Uniform Flying Height Slider Assembly With Improved Dynamic Air Bearing Characteristics

1. Technical Field

This invention relates generally to magnetic head slider assemblies for use in magnetic read/write systems employing rapidly moving recording media, and more particularly to a slider assembly which produces an air bearing characteristic of improved uniformity of flying height and dynamic response as the slider is skewed or is subjected to various dynamic forces as it moves relative to the recording media.

2. Background Art

As discussed in my recently issued U.S. Pat. No. 4,673,996 (referred to hereinafter as my '996 patent), issued June 16, 1987, magnetic recording systems utilizing transducers that are supported by an air bearing film as they move relative to the surface of a magnetic recording disk are well know in the art. Such transducers "fly" at just a few micro-inches above a rotating disk surface. The transducer is mounted in a slider assembly which has a contoured lower surface toward the recording medium. The air bearing film is produced by pressurization of the air as it flows between the disk and slider and is a consequence of the slider contour and relative motion of the two surfaces. The purpose of the air bearing is to provide, with minimal contact, a very narrow clearance between the slider and rotating disk. This allows a high density of magnetic data to be transferred and reduces the wear and damage to the magnetic assembly and recording medium during operation.

Typical sliders of the prior art utilize at least two lower rails having flat surfaces toward the recording medium, each of these rails having a tapered forward surface toward the direction of rotation of the recording medium, whereby the rotating medium forces air by viscous effects into the taper and thereby produces a pressure beneath each of the rails resulting in the air bearing. These sliders are typically gimbal mounted to a flexure which is attached to an arm. The arm is driven by an actuator which positions the transducer over the recording surface from one data track to another. The arm can move in a linear motion which is termed linear access or it can rotate which is termed rotary access. With rotary access, the slider will be positioned at varying angles with respect to the direction of disk rotation as the slider moves over the recording surface. This angular orientation is referred to as the "skew" angle.

When a typical slider is positioned having any angular skew, the rotation of the disk introduces pressurized air at the forward edge, thereby generating the air bearing. However, this air is pressurized at a reduced value because of the skew, and gives rise to a reduction in the flying height. Also, the skew angle gives rise to a roll of the slider such that the air bearing flying height is not uniform under both of the rails. Accordingly, the position of the transducer with respect to the recording medium can vary as the slider is caused to roll in one direction or the other or fly at different heights. Such variations in flying height adversely affect the data transfer between transducer and recording medium. Furthermore, the slider must move radially across the recording disk at a substantial rate of speed to access various portions of the disk. This motion also introduces air under one edge of each slider rail and results in a roll of the slider and a change in the spacing between the transducer and the recording medium. When any of these variations of spacing occur, particularly with a substantially reduced spacing between the slider and the disk, contact may occur between the slider (and its transducer) and the recording medium, or at least potentially rough surfaces thereof. Any such contact, of course, introduces wear into the slider and the recording surface.

In addition to my above-cited '996 patent, numerous magnetic head slider assemblies have been developed in the rapidly developing art of high speed recording/reading. Typical of these developments is the transducer assembly described in U.S. Pat. No. 3,823,416, issued to M. W. Warner on July 9, 1974. In this particular construction, there are two principal side rails having tapered front edges that produce the air film necessary to raise the transducer assembly above the recording medium. In addition, there is a center rail to which the transducer is attached at a trailing edge. By positioning the transducer along this center rail, the effects of roll upon the spacing of the transducer from the recording medium is minimized.

Another magnetic head slider assembly is that described in my U.S. Pat. No. 3,855,625, issued on Dec. 17, 1974. In this patent is described a slider support for a magnetic head assembly that is formed with a tapered flat or step flat forward edge on the outer rails, with a recessed portion delineated by a reverse step between the rails. This construction affects the air bearing to improve upon the stability and uniformity of flying height of the magnetic head of the device.

Another device in this general field is described in U.S. Pat. No. 4,218,715, issued to M. F. Garnier on Aug. 19, 1980. In this patent is taught the use of a negative pressure region between the rails and shallow recesses or reliefs formed in the rails so that the ambient pressure is substantially maintained in the areas of such recesses along the rails. This slider is alleged to be relatively insensitive to skew and disk curvature due to flutter or static deformation.

