Abstract:
In one embodiment, a plurality of axially oriented bearings defined along gaps between rotor and stator are provided to provide radial stiffness to the system; and these bearings are coupled together by radially oriented gaps. Grooves and/or magnets may be defined in order to maintain the stability and relative spacing of the gaps, while allowing free relative rotation of parts of the system with minimum power loss. A central conical bearing may be provided, having a fluid dynamic bearing around its conical surface, and being connected to an axially parallel but radially displaced axially oriented journal style bearing. The combined effects of these bearings is sufficient to maintain or even enhance the overall stability of the system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This invention is based on U.S. provisional patent application Ser. No. 60/351,641, filed Jan. 23, 2002, by Gunter K. Heine and Mohamed Mizanur Rahman and on U.S. provisional patent application Ser. No. 60/351,642, filed Jan. 23, 2002 by Gunter K. Heine and Mohamed Mizanur Rahman. The priority of these applications is claimed and the applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of fluid dynamic bearings, and more specifically to a design incorporating multiple fluid dynamic bearings to provide enhanced balance and rotational stability in the system. 
     BACKGROUND OF THE INVENTION 
     Disc drives are capable of storing large amounts of digital data in a relatively small area. A disc drive stores information on one or more spinning recording media. The recording media conventionally takes the form of a circular storage disk with a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across a surface of the disk by an actuator mechanism. 
     Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft supported from a base plate, and a hub to which the spindle is attached having a sleeve into which the shaft is inserted. Permanent magnets, which are typically attached to the hub, interact with a stator winding to rotate the hub relative to the shaft. This description is consistent with a fixed shaft motor; however, the invention to be described below is as easily useable with a motor comprising a rotating shaft, an end of the shaft supporting the hub for rotation to support the rotation of the disks. 
     In either case, to facilitate rotation and for best drive performances, one or more bearings are disposed between the hub or sleeve and the shaft. 
     Over time, disk drive storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has led to greater emphasis on restrictive tolerances in the manufacturing and operation of magnetic storage disk drives. For example, to achieve increased storage density, read/write heads must be placed increasingly close to the surface of the storage disk. 
     As a result, the bearing assembly which supports the storage disk is of critical importance. A typical bearing assembly of the prior art comprises ball bearings supported between a pair of bearing races which allow a hub of a storage disk to rotate relative to a fixed member. However, ball bearing assemblies have many mechanical problems such as wear, run-out and manufacturing difficulties. Moreover, resistance to operating shock and vibration is poor because of insufficient damping. 
     An important measure of the operating effectiveness of a fluid dynamic bearing motor is the stiffness to power ratio, where stiffness gives the ability of the system to perform better dynamically, and power is a measure of power consumed to start rotation and maintain the constant speed and rotation of the motor. Most known fluid dynamic bearings today in commercial use are made with oil as the fluid which is maintained in the bearing gap between the two relatively rotating surfaces. This maintains the proper stiffness and damping of the bearing which reduce non-repeatable run-out due to shock and vibration; however, because of the relatively high viscosity of such fluids, especially at lower temperatures such as at startup, considerable power is consumed to establish and maintain high speed rotation. 
     Finally, to maintain the required axial and radial stiffness and damping of the bearing, some minimum length of a journal and width or diameter of a cone or surface area of a cone or width or diameter of a thrust plate must be devoted to grooved surface, against which pressure can come to bear to maintain the stiffness and damping of the system. Therefore, typically known bearing systems have had a plurality of fluid dynamic bearings in series. For example, known systems include two conical bearings spaced along a shaft in cooperating to provide both axial and radial stiffness and damping; or a shaft with a thrust plate, with the journal bearings on the shaft and the thrust bearings on the thrust plate being arrayed in series to operatively cooperate and maintain the stiffness and damping of the system. However, all of this leads to fairly high profile designs to accommodate these serially arrayed bearings; the smaller disk drives which are the designed target for use in portable computers and the like cannot accommodate high profile drives. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide a bearing design in which stiffness and damping is maintained, but a lower power is achieved. 
     It is a further objective of the invention to provide a design in which wider bearing gaps may be used because the overall length of the bearing system is enhanced, without adding to the overall height of the system and machining capability and bearing performances are not hurt by bigger gap tolerances. 
     These and other objectives and advantages of the present invention are achieved by providing plural fluid dynamic bearings arrayed in parallel with one another and typically connected to one another along a common gap. In one embodiment, a plurality of axially oriented bearings defined along gaps between rotor and stator are provided to provide radial stiffness to the system; and these bearings are coupled together by radially oriented gaps. Grooves and/or magnets may be defined in order to maintain the stability and relative spacing of the gaps, while allowing free relative rotation of parts of the system with minimum power loss. 
