Abstract:
The present invention is related to a disk drive hub/back iron configuration that resists distortion upon changinging temperature of the disk drive. The hub/back iron configuration thus prevents distortion of the disks, reducing HDI problems.

Description:
[0001]    This application claims priority to U.S. Provisional Application Serial No. 60/390,387, filed Jun. 21, 2002; entitled, “Spindle Hub With Uniform Thermal Distortion”; Attorney docket number STL 3185. The foregoing patent application, which is assigned to the assignee of the present application, is incorporated herein by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Computer information is often written to and read from a rotating recording medium. The data is recorded in concentric tracks of a magnetic disk in the form of magnetic transitions. The disks are mounted on a spindle and the information is accessed by an actuator which moves a magnetic transducer radially over the surface of the disk and aligns the transducers with the concentric tracks. The disk and spindle are mounted for rotation on a support shaft and the disks are rotated at high speeds by means of an electric motor.  
           [0003]    Important requirements for magnetic disk files are quick access to data together with a high data rate. A key to both is high rotational speed of the disks. On average, it takes a half of a rotation of a disk for the desired data to reach the transducer after the actuator has positioned the transducer at the desired track. Thus, the higher the speed the disk rotates, the quicker the desired data can be accessed. Similarly, faster rotation of a disk causes more data to pass the transducer, increasing the data rate at the transducer.  
           [0004]    Increased capacity is also important and has been accomplished by increasing both the data density per disk and the number of disks in a given space. The number of disks able to occupy a given space has been increased by packing the disks closer together.  
           [0005]    The combination of higher spindle speeds and the increased number of disks has resulted in increasing the operating temperatures of high capacity, high performance disk drives. The changing temperature has a compounding effect in that increased temperature of the rotor reduces the motor efficiency and increases resistivity, thereby increasing the temperature even further due to the increased winding resistance.  
           [0006]    Spindle motors with separate rotor assemblies and stator assemblies are commonly used for disk drive applications. The rotor generally carries a multi-polar magnet, which is mounted about a lower periphery of the rotor. The stator typically includes a radially-oriented magnet, with the polarity of areas of the magnet alternated based on the location of the multi-polar magnet in the rotor. The multipolar magnet responds to the alternating magnetic field to rotate the rotor and disks.  
           [0007]    In a typical assembly of a separate rotor/stator configuration, the stator is mounted to a disk drive base plate, and the rotor assembly is mounted to bearings that are, in turn, mounted about a cylindrically shaped shaft.  
           [0008]    Various components of the rotor/stator assembly include the rotor shaft, bearings, a sleeve, a hub, the stator and stator magnet, a back iron, as well at least one disk. The increases in temperature in the disk environment may effect all components of the rotor/stator assembly. Moreover, the increases in temperature may affect the way in which the components are placed in relation to each other or interact with each other, as the various components are made of differing materials with different coefficients of expansion. Indeed, differing extents of thermal expansion in adjacent parts can distort the rotor/stator assembly as well as the disks, causing head/drive interface (HDI) problems.  
           [0009]    Thus, it is of interest in the art to develop a rotor/stator assembly that undergoes decreased distortion at high temperatures.  
         SUMMARY OF THE INVENTION  
         [0010]    An object of the present invention is to provide a hub and back iron assembly for a disk drive with decreased distortion during times of temperature change. Thus, the present invention provides a hub and back iron assembly for a disk drive, where the disk drive has a spindle and at least one disk, comprising: an annular hub having an inner side wall proximate the spindle; an outer side wall proximate the disk or disks; a top surface; and a bottom surface. The bottom surface has at least two notches—inner and outer notches—defined by a separating member. The inner notch accommodates a stator and the outer notch accommodates a back iron. In addition, the separating member has an outer sidewall. The hub and back iron assembly also includes a back iron disposed within the outer notch of the hub. The back iron has an inner surface proximate the spindle and coupled to the outer surface of the separating member of the hub, and an outer side wall proximate to the at least one disk and not coupled to the outer side wall of the hub. The coupling of the hub to the back iron may be accomplished by any number of means, including, but not limited to, gluing or press fitting.  
           [0011]    In addition, the present invention provides a disk drive comprising: a base; a spindle; an annular hub having an inner side wall proximate the spindle; an outer side wall proximate the at least one disk; a top surface; and a bottom surface having inner and outer notches defined by a separating member. The inner notch accommodates a stator, the outer notch accommodates a back iron. Further, the separating member has an outer sidewall. In addition, the disk drive includes a back iron disposed within the outer notch of the hub, where the back iron has an inner surface proximate the spindle and coupled to the outer surface of the separating member of the hub, and an outer side wall proximate to the at least one disk and not coupled to the outer side wall of the hub. Further, the disk drive includes a shaft supporting at least one end of the annular hub; a fluid dynamic bearing system comprising fluid in a gap between the shaft and the sleeve and the annular hub and the sleeve; a stator; and a cover adapted to couple with the base.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a top view representation of a magnetic disk drive.  
