Abstract:
A device streamlines air flow inside a hard disk drive with a stationary afterbody that is located adjacent to the disks. The device gradually expands the air flow so that the speed of the air flow gradually decreases while pressure increases. This design reduces losses in system momentum due to sudden expansion of the air in the drive. In addition, air flow moving toward the disk pack may be contracted to allow efficient energy conversion from pressure energy to kinetic energy prior to merging of the bypass air flow with the air flow among the disks. The device has a comb-like structure that is offset slightly from the spinning disk pack in the radial direction. The structure fulfills an aerodynamic function, reduces track misregistration, lowers overall aerodynamic dissipation and fulfills a filtration function.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates in general to an improved aerodynamic design for a diffuser and/or contraction and, in particular, to an improved system, method, and apparatus for diffusing and contracting air flow, especially within a hard disk drive to reduce flow-induced vibrations of the arm, suspension, and slider as well as the rotating disks.  
         [0003]     2. Description of the Related Art  
         [0004]     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).  
         [0005]     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.  
         [0006]     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.  
         [0007]     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.  
         [0008]     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, Japanese Patent JP53-47089, to Yasuaki, reveals a hard disk device in which air guides  20 ,  30  only guide a central portion of the flow of air back to the disks. Japanese Patent JP62-85997, to Wakatsuki, discloses a magnetic disk device ( FIGS. 3-5 ) in which a housing  31  with doors  20  guides the flow of air from the disks to a filter. U.S. Pat. No. 5,907,453, to Wood, reveals diverter ramps  220 ,  222  ( FIG. 9 ) that also only affect a central portion of the air flow.  
         [0009]     Currently known implementations of bypass channels such as these force a sudden widening of the air flow cross-section by as much as 50%. The sum of the thicknesses of the disk(s) in the disk pack is a significant fraction of the height of the bypass channel in the direction of the spindle axis. As a result, present designs cause objectionable disk base drag due to the disk wakes in the bypass channel. Moreover, there is also objectionable drag due to re-acceleration of the slow, bypass air flow around the actuator. Thus, an improved solution for streamlining air flow within a hard disk drive would be desirable.  
       SUMMARY OF THE INVENTION  
       [0010]     One embodiment of an apparatus for streamlining air flow inside of a hard disk drive is disclosed. The air flow is guided into a bypass channel. Each disk is provided with a stationary afterbody. The afterbody is shaped such that an expanding duct is created for the flow coming off each disk. An expanding aerodynamic duct is called a diffuser. In one embodiment, a diffuser provides a gradually expanding passage so that the speed of the air flow can gradually, rather than abruptly, decrease and the pressure can rise. This design reduces losses in system momentum due to sudden expansion of the air or gas in the drive.  
         [0011]     The present invention also ensures a smooth recovery process of pressure from kinetic energy in the entering flow field, which reduces the amount of power required by the spindle motor. The downstream diffuser receives air flow spun off the disks while reducing the rate of cross sectional expansion, and consequential turbulence, of the air as it travels from among the disk surfaces around the actuator and non-aerodynamic disk drive components. Upon return of the bypass flow to the disk pack, air flow reentering the disk pack is accelerated in a channel of diminishing cross section to allow efficient energy conversion from pressure energy to kinetic energy prior to merging of the bypass air flow with the air flow among the disks.  
         [0012]     The present invention utilizes a comb-like structure (diffuser or contraction) that is offset slightly from the spinning disk pack in the radial direction by approximately 0.5 mm, or whatever minimal distance is required due to mechanical tolerances. In one embodiment, the structure fulfills an aerodynamic function only. However, the structure may also be configured to perform a filtration function, in which case the structure may be formed from a filtration substance. The efficacy of the filtration material may be enhanced, for example, by incorporation of electric charges (electret). The structure may be provided with linear or rounded tapers. However, smooth, edge-free tapers are desirable. For example, since the contraction is required to re-accelerate the air flow into the disk pack, the leading edges of the contraction are preferably rounded.  
         [0013]     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 preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     So that the manner in which the features and advantages of the invention, as well as others 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 embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0015]      FIG. 1  is a schematic, top plan view of a hard disk drive constructed in accordance with the present invention.  
