Abstract:
Various embodiments of the present invention are generally directed to attenuating excitation energy of a rotatable storage medium using one or more plates each having a plurality of parallel channels to buffer fluid flow across an associated medium surface. A preferred embodiment includes a plurality of channels in facing relation to a common surface of a rotatable storage medium. Further included in a preferred embodiment, the plurality of channels are sequentially arranged into a first, second, and third channels with differing sidewall characterizations. In an alternative embodiment, a plurality of storage mediums which are axially aligned have a plurality of channels in facing relation to either a top or bottom surface of a rotatable storage medium.

Description:
FIELD OF THE INVENTION 
     The embodiments of the present invention relate generally to the field of data writing systems and more particularly without limitation to windage management for reducing fluid flow excitation of data writing components. 
     BACKGROUND 
     Modern data storage devices such as disc drives are commonly used in a multitude of computer environments to store large amounts of data in a form that is readily available to a user. Generally, a disc drive has a magnetic disc, or two or more stacked magnetic discs, that are rotated by a motor at high speeds. Each disc has a data storage surface divided into data tracks where data is stored in the form of magnetic flux transitions. 
     A data transfer member such as a magnetic transducer is moved by an actuator to selected positions adjacent the data storage surface to sense the magnetic flux transitions in reading data from the disc, and to transmit electrical signals to induce the magnetic flux transitions in writing data to the disc. The active elements of the data transfer member are supported by suspension structures extending from the actuator. The active elements are maintained a small distance from the data storage surface by a fluid bearing generated by fluid currents caused by the spinning discs. The term “fluid bearing” is synonymous with the term “air bearing” where the fluid utilized in the disc drive is air. Alternatively, the term “fluid bearing” is applicable to other embodiments utilizing a fluid other than air, such as helium. 
     A continuing trend in the data storage industry is toward ever-increasing the data storage capacity and the processing speed while maintaining or reducing the physical size of the disc drive. Consequently, the data transfer member and the supporting structures are continually being miniaturized, and data storage densities are continually being increased. One result is an overall increased sensitivity to vibration as a percentage of track width. 
     One source of vibration comes from the fluid currents, or windage, that is created by the spinning discs. Fluid flow perturbations, and especially turbulent fluid flow, can excite the actuator and/or the disc creating vibrations. During servo track writing operations, for example, such vibrations can create actuator positional control errors resulting in irregular servo track formatting such as but not limited to track squeeze. 
     While various proposed solutions have been found operable, there remains a continued need for improvements in windage management for attenuating excitation energy. It is to such improvements that the claimed invention is generally directed. 
     SUMMARY OF THE INVENTION 
     Various embodiments of the present invention are generally directed to attenuating excitation energy of a rotatable storage medium using one or more plates each having a plurality of parallel channels to buffer fluid flow across an associated medium surface. 
     In accordance with some embodiments, an apparatus comprises a stationary first plate having a plurality of channels extending therein in facing relation to a common surface of a rotatable storage medium, said channels each having a proximal and adjacent an outermost radius of the medium and a distal end adjacent an innermost radius of the medium, said channels further being parallel to one another to buffer fluid flow across :aid common surface. 
     In accordance with other embodiments, an apparatus comprises a rotatable storage medium having opposing top and bottom medium surfaces. The apparatus further comprises a stationary first surface adjacent the top medium surface having a plurality of top channels extending therein and parallel to one another to buffer fluid flow across said top medium surface. A first channel of said plurality of top channels has a leading edge surface with respect to said fluid flow which extends in non-orthogonal relation to the top medium surface and a second channel of said plurality of top channels has a leading edge surface with respect to said fluid flow that is substantially orthogonal to the top medium surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a data storage device constructed in accordance with embodiments of the present invention. 
         FIG. 2  is an isometric view of the data storage device of  FIG. 1  with the discs removed for clarity. 
         FIG. 3  is an elevational view of a related art fluid flow stripper and the discs. 
         FIG. 4  is a diagrammatic representation of a pressure field distribution created by the spinning disc within the related art fluid flow stripper of  FIG. 3 . 
