U.S. patent application number 09/837456 was filed with the patent office on 2001-12-06 for disc eccentricity measuring apparatus and method thereof and apparatus for recording and/or reproducing disc-shaped recording medium.
This patent application is currently assigned to Sony Corporation. Invention is credited to Kanai, Takashi, Nagano, Shuichi.
Application Number | 20010048646 09/837456 |
Document ID | / |
Family ID | 26545857 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010048646 |
Kind Code |
A1 |
Nagano, Shuichi ; et
al. |
December 6, 2001 |
Disc eccentricity measuring apparatus and method thereof and
apparatus for recording and/or reproducing disc-shaped recording
medium
Abstract
A recording and/or reproducing apparatus for a disc-shaped
recording medium includes an optical head, a disc rotationally
driving unit, a transfer unit, and an eccentricity amount measuring
unit. The eccentricity amount measuring unit includes a controller
and an error signal generator which generates an error signal
exhibiting the amount of relative displacement of a light beam
irradiated from the optical head onto the disc-shaped recording
medium with respect to a track on such medium. The controller
detects the peak and trough values of the error signal supplied
from the error signal generator and compares a difference signal
exhibiting a difference between the detected peak and trough values
and a reference value to calculate the amount of eccentricity of
the disc-shaped recording medium based on a comparison output
signal.
Inventors: |
Nagano, Shuichi; (Kanagawa,
JP) ; Kanai, Takashi; (Chiba, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Sony Corporation
Tokyo
JP
141-0001
|
Family ID: |
26545857 |
Appl. No.: |
09/837456 |
Filed: |
April 19, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09837456 |
Apr 19, 2001 |
|
|
|
08309907 |
Sep 21, 1994 |
|
|
|
6266304 |
|
|
|
|
Current U.S.
Class: |
369/44.28 ;
369/53.14; G9B/7.006; G9B/7.064 |
Current CPC
Class: |
G11B 7/00375 20130101;
G11B 7/0953 20130101 |
Class at
Publication: |
369/44.28 ;
369/53.14 |
International
Class: |
G11B 007/095 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 1993 |
JP |
P05-263092 |
Sep 28, 1993 |
JP |
P05-263093 |
Claims
What is claimed is:
1. An recording and/or reproducing apparatus for a disc-shaped
recording medium, comprising: an optical head for irradiating an
optical beam onto the disc-shaped recording medium; rotationally
driving means equipped with the disc-shaped recording medium for
rotationally driving the disc-shaped recording medium equipped;
transfer means for relatively transferring said optical head and
said rotationally driving means in a radial direction of the
disc-shaped recording medium; error signal generating means for
generating an error signal exhibiting the amount of the relative
shifting of a spot of a light beam irradiated from said optical
head, which is produced on the basis of an output signal from said
optical head, on the disc-shaped recording medium with respect to a
track on the disc-shaped recording medium; and control means which
detects a peak value and a trough value of the error signal
supplied from the error signal generating means and compares a
difference signal exhibiting a difference between the detected peak
value and the detected trough value with a reference value to
generate a drive signal to be supplied to the transfer unit on the
basis of a comparison output signal; wherein the drive signal from
said control means is supplied to said transfer means to shift said
optical head and said rotationally driving means in the radial
direction of the disc-shaped recording medium.
2. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 1, wherein said control means
comprises detecting means for sampling the error signal from said
error signal generating means and for comparing a sampled value
with a previously sampled value to detect said peak value and said
trough value; calculating means for calculating an average value on
the basis of said peak value and said trough value outputted rom
said calculating means; and comparing means for comparing the
average value outputted from said calculating means with a
reference value.
3. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 2, wherein said control means
further comprises analog-to-digital converting means for converting
the error signal from said error signal generating means into a
digital error signal, wherein the digital error signal from said
analog-to-digital converting means is supplied to said detecting
means.
4. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 2, wherein said detecting
means samples the error signal from said error signal generating
means and compares a sampled value with a previously sampled value
in a time-axial direction to detect said peak value and said trough
value.
5. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 2, wherein said control means
further comprises drive signal generating means for generating a
drive signal on the basis of the comparison output signal from said
comparing means.
6. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 5, wherein said comparing
means comprises a first comparator for comparing the average value
supplied from said calculating means with a first reference value,
and a second comparator for comparing said average value with a
second reference value, wherein said drive signal generating means
generates a first drive pulse signal on the basis of a comparison
output signal supplied from said first comparator and a second
drive pulse signal on the basis of a comparison output signal
supplied from said second comparator.
7. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 5, wherein said drive signal
generating means outputs a drive pulse signal so that a voltage
value is gradually lowered on the basis of the comparison output
signal from said comparing means.
8. An recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 5, wherein said drive signal
generating means outputs a drive pulse signal a voltage value of
which is changed step by step on the basis of the comparison output
signal from said comparing means and having a voltage value at a
falling time being lower than that at a rising time.
9. A method of measuring the amount of eccentricity of a
disc-shaped recording medium, comprising: a first step of
generating an error signal exhibiting the amount of relative
displacement of a spot of a light beam irradiated from the optical
disc onto the disc-shaped recording medium with respect to a track
on the disc-shaped recording medium on the basis of an output
signal from an optical head; a second step of detecting a peak
value and a trough value of the error signal generated to generate
a difference signal exhibiting a difference between the peak and
trough values detected; and a third step of calculating the amount
of eccentricity of the disc-shaped recording medium on the basis of
the difference signal.
10. A method of measuring the amount of eccentricity of a
disc-shaped recording medium as claimed in claim 9, wherein said
second step comprises the steps of sampling the error signal
generated means, comparing a sampled value with a previously
sampled value, detecting said peak value and said trough value on
the basis of a comparison result, and calculating an average value
from a difference between said peak value and said trough value
detected.
11. A method of measuring the amount of eccentricity of a
disc-shaped recording medium as claimed in claim 10, wherein said
third step comprises the step of comparing the average value
obtained in said second step with a reference value to calculate
the amount of eccentricity of the disc-shaped recording medium.
12. An apparatus for measuring the amount of eccentricity of a
disc-shaped recording medium, comprising: error signal generating
means for generating an error signal exhibiting the amount of
relative displacement of a spot of a light beam irradiated from an
optical head onto the disc-shaped recording medium with respect to
a track on the disc-shaped recording medium on the basis of an
output signal from the optical head; and calculating means which
detects a peak value and a trough value of the error signal
supplied from said error signal generating means to calculate the
amount of eccentricity of the disc-shaped recording medium on the
basis of a difference signal exhibiting a difference between the
peak and trough values detected.
