U.S. patent application number 09/859116 was filed with the patent office on 2002-01-31 for data recording and/or reproducing apparatus, and disc-shaped recording medium.
This patent application is currently assigned to Sony Corporation. Invention is credited to Hayashi, Nobuhiro.
Application Number | 20020012188 09/859116 |
Document ID | / |
Family ID | 16147995 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012188 |
Kind Code |
A1 |
Hayashi, Nobuhiro |
January 31, 2002 |
Data recording and/or reproducing apparatus, and disc-shaped
recording medium
Abstract
A data recording and/or reproducing apparatus is disclosed which
scans a head over a disc on which a servo pattern for moving the
head to a predetermined position is recorded in an arc forming a
part of a concentric circle. The apparatus comprises a track No.
detector and fine signal detector, for detection of the servo
pattern, a circumferential position detector to detect a
circumferential position on the disc, an offset calculator to
calculate an offset of a current position on the disc from the
detected circumferential position, and a positional difference
calculator. The calculated offset of the current position is added
to the positioning signal to control the head scanning orbit on the
disc to be spiral.
Inventors: |
Hayashi, Nobuhiro; (Tokyo,
JP) |
Correspondence
Address: |
Jay H. Maioli
Cooper & Dunham
1185 Avenue of the Americas
New York
NY
10036
US
|
Assignee: |
Sony Corporation
|
Family ID: |
16147995 |
Appl. No.: |
09/859116 |
Filed: |
May 15, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09859116 |
May 15, 2001 |
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09111402 |
Jul 7, 1998 |
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6292318 |
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Current U.S.
Class: |
360/75 ; 360/48;
G9B/5.188; G9B/5.221; G9B/5.223; G9B/7.033; G9B/7.066 |
Current CPC
Class: |
G11B 5/59627 20130101;
G11B 7/0938 20130101; G11B 7/08541 20130101; G11B 7/0953 20130101;
G11B 7/00736 20130101; G11B 5/59644 20130101; G11B 5/5526 20130101;
G11B 7/0901 20130101 |
Class at
Publication: |
360/75 ;
360/48 |
International
Class: |
G11B 021/02; G11B
005/09 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 1997 |
JP |
P09-184135 |
Claims
What is claimed is:
1. A data recording and/or reproducing apparatus in which a signal
recording and/or reproducing head is scanned over a disc-shaped
recording medium on which a positioning signal to move the signal
recording and/or reproducing head to a predetermined position is
recorded along an arc of a concentric circle, comprising: means for
detecting a positioning signal recorded along the arc; means for
detecting a circumferential position on the disc-shaped recording
medium; and means for calculating an amount of offset from a signal
indicative of the detected circumferential position; the calculated
offset amount being added to the positioning signal to control the
head for a scan along a spiral scanning orbit.
2. The apparatus as set forth in claim 1, wherein during idling
with no data recording or reproduction, the head is controlled to
scan along a concentric orbit over the disc-shaped recording
medium.
3. The apparatus as set forth in claim 2, further comprising a
means for holding the amount of offset, the offset amount held by
the holding means being added to the positioning signal to control
the head for a scan along a concentric orbit over the disc-shaped
recording medium during idling with no data recording or
reproduction.
4. The apparatus as set forth in claim 2, further comprising a
means for selecting, depending upon the type of a data to be
recorded, whether the head is to be controlled to scan along a
spiral or concentric orbit over the disc-shaped recording
medium.
5. The apparatus as set forth in claim 4, wherein the head is
controlled to scan along a spiral orbit over one side of the
disc-shaped recording medium adapted to record data on either side
thereof, and along an inverted spiral orbit over the other side of
the recording medium.
6. The apparatus as set forth in claim 2, wherein the arc forming a
part of the concentric circle, along which the positioning signal
is recorded, has a radius variable from one circumferential
position to another.
7. The apparatus as set forth in claim 1, further comprising a
means for selecting, depending upon the type of a data to be
recorded, whether the head is to be controlled for a scan along a
spiral or concentric orbit over the disc-shaped recording
medium.
8. The apparatus as set forth in claim 1, wherein the head is
controlled to scan along a spiral orbit over one side of the
disc-shaped recording medium adapted to record data on either side
thereof, and along an inverted spiral orbit over the other side of
the recording medium.
9. The apparatus as set forth in claim 1, wherein the arc forming a
part of the concentric circle, along which the positioning signal
is recorded, has a radius variable from one circumferential
position to another.
