Abstract:
An inlet to a disc drive&#39;s filter chamber is tapered to converge along most or all of its length so as to reduce drag and increase inflow volume and velocity. This accelerates the removal of particles from the disc drive&#39;s sealed chamber, reducing the likelihood of particle-induced data transfer errors or media damage.

Description:
FIELD OF THE INVENTION  
         [0001]    This application relates generally to removing stray particles from a disc drive and more particularly to controlling a flow through a particle filter so as to remove particles more quickly.  
         BACKGROUND OF THE INVENTION  
         [0002]    Disc drive machines record and reproduce information on a recording media. The media generally takes the form of circular information storage discs having a multiplicity of concentric tracks. Conventional hard disc drives include a disc pack holding a plurality of vertically aligned rotating information storage discs, each surface of which has an associated magnetic head that is adapted to transfer information between the disc and an external system. An elongated flexure arm supports each head so that the head flies a small distance from its respective data storage surface. The rotation of the discs creates an air bearing that controls fly height.  
           [0003]    It is extremely important to the operation of the disc drive to quickly establish and maintain a dust free environment within the drive. Fly heights are very small, typically 0.5 microinches or less. A disc drive typically contains many particles much larger than this, at least initially. These particles can cause read or write errors, and can even damage the data surfaces or the heads.  
           [0004]    To prevent dust particles from entering into the drive it is important to thoroughly filter any air that enters the drive from the outside. Drives are typically vented to the outside only through a breather filter that very efficiently filters dust particles from any air passing therethrough.  
           [0005]    It is also important to limit the number of particles generated inside the drive. Unfortunately, some of the actions that generate particles are unavoidable. At present, the principal source of dust within the drive is microparticles that flake off of the parking surfaces when the drive is started and stopped. Other parts that rub during operation can cause dust particles as well. Therefore, it is necessary to provide effective internal particle filtering.  
           [0006]    For improved performance, Seagate engineers have been working to reduce “cleanup time,” the time needed for a particle filter to remove substantially all of the dust particles suspended in the air inside a disc drive. Until recently, most of this effort has been confined to improving the quality of particle filters, not appreciating the importance of optimizing air flow through them. It is to this shortcoming that the present invention is directed.  
         SUMMARY OF THE INVENTION  
         [0007]    As with a conventional disc drive, the present invention includes an aperture for receiving gas flow from a rotatable disc stack within a sealed housing. To accelerate the filtering of particles, a disc drive of the present invention includes a means for receiving an initial flow and for providing to the chamber a modified flow at a higher flow rate.  
           [0008]    In a typical embodiment, this is accomplished by a tapered channel having inner and outer opposing walls. For specificity, many features of the channel are defined with respect to a fastest-flow path passing between these walls, with the disc drive operating under nominal conditions. The path extends beyond an inlet and an outlet of the channel, both of which are defined as closed planar cross sections having a solid circumference. The inlet is defined as an upstream-most closed planar cross section orthogonal to the path. The outlet is similarly defined as a downstream-most smallest-area planar cross section orthogonal to the path. The channel contains exactly one cross-section orthogonal to the path for each corresponding point on the path.  
           [0009]    Preferably, at least ⅔ of the length of the channel is substantially converging (i.e. having a cross sectional area that decreases at least 0.1% for each advance of R/100, where R is the nominal disc radius). Next, a shorter “conduit” that is substantially uniform passes the flow into the chamber. As a result of these features, under normal operating conditions, the average pressure in the filter chamber is significantly higher than that of the entire sealed chamber, significantly reducing the disc drive&#39;s cleanup time.  
           [0010]    Additional features and benefits will become apparent upon a review of the following drawings and the corresponding detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows a partially exploded, oblique view of a disc drive of the present invention.  
         [0012]    [0012]FIG. 2 shows a top view of a disc drive with a filter/chamber/inlet configuration of the prior art.  
         [0013]    [0013]FIG. 3 shows another configuration of the prior art.  
         [0014]    [0014]FIG. 4 shows a top view of a portion of a disc drive of the present invention.  
         [0015]    [0015]FIG. 5 shows a greatly magnified view of a circular portion of FIG. 4.  
