U.S. patent application number 13/908265 was filed with the patent office on 2014-11-27 for disk drive calibrating dynamic fly height write profile for fly height actuator.
The applicant listed for this patent is Western Digital Technologies, Inc.. Invention is credited to GALVIN T. CHIA, HUANXIANG RUAN, PRADEEP K. THAYAMBALLI.
Application Number | 20140347965 13/908265 |
Document ID | / |
Family ID | 51935319 |
Filed Date | 2014-11-27 |
United States Patent
Application |
20140347965 |
Kind Code |
A1 |
RUAN; HUANXIANG ; et
al. |
November 27, 2014 |
DISK DRIVE CALIBRATING DYNAMIC FLY HEIGHT WRITE PROFILE FOR FLY
HEIGHT ACTUATOR
Abstract
A disk drive is disclosed comprising a disk and a head actuated
over the disk, the head comprising a fly height actuator (FHA). The
disk drive further comprises control circuitry including disk
access circuitry, wherein during a calibration operation, the disk
access circuitry is configured into a calibration mode that
increases a heating of the head, and a fly height of the head is
measured periodically to generate periodic fly height measurements
that vary due to the heating of the head. A dynamic fly height
(DFH) write profile is generated based on the periodic fly height
measurements. During a write operation, the disk access circuitry
is configured into a write mode and a DFH control signal is
generated and applied to the FHA based on the DFH write
profile.
Inventors: |
RUAN; HUANXIANG; (Irvine,
CA) ; THAYAMBALLI; PRADEEP K.; (Fremont, CA) ;
CHIA; GALVIN T.; (Rancho Santa Margarita, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Western Digital Technologies, Inc. |
Irvine |
CA |
US |
|
|
Family ID: |
51935319 |
Appl. No.: |
13/908265 |
Filed: |
June 3, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61825641 |
May 21, 2013 |
|
|
|
Current U.S.
Class: |
369/13.26 ;
360/31 |
Current CPC
Class: |
G11B 5/012 20130101;
G11B 5/5534 20130101; G11B 5/6029 20130101; G11B 5/455 20130101;
G11B 5/607 20130101 |
Class at
Publication: |
369/13.26 ;
360/31 |
International
Class: |
G11B 21/12 20060101
G11B021/12 |
Claims
1. A disk drive comprising: a disk; a head actuated over the disk,
the head comprising a fly height actuator; and control circuitry
including disk access circuitry, the control circuitry operable to:
during a calibration operation, configure the disk access circuitry
into a calibration mode that increases a heating of the head, and
periodically measure a fly height of the head to generate periodic
fly height measurements that vary due to the heating of the head;
generate a dynamic fly height (DFH) write profile based on the
periodic fly height measurements; and during a write operation,
configure the disk access circuitry into a write mode and generate
a DFH control signal applied to the fly height actuator based on
the DFH write profile, wherein the head further comprises a laser
operable to heat the disk during the write operation, and the
control circuitry is operable to configure the disk access
circuitry into the calibration mode by applying a write power to
the laser.
2. The disk drive as recited in claim 1, wherein the calibration
mode is the same as the write mode.
3. The disk drive as recited in claim 1, wherein the control
circuitry is operable to configure the disk access circuitry into
the calibration mode by applying a write current to a write
element.
4. (canceled)
5. The disk drive as recited in claim 1, wherein the control
circuitry is operable to generate the DFH write profile based on a
magnitude of the periodic fly height measurements.
6. The disk drive as recited in claim 1, wherein the control
circuitry is operable to generate the DFH write profile based on a
phase of the periodic fly height measurements.
7. The disk drive as recited in claim 1, wherein the control
circuitry is further operable to repeat the calibration operation
and adjust the DFH write profile until the periodic fly height
measurements substantially match a target fly height.
8. The disk drive as recited in claim 1, wherein the control
circuitry is further operable to: during the write operation,
periodically measure the fly height of the head to generate write
fly height measurements; and adjust the DFH profile based on the
write fly height measurements.
