BACKGROUND OF THE INVENTION Data are commonly read from and written to spinning magnetic disks. The disks commonly have a series of closely spaced, concentric data tracks. A slider, including a data head, is mounted to a support arm which biases the slider towards the data surface of the disk. The slider is typically an air bearing slider and is supported just above the spinning data surface of the disk by a thin film of air. An actuator incremently moves the support arm so the slider is indexed to be registered with the desired data track.

To accommodate small manufacturing offsets in the slider surface relative to the data surface as well as small tilt variations caused by the movement of the data surface, the slider is typically mounted to the support arm through a gimbal arrangement. This gimballed mounting of the slider to the support arm permits the slider to pivot about a tangentially-directed axis in a radially-oriented plane, such pivotal movement commonly called roll, and about a radially-oriented axis in a tangentially-oriented plane, such movement commonly called pitch. This movement is illustrated in Fig. 1.

One problem associated with the manufacture of hard disk drives is that in an effort to get more information on the same size disk, the data tracks are spaced closer together. Presently, hard disks typically have about 4000 to 10,000 tracks per inch (about 1575 to 3900 tracks per cm); track densities of up to about 25,000 tracks per inch (about 9800 tracks per cm) are contemplated and even higher densities are expected in the future. These higher track densities and higher rotational speeds combine

to increase the problem of misregistration of the data head with the data track. One article discussing this disk misregistration problem states:"Current high performance disk drives have track densities approaching 6,000 TPI, or 166 micro inches between tracks. The head positioning servo system must hold the read/write element within 12% of the center of the track which means that relative radial displacement between the head and disk must be no more than 20 micro inches. At these high track densities, effects which were formally negligible now contribute significantly to track misregistration (TMR) in the 3.5 inch disk drives." ("The Effect of Disk Platter Resonances on Track <BR> <BR> <BR> <BR> Misregistration in 3.5 Inch Disk Drives,"IEEE Transaction Magnetics, Vol. 32, No. 3, May 1996, pp. 1762-1766.) With the track densities heading towards the 10,000 to 25,000 tracks per inch range, track misregistration problems become even more severe.

Disks have natural vibration modes, each characterized by a particular resonant frequency. At these frequencies the disk movement will be amplified by the resonant response to even small excitations. The driving excitations can be produced by imperfect bearings and motors as well as by aerodynamic instabilities in the air flow across the disk surface, particularly at the higher rotation rates. Although these vibrations are most easily characterized by the movement of the outer regions of the disk in a direction perpendicular to the surface, this motion necessarily must produce a tilting of the disk surface since the disks are clamped at the inside radius.

It can be shown that the neutral plane of the disk, the plane at the middle of the thickness, does not move radially to any significant degree. Due to the finite thickness of the disk, the tilting requires that the slider surface and the disk surface must move in opposite radial directions depending on the sense of the tilt. In latest drives these radial motions are large enough and at a high enough frequency as to challenge the ability of the drive servos to

keep the heads centered on the data tracks.

SUMMARY OF THE INVENTION The present invention is directed to a slider support assembly and method for supporting the slider which helps to prevent, or at least minimize, radial motion of the slider relative to the data surface as the disk tilts in response to disk vibration.

The present invention recognizes that a gimbaled slider contributes to the relative motion of the data track and slider. The stiffness of the air bearings will assure that the slider will follow the tilt motion of the disk.

Since, in the conventional slider suspension, the slider is designed to rotate about an axis which is located at or above the top surface of the slider, this rotation will result in a radial translation of the head across the data surface in a direction opposite to that of the track displacement. Thus it adds to the misalignment. Nothing can be done about the contribution of the disk to the problem. However, the effect of this track motion can be minimized if the slider suspension can be reconfigured in a way to make the slider response to tilt match that of the track, and thereby eliminating or minimizing the head/track relative motion. The present invention provides for the accomplishment of this goal by locating the roll axis of the slider to coincide with the roll axis of the disk, at the center plane of the disk.

The slider support assembly includes a support arm extendible over the data surface of a substrate, typically a magnetic disk. A slider, including a data head, is mounted to the support arm. The slider is mounted so the slider can pivot in a radially oriented plane about an effective roll axis located within the disk.

The effective roll axis is typically located centrally beneath the slider, preferably generally centered half way through the disk. By moving the effective roll axis from a position above the data surface, as found with

conventional gimbal-type slider supports, to a point below the data surface, pivotal radial movements of the slider relative to the data surface due to tilting of the data surface are reduced or eliminated.

According to the method aspect of the invention, the slider is supported along the data surface of the spinning disk by positioning the slider so the data head is aligned with a data track. Tilting movement of the data surface is accommodated by mounting the slider for pivotal movement in a roll plane about an effective roll axis. The roll plane is oriented generally perpendicular to the data track, that is, in a generally radial direction. The effective roll axis is oriented perpendicular to the roll plane and is located within the disk, preferably generally centered half-way through the disk.

