Abstract:
A disc drive system includes a disc drive chassis, a magnetic storage disc, a read/write transducer adjacent to the disc for reading and writing information on the disc, and a hydrodynamic bearing assembly. The hydrodynamic bearing assembly rotatably couples the magnetic storage disc to the disc drive chassis. The hydrodynamic bearing assembly includes a fluid path therethrough for circulating a fluid. A labyrinth seal and magnet shield is provided proximate the hydrodynamic bearing assembly.

Description:
This is a Continuation application of U.S. Ser. No. 09/111,127, filed Jul. 6, 1998, U.S. Pat. No. 6,055,126 entitled “DISC DRIVE HAVING HYDRODYNAMIC LABYRINTH SEAL AND MAGNET SHIELD”. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to disc drive systems for storing information. More specifically, the present invention relates to a hydrodynamic bearing assembly which provides support and rotation for a high speed spindle element. 
     The predominant trend in the disc drive industry for the past several years has been to increase track density in order to achieve increased data storage capacity. One of the difficulties which must be overcome in achieving this goal is the ability to maintain tracking position accuracy as the track density increases. 
     A major source of tracking position inaccuracy in a computer disc drive system is spindle bearing motion which is commonly referred to as “runout”. Conventional spindle bearings include ball bearing assemblies which are prone to numerous mechanical problems, such as large runout, substantial wear, capacious manufacturing requirements, and the like. 
     A hydrodynamic bearing is an alternative to conventional ball bearing spindle systems. In a hydrodynamic bearing assembly, a lubricating fluid functions as the actual bearing surface between a stationary base and the rotating spindle or hub. The lubricating fluid typically includes either air or liquid. The rotating hub causes the fluid to circulate through the hydrodynamic bearing. When the hub is stationary, the fluid is at rest. 
     Hydrodynamic bearing assemblies suffer from a number of disadvantages. For example, the hydrodynamic fluid must be sealed within the spindle so that it does not escape into the disc environment. Further, tolerance between components can be very small, particularly for disc density drives. The components are relatively delicate and can be damaged during assembly. 
     SUMMARY OF THE INVENTION 
     A disc drive system includes a disc drive chassis, a magnetic storage disc, a read/write transducer adjacent to the disc for reading and writing information on the disc, and a hydrodynamic bearing assembly. The hydrodynamic bearing assembly rotatably couples the magnetic storage disc to the disc drive chassis. The hydrodynamic bearing assembly includes a fluid path therethrough for circulating a fluid. A labyrinth seal and magnet shield is provided proximate the hydrodynamic bearing assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a magnetic disc drive including a labyrinth seal and magnet shield in accordance with the present invention. 
     FIG. 2 is a cross-sectional view of a spindle motor of FIG.  1 . 
     FIG. 3 is a more detailed cross-sectional view showing the labyrinth seal and magnet shield of the present invention. 
     FIG. 4 is a top plan view of the labyrinth seal and magnet shield. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a plan view of a disc drive  10  for use with the present invention. Disc drive  10  includes a chassis member  12  to which internal components of the disc drive  10  are mounted. Chassis member  12  couples to top cover  14  which forms a sealed environment for critical parts of the disc drive  10 . 
     Disc drive  10  includes at least one, but typically a plurality of discs  16  which are mounted for rotation on a spindle  18  having a bearing assembly (hub or sleeve)  20 . The bearing assembly  20  is described in greater detail below. Typically, a plurality of magnetic read/write heads  22  are mounted to an actuator  24  having an actuator body  26  and an actuator motor  28 . In the example shown at disc drive  10 , actuator  24  is a rotary actuator which is mounted for pivoting about a pivot axis  30 . Actuator  24  includes a number of head mounting arms  32  which couple the heads  22  to the actuator body  26  using a plurality of gimbal assemblies  34 . Actuator motor  28  is coupled to actuator body  26  to provide a force to move the heads  22  to a desired position on the surface of the disc  16  through arc  33 . 
