Title: Data storage device, head positioning apparatus and head positioning method
Abstract: A data storage device that can perform a track following process even when vibrations are produced by a wide range of frequencies.
Patent Number: 6,853,512 Issued on 02/08/2005 to Ozawa
| Inventors:
|
Ozawa; Yutaka (Fujisawa, JP)
|
| Assignee:
|
International Business Machines Corporation (Armonk, NY)
|
| Appl. No.:
|
251329 |
| Filed:
|
September 20, 2002 |
Foreign Application Priority Data
| Sep 21, 2001[JP] | 2001-289307 |
| Current U.S. Class: |
360/77.02; 318/561; 318/619; 360/75; 360/77.08 |
| Intern'l Class: |
G11B 005/59.6 |
| Field of Search: |
360/77.02,75,77.04,77.08
318/560,561,608,609,610,611,615,619,634,636
|
References Cited [Referenced By]
U.S. Patent Documents
| 5550685 | Aug., 1996 | Drouin | 360/77.
|
| 5610487 | Mar., 1997 | Hutsell | 360/77.
|
| 6219196 | Apr., 2001 | Semba et al. | 360/75.
|
| 6246536 | Jun., 2001 | Galloway | 360/78.
|
| 6417982 | Jul., 2002 | Ottesen et al. | 360/77.
|
| 6574065 | Jun., 2003 | Sri-Jayantha et al. | 360/75.
|
| Foreign Patent Documents |
| 03173217 | Jul., 1991 | JP.
| |
Primary Examiner: Tran; Sinh
Assistant Examiner: Habermehl; James L
Attorney, Agent or Firm: Feece; Ronald B.
Claims
What is claimed is:
1. A data storage device comprising:
a storage medium for storing user data and servo data;
a head for writing and reading said user data at a predetermined access
location on said storage medium, and for reading said servo data;
signal output means for employing said servo data read by said head to
output a position shift signal that represents the distance the position
of said head is shifted;
a filter for receiving said position shift signal, and for obtaining an
effective gain relative to a predetermined frequency that has been set;
phase comparison means for comparing the phase of said position shift
signal with the phase of a signal output by said filter;
frequency setting means for changing said predetermined frequency based on
the comparison results obtained by said phase comparison means;
control means for, based on said position shift signal and said signal
output by said filter, generating a control signal in order to position
said head at said access location, and for outputting said control signal;
and
a motor for driving said head based on said control signal.
2. The data storage device according to claim 1, wherein said frequency
setting means changes said predetermined frequency so that said
predetermined frequency can follow said frequency of said position shift
signal.
3. The data storage device according to claim 1, wherein, when the phase of
said position shift signal is not substantially shifted away from the
phase of said signal output by said filter, said frequency setting means
reduces said predetermined frequency.
4. The data storage device according to claim 1, wherein, when the phase of
said position shift signal is shifted 180.degree. away from the phase of
said signal output by said filter, said frequency setting means increases
said predetermined frequency.
5. A data storage device comprising:
a disk medium on which multiple tracks are formed;
a head for performing a seek for said disk medium and for accessing a
target track;
an actuator for receiving a control current, and for moving and positioning
said head above said target track; and
a controller for outputting said control current under feedback control,
wherein said controller outputs said control current to which a signal is
added that has a vibration attenuation function at a predetermined set
frequency, and
wherein said controller sets said predetermined frequency based on a phase
relationship between a signal indicating a deviation of said head relative
to said target track, and a preceding signal that has a vibration
attenuation function.
6. The data storage device according to claim 5, wherein, when there is a
predetermined deviation of said head relative to said target track, said
controller sets said predetermined frequency based on said phase
relationship between said signal indicating said deviation of said head
relative to said target track and said preceding signal that has said
vibration attenuation function.
7. The data storage device according to claim 5, wherein said controller
sets said predetermined frequency based on said phase relationship, so
that said predetermined frequency matches or is set close to the frequency
of said signal indicating said deviation of said head relative to said
target track.
