U.S. patent application number 11/825004 was filed with the patent office on 2007-11-08 for optical disc apparatus.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Kenji Fujiune, Yuuichi Kuze, Katsuya Watanabe, Shin-ichi Yamada.
Application Number | 20070258337 11/825004 |
Document ID | / |
Family ID | 18972142 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070258337 |
Kind Code |
A1 |
Fujiune; Kenji ; et
al. |
November 8, 2007 |
Optical disc apparatus
Abstract
An optical disk apparatus having a high reliability by evading
collision between a condensing lens and an optical disk regardless
whether the focus control is in the operative state or in the
inoperative state, thereby preventing damage to the condensing lens
and the optical disk. When the focus control is in the inoperative
state, by using a reflection light amount from the optical disk
(1), it is ascertained that the focus of the light beam is in the
vicinity of the information surface and the condensing lens (15) is
driven to be apart from the optical disk (1).
Inventors: |
Fujiune; Kenji;
(Moriguchi-shi, JP) ; Kuze; Yuuichi; (Settsu-shi,
JP) ; Yamada; Shin-ichi; (Katano-shi, JP) ;
Watanabe; Katsuya; (Nara-shi, JP) |
Correspondence
Address: |
HAMRE, SCHUMANN, MUELLER & LARSON P.C.
P.O. BOX 2902-0902
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Kadoma-shi
JP
571-8501
|
Family ID: |
18972142 |
Appl. No.: |
11/825004 |
Filed: |
July 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10475473 |
Oct 20, 2003 |
7257053 |
|
|
PCT/JP02/03745 |
Apr 15, 2002 |
|
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11825004 |
Jul 3, 2007 |
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Current U.S.
Class: |
369/44.11 ;
G9B/7.044; G9B/7.094 |
Current CPC
Class: |
G11B 7/24082 20130101;
G11B 7/08511 20130101; G11B 7/0946 20130101 |
Class at
Publication: |
369/044.11 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2001 |
JP |
2001-122433 |
Claims
1-33. (canceled)
34. An optical disk apparatus, comprising: a converging means for
converging and irradiating a light beam from a light source toward
a rotating information carrier; a focus displacement signal
detection means for generating a signal in accordance with a
positional displacement of a focus of the light beam with respect
to an information surface of the information carrier; a focus
shifting means for shifting the converging means in a direction
normal to the information surface of the information carrier; a
focus control means for driving the focus shifting means in
accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and a search means for shifting the converging means such
that the light beam is irradiated onto a desired track on the
information carrier; wherein the search means sets the focus
control means to an inoperative state if the focus control means is
operative and if the number of tracks across which the focus of the
light beam is shifted is a predetermined number or greater.
35. An optical disk apparatus, comprising: a converging means for
converging and irradiating a light beam from a light source toward
a rotating information carrier; a focus displacement signal
detection means for generating a signal in accordance with a
positional displacement of a focus of the light beam with respect
to an information surface of the information carrier; a focus
shifting means for shifting the converging means in a direction
normal to the information surface of the information carrier; a
focus control means for driving the focus shifting means in
accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and a search means for shifting the converging means such
that the light beam is irradiated onto a desired track on the
information carrier; wherein the search means sets the focus
control means to an inoperative state if the focus control means is
operative and if the direction in which the focus of the light beam
is shifted across the tracks is a direction toward the outer
periphery of the information carrier.
36. An optical disk apparatus, comprising: a converging means for
converging and irradiating a light beam from a light source toward
a rotating information carrier; a focus displacement signal
detection means for generating a signal in accordance with a
positional displacement of a focus of the light beam with respect
to an information surface of the information carrier; a focus
shifting means for shifting the converging means in a direction
normal to the information surface of the information carrier; a
focus control means for driving the focus shifting means in
accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and a search means for shifting the converging means such
that the light beam is irradiated onto a desired track on the
information carrier; wherein the search means sets the focus
control means to an inoperative state if the focus control means is
operative and if a target track to which the focus of the light
beam is to be shifted transversely is within a range of a
predetermined distance from the outermost periphery of the
information carrier.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Division of application Ser. No.
10/475,473, filed Oct. 20, 2003, which is a U.S. National Stage
application based on International Application No. PCT/JP02/03745,
filed on Apr. 15, 2002 and as amended on Oct. 2, 2002, which
applications are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to optical disk apparatuses
that record information on a rotating disk-shaped information
carrier (referred to as "optical disk" in the following) or
reproduce information recorded on the optical disk by converging
and irradiating a light beam coming from a light source toward the
optical disk. More specifically, the present invention relates to
optical disk apparatuses that are provided with a mechanism for
avoiding collisions between the optical disk and a condensing lens
for condensing the light beam, when recording or reproducing
information.
BACKGROUND ART
[0003] Conventional optical disk apparatuses reproduce information
by irradiating a relatively weak light beam with a constant light
amount onto an optical disk serving as an information carrier, and
detecting the reflected light whose strength has been modulated by
the optical disk. Moreover, information is recorded by irradiating
a light beam whose light amount is modulated in accordance with the
information to be recorded onto a recording material film on the
optical disk (see for example JP S52-80802A).
[0004] In read-only optical disks, information is recorded in
advance in a spiral shape with pits. Moreover, optical disks that
can be recorded and reproduced are fabricated by forming a film
made of an optically recordable/reproducible material (recording
material film) by a method such as vapor deposition on a substrate
surface having tracks of a spiral-shaped land-and-groove structure.
In order to record information on the optical disk or to read
information that has been recorded on the optical disk, a focus
control is necessary that controls the focus of a light beam in a
direction normal to the surface of the optical disk (referred to as
"focus direction" in the following), such that the light beam is
always in a predetermined converged state on the recording material
film.
[0005] Referring to FIG. 14, the following is an explanation of the
control operation of a conventional optical disk apparatus. As
shown in FIG. 14, an optical head 110 includes a semiconductor
laser 111, a coupling lens 112, a polarization beam splitter 113, a
1/4 wavelength plate 114, a condensing lens 115 serving as a
converging means, a focus actuator (referred to as "Fc actuator" in
the following) 116 serving as a focus shifting means, a tracking
actuator (referred to as "Tk actuator" in the following) 117
serving as a track shifting means, a detection lens 118, a
cylindrical lens 119, and an optical detector 120.
[0006] The light beam that is emitted from the semiconductor laser
111 is converted into a parallel beam by the coupling lens 112.
After this parallel beam has passed through the polarization beam
splitter 113 and the 1/4 wavelength plate 114, it is focused onto
the information surface of the disk-shaped optical disk 101 by the
condensing lens 115. Then, after the light beam reflected from the
optical disk 101 has passed again through the condensing lens 115
and the 1/4 wavelength plate 114, it is reflected by the
polarization beam splitter 113. Then, after this reflected light
beam has passed through the detection lens 118 and the cylindrical
lens 119, it is irradiated onto the optical detector 120, which is
partitioned into four sections. The condensing lens 115 is
supported by an elastic member (not shown in the drawings), and is
shifted by electromagnetic force in the focus direction, by letting
an electrical current flow through the Fc actuator 116.
[0007] The optical detector 120 sends detected light amount signals
to a focus error generator (referred to as "FE generator" in the
following) 130 serving as a focus displacement signal detection
means. The FE generator 130 uses the light amount signals from the
optical detector 120 to calculate an error signal indicating the
convergent state of the light beam on the information surface of
the optical disk 101, that is, a focus error signal (referred to as
"FE signal" in the following) corresponding to the positional
displacement of the focus of the light beam with respect to the
information surface of the optical disk 101. Then, the FE generator
130 sends this FE signal via a focus control filter (referred to as
"Fc filter" in the following) 131, which performs a phase
compensation, a driving selector 132, and a focus driver (referred
to as "Fc driver" in the following) 137 to the Fc actuator 116, in
order to stabilize the control operation of the focus control. The
Fc actuator 116 drives the condensing lens 115 in the focus
direction, such that the light beam converges in a predetermined
state on the information surface of the optical disk 101.
[0008] A fixed driving signal generator 136 sends to the driving
selector 132 a driving signal with which the Fc actuator 116 is
mechanically put in its natural state, that is, a state in which no
force is applied to the Fc actuator 116. If there is a positional
displacement of the focus of the light beam with respect to the
information surface of the optical disk 101, and this positional
displacement needs to be corrected for the recording or reproducing
of information, then the driving selector 132 sends the signal from
the Fc filter 131 to the Fc driver 137. Based on the signal from
the driving selector 132, the Fc driver 137 drives the Fc actuator
116. Then, the Fc actuator 116 drives the condensing lens 115 in a
focus direction, such that the light beam converges on the
information surface of the optical disk 101. In this state, it is
said that "the focus control is in an operative state." If it is
not necessary to correct positional displacements of the focus of
the light beam with respect to the information surface of the
optical disk 101, then the driving selector 132 sends the signal
from the fixed driving signal generator 136 to the Fc driver 137.
In this state, it is said that "the focus control is in a
inoperative state." Based on the signal from the driving selector
132, the Fc driver 137 drives the Fc actuator 116. If the focus
control is in the inoperative state, the Fc actuator 116 assumes
its natural state.
[0009] The light amount signal from the optical detector 120 is
also sent to the reflected light amount detector 161. Based on the
light amount signal from the optical detector 120, the reflected
light amount detector 161 detects a signal corresponding to the
light amount reflected from the optical disk 101, and sends it to a
focus anomaly detector (referred to as "Fc anomaly detector" in the
following) 181. If the time for which the signal from the reflected
light amount detector 161 is below a predetermined level continues
for at least an anomaly detection time TW, then the internal status
of the Fc anomaly detector 181 is set to a state indicating that
the focus control has been lost. That is to say, the Fc anomaly
detector 181 judges that a positional displacement of the focus of
the light beam with respect to the information surface of the
optical disk 101 has occurred.
[0010] As the density of optical disks increases, the optical disk
and the condensing lens become closer when positioning the focus of
the light beam on the information surface of the optical disk, and
the risk of collisions between the optical disk and the condensing
lens increases. The following two points are examples of the
problems that may occur in this case:
(1) If the focus control is in the inoperative state, that is, if
the optical disk apparatus is transported or moved, the condensing
lens and the optical disk may collide easily.
[0011] (2) With the focus anomaly detection using the reflected
light amount, the detection speed is slow, and the condensing lens
and the optical disk may collide easily. In particular, if the
optical head is moved to search the desired track with the focus of
the light beam, or if external vibrations or shocks act on the
optical disk apparatus, the focus control may be lost, and the
condensing lens and the optical disk may collide.