         [0016]      FIG. 2  is a front isometric view of a diffuser for the hard disk drive of  FIG. 1  and is constructed in accordance with the present invention.  
         [0017]      FIG. 3  is a rear isometric view of the diffuser of  FIG. 2 , and is constructed in accordance with the present invention.  
         [0018]      FIG. 4  is a front isometric view of the diffuser of  FIG. 2  showing one of the adjacent disks, and is constructed in accordance with the present invention.  
         [0019]      FIG. 5  is a front isometric view of a contraction for the hard disk drive of  FIG. 1  and is constructed in accordance with the present invention.  
         [0020]      FIG. 6  is a rear isometric view of the contraction of  FIG. 5 , and is constructed in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Referring to  FIG. 1 , a schematic drawing of one embodiment of an information storage system comprising a magnetic hard disk file or drive  111  for a computer system is shown. Drive  111  has an outer housing or base  113  containing a disk pack having at least one media 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  123 . A controller  119  is also mounted to base  113  for selectively moving the comb of arms  125  relative to disk  115 .  
         [0022]     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 is head and the slider  129 , which are mounted on suspension  127 . The slider  129  is usually bonded to the end of suspension  127 . The head is typically pico size (approximately 1250×1000×300 microns) and formed from ceramic or intermetallic materials. The head also may be of “femto” size (approximately 850×700×230 microns) and is pre-loaded against the surface of disk  115  (in the range two to ten grams) by suspension  127 .  
         [0023]     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  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.  
         [0024]     Referring now to  FIGS. 1 and 4 , 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 bypass channel  219  formed 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 disk pack or disks  115 . In the embodiment shown, the bypass channel  219  is located between an outer perimeter  217  ( FIG. 1 ) of the housing  113  and the actuator  121 , such that the bypass channel  219  completely circumscribes the actuator  121 . 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. When there is a partial bypass, the presence of a diffuser and contraction remains beneficial. Furthermore, in order to help the bypass flow negotiate substantial angular changes (channel bends), one or more turning vanes may be placed in those areas. The use of turning vanes is well known in wind tunnel design.  
         [0025]     As shown in  FIGS. 1 through 4 , one embodiment of the drive  111  constructed in accordance with the present invention also comprises a diffuser  221 . In the embodiment shown, the diffuser  221  is located in the bypass channel  219  and is positioned adjacent to the downstream side  213  of the disk pack or disks  115 . The diffuser  221  is also offset downstream from the disks  115  in the radial direction  207 , such that the diffuser  221  reduces air flow drag from the disks  115  due to disk wake in the bypass channel  219 . This type of aerodynamic drag is commonly called base drag.  
         [0026]     Alternatively, or operating in conjunction with the diffuser  221 , another embodiment of the drive  111  may include a contraction device or contraction  223  ( FIGS. 5 and 6 ). The contraction  223  is also located in the bypass channel  219 , but is adjacent to the upstream side  215  of the disk pack or disks  115 . Like the diffuser  221 , the contraction  223  is offset upstream from the disks  115 , but in a radial direction  209 . Each of the diffuser  221  and the contraction  223  may be spaced apart from outer edges  213 ,  215 , respectively, of the disks  115  in radial directions  207 ,  209 , respectively, by, for example, no more than approximately 0.5 mm. The contraction  223  is provided for re-accelerating a slow bypass air flow  225  ( FIGS. 1, 5 , and  6 ) from the contraction  223  to the disks  115  to provide efficient energy conversion for the air flow from pressure energy to kinetic energy prior to merging the slow bypass air flow  225  with air flow  205  ( FIG. 1 ) around the disks  115 .  
         [0027]     In another embodiment of the present invention, each of the diffuser  221  and/or the contraction  223  may further comprise an air filter(s) for filtering the air flowing through the bypass channel  219  and/or housing  113 . Either or both structures  221 ,  223  may be configured to perform this filtration function, in which case they may be formed from a filtration substance. In one particular embodiment, the diffuser  221  and the contraction  223  incorporate electrical charges to filter the air flowing through the bypass channel  219  and/or housing  113 . The efficacy of the filtration material may be enhanced, for example, by incorporation of electric charges (electret).  
