Title: Split VCM actuator
Abstract: A split actuator comprising two spring coupled actuators that share a common pivot bearing. The two reduced inertia actuators permit overlapping motions during a seek operation thereby reducing dead times in transfer of data between disk and transducers disposed on the actuators. A spring member that spring couples the two actuators boosts relative motions by storing and releasing spring potential energy selectively. The spring member is also configured so as to substantially restrict the relative motions of the two actuators to rotational motions about a common axis of the common pivot bearing. Rigidity of the spring member to non-rotational relative motions, as well as tuning of the spring member to provide a rigid response to selected frequencies, the spring member in conjunction with the common pivot bearing result in mechanical disturbance being substantially common to the two actuators, thereby allowing predictable and manageable disturbance corrections.
Patent Number: 6,847,504 Issued on 01/25/2005 to Bennett, et al.
| Inventors:
|
Bennett; George J. (Murrieta, CA);
Patton, III; Charles R. (Murrieta, CA)
|
| Assignee:
|
Western Digital Technologies, Inc. (Lake Forest, CA)
|
| Appl. No.:
|
137227 |
| Filed:
|
April 30, 2002 |
| Current U.S. Class: |
360/78.12; 360/77.02 |
| Intern'l Class: |
G11B 005/596 |
| Field of Search: |
360/78.12,78.04,75,77.02,77.06,97.01,97.02,25,31,245.2,245.7,264.4,264.5,264.7
|
References Cited [Referenced By]
U.S. Patent Documents
| 4943875 | Jul., 1990 | Reidenbach et al. | 360/245.
|
| 6005743 | Dec., 1999 | Price et al.
| |
| 6104581 | Aug., 2000 | Huang et al.
| |
| 6226156 | May., 2001 | Kasetty et al.
| |
| 6301073 | Oct., 2001 | Gillis et al. | 360/97.
|
| 6344938 | Feb., 2002 | Smith | 360/25.
|
| 6378037 | Apr., 2002 | Hall | 711/113.
|
| 6442002 | Aug., 2002 | Pan | 360/266.
|
| 6587301 | Jul., 2003 | Smith | 360/75.
|
| 6600622 | Jul., 2003 | Smith | 360/77.
|
| 6618221 | Sep., 2003 | Gillis et al. | 360/97.
|
| 6653763 | Nov., 2003 | Wang et al. | 310/369.
|
| 6680806 | Jan., 2004 | Smith | 360/31.
|
| 6683737 | Jan., 2004 | Gong et al. | 360/31.
|
| 6697214 | Feb., 2004 | Dimitri et al. | 360/97.
|
| 6710952 | Mar., 2004 | Smith | 360/31.
|
| 6747849 | Jun., 2004 | Le et al. | 360/245.
|
Primary Examiner: Tran; Sinh
Assistant Examiner: Tzeng; Fred
Attorney, Agent or Firm: Shara, Esq.; Milad G.
Knobbe Martens Olson & Bear LLP
Claims
What is claimed is:
1. A disk drive comprising:
a rotatable disk having a magnetic recording media formed on a surface of
the rotatable disk wherein the rotatable disk defines a plurality of
concentric data tracks;
a pivot point positioned adjacent the rotatable disk wherein the pivot
point defines an axis;
a rotatable pivot assembly positioned on the pivot point so as to rotate
about the axis defined by the pivot point;
a first actuator having a first transducer coupled to the pivot assembly so
as to be rotatable about the axis wherein the first actuator extends over
the surface of the rotatable disk such that rotation of the pivot assembly
results in movement of the first transducer over the surface of the
rotatable disk such that the first transducer can be positioned adjacent
selected data tracks;
a first coil that is disposed with respect to the first actuator so as to
induce movement of the first actuator and the first transducer with
respect to the surface of the disk;
a second actuator having a second transducer coupled to the pivot assembly
so as to be rotatable about the axis wherein the second actuator extends
over the surface of the rotatable disk such that rotation of the pivot
assembly results in movement of the second transducer over the surface of
the rotatable disk such that the second transducer can be positioned
adjacent selected data tracks;
a second coil that is disposed with respect to the second actuator so as to
induce movement of the second actuator and the second transducer with
respect to the surface of the disk; and
a mechanical interconnect structure that couples the first and second
actuators so as to permit limited relative movement of the first and
second actuators such that when the pivot assembly is rotated to a first
angular position with the first transducer in a first position adjacent a
first selected data track and the second transducer is in a second
position adjacent a second selected data track, the first transducer can
be moved by the first coil to a third position adjacent a third selected
data track without moving the second transducer from the second selected
data track.
2. The disk drive of claim 1, wherein the second actuator is coupled to the
pivot assembly by the mechanical interconnect structure thereby coupling
the first and second actuators wherein the first and second actuators are
influenced by a common vibration associated with the pivot assembly.
3. The disk drive of claim 2, wherein the disk drive comprises one or more
disks wherein each disk defines a top surface and a bottom surface.
4. The disk drive of claim 3, wherein each of the first and second
actuators comprises at least one arm wherein at least one transducer is
disposed on each of the at least one arm and wherein the at least one arm
of the first actuator is arranged with respect to the at least one arm of
the second actuator in an alternating manner such that the alternating
arms are arranged in an interleaving manner with respect to the one or
more disks.