DISCLOSURE OF THE INVENTION
[0012] To solve the problems of the related art, it is an object of
the present invention to provide a highly reliable optical disk
apparatus, with which collisions between the condensing lens and
the optical disk can be avoided and scratches on the condensing
lens or the optical disk can be prevented, regardless of whether
the focus control is in the operative state or in the inoperative
state.
[0013] In order to attain this object, a first configuration of an
optical disk apparatus according to the present invention
comprises:
[0014] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0015] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0016] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0017] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier;
[0018] an information surface detection means for detecting whether
the focus of the light beam is near the information surface of the
information carrier, if the focus control means is in a inoperative
state; and
[0019] a collision evasion means for generating a driving signal
for the focus shifting means such that the converging means is
displaced in a direction away from the information carrier if a
signal is generated by the information surface detection means.
[0020] With this first configuration of the optical disk apparatus,
if the focus control means is in the inoperative state, the
information carrier and the converging means do not become closer
than in the state in which the focus of the light beam is
positioned at the information surface of the information carrier,
so that collisions between the information carrier and the
converging means are avoided and scratches on the information
carrier and the converging means can be prevented, and an optical
disk apparatus with high reliability can be realized.
[0021] A second configuration of an optical disk apparatus
according to the present invention comprises:
[0022] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0023] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0024] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0025] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier;
[0026] a vibration detection means for detecting a vibration of the
apparatus; and
[0027] a collision evasion means for generating a driving signal
for the focus shifting means such that the converging means is
displaced in a direction away from the information carrier if a
signal of at least a predetermined value is generated by the
vibration detection means.
[0028] With this second configuration of the optical disk
apparatus, in a state in which the possibility of collisions
between the information carrier and the converging means due to
vibrations of the apparatus is high, collisions between the
information carrier and the converging means are avoided and
scratches on the information carrier and the converging means can
be prevented, and an optical disk apparatus with high reliability
can be realized.
[0029] In the first or second configuration of the optical disk
apparatus of the present invention, it is preferable that the
driving signal generated by the collision evasion means is a
two-value signal of a signal of a reference level and a signal of a
constant level that is such that the converging means is displaced
in the direction away from the information carrier. With this
preferable example, collisions between the information carrier and
the converging means can be avoided with a simple structure.
[0030] In the first or second configuration of the optical disk
apparatus of the present invention, it is preferable that the
driving signal generated by the collision evasion means is a pulse
signal having a predetermined peak value such that the converging
means is displaced in a direction away from the information
carrier. With this preferable example, the time for which the
driving signal of the collision evasion means is generated is
short, so that collisions between the information carrier and the
converging means can be avoided with low power consumption.
[0031] In the first or second configuration of the optical disk
apparatus of the present invention, it is preferable that the
driving signal generated by the collision evasion means is a ramp
signal having a constant slope. With this preferable example, the
driving signal generated by the collision evasion means becomes a
continuous signal, so that collisions between the information
carrier and the converging means can be avoided in a state in which
the load on the converging means and the focus shifting means is
reduced.
[0032] In the first or second configuration of the optical disk
apparatus of the present invention, it is preferable that the
driving signal generated by the collision evasion means if no
signal is generated by the information surface detection means or
the vibration detection means is a signal such that the converging
means is displaced with a predetermined slope in a direction
approaching the information carrier. With this preferable example,
when the information carrier and the converging means are
sufficiently spaced apart, the driving signal generated by the
collision evasion means becomes small, so that collisions between
the information carrier and the converging means can be avoided
with low power consumption.
[0033] In these cases, it is preferable that the driving signal
generated by the collision evasion means is saturated at an output
of a preset predetermined value. With this preferable example,
collisions between the information carrier and the converging means
can be avoided while preventing the converging means or the focus
shifting means being damaged due to the application of a large
driving signal by the collision evasion means.
[0034] A third configuration of an optical disk apparatus according
to the present invention comprises:
[0035] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0036] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0037] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0038] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and
[0039] a collision evasion means for constantly generating a
driving signal for the focus shifting means such that the
converging means is displaced in a direction away from the
information carrier if the focus control means is in an inoperative
state.
[0040] With this third configuration of the optical disk apparatus,
if the focus control means is in the inoperative state, the
positional relation between the information carrier and the
converging means is always in a state in which no collisions occur,
so that scratches on the information carrier or the converging
means can be prevented, and an optical disk apparatus with high
reliability can be realized.
[0041] A fourth configuration of an optical disk apparatus
according to the present invention comprises:
[0042] a converging means for converging and irradiating a light
beam from a light source toward an information carrier having a
spiral-shaped track that has a tiny fluctuation in radial direction
at a predetermined period;
[0043] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0044] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0045] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier;
[0046] a fluctuation amplitude detection means for detecting an
amplitude of the fluctuation of the track; and
[0047] an anomaly detection means for judging, from an amplitude
change over a predetermined time of a signal from the fluctuation
amplitude detection means, whether the operation of the focus
control means is anomalous, and generating a driving signal for the
focus shifting means such that the converging means is displaced in
a direction away from the information carrier.
[0048] With this fourth configuration of an optical disk apparatus,
even for recording media that cannot employ a method of detecting
whether the operation of the focus control means is anomalous from
the amplitude of the reproduction signal obtained when reproducing
information recorded on the information carrier, it can be detected
swiftly whether the operation of the focus control means is
anomalous, collisions between the information carrier and the
converging means can be avoided, and scratches on the information
carrier or the converging means can be prevented.
[0049] In the fourth configuration of the optical disk apparatus of
the present invention, it is preferable that the fluctuation
amplitude detection means is provided with a fluctuation detection
sensitivity switching means for switching a detection sensitivity
with which the amplitude of the fluctuation of the track is
detected, depending on whether information is being recorded or
information is being reproduced. With this preferable example, even
when the output of the light beam changes and the light amount
reflected from the information carrier changes depending on whether
information is being recorded or information is being reproduced,
the detection sensitivity of the fluctuation amplitude detection
means can be switched depending on whether information is recorded
or information is reproduced, thus canceling changes in the
reflected light amount, so that erroneous detections with the
anomaly detection means can be prevented.
[0050] In the fourth configuration of the optical disk apparatus of
the present invention, it is preferable that the anomaly detection
means is provided with an anomaly level switching means for
switching a signal change level of the fluctuation amplitude
detection means at which anomaly is judged, depending on whether
information is being recorded or information is being reproduced.
With this preferable example, even when the output of the light
beam changes and the light amount reflected from the information
carrier changes depending on whether information is being recorded
or information is being reproduced, and the signal from the
fluctuation amplitude detection means changes, the signal change
level of the fluctuation amplitude detection means at which anomaly
is judged can be switched depending on whether information is being
recorded or information is being reproduced, thus canceling changes
in the signal from the fluctuation amplitude detection means, so
that erroneous detections with the anomaly detection means can be
prevented.
[0051] It is preferable that the fourth configuration of the
optical disk apparatus of the present invention further comprises a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state, and a fluctuation detection sensitivity switching
means for switching a detection sensitivity of the fluctuation
amplitude detection means in accordance with a detection result of
the recorded region detection means. With this preferable example,
even when the light amount reflected from the information carrier
changes depending on whether the region on which the light beam is
irradiated is in a recorded or an unrecorded state, the detection
sensitivity of the fluctuation amplitude detection means can be
switched depending on whether the region on which the light beam is
irradiated is in a recorded or an unrecorded state, thus canceling
changes in the reflected light amount, so that erroneous detections
with the anomaly detection means can be prevented.
[0052] It is preferable that the fourth configuration of the
optical disk apparatus of the present invention further comprises a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state, and an anomalous level switching means for
switching a signal change level of the fluctuation amplitude
detection means at which anomaly is judged in accordance with a
detection result of the recorded region detection means. With this
preferable example, even when the light amount reflected from the
information carrier changes depending on whether the region on
which the light beam is irradiated is in a recorded or an
unrecorded state, and the signal from the fluctuation amplitude
detection means changes, the signal change level of the fluctuation
amplitude detection means at which anomaly is judged can be
switched depending on whether the region on which the light beam is
irradiated is in a recorded or an unrecorded state, thus canceling
changes in the signal from the fluctuation amplitude detection
means, so that erroneous detections with the anomaly detection
means can be prevented.
[0053] It is preferable that the fourth configuration of the
optical disk apparatus of the present invention further comprises a
track displacement signal detection means that generates a signal
in accordance with a positional displacement of the focus of the
light beam with respect to the track of the information carrier; a
track shifting means for shifting the converging means in a
direction traverse to the track of the information carrier; and a
tracking control means for driving the track shifting means in
accordance with the signal from the track displacement signal
detection means and performing a control such that the focus of the
light beam follows the track of the information carrier; wherein
the anomaly detection means operates only when the tracking control
means is in an operative state. With this preferable example, if
the tracking control means is in the inoperative state, erroneous
detection with the anomaly detection means due to disturbance of
the signal from the fluctuation amplitude detection means or the
signal from the focus displacement signal detection means can be
prevented.
[0054] It is preferable that the fourth configuration of the
optical disk apparatus of the present invention further comprises a
track displacement signal detection means that generates a signal
in accordance with a positional displacement of a focus of the
light beam with respect to the track of the information carrier; a
track shifting means for shifting the converging means in a
direction traverse to the track of the information carrier; and a
tracking control means for driving the track shifting means in
accordance with the signal from the track displacement signal
detection means and performing a control such that the focus of the
light beam follows the track of the information carrier; wherein
the anomaly detection means switches the detection time or the
amplitude change level of the signal amplitude change of the
fluctuation amplitude detection means at which it is judged that
the operation of the focus control means is anomalous, depending on
whether the tracking control means is in an operative state or an
inoperative state. With this preferable example, if the tracking
control means is in the inoperative state, erroneous detection with
the anomaly detection means due to disturbance of the signal from
the fluctuation amplitude detection means or the signal from the
focus displacement signal detection means can be prevented.
[0055] A fifth configuration of an optical disk apparatus according
to the present invention comprises:
[0056] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0057] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0058] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0059] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and
[0060] an anomaly detection means for judging that the operation of
the focus control means is anomalous when a change in the signal
from the focus displacement signal detection means over a
predetermined time is within a predetermined range, and generating
a driving signal for the focus shifting means that is such that the
converging means is displaced in a direction away from the
information carrier.