10. The apparatus as set forth in claim 1, wherein the disc-shaped
recording medium is rotated at a constant angular velocity.
11. A data recording and/or reproducing apparatus in which a signal
recording and/or reproducing head is scanned over a disc-shaped
recording medium having recorded along an arm of a concentric
circle having a radius variable from one circumferential position
to another a track address information signal under which the head
is moved to a predetermined radial position of the disc-shaped
recording medium, comprising: means for detecting, based on an
information read by the head, the track address information signal
recorded along the circular arc of the concentric circle; means for
detecting, based on the head-read information, a circumferential
position of the head on the disc-shaped recording medium; means for
detecting, based on the signal indicative of the circumferential
position on the disc-shaped recording medium, an amount of offset
with respect to the track address information signal; and means for
controlling, based on the track address information signal and
offset amount, the head for a scan along a spiral orbit over the
disc-shaped recording medium.
12. The apparatus as set forth in claim 11, wherein the head is
controlled to scan along a concentric orbit over the disc-shaped
recording medium during idling with no data recording or
reproduction.
13. The apparatus as set forth in claim 12, further comprising a
means for holding the amount of offset, the offset amount held by
the holding means being added to the positioning signal to control
the head for a scan along a concentric orbit over the disc-shaped
recording medium during idling with no data recording or
reproduction.
14. The apparatus as set forth in claim 12, further comprising a
means for selecting, depending upon the type of a data to be
recorded, whether the head is to be controlled to scan along a
spiral or concentric orbit over the disc-shaped recording
medium.
15. A disc-shaped recording medium having recorded along an arc
forming a part of a concentric circle thereon a positioning signal
to move a signal recording and/or reproducing head to a
predetermined position, the arc along which the positioning signal
is recorded having a-radius variable from one circumferential
position to another.
16. The disc-shaped recording medium as set forth in claim 15,
wherein the data track along which data is recorded is formed
spirally.
17. The disc-shaped recording medium as set forth in claim 15,
wherein data can be recorded on either side thereof and a data
track is formed in a spiral form on one of the disc sides and in an
inverted spiral form on the other side.
18. The disc-shaped recording medium as set forth in claim 15,
having formed thereon servo zones in which at least the position
information signal is recorded, and data zones into and/or from
which data is recorded and/or reproduced.
19. The disc-shaped recording medium as set forth in claim 18,
wherein the servo zone has recorded therein a signal indicative of
a circumferential reference position on the medium.
Description
[0001] BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for digitally
recording and/or reproducing data into and/or from a disc-shaped
recording medium such as a magnetic disc, optical disc or the like,
and a disc-shaped recording medium usable in the apparatus and into
and/or from which data is recorded and/or reproduced.
[0004] 2. Description of Related Art
[0005] Conventionally, to record information into a magnetic disc,
a magnetic head is moved radially of a magnetic disc based on a
positioning information to move a magnetic head to a predetermined
position, which is being reproduced.
[0006] The head positioning information is usually called "tracking
servo signal" and composed of a so-called track address indicative
of a data track number, and a fine signal indicative of a fine
position in the data track. Generally, the tracking servo signal is
recorded on a magnetic disc beforehand by means of a device called
"servo writer".
[0007] The tracking servo signal is recorded in zones defined by
segmenting a magnetic disc circumferentially. Of such zones, a one
where a tracking servo signal is recorded will be referred to as
"servo zone" herebelow, and a zone where no tracking servo signal
is recorded, namely, where data is recorded, will referred to as
"data zone" herebelow. Such a common disc format is illustrated by
way of example in FIG. 1. In the illustrated example in FIG. 1, the
servo zones count twelve in number but an actual disc consists of
tens to hundreds of servo zones.
[0008] The configuration of a common servo zone is illustrated in
detail by way of example in FIG. 2.
[0009] In the example illustrated in FIG. 2, the servo zone
consists of a track address indicative of a data track No., a fine
signal indicative in detail of a position in the data track, and a
clock mark located between the track address and fine signal to
extract a sync clock necessary for reproduction of these signals.
All these signals are recorded in a format which is already
disclosed, for example, in the U.S. patent application Ser. No.
08/588,020 of the Applicant of this patent application.
[0010] FIG. 3 illustrates the configuration of a general tracking
servo system of a magnetic disc drive, showing major components of
the system. It should be noted that other than the tracking servo
system is not illustrated in FIG. 3.