8. A positioning apparatus for employing an actuator to locate a
positioning object at a target position on an access object comprising:
signal output means for outputting a deviation signal that indicates a
deviation from said target position by said positioning object;
control means for, based on a deviation signal output by said signal output
means, outputting to said actuator a control signal that ensures said
positioning object follows said target position, and for controlling the
position of said positioning object; and
a digital peak filter for setting a predetermined frequency, or a frequency
band including said predetermined frequency, and for filtering said
received deviation signal and outputting a signal indicating the filtering
results,
wherein said control means outputs said control signal with said signal
output by said digital peak filter, and
wherein said digital peak filter increases or decreases said predetermined
frequency of a preceding output signal in accordance with a phase
difference between said preceding output signal and said deviation signal,
and employs the obtained predetermined frequency to perform filtering.
9. The positioning apparatus according to claim 8, wherein, when said phase
difference is substantially 0, said digital peak filter decreases said
predetermined frequency of said preceding output signal; and wherein, when
said phase difference is substantially 180.degree., said digital peak
filter increases said predetermined frequency of said output signal and
employs a newly obtained predetermined frequency to perform filtering.
10. The positioning apparatus according to claim 8, wherein said access
object is a data storage medium on which multiple tracks for the storage
of user data are concentrically formed; and wherein said positioning
object is a head for reading user data from said track or for writing user
data to said track.
11. The positioning apparatus according to claim 8, wherein, when a burst
pattern is formed on said data storage medium, said signal output means
outputs said deviation signal based on said burst pattern read by said
head.
12. A positioning method, for employing a deviation signal that indicates
the deviation of a positioning object relative to a target position on a
rotary disk to ensure said positioning object follows said target
position, comprising the steps of:
comparing the phase of said deviation signal, which indicates said
deviation of said positioning object from said target position, and the
phase of a filtering signal, which is obtained by filtering said deviation
signal at a predetermined frequency or in a frequency band including said
predetermined frequency;
employing the obtained relationship between said phase of said deviation
signal and said phase of said filtering signal to increase or decrease
said preceding predetermined frequency; and
adding a filtering signal at the resultant frequency to a control signal
that ensures said positioning object follows said target position.
13. The positioning method according to claim 12, wherein said relationship
is defined by matching or not matching said phases of said deviation
signal and said filtering signal.
14. The positioning method according to claim 12, wherein said filtering is
performed by a digital peak filter.
15. The positioning method according to claim 12, wherein said disk is a
magnetic disk for a hard disk drive; and wherein said positioning object
corresponds to a magnetic head for reading data from tracks that are
concentrically formed on said magnetic disk.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a data storage device such as a hard disk
drive, and in particular to an apparatus and a method for positioning a
head at a target position.
2. Background Art
A hard disk drive has magnetic heads for reading data from a magnetic disk,
or for writing data thereto. These magnetic heads are mounted on an
actuator mechanism that is driven by a VCM (Voice Coil Motor). When a
magnetic head reads or writes data, the actuator mechanism is driven and
moves and positions the magnetic head above a predetermined track. For the
moving and the positioning of the magnetic head at a predetermined
location, servo data recorded on the magnetic disk is employed.
On a magnetic disk, such as one in a hard disk drive, multiple data tracks
are concentrically formed, and identification data and a burst pattern are
stored in advance in the direction of the diameter of the disk. The
identification data represents the track addresses of the data tracks, and
based on the identification data read by a magnetic head, the rough
position of the magnetic head, i.e., the position of a magnetic head
relative to a data track, can be determined. A burst pattern includes
multiple burst pattern arrays wherein signal storage areas, the phases of
which differ, are arranged at predetermined intervals in the direction of
the diameter of the disk. A signal output by a magnetic head in accordance
with a burst pattern can be employed to detect even a slight position
shift of the magnetic head, i.e., a deviation wherein the position of the
magnetic head is shifted away from a data track relative to the magnetic
head.
To read data from or write data to a magnetic disk, first, while the
magnetic disk is rotating, identification data read from the magnetic head
is employed to determine the rough position of the magnetic head, and the
magnetic head is driven to move it to a specific data track. Then, a
signal output by the magnetic head in accordance with the burst pattern is
employed to precisely position the magnetic head relative to the specific
data track. Finally, data can be read from or written to the magnetic
disk. This process sequence is called a seek mode. Further, the feedback
control is performed so that even during the reading or writing of data,
based on a signal that is output by the magnetic head in accordance with
the burst pattern, the magnetic head can be positioned at a constant
location relative to a specific data track. This operation is called a
following mode.
