U.S. patent application number 11/012365 was filed with the patent office on 2005-06-30 for operating a rotatable media storage device at multiple spin-speeds.
This patent application is currently assigned to Matsushita Electric Industrial Co., Ltd.. Invention is credited to Ehrlich, Richard M., Schmidt, Thorsten, Tanner, Brian K..
Application Number | 20050141375 11/012365 |
Document ID | / |
Family ID | 32658876 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050141375 |
Kind Code |
A1 |
Ehrlich, Richard M. ; et
al. |
June 30, 2005 |
Operating a rotatable media storage device at multiple
spin-speeds
Abstract
A rotatable media storage device operates using multiple disk
spin-speeds, e.g., a reduced spin-speed and a nominal spin-speed. A
disk is spun up to a reduced spin-speed and an initial data
transfer is began while the disk spins at the reduced spin-speed,
if an amount of work that has been requested is below a threshold.
The disk is spun up to a further spin-speed (e.g., a nominal
spin-speed), which is greater than the reduced spin-speed, and the
initial data transfer is began while the disk spins at the further
spin-speed, if the amount of work that has been requested is above
the threshold. Alternative embodiments using multiple disk
spin-speeds are also provided.
Inventors: |
Ehrlich, Richard M.;
(Saratoga, CA) ; Schmidt, Thorsten; (Milpitas,
CA) ; Tanner, Brian K.; (San Jose, CA) |
Correspondence
Address: |
FLIESLER MEYER, LLP
FOUR EMBARCADERO CENTER
SUITE 400
SAN FRANCISCO
CA
94111
US
|
Assignee: |
Matsushita Electric Industrial Co.,
Ltd.
Kadoma-shi
JP
|
Family ID: |
32658876 |
Appl. No.: |
11/012365 |
Filed: |
December 15, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11012365 |
Dec 15, 2004 |
|
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10366237 |
Feb 13, 2003 |
|
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60530504 |
Dec 18, 2003 |
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60530491 |
Dec 18, 2003 |
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60436946 |
Dec 30, 2002 |
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Current U.S.
Class: |
369/47.38 ;
369/53.3 |
Current CPC
Class: |
G11B 19/26 20130101;
G11B 19/02 20130101; G11B 5/09 20130101 |
Class at
Publication: |
369/047.38 ;
369/053.3 |
International
Class: |
G11B 005/09 |
Claims
What is claimed is:
1. In a data storage device including a disk, a method for
controlling a spin-speed at which an initial data transfer occurs
after the disk begins to spin-up from rest, the method comprising:
(a) spinning the disk up to a reduced spin-speed and beginning to
perform the initial data transfer while the disk spins at the
reduced spin-speed, if an initial amount of work that has been
requested is below a threshold; and (b) spinning the disk up to a
further spin-speed, which is greater than the reduced spin-speed,
and beginning to perform the initial data transfer while the disk
spins at said further spin-speed, if the initial amount of work
that has been requested is above said threshold.
2. The method of claim 1, wherein the initial amount of work is
defined at least in part by an initial amount of data to be
transferred.
3. The method of claim 1, wherein the initial amount of work is
defined at least in part by an estimated amount of time necessary
to complete the work.
4. The method of claim 1, wherein the data transfer includes at
least one of reading data from the disk and writing data to the
disk.
5. The method of claim 1, wherein said further spin-speed comprises
a nominal spin-speed.
6. The method of claim 5, further comprising: (c) spinning the disk
up from said reduced spin-speed to said nominal spin-speed, if
additional work is requested while the initial data transfer is
being performed at said reduced spin-speed.
7. The method of claim 5, further comprising: (c) spinning the disk
up from said reduced spin-speed to said nominal spin-speed, if
additional work above said threshold is requested while the initial
data transfer is being performed at said reduced spin-speed.
8. The method of claim 5, further comprising: (c) spinning the disk
up from said reduced spin-speed to said nominal spin-speed, if
additional work above a further threshold is requested while the
initial data transfer is being performed at said reduced
spin-speed.
9. The method of claim 5, wherein: (c) spinning the disk up from
said reduced spin-speed to said nominal spin-speed, if enough
additional work is requested that a total amount of work exceeds
said threshold while the initial data transfer is being performed
at said reduced spin-speed.
10. The method of claim 6, wherein step (c) includes performing an
additional data transfer at said nominal spin-speed.
11. In a data storage device including a disk, a method for
controlling a spin-speed at which an initial data transfer occurs,
between a host and the disk of the data storage device, after the
disk begins to spin-up from rest, the method comprising: (a)
spinning the disk up to one of a plurality of different spin-speeds
at which the data storage device can operate, as instructed by the
host; and (b) beginning to perform a data transfer at said
instructed spin-speed.
12. The method of claim 11, wherein the plurality of spin-speeds
include a nominal spin-speed and a reduced spin-speed that is less
than said nominal spin-speed.
13. In a data storage device including a disk, a method for
controlling a spin-speed at which an initial data transfer occurs
after the disk begins to spin-up from rest, the method comprising:
(a) spinning the disk up to a reduced spin-speed and performing an
initial data transfer while the disk spins at said reduced
spin-speed; and (b) spinning the disk up to a nominal spin-speed,
which is greater than said reduced spin-speed, and performing an
additional data transfer while the disk spins at said nominal
spin-speed.
14. In a data storage device including a disk, an actuator assembly
having a head for reading from and/or writing to the disk, and a
load/unload ramp on which to park the head, a method for reducing
the amount of time it takes for a head to begin reading from and/or
writing to the disk after the actuator assembly has been parked on
the load/unload ramp, the method comprising: (a) monitoring a disk
spin-speed as the disk is spinning up to a selected spin-speed; (b)
beginning a ramp load operation before the disk spin-speed reaches
said selected spin-speed, but such that the disk will achieve said
selected spin-speed prior to the head reaching an outer diameter of
the disk; and (c) performing an initial data transfer at said
selected spin-speed.
