Abstract:
A disk storage device that utilizes an inner rotor spindle motor in which the spindle shaft is fixed to the disk mounting hub and rotates therewith. Support for the spindle is provided by a bearing tube that has a greater diameter and greater rigidity than the stationary shaft or post typically employed to support the disk stack in an outer rotor arrangement. The bearing tube supports the bearings in which the spindle shaft is journalled and allows wider axial spacing between the bearings, reducing spindle run out. At the same time, the bearing tube functions to entrap contaminants from the bearings within the internal motor space and reduces contamination in the clean chamber. By configuring the inner rotor, including the disk support hub, to rotate around the outer diameter of the bearing tube, an elongated “gap seal” is formed, allowing more efficient containment of contaminants from the bearings without need for expensive ferrofluicdic seals. One end of the bearing tube extends into an internal cavity formed within the disk support hub. This arrangement requires the hub to have a hollow interior, providing for a rotor structure having further reduced mass, further improving acceleration and vibration characteristics of the spindle.

Description:
This is a continuation of application Ser. No. 08/834,701, filed Apr. 1, 1997, now U.S. Pat. No. 5,877,916. 
    
    
     This invention relates to disk storage devices and, more particularly, to a disk storage device having a spindle motor with enhanced torque, acceleration and vibration characteristics. 
     BACKGROUND OF THE INVENTION 
     Disk storage devices, especially disk storage devices utilizing one or more rigid magnetic data storage disks directly coupled to the rotor of a spindle drive motor and housed within a “clean room” chamber, typically use an “outer rotor” brushless DC motor for rotating the storage disks past data read/write heads. The heads write and read digital data on the surface of the disks. in an “outer rotor” brushless motor, a rotor having an annular permanent magnet surrounds a multi-pole stator that is mounted concentric with the shaft defining the rotation axis of the motor. 
     An outer rotor motor employs a rotor that encompasses the stator element. The rotor therefore requires a diameter that adds to the mass and angular inertia of the rotor and increases the time required for the motor to reach the operating speed, which may be 6000 RPM or higher, at the time of startup. The radially displaced mass also amplifies vibrations due to imbalances, especially at higher operational speeds. 
     It is an object of the invention to provide a disk storage device that utilizes a spindle drive motor that has a reduced rotary mass and angular inertia and accordingly reduces the time required to accelerate the storage disks to operating speed at the time of startup. 
     It is another object to provide a disk storage device that utilizes a spindle motor that is not limited by the diameter of the disk support hub in providing sufficient torque to rapidly accelerate a stack of many disks at the time of startup. 
     It is a further object to provide a disk storage device that has an increased diameter spindle support structure to enhance the rigidity of the disk axis. 
     Still a further object is to provide a disk storage device that reduces the amount of spindle run out caused by play in the support bearings. 
     Another object is to provide a disk storage device that achieves an enhanced air gap seal between the clean chamber in which the disks operate and the spindle motor elements. 
     Yet another object is to provide a disk storage device that reduces radially-displaced spindle mass and is capable of operation at higher speeds with lower vibration. 
     SUMMARY OF THE INVENTION 
     The foregoing and other objects are achieved by providing a disk storage device that utilizes an inner rotor spindle motor in which the spindle shaft is fixed to the disk mounting rub and rotates therewith. Support for the spindle is provided by a bearing tube that has a greater diameter and greater rigidity than the stationary shaft or post typically employed to support the disk stack in an outer rotor arrangement. The bearing tube supports the bearings in which the spindle shaft is journalled and allows wider axial spacing between the bearings, reducing spindle run out. At the same time, the bearing tube functions to entrap contaminants from the bearings within the internal motor space and reduces contamination in the clean chamber. 
     By configuring the inner rotor, including the disk support hub, to rotate around the outer diameter of the bearing tube, an elongated “gap seal” is formed, allowing more efficient containment of contaminants from the bearings without need for expensive ferrofluidic seals. One end of the bearing tube extends into an internal cavity formed within the disk support hub. This arrangement requires the hub to have a hollow interior, providing for a rotor structure having further reduced mass, further improving acceleration and vibration characteristics of the spindle. 
     These and other objects, features and advantages of the invention are illustrated in the following description of preferred embodiments, as illustrated in the drawings as follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section taken along the spindle axis of a disk storage device employing a first embodiment of the invention. 
     FIGS. 2,  3 ,  4 , and  5  are cross-sections taken along the spindle axis, each illustrating a modified form of the spindle motor. 
