Abstract:
The present disclosure relates to a spindle motor having a shaft defining an axial bore that extends completely through the length of the shaft. At least a portion of the axial bore defines a fluid reservoir. A radial passageway extends radially from the fluid reservoir to an exterior surface of the shaft. The spindle motor also includes a pin that seals one end of the axial bore, and a plug that seals an opposite end of the axial bore. The motor further includes a rotor member that is rotatably mounted on the shaft. A bearing fluid forms a hydrodynamic bearing between the exterior surface of the shaft and the rotor member. The bearing fluid at least partially fills the fluid reservoir and the radial passageway.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to spindle motors for use in magnetic disc storage systems. More particularly, this invention relates to magnetic disc storage systems having spindle motors that use hydrodynamic bearings. 
     2. Description of Related Art 
     Data storage systems, such as disk drives, commonly make use of rotating storage disks. The storage disks are commonly magnetic disks but could also be optical. In a typical magnetic disk drive, a magnetic disk rotates at high speed and a transducing head uses air pressure to “fly” over the top surface of the disk. The transducing head records information on the disk surface by impressing a magnetic field on the disk. Information is read back using the head by detecting magnetization of the disk surface. The magnetic disk surface is divided in a plurality of concentric tracks. By moving the transducing head radially across the surface of the disk, the transducing head can read information from or write information to different tracks of the magnetic disk. 
     Spindle motors are commonly used to rotate magnetic disks at high speeds. Frequently, conventional spindle motors comprise small electric motors equipped with standard ball bearings. However, electric motors having ball bearings are known to experience problems such as runout or vibration that can prevent information from being accessed from disks rotated by the motors. This is especially true as advancements in data storage technology have increased magnetic disk storage densities. To overcome the problems associated with ball bearing electric motors, some disk drive systems now make use of electric motors having fluid hydrodynamic bearings. Bearings of this type are shown in U.S. Pat. No. 5,427,546 to Hensel, U.S. Pat. No. 5,516,212 to Titcomb and U.S. Pat. No. 5,707,154 to Ichiyama. 
     An exemplary hydrodynamic bearing typically includes a stationary shaft on which is mounted a rotary hub to which magnetic disks can be secured. There is no direct contact between the rotating hub and the shaft. Instead, a lubricating fluid forms a hydrodynamic bearing between the shaft and the rotary hub. Hydrodynamic pressure or pumping is frequently provided by a pattern of grooves, commonly in a herringbone configuration, defined either by the exterior surface of the shaft or the interior surface of the rotary hub. During rotation of the hub, the pattern of grooves provides sufficient hydrodynamic pressure to cause the lubricating fluid to act as a hydrostatic bearing between the shaft and the rotary hub. Frequently, capillary seals are used to retain the bearing fluid between the shaft and the rotary hub. 
     In certain prior art electric motors having hydrodynamic bearings, the shaft defines an axial bore that provides a reservoir for bearing fluid. In certain of such prior art motors, the axial bore has only one open end that is closed by a pin which is press fit within the bore. Because the bore has only one open end, the bore is difficult to clean. Consequently, it is possible for debris left within the bore to contaminate the bearing fluid. Additionally, when the pin is press fit within the bore, wear debris is generated by the pressing operation. This wear debris can contaminate the bearing fluid of the hydrodynamic bearing and lead to premature wear and failure of the electric motor. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention relates to a spindle motor including a shaft defining an axial bore extending completely through a length of the shaft. At least a portion of the axial bore defines a fluid reservoir. The shaft also defines a radial passageway extending radially from the fluid reservoir to an exterior surface of the shaft. A pin seals one end of the axial bore, while a plug seals the other end of the axial bore. The fluid reservoir is positioned between the pin and the plug. A rotor member to which a storage disk can be secured is rotatably mounted on the shaft. The motor further includes a bearing fluid adapted to form a hydrodynamic bearing between the exterior surface of the shaft and the rotor member. The bearing fluid at least partially fills the fluid reservoir and the radial passageway. In certain embodiments of the present invention, the plug and the pin are secured within the axial bore by adhesive. 
     Another aspect of the present invention relates to a spindle motor as described above that is incorporated within a data storage system. 
     These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings in which like reference numbers represent corresponding parts throughout: 
     FIG. 1 is a schematic diagram of a data storage system; 
     FIG. 2 is a top view of the system of FIG. 1; 
     FIG. 3 is a cross-sectional view bisecting an embodiment of a spindle motor constructed in accordance with the principles of the present invention; and 
     FIG. 4 is a cross-sectional view of the spindle motor of FIG. 3 with the shaft removed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description of the exemplary embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration the specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized as structural changes may be made without departing from the scope of the present invention. 