[0061] With this fifth configuration of an optical disk apparatus,
even for recording media that cannot employ a method of detecting
whether the operation of the focus control means is anomalous from
the amplitude of the reproduction signal obtained when reproducing
information recorded on the information carrier, it can be detected
swiftly whether the operation of the focus control means is
anomalous, collisions between the information carrier and the
converging means can be avoided, and scratches on the information
carrier or the converging means can be prevented.
[0062] It is preferable that the fifth configuration of the optical
disk apparatus of the present invention further comprises a
multiplication means for multiplying the signal from the focus
displacement signal detection means with a predetermined value; and
a gain switching means for switching a multiplication factor of the
multiplication means, depending on whether information is being
recorded or information is being reproduced. With this preferable
example, even if the output of the light beam changes and the
amount of light reflected from the information carrier changes
depending on whether information is being recorded or information
is being reproduced, the multiplication factor of the
multiplication means can be changed depending on whether
information is being recorded or information is being reproduced,
thus canceling changes in the amount of reflected light, so that
erroneous detection with the anomaly detection means can be
prevented.
[0063] In the fifth configuration of the optical disk apparatus of
the present invention, it is preferable that the anomaly detection
means further comprises a judgment level switching means for
switching, depending on whether information is being recorded or
information is being reproduced, a signal level at which the signal
of the focus displacement signal detection means that is compared
with that signal level is judged to be anomalous. With this
preferable example, even if the output of the light beam changes,
the amount of light reflected from the information carrier changes,
and the signal from the focus displacement signal detection means
changes depending on whether information is being recorded or
information is being reproduced, the signal level of the judgment
level switching means can be switched depending on whether
information is being recorded or information is being reproduced,
thus canceling changes in the signal from the focus displacement
signal detection means, so that erroneous detection with the
anomaly detection means can be prevented.
[0064] It is preferable that the fifth configuration of the optical
disk apparatus of the present invention further comprises a
multiplication means for multiplying the signal from the focus
displacement signal detection means with a predetermined value; a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state; and a gain switching means for switching a
multiplication factor of the multiplication means, in accordance
with a detection result of the recorded region detection means.
With this preferable example, even if the amount of light reflected
from the information carrier changes depending on whether the
region onto which the light beam is irradiated is in a recorded or
an unrecorded state, the multiplication factor of the
multiplication means can be switched depending on whether the
region onto which the light beam is irradiated is in a recorded or
an unrecorded state, thus canceling changes in the amount of
reflected light, so that erroneous detection with the anomaly
detection means can be prevented.
[0065] It is preferable that the fifth configuration of the optical
disk apparatus of the present invention further comprises a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state; and a judgment level switching means for
switching, in accordance with a detection result of the recorded
region detection means, a signal level at which the signal of the
focus displacement signal detection means that is compared with
that signal level is judged to be anomalous. With this preferable
example, even if the amount of light reflected from the information
carrier changes and the signal from the focus displacement signal
detection means changes depending on whether the region onto which
the light beam is irradiated is in a recorded or an unrecorded
state, the signal level of the judgment level switching means can
be switched depending on whether the region onto which the light
beam is irradiated is in a recorded or an unrecorded state, thus
canceling changes in the signal from the focus displacement signal
detection means, so that erroneous detection with the anomaly
detection means can be prevented.
[0066] It is preferable that the fifth configuration of the optical
disk apparatus of the present invention further comprises a track
displacement signal detection means that generates a signal in
accordance with a positional displacement of a focus of the light
beam with respect to the track of the information carrier; a track
shifting means for shifting the converging means in a direction
traverse to the track of the information carrier; and a tracking
control means for driving the track shifting means in accordance
with the signal from the track displacement signal detection means
and performing a control such that the focus of the light beam
follows the track of the information carrier; wherein the anomaly
detection means operates only when the tracking control means is in
an operative state.
[0067] A sixth configuration of an optical disk apparatus according
to the present invention comprises:
[0068] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0069] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0070] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0071] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier;
[0072] a focus integration means for integrating the signal from
the focus displacement signal detection means when a change of the
signal from the focus displacement signal detection means is within
a predetermined range;
[0073] a clearing means for clearing an integration value of the
focus integration means when the change of the signal from the
focus displacement signal detection means exceeds the predetermined
range; and
[0074] an anomaly detection means for judging that the operation of
the focus control means is anomalous when the absolute value of the
integration value of the focus integration means is at least a
predetermined value, and
[0075] generating a driving signal for the focus shifting means
that is such that the converging means is displaced in a direction
away from the information carrier.
[0076] With this sixth configuration of an optical disk apparatus,
even for recording media that cannot employ a method of detecting
whether the operation of the focus control means is anomalous from
the amplitude of the reproduction signal obtained when reproducing
information recorded on the information carrier, it can be detected
swiftly whether the operation of the focus control means is
anomalous, collisions between the information carrier and the
converging means can be avoided, and scratches on the information
carrier or the converging means can be prevented.
[0077] In the sixth configuration of the optical disk apparatus of
the present invention, it is preferable that the focus integration
means comprises a multiplication means for multiplying the signal
from the focus displacement signal detection means with at least
two kinds of multiplication factors, corresponding to the case that
information is being recorded and the case that information is
being reproduced, and wherein the result of the multiplication with
the multiplication means is integrated. With this preferable
example, even if the output of the light beam changes and the
amount of light reflected from the information carrier changes
depending on whether information is being recorded or information
is being reproduced, the multiplication factor multiplied with the
signal from the focus displacement signal detection means can be
switched depending on whether information is being recorded or
information is being reproduced, thus canceling changes in the
amount of reflected light, so that erroneous detection with the
anomaly detection means can be prevented.
[0078] In the sixth configuration of the optical disk apparatus of
the present invention, it is preferable that the clearing means
switches the range over which the change of the signal from the
focus displacement signal detection means is detected and compared,
depending on whether information is being recorded or information
is being reproduced. With this preferable example, even if the
output of the light beam changes, the amount of light reflected
from the information carrier changes and the signal from the focus
displacement signal detection means changes depending on whether
information is being recorded or information is being reproduced,
the range over which the change of the signal from the focus
displacement signal detection means is detected and compared can be
switched, thus canceling changes in the signal from the focus
displacement signal detection means, so that erroneous detection
with the anomaly detection means can be prevented.
[0079] It is preferable that the sixth configuration of the optical
disk apparatus of the present invention further comprises a
multiplication means for multiplying the signal from the focus
displacement signal detection means with a predetermined value; a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state; and a gain switching means for switching a
multiplication factor of the multiplication means, in accordance
with a detection result of the recorded region detection means.
With this preferable example, even if the amount of light reflected
from the information carrier changes depending on whether the
region onto which the light beam is irradiated is in a recorded or
an unrecorded state, the multiplication factor of the
multiplication means can be switched depending on whether the
region onto which the light beam is irradiated is in a recorded or
an unrecorded state, thus canceling changes in the reflected light
amount, so that erroneous detection with the anomaly detection
means can be prevented.
[0080] It is preferable that the sixth configuration of the optical
disk apparatus of the present invention further comprises a
recorded region detection means for detecting whether a region onto
which the light beam is irradiated is in a recorded or an
unrecorded state; wherein the clearing means switches the range
over which the change of the signal from the focus displacement
signal detection means is detected and compared, depending on a
detection result of the recorded region detection means. With this
preferable example, even if the amount of light reflected from the
information carrier changes and the signal from the focus
displacement signal detection means changes depending on whether
the region onto which the light beam is irradiated is in a recorded
or an unrecorded state, the range over which the change of the
signal from the focus displacement signal detection means is
detected and compared can be switched depending on whether the
region onto which the light beam is irradiated is in a recorded or
an unrecorded state, thus canceling changes in the signal from the
focus displacement signal detection means, so that erroneous
detection with the anomaly detection means can be prevented.
[0081] A seventh configuration of an optical disk apparatus
according to the present invention comprises:
[0082] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0083] an optical detection means for partitioning and receiving
the light beam reflected by the information carrier;
[0084] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier, by calculating a differential of partitioned
regions of the optical detection means;
[0085] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0086] an offset application means for applying an offset to the
signal from the focus displacement signal detection means;
[0087] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means and the offset application means, and performing a
control such that the focus of the light beam follows the
information surface of the information carrier; and
[0088] a vibration detection means for detecting a vibration of the
apparatus;
[0089] wherein, based on the signals from the vibration detection
means, the offset application means applies such an offset that the
converging means is displaced in a direction away from the
information carrier.
[0090] With this seventh configuration of the optical disk
apparatus, if the focus control means assumes an anomalous state,
and vibrations act on the apparatus during the time until the
anomalous state is detected, the focus control means generates a
driving signal that is such that the converging means is displaced
in a direction away from the information carrier, so that
collisions between the information carrier and the converging means
can be avoided, scratches on the information carrier or the
converging means can be prevented, and an optical disk apparatus
with high reliability can be realized.
[0091] In the seventh configuration of the optical disk apparatus
of the present invention, it is preferable that the offset
application means makes the applied offset amount larger, the
larger the signal from the vibration detection means is. With this
preferable example, the focus control means generates a driving
signal that is such that the converging means is displaced further
away from the information carrier, the larger the vibration acting
on the apparatus is, so that collisions between the information
carrier and the converging means can be avoided reliably.
[0092] In the seventh configuration of the optical disk apparatus
of the present invention, it is preferable that the focus
displacement signal detection means is provided with a balance
multiplication means that applies individual gains to the signals
before the differential calculation, and wherein the balance
multiplication means switches the gains such that an operating
point of the focus control means does not change, in accordance
with the offset applied by the offset application means. With this
preferable example, the focus control means generates a driving
signal that is such that the converging means is displaced further
away from the information carrier, without changing the operating
point, so that collisions between the information carrier and the
converging means can be avoided reliably.
[0093] In the seventh configuration of the optical disk apparatus
of the present invention, it is preferable that the offset applied
by the offset application means is saturated at a predetermined
level. With this preferable example, collisions between the
information carrier and the converging means can be avoided while
preventing damage to the converging means or the focus shifting
means due to the application of a large driving signal.