9. The disk drive as recited in claim 1, wherein the disk comprises
a plurality of servo sectors and the control circuitry is operable
to: configure the disk access circuitry into a read mode prior to
reading a first servo sector; and measure the fly height of the
head by reading data recorded in the first servo sector.
10. The disk drive as recited in claim 1, wherein: the disk
comprises a plurality of data tracks; the head comprises a read
element radially offset from a write element by at least one data
track; and during the calibration operation, the control circuitry
is operable to read data from a first data track to measure the fly
height of the head while the write element is over a second data
track.
11. The disk drive as recited in claim 10, wherein: the disk access
circuitry comprises write circuitry; and during the calibration
operation, the control circuitry is operable to read the data from
the first data track to measure the fly height of the head while at
least part of the write circuitry is enabled.
12. The disk drive as recited in claim 1, wherein prior to the
calibration operation the control circuitry is further operable to:
configure the disk access circuitry to increase the heating of the
head for a first interval; and after the first interval, configure
the disk access circuitry to decrease the heating of the head for a
second interval.
13. The disk drive as recited in claim 12, wherein the second
interval corresponds to a gap between a first write operation and a
second write operation.
14. A method of operating a disk drive comprising a disk, a head
actuated over the disk, the head comprising a fly height actuator,
and control circuitry including disk access circuitry, the method
comprising: during a calibration operation, configuring the disk
access circuitry into a calibration mode that increases a heating
of the head, and periodically measure a fly height of the head to
generate periodic fly height measurements that vary due to the
heating of the head; generating a dynamic fly height (DFH) write
profile based on the periodic fly height measurements; and during a
write operation, configuring the disk access circuitry into a write
mode and generate a DFH control signal applied to the fly height
actuator based on the DFH write profile, wherein the head further
comprises a laser operable to heat the disk during the write
operation, and the method further comprises configuring the disk
access circuitry into the calibration mode by applying a write
power to the laser.
15. The method as recited in claim 14, wherein the calibration mode
is the same as the write mode.
16. The method as recited in claim 14, further comprising
configuring the disk access circuitry into the calibration mode by
applying a write current to a write element.
17. (canceled)
18. The method as recited in claim 14, further comprising
generating the DFH write profile based on a magnitude of the
periodic fly height measurements.
19. The method as recited in claim 14, further comprising
generating the DFH write profile based on a phase of the periodic
fly height measurements.
20. The method as recited in claim 14, further comprising repeating
the calibration operation and adjusting the DFH write profile until
the periodic fly height measurements substantially match a target
fly height.
21. The method as recited in claim 14, further comprising: during
the write operation, periodically measuring the fly height of the
head to generate write fly height measurements; and adjusting the
DFH profile based on the write fly height measurements.
22. The method as recited in claim 14, wherein the disk comprises a
plurality of servo sectors and the method further comprises:
configuring the disk access circuitry into a read mode prior to
reading a first servo sector; and measuring the fly height of the
head by reading data recorded in the first servo sector.
23. The method as recited in claim 14, wherein: the disk comprises
a plurality of data tracks; the head comprises a read element
radially offset from a write element by at least one data track;
and during the calibration operation, the method further comprises
reading data from a first data track to measure the fly height of
the head while the write element is over a second data track.
24. The method as recited in claim 23, wherein: the disk access
circuitry comprises write circuitry; and during the calibration
operation, the method comprises reading the data from the first
data track to measure the fly height of the head while at least
part of the write circuitry is enabled.
25. The method as recited in claim 14, wherein prior to the
calibration operation the method further comprises: configuring the
disk access circuitry to increase the heating of the head for a
first interval; and after the first interval, configuring the disk
access circuitry to decrease the heating of the head for a second
interval.
26. The method as recited in claim 25, wherein the second interval
corresponds to a gap between a first write operation and a second
write operation.
27. A disk drive comprising: a disk; a head actuated over the disk,
the head comprising a fly height actuator; and control circuitry
including disk access circuitry, the control circuitry operable to:
during a calibration operation, configure the disk access circuitry
into a calibration mode that increases a heating of the head, and
periodically measure a fly height of the head to generate periodic
fly height measurements that vary due to the heating of the head;
generate a dynamic fly height (DFH) write profile based on the
periodic fly height measurements; and during a write operation,
configure the disk access circuitry into a write mode and generate
a DFH control signal applied to the fly height actuator based on
the DFH write profile, wherein the control circuitry is operable to
generate the DFH write profile based on a phase of the periodic fly
height measurements.