13. An apparatus for measuring the amount of eccentricity of a
disc-shaped recording medium as claimed in claim 12, wherein said
calculating means comprises detecting means which samples the error
signal from said error signal generating means and compares a
sampled value with a previously sampled value to detect said peak
value and said trough value, and average value calculating means
for calculating an average value on the basis of the peak and
trough values outputted from said detecting means, and comparing
means for comparing the average value outputted from said average
value calculating means with a reference value.
14. A recording and/or reproducing apparatus for a disc-shaped
recording medium, comprising: an optical head for irradiating an
light beam onto the disc-shaped recording medium, said optical head
including an objective lens which converges the light beam onto the
recording surface of the disc-shaped recording medium; disc
rotationally driving means equipped with the disc-shaped recording
medium, for rotationally driving the disc-shaped recording medium
equipped; transfer means for transferring said optical head and
said disc rotationally driving means relatively in a radial
direction of the disc-shaped recording medium; error signal
generating means for generating an error signal exhibiting the
amount of relative displacement of a spot of the light beam
irradiated from the optical disc, which is generated on the basis
of an output signal from said optical head, onto the disc-shaped
recording medium with respect to a track on the disc-shaped
recording medium; shifting direction detecting means for detecting
whether or not said objective lens shifts from an outer side of the
disc-shaped recording medium toward the inner side thereof on the
basis of the error signal outputted from said error signal
generating means; and control means which receives a detection
signal from said shifting direction detecting means, said control
means shifting said optical head and said disc rotationally driving
means relatively by supplying a drive signal to said transfer means
during a period for which the drive signal exhibiting that said
objective lens shifts from the outer side of the disc-shaped
recording medium toward the inner side thereof is supplied from
said shifting direction detecting means to said control means.
15. A recording and/or reproducing apparatus for a disc-shaped
recording medium as claimed in claim 14, wherein said shifting
direction detecting means comprises a detector which samples the
error signal from said error signal generating means and compares a
sampled value with a previously sampled value to detect said peak
value and said trough value, wherein the shifting direction of said
objective lens is detected on the basis of the peak and trough
values outputted from said detector.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a disc-shaped recording
medium eccentricity measuring apparatus and a method thereof, and
an apparatus for recording and/or reproducing the disc-shaped
recording medium. More particularly, the invention relates to a
disc-shaped recording medium eccentricity measuring apparatus for
measuring the disc-shaped recording medium on the basis of a
tracking error signal and a method thereof, and an apparatus for
recording and/or reproducing the disc-shaped recording medium,
which is equipped with the eccentricity measuring apparatus.
[0003] 2. Discussion of the Related Art
[0004] Disc recording or reproducing apparatus are equipped with
actuators for driving objective lenses for optical heads in
accordance with a tracking error signal obtained from track guide
information such as rows of pits or grooves for controlling the
optical spot tracking. The apparatus also include a sled mechanism
for displacing the relative position of the whole of the optical
head and the disc surface with respect to the direction of the
diameter of the disc.
[0005] Methods for the sled mechanism where the whole of the
optical head is shifted with respect to the disc, and where a
turntable on which the disc is mounted is shifted with respect to a
fixed position of the optical head are well known.
[0006] There is also a method where a sled error signal is
generated by extracting the low frequency component from the
tracking error signal by passing it through a low pass filter,
amplifying it, and then applying it to a drive motor as a drive
signal. The sled error signal is a signal exhibiting the amount of
the offset between the whole of the optical head and the objective
lens for which the actuator within the optical head drives the
tracking.
[0007] FIGS. 1a to 1c show the waveforms of those signals. FIG. 1c
is the tracking error signal which is supplied to a low pass filter
to generate the sled error signal shown in FIG. 1b. The sled drive
signal shown in FIG. 1a is then obtained.
[0008] The sled error signal in FIG. 1b exhibits the angle of
radiation of a light beam applied from the optical head with
respect to a disc surface. The sled mechanism should therefore
carry out shifting in such a direction that the angle of radiation
is vertical and the sled error signal becomes zero.
[0009] However, even if the sled drive signal is applied to the
sled motor, a point at which the shift of the optical head
commences depends on the stationary coefficient of friction of the
sled mechanism. As the stationary coefficient of friction disperses
depending on the apparatus in accordance with the sled load mass
and construction of the sled mechanism etc., it is difficult to
control the actual sled operation effectively just using this drive
voltage.
[0010] For example, in FIG. 1a, if the stationary coefficient of
friction is first exceeded so that motion commences at a point in
time when the sled drive voltage reaches a voltage S.sub.s, a
period between T.sub.1 and T.sub.2 becomes a dead band period where
there is no actual sled operation even though a voltage is being
applied. Also, design and adjustment is made extremely difficult
because this operation starting point disperses.
[0011] Further, when the sled mechanism starts the shift of the
optical head, as shown by the period from T.sub.2 to T.sub.3 in
FIG. 1b, the sled error signal is reduced until it is close to
zero, so that when the sled error signal becomes zero, the light
beam is applied vertically onto the disc surface. However, if the
motion coefficient of friction for the sled mechanism is large, it
will stop before the sled error signal becomes zero. This causes
that the optical beam will always be applied at an angle which is
slightly off from the vertical. As this motion coefficient of
friction also disperses, operation stoppage control using the drive
signal becomes difficult.
[0012] Also, as a voltage is always being applied to the sled
motor, the influence of voltage fluctuations going to other circuit
parts are ever present and this has a detrimental effect on the
equipment as a whole.
[0013] As a result of this, this applicant put forward a previous
technology in Japanese Patent Application No. 4-288196 where a sled
shift pulse is applied to a sled mechanism when the sled error
signal exceeds a certain threshold value.
[0014] This is as shown in FIGS. 2a to 2d, the sled error signal in
FIG. 2b obtained as the low frequency component of the tracking
error signal in FIG. 2c is compared with a prescribed threshold
value S.sub.TH. When, as in at the times T.sub.7 and T.sub.9, the
sled error signal reaches the threshold value S.sub.TH, pulses
shown in FIG. 2a is outputted as a drive signal. Here, a pulse
voltage Vs is set at a voltage sufficient to assimilate the
coefficient of friction. The threshold value S.sub.TH is then set
at a value which is such that the tracking control for the optical
head due to the actuator does not exceed a value of this trailing
limit. That is, a drive pulse is applied to the sled mechanism when
at a tracking trailing limit or when close to the limit using the
actuator, whereby the optical head is shifted.
[0015] If a fixed voltage pulse of a voltage which is sufficient to
assimilate the coefficient of friction is used for the drive signal
and the period for which this voltage is applied is set based on
the sled error signal, instabilities in the shift operation, which
depend on dispersion in the coefficient of friction, can be
resolved. As a result, an excellent shift operation can be achieved
so that the problems mentioned above may be resolved.
