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WO1994011865A1 - Tete d'enregistrement a support liquide et a faible trainee - Google Patents

Tete d'enregistrement a support liquide et a faible trainee Download PDF

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Publication number
WO1994011865A1
WO1994011865A1 PCT/US1993/010221 US9310221W WO9411865A1 WO 1994011865 A1 WO1994011865 A1 WO 1994011865A1 US 9310221 W US9310221 W US 9310221W WO 9411865 A1 WO9411865 A1 WO 9411865A1
Authority
WO
WIPO (PCT)
Prior art keywords
head
disk
pad
slider body
slider
Prior art date
Application number
PCT/US1993/010221
Other languages
English (en)
Inventor
William French
James U. Lemke
Turguy Goker
Walter Wong
William Repphun
David P. Danson
Original Assignee
Conner Peripherals, Inc.
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 Conner Peripherals, Inc. filed Critical Conner Peripherals, Inc.
Publication of WO1994011865A1 publication Critical patent/WO1994011865A1/fr

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Classifications

    • 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
    • G11B5/6005—Specially adapted for spacing from a rotating disc using a fluid cushion
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B17/00—Guiding record carriers not specifically of filamentary or web form, or of supports therefor
    • G11B17/32—Maintaining desired spacing between record carrier and head, e.g. by fluid-dynamic spacing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B33/00—Constructional parts, details or accessories not provided for in the other groups of this subclass
    • G11B33/14—Reducing influence of physical parameters, e.g. temperature change, moisture, dust
    • G11B33/148—Reducing friction, adhesion, drag

