Title: Electrostatic track following using patterned media
Abstract: A transducing head positioning system for use with patterned media. The patterned media comprises a plurality of data tracks and grooves. The grooved tracks can be used in connection with electrodes on a slider to create an electrostatic motor for microactuation of the slider.
Patent Number: 6,943,980 Issued on 09/13/2005 to Bonin, et al.
| Inventors:
|
Bonin; Wayne A. (North Oaks, MN);
Boutaghou; Zine-Eddine (Vadnais Heights, MN)
|
| Assignee:
|
Seagate Technology LLC (Scotts Valley, CA)
|
| Appl. No.:
|
055456 |
| Filed:
|
January 23, 2002 |
| Current U.S. Class: |
360/78.04 |
| Intern'l Class: |
G11B 005/59.6 |
| Field of Search: |
360/75,245.7,780.4
|
References Cited [Referenced By]
U.S. Patent Documents
| 4997521 | Mar., 1991 | Howe et al.
| |
| 5488519 | Jan., 1996 | Ishida et al.
| |
| 5729026 | Mar., 1998 | Mamin et al.
| |
| 5839193 | Nov., 1998 | Bennin et al.
| |
| 5844751 | Dec., 1998 | Bennin et al.
| |
| 5856672 | Jan., 1999 | Ried.
| |
| 5856896 | Jan., 1999 | Berg et al.
| |
| 5864445 | Jan., 1999 | Bennin et al.
| |
| 5943189 | Aug., 1999 | Boutaghou et al.
| |
| 5991114 | Nov., 1999 | Huang et al.
| |
| 5999303 | Dec., 1999 | Drake.
| |
| 6005736 | Dec., 1999 | Schreck.
| |
| 6044056 | Mar., 2000 | Wilde et al.
| |
Other References
Lin, C. and Massaro, D. J., IBM Technical Disclosure Bulletin, Electrostatically
Loaded Slider Bearing, vol. 12, No. 7, Dec. 1969.
|
Primary Examiner: Hudspeth; David
Assistant Examiner: Slavitt; Mitchell
Attorney, Agent or Firm: Kinney & Lange, P.A.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION(S)
This application claims priority from provisional application Ser. No. 60/267,305,
filed on Feb. 8, 2001, and entitled "Electrostatic Track Following using Patterned
Media" by Wayne Allen Bonin and Zine-Eddine Boutaghuo, which is herein incorporated
by reference.
Claims
1. A transducing head positioning system, the system comprising:
a first portion of an electrostatic motor comprising patterned data storage media
having a plurality of data tracks; and
a second portion of the electrostatic motor formed on a slider, wherein the electrostatic
motor is used to position a transducing head above a selected data track on the
patterned storage media.
2. The transducing head positioning system of claim 1 wherein the plurality of
data tracks comprises concentric data tracks.
3. The transducing head positioning system of claim 2 wherein each concentric
data track comprises a raised track and a groove.
4. The transducing head positioning system of claim 3 wherein a pitch of each
data track is about 2 microinches.
5. The transducing head positioning system of claim 3 wherein the second portion
of the electrostatic motor comprises a plurality of electrodes located on a media
opposing surface of the slider.
6. The transducing head positioning system of claim 5 wherein a width of the
electrodes is about equal to a width of the raised tracks on the patterned storage media.
7. The transducing head positioning system of claim 6 wherein a ratio of the
electrodes on the slider to the data track spacing on the patterned storage media
is 4 data tracks to 3 electrodes.
8. The transducing head positioning system of claim 7 and further comprising
a linear actuator for positioning the slider.
9. The transducing head positioning system of claim 5 wherein the plurality of
electrodes further comprises:
a plurality of phase one electrodes;
a plurality of phase two electrodes; and
a plurality of phase three electrodes.
10. An electrostatic slider positioning system, the system comprising:
patterned media comprising a plurality of data tracks; and
a slider located proximate the patterned media, wherein the slider includes a
plurality of electrodes configured to be selectively activated to cause an electrostatic
attraction between an electrode and a data track, and position the slider at a
selected data track.
11. The electrostatic slider positioning system of claim 10 wherein each data
track comprises a track and a groove.
12. The electrostatic slider positioning system of claim 11 wherein the plurality
of electrodes on the slider and the plurality of data tracks on the patterned media
form an electrostatic motor.
13. The electrostatic slider positioning system of claim 12 wherein a width of
each electrode is about the same as a width of a track on the disc.
14. The electrostatic slider positioning system of claim 13 wherein a ratio of
the spacing of the electrodes on the slider to the spacing of the data tracks on
the patterned storage media is 4 data tracks to 3 electrodes.
15. The electrostatic slider positioning system of claim 13 wherein the electrodes
have a length which allows the electrodes follow a curvature of data tracks at
both an inner and an outer diameter of the disc.
16. The electrostatic slider positioning system of claim 15 and further comprising
means for linear actuation of the slider as it tracks over the surface of the disc.
17. The electrostatic slider positioning system of claim 12 wherein the plurality
of electrodes on the slider comprises:
a first phase electrode;
a second phase electrode; and
a third phase electrode.