[0011] As seen from FIG. 3, a magnetic head 9 reproduces a signal
from a magnetic disc 11. The reproduced signal is amplified by a
reproduction amplifier 15, and then converted to a digital signal
by an A/D (digital/analog) converter 16. For acquisition of
tracking servo signals, the digital signal is passed to a track No.
detector 17 and a fine signal detector 19. From the digital signal,
the track No. detects a track No. while the fine signal detector 19
detects a fine signal. Thus, the track No. signal and fine signal
are extracted as tracking servo signals. When reproduced, the fine
signal shows a value of 0 when the magnetic head 9 is positioned in
the center of a data track, for example, and a value of .+-.0.5
when the magnetic head 9 is positioned .+-.1/2 of one track pitch
off the center of the data track.
[0012] A current position calculator 18 is provided to calculate
from the detected tracking servo signal a radial position where the
magnetic head 9 exists, and a value indicative of the radial
position is passed to a positional difference calculator 8 which is
also supplied with a value of a target position. In this positional
difference calculator 8, a difference between the radial and target
positions is determined.
[0013] Also a positioning compensator 14 is provided to generate a
VCM (Voice Coil Motor) control signal for the difference between
the radial and target positions to be zero. The VCM control signal
is converted to an analog signal by a D/A (digital/analog)
converter 13, and then passed to a VCM driver 12 which drives a VCM
(voice coil motor) 10. The voice coil motor (VCM) 10 moves the
magnetic head 9 radially over the magnetic disc 11.
[0014] It should be appreciated that for continuous recording and
reproduction of large amount of data, a faster access is possible
to a spiral data track rather than to a concentric data track. It
is assumed here that a greater amount of data than recordable on
one track for one round of a magnetic disc is to be recorded on the
magnetic disc. If the magnetic disc has data tracks formed
concentrically thereon, data for one data track is first recorded,
and then the magnetic head is moved to a next data track for
recording the rest of the data. On the contrary, if the magnetic
disc has a data track formed spirally thereon, data can be
continuously recorded on the track without the necessity of moving
the magnetic head from one track to another as in the magnetic disc
having the concentric data tracks.
[0015] Also in a magnetic disc having concentric data tracks, a
time required for the magnetic head to move from one to a next of
the concentric data tracks formed on the magnetic disc varies and
it is difficult to assure that the magnetic head can be moved from
one to another track within a predetermined time. Therefore, a
magnetic disc having such concentric data tracks is not so much
suitable for recording and reproducing an information which should
be real-time or continuously recorded or reproduced, such as image
information, for example. A magnetic disc having a data track
formed spirally thereon is suitably usable for such a purpose.
[0016] Usually, however, a tracking servo signal is recorded
concentrically on a magnetic disc, and it is extremely difficult to
record the signal spirally on a magnetic disc. For recording or
reproducing data with respect to a magnetic disc having concentric
data tracks formed thereon, it suffices to move the magnetic head a
half track pitch when a positioning information is recorded
concentrically on the magnetic disc by means of a servo writer. For
spiral recording of the positioning information, however, it is
necessary to move the magnetic head one over tens to one over
hundreds of one track pitch. It is very difficult to attain such a
high accuracy in moving the magnetic head over the magnetic
disc.
[0017] Conventionally, data recording and/or reproduction into
and/or from a magnetic disc is thus made with respect to the
concentric data tracks formed on the magnetic disc.
SUMMARY OF THE INVENTION
[0018] Accordingly, the present invention has an object to overcome
the above-mentioned drawbacks of the prior art by providing data
recording and/or reproducing apparatus adapted to form a spiral
data track on a disc-shaped recording medium without an improved
accuracy of the conventional servo writer, and a disc-shaped
recording medium usable in the apparatus.
[0019] The above object can be accomplished by providing a data
recording and/or reproducing apparatus in which a signal recording
and/or reproducing head is scanned over a disc-shaped recording
medium on which a positioning signal to move the signal recording
and/or reproducing head to a predetermined position is recorded
along an arc of a concentric circle, comprising, according to the
present invention, a means for detecting a positioning signal
recorded along the arc, a means for detecting a circumferential
position on the disc-shaped recording medium, and a means for
calculating an amount of offset from a signal indicative of the
detected circumferential position, the calculated offset amount
being added to the positioning signal to control the head for a
scan along a spiral orbit.
[0020] Also the above object can be accomplished by providing a
disc-shaped recording medium having recorded along an arc of a
concentric circle thereon a positioning signal to move a signal
recording and/or reproducing head to a predetermined position and
also having a data track formed spirally thereon.