     In a further alternative, a central conical bearing may be provided, having a fluid dynamic bearing around its conical surface, and being connected to an axially parallel but radially displaced axially oriented journal style bearing. The combined effects of these bearings is sufficient to maintain or even enhance the overall stability of the system. 
     In alternative embodiments, a plurality of generally axial, angularly oriented journal bearings may be provided, grooves on the facing surfaces of the gaps maintaining pressurization of the fluid to maintain the spacing and stiffness of the system. These axial or angularly oriented gaps are connected by generally radial connecting gaps; magnets or the like may be located adjacent these radial gaps to maintain the spacing of the gap and the relative orientation of the parts supporting the sides of the fluid bearings. 
     In an alternative approach or an approach in combination with these magnets along bearing gaps, the motor stator may be displaced relative to the motor magnet to establish either an axial or radial bias which would operate to maintain the spacing across the gaps within the fluid bearing system. 
     Other features and advantages of the invention will become apparent to a person of skill in the art who studies the following description of some exemplarian embodiments given with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. 
       It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a perspective view of a disk drive in which the bearing system of the present invention is especially useful. 
         FIG. 2  is a plan sectional view of a known bearing system as used in the prior art. 
         FIGS. 3 ,  4 ,  5 ,  6  and  7  are schematic views of various embodiments of the invention, each including fluid dynamic bearings in parallel. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates an example of a magnetic disk drive in which the invention may be employed. At least one magnetic disk  60  having a plurality of concentric tracks for recording information is mounted on a spindle  10 . The spindle is mounted on spindle support shaft  25  for rotation about a central axis. As the disks are rotated by the motor, a transducer  64  mounted on the end of an actuator end  65  is selectively positioned by a voice coil motor  66  rotating about a pivot axis  67  to move the transducer  64  from track to track across the surface of the disk  60 . The elements of the disk drive are mounted on base  40  in a housing  70  that is typically sealed to prevent contamination (a top or cover of housing  70  is not shown). The disks  60  are mounted on spindle  10 . 
       FIG. 2  illustrates a portion of a fluid dynamic bearing motor  100  that may be adapted to benefit from embodiments of the present invention. The motor  100  includes a shaft  52  that rotates within a stationary sleeve  70 . The rotating shaft  52  includes a reservoir  54  that supplies fluid through a groove  56  to the surface of a fluid dynamic bearing. The fluid dynamic bearing itself is formed between the outer surface  60  of the shaft  52  and the inner surface  72  of the sleeve  70 , which rotate relatively. The upper journal bearing surface  94  of the bearing terminates in a region generally indicated at  80  where the incline surface  82  slopes away from the recess  84  in the surface  60  to form a meniscus that will hold the fluid within the bearing. The upper journal surface  94  is separated from the lower journal bearing surface  96  by a bore  98  in the shaft  52  that feeds a fluid reservoir  99  defined within the shaft  52 . The lower journal bearing surface  96  of the bearing terminates at a region generally indicated at  90  where the rotating shaft meets a thrust plate  74 , the surface  60  including a recess  76  for enabling the joining of the thrust plate  74  to the rotating shaft  52 . The thrust plate  74  includes a surface  91  facing surface  92  across a gap to form a thrust bearing. Referring next to  FIGS. 3 ,  4  and  5 , these figures illustrate schematic examples of exemplary embodiments of the fluid dynamic bearings of the present invention. These include plural bearings in parallel, to minimize the height which must be provided to allow for effective bearing length to maintain the required stiffness and damping whereby the stability of the system in all dimensions. 
     Referring to  FIG. 3 , it can be seen that as compared to the prior art where two bearings are provided in series, in this embodiment two axial journal bearings  310 ,  320  defined along parallel gaps  312 ,  322  are provided. The necessary pressures to support rotation are established by grooves  324 ,  326  on one of the defining surfaces of the gap. The base  330  supports the stator windings  332  adjacent magnet  334 ; activation of the windings causes rotation of the hub  340 . This hub  340  can support one or more disks  342  for constant speed rotation under the urging of electrical signals supplied to the stator windings  332 . 
     In order to maintain the hub  340  seated on the stator  330  and the gap properly aligned, either magnet pair  325 ,  327  or magnet pair  329 ,  331  may be provided on either side of the gaps which couple the axial fluid bearings  320 ,  310 . These magnets would face each other across a fluid or gas filled gap  350 ,  354  so that the hub  340  and stator  330  would remain properly axially spaced and coupled together. The magnets could be sized to maintain the size of the gap, which could be filled with a fluid or gas to support relative rotation of the two elements. In operation, relative rotation of the grooved regions ( 370  or  371 ) that form fluid dynamic bearings creates axial forces of a thrust bearing to support relative rotation of stator and rotor; to prevent the gap at the fluid bearing from becoming too large, axially aligned magnets are provided facing each other across the same gap, and creating a force which is axially opposed to the axial force of the fluid bearing. 