Definitions

  • the invention relates to interactive elements commonly used in recording data on storage media in information storage devices. Specifically, the invention relates to a head design for use with recording an information apparatus utilizing a liquid bearing between the interactive element head and the storage disks.
  • Designers of information storage technology constantly seek to improve data storage capacity and performance of information storage devices. In one aspect, this involves improving the relationship between an interactive element and the storage medium.
  • the interactive element is a read/write head which interacts with a magnetic storage disk.
  • the read/write head is generally comprised of an active element, such as a transducer, mounted on a slider.
  • an active element such as a transducer
  • continual contact between the interactive element and the magnetic storage medium is advantageous from a magnetic perspective, such arrangement is undesirable because wear and material interactions lead to degraded system reliability and performance.
  • one paramount consideration in designing magnetic recording systems is the maintenance of spacing between the head and medium.
  • the read/write head "flies" over the disk-shaped recording medium by compressing a fine layer of air to form a very low friction gas bearing that maintains the head above, and out of contact with, the recording medium.
  • the head-disk interface distance or "flying height" is determined by such factors as the shape, load and size of the head.
  • the read/write head itself generally includes a transducer element to read and write flux transitions into the magnetic material of the recording medium.
  • Data is stored on the medium by the fringing magnetic field of the transducer element, generally a coil surrounding an active core providing two magnetic poles separated by a non-magnetic gap which is preferably oriented perpendicular to the disk surface. It is desireable to reduce the flying height of the recording head to increase the field gradient of the fringing flux of the transducer element incident to the storage medium and to increase the flux from the medium which reaches the head during playback.
  • Figs. 1 and 2 illustrate, in general form, the interaction between a conventional air bearing read/write head and a magnetic storage disk, and a conventional air bearing read/write head design, respectively.
  • the interface between a rigid disk medium 10 and a transducer 21, mounted on a slider 22, is maintained in an assembly including a means for rotating the disk 10, the means including a spindle 12 which fits through a central circular hole in the middle of the disk 10, and a spindle rotator 14.
  • Slider 22 is normally loaded by application of a force applied to slider 22 and directed toward disk 10. The force is applied by an assembly including actuator 16 swing arm 18, and gimballed spring suspension mechanism 20. The actuator pivots swing arm 18 to selectively position transducer 21 radially with respect to disk 10.
  • Gimballed spring suspension mechanism 20 loads slider 22 against disk 10 when disk 10 is stationary. When disk 10 rotates, an air bearing is generated which counterloads slider 22, lifting and maintaining slider 22 and transducer 21 above the surface of disk 10 to a flying height.
  • the spacing between transducer 21 and the surface of disk 10 is generally determined by the amount of loading exerted on slider 22, by the spring suspension, the aerodynamic design of slider 22 and the rotational velocity of the disk. It is to be understood that Fig. 1 is representative of the minimum complement of parts used to establish the operational interface between transducer 21 and disk 10.
  • a head-disk assembly normally makes provision for a plurality of parallel-spaced, coaxial disks which rotate on a common spindle together with a ganged array of transducer heads controlled by one or more actuator assemblies. While the disk rotates, conventional means, not shown, are used to operate the transducer 21 to electromagnetically read signals from, or write signals to, the disk.
  • the transducer includes a wound core with a recording gap.
  • Each head is thus comprised of two major parts: the slider, which provides the air bearing surface; and the transducer element, usually comprising a coil winding and recording gap, with the coil coupled to the control electronics of the disk drive with recording of data generated by the flux changes inducing magnetic changes in the recording medium. Rails, ramps and/or pads are incorporated onto the bottom portion of the slider to optimize flight characteristics for the head.
  • the transducer is generally positioned at the trailing edge of the slider relative to the motion of the slider with respect to the disk.
  • Fig. 2 illustrates a typical prior art read/write head support structure.
  • Slider 22 is suspended on a gimbal 24, which allows slider 22 to be parallel to disk 10 in response to forces applied to the slider in -in ⁇ directions normal to disk 10, while preventing lateral motion and yaw of the slider.
  • Slider 22 includes a pair of elongated rails 23, each with a flat bearing surface.
  • a narrow middle rail 25 is provided, also with a flat surface.
  • the leading edges of side rails 23 are beveled at 27, as is the leading edge of the center rail at 29.
  • Transducer 21 is mounted on slider 22 to place the recording gap 30 near the trailing edge of center rail 25, while transducer windings 32 are positioned below the recording gap on the trailing edge of the slider assembly beneath an anterior extrusion of center rail 25.
  • a layer of air (the "air bearing") builds up at the interface between the slider of Fig. 2 and disk 10.
  • the built-up layer of air reverse loads the slider on the flat bearing surfaces of rails 23, lifting the slider off of, or away from disk 10.
  • the art also encompasses other slider configurations, some of which eliminate the center rail and place the electromagnetic transducer element in one of the two laterally spaced slider rails 23.
  • F/A u dv/dy (1)
  • F is the force exerted on a stationary plate having a face with an area A by a parallel plate moving at a velocity v and spaced from the face at a distance (i.e., head-to-disk spacing) y by a liquid of viscosity u.
  • the shear rate dv/dy is linear with y, and is v/y.
  • u is a constant, the liquid is said to be Newtonian, and the classical equation of hydrodynamics, the Navier-Stokes equation, is valid.
  • Fig. 3 illustrates the relationship of Newtonian and pseudo-plastic and plastic liquids.
  • Fig. 3 illustrates the shear stress of a liquid as a function of time rate of deformation of the liquid (shear rate).
  • shear rate the shear stress of a liquid as a function of time rate of deformation of the liquid.
  • shape of each curve directly represents the change in viscosity of the liquid.
  • the curve labeled “Newtonian” shows a constant viscosity of a value corresponding to the slope of the curve.
  • the curves labeled “pseudo-plastic” and “plastic” indicate liquids whose viscosity apparently decreases with an increase in shear rate.
  • the plastic or pseudo-plastic nature of the liquid bearing is important since it allows very small power dissipation in the head-disk interface at the speeds and small spacings necessary for a very high density of information storage on the disk.
  • the force and power necessary for a non-Newtonian plastic or pseudo-plastic liquid are over an order of magnitude less than required with a Newtonian liquid.
  • head drag is a problem unique to recording apparatus utilizing either a Newtonian or non-Newtonian liquid bearing.
  • Drag is not a problem with air bearing heads because air imparts a drag of only 0.lg or less on an air bearing head.
  • head drag is a significant factor in the movement of the disk under a head with a liquid bearing between them.
  • achieving a practical recording device utilizing a liquid bearing involves providing a interactive recording head wherein the drag is below a predefined minimum level in relation to the rotational speed of the disk.
  • storage technology designers would like the power dissipated due to head drag in liquids to be even lower.
  • it is desireable to achieve a head design which would provide reduced drag when used in either a Newtonian or non-Newtonian liquid bearing.