[0016] However, in a disc which is scanned by the optical head when
recording or reproducing operation, eccentricity due to the
fabrication etc., eccentricity due to errors on the disc chucking
mechanism or eccentricity due to chucking shifts caused at the time
of loading or generated by disturbances occurs.
[0017] As a result of these eccentricities, the sled error signal
actually becomes of sine waveform shown in the expanded view of
FIG. 2d. The frequency of this waveform is the disc rotation
frequency, i.e. one period thereof is the equivalent to one
rotation period of the disc.
[0018] However, in the case where the shift operation of the
optical head is carried out in response to the level of the
aforementioned sled error signal, it is difficult to carry out
accurate shift operation during the execution of the shift
operation determination, that is, the comparison between the level
of the sled error signal and the threshold value S.sub.TH, as a
result of the effects of level fluctuations due to these
eccentricities.
[0019] A comparison result is therefore obtained which corresponds
to a measurement of the extent of the eccentricity taken with
respect to the loaded disc in order to cancel out the effects of
this eccentricity.
[0020] For example, from these kinds of conditions, the amount of
eccentricity for a disc in a disc player etc. can be measured.
[0021] A method of measuring this extent of eccentricity is, for
example, to half rotate the disc with the tracking servo turned
off. At this time, as the position to which the laser spot is
applied is fixed with the tracking servo turned off, if there is
any eccentricity, the beam spot crosses the track and a traverse
signal is therefore detected. The number of tracks which are
crossed over, that is, the traverse count number, is then taken as
the measurement of the eccentricity value at this time.
[0022] However, items such as a disc half rotation detecting means
are necessary with this kind of measuring method, which makes the
construction complicated. This is not suitable for adoption in
public use disc players etc.
[0023] Further, this cannot be carried out during operations such
as reproduction etc. because the tracking servo has to be turned
off. As a result, cases cannot be coped with whereby chucking
shifts due to disturbances etc. occur during reproduction etc. or
the eccentricity component is generated afresh.
SUMMARY OF THE INVENTION
[0024] It is therefore an object of the present invention to
provide an apparatus for recording and/or reproducing a disc-shaped
recording medium, which resolves the above-mentioned problems.
[0025] It is another object of the present invention to provide a
method of measuring the amount of eccentricity of a disc-shaped
recording medium, which resolves the above-mentioned problems.
[0026] It is further object of the present invention to provide an
apparatus for measuring the amount of eccentricity of a disc-shaped
recording medium, which resolves the above-mentioned problems.
[0027] According to the present invention, there is provided an
apparatus for recording and/or reproducing the disc-shaped
recording medium, including an optical head, a disc rotationally
driver, a transfer unit, an error signal generator and a
controller. The optical head irradiates an optical beam onto the
disc-shaped recording medium. The disc rotationally driver is
equipped with a disc-shaped recording medium and rotates the
disc-shaped recording medium equipped. The transfer unit transfers
the optical head and the disc rotationally driver relatively in a
radial direction of the disc-shaped recording medium. The error
signal generator generates an error signal exhibiting the amount of
the relative shifting of a spot of a light beam irradiated from the
optical head, which is produced on the basis of an output signal
from the optical head, on the disc-shaped recording medium with
respect to a track on the disc-shaped recording medium. The
controller detects a peak value and a trough value of the error
signal supplied from the error signal generator and compares a
signal exhibiting a difference between the detected peak value and
the detected trough value with a reference value to generate a
drive signal to be supplied to the transfer unit on the basis of a
comparison output signal. The transfer unit transfers the optical
head and the disc rotationally driver in the radial direction of
the disc-shaped recording medium by receiving the drive signal from
the controller.
[0028] According to the present invention, there is provided a
method of measuring the amount of eccentricity of the disc-shaped
recording medium, including first, second and third steps. In the
first step, an error signal exhibiting the amount of relative
displacement of a spot of a light beam irradiated from the optical
disc onto the disc-shaped recording medium with respect to a track
on the disc-shaped recording medium is generated on the basis of an
output signal from the optical head. In the second step, a peak
value and a trough value of the error signal thus generated are
detected to generate a difference signal exhibiting a difference
between the peak and trough values thus detected. In the third
step, the amount of eccentricity of the disc-shaped recording
medium is calculated on the basis of the difference signal.
[0029] According to the present invention, there is provided an
apparatus for measuring the amount of eccentricity of a disc-shaped
recording medium, including an error signal generator and a
calculator. The error signal generator generates an error signal
exhibiting the amount of relative displacement of a spot of a light
beam irradiated from the optical head onto the disc-shaped
recording medium with respect to a track on the disc-shaped
recording medium on the basis of an output signal from the optical
head. The calculator detects a peak value and a trough value of the
error signal supplied from the error signal generator to calculate
the amount of eccentricity of the disc-shaped recording medium on
the basis of a difference signal exhibiting a difference between
the peak and trough values thus detected.
[0030] According to the present invention, there is provided a
recording and/or reproducing apparatus for a disc-shaped recording
medium, including an optical head, a rotational driver, a transfer
unit, an error signal generator, a shifting direction detector and
a controller. The optical head irradiates an light beam onto the
disc-shaped recording medium, and includes an objective lens which
converges the light beam onto the recording surface of the
disc-shaped recording medium. The disc rotationally driver is
equipped with the disc-shaped recording medium, and rotates the
disc-shaped recording medium equipped. The transfer unit transfers
the optical head and the disc rotationally driver in the radial
direction of the disc-shaped recording medium relatively. The error
signal generator generates an error signal exhibiting the amount of
relative displacement of a spot of a light beam irradiated from the
optical head, which is generated on the basis of an output signal
from the optical head, onto the disc-shaped recording medium with
respect to a track on the disc-shaped recording medium. The
shifting direction detector detects whether or not the objective
lens shifts from the outer side of the disc-shaped recording medium
toward the inner side thereof on the basis of the error signal
outputted from the error signal generator. The controller receives
a detection signal from the shifting direction detector. The
controller also shifts the optical disc and the disc rotationally
driver relatively by supplying a drive signal to the transfer unit
during a period for which the drive signal exhibiting that the
objective lens shifts from the outer side of the disc-shaped
recording medium toward the inner side thereof is supplied from the
shifting direction detector to the controller.