15. The method of claim 14, further comprising: (d) adjusting said
spin-speed and performing a further data transfer at said adjusted
spin-speed.
16. The method of claim 14, wherein said selected spin-speed
comprises a nominal spin-speed.
17. The method of claim 14, wherein said selected spin-speed
comprises a reduced spin-speed that is less than a nominal
spin-speed.
18. The method of claim 14, wherein said selected spin-speed is
selected from a nominal spin-speed and a reduced spin-speed that is
less than said nominal-spin speed.
19. The method of claim 14, further comprising the step of
receiving an instruction, from a host, said instruction informing
the disk drive of said selected spin-speed.
20. The method of claim 14, further comprising selecting a
spin-speed based on a comparison of the initial data transfer to a
threshold.
21. The method of claim 20, wherein said threshold is defined by a
host.
Description
CLAIM OF PRIORITY
[0001] This application claims priority under 35 U.S.C. 119(e) to
U.S. Provisional Patent Application No. 60/530,504, filed Dec. 18,
2003, and entitled "Operating A Rotatable Media Storage Device At
Multiple Spin-Speeds."
[0002] This application also claims priority under 35 U.S.C. 119(e)
to U.S. Provisional Patent Application No. 60/530,491, filed Dec.
18, 2003, and entitled "Reducing the Time-To-Ready in a Rotatable
Media Storage Device."
[0003] This application is also a continuation-in-part of U.S.
patent application Ser. No. 10/366,237, filed Feb. 13, 2003, and
entitled "Intermediate Power Down Mode for a Rotatable Media Data
Storage Device," which claims priority under 35 U.S.C. 119(e) to
U.S. Provisional Patent Application No. 60/436,946, entitled
"Intermediate Power Down Mode for a Rotatable Media Data Storage
Device," filed Dec. 30, 2002.
[0004] Each of the above applications is incorporated herein by
reference.
FIELD OF THE INVENTION
[0005] The present invention relates generally to rotatable media
data storage devices, as for example magnetic or optical hard disk
drive technology.
BACKGROUND OF THE INVENTION
[0006] Disk drives typically include a number of rapidly rotating
disks having surfaces upon which data is written to and read from.
Each disk surface that is used to store data is matched with a head
which is held very close to the disk surface. The head can thereby
read and write data from/to the disk surface as it rotates under
the head.
[0007] A head suspension assembly (HSA) typically includes the head
attached to a slider, which is further attached to a flexible
suspension member (also known simply as a suspension). The
suspension is in-turn connected to a pivoting actuator arm, whose
motion is typically controlled using a voice coil motor. The
rotating or spinning of the disk creates air pressure beneath the
slider that lifts the slider and consequently the head off of the
surface of the disk, creating a micro-gap of typically less than
one micro-inch between the disk and the head. The suspension is
often bent or shaped to act as a spring such that a load force is
applied to the surface of the disk. The air bearing or cushion
created by the spinning of the disk resists the spring force
applied by the suspension, and the opposition of the spring force
and the air bearing to one another allows the head to trace the
surface contour of the rotating disk surface, which is likely to
have minute warpage, without contacting the disk surface.
[0008] It is preferred that the head and disk surface not come in
contact while the disk is rotating, since this can result in damage
to both the disk surface and the head. For example, data can be
permanently destroyed if excessive contact should occur. Also, the
head can be damaged by the contact. When the disk is rotating at a
sufficient speed, contact between the disk surface and head is
prevented by the air bearing, as just explained above.
[0009] It is also preferred that the head and disk surface not come
in contact while the disk is not rotating (e.g., when the hard
drive is not powered, or when there have been no recent read or
write requests, causing the disk drive to go into a power saving
mode where the disk stops spinning). This is because the head and
disk surface may stick together, if the disk and the head are at
rest and in contact for a period of time, resulting in damage to
the disk surface and/or head when the disk starts to rotate. Also,
since the disk starts spinning from rest, and a certain minimum
velocity is required for the head to float over the disk surface,
each startup of the hard drive can result in the head and disk
surface rubbing for a distance until the disk achieves sufficient
speed to form the aforementioned air cushion.
[0010] For the above mentioned reasons, load/unload ramp structures
and techniques have been used in many hard drives to hold a head
away from a disk surface while a disk is not spinning. In such
systems, the head is not released from the ramp structure until the
disk has achieved its normal operating spin-speed. Similarly, when
the disk drive is to be stopped, the slider is unloaded to a
standby position on the ramp structure before the disk rotation
speed is spun-down to rest.
[0011] Over the past few years, portable computing devices, such as
notebook computers, have become progressively thinner and lighter,
and battery technology has improved significantly. However, though
both thinner and lighter, portable computing devices have
incorporated ever-more powerful CPUs, larger and higher resolution
screens, more memory and higher capacity hard disk drives.
Feature-rich models include a number of peripherals such as
high-speed CD-ROM drives, DVD drives, fax/modem capability, and a
multitude of different plug-in PC cards. Each of these features and
improvements creates demand for power from system batteries. Many
portable electronics, such as MP3 players and personal digital
assistants, now use rotatable data storage devices as well, and by
their nature and size place great demands for power on
batteries.
[0012] The rotation of disks, within rotatable storage drives of
portable computing devices, consumes power from the batteries.
Accordingly, many manufacturers of rotatable data storage devices
have reduced demand on batteries by employing power savings
schemes. For example, many manufacturers perform a ramp unload, and
spin down the rotating storage medium to rest, after a period of
inactivity. While such schemes have been useful for extending
battery life, it would be beneficial if the rotation of disks could
be further optimized to save additional power.