         FIG. 5  is a plan view of a fluid flow stripper constructed in accordance with embodiments of the present invention. 
         FIG. 6  is a cross sectional view of the fluid flow stripper of  FIG. 5  taken generally along the section line  6 - 6  of  FIG. 5 . 
         FIG. 7  is a plan view of an ex-situ servo track writer constructed in accordance with embodiments of the present invention. 
         FIG. 8  is an isometric view of the servo track writer of  FIG. 7 . 
         FIG. 9  is an enlarged detail of a portion of  FIG. 8 . 
         FIG. 10  is a plan view of the fluid flow stripper of the servo track writer of  FIG. 7 . 
         FIG. 11  is a block diagram of a method for equalizing static pressure in accordance with embodiments of the present invention. 
         FIG. 12  is a bar chart indicating quantitative improvements associated with practicing embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings in general, and more particularly to  FIG. 1 , shown therein is a plan view of a data storage device  100  that is constructed in accordance with embodiments of the present invention. The data storage device  100  includes a base  102  to which various disc drive components are mounted, and a cover  104  (partially cutaway) which together with the base  102  and a perimeter gasket  105  form an enclosure providing a sealed internal environment for the data storage device  100 . 
     Mounted to the base  102  is a motor  106  to which one or more discs  108  are stacked and secured by a clamp ring  110  for rotation at a high speed. Where a plurality of discs  108  are stacked to form a disc stack, adjacent discs  108  are typically separated by a disc spacer  111  ( FIG. 3 ). An actuator  112  pivots around a pivot bearing  115  in a plane parallel to the discs  108 . The actuator  112  has actuator arms  116  (only one shown in  FIG. 1 ) that support load arms  118  in travel across the discs  108 . The load arms  118  are flex members that support data transfer members, such as read/write heads  120 , with each of the heads  120  operationally interfacing a surface of one of the discs  108  in a data reading and writing relationship. This relationship is maintained by a slider (not shown) which operably supports the head  120  on a fluid bearing sustained by fluid currents generated by the spinning discs  108 . In some embodiments the fluid can be air; in other embodiments the fluid can be something other than air such as but not limited to helium. 
     Each of the discs  108  has a data storage region comprising a data recording surface  122 . In some embodiments the head  120  is used to write servo information defining the track location; this is referred to as “in-situ” servo track writing. In other embodiments the servo information is prewritten to the discs  108  before they are installed into the data storage device  100 ; this is referred to as “ex-situ” servo track writing and is discussed below. The data tracks can be defined in various arrangements, such as being concentric or spiraled. In addition to in-situ servo track writing, the heads  120  are subsequently positioned adjacent a desired data track, from servo information feedback, in reading data from and writing data to the data storage surface  122 . Accordingly, the data storage device  100  is sometimes referred to as a data writing device or a data reading device. 
     As noted earlier, the motor  106  spins the discs  108  at a high speed while the head  120  writes and/or reads to/from the data storage surface  122 . The kinetic energy of the spinning discs is transferred by friction to the fluid at the disc/fluid boundary layer, thereby imparting a force vector to the fluid. The combined rotational and centrifugal forces from the spinning discs  108  creates a generally outwardly spiraling fluid flow pattern to the fluid surrounding the discs  108 . This fluid flow, or windage, can be attenuated to reduce excitation energy on the actuator  112  and the disc  108  to a level below an acceptable threshold level by practicing embodiments of the present invention. 
     In the illustrative embodiments of  FIG. 1 , the direction of disc  108  rotation is indicated by reference number  144 . A fluid flow stripper  140  is disposed upstream of the actuator  112 , with respect to the direction of disc  108  rotation.  FIG. 2  is an isometric view of the data storage device  100  with the discs  108  removed for better viewing of the stripper  140 . The stripper  140  has a body portion  146  and a number of plates  148  extending from the body  146 . The body portion  146  can be readily adapted for fastening to the base  102 . The plates  148  are spatially separated defining gaps therebetween for receivingly engaging one of the discs  108  in the disc stack. For example, the embodiments of  FIG. 2  illustrate a stripper  140  defining two gaps for use with a two-disc  108  stack. In alternative embodiments, the illustrative stripper  140  of  FIG. 2  can be used with three-disc and four-disc stacks where one of the plates  148  cooperates with either the base  102  or the cover  104  in enclosing the respective disc  108 . The relatively small gap between the plates  148  and the respective disc  108  creates a flow restriction that strips away, or diverts, a portion  160  of the fluid. 