5. The disk drive of claim 4, wherein the disk drive comprises two disks.
6. The disk drive of claim 5, wherein the first actuator comprises two arms
and wherein the second actuator comprises one arm interposed between the
two arms of the first actuator.
7. The disk of claim 4, wherein the disk drive comprises three disks.
8. The disk of claim 7, wherein the first actuator comprises two arms and
wherein the second actuator comprises two arms that alternate with the two
arms of the first actuator.
9. The disk drive of claim 2, wherein the pivot assembly comprises a
cylindrical member having a cylindrical axis that is substantially
co-axial with the axis defined by the pivot point wherein the cylindrical
member is adapted to allow mounting of the first and second actuators such
that the first and second actuators are mechanically coupled.
10. The disk drive of claim 1, wherein the mechanical interconnect
structure is a spring member that spring couples the first and second
actuators.
11. The disk drive of claim 10, wherein the spring member comprises a
plurality of flex sections wherein each flex section is a vertically
oriented panel with a first edge attached to a portion of the first
actuator and a second edge attached to a portion of the second actuator
wherein the first and second edges are two opposing edges.
12. The disk drive of claim 11, wherein the flex sections allow relative
motion of the first and second actuators in a first mode while resisting
other modes of the relative motion.
13. The disk drive of claim 12, wherein the first and second edges of the
flex section are inner and outer edges that attach to the first and second
actuators respectively.
14. The disk drive of claim 13, wherein the spring member comprises four
flex sections distributed substantially evenly circumferentially so as to
provide symmetry about the axis defined by the pivot wherein the symmetry
of the arrangement of the flex sections inhibits non-rotational relative
motion between the first and second actuators.
15. The disk drive of claim 11, wherein the flex sections allow a limited
spring-coupled rotational relative motion between the first and second
actuators.
16. The disk drive of claim 10, wherein the spring member acquires and
stores potential energy as the first and second actuators undergo relative
rotational displacement.
17. The disk drive of claim 16, wherein the spring member releases the
stored potential energy at a selected instance so as to facilitate
subsequent rotational relative motion of the first and second actuators.
18. The disk drive of claim 17, wherein each of the first and second
actuators has a reduced inertia thereby allowing greater acceleration for
a given applied power.
19. The disk drive of claim 18, wherein the spring member allows the first
transducer to begin moving in a seek operation while the second transducer
is performing a disk data transfer on a selected data track.
20. The disk drive of claim 19, wherein separate movements of the first and
second actuators reduces a dead time during which disk data transfer is
not being performed.
21. The disk drive of claim 20, wherein the dead time is substantially zero
for seek operations involving seek lengths less than a selected distance.
22. The disk drive of claim 16, wherein controlling of the motion of the
first and second actuators is performed so as to utilize the oscillatory
property of the spring member thereby enhancing the controlling effect on
the motion of the first and second actuators.
23. A disk drive comprising:
a rotatable disk having a magnetic recording media formed on a surface of
the rotatable disk wherein the rotatable disk defines a plurality of
concentric data tracks;
a first actuator having a first transducer and a first coil mounted to a
pivot assembly so as to be rotatable about an axis defined by the pivot
assembly wherein the first coil induces movement of the first actuator;
a second actuator having a second transducer and a second coil mounted on
the pivot assembly so as to be rotatable about the axis defined by the
pivot assembly wherein the second coil induces movement of the second
actuator; and
a spring member that interconnects and provides a spring coupling between
the first and second actuators such that motion of one actuator affects
the other actuator wherein the spring coupling allows the spring member to
acquire spring potential energy during a first relative motion of the
first and second actuators and release at least a selected portion of the
acquired spring potential energy during a second relative motion thereby
increasing the rate at which the second relative motion occurs and wherein
the spring coupling involves a force that is mutual between the two
actuators and generally isolated therebetween such that effects of the
force on other parts of the disk drive is reduced.
24. The disk drive of claim 23, wherein the spring coupling provided by the
spring member allows one of the two actuators to be controlled predictably
in response to motion of the other actuator.
25. The disk drive of claim 24, wherein the first actuator moves while the
second actuator remains over a selected data track wherein the second
actuator is controlled to compensate for the spring member acquiring the
spring potential energy thereby allowing the first transducer to initiate
a seek operation while the second transducer is performing a disk data
transfer.
26. The disk drive of claim 25, wherein mechanical disturbance experienced
by one actuator is transferred to the other actuator predictably via the
spring coupling thereby allowing the coupled mechanical disturbance to be
compensated in both actuators in a simplified manner.
27. The disk drive of claim 23, wherein the spring member includes a
structure that allows relative motion of the first and second actuators in
a first mode while resisting other modes of the relative motion.
28. The disk drive of claim 27, wherein the spring member allows a limited
range of rotational relative motion between the first and second actuators
about the axis defined by the pivot assembly wherein the spring member
also inhibits non-rotational relative motions between the first and second
actuators.
29. The disk drive of claim 28, wherein the spring member comprises a
plurality of flex sections wherein each flex section is a vertically
oriented panel with a first edge attached to a portion of the first
actuator and a second edge attached to a portion of the second actuator
wherein the first and second edges are two opposing edges.
