U.S. patent application number 09/731953 was filed with the patent office on 2002-06-06 for magnetic recording head burnishing method.
Invention is credited to Gillis, Donald Ray, Schouterden, Kris Victor.
Application Number | 20020067574 09/731953 |
Document ID | / |
Family ID | 24941581 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020067574 |
Kind Code |
A1 |
Gillis, Donald Ray ; et
al. |
June 6, 2002 |
Magnetic recording head burnishing method
Abstract
A slider burnishing method is introduced, in which the slider is
brought into a predetermined surface contact with the rotating disk
for a specified period. The predetermined surface contact and the
specified time period are selected together with the surface
condition of the rotating hard disk, such that smoothened slider
surface is abrasively formed. The smoothened slider surface is
substantially parallel to the disk surface and thus provides
reduced contact pressure during eventual operational contacting. In
addition, the smoothened slider surface creates a constant gap
together with the disk surface, which enhances the aerodynamic
properties of the air bearing surface and stabilizes a small fly
height.
Inventors: |
Gillis, Donald Ray; (San
Jose, CA) ; Schouterden, Kris Victor; (Los Gatos,
CA) |
Correspondence
Address: |
JOSHUA D. ISENBERG
LUMEN INTELLECTUAL PROPERTY SERVICES
SUITE 110
45 CABOT AVENUE
SANTA CLARA
CA
95051
US
|
Family ID: |
24941581 |
Appl. No.: |
09/731953 |
Filed: |
December 6, 2000 |
Current U.S.
Class: |
360/235.4 ;
G9B/5.036; G9B/5.229 |
Current CPC
Class: |
G11B 5/102 20130101;
Y10T 29/49025 20150115; G11B 5/60 20130101; Y10T 29/47
20150115 |
Class at
Publication: |
360/235.4 |
International
Class: |
G11B 005/60 |
Claims
What is claimed is:
1) A slider being fixated on a slider arm of a hard disk drive and
having a burnished surface in a substantially parallel orientation
to an opposing hard disk surface, wherein said parallel orientation
is defined by burnishing said slider on said opposing hard disk
surface.
2) The slider of claim 1, wherein said burnished surface is placed
on an air bearing surface adjacent to a contacting sensor.
3) The slider of claim 2, wherein said contacting sensor is a
magnetic read head.
4) The slider of claim 2, wherein said burnished surface is placed
on a slider having a crown.
5) The slider of claim 2, wherein said burnished surface is placed
on said slider having a camber.
6) The slider of claim 1, wherein said burnished surface is placed
on an air bearing surface overlapping with a contacting sensor.
7) The slider of claim 6, wherein said contacting sensor is a
magnetic read head.
8) The slider of claim 6, wherein said burnished surface is placed
on said slider having a crown.
9) The slider of claim 6, wherein said burnished surface is placed
on said slider having a camber.
10) The slider of claim 1, wherein said burnished surface has an
area extension corresponding to a predetermined fly characteristic
of said slider.
11) The slider of claim 1, wherein said burnished surface has an
area extension corresponding to a predetermined friction
characteristic of a contacting interface between said slider and
said opposing hard disk surface.
12) The slider of claim 1, wherein said burnished surface is
provided by applying a burnishing method.
13) A burnishing method for burnishing a slider on a hard disk
surface, said slider being mounted on a slider arm of a hard disk
drive, said burnishing method comprising the steps of: A) preparing
a hard disk surface by removing eventual topographic
inconsistencies; B) burnishing said slider; and C) checking a
burnishing result.
14) The burnishing method of claim 13, said burnishing method
further comprising the step of recognizing eventual topographic
inconsistencies being performed prior to said step A) of claim
13.
15) The burnishing method of claim 13, said burnishing method
further comprising the step of deriving a resistive reference
signal during a non-contacting condition of the slider.
16) The burnishing method of claim 15, wherein said resistive
reference signal is provided by a natural resistance of a read head
of said slider.
17) The burnishing method of claim 15, wherein said non-contacting
condition is provided by positioning said slider arm in an
operational parking position.
18) The burnishing method of claim 15, wherein said checking of
said burnishing result is a recognition process of a predetermined
fly characteristic of said slider.
19) The burnishing method of claim 18, wherein said fly
characteristic is determined by a resistive operational signal
derived from said read head and compared to said resistive
reference signal.
20) The burnishing method of claim 15, wherein said checking of
said burnishing result is a recognizing of a predetermined friction
characteristic of a contacting interface between said slider and
said hard disk surface.
21) The burnishing method of claim 20, wherein said friction
characteristic is determined by a resistive friction signal derived
from said read head and compared to said calibration signal.
22) The burnishing method of claim 13, said burnishing method
further comprising the step of sweeping said hard disk surface.
23) The burnishing method of claim 22, wherein said sweeping is
performed as a final step of said burnishing method.
24) The burnishing method of claim 22, wherein said sweeping is
performed by said slider with a centrifugal movement alternating
with a centripetal movement.
