Abstract:
A disk drive slit shroud mitigates a discontinuity in the bypass channel with an additional wall feature formed on the slit shroud. When installed, the wall feature fills the gap in the wall of the bypass channel that would otherwise be required to accommodate a slit shroud of sufficient surface area. The discontinuity in the channel wall is needed for manufacturing clearance during the installation of the slit shroud. The slit shroud design includes the wall feature which, when installed, fills up the gap in the channel wall to maintain a relatively flush conduit for the bypass channel.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to disk drives and, in particular, to an improved system, method, and apparatus for a slit shroud with an integrated bypass channel wall feature for disk drive applications. 
     2. Description of the Related Art 
     Generally, a data access and storage system consists of 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 (DASD) 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. Typically, one to six disks are stacked on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). 
     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 (ABS) 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. 
     In the prior art, a number of solutions have been proposed to enhance the air flow within hard disk drives, such as bypass channels located adjacent to the disk pack. For example, some disk drives have air guides that only guide a central portion of the flow of air back to the disks. Other disk drives have housings with doors that guide the flow of air from the disks to a filter, or they use diverter ramps that also only affect a central portion of the air flow. 
     For server class disk drive applications, the turbulence generated by the disk drive internal airflow is a significant contributor to the track misregistration (TMR) budget. To improve file performance and reliability, it is important to reduce the turbulence effects for the airflow around the HGA assembly. Two different techniques that are commonly used for turbulence reduction are the “dedicated flow bypass channel” and the “slit shroud.” 
     The dedicated flow bypass channel directs the upstream, highly turbulent airflow away from the HGA assembly region and returns it downstream of the HGA. The bypass channel is designed to have low resistance to airflow so that the extra motor torque needed to bypass the airflow around the HGA region is minimized. For effectiveness and manufacturing cost savings purposes, it is desirable to have the bypass channel designed into the base casting. 
     The purpose of the slit shroud is to maintain planar disk shrouding and to inhibit axial turbulent velocity components (i.e., relative to the planar orientation of the disks) that excite the HGA assembly. The slit shroud shields each individual suspension and the tail of the integrated lead suspension (ILS) from axial excitation from the mixing of highly turbulent radial flow coming off of the multiple spinning disks during operation. To increase the effectiveness of the slit shroud, the coverage area of the slit shroud adjacent the disks and HGAs must be maximized. Although these solutions are workable for some applications, other applications do not have sufficient coverage area for slit shrouds to operate effectively. Thus, an improved solution for disk drive applications having insufficient area to support conventional slit shrouds would be desirable. 
     SUMMARY OF THE INVENTION 
     One embodiment of a system, method, and apparatus for a disk drive slit shroud mitigates a discontinuity in the bypass channel with a wall feature in the slit shroud. When installed, the wall feature fills the gap in the wall of the bypass channel that would otherwise be required to accommodate a slit shroud of sufficient surface area. The bypass channel is most effective when designed into the base casting of the disk drive. In one embodiment, the discontinuity in the channel wall is needed for manufacturing clearance during the installation of the slit shroud. The slit shroud design includes the wall feature which, when installed, fills up the gap in the channel wall to maintain a relatively flush conduit for the bypass channel such that air leakage is minimized. 
     The invention is highly effective for some disk drive applications due to the limited disk drive “real estate” or surface area available in the disk drive, and for manufacturing process requirements. The bypass channel wall continuity must be compromised in some disk drive applications so that the slit shroud can be installed. The violation of the bypass wall continuity reduces the effectiveness of both the bypass channel because of reduced pressure and the slit shroud due to the addition of airflow disturbance from bypass channel leakage. The invention overcomes the limitations and makes limited area drives compatible with slit shrouds. 
     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, which will become apparent, are attained and can be understood in more detail, 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 which form a part of this specification. It is to be noted, however, that 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 one embodiment of a disk drive constructed in accordance with the present invention; 
         FIG. 2  is an isometric view of a base casting of the disk drive of  FIG. 1 , shown without installation of a slit shroud, and is constructed in accordance with the present invention; 
         FIG. 3  is an enlarged isometric view of a portion of the base casting of  FIG. 2 , shown with a slit shroud partially installed, and is constructed in accordance with the present invention; 
         FIG. 4  is an enlarged isometric view of a portion of the base casting of  FIG. 3 , shown with the slit shroud installed, and is constructed in accordance with the present invention; and 
         FIG. 5  is a high level flow diagram of a method in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , one embodiment of a system, method, and apparatus for an information storage system comprising a magnetic hard disk file or drive  111  for a computer system having a lightweight spoiler wing design is shown. Drive  111  has an outer housing including a base  113  and top cover (not shown). The housing contains a disk pack having at least one media disk, e.g., magnetic disk  115 . The 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  in the form of a comb that is movably or pivotally mounted to base  113  about a pivot assembly  123 . A controller  119  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 (HGA) is the head and the slider  129 , which are mounted on suspension  127 . 
     Suspensions  127  bias 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  133  free to move within a conventional voice coil motor magnet assembly  134  (top pole not shown) is also mounted to arms  125  opposite the head gimbal assemblies. Movement of the actuator  121  (indicated by arrow  135 ) by controller  119  moves the head gimbal assemblies along radial arcs across tracks on the disk  115  until the heads settle on their respective target tracks. The head gimbal assemblies operate in a conventional manner and always move in unison with one another, unless drive  111  uses multiple independent actuators (not shown) wherein the arms can move independently of one another. 
