Abstract:
In certain embodiments, a motor includes a shaft positioned adjacent a sleeve for relative rotation. The sleeve includes a first radial recirculation channel. The shaft and sleeve form first and second gaps. The first gap is configured to form a pump seal, is positioned above the first radial recirculation channel, and has a width measured between the shaft and sleeve. The second gap is configured to form a journal bearing, is positioned below the first radial recirculation channel, and has a width measured between the shaft and sleeve. The width of the first gap is greater than the width of the second gap.

Description:
RELATED APPLICATIONS 
       [0001]    The present application is a continuation application of U.S. application Ser. No. 11/903,435, filed on Sep. 22, 2007, the contents of which are incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    Disc drive memory systems are being utilized in progressively more environments besides traditional stationary computing environments. Recently, these memory systems are incorporated into devices that are operated in mobile environments including digital cameras, digital video cameras, video game consoles and personal music players, in addition to portable computers. These mobile devices are frequently subjected to large magnitudes of mechanical shock as a result of handling. As such, performance and design needs have intensified including improved resistance to a shock event, improved robustness and reduced power consumption. 
         [0003]    Disc drive memory systems store digital information that is recorded on concentric tracks of a magnetic disc medium. At least one disc is rotatably mounted on a spindle, and the information, which can be stored in the form of magnetic transitions within the discs, is accessed using read/write heads or transducers. A drive controller is typically used for controlling the disc drive system based on commands received from a host system. The drive controller controls the disc drive to store and retrieve information from the magnetic discs. The read/write heads are located on a pivoting arm that moves radially over the surface of the disc. The discs are rotated at high speeds during operation using an electric motor located inside a hub or below the discs. Magnets on the hub interact with a stator to cause rotation of the hub relative to the stator. One type of motor has a spindle mounted by means of a bearing system to a motor shaft disposed in the center of the hub. The bearings permit rotational movement between the shaft and the sleeve, while maintaining alignment of the spindle to the shaft. The read/write heads must be accurately aligned with the storage tracks on the disc to ensure the proper reading and writing of information. 
         [0004]    A demand exists for increased storage capacity and smaller disc drives, which has led to the design of higher recording areal density such that the read/write heads are placed increasingly closer to the disc surface. Because rotational accuracy is critical, disc drives currently utilize a spindle motor having fluid dynamic bearings (FDB) between a shaft and sleeve to support a hub and the disc for rotation. In a hydrodynamic bearing, a lubricating fluid provides a bearing surface between a fixed member and a rotating member of the disc drive. Hydrodynamic bearings, however, suffer from sensitivity to external loads or mechanical shock. Fluid can in some cases be jarred out of the bearing by shock events. 
         [0005]    Lubricant evaporation can limit the life of a hydrodynamic bearing motor. A sufficient amount of lubricant such as oil must be maintained to offset evaporation losses. The evaporation rate is further accelerated when special low viscosity oils are used to reduce power. The lower viscosity oils generally have a higher rate of evaporation. If a shock event occurs with a motor having an insufficient volume of lubricant, rotating surfaces may come in direct contact with stationary portions. Contact of the rotating surfaces can increase generated acoustic noise and motor run current. The dry surface-to-surface contact may also lead to particle generation or gall and lock-up of the motor during contact. Particle generation and contamination of the bearing fluid may also result in reduced performance or failure of the spindle motor or disc drive components. 
