WO2003058610A1 - Diminution de blocage par adherence de disques-tetes - Google Patents

Diminution de blocage par adherence de disques-tetes Download PDF

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Publication number
WO2003058610A1
WO2003058610A1 PCT/US2003/000417 US0300417W WO03058610A1 WO 2003058610 A1 WO2003058610 A1 WO 2003058610A1 US 0300417 W US0300417 W US 0300417W WO 03058610 A1 WO03058610 A1 WO 03058610A1
Authority
WO
WIPO (PCT)
Prior art keywords
head
disk
lubricant
voltage
dwell
Prior art date
Application number
PCT/US2003/000417
Other languages
English (en)
Inventor
James D. Kiely
Emil John Catoc Esmenda
Yiao-Tee Hsia
Original Assignee
Seagate Technology Llc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Seagate Technology Llc filed Critical Seagate Technology Llc
Priority to AU2003210457A priority Critical patent/AU2003210457A1/en
Publication of WO2003058610A1 publication Critical patent/WO2003058610A1/fr

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B21/00—Head arrangements not specific to the method of recording or reproducing
    • G11B21/16—Supporting the heads; Supporting the sockets for plug-in heads
    • G11B21/20—Supporting the heads; Supporting the sockets for plug-in heads while the head is in operative position but stationary or permitting minor movements to follow irregularities in surface of record carrier
    • G11B21/21—Supporting the heads; Supporting the sockets for plug-in heads while the head is in operative position but stationary or permitting minor movements to follow irregularities in surface of record carrier with provision for maintaining desired spacing of head from record carrier, e.g. fluid-dynamic spacing, slider
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
    • F16C33/02—Parts of sliding-contact bearings
    • F16C33/04—Brasses; Bushes; Linings
    • F16C33/06—Sliding surface mainly made of metal
    • F16C33/10—Construction relative to lubrication
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C33/00—Parts of bearings; Special methods for making bearings or parts thereof
    • F16C33/02—Parts of sliding-contact bearings
    • F16C33/04—Brasses; Bushes; Linings
    • F16C33/06—Sliding surface mainly made of metal
    • F16C33/10—Construction relative to lubrication
    • F16C33/102—Construction relative to lubrication with grease as lubricant
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
    • G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B5/60—Fluid-dynamic spacing of heads from record-carriers