28. A method of operating a disk drive comprising a disk, a head
actuated over the disk, the head comprising a fly height actuator,
and control circuitry including disk access circuitry, the method
comprising: during a calibration operation, configuring the disk
access circuitry into a calibration mode that increases a heating
of the head, and periodically measure a fly height of the head to
generate periodic fly height measurements that vary due to the
heating of the head; generating a dynamic fly height (DFH) write
profile based on the periodic fly height measurements; during a
write operation, configuring the disk access circuitry into a write
mode and generate a DFH control signal applied to the fly height
actuator based on the DFH write profile; and generating the DFH
write profile based on a phase of the periodic fly height
measurements.
29. A disk drive comprising: a disk; a head actuated over the disk,
the head comprising a fly height actuator; and control circuitry
including disk access circuitry, the control circuitry operable to:
during a calibration operation, configure the disk access circuitry
into a calibration mode that increases a heating of the head, and
periodically measure a fly height of the head to generate periodic
fly height measurements that vary due to the heating of the head;
generate a dynamic fly height (DFH) write profile based on the
periodic fly height measurements; during a write operation,
configure the disk access circuitry into a write mode and generate
a DFH control signal applied to the fly height actuator based on
the DFH write profile; and repeat the calibration operation and
adjust the DFH write profile until the periodic fly height
measurements substantially match a target fly height.
30. A method of operating a disk drive comprising a disk, a head
actuated over the disk, the head comprising a fly height actuator,
and control circuitry including disk access circuitry, the method
comprising: during a calibration operation, configuring the disk
access circuitry into a calibration mode that increases a heating
of the head, and periodically measure a fly height of the head to
generate periodic fly height measurements that vary due to the
heating of the head; generating a dynamic fly height (DFH) write
profile based on the periodic fly height measurements; during a
write operation, configuring the disk access circuitry into a write
mode and generate a DFH control signal applied to the fly height
actuator based on the DFH write profile; and repeating the
calibration operation and adjusting the DFH write profile until the
periodic fly height measurements substantially match a target fly
height.
31. A disk drive comprising: a disk; a head actuated over the disk,
the head comprising a fly height actuator; and control circuitry
including disk access circuitry, the control circuitry operable to:
during a calibration operation, configure the disk access circuitry
into a calibration mode that increases a heating of the head, and
periodically measure a fly height of the head to generate periodic
fly height measurements that vary due to the heating of the head;
generate a dynamic fly height (DFH) write profile based on the
periodic fly height measurements; and during a write operation,
configure the disk access circuitry into a write mode and generate
a DFH control signal applied to the fly height actuator based on
the DFH write profile, wherein: the disk comprises a plurality of
data tracks; the head comprises a read element radially offset from
a write element; and during the calibration operation, the control
circuitry is operable to read data from a first data track to
measure the fly height of the head while the write element is over
a second data track.
32. The disk drive as recited in claim 31, wherein: the disk access
circuitry comprises write circuitry; and during the calibration
operation, the control circuitry is operable to read the data from
the first data track to measure the fly height of the head while at
least part of the write circuitry is enabled.
33. A method of operating a disk drive comprising a disk, a head
actuated over the disk, the head comprising a fly height actuator,
and control circuitry including disk access circuitry, the method
comprising: during a calibration operation, configuring the disk
access circuitry into a calibration mode that increases a heating
of the head, and periodically measure a fly height of the head to
generate periodic fly height measurements that vary due to the
heating of the head; generating a dynamic fly height (DFH) write
profile based on the periodic fly height measurements; and during a
write operation, configuring the disk access circuitry into a write
mode and generate a DFH control signal applied to the fly height
actuator based on the DFH write profile, wherein: the disk
comprises a plurality of data tracks; the head comprises a read
element radially offset from a write element; and during the
calibration operation, the method further comprises reading data
from a first data track to measure the fly height of the head while
the write element is over a second data track.