[0021] According to the present invention, a servo writer having a
nearly same accuracy as in the conventional ones can be used to
record a tracking servo signal and a data track be formed spirally
based on the tracking servo signal, thereby permitting to record
and/or reproduce a large volume of data at a high speed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] These objects and other objects, features and advantages of
the present intention will become more apparent from the following
detailed description of the preferred embodiments of present
invention when taken in conjunction with the accompanying drawings,
of which:
[0023] FIG. 1 is a sketch of a common disc format;
[0024] FIG. 2 illustrates the configuration of a servo zone;
[0025] FIG. 3 is a schematic block diagram of a tracking servo
system in a common magnetic disc drive, showing its major
components of the system;
[0026] FIG. 4 is a schematic block diagram of a tracking servo
system in a magnetic disc drive according to a first embodiment of
the present invention, from the detected tracking servo signal,
showing major components of the system;
[0027] FIG. 5 is an explanatory drawing of a spiral data track
orbit on the magnetic disc in the first embodiment;
[0028] FIG. 6 is a schematic block diagram of a tracking servo
system in a magnetic disc drive according to a second embodiment of
the present invention from the detected tracking servo signal,
showing major components of the system;
[0029] FIG. 7 is a schematic block diagram of a tracking servo
system in a magnetic disc drive according to a third embodiment of
the present invention from the detected tracking servo signal,
showing major components of the system;
[0030] FIG. 8 is a schematic block diagram of a tracking servo
system in a magnetic disc drive according to a fourth embodiment of
the present invention from the detected tracking servo signal,
showing major components of the system;
[0031] FIG. 9 illustrates an example of an ideal fine signal
detection characteristic;
[0032] FIG. 10 illustrates an example of a fine signal detection
characteristic of an actual magnetic disc drive;
[0033] FIG. 11 illustrates, by way of example, a disc format in
which semi-circular data tracks are formed according to a fifth
embodiment of the present invention; and
[0034] FIG. 12 illustrates, by way of example, a disc format in
which quarter circular data tracks are formed according to a sixth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Prior to proceeding to a detailed description of the
preferred embodiments of the present invention, the principle of
the present invention will be discussed herebelow in comparison
with the prior art for a better understanding of the present
invention.
[0036] According to the present invention, a conventional servo
writer adapted to record on a magnetic disc a tracking servo signal
under which a magnetic head is moved about a half track pitch at
each time, can be used to record on each of concentric data tracks
formed on the magnetic disc a servo signal including a tracking
servo signal under which a data track is formed spirally on the
magnetic disc.
[0037] To this end, an information indicative of a circumferential
position on the magnetic disc is recorded beforehand in a part of
the tracking servo signal. By reproducing this information, it is
possible to know a relative angle 0 (radian) from a
disc-circumferential reference point at a position where the
magnetic head exists.
[0038] Of the tracking servo signal, a track address may be
regarded as an integer part of a radius of the magnetic disc, and a
fine signal as a decimal part of the radius. Therefore, under an
assumption that a track address provided by reproducing the
tracking servo signal is a and a fine signal is f
(-0.5<f<0.5), the radial position of the magnetic head can be
expressed as follows:
r=a+f (1)
[0039] Generally in the conventional apparatus, the magnetic head
is subjected to such a tracking servo control that a signal of zero
is obtainable from the fine signal, namely,
r=a (2)
[0040] On the contrary, the magnetic head is subjected to such a
tracking servo control that the radial position thereof is as
follows:
r'=a+.theta./2.pi. (3)
[0041] Thus, when the magnetic disc is rotated one around, a spiral
data track is formed which is offset one track pitch from the
preceding one.
[0042] Assume here that a magnetic disc has a number n of servo
zones and a number m of servo zones from a circumferential
reference point under data reproduction. Then, a following relation
can be obtained:
r'=a+m/n (4)
[0043] Therefore, no complicated calculation is required for
formatting the magnetic disc.
[0044] More particularly, the present invention permits to use a
servo writer having a nearly same accuracy as that of the
conventional servo writer to record a tracking servo signal under
which a data track can be formed spirally on a magnetic disc,
thereby permitting to record and/or reproduce a large amount of
data at a high speed.
[0045] To implement the above, the data recording and/or
reproducing apparatus (magnetic disc drive) according to the
present invention uses a magnetic disc formatted so that servo
zones and data zones are formed alternately as illustrated in FIG.