[0031] According to the present invention, an error signal
exhibiting the amount of relative displacement of a spot of a light
beam irradiated from the optical disc onto the disc-shaped
recording medium with respect to a track on the disc-shaped
recording medium is generated on the basis of an output signal from
the optical head so as to measure the amount of The calculator
detects a peak value and a trough value of the error signal
supplied from the error signal generator to calculate the amount of
eccentricity of the disc-shaped recording medium as a difference
between the peak value and the trough value of the error signal
generated. For that reason, according to the present invention, the
amount of eccentricity of the disc-shaped recording medium can be
measured with a simplified structure. Also, according to the
present invention, the amount of eccentricity of the disc-shaped
recording medium can be measured even during the recording or
reproducing operation for the disc-shaped recording medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIGS. 1a to 1c are explanatory diagrams showing a
conventional sled control operation;
[0033] FIGS. 2a to 2d are explanatory diagrams showing the sled
control operation;
[0034] FIG. 3 is an explanatory diagram showing the eccentricity
measuring operation in accordance with an embodiment of the present
invention;
[0035] FIGS. 4a to 4c are explanatory diagrams showing the sled
control operation in accordance with the embodiment of the
invention;
[0036] FIGS. 5a to 5e are explanatory diagrams showing the sled
control operation in accordance with the embodiment of the
invention;
[0037] FIG. 6 is a block diagram showing the essential parts of a
reproducing apparatus which makes up the embodiment of the
invention;
[0038] FIG. 7 is a block diagram showing the essential parts of a
further reproducing apparatus which makes up the embodiment of the
invention;
[0039] FIG. 8 is a conceptual block diagram showing the
construction of the essential parts of a system controller and a
servo controller in accordance with the embodiment of the
invention;
[0040] FIG. 9 is a flowchart showing the eccentricity measuring and
sled control processes in accordance with the embodiment of the
invention;
[0041] FIG. 10 is a flowchart showing the eccentricity measuring
and sled control processes in accordance with the embodiment of the
invention; and
[0042] FIG. 11 is a flowchart showing the eccentricity measuring
and sled control processes in accordance with the embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Hereinafter, description will be given of a disc
eccentricity measuring apparatus in accordance with an embodiment
of the present invention with reference to FIGS. 3 to 11.
[0044] FIG. 3 shows a sled error signal similar to that shown in
FIG. 2d. The disc eccentricity apparatus in accordance with this
embodiment calculates the amount of the eccentricity from this sled
error signal.
[0045] The waveform shown in FIG. 3 is a sine wave-shaped waveform
expressed in accordance with the influences of the deviation. It
follows that it's period is equivalent to one rotational period of
a disc and that a difference between a peak value .sub.2 and a
trough value P.sub.1 is equivalent to the amount of the
deviation.
[0046] This signal is therefore sampled at prescribed times and the
peak values P.sub.2 and the trough values P.sub.1 are detected. The
extent of the eccentricity is then obtained from the difference
between these two items.
[0047] At the point in time when the calculation of the
eccentricity commences, the first peak value P.sub.S is detected.
An initial extent of eccentricity is then calculated using the
trough value P.sub.1 and the peak value P.sub.2 detected after
this. It will not be at all certain that the peak value or trough
value detected first of all will be an extreme value as it depends
on a signal value from during the beginning of the sampling. There
is therefore an item to prevent the measuring of the extent of the
eccentricity using mistaken extreme values obtained in this way.
For example, if the sampling starts at a time T.sub.0, then the
first peak value detected is P.sub.E. If the extent of the
eccentricity is then calculated using the difference between the
trough value P.sub.F detected next and the peak value P.sub.E, this
value will be inaccurate. The trough value P.sub.1 and the peak
value P.sub.2 used in the calculations are obtained after the
onetime peak value Ps has been confirmed.
[0048] After the trough value P.sub.1 and the peak value P.sub.2
have been obtained in this way, from the following period onwards
the trough values and the peak values are used as the trough values
P.sub.1 and the peak values P.sub.2 in the calculations for the
extent of the eccentricity without modification as there will be no
mistaken detection of extreme values of the kind described
above.
[0049] By obtaining the extent of the eccentricity from the trough
values P.sub.1 and the peak values P.sub.2 for the sled error in
this way in this embodiment, the extent of the eccentricity can be
obtained, for example, every rotational period during reproducing
operation etc.
[0050] By doing this, sled control in which the influence of
eccentricity can be canceled can be carried out based on
measurements for the extent of deviation taken in this way.
[0051] The sled error signal exhibits the whole offset amount for
the objective lens and the optical head. With the waveform shown in
FIG. 3, it is shown that the objective lens is driven by the
tracking operation in a direction which negates the influence of
the eccentricity. The average value of the trough value P.sub.1 and
the peak value P.sub.2 (CT in the diagram) is an offset amount for
canceling the effects of the eccentricity. It is therefore
preferable to work out the shift for the relative positions of the
optical head and disc based on this average value CT.
[0052] Each of the various examples of sled control carried out
based on the average value CT is shown in FIGS. 4a to 5e.
[0053] FIG. 4a shows the slide error signal while the extent of the
offset for the objective lens with respect to the whole of the
optical head is being amplified as far as the region of the
trailing limit. An average value C.sub.T is obtained from this sled
error signal every eccentricity component cycle. Then, when it is
intended to carry out a shift, the threshold value TH.sub.1 to be
taken as the offset amount is set up and the calculated average
value CT is compared with this threshold value TH.sub.1.
[0054] In that taken as a first example of a drive pulse used in
the sled control, as shown in FIG. 4b, a drive pulse is generated
for a predetermined duration from the time when the average value
CT exceeds the threshold value TH.sub.1.
[0055] The time when the average value CT can be detected to have
exceeded the threshold value TH.sub.1 is when the peak value
P.sub.2 is detected. An average value CT is then calculated from
this peak value P.sub.2 and the previous trough P.sub.1, and this
is then compared with the threshold value TH.sub.1. It therefore
follows that the output for the drive pulse occurs after the time
T.sub.1 at which the peak value P.sub.2 is detected.
[0056] An appropriate operation of the optical head which cancels
out the effects of the eccentricity can therefore be achieved by
carrying out the sled control by comparing the average value CT for
the extent of the offset and the threshold value TH.sub.1.
[0057] In a second example of a drive pulse used in a sled control,
as shown in FIG. 4b, a drive pulse is generated for a prescribed
period from the time when it is detected that the average value CT
has exceeded the threshold value TH.sub.1. Also, the level of the
drive pulse comes down gradually while the drive is in halt.
[0058] If supply of the drive pulse is rapidly suspended, the
optical head will come to an abrupt halt, which will cause
disturbance to the tracking servo. However, as shown in FIG. 4c,
having the level of the drive pulse come down gradually means that
the shift acceleration of the optical head is also reduced
gradually. This shifting then negates the coefficient of frictional
motion so as to make the shifting speed of the entire optical head
slower until it comes to a halt. By halting the shifting of the
optical head in this gentle manner, disturbances to the tracking
servo can be prevented.
[0059] A third example of a drive pulse used in sled control is
actually a development on from the first example of the drive pulse
used in the sled control. Here, if the stationary friction
coefficient of the sled mechanism is large, even if a drive pulse
is applied, the shift of the optical head will not occur, as shown
in FIG. 4b. Instead, as shown in FIG. 5a, the level of the sled
error signal, that is, the extent of the offset is amplified
without being modified. If this continues without change, it will
not be possible to follow the tracking and it will therefore not be
possible to read signals from the disc.