18. The electrostatic slider positioning system of claim 17 and further comprising
a control system for controlling the electrostatic motor by selectively applying
a voltage to the first, second, and third phase electrodes.
19. A method of controlling the position of a transducing head above the surface
of a patterned electronic storage medium, the method comprising:
suspending a slider above a surface of the storage medium, wherein the slider
comprises a plurality of electrodes on a storage medium opposing surface; and
moving the transducing head to a desired data track on the storage medium by
actuating an electrostatic motor formed by the plurality of electrodes on the slider
and tracks on the patterned electronic storage medium.
20. The method of claim 19 and further comprising coarsely positioning the slider
using a linear actuator.
21. The method of claim 19 wherein actuating the electrostatic motor comprises
applying a voltage to an electrode of the electrostatic motor to create an electrostatic
attraction between the electrode and a track on the medium.
22. The method of claim 21 wherein actuating the electrostatic motor further
comprises applying a voltage to selected electrodes.
23. The method of claim 22 wherein applying a voltage to selected electrodes comprises:
configuring the plurality of electrodes to comprise a first phase electrode,
a second phase electrode, and a third phase electrodes; and
controlling the application of a voltage to the first, second, and third phase
electrodes to move the slider across the storage medium.
24. A transducing head positioning system, the system comprising:
patterned data storage media comprising a plurality of data tracks, wherein each
data track comprises a raised track and a groove, the patterned data storage media
forming a first portion of an electrostatic motor; and
a slider carrying a second portion of the electrostatic motor, wherein the second
portion of the electrostatic motor comprises a plurality of electrodes located
on a media opposing surface of the slider, wherein a width of the electrodes is
about equal to a width of the raised tracks on the patterned storage media, and
wherein the electrostatic motor is used to position a transducing head above a
selected data track on the patterned storage media.
25. The transducing head positioning system of claim 24 wherein a ratio of the
electrodes on the slider to the data track spacing on the patterned storage media
is 4 data tracks to 3 electrodes.
26. The transducing head positioning system of claim 25 and further comprising
a linear actuator for positioning the slider.
27. An electrostatic transducer positioning system, the system comprising:
patterned media comprising a plurality of data tracks, wherein each data track
comprises a track and a groove; and
a transducer located proximate the patterned media, wherein the transducer comprises
a plurality of electrodes which form an electrostatic motor together with the plurality
of data tracks, the plurality of electrodes comprising a first phase electrode,
a second phase electrode, and a third phase electrode which can be selectively
activated to cause an electrostatic attraction between an electrode and a data
track.
28. The electrostatic transducer positioning system of claim 27 and further comprising
a control system for controlling the electrostatic motor by selectively applying
a voltage to the first, second, and third phase electrodes.
29. A method of controlling the position of a transducer above patterned media,
the method comprising:
suspending a transducer above a surface of the media, wherein the transducer
includes a plurality of electrodes on a media opposing surface; and
moving the transducer to a desired data track on the media by applying a voltage
to at least one of the plurality of electrodes to create an electrostatic attraction
between the electrode and a data track on the media.
30. The method of claim 29 wherein moving the transducer further comprises:
selecting three of the plurality of electrodes; and
applying a voltage to one of the three selected electrodes.
31. The method of claim 29 wherein applying a voltage to at least one of the
plurality of electrodes comprises:
configuring the plurality of electrodes to comprise a first phase electrode,
a second phase electrode, and a third phase electrode; and
controlling the application of a voltage to the first, second, and third phase
electrodes to move the transducer across the media.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a disc drive system. In particular, the present
invention relates to a head positioning system capable of accommodating ever higher
areal density of computer discs.
Disc drive systems are well known in the art and comprise several discs, each
disc having concentric data tracks for storing data. The discs are mounted on a
spindle motor, which causes the discs to spin. As the discs are spinning, a slider
suspended from an actuator arm "flies" a small distance above the disc surface.
The slider carries a transducing head for reading from or writing to a data track
on the disc.
In addition to the actuator arm, the slider suspension comprises a bearing about
which the actuator arm pivots. A large scale actuator motor, such as a voice coil
motor (VCM), is used to move the actuator arm over the surface of the disc. When
actuated by the VCM, the slider can be moved from an inner diameter to an outer
diameter of the disc along an arc until the slider is positioned above a desired
data track on the disc. Called tracking, this method of positioning the slider
above the desired track on the disc allows the transducing head on the slider to
either read from or write data to a selected track on the disc.
The areal recording density of the disc is typically given in tracks per inch
(TPI). There is constant pressure to increase the areal density of discs, and thus
increase the number of tracks per inch on the disc. As the tracks per inch increase,
the accuracy of the system used to position the transducing head above the desired
track on the disc must increase in proportion. This requires increasing the bandwidth
of the servo system used to position the actuator arm.
There are many sources of error which reduce the track positioning accuracy
of current slider suspension systems. The actuator arm is designed to be flexible
to improve the ability of the slider to more closely follow the surface of the
disc. However, this flexibility can result in the occurrence of unwanted resonances
in the suspension as the suspension is moved across the disc surface during tracking.
