U.S. patent application number 09/732410 was filed with the patent office on 2002-06-06 for method for detecting mechanical damage in a parking zone of a hard disk drive.
Invention is credited to Kwon, Haesung, Lee, Kangseok, Yang, Wonchoul.
Application Number | 20020067561 09/732410 |
Document ID | / |
Family ID | 24943418 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067561 |
Kind Code |
A1 |
Yang, Wonchoul ; et
al. |
June 6, 2002 |
Method for detecting mechanical damage in a parking zone of a hard
disk drive
Abstract
A method for detecting an asperity in a non-data parking zone of
a disk in a hard disk drive. The method includes the steps of
moving the heads of the disk drive adjacent to the parking zones of
the disks, and then detecting asperities in the parking zones with
a thermal asperity detection circuit.
Inventors: |
Yang, Wonchoul; (San Jose,
CA) ; Lee, Kangseok; (Cupertino, CA) ; Kwon,
Haesung; (San Jose, CA) |
Correspondence
Address: |
Ben J. Yorks
IRELL & MANELLA LLP
Suite 400
840 Newport Center Drive
Newport Beach
CA
92660
US
|
Family ID: |
24943418 |
Appl. No.: |
09/732410 |
Filed: |
December 6, 2000 |
Current U.S.
Class: |
360/25 ; 360/75;
G9B/5.024 |
Current CPC
Class: |
G11B 5/012 20130101 |
Class at
Publication: |
360/25 ;
360/75 |
International
Class: |
G11B 005/02 |
Claims
What is claimed is:
1. A hard disk drive, comprising: a disk that has a parking zone; a
spindle motor that rotates said disk; a head that is coupled to
said disk; an actuator arm that is coupled to said head; a voice
coil motor that is coupled to said actuator arm and can be
activated to move said head relative to said disk; a thermal
asperity detection circuit that is coupled to said head and can
detect an asperity on said disk; a controller that is coupled to
said voice coil motor and said thermal asperity detection circuit,
said controller causes said voice coil motor to move said head into
said parking zone so that said thermal asperity detection circuit
can detect an asperity in the parking zone.
2. The disk drive of claim 1, wherein said controller causes said
voice coil motor to move said head across said parking zone in
accordance with a seek routine.
3. The disk drive of claim 1, wherein a detection of an asperity is
stored in memory.
4. The disk drive of claim 3, wherein a location of an asperity is
stored in memory.
5. The disk drive of claim 1, wherein said thermal asperity
detection circuit includes a threshold detector.
6. The disk drive of claim 5, wherein said thermal asperity
detection circuit includes a compensation circuit.
7. The disk drive of claim 1, wherein said head includes a
magneto-resistive read element.
8. A method for detecting an asperity in a parking zone of a disk
located within a hard disk drive, comprising: rotating a disk that
has a parking zone; moving a head to the parking zone, said head
providing a signal; and detecting an asperity in the parking zone
from the signal provided by the head.
9. The method of claim 8, wherein the signal is compared with a
threshold value to determine the asperity.
10. The method of claim 8, wherein the head is moved across the
parking zone in accordance with a seek routine.
11. The method of claim 10, wherein the detection of the asperity
is stored in memory.
12. The disk drive of claim 11, wherein a location of the asperity
is stored in memory.
13. A circuit for a hard disk drive that has a head which is
coupled to a disk, the disk has a parking zone, the head provides a
signal, comprising: a controller that can move the head to the
parking zone of the disk; and, a thermal asperity detection circuit
that receives the signal from the head and can detect an asperity
in the parking zone.
14. The circuit of claim 13, wherein said controller causes the
head to move across the parking zone in accordance with a seek
routine.
15. The circuit of claim 13, wherein the detection of the asperity
is stored in memory.
16. The circuit of claim 15, wherein a location of the asperity is
stored in memory.
17. The circuit of claim 13, wherein said thermal asperity
detection circuit includes a threshold detector.
18. The circuit of claim 17, wherein said thermal asperity
detection circuit includes a compensation circuit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for detecting an
asperity on a parking zone of a disk.
