Abstract:
The present invention relates to the field of fluid dynamic bearings. Specifically, the present invention provides a secondary fluid reservoir for the fluid used in a fluid dynamic bearing in a high-speed spindle motor assembly.

Description:
CROSS REFERENCE TO A RELATED APPLICATION 
     This application claims priority to provisional application Serial No. 60/390,388, filed Jun. 21, 2002, entitled “FDB Secondary Capillary Seal Reservoir” invented by Robert A. Nottingham, Norbert S. Parsoneault, Jeffrey A. LeBlanc, and Troy M. Herndon, assigned to the assignee of the present application, and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of computer disk drives, specifically, those having fluid dynamic bearings. 
     BACKGROUND OF THE INVENTION 
     Disk drive memory systems have been used in computers for many years for the storage of digital information. Information is recorded on concentric tracks of a magnetic disk medium, the actual information being stored in the forward magnetic transitions within the medium. The disks themselves are rotatably mounted on a spindle. Information is accessed by a read/write transducer located on a pivoting arm that moves radially over the surface of the rotating disk. The read/write heads or transducers must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information. 
     During operation, the disks are rotated at very high speeds within an enclosed housing using an electric motor generally located inside a hub or below the disks. Such spindle motors may have a spindle mounted by two ball bearing systems to a motor shaft disposed in the center of the hub. The bearing systems are spaced apart, with one located near the top of the spindle and the other spaced a distance away. These bearings allow support of the spindle or hub about the shaft, and allow for a stable rotational relative movement between the shaft and the spindle or hub while maintaining accurate alignment of the spindle and shaft. The bearings themselves are normally lubricated by highly refined grease or oil. 
     The conventional ball bearing system described above is prone to several shortcomings. First is the problem of vibration generated by the balls rolling on the bearing raceways. This is one of the conditions that generally guarantees physical contact between raceways and balls, in spite of the lubrication provided by the bearing oil or grease. Bearing balls running on the microscopically uneven and rough raceways transmit the vibration induced by the rough surface structure to the rotating disk. Such vibration results in misalignment between the data tracks and the read/write transducer, limiting the data track density and the overall performance of the disk drive system. Further, mechanical bearings are not always scalable to smaller dimensions. This is a significant drawback, since the tendency in the disk drive industry has been to shrink the physical dimensions of the disk drive unit. 
     As an alternative to conventional ball bearing spindle systems, much effort has been focused on developing a fluid dynamic bearing (FDB). In these types of systems, lubricating fluid, either gas or liquid, functions as the actual bearing surface between a shaft and a sleeve or hub. Liquid lubricants comprising oil, more complex fluids, or other lubricants have been utilized in such fluid dynamic bearings. 
     The reason for the popularity of the use of such fluids is the elimination of the vibrations caused by mechanical contact in a ball bearing system and the ability to scale the fluid dynamic bearing to smaller and smaller sizes. In designs such as the single plate FDB, two thrust surfaces generally are used to maintain the axial position of the spindle/shaft assembly in relation to other components such as the sleeve. 
     Clearly, it is essential to maintain the volume, position and integrity of the fluid in a fluid dynamic bearing system. Accordingly, there have been improvements to almost every component of such systems, including the addition of seals, various designs for bearing shapes, specific fluids to be used, and the like. 
     Thus, there is an interest in the art to assure the volume, position and integrity of fluid in a fluid dynamic bearing system. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to provide a fluid reservoir to maintain the volume and integrity of the fluid in a fluid dynamic bearing assembly. This and other objectives and advantages are achieved by providing a secondary reservoir in a fluid dynamic bearing design between a bearing and an adjacent component such as a bearing sleeve or seal member. 
     Specifically, the present invention provides an annular bearing cone for a fluid dynamic bearing in a disk drive comprising: a bottom, a top and a middle; a central annular opening; upper walls angling out from the top to the middle; lower walls angling out from the bottom to the middle to meet the upper walls; and axial grooves in the upper walls of the annular bearing cone. The annular cone may also have at least one recirculation hole in communication with the central annular opening where there are axial grooves on the walls of the central annular opening between the recirculation hole and the top of the bearing cone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference is made to the accompanying drawings in the following detailed description. 
     FIG. 1 illustrates an example of a magnetic disk drive in which the invention may be employed; 
     FIG. 2 is a vertical sectional view of a fluid dynamic bearing cartridge; 
     FIG. 3 is an exploded view of the fluid dynamic bearing cartridge of FIG. 2; and 
     FIG. 4 is a cross-sectional view of the reservoir system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it is to be understood that the described embodiments are not intended to limit the invention solely and specifically to only those embodiments, or to use solely in the disk drive which is illustrated. On the contrary, the invention is intended to cover alternatives, modifications and equivalents that may be included within the spirit and scope of the invention as defined by the attached claims. Further, both hard disk drives and spindle motors are both well known to those of skill in this field. In order to avoid confusion while enabling those skilled in the art to practice the claimed invention, this specification omits such details with respect to known items. The embodiments of the present invention are intended to maintain the volume and integrity of a fluid in a fluid dynamic bearing system. 
     FIG. 1 illustrates an example of a magnetic disk drive in which the invention may be employed. At least one magnetic disk  5  having a plurality of concentric tracks for recording information is mounted on a spindle  7 . The spindle is mounted on spindle support shaft  6  for rotation about a central axis. As the disks are rotated by the motor, a transducer  8  mounted on the end of an actuator end  4  is selectively positioned by a voice coil motor  2  rotating about a pivot axis  3  to move the transducer  8  from track to track across the surface of the disk  5 . The elements of the disk drive are mounted on base  1  in a housing  9  that is typically sealed to prevent contamination (a top or cover of housing  9  is not shown). The disks  5  are mounted on spindle  7 . 