       SUMMARY 
       [0006]    The present invention provides a novel fluid dynamic bearing motor. A fluid dynamic bearing containing fluid is defined between an inner component and an outer component, wherein the inner component and the outer component are positioned for relative rotation. In an embodiment, a central region of the fluid dynamic bearing is situated between a first axial end of the fluid dynamic bearing and a second axial end of the fluid dynamic bearing. A radial gap is defined between the inner component and the outer component, wherein the first axial end of the fluid dynamic bearing has a larger radial gap as compared to the central region of the fluid dynamic bearing. A capillary seal or a grooved pumping seal is situated between the inner component and the outer component, for containing fluid with the fluid dynamic bearing motor. These and various other features and advantages will be apparent from a reading of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
           [0008]      FIG. 1  is a top plan view of a disc drive data storage system in which the present invention is useful, in accordance with an embodiment of the present invention; 
           [0009]      FIG. 2  is a sectional side view of a fluid dynamic bearing spindle motor that can be used in a disc drive data storage system as in  FIG. 1 , wherein a thrust bearing is utilized at one journal end and a fluid seal is utilized at an opposing end, in accordance with an embodiment of the present invention; 
           [0010]      FIG. 3  is a sectional side view of a portion of a fluid dynamic bearing spindle motor taken at an end of a journal bearing, illustrating a first axial end of the journal bearing and a fluid reservoir having a larger radial gap as compared to a central region of the journal bearing, in accordance with an embodiment of the present invention; 
           [0011]      FIG. 4A  is a sectional side view of a portion of a fluid dynamic bearing spindle motor, illustrating a fluid recirculation passageway, wherein a first connecting portion of the fluid recirculation passageway connects with the journal bearing between a first axial end of the journal bearing and a central region of the journal bearing, and a second connecting portion of the fluid recirculation passageway connects with a second axial end of the journal bearing via a thrust bearing, in accordance with an embodiment of the present invention; and 
           [0012]      FIG. 4B  is a sectional side view of a portion of a fluid dynamic bearing spindle motor, illustrating a fluid recirculation passageway similar to the one shown in  FIG. 4A , except that a second connecting portion of the fluid recirculation passageway connects with a central region of the journal bearing, in accordance with another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Exemplary embodiments are described with reference to specific configurations. Those of ordinary skill in the art will appreciate that various changes and modifications can be made while remaining within the scope of the appended claims. Additionally, well-known elements, devices, components, methods, process steps and the like may not be set forth in detail in order to avoid obscuring the invention. 
         [0014]    A system and method are described herein for providing a fluid dynamic bearing (FDB) motor with relatively rotatable components having facing surfaces that are reliably lubricated in case of contact or a shock event. In an embodiment, a recirculation passageway and a fluid reservoir also join to the FDB bearing. The present invention increases robustness of the FDB motor, and reduces sensitivity to external loads or mechanical shock events. The present invention also averts dry surface-to-surface contact of bearing surfaces, and the resulting reduced performance or failure of the motor or disc drive components. The use of diamond-like coating (DLC) on relatively rotatable fluid bearing surfaces may also be reduced or eliminated. 
         [0015]    It will be apparent that features of the discussion and claims may be utilized with disc drives, low profile disc drive memory systems, spindle motors, various fluid dynamic bearing designs, hydrodynamic and hydrostatic bearings, and other motors employing a stationary and a rotatable component, including motors employing conical bearings. Further, embodiments of the present invention may be employed with a fixed shaft or a rotating shaft. Also, as used herein, the terms “axially” or “axial direction” refers to a direction along an axis of rotation, or along a centerline axis length of the shaft (i.e., along axis  240  of shaft  202  as shown in  FIG. 2 ), and “radially” or “radial direction” refers to a direction perpendicular to the centerline length of the shaft  202 . Also, as used herein, the expressions indicating orientation such as “upper”, “lower”, “top”, “bottom”, “height” and the like, are applied in a sense related to normal viewing of the figures rather than in any sense of orientation during particular operation, etc. These orientation labels are provided simply to facilitate and aid understanding of the figures and should not be construed as limiting. 
         [0016]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views.  FIG. 1  illustrates a top plan view of a disc drive data storage device  110  in which the present invention is useful. Clearly, as described herein, features of the discussion and claims are not limited to this particular design, which is shown only for purposes of the example. Disc drive  110  includes housing base  112  that is combined with cover  114  forming a sealed environment to protect the internal components from contamination by elements outside the sealed environment. Disc drive  110  further includes disc pack  116 , which is mounted for rotation on a motor design (described in  FIG. 2 ) by disc clamp  118 . Disc pack  116  includes a plurality of individual discs, which are mounted for co-rotation about a central axis. Each disc surface has an associated head  120  (a read head and a write head), which is mounted to disc drive  110  for communicating with the disc surface. In the example shown in  FIG. 1 , heads  120  are supported by flexures  122 , which are in turn attached to head mounting arms  124  of actuator body  126 . The actuator shown in  FIG. 1  is a rotary moving coil actuator and includes a voice coil motor, shown generally at  128 . Voice coil motor  128  rotates actuator body  126  with its attached heads  120  about pivot shaft  130  to position heads  120  over a desired data track along arc path  132 . This allows heads  120  to read and write magnetically encoded information on the surfaces of discs  116  at selected locations. 