25) The burnishing method of claim 24, wherein said slider is
contacting said hard disk surface during said centrifugal movement
and distancing from said hard disk surface during said centripetal
movement.
26) The burnishing method of claim 25, wherein said contacting and
said distancing are performed by changing an environment
pressure.
27) The burnishing method of claim 25, wherein said contacting and
said distancing are performed by changing the rotational speed of
said hard disk.
28) The burnishing method of claim 13, wherein said preparing of
said hard disk surface is provided by a stepped reduction of a disk
surface burnishing speed.
29) The burnishing method of claim 13, wherein said preparing of
said hard disk surface is provided by a stepped reduction of an
environment pressure.
30) The burnishing method of claim 13, wherein said burnishing of
said slider is provided by applying a contacting force together
with a rotational hard disk speed that corresponds to an abrasion
characteristic of said hard disk surface.
31) The burnishing method of claim 13, wherein said burnishing of
said slider is provided by applying said contacting force together
with said rotational hard disk speed that corresponds to a debris
clogging characteristic of a contacting interface between said
slider and said hard disk surface.
32) A hard disk drive having a slider being fixated on a slider arm
of said hard disk drive, said slider having a burnished surface
being burnished by an opposing hard disk surface in a substantially
parallel orientation to said opposing hard disk surface.
33) The hard disk of claim 32, wherein said burnished surface is
placed on an air bearing surface adjacent to a contacting
sensor.
34) The hard disk drive of claim 33, wherein said contacting sensor
is a magnetic read head.
35) The hard disk drive of claim 32, wherein said burnished surface
is placed on an air bearing surface overlapping with a contacting
sensor.
36) The hard disk drive of claim 35, wherein said contacting sensor
is a magnetic read head.
Description
BACKGROUND OF INVENTION
[0001] The continuous development of magnetic recording disk drives
results in ever increasing data storage densities in the storing
layers. To read and write the magnetic signals, the read and write
heads have to be kept in ever-closer distance to the rotating disc
surface where the storing layers are deposited.
[0002] The read and write heads are typically integrated in the
so-called sliders, which provide specifically designed
three-dimensional features on their bottom side that is next to the
disk surface. These three-dimensional features utilize the
viscosity and kinetic energy of a rotating air stream induced by
the spinning disk to lift the sliders on a predetermined fly height
during the hard disk operation.
[0003] The viscosity of the air stream depends mainly on the air
temperature and the air pressure.
[0004] The kinetic energy of the rotating air stream depends on its
velocity relative to the slider and subsequently on the rotational
speed of the hard disk.
[0005] The bottom side performs the function of an air bearing in
closest proximity to the disk surface. As a result fly heights in
the nanometer range can be implemented.
[0006] Such small fly heights require high precision of the disk
surface since even the smallest surface inconsistencies result in a
contacting of the slider with the fast moving disk surface. Even
though the utilized fabrication processes provide for sufficient
surface evenness of the hard disk, special wear-in procedures are
commonly performed to eliminate eventual and/or recognized surface
unevenness. These wear-in procedures are typically performed by
reducing the fly height below the operational level and moving the
slider over the surface until no contacting is recognized anymore.
The slider, which is made of a relatively hard material is thereby
utilized as an abrasive tool to remove any interfering surface
inconsistencies from the relatively soft top layers of the hard
disk.
[0007] The fly height is typically reduced by changing the
rotational speed of the hard disk and/or by changing the air
pressure.
[0008] A number of U.S. patents discloses variations of the hard
disk wear-in procedure, which is commonly referred to as
burnishing.
[0009] U.S. Pat. No. 5,696,643 and U.S. Pat. No. 5,863,237, for
instance, describe methods to burnish away topographic
irregularities from the disk surface. After recognizing an surface
irregularity via a thermal contacting signal, the rotational speed
of the hard disk is reduced and the fly height of the read/write
head is lowered. The burnishing is performed over a certain time
period, during which the height of the surface irregularities is
continuously reduced. After finishing the disk burnishing the
interference signals no longer occur during operational rotation of
the hard disk.
[0010] Japanese Patent JP 06309636 describes a similar burnishing
method, except that the read/write head is lowered by reducing the
air pressure under which the hard disk drive operates.
[0011] The thermal contacting signal results from a dynamic
resistance change in the read head, which is thermally induced by
the frictional energy created during the contacting of the
head.
[0012] The dynamic resistance change itself may be recognized with
various methods. In one method, it is recognized during the regular
read operation of the hard disk. This requires a fully functioning
hard disk drive, including a partitioned hard disk. U.S. Pat. No.
5,751,510 describes such a method.
[0013] In another method, the dynamic resistance change is obtained
by the read/write head without reading any data from the hard disk.
In such a case, an electrical stimulus voltage is applied to the
read head. This method can be performed at an earlier hard disk
fabrication stage since it does not require operational data read
from the hard disk surface. A calibration signal and/or a
calibration value has to be obtained for a known non-interference
condition. U.S. Pat. No. 5,806,978, for instance, describes such a
method.