     FIGS. 2 and 3 show an exemplary design of a bearing cartridge  26  that may be part of the spindle identified in FIG.  1 . Bearing cartridge  26  supports a spindle hub assembly  27 , which is comprised of a back iron  28  and a cover  29 . Bearing cartridge  26  includes a central spindle shaft  30  may be press fit within a bottom mounting flange  31  which is threadably secured to base  12 . Bearing cartridge  26  also includes an upper bearing sleeve  32  and a lower bearing sleeve  33 . Both upper bearing sleeve  32  and lower bearing sleeve  33  include conical bearing surfaces  34 . Bearing surfaces  34  engage a pair of bearing cones  35  and  36 . 
     Bearing cartridge  26  also includes upper and lower seal cones  37  and  38 , seal O-rings  39  and  40 , and shield seals  41  and  42 . Seal cones  37  and  38  are press fit onto spindle shaft  30  and shield seals  41  and  42  are press fit onto bearing sleeves  32  and  33 . The spindle motor includes stator windings  43  which are secured about spindle shaft  30  by means of a clip  44  and magnets  45 , which are secured to back iron  28 . 
     An electric connector assembly  47  is mounted within the lower end of spindle shaft  30  and includes electrical leads that are connected to the electrical windings of the motor. Connector assembly  47  also includes connector pins  48 , which provide for reception for connector from an electrical power source. 
     FIG. 4 shows an embodiment of a reservoir system of the present invention. FIG. 4 shows a shaft  500 , a shield seal member  502 , a bearing sleeve  504 , a bearing cone  506 , and a fill hole  520  in shield seal member  502 . 
     A fluid reservoir A is shown at  510 . Reservoir A provides fluid between bearing cone  506  and shield seal member  502 , and bearing cone  506  and bearing sleeve  504 . A second reservoir, reservoir B, is shown at  514  and is connected to reservoir A  510  by passage  512 , which creates a capillary path between reservoir A  510  and reservoir B  514 . In one embodiment, there may be an axial groove or grooves  513  down the side of bearing cone  506 . Axial groove  513 , if present, can be longitudinal notches or scratches along the cone  506  in passage  512  from reservoir A  510  to reservoir B  514 . Such longitudinal scratches or grooves  513  enhance the ability of the passage  512  to provide a capillary path to facilitate the flow of fluid between the reservoirs. 
     Fluid can be added to the system through fill hole  520 . When fluid is added to the system both reservoirs A and B fill with fluid. Initially the gap of reservoir B  514  between annular seal member  522  and bearing cone  506  is tighter than the gap for reservoir A between bearing cone  506  and shield seal member  502 . The capillary action is such that fluid is first drawn in to reservoir B  514 . 
     However, should reservoir A  510  get depleted and reservoir B  514  be filled, the gap between bearing cone  506  and shield seal member  502  for reservoir A  510  will be smaller than the gap for reservoir B  514  between annular shield member  522  and bearing cone  506  (i.e., the meniscus width of reservoir A becomes smaller than the meniscus width of reservoir B). Capillary action will now act such that fluid will travel from reservoir B to reservoir A via passage  512 . The gap and meniscus size for reservoir A for  510  and reservoir B  514  are variable depending on the fill level of each reservoir. If the levels of reservoirs A and B are full and stay full, there will be no net movement of fluid from reservoir B to A or from A to B. If the meniscus width of reservoir A becomes smaller than that of B, there will be net movement of fluid from reservoir B to reservoir A. 
     Note that the embodiment of FIG. 4 shows a shield seal member  502  abutting sleeve  504  adjacent bearing cone  506  to form reservoir A, and an annular seal  522  adjacent bearing cone  506  to form reservoir B. An alternative embodiment to this embodiment might simply be to configure the bearing sleeve in such a way to serve the purpose of all three elements; that is, the bearing sleeve, the shield seal member and the annular seal, or two out of three of these elements. Essentially, one skilled in the art should note that the present invention requires merely a structure adjacent bearing cone  506  to form reservoirs A and B and passage  512 ; and the present invention should not be limited to a particular structure or set of structures. 
     Another aspect of the present invention is shown in FIG. 4. A cross-section of a recirculation hole  518  is shown. Recirculation hole  518  is a structural element of an exemplary fluid redistribution system of a fluid dynamic bearing. Such recirculation holes are common in fluid dynamic bearing systems to assure that the distribution of fluid throughout the system is even. In this case, reservoir B  514  is connected to recirculation hole  518  by passage  516 . Passage  516  may also have axial grooves thereon similar to axial grooves  513  on the outside of bearing cone  506 . Passage  516  provides a capillary path from recirculation hole  518  to reservoir B. Capillary passage  516  can be used in addition to, or as an alternative to, the passage  512  between reservoir A  510  and reservoir B  514 . Thus, passage  516  between reservoir B  514  and recirculation hole  518  could be used to remove fluid from reservoir B instead of using passage  512  and the optional axial groove  513  for transfer of fluid from reservoir B  514  to reservoir A  510 . 
     Other features and advantages of the invention will become apparent to a person of skill in the art who studies the following disclosure of preferred embodiments.