Still another device is described in U. S. Pat. No. 4,285,019, issued to J. C. Scott, et al., on Aug. 18, 1981. The slider of this patent is manufactured to have a substantially continuous curved surface from the front to the back of the slider rather than a planar surface as in other of the above-cited devices. With this construction, it is alleged that the trailing edge, by being along a curve, is better protected from making contact with the recording medium during operation or start/stop conditions, thereby minimizing damage to the transducer. This patent also teaches that a continuous curvature can exist across the slider as would be produced by machining the entire lower surface of the slider to a spherical contour.

Still another patent of this technology is U.S. Pat. No. 4,475,135, issued to M. W. Warner, et al., on Oct. 2, 1984. The slider of this patent has a continuously tapered surface across the front edge thereof to pressurize the air, a pair of axially extending rails, and an area between the two that is recessed to provide a region of negative pressure. This construction is alleged to provide an extremely fast lift off of the slider from the disk surface as the disk begins to rotate. Thus, minimum wear occurs during initial startup and stopping of the disk.

Although several of the above-referenced patents acknowledge the existence of a roll of the slider during operation, none of them, except for my '996 patent, appears to address the problem of preventing such roll.

According to the teaching of my above-cited 996 patent, a reduction of roll and flying height variations is achieved by providing both longitudinal edges of each rail with a transverse pressurization contour (TPC); i.e., a contour whereby pressurization is produced in the contour at one transverse edge of the rail and expansion is produced in the contour along the other transverse edge of the rail when there is a transverse component of airflow across the face of the rail. When a pair of rails are used, the patent calls for TPC's along the side edges of both rails. This arrangement provides flying height uniformity and control when the skew angle varies considerably with a near even split (negative to positive) from an inside track to an outside track (e.g. -15 degrees to +15 degrees). There are also disk configurations and skew arrangements that do not lend themselves to flying height uniformity with the inclusion of TPC sections along each side edge of each rail. For example, consider a 31/2 inch disk spinning at 3600 rpm. With a near zero skew angle at the inside radius and moderate positive skew (such as +15 degrees) at the outside radius, a conventional taper-flat slider without TPC sections will increase moderately in flying height across the data band. Addition of TPC sections along each rail side edge in this case will not provide a more uniform flying height profile. In fact, TPC's along both edges would produce a flying height profile with greater variation, since the primary influence of the TPC sections is to produce more lifting support to the slider at a skewed orientation. This is in contrast to a desire for a more uniform flying height profile across the data band of a data storage disk.

Accordingly, it is a principal object of the present invention to provide a highly controlled thin pressurized film of air between the magnetic assembly and the spinning magnetic disk.

It is a further object of the present invention to provide an improved magnetic head air bearing slider for magnetic recording systems that displays a high degree of insensitivity of clearance and roll angle to the slider skew.

It is another object of the present invention to provide a slider whose flying height and roll angle are highly insensitive to slider access velocity.

It is also an object of the present invention to provide a slider that exhibits a rapid lift off from the disk surface when rotation is started with the slider in a skewed position in contact with the disk.

It is another object of the present invention to provide a slider processing substantial ability to satisfactorily perform without contact by roughness on the disk surface during skewed slider orientation and/or rapid slider access over the recording medium.

A further object of the present invention is to provide a slider assembly with increased air bearing damping which improves its stability of motion and which allows the slider to settle more quickly after being subjected to impulse loading or other forces.

Also an object of the present invention is to provide a slider assembly with a high degree of insensitivity of clearance and roll angle to radial position on the magnetic disk as both the skew angle and disk velocity vary.

Another object of the present invention is to provide a magnetic head air bearing assembly that exhibits a substantially uniform flying height when a zero skew angle exists at either an inner or outer radius of the magnetic disk, and a substantial skew angle exists at the opposite extreme radius of the disk.

It is an additional object of the present invention to provide a slider that is easy to manufacture and which does not require a significant increase in cost over the conventional slider assemblies that are presently in use.

Other objects of the present invention will become apparent upon consideration of the drawings set forth hereinafter, and a complete discussion of the invention with respect to those drawings.

According to the present invention, an air bearing surface of a magnetic head air bearing slider is described by two or more coplanar rails extending rearwardly from a forward edge and separated by an ambient pressure relief slot. Each air bearing rail is sloped at its forward edge so as to pressurize incoming air flow to produce lift for the slider assembly. Furthermore, each of the rails is provided with an edge contour along at least one edge (a corresponding side edge of the rails). These edge contours are referred to as transverse pressurization contours (TPC). Depending upon the disk size and relationship of the skew angle between an inner radius and an outer radius of the magnetic disk, the edge selected for the contour is such that the air bearing formed between the slider and the recording medium is not degraded by slider skew angle or access velocity. This results in very little roll and very little tendency to change the flying height due to skew or access, and provides rapid lift off when the slider is in a skewed position relative to the direction of rotation of the recording disk. This permits a wider range of skew angles, and a higher access velocity than can be utilized without the advantages produced by the present invention. The TPC's can have various configurations; however, each configuration has an average angle with respect to the bottom of the rails of about 0.05 to about 5.0 degrees.