These unwanted resonances in the suspension reduce the ability to accurately control
the slider positioning system at the required frequency. In addition, forces acting
at the VCM, the bearing, and the actuator arm may all introduce potential error
into the final tracking ability of the slider by adding to the resonance experienced
in the actuator arm.
In an attempt to manage the amount of resonance in the suspension, secondary
microactuators
have been placed between the suspension and the slider. Moving the slider directly
by using a form of microactuator has reduced, but has not eliminated the effect
of suspension resonances. In particular, as the actuation force is applied to the
slider by the microactuator, an equal and opposite reaction force is applied to
the suspension, which in turn can create other resonance disturbances in the suspension.
Control systems have been developed which attempt to compensate for the resonance
and vibration experienced by the slider. However, such attempts reduce, but do
not eliminate the effect of suspension resonances.
Microactuators and control systems have improved the tracking accuracy
of sliders to where areal densities of up to 200,000 TPI may be possible. However,
current goals are for discs having areal densities of as high as 500,000 to 1,000,000
TPI. At such areal densities, current slider positioning methods become inadequate.
Thus, there is a need in the art for an improved head positioning system which
is capable of accommodating discs with ever higher areal densities.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a head positioning system capable of positioning
a slider over a medium having up to 500,000 to 1,000,000 TPI. The head positioning
system comprises a slider positioned over a patterned media. The patterned media
comprises a disc having a plurality of tracks and grooves. Located on the slider's
medium opposing surface are a plurality of electrodes. The electrodes can be selectively
activated so that together with the tracks on the disc, the electrodes operate
as an electrostatic motor. Using the electrostatic motor, the slider can be finely
positioned at a desired track on the disc.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a disc drive actuation system for positioning
a slider over a track on a disc.
FIG. 2 is an greatly enlarged side view of a slider having a plurality of electrodes
positioned above a grooved media.
FIG. 3 shows a simplified diagrammatic view of a slider positioned at various
locations on a disc.
FIG. 4 is an illustration of the curvature depth of a curve.
FIG. 5 is a table illustrating the curvature depth in microinches and the change
in curvature with respect to a 28 millimeter radius.
FIG. 6 is a bottom plan view of a slider illustrating the air bearing surface.
DETAILED DESCRIPTION
FIG. 1 is a perspective view of a disc drive actuation system
10 for
positioning a slider
12 over a selected data track
14 of a magnetic
storage medium
16, such as a disc. The actuation system
10 includes
a voice coil motor (VCM)
18 arranged to rotate a slider suspension
20
about an axis
22. The slider suspension
20 includes a load beam
24
connected to an actuator arm
26 at a slider mounting block. A flexure
28
is connected to the end of the load beam
24, and carries the slider
12.
The slider
12 carries a magneto-resistive (MR) element (not shown) for reading
and/or writing data on the concentric tracks
14 of the disc
16.
The disc
16 rotates around an axis
30, which causes the slider
12 to "fly" a small distance above the surface of the disc
16. To
position the slider
12 at a desired track
14 on the disc
16,
the VCM
18 actuates the slider suspension
20 about the axis
22
so that the suspension
20 is moved in an arc across the surface of the disc
16. This arc shaped movement allows the slider
12 to be moved from
an inner diameter to an outer diameter of the disc
16 so that the slider
can be positioned above the desired track
14 on the disc
16. A variety
of sources of positioning error are introduced during this process and while the
disc drive
10 is capable of operation at up to 200,000 TPI, it is inadequate
for TPI's in excess of that number.
The present invention improves upon the disc drive illustrated in FIG. 1 to allow
for TPI of up to 500,000 to 1,000,000 TPI. FIG. 2 is a greatly enlarged side view
of a slider
40 positioned above a patterned medium
42, such as a
disc. The slider
40 comprises a slider substrate
44 and a disc opposing
surface
46. On the disc opposing surface
46 are a plurality of phase
1 electrodes
48, phase
2 electrodes
50, and phase
3
electrodes
52.
The patterned media
42 comprises a disc having a plurality of tracks
54,
labeled A-E, and grooves
56. It is anticipated that such a patterned media,
in the form of tracks
54 and grooves
56, will be necessary in order
to increase the bit density possible before the onset of the superparamagnetic
limit, which currently sets a lower size limit on the magnetic particle size of
the storage media.
The tracks
54 on the disc
42 can be used in conjunction with the
phase
1,
2, and
3 electrodes
48-
52 to form an
electrostatic motor
58 for microactuation of the slider
40. An application
of a voltage to a phase
1,
2, or
3 electrode
48-
52,
causes an electrostatic attraction between the activated electrode
48-
52
and the closest track
54 on the disc
42 over which the activated
electrode
48-
52 is located. By controlling the application of voltage
to selected phase
1,
2, or
3 electrodes
48-
52,
it is possible to finely position the slider
40 above a selected location
on the disc
42.
When moving the slider
40 using the electrostatic motor
58, an
electrostatic force is generated between the disc
42 and the slider
40.
As a result, unlike using a microactuator between the slider and the suspension
to move the slider, there is no reactive force acting on the suspension when using
the electrostatic motor. This reduces the negative effects of suspension resonances
on the tracking ability of the slider
40.