34. The method as recited in claim 33, wherein: the disk access
circuitry comprises write circuitry; and during the calibration
operation, the method comprises reading the data from the first
data track to measure the fly height of the head while at least
part of the write circuitry is enabled.
35. A disk drive comprising: a disk; a head actuated over the disk,
the head comprising a fly height actuator; and control circuitry
including disk access circuitry, the control circuitry operable to:
during a calibration operation, configure the disk access circuitry
into a calibration mode that increases a heating of the head, and
periodically measure a fly height of the head to generate periodic
fly height measurements that vary due to the heating of the head;
generate a dynamic fly height (DFH) write profile based on the
periodic fly height measurements; and during a write operation,
configure the disk access circuitry into a write mode and generate
a DFH control signal applied to the fly height actuator based on
the DFH write profile, wherein prior to the calibration operation
the control circuitry is further operable to: configure the disk
access circuitry to increase the heating of the head for a first
interval; and after the first interval, configure the disk access
circuitry to decrease the heating of the head for a second
interval.
36. A method of operating a disk drive comprising a disk, a head
actuated over the disk, the head comprising a fly height actuator,
and control circuitry including disk access circuitry, the method
comprising: during a calibration operation, configuring the disk
access circuitry into a calibration mode that increases a heating
of the head, and periodically measure a fly height of the head to
generate periodic fly height measurements that vary due to the
heating of the head; generating a dynamic fly height (DFH) write
profile based on the periodic fly height measurements; and during a
write operation, configuring the disk access circuitry into a write
mode and generate a DFH control signal applied to the fly height
actuator based on the DFH write profile, wherein prior to the
calibration operation the method further comprises: configuring the
disk access circuitry to increase the heating of the head for a
first interval; and after the first interval, configuring the disk
access circuitry to decrease the heating of the head for a second
interval.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to provisional U.S. Patent
Application Ser. No. 61/825,641 (Atty. Docket No. T6397.P), filed
on May 21, 2013, which is hereby incorporated by reference in its
entirety.
BACKGROUND
[0002] Disk drives comprise a disk and a head connected to a distal
end of an actuator arm which is rotated about a pivot by a voice
coil motor (VCM) to position the head radially over the disk. The
disk comprises a plurality of radially spaced, concentric tracks
for recording user data sectors and embedded servo sectors. The
embedded servo sectors comprise head positioning information (e.g.,
a track address) which is read by the head and processed by a servo
controller to control the actuator arm as it seeks from track to
track.
[0003] Data is typically written to the disk by modulating a write
current in an inductive coil to record magnetic transitions onto
the disk surface in a process referred to as saturation recording.
During readback, the magnetic transitions are sensed by a read
element (e.g., a magnetoresistive element) and the resulting read
signal demodulated by a suitable read channel. Heat assisted
magnetic recording (HAMR) is a recent development that improves the
quality of written data by heating the disk surface with a laser
during write operations in order to decrease the coercivity of the
magnetic medium, thereby enabling the magnetic field generated by
the write coil to more readily magnetize the disk surface.
[0004] FIG. 1 shows a prior art disk format 2 as comprising a
number of servo tracks 4 defined by servo sectors 6.sub.0-6.sub.N
recorded around the circumference of each servo track. Each servo
sector 6.sub.i comprises a preamble 8 for storing a periodic
pattern, which allows proper gain adjustment and timing
synchronization of the read signal, and a sync mark 10 for storing
a special pattern used to symbol synchronize to a servo data field
12. The servo data field 12 stores coarse head positioning
information, such as a servo track address, used to position the
head over a target data track during a seek operation. Each servo
sector 6.sub.i further comprises groups of servo bursts 14 (e.g., N
and Q servo bursts), which are recorded with a predetermined phase
relative to one another and relative to the servo track
centerlines. The phase based servo bursts 14 provide fine head
position information used for centerline tracking while accessing a
data track during write/read operations. A position error signal
(PES) is generated by reading the servo bursts 14, wherein the PES
represents a measured position of the head relative to a centerline
of a target servo track. A servo controller processes the PES to
generate a control signal applied to a head actuator (e.g., a voice
coil motor) in order to actuate the head radially over the disk in
a direction that reduces the PES.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 shows a prior art disk format comprising a plurality
of servo tracks defined by embedded servo sectors.
