Abstract:
The present invention provides a spindle motor and a method of manufacturing a spindle motor wherein a bearing unit is manufactured as a discrete modular component. A spindle motor that meets a set of specific technical requirements can be easily manufactured by combining such a bearing unit with other spindle moor components.

Description:
FIELD OF INVENTION 
   The following application relates to the field of spindle motors and more specifically to a design that allows for more efficient manufacture of such motors. 
   BACKGROUND OF THE INVENTION 
   Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a shaft or “spindle”, the information being accessed by means of transducers located on a pivoting arm, which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable. 
   Electric spindle motors are used to rotate the discs in disc drive systems. Such spindle motors may have either a fixed shaft and a rotating sleeve or a fixed sleeve and a rotating shaft. Depending on the type of spindle motor, a rotor hub is affixed to either the rotating shaft or to the rotating sleeve. The disc is then mounted on the rotor hub. 
   The spindle motor&#39;s shaft and sleeve must be rotatably mounted to each other so as to allow relative rotation between the shaft and sleeve, but so as to minimize lateral and axial motion as well as tilting motion. Fluid dynamic bearings are the preferred method of providing such mounting, although conventional ball bearings are sometimes used. 
   In fluid dynamic bearings, a thin film of a lubricating fluid—either gas or liquid—functions as the bearing surface between the sleeve and the shaft. Pressure generating grooves on either the sleeve or the shaft generate pressure gradients in the fluid that prevent the sleeve and the shaft from contacting each other during motor operation. The bearing properties such as stiffness and energy consumption as well as the cost of the bearing are dependant upon many factors such as the bearing dimensions and shape, the positioning of the grooves, and the size of the gaps between the sleeve and shaft. 
   The requirements for a specific spindle motor vary depending on the application in which the spindle motor will be used. Since hard disc drives are used for a large variety of applications, there is a need for a variety of types of spindle motors to meet the specific requirements of the various applications. Accordingly, there is a need to efficiently manufacture a variety of types of spindle motors, where each type of spindle motor is closely matched to the specific requirements of the applications for which it will be used. 
   The manufacture of fluid dynamic bearings is a labor intensive process that requires numerous steps including machining the components, etching the grooves, applying oil repellent film, assembling the components, and adding the lubricant. In the prior art, as shown in  FIG. 1 , the bearing and the spindle motor are manufactured together as a single unit and the bearing is an integral part of the spindle motor. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a spindle motor and a method of manufacturing a spindle motor that improves manufacturing efficiency and that allows for easily matching design specifications with manufacturing requirements. 
   One aspect of the present invention is a bearing unit preferably a hydrodynamic bearing unit for use in a spindle motor where the bearing unit is a discrete component. Another aspect of the present invention is a spindle motor comprised of modular interchangeable units such as bearing units, rotor units, and stationary units, which can be combined to meet the specific needs of a particular application. A further aspect of the present invention is a method of manufacturing a spindle motor whereby the bearing unit is manufactured separately from the other components of the motor and is thereafter combined with the other motor components. A further aspect of the present invention is a method of manufacturing a motor wherein modular motor components are manufactured, requirements for a specific application are received, and a motor meeting those requirements is manufactured by selecting the appropriate components and combining them to make a motor that meets the received requirements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is illustrated by way of example and not limitation and the figures of the accompanying drawings in which like references denote like or corresponding parts, and in which: 
       FIG. 1  is a cross sectional drawing showing a prior art spindle motor. 
       FIG. 2  is a cross sectional drawing showing a spindle motor embodying an aspect of the present invention. 
       FIG. 3  is a cross sectional drawing showing a bearing unit embodying an aspect of the present invention. 
   

   DETAILED DESCRIPTION 
   A spindle motor embodying the present invention is shown in FIG.  2 . The spindle motor is comprised of bearing unit  1 , rotating unit  2 , and stationary unit  3 . Bearing unit  1  allows rotating unit  2  to rotate with respect to stationary unit  3 . 
   As shown in  FIG. 2 , rotating unit  2  is comprised of rotor hub  21 , yoke  22 , and magnets  23 . A disc (not shown) can be mounted on rotor hub  21 . Yoke  22  mounts magnets  23  to rotor hub  21 . 
   As shown in  FIG. 2 , stationary unit  3  is comprised of bracket  31 , core  32 , and coils  33 . Bracket  31  allows the spindle motor to be attached to a hard disc drive. Core  32  and coils  33  are mounted to bracket  31  and they generate a rotating electric field. 
   As shown in  FIG. 3 , bearing unit  1  is comprised of fixed shaft  11 , rotating sleeve  12 , conical bearings  13 , expansion joint  14 , and bushing  15 . Conical bearings  13  are hydrodynamic bearings that allow rotating sleeve  12  to rotate about fixed shaft  11  without contacting fixed shaft  11 . Bushing  15  is affixed to rotating sleeve  12 . Expansion joint  14  allows for thermal expansion in the bearing unit. 
   Fixed shaft  11  of bearing unit  1  is affixed to bracket  31  of stationary unit  3 . Bushing  15  of bearing unit  1  is affixed to rotor hub  21  of rotating unit  2 . During spindle motor operation, core  32  and coil  33  generate a rotating electric field that applies a rotational force to magnets  23  that is coupled to rotating sleeve  12  through yoke  22 , rotor hub  21 , and bushing  15 . Accordingly, rotating sleeve  12  and rotating unit  2  rotate about fixed shaft  11 . 
   A spindle motor according to the present invention can be manufactured with a rotating shaft and a stationary sleeve instead of a fixed shaft and a rotating sleeve. In which case, the rotating shaft would be affixed to the rotating unit and the stationary sleeve would be affixed to the stationary unit. Additionally, the bearings in the bearing unit need not be hydrodynamic conical bearings. Other types of bearings can be used such as hydrodynamic thrust bearings, hydrodynamic journal bearings, pivot bearings, or ball bearings. 
   In one aspect of the present invention, bearing unit  1  is manufactured separately from the other components of the spindle motor. It is then affixed to rotating unit  2  and to stationary unit  3  to form a spindle motor. Manufacturing bearing unit  1  as a separate component increases the ease with which the bearing can be handled and reduces the overall cost of manufacturing a spindle motor. 
   In another aspect of the present invention, a plurality of interchangeable types of bearing units are manufactured with a variety of bearing properties such as stiffness, energy consumption, durability, cost, operating temperature range, etc. Depending upon the particular application in which the spindle motor is to be used, the appropriate bearing unit is selected and then combined with a rotating unit and a stationary unit. Additionally, a plurality of interchangeable types of rotating units and a plurality of interchangeable types of stationary units can be manufactured, where each type of rotating unit and each type of stationary unit has distinct properties. Depending upon the performance requirements of a particular application in which a spindle motor is to be used, an appropriate type of bearing unit, an appropriate type of stationary unit, and an appropriate type of rotating unit is selected to manufacture a spindle motor that will meet the performance requirements while minimizing the cost of the motor. 
   The drawings and descriptions of the preferred embodiments are made by way of example rather than to limit the scope of the inventions, and they are intended to cove all such changes and modifications as are within the spirit and scope of the inventions.