As used in this application, radial and tangential refer to those directions defined by the data tracks. Also, the terms above and below the data surface refer to these directions when the data substrate is generally horizontal and the data surface is the upper surface. However these terms are intended to cover other situations, such as when the data substrate is at a 45° angle and the data surface is generally downwardly-facing; in this situation"above"the data surface is actually downward and away from the data surface.

A primary advantage of the invention is the recognition that flutter or other excursions of the data substrate, especially near the outer edge of a spinning disk, (1) involves very small angular distances as measured from the center of the disk, and (2) can be thought of as a twisting of the disk about a position centrally beneath the slider and generally centered within the body of the disk.

Therefore, by pivotally mounting the slider so its effective roll axis passes through the disk, or other substrate, and preferably half-way through the disk, relative radial sliding movement due to disk tilting can be minimized or eliminated.

This pivotal mounting in the radially oriented roll plane is preferably provided using a pivotal mounting structure to mount the slider to the support arm. This pivotal mounting structure preferably uses a trapezoidal suspension. In one embodiment a pair of links extend from the slider to the distal end of the support arm. The links are pivotally mounted at each of their ends or are effectively pivotally mounted by or through flexible or elastic couplings at each of their ends. The links diverge outwardly away from one another as they extend from the slider to the support arm. The lengths and orientations of the links are designed so that the effective roll axis of the slider lies within the body of the disk, and preferably half-way through of the body of the disk. With the trapezoidal suspension, the support arm is typically a radially-extending support arm; the support arm could extend at other orientations, such as tangentially to the data tracks.

Another embodiment of the pivotal mounting structure for the slider is provided by rotatably mounting the proximal end of the support arm to the actuator. This rotatable mounting of the support arm allows the support arm to pivot about a support arm axis, the support arm axis preferably passing through a point centered beneath the slider midway through the thickness of the disk. In this case, the effective roll axis of the slider would be defined by the support arm axis and would be located about half-way through the body of the disk, rather than above the data surface of the disk as is conventional, to help keep the data head aligned with the data track as the disk undergoes flutter.

The roll axis has been described as an effective roll axis. This is because the location of the actual roll axis of the slider may shift or move as, for example, the links pivot. That is, during use the slider may define a range of locations for its roll axis, all a short distance from the average or effective roll axis. The change in

position of the actual roll axis is small because the excursions of the data surface are small. Therefore this range of roll axes can be characterized as an effective roll axis.

Other features and advantages will appear from the following description in which the disclosed embodiments are set forth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a conventional air bearing slider mounted to the distal end of a tangentially-oriented support arm through a gimballed slider support, the figure illustrating pivotal movement of the slider in a radially- oriented roll plane and in a tangentially-oriented pitch plane; Fig. 2A schematically illustrates a conventional gimballed slider with the head properly oriented with a track of the disk; Fig. 2B illustrates the slider and disk of Fig.

2A, after flutter of the disk caused the disk to effectively tilt causing the track to move to the right and the head to move to the left so the head becomes misaligned with the track; Fig. 3 illustrates, in simplified form, a slider support assembly made according to the invention using a radially-directed support arm; Fig. 4A is a simplified side view, taken along line 4A-4A of Fig. 3, of the distal end of the support arm, the slider and a portion of the disk showing a trapezoidal suspension supporting the slider adjacent to the data surface of the disk with the data head and data track aligned; Fig. 4B illustrates the result of flutter of the disk in which the data surface has been shown, in exaggerated form, to have been tilted relative to the support arm thus causing the links of the trapezoidal

suspension to pivot but showing that the data head and data track remain substantially aligned due to the pivotal movement of the slider about an effective roll axis passing through the center of the body of the disk; Fig. 5A illustrates the effect on the position of the effective roll axis of Figs. 4A and 4B as the links are pivoted inwardly so that their upper ends are closer to one another causing the roll axis to move, in the figure, downwardly ; Fig. 5B illustrates the situation in which the two links are parallel to one another which results in the roll axis being located at infinity, in this figure infinity being above the slider; Fig. 5C illustrates the effect of continuing to move the upper ends of the links towards one another causing the roll axis to move downwardly towards the support arm, this position being similar to the roll axis position of the prior art slider of Fig. 2A; and Fig. 6 is a simplified side view of an alternative embodiment of the invention in which the support arm is tangentially directed, similar to the support arm of Fig. 1, but in which the proximal end of the support arm is rotatably mounted to the actuator for rotational movement about a roll axis, the roll axis passing through a point located directly beneath the slider about half-way through the thickness of the disk; and Fig. 7 is a simplified side view of a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 illustrates a conventional support arm 2 supporting an air bearing slider 4 above the data surface 6 of a spinning disk 8. Disk 8 has a series of closely spaced data tracks 10, such as 6,000 tracks 10 per radial inch.

Slider 4 has a data head 12 which is alignable with selected ones of data tracks 10 through the radial movement of support arm 2 by an actuator, not shown in Fig. 1, in the

direction of arrow 13.

Fig. 2A is a simplified enlarged view of the conventional disk and slider taken along line 2A-2A of Fig.

1 illustrating the gimballed slider support 14 having a pivot point 16 located above slider 4. Gimballed support 14 provides for pivotal movement in the radially directed roll plane 18, as well as in the tangentially directed pitch plane 19.