One method of operating the electrostatic motor
58 is to apply a voltage
to only one set of either the phase
1, phase
2, or phase
3
electrodes
48-
52 at any given time. The set of electrodes
48-
52
is activated by applying an electrical potential to the selected electrodes
48-
52
while the other electrodes
48-
52 remain at ground potential, as does
the disc
42. More specifically, activating the phase
1 electrodes
48 will cause the phase
1 electrodes
48 to center over the
closest data track
54 on the disc
42, or tracks A and E as shown
in FIG.
2. Activating the phase
2 electrodes
52 and deactivating
the phase
1 electrodes
50 will cause the slider
40 to move
⅓ of a track
56 to the left (as viewed in FIG. 2) so that the phase
2 electrode
50 is centered over track B. Similarly, activating the
phase
3 electrodes
52 and deactivating the phase
1 electrodes
48 will cause the slider
40 to move ⅓ of a track
54
to the right, so that the phase
3 electrode
52 is centered over data
track D. Thus, by properly sequencing the application of voltage to phase
1,
phase
2, and phase
3 electrodes
48-
52, it is possible
to move the slider
40 any desired distance across the disc surface
42.
A control system can be used to control the tracking of the slider
40
by
controlling the application of voltage to the electrodes
48-
52. Such
a control system can be used to cause the slider
40 to lock onto a desired
track
54 by selectively activating the electrodes
48-
52. In
doing so, the control system causes the electrostatic motor
58 to act similar
to a stepper motor. As a result, the control system allows for automatic track
following without a closed loop servo feedback system.
For instance, a positioning resolution of ⅙ of a track can be obtained
by first activating the phase
1 electrodes
48, centering the phase
1 electrodes over tracks A and E. Next, both phase
1 electrodes
48
and phase
3 electrodes
52 are activated, causing the slider to move
slightly so that the phase
1 electrodes
48 are no longer centered
over tracks A and E, but are shifting slightly to the right (as viewed in FIG.
2). Finally, activating the phase
3 electrodes
52 but not
the phase
1 electrodes
48 results in the slider moving to the right
(as viewed in FIG. 2) until the phase
3 electrode
52 is centered
over track D. As a result of this sequence of activation, the slider is moved ⅓
track to the right. Thus, continuos analog positioning can be obtained by adjusting
the voltages applied to the electrodes
48-
52 in a continuous analog
manner, rather than by simple digital switching.
The patterned media
42 may have various ratios of tracks
54 to
grooves
56. For instance, as is illustrated in FIG. 2, the width of the
tracks
54 may be equal to the width of the grooves
56. Other ratios
may be suitable for use with the present invention as well, including a track width
to groove width ratio of 60/40. Similarly, the spacing of the electrodes
48-
52
on the slider
40 may vary based on the track
54 spacing on the disc
42. In FIG. 2, the spacing of the electrodes
48-
52 on the
slider
40 is 4/3 of the track
54 to track
54 spacing on the
disc
42.
Regardless of the spacing of the tracks
54, it is desirable that
the width of the electrodes
48-
52 on the slider
40 be about
equal to the width of the tracks
54 on the disc
42. If the electrodes
48-
52 are wider than the tracks
54, the ability of the electrodes
48-
52 to follow the tracks
54 is diminished. If the electrodes
48-
52 are narrower than the tracks
54, the electrodes
48-
52
may wander the width of the tracks
54, reducing the performance and accuracy
of the tracking ability of the slider
40.
The maximum force available for moving or holding the slider
40 with respect
to the tracks
54 on the disc
42 depends on several factors, including:
the number and length of active electrodes
48-
52; the gap between
the slider
40 and the disc
42; and the voltage applied to the active
electrodes
48-
52. The relationship of these factors is given in the
below equation:
##EQU1##
Where F
lat is the lateral force in newtons, N is the number of active
electrodes, d is the gap between the disc and slider electrodes in meters, ε
0,
is the dielectric constant of the gap (8.854×10
-12 F/m for air
or a vacuum), L is the length of the active electrodes in meters, and V is the
voltage between the active slider electrodes and the disc.
When an active electrode
48-
52 is positioned directly above a
track
54, the alignment force is essentially zero. Once the slider starts
moving off a track, the lateral force begins to increase. The maximum lateral force
occurs when the active electrode is misaligned from a track by about the fly height,
or gap. The lateral force stays essentially at the maximum until the active electrode
48-
52 moves further away from a track
54 than the fly height.
As is shown in the above equation, the lateral positioning force varies with
the
square of the voltage between the slider electrodes
48-
52 and the
disc
42. The amount of voltage that can be applied to the slider electrodes
48-
52 is limited by a variety of factors. At a gap of 0.1 microinches
(about 2.5 nanometers), the voltage limit is not due to the electrical breakdown
strength of air, which actually increases for air at standard pressure for a spacing
of less than about 7 micrometers. Rather, at gaps of less than about 1 nanometer,
electron tunneling currents are likely to be the limiting factor.