     To some extent, the portion of the fluid flow admitted into the gaps between the stripper  140  and the discs  108  is attenuated for reduced excitation acting on the downstream actuator  112  ( FIG. 1 ). However,  FIG. 3  is an elevational view of a related art stripper  141  comprising a plurality of plates  149  with planar surfaces in close mating relationship with the discs  108 .  FIG. 4  diagrammatically illustrates a problem associated with this type of related art stripper  141  is that a pressure gradient is created across the disc  108 . That is, the outwardly spiraling fluid flow creates a lowest pressure area  143  at the inner diameter and a highest pressure area  145  at the outer diameter, with intermediate pressure areas therebetween. This pressure gradient can create eddy currents and even turbulent flows that adversely excite the downstream actuator  112  ( FIG. 1 ). The embodiments of the present invention address this problematic pressure gradient by equalizing the static pressure of the fluid flowing through the stripper  140  ( FIG. 1 ). 
       FIG. 5  is a plan view of the stripper  140  receivingly engaging the disc  108 , which rotates about central axis  161 . In the illustrative embodiments of  FIG. 5 , the stripper  140  defines three zones through which the fluid passes. At the inlet to the first zone  162  a flow restriction is created for diverting the portion  160  away from the actuator  112  ( FIG. 1 ). The portion of the fluid that is admitted to the stripper  140  then passes through the first zone  162 , which has opposing planar surfaces in a close mating relationship with the disc  108  creating a relatively high pressure disc damping zone. The fluid then continues on to a second zone  164  and a third zone  166 , which have radially disposed baffles defining channels that distribute the fluid dynamic pressure in order to equalize the static pressure across the disc. 
       FIG. 6  is a cross sectional view taken generally along the line  6 - 6  of  FIG. 5 . In the first zone  162  opposing spatially disposed planar surfaces  170 ,  172  are substantially parallel with the disc  108 , defining a gap therebetween for receivingly engaging the disc  108  in a close mating relationship. The fluid in the small gap exerts a relatively high pressure for damping the disc  108 . 
     In the second zone  164  a protuberant surface  174  defines a radially extending channel  176  at the outlet of the damping zone  162 . For illustrative purposes the radially extending channel  176  has an angled leading edge  178  to more smoothly transition the flow leaving the damping zone  162 , and an orthogonal trailing edge  180  to more abruptly slow the fluid velocity leaving the channel  176 . This arrangement serves to momentarily pressurize the channel  176  as the fluid passes therethrough. Some of the pressurized fluid will flow radially inward within the channel  176 , rather than flowing out of the channel  176 , thereby partially equalizing the static pressure gradient across the disc  108 . 
     An opposing protuberant surface  182  defines a radially extending channel  184  on the opposing side of the disc  108 . In the illustrative embodiments of  FIG. 6  the opposing channels  176 ,  184  are aligned and shaped equivalently to equalize the static pressure evenly on opposing sides of the disc  108 . 
     Within the zone  164 , additional protuberant surfaces  186 ,  188  and  190  define substantially rectangular channels  192 ,  194  and  196 . Opposing channels  198 ,  200 , and  202  are aligned and shaped equivalently therewith. As indicated by the fluid flow eddy currents, the dynamic pressure within the channels diminishes as the fluid flows sequentially through the channels, as the fluid flow loses energy as a result of the stages of dynamic pressure equalization having taken place in upstream channels. Even at the reduced dynamic pressures, however, the static pressure equalization continues within each downstream channel. 
