Disk drive apparatus and read error recovery method in a disk drive apparatus

12 Pages·2013·0.95 MB·English

‘ US005754355A ‘
United States Patent [191 [11] Patent Number: 5,754,355
Nakamura et al. [45] Date of Patent: *May 19, 1998
[54] DISK DRIVE APPARATUS AND READ 5,461,521 10/19‘95 Ito et al. ................................. .. 360/75
ERROR RECOVERY METHOD IN A DISK 5,527.110 6/1996 Abraham et a1. .. 360/75 X
DRIVE APPARATUS
5.537.034 7/1996 Lewis . . . . . . . . . . . . . . . . . . . . . .. 324/212
5,612,830 3/1997 Gregory et al. .................... .. 360/71 X
[75] Inventors: Takashi Nakamura. Fujisawa; Isao
FOREIGN PATENT DOCUMENTS
Yoneda; Yuji Yokoe. both of
Yokohama; Kazushi Tsuwako. 010594 4/1984 European Pat. Off. .. 360/75
Machida; F ujio Harako. Fujisawa; 0044123 4/1981 Japan .................. .. 360/75
Katsumi Suda; Michio Nakajima. 0184679 8/1987 Japan ..................................... .. 360/75
both of Sagamihara; Kenji Ogasawara. 0528472 2/1993 Japan.
Fujisawa. all of Japan
UT HER PUBLICATIONS
[73] Assignee: International Business Machines Patent Abstracts of Japan. vol. 17. No. 311. P-l556. Jun. 14.
Corporation. Armonk. NY. 1993.
IBM Technical Disclosure Bulletin. vol. 34. No. 11. Apr.
[*1 Notice: The term of this patent shall not extend 1992. pp. 217-219. Fast Otfset Recovery for Thermal Asper
beyond the expiration date of Pat. No. ity Data Recovery Procedure.
5.696.643.
Primary Examiner—Andrew L. Sniezek
[21] Appl. No.: 633,596 Attorney Agent, or Firm—Matthew J. Bussan
[22] Filed: Apr. 17, 1996 [57] ABSTRACT
[30] Foreign Application Priority Data A disk drive apparatus and read error recovery method in a
disk drive apparatus removes thermal asperities on disk
Sep. 21, 1995 [JP] Japan .................................. .. 7-242832
surfaces. A projection. such as a thermal asperity. on the
[51] Int. Cl.6 ................................................... .. G11B 15/46 recording surfaces of disks is detected when a signal trans
ducer head contacts the projection. The ?ying height of the
[52] US. Cl. .......................... .. 360/7303; 360/75: 360/53
signal transducer head is lowered. e.g.. by changing the disk
[58] Field of Search .................................. .. 360/75. 73.03.
rotation speed from the normal rotation speed in read/write
360/137. 73.01. 70. 31. 105. 109. 113.
operations or by heating a suspension having a bimetal
53. 78.04. 78.08. 78.14
element. while the signal transducer head is positioned over
[56] References Cited the detected projection on the track. The signal transducer
head strikes the projection to break the projection. This
U.S. PATENT DOCUMENTS avoids a subsequent error from being caused by the thermal
asperity.
4,635,139 H1987 Nguyen et a1. 360/25
4.669.011 5/1987 Lemke ............ .. .. 360/103
5,233,482 8/1993 Galbraith et al. ....................... .. 360/46 15 Claims, 6 Drawing Sheets
Data read opera t Inn
71
Bin
read error
nrcur
?
YES
nenmrs error to host
as hardware error.
79
Continues read process .
US. Patent May 19, 1998 Sheet 1 0f 6 5,754,355
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US. Patent May 19, 1998 Sheet 2 of 6 5,754,355
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US. Patent May 19, 1998 Sheet 3 0f 6 5,754,355
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US. Patent May 19, 1998 Sheet 4 of 6 5,754,355
Data read operation
Did
read error
occur
YES
/72
Starts error recovery
Drocess. Jr
73
Adjusts MR device /
Dias. AGC. etc.
was
error recovered
/75
Disk rotation soeed
is reduced.
l ..+
Returns to normal /
rotatlon soeed.
l 77
Re-reads data.
W85
error recovered YES
78
Reports error to host
as hardware error.