     FIG. 1 shows a schematic diagram of a data storage system  10  suitable for practicing the present invention. System  10  comprises a plurality of magnetic recording disks  12 . Each disk has a plurality of concentric data tracks. Disks  12  are mounted on a spindle motor shaft  14  which is connected to a spindle motor  16 . Motor  16  is mounted to a chassis  18 . The disks  12 , spindle  14 , and motor  16  comprise a disk stack assembly  20 . 
     A plurality of sliders  30  having read/write heads are positioned over the disks  12  such that each surface of the disks  12  has a corresponding slider  30 . Each slider  30  is attached to one of the plurality of suspensions  32  which in turn are attached to a plurality of actuator arms  34 . Arms  34  are connected to a rotary actuator  36 . Alternatively, the arms  34  may be an integral part of a rotary actuator comb. Actuator  36  moves the heads in a radial direction across disks  12 . Actuator  36  typically comprises a rotating member  38  mounted to a rotating bearing  40 , a motor winding  42  and motor magnets  44 . Actuator  36  is also mounted to chassis  18 . Although a rotary actuator is shown in the preferred embodiment, a linear actuator could also be used. The sliders  30 , suspensions  32 , arms  34 , and actuator  36  comprise an actuator assembly  46 . The disk stack assembly  20  and the actuator assembly  46  are sealed in an enclosure  48  (shown by dashed line) which provides protection from particulate contamination. 
     A controller unit  50  provides overall control to system  10 . Controller unit  50  typically contains a central a processing unit (CPU), memory unit and other digital circuitry. Controller  50  is connected to an actuator control/drive unit  56  which in turn is connected to actuator  36 . This allows controller  50  to control the movement of sliders  30  over disks  12 . The controller  50  is a connected to a read/write channel  58  which in turn is connected to the heads of the sliders  30 . This allows controller  50  to send and receive data from the disks  12 . Controller  50  is connected to a spindle control/drive unit  60  which in turn is connected to spindle motor  16 . This allows controller  50  to control the rotation of disks  12 . A host system  70 , which is typically a computer system, is connected to the controller unit  50 . System  70  may send digital data to controller  50  to be stored disks  12 , or may request that digital data be read from disks  12  and sent to the system  70 . The basic operation of DASD units is well known in the art and is described in more detail in  Magnetic Recording Handbook , C. Dennis Mee and Eric D. Daniel, McGraw Hill Book Company, 1990. 
     FIG. 2 shows top view of system  10 . A loading ramp member  80  is located at the edge of the disk stack assembly  20 . Member  80  automatically unloads the sliders  30  from the disks  12  as actuator  36  moves the sliders  30  to the outer disk position. To unload a slider or head means to move it a vertical distance away from its corresponding disk surface. The ramp  80  is optional. Alternatively, the sliders  30  may be placed permanently in the loaded position between the disks. 
     FIG. 3 is diagramatic cross-sectional view of a spindle motor  120  that is an embodiment of the present invention. A preferred application of the spindle motor is in data storage systems such as the disk drive system  10  illustrated in FIGS. 1 and 2. 
     The spindle motor  120  generally includes a stationary shaft  122  and a rotor member  124  rotatably mounted on the shaft  122 . A thrust plate  126  is fixedly connected to the shaft  122 . The thrust plate  126  is captured between a shoulder  128  of the rotor member  124  and a cover plate  130  that is fixedly connected to the rotor member  124 . Interference between the cover plate  130  and the thrust plate  126 , and between the shoulder  128  and the thrust plate  126 , prevent the rotor member  124  from becoming axially displaced from the shaft  122 . The spindle motor  120  also includes a stator  132  that is fixedly connected to a base  133  in which a lower end of the shaft  122  is press fit. The stator includes a plurality of laminar plates  134  and coils  136  disposed about the plates  134 . One or more magnet elements  135  are positioned directly outside the stator  132 . The magnetic elements  135  are secured to the inside of the rotor member by a magnetic sleeve or back iron  140 . The rotor member  124  includes a flange  142  that projects radially outward from a main body of the rotor member  124 . A storage medium  144  such as a magnetic disk is secured to the flange  142 . 
     The shaft  122  of the spindle motor  120  includes an axial bore  146  that extends completely through a length L of the shaft  122 . An upper portion  148  and a lower portion  150  of the axial bore  146  have been tapped with internal threads. The tapped upper portion  148  allows a cover to be bolted to the spindle motor  120 , while the tapped lower portion  150  allows the shaft  122  to be bolted to a disk drive chassis such as the chassis  18  of the data storage system  10  shown in FIGS. 1 and 2. 
     The spindle motor  120  also includes a pin  152  that seals one end of the axial bore  146  and a plug  154  that seals an opposite end of the axial bore  146 . The plug  154  is generally cylindrical. The pin  152  includes a head portion  156  and an elongate portion  158  that extends longitudinally from the head portion  156  along the axial bore  146 . The head portion  156  of the pin  152  includes a generally cylindrical portion  160  and a lip portion  162  that projects radially outward from the cylindrical portion  160 . 
