U.S. patent application number 15/246332 was filed with the patent office on 2017-03-30 for data storage device concurrently controlling and sensing a secondary actuator for actuating a head over a disk.
The applicant listed for this patent is Western Digital Technologies, Inc.. Invention is credited to JAESOO BYOUN, TIMOTHY A. FERRIS.
Application Number | 20170092310 15/246332 |
Document ID | / |
Family ID | 56878247 |
Filed Date | 2017-03-30 |
United States Patent
Application |
20170092310 |
Kind Code |
A1 |
FERRIS; TIMOTHY A. ; et
al. |
March 30, 2017 |
DATA STORAGE DEVICE CONCURRENTLY CONTROLLING AND SENSING A
SECONDARY ACTUATOR FOR ACTUATING A HEAD OVER A DISK
Abstract
A data storage device is disclosed comprising a voice coil motor
(VCM) and a secondary actuator configured to actuate a head over a
disk. A control signal is applied to the secondary actuator while
processing a sensor signal generated by the secondary actuator. A
vibration signal is generated based on the sensor signal, wherein
the vibration signal has a cut-off frequency between ten percent
and ninety percent of a bandwidth of a control loop for controlling
the secondary actuator.
Inventors: |
FERRIS; TIMOTHY A.; (MISSION
VIEJO, CA) ; BYOUN; JAESOO; (IRVINE, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Western Digital Technologies, Inc. |
Irvine |
CA |
US |
|
|
Family ID: |
56878247 |
Appl. No.: |
15/246332 |
Filed: |
August 24, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14865858 |
Sep 25, 2015 |
9437231 |
|
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15246332 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/5582 20130101;
G11B 5/5552 20130101; G11B 5/5565 20130101; G11B 5/5526
20130101 |
International
Class: |
G11B 5/55 20060101
G11B005/55 |
Claims
1. A method of operating a data storage device, the method
comprising: actuating a head over a disk using a voice coil motor
(VCM) and a secondary actuator; applying a control signal to the
secondary actuator and concurrently process a sensor signal
generated by the secondary actuator; and generating a vibration
signal based on the sensor signal and a sensor capacitor, wherein a
capacitance of the sensor capacitor is at least two times less than
a capacitance of the secondary actuator.
2. The method as recited in claim 1, wherein the vibration signal
has a cut-off frequency between ten percent and ninety percent of a
bandwidth of a control loop for controlling the secondary
actuator.
3. The method as recited in claim 1, wherein: a control loop for
controlling the secondary actuator has a high-pass response; and
the vibration signal has a cut-off frequency above a cut-off
frequency of the high-pass response of the control loop for the
secondary actuator.
4. The method as recited in claim 1, wherein the vibration signal
has a cut-off frequency higher than a cut-off frequency of a
response of a control loop for controlling the VCM.
5. The method as recited in claim 1, further comprising: generating
a sensor current proportional to a current applied to the secondary
actuator due to the control signal; estimating a capacitive voltage
of the secondary actuator based on the sensor current; and
generating the vibration signal based on a difference between the
sensor signal and the estimated capacitive voltage.
6. The method as recited in claim 5, further comprising estimating
the capacitive voltage of the secondary actuator by applying the
sensor current to the sensor capacitor.
7. The method as recited in claim 5, further comprising adapting a
gain of the sensor capacitor based on the sensor signal and the
estimated capacitive voltage.
8. The method as recited in claim 7, further comprising: low pass
filtering a difference between the sensor signal and the estimated
capacitive voltage to generate a low-pass signal; and adapting the
gain of the sensor capacitor based on the low-pass signal.
9. The method as recited in claim 1, further comprising generating
a feed-forward compensation signal applied to the secondary
actuator based on the vibration signal.