1. The servo zone in the disc format has a detail configuration as
illustrated in FIG. 2. As seen from FIG. 2, one round of the
magnetic disc includes tens to hundreds of servo zones. Of the
servo zones, a certain one (or some) has recorded in a track
address recording zone a special pattern indicative of a
disc-circumferential reference point (will be referred to as "home
index" hereafter). When reproduced, the special pattern reveals the
position of the home index.
[0046] FIG. 4 shows the configuration of a tracking servo system
consisting of major components in a magnetic disc drive according
to the first embodiment of data recording and/or reproducing
apparatus of the present invention. It should be noted that other
than the configuration of the tracking servo system is not
illustrated in FIG. 4.
[0047] As illustrated in FIG. 4, a signal reproduced from a
magnetic disc 21 by a reproducing or magnetic head (will be
referred to simply as "head" hereinafter) 40 is amplified by a
reproduction amplifier 25, and then converted to a digital signal
by an A/D converter 26. From this digital signal, a track No.
detector 27 detects a track No. while a fine signal detector 29
detects a fine signal. These track No. and fine signals are
extracted as the tracking servo signals. When the fine signal is
reproduced, a value of 0 is provided when the head 40 is positioned
in the center of a data track, for example, and a value of .+-.0.5
is provided when the head 40 is offset .+-.1/2 of one track pitch
from the center of the data track.
[0048] A current position calculator 28 is provided to calculate a
radial position of the head 40 from the detected tracking servo
signal, and a value indicative of the radial position is passed to
a positional difference calculator 41.
[0049] Further, a circumferential position detector 30 is provided
to detect, from the digital signal delivered from the A/D converter
26, how many servo zones have been counted from the disc
circumferential reference point. To this end, the circumferential
position detector 30 comprises a home index detector and a counter
which counts servo zones over which the head 40 has moved after
passing by the home index.
[0050] An offset calculator 31 is provided to calculate an offset
amount from the current servo zone No. Under an assumption that a
number of servo zones per round of the magnetic disc is m and the
current servo zone No. is n (0<n<m), the offset calculator 31
calculates the offset amount using the following relation:
Offset=n/m-0.5 (5)
[0051] The offset amount calculated by the offset calculator 31 is
supplied to the positional difference calculator 41.
[0052] The positional difference calculator 41 is also supplied
with a signal indicative of a target position, and determines a
difference between a sum of the target position and offset amount
and the current radial position.
[0053] Also a positioning compensator 24 is provided to generate a
VCM control signal for no difference between the sum of the target
position and offset amount and the current radial position. The VCM
control signal is converted to an analog signal by a D/A converter
23, and then supplied to a VCM driver 22 which drives a VCM 20. The
voice coil motor (VCM) moves the head 40 radially over the magnetic
disc 21.
[0054] The aforementioned tracking servo system in the magnetic
disc drive according to the first embodiment of the present
invention functions as will be described herebelow with reference
to FIG. 5:
[0055] In FIG. 5, imaginary concentric circles are depicted with
solid lines. A servo signal for each track is recorded on the
magnetic disc 21 concentrically along each circle shown with the
solid line. Each of the imaginary concentric circles is depicted
with a continuous solid line, but it should be appreciated that
actual servo zones and data zones are formed alternately as
illustrated in FIG. 1. As illustrated in FIG. 5, a servo signal
indicative of a track No. t given as a target position is recorded
in a concentric track indicated with a reference SPt.
[0056] The amount of offset calculated by the offset calculator 31
is -0.5 when the head 40 in a servo zone in which the home index is
just present. It will increase as the magnetic disc 21 rotates, and
becomes zero when the magnetic disc 21 has rotated a half round
from the home index. As the magnetic disc 21 further rotates, the
offset amount will be about +0.5 when the head 40 comes in a servo
zone just before a next home index.
[0057] The amount of offset is added to the target position for
positioning the head 40 so that when the magnetic disc 21 has
rotated one turn, the head 40 will move across one track obliquely
for a servo signal recorded concentrically. Namely, the head 40
will delineate a spiral scanning orbit TL as indicated with a
dashed line in FIG. 5.
[0058] When the head 40 comes to a servo zone in which a next home
index exists, a track No. t+1 is given as a target position, so
that the head 40 will be positioned along a continuous spiral
scanning orbit.
[0059] By recording or reproducing data while positioning the head
40 as in the above, a spiral data track can be formed in a data
zone.
[0060] It should be appreciated that the signal processing by the
offset calculator 31, current position calculator 28, positional
difference calculator 41 for calculation of a difference between a
target position and a current position, positioning compensator 24,
etc. as in FIG. 4 can be done by a software called "Digital Signal
Processor (DSP)".