         [0016]    [0016]FIG. 6 shows a plot of cross-sectional areas versus position, for the channel and conduit shown in FIGS. 4&amp;5. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring to the drawings in general, and more particularly to FIG. 1, shown there is a disc drive  100  configured to implement the present invention. Disc drive  100  includes a housing  102  containing several discs  108  in a stack arranged for co-rotation in a conventional manner. Preferably, the discs  108  are each at least 50 mils thick to minimize the flutter that can result from having gaps in the shroud circumscribing the disc stack. The cover  120  is configured to engage with the housing to provide a conventional sealed chamber. The chamber is sealed to resist the introduction of contaminants. The top and bottom flat surfaces of each disc  108  each include many thousands of circular tracks  148  containing data. A rotary actuator  110  supports several transducer heads  160  each supported on a respective arm adjacent a respective surface of a disc  108 . A conventional voice coil motor (comprising at least one magnet  177  and at least one voice coil  154 ) controls the position of the actuator  110  so that a selected one of the heads  160  is positioned on its arc  190  adjacent a selected track  148 . Once the head  160  is following the selected track  148 , data can be retrieved from or written to the track  148  via a flex connector  164  through which data signals flow.  
         [0018]    A spindle motor  144  causes the discs  108  to spin, counterclockwise as shown, at a tightly-controlled nominal frequency of several thousand revolutions per minute. This causes a wind of hundreds of feet per second to be carried along all about the circumference of discs. At the same time, head  160  flies a very small distance (less than 1 microinch) above its respective disc  108 . This fly height must be small enough for strong magnetic interactions, but large enough to prevent damaging collisions. As it turns out, this distance is small enough that dust particles play a very significant role.  
         [0019]    To reduce the number of dust particles, a particle filter  180  is positioned to permit air to flow through it whenever the disc stack spins. According to the present invention, a tapered inlet is provided to increase the amount of air that will enter the filter chamber, which in turn increases the amount of air that flows through the chamber. The height  183  of the sealed chamber is also shown. For present purposes, it can be assumed that all open portions of the sealed chamber of all disc drives have this uniform height. Lengths and widths of items shown are therefore also representative of vertical cross-sectional areas. This is especially significant in the description of FIG. 6 below.  
         [0020]    [0020]FIG. 2 shows a top view of a disc drive  200  with a filter/chamber/inlet configuration of the prior art, drawn to scale. Particle-capturing filter  280  is supported between opposing C-shaped gaps on the housing  202 . One of the C-shaped gaps is on a column  289  of the housing that extends to contact the cover (not shown) of the disc drive  200 . The corner of the disc drive  200  shown is essentially uniform throughout the height of the chamber  279  and channel. For present purposes the dimensions are height-normalized so that the widths as shown in FIG. 2 directly represent the cross-sections of each depicted item.  
         [0021]    As discs  208  spin in direction  228 , air enters the filter chamber  279  through a channel having a substantially converging portion  232  and a substantially uniform portion  240 . Filter  280  forms one side of chamber  279 , so that all air flowing into chamber  279  flows out through filter  279 . The channel has an inlet  291  and an outlet  292  that are both planar and substantially vertical. For specificity, the inlet  291  is defined so that its point  261  of fastest flow has a flow direction that is perpendicular to the inlet  291 , and that the inlet is the leftmost (upstream-most) cross section having a closed boundary. The outlet  292  is similarly defined so that its point  262  of fastest flow has a flow direction that is perpendicular to the outlet  292 . Connecting the points  261 , 262  of fastest flow is a path  230  of fastest flow. Each point on path  230  downstream from inlet  261  has a corresponding cross-section of the channel which has a corresponding area. Outlet  292  is further defined so that the area is equal to the minimum of these areas.  
         [0022]    Note that the boundary of the inlet  291  intersects inner and outer walls  281 , 282  that extend along the channel. Note also that “substantially uniform” portion  240  is so named because its cross-sectional area (perpendicular to path  230 ) varies by less than 0.1%, as measured by planes at any two points separated along the path  230  by exactly R/1000, R being the nominal radius of the discs  208 . As used herein, similarly, a “substantially” converging or diverging portion such as  232  is one having a cross section that decreases too significantly, over too long a downstream or upstream path, to qualify as “substantially uniform.” 