  • PW50 is an especially accurate reflection of the electrical performance of the head in terms of evaluating heads.
  • European Patent Application No. 0,367510 published September 5, 1990, teaches a hard disk drive assembly using a low viscosity liquid lubricant on the disk surface to support the slider. Also shown therein is a slider configuration utilizing three triangular pads. One pad is positioned at the leading edge of the slider, while two pads are positioned adjacent the trailing edge of the slider. Each pad is positioned so that an included angle faces the leading edge of he slider, and one side is parallel to the "axis" of the slider. This "inclined" side, forming an angle of about 10° with the included angle, faces the outer edge of the slider with respect to the hub of the disk.
  • each of the pads is at a height of about 25-50 microns above the surface of the slider, and there is no teaching that these pads or any part of any of their surfaces be ramped, or angled with respect to the disk during operation.
  • the drive assembly specifically requires that the bearing lubricant be maintained at a level of approximately one micron on the disk surface and should not exceed 5 microns (39.4 ⁇ " to 196.5 ⁇ ").
  • an object of the invention is to provide a low drag read/write head for use with a disk drive having a liquid bearing at the head/disk interface.
  • a further object of the invention is to provide a low drag head having the capability to maintain a relatively constant head-disk interface distance in relation to the movement of the head in relation to the storage medium.
  • a further object of the invention is to minimize that portion of the head running on a fluid bearing which is subject to a high shear rate.
  • Yet another object of the invention is to provide a head in accordance with the above objects which may be advantageously used with a bearing liquid having non-
  • a further object of the invention is to provide the above objects in a head design which utilizes a number of pads and which does not require the plane which all the pads have in common to be parallel to the medium surface or to the pad surfaces themselves during normal operation.
  • a further object of the invention is to achieve the above objects in a slider design which utilizes a pad height, fluid thickness and disk speed which renders drag on areas of the slider other than low-area pad surfaces insignificant.
  • the head includes a slider body, the slider body having at least a first and second regions; and a transducer element, mounted on the first region of the slider body, wherein the first region of the slider body has a substantially higher drag on the disk, through the liquid bearing when moving through the liquid when the disk is rotating than the second region.
  • the slider body has at least a first and second ends wherein the second end of the slider body travels at a flying height which is substantially greater with respect to the disk when the disk is rotating than a flying height achieved by the first end.
  • the slider body has a top, bottom, first side, second side, front end and rear end.
  • First and second pad elements are positioned on the bottom of the slider in axial alignment with respect to the length of the slider body.
  • One of the pads, the core pad is formed to have a recording gap therein coupled to a transducer element.
  • the leading edge of the non-core pad is beveled to cause it to fly higher than the core pad.
  • the slider includes first and second pads, positioned on the bottom of the slider body adjacent the leading edge at a spaced distance apart, the first pad being adjacent the first side and the second pad being adjacent the second side, each pad being roughly rectangular in shape and having a ramped front edge. Further, a third pad is positioned adjacent the trailing edge of the slider body and the first side. Finally, a transducer element is positioned at the rear end of the slider body, and coupled to magnetic elements on the surface of the third pad for writing and reading information.
  • a first and second pads are positioned adjacent the front end of the slider body at a spaced distance apart, each pad being roughly rectangular in shape and having a tapered edge.
  • third and fourth pads are positioned at the rear end of the slider body at the spaced distance apart.
  • the first and second pads are provided with a tapered leading edge to increase the lift of the pads.
  • the non-core rear pad is also provided with a beveled leading edge so that only the pad associated with the transducer element travels at low flying height.
  • Figure 1 is a simplified diagram of a typical prior art arrangement of a head-disk assembly
  • Figure 2 illustrates an enlarged view of the underside of a typical prior art head which utilizes an air bearing interface between a head and a disk;
  • Figure 3 is a graphic representation of the apparent viscosity of Newtonian fluids as compared with the apparent viscosity of plastic or pseudo-plastic fluids.
  • Figures 4A-4E are simplified, bottom views of pads utilized in a liquid bearing read/write head showing coplanarity data for 5 different core pads;
  • Figure 5 is an enlarged, bottom plan view of a core pad of a thin film liquid bearing read/write head
  • Figures 6A through 6C are end, bottom plan, and side views, respectively, of a two-pad slider in accordance with the present invention
  • Figure 6D is an end view of the two-pad slider shown in Figs. 6A-6C illustrating the orientation characteristics of a head in accordance with the present invention when the head is travelling relative to the disk surface;
  • Figures 7A through 7C illustrate enlarged front, bottom plan, and side views, respectively, of a four-pad read/write head in accordance with the present invention
  • Figure 7D illustrates the orientation characteristics of a head as shown in Figs. 7A-7C in accordance with the present invention when the head is travelling relative to the disk surface;
  • Figure 7E is an enlarged view of the front pad of the head shown in Figures 7A-7C illustrating ramp length and angle for a single pad of the slider;
  • Figure 7F is an enlarged, bottom plan view of an alternative embodiment of a four-pad read/write head in accordance with the present invention
  • Figures 8A through 8C illustrate enlarged front, bottom plan, and side views, respectively, of a first embodiment of a three-pad head in accordance with the present invention
  • Figure 8D is a bottom plan view of a second embodiment of a three-pad head in accordance with the present invention.
  • Figure 8E is a bottom plan view of a third embodiment of a three-pad head in accordance with the present invention
  • Figure 9 is a representation of the respective flying heights of the right rear active pad, and the front right and front left pads, respectively, of a three-pad read/write head such as that shown in Figures 8A-8C
  • Figure 10 illustrates the respective flying heights of a three-pad head such as that shown in Figures 8A-8C having ramps lapped into the front pads with a first ramp length and angle
  • Figures 11A and 11B illustrate respective flying heights of a three pads of a three-pad head first having no ramps on the leading edge pads (Fig. 11A) , and subsequently having ramps placed into the pads (Fig. 11B)
  • Figure 12 illustrates the respective flying heights of three pads of a three-pad head such as that shown in Figures 8A-8C having a second ramp length and ramp angle
  • FIG. 11A illustrates the respective flying heights of three pads of a three-pad head such as that
  • Figure 13 is a graph representing the relationship between disk speed, head drag and flying height
  • Figures 14A-14D illustrate a method for manufacturing a read/write head in accordance with the present invention
  • Figure 15 is a perspective view of the major components of a two and one-half inch form factor disk drive in which the read/write head of the present invention is suitable for use.
  • the present invention achieves the above objects of providing a novel head for use in an information storage device having high data storage, capacity in a small physical form factor wherein a liquid bearing lubricant is utilized at the interface of the storage medium and an interactive element used to transfer data to and from the storage medium.
  • the storage device comprises a Winchester-type, magnetic storage disk drive.
