Abstract:
A hard disk drive has a recirculation filter that shrouds the rims of disks at the inlet and outlet of the filter. The shroud is aerodynamically shaped to reduce flow-induced disk vibration of the read/write head. A significant improvement in non-repeatable run-out is provided when the inlet and outlet are shrouded along the rims of the disks.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to hard disk drives and, in particular, to an improved system, method, and apparatus for a hard disk drive having a recirculation filter with shrouding that shrouds the rims of disks at the inlet and outlet of the filter. 
     2. Description of the Related Art 
     Data access and storage systems typically comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. One to six disks are usually stacked on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute. 
     A typical HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The surface of the slider facing the disk is aerodynamically shaped to create an air bearing in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. 
     Typically, a slider is formed with an aerodynamic pattern of protrusions on its air bearing surface that enables the slider to fly at a substantially constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk&#39;s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system. 
     The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops a torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track. 
     Some disk drive designs use an air recirculation filter to reduce contamination inside the disk drive. Since the amount of available space inside a disk drive enclosure is typically very limited, it can be difficult to accommodate such a filter. One difficulty in determining the proper location for a recirculation filter is selecting a space that is suitable for both good clean up efficiency and one that will have a minimum impact on other important criteria, specifically track misregistration (TMR) and aerodynamic power consumption. 
     In small form factor drives, the lack of space usually results in placing the recirculation filter  11  at the so-called “11 o&#39;clock” location.  FIGS. 1-3  depict one type of prior art placement of a filter at the 11 o&#39;clock position with unshrouded inlet  13  and outlet  15 . As best shown in  FIG. 2 , the rim  17  of the disk  19  is completely exposed at both the inlet  13  and at the outlet  15  in front of the air filter  11 . As shown in  FIG. 3 , the filter inlet  13  and outlet  15  are open all the way to the casting floor  21 . 
     Wherever the disk is not shrouded the airflow separates from the disk in a highly turbulent and unsteady manner. The result is undesirable unsteady forces on the disk which contribute to position errors (as indicated by the position error signal (PES)) of the read/write head. With such physical interruptions adjacent to the disks, disk flutter is exacerbated due to an increase in flow turbulence in between and around the filter. 
     The unsteadiness of the aerodynamic forces has frequency components that are beyond the bandwidth of current servo systems. Such forces cannot be corrected or, worst yet, are even amplified by the servo system. In principle, the high frequency components could be counteracted with systems based on micro-actuators and the like, but such systems can be quite expensive and prone to their own increased aerodynamic excitation. Thus, an improved solution for overcoming the limitations and problems associated with the prior art would be desirable. 
     SUMMARY OF THE INVENTION 
     Embodiments of a system, method, and apparatus for a hard disk drive having a recirculation filter with shrouding that shrouds the rims of disks at the inlet and outlet of the filter are disclosed. The aerodynamic shaping utilized by the invention is a highly effective and economical means of reducing flow-induced disk vibration or flutter compared to prior art solutions. 
     The invention provides a significant improvement in non-repeatable run-out (NRRO) when the inlet and outlet are shrouded along the rims of the disks. An NRRO reduction of about 0.2% TP (track pitch) at the disk outer diameter (OD) is realized in some applications. Such improvements result in a reduction in disk flutter modes, particularly in the sensitive OD region. 
     The invention advantageously reduces disk flutter and NRRO, and reduces the overall part count for the disk drive to reduce its cost (i.e., no extra part is needed as a filter holder). The invention also allows the filter to be placed at the 11 o&#39;clock position and reduces power consumption by the disk drive. In one embodiment, the rims of the disks are completely shrouded while allowing the recirculation flow to pass through the filter. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the present invention are attained and can be understood in more detail, a more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the appended drawings. However, the drawings illustrate only some embodiments of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a plan view of a conventional disk drive with cover removed; 
         FIG. 2  is an enlarged plan view of a portion of the conventional disk drive of  FIG. 1 ; 
         FIG. 3  is an isometric view of the portion of the conventional disk drive of  FIG. 1  with the disk and filter removed; 
         FIG. 4  is a plan view of one embodiment of a disk drive constructed in accordance with the invention and shown with cover removed; 
         FIG. 5  is an enlarged plan view of a portion of the disk drive of  FIG. 4  and is constructed in accordance with the invention; 
         FIG. 6  is an isometric view of the portion of the disk drive of  FIG. 5  with the disk and filter removed; and 
         FIG. 7  is an isometric view of the portion of the disk drive of  FIG. 6  shown with the top disk transparent. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 4 , one embodiment of a system, method and apparatus for a hard disk drive having a recirculation filter with shrouding that shrouds the rims of disks at the inlet and outlet of the filter is disclosed. The drive  111  has an outer housing or base  113  containing a disk pack having at least one medium or magnetic disk  115 . The disk or disks  115  are rotated (see arrows  205 ) by a spindle motor assembly having a central drive hub  117 . An actuator  121  comprises a plurality of parallel actuator arms  125  (one shown) in the form of a comb that is movably or pivotally mounted to base  113  about a pivot assembly. A controller is also mounted to base  113  for selectively moving the comb of arms  125  relative to disk  115 . 
     In the embodiment shown, each arm  125  has extending from it at least one cantilevered load beam and suspension  127 . A magnetic read/write transducer or head is mounted on a slider  129  and secured to a flexure that is flexibly mounted to each suspension  127 . The read/write heads magnetically read data from and/or magnetically write data to disk  115 . The level of integration called the head gimbal assembly consists of the head and the slider  129 , which are mounted on suspension  127 . The slider  129  is usually bonded to the end of suspension  127 . 