[0013] As mentioned above, a head is typically not released from a
ramp structure until the disk has achieved its normal operating
spin-speed. This affects a drive's "time-to-ready," meaning the
time to which the head can start reading data from, or written data
to, the disk. It would be beneficial if a disk drive's
"time-to-ready" could be reduced.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 is a diagram showing components of an exemplary disk
drive that can be used to implement embodiments of the present
invention.
[0015] FIG. 2 shows additional details of the actuator assembly
from FIG. 1 and related elements.
[0016] FIG. 3 shows additional details of the voice coil motor
(VCM) driver from FIG. 1, and related elements.
[0017] FIGS. 4A and 4B shows additional details of the spindle
motor (SM) driver from FIG. 1, and related elements.
[0018] FIG. 5 is an exemplary graph of disk spin-speed versus time,
which is useful for explaining embodiments of the present
invention.
[0019] FIGS. 6-9 are high level flow diagrams that are useful for
describing various embodiments of the present invention.
[0020] FIG. 10 is an exemplary graph that shows the number of
blocks to transfer (during a read or write operation) versus the
amount of time necessary to perform the data transfer, assuming the
disk is spinning up from rest.
[0021] FIG. 11 is a high level flow diagram that is useful for
describing embodiments of the present invention in which a disk can
be read from or written to at more than one spin-speed.
DETAILED DESCRIPTION
[0022] Embodiments of the present invention are useful for reducing
the amount of time it takes for a head to begin reading from and/or
writing to a disk, after an actuator assembly has been parked on a
load/unload ramp and the disk has not been rotating. In accordance
with an embodiment of the present invention, a disk spin-speed is
monitored as a disk spins up from rest. The disk may have been at
rest, for example, because the drive had just been powered on, or
because the drive had been in a power saving (e.g., idle) mode. In
accordance with an embodiment of the present invention, the drives
"time-to-ready" is reduced by beginning a ramp load operation
before the disk spin-speed reaches its nominal spin-speed, and in
accordance with specific embodiments, even before the disk
spin-speed achieves a minimum float spin-speed for causing the head
to float over a surface of the disk. However, before explaining
further details and embodiments of the present invention, it is
first useful to describe exemplary environments in which
embodiments of the present invention can be useful.
[0023] FIG. 1 shows an exemplary disk drive 100, which includes at
least one rotatable storage medium 102 (i.e., disk) capable of
storing information on at least one of its surfaces. In a magnetic
disk drive as described below, the storage medium 102 is a magnetic
disk. The numbers of disks and surfaces may vary from disk drive to
disk drive. A closed loop servo system, including an actuator
assembly 106, can be used to position a head 104 over selected
tracks of the disk 102 for reading or writing, or to move the head
104 to a selected track during a seek operation. In one embodiment,
the head 104 is a magnetic transducer adapted to read data from and
write data to the disk 102. In another embodiment, the head 104
includes separate read and write elements. For example, the
separate read element can be a magnetoresistive head, also known as
an MR head. It will be understood that various head configurations
may be used with embodiments of the present invention.
[0024] A servo system can include a voice coil motor driver 108 to
drive a voice coil motor (VCM) 130 for rotation of the actuator
assembly 106, a spindle motor driver 112 to drive a spindle motor
132 for rotation of the disk 102, a microprocessor 120 to control
the VCM driver 108 and the spindle motor driver 112, and a disk
controller 128 to accept information from a host 122 and to control
many disk functions. The host 122 can be any device, apparatus, or
system capable of utilizing the disk drive 100, such as a personal
computer or Web server. The disk controller 128 can include an
interface controller in some embodiments for communicating with the
host 122, and in other embodiments a separate interface controller
can be used. Servo fields on the disk 102 are used for servo
control to keep the head 104 on track and to assist with
identifying proper locations on the disk 102 where data is written
to or read from. When reading servo fields, the head 104 acts as a
sensor that detects position information to provide feedback for
proper positioning of the head 104.
[0025] The microprocessor 120 can also include a servo system
controller, which can exist as circuitry within the drive or as an
algorithm resident in the microprocessor 120, or as a combination
thereof. In other embodiments, an independent servo controller can
be used. Additionally, the microprocessor 120 may include some
amount of memory such as SRAM, or an external memory such as SRAM
110 can be coupled with the microprocessor 120. The disk controller
128 can also provide user data to a read/write channel 114, which
can send signals to a current amplifier or preamp 116 to be written
to the disk 102, and can send servo signals to the microprocessor
120. The disk controller 128 can also include a memory controller
to interface with memory 118. Memory 118 can be DRAM, which in some
embodiments, can be used as a buffer memory.
[0026] Although shown as separate components, the VCM driver 108
and spindle motor driver 112 can be combined into a single "hard
disk power-chip." It is also possible to include the spindle speed
control circuitry in that chip. The microprocessor 120 is shown as
a single unit directly communicating with the VCM driver 108,
although a separate VCM controller processor (not shown) may be
used in conjunction with processor 120 to control the VCM driver
108. Further, the processor 120 can directly control the spindle
motor driver 112, as shown. Alternatively, a separate spindle motor
controller processor (not shown) can be used in conjunction with
microprocessor 120.
[0027] FIG. 2 shows some additional details of the actuator
assembly 106. As shown in FIG. 2, the actuator assembly 106
includes an actuator arm 204 that is positioned proximate the disk
102, and pivots about a pivot point 206 (e.g., which may be an
actuator shaft). Attached to the actuator arm 204 is the read/write
head 104, which can include one or more transducers for reading
data from and writing data to a magnetic medium, an optical head
for exchanging data with an optical medium, or another suitable
read/write device. Also, attached to the actuator arm 206 is an
actuator coil 210, which is also known as a voice coil or a voice
actuator coil.