[0094] An eighth configuration of an optical disk apparatus
according to the present invention comprises:
[0095] a converging means for converging and irradiating a light
beam from a light source toward a rotating information carrier;
[0096] a focus displacement signal detection means for generating a
signal in accordance with a positional displacement of a focus of
the light beam with respect to an information surface of the
information carrier;
[0097] a focus shifting means for shifting the converging means in
a direction normal to the information surface of the information
carrier;
[0098] a focus control means for driving the focus shifting means
in accordance with the signal from the focus displacement signal
detection means, and performing a control such that the focus of
the light beam follows the information surface of the information
carrier; and
[0099] a search means for shifting the converging means such that
the light beam is irradiated onto a desired track on the
information carrier;
[0100] wherein the search means sets the focus control means to an
inoperative state when the focus control means is operative.
[0101] With this eighth configuration of the optical disk
apparatus, if the search means is in a state in which the
possibility of collisions between the information carrier and the
converging means due to vibrations during the search operation is
high, then collisions between the information carrier and the
converging means can be avoided, scratches on the information
carrier or the converging means can be prevented, and an optical
disk apparatus with high reliability can be realized.
[0102] In the eighth configuration of the optical disk apparatus of
the present invention, it is preferable that the search means sets
the focus control means to an inoperative state if the number of
tracks across which the focus of the light beam is shifted is a
predetermined number or greater. With this preferable example, if
the search means is in a state in which the possibility of
collisions between the information carrier and the converging means
due to large vibrations occurring during a long search operation is
high, then collisions between the information carrier and the
converging means can be avoided.
[0103] In the eighth configuration of the optical disk apparatus of
the present invention, it is preferable that the search means sets
the focus control means to an inoperative state if the direction in
which the focus of the light beam is shifted across the tracks is a
direction toward the outer periphery of the information carrier.
With this preferable example, if it is in a state in which there is
a high possibility of collisions between the information carrier
and the converging means due to large vibrations occurring during a
search operation in the direction toward the outer periphery of an
information carrier with a high possibility of collisions between
the information carrier and the converging means due to the
influence of surface fluctuations of the information carrier or the
like, then collisions between the information carrier and the
converging means can be avoided.
[0104] In the eighth configuration of the optical disk apparatus of
the present invention, it is preferable that the search means sets
the focus control means to an inoperative state if a target track
to which the focus of the light beam is to be shifted transversely
is within a range of a predetermined distance from the outermost
periphery of the information carrier. Also with this preferable
example, if it is in a state in which there is a high possibility
of collisions between the information carrier and the converging
means due to large vibrations occurring during a search operation
in the direction toward the outer periphery of an information
carrier with a high possibility of collisions between the
information carrier and the converging means due to the influence
of surface fluctuations of the information carrier or the like,
then collisions between the information carrier and the converging
means can be avoided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0105] FIG. 1 is a block diagram showing an optical disk apparatus
according to a first embodiment of the present invention.
[0106] FIG. 2A shows the signal that is output from the reflected
light amount detector in the first embodiment of the present
invention, FIG. 2B shows the signal that is output from the
information surface detector in the first embodiment of the present
invention, FIG. 2C shows the signal that is output from the evasion
driving signal generator in the first embodiment of the present
invention, FIG. 2D shows the signal that is output from the driving
limiter in the first embodiment of the present invention, and FIG.
2E shows the positional relation between the optical disk and the
condensing lens in the first embodiment of the present
invention.
[0107] FIG. 3 is a block diagram showing an optical disk apparatus
according to a second embodiment of the present invention.
[0108] FIG. 4A is a magnified view showing an optical disk for the
case that there is no wobble in the second embodiment of the
present invention, and FIG. 4B is a magnified view showing an
optical disk for the case that there is wobble in the second
embodiment of the present invention.
[0109] FIG. 5A shows the signal that is output from the wobble
amplitude detector in the second embodiment of the present
invention, FIG. 5B shows the signal that is output from the
recording operation indicator in the second embodiment of the
present invention, FIG. 5C shows the signal that is output from the
recording region detector in the second embodiment of the present
invention, FIG. 5D shows the signal that is output from the
variable multiplier in the second embodiment of the present
invention, and FIG. 5E shows the internal status of the Fc anomaly
detector in the second embodiment of the present invention.
[0110] FIG. 6 is a block diagram showing an optical disk apparatus
in accordance with a third embodiment of the present invention.
[0111] FIG. 7 shows the signal of the FE generator for the case
that the focus of the light beam has passed in the focus direction
through the information surface of the optical disk in the third
embodiment of the present invention.
[0112] FIG. 8A shows the signal that is output from the FE
generator in the third embodiment of the present invention, FIG. 8B
shows the signal that is output from the recording operation
indicator in the third embodiment of the present invention, FIG. 8C
shows the signal that is output from the recording region detector
in the third embodiment of the present invention, and FIG. 8D shows
the signal that is output from the variable multiplier in the third
embodiment of the present invention.
[0113] FIG. 9A shows the signal that is output from the variable
multiplier in the third embodiment of the present invention, FIG.
9B shows the reference level of the level change detector in the
third embodiment of the present invention, FIG. 9C shows the
counter value of the level change detector in the third embodiment
of the present invention, FIG. 9D shows the signal that is output
from the multiplier in the third embodiment of the present
invention, and FIG. 9E shows the internal status of the Fc anomaly
detector in the third embodiment of the present invention.
[0114] FIG. 10 is a block diagram showing an optical disk apparatus
in accordance with a fourth embodiment of the present
invention.
[0115] FIG. 11 is a graph of the input/output characteristics of
the offset generator in the fourth embodiment of the present
invention.
[0116] FIG. 12A shows the signal that is output from the adder when
there is no vibration in the fourth embodiment of the present
invention, FIG. 12B shows the signal that is output from the adder
when vibration is detected and when there is no output from the
balance signal generator in the fourth embodiment of the present
invention, and FIG. 12C shows the signal that is output from the
adder when vibration is detected and when there is an output from
the balance signal generator in the fourth embodiment of the
present invention.
[0117] FIG. 13 is a block diagram showing an optical disk apparatus
in accordance with a fifth embodiment of the present invention.
[0118] FIG. 14 is a block diagram showing a conventional optical
disk apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
[0119] The following is a more detailed description of the present
invention, with reference to embodiments.
First Embodiment
[0120] FIG. 1 is a block diagram showing an optical disk apparatus
according to a first embodiment of the present invention.
[0121] As shown in FIG. 1, an optical head 10 includes a
semiconductor laser 11 serving as a light source, a coupling lens
12, a polarization beam splitter 13, a 1/4 wavelength plate 14, a
condensing lens 15 serving as a converging means that converges and
irradiates a light beam coming from the light source toward a
rotating disk-shaped optical disk 1 serving as a information
carrier, a focus actuator (referred to as "Fc actuator" in the
following) 16 serving as a focus shifting means for shifting the
condensing lens 15 in a direction normal to the information surface
of the optical disk 1, a tracking actuator (referred to as "Tk
actuator" in the following) 17 serving as a track shifting means
for shifting the condensing lens 15 in a direction transverse to
the tracks on the optical disk 1, a detection lens 18, a
cylindrical lens 19, and an optical detector 20.
[0122] The light beam emitted from the semiconductor laser 11 is
converted into a parallel beam by the coupling lens 12. After this
parallel beam has passed through the polarization beam splitter 13
and the 1/4 wavelength plate 14, it is focused onto the information
surface of the optical disk 1 by the condensing lens 15.
[0123] After the light beam reflected from the optical disk 1 has
passed again through the condensing lens 15 and the 1/4 wavelength
plate 14, it is reflected by the polarization beam splitter 13.
Then, after this reflected light beam has passed through the
detection lens 18 and the cylindrical lens 19, it is irradiated
onto the optical detector 20, which is partitioned into four
sections. The condensing lens 15 is supported by an elastic member
(not shown in the drawings), and is shifted by electromagnetic
force in the focus direction, by letting an electrical current flow
through the Fc actuator 16.
[0124] The optical detector 20 sends the detected light amount
signals to a focus error generator (referred to as "FE generator"
in the following) 30 serving as a focus displacement signal
detection means for generating a signal corresponding to the
positional displacement of the focus of the light beam with respect
to the information surface of the optical disk 1. The FE generator
30 uses the light amount signals from the optical detector 20 to
calculate an error signal indicating the convergent state of the
light beam on the information surface of the optical disk 1, that
is, a focus error signal (referred to as "FE signal" in the
following) corresponding to the positional displacement of the
focus of the light beam with respect to the information surface of
the optical disk 1. Then, the FE generator 30 sends this FE signal
via a focus control filter (referred to as "Fc filter" in the
following) 31, which performs a phase compensation, a driving
selector 32, and a focus driver (referred to as "Fc driver" in the
following) 37 to the Fc actuator 16, in order to stabilize the
control operation of the focus control. The Fc actuator 16 drives
the condensing lens 15 in the focus direction, such that the light
beam converges in a predetermined state on the information surface
of the optical disk 1.
[0125] A reflected light amount detector 61 and an information
surface detector 62 constitute an information surface detection
means for detecting whether the focus of the light beam is near the
information surface of the optical disk 1. The light amount signal
of the optical detector 20 is sent to the reflected light amount
detector 61. Based on the light amount signal from the optical
detector 20, the reflected light amount detector 61 detects a
signal corresponding to the light amount reflected from the optical
disk 1 (reflected light amount signal), and, sends it to the
information surface detector 62. The information surface detector
62 can be configured with a comparator or the like. If the
reflected light amount signal from the reflected light amount
detector 61 is greater than a comparison level A, then the
information surface detector 62 sends a high-level signal, and if
it is lower than the comparison level A, then the information
surface detector 62 sends a low-level signal to an evasion driving
signal generator 63 serving as a collision evasion means.
[0126] A driving limiter 64 sends to the evasion driving signal
generator 63 a signal for restricting the signal from the evasion
driving signal generator 63 such that it does not become greater
than zero-level. If the signal from the driving limiter 64 is
low-level, then the evasion driving signal generator 63 generates a
driving signal such that the condensing lens 15 is displaced at a
predetermined speed (slope) away from the optical disk 1 when the
signal from the information surface detector 62 is high-level, and
generates a driving signal such that the condensing lens 15 is
displaced at a predetermined speed (slope) toward the optical disk
1 when the signal from the information surface detector 62 is
low-level. Then, the evasion driving signal generator 63 sends the
generated driving signal to the driving selector 32 and the driving
limiter 64.