79
/ FIG. 4
Continues read DFOCESS.].'__—
US. Patent May 19, 1998 Sheet 5 0f 6 5,754,355
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May 19, 1998 Sheet 6 of 6 5,754,355
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FIG. 6B
5.754.355
1 2
DISK DRIVE APPARATUS AND READ read error occurs. a disk drive apparatus according to an
ERROR RECOVERY METHOD IN A DISK embodiment of this invention lowers the ?ying height of the
DRIVE APPARATUS signal transducer head by changing the disk rotation speed
and makes the surface of a component of the signal trans
BACKGROUND OF THE INVENTION ducer head hit a projection on the disk to scrub it away. As
one of the data recovery operations. this removes the basic
1. Technical Field
cause of the thermal asperity.
This invention relates to a disk drive apparatus and. more
This embodiment may be con?gured to use a positive
speci?cally. to a disk drive apparatus and method for elimi
pressure signal transducer head. which increases its ?ying
nating read errors on the disk surface. which are caused by
height as the disk rotation speed increases. In the positive
projections. such as thermal asperities.
pressure signal transducer head con?guration. this embodi
2. Description of the Prior Art ment lowers the ?ying height of the signal transducer head
A magnetic disk drive apparatus is an apparatus for by reducing the disk rotation speed from the normal speed
recording and reading data on the surfaces of disks through used in read or write operation. As a result. a surface of the
the use of a changing magnetic ?eld. A transducer head is signal transducer head known as the Air Bearing Surface
positioned over a speci?c position on a disk track on which (ABS) hits and scrubs a projection on the disk to break the
data is recorded. and reads or writes data on the track of the projection.
disk spinning at high speed. The head is slightly apart from
Alternatively. this embodiment may be con?gured to use
the disk surface and positioned over the speci?c track. a negative pressure signal transducer head. which decreases
Recently. a magnetoresistive (MR) head is used as a trans 20 its ?ying height as the disk rotation speed increases. In the
ducer head. The output resistance of this head changes in negative pressure signal transducer head con?guration. this
response to changes in the magnetic ?eld. This resistance embodiment lowers the ?ying height of the signal transducer
change is converted into a direct current voltage signal by head by increasing the disk rotation speed from the normal
applying a predetermined electric current to the MR head to speed in read or write operation. As a result. the ABS side
read data. 25 strikes against and scrubs a projection on the disk to elimi
A thermal asperity is a projection produced on a disk nate the projection.
which prevents the reading and writing of data on the disk In a disk drive apparatus according to another embodi
The thermal asperity may increase the temperature of the ment of this invention. a servo clock is supplied in accor
MR stripe of an MR head locally by 100° C. or more. This dance with a change of the disk rotation speed. In this
temperature rise is caused by a mechanical collision between embodiment. a servo signal recorded on the disk is read
a head area containing the MR stripe and a projection on the while the disk rotation speed is changed. and thereby accu
disk surface. Because a change in resistance of the MR head rate position control is accomplished to remove a projection.
caused by a change in the magnetic ?eld on a magnetic
Furthermore. in a disk drive apparatus according to yet
media resulting from a normal read operation is less than one
another embodiment of this invention. a birnetal element and
percent of the MR stripe’s resistance. a signal change caused 35
a heating element are attached to a head suspension. which
by a temperature rise may substantially exceed the resistance
is a mounting structure for a signal transducer head. In this
change caused by a normal read signal. preventing the
embodiment. when the heating element is heated. the
normal read of data.
birnetal element is ?exed to force the ?ying height of the
One prior approach to solve the thermal asperity problem signal transducer head lower to scrub away a projection.
with read data is. when a drastic signal change which is such as a thennal asperity.
likely to be caused by a thermal asperity occurs. to make an Other features and advantages of this invention will
appropriate modi?cation to the read signal so that it can be become apparent from the following detailed description of
used as normal read data. Another prior approach is to the presently preferred embodiment of the invention. taken
correct an erroneous read signal by using an appropriate in conjunction with the accompanying drawings.
45
error correction method. such as an error correcting code
(ECC) method. However. these approaches have disadvan BRIEF DESCRIPTION OF THE DRAWINGS
tages. First. additional hardware is required to be added FIG. 1 is a schematic diagram of a disk drive apparatus
externally. Second. large burst errors unrecoverable by using according to an embodiment of this invention.
ECCs cannot be corrected. and eventually must be treated as
FIGS. 2A. 2B and 2C are diagrams showing states of
unreadable hardware error. Thus. these prior approaches do 50
operation in a disk drive apparatus according to an embodi
not provide an adequate solution to the thermal asperity
ment of this invention.
problem.
FIGS. 3A and 3B are diagrams showing read signals in a
OBJECTS OF THE INVENTION disk drive apparatus according to an embodiment of this
55 invention.