[0060] The threshold value TH.sub.2 is therefore set at a level
which is higher than the threshold value TH.sub.1 and the average
value CT is then compared with this threshold value TH.sub.2.
[0061] Then, as shown in FIG. 5b, an ordinary level drive pulse is
generated when the average value CT becomes higher than the
threshold value TH.sub.1. However, the shifting of the optical head
is not carried out without any modifications taking place so that
when the average value CT exceeds the threshold value TH.sub.2, the
drive pulse is generated as a higher voltage pulse. In this way,
the shifting of the optical head can be carried out more
accurately.
[0062] In a fourth example of a drive pulse used in sled control,
this third example of the drive pulse used in the sled control is
combined with the second example of the drive pulse used in the
sled control (FIG. 4c) so that a drive pulse as shown in FIG. 5c is
generated.
[0063] A fifth example of a drive pulse used in sled control is a
development of the third example of the drive pulse used in the
sled control (FIG. 5b). In this case, a higher voltage pulse is
generated as the drive pulse when the average value CT exceeds the
threshold value TH.sub.2. However, if a high level pulse is
continually applied in order that a simple pulse drive will provide
uniform acceleration, the shifting speed will become too high. As a
result of this, the amount of shifting will become excessive and
the control will b considered to be unstable. Therefore, as shown
in FIG. 5d, a high level pulse is applied only for the first
prescribed period and ordinary level voltages are applied as the
drive pulses after that. By making the drive pulse a composite
pulse in this way, the drive can be started with a voltage which is
sufficient with respect to the initial stationary friction
coefficient and a stable shift of the optical head can be carried
out at normal speed using a normal level pulse after this time.
[0064] A sixth example of a drive pulse used in a sled control is a
composition of the first to fifth examples of the drive pulses used
in the sled control and generates a drive pulse shown in FIG. 5e.
That is, in this example of the drive pulse used in the sled
control, the influences of the eccentricity on the sled operation
are canceled, the generation of disturbances in the tracking servo
due to rapid sled halting is prevented, and the inability to follow
the tracking due to poor sled starting caused by irregularities in
the stationary friction coefficient is resolved, as are control
instabilities due to the rapidness of the shift speed.
[0065] Here, the applied voltage was selected using two stage
threshold values TH.sub.1 and TH.sub.2. However, finer control can
be achieved by applying voltage values using threshold values of
three stages or more.
[0066] Also, as becomes clear from the first to sixth examples of
the drive pulses used in the sled control, the drive pulse is
applied directly after or at a prescribed period after a time
(T.sub.1, T.sub.2, T.sub.3) at which a peak P.sub.2 is detected due
to an average value CT exceeding a threshold value TH.sub.1 or
TH.sub.2 i.e. the period for which the drive pulse is supplied it
takes for the sled error signal to go from a peak point to a trough
point. This is the period for the objective lens to be shifted from
the outer side of the disc to the inner side by the tracking servo.
As this period can be considered to be that of the drive pulse,
then the whole of the optical head shifts from the inner side of
the optical disc to the outer side i.e. the opposite way to that of
the objective lens.
[0067] In this way, the objective lens acceleration can be made
small during the sled operation and the tracking control can be
made stable, as can the shifting of the optical head which
accompanies it.
[0068] Taking into consideration the period where the sled error
signal goes the opposite way from this i.e. from a trough to a
peak, that is to say, the period of the sled error pulse where the
objective lens is shifted from the inner side to the outer side of
the disc, if the whole of the optical head is shifted from the
inner side of the disc to the outer side, the optical head shifting
process cannot be carried out in a stable manner as the
acceleration has to be greatly increased to shift the objective
lens to the outer circumference.
[0069] For these reasons, the drive pulse is a fixed period pulse
so that the shifting of the optical head is completed in the period
where the sled error signal goes from a peak to a trough. This
fixed period is decided based on the rotational period of the disc.
For example, in the case of a compact disc player, the drive pulse
output period is in the region of 30 to 50 msecs as the disc
rotates about 200 to 500 times a minute.
[0070] For example, in the slide drive pulse in FIG. 5e, after a
normal level pulse is applied for about 36 msecs, the level
gradually comes down. Also, the high level pulse for when the
average value CT exceeds the threshold value TH.sub.2 is only
applied for the first 4 msecs.
[0071] Rather than setting the application of the drive pulse to a
prescribed period, the application of the drive pulse could also be
completed by detecting when the shifting of the objective lens
towards the inner side of the disc has been completed.
[0072] Hereinafter, description will be given in more detail of a
disc reproducing apparatus in accordance with an embodiment of the
present invention where eccentricity is measured using a sled error
signal, an average value CT is obtained, and the sled control in
FIG. 5e is carried out.
[0073] First, the construction of the essential parts of the disc
reproducing apparatus into which the disc eccentricity measuring
apparatus is installed so as to make up this embodiment will be
described with reference to FIGS. 6 and 7.
[0074] In FIG. 6, reference numeral 1 indicates an optical disc
such as, for example, a compact disc etc. which is rotatably driven
by a spindle motor 2. Information recorded on the optical disc 1 is
read by the optical head 3. At the optical head 3, an optical beam
outputted from, for example, a semiconductor laser is converged
from the objective lens onto the recording surface of the optical
disc 1 as a beam spot via an optical system made up from a
diffraction grating, beam splitter and a 1/4 wavelength plate. The
light reflected back is then inputted into a detector by the
optical system so that pit playback information is obtained.
[0075] As the objective lens controls the focus of the beam spot
converged on the recording surface of the optical disc and controls
the tracking, it is supported by an actuator capable of taking it
in a direction away from the optical disc 1 as well as in a
direction along the diameter of the disc.
[0076] Information as electrical signals corresponding to the
amount of light detected by the detector in the optical head 3 is
supplied to an RF amplifier 4 which undergoes processing such as
arithmetic operations and amplification etc. Reproduced signals
such as musical data etc. as well as tracking error signals TE and
focus error signals FE etc. are extracted from the RF amplifier
4.
[0077] After the reproduced signal outputted from the RF amplifier
4 has undergone error correction processing and demodulation
processing etc.in a signal processor 5 after it has been sent to
the signal processor 5, it is outputted as, for example, L and R
audio signals from the terminal 7 after having gone via the D/A
converter. Also, the number of rotations of the spindle motor 2 is,
for example, CLV (Constant Linear Velocity) controlled using a
pulse generated by the internal PLL taken from the reproduced
signal.