At gaps of 2.5 nanometers, the voltage limit will likely be due to field emission.
The electric field at which significant field emission occurs varies greatly depending
on the material used for the electrodes
48-
52. The table below gives
the magnetic field strength at which significant field emission occurs for a variety
of materials:
| |
| Material |
Electric Field (in Volts per meter) |
| |
| Tungsten |
1.4 × 1010 |
| Lanthanum hexaboride |
3.7 × 109 |
| specially prepared metal/insulator |
5 × 108 |
| system using Beryllia particles |
| p-doped diamond material |
15 to 30 × 107 |
| |
Using the above values for maximum electric field strength, the maximum possible
voltage for a gap of 2.5 nanometers would be 35 volts for Tungsten, 9.25 volts
for Lanthanum hexaboride, 1.25 volts for the Beryllia particle metal/insulator
system, and 0.175 for the p-doped diamond material.
Another limiting factor for electrode voltage is the normal attraction force
between the disc and the slider electrodes. The normal force is given in the below
equation:
##EQU2##
where w is the width of the slider electrodes and all the variables are the
same as those previously defined above.
The normal force (F
n) is equal to the lateral force (F
lat)
multiplied by w/d. Thus, for slider electrodes having a width of 25 nanometers
and a gap of 2.5 nanometers, the normal force is 10 times larger than the lateral
positioning force. Typically, the total pre-load force supported by the air bearing
in current slider designs is about 2.5 grams. As such, the electrostatic attraction
force needs to be limited to about 1 gram unless a drastic redesign of the air
bearing is performed because of the risk that the normal force will overcome the
pre-load force such that the slider crashes into the disc.
In addition to the amount of voltage applied to the electrodes, the lateral positioning
force available for moving or holding the slider
40 depends on the length
of the electrodes on the slider. The patterned storage medium is typically a disc
having concentric data tracks on its surface. The curvature of the concentric data
tracks on the disc limits the length of the electrodes on the slider. This is because
the radius of the data tracks at the inner diameter of the disc will be smaller
than the radius of the data tracks at the outer diameter of the disc. As a result,
the depth of curvature of the data tracks at the inner diameter is not equal to
the depth of curvature of the data tracks at the outer diameter of the disc. Thus,
the electrodes must be of a length that allows them to "fit" the depth of curvature
of the data tracks at both the inner diameter, as well as at the outer diameter.
To illustrate this, FIG. 3 shows a simplified diagrammatic view of a slider positioned
at various locations on a disc. Shown in FIG. 3 are several data tracks
60
having varying depths of curvature corresponding to data tracks on a disc at the
inner diameter moving toward the outer diameter. In addition, a slider
62
having two electrodes
64 is shown. At a first position
66, the slider
62 is positioned closest to the inner diameter. When so positioned, the
electrodes
64 on the slider
62 do not match the data tracks
60.
Similarly, at a third position
70, corresponding to an outer diameter of
the disc, the electrodes
64 on the slider
62 likewise do not match
the data tracks
60. The only time the electrodes
64 are exactly aligned
with the data tracks
60 is when the slider
62 is located at a second
position
68, located somewhere between the inner and outer diameter of the disc.
The longer the electrodes
64, the more difficult it is to ensure that
the electrodes
64 properly align with the data tracks
60 at both
the inner diameter and the outer diameter such that the electrodes
64 can
efficiently be used to position the slider
62. As such, it is desired to
have electrodes
64 with a length that will minimize the misalignment of
the electrodes
64 and data tracks
60.
FIG. 4 is an illustration of curvature depth of a circle. For a circle defined
by r
2=x
2+y
2, the curvature depth d is a function
of the radius r and the distance y from the radius. This relationship is given
by the following equation:
FIG. 5 is a table
80 illustrating the amount of track curvature, and
the difference in that curvature with respect to a radius of 28 millimeters, for
various radii from 16 to 44 mm. Each cell of the table
80 contains two numbers.
The upper number is the curvature, and the lower number is the change in curvature
between that radius and the 28 millimeter radius. The far left column of the table
80 represents the orthogonal offsets from the radius line of between 0.000
and 0.100 mm. This offset in the y axis corresponds to the length of the electrodes
on the slider.
As illustrated in FIG. 3 above, as the change in curvature with respect to the
28 mm radius increases, the misalignment between the slider electrodes and the
data tracks will increase. Thus, the maximum tolerable y value is limited by the
change in curvature with respect to the 28 mm radius. Because the curvature is
symmetric about the radius line, the electrode length can be twice the maximum
tolerable y value in the table
80.
The misalignment typically occurs at the ends of the slider electrodes. For the
500,000 TPI example illustrated above, if the misalignment between the ends of
the electrodes and the data tracks exceeds 1 microinch, that portion of the electrode
will be attracted more strongly to the adjacent track than the correct track, and
the net positioning force will be reduced. However, the curvature mismatch at the
ends of the slider electrodes will cause an offset in the opposite direction at
the center, so the actual amount of curvature mismatch before the ends of the slider
electrodes provide a negative contribution to the positioning force will be greater
than 1 microinch but less than 2 microinches.