Definitions

  • the invention relates to the reduction of stiction between to bodies and more particularly relates to field of disk drives and the reduction of head-disk stiction.
  • Stiction is caused by a combination of interfacial friction and interfacial liquid meniscus forces.
  • Conventional means for reducing stiction include artificially increasing the roughness of a landing zone on media and/or artificially increasing the roughness on certain regions of the head' s air-bearing surface or by providing bumps or pads on the air bearing surfaces.
  • the media is roughened to provide a landing zone, a segment of the disk that could otherwise be used for data storage is sacrificed. This is undesirable in today's disk drives; and as areal density increases, the storage capacity sacrificed by this landing zone increases.
  • Attempts to employ ' artificially roughened heads on unroughened, smooth media have been unsuccessful in reducing stiction sufficiently. Other methods of reducing stiction are needed.
  • the invention comprises reducing stiction between two bodies separated by a lubricant through the application of electrostatic fields when the two bodies are dwelling statically.
  • the electrostatic field is removed prior to causing the two bodies to begin sliding contact.
  • the electrostatic field is created by applying a small voltage between the head and the disk while disk rotation is stopped and the head is dwelling on the disk. This voltage is removed just prior to applying power to the spindle motor.
  • the spindle motor overcomes stiction and disk rotation begins.
  • the applied electrostatic field creates a capacitance attraction between the head and the disk. This attraction squeezes lubricant away from the interface between the two. When the electric field is removed, the capacitance attraction is removed thereby causing a net separation force between the head and disk. However, the lubricant is viscous and it does not immediately flow back to replace the lubricant that was squeezed out.
  • the increased separation between the head and disk coupled with the slowness of lubricant movement creates voids in the lubricant contact area between the head and disk. This reduction in lubricant contact area reduces lubricant meniscus forces between head and disk and the lubricant. The reduction in meniscus forces in turn reduces stiction.
  • Disk drive lubricants exhibit dielectrophoresis .
  • the applied electrostatic field causes lubricant to move and spatially aggregate at locations of highest field intensity which are the areas of closest contact between the head and disk.
  • the lubricate aggregates around these points and thins elsewhere. This, in turn, reduces the surface area of contact between the disk lubricant and interfacing surfaces.
  • the reduction in surface area of contact reduces the meniscus force between the lubricant and the interfacing surfaces.
  • the reduction in meniscus forces reduces stiction.
  • Fig. 1 is a schematic view of the essential components of the disk drive necessary to carry out the present invention.
  • Fig. 2 is a schematic of an additional lead connected between a flex circuit and a magnetic head that applies the electrostatic voltage of the present invention to the head.
  • Fig. 3 is a chart comparing stiction values with and without the invention.
  • Fig. 4 is a chart summarizing the reduction in stiction.
  • Fig. 5 is an ellipsometric image of a disk showing lubricant thickness when a head has been dwelling on the disk with an electrostatic voltage applied.
  • Fig. 6 is an ellipsometric image of the disk of
  • Fig. 5 one day after the electrostatic voltage has been removed.
  • Fig. 1 illustrates the essential disk drive components required to implement the current invention. Shown in the figure is magnetic disk 10 mounted on disk drive spindle 22. Magnetic head 16, which is mounted on flexure 14, is shown in contact with the magnetic disk 10. In most disk drives, this point of contact would be located at a landing zone which is located adjacent spindle 22.
  • Flexure 14 is in turn connected to a flex circuit 18, that is electrically connected, through switch 24, to positive voltage supply 20.
  • a first means is to simply apply the voltage to the flexure 14, which in turn supplies the voltage to the head 16.
  • a separate lead 26 may be provided between the flex circuit 18 and the head 16 if it is desired to electrically isolate the head 16 from flexure 14.
  • this lead 26 comprises one of the leads 28 that bond to bonding pads (not shown) and connect the head' s active transducers components to the flex circuit 18.
  • the magnetic disk 10 is further connected to ground 12. Any number of means may be used to accomplish this. However the most common means would be to provide an electrically conductive bearing fluid or grease in the disk drive's spindle motor (not shown) that drives spindle 22.
  • the switch 24 is closed to connect voltage source 20 to the head after the disk 10 has come to a halt.
  • This "dwell voltage” creates an electrostatic field between the head and disk across the lubricant. It is left connected until it is again desired to begin rotation of the magnetic disk 10 for normal disk drive operation. At that time, switch 24 is opened to disconnect voltage 20 from the head. Alternatively to save power, it may be sufficient to apply the dwell voltage for a short time just prior to the start of disk rotation.
  • the preferred electric dwell voltage differential between the head 16 and disk 10 is on the order of two volts. Dwell voltages may range, however, from a effective lower limit, approximately lOOmV, to an effective upper limit set primarily to avoid potentially harming the read/write transducer. Two volts is the upper limit with today's highly sensitive transducers. However, dwell voltages different from these voltages may also be used without limitation on the scope of the present invention.
  • the lubricant In order to conserve power, it is desirable that the lubricant not be conductive. This is also desirable to maximize the "capacitor" effect of having the head and disk cooperate together as conductive "plates" separated by a dielectric.
  • the lubricant commonly used in disk drives, including the functional and non functional lubricants described herein, are dielectrics.
  • Lubricants commonly used in magnetic disk drives are dielectrics. These dielectric lubricants have recently been shown to be susceptible to dielectrophoretic effects. The lubricants move when they are exposed to an electric field gradient.
  • Dielectrophoresis is an electrical phenomenon that allows particles to be trapped or manipulated by applying nonuniform electrical fields. These non uniform electric fields induce electrical polarization in the particles. Depending on the polarizability of the particles with respect to the medi f um in which it is suspended, they will move toward or away from regions of high field intensity. Motion toward the regions of high field intensity is termed positive dielectrophoresis. Motion away from them is termed negative dielectrophoresis.
  • functional lubricants include functional perfluoropolyether lubricants (e.g., FOMBLIN® Z-DOL and Z-tetraol) , available from Ausimont USA, a subsidiary of Montedison S.P.A of Milan, Italy.
  • functional perfluoropolyether lubricants e.g., FOMBLIN® Z-DOL and Z-tetraol
  • non-functional lubricants that are also used on occasion exhibit some dielectrophoresis, though not as pronounced as functional lubricants.
  • An exemplary non-functional lubricant is FOMBLIN® Z, available > from Ausimont USA, a division of Montedison, S.P.A., of Milan Italy.
  • the use of a functional lubricant is preferred to enhance dielectrophoresis in the presence of the applied electrostatic field of the present invention.
  • Fig. 5 is an ellipsometric image from a disk that had 2V applied between it and a head.
  • the lighter areas are the disk lubricant.
  • the darker areas, particularly at the dark points of contact 50, are areas of less or no lubricant.
  • the applied electrostatic fields has caused the lubricant to accumulate and form menisci in regions 52 near points contact 50 between the head and the disk. This accumulation in turn thins the lubricant at locations 54 away from these points of contact 50.
  • a head contacts a disk surface via a plurality point contacts, dark spots 50, scattered about the head/disk interface.
  • These point contacts 52 are caused by carbon bumps or pads formed on the rails of a slider that are intended to reduce the area of contact between disk and the head. They may also be caused by unintended asperities.
  • Fig. 6 is an ellipsometric of the same disk area imaged one day later during which time no dwell voltage was applied between the head and the disk.
  • the change in lubricant thickness from the first image shown in Fig. 6. One day is sufficient time for lubricant to reflow back to its equilibrium state.
  • the areas 62 that had thicker lubricant due to dielectrophoretic attraction now shows a negative change in lube thickness and appear dark.
  • the areas 60 under the points of contact show a positive change in lubricant thickness. They appear brighter.
  • Figs. 5 and 6 together show that capacitive squeeze expels lubricant from beneath the bumps or pads.
  • the dwell voltage on the head increases capacitive force, bringing the head closer to the disk. This increased force between head and the disk squeezes some lubricant out from the interface between the two.
  • the figures also show that removing the dwell voltage lifts the head slightly, back towards its 'normal, ' zero-volts-applied, position. This permits the squeezed-out lubricant at the points of contact 50/62 to flow back.
  • Disk lubricant is highly viscous and flows slowly. When the dwell voltage is removed, the lubricant cannot immediately react to this sudden movement. The accumulated lubricant menisci either break or shrink. Both broken menisci and less meniscus contact area result in lower stiction.
  • a magnetic head comprising a conductive A1203/TiC slider body 16 was connected to a 2V DC voltage 20 through a conductive lead 26 from the slider bond pads to the flex circuit 18.
  • the head' s reader and writer transducers were not connected in this configuration, as this investigation was focused only on stiction performance.
  • the disk remained at ground, giving a 2V potential across the head-disk interface.
  • dwell voltage reduces stiction.
  • the heads were mounted on a tribology spinstand to measure stiction.
  • a tribology spinstand is a device that measures stiction and friction forces between heads and disks in conditions that mimic those found in a disk drive.
  • the head is mounted on a calibrated strain gauge force sensor.
  • the strain gauge output is combined with the disk rotational rate to determine head-disk forces at the start of spin-up (stiction) and during flying (friction) .
  • a production head and production disk were loaded onto a tribology spinstand, with the head making contact with the data zone of the disk.
  • the head was allowed to dwell in one location for one hour. This is sufficient time for mobile lubricant to move either as a result of the capacitance squeeze effect or as a result of the menisci migrating to areas of high electric field strength due to dielectrophoresis.
  • the stiction value was measured by accelerating the disk and measuring the interfacial force.
  • the disk was decelerated to zero RPM and the head was allowed to dwell for another hour. During this second dwell, a voltage (2V DC) was applied to the head.
  • Fig. 3 is a chart of the results of this test.
  • the chart compares stiction in grams vs. test cycles.
  • the data shows a significant decrease in stiction when 2V DC was applied, line 30, versus when 0V DC is applied, line 32.
  • a paired T-test analysis on this data yielded a mean decrease of 1.3 grams (a reduction of 32%) and a 100% confidence that there was a stiction decrease when a dwell voltage was first applied.
  • head and disk combinations were put through contact-start-stop tests that included cycles of seeking (moving from the inner diameter of the data zone to the outer diameter at 10Hz for 3 seconds) .
  • This type of test is believed to accelerate lubricant accumulation on the head.
  • the head was allowed to dwell on the data zone of the disk for 24 hours. Stiction was then measured. This is a generally accepted test procedure for measuring "dwell stiction. "
  • Fig. 4 is a chart of the test data from this experiment. It compares measured stiction values in grams of six pairs of tests. The data shows a decrease in stiction in the case of dwell with an applied voltage, bars 40, versus those with zero volts, bars 42. The mean decrease in stiction in these paired tests was 0.85 grams, with 92% confidence that there was a decrease in stiction.