  • the present invention may be utilized in any storage device wherein the drag between an interactive element and the storage medium is critical. For purposes of explanation, the present invention will be described with respect to its application in a magnetic storage disk drive.
  • the acceptable level of drag for any storage medium travelling under a head with a liquid bearing is determined by limitations on the power of the actuator utilized to move the head relative to disk and the power of the spindle motor to rotate the disk relative to the head.
  • an additional concern is the capacity of the storage battery used as the power source.
  • the power consumption of such portable computers should be minimal.
  • a drag level of approximately 1.2 grams or less at a disk speed of 340 inches per second (ips) would be acceptable.
  • the PW50 for the head be under 55 ns, and preferably even lower, at 340 ips to achieve recording densities at desireable levels, as the 65mm diameter disks used in 2-1/2" disk drives travel in a range of 250 ips at the inner data track to 450 ips at the outer data track.
  • this means the recording gap must be approximately l ⁇ " high during operation.
  • Slider configurations for an information storage device using a liquid bearing at the head/disk interface generally attempt to reduce the areas of high pressure with respect to the fluid by utilizing pads on the lower surface of the slider body, as shown in European Patent Application No. 0367510. Any number of pads may be provided, with one of the pads including a magnetic gap coupled to transducer coils. The presence of the pads serves to reduce the effective area of the slider in the bearing lubricant.
  • heads are manufactured so that the areas adjacent to the disk, but not actually pad areas, are receded 2 to 4 mils (milli-inches) from the pad surfaces.
  • Drag is also created because of momentum transfer. Any part of the slider that is impacted by the sheet of fluid that is on the disk will experience a force due to the deceleration of the fluid. The contribution of drag as a result of momentum transfer is very difficult to measure or estimate. It is directly proportional to the thickness of fluid on the disk, the fluid density, head speed, and the head area impacted. It can also be affected by the degree to which those impacted areas are streamlined.
  • the drag values measured and discussed herein are a sum of terms from pad shear, non-pad shear, and momentum transfer.
  • the size of a particular slider is on the order of 112 mils long x 88 mils wide, and manufacturing tolerances of the suspension mechanism for the head physically limit the minimum size of such sliders.
  • Pads cannot be made arbitrarily small because the disk and head would become subject to damage due to shock and vibration incident to the drive.
  • the pressure that any head pad and the disk are subjected to during a shock is proportional to the mass of the slider. If a shock creates a pressure greater than the yield strength of the slider material and/or the disk surface then one or both can be permanently deformed during the shock.
  • the mass of the slider must be scaled down with the total pad area. It is also advantageous to shape the slider body and position the pads on it so that shocks will load all the pads with roughly the same pressure. There are practical limits to how small sliders can be made, but as the state of this art progresses, it will clearly be possible to scale down slider and pad sizes to reduce drag further.
  • the orientation of the slider must be such that the recording gap, whether positioned at the rear of the slider or on another "active" pad on the bottom surface of the slider, is positioned such that the pole tips are relatively parallel to the surface of the disk.
  • any variation in the angle of the pole tips with respect to the surface of the disk can alter the area of maximum intensity of the flux incident upon the disk surface, and the flying height of the gap.
  • the orientation of the slider body is generally irrelevant, but the orientation of the planar surface of the pads is critical. If a slider is positioned against a disk, there is no guarantee that all the points on all the pads are actually in contact with the disk. In general, only one point from each pad will contact the disk. More points can be made to contact the disk by increasing the force pressing the slider and disk together and causing the slider and disk to deform, or by making the slider with the pads more nearly co- planar.
  • the relationship of the planar pad surfaces to the planar disk surface is generally referred to as coplanarity.
  • Measurements made of the coplanarity of pads is possible by observing the pads with an interferometer made by Wyko Corporation, Arlington, Arizona. This instrument measures the height of a number of points on each pad with respect to an optical flat. The instrument then establishes a "best fit" plane for all the points observed on all the pads. It also establishes a best fit plane for each pad using only points on that pad.
  • the plane for each pad is not quite parallel to the common plane.
  • the slopes of these pad planes, with respect to the common plane, together with the pad dimensions, can be used to estimate which corner of the pad would touch the disk first and how high above the disk the other corners would be.
  • Figures 4A-4E show data taken in this manner for the core pads of 5 heads.
  • the deviations from coplanarity of the front pads are of a similar magnitude, but are less important because there is no write/read transducer on the front pads and because their flying height is determined, as discussed below, in a different manner in accordance with the present invention. Points on the ramps were not used in any of the coplanarity calculations.
  • the corner of each pad marked with a "0" is the corner that would touch the disk.
  • the numbers near the other corners show the height in microinches that these corners would be at if the disk were not spinning, assuming that the pad is a plane.
  • the pole tips are, in general, not located on the corners of the pads, the pole tips will, in general, be positioned at some height above the disk surface even when the disk is not moving. The exact spacing depends on the angles the pad is making with the disk, the force between the slider and disk, the size of the pad, and the location on the pad of the pole tips. In Fig. 4, the pole tips are approximately two-thirds of the height from the bottom of the pad and centered on the pad. When the disk is spinning under normal operating conditions, the front pads typically lift away from the disk to a flying height of approximately 5 ⁇ " . Since the pads are approximately 100 mils apart and 3 mils long in the direction of motion, the slider body will tilt when the disk is moving so that the corners on the front edges of the core pads will be lifted approximately 0.15 ⁇ " further from the disk, simply due to geometry.
  • the transducer is constructed on the slider using multilayer manufacturing processes.
  • a first layer of overcoat material is deposited, using semiconductor manufacturing processes, then a first magnetically permeable material is deposited on the head substrate to form a first magnetic pole. Deposition of this material may be carried out by sputtering or plating or other such processes.
  • spiral loops of electrically conductive material are deposited to produce a plurality of coiled turns occupying substantially the same plane.
  • two to three layers of coils may be deposited.
  • a second layer of magnetically permeable material is deposited to form the second pole.
  • a second layer of overcoat material is deposited. The poles imbedded in these two overcoat layers are shown in Fig. 5.
  • a pad is typically not actually a totally planar surface.
  • Current manufacturing processes typically result in the substrate and overcoat parts of the pad being planar, but the plane of the substrate is slightly higher than the plane of the overcoat; if the pad is placed against a disk, the substrate area will be closer than the overcoat.
  • the height difference between these planes is typically from approximately 0.2 ⁇ " to approximately 1.5 ⁇ ".
  • the pole tips are typically not coplanar with the overcoat.
  • sliders have pole surfaces 40a,40b that are parallel to the overcoat but from 0.2 ⁇ " above to 0.2 ⁇ " below the overcoat surface.
  • the sum of these two steps is usually called pole tip recession, and is typically approximately 0.5 ⁇ ".