In light of this effect, the numbers in the table illustrated in FIG. 5 can assist
in determining suitable lengths of electrodes. The numbers in area
82 indicate
a positive contribution to positioning force for the entire length of the electrodes.
The numbers in area
84 indicate a possible negative contribution from part
of the length of the electrodes. Finally, the numbers in area
86 indicate
a definite negative contribution from part of the electrode length. Thus, as can
be determined from table
80 in FIG. 5, for a minimum track radius of 20
millimeters and a maximus radius of 44 millimeters, with the slider electrodes
centered about the radius line, the length of the slider electrodes for maximum
force is between 0.12 millimeters and 0.16 millimeters (2×0.060 and 2×0.080 mm).
To help maintain proper alignment of the slider electrodes to the tracks on the
disc as the slider moves from the inner diameter to the outer diameter of the disc,
it is necessary to utilize a suspension mechanism which maintains a fixed, rather
than a rotating orientation of the slider to the disc. Currently, the slider is
moved over the disc using a VCM with a central pivot bearing, such as that illustrated
in FIG. 1 above. Using a VCM results in an arc shaped path as the slider moves
over the disc, rather than a linear shaped path. One method of obtaining the required
linear path of the slider over the disc is to utilize linear actuation mechanisms.
One suitable linear actuation mechanism involves adding compliant springs between
the slider and the slider suspension, similar to springs used in connection with
other head level microactuators. A VCM or other primary positioning mechanism can
still be used for coarse positioning and seeking to within some relatively small
distance of the desired track. Once the primary positioning mechanism has positioned
the slider to within about a half of a track of the desired position, the electrostatic
motor can be actuated by activating the proper slider electrodes. The compliant
springs will allow the slider to lock in and follow the desired track. Using the
electrostatic motor allows for fine positioning, with no additional servo feedback
required. In addition, if initial positioning error results in the slider being
off by one or more tracks, the electrostatic positioning can also be used to step
to the desired track.
A second method of linear actuation, though similar to the first, reduces the
mass
that must be moved by the electrostatic actuation. Reducing the moving mass greatly
reduces the seek time of the electrostatic motor. Placing the compliant springs
between slider and the slider suspension, as in method
1, requires moving
the entire slider. In contrast, the second method involves placing compliant springs
between the head and the slider. To do so, the compliant springs may be fabricated
during the slider and transducing head manufacturing process. When the compliant
springs are located between the head and the slider, only the head (and a thin
substrate and overcoat encapsulating the head) must be actuated using the electrostatic
motor. As a result, the moving mass is greatly reduced, and the electrostatic positioning
acceleration is increased by 10 to 100 times.
A third method of linear actuation requires eliminating the primary positioning
system entirely. In its place, only the electrostatic actuation is used for both
track following and the coarse positioning used during seeking. To provide the
required alignment of the slider electrodes to the disc as the slider sweeps across
the disc surface, a folded flexure suspension mechanism may be used. The folded
flexure suspension mechanism will increase the mass that must be moved by the electrostatic
motor. As a result, seek times will be longer. Due to the longer seek times, this
method may be better suited to low cost applications where speed is not the most
important parameter.
In addition to the length of the electrodes, the number of the slider electrodes
located on the slider will have an effect on the performance of the electrostatic
motor. FIG. 6 is a simplified bottom plan view of a slider illustrating the medium
opposing surface of a slider
90. The slider
90 has a trailing edge
92 and an air bearing surface (ABS)
94. Located on the ABS are the
electrodes, indicated generally by
96. The number of slider electrodes
96
is determined by the TPI and the width of the trailing edge air bearing surface
94.
A slider may have an ABS width of about 110 micrometers. The entire width of a
slider may be 1 millimeter, in which case the ABS amounts to about one tenth of
the total slider width. Based on a slider having these parameters, the number of
electrodes which can be located on the ABS is approximately 541: (100 μm)(500
tracks/microinch)/(25.4 μm/microinch)(¼ active electrodes per data track)=541.
If the entire width of the trailing edge of the slider, rather than just the
width
of the ABS, was used for the electrodes, the number of electrodes could be increased
by about 9 times. However, any such attempt to place electrodes on the entire width
of the slider would require a drastic redesign of the air bearing.
Tables 2a-2c and 3a-3c below provide a comparison of the results of modeling
the performance of electrostatic slider positioning systems having: 1) electrodes
across the trailing edge ABS; and 2) having electrodes across the entire trailing
edge. Each table shows the lateral positioning force, F
lat, and normal
attraction force, F
n, as well as the resulting lateral accelerations
possible at selected voltages.