[0003] 2. Background Information
[0004] Hard disk drives contain a plurality of heads that are
coupled to a number of magnetic disks. The heads can read
information by sensing the magnetic fields of the disks, and write
information by varying the magnetic fields of the disks.
Information is typically stored within data sectors that are
located on annular tracks of the disks.
[0005] The heads are typically attached to an actuator arm and a
voice coil motor. The voice coil motor can be energized to move the
heads to different tracks of the disks.
[0006] Each read/write head has an air bearing surface that
cooperates with an airflow generated by the rotating disk to create
an air bearing between the head and the disks surface. The air
bearing reduces mechanical wear between the head and the adjacent
disk surface. It is desirable to design an optimum air bearing that
will minimize mechanical wear while maximizing the magnetic
coupling between the disk and the head.
[0007] Some heads contain a magneto-resistive (MR) material that is
used to sense the magnetic field of the disks. The resistance of
the magneto-resistive material will vary linearly with variations
in the magnetic field. The magneto-resistive material is coupled to
a current source. Variations in the magnetic field of the disk will
cause a corresponding change in the magneto-resistive resistance
and the voltage sensed across the magneto-resistive element. MR
heads typically have a higher bit density than other types of disk
drive heads.
[0008] The disks may have one or more asperities that make physical
contact with the heads. The asperity may be a particle that resides
on the disk, or an irregularity in the disk surface. The contact
between the asperity and the head may cause a momentary increase in
temperature of the magneto-resistive material. The increase in
temperature will increase the resistance and corresponding voltage
sensed across the magneto-resistive element. There have been
developed thermal asperity detection circuits that will detect and
compensate for the variation in the read signal caused by contact
between the head and an asperity.
[0009] During operation of the disk drive the heads are located
adjacent to the data fields of the disks. When the disk drive is
powered down the heads may be moved to parking zones of the disks.
The parking zones are typically areas of the disks that have no
data. The disk drive may be subject to shock and/or vibration loads
that cause the heads to slap the disks. Head slapping may cause
damage to the disks and/or heads. Placing the heads in non-data
parking zones of the disks insure that data is not corrupted from a
head slapping event.
[0010] The surfaces of the disks are typically inspected with a
disk certifier before being assembled into a hard disk drive. The
disk certifier may include optical elements that are used to detect
the surfaces of the disks. The certifiers are used to detect and
possibly correct defective disks.
[0011] Sometimes an asperity is formed after the disks have been
inspected and assembled into a drive. For example, an asperity may
be formed in the parking zone of a disk during the assembly
process. The asperity may decrease the life and reliability of the
disk drive. It would be desirable to detect an asperity in the
parking zone of a disk after the disk drive has been assembled to
screen for defective products before the drive is shipped to a
customer.
BRIEF SUMMARY OF THE INVENTION
[0012] One embodiment of the present invention is a hard disk drive
which has a controller that can move a head to a parking zone of a
disk. The disk drive may include a thermal asperity detection
circuit that is coupled to the head and can detect an asperity in
the parking zone of the disk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a top view of an embodiment of a hard disk drive
of the present invention;
[0014] FIG. 2 is a schematic of an electrical system of the hard
disk drive;
[0015] FIG. 3 is a schematic of a thermal asperity detection
circuit of the electrical system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] In general the present invention provides a method for
detecting an asperity in a non-data parking zone of a disk in a
hard disk drive. The method includes the steps of moving the heads
of the disk drive adjacent to the parking zones of the disks, and
then detecting asperities in the parking zones with a thermal
asperity detection circuit.
[0017] Referring to the drawings more particularly by reference
numbers, FIG. 1 shows an embodiment of a hard disk drive 10 of the
present invention. The disk drive 10 may include one or more
magnetic disks 12 that are rotated by a spindle motor 14. The
spindle motor 14 may be mounted to a base plate 16. The disk drive
10 may further have a cover 18 that encloses the disks 12.