30. The disk drive of claim 29, wherein the first and second edges of the
flex section are inner and outer edges that attach to the first and second
actuators respectively.
31. The disk drive of claim 30, wherein the spring member comprises four
flex springs distributed substantially evenly circumferentially so as to
provide symmetry about the axis defined by the pivot wherein the symmetry
of the arrangement of the flex springs inhibits non-rotational relative
motion between the inner and outer portions.
32. The disk drive of claim 23, wherein the spring member acquires and
stores potential energy as the first and second actuators undergo relative
rotational displacement.
33. The disk drive of claim 32, wherein the spring member releases the
stored potential energy at a selected instance so as to facilitate
subsequent rotational relative motion of the first and second actuators.
34. The disk drive of claim 33, wherein each of the first and second
actuators has a reduced inertia thereby allowing greater acceleration for
a given applied power.
35. The disk drive of claim 34, wherein the spring member allows the first
transducer to begin moving in a seek operation while the second transducer
is performing a disk data transfer on a selected data track.
36. The disk drive of claim 32, wherein separate movements of the first and
second actuators reduces a dead time during which disk data transfer is
not being performed.
37. The disk drive of claim 36, wherein the dead time is substantially zero
for seek operations involving seek lengths less than a selected distance.
38. The disk drive of claim 32, wherein controlling of the motion of the
first and second actuators is performed so as to utilize the oscillatory
property of the spring member thereby enhancing the controlling effect on
the motion of the first and second actuators.
39. A method of performing a seek operation in a hard disk drive comprising
a rotatable disk having a magnetic recording media, and an actuator
assembly that includes a first transducer mounted on a first rotatable
actuator and a second transducer mounted on a second rotatable actuator,
the method comprising:
initiating movement of the first actuator at time T0 while maintaining the
second transducer at a first location on the disk to perform a disk data
transfer, wherein the resulting relative motion of the first and second
actuators causes an interaction of the first and second actuators wherein
the interaction causes some of kinetic energy of the relative motion to be
stored as potential energy; and
terminating the disk data transfer of the second transducer at the first
location at time T1 and initiating movement of the second actuator wherein
at least a portion of the potential energy stored as a result of the
interaction of the first and second actuators is converted into kinetic
energy of the second actuator thereby increasing the rate of the second
actuator's movement.
40. The method of claim 39, wherein initiating movement of the first
actuator comprises initially supplying the first actuator with a
substantially full power available to both actuators so as to cause an
increased acceleration of the first actuator.
41. The method of claim 40, wherein the increased acceleration of the first
actuator reduces duration of first actuator's movement.
42. The method of claim 39, wherein maintaining the second transducer at
the first location while the first actuator is moving comprises supplying
the second actuator with controlled power to compensate for interaction
between the first and second actuators.
43. The method of claim 42, wherein the interaction between the first and
second actuators is a spring-coupled interaction.
44. The method of claim 43, wherein initiating movement of the second
actuator comprises releasing the second actuator by stopping the
controlled power thereby allowing the spring-coupled second actuator to be
accelerated along with the first actuator.
45. The method of claim 44, wherein the spring coupling reduces duration of
the second actuator's movement.
46. The method of claim 39, further comprising stopping the first actuator
and performing a disk data transfer with the first transducer while the
second actuator is still in motion.
47. The method of claim 46, wherein switching of the second transducer to
the first transducer as the disk operating transducer reduces a dead time
during which disk data transfer is not being performed.
48. The method of claim 47, wherein the dead time is substantially zero for
seek operations involving seek lengths less than a selected distance.
49. The method of claim 46, wherein stopping the first actuator comprises
supplying the first actuator with a substantially full power available to
both actuators so as to cause an increased deceleration of the first
actuator.
50. The method of claim 39, further comprising stopping the first actuator
and utilizing the spring member to facilitate stopping of the second
actuator wherein the second transducer performs a disk data transfer after
the second actuator has stopped.
51. The method of claim 50, wherein stopping the second actuator comprises
controlling the deceleration of the first and second actuators such that
oscillatory motion between the two actuators due to the spring interaction
enhances the effects of the controlled deceleration.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to computer data storage and, in particular, relates
to a disk drive having a split VCM actuator that provides advantages in
performance and cost savings.
2. Description of the Related Art
Disk drive storage devices are an important component in virtually all
computer systems. In particular, disk drives provide computer systems with
the ability to store and retrieve data in a non-volatile manner such that
the data is maintained even if power is removed from the device. The
popularity of these devices is based on their ability to quickly store and
retrieve large quantities of digital information at low cost.
The typical disk drive comprises one or more pivotally mounted disks (also
referred to as platters) having a magnetic recording layer disposed
thereon and one or more magnetic transducer elements for affecting and
sensing the magnetization states of the recording layer. Typically one
transducer is associated with one magnetic layer of the disk. Thus, for
example, a single disk having two recording layers has one transducer
disposed adjacent each of the two recording layers, for a total of two
transducers.