In a hard disk drive, a magnetic disk is so provided that it encircles the
outer circumference of a spindle that is rotated by a motor. However, due
to manufacturing errors, the center of such a magnetic disk tends to be
slightly eccentric relative to the rotational center of the spindle. This
eccentricity can serve as a feedback control system disturbance that
governs the positioning of the magnetic head at a constant location
relative to a specific data track.
Specifically, the feedback control system defines, as a feedback element, a
signal that is output by the magnetic head in accordance with the burst
pattern, and employs the position of the magnetic head relative to a data
track, which is obtained from this signal, and a deviation signal, which
represents the deviation from the target position of the magnetic head, to
generate and output a control signal that matches the positioning of the
magnetic head with the target. In this manner, the feedback control system
determines the positioning of the magnetic head. However, even when the
positioning of the magnetic head can match the target position, because of
the above described eccentricity, a disturbance (a repeatable run out,
hereinafter referred to as an RRO) that increases the deviation is added
at every predetermined cycle. Therefore, the control by the feedback
control system can not follow the RRO, so that conventionally the shifting
from the target position of the position of the magnetic head exceeds a
permissible value. Accordingly, errors occur repetitively; for example,
part of the information read from the data track is lost, or part of the
information to be written to the data track can not be written normally.
To resolve these problems, one hard disk drive has been proposed that
employs a digital peak filter for obtaining a high gain, i.e., an
effective gain, only for an element having a specific, comparatively low
frequency (e.g., 60 Hz) that is included in a deviation signal. An input
deviation signal is input to the digital peak filter, whereat a control
signal is generated, by adding a signal produced by the digital peak
filter, and is output. For the hard disk drive, since the specific
frequency matches the frequency corresponding to an RRO occurrence cycle,
the head can follow the data track without changing the configuration of
other sections of the control system.
However, an RRO having a high frequency occurs in a hard disk drive, due
not only to the eccentricity of the center of a magnetic disk relative to
the rotational center of a spindle, but also because the bearing of the
motor that rotates the spindle is not circular. An RRO having a high
frequency becomes a problem, especially when the pitches at which data
tracks are formed on the magnetic disk are reduced (the distances are
smaller) in order to increase the data recording density of the magnetic
disk. On the other hand, when for the hard disk drive the frequency for
increasing the gain of the digital peak filter is simply increased, the
stability of the control system is deteriorated.
Further, for a notebook PC, for example, vibration sources, such as a
floppy disk drive, a CD-ROM drive, a cooling fan and a loudspeaker, are
internally provided. And in addition, depending on the environment in
which the notebook PC is used, external vibrations may be transmitted to
the hard disk drive. Thus, it is difficult to designate a frequency for
all the vibrations that may be transferred to the hard disk drive. And
therefore, while a digital peak filter for a hard disk drive may
effectively handle a specific, fixed frequency, it is impossible to
suppress the whole range of frequencies which produce vibrations that can
be conveyed to the hard disk drive.
SUMMARY OF THE INVENTION
It is one advantage of the present invention that it provides a data
storage device that can perform a track following process even when
vibrations are produced by a wide range of frequencies. It is another
object of the present invention to provide an appropriate head positioning
apparatus and head positioning method for such a data storage device.
For the present invention, the performance of a stable track following
process that employs the above described digital filter was discussed. To
stabilize the track following, a frequency set for the digital peak filter
may follow a frequency for a generated vibration or impact. For example,
for a magnetic head, a deviation signal that is known as a PES (Position
Error Signal) may be analyzed to detect a frequency. Then, only the
detected frequency need be employed to appropriately change the frequency
set for the digital peak filter. However, since an enormous number of
calculations is required to detect a frequency through the analysis of a
PES, this method, therefore, this is not a practical resolution means.
The present inventor discovered that for track following an operation using
the digital peak filter, an interesting relationship is established
between the phase of the PES and the phase of the signal output by the
digital peak filter. According to this relationship, when the phase of the
PES matches the phase of the signal output by the digital peak filter, the
frequency of the PES is slower than the signal output by the digital peak
filter, and when these phases are shifted 180.degree., the frequency of
the PES is faster than the signal output by the digital peak filter. This
relationship will now be described while referring to FIGS. 10 to 12.