It is an object of this invention to provide a disk drive
FIG. 4 is a ?owchart showing a data recovery method
apparatus and method whereby. when a thermal asperity is
according to an embodiment of this invention.
encountered. the projection on the disk which causes the
FIG. 5 is a block diagram showing a disk drive apparatus
thermal asperity is removed to avoid a subsequent error from
according to another embodiment of this invention.
being caused by the thermal asperity. This makes it possible
FIGS. 6A and 6B are top and side views. respectively. of
to resolve the above mentioned disadvantages of prior
a suspension structure according to yet another embodiment
thermal asperity counter measures.
of this invention.
SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED
In order to realize the above mentioned and other objects. 65 EMBODIMENT
when a drastic signal change caused by a thermal asperity is FIG. 1 shows a hard disk drive apparatus (HDD) accord
detected by the MR head for reading data. or when a data ing to an embodiment of this invention. As shown in FIG. 1.
5.754.355
3 4
the disk drive apparatus 10 comprises a disk assembly 11 set to 2060 rpm. The signal transducer head is lowered until
and hard disk controller (HDC) 30 containing a local CPU. its closest point to the disk nearly contacts the surface of the
The disk assembly 11 comprises a disk drive (spindle motor) disk. The lowered height depends on the shape and weight
14 which rotates a shaft 12 at a high speed. A cylindrical of the signal transducer head. It is desirable that an appro
support structure 16 is mounted on the shaft 12 in such a priate level is selected accordingly. When the signal trans
manner that they are concentric with each other. One or ducer head is lowered. it may remain in read mode or in the
more data storage disks for 18A. 18B are mounted on the off state. For example. approximately 100 msec after the
outer surface of the supporting structure 16 at predetermined rotation speed reduction is started. the disk is brought into a
intervals. The disks 18A. 18B rotate together with the
low speed state. kept at this speed for 2 to 3 seconds. then
supporting structure 16 as one united body when the shaft 12
returned to the normal rotation speed. After returning to the
is rotated by the disk drive 14.
normal rotation speed. the read operation is performed again
Signal transducer heads 20A. 20B. 20C. 20D are held by
and the removal of the error is checked.
access arms 22A. 22B. 22C. 22D and face each disk surface.
The data recovery operation ends with the break-011E of the
respectively. The access arms 22A. 22B. 22C. 22D are
projection. i.e.. thermal asperity. and the disk is returned to
connected to a signal transducer head drive (voice coil
its normal rotation speed. When the disk returns to the
motor) 28 through a shaft 26. The signal transducer heads
normal rotation speed. the ?ying height of the signal trans
20A. 20B. 20C. 20D are positioned at a predetermined
ducer head increases. FIG. 3B shows the read signal after the
position by rotation of the shaft 26. The disk drive 14 and
data recovery operation. The steep signal change observed in
signal transducer head drive 28 are connected to the HDC
FIG. 3Ais eliminated. indicating that the projection (thermal
30. The number of rotations and rotation speed of shaft 26
20 asperity) has been removed.
are controlled by the HDC 30. The HDC 30 can be con
An embodiment of a data recovery method for removing
nected to a host 32.
a projection (thermal asperity) according to the present
FIGS. 2A. 2B and 2C schematically show how a projec
invention is described below with reference to FIG. 4. FIG.
tion on a data recording surface of the disk is broken by
4 is a ?owchart showing an error recovery method according
contact with a positive pressure signal transducer head
25 to an embodiment of the present invention. After a read error
according to an embodiment of this invention. FIG. 2A
is detected at step 71. the data error recovery process starts
shows the state in which a signal transducer head 20
at step 72. At step 73. conventional error recovery processes.
equipped with an MR head 42 contacts a projection 52 on
for example. bias current change of the MR head. AGC gain
the disk 18 while reading data on the disk 18. The signal
transducer head 20 includes the MR head 42 and an Air adjustment. or some other error recovery processes are
performed. After the error recovery processes. the data is
Bearing Surface (ABS) 44 holding the MR head 42. The
re-read and if the data is read successfully. the operation
signal transducer head 20 is tilted with respect to the
direction of rotation by air pressure produced by the rotation exits the error recovery process routine (step 74) to return to
the normal data read operation (step 79).
of the disk. This tilt angle is called the “pitch angle." The
pitch angle increases as the number of disk rotations If the error is not corrected by these conventional steps.