[0014] With continuously decreasing fly heights a contacting and
non-contacting operational conditions in the head/disk interface
become less and distinctly able. Read/write heads operate typically
with their air bearing surface in an angulated orientation relative
to the disk surface.
[0015] The microscopic air bearing features are typically
fabricated with a common protrusion direction normal to the
substrate plane, which results in essentially coplanar surfaces and
linear edges. The design of the air bearing surface defines the
primary contacting edge, which initially contacts the moving disk
surface. In the case where the front portion of the air bearing
surface is raised sufficiently, the primary contacting edge becomes
the front edge with the read and write elements. In such a case,
the contacting of the slider during the regular hard disk operation
occurs mainly with the slider front edge.
[0016] The linear contacting of the slider with the primary
contacting edge results in relatively high surface pressures, which
result in wear of the disk surface and/or the slider. As a result
of disk wear, debris may adhesively build up on the primary
contacting edge. Since it is desirable to have the read/write heads
in closest proximity to the disk surface, they are preferably in an
area adjacent to the primary contacting edge. Debris built-up
alters the read and write characteristic of the heads and needs to
be prevented. U.S. Pat. No. 6,088,199, for instance, discloses an
abrasive section placed on the hard disk to remove eventual debris
built-up on the slider. The patent does not prevent debris from
building up, however. It provides only a cleaning method.
[0017] Wear in the head/disk interface related to operational
slider contact is explored in a number of scientific
disclosures.
[0018] In IEEE Trans. Magn. (USA) vol 34, no.4, pt.1, p. 1714-16, a
conference/journal paper is disclosed, which describes the abrasive
wear and adhesion of the slider surface.
[0019] In the 1996 AME/STLE Tribology Conference (TRIB-Vol.6)
p.17-23, a conference paper is disclosed, which describes new
techniques for evaluating slider wear and burnishing of the
head/disk interface.
[0020] Further, in the Proceedings of the SPIE--The International
Society of Optical Engineering (USA) vol.2604 p.236-43, contact
force measurements at the head/disk interface for contact recording
heads in magnetic recording are disclosed and correlated to the
burnishing in the head/disk interface.
[0021] Finally, in the Journal of Materials Research vol.8, no.7 p.
1611-28, friction and wear studies of silicon in sliding contact
with thin-film magnetic rigid disks are disclosed.
[0022] The ever decreasing fly heights make the limitations
described in the above scientific paper increasingly stringent.
[0023] The present invention addresses these limitations and
provides a solution for them.
OBJECTS AND ADVANTAGES
[0024] It is a primary object of the present invention to provide a
slider head in a wear reducing configuration and a method for
creating the same.
[0025] It is another object of the present invention to provide a
method for creating the wear-reducing configuration with feasible
fabrication effort.
SUMMARY
[0026] A slider burnishing method is introduced, in which a primary
contacting area of the slider is flattened in an abrasive way.
[0027] The primary contacting area is defined by the operational
orientation of the slider relative to the hard disk surface. In the
case of a planar slider, the contacting area is essentially a
contacting edge at the front end of the slider where the read and
write heads are located.
[0028] There are techniques known to those skilled in the art that
apply a bending in the form of a crown and/or camber to the air
bearing surface. The bending of the air bearing surface results in
a smoother contacting of the air bearing surface with the hard disk
surface. In such a case the contacting area may be at a more
central location of the slider adjacent to the location of the read
and write heads.
[0029] The abrasive flattening of the contacting area is
accomplished by applying a slider burnishing method during which
the slider is kept in contact with the rotating hard disk. The
slider burnishing method is designed for:
[0030] preventing damage of the relatively soft surface layers of
the hard disk;
[0031] preventing debris accumulation in the contacting area during
the slider burnishing;
[0032] keeping the thermal rise in the slider below a critical
maximum; and
[0033] creating a predetermined flattened area.
[0034] The slider burnishing creates a flattened area that is
planar and essentially parallel to the hard disk surface. An
eventual contacting of the slider with the hard disk surface
results in reduced surface pressure in the contacting area, which
is commonly referred to as the head/disk interface. The slider
contacting may either be intermediate or permanent.
[0035] Under operational conditions where a fly height needs to be
maintained, the flattened area defines, together with the hard disk
surface, an even air bearing gap. This air bearing gap enhances the
aerodynamic properties of the air bearing surface, such that
smaller fly heights can be utilized in a stable fashion.
[0036] The slider burnishing method consists of a number of
individual steps with various contacting forces and rotational disk
speeds. The main steps perform the following tasks:
[0037] preparing the hard disk surface by removing eventual
topographic inconsistencies;
[0038] burnishing the slider; and
[0039] checking the burnishing result.
[0040] In an alternate embodiment the slider burnishing process is
mainly performed by the following steps:
[0041] deriving a resistive reference signal during a
non-contacting condition of the slider.