         [0023]    [0023]FIG. 3 shows a portion of another disc drive  300  of the prior art, including a particle-capturing filter  380 . Discs  308  having a nominal radius  385  rotate counterclockwise  328  about axis  325 , permitting heads  376  to fly adjacent corresponding surfaces of discs  308 . (In the disc drive arts, note that the “vertical” direction is conventionally defined by the axis  325  of the disc stack, not by the planet&#39;s center). A series of time-averaged maximum flow points  331 , 333 , 335 , 337  is shown. Note that the channel is bounded by an inlet  391  and an outlet  392 , and that points  333  and  335  are within substantially divergent parts of the channel. Interleaved therewith are three substantially convergent parts  332 , 334 , 336  of the channel. As with FIG. 2, FIG. 3 is drawn to scale. Vertical surfaces shown therein are essentially uniform and essentially extend between a flat floor and a flat ceiling. A close examination of FIG. 3 will thus reveal that along an estimated fastest-flow path connecting the reference points  331 , 333 , 335 , 337 , less than ⅔ of the length of the channel is within a substantially converging portion.  
         [0024]    As used here and consistent with industry usage, “substantially convergent” refers to a portion of a channel or conduit having a cross section that decreases at least 0.1% for each advance of R/100 along the fastest-flow path, where R is the nominal radius of a disc in the stack. A conduit is “substantially uniform” if it is neither substantially convergent nor substantially divergent. Note that a conduit may thus be “substantially uniform” even if it is textured.  
         [0025]    Concerning FIGS. 2 &amp; 3, note that the described features concerning the maximum flow path, perpendicular cross sections, and convergent portions of channels are not conventionally referenced or known in the art. Rather, the drives  200 , 300  themselves are in public use. The features described above are inherent in these prior art designs, however, these inherent features are useful in contrasting designs of the present invention.  
         [0026]    [0026]FIG. 4 shows a portion of a disc drive  400  of the present invention. Disc drive  400  includes a sealed housing  402  containing air. A stack of one or more discs  408  having a nominal radius  485  rotate counterclockwise  428  at a nominal frequency about axis  425  using means like those of FIG. 1. As a result, air flows into a flow-directing channel  474  having inner and outer opposing walls  481 , 482  and a curvilinear fastest-flow path  430  passing therebetween. The channel  474  is bounded by an inlet  491 , an outlet  492 , vertical walls  481  and  482 , and a horizontal ceiling and floor. Inlet  491  is defined as the upstream-most closed cross section orthogonal to path  430 . Outlet  492  is defined as the downstream-most smallest-area cross section orthogonal to path  430 .  
         [0027]    Channel  474  contains exactly one cross-section orthogonal to the path for each corresponding point on the path, the channel having a length along the path bounded by inlet  491  and outlet  492 . Unlike any conventional disc drives, at least ⅔ of the length is within a substantially convergent portion  475  of the channel  474 . (Note that the convergent portion  475  is 100% of the channel, in the example of FIG. 4).  
         [0028]    Because of this convergence, chamber  479  receives more air from channel  474  than a similarly constructed design of the prior art. The volume-averaged air pressure in chamber  479  is at least 5% to 50% higher than the volume-averaged air pressure within the entire disc drive cavity within housing  402 . (All gas pressures mentioned in this document are absolute pressures, not gauge pressures.)  
         [0029]    In the preferred embodiment as shown, to scale, particle-capturing filter  480  has a width  481  at least 20% to 50% of the nominal radius  485  (R). Additionally, the gap between the downstream side of the filter  480  and the discs  408  has a smallest-area cross-section  445  that is entirely within a horizontal distance  447  of the discs  408  that is less than 5% to 50% of R. Because the cross-section  445  has a width greater than 10% to 50% of R, also, the “fastest flow” path of the filter outlet gap has no special importance.  
         [0030]    Turning now to FIG. 5, there is shown a greatly magnified view of a circular portion  499  of FIG. 4. The widths of several cross sections  500 , 501 , 502 , 503 , 504 , 505 , 506 , 507 , 508 , 509 , 510 , 511 , 512  are shown, all in planes perpendicular to fastest-flow path  430 . The leftmost cross section  500  is constructed as far to the left as possible, in FIG. 5, while being closed by inner wall  481 . Cross section  500  thus is identical to inlet  491 . Each cross section is separated from its successor along path  430  by exactly R/100.  