  • the numbers given in Fig. 4 for coplanarity of the core pads were actually derived from points on the substrate only.
  • the pole tips would actually be approximately 0.5 ⁇ " further from the high point than the 0.03 and 0.29 ⁇ " numbers shown.
  • a single pad head having an extremely small area would provide the minimum drag in a drive with a liquid bearing.
  • there are several practical problems with such a one head pad there are several practical problems with such a one head pad.
  • a practical solution to the problem of head drag has been devised wherein only a portion of the total slider body of any particular slider is allowed to fly close to the disk surface while the head is supported by, a liquid bearing interface.
  • the area of the head which is subject to drag is substantially reduced.
  • a recording gap is provided in a pad and the portion of the slider wherein this active core pad is located is caused to fly at a relatively low flying height with respect to the disk, while the balance of the slider is caused to fly at a much greater distance with respect to the disk.
  • the non- active, relatively high flying pad or pads define a linear or planar surface with the active pad, and maintain stability for the slider body at the head disk interface.
  • the portion of the slider body including the recording gap, or other interactive element is allowed to fly close enough to the storage medium to assure adequate performance.
  • the second portion of the slider body flies at a greater height with respect to the medium and acts to stabilize the head, with a practical gimbal connected to the slider to allow the head loading force to press the head into an orientation that results in the portion including the transducer to be parallel enough to the storage medium.
  • This second region of the slider is made to fly far enough from the medium that it does not create significant drag.
  • Fig. 6A is a rear view
  • Fig. 6B a bottom view
  • Fig. 6C a partial side view of a two-pad head in accordance with the present invention.
  • the head may comprise a thin film head.
  • the two-pad head includes a slider body 35 affixed to a flexure 42 which may be bonded or staked to an actuator arm 43 positioned by conventional means such as a voice coil motor. Slider 35 is effectively bonded to flexure 42 with upper arm 42a and lower arm 42b at a position which is at the same height above the disk as the center of mass of slider body 35.
  • slider body 35 is formed to have two pads 36a and 36b.
  • thin film head windings 38 are coupled to a recording gap 40 on core pad 36a.
  • the motion of the disk relative to the slider body 35 is shown by arrow 50 in Figs. 6B and 6C.
  • Each pad 36a,36b has an approximate length, l p , of 3 mils, and an approximate width, w p of 2 mils.
  • the slider 35 shown in Figs. 6A-6C has an extremely low mass because of the relative shortness of the slider.
  • slider 35 may have a width W of about 88 mils, the current standard width of a so-called 70% slider -- the industry standard size air bearing recording head.
  • Slider 35 generally has a length L of 12 mils.
  • any torques that might be created during the radial acceleration or deceleration of the head during track-to-track seeks or shocks will not tend to lift the head off the disk. Both these factors make the head very shock proof. As shown in Figs.
  • the non-core pad 36b may be provided with a ramp 37 which induces the non- core pad to travel at a greater flying height (h 2 ) with respect to a disk 10 than the flying height (h,) achieved by core pad 36a, as shown in Fig. 6D.
  • a 5 ⁇ " difference in the respective flying heights between non-core pad 36b and core pad 36a will result in only a negligible change in the orientation of the core pad with respect to the disk; hence, recording gap 40 remains relatively parallel to the surface of the disk.
  • this two-pad head could be made to have less drag by reducing pad size and head load, while maintaining the same shock resistance as a four-pad head, discussed below.
  • Figs. 7A-7C are rear, bottom, and side views, respectively, showing a first embodiment of four-pad head in accordance with the present invention.
  • the head described with respect to Figs. 7A-7F is generally referred to as a compolithic-type head manufactured by AMC Corporation.
  • a four-pad embodiment of a recording head for use in accordance with the present invention includes a slider 60 having four slider pads 62 with flat bearing surfaces 64. Each pad has a length l p of 3 mils and a width w p , of 2 mils. It is noteworthy that the length and width of the pads may vary within a range of 0.5 to 4.0 mils. Slider 60 has a length L' of about 118 mils and a width W" of about 88 mils. Slider 60 may be mounted at the trailing end of a suspension assembly coupled to an actuator arm, as discussed above.
  • a pair of bearing pads 62a !. -, and 62b,. 2 are carried on each side of slider 60.
  • Transducer coils 67 are mounted on the rear pads 62b,. 2 on each side of slider 60.
  • a recording gap (not shown) is formed in at least one of pads 62b, which carry transducer coils 67.
  • Slider 60 has heads on only the rear of both trailing pads. Only the outside transducer head (closest the edge of the disk) is generally active in data taking.
  • each of the front bearing pads 62a,. 2 has a forward surface 66.
  • Each surface or "ramp" 66 has a length l r which may vary in accordance with the amount of lift desired from the front pads in relation to the rear pads.
  • pads 62a,. 2 , 62b,. 2 may be slightly rounded or "blended" as is known in the art as shown in 66a in exaggeration.
  • Ramps 66 shown on the front pads 62a,, 62a 2 have a slope ⁇ of 0.8°-3.0°, as shown in Fig. 7F, and have a length l r of about 3.0 ( ⁇ 0.5) mils.
  • Pads 62 are generally manufactured to be 3-4 mils above the bottom surface of the slider.
  • the load is 5 grams and is applied at a point 61 that results in equal pressure on all pads when the disk is stopped. It should be noted that the drag effectively shifts the load point 61 forward a small distance when the disk is spinning.
  • Fig. 7D shows the effect of providing ramps 66 on front pads 62a.
  • ramps 66 cause the forward portion 63 of slider body 60 to travel at a height h 2 with respect to disk 10 while the rear portion 65 of slider body travels is at height h, which is substantially less than h 2 .
  • the increased flying height h 2 of the leading edge pads results in substantially lower drag for the head as a whole, whether the head travels on a Newtonian or non- Newtonian fluid.
  • the rear pads 62b,. 2 thus contribute the majority of the total drag of the slider 60 in the lubricant in the case where neither rear pad 62b,_ 2 is ramped.
  • Fig. 7F shows a bottom view of an alternative embodiment of a four-pad head in accordance with the present invention wherein a ramped leading edge 68 may be provided on pad 62b,, where pad 62b 2 is used as the active head in reading to and writing from the disk.
  • Provision of ramp 68 on the rear, non-active pad 62b induces a higher flying height in pad 62b, with respect to the disk, such height being on the order of h, achieved by pads 62a, _ 2 .
  • only the active pad, coil 62b 2 would remain at a low flying height with respect to the disk surface, while the remaining three pads fly at higher levels.
  • a four-pad head without ramps loaded with 5 grams at its center point had a measured drag of 3 grams, and a PW50 of 50 ns. After application of ramps, loaded with 5 grams at the center point, the drag was reduced to 1.5 grams, while the PW50 remained at 50 ns.
  • Shown in Figs. 8A-8C is an alternative, three-pad head design for a low drag head in accordance with the present invention.
  • Figs. 8A-8C show a rear view, bottom view and side view, respectively, of the three-pad thin film head in accordance with the present invention. Again, the principles taught herein with respect to a magnetic, thin film head apply equally to various types of recording technology.
  • Slider 70 has three flat bearing surfaces 74, including two front slider pads 72a, and 72a 2 and a rear slider pad 72b,. (It should be understood that the terms front and rear are relative to the motion of the disk, designated by arrow 50 in Fig. 8A-8C.)
  • the rear pad 72b contains a recording gap, similar to that shown with respect to Fig. 5, coupled to a coil arrangement (not shown) .