     FIGS. 6 and 7 are partial cross-section of the preceding embodiments, showing machining details for relevant portions of the lower housing wall, hub, and bearing tube. 
     FIG. 8 is a cross-section taken along the spindle axis of a disk storage device employing a still further embodiment of the invention. 
     FIG. 9 is a cross-section taken along line  9 — 9  of FIG. 8 perpendicular to the spindle axis, showing how the stator lamination and windings interact with the magnet ring of the rotor. 
     FIG. 10 is a cross-section taken along the spindle axis showing another modified form of the spindle motor. 
     FIG. 11 is a similar view illustrating yet another embodiment of the spindle motor. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, the disk storage device, which may be, for example, a magnetic hard disk drive (HDD), includes a housing having an upper partition or wall  10  and a lower partition or wall  12  which adjoin side walls (not shown) to enclose a substantially sealed “clean room chamber” CR. Clean room chamber CR is a finally sealed clean room manufactured to HDD industry contamination standards. One or more data storage disks  30  are located within the clean room chamber and cooperate with read/write heads  32 . During operation the heads “fly” on a thin layer of air proximate to the surface of the rotating disks and function as transducers for magnetically reading and recording (writing) digital data in tracks on the surfaces of the disks. 
     The disks  30  are rotated at an operating speed that may be in the range of 3,000 to 10,000 RPM. The disks are mounted on a hub  22  that is part of a rotor assembly  20  of a brushless DC spindle motor. The drive elements of the spindle motor are supported inside the clean room chamber within a recessed portion  13  of the lower wall  12  of the HDD housing. Hub  22  is cylindrically shaped and dimensioned to fit through the center opening of the disks. The hub has a radially extending shoulder  28  for supporting the lower disk  30  that may be part of a disk stack. The hub  22  may be made of an aluminum alloy, which is a material that is suitable for use after machining in a clean room environment. One or more spacer rings  34  separate the disks and a clamping element  36  is fastened to the closed end of the rotor  20  and presses against the disk stack to couple the disks to the hub  22 . 
     The rotor assembly  20  rotates on a shaft  23  that is press-fit into or otherwise attached to the closed end of the rotor. Shaft  23  is supported to rotate about the spindle axis  15  by a pair of axially spaced bearings  16  and  18 . Bearings  16  and  18  are mounted within a bearing tube  14  or other form of cylindrical support member that is an integral part of, or is attached to, the recessed wall portion  13 . Bearing spacer member  39  maintains the bearings  16  and  18  in the correct axial locations. The recessed wall portion  13  may be an integral part of the HDD housing wall  12 , or it may be in the form of a detachable assembly flange. If the latter, the spindle motor can be manufactured as a separate unit that is installed into an opening in the HDD housing at the time of final HDD assembly. 
     The spindle motor further includes a permanent magnet  24  that is in the form of an annular ring affixed to a cylindrical ferromagnetic support member  26 . The latter is attached to the lower end of the rotor hub portion  22 . Hub  22  has a cylindrically-shaped central cavity  29  that fits over the upper end of bearing tube  14 . A narrow gap  50  is formed between the outer surface of the bearing tube and the inner surface of the rotor  20  and forms a “gap seal” to reduce the transfer of particles and other contaminants emanating from the bearings  16  and  18  into the clean room chamber. A sealing washer  38   b  is inserted above bearing  18  to further enhance the effect of the seal. Conforming interior surfaces  19   a  and  19   b  of the housing wall  12  surround the edge of the disk mounting flange  28  of the hub  22 . A narrow gap  52  is formed between the outer periphery of the flange  28  and the surfaces  19   a  and  19   b  and functions as a further gap seal to retard the transfer of contaminants into the clean room chamber. A cap  38   a  is inserted to close the opening at the lower end of bearing tube  14 . 
     A stator assembly  40  is supported within the recessed wall portion  13  and encircles the rotor magnet  24 . The stator  40  has windings  42  wound on the stator laminations  43  and a plurality of poles separated from the magnet  24  by a cylindrically-shaped air gap  25 . As shown in FIG. 9, which illustrates the stator arrangement of the similar spindle motor of FIG. 8, the stator  40  (shown as  140  in FIG. 9) may, for example, include twelve equally spaced poles and associated windings, that cooperate with, for example, eight rotor poles (shown schematically by dots on magnet  24 ). A motor driving circuit (not shown) switches timed current pulses into the stator windings to generate flux that interacts with the flux produced by magnet  24  to generate torque on the rotor  20 . This rotates the rotor and enables data transfer to occur between the read/write heads  32  and the recording surfaces of disks  30 . 