The recording layer comprises a large number of relatively small domains
disposed thereon that can be independently magnetized according to a
localized applied magnetic field and that can be maintained in the
magnetized state when the external field is removed. The domains are
grouped into concentric circular tracks each having a unique radius on the
disk, and data is written to or read from each track by positioning the
transducer over the disk at the corresponding radius while the disk is
rotated at a fixed angular speed.
To position the transducer with respect to the disk, the typical disk drive
further comprises a pivotally mounted actuator, typically using a pivot
bearing. The transducer is typically mounted on one end of the actuator,
and the other end of the actuator comprises a coil that forms part of a
voice coil motor (VCM). The actuator is mechanically balanced with respect
to the pivot bearing so as to facilitate rotation of the actuator, and
thus the movement of the transducer, by a torque exerted by the VCM in a
manner known in the art. To apply the torque to the actuator in a
controlled manner, the disk drive further comprises a servo-controller for
controlling the VCM. The VCM comprises a coil of conducting wire wound
into a plurality of loops and a permanent magnet disposed adjacent the
coil. The servo-controller initiates movement of the actuator arm by
directing a control current to flow through the coil that generates a
torque that causes rotation of the actuator about its pivot bearing.
Because the direction of the torque is dictated by the direction of
control current flow, the servo-controller is able to move the transducer
to a different location by first directing the control current through the
coil so as to angularly accelerate the actuator in a first direction and
then reversing the control current so as to angularly decelerate the
actuator.
The movement of the transducer in the foregoing manner is known as a seek
operation, wherein the transducer is moved from a first track location to
a second track location. The distance between the first and second track
locations is known as a seek length, and is typically expressed as the
number of tracks between the first and second track locations. The time
required to complete the seek operation is known as a seek time, and the
seek time is one of the parameters that contribute to the overall
performance of the disk drive.
A traditional actuator that performs the aforementioned seek operation is
typically configured such that all the transducers mounted thereon are
substantially fixed relative to each other. As a result, the transducers
mounted on the common actuator move in unison during seek operations. Such
fixed configuration of the transducers and the common actuator has
drawbacks that are well known in the art.
One drawback associated with the common actuator with multiple transducers
relates to a relatively large moment of inertia resulting from such a
configuration. As is understood in the art, moment of inertia of a
rotating object is inversely proportional to its angular acceleration
resulting from a given applied torque. Thus the common actuator having a
relatively large moment of inertia accelerates at a lower rate,
disadvantageously resulting in longer seek times. One way to compensate
for the relatively large moment of inertia of the actuator, so as to
achieve greater acceleration, is to increase the torque applied to the
actuator. As is also understood in the art, such increase in applied
torque disadvantageously requires greater power expenditure or use of
higher torque generating (and higher cost) magnets.
Another drawback associated with the common actuator relates to the common
motion of the transducers during seek operations. Because the transducers
move in unison, seek operations result in "dead times" during which data
is not transferred between the transducer(s) and the recording layers
(read or write). Data transferred between the transducer(s) and the
recording layers (read or write) is called a disk data transfer. The dead
times disadvantageously leave gaps interspersed between active time
segments of available data transfer time that affects the rate at which
information can be transferred between the disk and a host computer
(referred to as throughput). Host to disk data transfers are distinguished
from internal transfers by calling them host data transfers.
To maintain a specified throughput capability of the disk drive, the dead
time gaps can be compensated for in various manners. A general solution is
to increase the rate at which data is transferred from the disk to the
host computer during the "live" (non-dead) times. This objective can be
achieved by increasing the bandwidth of a data channel through which the
data to and from the disk is processed. Concurrently, the rate of data
transfer between the transducer and the disk can be increased. One way to
achieve increase in the data transfer rate between the transducer and the
disk is to increase the rotational speed of the disk. As is understood in
the art, increasing the rotational speed of the disk increases the rate at
which the transducer interacts with the magnetic domains disposed on the
tracks.
Spinning the disk faster, however, has drawbacks. For example, spinup time
is longer for a faster spinning disk. Also, the track density of the disk,
typically expressed as tracks per inch (TPI), needs to be decreased in
order to accommodate effects associated with increase in rotational speed
of the disk. These effects include aerodynamic vibrations between the
transducer and the disk, bearing vibrations, and other disturbance
producing forces. Thus in order to maintain a specified storage capacity
of the disk drive, the number of disks needs to increase to compensate for
the reduction in TPI. Such an increase in the number of disks, along with
the increase in rotational speed, lead to additional heat generation and
acoustic effects that need to be dealt with. Furthermore, material cost
associated with additional disks is a substantial amount.
From the foregoing, it will be appreciated that various solutions are
implemented to compensate for the dead time gaps in data transfer
associated with the common actuator. Each of the various solutions
described has advantages and drawbacks associated with it. Hence, as is
well known in the art, a great deal of effort is made in the disk drive
industry to reduce or eliminate the seek time.
One solution proposed for reducing or eliminating the dead time gaps in
data transfer is to perform overlapping seek operations using two or more
independent actuators. The dead time gaps may be eliminated in such a
multiple actuator disk drive by, for example, performing a seek operation
with a first transducer mounted on a first actuator while a second
transducer mounted on a second actuator is performing a data transfer
operation. Thus, seek operations performed by each of the actuators is
hidden such that dead time gaps do not exist in the overall data transfer.