The output (Fout) of the digital peak filter produced by a common Z
conversion can be represented by the equation below:
Fout=(KaZ.sup.2 -KbZ)/(Z.sup.2 -2 cos(.omega..multidot.T)Z+1),
wherein Z denotes a signal output immediately before by the digital peak
filter, and is called a state variable. Ka and Kb denote gains, and
.omega. and T denote an angular frequency and a set frequency. The
waveforms of the state variable Z and the PES are shown in FIGS. 10 to 12.
FIG. 10 is a graph showing an example wherein the frequency of the PES
matches the frequency of the state variable Z, i.e., the frequency of the
signal output by the digital peak filter. In this case, since the digital
peak filter is effective, the PES is suppressed.
FIG. 11 is a graph showing a case wherein the frequency of the PES is
slower than the frequency of the signal output by the digital peak filter.
It is apparent from this graph that the phase of the PES matches the phase
of the signal output by the digital peak filter. FIG. 12 is a graph
showing a case wherein the frequency of the PES is faster than the
frequency of the signal output by the digital peak filter. In this case,
the phase of the PES is shifted 180.degree. from the phase of the signal
output by the digital peak filter.
As is described above, when the phases of the PES and the state variable
are compared, it can be found that the frequency of the PES is slower or
faster than the frequency set for the digital peak filter. Therefore,
based on the relationship between the phases of the two signals, the
frequency set for the digital peak filter can follow the PES.
Based on the above described idea, according to the present invention, a
data storage device comprises: a storage medium for storing user data and
servo data; a head for writing and reading the user data at a
predetermined access location on the storage medium, and for reading the
servo data; signal output means for employing the servo data read by the
head to output a position shift signal that represents the distance the
position of the head is shifted; a filter for receiving a position shift
signal, and for obtaining an effective gain relative to a predetermined
frequency that has been set; phase comparison means for comparing the
phase of the position shift signal with the phase of a signal output by
the filter; frequency setting means for changing the predetermined
frequency based on the comparison results obtained by the phase comparison
means; control means for, based on the position shift signal and the
signal output by the filter, generating a control signal in order to
position the head at the access location, and for outputting the control
signal; and a motor for driving the head based on the control signal.
According to the data storage device of the invention, since the phase of
the position shift signal is compared with the phase of the preceding
signal output by the digital peak filter, the relationship of the
frequency of the filter output signal to the frequency of the position
shift signal can be obtained. That is, comparison results can be
introduced indicating that the frequency of the filter output signal is
faster or slower than the frequency of the position shift signal. Based on
the comparison results, a predetermined frequency for a new signal to be
output by the filter is appropriately changed. Of course, this change is
made for the purpose of ensuring that the predetermined frequency of the
new signal output by the filter follows the frequency of the position
shift signal. The change or the following of the predetermined frequency
of the filter suppresses the position shift of the head across a wide
frequency band.
With this arrangement, it is preferable that the frequency setting means
for the data storage device of the invention changes the predetermined
frequency so that the predetermined frequency can follow the frequency of
the position shift signal.
Further, when the phase of the position shift signal is not substantially
shifted away from the phase of the signal output by the filter, the
frequency setting means of the data storage device of the invention
reduces the predetermined frequency so it is lower than the previously set
frequency. And when the phase of the position shift signal is shifted
180.degree. away from the phase of the signal output by the filter, the
frequency setting means increases the predetermined frequency so it is
higher than the previously set frequency.
The signal (hereinafter referred to as a filter signal) output by the
digital peak filter has as a function the attenuation of the vibration of
the head. The filter signal having the vibration attenuation function is
added to a control current under feedback control. According to the
invention, the frequency set for this filter signal is changed as needed.
Therefore, in accordance with the present invention, a data storage device
comprises: a disk medium on which multiple tracks are formed; a head for
performing a seek for the disk medium and for accessing a target track; an
actuator for receiving a control current, and for moving and positioning
the head above the target track; and a controller for outputting the
control current under feedback control, wherein the controller outputs the
control current to which a signal is added that has a vibration
attenuation function at a predetermined set frequency, and wherein the
controller sets the predetermined frequency based on a phase relationship
between a signal indicating a deviation of the head relative to the target
track, and a preceding signal that has a vibration attenuation function.