Fig. 2B illustrates the elements of Fig. 2A after disk 8 has been deflected due to disk flutter; the deflection is exaggerated for purposes of illustration.

Comparing Figs. 2A and 2B, it is seen that because slider 4 been pivoted around pivot point 16, data track 10 and data head 12 slide relative to one another in a radial direction, that is in roll plane 18, with data head 12 moving to the left and data track 10 moving to the right. Data head 12 and data track 10 are no longer aligned resulting in track misregistration.

Fig. 3 shows a slider support assembly 20 made according to the invention. Support assembly 20 has many of the same elements illustrated in Figs. 1-2B so that like elements will be referred to with like reference numerals.

The proximal end 22 of support arm 2 extends from an actuator 24 which indexes the distal end 26 of support arm 2, and slider 4 therewith, to different radial positions as indicated by arrow 28. Radially-extending support arm 2 could be oriented in a different direction, such as tangentially as in Fig. 1.

In comparing Figs. 4A and 2A, it is seen that gimballed slider support 14 has been replaced by a trapezoidal suspension 30 for pivotal movement about a roll axis. Trapezoidal suspension 30 includes a pair of links 32,34 secured at their lower ends 36,38 to slider 4 and at their upper ends 40,42 to distal end 26 of support arm 2.

The junctions of ends 36,38,40,42 with slider 4 and support arm 2 are effectively pivotal connection points.

That is, these junctions can be true pivotal connections or

can be, for example, elastic connections which effectively function as pivotal connections. Trapezoidal suspension 30 is used to permit slider 4 to pivot in roll plane 18.

Other, typically conventional, mounting structure, not shown, can be used to provide for the pivotal mounting of slider 4 to support arm 2 for movement in pitch plane 19.

The lengths and orientations of links 32,34 provide an effective roll axis 44 located essentially beneath slider 4 and at about half-way through the thickness of disk 8. That is, for small rolling motions (pivotal motions in roll plane 18) of slider 4, roll axis 44 remains generally centered within disk 8. Therefore, as disk 8 deflects, slider 4 moves with the disk and undergoes insignificant relative sliding motion along roll plane 18.

This is indicated by the fact that data head 12 and data track 10 remain aligned as slider 4 and disk 8 move from the configuration of Fig. 4A to the configuration of Fig. 4B.

The lengths, locations, angles and configurations of links 32,34 determine the location of roll axis 44.

While movement of disk 8 as indicated in Figs. 4A and 4B will cause the location of roll axis 44 to shift, the amount of shift is small so that the effective roll axis location can be considered stationary.

Fig. 5A illustrates what would happen to roll axis 44 if upper ends 40,42 of links 32,34 were moved closer to one another, but not so close that links 32,34 are parallel. The location of roll axis 44 in this event would move in the direction of arrow 46, that is, much farther away from slider 4.

Fig. 5B illustrates the fact that if links 32,34 are made parallel to one another, suspension 30 becomes a parallelogram suspension so that the pivot point is effectively at infinity. That is, there would be no pivoting and thus no roll. Fig. 5C illustrates the result of continuing pivotal movement of links 32,34 in the direction of the arrows so that their upper ends 40,42 are closer together than their lower ends 36,38. This causes

roll axis 44 to move towards slider 4, in the example still above support arm 2.

Fig. 6 illustrates, in a very schematic form, an alternative embodiment of the invention in which support arm 2a is a tangentially oriented support arm, similar to the orientation of the support arm in Fig. 1. The proximal end 22a of support arm 2a is rotatably mounted to actuator 24a for relatively free rotational movement about a roll axis 44a. Roll axis 44a passes through a point 50 situated generally beneath slider 4 and midway through the thickness of disk 8. Doing so permits slider 4 to roll or pivot in roll plane 18a to help maintain the alignment of data track 10 with data head 12 as shown in Figs. 4A and 4B. It can be appreciated that the angles of roll axis 44a and roll plane 18a have been exaggerated for purposes of illustration.

Slider 4 could be mounted to the distal end 26 of a support arm 2a as shown in Fig. 7. Support arm 2a has a semi-spherical surface 52 engaging a plurality of low- friction bearings 54 carried by slider 4a. Surface 52 is sized so that its center is coincident with roll axis 44 centered within disk 8. Bearings 54 could be replaced by very short spacer links; because of the very small movements involved, short spacer links would act similarly to bearings 54 causing slider 4a to pivot about roll axis 44.

The present invention is particularly adapted for use with magnetic disks. However, the invention can also be used with other data storage and retrieval technologies.

For example, the invention can be used with a technology called solid immersion lens recording, a type of magneto- optical recording technology. TeraStar Corporation of San Jose, California has been developing new field recording technology using a flying optical head with optical elements including a solid immersion lens. The invention would help to ensure proper alignment of the lens with the data tracks on a spinning disk. In this case the lens would act as the data head.

Other modifications and variations can be made to the disclosed embodiments without departing from the subject of the invention as defined in the following claims.