[0006] FIG. 2A shows a disk drive according to an embodiment
comprising a head actuated over a disk.
[0007] FIG. 2B shows a head according to an embodiment comprising a
fly height actuator.
[0008] FIG. 2C is a flow diagram according to an embodiment for
generating a dynamic fly height (DFH) write profile based on fly
height measurements taken during a calibration operation.
[0009] FIG. 3A shows a prior art DFH write profile comprising a
step decrement in order to compensate for a heating effect of a
write mode.
[0010] FIG. 3B shows a DFH write profile according to an embodiment
to compensate for the heating effect of the write mode.
[0011] FIG. 4 is a flow diagram according to an embodiment wherein
the calibration operation is iterated until the DFH write profile
converges.
[0012] FIG. 5 is a flow diagram according to an embodiment wherein
the DFH write profile may be adjusted during a normal write
operation.
[0013] FIG. 6 shows an embodiment wherein the DFH write profile is
phase shifted to compensate for a thermal response of the fly
height actuator.
[0014] FIG. 7 shows a head according to an embodiment comprising a
laser for heating the disk during a write operation.
[0015] FIG. 8 shows an embodiment wherein a fly height measurement
is taken at each servo sector.
[0016] FIG. 9 shows an embodiment wherein during the calibration
operation a fly height pattern is read from a first data track
while writing data to a second data track.
[0017] FIGS. 10A and 10B illustrate an embodiment where a DFH write
profile may be calibrated for a gapped write operation.
DETAILED DESCRIPTION
[0018] FIG. 2A shows a disk drive according to an embodiment
comprising a disk 16 and a head 18 (FIG. 2B) actuated over the disk
16, the head 18 comprising a fly height actuator (FHA) 20. The disk
drive further comprises control circuitry 22 including disk access
circuitry, the control circuitry operable to execute the flow
diagram of FIG. 2C wherein during a calibration operation (block
24), the disk access circuitry is configured into a calibration
mode that increases a heating of the head (block 26), and a fly
height of the head is measured periodically to generate periodic
fly height measurements that vary due to the heating of the head
(block 28). A dynamic fly height (DFH) write profile is generated
based on the periodic fly height measurements (block 30). During a
write operation (block 32), the disk access circuitry is configured
into a write mode (block 34) and a DFH control signal 38 is
generated and applied to the FHA based on the DFH write profile
(block 36).
[0019] In the embodiment of FIG. 2B, the head 18 comprises a
suitable read element 40, such as a magnetoresistive element, and a
suitable write element 42, such as an inductive coil. In one
embodiment, the write element 42 may be used to write a fly height
pattern on the disk 16, and the head 18 used to read the fly height
pattern from the disk 16 in order to generate a fly height
measurement when calibrating the DFH write profile. In another
embodiment, the head 18 may comprise a suitable fly height sensor,
such as a magnetoresistive sensor or capacitive sensor, operable to
generate a fly height signal that is processed to generate the fly
height measurements when calibrating the DFH write profile.
[0020] Any suitable FHA 20 may be integrated into the head 18, such
as a heater that actuates through thermal expansion, or a
piezoelectric (PZT) element that actuates through mechanical
deflection. In one embodiment, the FHA 20 is controlled in order to
maintain a target fly height for the head 18 during write and read
operations. For example, maintaining a target fly height during a
write operation may help ensure the disk surface is adequately
saturated by the magnetic field generated by the write element 42.
However, during a write operation the head 18 typically undergoes
additional thermal expansion due to a heating effect of a write
component, such as a heating effect of the write element 42 and/or
a heating effect of a laser used to heat the disk surface in a HAMR
disk drive. To compensate for the fly height deviation due to the
heating effect during a write operation, the DFH control signal 38
applied to the FHA 20 is typically reduced.