Abstract

Selon la présente invention, le blocage par adhérence de disques-têtes est diminué par application d'un champ électrostatique entre la tête (16) et le disque (10) alors que la tête demeure en contact avec la surface du disque. Juste avant que le lecteur de disque ne commence à faire tourner le disque de sorte que les têtes décollent, le champ électrostatique est supprimé.
PCT/US2003/000417 2002-01-07 2003-01-07 Diminution de blocage par adherence de disques-tetes WO2003058610A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003210457A AU2003210457A1 (en) 2002-01-07 2003-01-07 Head-disk stiction reduction

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US34643302P 2002-01-07 2002-01-07
US60/346,433 2002-01-07

Publications (1)

Publication Number Publication Date
WO2003058610A1 true WO2003058610A1 (fr) 2003-07-17

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AU (1) AU2003210457A1 (fr)
WO (1) WO2003058610A1 (fr)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3732552A (en) * 1970-08-29 1973-05-08 Philips Corp Floating magnetic head system with variable curvature shoe
JPS55108964A (en) * 1979-02-13 1980-08-21 Nec Corp Magnetic disc device
US4479090A (en) * 1982-09-30 1984-10-23 International Business Machines Corporation Circuitry for measuring magnetic head flying characteristics
US4589036A (en) * 1984-12-03 1986-05-13 International Business Machines Corporation Apparatus and method for instrumented radial translation of a read/write transducer at start-up of a rotating disk file

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3732552A (en) * 1970-08-29 1973-05-08 Philips Corp Floating magnetic head system with variable curvature shoe
JPS55108964A (en) * 1979-02-13 1980-08-21 Nec Corp Magnetic disc device
US4479090A (en) * 1982-09-30 1984-10-23 International Business Machines Corporation Circuitry for measuring magnetic head flying characteristics
US4589036A (en) * 1984-12-03 1986-05-13 International Business Machines Corporation Apparatus and method for instrumented radial translation of a read/write transducer at start-up of a rotating disk file

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 004, no. 160 (P - 035) 8 November 1980 (1980-11-08) *

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