FIG. 1 is a drawing illustrating skew angle as applied to a magnetic head slider assembly, i.e., the included angle between the direction of disk velocity and the -longitudinal axis of the slider.

FIG. 2 is an isometric bottom view of a typical slider assembly according to my above-cited patent wherein transverse pressurization contains are provided along both edges of the slider rails.

FIG. 3 is an isometric bottom view of one embodiment of the present invention showing the application of a transverse pressurization contour as applied to one corresponding side edge of each of the rails of the slider assembly.

FIG. 4 is a transverse cross-section of one rail of a slider assembly illustrating one embodiment of a single transverse pressurization contour.

FIG. 5 is a transverse cross-section of one rail of a slider assembly illustrating another configuration of a single transverse pressurization contour.

FIG. 6 is a transverse cross-section of one rail of a slider assembly illustrating still another configuration of a single transverse pressurization contour.

FIG. 7 is a transverse cross-section of one rail of a slider assembly illustrating the same configuration of transverse pressurization contour as shown in FIGS. 3 and 6 except that it is along an opposite edge-of the rail.

FIG. 8 is an isometric drawing showing the bottom surface of another embodiment of the slider assembly employing the transverse pressurization contour of FIG. 6.

FIG. 9 is a computer generated simulation of flying height variation after subjecting a slider head assembly to a selected vertical impulse. This slider had no transverse pressurization contours.

FIG. 10 is a computer generated simulation of flying height variation after subjecting a slider head assembly to the same vertical impulse as for the slider used for FIG. 9; however, significant damping of oscillations is achieved due to transverse pressurization contours.

FIG. 11 is an isometric bottom view of another embodiment of the present invention showing a deep transverse recess and a single TPC in corresponding edges of the rails of the slider.

FIG. 12 is a plot, as obtained by computer simulation, of flying height variation or profiles for a conventional taper-flat slider assembly without transverse pressurization contours when the skew angle magnitude is approximately equal at inside and outside radius. The results for two cases are plotted.

FIG. 13 is a plot, as obtained by computer simulation of flying height variation for a slider incorporating TPC step sections along each side edge of the two rails. The skew angle magnitude is equal at inside and outside radius.

As stated above, the angular relationship between the longitudinal axis of a magnetic head slider and the direction of movement of the magnetic disk is referred to as "skew angle". This relationship is illustrated in FIG. 1. The slider can be pivotally positioned such that a slider rail 10 has a zero skew angle between the longitudinal axis 12 thereof and the direction 14 of movement of the recording medium. This mounting can result in a positive or negative skew angle as the slider head is accessed to the maximum radius of the disk. Similarly, the slider can be pivotally mounted such that the skew angle is zero at the outer radius of the disk, with a resulting positive or negative skew angle at the inner radius. A slider can also be pivotally mounted to provide approximately equal skew angle magnitudes at the minimum radius and outer radius.

The slider head, illustrated in FIG. 2, is typical of the invention set forth in my above-identified U.S. Pat. No. 4,673,996 which is incorporated herein by reference. In this and other drawings depicting embodiments of the invention, the units are enlarged and not necessarily to scale in order to better show the transverse pressurization contours. This slider assembly is indicated generally at 16. In this embodiment, there are a pair of rails 18, 20 separated by a deeply recessed region 22 in a substantially conventional manner. This recessed area prevents the entire body from providing an air bearing support and thus allows for low flying heights when low or moderate loads are applied to the slider. The slider 16 has a forward or leading edge 24 and a rear or trailing edge 26. Each of the rails 18, 20 consist of a converging inlet slope 28, 30, respectively, leading to a substantially flat air bearing surface 32, 34, respectively. Further, the air bearing surface 32 is provided with transverse pressurization contours 36, 38; and air bearing surface 34 is provided with transverse pressurization contours 40, 42. This type of slider is referred to hereinafter as a Type III slider. Typically, the converging inlet slope has a linear taper at an angle of about 0.5 to about 2 degrees with respect to the bearing surfaces 32, 34. The TPC can be defined as having an "average angle" with respect to the air bearing surface. For this step-type TPC, this average angle, .theta., can be determined from the equation: Tan .theta.=B/C, where B is the height of the step and C is the width of the step (see FIG. 6). As described in greater detail hereinafter, this average angle can vary from about 0.05 to about 5 degrees.