[0021] FIG. 3A shows a prior art DFH write profile employed during
a write operation wherein the DFH control signal 38 is adjusted
(e.g., increased) during a preheat interval in order to adjust the
fly height of the head to the target fly height. When the disk
access circuitry is configured into the write mode, the DFH control
signal is decreased by a step decrement in order to compensate for
the heating effect of the write mode. Employing a step decrement in
the DFH write profile causes the fly height of the head to increase
initially due to the cooling response of the FHA 20, and then
decrease toward the target fly height as the heating response of
the write mode begins to reduce the fly height as illustrated in
FIG. 3A. This fly height transient at the beginning of a write
operation may result in inadequate saturation of the disk surface
for one or more data sectors.
[0022] FIG. 3B illustrates an embodiment of the present invention
which helps reduce the fly height transient at the beginning of a
write operation due to the prior art step decrement in the DFH
write profile. In this embodiment, a fly height measurement is
generated periodically at the beginning of a write operation as
represented by the black dots on the fly height curve of FIG. 3B. A
DFH write profile is then generated based on the periodic fly
height measurements. In the embodiment shown in FIG. 3B, the DFH
write profile comprises a step decrement at each corresponding fly
height measurement. However, any suitable DFH write profile may be
generated based on the fly height measurements, where the DFH write
profile may differ for different disk drive configurations, such as
different head geometries, different FHA 20 response times,
different write heating response times, with or without a laser for
HAMR, etc.
[0023] In one embodiment, the DFH write profile may be generated
through multiple iterations until a suitable criterion has been
satisfied, such as the measured fly height remaining near a target
fly height at the beginning of the write mode. This embodiment is
illustrated in the flow diagram of FIG. 4 which is an extension of
the flow diagram of FIG. 2C, wherein after generating the initial
DFH write profile (block 30), the calibration operation is repeated
by configuring the disk access circuitry into the calibration mode
(block 44) and generating a fly height measurement periodically
(block 46) while applying the initial DFH write profile to the FHA
(block 45). A criterion is then evaluated (block 48) to determine
whether the initial DFH write profile adequately compensated for
the fly height transient. For example, the fly height measurements
may be evaluated to determine whether they remain at a target fly
height within a predetermined tolerance, or whether a derivative of
the fly height measurements falls below a threshold, or whether a
derivative of the DFH write profile falls below a threshold, etc.
If the criterion is not met at block 48, then the DFH write profile
is adjusted based on the fly height measurements (block 50) and the
flow diagram is repeated from block 44 until the criterion is
satisfied at block 48.
[0024] The disk access circuitry may be configured into the
calibration mode at step 26 of FIG. 2C in any suitable manner. In
one embodiment, the calibration mode at step 26 is the same as the
write mode at step 34, such as applying a write level current to
the write element 42 and optionally applying a write level power to
a laser for HAMR. In another embodiment, a lower level write
current and/or a lower level laser power may be employed when
calibrating the DFH write profile. In general, the disk access
circuitry is configured into the calibration mode in order to
increase the heating of the head 18 similar to a normal write
operation so that the DFH write profile may be calibrated.
[0025] In one embodiment, the DFH write profile is calibrated by
executing the flow diagram of FIG. 2C, for example, as part of a
manufacturing process before the disk drives are deployed in the
field. FIG. 5 is a flow diagram according to an embodiment which
extends on the flow diagram of FIG. 2C, wherein when a normal write
operation is executed while the disk drive is deployed in the field
(block 52), the disk access circuitry is configured into the write
mode (block 54) and the DFH control signal 38 is generated based on
the DFH write profile (block 56). During the beginning of the write
operation, the fly height measurements are periodically generated
(block 58), and the fly height measurements are used to adjust the
DFH write profile (block 60). In this manner, the DFH write profile
may be adjusted over the life of the disk drive which may help
compensate for changes that occur over time, such as changes to the
thermal response time of the FHA or other write components.