For the data storage device of the invention, when there is a predetermined
deviation of the head relative to the target track, the controller sets
the predetermined frequency based on the phase relationship between the
signal indicating the deviation of the head relative to the target track
and the preceding signal that has the vibration attenuation function. For
this setting, the phase relationship is employed to match or set the
predetermined frequency close to the frequency of the signal indicating
the deviation of the head relative to the target track.
According to the invention, the following appropriate positioning apparatus
is provided for the thus arranged data storage device. According to the
present invention, a positioning apparatus for employing an actuator to
locate a positioning object at a target position on an access object
comprises: signal output means for outputting a deviation signal that
indicates a deviation from the target position by the positioning object;
control means for, based on a deviation signal output by the signal output
means, outputting to the actuator a control signal that ensures the
positioning object follows the target position, and for controlling the
position of the positioning object; and a digital peak filter for setting
a predetermined frequency, or a frequency band including the predetermined
frequency, and for filtering the received deviation signal and outputting
a signal indicating the filtering results, wherein the control means
outputs the control signal with the signal output by the digital peak
filter, and wherein the digital peak filter increases or decreases the
predetermined frequency of a preceding output signal in accordance with a
phase difference between the preceding output signal and the deviation
signal, and employs the obtained predetermined frequency to perform
filtering.
According to the positioning apparatus of the invention, when the phase
difference is substantially 0, the digital peak filter decreases the
predetermined frequency of the preceding output signal. And when the phase
difference is substantially 180.degree., the digital peak filter increases
the predetermined frequency of the output signal and employs a newly
obtained predetermined frequency to perform filtering. For the positioning
apparatus of the invention, the access object is a data storage medium on
which multiple tracks for the storage of data are concentrically formed,
and the positioning object is a head for reading data from a track or for
writing data to a track. When a burst pattern is formed on the data
storage medium, the signal output means outputs the deviation signal based
on the burst pattern read by the head.
According to the invention, the following positioning method is provided
for the data storage device and the positioning apparatus described above.
The positioning method, for employing a deviation signal that indicates
the deviation of a positioning object relative to a target position on a
rotary disk to ensure the positioning object follows the target position,
comprises the steps of: comparing the phase of the deviation signal, which
indicates the deviation of the positioning object from the target
position, and the phase of a filtering signal, which is obtained by
filtering the deviation signal at a predetermined frequency or in a
frequency band including the predetermined frequency; employing the
obtained relationship between the phase of the deviation signal and the
phase of the filtering signal to increase or decrease the preceding
predetermined frequency; and adding a filtering signal at the resultant
frequency to a control signal that ensures the positioning object follows
the target position.
According to the positioning method of the invention, the relationship is
defined by matching or not matching the phases of the deviation signal and
the filtering signal. When the phases are not matched, the phase
difference is 180.degree..
According to the present invention, the filtering is performed by a digital
peak filter. The positioning method of the invention can be applied for a
hard disk drive, and in this case, the disk of the invention is a magnetic
disk for the hard disk drive, and the head of the invention corresponds to
a magnetic head for reading data from tracks that are concentrically
formed on the magnetic disk.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram showing the essential configuration of a hard
disk drive according to one embodiment of the present invention.
FIG. 2 is a conceptual diagram showing the contents stored on a magnetic
disk according to the embodiment.
FIG. 3 is a conceptual diagram showing the contents stored on the magnetic
disk according to the embodiment.
FIG. 4 is a diagram showing the structure of an MPU/HDC according to the
embodiment.
FIG. 5 is a diagram showing the structure for the feedback control in a
seek mode.
FIG. 6 is a diagram showing the structure for the feedback control in a
settling mode.
FIG. 7 is a diagram showing the structure by which feedback control is
provided for a following mode.
FIG. 8 is a flowchart showing the processing performed to set a frequency
for a digital peak filter in a following mode.
FIG. 9 is a graph showing the relationship between the frequency of a
vibration provided for the hard disk drive and the accuracy for following
the target position at each frequency.