Examples of disk drives that utilize multiple actuators and thus are
adaptable for such hidden seek tasks are disclosed in U.S. Pat. No.
5,343,345 to Gilovich, U.S. Pat. No. 5,761,007 to Price et al (assigned to
International Business Machines Corporation), and U.S. Pat. No. 5,901,010
to Glover et al (assigned to Cirrus Logic, Inc.).
Unfortunately the independent actuators exemplified in the disclosed
patents suffer from drawbacks, including mechanical disturbance crosstalk
between the two actuators. Specifically, each of the two actuators is
mounted on its own pivot bearing assembly, typically in the form of a ball
bearing. Each actuator and bearing generates a mechanical disturbance that
is independent of the other actuator and its bearing. The two sources of
vibration are known to combine in a manner that makes compensation of each
transducer substantially difficult. Expected performance gains have not
been realized because of these problems, and the dual actuator drives have
not done well in the market as a result.
Thus from the foregoing drawbacks associated with the common actuator and
problems encountered by proposed solutions, it will be appreciated that
there is a continuing need for improving the manner in which transducers
are moved. To this end, there is a need for an apparatus that allows seeks
to be overlapped effectively so as to reduce or eliminate dead time gaps
in the data transfer to and from the disk. There is a need for an actuator
that performs such operations while effectively compensating for the
debilitating vibrations.
SUMMARY OF THE INVENTION
One aspect of the invention relates to a disk drive comprising a rotatable
disk having a magnetic recording media formed on a surface of the
rotatable disk. The rotatable disk defines a plurality of concentric data
tracks. The disk drive further comprises a pivot point positioned adjacent
the rotatable disk wherein the pivot point defines an axis. The disk drive
further comprises a rotatable pivot assembly positioned on the pivot point
so as to rotate about the axis defined by the pivot point. The disk drive
further comprises a first actuator having a first transducer coupled to
the pivot assembly so as to be rotatable about the axis. The first
actuator extends over the surface of the rotatable disk such that rotation
of the pivot assembly results in movement of the first transducer over the
surface of the rotatable disk such that the first transducer can be
positioned adjacent selected data tracks. The disk drive further comprises
a first coil that is disposed with respect to the first actuator so as to
induce movement of the first actuator and the first transducer with
respect to the surface of the disk. The disk drive further comprises a
second actuator having a second transducer coupled to the pivot assembly
so as to be rotatable about the axis. The second actuator extends over the
surface of the rotatable disk such that rotation of the pivot assembly
results in movement of the second transducer over the surface of the
rotatable disk such that the second transducer can be positioned adjacent
selected data tracks. The disk drive further comprises a second coil that
is disposed with respect to the second actuator so as to induce movement
of the second actuator and the second transducer with respect to the
surface of the disk. The disk drive further comprises a mechanical
interconnect structure that couples the first and second actuators so as
to permit limited relative movement of the first and second actuators such
that when the pivot assembly is rotated to a first angular position with
the first transducer in a first position adjacent a first selected data
track and the second transducer is in a second position adjacent a second
selected data track, the first transducer can be moved by the first coil
to a third position adjacent a third selected data track without moving
the second transducer from the second selected data track.
In one embodiment, the second actuator is coupled to the pivot assembly by
the mechanical interconnect structure thereby coupling the first and
second actuators. The first and second actuators are influenced by a
common vibration associated with the pivot assembly. The disk drive
comprises one or more disks wherein each disk defines a top surface and a
bottom surface. Each of the first and second actuators comprises at least
one arm. At least one transducer is disposed on each of the at least one
arm and the at least one arm of the first actuator is arranged with
respect to the at least one arm of the second actuator in an alternating
manner such that the alternating arms are arranged in an interleaving
manner with respect to the one or more disks.
In one embodiment, the disk drive comprises two disks. The first actuator
comprises two arms and wherein the second actuator comprises one arm
interposed between the two arms of the first actuator. In another
embodiment, the disk drive comprises three disks. The first actuator
comprises two arms and wherein the second actuator comprises two arms that
alternate with the two arms of the first actuator.
In one embodiment, the pivot assembly comprises a cylindrical member having
a cylindrical axis that is substantially co-axial with the axis defined by
the pivot point. The cylindrical member is adapted to allow mounting of
the first and second actuators such that the first and second actuators
are mechanically coupled. The mechanical interconnect structure is a
spring member that spring couples the first and second actuators. The
spring member comprises a plurality of flex sections wherein each flex
section is a vertically oriented panel with a first edge attached to a
portion of the first actuator and a second edge attached to a portion of
the second actuator. The first and second edges are two opposing edges.
The flex springs allow relative motion of the first and second actuators
in a first mode while resisting other modes of the relative motion.
In one embodiment, the first and second edges of the flex section are inner
and outer edges that attach to the first and second actuators
respectively. The spring member comprises four flex sections distributed
substantially evenly circumferentially so as to provide symmetry about the
axis defined by the pivot. The symmetry of the arrangement of the flex
sections inhibits non-rotational relative motion between the first and
second actuators. The flex sections allow a limited spring-coupled
rotational relative motion between the first and second actuators.