[0026] The DFH write profile may be generated in any suitable
manner based on the periodic fly height measurements as shown in
FIG. 3B. In one embodiment, the values in the DFH write profile are
generated and optionally adapted based on the magnitude of each fly
height measurement. As described above, the values of the DFH write
profile may be adapted based on the subsequent magnitude of the fly
height measurements until the magnitude of the fly height
measurements reach a target fly height within a predetermined
tolerance. In one embodiment, the values of the DFH write profile
may also be generated based on a phase of the fly height
measurements. For example, in one embodiment the delayed thermal
response of the FHA 20 (transient response) may be taken into
account when generating the DFH write profile by phase shifting the
DFH write profile as illustrated in FIG. 6. Inducing a phase shift
in the DFH write profile may help reduce the fly height error as
compared to FIG. 3B, wherein in one embodiment the phase shift may
be induced explicitly or it may be an inherent result of adjusting
the magnitude of the DFH write profile values over time.
[0027] FIG. 7 shows an embodiment wherein the head 18 comprises a
laser 62 used to heat the disk surface during write operations in a
HAMR disk drive. Any suitable laser 62 may be employed, such as a
laser diode, together with suitable optics for focusing the laser
light onto the disk surface, such as a wave guide and a near field
transducer (NFT). In one embodiment, the laser power may be
increased during the preheat interval shown in FIG. 6 in order to
reduce the fly height transient after transitioning in to the write
mode. In one embodiment, both the FHA 20 and the laser 62 may be
controlled during the preheat interval to adjust the head toward
the target fly height prior to transitioning into the write
mode.
[0028] When initially calibrating and/or adapting the DFH write
profile, the fly height measurements may be generated periodically
in any suitable manner. FIG. 8 shows an embodiment wherein a fly
height measurement may be generated while reading a fly height
pattern from each servo sector of a servo track. Each servo sector
may comprise a dedicated field for storing the fly height pattern,
or the fly height pattern may be based on an existing field, such
as a preamble or a servo burst field. In one embodiment, the fly
height pattern comprises a periodic pattern and the fly height
measurement is generated based on a harmonic ratio technique
(Wallace spacing equation) that measures an absolute head-media
spacing (HMS) according to the ratio of the amplitude of the read
signal at two different harmonics. In one embodiment, the fly
height measurements generated at each servo sector as shown in FIG.
8 may be interpolated in order to increase the resolution of the
measurements and the corresponding resolution of the DFH write
profile. In another embodiment, the DFH write profile values may be
interpolated to increase the resolution of the adjustments made to
the DFH control signal.
[0029] FIG. 9 is a flow diagram according to another embodiment
wherein the disk comprises a plurality of data tracks, and the head
comprises a read element 40 radially offset from a write element 42
by at least one data track. When calibrating the DFH write profile,
the control circuitry 22 is operable to read data from a first data
track 64 to measure the fly height of the head while the write
element 42 is over a second data track 66. In this manner, the disk
access circuitry may be configured into the calibration mode (e.g.,
write mode) while simultaneously reading the data (e.g., fly height
pattern) from the first data track 64. Because the write element 42
is radially offset from the read element 40, the data recorded in
the first data track 64 is not erased by the write element 42. This
enables the control circuitry 22 to generate a fly height
measurement at any desired resolution along the first data track,
and thereby generate a corresponding DFH write profile at any
suitable resolution.
[0030] In one embodiment, the control circuitry may receive two or
more host write commands for writing data to the same data track
with a gap between the write operations. This illustrated in FIG.
10B wherein the control circuitry may execute a first write
operation during a first interval, wait a second interval for the
disk to spin, and then execute a second write operation. If the
second interval is relatively short, the head 18 may not fully cool
to a steady state before executing the second write operation.
Therefore, when a DFH write profile is calibrated for a fully
cooled head, the DFH write profile may not be optimum when
executing a second write operation after a short gap since the
write heating response shown in FIG. 3A will be different. In one
embodiment, the DFH write profile for a gapped write operation may
be generated by modifying the DFH write profile for a non-gapped
write operation, such as by modifying the magnitude and/or phase of
a non-gapped DFH write profile based on the length of the gap.