[0028] The voice coil 210 moves relative to one or more magnets 212
when current flows through the voice coil 210. The magnets 212 and
the actuator coil 210 are parts of the voice coil motor (VCM) 130,
which applies a force to the actuator arm 204 to rotate it about
the pivot point 206. The actuator arm 204 includes a flexible
suspension member 226 (also known simply as a suspension). At the
end of the suspension 226 is a mounted slider (not specifically
shown) with the read/write head 104.
[0029] The VCM driver 108, under the control of the microprocessor
120 (or a dedicated VCM controller, not shown) guides the actuator
arm 204 to position the read/write head 104 over a desired track,
and moves the actuator arm 204 up and down a load/unload ramp 224.
The ramp 224 will typically include a latch (not shown) to hold the
actuator arm 204 when in the parked position. The drive 100 also
includes crash stops 220 and 222. Additional components, such as a
disk drive housing, bearings, etc. which have not been shown for
ease of illustration, can be provided by commercially available
components, or components whose construction would be apparent to
one of ordinary skill in the art reading this disclosure.
[0030] Disk(s) 102 generally rotate at a constant set rate ranging
from 3,600 to 15,000 RPM, with speeds of 4,200 and 5,400 RPM being
common for hard disk drives designed for mobile environments, such
as laptops. The actuator assembly sweeps an arc between the inner
and outer diameters of the disk 102, that combined with the
rotation of the disk 102 allows a read/write head 104 to access
approximately an entire surface of the disk 102. The head 104 reads
and/or writes data to the disks 102, and thus, can be said to be in
communication with a disk 102 when reading or writing to the disk
102. Each side of each disk 102 can have an associated head 104,
and the heads 104 are collectively arranged within the actuator
assembly such that the heads 104 pivot in unison. As mentioned
above, the spinning of the disk 102 creates air pressure beneath
the slider to form a micro-gap of typically less than one
micro-inch between the disk 102 and the head 104.
[0031] FIG. 3 shows exemplary details of the VCM driver 108 of FIG.
1 as connected to the VCM 130. As shown, the exemplary VCM driver
108 includes a VCM current application circuit 350, which applies
current to the coil 210 of the VCM 130 with a duration and
magnitude controlled based on a signal received from the
microprocessor 120 (or separate VCM controller). The coil 210 is
modeled in FIG. 3 to include a coil inductance L.sub.coil, a coil
resistance R.sub.coil and a back emf voltage generator 370. Current
provided through the coil 210 controls movement of a rotor 350, and
likewise movement of the rotor 350 generates a back emf voltage in
the back emf voltage generator 370.
[0032] The VCM driver 108 further includes a back emf detection
circuit 352 for sensing the velocity of the actuator arm 204 based
on an estimate of the open-circuit voltage of the VCM 130. The
open-circuit voltage of the VCM 130 is estimated by observation of
the actual VCM voltage and the VCM current (either the commanded
current or the sensed current, sensed using a series sense resistor
R.sub.sense), and multiplication of the current by an estimated VCM
coil resistance (R.sub.coil) and subtraction of that amount from
the measured coil voltage. Referring briefly back to FIG. 2, during
shut down, the actuator arm 204 is positioned on the ramp 224
situated off to the side of the disk 102 to prevent contact between
the head 104 and the disk 102. During startup, actuator velocity
down the ramp 224 is controlled using measurements from the VCM
back emf detection circuit 352 to ensure that the head 104 "flies"
or "floats" when it gets to the bottom of the ramp 224 and does not
contact the disk 102.
[0033] FIG. 4A shows exemplary details of the spindle motor 132
supporting a rotor shaft 470, and the spindle motor driver circuit
112. The exemplary spindle motor 132 includes a coil 460 with three
windings 462, 464 and 466 electrically arranged in a Y
configuration. A rotor 468 of the spindle motor 132 has magnets
that provide a permanent magnetic field. The spindle motor driver
circuit 112 supplies current to windings 462-466 to cause the rotor
468 to rotate at a desired operating spin-rate. The spindle motor
driver 112 includes a commutation and current application circuit
450 to apply different commutation state currents across windings
462-466 at different times. The commutation and current application
circuit 450 applies the commutation state currents based on signals
received from the microprocessor 120. The microprocessor 120
monitors the time period between back emf zero crossings using a
spindle motor back emf detector 452 and uses this time period
information to determine the speed of spindle motor 132. The speed
indication can then used by the microprocessor 120 (or separate SM
controller) to control the commutation voltages applied across
windings 462-466 to accomplish a desired speed. In accordance with
embodiments of the present invention described below, the speed
indication can also be used by the microprocessor 120 for
triggering certain events, such as initiation of a ramp load
operation.
[0034] FIG. 4B shows an alternative configuration of the spindle
motor driver circuit 112. As shown, the commutation and current
application circuit 450 receives the back emf zero crossing signals
from the spindle motor back emf detector 452. In this embodiment,
the commutation circuit 450 includes circuitry to calculate the
current application states needed to obtain a desired speed based
on a spindle motor speed indication determined from the spindle
motor back emf detector 452 (during steady-state operation; during
open-loop startup, commutation states are determined internally or
provided from the microprocessor 120). In the embodiment of FIG.
4B, some (or all) of the processing that was performed by the
microprocessor 120 in the configuration of FIG. 4A, is included in
the commutation circuit 450. Thus, in the configuration of FIG. 4B,
the microprocessor 120 may only provide clocking or desired spindle
motor speeds to the commutation circuit 450.