The spring member acquires and stores potential energy as the first and
second actuators undergo relative rotational displacement. The spring
member releases the stored potential energy at a selected instance so as
to facilitate subsequent rotational relative motion of the first and
second actuators. In one embodiment, each of the first and second
actuators has a reduced inertia thereby allowing greater acceleration for
a given applied power.
In one embodiment, the spring member allows the first transducer to begin
moving in a seek operation while the second transducer is performing a
disk data transfer on a selected data track. Separate movements of the
first and second actuators reduces a dead time during which disk data
transfer is not being performed. The dead time is substantially zero for
seek operations involving seek lengths less than a selected distance. In
one embodiment, controlling of the motion of the first and second
actuators is performed so as to utilize the oscillatory property of the
spring member thereby enhancing the controlling effect on the motion of
the first and second actuators.
Another aspect of the invention relates to a disk drive comprising a
rotatable disk having a magnetic recording media formed on a surface of
the rotatable disk wherein the rotatable disk defines a plurality of
concentric data tracks. The disk drive further comprises a first actuator
having a first transducer and a first coil mounted to a pivot assembly so
as to be rotatable about an axis defined by the pivot assembly wherein the
first coil induces movement of the first actuator. The disk drive further
comprises a second actuator having a second transducer and a second coil
mounted on the pivot assembly so as to be rotatable about the axis defined
by the pivot assembly wherein the second coil induces movement of the
second actuator. The disk drive further comprises a spring member that
interconnects and provides a spring coupling between the first and second
actuators such that motion of one actuator affects the other actuator. The
spring coupling allows the spring member to acquire spring potential
energy during a first relative motion of the first and second actuators
and release at least a selected portion of the acquired spring potential
energy during a second relative motion thereby increasing the rate at
which the second relative motion occurs and wherein the spring coupling
involves a force that is mutual between the two actuators and generally
isolated therebetween such that effects of the force on other parts of the
disk drive is reduced.
The spring coupling provided by the spring member allows one of the two
actuators to be controlled predictably in response to motion of the other
actuator. In one embodiment, the first actuator moves while the second
actuator remains over a selected data track. The second actuator is
controlled to compensate for the spring member acquiring the spring
potential energy thereby allowing the first transducer to initiate a seek
operation while the second transducer is performing a disk data transfer.
Mechanical disturbance experienced by one actuator is transferred to the
other actuator predictably via the spring coupling thereby allowing the
coupled mechanical disturbance to be compensated in both actuators in a
simplified manner.
In one embodiment, the spring member includes a structure that allows
relative motion of the first and second actuators in a first mode while
resisting other modes of the relative motion. The spring member allows a
limited range of rotational relative motion between the first and second
actuators about the axis defined by the pivot assembly wherein the spring
member also inhibits non-rotational relative motions between the first and
second actuators. The spring member comprises a plurality of flex sections
wherein each flex section is a vertically oriented panel with a first edge
attached to a portion of the first actuator and a second edge attached to
a portion of the second actuator. The first and second edges are two
opposing edges.
In one embodiment, the first and second edges of the flex section are inner
and outer edges that attach to the first and second actuators
respectively. The spring member comprises four flex springs distributed
substantially evenly circumferentially so as to provide symmetry about the
axis defined by the pivot wherein the symmetry of the arrangement of the
flex springs inhibits non-rotational relative motion between the inner and
outer portions.
The spring member acquires and stores potential energy as the first and
second actuators undergo relative rotational displacement. The spring
member releases the stored potential energy at a selected instance so as
to facilitate subsequent rotational relative motion of the first and
second actuators. In one embodiment, each of the first and second
actuators has a reduced inertia thereby allowing greater acceleration for
a given applied power. The spring member allows the first transducer to
begin moving in a seek operation while the second transducer is performing
a disk data transfer on a selected data track. Separate movements of the
first and second actuators reduces a dead time during which disk data
transfer is not being performed. The dead time is substantially zero for
seek operations involving seek lengths less than a selected distance. In
one embodiment, controlling of the motion of the first and second
actuators is performed so as to utilize the oscillatory property of the
spring member thereby enhancing the controlling effect on the motion of
the first and second actuators.
Another aspect of the invention relates to a method of performing a seek
operation in a hard disk drive comprising a rotatable disk having a
magnetic recording media, and an actuator assembly that includes a first
transducer mounted on a first rotatable actuator and a second transducer
mounted on a second rotatable actuator. The method comprises initiating
movement of the first actuator at time T0 while maintaining the second
transducer at a first location on the disk to perform a disk data
transfer. The resulting relative motion of the first and second actuators
causes an interaction of the first and second actuators wherein the
interaction causes some of kinetic energy of the relative motion to be
stored as potential energy. The method further comprises terminating the
disk data transfer of the second transducer at the first location at time
T1 and initiating movement of the second actuator wherein at least a
portion of the potential energy stored as a result of the interaction of
the first and second actuators is converted into kinetic energy of the
second actuator thereby increasing the rate of the second actuator's
movement.
In one implementation, initiating movement of the first actuator comprises
initially supplying the first actuator with a substantially full power
available to both actuators so as to cause an increased acceleration of
the first actuator. The increased acceleration of the first actuator
reduces duration of first actuator's movement. Maintaining the second
transducer at the first location while the first actuator is moving
comprises supplying the second actuator with controlled current to
compensate for interaction between the first and second actuators.