35 the ?ying height of the signal transducer head is changed by
increases. It decreases as the number of disk rotations. and
therefore wind pressure. decreases. In FIG. 2A. the closest changing the disk rotation speed in accordance with this
to-disk point of the ABS 44 of the signal transducer head 20 embodiment of the invention. At step 75. the disk speed is
contacts the projection 52. reduced. for example. from 4870 rpm to 2060 rpm as
When the signal transducer head 20 is brought into mentioned above. After a predetermined period of time. for
40
example. 2 to 3 seconds. the normal rotation speed is
contact with the projection 52 as shown in FIG. 2A. the
returned (step 76). Then. at step 77. the data is re-read and
temperature of the signal transducer head 20 rises as
described earlier. and consequently. the resistance of the MR if the data is read successfully. the error recovery process
head 42 changes. and the read signal provided by the MR ends to return to the normal read operation (step 79). If the
head 42 changes drastically. FIG. 3A shows this change in data read still fails. the error is reported as a hardware error
45
the read signal. In FIG. 3A. the drastic change point 62 in the to the host (step 78) and an appropriate action. such as data
signal pattern that can be seen when the projection is write to an alternative area. is performed.
detected is caused by the temperature change of the MR An apparatus and method of another embodiment of this
head 42 and therefore ultimately by the projection 52. Such invention are described below. This embodiment uses a
a projection. as described earlier. causes a drastic change in 50 servo signal recorded on a disk to control the position of a
temperature of the head‘s MR stripe. and is often called a signal transducer head to scrub and remove a projection.
thermal asperity. A read signal produced by a thermal such as a thermal asperity.
asperity is distinct from normal data signals. Therefore. if a When an error caused by a thermal asperity is
steep read signal which is likely to be caused by a thermal encountered. the spindle motor is braked to spin-down more
asperity is detected. a data recovery operation is performed. quickly. FIG. 5 is a block diagram that shows the main
55
FIG. 2B shows the positions of the disk 18 and signal components of a disk drive apparatus of this embodiment.
transducer head 20 when the rate of disk rotation is In FIG. 5. a servo signal detected by a magnetic head 71
decreased by the data recovery operation according to an is ampli?ed by a preampli?er 72. then a peak servo signal is
embodiment of this invention. The ?ying height of the signal detected and a pulse sequence is generated by a signal
transducer head 20 is lowered and comes closer to the disk processing circuit 73. Based on this pulse sequence. a servo
18. The pitch angle becomes smaller. That is. the signal information processing circuit 74 detects a data identi?er
transducer head 20 comes nearer to a position parallel to the and generates a sample-and-hold timing. The clock used in
disk. As a result. the side of the ABS 44 of the signal this process is generated and supplied by a clock synthesizer
transducer head 20 hits the projection 52. The strike breaks 76. which generates any frequency. or by a crystal oscillator
the projection 52 as shown in FIG. 2C. 78. which generates a frequency speci?c to a crystal oscil
For example. assum'ng the disk rotation speed is 4870 lator element 77. Either clock synthesizer 76 or crystal
rpm during read/write operation. a reduced rotation speed is oscillator 78 is selected by a change-over switch 79. which
5.754.355
5 6
is activated by a local controller 75. That is. the switching is embodiment. The suspension 91 ?xed on a head arm 99
made according to a disk rotation speed. comprises of a bimetal element. that is. an element formed
Based on the servo information obtained as described of a ?rst material 92 with a higher linear thermal expansion
above. the local controller 75 controls. via a motor driver 80. coe?icient. for example SUS 303. and a second material 93
a current ?owing into a voice coil motor (VCM) 81 to with a lower linear thermal expansion coe?icient. for
control the position of the head. Speed reduction of a spindle example SUS 406. bonded together. A heating element 94 is
motor which drives a disk is accomplished by short formed on the material 93 of the suspension by printing a
circuiting a switch 83 inserted between two different phases resistance element made of a material such as carbon. The
of a spindle motor 82 to apply a brake to the spindle motor heating can be controlled by a DC voltage source 96 and a
82. Thus. the speed reduction is accomplished in a short switch 95. When the switch 95 is closed. electric current is
time. conducted through the heating element and a difference
When an error caused by a projection. such as a thermal between the linear coe?icients of the two materials causes
asperity. is detected in the disk drive apparatus shown in the suspension to ?ex. This. in turn. moves a signal trans
FIG. 5. the revolution speed of the spindle motor 82 is ducer head 97 close to a disk 98. causing the ?ying height
reduced. for example. to one half of the normal speed. In of the signal transducer head 97 to decrease.