         [0031]    A single-disc implementation of the embodiment of FIGS. 4&amp;5, Seagate&#39;s “Snowmass” product, has an actual nominal rotation rate of 7200 rotations per minute. By replacing a prior design with a tapered inlet design substantially as shown, the cleanup time was reduced by more than 20%. More particularly, the operating time until substantially all of the particles in the size range of 0.09 to 0.20 microns were eliminated was reduced from 23 seconds to 18 seconds. For modern disc drives with heads that fly about 0.5 microinches or less above the disc, this is a meaningful risk reduction.  
         [0032]    [0032]FIG. 6 shows a plot of widths  698  versus position  697 , both tick-marked in accurate increments of R/100. Width points  600 , 601 , 602 , 603 , 604 , 605 , 606 , 607 , 608 , 609 , 610 , 611 , 612  correspond to each respective cross section  500 , 501 , 502 , 503 , 504 , 505 , 506 , 507 , 508 , 509 , 510 , 511 , 512  of FIG. 5. Cross sectional area  618  is also plotted vertically, in areal units scaled so that each cross section has a width and area point exactly overlaid. Note that this assumes a constant channel and chamber height, which is graphically helpful but not fundamental to the present invention.  
         [0033]    Note that at the inlet (where position=0), width has its maximum finite value. To the left of the inlet  491 , width is infinite. Moving downstream, cross sectional area  618  decreases steadily to a minimum value  650 , defining the channel outlet  492  at position  651 . A small distance to the right of cross section  512 , cross sectional area  618  jumps to a very large value.  
         [0034]    Alternatively characterized, a first embodiment of the present invention is a disc drive (such as  100 ) that includes a sealed housing (such as  102 ), a rotatable stack of discs (such as  108 ), and a chamber adjacent a particle filter (such as  180 ). The chamber is configured to receive a gas flow through a channel (such as  174 , 474 ) that converges along most or all of its length. The chamber has a volume-averaged gas pressure last least 5% larger than that of the sealed housing. In this preferred embodiment, the chamber has a larger volume than that of the channel, and the filter is wider than R/10, where R is the nominal radius of a disc (such as  408 ) in the stack.  
         [0035]    In a second embodiment, the channel has inner and outer opposing walls (such as  481 , 482 ) and a curvilinear fastest-flow path (such as  430 ) passing between them. The path extends beyond an inlet and an outlet of the channel. For specificity, the inlet (such as  491 ) is defined as an upstream-most closed planar cross section orthogonal to the path. The outlet (such as  492 ) is similarly defined as a downstream-most smallest-area planar cross section orthogonal to the path. The channel contains exactly one cross-section orthogonal to the path for each corresponding point on the path. The channel has a length along the path bounded by the inlet and the outlet. The length is between 5% and 20% of R.  
         [0036]    In a third embodiment, the inlet (such as  491 ) is a planar cross section configured to receive from the disc stack an initial flow characterized by V1, where V1 is a volume flow rate across the cross section. The initial flow is received into a means (such as channel  474 ) for receiving the initial flow and for providing to a filter chamber (such as  479 ) a modified flow characterized by V2&gt;V1, where is a volume flow rate of the modified flow.  
         [0037]    In a fourth embodiment, a continuously converging portion (such as  571 ) of the channel contains at least ⅔ of the channel&#39;s length (i.e. along the fastest-flow path). The portion contains a series of several cross sectional areas (such as  500  through  510 ) each orthogonal to the path and defining successive pairs of the areas. Each of the successive pairs is separated by a distance along the path of R/100. Each of the successive pairs consists of a downstream one A i+1  and an upstream one A i . The portion converges steadily enough so that 0.80&lt;(A i+1 /A i )&lt;0.99 for each of the successive pairs.  
         [0038]    In a fifth embodiment, the narrowest portion of the channel/filter combination occurs at one nominally uniform, contiguous conduit that overlaps the channel and the chamber. The conduit has a nominal cross section and two ends, the ends each abutting a respective region having a larger-than-nominal cross section. To promote laminar flow while minimizing drag, the conduit having a length between 1% and 5% of R.  
         [0039]    In a sixth embodiment, reference is made to the volume-averaged, time-averaged flow speed that is an inherent attribute of the chamber and of the channel. In this preferred embodiment, this flow speed is greater for the channel than for the chamber. As a result of this flow speed increase, the stagnation pressure within the filter chamber increases non-linearly.  
         [0040]    It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. For example, while the various embodiments of the present invention have been described with respect to a disc drive, the present invention is also applicable to, and may be implemented in, other data storage devices such as optical disc drives and magneto-optical disc drives. Numerous other changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.