[0078] On the other side, the tracking error signal TE and the
focus error signal FE are provided to a servo controller 8. Then,
after processing such as phase compensation is carried out by the
servo controller 8, this is sent to an actuator driver 9 which
drives the actuator as tracking drive signals and focus drive
signals. The drive voltage outputted from the actuator driver 9 is
applied to the actuator in the optical head 3 and the shifting of
the objective lens is controlled in the tracking direction and the
focusing direction in such a manner that the respective error
signals become zero.
[0079] Further, at the servo controller 8, after the tracking error
signal TE has undergone phase compensation, it's low frequency
component is extracted by a low pass filter and this is taken as
the sled error signal.
[0080] As described in the following, the sled drive signal based
on the sled error signal is provided to the driver 10. The driver
10 applies a driving voltage to a slide motor 11 based on the drive
information. The rotational force of the slide motor 11 is
decelerated to a prescribed level using gear ratios, for example,
transmission is carried out via the rack gear 3a of the optical
head 3 and the whole of the optical head 3 is shifted across the
diameter of the optical disc 1.
[0081] Reference numeral 12 indicates a system controller formed
from a microcomputer, which outputs the operation control signals
for each part. For example, the system controller 12 performs
control such as the loop opening and closing of the servo system,
acceleration pulses, and deceleration pulses etc. for the servo
controller 8. Also, it also controls the taking of eccentricity
measurements and the generation of the drive pulses, which are to
be described later.
[0082] FIG. 7 is a further example of a structure for a reproducing
apparatus. Portions which are the same as portions in FIG. 6 are
given the same numerals and their descriptions are omitted. In this
case, the optical disc 1 is loaded on a turntable 13 and is rotated
as a result of the turntable 13 being rotated by the spindle motor
2. On the other hand, the optical head is fixed, the turntable 13
has, for example, a rack gear 13a set up on it and this then
interlocks with a gear which transmits the rotational force of the
slide motor 11. By then shifting the turntable 13 using the slide
motor 11, the relative positions of the optical head 3 and the
optical disc 1 can be displaced along the direction of the diameter
of the disc.
[0083] It is also possible to use a linear motor at the sled
mechanism in the structures in FIGS. 6 and 7.
[0084] The structures for the reproducing apparatus in FIGS. 6 and
7 are applied to the embodiment in this invention. However, the
system controller 12 and the servo controller 8 in FIGS. 6 or 7
also carry out the eccentricity measurement operation and the sled
operation in this invention. A block diagram of the of the
structure of the processes carried out by the internal hardware and
software and the process for the tracking error signal is therefore
provided in FIG. 8.
[0085] The system controller 12 actually consists of a
microcomputer made up of a CPU, ROM, RAM and interface. In FIG. 8,
a conceptual block diagram of the structure of the hardware which
carries out these operations using software is shown.
[0086] Reference numeral 8a in FIG. 8 indicates a phase
compensation circuit which carries out phase compensation on the
tracking error signal TE shown in FIG. 1c which is provided to the
servo controller 8 and outputs the tracking drive signal for the
actuator 9. The low frequency component of the output from the
phase compensation circuit 8a is extracted by the low pass filter
8b and a sled error signal is generated.
[0087] The sled error signal is made into digital data by passing
it through the A/D converter 8d and it is then inputted into the
system controller 12, so as to be taken in by the input register
31. The A/D converter may be set up internally within the system
controller 12 or may be set up as an external circuit.
[0088] At the system controller 12, there is a filter 32 for
carrying out filter operations on the inputted sled error data
which was sampled by the A/D converter, an extreme value detection
calculating section 33 which obtains the peak values (P.sub.S,
P.sub.2) and the trough values (P.sub.1) using the sled error data
obtained via the filter 32, a comparing memory 35 which serves as a
register for the extreme detection operation, a P.sub.1 memory 36
and P.sub.2 memory 37 for holding the detected peak value (P.sub.2)
and the trough value (P.sub.1) and an average value calculating
section 34 for calculating the average value CT from the detected
peak value (P.sub.2) and the trough value (P.sub.1).
[0089] Also, a threshold value TH.sub.1 generating section 38, a
threshold value TH.sub.2 generating section 39 and comparing
sections 40 and 41 are set up for comparing the average value CT
with the threshold values TH.sub.1 and TH.sub.2 and a slide control
processing section 42 is set up for carrying out slide drive
control in accordance with the comparison results for the comparing
sections 40 and 41.
[0090] The slide control processing section 42 outputs the slide
control signal to the drive pulse generator 8c in the servo
controller 8 in accordance with the comparison results from the
comparing sections 40 and 41 and in accordance with the sum of the
tracking gain timer 43, the sled drive timer 44 and the decrement
counter 45.
[0091] Eccentricity measurements and slide control operations
carried out using this kind of system controller 12 and servo
controller 8 are described in the flowcharts shown in FIGS. 9 to
11. These flowcharts show software based control operations which
use the aforementioned conceptual structure.
[0092] The flowcharts in FIGS. 9 to 11 show process routines which
are carried out, for example, every four msecs. The process at the
system controller 12 goes to step F101 every four msecs and
determines whether or not reproduction is currently taking place.
If the system controller determines in step F101 that reproduction
is not taking place, the following processes shown in FIGS. 9 to 11
are not carried out, and the process is completed. This routine
will then not take place for a further four msecs.
[0093] If the reproducing operation is taking place so that the
process routine is entered, step F102 is gone onto. During
reproducing, the sled error signal is sampled by the A/D converter
8d, converted to digital data, and inputted, as described above.
The system controller 12 therefore reads the sled error signal
value at a period which is a number of milliseconds, in this case,
4 msecs, because the frequency band for the sine wave-shaped
waveform which depends on the effects of the eccentricity is a low
frequency of a number of Hz.
[0094] As a result of this, a sampling period of, for example, 4
msecs is taken as the sampling period at, for example, the A/D
converter 8d and the sled error signal is converted to digital
data. It is then determined during reproduction that the sampling
timing is present in step F102, step F103 is gone onto and the
sampled digital data is taken into the input register 31.
[0095] Digital filter arithmetic (F104) is then carried out by the
filter 32 in order to remove the noise component from the sled
error data which has been read in.
[0096] Next, at the system controller 12, it is determined whether
or not the current drive pulse is being generated from the drive
pulse generator 8c so that the sled motor 11 is being driven
(F105). If the drive pulse is not being applied, the process
proceeds to step F106 for the arithmetic processing to determine
the extent of the eccentricity. If the drive pulse is being
applied, the process goes to [NEXT2] so as to go on to the process
shown in FIG. 11.
[0097] In the arithmetic process to determine the extent of the
eccentricity, first, it is determined whether the peak value Ps has
already been detected by confirming to see if the P.sub.S detection
flag is present (F106).