  • each forward pad 72a,. 2 contains a ramp 76 to enable slider 70 to attain flying height characteristics similar to that shown in Fig. 7D for slider 60.
  • a load point 78 for slider 70 which achieves an optimal flight characteristics for this particular read/write head.
  • load point 78 is positioned such that the load applied by the suspension assembly is evenly distributed to all three pads. In certain embodiments, it may be advantageous to move load point 78 to shift the load toward the trailing edge of the slider, or closer to either side of the slider, to alter the flying heights of the respective pads.
  • Fig. 8D shows an alternative embodiment of a three- pad head in accordance with the present invention.
  • slider 70-1 includes only a single leading edge pad 72a, and two trailing edge pads 72b,, 72b 2 .
  • rear pad 72b 2 is provided with a ramp 76 similar to leading edge pad 72a,m while core pad 72b, has no ramp.
  • core pad 72b will remain at a position relatively close to the disk surface when travelling in the fluid (e.g., at height h,) , while pad 72a, and 72b 2 will achieve greater flying heights (e.g., heights h 2 ) with respect to the disk surface.
  • Figs. 8E and 8F are yet another embodiment of a three-pad head in accordance with the present invention.
  • Slider 70-2 as shown in Fig. 8E includes first and second leading edge pads 72a,, 72a 2 with ramps, and a single trailing edge core pad 72b 2 .
  • Triangular areas 77 are provided in front of leading pads 72a,, 72a 2 and 72b 2 . These triangular areas 76a are parallel to the pad surfaces and lower than the pad areas by >5 ⁇ "; that is, they will be approximately 5 ⁇ " further from the disk during operation than the pad areas. They are designed to function in a similar way to the triangular pads in European Patent Application Serial No. 0 367510.
  • Pad 74 in Figs. 8E-8F has generally the same area as the -pads shown with respect to Figs. 8A-8D.
  • Ramps 76a are provided on the surface of pads 72a,, 72a 2 . Such ramp 76a would tend to streamline the pads and reduce momentum transfer drag and generally create lift on the front pad 72a,, 72a 2 so that they no longer create any significant drag. Providing front pads 72a, and 72a 2 approximately I ⁇ " above ramp 76a greatly reduces the drag contributed by front pads 72a. In addition, since the tips of the triangular areas 77 are receded, they generally do not contact the disk surface, thereby preventing any damage due to chipping of ramp tip 77.
  • the ramps herein described need not be a simple plane at an angle to the pad.
  • the ramped area can be a curved surface that roughly approximates the dimensions of the ramps described.
  • the ramped area can also be parallel to the pad but separated from it by roughly the same distance as the highest part of the ramps described. For example, a planar ramp area 300 ⁇ " long parallel to the planar pad area, and approximately 5.2 ⁇ " further from the disk surface when the disk is stopped would have essentially the same tendency to lower drag by lifting the pad as would a planar ramp 300 ⁇ " long at 1° to the disk surface.
  • Fig. 9 shows measured, respective flying heights for a three-pad head, such as that shown in Figs. 8A-8C.
  • the liquid bearing used is a perfluro-polyether, such as Galden D02, manufactured by Montefluos, Milan, Italy, and measurements taken by an interferometer.
  • a perfluro-polyether such as Galden D02, manufactured by Montefluos, Milan, Italy, and measurements taken by an interferometer.
  • the numerical values shown with respect to each pad represents the relative flying heights of the pads with respect to the disk over an average of many points on the head and many disk rotations.
  • the average flying height (h,) of the right rear active pad is 0.4 ⁇ ".
  • the ramp length of the front right pad 62a 2 was 6.66 micrometers, while the ramp angle ⁇ was 2.15°.
  • the ramp length for the front left pad 62a is 7.74 micrometers, with a ramp angle ⁇ of 1.69°.
  • the respective flying heights average 4.3 and 6.0 ⁇ " for the front left and front right pads, respectively. This flying height is approximately 11 to 15 times greater than the flying height of the rear, active pad at 0.4 ⁇ ".
  • Fig. 10 shows the flying height characteristics for pads of a three pad slider 70 as shown in Figs. 8A-8C.
  • the respective flying heights for the front left pad and front right pad as 2.7 ⁇ " and 3.7 ⁇ " respectively, while the active pad is at 0.4 ⁇ ".
  • the flying height for the front left pad is achieved with a ramp length of 2.43 micrometers and a ramp angle ⁇ of 0.70°.
  • the front right pad is provided with a ramp length of 2.39 micrometers, and a ramp angle ⁇ of 0.88°.
  • the total drag for the head has been measured at .84 grams at 340 ips.
  • the ratio of the flying heights between the front pads and the rear pad is between 6.75:1 and 9.25:1.
  • Fig. 11A shows the flying height characteristics of each of the three pads of a particular three-pad head wherein no ramps 76 are included on the forward pads 72a.
  • the flying height for the front left pad 72a, and front right pad 72a 2 is approximately 1.2 ⁇ " and l.O ⁇ ", respectively, while the core pad height is 1.2 ⁇ ".
  • the total measured drag on this particular head is 1.65 grams at 340 ips, significantly greater than the measured drag of the three-pad heads with ramps discussed above.
  • Fig. 11A shows the flying height characteristics of each of the three pads of a particular three-pad head wherein no ramps 76 are included on the forward pads 72a.
  • the flying height for the front left pad 72a, and front right pad 72a 2 is approximately 1.2 ⁇ " and l.O ⁇ ", respectively, while the core pad height is 1.2 ⁇ ".
  • the total measured drag on this particular head is 1.65 grams at 340 ips, significantly greater than the measured drag of the three-pad heads with ramps discussed above.
  • FIG. 11B shows the effect of adding ramps to the same head described with respect to Fig. 11A.
  • the front left and right pads have flying height of 3.4 ⁇ " and 5.2 ⁇ " respectively, while the core pad has a flying height of 0.8 ⁇ ".
  • the provision of ramps on the forward pads will yield the desired flight characteristics for the head and significantly reduce drag whether using a plastic or pseudo-plastic non-Newtonian liquid bearing or a Newtonian fluid.
  • Fig. 12 Shown in Fig. 12 is flight data for a three-pad head, wherein a front left pad with a ramp length of 14.34 micrometers and a ramp angle of 2.16° has an average flying height of 5.7 ⁇ "; a front right pad having a ramp length of 10.84 micrometers and a ramp angle of 1.94° has an average flying height of 4.4 ⁇ "; and the rear active pad no ramp angle has an average flying height of 0.8 ⁇ ".
  • the total drag on the head configured as described above is .5 grams, less than that taught with respect to the head shown in Fig. 10.
  • the ratio between the flying heights of the front pads and the rear pad for the head described with respect to Fig. 12 is approximately 5:1 to 7:1.
  • increasing ramp lengths and ramp angles for a particular head design will yield a rather significant increase in flying height relative to the non-ramped rear pad.
  • PW50 is a measurement of head performance which more accurately reflects how the head will perform in a drive. Table 2, set forth below,
  • PW50 depends very sensitively on the flying height; the fact that PW50 did not change means flying height did not change.
  • Fig. 13 shows the relationship between the measured drag and observed bearing thickness (or flying height) , and the speed of the disk in inches per second. As shown therein, both drag and flying height increase only very slightly in accordance with the increase in speed of the disk. Flying height, in general, is less sensitive to changes in speed than drag.
  • the measurements were taken for a three-pad slider loaded with 5 grams, with two ramped pads in front and one 2.5 mil x 2.5 mil pad in the rear. As shown therein, the crosses (+) represent the slider drag in grams, while the circles (o) represent the core pad liquid bearing thickness in ⁇ ". As shown therein, the drag increases, but the pad flying height is relatively independent of speed.
  • a three-pad head has less drag than the four-pad head in that only one non-ramped pad at the rear is flying at a low flying height within the fluid and thus contributing significantly to the total drag of the head.