[0127] If the signal from the driving limiter 64 is high-level,
then the evasion driving signal generator 63 clears the output
driving signal to zero, and sends the generated driving signal to
the driving selector 32 and the driving limiter 64. The driving
limiter 64 sends to the evasion driving signal generator 63 a
high-level signal if the driving signal from the evasion driving
signal generator 63 is zero or greater, and a low-level signal if
the driving signal from the evasion driving signal generator 63 is
smaller than zero. The driving selector 32 performs signal
switching such that the signal from the Fc filter 31 is sent via
the Fc driver 37 to the Fc actuator 16 if the focus control is in
the operative state, and the signal from the evasion driving signal
generator 63 is sent via the Fc driver 37 to the Fc actuator 16 if
the focus control is in the inoperative state.
[0128] Referring to FIG. 2, the following is an explanation of the
operation of collision evasion between the condensing lens 15 and
the optical disk 1 if the focus control is in the inoperative
state. FIG. 2A shows the reflected light amount signal that is
output from the reflected light amount detector 61, FIG. 2B shows
the signal that is output from the information surface detector 62,
FIG. 2C shows the driving signal that is output from the evasion
driving signal generator 63, and FIG. 2D shows the signal that is
output from the driving limiter 64. FIG. 2E shows the positional
relation between the optical disk 1 (indicated by the broken line)
and the condensing lens (indicated by the solid line).
[0129] If the focus control is in the inoperative state, the
driving selector 32 constantly sends the signal from the evasion
driving signal generator 63 to the Fc actuator 16. Since the focus
control is in the inoperative state, the distance between the
condensing lens 15 and the optical disk 1 changes depending on
surface fluctuations of the optical disk 1 or the like. When the
condensing lens 15 and the optical disk 1 come close to one
another, and the focus of the light beam thus comes close to the
information surface of the optical disk 1, the reflected light
amount signal that is output from the reflected light amount
detector 61 increases, as shown in FIG. 2A. When the focus of the
light beam becomes even closer to the information surface of the
optical disk 1, and the reflected light amount signal that is
output from the reflected light amount detector 61 exceeds a
reference level A, the signal that is output from the information
surface detector 62 becomes high-level, as shown in FIG. 2B.
[0130] When the signal that is output from the information surface
detector 62 has become high-level, the evasion driving signal
generator 63 generates a driving signal for the Fc actuator 16,
such that the condensing lens 15 is displaced in a direction away
from the optical disk 1, as shown in FIG. 2C. Thus, the condensing
lens 15 and the optical disk 1 gradually move away from one
another, and the reflected light amount signal that is output from
the reflected light amount detector 61 decreases, as shown in FIG.
2A.
[0131] When the condensing lens 15 and the optical disk 1 are more
than a predetermined distance apart, and the reflected light amount
signal that is output from the reflected light amount detector 61
becomes lower than the comparison level A, then, the signal that is
output from the information surface detector 62 becomes low-level,
as shown in FIG. 2B. When the signal that is output from the
information surface detector 62 becomes low-level, the evasion
driving signal generator 63 generates a driving signal for the Fc
actuator 16, such that the condensing lens 15 is displaced in a
direction toward the optical disk 1, as shown in FIG. 2C.
[0132] When the driving signal that is output from the evasion
driving signal generator 63 (see FIG. 2C) becomes zero, the signal
that is output from the driving limiter 64 becomes high-level, as
shown in FIG. 2D. Then, as shown in FIG. 2C and FIG. 2D, if the
signal that is output from the driving limiter 64 is high-level,
the driving signal that is output from the evasion driving signal
generator 63 takes on a constant value that does not become greater
than zero.
[0133] Thus, when the condensing lens 15 and the optical disk 1
approach one another, the condensing lens 15 is driven such that it
is displaced in a direction away from the optical disk 1, so that
collisions between the condensing lens 15 and the optical disk 1
can be avoided.
[0134] It should be noted that in the present embodiment, the
extent to which the condensing lens 15 and the optical disk 1 have
approached one another is detected using the reflected light
amount, but the present invention is not necessarily limited to
this configuration. It is also possible to detect the extent to
which the condensing lens 15 and the optical disk 1 have approached
one another using, for example, the amplitude of the signal
recorded on the information surface of the optical disk 1, the
amplitude of the FE signal serving as the error signal used by the
focus control, or the amplitude of a tracking error signal
(referred to in the following as "TE signal") serving as the error
signal used for the tracking control.
[0135] Moreover, if the information surface of the optical disk 1
is made of tracks with wobble as shown in FIG. 4B, then a signal
corresponding to the wobble component of the tracks may be detected
by the information surface detector 62, and that the distance
between the condensing lens 15 and the optical disk 1 has become
close may be detected using the amplitude of that signal. Moreover,
it is also possible to configure the information surface detector
62 by attaching a position sensor to the optical head 10, and to
directly detect the distance to the optical disk 1.
[0136] It is also possible to devise a configuration in which an
acceleration sensor serving as a vibration detection means is
attached to the casing of the overall apparatus, the detected
acceleration signal, that is, a signal corresponding to an external
vibration is detected, and the evasion driving signal generator 63
foresees when the distance between the condensing lens 15 and the
optical disk 1 becomes close to vibrations and generates a driving
signal such that a collision between them is avoided.
[0137] Moreover, the present embodiment is configured such that
when the condensing lens 15 and the optical disk 1 start to become
close to one another, a triangular driving signal decreasing with a
constant slope, and when they then start to move away from one
another, a triangular driving signal increasing with a constant
slope is output from the evasion driving signal generator 63 (see
FIG. 2C), but the present invention is not necessarily limited to
this configuration. For example, the same effect can also be
attained with a configuration in which a pulse signal having a
predetermined peak value such that the condensing lens 15 is
displaced in a direction away from the optical disk 1 is output
from the evasion driving signal generator 63. And the same effect
can also be attained with a configuration in which a ramp signal
having a constant slope is output from the evasion driving signal
generator 63.
[0138] The driving signal that is output from the evasion driving
signal generator 63 is saturated at a preset predetermined value
due to the action of the driving limiter 64. Therefore, more than
the necessary current will not flow through the Fc actuator 16 due
to the driving signal that is output from the evasion driving
signal generator 63. As a result, more than the necessary heat is
not generated by the Fc actuator 16, so that damage to the optical
head 10 can be prevented.
[0139] Furthermore, the same effect can also be attained with a
configuration in which the evasion driving signal generator 63
outputs a two-value signal with a reference level corresponding to
the case that the condensing lens 15 and the optical disk 1 are
away from one another, and a very low constant level at which the
condensing lens 15 does not collide with the optical disk 1 when
the condensing lens 15 and the optical disk have become close to
one another.
[0140] In the present embodiment, when the focus control is in the
inoperative state, and the condensing lens 15 has moved close to
the optical disk 1, the evasion driving signal generator 63
generates a driving signal such that the condensing lens 15 is
displaced with a predetermined speed in a direction away from the
optical disk 1, but there is no limitation to this configuration.
For example, collisions between the condensing lens 15 and the
optical lens 1 when the focus control is in the inoperative state
can be reliably prevented with a configuration in which the evasion
driving signal generator 63 outputs a very low constant signal such
that the condensing lens 15 is constantly displaced from the
optical disk 1 if the focus control is inoperative, even when the
condensing lens 15 is not approaching the optical disk 1.
Second Embodiment
[0141] FIG. 3 is a block diagram showing an optical disk apparatus
according to a second embodiment of the present invention. It
should be noted that structural elements that are the same as in
FIG. 1 of the first embodiment have been denoted by the same
numerals, and their further explanation has been omitted.
[0142] As shown in FIG. 3, in the present embodiment, a variable
power laser 21 is used as the semiconductor laser. Moreover, in the
optical disk apparatus of the present embodiment, the FE generator
30 sends the FE signal via the Fc filter 31 and the Fc driver 37 to
the Fc actuator 16. That is to say, different from the first
embodiment, the FE signal from the FE generator 30 is sent to the
Fc actuator 16 not via the driving selector 32 (see FIG. 1), but
only via the Fc filter 31 and the Fc driver 37.
[0143] The optical detector 20 sends the detected light amount
signal to the FE generator 30, a tracking error generator (referred
to as "TE generator" in the following) 40, a wobble amplitude
detector 65, and a recording region detector 70. The TE generator
40 serves as a track displacement signal detection means for
generating a signal corresponding to the positional displacement of
the focus of the light beam with respect to the track on the
optical disk 1. The wobble amplitude detector 65 serves as a
fluctuation amplitude detection means for detecting an amplitude of
the fluctuation in the spiral-shaped track, which has a tiny
fluctuation in the radial direction at a predetermined period, on
the optical disk 1. The recording region detector 70 serves as a
recorded region detection means for detecting whether the region
irradiated by the light beam is in a recorded or an unrecorded
state.
[0144] The TE generator 40 calculates a tracking error signal
(referred to as "TE signal" in the following) that corresponds to
the positional displacement between the focus of the light beam and
the track on the optical disk 1, using the light amount signal from
the optical detector 20. Then, the TE generator 40 sends this TE
signal to a tracking control filter 41 (referred to as "Tk filter"
in the following) serving as a tracking control means. Based on the
TE signal from the TE generator 40, the Tk filter 41 sends a
driving signal causing the focus of the light beam to follow the
track to the Tk actuator 17, via the switch 42 and a tracking
driver (referred to as "Tk driver" in the following) 44.
[0145] The Tk actuator 17 moves the condensing lens 15 in the
radial direction of the optical disk 1, in accordance with the
driving signal from the Tk driver 44. A tracking control operation
indicator (referred to as "Tk control operation indicator" in the
following) 68 sends to a focus anomaly detector (referred to as "Fc
anomaly detector") 67, which serves as an anomaly detection means,
and the switch 42 a high-level signal when tracking control is
performed, and a low-level signal when tracking control is not
being performed.
[0146] The switch 42 sends the signal from the Tk filter 41 to the
Tk actuator 17 if the signal from the Tk control operation
indicator 68 is high-level, and sends a zero to the Tk actuator 17
if the signal from the Tk control operation indicator 68 is
low-level.
[0147] Referring to FIG. 4, the following is an explanation of the
track wobble. FIG. 4A is a magnified view showing the optical disk
1 for the case that there is no wobble, and FIG. 4B is a magnified
view showing the optical disk 1 for the case that there is wobble.
The track wobble shown in FIG. 4B has a frequency that is higher
than the frequency band of the tracking control, so that the focus
of the light beam scans the vicinity of the track center,
regardless of whether there is wobble or not. The wobble amplitude
detector 65 detects the amplitude of wobble of a predetermined
frequency in the tracks on the optical disk shown in FIG. 4B, and
sends this amplitude to a variable multiplier 66.
