U.S. patent application number 10/924449 was filed with the patent office on 2006-03-02 for detection of fly height change in a disk drive.
Invention is credited to Yiping Ma.
Application Number | 20060044658 10/924449 |
Document ID | / |
Family ID | 35942657 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060044658 |
Kind Code |
A1 |
Ma; Yiping |
March 2, 2006 |
Detection of fly height change in a disk drive
Abstract
A method for detecting a change in fly-height comprises
measuring a baseline position error signal, measuring a position
error signal at later time, and comparing the measured change in
PES to a predetermined value. If the measured change in PES is
greater than the predetermined value, it is determined that a
decrease in fly-height has occurred. Depending on whether the disk
drive has a head cleaner or whether the PES signal changes occur
only at the certain diameter of the disk, a head cleaning is
initiated to correct the fly-height change. If no head cleaning is
necessary, a general error signal may be generated to indicate
potential drive failure.
Inventors: |
Ma; Yiping; (Layton,
UT) |
Correspondence
Address: |
IOMEGA CORPORATION
PATENT DEPARTMENT
10955 VISTA SORRENTO PARKWAY
SAN DIEGO
CA
92130
US
|
Family ID: |
35942657 |
Appl. No.: |
10/924449 |
Filed: |
August 24, 2004 |
Current U.S.
Class: |
360/31 ; 360/75;
G9B/5.144; G9B/5.145; G9B/5.23 |
Current CPC
Class: |
G11B 5/6029 20130101;
G11B 5/6005 20130101; G11B 5/41 20130101; G11B 5/455 20130101 |
Class at
Publication: |
360/031 ;
360/075 |
International
Class: |
G11B 27/36 20060101
G11B027/36; G11B 21/02 20060101 G11B021/02 |
Claims
1. A method for detecting a change in fly-height comprising:
measuring a baseline position error signal; measuring a subsequent
position error signal (PES); comparing the change in PES to a
predetermined value; and determining a decrease in fly-height if
the change in PES is greater than the predetermined value.
2. The method of claim 1, further comprising generating an error
condition upon determination of the decrease in fly-height.
3. The method of claim 1, further comprising initiating a head
cleaning procedure upon determination of the decrease in
fly-height.
4. The method of claim 1, further comprising measuring the PES at
an inner-diameter of a disk.
5. The method of claim 1, further comprising measuring a
corresponding PES for each head of a drive.
6. The method of claim 5, further comprising generating an error
condition if any of the position error signals corresponding to
each head of a drive has changed more than the predetermined
value.
7. The method of claim 6, further comprising initiating a head
cleaning upon generation of the error condition.
8. A method of initiating head cleaning in a disk drive comprising:
establishing a baseline PES; measuring a transient PES; and
calculating change in average absolute PES and initiating head
cleaning if the change in average absolute PES exceeds a
threshold.
9. The method of claim 8, wherein the PES is measured at an inner
diameter of the disk drive.
10. The method of claim 8, further comprising measuring the PES at
a plurality of different radii of the disk drive.
11. The method of claim 10, further comprising generating an error
condition and canceling the head cleaning if the change in average
absolute PES exceeds the threshold at all the plurality of
different radii.
Description
TECHNICAL FIELD
[0001] This invention relates to computer storage products, and
more particularly to detecting changes in fly height for disk
drives.
BACKGROUND
[0002] A disk drive is a data storage device that stores data in
concentric tracks on a disk. Data is written to or read from the
disk by spinning the disk about a central axis while positioning a
transducer near a target track of the disk. During a read
operation, data is transferred from the target track to an attached
host through the transducer. During a write operation, data is
transferred in the opposite direction.
[0003] During typical disk drive operation, the transducer does not
contact the surface of the disk. Instead, the transducer rides
along a cushion of air generated by the motion of the disk. The
transducer is normally mounted within a slider structure that
provides the necessary lift in response to the air currents
generated by the disk. The distance between the transducer/slider
and the disk surface during disk drive operation is known as the
"fly height" of the transducer.
