Abstract:
A low-profile pivot assembly is disclosed. The assembly includes two generally coaxial bearings having differing diameters so as to define inner and outer bearings. This arrangement permits the pivot assembly to be constructed with a lower profile than conventional pivot bearings. These and other and benefits will become apparent upon a review of the attached figures and the accompanying description.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/282,798, filed Apr. 10, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of hard disc drive data storage devices, and more particularly, but not by way of limitation, to rotational support of disc drive actuators.  
         BACKGROUND OF THE INVENTION  
         [0003]    Disc drives of the type known as “Winchester” disc drives, or hard disc drives, are well known in the industry. Such disc drives magnetically record digital data on a plurality of circular, concentric data tracks on the surfaces of one or more rigid discs. The discs are typically mounted for rotation on the hub of a brushless DC spindle motor. In disc drives of the current generation, the spindle motor rotates the discs at speeds of up to 15,000 RPM.  
           [0004]    Data are recorded to and retrieved from the discs by an array of vertically aligned read/write head assemblies, or heads, which are controllably moved from track to track by an actuator assembly. The read/write head assemblies typically consist of an electromagnetic transducer carried on an air bearing slider. This slider acts in a cooperative pneumatic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. In order to maintain the proper flying relationship between the head assemblies and the discs, the head assemblies are attached to and supported by flexures attached to the actuator.  
           [0005]    The actuator assembly used to move the heads from track to track has assumed many forms historically, with most disc drives of the current generation incorporating an actuator of the type referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing base member closely adjacent the outer diameter of the discs. The pivot shaft is mounted such that its central axis is normal to the plane of rotation of the discs. The actuator is mounted to the pivot shaft by precision ball bearing assemblies within a bearing housing. The actuator supports a flat coil which is suspended in the magnetic field of an array of permanent magnets, which are fixedly mounted to the disc drive housing base member.  
           [0006]    On the side of the actuator bearing housing opposite to the coil, the actuator assembly typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. These actuator arms extend between the discs, where they support the head assemblies at their desired positions adjacent the disc surfaces. When controlled DC current is applied to the coil, a magnetic field is formed surrounding the coil which interacts with the magnetic field of the permanent magnets to rotate the actuator bearing housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator bearing housing rotates, the heads are moved generally radially across the data tracks of the discs along an arcuate path.  
           [0007]    In the past, disc drives were typically used for storage of data in personal computers and in storage arrays for storing huge amounts of data in enterprise applications. Presently, however, drives are being contemplated for use in a wide variety of consumer products, such as television set-top video recorders, video game consoles, and hand-held computers. These applications present a new set of challenges to the drive industry, requiring that drives be more quiet and smaller than ever before. In particular, there is a need to produce drives having a height which is decreased relative to that of conventional drives to enable use in hand-held and card-type applications.  
           [0008]    A primary factor in limiting potential decreases in drive height is the actuator pivot. A typical pivot mechanism has two ball bearing assemblies having ball bearings which roll between inner and outer races, a stationary shaft attached to the inner races and a rotating sleeve attached to the outer races. The sleeve is typically secured within a bore in the actuator body and the stationary shaft typically is attached to the base deck and the top cover of the disc drive. The bearings are preloaded such that the inner races are forced toward one another. The inner and outer races of each bearing assembly are thereby slightly offset so as to take up radial clearances built into the bearing assemblies. Without preload, the sleeve would be more free to move along the pivot axis, to translate horizontally or to pivot about a horizontal axis, causing unwanted head movement. In addition, lack of preload would lead to unwanted vibrations, contributing to the likelihood of resonance within the actuator system. It is the provision of two bearing assemblies which allows preload. However, one disadvantage of this arrangement is that absolute minimum drive height is limited by the combined height of the two bearing assemblies in addition to the vertical spacing between them.  
           [0009]    What the prior art has been lacking is a low profile actuator pivot assembly which is easily assembled, inexpensive and which exhibits adequate stiffness to prevent excess vibration of the actuator assembly.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is directed to a low-profile actuator pivot bearing assembly. The assembly includes two generally coaxial bearings having differing diameters so as to define inner and outer bearings. This arrangement permits the pivot assembly to be constructed with a lower profile than conventional pivot bearings. These and other and benefits will become apparent upon a review of the attached figures and the accompanying description.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 shows an exploded view of a disc drive incorporating the bearing mounting assembly of the present invention.  
         [0012]    [0012]FIG. 2 shows an exploded view of an actuator incorporating an embodiment pivot assembly of the present invention.  
         [0013]    [0013]FIG. 3 depicts a cross-sectional view of an actuator mounted to one embodiment of a pivot assembly.  