[0098] Detection of the peak value P.sub.S is something which is
only carried out once at initialization conditions. Initialization
conditions are when the disc is installed or when a track jump is
completed.
[0099] If the peak value P.sub.S is not detected under
initialization conditions, the process goes to step F107. It is
then determined if the sled error value inputted on this occasion
is smaller than the sled error value inputted on the previous
occasion. If the sled error value is larger than on the previous
occasion then the sled error waveform is going towards a peak value
and alternatively, if the sled error value is smaller than the
previous value it is going towards a trough value. It follows that
the time when it is first detected that the inputted slide error
value is smaller than the previous value is the time when the peak
value has been exceeded. This means that the value for the previous
time was a peak value.
[0100] Here, the comparison operation is carried out in step F107
at the extreme detection calculator 33. If the inputted sled error
value is larger than the sled error value for the previous time,
the data in the comparing memory 35 is rewritten with this inputted
value (F108) and the next sampling timing is waited for.
[0101] That is to say that the data in the comparing memory 35 is
compared with the sled error value inputted in step F107 and is
made to be the sled error value for the previous time.
[0102] When starting at a certain time, at the comparison process
in step F107 of the process routine in FIG. 9, the sled error value
for the current time will become smaller than the sled error value
for the previous time stored in the comparing memory 35. When this
happens, the process moves on to step F109, it is taken that the
initial peak value P.sub.S has been detected from initialization
conditions and the P.sub.S detection flag is set to "ON".
[0103] Next, the detecting P.sub.1 flag is set to "ON" so that the
process for detecting the trough value P.sub.1 can be gone to
(F110). Then, the sled error value for this time is re-written with
the current sled error value and stored in a comparing memory 35 so
that it can be used in the comparison process for detecting the
point P.sub.1, and the routine is completed.
[0104] Once the Ps detection flag has been set to "ON", the process
routine goes on to steps F106 to F112. Then, if it is detected in
step F112 that the detecting P.sub.1 flag is on, the process for
detecting the trough value P.sub.1 has been carried out, and the
detecting P.sub.1 flag is turned off, the process in FIG. 10 is
gone to, as is shown by [NEXT1] in the diagram, and the detecting
P.sub.2 flag is confirmed in step F119. If the detecting P.sub.2
flag is on, the process for detecting the peak value P.sub.2 is
carried out.
[0105] As described above, after the peak value P.sub.S has been
detected from the initialization conditions, the detecting P.sub.1
flag is set so that the process goes on to step F113 and the
extreme detection operator 33 compares the sled error value for
this time with the sled error value for the previous time stored in
the comparing memory 35. Then, if the sled error value for this
time is smaller than the sled error value for the previous time,
the current sled error signal is going towards a trough value. The
value in the comparing memory 35 is therefore renewed with the sled
error value for this time in step F118.
[0106] In step F113, if the sled error value for this time is
larger than that for the previous time then it has gone beyond the
trough value P.sub.1, that is to say that at this point in time the
sled error value stored in the comparing memory 35 is the trough
value P.sub.1.
[0107] Here, the detecting P.sub.1 flag is reset so that the
detection of the trough value P.sub.1 can be completed (F114) and
the detecting P.sub.2 flag is set (F115) so that the detection
process for the following peak value P.sub.2 can be carried out.
The sled error value for the previous time stored in the comparing
memory 35 at this point in time is then stored in the P.sub.1
memory 36 (F116) as the trough value P.sub.1 so as to fix the
trough value P.sub.1. At this time, it would also be possible to
take the current sled error value as the trough value P.sub.1 and
store it in the P.sub.1 memory 36.
[0108] The comparing memory 35 then has to be renewed with the sled
error value for this time (F117) so that this can be used in the
comparison process for detecting the peak values P.sub.1 from
hereinafter, and the process is completed.
[0109] In the process from the next time onwards, the process goes
to the step F119 in FIG. 8 which is shown by [NEXT1] because the
P.sub.S detection flag is on, the detecting P.sub.1 flag is reset
and the detecting P.sub.2 flag is confirmed. The detection process
for the peak value P.sub.2 is then executed because the detecting
P.sub.2 flag is on.
[0110] Here, if the detecting P.sub.2 flag is off, that is, if the
detecting P.sub.1 flag and the detecting P.sub.2 flag are both
reset, the process will come to an end. However, after the point
P.sub.S has been detected from the initialization conditions, the
trough values P.sub.1 and the peak values P.sub.2 are
intermittently and reciprocally detected, so that unsettled results
do not occur in step F119 under normal operating conditions.
[0111] In step F120 it is determined whether the sled error value
for this time is smaller than the sled error value stored in the
comparing memory 35 for the previous time.
[0112] If the sled error value for this time is larger than the
sled error value for the previous time, the current sled error
signal is in the middle of going towards a peak value. Therefore,
in step F125, the value in the comparing memory 35 is renewed with
the sled error value for this time and the process is
completed.
[0113] In step F120, if the sled error value for this time is
smaller than that for the previous time, then it has gone beyond
the peak value P.sub.2, that is to say that at this point in time
the sled error value stored in the comparing memory 35 is the peak
value P.sub.2.
[0114] The detecting P.sub.2 flag is reset so that the detection of
the peak value P.sub.2 is completed (F121) and the detecting
P.sub.1 flag is set (F122) so that the detection process for the
following trough value P.sub.1 can be shifted to. The sled error
value for the previous time stored in the comparing memory 35 at
this time is taken as the peak value P.sub.2 and stored in the
P.sub.2 memory 37 (F123) so that the peak value P.sub.2 becomes
fixed. Now, taking the value decided in the process in step F116
occurring in the previous process as the trough value P.sub.1, when
the current value for the sled error value at this time is taken as
the trough value P.sub.1 and stored in the P.sub.1 memory 36, the
sled error value for this time is also taken as the peak value
P.sub.1 in this step F123 and stored in the P.sub.2 memory 37.
[0115] Then, the comparing memory 35 is renewed (F124) with the
sled error value for this time so that this can be used in the
comparison process for detecting the peak value P.sub.1
hereinafter.
[0116] Here, as the trough value P.sub.1 and the peak value P.sub.2
have been detected, an average value CT is obtained at the average
value calculation section 34 from the trough value P.sub.1 stored
in the P.sub.1 memory 36 and the peak value P.sub.2 stored in the
P.sub.2 memory 37. A sled error value for which the eccentricity
component is canceled is therefore obtained (F126).
[0117] As this average value CT for the sled error value is the
average value for the extent of the offset of the entire optical
head and the objective lens, it is compared with the threshold
value TH.sub.1 at the comparing section 40. It is then determined
whether or not the relative shifting between the optical head and
the optical head is necessary to bring the operation of the
objective lens in to within the range for which the eccentricity
can be brought in by the tracking servo (F127).