[0004] The fly height is controlled by the suspension attached to
the slider and the airbearing of the slider. For magnetic purposes,
the fly height is measured as a distance between the read/write
elements and the magnetic surface. There are several conditions
that create disturbances between the airbearing and the disk
surface that can change the fly height. These conditions include
altitude, temperature, and contamination. An extreme in any of
these conditions will degrade the error rate performance of the
drive. These conditions are taken into account during the
development of the airbearing designs.
[0005] Because the transducer is held aloft during disk drive
operation, friction and wear problems associated with contact
between the transducer and the disk surface are usually avoided.
However, due to the extremely close spacing of the heads and disk
surface, any contamination of the read-write heads or disk platters
can lead to a head crash--a failure of the disk in which the head
scrapes across the platter surface, often grinding away the thin
magnetic film. For giant magnetoresistive head technologies (GMR
heads) in particular, a minor head contact due to contamination
(that does not remove the magnetic surface of the disk) could still
result in the head temporarily overheating, due to friction with
the disk surface, and renders the disk unreadable until the head
temperature stabilizes.
[0006] What is needed is a disk drive that can monitor the
fly-height and take corrective action upon the first indication of
a change in the fly-height. Preferably this monitoring would be
accomplished without adding components to the increase the cost of
the drive.
SUMMARY
[0007] A method for detecting a change in fly-height comprises
measuring a baseline position error signal, measuring a position
error signal at later time, and comparing the measured change in
PES to a predetermined value. If the measured change in PES is
greater than the predetermined value, it is determined that a
decrease in fly-height has occurred. Depending on whether the disk
drive has a head cleaner or whether the PES signal changes occur
only at the certain diameter of the disk, a head cleaning is
initiated to correct the fly-height change. If no head cleaning is
necessary, a general error signal may be generated to indicate
potential drive failure.
DESCRIPTION OF DRAWINGS
[0008] These and other features and advantages of the invention
will become more apparent upon reading the following detailed
description and upon reference to the accompanying drawings.
[0009] FIG. 1 is a diagrammatic view of an apparatus which is an
information storage system that embodies aspects of the present
invention.
[0010] FIG. 2 is a flowchart illustrating a process for determining
fly height decrease in a disk drive by monitoring the PES.
[0011] FIG. 3 is a flowchart illustrating a process for determining
fly height decrease in a disk drive by monitoring multiple
PESs.
DETAILED DESCRIPTION
[0012] In a disk drive, a position error signal (PES) is indicative
of the position of the head with respect to the center of a
particular track. Particularly, during track following, a servo
system generates the PES from the received servo information and
then uses the PES to generate a correction signal which is provided
to a power amplifier to control the amount of current through the
actuator coil, in order to adjust the position of the head
accordingly. Typically, the PES is presented as a position
dependent signal having a magnitude indicative of the relative
distance between the head and the center of a track and a polarity
indicative of the direction of the head with respect to the track
center.
[0013] A position error signal is determined by comparing the
amplitude of the signals read from neighboring bursts. The PES is
proportional to the difference between the signal amplitudes of the
neighboring bursts, divided by the sum of their signal amplitudes.
Thus, the PES represents the offset distance between the head and
track centerline as defined by the servo information embedded in
the disk. The PES is then used as part of a closed loop servo
system to correct the position of the head with respect to the
track.
[0014] FIG. 1 is a diagrammatic view of an apparatus which is an
information storage system 10, and which embodies aspects of the
present invention. The system 10 includes a receiving unit or drive
12 which has a recess 14, and includes a cartridge 16 which can be
removably inserted into the recess 14.
[0015] The cartridge 16 has a housing, and has within the housing a
motor 21 with a rotatable shaft 22. A disk 23 is fixedly mounted on
the shaft 22 for rotation therewith. The side of the disk 23 which
is visible in FIG. 1 is coated with a magnetic material of a known
type, and serves as an information storage medium. This disk
surface is conceptually divided into a plurality of concentric data
tracks. In the disclosed embodiment, there are about 50,000 data
tracks, not all of which are available for use in storing user
data.