     FIG. 2 shows a second embodiment of a disk storage device having a modified form of rotor assembly  20 ′. The aluminum hub  22 ′ is fitted with a ferromagnetic insert  37  conforming generally to and spaced from the upper side of winding  42  and curving down to a closely-spaced gap from inner peripheral surface  19   b  of housing wall  12 . Insert  37  acts as a shield to prevent stray magnetic flux from impinging on the data storage disks. Ferromagnetic magnet support member  26 ′ is extended along, and uniformly spaced from, substantially the entire length of bearing tube  14 . The outer surface of bearing tube  14  and the inner surface of support sleeve  26 ′ are precisely machined to leave a narrow “gap seal” running between them. 
     FIG. 3 shows a third embodiment of a disk storage device having a modified form of rotor assembly  20 ″. The aluminum hub  22 ″ is fitted with a flat ferromagnetic shielding insert  37 ′ spaced from the upper side of stator winding  42 . Flange  28 ′ of hub  22 ″ is terminated in beveled surface  35  that forms a gap seal with a corresponding surface  19   c  of housing  12 . Surface  19   c  replaces surfaces  19   a  and  19   b  of FIG.  2 . Particularly for devices of reduced dimensions, the configuration of FIG. 3 simplifies manufacture and reduces cost. 
     In the embodiment of FIG. 4, a steel hub  49  replaces the aluminum hub of previous embodiments and eliminates the need for separate magnetic yoke and magnetic shielding parts. This configuration enables further reduction of dimensions while also enabling reduced manufacturing cost. 
     In the embodiment of FIG. 5, magnetic shielding yoke  57  replaces ferromagnetic insert  37  and ferromagnetic magnet support  26  of FIG.  2  and is fitted inside a further modified machined form of aluminum hub  22 ′″. This embodiment also shows a separate assembly flange  59  supporting the spindle motor and mounted to lower wall  12  of the clean room housing. 
     FIGS. 6 and 7 show the surfaces, with heavy lines, of the base plate  13  and hub  22  requiring machining for relatively close tolerances in the embodiment of FIG.  1 . These surfaces include surfaces  19   a  and  19   b , the vertical and top surfaces of bearing tube  14 , and the surface of lower wall  12  where the lower edge of rotor  20  must pass over it. As shown in FIG. 7, the close tolerance surfaces of hub  22  are those at the periphery of flange  28  and inner cavity of hub  22 . Preferably, these surfaces should be machined in a single chucking step to assure a close fit. 
     In the embodiment of FIG. 8, the illustrated disk storage device is similar in most respect to that of FIG.  1 . It includes a housing having an upper partition or wall  110  and a lower partition or wall  112  which adjoin side walls (not shown) to enclose a substantially sealed “clean room chamber” CR similar to that of FIG.  1 . Data storage disks  130  are mounted on a hub  122  that is part of a rotor assembly  120  of a brushless DC spindle motor. The drive elements of the spindle motor are supported inside the clean room chamber within a recessed portion  113  of the lower wall  112  of the HDD housing. Hub  122  is cylindrically shaped and dimensioned to fit through the center opening of the disks. The hub has a radially extending shoulder  128  for supporting the lower disk  130  that may be part of a disk stack. The hub  122  may be made of an aluminum alloy, which is a material that is suitable for use after machining in a clean room enviromnent. One or more spacer rings  134  separate the disks and a clamping spring  136  is fastened to the closed end of the rotor  120  and presses against the upper spacer ring  134  to couple the disks to the hub  122 . 
     The rotor assembly  120  rotates on a shaft  123  that is press-fit into or otherwise attached to the closed end of the rotor. Shaft  123  is supported to rotate about the spindle axis  115  by a pair of axially spaced bearings  116  and  118 . Bearings  116  and  118  are mounted within a bearing tube  114  or other form of cylindrical support member that is an integral part of, or is attached to, the recessed wall portion  113 . The recessed wall portion  113  may be an integral part of the HDD housing wall  112 , or it may be in the form of a detachable assembly flange. If the latter, the spindle motor can be manufactured as a separate unit that is installed into an opening in the HDD housing at the time of final HDD assembly. 