[0035] In the configurations of both FIGS. 4A and 4B, measurements
of spindle motor speed, and thus of disk spin-speed, can be made
using the spindle motor back emf detector 452. The spindle motor
back emf information is provided to the microprocessor 120. After
the head 104 is over the disk 102, the processor 120 can also
determine spin-speed using the servo data from disk 102.
[0036] Reducing Time-to-Ready
[0037] Referring back to FIG. 2, the load/unload ramp 224 is used
to hold the head 104 away from a disk surface while the disk 102 is
not spinning. As mentioned above, conventionally the head 104 is
not released from the ramp (i.e., does not begin moving down the
ramp 224) until the disk 102 has achieved its normal operating
spin-speed. This effects a drive's "time-to-ready," meaning the
time to which data can start being read from, or written to, a
disk. Embodiments of the present invention, discussed with
reference to FIGS. 5-7, are used to reduce a disk drive's
"time-to-ready."
[0038] FIG. 5 is an exemplary graph of disk spin-speed versus time.
Three different spin-speeds are labeled on the vertical axis,
including nominal spin-speed 506, minimum "float" spin-speed 504,
and a spin-speed 502 when a ramp load operation begins, in
accordance with an embodiment of the present invention. The nominal
spin-speed 502 is the spin-speed at which the drive is designed to
normally read and write data. The nominal spin-speed 502 is shown
as occurring at a time 516, labeled t.sub.nom, after the disk
begins to spin-up from rest. The minimum "float" spin-speed 504, is
the minimum spin-speed at which a sufficient air-gap is formed
between the slider and the disk's surface to prevent the head 104
from contacting the disk 102 following a ramp load operation (i.e.,
when the head 104 leaves the ramp 224 and is positioned over an
outer diameter of the surface of disk 102). The minimum float
spin-speed is shown as occurring at a time 514, labeled t.sub.min.
The minimum float spin-speed 504, which is typically be about
two-thirds of the nominal spin-speed 502, can be determined through
simple experiments. As will be discussed in more detail below, in
accordance with some embodiments of the present invention, a drive
is designed to read and write at more than one spin-speed (e.g., at
a reduced spin-speed and a nominal spin-speed). In such
embodiments, it is assumed that the nominal spin-speed is higher
than the lowest spin-speed at which the drive can read and
write.
[0039] A ramp load operation is the operation in which the head 104
is moved from a parked position on the ramp 224, down the ramp 224
toward the disk 102, and eventually over the surface of the disk
102. The terms "on the ramp" and "down the ramp" are not meant to
convey that the head itself contacts the ramp 224. Rather, it is
more likely that a lift tab (not shown) or similar lifting feature
associated with the head suspension assembly, engages the ramp 224.
A ramp load operation begins at the time when the head 104 begins
to moved from the parked position toward the disk 102.
[0040] Conventionally, a ramp load operation is not began until the
disk 102 has achieved its nominal spin-speed 502. In accordance
with an embodiment of the present invention, discussed below with
reference to the high level flow diagram of FIG. 6, the ramp load
operation begins at a spin-speed 506 that is less than the minimum
float speed 504. The time at which the load operation begins is
shown as occurring at a time 512, labeled toad.
[0041] Referring to FIG. 6, the spin-speed of the disk (i.e., the
disk spin-speed) is monitored as the disk spins-up from rest, as
specified at a step 602. The disk may have been at rest because the
disk-drive was just powered up, or because the disk drive was in a
power saving mode in which the disk was spun down to rest. As
mentioned above, the head suspension assembly is parked on the ramp
while the disk is at rest.
[0042] At a next step 604, a ramp load operation is began before
said disk spin-speed reaches a minimum float spin-speed for causing
the head to float over a surface of the disk. This includes
beginning to move the head from a parked position on the ramp
toward the disk. The initiating of the ramp load operation can be
triggered when the disk spin-speed reaches a threshold spin-speed,
that is less than said minimum float spin-speed, yet fast enough
that the spin-speed will reach the minimum float speed by the time
the head reaches the outer diameter of the disk.
[0043] In accordance with an embodiment of the present invention,
tests are performed to determined the amount of time it takes for
the disk to spin from rest up to the minimum float spin-speed.
Tests are also performed to determine the amount of time it takes
for the head to move from the parked position to the outer diameter
of the disk, once a ramp load operation is initiated (i.e.,
begins). Using the results of these tests, a graph of time versus
spin-speed, resembling the graph in FIG. 5, can be produced. A
determination can be made of the earliest time (and corresponding
earliest spin-speed) at which the ramp load operation can begin,
such that the minimum float speed will be achieved just prior to
the head reaching the outer diameter of the disk.
[0044] For example, starting from rest, assume that it takes 2.000
seconds for the disk to reach its nominal spin-speed, yet only
1.500 seconds for the disk to reach its minimum float spin-speed.
Also assume that it takes 200 msec. (i.e., 0.200 seconds) for the
head to move from the parked position to the outer diameter of the
disk during a ramp load operation. Thus, if a ramp load operation
begins at, or slightly later than, 1.300 seconds after the disk
begins to spin-up from rest, then the disk should achieve the
minimum float speed by the time the head moves from the parked
position to the outer diameter of the disk. Also assume that the
nominal spin-speed of the disk is 5,400 rpm, and that the minimum
float speed is 4,000 rpm. Further, assume that at 1.300 seconds
after the disk begins to spin-up from rest that disk achieves a
spin-speed of 3,200 rpm. Using these exemplary assumptions, the
threshold spin-speed could be set at (or slightly above) 3,200 rpm.