[0016] The disk surface is also conceptually configured to have a
plurality of circumferentially spaced sectors, two of which are
shown diagrammatically at 26 and 27. These sectors are sometimes
referred to as servo wedges. The portions of the data tracks which
fall within these sectors or servo wedges are not used to store
data. Data is stored in the portions of the data tracks which are
located between the servo wedges. The servo wedges are used to
store servo information of a type which is known in the art. The
servo information in the servo wedges conceptually defines a
plurality of concentric servo tracks, which have a smaller width or
pitch than the data tracks. In the disclosed embodiment, each servo
track has a pitch or width that is approximately two-thirds of the
pitch or width of a data track. Consequently, the disclosed disk 23
has about 73,000 servo tracks. The servo tracks effectively define
the positions of the data tracks, in a manner known in the art.
[0017] Data tracks are arranged in a concentric manner ranging from
the radially innermost tracks 36 to the radially outermost tracks
37. User data is stored in the many data tracks that are disposed
from the innermost tracks 36 to the outermost tracks 37 (except in
the regions of the servo wedges).
[0018] The drive 12 includes an actuator 51 of a known type, such
as a voice coil motor (VCM). The actuator 51 can effect limited
pivotal movement of a pivot 52. An actuator arm 53 has one end
fixedly secured to the pivot 52, and extends radially outwardly
from the pivot 52. The housing of the cartridge 16 has an opening
in one side thereof. When the cartridge 16 is removably disposed
within the drive 12, the arm 53 extends through the opening in the
housing, and into the interior of the cartridge 16. At the outer
end of the arm 53 is a suspension 56 of a known type, which
supports a read/write head 57. In the disclosed embodiment, the
head 57 is a component of a known type, which is commonly referred
to as a giant magneto-resistive (GMR) head. However, it could
alternatively be some other type of head, such as a
magneto-resistive (MR) head.
[0019] During normal operation, the head 57 is disposed adjacent
the magnetic surface on the disk 23, and pivotal movement of the
arm 53 causes the head 57 to move approximately radially with
respect to the disk 23, within a range which includes the innermost
tracks 36 and the outermost tracks 37. When the disk 23 is rotating
at a normal operational speed, the rotation of the disk induces the
formation between the disk surface and the head 57 of an air
cushion, which is commonly known as an air bearing. Consequently,
the head 57 floats on the air bearing while reading and writing
information to and from the disk, without direct physical contact
with the disk. As stated above, the distance the head floats above
the disk is known as the "fly-height."
[0020] The drive 12 includes a control circuit 71, which is
operationally coupled to the motor 21 in the cartridge 16, as shown
diagrammatically at 72. The control circuit 71 selectively supplies
power to the motor 21 and, when the motor 21 is receiving power,
the motor 21 effects rotation of the disk 23. The control circuit
71 also provides control signals at 73 to the actuator 51, in order
to control the pivotal position of the arm 53. At 74, the control
circuit 71 receives an output signal from the head 57, which is
commonly known as a channel signal. When the disk 23 is rotating,
segments of servo information and data will alternately move past
the head 57, and the channel signal at 74 will thus include
alternating segments or bursts of servo information and data.
[0021] The control circuit 71 includes a channel circuit of a known
type, which processes the channel signal received at 74. The
channel circuit includes an automatic gain control (AGC) circuit,
which is shown at 77. The AGC circuit 77 effect variation, in a
known manner, of a gain factor that influences the amplitude of the
channel signal 74. In particular, the AGC circuit uses a higher
gain factor when the amplitude of the channel signal 74 is low, and
uses a lower gain factor when the amplitude of the channel signal
74 is high. Consequently, the amplitude of the channel signal has
less variation at the output of the AGC circuit 77 than at the
input thereof.
[0022] The control circuit 71 also includes a processor 81 of a
known type, as well as a read only memory (ROM) 82 and a random
access memory (RAM) 83. The ROM 82 stores a program which is
executed by the processor 81, and also stores data that does not
change. The processor 81 uses the RAM 83 to store data or other
information that changes dynamically during program execution.
[0023] The control circuit 71 of the drive 12 is coupled through a
host interface 86 to a not-illustrated host computer. The host
computer can send user data to the drive 12, which the drive 12
then stores on the disk 23 of the cartridge 16. The host computer
can also request that the drive 12 read specified user data back
from the disk 23, and the drive 12 then reads the specified user
data and sends it to the host computer. In the disclosed
embodiment, the host interface 86 conforms to an industry standard
protocol which is commonly known as the Universal Serial Bus (USB)
protocol, but could alternatively conform to any other suitable
protocol, including but not limited to the IEEE 1394 protocol.