[0148] The recording region detector 70 serving as the recorded
region detection means detects the amplitude value of the light
amount signal from the optical detector 20, and a high-level signal
is sent to the variable multiplier 66 if the light beam is
irradiated onto a recorded region of the optical disk 1, whereas a
low-level signal is sent to the variable multiplier 66 if the light
beam is irradiated onto an unrecorded region of the optical disk
1.
[0149] A recording operation indicator 69 sends a low-level signal
to the variable multiplier 66 and the variable power laser 21 if
information recorded on the optical disk 1 is being reproduced, and
sends a high-level signal to the variable multiplier 66 and the
variable power laser 21 if information is being recorded on the
optical disk 1. The variable power laser 21 emits at reproducing
power if the signal from the recording operation indicator 69 is
low-level, and emits pulses at recording power if the signal from
the recording operation indicator 69 is high-level.
[0150] The variable multiplier 66 switches the multiplication
factor with which the signal from the wobble amplitude detector 65
is multiplied in accordance with the logical state of the signal
from the recording operation indicator 69 and the recording region
detector 70, and sends the thusly obtained signal to the Fc anomaly
detector 67. If the time at which the signal from the variable
multiplier 66 becomes lower than a predetermined level compared to
a reference level continues for more than an anomaly detection time
TW, then the internal status of the Fc anomaly detector 67 is set
to a state indicating that the focus control has been lost. The Fc
anomaly detector 67 switches the anomaly detection time TW based on
the signal from the Tk control operation indicator 68.
[0151] Referring to FIG. 5, the following is an explanation of the
operation of focus anomaly detection for the case that the tracking
control is in a inoperative state. FIG. 5A shows the signal that is
output from the wobble amplitude detector 65, FIG. 5B shows the
signal that is output from the recording operation indicator 69,
FIG. 5C shows the signal that is output from the recording region
detector 70, and FIG. 5D shows the signal that is output from the
variable multiplier 66. FIG. 5E shows the internal status of the Fc
anomaly detector 67.
[0152] In the following explanations, it is assumed that first,
information is recorded on an unrecorded region, then information
on an unrecorded region is reproduced, then information on a
recorded region is reproduced, and then the focus control is lost
during the reproduction operation for the recorded region.
[0153] Since no tracking control is carried out, that is, since the
tracking control is in the inoperative state, the signal from the
Tk control operation indicator 68 is low-level, and the driving
signal sent to the Tk actuator 17 is zero. The light beam traverses
the tracks in accordance with the eccentric state of the tracks on
the optical disk 1. The wobble amplitude detector 65 detects the
wobble for on-track states, but the more off-track the state
becomes, the less can the wobble be detected. Therefore, the signal
that is output from the wobble amplitude detector 65 fluctuates, as
shown in FIG. 5A.
[0154] When transitioning from the state of recording information
to a state of reproducing information, the signal that is output
from the recording operation indicator 69 changes from high-level
to low-level, as shown in FIG. 5B.
[0155] When the position to which the light beam is irradiated
transitions from an unrecorded region on the optical disk 1 to a
recorded region, the signal that is output from the recording
region detector 70 changes from low-level to high-level, as shown
in FIG. 5C. The wobble amplitude detector 65 detects the wobble
amplitude from the reflected light, so that the detection result
depends on the reflected light amount.
[0156] That is to say, as shown in FIG. 6A, even for the same
unrecorded region (when the signal that is output from the
recording region detector 70 in FIG. 5C is low-level), the wobble
amplitude detected by the wobble amplitude detector 65 is larger in
the case that information is being recorded (when the signal that
is output from the recording operation indicator 69 in FIG. 5B is
high-level) than in the case that information is being reproduced
(when the signal that is output from the recording operation
indicator 69 in FIG. 5B is low-level). And also for the same state
in which information is being reproduced (when the signal that is
output from the recording operation indicator 69 in FIG. 5B is
low-level), the wobble amplitude detected by the wobble amplitude
detector 65 is larger in the case that the light beam is irradiated
on an unrecorded region (when the signal that is output from the
recording region detector 70 in FIG. 5C is low-level) than in the
case that the light beam is irradiated on a recording region (when
the signal that is output from the recording region detector 70 in
FIG. 5C is high-level).
[0157] These changes in the detection sensitivity of the wobble
amplitude detector 65 are constant, so that the changes in the
detection sensitivity of the wobble amplitude detector 65 can be
corrected by providing the wobble amplitude detector 65 with a
fluctuating detection sensitivity switching means (not shown in the
drawings) that sends to the variable multiplier 66 a signal that
switches the multiplication factor of the variable multiplier 66 in
accordance with the emission power of the variable power laser 21
and the reflectivity of the optical disk 1, depending on whether
information is being recorded or information is, being reproduced.
That is to say, even if the output of the light beam changes and
the light amount reflected from the optical disk 1 changes
depending on whether information is being recorded or information
is being reproduced, the change in the reflected light amount can
be canceled by switching the detection sensitivity of the wobble
amplitude detector 65 between the case that information is being
recorded and the case that information is being reproduced, so that
the amplitude of the signal that is output from the variable
multiplier 66 can be made constant, as shown in FIG. 5D. As a
result, erroneous detection with the Fc anomaly detector 67 can be
prevented. Moreover, by providing the wobble amplitude detector 65
with a fluctuating detection sensitivity switching means (not shown
in the drawings) that sends to the variable multiplier 66 a signal
that switches the multiplication factor of the variable multiplier
66 depending on whether the region on which the light beam is
irradiated is in a recorded or an unrecorded state, the change in
the reflected light amount can be similarly canceled by switching
the detection sensitivity of the wobble amplitude detector 65 even
if the output of the light beam changes and the light amount
reflected from the optical disk 1 changes depending on whether a
recorded region is irradiated or an unrecorded region is
irradiated, so that erroneous detection with the Fc anomaly
detector 67 can be prevented.
[0158] Since the signal from the Tk control operation indicator 68
is low-level, the Fc anomaly detector 67 selects the anomaly
detection time TW for the case that the tracking control is in the
inoperative state. Then, the Fc anomaly detector 67 measures the
time that the state continues in which the signal from the variable
multiplier 66 is lower than the anomaly detection level TL, and
when this time becomes longer than the anomaly detection time TW,
the internal status of the Fc anomaly detector 67 is set to the
state indicating that the focus control has been lost. In this
case, by making the anomaly detection time TW longer than the
period in which the light beam traverses the tracks, a erroneous
detection in the off-track state can be prevented. When the focus
control is lost, the signal that is output from the wobble
amplitude detector 65 becomes zero, so that the internal status of
the Fc anomaly detector 67 is set to the state indicating that the
focus control has been lost after an anomaly has occurred and after
the anomaly detection time TW has passed.
[0159] The reflected light is detected over a broad range from the
state in which the focus of the light beam is positioned on the
information surface of the optical disk 1, so that there is a
constant limit to the detection speed of the focus anomaly
detection using the reflected light amount. On the other hand,
since the detected range of the wobble amplitude is small compared
to that of the reflected light, the detection speed can be
increased with a focus anomaly detection using the wobble
amplitude.
[0160] If the tracking control is in the operative state, the light
beam always follows the tracks, so that the signal that is output
from the wobble amplitude detector 65 does not fluctuate as it does
when the tracking control is in the inoperative state. Therefore,
if the anomaly detection time TW of the Fc anomaly detector 67 is
longer than the wobble period, erroneous detections by the Fc
anomaly detector 67 can be prevented, so that the anomaly detection
time TW can be set shorter than when the tracking control is in the
inoperative state. Consequently, it becomes possible to perform a
very fast anomaly detection.
[0161] It should be noted that in the present embodiment, the Fc
anomaly detector 67 serving as the anomaly detection means is
operated also when the tracking control is in the inoperative
state. If the tracking control is in the inoperative state, the
focus of the light beam traverses the tracks on the optical disk 1,
and the detection sensitivity of the wobble amplitude detection
differs for the case that the light beam is irradiated on a track
and the case that the light beam is irradiated between tracks (if
the light beam is irradiated between tracks, the detection
sensitivity decreases). Therefore, an accurate wobble amplitude
cannot be obtained, and the Fc anomaly detector 67 produces a
erroneous detection. Consequently, if the Fc anomaly detector 67 is
operated only when the tracking control is in the operative state,
then the Fc anomaly detector 67 is not affected by track traversing
due to eccentricity, and the wobble signal components are
emphasized, so that the detection precision of the Fc anomaly
detector 67 can be increased.
[0162] Moreover, in the present embodiment, the signal from the
wobble amplitude detector 65 is multiplied with different values
depending on whether the light beam is irradiated on a recorded
region of the optical disk 1 or irradiated on an unrecorded region,
and erroneous detections by the Fc anomaly detector 67 are
prevented, but the same effect can also be attained with a
configuration in which the signal level at which it is judged that
the focus control is lost is changed in the Fc anomaly detector 67,
depending on whether the light beam is irradiated on a recorded
region of the optical disk 1 or irradiated on an unrecorded region.
Furthermore, it is also possible to provide the Fc anomaly detector
67 with an anomaly level switching means (not shown in the
drawings) that switches the signal change level of the wobble
amplitude detector 65 at which it is judged that the focus control
is lost, that is, at which it is judged that there is an anomaly,
in accordance with the result detected by the recording region
detector 70, depending on whether the light beam is irradiated on a
recorded region of the optical disk 1 or irradiated on an
unrecorded region.
[0163] Moreover, the present embodiment has been explained by
giving an example in which erroneous detections of the Fc anomaly
detector 67 are prevented by switching the value with which the
signal from the wobble amplitude detector 65 is multiplied by the
variable multiplier 66 depending on whether information is being
recorded or information is being reproduced, but it is also
possible to change the level at which the Fc anomaly detector 67
judges that the focus control is lost, depending on whether
information is being recorded or information is being reproduced.
Moreover, a configuration is also possible in which the Fc anomaly
detector 67 is provided with an anomaly level switching means (not
shown in the drawings) that switches the signal change level of the
wobble amplitude detector 65 at which it is judged that focus
control has been lost, that is, that there is an anomaly, in
accordance with the result detected with the recording region
detector 70.
Third Embodiment
[0164] FIG. 6 is a block diagram showing an optical disk apparatus
in accordance with a third embodiment of the present invention. It
should be noted that structural elements that are the same as in
FIG. 1 of the first embodiment have been denoted by the same
numerals, and their further explanation has been omitted.