Tables 2a-2c illustrate the performance of an electrostatic slider positioning
system with electrodes located across the trailing edge ABS. The data in Tables
2a-2c is based on a slider having 541 active slider electrodes covering a width
of about 110 microns, which is typical of the width of a trailing edge airbearing
surface. In addition, the length of the electrodes was about 1.20×10
-4
meters, while the gap between the disc and the slider electrodes was about
2.50×10
-9 meters.
| |
|
Flat |
Fn |
Acceleration |
| |
Volts |
(N) |
(gram) |
(g) |
| |
|
| |
1 |
1.15E-04 |
0.12 |
19.6 |
| |
1.5 |
2.59E-04 |
0.26 |
44.0 |
| |
2 |
4.60E-04 |
0.47 |
78.2 |
| |
2.5 |
7.19E-04 |
0.73 |
122.2 |
| |
3 |
1.03E-03 |
1.06 |
176.0 |
| |
5 |
2.87E-03 |
2.93 |
488.8 |
| |
7 |
5.63E-03 |
5.75 |
958.0 |
| |
10 |
1.15E-02 |
11.73 |
58653.2 |
| |
|
| TABLE 2b |
| |
| Pico AlTiC Slider |
| |
|
Flat |
Fn |
Acceleration |
| |
V |
(N) |
(gram) |
(g) |
| |
|
| |
1 |
1.15E-04 |
0.12 |
7.3 |
| |
1.5 |
2.59E-04 |
0.26 |
16.5 |
| |
2 |
4.60E-04 |
0.47 |
29.3 |
| |
2.5 |
7.19E-04 |
0.73 |
45.8 |
| |
3 |
1.03E-03 |
1.06 |
66.0 |
| |
5 |
2.87E-03 |
2.93 |
183.3 |
| |
7 |
5.63E-03 |
5.75 |
359.3 |
| |
10 |
1.15E-02 |
11.73 |
733.2 |
| |
|
Table 2a provides the acceleration in g's for a Femco Si slider having amass
of 6×10
-7 kilograms. Table 2b provides the acceleration in g's
for a Pico AlTiC slider having a mass of 1.6×10
-6 kilograms. Looking
at Tables 2a and 2b, a 1 gram normal force (F
n) imposes a 3 volt limit
on the electrode voltage, which generates 1.0 mN of positioning force (F
lat).
As shown in Table 2a, moving the entire slider would provide an acceleration of
176 g's for a 0.6 mg Femco Silicon slider. As shown in Table 2b, an acceleration
of 66 g's can be achieved for a 1.6 mg AlTic Pico slider.
An acceleration of 176 g's is near the maximum anticipated acceleration for seeking
in high performance drives. In comparison, an acceleration pf 66 g's is rather
modest performance which would have limited applications in high performance drives.
If a simple air bearing design change allowed operation of the electrodes at 5
volts, the resulting normal attractive force of 2.9 grams, and a lateral force
of about 219 mN, the Femco Silicon slider would have an acceleration of 488 g's
and the AlTiC Pico slider would have an acceleration of about 183 g's. Both such
performances would be suitable for high performance drives.
Table 2c shows the accelerations in g's for four head level actuators, such
as by using compliant springs between the slider and head as described above. Table
2c shows the results of modeling four actuators each having a different moving
mass. As can be seen in Table 2c, the head level actuators achieve high seek acceleration
even at one volt electrode potential.
For a 30 microgram moving mass and a one volt potential, the resulting acceleration
is 390 g's. This acceleration allows for a single track switch (for a disc having
500,000 TPI) in about 11 microseconds, neglecting settling time. With springs that
allow one micrometer of motion, up to 20 tracks could be covered in 50 microseconds.
With springs that allow five micrometers of travel, up to 100 tracks could be covered
in 110 microseconds. At two volts, these times are reduced by a factor of two.
| TABLE 2c |
| |
| Transducer Level Actuators |
| |
2E-08 kg |
3E-08 kg |
5E-08 kg |
1E-07 kg |
| |
moving |
moving |
moving |
moving |
| |
mass |
mass |
mass |
mass |
| |
Flat |
Fn |
Accel. |
Accel. |
Accel. |
Accel. |
| V |
(N) |
(gram) |
(g) |
(g) |
(g) |
(g) |
| |
| 1 |
1.15E-04 |
0.12 |
586.5 |
391.0 |
234.6 |
117.3 |
| 1.5 |
2.59E-04 |
0.26 |
1319.7 |
879.8 |
527.9 |
263.9 |
| 2 |
4.60E-04 |
0.47 |
2346.1 |
1564.1 |
938.5 |
469.2 |
| 2.5 |
7.19E-04 |
0.73 |
3665.8 |
2443.9 |
1466.3 |
733.2 |
| 3 |
1.03E-03 |
1.06 |
5278.8 |
3519.2 |
2111.5 |
1055.8 |
| 5 |
2.87E-03 |
2.93 |
14663.3 |
9775.5 |
5865.3 |
2932.7 |
| 7 |
5.63E-03 |
5.75 |
28740.1 |
19160.1 |
11496.0 |
5748.0 |
| 10 |
1.15E-02 |
11.73 |
58653.2 |
39102.2 |
23461.3 |
11730.6 |
| |
Tables 3a-3c illustrate the results of modeling the performance of an electrostatic
slider positioning system having electrodes located across the entire trailing
edge of the slider. Shown in Tables 3a-3c are the lateral positioning force (F
lat)
and normal attraction force (F
n), and the resulting lateral acceleration
possible for various cases of moving mass at voltages from 0.5 to 5 volts. The
data in Tables 3a-3c is based on a slider having 4920 active slider electrodes
covering the entire width of the slider, or about 1000 microns. The length of the
electrodes was about 1.20×10
-4 meters, while the gap between the
disc and the slider electrodes was about 2.50×10
-9 meters.