10. Control circuitry configured to control a voice coil motor
(VCM) and a secondary actuator to actuate a head over a disk, the
control circuitry configured to: apply a control signal to the
secondary actuator and concurrently process a sensor signal
generated by the secondary actuator; and generate a vibration
signal based on the sensor signal and a sensor capacitor, wherein a
capacitance of the sensor capacitor is at least two times less than
a capacitance of the secondary actuator.
11. The control circuitry as recited in claim 10, wherein the
vibration signal has a cut-off frequency between ten percent and
ninety percent of a bandwidth of a control loop for controlling the
secondary actuator.
12. The control circuitry as recited in claim 10, wherein: a
control loop for controlling the secondary actuator has a high-pass
response; and the vibration signal has a cut-off frequency above a
cut-off frequency of the high-pass response of the secondary
actuator.
13. The control circuitry as recited in claim 10, wherein the
vibration signal has a cut-off frequency higher than a cut-off
frequency of a response of a control loop for controlling the
VCM.
14. The control circuitry as recited in claim 10, further
configured to: generate a sensor current proportional to a current
applied to the secondary actuator due to the control signal;
estimate a capacitive voltage of the secondary actuator based on
the sensor current; and generate the vibration signal based on a
difference between the sensor signal and the estimated capacitive
voltage.
15. The control circuitry as recited in claim 14, further
configured to estimate the capacitive voltage of the secondary
actuator by applying the sensor current to the sensor capacitor
that is proportional to a capacitance of the secondary
actuator.
16. The control circuitry as recited in claim 14, further
configured to adapt a gain of the sensor capacitor based on the
sensor signal and the estimated capacitive voltage.
17. The control circuitry as recited in claim 16, further
configured to: low pass filter a difference between the sensor
signal and the estimated capacitive voltage to generate a low-pass
signal; and adapt the gain of the sensor capacitor based on the
low-pass signal.
18. The control circuitry as recited in claim 10, further
configured to generate a feed-forward compensation signal applied
to the secondary actuator based on the vibration signal.
19. A data storage device comprising: a disk; a head; a voice coil
motor (VCM) and a secondary actuator configured to actuate the head
over the disk; and control circuitry configured to: apply a control
signal to the secondary actuator and concurrently process a sensor
signal generated by the secondary actuator; and generate a
vibration signal based on the sensor signal, wherein the vibration
signal has a cut-off frequency between ten percent and ninety
percent of a bandwidth of a control loop for controlling the
secondary actuator.
20. The data storage device as recited in claim 19, wherein: the
control loop for controlling the secondary actuator has a high-pass
response; and the vibration signal has a cut-off frequency above a
cut-off frequency of the high-pass response of the control loop for
the secondary actuator.
21. The data storage device as recited in claim 19, wherein the
vibration signal has a cut-off frequency higher than a cut-off
frequency of a response of a control loop for controlling the
VCM.
22. The data storage device as recited in claim 19, wherein the
control circuitry is further configured to: generate a sensor
current proportional to a current applied to the secondary actuator
due to the control signal; estimate a capacitive voltage of the
secondary actuator based on the sensor current; and generate the
vibration signal based on a difference between the sensor signal
and the estimated capacitive voltage.
23. The data storage device as recited in claim 22, wherein the
control circuitry is further configured to estimate the capacitive
voltage of the secondary actuator by applying the sensor current to
a sensor capacitor that is proportional to a capacitance of the
secondary actuator.
24. The data storage device as recited in claim 23, wherein the
control circuitry is further configured to adapt a gain of the
sensor capacitor based on the sensor signal and the estimated
capacitive voltage.
25. The data storage device as recited in claim 24, wherein the
control circuitry is further configured to: low pass filter a
difference between the sensor signal and the estimated capacitive
voltage to generate a low-pass signal; and adapt the gain of the
sensor capacitor based on the low-pass signal.
26. The data storage device as recited in claim 23, wherein a
capacitance of the sensor capacitor is at least two times less than
the capacitance of the secondary actuator.