         [0013]    [0013]FIG. 2 is a cross-sectional illustration of a hub, back iron and magnet assembly.  
         [0014]    [0014]FIG. 3 is a cross-sectional illustration of a prior art hub, back iron and magnet assembly.  
         [0015]    [0015]FIG. 4 is a cross-sectional illustration of an embodiment of a hub, back iron and magnet assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    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 disc 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, hard disc drives are 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.  
         [0017]    [0017]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 plate  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 .  
         [0018]    [0018]FIG. 2 is a cross section of an exemplary hub, back iron and magnet assembly. The disk drive is comprised of hub  102  (including hub regions  120  and  122 ), disks  60 , spacer  106  and magnet  108 . Magnet  108  is, at its top adjacent to hub  120 , at its outside edge adjacent to back iron  118 , and at its inside edge adjacent to the stator assembly  110 . FIG. 2 additionally shows a sleeve  116  coupled to a spindle  10 , and fluid dynamic bearing cones  114 . Back iron  118  has an inner surface  124  and an outer surface  126 . Regions or surface of components proximate the spindle  10  are referred to as inner or inside, and regions or surfaces of components proximate the disks  60  are referred to as outer or outside.  
         [0019]    The thermal expansion of hub  102  at its outer diameter  122  must closely match the thermal expansion of the disks  60 . As the back iron is typically glued, shrunk, or pressed against hub  102 , the interaction of back iron  118  with hub  102  changes how the hub outer diameter  122  expands. In prior art configurations, the outer region  126  of back iron  118  is joined to the inner surface of region  122  of hub  102 . In such a prior art configuration, any expansion in the hub outer diameter  122  tends to distort disks  60 , and such distortion of disks  60  leads to HDI problems. A prior art version of the attachment of back iron  118  of hub  102  is shown in FIG. 3.  
         [0020]    In the present invention, and as shown in FIG. 2, back iron  118  is coupled to hub  102  only at the upper region of the inner surface  124  of back iron  118  and the outer surface of the small region  120  of hub  102 . Such coupling can be done by means known in the art, including using glues or other adhesives, press fitting or other coupling means. Back iron  118  is not coupled to hub  102  at the outer surface  126  of back iron  118 . Since the coupling of back iron  118  to hub  102  is at a junction distal to disks  60 , any distortion or configuration change in back iron  118  is unlikely to affect, or at the least will have less effect on, disks  60 .  
       EXAMPLE  
       [0021]    [0021]FIG. 3 illustrates a prior art hub, back iron and magnet assembly. In this figure, there is a sleeve  116 , hub  102 , magnet  108 , and back iron  119 . Note that the configuration of back iron  119  is that of an upside down “L”, and that region  123  of hub  102  contacts back iron  119  along area  125 . In this configuration, and in any configuration where the back iron is coupled to the outer wall of the hub, distortion in the back iron  119  would affect region  123  of hub  102 . Region  123  is that region of hub  102  that is adjacent to the disks (not shown). Thus, the distortion caused by back iron  119  of hub region  123  would affect the disks (not shown). The shading of the hub/back iron/magnet assembly in FIG. 3 shows expansion as a result of heating. If the expansion of the assembly were uniform, the shading would be in vertical “stripes”. The angle shows that the top of the hub is moving more than the bottom of the hub with increasing temperature. Note that the hub area  123  (typically composed aluminum) coupled to the back iron (typically composed of steel) has several shadings—indicative of uneven expansion.  
         [0022]    [0022]FIG. 4 shows an embodiment of the hub, back iron and magnet configuration of the present invention. Note that the configuration of hub  102  and back iron  118  has been changed from the prior art. Note that back iron  118  is not attached to hub region  122 . Instead, back iron  118  is attached to the inner surface of hub region  120  at junction  124 . In this configuration, back iron  118 , when distorted, affects region  120  of hub  102 , not region  122  of hub  102 . Thus region  122 , the region of the hub adjacent the disks (not shown), is not affected by distortion of back iron  118 . The shading of the hub/back iron/magnet assembly in FIG. 4 shows expansion as a result of heating similar to that in FIG. 3. However, note that, though still angled, there are not as many varying areas of differential expansion. In FIG. 4, the hub area  123  (typically composed aluminum) coupled to the back iron (typically composed of steel) has only two shadings and that the majority of hub area  123  is only one shade.