     The disks  115  define an axis  201  of rotation  205  and radial direction  207  relative to the axis  201 . The 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 bypass channel  219  located in the housing  113  for directing the air flow generated by rotation of the disks  115  from the downstream side  213  of the disk pack or disks  115  to the upstream side  215  of the disks  115 . In this way the airflow substantially bypasses the actuator. 
     In the embodiment shown, the bypass channel  219  is located between an outer perimeter  217  of the housing  113  and the actuator  121 , such that the bypass channel  219  completely circumscribes the actuator  121 . The elements that define the bypass channel  219  may be integrally formed (e.g., cast) with the base  113 . In some HDD designs where there is not sufficient space to implement a full bypass channel (shown) the bypass channel  219  may be interrupted (not shown). This is known as a partial bypass. Furthermore, in order to help the bypass airflow negotiate substantial angular changes (channel bends), one or more turning vanes may be placed in those areas. 
     Referring now to  FIGS. 1-4 , one embodiment of the drive  111  also comprises a slit shroud  300 . The slit shroud  300  is designed to be integrated and work with the bypass channel  219 . The bypass channel  219  includes inner and outer walls  301 ,  303  that define the conduit for the airflow. At least one opening  305  ( FIGS. 2 and 3 ) is formed in the inner wall  301  adjacent the actuator  121 . The slit shroud  300  may be mounted to the housing adjacent the actuator  121  for maintaining planar shrouding of the media disk(s)  115  and inhibit axial turbulent velocity components with respect to the actuator  121 . The slit shroud  300  has a wall feature  307  that is located in and closes the opening  305  when fully installed ( FIG. 4 ) at the inner wall  301  of the bypass channel  219 . The wall feature  307  is complementary to the inner wall  301  and, in one embodiment, flush with it as well for contiguous airflow through the conduit and to reduce drag. 
     In one embodiment, the wall feature  307  of the slit shroud  300  and the inner wall  301  of the bypass channel  219  extend in an axial direction (e.g., vertically) from the housing. The wall feature  307  and the opening  305  may span a linear gap of approximately 1 mm to 20 mm. For example, a typical 3.5-inch server class drive the gap may comprise about 5 mm. As shown in the drawings, the opening  305  may comprise a flat rectangular hole, and the wall feature  307  is a flat rectangular panel that completely covers opening  305 . 
     As shown in the illustrated embodiment of  FIG. 2 , the opening  305  in the inner wall  301  of the bypass channel  219  is located on the upstream side  215  (reference  FIG. 1 ) of the media disk  115  but spaced apart from the media disk  115 . The opening  305  separates the inner wall  301  into an upstream portion  309  to the right of opening  305  in  FIG. 2  and a downstream portion to the left of opening  305  in  FIG. 2 . The downstream portion of the inner wall  301  extends from the downstream side  213  of the media disk  115  and around the actuator  121  opposite the media disk  115 . The upstream portion  309  of the inner wall  301  is located only directly adjacent the upstream side  215  of the media disk  115 , such that the downstream portion of the inner wall  301  is much longer and represents more of the inner wall  301  than the upstream portion  309  of the inner wall  301 . 
     In addition, the slit shroud  300  comprises one or more planar platforms  311  that may be equal in number to the number of media disks  115 . The platforms  311  are axially aligned with and parallel to the media disks  115 . As shown in  FIG. 4 , the platforms  311  have a planar surface area that extends from the perimeters of the media disks  115  outward toward the wall feature  307  of the slit shroud  300 . 
     In some disk drive embodiments, a load/unload ramp is required for suspensions  127 . For those applications, the “sliding” installation of slit shroud  300  relative to suspensions  127  (i.e., parallel to the planes defined by suspensions  127 ) prevents damage to the components of the drive. If no load/unload ramp is required, the slit shroud  300  (i.e., wall feature  307 ) may be installed directly downward into opening  305  by motion perpendicular to the planes defined by suspensions  127 . 
     Referring now to  FIG. 5 , the invention also comprises a method of directing airflow in a disk drive. In one embodiment the method begins as indicated at step  501 , and comprises providing the disk drive with a media disk, an actuator, and a bypass channel (step  503 ); shrouding the actuator with a slit shroud and defining at least a portion of the bypass channel with the slit shroud (step  505 ); directing airflow through the bypass channel such that at least a portion of the airflow is directed by the slit shroud (step  507 ); before ending as indicated at step  509 . 
     The method may further comprise directing airflow with the bypass channel from a downstream side of the media disk to an upstream side of the media disk, and providing the slit shroud with a wall feature that defines said at least a portion of the bypass channel. In another embodiment, the method may comprise substantially bypassing airflow around the actuator with the bypass channel, and providing the bypass channel with a wall that defines a conduit for the airflow and an opening in the wall adjacent the actuator, and wherein the slit shroud maintains planar shrouding of the media disk and inhibits axial turbulent velocity components with respect to the actuator, and the slit shroud has a wall feature that closes the opening in the wall of the bypass channel, such that the wall feature is complementary to the wall. In addition the method may further comprise making the slit shroud flush with the bypass channel. 
     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.