  • three pads are the minimum necessary to allow the pads to be pressed against the disk surface and assume an orientation nearly parallel to the disk owing to the flexing of the gimbal. This makes it easier to orient the active pad of the three-pad head in a parallel relationship relative to the disk surface.
  • the front pads are flying at a significantly higher flying height than the rear pad, because of the length between the front and rear pads, a change in the respective flying heights between the front and rear pads does not significantly alter the relationship of the gap with respect to the disk.
  • the liquid bearing can comprise either a Newtonian or a non- Newtonian bearing
  • the advantages attenuant with using the above-defined head designs with a non- Newtonian bearing provide significant advantages over using this design with the Newtonian bearing.
  • Fig. 3 because the viscosity of a non-Newtonian liquid decreases with respect to that of a Newtonian fluid as the shear rate increases, the higher shear rates which are caused by the lower flying pad will allow the flying height of the lower flying pad to be maintained while drag is minimized.
  • a significantly low level of fluid is required for operation of the head.
  • Figs. 14A-14D show the process steps utilized to manufacture a four-pad head in accordance with the present invention. It will be realized by those skilled in the art that the description with respect to the four-pad head may be readily adapted to manufacture a three- or two-pad head in accordance with the present invention. Again, it should be realized that Figs. 14A- 14D are not drawn to scale. Fig.
  • 14A is a bottom view of a conventional slider with two rails 80 and 82 formed in the base of the slider in a conventional manner.
  • the head has been lapped to create the best surface finish and pole tip recession possible.
  • Rails 80 and 82 are generally the same size as an air bearing slider, hence a conventional lapping process generally used with air bearing sliders may be utilized at this stage of manufacture.
  • Rails 80 and 82 are thereafter etched by conventional pattern etching techniques to create a step 84 in rails 80 and 82.
  • Step 84 lowers the etched surface approximately 50 to lOO ⁇ " below the surrounding material which will eventually define the pad areas.
  • the raised area 80a and 82a, of rails 80 and 82, respectively, is provided with the final intended path width, approximately 2 mils. Since the extended raised portions 80a and 82a extend the entire length of the slider, and off the ends of the slider, mask alignment along the length of the head is not a problem. Lateral alignment is not critical and the conventional transverse pressure contour (TPC) head tooling is in place to perform this function.
  • TPC transverse pressure contour
  • etching processes such as ion milling can create some redeposited material during etching, thus it may be necessary to briefly lap the slider after milling to remove redeposited material. The process would be somewhat easier with rails extending the length of the slider because the area is bigger and loads can be greater. It is actually not necessary that step 84 be created along the length of each rail, but only at those areas where the pads will eventually be formed.
  • Fig. 14D is a cross-sectional view of Fig. 14C, both of which show how the center portion 85 of the slider body is removed by a dicing process to define the front edges of the rear pads and the rear edges of the front pads.
  • This process has several advantages. Namely, experience has shown that a diced edge will function well at the critical leading edge of the rear pad. It is not desireable to create a blend at the leading edge of the rear pad. Conventional lapping processes that have been performed on the rear pad after it was made to final size, generally 2 by 3 mils, run a risk of putting a tiny blend on the front edge that would cause the rear pad to fly at a much higher level.
  • the dicing process will generally define the lengths of the pads much more than etching. The present state-of-the- art in etching mask alignment allows the pad to be positioned along the length of the slider at a position of plus or minus 0.5 mils.
  • etching generally creates some blend on the outside edges of the pads, as long as the leading edge of the pad is created without a blend, the slider will function properly.
  • a blend at the outside edges of the slider would probably confer some greater resistance to the head scratching the disk during crash stop when, in general the actuator arm engages a crash stop and inertial forces causes the head to yaw as the disk slows and the head settles to the disk surface.
  • a "sharp" edge contributes more damage than the blended edge.
  • Such a blend would not really affect slider performance as long as the blend area was small compared to the pad area, and its angle is much bigger than the approximately 1° shown to cause lift.
  • the ramped leading edge of the pads may thereafter be provided by lapping the front edges of the leading edge pads.
  • the lapping may be performed before or after the etching step. It is also conceivable that the etching step may be utilized to create the forward ramps, however greater care in mask alignment must be taken, and a "kiss" lapp to remove residue will likely be required.
  • the core pad can be extremelyly sensitive to blends on the front edge of the core pad.
  • the very fine finishes on the pads are generally made by a succession of lapping processes that go to finer and finer grit sizes.
  • This art is well known in the industry, as is the fact that the edges of surfaces polished in this way will generally have some degree of roll-off or blending, as it is called. This can be minimized by proper technique, but there will always be some edge effect.
  • a group of three-pad heads was tested that were made by first defining the pad, typically 2.5 mils wide and 3.0 mils long, and second by performing a final polish on the pads, consistent with state of the art practices in the industry, with the intention of minimizing any edge blend. These were three-pad heads very similar to the head shown in Fig. 6A-6C. Tests at 340 ips showed an average drag of .65 grams and an average PW50 of 52 ns. The front edges of the core pads were then redefined by dicing away approximately .2 mils to make the core pads approximately 2.8 mils long. The pad surface was protected by wax from any erosion by the dicing wheel slurry during this process.
  • etching is a superior method of defining the pad edges.
  • the etched pat blends on the sides of the pads have not been any problem, but they could be if they were more effective at creating lift. This is because in a typical disk drive, the head is moved radially by a rotary actuator and is always operating at some skew angle with respect to the disk motion vector.
  • the skew angle can be as much as 15°. If the sides of the pads have any tendency to create lift, then they would start to do so as the skew angle gets bigger and a disk velocity component perpendicular to the pad side develops.
  • Etched heads tested with blends due to etching vary widely in shape, being somewhat rounded, but blends are approximately between 10 and 30° and between 20 and 75 ⁇ " long. Such blends on the side of the core pad had little effect at up to a 15° skew angle.
  • head disk assembly 100 generally includes disk 110, actuator assembly 120, header assembly 130, all mounted in a base 105 which, when coupled to cover 107, provides a controlled environment in which the disk 110, actuator assembly 120, and header assembly 130 are maintained.
  • the controlled environment between cover 107 and base 105 allows for a maintenance of a liquid bearing on the disk surface.
  • a wicking assembly 140 transports liquid bearing material to the disk surface while disk 110 is rotating to ensure constant lubrication of the surface for slider 70.
  • Slider 70 is carried by an actuator arm 124 which is part of actuator assembly 120.
  • Actuator assembly 120 includes a voice coil motor which, under the control electronics located on printed circuit board 150, operates responsive to control signals from the host computer to position the head at various data locations on the disk.
  • a spindle motor (not shown) is also located on base 105 and within the controlled environment to rotate disk 110 responsive to control signals from the control electronics on PCB 150.