[0018] The disk drive 10 may include a plurality of heads 20
located adjacent to the disks 12. The heads 20 may have separate
write and read elements (not shown) that magnetize and sense the
magnetic fields of the disks 12. By way of example, the heads 20
may include magneto-resistive read elements.
[0019] Each head 20 may be gimbal mounted to a flexure arm 22 as
part of a head gimbal assembly (HGA). The flexure arms 22 are
attached to an actuator arm 24 that is pivotally mounted to the
base plate 16 by a bearing assembly 26. A voice coil 28 is attached
to the actuator arm 24. The voice coil 28 is coupled to a magnet
assembly 30 to create a voice coil motor (VCM) 32. Providing a
current to the voice coil 28 will create a torque that swings the
actuator arm 24 and moves the heads 20 across the disks 12.
[0020] The voice coil motor 32 can move the heads 20 to a parking
zone 34 of each disk 12. The parking zone 34 is an area that does
not contain any data. The heads 20 are typically moved to the
parking zones 20 when the disk drive 10 is powered down.
[0021] The hard disk drive 10 may include a printed circuit board
assembly 36 that includes a plurality of integrated circuits 38
coupled to a printed circuit board 40. The printed circuit board 38
is coupled to the voice coil 28, heads 20 and spindle motor 14 by
wires (not shown).
[0022] FIG. 2 shows a schematic of an electrical system 50 that can
control the disk drive 10. The system 50 includes a controller 52
that is connected to an input/output (I/O) buffer 54, voice coil
motor control circuit 56, spindle motor control circuit 58,
read/write channel circuit 60, memory 62 and a thermal asperity
detection circuit 64. The I/O buffer 54 provides an interface with
an external source such as a personal computer. The voice coil
control circuit 56 and spindle motor control circuit 58 contain
drivers, etc. to control the voice coil motor and spindle motor,
respectively. The voice coil motor circuit 56 and spindle motor
control circuit 58 operate in accordance with signals, commands,
etc. from the controller 52.
[0023] The controller 52 may be a processor that can perform
software routines in accordance with instructions and data. Memory
62 may include both volatile and non-volatile memory. The thermal
asperity circuit 64 can detect an asperity on the disks 12. The
thermal asperity circuit 64 can provide an output signal, command,
etc. to the controller 52 when an asperity is detected.
Additionally, the thermal asperity circuit 64 may provide the
output signal, command, etc. to the I/O buffer 54 for transmission
to an external device such as a test station.
[0024] FIG. 3 shows an embodiment of a thermal asperity circuit 64
of the present invention. The thermal asperity compensation circuit
64 includes a preamplifier 66 that is coupled to one of the heads
20. When reading data the head 20 generates a read signal that
corresponds to the magnetic field of the disk 12. The read signal
is first amplified by the preamplifier 66, and then provided to a
variable gain amplifier (VGA) 68. The amplified read signal is also
provided as one input to the noninverting terminal of a threshold
detector 70. The inverting terminal of the threshold detector 70 is
coupled to a threshold signal which is representative of a typical
level of a thermal asperity. The threshold signal may be provided
by the controller 52. The output of the threshold detector 70 is
used to control a multiplexor 72, a feedforward filter 74 and a
feedback filter 76, as described in detail in the following
sections.
[0025] The VGA 68 amplifies the read signal that is then provided
to a continuous time filter 78. The output of the VGA 68 is a
function of a gain correction signal S.sub.G of a gain tracking
loop 80 and a gain loop acquisition loop 82. In one embodiment, the
continuous time filter 78 is a 7-pole, 2-zero equi-ripple filter
for standard signal conditioning, as is known in the art. In
particular, the continuous time filter 78 limits the received
signal's bandwidth to prevent aliasing. As such, the continuous
time filter 78 is a low pass filter with a cut-off frequency that
is less than half the sampling rate of sampler 84. Continuous time
filter 78 may also provide some equalization of the analog signal.
The output of the continuous time filter 78 is provided to a
sampler 84, which samples the amplified read signal to provide a
sequence of analog samples RSAM of the amplified read signal.
