Abstract:
A method and apparatus for improving flying height stability at lower speeds is achieved by an ABS with a channel and pocket. The channel and pocket are configured to achieve a desired flying height profile.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to hard disk drives. In particular, the present invention relates to an improved design for an air bearing slider. 
       BACKGROUND 
       [0002]    Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk&#39;s data tracks. The high speed rotation of a magnetic disk generates a stream of air flow along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions. 
         [0003]    As portable devices such as handheld music/video players, cell phones, and digital cameras have become more prevalent, the market for small form factor (0.85″ to 1.8″) hard disk drives (SFF HDD) has increased substantially. SFF HDDs offer high recording capacity at a relatively inexpensive price. One design requirement critical for good reliability in SFF HDDs is a stable gap or flying height (FH) between the magnetic head (embedded in the slider) and the media (disk) in all possible environments where consumer electronics might be used. 
         [0004]    The design of SFF HDDs presents many unique challenges. One such challenge is achieving a high enough flying height at very low linear speeds. The air bearing is generated by the air flow created by the rotation of the magnetic disk under the slider. A larger relative speed (i.e. a faster spinning disk or a disk with a larger radius) makes it easier to lift an air bearing. A typical speed at the inner diameter (“ID”) for a 3.5″ HDD like the ones used in desktop computers is approximately 18 m/s; while for a 0.85″ disk drive the speed at the ID is only approximately 2 m/s. This much lower speed makes it very difficult to generate enough air bearing force to fly the slider at a height that can avoid disk contact at the inner radius of a disk. 
         [0005]    A related issue is the challenge of achieving a uniform flying height across the radii of the disk. The linear velocity of the disk increases at larger radii, making it more difficult to achieve a uniform flying height. In a typical 3.5″ HDD the sliders can be designed to reach a saturation level where the slider will continue to fly at a relatively constant height across varying radii (i.e. at varying linear velocities). Low linear velocities makes achieving a constant flying height across the radii of SFF HDDs more challenging. 
         [0006]    Another challenge in designing SFF HDDs is large disk clamp distortion at the ID. SFF HDDs require thin disks, but thin disks usually have large distortions caused by disk clamping forces, leading to undulated disk surfaces and large FH variations at different radii. Disk distortion is typically more pronounced at the ID than at the OD. 
         [0007]    In addition to the challenges mentioned above, there are many unique challenges presented by specific requirements of the consumer electronic devices that utilize SFF HDDs. For example, consumer electronics devices must operate in a large temperature range (from −20° C. to 80° C.). At varying temperatures, the slider and other disk drive components can experience thermal contraction or expansion. In order to achieve a stable flying height, an ABS design must compensate for the physical distortions that different temperatures can cause. 
         [0008]    In addition to operating at a range of temperatures, consumer electronics and the SFF HDDs inside them must also be able to operate at different altitudes, ranging anywhere from below sea level to twenty thousand feet above sea level. The lower air density at high altitudes relative to sea level makes achieving an adequate lift force, and thus a stable flying height, more difficult. 
         [0009]    Consumer electronics devices also have stringent shock requirements. The types of devices utilizing SFF HDDs frequently operate while moving and thus need to be able to withstand sudden impacts. A mechanical shock, such as being dropped to the ground, can cause the flying height between the magnetic head and the disk to suddenly change or even drop to zero, leading to head-disk contact. Therefore, an ABS design should be able to prevent head-disk contact under a certain level of shock. 
         [0010]    In light of the foregoing challenges, a need in the art exists for an improved ABS design for use in SFF HDDs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows an ABS design as known in the art. 
           [0012]      FIG. 2  shows an ABS design with a central air tunnel and pocket apparatus for achieving a higher flying height at low linear velocities and a relatively constant flying height across varying radii. 
           [0013]      FIG. 3  shows the air pressure profile at sea level for an ABS embodying aspects of embodiments the present invention. 
           [0014]      FIG. 4  shows the flying height profile at sea level and ten-thousand feet for an ABS embodying aspects of embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  shows a typical design of an ABS for achieving a uniform flying height in a typical 3.5″ drive. The ABS has a leading edge  101  and a trailing edge  102 , with a center pad  103  and read/write element  104  at the trailing edge  102 . At the inner radius, the air flow generally comes from the direction shown by the arrows  151 . At the outer radius, the air flow generally comes from the direction of the arrows  152 . The ABS utilizes two edge lines  111  and  112  to form a sub-ambient pressure cavity  113  that provides the lift force for the ABS. At the ID, edge line  111  is at the air influx side of the ABS. The height and length of edge line  111  can be modified to determine the amount of air that is blocked and the amount of air that is allowed to enter the sub-ambient pressure cavity  113  when the ABS is at the ID. 