The interaction between the first and second actuators is a spring-coupled
interaction. Initiating movement of the second actuator comprises
releasing the second actuator by stopping the controlled power thereby
allowing the spring-coupled second actuator to be accelerated along with
the first actuator. The spring coupling reduces duration of the second
actuator's movement.
In another implementation, the method of performing a seek operation
further comprises stopping the first actuator and performing a disk data
transfer with the first transducer while the second actuator is still in
motion. Switching of the second transducer to the first transducer as the
disk operating transducer reduces the dead time during which disk data
transfer is not being performed. The dead time is substantially zero for
seek operations involving seek lengths less than a selected distance. In
one implementation, stopping the first actuator comprises supplying the
first actuator with a substantially full power available to both actuators
so as to cause an increased deceleration of the first actuator.
In one implementation, the method of performing a seek operation further
comprises stopping the first actuator and utilizing the spring member to
facilitate stopping of the second actuator wherein the second transducer
performs a disk data transfer after the second actuator has stopped. In
one implementation, stopping the second actuator comprises controlling the
deceleration of the first and second actuators such that oscillatory
motion between the two actuators due to the spring interaction enhances
the effects of the controlled deceleration.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A illustrates a top view of a typical prior art hard disk drive;
FIG. 1B illustrates a side view of the prior art hard disk drive;
FIG. 2 illustrates a symbolic functional representation of a split
actuator;
FIG. 3A illustrates an isolated exploded view of one embodiment of the
split actuator comprising a combination of a first actuator and a second
actuator wherein both are mounted on a common pivot bearing;
FIG. 3B illustrates a side view of a two platter disk drive in which the
split actuator of FIG. 3A may be utilized;
FIG. 3C illustrates a side view of a multiple platter disk drive in which
another embodiment of the split actuator may be utilized;
FIG. 3D illustrates a plan view of the first actuator in relation to the
common pivot bearing, wherein the first actuator is fixedly mounted to the
common pivot bearing;
FIG. 3E illustrates a plan view of the second actuator in relation to the
common pivot bearing and a spring member, wherein the second actuator is
coupled to the common pivot bearing by the spring member so as to spring
couple the first and second actuators;
FIG. 3F illustrates a plan view of another embodiment of the actuator
wherein the spring member is directly attached to the first and second
actuators;
FIG. 4A illustrates an isometric view of the spring member comprising four
flex sections arranged circumferentially;
FIG. 4B illustrates a top sectional view of the spring member showing the
flex sections that spring couple inner portion and outer portion of the
spring member, thereby spring coupling the first and second actuators;
FIG. 5 illustrates a manner in which the spring coupling allows limited
relative rotational motion between the first and second actuators;
FIG. 6A illustrates profiles of applied current to the first and second
actuators performing overlapping motions during a seek operation;
FIG. 6B illustrates profiles of transducer velocity of the first and second
actuators performing the overlapping motions;
FIG. 6C illustrates profiles of transducer displacement of the first and
second actuators performing the overlapping motions;
FIG. 7A illustrates profiles of transducer velocity of the first and second
actuators performing a slingshot style seek operation;
FIG. 7B illustrates profiles of transducer displacement of the first and
second actuators performing the slingshot seek operation; and
FIG. 8 illustrates a generalized diagram showing a series of seek
operations, wherein the split nature of the actuator and the spring
coupling provide reduction in effective seek time.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Reference will now be made to the drawings wherein like numerals refer to
like parts throughout. FIG. 1A schematically illustrates an exemplary disk
drive 100 of the prior art for storing information. The disk drive 100
includes one or more disks 102 (also called platters) that have a magnetic
media 103 formed on the surfaces 101 of the disks 102. The magnetic media
103 is programmable such that application of an external magnetic field
results in a change of the magnetic state of the media which permits the
magnetic media 103 to be selectively magnetized to store data. The disks
102 are typically organized into a plurality of concentric magnetic tracks
106 which include servo bursts 110 that are arranged so as to be equally
spaced from an axis of a spindle 104 about which the disk 102 rotates. The
servo bursts 110 on a given track 106 are spaced circumferentially in a
periodic manner and they provide positional information used by a voice
coil motor (VCM) servo system during reading and writing operations, and
seeking and settling operations, in a manner known in the art.
The disk drive 100 further comprises a transducer 114 mounted on an
actuator 116 that rotates about a pivot point defined by a pivot assembly
due to a controlled torque applied by a VCM 122. The pivot assembly
typically comprises a pivot bearing 120. A signal bus 124 interconnects
the transducer 114 and the VCM 122 to a controller 128 such that the
controller 128 can control the movement of the actuator 116 in a manner
well known in the art. Furthermore, the controller 128 sends and receives
signals to and from the transducer 114 so as to permit the transducer to
read, write, and erase information contained on the disk 102.