     In operation, the spindle  18  causes disc  16  to rotate. Electronic circuitry  36  energizes the actuator motor  28  causing the actuator  24  to rotate about pivot axis  30  whereby the magnetic read/write head  22  is moved through arc  33  radially across the surface of the disc  16 . Actuator  24  positions head  22  over a concentric track. This allows the electronic circuitry  36  to read back or write information at desired locations on disc  16 . 
     As shown in FIG. 2, the hub/sleeve  20  is rotatably coupled to a bearing assembly  54 . The spindle motor  18  includes a stator assembly  78  preferably coupled to the chassis member  12  and a magnetized magnet  76  coupled to the hub/sleeve  20 . Interaction between the stator assembly  78  and the magnet  76  causes the hub/sleeve  20  to rotate about the bearing assembly  54 . 
     The bearing assembly  54  includes a shaft  56  connected to the chassis member  12 . The shaft  56  includes a bore  58  and a side opening  60 . A thrust plate  62  is connected to one end of the shaft  56  to secure the hub/sleeve  20  to the bearing assembly  54 . A counterplate  64  is connected to the hub/sleeve  20  and covers the opening  52 . Preferably, the inside diameter of the bore  50  is greater than the outside diameter of the shaft  56  so as to create a chamber  66  between the shaft  56  and the hub/sleeve  20 . The chamber  66  is filled with a lubricating fluid which is used to form a hydrodynamic bearing. The fluid is sealed within the chamber  66 . 
     When the hub/sleeve  20  is not rotating, the fluid within the chamber  66  is at rest. The counterplate  64  is in contact with the thrust plate  62  if the disc drive  10  (shown in FIG. 1) is in the horizontal position; or the shaft  56  is in contact with the hub/sleeve  20  if the disc drive  10  (shown in FIG. 1) is in the vertical position. When the hub/sleeve  20  is rotating, pressure differentials within chamber  66  cause the fluid to circulate through the chamber  66 . The fluid circulates through the bore  58  and side openings  60  and around the shaft and thrust plate  62 . When the hub/sleeve is rotating, the fluid suspends the counterplate  64  away from the thrust plate  62  such that the hub/sleeve can freely rotate about the shaft  56  and thrustplate  62 . 
     FIG. 2 also shows a labyrinth seal and magnet shield  90  in accordance with one embodiment of the present invention. As shown in FIG. 2, shield  90  is configured to fit within one end of hub/sleeve  20  near magnet  76 . FIG. 3 is a more detailed view of shield  90  in motor  18 . Shield  90  fits in a cut out section  92  of hub/sleeve  20  and includes a raised inner diameter portion  94  and an outer diameter portion  96 . Vertical section  98  extends between portions  94  and  96 . 
     In one preferred embodiment, shield  90  is formed from thin aluminum and is press fit into cut out section  92 . FIG. 4 is a top plan view of shield  90  showing sections  94 ,  96  and  98 . An inner opening  100  fits around shaft  56 . Preferably, the gap between shaft  56  and shield  90  is sufficiently small to form a labyrinth seal for any oil or other debris escaping from the capillary seal of the hydrodynamic bearing. Further, outer diameter portion  96  is positioned under magnet  76  to protect magnet  76  during manufacturing and assembly of the disc drive system. 
     Thus, shield  90  of the present invention may be easily implemented with existing spindle motors which employ hydrodynamic bearing. Further, the shield  90  protects the bottom side of magnet  76  from chipping during handling and assembly of the disc drive after magnet  76  has been mounted to hub/sleeve  20  but prior to final assembly. 
     The present invention offers a number of advantages over the prior art system. With the present invention, the magnet is protected such that the magnet is less likely to be damaged which could require the entire motor assembly to be replaced. Further, the invention provides additional sealing through a labyrinth seal such that evaporation of hydrodynamic fluid or other contaminants are inhibited so as to not contaminate the region containing the storage disc. Further, the invention can be easily retrofit with the existing designs. For example, the labyrinth seal and magnet shield on the invention can be fit into a recess region formed in a hub/sleeve of an existing motor design. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the labyrinth seal and magnet shield of the present invention may be formed of any appropriate material and have any shape as desired for a particular motor configuration, and may be implemented in any shape or using any technique as desired. Materials include stainless steel, plated metal, plastic, aluminum, etc.