27. The data storage device as recited in claim 19, wherein the
control circuitry is further configured to generate a feed-forward
compensation signal applied to the secondary actuator based on the
vibration signal.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/865,858 (Atty. Docket No. T8190), filed on
Sep. 25, 2015, entitled "DATA STORAGE DEVICE CONCURRENTLY
CONTROLLING AND SENSING A SECONDARY ACTUATOR FOR ACTUATING A HEAD
OVER A DISK," which is hereby incorporated by reference in its
entirety
BACKGROUND
[0002] Data storage devices such as 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 servo sectors. The servo sectors comprise head positioning
information (e.g., a track address) which is read by the head and
processed by a servo control system to control the actuator arm as
it seeks from track to track.
[0003] FIG. 1 shows a prior art disk format 2 as comprising a
number of servo tracks 4 defined by servo sectors 60-6N recorded
around the circumference of each servo track. Each servo sector 6i
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 6i 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
[0004] FIG. 1 shows a prior art disk format comprising a plurality
of servo tracks defined by servo sectors.
[0005] FIG. 2A shows a data storage device in the form of a disk
drive according to an embodiment comprising a head actuated over a
disk by a voice coil motor (VCM) and a secondary actuator.
[0006] FIG. 2B is a flow diagram according to an embodiment wherein
a control signal is applied to the secondary actuator while
processing a sensor signal generated by the secondary actuator,
wherein a high-pass vibration signal is generated based on the
sensor signal.
[0007] FIG. 2C shows an embodiment wherein the secondary actuator
control loop has a high-pass response, and the vibration signal has
a cut-off frequency above a cut-off frequency of the high-pass
response of the secondary actuator.
[0008] FIG. 3 shows control circuitry according to an embodiment
wherein the vibration signal is generated based on a difference
between the sensor signal and an estimated capacitive voltage of
the secondary actuator.
[0009] FIG. 4 shows control circuitry according to an embodiment
wherein a gain of a sensor capacitor is adapted based on the sensor
signal and the estimated capacitive voltage of the secondary
actuator.
[0010] FIG. 5 shows an embodiment wherein the vibration signal has
a cut-off frequency higher than a cut-off frequency of the VCM
control loop.
DETAILED DESCRIPTION
[0011] FIG. 2A shows a data storage device in the form of a disk
drive according to an embodiment comprising a voice coil motor
(VCM) 16 and a secondary actuator 18 configured to actuate a head
20 over a disk 22. The disk drive further comprises control
circuitry 24 configured to execute the flow diagram of FIG. 2B,
wherein a control signal is applied to the secondary actuator while
processing a sensor signal generated by the secondary actuator
(block 26). A vibration signal is generated based on the sensor
signal, wherein the vibration signal is a high-pass signal (block
28).
[0012] In the embodiment of FIG. 2A, the disk 22 comprises a
plurality of servo sectors 300-30N that define a plurality of servo
tracks 32, wherein data tracks are defined relative to the servo
tracks at the same or different radial density. The control
circuitry 24 processes a read signal 34 emanating from the head 20
to demodulate the servo sectors 300-30N and generate a position
error signal (PES) representing an error between the actual
position of the head and a target position relative to a target
track. The control circuitry 24 filters the PES using a suitable
compensation filter to generate a control signal 36 applied to the
voice coil motor (VCM) 16 which rotates an actuator arm 38 about a
pivot in order to actuate the head 20 radially over the disk 22 in
a direction that reduces the PES. The control circuitry 24 also
generates a control signal 40 applied to the secondary actuator 18
in order to actuate the head 20 over the disk 22 in fine movements.
The servo sectors 300-30N may comprise any suitable head position
information, such as a track address for coarse positioning and
servo bursts for fine positioning. The servo bursts may comprise
any suitable pattern, such as an amplitude based servo pattern or a
phase based servo pattern.