In operation, the disk 102 rotates about the axis of the spindle 104 at
selected angular speed such that the surface 101 of the disk 102 moves
relative to the transducer 114. The transducer's radial position on the
disk 102 is changeable by the rotation of the actuator 116 so as to be
able to position the transducer 114 on a desired data track 106. The
transducer's radial and circumferential position on the disk 102 is
determined by reading of the information contained in the servo bursts 110
in a manner well known in the art. Once the transducer 114 is positioned
on the desired data track 106 within desirable limits, data can be written
to or read from a circular arc between the servo bursts 110.
FIG. 1A further illustrates a coil 118 located at the end of the actuator
116, opposite from the transducer 114. As is well known in the art, when a
current is passed through the coil 118, the coil forms an electromagnet
that interacts with an existing magnetic field from a source such as a
permanent magnet. The coil 118 and the permanent magnet are configured
such that passing of the current in the coil 118 in one direction causes
the actuator 116 to rotate in a first direction. When the current is
passed through the coil 118 in the opposite direction, the actuator 116
rotates in a second direction that is substantially opposite from the
first direction.
FIG. 1B illustrates a side view of the exemplary disk drive 100 of the
prior art, showing that the disk drive 100 may have more than one disk 102
mounted on a common spindle 104. Associated with each disk surface 101 is
a transducer 114 mounted to a common actuator 116. Thus, the disks 102
rotate in unison, and the transducers 114 move in unison relative to the
rotating disks 102.
FIG. 2 illustrates a functional schematic diagram of one embodiment of a
split actuator 140. The split actuator 140 comprises a first actuator 142
coupled to a second actuator 144. In one embodiment, the first and second
actuators 142 and 144 are rotatably mounted on a pivot bearing 146 such
that the first and second actuators 142, 144 rotate about a common axis
defined by the pivot bearing 146 in a manner described below. The first
actuator 142 comprises a first transducer 150 disposed thereon and a first
coil 152 that drives movement of the first actuator 142. Similarly, the
second actuator 144 comprises a second transducer 154 disposed thereon and
a second coil 156 that drives movement of the second actuator 144.
FIG. 2 further illustrates a controller 400 interconnected to the first and
second actuators 142 and 144 by a bus 402. In one embodiment, the function
of the controller 400 includes controlling movements of the first and
second actuators 142 and 144.
Because the first and second actuators 142, 144 share a common axis of
rotation about the pivot bearing 146, the first and second actuators 142,
144 may move in a first relative direction 162 or a second relative
direction 164. Specifically, the first relative direction 162 may be
defined as the first and second transducers 150, 154 moving away from each
other, and the second relative direction 164 may be defined as the first
and second transducers 150, 154 moving towards each other. Thus, for
example, if the first transducer 150 is stationary with respect to the
disk and the second transducer 154 moves away from the first transducer
150, then the first and second actuators 142, 144 are moving in the first
relative direction 162.
As schematically indicated by a spring in FIG. 2, the split actuator 140
further comprises a mechanical coupling 160 that couples the first and
second actuators 142, 144. One aspect of the split actuator relates to the
split actuator 140 being able to store a portion of the energy associated
with the relative movement of the first and second actuators 142, 144 in
the mechanical coupling 160, such that the stored energy can be utilized
to aid the subsequent relative movement of the first and second actuators
142, 144. As described below in greater detail, the combination of dual
actuators and energy storing capability permits the split actuator 140 to
advantageously perform various seek operations with either reduced or
substantially hidden seek times. Another aspect of the split actuator
relates to the structure of the mechanical coupling that permits
overcoming of at least some of the problems associated with dual
actuators.
Splitting an actuator into two separate structures and coupling them allow
aforementioned advantages to be implemented in a manner described below.
In one embodiment, for example, each of the two split actuators has
approximately half the inertia as the unsplit actuator because each
actuator needs to support half the number of transducers. The VCM torque
constant can correspondingly be reduced by approximately half while
maintaining a specified level of angular acceleration for the split
actuators. As a consequence, coil dimensions and magnet size for each coil
can also be reduced. Alternatively, since the specified level of
acceleration can be achieved by approximately half of the original
current, if the VCM torque constant is left unchanged from that of a
standard actuator, a full original current can, if desired, provide one
split actuator with approximately twice the specified acceleration of a
standard actuator if the desired seek distance is small.
The split actuator implementation described herein addresses the drawbacks
referred to in the Description of the Related Art section in a manner
described below. In particular, the structure (and advantages derivable
therefrom) of the mechanical coupling between the first and second
actuators is described.
FIGS. 3A-B illustrate a split actuator 180 that represents one possible
embodiment of the coupled split actuator described above in reference to
FIG. 2. The split actuator 180 is configured to be used with a two-platter
disk drive comprising a top platter and a bottom platter. The top platter
defines a top surface and a bottom surface, and the bottom platter
similarly defines a top surface and a bottom surface. It will be
appreciated that while the exemplary configuration of the split actuator
is described in context of the two platter disk drive, the implementation
of the split actuator is not limited to such a disk drive. The split
actuator may be adapted and implemented in disk drives with any number of
platters without departing from the spirit of the invention. As an
example, a three platter disk drive and a modified split actuator is
described below in reference to FIG. 3C.
FIG. 3A illustrates an exploded view of the split actuator 180, showing
that the split actuator 180 comprises a first actuator 182 and a second