The system illustrated in Tables 3a-3c requires a substantially redesigned trailing
edge airbearing that also covers the entire width of the slider at the trailing
edge. This embodiment, used with a primary positioning means for coarse track seeking
and compliant springs between the slider and the suspension for electrostatic microactuation,
provides higher performance than the embodiment illustrated in Tables 2a-2c.
| TABLE 3a |
| |
| Femco Silicon Slider |
| |
|
Flat |
Fn |
Acceleration |
| |
V |
(N) |
(gram) |
(g) |
| |
|
| |
0.5 |
2.61E-04 |
0.27 |
44.5 |
| |
0.7 |
5.12E-04 |
0.52 |
87.1 |
| |
1 |
1.05E-03 |
1.07 |
177.8 |
| |
1.5 |
2.35E-03 |
2.40 |
400.1 |
| |
2 |
4.18E-03 |
4.27 |
711.2 |
| |
2.5 |
6.53E-03 |
6.66 |
1111.3 |
| |
3 |
9.41E-03 |
9.60 |
1600.2 |
| |
5 |
2.61E-02 |
26.66 |
4445.1 |
| |
|
| TABLE 3b |
| |
| Pico AlTic Slider |
| |
|
Flat |
Fn |
Acceleration |
| |
V |
(N) |
(gram) |
(g) |
| |
|
| |
0.5 |
2.61E-04 |
0.27 |
16.7 |
| |
0.7 |
5.12E-04 |
0.52 |
32.7 |
| |
1 |
1.05E-03 |
1.07 |
66.7 |
| |
1.5 |
2.35E-03 |
2.40 |
150.0 |
| |
2 |
4.18E-03 |
4.27 |
266.7 |
| |
2.5 |
6.53E-03 |
6.66 |
416.7 |
| |
3 |
9.41E-03 |
9.60 |
600.1 |
| |
5 |
2.61E-02 |
26.66 |
1666.9 |
| |
|
Table 3a provides the acceleration in g's for a Femco Si slider having a mass
of 6×10
-7 kilograms. Table 3b provides the acceleration in g's
for a Pico AlTic Slider having a mass of 1.6×10
-6 kilograms. The
tables illustrate that acceptable performance for high performance drives is obtained
at as low as 1.5 volts for the heavier Pico AlTiC slider and 1.0 volts for the
Femco silicon slider.
As can be seen by comparing Tables 3a and 3b with Tables 2a and 2b, the wider
trailing edge air bearing associated with Tables 3a and 3b allows greater normal
force, possibly up to ten times greater, than the normal forces provided by the
similar sliders illustrated in Tables 2a-2b. In addition, as shown in Tables 3a
and 3b, at a voltage of three volts the acceleration of the Femco Silicon slider
is 1600 g's and the acceleration of the Pico AlTiC slider is 600 g's. Both of these
accelerations are significantly greater than the accelerations of 176 g's and 66
g's achieved by the Femco Silicon slider of Table 2a and the Pico AlTiC slider
of Table 2b at the same voltage.
Table 3c below illustrates that for a lower performance, low cost drive, the
primary positioning means can be entirely replaced by a simple folded flexure suspension
that allows the slider to sweep the entire inner diameter to outer diameter range
of the disc using only the electrostatic stepping action of the slider electrodes
and the disc tracks. Though larger mass, the need for a primary positioning means
is eliminated.
| TABLE 3c |
| |
| Slider with Folded Flexure Suspension |
| |
5E-06 kg |
1E-05 kg |
2E-05 kg |
4E-05 kg |
| |
moving |
moving |
moving |
moving |
| |
mass |
mass |
mass |
mass |
| |
Flat |
Fn |
Accel. |
Accel. |
Accel. |
Accel. |
| V |
(N) |
(gram) |
(g) |
(g) |
(g) |
(g) |
| |
| 0.5 |
2.61E-04 |
0.27 |
5.3 |
2.7 |
1.3 |
0.7 |
| 0.7 |
5.12E-04 |
0.52 |
10.5 |
5.2 |
2.6 |
1.3 |
| 1 |
1.05E-03 |
1.07 |
21.3 |
10.7 |
5.3 |
2.7 |
| 1.5 |
2.35E-03 |
2.40 |
48.0 |
24.0 |
12.0 |
6.0 |
| 2 |
4.18E-03 |
4.27 |
85.3 |
42.7 |
21.3 |
10.7 |
| 2.5 |
6.53E-03 |
6.66 |
133.4 |
66.7 |
33.3 |
16.7 |
| 3 |
9.41E-03 |
9.60 |
192.0 |
96.0 |
48.0 |
24.0 |
| 5 |
2.61E-02 |
26.66 |
533.4 |
266.7 |
133.4 |
66.7 |
| |
Although the present invention has been described with reference to preferred
embodiments, workers skilled in the art will recognize that changes may be made
in form and detail without departing from the spirit and scope of the invention.
*