During operation of a system employing these sliders, most of the static load developed by a rail is carried by the central flat portion (i.e., surfaces 32, 34) of each rail. When the slider is subjected to dynamic forces which cause the slider to translate, pitch or roll, the effective width of the slider rail enlarges to include most of the width of the TPC sections as well. This increased effective air bearing surface area provides more support to the slider during dynamic excursions and allows the slider to settle more quickly after being subjected to such dynamic forces. Examples of these dynamic forces which alter the slider static flying orientation include those associated with: rapidly accessing the slider (and magnetic head) from one data track to another; non-flat run-out conditions on the disk which causes the slider to come in close proximity to the disk; etc. Localized asperities on the disk which disturb the air film between the slider and the disk are problems to the stability of the slider, also. Depending on the size, shape and distribution of such asperities, the slider may or may not perform satisfactorily.

One desired characteristic o the slider is to quickly return to equilibrium position after an encounter with disk disturbance or due to access motion radially across the disk. Such decreased settling time enhances the stability of the slider and minimizes the possibility of a "head crash" of the slider into the disk as the slider is repeatedly subjected to dynamic input. This damping feature was not fully recognized at the time of filing the application for my above-cited patent.

Two plots showing the effect of damping can be seen in FIGS. 9 and 10. These plots were generated by computer simulation. The simulation is based on a theory which includes three degrees of freedom for the slider motion and isothermal compressibility and molecular slip for the air film. The air film is thus viscous, compressible and slightly rarefied. The plot in FIG. 9 is for a conventional taper-flat rail having a pad width of 0.015 inch; and that in FIG. 10 is for a similar rail having a TPC section along each edge. The sliders were each subjected to the same vertical impulse. In each case, the slider overall dimensions, load force, mass and moments of inertia were the same. Also, the static minimum flying heights were the same. For each slider, the dimensionless change in flying height, H, is plotted versus the dimensionless time, T, (the time value of unity corresponds to the time required for a point on the disk surface to travel the length of the slider). It can be seen that the TPC slider quickly returns to equilibrium in contrast to a non-TPC slider indicating significantly increased damping to impulse. These results are for a slider flying at a height of about six micro-in cheso above a 51/4 inch disk rotating at 3600 rpm.

The provision of a TPC along each edge of each rail provides, as stated in my cited '996 patent, improvement in flying height uniformity and low roll angle. During slider access in one direction, the TPC along the rail in that direction provides support. The TPC along the opposite edge provides support when the access motion is in that opposite direction. In many situations, the Type III slider also provides static flying height uniformity when there is a substantial balance in the skew angle (positive and negative) from the inner radius of the recording medium to the outer radius. The degree of static flying height uniformity possible with a Type III slider is influenced primarily by the disk size, the skew angle distribution across the recording band, and the desired static flying height. With a 51/4 inch or larger disk and substantial negative to positive skew angle variation across the recording band, the static flying height tends to increase, reach a maximum, and then decrease from inside to outside radius (see FIG. 12) for the case of a typical taper-flat slider without TPC sections. By incorporating TPC sections along both side edges of each rail, the static flying height can be controlled to a near constant value across the data band. In order to achieve a uniform flying height with radius, the average angle of the TPC sections on each rail are usually different. Typically, the average angle for the TPC section along the inside edge of each rail is between 1/4 to 1/2 that for the TPC section along each outside edge. Flying height profiles are presented on FIG. 13 for the case where TPC step sections are utilized along each side edge of a two rail slider. Steps along the inside edges are one micron deep while those along the outside edges are three microns deep.

With a 31/2 inch or smaller disk spinning at 3600 rpm, there is more of a tendency for the static flying height to increase monotonically with disk radius. This is caused primarily by the decreased tangential velocities associated with the smaller disk. In order to achieve a given flying height level, the slider rail widths will generally be greater than those used with a larger disk. This causes the static flying height to increase across the recording band (as the velocity changes) even though the skew angle may be substantial and vary considerably. That is, with a 31/2 inch disk, the static flying height is more sensitive to velocity change than the case with a 51/4 inch disk. This variation in flying height sensitivity with disk size then requires a variation in TPC distribution in order to provide static flying height uniformity over the recording band of some small disk applications.