[0042] preparing the hard disk surface by removing eventual
topographic inconsistencies;
[0043] burnishing the slider;
[0044] checking the burnishing result; and
[0045] sweeping the disk surface to remove debris.
[0046] The calibration signal is derived prior to the slider
burnishing, to have a reference value so as to determine the
contacting signal. Calibration signal and contacting signal are a
function of the read head resistance, which influences a bias
voltage applied to the read head during the slider burnishing. The
read head resistance is dependent on the read head temperature and
changes during frictional contact with the disk surface, as is
known to those skilled in the art.
[0047] The contacting signal is utilized to observe the contacting
characteristic during the following steps of the slider burnishing
method.
[0048] During the disk surface preparation the fly height is
consecutively lowered in correspondence with a reduction of the
rotational disk speed. Topographic inconsistencies are thereby
removed without creating abrasive deposits on the contacting
area.
[0049] The slider burnishing is the most time consuming step of the
slider burnishing method and is performed with a predetermined
contacting force at a relatively low rotational speed. Since the
disk surface has been smoothened sufficiently a permanent slider
contact can be maintained without the risk of vibrations and/or
excessive abrasion induced by eventual topographic inconsistencies.
During the slider burnishing, the slider is continuously moved over
the rotating disk surface to prevent local thermal rise in the disk
surface. Rotational speed and contacting force are also selected to
keep thermal rise of the slider below a critical level at which the
heat sensitive components of the slider may be damaged and/or
debris may weld on the contacting area.
[0050] During the clearance check the fly height is raised to a
level at which no contacting signal is recognized anymore.
[0051] The final sweeping step removes any debris accumulated on
the disk surface during the prior burnishing operation.
[0052] The slider burnishing method is performed with various
rotational speeds and independently defined fly heights and/or
contact forces between the slider and the hard disk surface. To
adjust the fly heights and/or the contact forces in an independent
fashion to the rotational speeds, the air pressure under which the
slider burnishing is performed is correspondingly adjusted.
BRIEF DESCRIPTION OF THE FIGURES
[0053] FIG. 1 shows a three-dimensional view of a simplified hard
disk drive with a removed housing portion such that a hard disk and
a slider attached on a slider arm are visible.
[0054] FIG. 2 shows an enlarged detailed view of the interface
between the slider and the hard disk of FIG. 1 in a direction
perpendicular to a reference plane also shown in FIG. 1.
[0055] FIG. 3 shows a simplified slider with an essentially planar
adaptation surface.
[0056] FIG. 4 shows a simplified slider with a first curved
adaptation surface having a curvature axis that is collinear with a
symmetric plane of the slider.
[0057] FIG. 5 shows a simplified slider with a second curved
adaptation surface having a curvature axis that is perpendicular to
a symmetric plane of the slider.
[0058] FIG. 6 shows a simplified slider with a third curved
adaptation surface having the first and second curvature axes.
[0059] FIG. 7 shows a simplified graph of a control signal change
during the slider burnishing process for an exemplary case where
the control signal sensor is within the burnishing area.
[0060] FIG. 8 shows a simplified graph of a control signal change
during the slider burnishing process for an exemplary case where
the control signal sensor is outside the burnishing area.
[0061] FIG. 9 shows a block diagram of a preferred embodiment of a
burnishing method.
[0062] FIG. 10 shows a block diagram of an alternate embodiment of
the burnishing method.
[0063] FIG. 11 shows a graph of four exemplary control signal
voltages of four different sliders during their burnishing
process.
[0064] FIG. 12 shows a graph of four relative resistance changes of
read heads operating as contacting sensors during the burnishing
process of the four sliders referred to in FIG. 11.
DETAILED DESCRIPTION
[0065] Although the following detailed description contains many
specifics for the purposes of illustration, anyone of ordinary
skill in the art will appreciate that many variations and
alterations to the following details are within the scope of the
invention. Accordingly, the following preferred embodiment of the
invention is set forth without any loss of generality to, and
without imposing limitations upon, the claimed invention.
[0066] FIG. 1 shows the a simplified hard disk drive HDD with the
main operational components involved in the slider burnishing being
visible through a removed housing portion of the hard disk drive
HDD. A slider 1 is attached to a slider arm iC, which pivots around
a slider arm axis iD. The slider has a front face 1B and a
symmetric plane IF. FIG. 1 also shows a hard disk 2 having a hard
disk surface 2A and a spinning axis 2B.
[0067] During the slider burnishing, the slider arm IC pivots
around the slider arm axis iD such that the slider 1 performs
centripetal and centrifugal movements along the hard disk surface
2A of the spinning hard disk 2.
[0068] Dependent on the velocity of the centripetal and centrifugal
slider movements relative to the rotational speed of the hard disk
surface, the symmetric plane IF defines a movement angle together
with the resulting movement vector in the interface between the
slider 1 and the hard disk surface 2A. In the case where the slider
arm iC does not move, the movement angle is approximately zero. It
is clear to one skilled in the art how the geometric and dynamic
conditions of the hard disk 2 and the slider arm 1C precisely
define the movement angle.