         [0016]    At the OD, edge line  112  is at the air influx side of ABS, and likewise the height and length of edge line  112  can be selected to determine the amount of air that is blocked and the amount of air that is allowed to enter the sub-ambient pressure cavity  113 . In a typical drive, the amount of incoming airflow at the OD will be significantly greater than the amount of airflow at the ID. Therefore, in order to achieve a constant flying height, the edge lines  111  and  112  will typically be configured to block more air at the OD than at the ID, and consequently to allow more air to enter the sub-ambient pressure cavity  113  at the ID than at the OD. 
         [0017]    The design of  FIG. 1  works well for high speed 3.5″ disk drives; however, for SFF HDDs a more complex design is needed to achieve a desirable flying height profile.  FIG. 2  shows an ABS embodying aspects of the present invention. Like the design shown in  FIG. 1 , the embodiment shown in  FIG. 2  contains a leading edge  201 , a trailing edge  202 , and a center pad  203 , with a read/write element  204  at the trailing edge  202 . The ABS can also has two sub-ambient pressure cavities  205   a  and  205   b  as well as side pads  231   a  and  231   b  which also produce a lifting force. 
         [0018]    An aspect of the present invention calls for using ABS rails (such as  210 ,  211 , and  212 ) to create a central air channel  221  and pocket apparatus  220 . The height, width, angles, spacing, and other characteristics of the rails can be altered to change the pressure, and as a result the lifting force, created by the central air channel  221  and the pocket  220 . In a typical embodiment, the air channel  221  and pocket  220  can be designed to provide a lift force at the trailing edge  202  of the ABS. 
         [0019]    In a typical ABS embodying aspects of the present invention, as the ABS moves from the ID to the MD to the OD and the air flow increases, the lifting force created by air going into the pocket  220  and into the air channel  221  may reduce. The increased airflow, however, may cause the lifting force at sub-ambient pressure cavities  205   a  and  205   b  and side pads  231   a  and  231   b  to increase in a manner that offsets the lower lifting force at the pocket  220  and air channel  221 . Having multiple apparatuses that can independently alter the lift force of the ABS based on its orientation and linear velocity can make it possible for a designer to achieve a desired flying height profile across the varying radii of a disk. For example, even in spite of the substantially lower linear velocity at the ID, aspects of the present invention make it possible to configure an ABS to result in a higher flying height at the ID than at the OD. A configuration that results in a higher flying height at the ID might be desirable in order to avoid certain types of disk failure which occur disproportionately at the ID. 
         [0020]    At the inner radius, the air flow generally comes from the direction shown by the arrows  251 . Rails  210  and  211  and a trapper  213  form a pocket  220 , which acts as an air-pressurized chamber to lift the trailing edge  202 . The length and height of rail  210 , as well as the separation between rails  210  and  211  and the angle and height of the trapper  213  can all be adjusted to create a desired lifting force, and as a result, a desired flying height. At the ID, air flow  251  is typically at its lowest, meaning the air pocket  220  needs to be configured to trap more air at the ID than at other radii on the disk by toward to the air flow direction at ID. 
         [0021]    At the middle radius, the air flow generally comes from the direction of the arrows  252 . Rails  211  and  212  form a central air channel  221 . The opening of the central air channel  221  has a partial deflector  214 . The height, length, and deflect angle of the partial deflector  214  as well as the separation of rails  211  and  212  can be varied to increase or decrease the amount of air entering the air channel  221 , and as result the lifting force of the channel  221 . 
         [0022]    At the outer radius, the air flow generally comes from the direction of the arrows  253  and is greater than at other radii on the disk. With the greater lift force created by the increased airflow at the OD, the ABS may be configured to direct less air into the channel  221  and pocket  220 . This can be achieved by configuring rail  212  to block air flow. The decrease in lift force created by the channel  221  and pocket  220  can be offset by the increased lift force at sub-ambient pressure cavities  205   a  and  205   b  and side pads  231   a  and  231   b,  resulting in a desired flying height profile. 
         [0023]      FIG. 3  shows an air pressure profile at the ID for an ABS embodying aspects of embodiments of the present invention. In addition to the lift force created by the side pads  231   a - b  and  232   a - b  (shown at  331   a - b  and  332   a - b  on the pressure profile), the air tunnel  221  and pocket  220  create a relatively large additional lift force (shown at  321  and  320  on the pressure profile). The lift force is greatest at the trailing edge  202  ( 302  on the pressure profile) where the read/write element is located. As the ABS moves from the ID to the OD, the lift forces at the tunnel  221  and pocket will decrease and the lifts forces at the side pads  231   a - b  and  232   a - b  will increase in a manner that will achieve a desired flying profile. 
         [0024]      FIG. 4  shows the flying height of an ABS with a central air tunnel and pocket apparatus according to embodiments of the present invention. At 10K as well as at sea level, the flying height at the ID is higher than that at the OD, which will dramatically improve the reliability of small platform drives. 
         [0025]    The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments without the use of inventive faculty. For example, some or all of the features of the different embodiments discussed above may be deleted from the embodiment. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope defined only by the claims below and equivalents thereof.