In other words, if the ramp-load operation is initiated when the
disk spin-speed reaches 3,200 rpm, then the disk will have just
achieved the minimum float spin-speed of 4,000 rpm by the time the
head reaches the outer diameter of the disk. Then, as soon as the
disk reaches its nominal spin-speed, the head should ready for
servoing and reading and/or writing. Or, if reading and writing can
occur at less than the nominal spin-speed, e.g., at a reduce
spin-speed, as explained below, then the head will be ready to read
and write once the reduced spin-speed is reached.
[0045] It is also possible, in accordance with an embodiment of the
present invention, that the drive can use measures of back EMF to
get the heads close to a desired track on the disk (for reading or
writing), even before the disk reaches a spin-speed at which the
drive can begin servoing (e.g., the nominal spin-speed). For
example, if the drive knows that the first track to read from or
write to is near the inner diameter of the disk, then the drive can
use measures of back EMF to guide the head toward a location near
the inner diameter of the disk such that once the disk reaches a
desired spin-speed (e.g., the nominal spin-speed) at which it can
begin servoing, there is less distance that the actuator arm will
need to travel in order to place head over the desired track.
[0046] In the above manners, the time-to-ready can reduced. It is
noted that the above mentioned spin-speeds and times are just
exemplary values, which are not meant to be limiting.
[0047] To the knowledge of the inventor, a disk drive's nominal
spin-speed has always been higher than the minimum float
spin-speed. Also, to the knowledge of the inventor, reading and/or
writing have not been performed at less than a disk drive's nominal
spin-speed. In accordance with embodiments of the present
invention, a disk drive is adapted to perform reading and/or
writing at the minimum float spin-speed, and/or at some other
spin-speed that is less than the nominal spin-speed. Such
embodiments are discussed below in the "Multiple Spin-speed"
section. As will be appreciated from the discussion of the multiple
spin-speed embodiments, it can be beneficial to combine the above
discussed embodiments (relating to early initiation of a ramp load
operation) with the embodiments relating to multiple
spin-speeds.
[0048] As explained above with reference to FIGS. 4A and 4B, the
disk spin-speed can be monitored by monitoring the spin-speed of
the spindle motor 132 that rotates the disk 102. This can be
accomplished, for example, by using measurements of back EMF
determined by the spindle motor back emf detection circuit 452.
Alternative schemes for monitoring disk spin-speed, while the head
104 is not over the disk 102, can also be used.
[0049] In accordance with a further embodiment of the present
invention discussed with reference to the flow diagram of FIG. 7,
the spin-up time since the disk began to spins-up from rest is
monitored, at a step 702. In this manner, at a step 704 a ramp load
operation is initiated before the spin-up time reaches a predicted
time at which the disk achieves a minimum float spin-speed for
causing the head to float over a surface of the disk. The threshold
spin-up time should be selected such that the disk will achieve the
minimum float spin-speed prior to the head reaching an outer
diameter of the disk. For example, a ramp load operation can be
initiated when time since spin-up began reaches a threshold spin-up
time, which that is less than the predicted time at which the disk
will achieve the minimum float spin-speed. Using the exemplary
values just discussed above, the threshold spin-up time can be
1.300 seconds, for example.
[0050] In the above described embodiments, the head 104 should
reach the outer diameter of the disk 102 after the disk spin-speed
reaches the minimum float spin-speed, but before the disk reaches
the nominal spin-speed. In accordance with alternative embodiments
of the present invention, the ramp load operation can be initiated
prior to the disk spin-speed reaching nominal spin-speed, but such
that by the time the head 104 reaches the outer diameter of the
disk 102, the disk spin-speed will have reached the nominal
spin-speed (which is always at least as great as the minimum float
spin-speed). In these embodiments, summarized in the flow diagrams
of FIGS. 8 and 9, it is possible that the ramp load operation may
not even begin until after the disk spin-speed reaches the minimum
float spin-speed. Nevertheless, the time-to-ready will still be
less than if the ramp load operation did not begin until after the
disk spin-speed reached the nominal spin-speed. In such
embodiments, the time since spin-up from rest and/or the spin-speed
can be monitored, as discussed above. Similarly, a spin-up speed
threshold or a time threshold (since spin-up began) can be used as
the triggering threshold to begin a ramp load operation. In another
embodiment, where reading and writing can occur at a reduced
spin-speed (which is less than the nominal spin-speed), the ramp
load operation can be initiated prior to the disk spin-speed
reaching the reduced spin-speed, but such that by the time the head
104 reaches the outer diameter of the disk 102, the disk spin-speed
will have reached the reduced spin-speed.
[0051] For all of the embodiments discussed above, it would be
useful to have a safety feature that causes the head 104 to retract
back up the ramp 224 if the head is about to reach the outer
diameter of the disk, but the disk has not yet reached the minimum
float spin-speed (or some other predetermined spin-speed).
Generally, the exact location of the head 104 is difficult to
determine while the head suspension assembly moving along the ramp
224. However, there are certain ways that a location of the head
can be approximated. For example, the location of the head 104 can
be estimated using angular velocity measurements that are made,
e.g., using the VCM back emf detection circuit 352, discussed with
reference to FIG. 3. Such measurements of angular velocity can be
used to estimate where the head 104 is along the ramp 224. Most
ramps 224 have a flat portion followed by a declined portion
adjacent the outer diameter of the disk 102. When the head 104
begins to move down the declined portion of the ramp 224, the
velocity of the head 104 will typically increase, as compared to
when the head is moving along the flat portion of the ramp 224.
This increase in acceleration can be detected by the VCM back emf
detection circuit 352. In these manners, the location of the head
104 relative to ramp 224 can be estimated. In accordance with an
embodiment of the present invention, if the disk spin-speed has not
reached the minimum float spin-speed (or some other predetermined
threshold) by the time the head 104 reaches a predefined location
with respect to the ramp 224, then the VCM driver 108 is instructed
to abort the ramp load operation for the time being, and to move
the head back up the ramp 224 (e.g., to the parked position).