[0069] FIG. 2 shows an enlarged view of the interface between the
slider 1 and the hard disk 2 in a direction perpendicular to the
reference plane iF. The main physical characterizing elements of
the present invention in the slider/disk interface are:
[0070] the hard disk surface 2A;
[0071] adaptation surfaces 1E, 11E, 12E, 13A (see FIGS. 3-6);
[0072] front faces 1B, 11B, 12B, 13B (see FIGS. 3-6);
[0073] burnishing areas 1A, 11A, 12A, 13A (see FIGS. 3-6); and
[0074] burnishing sensors 1R, 11R, 12R, 13R (see FIGS. 3-6).
[0075] The front faces 1B, 11-13B are shown in planar configuration
for the purposes of general understanding. It is noted that front
faces of sliders may have any shape without affecting the core of
the invention.
[0076] For general understanding, the introductory example
described in FIG. 2 refers to the slider 1 having a planar
adaptation surface 1E perpendicular to the symmetric plane 1F. The
adaptation surface 1E is oriented with an adaptation angle 3A
relative to the hard disk surface. In the preferred embodiment of
the invention, the adaptation angle 3A is essentially identical
with an operational angle (not shown) under which the adaptation
surface 1E will be kept in position during the operational use of
the hard disk drive.
[0077] The core of the invention also applies to a case where the
adaptation angle 3A is different from the operational angle.
[0078] During the slider burnishing a contacting condition is
provided between the adaptation surface 1E and the hard disk
surface 2A, which results in a burnishing area 1A abrasively formed
by the hard disk surface 2A. In the preferred embodiment the
contacting condition is provided by altering dynamic and/or static
fluid properties that influence a fly height of the slider 1 above
the hard disk surface 2A, as is known to those skilled in the art.
The dynamic fluid properties are, for instance, altered by changing
the rotational speed of the hard disk 2, such that the velocity of
a concentrically circulating fluid stream is reduced.
[0079] The static fluid properties are, for instance, altered by
changing the fluid viscosity, for instance, by reducing the static
pressure of a compressible fluid.
[0080] The fluid utilized for the slider burnishing may be
identical to/or different from the operational fluid under which
the hard disk drive is operated. In the preferred embodiment the
burnishing fluid is air.
[0081] It is noted that the burnishing fluid may be any gaseous or
liquid material that is suitable for providing the contacting
characteristic. The preferred gaseous burnishing fluid is air.
Alternate gaseous burnishing fluids may be, for instance He, or Ne,
which may introduce a reduced fly height due to their low viscosity
relative to the viscosity of the operational fluid in the preferred
form of air. In general, the fly height may be adjusted during the
burnishing process by altering the composition of the burnishing
fluid and consequently the viscosity relative to the composition of
the operating fluid. The operating fluid is the fluid, which fills
the space between the slider and the disk surface during the
operational use of the hard disk. In addition, the inert nature of
He and Ne protect the slider and disk surface against oxidation,
which may result from the elevated temperatures in the burnishing
interface between slider and disk surface. In addition, any
burnishing enhancing material may be applied to the hard disk
surface 2A and/or the adaptation surface 1E, 11-13E to enhance the
slider burnishing process. In particular, slider burnishing
enhancing materials that overcome the limitations imposed by the
operational softness of the hard disk surface 2A relative to the
operational hardness of the adaptation surface 1E may be applied to
the hard disk surface 2A prior to the slider burnishing process.
This burnishing enhancing material may be applied in a fashion that
corresponds to the burnishing process such that at the end of the
burnishing process the burnishing enhancing material itself is
abraded and no longer present on the hard disk surface 2A.
[0082] During the slider burnishing process, material is removed
from the slider 1. The removed material 1G leaves a burnished area
1A behind. The removal material height 3B defines, together with
slider shape, the removed material volume. The removed material
volume influences the slider burnishing time. To keep the slider
burnishing time to a minimum the contacting characteristic has
preferably a contact force gradient that corresponds to the
increase of burnishing area during the slider burnishing. As a
result, the contact pressure in the slider/disk interface remains
constant and below a critical level. The critical pressure level is
defined by the abrasion resistance of the hard disk surface 2A and
the thermal drain capacity of the slider.
[0083] The adaptation angle 3A influences a fly characteristic of
the slider 1 above the hard disk surface 2A. The fly characteristic
keeps the slider 1 in a predetermined fly height range under
operational conditions as is known to those skilled in the art. The
burnished areas 1A, 11-13A define, together with the hard disk
surface 2A, an operational gap that has stabilizing influence on
the fly characteristic. In the preferred embodiment where the
adaptation angle 3A is essentially equal to the operational angle
the operational gap has a consistent width. As a result, the fluid
stream in the gap has a constant velocity resulting in a balanced
fluid pressure in the gap. In case of a contacting of the slider 1
with the hard disk surface 2A, the burnished areas 1A, 11-13A
contact snuggly with the hard disk surface 2A, which avoids
unfavorable abrasion of the hard disk surface 2A.