         [0017]    A flex assembly provides the requisite electrical connection paths for the actuator assembly while allowing pivotal movement of the actuator body  126  during operation. The flex assembly (not shown) terminates at a flex bracket for communication to a printed circuit board mounted to the bottom side of disc drive  110  to which head wires are connected; the head wires being routed along the actuator arms  124  and the flexures  122  to the heads  120 . The printed circuit board typically includes circuitry for controlling the write currents applied to the heads  120  during a write operation and a preamplifier for amplifying read signals generated by the heads  120  during a read operation. 
         [0018]    Referring to  FIG. 2 , a sectional side view is illustrated of a fluid dynamic bearing motor  210  in which the present invention is useful. The fluid dynamic bearing motor  210  is the type that can be used in a disc drive data storage system  110  as in  FIG. 1 . The motor includes a stationary component and a rotatable component that is relatively rotatable about the stationary component, defining a journal bearing  223  therebetween. In this example, the rotatable components include sleeve  230  and hub  232 . Hub  232  includes a disc carrier member, which supports disc pack  116  (shown in  FIG. 1 ) for rotation about shaft  220 . Sleeve  230  and hub  232  additionally are affixed to backiron  228  and magnet  238 . One or more magnets  238  are attached to a periphery of backiron  228 . The magnets  238  interact with a stator winding  236  attached to the base  234  to cause the hub  232  to rotate. Magnet  238  can be formed as a unitary, annular ring or can be formed of a plurality of individual magnets that are spaced about the periphery of hub  232 . Magnet  238  is magnetized to form one or more magnetic poles. 
         [0019]    In this example, the stationary components include shaft  220  and stator  236 , which are affixed to base plate  234 . The shaft  220  is affixed to a top cover  222  of the fluid dynamic bearing motor  210 . A fluid dynamic journal bearing  223  is established between the rotating sleeve  230  and the stationary shaft  220 . A fluid, such as lubricating oil or a ferromagnetic fluid fills interfacial regions between shaft  220  and sleeve  230  as well as between other stationary and rotatable components. While the present figure is described with a lubricating fluid, those skilled in the art will appreciate that useable fluids include a lubricating liquid or gas. 
         [0020]    This magnetically biased motor design includes a bearing design that cooperates with the magnetically biased circuit or element to establish and maintain fluid pressure in the bearing areas. The bearing design provides an axial magnetic force, especially in designs where a thrust bearing is defined in a gap at an end of the shaft  220 . In the motor illustrated in  FIG. 2 , a thrust bearing  226  is utilized at one journal end and a fluid seal (described in  FIG. 3 ) is utilized at an opposing journal bearing end. Thrust bearing  226  provides the described axial magnetic force. 
         [0021]    Turning now to  FIG. 3 , a sectional side view is illustrated of a portion of a fluid dynamic bearing spindle motor as in  FIG. 2 , taken at an end of a journal bearing  223 . The journal bearing  223  includes a first axial end  224 A, a second axial end  224 C, and a central region  224 B situated between the first axial end  224 A and the second axial end  224 C (as more fully illustrated and shown in  FIG. 2 ). Upper radial gap  304  and central radial gap  306  are defined by the journal bearing  223  between the shaft  220  and the sleeve  230 . Upper radial gap  304  is defined at first axial end  224 A, and central radial gap  306  is defined at central region  224 B of the journal bearing  223 . In another embodiment, central radial gap  306  is defined at central region  224 B and further defined at second axial end  224 C. Upper radial gap  304  is structured with a larger radial gap as compared with central radial gap  306 . In an embodiment, upper radial gap  304  is established with a radial gap in the range of 10 microns to 20 microns, and central radial gap  306  is established with a radial gap in the range of 1 micron to 6 microns. In a particular embodiment, upper radial gap  304  has a 15 micron radial gap, and central radial gap  306  has a 3 micron radial gap. 
         [0022]    A fluid reservoir  310  is also situated between the shaft  220  and the sleeve  230 , and is in fluid communication with the journal bearing  223 . The first axial end  224 A of the journal bearing  223  is situated between the fluid reservoir  310  and the central region  224 B of the journal bearing  223 . Fluid reservoir  310  is structured with a larger radial gap as compared to central radial gap  306 . In an embodiment, fluid reservoir  310  has a tapered radial gap that is radially larger than upper radial gap  304 . Alternatively, fluid reservoir  310  is structured with a radial gap equivalent to upper radial gap  304 . 
