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. Further, the motor elements are located outside the clean room chamber, further enhancing the cleanliness of the environment surrounding the data storage disks.

Description:
This is a continuation of application Ser. No. 08/834,700, filed Apr. 1, 1997, now U.S. Pat. No. 6,005,746. 
    
    
     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 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 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 allow location of the drive elements of the spindle motor outside the clean room chamber without significantly increasing the mass or angular inertia of the rotating 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 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. Further, the motor elements are located outside the clean room chamber, further enhancing the cleanliness of the environment surrounding the data storage disks. 
     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-sectional view taken along the spindle axis of a first embodiment of disk storage device according to the invention. 
     FIG. 1 a  is a cross-sectional view taken along the line  1 a— 1 a of FIG. 1 showing how the stator cooperates with the rotor and rotor magnet. 
     FIG. 2 is a cross-sectional view taken along the spindle axis of a second embodiment of disk storage device according to the invention. 
     FIG. 3 is a cross-sectional view of a portion of a third embodiment of the invention showing an alternate form of electrical contact device for connecting the stator windings to control circuitry that is mounted external to the housing of the disk storage device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a first embodiment of a disk storage device according to the invention includes a housing having a base plate  10  and a partition  12 . Base plate  10  and partition  12  cooperate with side walls (not shown) to define a clean room chamber CR. The chamber CR is a finally sealed clean room manufactured to HDD industry contamination standards for controlling the amount of particulate matter and other contaminants coming into contact with the storage disks. 
     Data storage disks  30 , which may be magnetic hard disks, are located within the clean-room and cooperate with data read/write transducers  32 . Transducers  32  are mounted on actuator arms to move relative to the surface of the disks to read and write (record) data in tracks on the storage surfaces. Each storage disk  30  has a central opening of standard diameter that fits over the disk mounting portion of a hub  14 . The hub  14  is press-fit on, or otherwise attached to, a shaft  16  that is supported to rotate about spindle axis  19 . The storage disks  30  are coupled to the hub  14  by a radially-extending disk support flange  15 , spacer ring  33 , and clamping ring  31  in a conventional manner. 
     The shaft  16  and hub  14  are rotatably driven by a brushless D.C. motor having a rotor  17  and stator  28 . Rotor  17  may be made of a ferromagnetic material such as soft iron or steel and is circular with a cylindrical flange at its periphery. An annular permanent magnet  18  is affixed to the peripheral flange of the rotor. Magnet  18  is surrounded by the stator lamination  28  and is spaced from the stator pole faces to form a cylindrical air gap AG. 
     The relationship between the stator elements and the rotor are illustrated in FIG. 1 a . The stator is supported on a cylindrical projection  26  which is part of an assembly flange  22  (FIG.  1 ). Flange  22  fits into a circular opening in the base plate  10  and is attached thereto by fasteners such as screws. Assembly flange  22  includes a bearing tube  24  that is concentric with the spindle axis  19 . Bearing tube  24  supports on its cylindrical inner surface a pair of axially spaced bearings  20 A and  20 B that rotatably support shaft  16 . 
     Timed current pulses are supplied from a motor control circuit (not shown) through a contact member  38  to the stator windings. Magnetic flux generated by the stator windings within lamination  28  interacts with the flux produced by the rotor magnet  18  to apply torque to rotor  17 . The latter in turn rotates the shaft  16 , hub  14  and disks  30  to move the storage surfaces of the disks past read/write heads  32  so that data transfer occurs between the heads and the data storage tracks on the disks. A ferromagnetic shielding ring  21  is affixed to the flange  22  adjacent the magnet  18 , air gap and stator  28 . The ring  21  prevents any stray flux produced by the motor parts from penetrating the clean-room and impinging on the data storage surfaces of the disks. 
     Contaminants such as particulate matter emanating from the stator and rotor elements cannot migrate into the clean room because the motor is mounted outside the clean room on the opposite side of the base plate  10 . A cover (not shown) may be affixed to the projection  26  to enclose the stator and rotor to keep foreign objects from interfering with motor operation. However, a printed circuit board supporting the motor control circuitry and other circuit elements may be affixed in a frame suspended below the base plate to serve the same function, making a separate motor cover unnecessary. 