         [0014]    [0014]FIG. 4 shows a cross-sectional view of an actuator mounted to another embodiment of a pivot assembly.  
         [0015]    [0015]FIG. 5 depicts a cross-sectional view of an embodiment in which two discs may be accessed by head assemblies.  
         [0016]    [0016]FIG. 6 depicts a cross-sectional view of another embodiment in which two surfaces of the same disc may be accessed by head assemblies. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0017]    Turning now to the drawings and specifically to FIG. 1, shown is an exploded view of an example of a disc drive  100  in which the present invention is particularly useful. Of course, the illustrated drive is merely exemplary in nature; the pivot assembly  400  of the present invention may be utilized in any number of storage devices. It is further contemplated that the disclosed pivot assembly  400  may be implemented in other device requiring pivotal mounting of a rotating element. The illustrated disc drive  100  includes a base  110  to which all other components are directly or indirectly mounted and a top cover  120  which, together with the base  110 , forms a disc drive housing which encloses delicate internal components and isolates these components from external contaminants.  
         [0018]    The illustrated disc drive  100  includes a plurality of discs  200  which are mounted for rotation on a spindle motor (not shown). The discs  200  include on their surfaces a plurality of circular, concentric data tracks  210  on which data are recorded via an array of vertically aligned head assemblies (one of which is shown at  310 ). The head assemblies  310  are supported by flexures  320 , which are attached to arm portions of actuator  300 . The actuator  300  is mounted to a pivot assembly  400  about which the actuator  300  rotates.  
         [0019]    Power to drive the actuator  300  about the pivot assembly  400  is provided by a voice coil motor (VCM). The VCM consists of a coil  330  which is supported by the actuator  300  within the magnetic field of a permanent magnet assembly having spaced upper and lower magnets  340 . The magnets  340  may be mounted to spaced pole pieces  350  which may be fixed to the deck  110  and spaced from one another by spacers  360 . Electronic circuitry is provided on a printed circuit board (PCB, not shown) mounted to the underside of the deck  110 . Control signals to drive the VCM are carried between the PCB and the moving actuator  300  via a flexible printed circuit cable (PCC)  500 , which also transmits data signals to and from the heads  310 .  
         [0020]    [0020]FIG. 2 shows an exploded view of an embodiment of a low-profile actuator pivot assembly  400  in combination with an actuator  300 . In one embodiment of the invention illustrated here, the actuator  300  is a “single-stage” actuator, meaning it has only one arm and may be, as in this case, generally planar.  
         [0021]    As shown in FIG. 2, pivot assembly  400  includes two bearings  420 , 450 , each comprising a number of balls  422 , 452 . The balls  422  are positioned between an innermost sleeve  410  and an intermediate sleeve  430 . The innermost sleeve  410  does not rotate and includes a raceway  412 . Intermediate sleeve  430  includes an inner raceway  432  and is fixed to the actuator  300 . Balls  422  roll within raceways  412 , 432  such that intermediate sleeve  430  is free to rotate about fixed innermost sleeve  410 . Because actuator  300  is fixed to the intermediate sleeve, the actuator  300  is also free to rotate.  
         [0022]    Balls  452  are positioned between an outermost sleeve  460  and the intermediate sleeve  430 . The outermost sleeve  460  does not rotate and includes a raceway  462 . Intermediate sleeve  430  includes an outer raceway  434 . Balls  452  roll within raceways  462 , 434  such that intermediate sleeve  430  is free to rotate within outermost sleeve  460 . As mentioned above, the actuator  300  is fixed to the intermediate sleeve  430  and is also free to rotate about a vertical axis.  
         [0023]    [0023]FIG. 3 depicts a cross-sectional view of one embodiment of the present invention. Balls  422  make up lower bearing  420 , while balls  452  make up upper bearing  450 . Unlike conventional pivots, however, in which upper and lower bearings are vertically spaced and have identical dimensions, the upper and lower bearings of FIG. 3 have different dimensions. Upper bearing  450  has a diameter which is greater than that of lower bearing  420 . This arrangement permits the vertical spacing between the upper and lower bearings  420 , 450  to be significantly reduced relative to conventional pivots. In fact, portions of upper and lower bearings  420 , 450  may even share a common horizontal plane, such as the one designated  470  in FIG. 3. As such, the height of pivot assembly  400  is capable of being constructed with an overall height significantly lower than that of conventional pivots.  
         [0024]    Another advantage of this arrangement is that outer balls  452  can be made larger than inner balls  422  as illustrated in FIG. 3. Use of larger balls increases axial, and radial and rotational stiffness of the pivot assembly  400 .  