[0165] As shown in FIG. 6, also in the present embodiment, a
variable power laser 21 is used as the semiconductor laser, as in
the second embodiment. Moreover, also in the present embodiment, as
in the second embodiment, the FE generator 30 sends the FE signal
via the Fc filter 31 and the Fc driver 37 to the Fc actuator 16.
That is to say, different from the first embodiment, the FE signal
from the FE generator 30 is sent to the Fc actuator 16 not via the
driving selector 32 (see FIG. 1), but only via the Fc filter 31 and
the Fc driver 37. The FE signal from the FE generator 30 is also
sent to the variable multiplier 66 serving as a multiplication
means and a gain switching means.
[0166] The optical detector 20 sends the detected light amount
signal to the FE generator 30 and the recording region detector
70.
[0167] Detecting the amplitude of the light amount signal from the
optical detector 20, the recording region detector 70 sends a
high-level signal to the variable multiplier 66 if the light beam
is irradiated onto a recorded region of the optical disk 1, whereas
a low-level signal is sent to the variable multiplier 66 if the
light beam is irradiated onto an unrecorded region of the optical
disk 1.
[0168] A recording operation indicator 69 sends a low-level signal
to the variable multiplier 66 and the variable power laser 21 if
information recorded on the optical disk 1 is being reproduced, and
sends a high-level signal to the variable multiplier 66 and the
variable power laser 21 if information is being recorded on the
optical disk 1. The variable power laser 21 emits at reproducing
power if the signal from the recording operation indicator 69 is
low-level, and emits pulses at recording power if the signal from
the recording operation indicator 69 is high-level.
[0169] The variable multiplier 66 switches the multiplication
factor with which the signal from the FE generator 30 is multiplied
in accordance with the logical state of the signal from the
recording operation indicator 69 and the signal from the recording
region detector 70, multiplies this multiplication factor with the
signal from the FE generator 30, and sends the thusly obtained
signal to a level change detector 71.
[0170] The level change detector 71 performs an integration of the
focus displacement signal by increasing a counter value when the
signal from the variable multiplier 66 falls into a predetermined
level range W with respect to a reference level.
[0171] Moreover, when the signal from the variable multiplier 66
does not fall into a predetermined level range W with respect to a
reference level (that is, when the predetermined level range W is
exceeded), the level change detector 71 clears the counter value to
zero with a clearing means (not shown in the drawings) provided in
the level change detector 71, and sets the signal level of the
variable multiplier 66 to the reference level. The level change
detector 71 sends the reference level and the counter value of the
counter provided in the level change detector 71 to a multiplier
72. By multiplying the counter value of the variable multiplier 66
and the absolute value of the reference level in the focus
integration means constituted by the counter and the multiplier 72,
the multiplier 72 calculates a value corresponding to the
integrated focus displacement signal, and sends the result of this
multiplication to an Fc anomaly detector 73 serving as an anomaly
detection means.
[0172] If the signal from the multiplier 72 is at or below an
anomaly detection level, then the internal status of the Fc anomaly
detector 73 is set to a state indicating that the focus control is
in normal condition, and if the signal from the multiplier 72 is
larger than the anomaly detection level, then the internal status
of the Fc anomaly detector 73 is set to a state indicating that the
focus control has been lost.
[0173] Referring to FIGS. 7 to 9, the following is an explanation
of the operation of the focus anomaly detection according to the
present embodiment.
[0174] FIG. 7 shows the signal of the FE generator 30 for the case
that the focus of the light beam has passed in the focus direction
through the information surface of the optical disk 1. As shown in
FIG. 7, if the focus of the light beam is near the information
surface of the disk 1, a focus direction error signal appears, and
if the focus of the light beam is to a certain extent removed from
the information surface of the optical disk 1, then the signal of
the FE generator 30 assumes a constant value.
[0175] FIG. 8 illustrates how the detection signal is generated.
FIG. 8A shows the signal that is output from the FE generator 30,
FIG. 8B shows the signal that is output from the recording
operation indicator 69, FIG. 8C shows the signal that is output
from the recording region detector 70, and FIG. 8D shows the signal
that is output from the variable multiplier 66.
[0176] To facilitate the understanding of the operation in the
following, a case is explained in which, first, information is
recorded on an unrecorded region, and then information is a
reproduced from an unrecorded region and then from a recorded
region. Even when the focus control is in the operative state, the
focus error is not eliminated completely, and, as shown in FIG. 8A,
a residual difference due to surface fluctuations, scratches in the
disk or surface roughness remains.
[0177] When transitioning from a state in which information is
recorded to a state in which information is reproduced, the signal
that is output from the recording operation indicator 69 changes
from high-level to low-level, as shown in FIG. 8B.
[0178] When the position on which the light beam is irradiated
transitions from an unrecorded region to a recorded region on the
optical disk 1, the signal that is output from the recording region
detector 70 changes from low-level to high-level, as shown in FIG.
8C.
[0179] Since the FE generator 30 detects the FE signal from the
reflected light, the detection result differs depending on the
reflected light amount. That is to say, as shown in FIG. 8A, even
for the same unrecorded region (when the signal that is output from
the recording region detector 70 in FIG. 8C is low-level), the
amplitude of the FE signal generated with the FE generator 30 is
larger in the case that information is being recorded (when the
signal that is output from the recording operation indicator 69 in
FIG. 8B is high-level) than in the case that information is being
reproduced (when the signal that is output from the recording
operation indicator 69 in FIG. 8B is low-level). And also for the
same state in which information is being reproduced (when the
signal that is output from the recording operation indicator 69 in
FIG. 8B is low-level), the amplitude of the FE signal generated
with the FE generator 30 is larger in the case that the light beam
is irradiated on an unrecorded region (when the signal that is
output from the recording region detector 70 in FIG. 8C is
low-level) than in the case that the light beam is irradiated on a
recording region (when the signal that is output from the recording
region detector 70 in FIG. 8C is high-level).
[0180] These changes in the detection sensitivity of the FE
generator 30 are constant, so that by providing the variable
multiplier 66 with a gain switching means (not shown in the
drawings) that switches the multiplication factor of the variable
multiplier 66 in accordance with the emission power of the variable
power laser 21 and the reflectivity of the optical disk 1 depending
on whether information is being recorded or information is being
reproduced, it is possible to cancel changes in the reflected light
amount by switching the multiplication factor of the variable
multiplier 66 depending on whether information is being recorded or
information is being reproduced, even when the output of the light
beam changes and the reflected light amount from the optical disk 1
changes depending on whether information is recorded or information
is reproduced, so that it is possible to attain a constant
amplitude of the signal that is output from the variable multiplier
66, as shown in FIG. 8D. As a result, erroneous detection of the Fc
anomaly detector 73 can be prevented.
[0181] Moreover, by providing the variable multiplier 66 with a
gain switching means (not shown in the drawings) that switches the
multiplication factor of the variable multiplier 66 depending on
whether the light beam is irradiated on a recorded region or an
unrecorded region, it is similarly possible to cancel changes in
the reflected light amount by switching the multiplication factor
of the variable multiplier 66, even when the output of the light
beam changes and the reflected light amount from the optical disk 1
changes depending on whether the light beam is irradiated on a
recorded region or on an unrecorded region, so that erroneous
detection of the Fc anomaly detector 73 can be prevented.
[0182] FIG. 9 illustrates how the focus control is lost from a
normal state, while the focus control is in an operative state.
FIG. 9A shows the signal that is output from the variable
multiplier 66, FIG. 9B shows the reference level of the level
change detector 71, FIG. 9C shows the counter value of the level
change detector 71, and FIG. 9D shows the signal that is output
from the multiplier 72. Moreover, FIG. 9E shows the internal status
of the Fc anomaly detector 73.
[0183] As shown in FIG. 9A, by making the compared level range W,
which is a parameter for changing the reference level of the level
change detector 71, smaller than the residual difference of the
focus control, the reference level of the level change detector 71
is frequently rewritten due to the residual difference of the focus
control, as shown in FIG. 9B, if the focus control is in the normal
state, so that the counter value of the level change detector 71
does not become large, as shown in FIG. 9C.
[0184] When the focus control deviates from the normal state, the
signal that is output from the variable multiplier 66 takes on a
constant value, as shown in FIG. 9A, so that the counter value of
the level change detector 71 is incremented, as shown in FIG. 9C,
and at the same time, also the signal that is output from the
multiplier 72 increases, as shown in FIG. 9D. When the signal that
is output from the multiplier 72 reaches the anomaly detection
level, the internal status of Fc anomaly detector 73 is set to a
state indicating that the focus control has been lost, as shown in
FIG. 9E.
[0185] Here, the light amount reflected from the optical disk 1
differs depending on whether the focus of the light beam is
positioned on a track of the optical disk 1 or positioned between
tracks the Fc anomaly detection 73 occasionally may make a
erroneous detection when the detection speed of the focus anomaly
detection due to the reflected light amount is increased. For this
reason, if the tracking control is in the inoperative state,
[0186] With the focus anomaly detection in the present embodiment,
the detection speed can be made faster, regardless of whether the
tracking control is in the operative state or in the inoperative
state.
[0187] It should be noted that in the present embodiment, the
results of a multiplication of the reference level and the counter
value of the level change detector 71 are sent to the Fc anomaly
detector 73, but there is no limitation to this configuration. For
example, it is also possible to send only the counter value to the
Fc anomaly detector 73, compare the counter value with the anomaly
detection level, and when the counter value is above the anomaly
detection level, set the internal state of the Fc anomaly detector
73 to a state indicating that the focus control has been lost.
[0188] Moreover, in the present embodiment, erroneous detections
with the Fc anomaly detector 73 are prevented by switching the
multiplication factor of the variable multiplier 66 depending on
whether the light beam is irradiated onto a recorded region or onto
an unrecorded region, or depending on whether information is being
recorded or reproduced, and multiplying the signal from the FE
generator 30 with this multiplication factor, but there is no
limitation to this configuration. For example, the same effect can
also be attained without providing the variable multiplier 66, by
providing a judgment level switching means (not shown in the
drawings) that switches the signal level of the Fc generator 30
that is judged to be anomalous by changing the compared level range
W, which is a parameter for altering the reference level of the
level change detector 71, depending on whether information is
recorded or reproduced. It is also possible to provide a judgment
level switching means (not shown in the drawings) that switches the
signal level of the Fc generator 30 that is judged to be anomalous
by changing the compared level range W depending on whether the
light beam is irradiated onto a recorded region or onto an
unrecorded region.