order to reduce the speed quickly. the spindle motor 82 is In the suspension shown in FIGS. 6A and 6B. when the
braked. The braking may be accomplished by applying short heating element 94 is heated while the signal transducer
circuit between phases of the spindle motor 82 as described head 97 is over the proximity of a track on which an error
above. or by exciting the spindle motor 82 to bring it to a occurred. the bimetal element bends in the direction which
phase opposite to a normal phase. 20 moves the signal transducer head 97 closer to the surface of
The servo clock supply source is switched from the disk 98. and as a result. the ?ying height of the signal
crystal oscillator 78 to the clock synthesizer 76. The output transducer head 97 is reduced. While the ?ying height is
frequency of the clock synthesizer 76 is preset to one half of reduced. scrubbing operation is performed over the track on
the frequency of a normal servo clock. that is. the servo which the error occurred and over its proximity to remove a
clock based on the crystal oscillator 78. Thus. the servo data projection. such as a thermal asperity. After scrubbing. the
recorded on the disk. the rotation speed of which is reduced. signal transducer head 97 returns to its normal ?ying height
can be read by using the magnetic head 71. for data read/write operations. That is. the heating of the
heating element 94 is stopped. The read/Write operation is
Under the conditions allowing servo data on the disk to be
read. the magnetic head 71 is positioned over a track on retried to ensure that the projection was removed.
which an error occurs and moved forward and backward. for It will be appreciated that. although speci?c embodiments
example +l~50 tracks. from that track to make the ABS side of the invention have been described herein for purposes of
of the signal transducer head scrub away a projection. such illustration. various modi?cations may be made without
as a thermal asperity. The servo data read from the disk departing from the spirit and scope of the invention. In
during this operation enables the signal transducer head to particular. the data recovery method for an embodiment
be positioned accurately for scrubbing. After scrubbing for 35 using a positive pressure signal transducer head con?gura
a predetermined period of time. the disk rotation speed is tion is described with reference to the ?owchart shown in
returned to a normal speed. the servo clock supply source is FIG. 4. In that embodiment. the ?ying height of the signal
switched back to the crystal oscillator 78. and then a transducer head decreases as the disk rotation speed
read/wlite operation is retried. decreases. In an embodiment using a negative pressure
Because the signal transducer head performs the scrub 40 signal transducer head con?guration. on the other hand. the
bing operation while reading servo data. accurate control can disk rotation speed is increased to lower the ?ying height of
be achieved. For example. it can be moved 50 tracks inward the signal transducer head. Also. the order of error recovery
or outward from a track on which an error occurred The processes is not limited to the order shown in FIG. 4. For
movement of the signal transducer head may be controlled example. an error recovery process for an error cause which
by specifying X tracks inward or outward as the target occurs most frequently may be performed ?rst. Accordingly.
tracks. or by specifying the number of tracks to be sldpped. the scope of protection of this invention is limited only by
The signal transducer head may be moved one track for one the following claims and their equivalents.
disk rotation or several tracks for one disk rotation. We claim:
1. A disk drive apparatus which rotates a data storage disk
Since a track on which an error occurred might cause
50
and reads data on said disk using a signal transducer head
additional errors. an alternative area on the disk may be used
instead of the erroneous track by changing the address to ?oating at a ?rst ?ying height over a track on said disk. said
disk drive apparatus comprising:
ensure the reliability of subsequent data read/write opera
tions. detecting means for detecting a read error in a read signal
In yet another embodiment of this invention. a bimetal 55 output from said signal transducer head when said
element and a heating element are attached to a head signal transducer head is ?oating at said ?rst ?ying
suspension. which is a mounting structure of a signal trans height over said track‘. and
ducer head. If the disk drive apparatus detects an error. it read error recovery means. responsive to said detecting
heats the heating element on the suspension while the means detecting a read error. for recovering from said
element is in the proximity of a track on which the error read error by reducing the ?ying height of said signal
occurred. Heat from the heating element ?exes the bimetal transducer head from said ?rst ?ying height while said
element to force the signal transducer head to reduce its signal transducer head is ?oating over said track to
?ying height. While the ?ying height being reduced. the make said signal transducer head strike and break a
signal transducer head traverses the disk to scrub away a projection on said disk.
projection. such as a thermal asperity. 2. A disk drive apparatus as recited in claim 1. wherein:
65
FIGS. 6A and 6B are top and side views. respectively. of said signal transducer head includes a magnetoresistive
a suspension having a bimetal element according to this (MR) head. and said read error is caused when the