FIG. 10 is a graph showing, for comparison, the waveforms of a state
variable Z and a PES in the feedback control.
FIG. 11 is a graph showing, for comparison, the waveforms of the state
variable Z and the PES in the feedback control.
FIG. 12 is a graph showing, for comparison, the waveforms of the state
variable Z and the PES in the feedback control.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The preferred embodiment of the present invention will now be described in
detail by employing a hard disk drive as an example.
FIG. 1 is a block diagram showing the essential portion of a hard disk
drive 1. The hard disk drive 1 is a data storage/reproduction apparatus
wherein a magnetic head 4 performs a seek operation for a magnetic disk 2
that is driven by a spindle motor 3, and remains at a predetermined track
(position) to write data to or to read data from the magnetic disk 2. A
single or a plurality of magnetic disks 2 can be mounted, as needed,
within the hard disk drive 1, but in this embodiment, only one magnetic
disk 2 is so employed.
When the hard disk drive 1 is driven, the magnetic disk 2 is rotated at the
spindle shaft of the spindle motor 3, and when the hard disk drive 1 is
inactive, the magnetic disk 2 is halted (is stationary). As is shown in
FIG. 2, on each recording face of the magnetic disk 2, multiple position
detection data storage areas 30 are formed radially in the direction of
the diameter of the magnetic disk 2, and the remaining areas are defined
as data track areas 32. In FIG. 3, part of the position detection data
storage area 30 and the data track area 32 are shown. Multiple data tracks
are formed concentrically at set pitches in the data rack area 32, and
part of these tracks, i.e., data tracks 34A, 34B, 34C and 34D, are shown
in FIG. 2. The magnetic head 4, which will be described later, reads or
writes data along each data track 34 in the circumferential direction
(direction indicated by an arrow A in FIG. 3) of the magnetic disk 2.
A track identification data storage area 30A and a burst pattern storage
area 30B are formed in the position detection data storage area 30. In the
track identification data storage area 30A, track identification data,
which represents the track address of each data track 34 by using a Gray
code (cyclic binary code), is stored in consonance with each data track
34. Further, a burst pattern is formed in the burst pattern storage area
30B. As is shown in FIG. 3, the burst pattern consists of four burst
pattern arrays A to D wherein signal storage areas (hatched portions in
FIG. 3) are arranged in the direction in which the data tracks 34 are
positioned, i.e., in the direction of the diameter of the magnetic disk 2.
For the individual signal storage areas constituting each burst pattern
array, the size of the signal storage area and the interval between the
adjacent areas in the direction of the diameter of the magnetic disk 2 are
equal to the pitch P of the data tracks 34.
The signal storage areas 30a of the burst pattern array A, and the signal
storage areas 30b of the burst pattern array B are arranged in a zigzag
shape in the direction of the diameter of the magnetic disk 2. The sides
at both ends of each area in the direction of the disk diameter correspond
to the widthwise center portion of a data track 34, and the burst pattern
arrays A and B are formed by storing a signal in each area. The signal
storage areas 30c of the burst pattern array C and the signal storage
areas 30d of the burst pattern array D are also arranged in a zigzag shape
in the direction of the diameter of the magnetic disk 2. Further, the
sides at both ends of each area in the direction of the disk diameter
correspond to boundaries between the data tracks 34, and the burst pattern
arrays C and D are formed by storing a signal in each area.
At the distal end of an actuator 5, the magnetic heads 4 are held in
consonance with the obverse and reverse faces of the magnetic disk 2. The
magnetic head 4 reads data from and writes data to the magnetic disk 2,
and also reads servo data from the magnetic disk 2. The magnetic head 4 is
moved with the actuator 5 in the radial direction of the magnetic disk 2.
A lamp (not shown) is located outside the magnetic disk 2 and is retracted
when the magnetic head 4 is not driven.
A read/write circuit 11 performs data reading/writing. That is, write data
transferred by a host computer via an MPU/HDC 12 is converted into a write
signal (current), and the write signal is transmitted to the magnetic head
4. Based on the write current, the magnetic head 4 writes data to the
magnetic disk 2. Further, the magnetic head 4 converts a signal (current)
read from the magnetic disk 2 into digital data, and outputs the digital
data to a host computer via the MPU/HDC 12. The servo data is also
included in the digital data.