Fourth Embodiment
[0189] FIG. 10 is a block diagram showing an optical disk apparatus
in accordance with a fourth embodiment of the present invention. It
should be noted that structural elements that are the same as in
FIG. 1 of the first embodiment have been denoted by the same
numerals, and their further explanation has been omitted.
[0190] As shown in FIG. 10, in the present embodiment, a focus
displacement signal detection means corresponding to the FE
generator 30 in FIG. 1 is constituted by a balance calculator 33, a
differential amplifier 34, and an adder 35. As an optical detector,
an optical detector 22 is used that is different from the optical
detector 20 in FIG. 1. The optical detector 20 in FIG. 1 outputs
signals corresponding to the received light amounts at a plurality
of light-receiving portions in the detector, whereas the optical
detector 22 of the present embodiment additionally calculates a
differential signal for generating a focus displacement signal and
outputs this differential signal.
[0191] The optical detector 22 generates two differential input
signals for detecting a focus error from the detected light amount
signals, and sends these differential input signals to the balance
calculator 33.
[0192] If the balance signal from the balance signal generator 76
is larger than zero (reference level), then the balance calculator
33 performs a balance calculation with which one of the two
differential input signals output from the optical detector 22 is
amplified a lot, and the other differential input signal is
amplified a little. That is to say, balance calculations such as
"one differential input signal".times.(1+balance signal) and "other
differential input signal".times.(1-balance signal) are performed.
Then, the balance calculator 33 sends the two signals to the
differential amplifier 34. The differential amplifier 34 generates
a differential output of the two signals from the balance
calculator 33, and sends this differential output to the adder
35.
[0193] The adder 35 adds the signal from the differential amplifier
34 and the signal from an offset generator 75, and sends the
resulting signal to the Fc filter 31.
[0194] An acceleration sensor 74 made of a device such as a
piezoelectric element or the like serving as a vibration detection
means detects vibrations acting on the optical disk apparatus as an
electric charge amount, and detects the vibration of the optical
disk apparatus by converting this electric charge amount into a
voltage. An acceleration signal corresponding to the vibration
magnitude detected by this acceleration sensor 74 is sent to a
limiter 77 via an offset generator 75.
[0195] FIG. 11 shows an example of the input/output characteristics
of the offset generator 75. As shown in FIG. 11, the offset
generator 75 is designed such that its output is larger, the larger
the acceleration signal from the acceleration sensor 74 is.
[0196] The limiter 77 restricts the signal from the offset
generator 75 such that it does not become greater than a
predetermined level, and sends this signal to the adder 35 and to
the balance signal generator 76. The balance signal generator 76
generates a balance signal for switching the gains of the balance
calculator 33 such that the operating point of the adder 35 does
not change, in accordance with the signal from the offset generator
75, and sends the generated balance signal to the balance
calculator 33. Ensuring that the operating point of the adder 35
does not change ensures that also the operating point of the Fc
filter 31 does not change.
[0197] Referring to FIG. 12, the following is an explanation of the
operation of the collision evasion in accordance with the present
embodiment. FIG. 12A shows the signal that is output from the adder
35 when there is no vibration, FIG. 12B shows the signal that is
output from the adder 35 when vibration is detected and when there
is no output from the balance signal generator 76, and FIG. 12C
shows the signal that is output from the adder 35 when vibration is
detected and when there is an output from the balance signal
generator 76. All diagrams of FIG. 12 show the signals for the case
that the focus control is inoperative, and the focus of the light
beam passes through the information surface of the optical disk
1.
[0198] When there is no vibration, the signal that is output from
the adder 35 takes on the state as shown in FIG. 12A, and the focus
of the light beam is regulated to the information surface of the
optical disk 1 by the focus control.
[0199] When there is vibration, the offset generator 75 generates
an offset signal corresponding to the vibration magnitude, and if
vibration occurs and the balance signal does not change before and
after the offset signal from the offset generator 75 changes, then
the signal that is output from the adder 35 takes on the state as
shown in FIG. 12B. That is to say, outside the focus error (FE)
detection range, the signal that is output from the adder 35
becomes even smaller. The Fc filter 31 can generate a driving
signal for the Fc actuator 16 that displaces the condensing lens 15
in a direction away from the optical lens 1, the displacement being
greater the smaller the signal that is output from the adder 35 is
(the larger the vibration acting on the apparatus is).
[0200] Thus, even when the focus control is lost due to vibrations
or shock and the focus of the light beam has left the FE detection
range, a driving signal is applied to the Fc actuator 16 that
causes the condensing lens 15 to be displaced considerably in a
direction away from the optical disk 1, in accordance with the
magnitude of the vibration acting on the optical disk apparatus, so
that collisions between the condensing lens 15 and the optical disk
1 can be prevented.
[0201] As shown in FIG. 12B, when a vibration occurs in the case
that the focus control is in the normal state, the focus of the
light beam is not controlled to the information surface of the
optical disk 1 anymore. In this case, the balance signal generator
76 sends a balance signal in accordance with the offset value of
the offset generator 75 to the balance calculator 33, and by
performing the balance calculation with the balance calculator 33,
the focus of the light beam can be controlled to the information
surface of the optical disk 1, as shown in FIG. 12C.
[0202] Moreover, when the offset generator 75 generates an offset
amount that is too large, a large driving signal is applied to the
Fc actuator 16 if the focus control has been lost, and there is the
risk that the optical head 10 is damaged due the heat generated by
the Fc actuator 16. In order to prevent this, the offset signal
generated by the offset generator 75 is saturated at a
predetermined level by the limiter 77.
[0203] As explained above, with the present embodiment, while
maintaining a state in which the focus of the light beam is
controlled to the information surface of the optical disk 1 if the
focus control is in the normal state, a force that drives the
condensing lens 15 away from the optical disk 1 can be increased in
accordance with vibrations acting on the optical disk apparatus if
the focus control is lost, so that collisions between the
condensing lens 15 and the optical disk 1 can be prevented.
Fifth Embodiment
[0204] FIG. 13 is a block diagram showing an optical disk apparatus
in accordance with a fifth embodiment of the present invention. It
should be noted that structural elements that are the same as in
FIG. 1 of the first embodiment have been denoted by the same
numerals, and their further explanation has been omitted.
[0205] As shown in FIG. 13, the signal from the Fc filter 31 is
sent via the switch 42 and the Fc driver 37 to the Fc actuator 16.
A signal related to the shifting distance, which is indicated by a
search operation indicator 78 serving as a searching means for
shifting the condensing lens 15 such that the light beam is
irradiated onto the desired track on the optical disk 1, is sent to
a search driving signal generator 79 and a focus control operation
indicator (referred to as "Fc control operation indicator" in the
following) 80.
[0206] Moreover, the driving signal from the search driving signal
generator 79 is sent to a transport motor 43 and to the Fc control
operation indicator 80.
[0207] The transport motor 43 moves the optical head 10 in a radial
direction of the optical disk 1, in accordance with the driving
signal from the search driving signal generator 79. Here, the
surface fluctuations of the optical disk 1 increase at its outer
periphery, so that when the focus control is in the inoperative
state, the possibility that the optical lens 15 collides with the
optical disk 1 at the outer periphery of the optical disk 1 is very
high.
[0208] Moreover, when a search over a long distance is carried out,
there is the risk that the condensing lens 15 is shaken through the
casing of the optical head 10 due to the vibrations caused by that
search, and the focus control is lost.
[0209] To address this problem, if the direction in which the focus
of the light beam is moved across the tracks is the direction
toward the outer periphery of the optical disk 1, and if the moving
distance that is instructed by the search operation indicator 78 is
the risk distance K or greater, wherein the risk distance K is
defined as the search distance for which there is the risk that the
focus control is lost, then the following signal is output from the
Fc control operation indicator 80 to the switch 42. That is, the Fc
control operation indicator 80 sends a low-level signal to the
switch 42 if the search driving signal generator 79 generates a
driving signal, and sends a high-level signal to the switch 42 if
the search driving signal generator 79 does not generate a driving
signal.
[0210] If the moving distance instructed from the search operation
indicator 78 is smaller than the risk distance K, then the Fc
control operation indicator 80 sends a high-level signal to the
switch 42. If the signal from the Fc control operation indicator 80
is high-level, then the switch 42 sends the signal from the Fc
filter 31 to the Fc actuator 16, and if the signal from the Fc
control operation indicator 80 is low-level, then the switch 42
sends a zero to the Fc actuator 16.
[0211] The following is an explanation of the operation in the case
that the moving distance (search distance) instructed by the search
operation indicator 78 is longer than the risk distance K. While a
search operation is performed, a driving signal is generated by the
search driving signal generator 79, and a low-level signal is sent
from the Fc control operation indicator 80 to the switch 42. During
that time, the switch 42 sends a zero to the Fc actuator 16, so
that the focus control becomes inoperative, and the condensing lens
15 is removed at a position at which it does not collide with the
optical disk 1.
[0212] When the searching operation is finished and no driving
signal is generated anymore by the search driving signal generator
79, a high-level signal is sent to the switch 42, and the focus
control becomes operative again.
[0213] As explained above, with the present embodiment, if a search
is performed over long distance of at least 1/3 stroke toward the
outer periphery of the optical disk 1, then collisions between the
condensing lens 15 and the optical disk 1 can be prevented by
making the focus control inoperative, and ensuring a large distance
between the condensing lens 15 and the optical disk 1, so that the
practical effects are considerable.
[0214] Moreover, a configuration is also possible in which the
search operation indicator 78 sets the focus control to the
inoperative state, if the target track to which the focus of the
light beam is to be moved is within a range of a predetermined
distance from the outermost periphery of the optical disk 1.
[0215] Furthermore, a configuration is also possible in which the
distance to which the focus of the light beam is moved is converted
into a corresponding number of tracks, and if this converted number
of tracks is greater than a predetermined number (for example the
number of tracks corresponding to the risk distance K), then the
search operation indicator 78 sets the focus control to the
inoperative state.
INDUSTRIAL APPLICABILITY
[0216] As described above, with the present invention, collisions
between the condensing lens and the optical disk can be avoided
regardless whether the focus control is in the operative state or
in the inoperative state, so that it can be used for optical disk
apparatuses that are equipped with high-density optical disks, for
which the possibility of collisions between the condensing lens and
the optical disk is high.
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