     Suspensions  127  have a spring-like quality, which biases or urges the air bearing surface of the slider  129  against the disk  115  to cause the slider  129  to fly at a precise distance from the disk. A voice coil that is free to move within a conventional voice coil motor magnet assembly is also mounted to arms  125  opposite the head gimbal assemblies. Movement of the actuator  121  by the controller moves the head gimbal assemblies along radial arcs across tracks on the disk  115  until the heads settle on their respective target tracks. 
     Referring now to  FIGS. 4-7 , the disk pack and disks  115  (one shown) define an axis  201  of rotation  205  and radial directions  207 ,  209 , relative to the axis  201 . The disk pack and disks  115  have a downstream side  213  wherein air flows away from the disks  115 , and an upstream side  215  wherein air flows toward the disks  115 . 
     The drive  111  also has a shroud  219  (best shown in  FIG. 6 ) that is formed in the housing  113 . In the embodiment shown, shroud  219  is integrally formed with the base casting or housing  113 . Shroud  219  directs the air flow generated by rotation of the disks  115  from the downstream side  213  of the disk pack or disks  115 , through a filter channel  221 , an air filter  223  located in filter channel  221 , and then to the upstream side  215  of the disk pack or disk  115 . The body of the shroud  219  reduces air flow drag from and to the disks  115  due to disk wake in and through the filter channel  221 . The mixing of air inside the disk pack with that from outside the disk pack causes tangential Reynolds stress. The work done by this Reynolds stress must be supplied by the spindle motor. To minimize both excitation and the amount of power required by the spindle, turbulent mixing must be minimized. 
     In the embodiment shown, the shroud  219  is located between an outer perimeter  217  of the housing  113  and the disk  115 . In one embodiment, the shroud  219  is located in what is commonly referred to as the “11 o&#39;clock position” (see upper left portions of  FIGS. 4 and 5 ). This may comprise locating the shroud  219  on the opposite side of disk  215  relative to actuator  121  (see  FIG. 4 ), which is located adjacent to the “5 o&#39;clock position.” In one embodiment, the shroud  219  may extend in an arcuate or circumferential span from about the 9 o&#39;clock position (see line  220 ) to about the 12 o&#39;clock position (see line  222 ) or beyond. 
     A seal  225  extends near and around the outer perimeter  217  to seal the cover (not shown) to housing  113 . The shroud  219 , filter channel  221  and air filter  223  are located completely within the seal  225  to protect them from exposure to external contaminants relative to drive  111 . 
     In the two-disk configuration shown in  FIGS. 6 and 7 , the shroud  219  is provided with two edge walls  231  that closely follow the external contours (i.e., rims  232  in  FIG. 6 ) of the two disks  115 . However, the shroud may be provided with more or fewer edge walls depending on the number of disks contained within a particular drive. The edge walls  231  are arcuate and complimentary in shape to the perimeters or rims  232  of the disks  115 . The edge walls  231  are radially spaced apart from the rims  232  by a radial clearance that is typically greater than 0 mm but less than 1 mm. For example, the radial clearance may comprise no more than about 0.2 mm. 
     Each of the edge walls  231  of the shroud  219  has a generally cylindrical transverse surface extending in the axial direction that flatly faces the rims  232  of the disks  115 . The transverse surfaces are located immediately adjacent to respective ones of the disks  115  (see  FIGS. 4 ,  5  and  7 ) and is substantially perpendicular to the planar orientations of the disks  115 . The edge walls  231  have arcuate contours that are complementary in shape with respect to circular outer edges  232  of the disks  115 . 
     Again referring to  FIGS. 6 and 7 , the edge walls  231  have axial dimensions or thicknesses  233  that are equal to or greater than the axial dimensions or thicknesses  235  of their respective disks  115 . In addition, the entire thickness  235  of each disk  115  is axially aligned with or located within the axial direction and dimension  233  of respective ones of the edge walls  231 . 
     Arcuate slotted openings  241 ,  243  formed between the edge walls  231  provide ingress and egress, respectively, for filter channel  221 . Opening  241  is formed on the downstream side  213  of disk  115 , while opening  243  is formed on the upstream side  215  ( FIG. 5 ) of disk  115 . The openings  241 ,  243  may be divided by a partition  245  ( FIG. 6 ) as shown, which may be located at the 11 o&#39;clock position. Also in the embodiment shown, the filter  223  ( FIGS. 5 and 7 ) is located only adjacent to the downstream side  215  ( FIG. 5 ) of the disk, rather than the upstream side  213  or both sides. 
     In one embodiment, the shroud is located between the filter channel and the disk adjacent to both the downstream and upstream sides of the disk. The shroud has arcuate edge walls that are complementary in shape to the outer rim of the disk and closely follow an external contour of the outer rim of the disk. The arcuate edge walls are complimentary in shape to the outer rim of the disk and have generally cylindrical transverse surfaces extending in the axial direction that flatly face the outer rim of the disk. The transverse surfaces are located immediately adjacent to the outer rim of the disk substantially perpendicular to a planar orientation of the disk. The shroud has arcuate slotted openings formed adjacent to the arcuate edge walls to provide ingress and egress, respectively, for the filter channel. 
     The air filter  223  filters the air flowing through the filter channel  221  and/or housing  113 . In one embodiment, the air filter  223  incorporates electrical charges to filter the air flowing through the filter channel  221  and/or housing  113 . The efficacy of the filtration material may be enhanced, for example, by incorporation of electric charges (electret). 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.