     In zone  166 , protuberant surfaces  190 ,  204 , and  206  define angled transition surfaces and radiused edges defining channels  208  and  210 . In like manner, protuberant surfaces  212 ,  214 , and  216  define aligned and equivalent channels  218 ,  220  on the opposing side of the disc  108 . The smoother channels of the zone  166  are less obtrusive to the fluid flow, being related to the generally reduced dynamic pressure of the fluid flow in comparison to that upstream. The smoother channel also advantageously tends to straighten the flow leaving the stripper  140 . 
     The illustrative embodiments of  FIG. 6  thus include a transition channel  176  followed by three sharp rectangular channels  192 ,  194 ,  196  in zone  164  and two smooth v-shaped channels  208 ,  210  in zone  166 . This arrangement has been proven effective in equalizing the fluid pressure and straightening the fluid flow leaving the stripper  140  so as to not excite the downstream actuator  112  ( FIG. 1 ). 
     Turning now to  FIGS. 7-9 , embodiments of the present invention are now addressed with regard to an ex-situ servo track writing device  300  that is used to write servo data information to a multi-disc stack of discs  108 . The device  300  includes an actuator assembly  302  for positioning an actuator  303  supporting servo recording heads  304  at a distal end thereof for recording the servo information. A motor hub assembly  306  rotationally presents the discs  108  to the recording heads  304 . A vacuum chuck  308  secures the actuator assembly  302  between a servo writing position, shown in  FIG. 9 , and a retracted position where the multi-disc stacks are loaded and unloaded, shown in  FIG. 8 . A laser interferometer  310  provides position control for the angular displacement of the servo recording heads  304 . 
     A base  312 , such as a granite slab, supports the device  300  components. A linear slide  314  defines a constrained lateral movement for the actuator assembly  302  between the servo writing and the load/unload positions. With the actuator assembly  302  in the load/unload position ( FIG. 8 ) a spindle hub  328  supporting the plurality of discs  108  is loaded to the motor  306 . A fluid flow stripper  330  and a fluid flow dam  332  are then articulated to partially enclose the plurality of discs  108 . The actuator assembly  302  is then moved laterally by the slide  314  into operable engagement with the multi-disc stack. A comb  334  pivots to clearingly engage the plurality of servo recording heads  304  with the respective discs  108  so that the actuator  303  can be loaded to the multi-disc stack. With the actuator  303  loaded, the motor  306  spins the multi-disc stack and servo track writing begins. 
     As above, the spinning discs  108  create windage that can adversely excite the actuator  303  and the discs  108 . The stripper  330  attenuates the windage energy to prevent this adverse excitation. The stripper  330  has a body portion  342  and a plurality of spatially disposed plates  344  defining gaps therebetween that are receivingly engageable with the discs  108 . Here, however, the body portion  342  is journalled by pivots  346  for articulating movement between the retracted position ( FIG. 8 ) and the engaged position ( FIG. 9 ). In the retracted position the plates  344  are clearingly disengaged from the disc  108  permitting movement of the disc  108  along the axis of disc  108  rotation for loading and unloading the multi-disc stack to the device  300 . 
       FIG. 10  is an enlarged elevational view of the stripper  330  of  FIG. 9 . The body  342  defines a passageway  348  through which the plates  344  strip away and divert a portion  350  of the windage created by the spinning discs  108 . Otherwise, the portion of the fluid entering the stripper  330  is acted upon to attenuate fluid flow excitation energy that would otherwise adversely affect the downstream actuator  303 . The plates  344  are configured in the same manner as described above and shown particularly in  FIGS. 5 and 6 , so as to provide a multi-zoned arrangement whereby the admitted fluid passes first through the disc damping zone  162 , then the first and second baffle zones  164 ,  166 . 
       FIG. 11  illustrates a method  400  of EQUALIZING STATIC PRESSURE illustrating steps for practicing the embodiments of the present invention. The method  400  includes placing the stripper  140 ,  330  around the disc  108  at a location upstream of the actuator  112 ,  203  in block  402 . Clearly, in alternative embodiments the stripper  140 ,  330  could be placed in other locations to attenuate windage excitation, such as but not limited to placing the stripper  140 ,  330  upstream of a filter device. In block  404  the disc  108  is rotated, creating the windage addressed by the embodiments of the present invention. In block  406  an upstream portion of the windage is diverted away from the actuator  112 ,  203  by the stripper  140 ,  330 . In block  408  the rest of the fluid flow is admitted into the gap between the stripper  140 ,  330  and the disc  108 . In block  410  the admitted fluid flow passes through a disc damper zone. In block  412  the admitted fluid flow passes through a radially-extending baffle zone. 