[0084] In FIGS. 3-6 a number of configurations of the sliders 1,
11-13 is shown. The configurations of the sliders 1, 11-13 are
shown with the adaptation surfaces 1E, 11-13E, the contacting
sensors in the preferred form of data read heads 1R, 11-13R, write
heads 1W, 11-13W, the burnished areas 1A, 11-13A and the front
faces 1B, 11-13B.
[0085] The sliders 1, 11 of FIGS. 3 and 4 have their data read
heads 1R and 11R within the burnished area 1A, 11A.
[0086] The sliders 12, 13 of FIGS. 5 and 6 have their data read
heads 12R and 13R outside the burnished area 12A, 13A.
[0087] In FIG. 4, the adaptation surface 11E has a curvature with a
curvature axis 11F. The curvature of the adaptation surface 11E is
known to those skilled in the art as camber.
[0088] In FIG. 5, the adaptation surface 12E has a curvature with
curvature axis 12F. The curvature of the adaptation surface 12E is
known to those skilled in the art as crown.
[0089] In FIG. 6, the adaptation surface 13E has a curvature with a
curvature axes 13F and 13G. The curvature of the adaptation surface
13E is a combination of crown and camber.
[0090] For the exemplary sliders 1, 11 the adaptation angle 3A
remains constant during the slider burnishing process. For the
exemplary sliders 12, 13 the adaptation angle 3A increases during
the slider burnishing process.
[0091] At the start of the slider burnishing the sliders 1, 11-13
have initial burnishing contacts with the hard disk surface 2A. At
the initial burnishing contacts the burnishing areas 1A, 11-13A
start to form and to expand.
[0092] For the slider 1, the initial burnishing contact is an edge
of the front face 1B and the adaptation surface 1E.
[0093] For the slider 11, the initial burnishing contact is a point
on the edge of the front face 2B and the adaptation surface 2E.
[0094] For the slider 12, the initial burnishing contact is a
initial contacting line parallel to the curvature axis 12F.
[0095] The distance of the initial contacting line to the data read
head 12R depends on the overall orientation of the slider 12 to the
hard disk surface 2A.
[0096] For the slider 13, the initial burnishing contact is an
initial contacting point. The distance of the initial contacting
point to the data read head 13R depends on the overall orientation
of the slider 13 to the hard disk surface 2A.
[0097] The burnishing areas 1A, 12A have a first extension
direction essentially perpendicular to the front faces 1B and
11B.
[0098] Since the sliders 1, 11-13 are shown with final fabricated
burnishing areas 1A, 11-13A, the initial burnishing contacts are no
longer present and therefore not shown.
[0099] During the slider burnishing of the slider 1, the burnishing
area 1A expands away form the edge between the front face 1 and the
adaptation surface 1E. As shown for the slider 1, the burnishing
area 1A expands beyond the data read head 1R and the write head
1W.
[0100] During the slider burnishing of the slider 11, the
burnishing area 11A expands away form the initial contacting point
on the edge between the front face 2B and the adaptation surface
2E. As shown for the slider 11, the burnishing area 11A expands
beyond the data read head 11R and the write head 11W.
[0101] During the slider burnishing of the slider 12, the
burnishing area 12A expands away form the initial contacting line.
As shown for the slider 12, the initial contacting line is at a
distance to the data read head 12R, such that the final expanded
burnishing area 12A does not overlap with the data read head 12R
and the write head 12W.
[0102] During the slider burnishing of the slider 13, the
burnishing area 13A expands away form the initial contacting point.
As shown for the slider 13, the initial contacting point is in a
distance to the data read head 13R such that the final expanded
burnishing area 13A does not overlap with the data read head 13R
and the write head 13W. It is clear to one skilled in the art that
the configurations of the sliders 1, 11-13 may be defined such that
the burnishing areas 1A, 11-13A may or may not overlap with the
data read heads 1R, 11-13R.
[0103] It is clear to one skilled in the art that the adaptation
surfaces 1E, 11-13E may have any shape or configuration.
Furthermore, the adaptation surfaces 1E, 11-13E may form an air
bearing surface at is known to those skilled in the art, and/or may
be a component of an air bearing surface.
[0104] The slider burnishing process is monitored by use of a
contacting sensor. In the preferred embodiment the contacting
sensors are the data read heads 1, 11-13R as they are known to
those skilled in the art for the recognition of disk surface
contact recognition.
[0105] In the preferred embodiment the natural resistance of the
data read heads 1R, 11-13R is recognized prior to the slider
burnishing process and utilized as a reference value. During the
slider burnishing a dynamic and static resistance changes may occur
in the data read heads 1R, 11-13R.