[0061] As having been described in the foregoing, the first
embodiment of the present invention permits to record a tracking
servo signal using a servo writer having a generally same accuracy
as the conventional one, that is to say, a servo writer which
provides a tracking servo signal to move the head a half track
pitch, form a data track spirally based on the tracking servo
signal, and thus record or reproduce a large amount of data at a
high speed.
[0062] In the first embodiment, the head is continuously moved from
the inner toward the outer circumference of the magnetic disc, for
example, while the head is under tracking. Therefore, in case
recording, for example, of a certain amount of data is followed by
a slight idling time before a next data is transmitted from a host
computer, and then followed by recording of remaining data in a
data track next to a one where the data has been recorded, that is
to say, when an intermittent recording is done, the head will have
moved continuously along the spiral data track orbit toward the
outer circumference. Therefore, a seek operation for return to a
position where the recording is complete, is required.
[0063] To meet the above requirement, the second embodiment of the
present invention further comprises a hold circuit 32 as
illustrated in FIG. 6, in addition to the major components shown in
FIG. 4. Thus, it is also possible to change or hold an amount of
offset depending upon whether the apparatus is recording or
reproducing data or idling. It should be noted that in FIG. 6, same
components as in FIG. 4 are indicated with same references and they
will not be further described.
[0064] In the second embodiment, when an operation-mode designate
signal supplied from a host computer, for example, indicates that a
data recording or reproduction is in progress, an offset amount as
in the first embodiment is added to a target position by the hold
circuit 32. Thus, the head 40 is spirally tracked during the data
recording or reproduction.
[0065] On the contrary, when the operation-mode designate signal
indicates an idling for no data recording or reproduction, the hold
circuit 32 holds an offset amount against changing. Thus, during
the idling, the head 40 is tracked concentrically and thus stays
continuously at a same radius on the magnetic disc 21.
[0066] As having been described in the foregoing, the second
embodiment of he present invention permits to prevent the head from
moving along the spiral data track orbit during suspension of an
intermittent data recording or reproduction, thereby making it
unnecessary, for resuming the interrupted recording or
reproduction, to return the head to a position where the recording
or reproduction has been interrupted.
[0067] Therefore, the recording or reproduction once suspended can
be resumed quickly, that is to say, a speedy access is possible to
a desired data track.
[0068] For continuous recording or reproducing a large amount of
data, a spiral data track is advantageous in that speedy access to
a data track. According to the present invention, however,
concentric data tracks can be formed for the purpose of frequent
intermittent recording or reproducing a relatively small data such
as character information.
[0069] FIG. 7 illustrates an example of the configuration of the
third embodiment which can implement the above. It should be noted
that in FIG. 7, same components as in FIG. 5 are indicated with
same references and they will not be further described.
[0070] According to this embodiment, the magnetic disc drive is
adapted to form on a magnetic disc 21 a zone in which concentric
data tracks are formed and a zone in which a spiral data track is
formed. For this purpose, the magnetic disc drive further
comprises, in addition to the major components shown in FIG. 4, a
concentric/spiral switching circuit 33, and a switch 35.
[0071] The concentric/spiral switching circuit 33 selects which is
to be formed on the magnetic disc 21 concentric data tracks or a
spiral data track. The switch 35 is turned on or off, under a
select signal supplied from the concentric/spiral switching circuit
33, to supply or not an offset amount from the offset calculator 31
to the positional difference calculator 41.
[0072] To form a spiral data track, for example, on the magnetic
disc 21, the concentric/spiral switching circuit 33 delivers a
switch-on signal to close the switch 35 through which the offset
amount is added to the target position. Thus, the head 40 is
tracked spirally.
[0073] On the other hand, when it is intended to form concentric
data tracks on the magnetic disc 21, a switch-off signal is
supplied from the concentric/spiral switching circuit 33 to the
switch 35 which will thus be turned off so that the offset amount
will not be added to the target position. Thus, the head 40 is
tracked concentrically.
[0074] As having been described in the foregoing, the third
embodiment permits to form on a same magnetic disc 21 a spiral data
track and concentric data tracks together either of which can be
used depending on the type of an information to be recorded or
reproduced, thereby permitting an optimum run of the magnetic disc
drive.