The actuator 5 is driven by a voice coil motor (VCM) 6, and it can
therefore be said that the VCM 6 drives the magnetic head 4. The VCM 6 is
constituted by a movable element having as an element a coil and as an
additional element a fixed element having a permanent magnet. When a
predetermined current is supplied to the coil by a VCM driver 8, the
movable element is driven and the magnetic head 4 is moved to, or halted
at, a predetermined position on the magnetic disk 2.
The MPU/HDC 12 determines the position of the magnetic head 4 based on a
signal received from the read/write circuit 11, employs the deviation
between the determined position of the magnetic head 4 and the target
position thereof to generate, in a manner that will be described later, a
control signal for controlling the positioning of the magnetic head 4, and
outputs the control signal to the DAC 7 connected to the MPU/HDC 12. That
is, the control signal is a motor current control signal for controlling a
current that flows across the voice coil of the VCM 6. The detailed
operation of the MPU/HDC 12 will be described later.
The DAC 7 converts the control current received from the MPU/HDC 12 into an
analog signal (voltage signal), and outputs it to a VCM driver 8.
The VCM driver 8 converts the voltage signal received from the DAC 7 into a
drive current, and transmits the drive current to the VCM 6. A ROM 13 and
a RAM 14 are provided for the hard disk drive 1.
According to the embodiment, three modes are used for the positioning of
the magnetic head 4 of the hard disk drive 1: a seek mode, a settling mode
and a following mode. In this embodiment, in the following mode, an
innovative positioning process is performed for the magnetic head 4.
The configuration for the feedback control in the seek mode is shown in
FIG. 5. As is shown in FIG. 5, the seek mode is the feedback velocity
control that makes the current velocity of the magnetic head 4 follow the
target velocity. In FIG. 5, u(n) indicates a current positioning control
(DAC out) that is output to the DAC 7 in the seek mode.
The structure of the feedback control in the settling mode is shown in FIG.
6. As is shown in FIG. 6, the settling mode provides position-velocity
control for the feedback for the distance between the current position of
the magnetic head 4 and the target position, and the current velocity. In
FIG. 6, u(n) indicates the control current DAC out that is output to the
DAC 7 in the settling mode.
An explanation will now be given for the feedback control in the following
mode. FIG. 4 is a functional block diagram showing a control system that
implements the functions of the MPU/HDC 12 by which, while the magnetic
head 4 is reading or writing data, the position of the magnetic head 4 is
controlled so as to follow a predetermined position corresponding to each
data track 34 (in order to perform the following operation).
A signal is output by the read/write circuit 11 to a current head position
calculator 122 and a burst pattern detector 123. Based on the received
signal, the burst pattern detector 123 determines whether the magnetic
head 4 corresponds to the burst pattern storage area 30B, and outputs the
determination results to the current head position calculator 122. When
the burst pattern detector 123 determines that the magnetic head 4
corresponds to the burst pattern storage area 30B, the current head
position calculator 122 fetches a signal output by the read/write circuit
11, and employs this signal to calculate and output the position (the
current position of the magnetic head 4) to which the magnetic head 4
corresponds along the diameter of the magnetic disk 2. Therefore, the
current head position is periodically output by the current head position
calculator 122.
A target head position setting unit 125 sets and outputs the target
position for the magnetic head 4 in the direction of the diameter of the
magnetic disk 2. When the center position of a gap corresponding to the
read element of the magnetic head 4 is longitudinally shifted from the
center of a gap corresponding to the write element, the target head
position setting unit 125 sets and outputs a different value for the
target position for the magnetic head 4 for the reading of data from and
the writing of data to the data track 34 (e.g., for the data reading, a
value whereat the center of the gap of the read element matches the center
of the data track 34, or for the data writing, a value whereat the center
of the gap of the write element matches the center of the data track 34).
The current head position output by the current head position calculator
122, and the target head position output by the target head position
setting unit 125 are transmitted to a head position signal generator 124.
The head position signal generator 124 compares the current head position
with the target head position, and outputs a head position signal y(n)
that represents the size and direction of the deviation of the current
head position from the target head position (to which side the current
head position is shifted from the target head position, either the inner
side or the outer side). The head position signal y(n) stands for a PES.