     In the embodiment of  FIG. 3 , the magnets, either magnetic pair  325 ,  327 , or magnet pair  329 ,  331  are provided on either side of an axial gap. If the magnets  325 ,  327  are provided they are generally annular in shape, having a central axis which is in common with the center axis of the entire system. In either case, the magnets are sized and positioned to provide an attractive force across the gap where they are located; the fluid bearing gap of the journal and thrust bearings, to maintain the gap spacing. Two different arrangements are possible with the design of  FIG. 3 . If the magnet pair  329 ,  331  is provided at the central axis of the gap, then the grooves  370  would be provided in the distant (annular) gap section  370 . Under non-spinning conditions, the groove surfaces at the gap section  370  would be in contact with each other, but not the magnetic surfaces, that is the axial gap surfaces where the magnets  329 ,  331  are located. Under spinning conditions, the groove surfaces at section  370  would spin up out of contact and establish a gap which could be optimized for performance of the system, with the magnets  329 ,  331  being attractive magnets limiting the size of the groove bearing gap by their attractive force. 
     The opposite condition is also possible. The magnets  325 ,  327  are provided attractive to each other across the annular axial annular gap  350  and the grooves  371  are provided at the centerline gap. The groove surfaces of gap  371  rest upon each other in the rest condition, but the magnet surfaces do not, as it would become too difficult to spin up the system. When the system spins up, then the gap at grooves  371  would be established, with an axial extent limited by the attractive force of magnets  325 ,  327 . 
     It should be noted that the magnet  334  which is a part of the motor could be offset from the stator  332  to either supplement or diminish this magnetic attractive force in order to further find tune the size of the gap. 
     In similar fashion, as shown in  FIG. 4 , generally axial but angular gaps  410 ,  420  could be defined connected by radial gaps  412 ,  422 . As in the previous example, the stator  430  supports the hub  440  for rotation by virtue of the grooved fluid dynamic bearings  410 ,  420 . The angular nature of the gaps provides both axial and radial support for the system. The hub and stator are kept together in proper axial alignment and the fluid bearing gaps kept in proper spacing by the provision of magnets  432 ,  442  facing each other across the radial gap  412 , and/or magnets  444 ,  446  located at or near the center line of the system. As in the previous design, air or fluid may be provided in this gap to maintain the separation of these parts to provide for non-frictional relative rotation; and in this embodiment it is further shown that the grooves that define the bearings  410 ,  420  may be axially offset from one another. As with the previous embodiment, the rotation of the hub  440  relative to the stator  430  is achieved by the interaction of magnet  460  and stator windings  462  which are energized in a known fashion. As will be explained below with reference to  FIG. 5 , the axial and/or radial alignment of the hub  440  and stator  430  can also be achieved and/or maintained, in whole or in part, by an offset of the magnetic interaction between the stator  462  and its associated magnet  460 . 
     The axial forces generated in the bearing gaps  410  and  420  are used to support in part separation of the system&#39;s rotor  440  from stator  430  and thereby the reliable operation of the system. Therefore, considering the possibilities, in one approach the magnets  444 ,  446  would be provided across gap  422 , and grooves would be provided in gap  412 . Under this condition the magnets  444 ,  446  would provide an attractive force across the gap; this force would operate in opposition to the force generated by the grooves at gap  412 , restraining excessive separation across that gap. 
     Alternatively, the magnets  442 ,  432  could be provided, with grooving in the gap  414 . In this case, the magnets also would be attractive, and the grooved surfaces  414  would operate to create an axial separating force which would be counter-balanced by the magnetic attraction force. In each case, the magnetic axial attraction balances the axial forces generated by the grooved bearing. In each of these cases, the magnetic attraction force from the magnets located at the gap could be supplemented or diminished by an offset between the magnet  460  and stator  462  of the rotational propulsion motor. 
     Also because of the presence of grooves in the gaps  410 ,  420  which are angled with respect to the vertical axis, these grooves will create an axially directed force under rotational conditions. Therefore, since under rotating conditions these grooves will be active in creating an axial force which would cause the hub/rotor  440  to separate from the base  430 , then several alternatives are possible with respect to the magnet placement without further grooving in the gap regions  412 ,  414  being required. Either magnets  442  and  432  could be provided; or magnets  444  and  446  could be provided to generate an attractive force; or both sets of magnets could be provided. In all instances, because of the axial force being generated in gaps  410 ,  420 , no grooving is required in the gaps  412 ,  414 . Again, the magnetic force of these magnets can be modulated by an offset of magnet  460  relative to stator  452 . 