         [0028]     In the embodiments illustrated, both the diffuser  221  and the contraction  223  are equipped with a plurality of airfoils  231 ,  233 , respectively. The airfoils  231 ,  233  may be identical but, as shown in the illustrations, they may be configured differently as well. The airfoils  231 ,  233  are axially apart from each other, respectively, in the axial direction. Each of the airfoils  231 ,  233  has a generally planar orientation in the radial direction. As shown, for example, in  FIG. 4 , the airfoils  231  (only one shown for clarity) are axially aligned with one of the disks  115 . The airfoils  231 ,  233  also having a maximum axial thickness  235  ( FIG. 2 ) that is preferably equal to an axial thickness  237  ( FIG. 4 ) of a respective one of the disks  115 . The diffuser shape must be such as to promote adherence of the flow to the surface while avoiding flow separation. It is well known in the art that flow separation occurs when the diffuser widens too suddenly. Furthermore, it will be understood that an array of flow conditioning measures can be applied to the basic diffuser shape shown for the purpose of promoting adherence of the flow to the diffuser walls. Among these measures are turbulators consisting of surface roughness elements, for example ridges, vortex generators, boundary layer tripping devices and the like. Other flow conditioning measure is irradiation of the flow with sound. The mentioned flow conditioning techniques are known in the art of aerodynamic design.  
         [0029]     Each of the airfoils  231  of the diffuser  221  has a leading edge  241  with a generally cylindrical transverse surface  243  extending in the axial direction that flatly faces the disks  115 . Transverse surface  243  is located immediately adjacent to a respective one of the disks  115  (see  FIGS. 1 and 4 ) and is substantially perpendicular to a planar orientation of a respective one of the disks  115 . Each of the airfoils  233  of the contraction  223  has a trailing edge  251  located immediately adjacent to a respective one of the disks  115 , and a leading edge  253  with a rounded surface  255  that is located opposite the trailing edge  251 .  
         [0030]     The leading edges  241  of the airfoils  231  of the diffuser  221  and the trailing edges  251  of the airfoils  233  of the contraction  223  have arcuate contours that are complementary in shape with respect to circular outer edges  213 ,  215  of the disks  115 . The airfoils  231  of the diffuser  221  also have trailing portions  245  located opposite the leading edges  241 . The trailing portions  245  taper down in axial thickness in the air flow direction away from the disks  115  to define gradually expanding passages  249 . The air flow transitions from the disks  115  to the trailing portions  245  along the tapers to gradually decrease a speed of the air flow.  
         [0031]     As shown in  FIGS. 2-4 , the tapers on the airfoils  231  of the diffuser  221  are smooth and edge-free from the leading edges  241  to the trailing portions  245 . Alternatively, the tapers may be configured with linear tapers. The airfoils  233  of the contraction  223  may be provided with similar smooth and edge-free tapers extending from their respective leading edges  253  to their respective trailing edges  251 . In addition, the trailing portions  245  of the airfoils  231  of the diffuser  221  and the leading edges  253  of the airfoils  233  of the contraction  223  have linear edges that are substantially perpendicular to the directions of the air flow at the downstream and upstream sides  213 ,  215 , respectively, of the disk pack or disks  115 . Furthermore, the leading edges  253  of the airfoils  233  of the contraction  223  are preferably rounded  255 , as shown in  FIGS. 5 and 6 .  
         [0032]     The present invention has several advantages, including the ability to streamline air flow in a hard disk drive. The air flow is smoothed into the bypass channel with a stationary afterbody. The diffuser provides a gradual expanding passage so that the speed of the air flow can gradually decrease and the pressure can rise. This design reduces losses in system momentum due to sudden expansion of the air or gas in the drive, and ensures a smooth recovery of pressure from kinetic energy in the entering flow field. As a result, the amount of power required by the spindle motor is reduced. Alternatively, air flow moving toward the disk pack is contracted to allow efficient energy conversion from pressure energy to kinetic energy prior to merging of the bypass air flow with the air flow among the disks. The structure also may be used to filter the air flow. It will be understood that the present invention encompasses designs in which the diffuser or contraction are not implemented. The usual reason being interference with other drive components.  
         [0033]     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.