[0106] A dynamic resistance change is mainly induced by a thermal
friction energy resulting from a disk surface contacting of the
contacting sensors and/or surrounding areas of the sliders 1,
11-13.
[0107] A static resistance change is mainly induced in a case where
the contacting sensors are or become part of the burnishing area
during the slider burnishing as it is shown with the sliders 1, 11.
The removing of material 1G includes a removing of the contacting
sensor material, which results in a static resistance change of the
contacting sensor.
[0108] In FIG. 7 a simplified graph shows a curve 22A representing
the static resistance change and a curve 22D representing the
dynamic resistance change for a case where the data read heads 1R,
11-13R are overlapped by the burnishing areas 1A, 11-13A.
[0109] The vertical axis 20 (see also FIG. 8) represents the
resistance change relative to the total read head resistance. The
horizontal axis 21, 31, 41 (see FIGS. 8, 11, 12) represent a number
of burnishing cycles during which the sliders 1, 11-13 are moved
back and forth on the disk surface 2A.
[0110] Prior to the slider burnishing, a reference value 22R, 23R,
32R and 42R (see also FIGS. 8, 11, 12) is recognized preferably on
a slider position for which a non-contacting condition is secured.
Such a slider referencing position is preferably on a parking ramp
where the slider arm 1C is parked during non-operation of the hard
disk drive.
[0111] The curve 22A has an initial incline angle and becomes
flatter during the slider burnishing. The curve 22A approaches
asymptotically to a theoretical maximum line 22E. The incline angle
of the curve 22A over its length corresponds to the increasing
removed material height 3B. The burnishing areas 1A, 11-13A start
to form from a contacting line or a contacting point, such that a
relatively low amount of initially removed material 1G results in a
relatively high gain of removed material height 3B.
[0112] With continuing material removal the burnishing areas 1A,
11-13A extend. As a result, for a given amount of removed material
the gain of removed material height 3B becomes ever smaller. The
increase of the burnishing areas 1A, 11-13A also results in a
reduced contacting pressure for a given contacting force. Since the
contacting force is limited to prevent thermally induced damages to
the disk surface 2A and/or the sliders 1, 11-13, the contacting
pressure reaches a level at which abrasion of the slider material
no longer occurs. The material properties of the sliders 1, 11-13,
the abrasive properties of the hard disk surface 2A and the maximum
contacting force define a theoretical maximal burnishing area
extension, which is recognized by the theoretical maximum line
22E.
[0113] In FIG. 8 the curve 23A corresponds to the curve 22A, except
for the case where the contacting sensors do not become overlapped
by the burnishing areas 1A, 11-13A. Hence, the contacting sensors,
e.g. the data read heads 1R, 11-13R, are not exposed to the
material removal process. Consequently, the data read heads 1R,
11-13R do not change their static resistance, and the curve 23A is
horizontal.
[0114] The curves 22D, 23D (see FIG. 8) provide examples for the
dynamic resistance change during the slider burnishing. After
recognizing the reference resistance 22R, 23R, 32R, 42R the slider
burnishing process is initiated by bringing the sliders 1, 11-13
into contact with the rotating disk surface 2A. Initially, the
dynamic resistance change has a relatively volatile nature. The
reason for this is topographic inconsistencies in the hard disk
surface that impose varying contacting conditions. During the
slider burnishing these topographic inconsistencies are removed and
the dynamic resistance change becomes smaller and smaller. This is
shown in FIGS. 7 and 8 by the upper boundary curves 22C, 23C and
the lower boundary curves 22B and 23B.
[0115] It is noted that the contacting sensor may be any device
known to those skilled in the art to recognize the contacting
characteristic. The contacting sensor may or may not utilize a
reference signal.
[0116] It is further noted that the reference signal may be a
predetermined signal derived independently from the hard disk drive
subject to the slider burnishing. The reference signal may be
statistically, empirically, or theoretically predetermined.
[0117] The slider burnishing is performed by a burnishing method in
which the burnishing parameters are variously specified such that
distinctive slider burnishing steps are created.
[0118] FIG. 9 shows a block diagram of the steps of a burnishing
method of the preferred embodiment. The burnishing method begins
with preparing the hard disk surface, followed by burnishing the
slider and finally checking the burnishing result.
[0119] During the preparation of the hard disk surface 2A, the
sliders 1, 11-13 are continuously lowered, preferably by changing
the rotational speed of the hard disk 2 and/or by reducing the
environment pressure. The lowering may be performed either in a
predetermined fashion, or in correspondence with recognized dynamic
resistance fluctuations. Dynamic resistance fluctuations indicate
the contacting dynamic. In other words, it is important to prevent
the sliders 1, 11-13 from vibrating and from shifting their pitch
angles to a negative value when hitting topographic
inconsistencies. Topographic inconsistencies may be bumps, waves or
the like on the hard disk surface 2A as known to those skilled in
the art. The pitch angle corresponds to the adaptation angle 3A. A
negative pitch angle would cause the slider to plow into the hard
disk surface 2A. This needs to be prevented at any cost.