       FIG. 5  illustrates a further alternative of the present invention in schematic format. In this alternative, the angular dynamic bearing  510  is defined by an internal cone  520  which supports the hub  524  on an end thereof. The surface  526  of the cone  526  defines with an interior surface of the sleeve or stator  530  a conical bearing  542  capable of generating both radial and axial forces. An exterior surface  532  of the sleeve cooperates with an interior surface  534  of the hub to define a radial bearing gap  538 . This bearing gap  538  has grooves on at least one wall surface thereof, defining a journal bearing. The combination of this bearing and the conical bearing  510  which is established by grooves  542  provides both radial and axial stability to the system. However, to further enhance the stability of the system it may be desirable to provide annular magnets  550  on the axially upper and lower surfaces of the radial gap  554  to maintain the gap and maintain the stability of the rotor  524  relative to the stator  530 . 
     The conical bearing  542  generates both axial and radial forces in rotation. Therefore, the axial component of these fluid bearing forces would typically generate forces in opposition to the attractive force of the magnets. In this embodiment, the magnets at  550 ,  551  which are annular about the central axis  501  of the design are in opposition so that when the system is at rest the magnetic surfaces do not rest upon each other. When the system rotates, the conical bearing surface moves away from sleeve  530 , closing down the gap of the bearing  542 . In rotation, as the conical bearing  526  rotates, axial forces are generated in the direction of arrow  560 , the axial force acting in opposition to the repulsive force of the magnets  550 ,  551  to properly set the conical bearing gap for optimum operation while the facing surfaces which carry the magnets  550 ,  551  remain separated. 
     Of course, magnets  550 ,  554  could be eliminated. As alternatives, grooves  521  could be in the same gap, creating pressure against arrow  560 ; or the bias from magnet  564  could be used. 
     It should be noted that the bearings in all of the figures could be multi-fluid bearings. In each case, either the inner bearings could be liquid with the outer bearing being air; or both could be liquid, with different liquids being possible, separated by capillary seals or other seals effective in such operation, or both bearings could be air. 
     This stability and positioning is further enhanced by a modification of the active sections of the motor generally indicated at  560  as comprising stator laminations and windings  562  and associated magnet  564 . In a first embodiment on the left side of the figure, the windings  562  are offset from the magnet  564  to establish a force as indicated by the vector  566  which relatively positions the hub and the stator in the axial direction. In an alternative approach, the stator is repositioned or rotated 90° relative to the hub so that now the stator  570  and its laminations and windings lies primarily in the radial place and is now associated with a magnet  572  and axial surface  574  of hub  524 . By adopting this orientation, forces may be established as indicated by the vectors  576 ,  578  to position the hub relative to the stator in both the axial and radial directions. 
     In all of these embodiments, fluid is typically found in the gaps indicated by the grooves which are shown in each of the figures; as is known in this technology, capillary seals would be found at either end of these fluid sections. In this way, different liquids could be used in different bearing sections along the same gaps or liquid could be the fluid in an inner bearing, with air in an outer bearing; or air could be used in all bearings. 
     Other alternatives are also available. For example, where the outer bearing is an axial journal bearing such as bearing  320  in  FIG. 1  then this can have a larger gap than the inner bearings. 
     Also, in all the above embodiments, the outer bearing can be established with a net pumping pressure toward the inner bearing. For example, in  FIG. 4 , the bearing  410  may have a net pumping effect toward bearings  412 ,  420 ,  422 . This bearing thereby actgs as a seal for the inner bearings. This effect also reduces the lubricant evaporation and increases the load carrying capacity of the inner bearing. For example in  FIG. 4 , as bearing  410  pumps inward into the bearing system, increasing the pressure in bearings generating axial force such as bearings  412 ,  414 . 
     Further, alternative embodiments appear in  FIGS. 6 and 7 . In these two axial sections  610 ,  620  or  710 ,  720  are provided in parallel along a common gap,  630 ,  730  and plural journal bearings  640 ,  650  or  740 ,  750  are provided along the same gap which rather than being parallel include one axial journal bearing  650 ,  750  and one bearing  660 ,  760  at a shallow angle to the axis. 
     As in the other embodiments, grooves are provided in one of the axial sections. The other typically has attracting magnets on either axial side to control gap width in operation. However, these magnets may be omitted, or supplemented, by magnetic bias created by offsetting magnet  682  from stator  782 . 
     Further, some physical restraint such as a shoulder, retaining clip ring or the like is typically incorporated in all the above designs to prevent axial separation under shock or other circumstance. 
     While foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.