[0026] Samples r.sub.SAM of the amplified read signal are also
provided to the gain loop acquisition circuit 82 and a timing loop
acquisition circuit 86. The output of the summing circuit 88 is
provided to the gain loop tracking circuit 80 and a timing loop
tracking circuit 90. A gain correction signal S.sub.G generated by
the gain loop tracking circuit 80 and the gain loop acquisition
circuit 82, is provided as a variable gain set point for the VGA
68. The timing correction signal S.sub.T generated by the timing
loop tracking circuit 90 and the timing loop acquisition circuit
86, which provides timing corrections to the sampling rate, is
provided to a phase/frequency detector 92. Phase and frequency
errors are provided to a charge pump 94 which accumulates a charge
proportional to the timing correction signal S.sub.T. In response,
the charge pump 94 outputs the accumulated charge due to timing
error as a voltage to a voltage controlled oscillator (VCO) 96. The
VCO 96 generates a signal with a corrected frequency which is used
to control the sampling frequency of the sampler 84, and which is
simultaneously fed back to the phase/frequency detector 92 for
comparison with the timing correction signal S.sub.T generated by
the timing loop tracking circuit 90.
[0027] During normal operation, the output of the sampler 84 is
directly provided to a FDTS detector 98 via multiplexor 72. The
feedforward filter 74 and the feedback filter 76 in the FDTS
detector 98 will also utilize a first set of predetermined
parameters (such as taps) for normal operation. However, when a
thermal asperity is detected by threshold detector 70, the
threshold detector 70 generates a signal to select the multiplexor
72 to multiplex the samples r.sub.TA(t).sub.SAM from a 1-D sample
filter 100, to the FDTS detector 98. The 1-D sample filter 100
first differentiates the sample stream and then removes the level
shift from the resulting sample stream. In one embodiment, the
sample filter 100 is a discrete time filter having a transfer
function of T(D)=1-D, where D is a delay factor. Depending upon
system partial response parameters, D may be vary from D.sup.2 to
D.sup.N, where N is an integer. When a thermal asperity is
encountered, the multiplexor 72 also provides a signal to the
feedforward filter 74 and the feedback filter 76 in the FDTS
detector 98, to utilize a second set of predetermined parameters
(such as taps) for processing the read signal. Samples from the
FDTS detector 98 are then generated as output signal r.sub.OUT(t).
The threshold detector 100 also provides an output that is provided
to the controller 52. The circuit shown in FIG. 3 is also disclosed
in Application No. 049,494, which is assigned to the same assignee,
and is hereby incorporated by reference.
[0028] Referring to FIGS. 1-3, in operation, the disks 12 are
rotated by the spindle motor 14 and the controller 52 may establish
a threshold parameter for the threshold detector 70. The controller
52 may then generate signals, commands, etc. to move the heads 20
to the parking zones 34 of the disks 12. The heads 20 may fly for a
predetermined time interval to insure that the system is stable.
For example, the heads may fly in the parking zone for 5 minutes.
An asperity on the disks 20 may cause a variation in the sensing
voltage of the head 20 to exceed the threshold value provided to
the threshold detector 70. The threshold detector 70 then provides
an output to the controller 52. The controller 52 may have the
detection stored in memory 62 and/or provided to the I/O buffer 54
for transmission to an external source such as a test station.
[0029] The controller 52 can further generate signals, commands,
etc. to incrementally move the heads 20 across the parking zones in
accordance with a seek routine. The thermal asperity circuit 64 can
detect asperities as the heads 20 are incrementally moved across
the parking zones. Both the presence of an asperity and the
location of the asperity may be stored in memory 62 and/or provided
to the I/O buffer 54.
[0030] The present invention thus provides a technique to detect
asperities in the parking zones of the disks 20 assembled within a
disk drive without significantly changing the disk drive 10.
[0031] While certain exemplary embodiments have been described and
shown in the accompanying drawings, it is to be understood that
such embodiments are merely illustrative of and not restrictive on
the broad invention, and that this invention not be limited to the
specific constructions and arrangements shown and described, since
various other modifications may occur to those ordinarily skilled
in the art.
* * * * *