     Both the pin  152  and the plug  154  are preferably secured within the axially bore  146  by an adhesive such as epoxy. For example, the pin  152  is secured within the axial bore  146  by a layer of adhesive  164  positioned between the generally cylindrical portion  160  of the plug  154  and the interior surface of the shaft  122 . Similarly, the plug  154  is shown secured within the axial bore  146  by an adhesive layer  168  positioned between the outer surface of the plug  154  and the interior surface of the shaft  122 . Each of the adhesive layers  164  and  168  preferably has a thickness in the range of 5-20 microns. 
     By way of nonlimiting example, the axial bore  146  can have a diameter d 1 , in the range of 2-2.5 millimeters, the plug  154  and the cylindrical portion  160  of the pin  152  can have diameters d 2  in the range of 2-2.5 millimeters, the elongated portion  158  of the pin  152  can have a diameter d 3  in the range of 1.9-2.4 millimeters, and the lip portion  162  of the pin  152  can have a diameter d 4  in the range of 2.5-3 millimeters. For certain embodiments, the diameters d 2  of the cylindrical portion  160  and the plug  154  are in the range of 5-20 microns smaller than the diameter d 2  of the axial bore  146 . In such embodiments, a clearance of 5-20 microns exist between the cylindrical portion  160  and the interior surface  166  of the shaft, and between the plug  154  and the interior surface  166  of the shaft  122 . Such clearance provides volume or space for allowing a desired thickness of adhesive to be placed between the cylindrical portion  160  and the interior surface  166  of the shaft  122 , and between the plug  154  and the interior surface  166  of the shaft  122 . 
     The pin  152  and the plug  154  can also be secured within the axial bore  146  by a heat shrinking technique. For example, the shaft  122  can be cooled prior to placing the pin  152  and the plug  154  within the bore  146 . By cooling the shaft  122  with a coolant such as liquid nitrogen, the diameter of the bore  146  of the shaft  122  is expanded. The pin  152  and the plug  154  are placed in the bore  146  while the shaft is cold. Subsequently, the shaft  122  is allowed to warm to room temperature. As the shaft  122  warms, the diameter of the bore  146  constricts causing the pin  152  and the plug  154  to be pressed within the bore  146 . In this manner, friction retains the pin  152  and the plug  154  within the bore  146 . A shrink fit connection, as described above, can also be provided by cooling the pin  152  and the plug  154  as opposed to the shaft  122 . 
     Because the axial bore  146  extends completely through the length L of the shaft  122 , of the interior surface  166  of the shaft  122  can effectively be cleaned by conventionally known techniques such as an ultrasonic bath. Also, because the pin  152  and the plug  154  are glued or shrink-fitted into the axial bore  146 , debris associated with press-fit operations is not generated. 
     Friction between the shaft  122  and the rotor member  124  is inhibited through the use of upper and lower hydrodynamic bearings  170  and  172 . The upper hydrodynamic bearing  170  includes a bearing fluid  174  such as lubricating fluid or oil. The bearing fluid  174  is positioned between the shaft  122  and the rotor member  124 , between the thrust plate  126  and the rotor member  124 , and between the top of the thrust plate  126  and the bottom of the cover plate  130 . The bearing fluid  174  is also provided in a fluid reservoir  176  formed between the elongate portion  158  of the pin  152  and the interior surface  166  of the shaft  122 . Fluid communication between an exterior surface  177  of the shaft  122  and the fluid reservoir  176  is provided by radial passageways  178  that extend radially from the fluid reservoir  176  to the exterior surface  177  of the shaft  122 . 
     The lower hydrodynamic bearing  172  is formed by a bearing fluid  180  such as lubricating fluid or oil. The bearing fluid  180  is positioned between the exterior surface  177  of the shaft  122  and the rotor member  124 . A volume  182  between the upper and lower hydrodynamic bearings  170  and  172  is typically filled with air. Bearing fluid movement between the upper and lower hydrodynamic bearings  170  and  172  is preferably inhibited by conventional techniques such as capillary seals. Similarly, the bearing fluid is inhibited from escaping the spindle motor  122  by similar conventionally known sealing techniques. 
     Hydrodynamic pressure for pressurizing the bearing fluid  174  and  180  is preferably provided by any number of known techniques. For example, as shown in FIG. 4, herringbone patterns of grooves  185  have been provided within the interior surface of the rotor member  124  at positions adjacent to the upper and lower hydrodynamic bearings  170  and  172 . When the rotor member  124  is rotated relative to the shaft  122 , the herringbone patterns of grooves  185  generate pumping actions which pressurize the bearing fluids  174  and  180 . It will be appreciated that a similar herringbone pattern is also preferably provided on the top and bottom surfaces of the thrust plate  126 . Additionally, it will be appreciated that a herringbone pattern can also be formed on the exterior surface  177  of the shaft  122  to achieve a similar pumping effect. 
     The foregoing description of the exemplary embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not with this detailed description, but rather by the claims appended hereto.