels which are set to comparators 104a and 104b (FIG.
10). The comparators 104a and 104b compare the set levels with the
level detected by using the sample pulse B.
[0067] The levels set to the comparators 104a and 104b are shown in
FIG. 9H together with the reflection light during overwrite. The
solid line in FIG. 9H shows the reflection light amount without
power correction, and the broken line shows the erase level with
power correction. In accordance with the signals output from the
comparators 104a and 104b, a current reduction signal shown in FIG.
9G is obtained. This current reduction signal is supplied to the
laser driver 14 to change the power. The reflection light level
detected at each sample pulse A by using a newly set erase power is
compared with the reflection light level detected at the next
sample pulse B. If the latter level exceeds the level set to the
comparator 104b, it can be judged that the light absorption is in
the area of the mark so that the power is lowered, whereas if it
exceeds the level set to the comparator 104a, it can be judged that
the light absorption is in the area of the space so that the power
is increased.
[0068] FIG. 10 shows the record level detector 12 according to
another embodiment of the invention. An output of the pre-amplifier
8 is input to two sample/hold circuits 100a and 100b operating in
response to the sample pulses A and B shown in FIGS. 9C and 9D. A
level sampled and held in response to the sample pulse A is
supplied to a non-inverting amplifier 101 and to an inverting
amplifier 102 having the gains of +1/G (G is an optional constant)
and -1/G to generate the positive and negative levels smaller than
in absolute value than the level to be caused by a light absorption
difference. These levels and the level detected in response to the
sample pulse A are supplied to two addition amplifiers 103a and
103b having the gain "1" or the same gain, the outputs from the
amplifiers 103a and 103b being set to the comparators 104a and 104b
as reference levels.
[0069] A level detected in response to the sample pulse B is
supplied to the comparators 104a and 104b whose outputs are
supplied to a NOR circuit 105. Only when the two outputs of the
comparators 104a and 104b have the "low" level, the current
reduction signal takes the "high" level, and in other cases, it
takes the "low level". This signal is delayed by a delay circuit
106 by a time corresponding to the sample pulse. If the current
reduction signal takes the "high level", the power applied to the
recording medium is lowered, whereas if it takes the "low level",
the power is set to the initial value so that the power can be
changed at the non-record area and at the record area.
[0070] FIG. 11 shows the laser driver 14 for generating a record
waveform according to another embodiment of the invention. Although
the fundamental operation is the same as the laser driver 14 shown
in FIG. 4, the controller 19 sets beforehand the reference powers
and corrected powers lowered by the amount corresponding to light
absorption for each record pulse train. The current reduction
signal described with FIG. 10 is used for turning on and off the
switches 110. If the current reduction signal takes the "low
level", the switches 110 are opened so that the reference powers
.DELTA.Pw1, .DELTA.Pw2 and .DELTA.Pe shown in FIG. 3A are output,
whereas if the current reduction signal takes the "high level", the
switches 110 are closed so that the corrected powers
.DELTA.Pw1-.delta.PW1, .DELTA.Pw2-.delta.Pws and
.DELTA.Pe-.delta.Pe are output which are lowered by an amount
corresponding to light absorption. Like parts to those shown in
FIG. 4 are represented by using identical reference numerals, and
the description thereof is omitted.
[0071] With the above operations, the power can be corrected at
high speed with simplified circuit structure. Therefore, the
reliability of data can be improved and data can be recorded at
high transfer speed.
[0072] A method of measuring beforehand light absorption factors
according to an embodiment of the invention will be described.
Referring to FIG. 12A, a repetitive pattern of, for example, a mark
length 4Tw and a space length 4Tw is recorded in a test area (an
area excepting the data field) of a recording medium at powers of
.DELTA.Pw1, .DELTA.Pw2 and .DELTA.Pe shown in FIG. 3A. This test
area is in the non-record state and a record mark can be recorded
correctly without being affected by a light absorption factor. FIG.
12B shows a reflection light obtained by applying a constant power
.DELTA.Pe (DC erase power) to the record marks and space. The solid
line indicates the reflection light with the record mark, and the
broken line indicates the reflection light without the record mark.
The level of the reflection light is detected at each sample pulse
shown in FIG. 12C. The record level detector is similar to that
shown in FIG. 7. The measured level with the record mark is Ve and
that without the record mark is Vw. The corrected powers
(.delta.Pe, .delta.Pw1 and .delta.Pw2 are calculated from the
reference powers .DELTA.Pe, .DELTA.Pw1 and .DELTA.Pw2 as in the
following:
.delta.Pe=.DELTA.Pe.times.Vw/Ve
.delta.Pw1=.DELTA.Pw1.times.Vw/Ve
.delta.Pw2=.DELTA.Pw2.times.Vw/Ve
[0073] The corrected powers lowered by the amount corresponding to
light absorption used in FIG. 11 can be easily set as described
above. If these levels are detected before the record operation, a
variation of light absorption factors of recording media can be
detected so that a compatibility between recording media can be
improved.
[0074] In the above embodiments of the invention, a change in the
reflection light level is detected by using the erase power. This
change can also be detected by using the record power to perform
the above-described power correction method. It is therefore
possible to detect the change in the reflection light level by
using both the erase and record powers to correct the power.
Namely, if at least one of the erase power Pe and record powers Pw1
and Pw2 is corrected, the change in the shape of the record mark
can be suppressed. The more the change can be suppressed, the more
the number of powers to be corrected is increased.
[0075] In the above embodiments, the power correction program shown
in FIG. 8 is stored in the controller 19 to execute it. Instead,
the program may be stored in a storage medium. When new record
marks are recorded in a recording medium, i.e., when new data is
recorded, the program is read from the storage medium into the
controller 19 to execute it. The controller 19 therefore has at
least a storage device for storing the program and a processing
unit for executing the program.
[0076] The power correction method of the embodiment used when
record marks are recorded, particularly when record marks are
overwritten, can obviously be applied to both when data is written
in the center of the record mark and when data is written along the
boarder of the record mark.
* * * * *