Landscapes

  • Adjustment Of The Magnetic Head Position Track Following On Tapes (AREA)
  • Supporting Of Heads In Record-Carrier Devices (AREA)

Abstract

Elément interactif pour un appareil d'enregistrement d'informations, ledit appareil d'enregistrement d'informations étant doté d'un support liquide lubrifiant entre un support de stockage et l'élément interactif qui se déplace par rapport au support de stockage. Selon un aspect de la présente invention, l'élément comporte un corps de glissement, ledit corps de glissement (70) ayant au moins des première et deuxième régions, et un élément d'interface monté sur la première région du corps de glissement. Lorsque la première région se déplace au-dessus du support liquide quand l'élément interactif se déplace par rapport au support de stockage, ladite première région du corps de glissement présente une traînée considérablement plus élevée que celle de la deuxième région. Dans un mode de réalisation, l'élément est une tête d'enregistrement pour une unité de disques, ladite unité de disques comportant un support liquide entre un disque de stockage rotatif et la tête. La tête d'enregistrement comprend un corps de glissement (70), ledit corps de glissement possédant des première et seconde extrémités, et un élément transducteur monté sur la première extrémité du corps de glissement. La seconde extrémité du corps de glissement se déplace avec un écart par rapport au disque qui est considérablement plus important, lorsque le disque tourne, que l'écart atteint par la première extrémité.
PCT/US1993/010221 1992-11-13 1993-10-22 Tete d'enregistrement a support liquide et a faible trainee WO1994011865A1 (fr)

Applications Claiming Priority (2)

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US97644292A 1992-11-13 1992-11-13
US07/976,442 1992-11-13

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0689198A3 (fr) * 1994-06-20 1997-01-29 Quantum Corp Support glissant pour transducteur d'unité à disque dur ayant un patin de contact avec contrÔle du tangage et du roulis
US6118635A (en) * 1994-10-20 2000-09-12 Hitachi, Ltd. Magnetic storage apparatus having a head with sliding pads
EP0962932A3 (fr) * 1998-06-02 2002-01-02 Texas Instruments Incorporated Utilisation de la méthode des ratios des surfaces des signals maximums pour déteminer le signal pw50 et la distance de survol d'une tête de détection

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6148182A (ja) * 1984-08-10 1986-03-08 Fujitsu Ltd 浮動形磁気ヘツド
JPS6396722A (ja) * 1986-10-09 1988-04-27 Hitachi Ltd 浮動型磁気ヘツド
US5193046A (en) * 1988-10-17 1993-03-09 Conner Peripherals, Nc. Information recording apparatus with a liquid bearing

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6148182A (ja) * 1984-08-10 1986-03-08 Fujitsu Ltd 浮動形磁気ヘツド
JPS6396722A (ja) * 1986-10-09 1988-04-27 Hitachi Ltd 浮動型磁気ヘツド
US5193046A (en) * 1988-10-17 1993-03-09 Conner Peripherals, Nc. Information recording apparatus with a liquid bearing

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0689198A3 (fr) * 1994-06-20 1997-01-29 Quantum Corp Support glissant pour transducteur d'unité à disque dur ayant un patin de contact avec contrÔle du tangage et du roulis
US6118635A (en) * 1994-10-20 2000-09-12 Hitachi, Ltd. Magnetic storage apparatus having a head with sliding pads
EP0962932A3 (fr) * 1998-06-02 2002-01-02 Texas Instruments Incorporated Utilisation de la méthode des ratios des surfaces des signals maximums pour déteminer le signal pw50 et la distance de survol d'une tête de détection
KR100762017B1 (ko) * 1998-06-02 2007-09-28 텍사스 인스트루먼츠 인코포레이티드 인가된 피크 면적비를 이용한 신호 ｐｗ50 및 헤드 플라이 높이 결정

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