     The spindle motor further includes a permanent magnet  124  that is in the form of an annular ring affixed to a cylindrical ferromagnetic support member  126 . The latter is attached to the lower end of the rotor hub portion  122 . Hub  122  has a cylindrically-shaped central cavity  129  that fits over the upper end of bearing tube  114 . The magnet support member  126  encircles the bearing tube  114 . A narrow gap  150  is formed between the outer surface of the bearing tube and the inner surface of the rotor  120  and forms a “gap seal” to reduce the transfer of particles and other contaminants emanating from the bearings  116  and  118  into the clean room chamber. A ring  144  is set into the housing wall  112  and surrounds the disk mounting flange  128  of the hub  122 . A narrow gap  152  is formed between the outer periphery of the flange  128  and the inner periphery of the ring  144  and functions as a further gap seal to retard the transfer of contaminants into the clean room chamber. 
     A stator assembly  140  is supported within the recessed wall portion  113  and encircles the rotor magnet  124 . The stator  140  has windings  142  wound on the stator laminations and a plurality of poles separated from the magnet  124  by a cylindrically-shaped air gap  125 . As shown in FIG. 9, the stator  140  may, for example, include twelve equally spaced poles and associated windings, that cooperate with, for example, eight rotor poles (shown schematically by dots on magnet  124 ). A motor driving circuit (not shown) switches timed current pulses into the stator windings to generate flux that interacts with the flux produced by magnet  124  to generate torque on the rotor  120 . This rotates the rotor and enables data transfer to occur between the read/write heads  132  and the recording surfaces of disks  130 . 
     FIG. 10 shows another embodiment of a disk storage device having a modified form of rotor assembly  120 ′. The underside of the closed end of the hub  122 ′ is provided with an annular groove  154  that mates with the extended upper end of the bearing tube  114  to form a labyrinth seal  156  that further enhances retardation of contaminant particle movement toward the clean room chamber. FIG. 10 also shows that modified rotor assembly  122 ′ employs a ferromagnetic magnet support member  126 ′ that has a radially-extending lip  127  projecting into the disk support flange  128 ′. The lip  127  extends across the end of the magnet  124 , the air gap  125  and partially encloses the pole faces of the stator lamination. Any stray flux that may emanate from the area of the motor air gap will be contained by the lip  127  and prevented from impinging on the data storage disks  130 . 
     FIG. 11 illustrates a still further embodiment of data storage device having a further modified spindle motor. The rotor assembly  160  is provided with an internal sleeve  162  that is press fit or glued inside the hub portion  164 . The permanent magnet ring  167  and ferromagnetic support member  166  are affixed about an end of the sleeve  162 . Sleeve  162  can be formed of an aluminum alloy and has a precisely machined inner diameter. The outer diameter of the bearing tube  114  may also be precisely machined to permit close spacing with respect to the sleeve  162  so that gap seal  150  is made very narrow and hence more effective in retarding transfer of contaminant particles toward the clean room CR. 
     Sleeve  162  also positions the magnet ring  167  and air gap further away from the axis of rotation. This increases the radius of the magnet  167  and the air gap  125  so that the magnet and air gap both have diameters substantially exceeding the diameter of the disk mounting hub  164 . In this regard, the embodiment of FIG. 11 is similar to that of FIG.  1 . This permits generation of a higher motor torque without increasing the height of the spindle or the diameter of the hub. In fact, the motor arrangement of the invention allows the torque produced by the motor to be essentially independent of both the spindle height and hub diameter. 
     As illustrated in the above, the inner rotor-rotating shaft design of the disk storage device of the present invention provides several advantages. Among these are the following. 
     The rotor assembly has reduced mass because the hub portion is essentially hollow and the magnetic ring and ferromagnetic support member are not affixed to a radially-extending support structure, as is required in an outer rotor design, allowing the rotor mass to be reduced and located closer to the axis of rotation. These features allow the same drive torque to accelerate the spindle assembly to the required operating speed in a shorter time and reduce vibrations at higher operating speeds. Further, the motor diameter can be increased without incurring a proportionate increase in rotor mass. 
     Still further, the spindle axis is fixed by a relatively large diameter bearing tube or cylindrical structure, which is more rigid than the stationary shaft or post usually used to support the spindle. 
     In addition, because the stator components are located away from the spindle axis, there is more room in the center of the assembly for the bearings and they can be spaced further apart to reduce spindle run out due to play in the bearings. 
     Still further, the rotor configuration allows for an extended-length cylindrical gap seal for providing enhanced isolation of the bearings from the clean room. The gap seal may be used along with one or more labyrinth seals (such as formed by the gap  156  shown in FIG. 10) to further retard the migration of contaminants into the clean room chamber. 
     Although we have shown and described this invention in connection with certain embodiments, additional alternatives, modifications, and variations may be apparent to those skilled in the art in view of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and scope of the appended claims.