The head position signal y(n) is transmitted to a main controller 121. FIG.
7 is a conceptual block diagram showing a process performed by the main
controller 121 based on the relationship between the input and output
effected through this process. As is shown in FIG. 7, the following mode
is a control process for adding an integrator to the settling mode. In
FIG. 7, u(n) is the DAC out that is output to the DAC 7 in the following
mode. In the following mode, as is shown in FIG. 7, a digital peak filter
20 is provided. The output Fout of the digital peak filer 20 can be
represented by the equation below.
Fout=(KaZ.sup.2 -KbZ)/(Z.sup.2 -2 cos(.omega..multidot.T)Z+1),
wherein Z denotes a signal output immediately before by the digital peak
filter 20, and is called a state variable. Ka and Kb denote gains, and
.omega. and T denote an angular frequency and a set frequency. The output
Fout is output by being added to the DAC out, which is the control signal
in the feedback control.
For the feedback control in the following mode, a comparator 21 is
provided. The comparator 21 receives a signal output immediately before by
the digital peak filter 20, and also a deviation signal PES (y(n)), and
compares the phases of these two signals. When the phase of the PES
matches the phase of the output signal of the digital peak filter 20, the
comparator 21 instructs the digital peak filter 20 to slow down the set
frequency T. And when the phase of the PES is shifted 180.degree. from the
phase of the output signal of the digital peak filter 20, the comparator
21 instructs the digital peak filter 20 to accelerate the set frequency T.
The processing in the following mode performed by the thus arranged hard
disk drive 1 will now be described while referring to the flowchart in
FIG. 8.
In the following mode, a check is performed to determine whether the PES
exceeds a predetermined value A (step S101 in FIG. 8). This is because the
method of the embodiment for following the frequency of the digital peak
filter 20 is employed only when the vibration is large.
When the PES exceeds the predetermined value A, the comparator 21
determines whether the phase of the signal output immediately before by
the digital peak filter 20 matches the phase of the PES (step S103 in FIG.
8). When the phase of the preceding signal output by the digital peak
filter 20 matches the phase of the PES, the frequency of the preceding
signal output by the digital peak filter 20 is faster than the frequency
of the PES. Therefore, the frequency T set for the digital peak filter 20
is reduced (step S107 in FIG. 8). When the phase of the preceding signal
output by the digital peak filter 20 does not match the phase of the PES,
the frequency of the preceding output signal of the digital peak filter 20
is slower than the frequency of the PES. Therefore, the frequency T set
for the digital peak filter 20 is increased (step S105 in FIG. 8). When
the phase of the preceding signal output by the digital peak filter 20
does not match the phase of the PES, the two phases are shifted 180. By
repeating this processing, the PES is adjusted so as to fall to a value
equal to or smaller than the predetermined value A.
FIG. 9 is a graph showing the relationship between the frequency
(horizontal axis) of a vibration provided for the hard disk drive 1 and
the accuracy (vertical axis) for following the target position at each
frequency. When the numerical value is small, the following accuracy is
favorable. A comparison example is one using the digital peak filter 20
that has four fixed, set frequencies T.
It is apparent from FIG. 9 that, according to the embodiment, the vibration
attenuation function is effective across the entire frequency range that
was measured, and favorable following accuracy is provided. On the other
hand, in the comparison example the following accuracy is improved for
each set frequency T, but is apparently deteriorated in the other
frequency bands.
As is described above, since the hard disk drive 1 of the embodiment
permits the frequency T set for the digital peak filter 20 to follow the
PES, the vibration attenuation function can be obtained for a vibration
across a wide frequency range. Especially in this embodiment, since the
phase of a preceding signal output by the digital peak filter 20 is
compared with the phase of the PES, the set frequency T of the digital
peak filter 20 can be changed. This is a simpler method than the one
whereby the detection of the frequency is performed by analyzing the PES.
In this embodiment, the hard disk drive 1 has been employed as the data
storage device; however, the present invention can be also applied for
another data storage device. Further, the positioning apparatus or the
positioning method of the embodiment can also be applied for an
application other than the data storage device.
As will be appreciated from the above description, the present invention
advantageously allow the head to be controlled so that in the following
mode it can follow the data track.
*