         [0025]    [0025]FIG. 3 also shows one embodiment of an intermediate sleeve  430 . In this embodiment, outer raceway  434  is formed in an outer sleeve  435  while inner raceway  432  is formed in an inner sleeve  445 . Inner and outer sleeves  445 , 435  may be manufactured separately and fixed together in any of a number of ways. For example, adhesives may be used to fasten them together, or inner sleeve  445  may be press-fit, welded, or attached by conventional mechanical fasteners such as screws within outer sleeve  435 . It should also be recognized that intermediate sleeve  430  may instead be manufactured as a single piece so as to reduce parts and assembly steps. Such a sleeve could have integrally formed portions  435 , 445  or could take the form of a single sleeve such as  445  having inner and outer raceways  432 , 434  formed therein. What is important is that intermediate sleeve  430  have inner and outer raceways  432 , 434  which are vertically spaced from one another.  
         [0026]    [0026]FIG. 3 also depicts one method for attaching an actuator  300  or other rotatable element to pivot assembly  400 . In this embodiment, actuator  300  includes an aperture aligned with the axis of rotation of the pivot assembly  400 . A portion  380  of the actuator  300  surrounding the aperture is deformed so as to be expanded against an inner surface of the intermediate sleeve  430 . This type of operation is known as “swaging.” However, it is also contemplated that the actuator  300  could be attached to intermediate sleeve  430  by other means, such as adhesive, welding, or conventional mechanical fasteners such as screws. Portion  380  could also be formed as a protrusion so as to facilitate a simple press-fit within intermediate sleeve  430  is swaged to intermediate sleeve  430 .  
         [0027]    [0027]FIG. 3 also shows one arrangement for effecting preload of the pivot assembly  400 . Preloading is a procedure by which inner and outer races of each bearing are slightly offset from one another so as to take up radial clearances built into the bearing assemblies. If these clearances were to remain, intermediate sleeve  430  would be free to move in undesirable ways. Small amounts of vertical and horizontal translation would be possible, as would rocking about a horizontal axis, causing unwanted movement of actuator  300 . Where applied in a disc drive, a supported read/write head would also move uncontrollably, causing read/write errors, head-disc contact and even catastrophic drive failure. In addition, lack of preload would lead to unwanted vibrations, contributing to the likelihood of resonance within the actuator system. As seen in FIG. 3, base  110  may be provided with a circular land portion  112  as well as a threaded bore  114 . As an initial step for installing pivot assembly  400  within on the deck, outermost sleeve  460  is aligned with and lowered onto land  112 . Innermost sleeve  410  is simultaneously lowered about coaxial threaded bore  114 . Threaded member  115  is then threaded into bore  114 . Threaded member  115  includes a head portion which contacts an upper surface of innermost sleeve  410  as threaded member  115  descends into bore  114 . Innermost sleeve  410  is thereby forced downwardly until clearances are removed from between balls  422 , 452  and their respective raceways  412 , 432 , 434 , 462 . This causes balls  422 , 452  to loaded against the curved surfaces of their respective raceways  412 , 432 , 434 , 462 , such that a line of force is set up a small angle, called a “contact angle,” relative to the horizontal plane of the bearing. For purposes of illustration, approximations of the contact angles are illustrated in FIG. 3 as lines  425  and  455 . One advantage of the preload arrangement of FIG. 3 is that preload may be adjusted easily by simply turning fastener  115 . Thus one pivot assembly  300  may be suitable for a variety of different applications requiring different preloads.  
         [0028]    [0028]FIG. 4 depicts an embodiment of pivot assembly  400  in which preload is applied in a manner different from that shown in FIG. 3. In this embodiment, base  110  is provided with a central land portion  116  as well as a cylindrical wall  118 . As an initial step for installing pivot assembly  400  on the base  110 , innermost sleeve  410  is aligned with and lowered onto land  116 . Outermost sleeve  460  is simultaneously lowered within coaxial cylindrical wall  118 . The outer surface of outermost sleeve  460  is dimensioned to fit closely within the inner surface of wall  118 , and is configured to be secured to it by any of a number of methods, such as press-fitting, adhesive, threads or some other appropriate fastener. The outermost sleeve  460  is pressed downwardly until the desired preload is reached, taking up the clearances between balls  422 , 452  and their respective raceways  412 , 432 , 434 , 462 . If press-fit, assembly is complete and downward pressure is removed from outermost sleeve  460 . Otherwise, the fastening means is applied, after which assembly is complete and only then is downward pressure removed from the outermost sleeve  460 . For purposes of illustration, approximations of the contact angles are illustrated in FIG. 4 as lines  425  and  455 . Note that the contact angles in FIG. 4 are sloped oppositely to those of FIG. 3.  