[0075] In the first embodiment having previously been described,
the amount of offset is calculated using the following:
Offset=n/m-0.5 (6)
[0076] However, to select whether a spiral data track along which
the head 40 will be moved from the inner toward outer
circumference, or vice versa, is formed on the magnetic disc 21,
the above relation is changed as follows for use in the fourth
embodiment of the present invention:
Offset=-(n/m-0.5) (7)
[0077] FIG. 8 illustrates an example of the configuration of the
fourth embodiment which can implement the above. It should be noted
that in FIG. 8, same components as in FIG. 5 are indicated with
same references and they will not be further described
[0078] The fourth embodiment will be explained concerning an
example in which a spiral data track is formed on one of the front
and rear sides of a magnetic disc 21. A spiral data track formed on
one side being an inversion of a one formed on the other side.
[0079] The magnetic disc drive according to the fourth embodiment
illustrated in FIG. 8 further comprises, in addition to the major
components shown in FIG. 4, a sign inversion circuit 34 which is
supplied with a side designate signal from a host computer or the
like, for example. The side designate signal designates either the
front or rear side of a magnetic disc 21 where a spiral data track
is to be formed. Thus, a spiral data track can be formed on one
side of the magnetic disc 21 to be an inversion of a one that is
formed on the other side.
[0080] A spiral data track along which the head 40 is moved from
the inner toward outer circumference can be formed on the front
side, for example, of a magnetic disc 21, while a spiral data track
along which the head 40 is moved from the outer toward inner
circumference can be formed on the rear side.
[0081] Assume here that data recording is to be started at the
inner circumference of the front side of the magnetic disc 21 and
made in all data zones on the front side. In this case, the head 40
will stay at the outermost circumference of the front side of the
magnetic disc 21. With the head 40 moved to a position for reading
the rear side of the magnetic disc 21 and the sign of the offset
amount changed by the sign inversion circuit 34, the head 40 can
record data along the spiral data track while moving from the outer
toward inner circumference.
[0082] If a double head 40 consisting of two heads for the front
and rear sides, respectively, of a magnetic disc 21 is used and
both the heads are movable by a head arm while being interlocked
with each other, could be used, it will not be necessary that a
single head 40 should be moved from the front to rear side of a
magnetic disc 21, or vice versa, for reading or writing data on
each side of the, magnetic disc 21.
[0083] As having been described in the foregoing, the fourth
embodiment of the present invention permits to form a spiral data
track on the front side of a magnetic disc 21 and on the rear side
an inverted one of the spiral data track formed on the front side.
Also, if the double head 40 consisting of two heads for the front
and rear sides, respectively, of a magnetic disc 21, both the heads
being movable by a head arm while being interlocked with each
other, could be used as mentioned above, a larger amount of data
than recordable on one side of the magnetic disc 21 can be
continuously recorded onto the magnetic disc without a head seek
time which would be required for moving a single head 40 from one
magnetic disc side where data reading is complete to the other disc
side, and thus data can be recorded or reproduced at a high
speed.
[0084] In each of the aforementioned embodiments of the present
invention, a fine signal detected by the fine signal detector 29
should preferably have an ideal characteristic as shown in FIG. 9.
That is to say, it is ideal that the fine signal has a value of 0
when the reproduction or head 40 is just aligned with the data
track and it has values of .+-.0.5 when the head 40 is a half track
pitch off the track. In practice, however, as the head 40 is off,
that is to say, beyond or short of, the center of the data track
because the track pitch is not precisely coincident with the width
of the head 40 or for a similar reason, the characteristic line
will deviate from a straight line illustrated in FIG. 9, as
illustrated in FIG. 10. If the characteristic line is much off the
straight line, the radial position of the head 40 will not
accurately reflect an offset amount calculated in the manner having
been described concerning the first to fourth embodiments as the
case may be.
[0085] Take a case, for example, in which when the offset
calculator 31 provides an offset amount of 0.5 in order to position
the head 40 a half track pitch off the center of the servo signal
where near the home index, the fine signal characteristic is on the
order of 0.4 as illustrated in FIG. 10. In this case, since the
positional difference of the head 40 with respect to the target
position is not 0, no normal positioning is possible.
[0086] Therefore, no spiral data track can be formed accurately in
the spiral form in this case.
[0087] To solve the above problem, the fifth embodiment is proposed
according to which servo signals shifted a half track pitch from
one to another at every half round of the magnetic disk are
generated as illustrated in FIG. 11. For example, same servo
signals are recorded at a position of a same radius for one half
round from the home index, while for the other half round, servo
signals are recorded at a position of a radius shifted a half track
pitch from that in the former half round. The servo writer
functions to record fine signals A, B, X and Y at positions shifted
a half track pitch from one another, so that a pattern can be
easily formed in which servo signals are recorded at positions
shifted a half track pitch for each half round of a magnetic
disc.