Due to the influences cited above, there are disk and skew configurations in which a TPC section along only a single corresponding side edge of each rail may be adequate or even required for control of static flying height and roll angle across the recording band. One such configuration occurs when the skew angle is near zero at the inside radius and significantly non-zero at the outside radius. As an example, consider a 31/2 inch diameter disk spinning at 3600 rpm. The inside skew angle can be zero while the outside skew angle can be +15 degrees. A conventional taper-flat slider such as is found in current disk drives increases moderately in static flying height from inside to outside radius. If TPC sections of the same size and geometry were utilized along each side edge of the slider, the flying height would increase more across the recording zone than for the slider with no TPC sections. However, by including a TPC section only along the inside longitudinal edge of each rail (i.e., the edge closer to the center of disk rotation), the flying height can be controlled at a nearly constant value from inside to outside disk radius. In this case, the TPC sections produce subambient pressure which increases in magnitude as the skew angle (and radius) increases. This effect causes the slider to be attracted toward the disk and provides a more uniform flying height profile across the recording band. With this particular disk size and skew distribution, a nearly uniform flying height profile can only be produced with the single TPC section per rail.

An example where near uniform static flying height may be achieved with either single or dual TPC sections occurs with a 51/4 inch disk at 3600 rpm and a skew angle which varies from zero at the inside track radius to +20 degrees at the outside radius. In this case, most of the flying height augmentation is provided by the TPC sections along the rail outside edges as they produce pressurization and lift.

A modified slider having one TPC per rail is illustrated at 16A in FIG. 3. This embodiment is designated as Type I slider. There are a pair of rails 18', 20' separated by the deep recess 22. The forward ends of the rails are each provided with converging inlet slopes 28, 30. Each rail 18', 20' is provided with a single TPC, i.e., 36, 40, respectively. These are on corresponding edges of the rails, 18', 20', as shown, and are in those edges toward the center of rotation of a recording disk when there is substantially zero skew angle at the inner radius of the disk and a large positive skew angle at a maximum radius. Typical step heights are 0.00002 to 0.0002 in., and typical widths are about 0.005 in. However, other step sizes can be used. The remaining flat region is typically 0.015 to 0.02 in. As stated above, the average angle defined by the step TPC is about 0.05 to about 5 degrees.

Shown in FIG. 7 at 16B is a slider designated as a Type II slider. In this embodiment, the TPC's, e.g 40, are on opposite edges of the rails 18', 20', as compared with FIG. 3, when there is zero skew angle at the inner radius of the disk and a large negative skew angle at the outer radius.

The following table illustrates the conditions for choosing between a Type I and Type II slider.

The step-type TPC's of FIGS. 2-3 can be manufactured by several conventional methods. For those units where the height of the step is small (small average angle) the step can be produced by ion milling or etching techniques. The deeper steps can be achieved by these techniques or by machining.

Although step-type TPC's are relatively easy to manufacture; similarly, a TPC of a uniform taper as illustrated at 16C in FIG. 4 can be easily produced by lapping, etc. Such uniform tapers have an angle of also about 0.05 to about 5 degrees. In addition, these TPC's can have a convex configuration as disclosed in my above-cited '996 patent and illustrated at 16D in FIG. 5. These configurations will also have an average angle, as computed above, of about 0.05 to about 5 degrees.

In addition to the several variations of a single TPC per rail and a double TPC per rail, the sliders of the present invention can utilize other features often found in conventional sliders. One such configuration is illustrated at 16E in FIG. 8. This embodiment is similar to that of FIG. 2 except that a cross-bar 44 joins the two rails. Although each rail is illustrated as having a TPC along a single edge, a similar construction could have two TPC's per rail. The cross-bar 44, which divides the recess into two portions 22A, 22B, causes a subambient pressure to be developed within the recess 22B behind the cross-bar and therefore the flying height is reduced.

Still another slider is shown at 16F in FIG. 11. In this embodiment there is at least one deep transverse recess 46 in addition to the longitudinal recess 22. This construction permits the use of wider rails thus providing for increased space for housing electronics components. As in the other embodiments, a single TPC per rail can be utilized.

From the foregoing, it will be understood by those versed in the art that, depending upon the operating conditions of a particular slider/disk construction, a slider can be selected having increased resistance to changes in flying height. Further, the slider of the types disclosed herein provide increased damping characteristics such that the slider flying height will quickly stabilize after being subjected to a dynamic input.

Although only specific embodiments of the present invention are shown and described herein, the invention is not to be limited by these embodiments. Rather, the scope of the invention is to be defined by these descriptions taken together with the attached claims and their equivalents.