[0120] Once the dynamic resistance fluctuations have reached a
minimal level indicating a required planarity and/or smoothness of
the hard disk surface 2A, the burnishing parameters are adjusted to
levels that create a contacting characteristic primary defined to
perform the slider burnishing. The slider burnishing step may be
initiated by recognizing the dynamic resistance fluctuations and/or
after a predetermined surface preparation period.
[0121] Following the slider burnishing step, the hard disk drive is
brought into operational mode, which includes, for instance, the
adjustment of the environment pressure and/or the adjustment of the
hard disk speed to operational levels. The contacting sensor
recognizes then the actual fly height achieved by fabricating the
predetermined burnishing areas 1A, 11-13A.
[0122] FIG. 10 shows a block diagram of the preferred embodiment
with the additional steps of deriving a resistive reference signal
during a non-contacting condition of the slider and sweeping the
disk surface to remove debris.
[0123] The resistive reference signal may be the natural resistance
of a resistive contacting sensor like, in the preferred embodiment,
a magnetic read head as is known to those skilled in the art.
[0124] The sweeping of the disk surface 2A may be performed with a
sequence of centrifugal slider movements in disk contact
alternating with centripetal slider movements without disk contact.
Disk contacting and non-contacting may be provided, for instance,
by changing the rotational speed of the hard disk 2 or the
environment pressure.
[0125] In the case where the resistive reference signal is
utilized, the checking of the burnishing result is performed by
comparing an operational resistive signal of the contacting sensor
derived under operational conditions of the hard disk drive. A
non-contacting operation of the sliders 1, 11-13 at a fly height
that is accomplished by the defined burnishing areas 1A, 11-13A is
established when the operational resistive signal is within a
specified range of the resistive reference signal.
[0126] FIG. 11 shows four curves 34A-D, each having one of the line
styles 33. The vertical axis 30 represents a voltage level of the
contacting signal in the approximate occurring range during the
burnishing method. The four curves 34A-D are derived from
experimental slider burnishing performed on sliders that are
different from those described in the above. The four curves 34A-D
are shown for the sole purpose of general understanding without any
claim of accuracy. The four curves 34A-D are integrated from a
filtered measured signal and correspond to the simplified curve
22D. The filtered measured signal is cleared of electronic noise
and other high and low frequencies, which do not relate to the
burnishing process.
[0127] The burnishing method is applied during the period 31A (see
also FIG. 12). The preparation of the slider surface is performed
during the period 31B (see also FIG. 12). The slider burnishing is
performed during the period 31C (see also FIG. 12).
[0128] During the period 31B the voltage level has strong
fluctuations as explained above. Towards the end of the period 31B
the voltage level change becomes more steady, which indicates the
successful preparation of the hard disk surface 2. When the
burnishing parameters are changed according to the requirements for
the slider burnishing, the voltage level has again strong
fluctuations for a short period 31E. This indicates that hit
clearance is not obtained yet, which means that the slider is still
hitting the disk surface.
[0129] During the period 31D at the end of the slider burnishing
process, the rotational speed of burnished hard disk is gradually
increased again and the regular operational conditions are
established. An operational voltage signal 32I is derived. The
operational voltage signal 321 has a level discrepancy 31F to a
reference voltage signal 32R that indicates a predetermined
clearance increase and the successful slider burnishing as
described above.
[0130] FIG. 12 shows four curves 44A-D, each having one of the line
styles 44. The vertical axis 40 represents the static resistance
change relative to the total resistance in magnetic read heads that
are utilized as contacting sensors.
[0131] The four curves 44A-D are derived during the same
experimental slider burnishing as described in FIG. 11. The four
curves 44A-D are shown for the sole purpose of general
understanding without any claim of accuracy.
[0132] The fluctuating static resistance change at the begin of the
period 31B results from the disk surface preparation, during which
also the slider is exposed to a certain abrasion.
[0133] Once the topographic inconsistencies are removed, the
relative static resistance change goes into a steady incline.
During the change from the disk preparation step to the slider
burnishing step the curves 44A-D have a short inconsistency as
described in FIG. 11. During the period 31C the tangential angle of
the four curves 44A-D goes towards zero, which indicates that the
maximum burnishing areas are reached. The curves 44A-D are
practically obtained curves that correspond to the simplified curve
22A.
[0134] It is noted that the disk surface preparation may be
optionally and eventually initiated after performing a disk surface
verification process in which the evenness of the hard disk surface
is recognized. The verification process may be performed by
lowering the sliders 1, 11-13 and recognizing the magnitude of the
contacting signal fluctuations to derive information about the
topographic inconsistencies. The verification process may be
performed only for a relatively short period compared to the
surface preparation process, since it does not perform a
fabrication but only a measurement.
[0135] Accordingly, the scope of the invention described in the
specification above is set forth by the following claims and their
legal equivalent.
* * * * *