[0118] If the average value CT does not exceed the threshold value
TH.sub.1, the sled operation is not necessary and the sled control
processing section 42 goes from this comparison result to the step
F128 so that the sled servo is turned off and the process is
complete.
[0119] By carrying out this process from step F101 every 4 msecs,
the trough value P.sub.1 and the peak value P.sub.2 can be detected
every period of the sled error signal. The average vale CT can then
be obtained after the peak value P.sub.2 has been detected.
However, as the sled servo is off and the relative shifting between
the optical head and the optical disc is not carried out, the
offset between the objective lens and the entire optical head
gradually increases. As a result of this, at some point in time it
will be detected that the average value CT will have exceeded the
threshold value TH.sub.1.
[0120] After doing this, the process goes onto step F129 where it
is determined by the comparing section 41 whether or not the
average value CT has exceeded the threshold value TH.sub.2 from the
comparison result.
[0121] If the average value CT has not exceeded the threshold value
TH.sub.2, a normal sled operation of the kind shown at the time
T.sub.1 in FIG. 5e is carried out.
[0122] Namely, in step F130, the sled control process section 42
sets a normal voltage level L.sub.1 as a drive pulse and sends this
information to the drive pulse generator 8c.
[0123] Then, the tracking gain is to be raised for a fixed period
of time so that the tracking does not go out during the relative
shifting between the optical head and the optical disc, so the
tracking gain timer is set (F132) in order to do this. The tracking
gain is then raised up to a prescribed level (F133). The conceptual
block diagram for this operational function is not shown in FIG. 8,
but the system controller 12 carries out the control of the
increasing of the tracking gain for the servo controller 8 in a
period which is dictated by the tracking gain timer 43.
[0124] Further, as the control is carried out for a drive pulse
application period of, for example, 36 msecs, after the drive timer
44 has been set (F134), the sled control processing section 42
commences the application of the prescribed voltage pulse (F135)
shown by the pulse applied at a point in time directly after the
time T.sub.1 in FIG. 5e to the sled motor 11 from the slide drive
pulse generator 8c via the driver 10.
[0125] The process then goes from step F105 to [NEXT2] and on to
step F136 in FIG. 11 after the application of this pulse voltage
has commenced.
[0126] Then, at a certain point in time it is determined whether
the tracking gain timer 43 has overflowed or not, and then after a
fixed period of time set at the tracking gain timer 43 has elapsed
since the start of the shifting, the tracking gain is returned to
normal conditions (F137).
[0127] In the process which follows the four milliseconds after the
relative shifting of the optical head and the optical disc has
started, the process moves on to step F139 in FIG. 11 and the drive
pulse is set to a normal voltage level L.sub.1. At this time during
the starting of the shift starting, when a normal voltage level
L.sub.1 has been set in step F130, the drive pulse according to
this step F139 is not changed.
[0128] Then, the drive timer 44 in step F140 is verified and it is
determined whether or not 36 msecs have passed. A normal level
drive pulse is then applied intermittently in the way as with the
pulse directly after the time T1 in FIG. 5e.
[0129] The process from FIG. 9 is carried out every 4 msecs. It is
therefore determined in the ninth process routine from the start of
the relative shifting between the optical head and the optical disc
in step F140 that 36 msecs has passed using the slide drive timer
44. The process then goes from step 141 to step 143, the decrement
counter 45 is set and the process to gradually lower the pulse
voltage is started.
[0130] Then, in the process from the next time, as the applied
voltage is being decreased, the step F139 is not gone through, the
process goes from step F138-F140-F141 and the voltage decrement
control is intermittently carried out in step F143 until the
decrement counter 45 overflows.
[0131] By overflowing the decrement counter 45, the sled servo is
turned off, and the outputting of the drive pulse is completed. In
this way, as shown in FIG. 5e, a drive pulse of a normal voltage
level L.sub.1 is outputted within the period from a time directly
after the time T.sub.1 until the next trough value P.sub.1 is
detected. Also, the pulse voltage is gradually lowered while the
sled is in halt.
[0132] The process for detecting the trough value P.sub.1 is
shifted to after the subsequent four milliseconds after this
completion.
[0133] It can be seen from FIGS. 4a and 4b that the relative
shifting between the optical head and the optical disc can be
carried out using drive pulses of this kind of normal voltage level
L.sub.1. but, depending on the circumstances, there are also cases
where the stationary coefficient of friction may be large or
correct sliding cannot be carried out. In this kind of case, as
shown in FIG. 5a, the offset between the objective lens and the
optical head will increase and the average value CT will become
higher.
[0134] If the sled operation remains incorrect, the average value
CT calculated after the detection of the peak value P.sub.2 at a
time T.sub.3 will exceed the threshold level TH.sub.2.
[0135] In this case, the process goes from the step F129 to F131 in
FIG. 10, and the voltage applied as the slide drive pulse is set to
be a high level L.sub.2. The relative shifting between the optical
disc and the optical head is then started using the L.sub.2 level
drive pulse via the process in steps F132 to F135.
[0136] This applied voltage L.sub.2 is made to be sufficient to
negate the stationary coefficient of friction of the sled mechanism
and provide an immediate sled operation response and should be, for
example, a level which is twice that of the normal level L.sub.1.
It follows that the relative shifting between the optical head and
the optical disc commences immediately after the time T.sub.3 as a
result of the application of the slide pulse.
[0137] The process at the time after the application of this kind
of high level pulse voltage has started goes on from step F105 to
step F136 in FIG. 11, and on to step F139. Here, the pulse voltage
level is set to a normal level L.sub.1. Therefore, the drive pulse
is made to be a high level pulse just for the first four
milliseconds, as shown by the pulse after the time T.sub.3 in FIG.
5e, and thereafter becomes a normal level composite pulse until 36
milliseconds have passed since the start of the sled operation.
[0138] After these 36 milliseconds have passed, the applied voltage
is gradually decreased to gear for the halting of the sled
operation in the aforementioned way.
[0139] By carrying out the above process intermittently, sled
control can be carried out using the drive pulse shown in FIG.
5e.
[0140] Detailed descriptions of the respective slide control
methods in FIGS. 4b and 4c or FIGS. 5b to 5d have been omitted but
these can be carried out with the modification of just one part of
the process in FIGS. 9 to 11.
[0141] Also, the average value CT was obtained from the trough
value P.sub.1 and the peak value P.sub.2, but, naturally, this
could also be obtained from the peak value P.sub.2 and the
following trough value P.sub.1.
[0142] The present invention is particularly applicable to
eccentricity measuring apparatus for disc recording medium playback
apparatus, recording apparatus and recording/playback apparatus but
can also be used for other processes where the measured degree of
eccentricity is for items other than slide drives, such as servo
band setting control which corresponds to degrees of
eccentricity.
* * * * *