         [0029]    Of course, it should be understood that the device described herein may be modified without departing from the spirit of the invention. For example, while a single, planar actuator arm  300  is advantageous for its ease of manufacture, low profile and low inertia, it is contemplated that additional arms  305  could be added for the purpose of accessing additional disc surfaces as shown in FIG. 6. It is also contemplated that actuator  300  could be provided with two heads  310  and support assemblies  320  and installed between two discs  200  as in FIG. 5, so as to allow access to two disc surfaces while maintaining the advantages described above with respect to a single, planar actuator.  
         [0030]    Alternatively characterized, a first contemplated embodiment of the invention takes the form of a pivot assembly (such as  400 ) including a stationary outer annular element (such as  460 ), a stationary inner element (such as  410 ) extending along an axis of the outer element (such as  460 ), and a rotatable annular element (such as  430 ) coaxial with and intermediate the inner and outer elements (such as  410 , 460 ). A first plurality of balls (such as  420 ) is positioned between the inner and intermediate elements (such as  410 , 430 ) and a second plurality of balls (such as  450 ) is positioned between the outer and intermediate elements (such as  460 , 430 ). The first plurality of balls (such as  420 ) may lie in a first plane and centers of the second plurality of balls (such as  450 ) may lie in a second plane spaced from the first plane. A portion of each ball (such as  422 , 452 ) of the first and second plurality of balls (such as  420 , 450 ) may lie in a common plane (such as  470 ). Each of the second plurality of balls (such as  450 ) may have a diameter greater than a diameter of each of the first plurality of balls (such as  420 ). The inner, outer and intermediate elements (such as  410 , 460 , 430 ) may exert a preload on each ball (such as  422 , 452 ) of the first and second plurality of balls (such as  420 , 450 ). The pivot assembly (such as  400 ) may be implemented in a disc drive (such as  100 ) having a base (such as  110 ) and an actuator (such as  300 ), in which the outer and inner elements (such as  460 , 410 ) are mounted to the base (such as  110 ) and the actuator (such as  300 ) is mounted to the intermediate element (such as  430 ). In this embodiment, the outer and inner elements (such as  460 , 410 ) may exert a preload on each ball (such as  422 , 452 ) of the first and second plurality of balls (such as  420 , 450 ).  
         [0031]    Alternatively characterized, a second contemplated embodiment of the invention takes the form of a disc drive (such as  100 ) including a base (such as  110 ), an actuator (such as  300 ) and a pivot assembly (such as  400 ) for rotatably mounting the actuator (such as  300 ) to the base (such as  110 ). The pivot assembly (such as  400 ) includes a stationary annular outer element (such as  460 ) mounted to the base (such as  110 ), an annular inner element (such as  430 ) coaxial with and rotatable with respect to the outer element (such as  460 ). The actuator (such as  300 ) is mounted to the inner annular element (such as  430 ). A first plurality of balls (such as  450 ) is positioned between the inner and outer annular elements (such as  430 , 460 ). A preload member is positioned within the inner annular element (such as  430 ) and is configured to exert a preload on each of the first plurality of balls (such as  450 ). The preload member may take the form of an innermost element (such as  410 ) mounted to the base (such as  110 ) and a second plurality of balls (such as  420 ) positioned between the inner element (such as  430 ) and the innermost element (such as  410 ). Optionally the disc drive (such as  100 ) may further include a threaded bore (such as  114 ) in the base (such as  110 ) and a threaded member (such as  115 ) configured to exert a force on the preload member as the threaded member (such as  115 ) is rotated within the threaded bore (such as  114 ). Each of the first plurality of balls (such as  450 ) may have a diameter greater than a diameter of each of the second plurality of balls (such as  420 ). The inner annular element (such as  430 ) may take the form of a first sleeve (such as  445 ) fixedly mounted within a second sleeve (such as  435 ). The inner annular element (such as  430 ) may include a first raceway (such as  434 ) engaging the first plurality of balls (such as  450 ) and a second raceway (such as  432 ) engaging the second plurality of balls (such as  420 ). Optionally, the actuator (such as  300 ) may be swaged to the inner annular element (such as  430 ).  
         [0032]    From the foregoing, it is apparent that the present invention is particularly suited to provide the benefits described above. While particular embodiments of the invention have been described herein, modifications to the embodiments which fall within the envisioned scope of the invention may suggest themselves to one of skill in the art who reads this disclosure.