[0024] As the heads 57 get dirty, the fly height decreases. The
decrease in the fly height increases the friction between the heads
57 and the disk 23, which causes the slider to get off-track, thus
increasing the PES. Therefore, monitoring the PES can be used to
indicate a change in the fly height.
[0025] FIG. 2 is a flowchart showing the process 200 for detecting
the fly height change in the present invention. The process 200
begins at a START block 205. Proceeding to block 210, the process
200 establishes a baseline PES for the drive 12. The baseline PES
represents the PES at the initial life of the disk and may be
stored in memory for comparison purposes.
[0026] Proceeding to block 215, the process 200 measures the
current PES of the drive 12. As stated above, over time the heads
57 of the drive 12 may get dirty and thereby affect the value of
the PES. The PES at block 215 may be measured at a regular
interval. Also, the PES may be measured on one or more heads 57 of
the drive. After the current PES is measured, the process 200
proceeds to block 220. In block 220, the change in the average
absolute PES is calculated by comparing the current measured PES
(or an average of a predetermined number of measured PESs) to the
baseline PES.
[0027] Proceeding to block 225, the change in the absolute PES is
compared to a threshold value. The threshold value may be selected
in a variety of manners, including being predetermined, measured,
or calculated. If the change in the absolute PES is below the
threshold value, the process 200 proceeds along the NO branch back
to block 215 to measure the next current PES at an appropriate
interval. If the change in the absolute PES is above the threshold
value, the process 200 proceeds along the YES branch to block 230
where an error condition is generated by the drive 12.
[0028] Proceeding to block 235, the process 200 determines whether
the drive 12 has a head cleaner. If the drive 12 has a head
cleaner, the process 200 proceeds along the YES branch to block 240
where a head cleaning procedure is initiated. As stated above, if
the heads 57 of the drive 12 get dirty, then the PES may be
changed. By cleaning the heads 57, the fly height should return to
normal and the PES should therefore return to a value close to the
baseline PES. After the head cleaning is initiated, or if the drive
12 is determined not to be a removable hard drive in block 235, the
process terminates in END block 245.
[0029] FIG. 3 discloses a process 300 according to an alternative
embodiment of the present invention. The process 300 begins at a
START block 305. Proceeding to block 310, the process 300 detects
the error condition generated in block 230 and then proceeds to
block 315 where the absolute changes in the PES are compared at
both the inner diameter 36 and the outer diameter 37 of the disk
23. This is accomplished by having a first baseline PES measured at
the inner diameter 36 and a second baseline PES measured at the
outer diameter 37. These first and second baseline PESs are then
compared to corresponding first and second transient PESs.
[0030] Proceeding to block 320, the changes in both PES at both the
inner diameter 36 and the outer diameter 37 are compared against
corresponding thresholds. If the change in the PES at both the
inner diameter 36 and the outer diameter 37 exceed the threshold,
the process 300 proceeds along the YES branch to block 325. In
block 325, a general error condition is generated indicating a
possible future failure of the drive. It has been discovered that
if the PES is changing due to contamination issues, the PES will be
affected at certain diameter first depending on the slider design.
Thus, if the change in both the first and second PESs exceed the
threshold, it is likely the result of another factor such as a
vibration problem.
[0031] Returning to block 320, if the change in the inner diameter
36 PES exceeds the threshold but the change in the outer diameter
37 PES does not exceed the threshold, the process proceeds along
the NO branch to block 330. In block 330, a head cleaning procedure
is initiated. A change in the inner diameter PES and not the outer
diameter PES is typically indicative of dirty heads 57. By cleaning
the heads 57, the fly height should return to normal and the PES
should therefore return to a value close to the baseline PES. After
the head cleaning is initiated, or after the general error
condition is generated in block 325, the process terminates in END
block 335.
[0032] Numerous variations and modifications of the invention will
become readily apparent to those skilled in the art. Accordingly,
the invention may be embodied in other specific forms without
departing from its spirit or essential characteristics.
* * * * *