[0013] The secondary actuator 18 may comprise any suitable elements
for actuating the head 20 over the disk 22, such as one or more
piezoelectric elements. Further, the secondary actuator 18 may
actuate the head 20 in any suitable manner, wherein in the example
of FIG. 2A, the secondary actuator 18 actuates a suspension 41
about the distal end of the actuator arm 38. In other embodiments,
the secondary actuator 18 may actuate the head 20 about the distal
end of the suspension 41. In yet other embodiments, the secondary
actuator may comprise multiple actuators, such as a milliactuator
configured to actuate the suspension 41 about the actuator arm 38,
and a microactuator configured to actuate the head 20 about the
suspension 41.
[0014] In one embodiment, the secondary actuator 18 may operate as
a sensor for sensing vibrations affecting the disk drive. That is,
a vibration may cause a rotational displacement of the actuator arm
38 which may induce an electrical response (sensor signal) in the
secondary actuator 18. In one embodiment, the sensor signal may
manifest on the same electrical lead used to apply the control
signal 40 to the secondary actuator 18, and in other embodiments,
there may be a dedicated lead coupled to the secondary actuator 18
for conducting the sensor signal. In one embodiment, the sensor
signal may be processed to generate a vibration signal representing
a vibration affecting the disk drive (magnitude and/or phase). The
vibration signal may be used for any suitable purpose, such as for
aborting a write operation to prevent an off-track write, or for
generating a feed-forward control signal that compensates for the
vibration in the servo control loop.
[0015] FIG. 2C shows an embodiment wherein the vibration signal 42
generated based on the sensor signal 40 emanating from the
secondary actuator 18 is a high pass signal meaning that the
vibration signal 42 is responsive to higher frequency vibrations
affecting the disk drive (above a cut-off frequency) with
essentially no response at DC. In one embodiment, the vibration
signal has a cut-off frequency between ten percent and ninety
percent of a bandwidth of the control loop for controlling the
secondary actuator 18. In another embodiment, the control loop for
controlling the secondary actuator 18 has a high-pass response 44
such as shown in FIG. 2C, and the high-pass vibration signal has a
cut-off frequency above a cut-off frequency of the high-pass
response of the secondary actuator control loop. In yet another
embodiment shown in FIG. 5, the high-pass vibration signal 42 has a
cut-off frequency higher than a cut-off frequency of a response of
the VCM control loop 46. In one embodiment, generating the
high-pass vibration signal 42 above the response of the VCM control
loop 46 helps attenuate cross-talk interference from the VCM
control loop when using the vibration signal as feed-forward
compensation for the secondary actuator control loop.
[0016] FIG. 3 shows control circuitry according to an embodiment
comprising a read/write channel 48 configured to process the read
signal 34 emanating from the head 20 when reading the servo
sectors. The read/write channel 48 demodulates the read signal 34
into a measured position 50 of the head 20 over the disk 22. The
measured position 50 is subtracted from a reference position 52 to
generate a position error signal (PES) 54. A VCM compensator 56
processes the PES 54 to generate the control signal 36 applied to
the VCM 16, and a secondary actuator compensator 58 processes the
PES 54 to generate the control signal 40 applied to the secondary
actuator 18. In the embodiment of FIG. 3, the secondary actuator
compensator 58 generates a digital control signal 60 that is
adjusted at adder 62 by a feed-forward compensation signal 64. The
resulting digital control signal 66 is converted into an analog
control signal 40 by a digital-to-analog converter (DAC) 68. The
analog control signal 40 is processed at block 70 to estimate a
capacitive voltage 72 of the secondary actuator 18, and at block
74, a vibration signal 76 is generated based on the estimated
capacitive voltage 72 and the analog control signal 40. Block 78
processes the vibration signal 76 to generate the feed-forward
compensation signal 64, wherein block 78 may implement any suitable
conversion algorithm to convert the vibration signal 76 (an
acceleration signal) into a feed-forward control signal 64. In the
embodiment of FIG. 3, the feed-forward control signal 64
compensates for the vibration by essentially anticipating the
effect of the vibration on the PES 54 and controlling the position
of the head 20 so as to follow the vibration.