[0088] The configuration of the apparatus for forming a spiral data
track on a magnetic disc 21 thus formatted is the same as in FIG.
4. In this embodiment, however, the offset calculator 31 calculates
an amount of offset as will be discussed below. Namely, it is
assumed now that the magnetic disc 21 has formed thereon a number m
of servo zones per round and a current servo zone number within
which the head 40 stays is n (0<n<m). Under this assumption,
an amount of offset is calculated as follows:
When n<m/2,
Offset=n/m-0.25 (8)
When n>m/2,
Offset=n/m-0.75 (9)
[0089] The tracking servo system of a magnetic disc drive working
as in the fifth embodiment functions as will be described herebelow
with reference to FIG. 11.
[0090] In FIG. 11, imaginary concentric circles are depicted by
semi-circles (two concentric semi-circles, inner and outer)
indicated with solid lines. As shown, a signal indicative of a
track No. t given as a target position is recorded on a
semi-circular track indicated with a reference SPt.
[0091] The amount of offset calculated by the offset calculator 31
is -0.25 when the head 40 is within a servo zone including the
servo index. The offset amount will increase as the magnetic disc
21 rotates. When the magnetic disc 21 has rotated a quarter round
from the home index, the amount of offset will be 0. As the
magnetic disc 21 further rotates, the amount of offset will
increase correspondingly. When the magnetic disc 21 reaches a
position just before it will have rotated a quarter round from the
home index, the offset amount will be +0.25. Furthermore, when the
head 40 is within a next servo zone, the offset amount is -0.25. As
the magnetic disc 21 rotates, the offset amount will increase as
mentioned above. When the magnetic disc 21 has rotated three
fourths of a round from the home index, the offset amount will be
0. As the magnetic disc 21 further rotates, the offset amount will
increase correspondingly. When the magnetic disc reaches a position
just before a next home index, the offset amount will be +0.25.
[0092] By adding the amount of offset to the target position as in
the above, the head 40 is positioned based on servo signals
recorded in the semi-circles (two concentric semi-circles, inner
and outer) so that it moves obliquely across one track as the
magnetic disc 21 rotates one turn. That is to say, a spiral orbit
TL will be delineated as indicated with a dashed line in FIG.
11.
[0093] Given a track No. t+1 as a target position when the head 40
has come to a servo zone including a next home index, the head 40
will be positioned along the continuous spiral orbit.
[0094] By recording or reproducing data while positioning the head
40, a full spiral data track can be formed in a data zone.
[0095] For positioning with respect to the magnetic disc on which
data is recorded in the servo format as in the fifth embodiment,
the head 40 is moved only within a range of .+-.0.25 from the track
center as evident from FIG. 11. Namely, since the head 40 is moved
only within a range of .+-.0.25 in which the offset amount changes
with a substantial linearity, a data track can be formed in an
accurately spiral form.
[0096] The fifth embodiment of the present invention has been
described concerning the example in which servo signals are
recorded in semi-circles (two concentric semi-circles, inner and
outer). With a servo writer capable of a higher resolution of the
head moving pitch, servo signals may be recorded at smaller
intervals.
[0097] As illustrated in FIG. 11, by recording servo signals on
quarter-circles (four concentric quarter-circles), for example, the
head 40 can be moved only within a range of .+-.0.125 from the
track center, so that the head 40 can be moved only within a range
in which the fine signal linearity is much better.
[0098] As having been described in the foregoing, the fifth
embodiment allows to form a spiral data track accurately since the
head 40 is moved only within a range in which the linearity is
relatively good, even if the linearity of a fine signal is not
good, for example, about .+-.0.5.
[0099] The embodiments of the present invention have been described
concerning a magnetic disc as a disc-shaped recording medium. It
should be appreciated, however, that the present invention is
applicable for an optical disc having similar concentric servo
zones to those formed on the magnetic disc as mentioned in the
foregoing.
[0100] According to the present invention, a positioning signal
recorded on an arc forming a part of a concentric circle on a
disc-shaped recording medium is detected, a circumferential
position on the disc-shaped recording medium is detected, and an
offset with respect to the positioning signal is determined from
the circumferential position signal to control the head for a scan
along a spiral orbit, thereby permitting to form a spiral data
track without a higher accuracy of the conventional servo
writer.
* * * * *