         [0023]    In a further embodiment, a fluid recirculation passageway  320  is formed through the sleeve  230  to recirculate fluid through journal bearing  223 , and to facilitate purging air from journal bearing  223  via fluid reservoir  310 . Fluid recirculation passageway  320  includes axially extending portion  320 A and radially extending portion  320 B. Radially extending portion  320   l  fluidly connects to journal bearing  223  between first axial end  224 A, and central region  224 B of the journal bearing  223 . The arrows show an example direction of fluid flow through the fluid recirculation passageway  320  and the fluid dynamic bearing  223 . Alternatively, fluid may be caused to flow in the opposite direction. Alternative embodiments of fluid recirculation passageway  320  are described in  FIGS. 4A and 4B . 
         [0024]    The invention utilizes and makes use of the properties of a grooved pumping seal and a centrifugal capillary seal to contain fluid with the fluid dynamic bearing motor, in an embodiment. The first axial end  224 A of the journal bearing  223  includes a grooved pumping surface  330 A having a grooved pumping seal zone  312 . A grooved pumping surface may alternatively be formed on the surface of the shaft  220 , rather than on the sleeve  230 . When fluid is situated within pump seal zone  312 , grooved pumping surface  330 A creates a grooved pumping seal (a high stiffness seal) that pumps fluid toward central region  224 B, serving to contain fluid with the fluid dynamic bearing motor. 
         [0025]    In yet a further embodiment, the first axial end  224 A includes a smooth surface  330 B having a centrifugal capillary seal zone  314 . A smooth surface is formed on both the shaft  220  and the sleeve  230  between the grooved pump seal surface  330 A and the radially extending portion  320 B of the recirculation passageway  320 . The radial gap at the centrifugal capillary seal zone  314  is a larger radial gap as compared with the radial gap at the central region  224 B of the journal bearing  223 . A centrifugal capillary seal, defined between shaft  220  and sleeve  230 , contained on an end by seal meniscus at the centrifugal capillary seal zone  314 , is utilized for containing fluid within the fluid dynamic bearing motor. Fluid within the centrifugal capillary seal zone  314  is forced toward recirculation zone  316  by centrifugal force when shaft  220  and sleeve  230  are in relative rotational motion. Alternatively, a centrifugal capillary seal is defined between shaft  220  and sleeve  230  within fluid reservoir  310 , for containing fluid within the fluid dynamic bearing motor. 
         [0026]    Further, one of shaft  220  and sleeve  230  includes sections of pressure generating grooves facing the fluid dynamic bearing  223  at the central region  224 B, including asymmetric and symmetric grooves, in an embodiment. The groove pattern can include a herringbone pattern or a sinusoidal pattern. These grooves induce fluid flow in the interfacial region of the journal bearing  223  and generate a localized region of dynamic high pressure and radial stiffness. As sleeve  230  rotates, pressure is built up in each of its grooved regions. In this way, shaft  220  easily supports hub  232  for constant high speed rotation. 
         [0027]      FIG. 4A  is a sectional side view of a portion of a fluid dynamic bearing spindle motor, illustrating a fluid recirculation passageway, in accordance with an embodiment of the present invention. A radially extending portion  320 B of the fluid recirculation passageway connects with the journal bearing between a first axial end  224 A of the journal bearing and a central region  224 B of the journal bearing. A lower portion of the axially extending portion  320 A of the fluid recirculation passageway connects with a second axial end  224 C of the journal bearing via thrust bearing  226 . The thrust bearing  226  is defined between sleeve  230  and baseplate  234 . 
         [0028]      FIG. 4B  shows another sectional side view of a portion of a fluid dynamic bearing spindle motor, illustrating a fluid recirculation passageway, in accordance with another embodiment of the present invention. In this embodiment the axially extending portion  320 A of the fluid recirculation passageway connects to a radially extending portion  420 . The radially extending portion  420  of the fluid recirculation passageway connects with the central region  224 B of the journal bearing  223 . 
         [0029]    Modifications and variations may be made to the disclosed embodiments while remaining within the spirit and scope of the invention. The implementations described above and other implementations are within the scope of the following claims.