     The passing the admitted portion step can comprise passing the fluid past two or more equivalent baffles in the baffle zone. The passing the admitted portion step can further comprise passing the fluid through differently configured baffles, such as sharp and smooth edged baffles. Preferably, like baffles are formed and aligned on opposing sides of the disc. 
       FIG. 12  illustrates results of testing the stripper  140 ,  330  of the present invention. The grouping of data  450  indicates the amount of track squeeze present in a sample of heads and measured both at the disc  108  inner and outer diameters, for a stripper in accordance with related art embodiments such as illustrated by stripper  141  in  FIG. 3 . The grouping of data  452  indicates the results of the same measurement for the stripper  140 ,  330  of the embodiments of the present invention. For the latter, a total track squeeze improvement of over 20% was observed. 
     Summarizing generally, a stripper (such as  140 ,  330 ) is provided for attenuating windage created by a rotating disc (such as  108 ) that can otherwise create disturbances acting on the disc an on a downstream actuator (such as  112 ,  303 ) disposed in a data reading and writing relationship with the disc. 
     The stripper can comprise a body (such as  146 ,  342 ) and a pair of spatially disposed plates (such as  148 ,  344 ) extending from the body defining a gap therebetween that is receivingly engageable with the disc. In a disc damping zone (such as  162 ) the plates are substantially planar and parallel with the discs in a close mating relationship. A first baffle zone (such as  164 ) has a protuberant surface (such as  174 ,  186 ,  188 ,  190 ) defining one or more radially extending channels (such as  176 ,  192 ,  194 ,  196 ) where the fluid dynamic pressure partially equalizes the fluid static pressure radially across the disc. The first baffle zone can have a protuberant surface defining one or more channels (such as  184 ,  198 ,  200 ,  202 ) on the opposing side of the disc. Preferably, the opposing channels are aligned and of like structural arrangement. A second baffle zone (such as  166 ) has a protuberant surface (such as  190 ,  204 ,  206 ) defining one or more differently configured radially extending channels (such as  208 ,  210 ) for further equalization. Opposing channels (such as  218 ,  220 ) can be provided in the second baffle zone on the opposing side of the disc. 
     In some embodiments the body is adapted for articulating movement between a retracted position and an engaged position, such that in the retracted position the plates are clearingly disengaged from the disc permitting movement of the disc in a direction along an axis of disc rotation. 
     Preferably, the actuator operably engages a disc stack having a plurality of spaced-apart discs, and the stripper comprises a plurality of plates with each of the plurality of plates disposed adjacent to a side of one of the plurality of discs. 
     In some embodiments a method (such as  400 ) is provided for equalizing static pressure created by the rotating disc. The method comprises admitting the flow into a gap between the disc and the stripper (such as  408 ), and passing the flow past the radially extending baffle (such as  412 ). 
     In some embodiments a fluid flow stripper device is provided for a rotating disc, comprising a pair of spatially disposed plates defining a gap for receivingly engaging the disc, and protuberant surfaces on the plates attenuating fluid flow disturbances by steps for equalizing the static pressure in the fluid across the disc. In some embodiments the steps for equalizing can be characterized by passing the fluid through a zone comprising one or more radially disposed sharp baffles. In some embodiments the steps for equalizing can be characterized by passing the fluid through a zone comprising one or more radially disposed smooth baffles. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with the details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the number and arrangement of the baffle channels without departing from the scope and spirit of the present invention. In addition, although the preferred embodiments described herein are directed to a data writing device, it will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the spirit and scope of the present invention. 
     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 presently preferred embodiments have been described for purposes of this disclosure, numerous changes may be made which 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.