[0052] Other schemes for determining the position of the head 104
relative to the ramp 224 can alternatively or additionally be used,
in order to determine whether to abort the ramp load operation. For
example, it would be possible to use the teachings in commonly
assigned U.S. patent application Ser. No. 10/349,798, entitled
"Ramp Arrangement and Method for Measuring the Position of an
Actuator Arm in a Rotating Media Storage Device," which is
incorporated herein by reference. As taught in the just mentioned
application, the ramp 224 can be electrically connected with the
actuator assembly (e.g., with the lift tab or suspension), such
that a closed circuit is formed when a portion of the actuator
assembly contacts a portion of the ramp 224. The closed circuit has
a resistance that varies when the actuator assembly moves along the
ramp, as would the resistance in a potentiometer including an
adjustable wiper. By measuring the resistance, or changes in
resistance, the position of the head 104 relative to the ramp 224
can be determined.
[0053] Multiple Spin-Speeds
[0054] As mentioned above, the minimum float spin-speed for a disk
drive is typically about two-thirds of the disk drive's nominal
spin-speed (i.e., the spin-speed at which the drive is designed to
read and write data). Typically, the faster the nominal spin-speed,
the faster data can be read from and written to a disk. However,
the faster the nominal spin-speed, the more power necessary to spin
the disk. Accordingly, the nominal spin-speed selected for use in a
portable computing device (and more specifically, in a rotatable
data storage device of the portable computing device) is typically
selected with both performance and power consumption in mind. In
other words, the nominal spin-speed of the disk drive can be
selected to provide an acceptable trade-off between performance and
power.
[0055] Embodiments of the present invention, which shall now be
explained, also relate to methods and systems in which more than
one spin-speed is used for reading from and writing to a disk. More
specifically, in accordance with an embodiment of the present
invention, a reduced spin-speed is used in certain situations,
wherein the reduced spin-speed is greater than or equal to the
minimum float spin-speed, yet less than the nominal spin-speed. It
should be understood that for each of the embodiments involving
multiple spin-speeds, the read/write channel (e.g., 114) of the
rotatable media storage device implementing the inventions should
be designed to operate at multiple frequencies (i.e., one for each
spin-speed).
[0056] There are many instances where a host may need read a small
amount of data from, or write a small amount of data to, a disk
which has been spun down to rest. In such instances, it may often
be faster and less power consuming for the host to perform the read
or write operation while the disk rotates at a spin-speed that as
less than its nominal spin-speed. This is because it takes less
time to achieve the reduced spin-speed, thereby reducing the
time-to ready, and enabling the host to begin reading and/or
writing at an earlier point in time. Additionally, less power is
consumed at the reduced spin-speed than would be consumed a higher
nominal spin-speed.
[0057] FIG. 10 is an exemplary graph that shows the number of
blocks to transfer (during a read or write operation) versus the
amount of time necessary to perform the data transfer, assuming the
disk is spinning up from rest. As can be seen from the graph, if
the amount of data is less than X blocks, then it will take less
time to transfer the data at the reduced speed. This is because the
transfer can begin sooner (i.e., at time t1, as opposed to at time
t2) if the reduced spin-speed is used.
[0058] However, as can also be seen from the graph, if the amount
of data is greater than X blocks, then it would be faster to wait
until the disk reached the nominal spin-speed (at time t2) to begin
the data transfer. Nevertheless, even though an entire data
transfer may occur faster if the transfer does not begin until the
disk reaches the nominal spin-speed, there are other advantages to
beginning a data transfer at the reduced spin-speed. For example,
if a user makes a request for information stored as data on a disk
that is at rest (i.e., not spinning), the response time (i.e., the
time it takes to display at least a portion of the information to
the user) may be quicker if the data is read from the disk at the
reduced spin-speed. For a more specific example, a user of a laptop
computer may click on a HELP button in an attempt to learn about
certain features of a software program. Assume that the information
necessary to display an initial HELP screen is stored on a disk
that is at rest, and that the sooner the HELP screen can be
displayed the better (from the standpoint of the user). If the
information (relating to the initial HELP screen) is read from the
disk as soon as the disk reaches the reduced spin-speed, then the
user will experience a faster response time. Then, while the user
provides more details about the help that they desire (e.g., as
prompted by the initial HELP screen), the disk can be spun-up to
the nominal spin-speed (although this is not necessary).
[0059] In accordance with an embodiment of the present invention,
if less than a specific amount of work is to be performed (e.g., a
transfer of less than X blocks of data) following a disk spinning
up from rest, then the disk is spun up to its reduced spin-speed
and the work is began at the reduced spin-speed.
[0060] Further embodiments of the present invention, which will now
be described, provide systems and methods for controlling a
spin-speed at which an initial data transfer occurs after a disk
begins to spin-up from rest. The disk may have been at rest because
the storage device was powered down (i.e., off), or because the
disk was purposefully spun-down to conserve power (i.e., as part of
a power saving scheme). In either situation, it is likely that the
head is parked on a ramp when the disk is at rest, to prevent the
head from contacting the disk, as was explained above.
[0061] As will be described with reference to FIG. 11, in
accordance with embodiments of the present invention, whether the
initial data transfer occurs at a reduced spin-speed or a nominal
spin-speed can be based on whether an amount of work to be
performed is less than a threshold. This determination, which is
performed at a step 1102, can be performed, for example, by a disk
controller, by a microprocessor within a storage device, or by a
host that is interfacing with the storage device, or any
combination thereof. In accordance with an embodiment of the
present invention, the amount of work can be defined at least in
part by an amount of data to be transferred (i.e., read from or
written to the disk). In accordance with another embodiment of the
present invention, the amount of work can be defined at least in
part by an estimated amount of time necessary to complete the work.