[0031] In another embodiment, the DFH write profile may be
calibrated for a gapped write operation for different gap lengths,
and then the calibrated DFH write profile is used to execute a
gapped write operation. This embodiment is understood with
reference to the flow diagram of FIG. 10A, wherein when calibrating
a DFH write profile (block 68), the disk access circuitry is
configured into the calibration mode to increase the heating of the
head (block 70) for a first interval representing a first write
operation (block 72). The disk access circuitry is then configured
to decrease the heating of the head (block 74) for a second
interval representing a gap between the first write operation and a
second write operation (block 76) as illustrated in FIG. 10B. The
disk access circuitry is again configured into the calibration mode
to increase the heating of the head (block 78) and a fly height
measurement is periodically measured (block 80). A DFH write
profile for the gap corresponding to the second interval is then
generated based on the fly height measurements. The flow diagram of
FIG. 10A may be repeated for a number of different gap lengths in
order to generate a corresponding number of DFH write profiles.
During normal operation, when a gapped write operation is detected,
the corresponding gapped DFH write profile is selected to execute
the gapped write operation. Similar to the embodiment described
above with reference to FIG. 5, the gapped DFH write profiles may
be further adapted when executing gapped write operations during
normal operation of the disk drive.
[0032] In one embodiment, the control circuitry 22 of FIG. 2A may
comprise a servo control system that dynamically controls the fly
height of the head based on a measured topography of the disk
surface. The servo control system may employ feedback control
and/or feed-forward control which adjusts the DFH control signal 38
in real time so that the fly height follows the topography of the
disk surface during access operations. In one embodiment, the DFH
write profile described above is injected into this servo control
system as a feed-forward control signal so that the head follows
the topography of the disk surface in addition to compensating for
the thermal response of the head 18 and the FHA 20 at the beginning
of a write operation.
[0033] Any suitable control circuitry may be employed to implement
the flow diagrams in the above embodiments, such as any suitable
integrated circuit or circuits. For example, the control circuitry
may be implemented within a read channel integrated circuit, or in
a component separate from the read channel, such as a disk
controller, or certain operations described above may be performed
by a read channel and others by a disk controller. In one
embodiment, the read channel and disk controller are implemented as
separate integrated circuits, and in an alternative embodiment they
are fabricated into a single integrated circuit or system on a chip
(SOC). In addition, the control circuitry may include a suitable
preamp circuit implemented as a separate integrated circuit,
integrated into the read channel or disk controller circuit, or
integrated into a SOC.
[0034] In one embodiment, the control circuitry comprises a
microprocessor executing instructions, the instructions being
operable to cause the microprocessor to perform the flow diagrams
described herein. The instructions may be stored in any
computer-readable medium. In one embodiment, they may be stored on
a non-volatile semiconductor memory external to the microprocessor,
or integrated with the microprocessor in a SOC. In another
embodiment, the instructions are stored on the disk and read into a
volatile semiconductor memory when the disk drive is powered on. In
yet another embodiment, the control circuitry comprises suitable
logic circuitry, such as state machine circuitry.
[0035] The various features and processes described above may be
used independently of one another, or may be combined in various
ways. All possible combinations and subcombinations are intended to
fall within the scope of this disclosure. In addition, certain
method, event or process blocks may be omitted in some
implementations. The methods and processes described herein are
also not limited to any particular sequence, and the blocks or
states relating thereto can be performed in other sequences that
are appropriate. For example, described tasks or events may be
performed in an order other than that specifically disclosed, or
multiple may be combined in a single block or state. The example
tasks or events may be performed in serial, in parallel, or in some
other manner. Tasks or events may be added to or removed from the
disclosed example embodiments. The example systems and components
described herein may be configured differently than described. For
example, elements may be added to, removed from, or rearranged
compared to the disclosed example embodiments.
[0036] While certain example embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions disclosed herein.
Thus, nothing in the foregoing description is intended to imply
that any particular feature, characteristic, step, module, or block
is necessary or indispensable. Indeed, the novel methods and
systems described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the methods and systems described herein may be made
without departing from the spirit of the inventions disclosed
herein.
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