     Bearings  20 A and  20 B are also a source of contaminants. A sealing member  34 , such as a ferrofluidic sealing ring, is inserted at the end of bearing tube  24  closest to the clean room to prevent contaminants from entering the clean room. Alternatively, the underside of hub  14  and the outer diameter of the upper portion of bearing tube  24  can be precisely machined to establish at narrow gap  36 . Gap  36  may operate as a “gap seal,” making it possible to eliminate the seal  34  or replace it with a simple ring or washer  35 , as illustrated in FIG.  2 . 
     Because the rotor  17  is arranged as an inner rotor, it has a reduced radial dimension as compared to an outer rotor of comparable torque. This enables the mass of the rotor to be reduced and displaced inwardly so that the moment of inertia of the rotating structure is reduced, allowing more rapid acceleration of the spindle at the time of startup. Further, placement of the stator at the periphery of the motor frees up space near the spindle axis. This allows the bearings to be separated by a greater axial distance without increasing the height of the spindle. As a result a more compact disk storage device can be constructed without the need to position the motor inside the clean room. 
     Referring to FIG. 2, the embodiment there shown is similar to that of FIG. 1 but uses gap-type seals in place of ferrofluidic seal  34 . The spindle motor of FIG. 2 is integrated into the base plate  10 , rather than mounted on a separate assembly flange as shown in FIG.  1 . It also employs an integral hub and shaft  14 ′ i.e., the shaft and hub are formed together as a one-piece unit out of a material such as an aluminum alloy or steel. A washer  35  is inserted near the top of bearing tube  24 ′ and functions to entrap particles from the bearings within the bearing tube. Particles that escape through the narrow gap between the shaft portion of the hub/shaft  14 ′ and washer  35  enter a gap  50  formed between the underside of hub  14 ′ and the top of bearing tube  24 ′. An annular groove  44  in the underside of the hub meshes with the upper end of the bearing tube so that gap  50  is in the form of a labyrinth seal. This seal further retards the migration of contaminant particles toward the clean room. Additional labyrinth seals may be provided via further annular grooves, such as those shown at  46  and  48 , machined into the underside of the hub. These grooves mesh with raised annular projections formed on the upper side of the base plate  10 ′, providing two additional labyrinth seals for retarding the transfer of contaminants still further. 
     FIG. 2 also shows a printed circuit board (PCB)  40  suspended on a frame (not shown) parallel to the base plate in the area of the spindle motor. PCB  40  supports motor control circuitry for generating the timed current pulses that energize the stator windings of the motor. Electrical connection of the stator circuits with the control circuitry is achieved through use of a connector pin  42  mounted within in an insulating bushing on the outside of base plate  10 ′. This type of connection simplifies the manufacturing process and facilitates easy removal of PCB  40  for testing and repair purposes. 
     FIG. 3 shows a modified form of quick-disconnect contact member that includes a contact pin  62  mounted in base plate  10 ″ within an insulated housing  63 . A spring  64  biases contact pin  62  toward PCB  60 . A conductive pad  61  is provided on PCB  60  to conductively engage the tip of contact  62 . Stator leads  66  are connected to contact pin  62  to couple the control pulses to the stator windings. Pin  62  and pad  61  may be plated with a highly conductive material such as gold or silver to enhance the electrical integrity of the connection. 
     The disk storage device of the invention provides several advantages. The motor elements can be located outside the clean room, whereby the danger of clean room contamination is reduced, while reducing, or at least without materially increasing, the mass or angular inertia of the rotating elements. This, in turn, improves the acceleration characteristics of the disk drive at the time of startup. Further, the mass of the rotating elements of the spindle motor is both reduced and displaced toward the axis of rotation, enabling improvement in acceleration characteristics and reducing vibrations caused by imbalance in the rotating parts. Still further, removal of the stator from the area immediately surrounding the spindle axis leaves more space in that region that is utilized for achieving greater axial separation of the bearings. This reduces spindle run out caused by bearing wear and play. Additionally, the spindle assembly is supported for rotation by a bearing tube that increases the rigidity of the spindle axis. 
     Although the invention has been described in connection with preferred embodiments and certain alternatives, other alternatives, modifications and variations may be apparent to those skilled in the art in view of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.