[0017] Any suitable control circuitry may be employed to implement
blocks 70 and 74 in FIG. 3. FIG. 4 shows control circuitry
according to an embodiment comprising a sensor capacitor 80
comprising a capacitance C' and a gain K that effectively estimate
the capacitance C within the secondary actuator 18. The control
circuitry of FIG. 4 further comprises a suitable current mirror F
that generates a sensor current 82 proportional to a current
applied to the secondary actuator 18 due to the control signal 40.
An estimated capacitive voltage 72 of the secondary actuator 18 is
generated by applying the sensor current 82 to the sensor capacitor
80, and the vibration signal 76 is generated at adder 84 based on a
difference between the sensor signal 40 and the estimated
capacitive voltage 72. This embodiment effectively cancels the
voltage component in the sensor signal 40 due to the capacitance C
of the secondary actuator 18 so that the vibration signal 76
represents mainly the voltage component 88 generated by the
secondary actuator 18 due to the effect of the vibration on the
disk drive.
[0018] In the embodiment of FIG. 4, the control circuitry adapts
the gain K of the sensor capacitor 80 based on the sensor signal 40
and the estimated capacitive voltage 72. In one embodiment, a
difference signal 86 is generated at adder 89 based on a difference
between the absolute value (block 90A) of the control signal 40 and
the absolute value (block 90B) of the estimated capacitive voltage
72. In the embodiment of FIG. 4, the control circuitry comprises a
proportional-integral-derivative (PID) compensator 92 that low pass
filters the difference signal 86 to generate a low-pass signal 94,
and adapts the gain K of the sensor capacitor 80 based on the
low-pass signal 94. In this manner, the gain K of the sensor
capacitor 80 is adapted substantially based on the control signal
generated by the secondary actuator compensator 58 rather than on
the sensor signal 40 due to the response of the secondary actuator
18 to vibrations. In one embodiment, the gain K is adapted until
the low-pass signal 94 is substantially zero wherein the
capacitance of the sensor capacitor 80 will substantially match the
capacitance C of the secondary actuator 18.
[0019] In one embodiment, the ratio of the current mirror F and the
gain K are selected to enable the capacitance C' of the sensor
capacitor 80 to be significantly less than the capacitance C of the
secondary actuator 18 (e.g., two times less). In this manner, the
capacitor C' in the sensor capacitor 80 may be fabricated as part
of an integrated circuit rather than implemented as a more
expensive external capacitor. For example, if the capacitor C' is
fabricated to be approximately two times smaller than the capacitor
C of the secondary actuator 18, the current mirror F may be
fabricated with an approximately unitary ratio and the gain K
adapted to approximately two. In other embodiments, the ratio of
the current mirror F and/or the gain K may be selected so that the
capacitor C' of the sensor capacitor 80 may be larger than the
capacitor C of the secondary actuator 18.
[0020] 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 other embodiments, the control circuitry may be
implemented within a suitable preamp circuit, within a power large
scale integrated (PLSI) circuit, or within a stand-alone integrated
circuit.
[0021] 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. In some
embodiments, the control circuitry may comprise suitable conversion
circuitry so that at least some of the operations are implemented
in the digital domain, and in other embodiments at least some of
the operations are implemented in the analog domain.
[0022] In various embodiments, a disk drive may include a magnetic
disk drive, an optical disk drive, etc. In addition, while the
above examples concern a disk drive, the various embodiments are
not limited to a disk drive and can be applied to other data
storage devices and systems, such as magnetic tape drives, solid
state drives, hybrid drives, etc. In addition, some embodiments may
include electronic devices such as computing devices, data server
devices, media content storage devices, etc. that comprise the
storage media and/or control circuitry as described above.
[0023] 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.
[0024] 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 embodiments disclosed
herein.
* * * * *