A disk controller, microprocessor and/or host may perform such an
estimate, e.g., using a lookup table, model, etc. These are just
examples, which are not meant to limit the present invention.
[0062] The threshold, which can be predefined or selectable (e.g.,
by the host) should be consistent with how the amount of work is
defined. For example, if the amount of work is defined by the
amount of data blocks to be transferred between a disk and a host,
then the threshold should specify a threshold number of data
blocks. For example, referring back to FIG. 10, the threshold can
be set as X data blocks, which is the point at which it would be
faster to wait until the disk spins up to the nominal spin-speed to
begin the data transfer, rather than begin the data transfer at the
reduced speed.
[0063] As specified at step 1104, if it is determined that the
amount of work is less than the threshold, then the disk is spun-up
to the reduced spin-speed, at which point the initial data transfer
can begin. If, however, it is determined that the amount of work is
greater than the threshold, then the initial data transfer does not
begin until the disk is spun-up to the nominal spin-speed, as
specified at step 1106.
[0064] As was explained above with reference to FIGS. 4A and 4B,
the spindle motor back EMF detection circuit 452 can be used to
monitor the spin-speed of the disk. Referring back to FIG. 1, the
disk controller 128 can be used to be used to control the reading
from and writing to the disk 102. The microprocessor 120 and/or the
VCM driver 108 can control the spin-speed of the VCM 130, and
thereby the spin-speed of the disk 102.
[0065] While an initial data transfer is being performed at a
reduce spin-speed (or after the transfer is complete), the storage
device may receive instructions to perform additional work (e.g.,
transfer more data). Referring again to FIG. 11, in accordance with
an embodiment of the present invention, if the addition work is
requested, then the disk is spun-up from the reduced spin-speed to
the nominal spin-speed, and the additional work (e.g., data
transfers) are performed at the nominal spin-speed, as specified at
step 1112. For example, this can occur regardless of the extent of
the additional work (as shown by the dashed line), or
alternatively, only if the additional work is above the a
threshold, as expressed by step 1108. This threshold can be the
same threshold used in step 1102, or it may be that the additional
work requested must be above a further threshold in order to cause
the disk to be spun-up to the nominal spin-speed. In still another
embodiment, the disk is spun up to the nominal spin-speed if the
additional work causes a total amount of work to exceed a threshold
(e.g., the threshold used in step 1102, or some other threshold),
or if a total amount of remaining work exceeds a threshold. If the
additional work does not exceed a threshold, in accordance with how
the threshold is defined, the spin-speed can be kept at the reduced
spin-speed to save power, as specified at steps 1108 and 1110.
Further, a ramp unload operation can be performed and the disk can
be spun back down to rest, if a defined period of inactivity is
exceeded, e.g., following step 1104, 1106, 1110 or 1112.
[0066] In accordance with another embodiment, an initial data
transfer, after the disk has been at rest, is performed at the
reduced spin-speed regardless of the amount of data to be
transferred. Then the disk is spun up to the nominal spin-speed so
that additional data transfers (if necessary) can be performed at
the nominal spin-speed. Such an embodiment is especially useful in
situations where a user makes a request for information that
requires data to be read from a disk that is at rest at the time of
the request, because at least a portion of the information can be
presented to the user more quickly (than if the disk had to spin-up
to the nominal spin-speed before performing a read). This was
explained above in some more detail.
[0067] In accordance with some embodiments of the present
invention, it is the host that decides the appropriate spin-speed
at which to read and write to a disk. In such embodiments, the host
instructs the storage device to achieve a specific spin-speed at
which to perform data transfers (initial or otherwise). More
generally, the drive will perform data transfers at instructed
spin-speeds that are specified by the host.
[0068] The embodiments just described above, which relate to
performing reads and writes at more than one speed, can be combined
with the other embodiments discussed above relating to beginning
ramp loads operations at lower spin-speeds and/or earlier times
than is conventional. Such combinations can be used to further
reduce a time-to-ready in a rotatable media storage device. For
example, assume a storage device can read or write to a disk at
both a reduced spin-speed and a nominal spin-speed, and that the
reduced spin-speed is used for initial data transfers (e.g., if an
initial data transfer does not exceed a threshold). In accordance
with an embodiment of the present invention, a ramp load operation
is initiated before the disk spin-speed reaches the reduced
spin-speed, such that the disk will achieve the reduced spin-speed
just prior to a head reaching an outer diameter of the disk.
[0069] It is also possible that more that two spin-speeds can be
used. For example, there can be a low spin-speed, a medium
spin-speed and a high spin-speed, or even more than three different
spin-speeds. Thresholds, similar to those described above, can be
used to select which of the spin-speeds should be used to perform
initial data transfers and/or further data transfers following the
initial data transfers. Unless otherwise specified, it should be
assumed that the lowest spin-speed (i.e., a reduced spin-speed) is
not the nominal spin-speed, and that any spin-speed greater than
the lowest spin-speed may be defined as the nominal spin-speed.
[0070] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example, and not limitation. It will be
apparent to persons skilled in the relevant art that various
changes in form and detail can be made therein without departing
from the spirit and scope of the invention.
[0071] The present invention has been described above with the aid
of functional building blocks illustrating the performance of
specified functions and relationships thereof. The boundaries of
these functional building blocks have often been arbitrarily
defined herein for the convenience of the description. Alternate
boundaries can be defined so long as the specified functions and
relationships thereof are appropriately performed. Any such
alternate boundaries are thus within the scope and spirit of the
claimed invention.
[0072] The breadth and scope of the present invention should not be
limited by any of the above-described exemplary embodiments, but
should be defined only in accordance with the following claims and
their equivalents.
* * * * *