Patent Publication Number: US-6903903-B1

Title: Disk drive head stack assembly having a tapered pivot bearing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation-in-part of, and claims priority under 35 U.S.C. §120 to, U.S. patent application Ser. No. 09/354,400, that is entitled “ACTUATOR ARM ASSEMBLY STACK COMPRESSED WITH SPRING WASHER,” that was filed on Jul. 15, 1999, now abandoned and the entire disclosure of which is incorporated by reference in its entirety herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to disk drives and, more particularly, to using at least one retainer ring to at least generally assist in maintaining an association of at least one head/arm assembly and a pivot bearing during disk drive operations (e.g., read and/or write operations). 
     BACKGROUND OF THE INVENTION 
     Disk drive systems have undergone significant evolution in a relatively short time. Current designs often have a plurality of disks maintained in a common stack, along with a head stack assembly that may include a unitary, rigid actuator arm body (e.g., “E” block) having a plurality of rigid, non-deflectable, vertically spaced actuator arms or tips on which a plurality of flexible suspensions or load beams are fixedly mounted (e.g., via staking). Heads are mounted on the individual load beams and read/write information from the plurality of disks, with two load beams extending into the space between adjacent disks. 
     Each disk includes a plurality of tracks which are concentrically disposed about an axis about which the plurality of disks rotate. Information may be stored in each of these tracks. Access to other tracks, and thereby other data storage areas on a disk, is provided by moving (e.g., pivoting) the actuator body via a voice coil motor or the like to simultaneously move all load beams and their corresponding heads to a different radial position relative to their corresponding disk. There is at least one known disk drive design which is admitted to be prior art which mounts a plurality of individual actuator arms on a bearing hub, and which clamps these individual actuator arms together and maintains the same in a certain fixed positional relation by a threaded interconnection. Specifically, an external portion of the bearing hub is threaded and a nut is engaged therewith to clamp the actuator arms “down” onto the bearing hub. 
     Both of the above-noted designs suffer from a number of disadvantages in at least some respect. Solid actuator bodies with load beams separately attached thereto can be relatively costly to fabricate, assemble, test, and rework. Threaded interconnections increase the potential for the generation of particulates within the disk drive encasement which can adversely affect one or more aspects of its operation. Therefore, it would be desirable to have a more cost effective approach for assembling a head stack assembly which avoided particulate generation, particularly for the “low end” disk drive market. 
     Retainer rings have been used to mount a head/arm assembly on a pivot bearing. In this regard, the head/arm assembly is mounted on the pivot bearing so as to be located between a flange of the pivot bearing and a retainer ring slot that is formed on an outer wall of the pivot bearing. A frustumly-shaped arbor is disposed against the end of the pivot bearing to allow a retainer ring to be mounted on the outer wall of the pivot bearing. Advancing the retainer ring relative to the arbor expands the same to a sufficient diameter so as to be able to be disposed on the outer wall of the pivot bearing. Once on the outer wall of the pivot bearing, the retainer ring is advanced along a constant diameter portion of the pivot bearing until it “snaps” into the retainer ring slot. This approach provides at least certain advantages in the assembly of a head stack assembly. However, it still requires additional tooling. 
     BRIEF SUMMARY THE INVENTION 
     The present invention generally relates to the assembly of a head stack assembly for disk drives. More specifically, the present invention generally relates to the manner in which one or more head/arm assemblies are mounted on a pivot bearing. 
     A first aspect of the present invention generally relates to a method for assembling a disk drive head stack assembly. A first actuator arm is mounted on an outer wall of the pivot bearing. A retainer ring, clip, or the like is used to mount the first actuator arm on the pivot bearing. In this regard, the retainer ring is disposed against a portion of the outer wall of the pivot bearing. The retainer ring is advanced relative to the pivot bearing in a direction of a retainer ring slot or groove formed on the outer wall of the pivot bearing. At least a portion of this advancement expands the retainer ring by its continued engagement with the pivot bearing to facilitate the disposition of the retainer ring within the retainer ring slot formed on the outer wall of the pivot bearing. 
     Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The head stack assembly associated with the first aspect may include a single actuator arm. Multiple individual actuator arms may be secured to the pivot bearing in accordance with the first aspect of as well. Each actuator arm may be part of the head/arm assembly that includes a rigid actuator arm, a flexible suspension, and a head (e.g., a slider and one or more transducers) that is appropriately mounted on the suspension. 
     Only relative movement is required between the retainer ring and the pivot bearing in case of the first aspect. Typically the pivot bearing will remain stationary, while the retainer ring is advanced. In any case, the movement of the retainer ring relative to the pivot bearing in accordance with the first aspect may be along a direction that is at least generally parallel with a rotational axis associated with the pivot bearing. The expansion of the retainer ring need not, but may, occur over the entire time that the retainer ring is advanced relative to the pivot bearing, during its engagement with the pivot bearing, so as to direct the retainer ring within the retainer ring slot. In one embodiment, the retainer ring engages a short cylindrical section of the outer wall of the pivot bearing immediately prior to being directed within the retainer ring slot. Continued movement of the retainer ring along the outer wall of the pivot bearing would thereby not further expand the retainer ring when engaged with this cylindrical section. In another embodiment, the retainer ring expands by its engagement with the outer wall of the pivot bearing until being directed within the retainer ring slot. Movement of the retainer ring into the retainer ring slot on the outer wall of the pivot bearing may be provided by the elastic forces that are stored within the retainer ring while being expanded in accordance with this first aspect. Preferably, the retainer ring exerts a contractive force on the pivot bearing after being disposed within its retainer ring slot. 
     The retainer ring may be initially mounted on the outer wall of the pivot bearing without having to substantially increase the size thereof in the case of the first aspect. In one embodiment, the size of the retainer ring need not be increased at all to initially dispose the retainer ring on the outer wall of the pivot bearing and so as to be in interfacing relation therewith. No separate tooling is thereby required to initially position the retainer ring on the outer wall of the pivot bearing. Stated another way, the retainer ring may be manipulated solely by hand to dispose the retainer ring on the outer wall of the pivot bearing. Stated yet another way, the inner diameter of the retainer ring in an undeformed state is larger than an outer diameter of a portion of the outer wall of the pivot bearing to initially position the retainer ring on the outer wall for subsequent expansion of the retainer ring in one embodiment of the first aspect. It should be appreciated that an appropriate pliers could be used to increase the inner diameter of the retainer ring to initially dispose the same on the outer wall of the pivot bearing, and thereafter the retainer ring could be expanded in accordance with the first aspect. In any case, once the retainer ring is initially on the outer wall of the pivot bearing, the size of the retainer ring is increased by at least about 8% in one embodiment, and by at least about 10% in another embodiment, prior to being disposed within the retainer ring slot. This also may be done solely by hand. Expansion of the retainer ring in accordance with the first aspect preferably does not exceed the elastic limit of the retainer ring or “over stretch” the retainer ring by an amount that would adversely affect its ability to be retained within the retainer ring slot. 
     There are a number of ways in which the expansion of the retainer ring may be described in the case of the first aspect. One is that the effective diameter of the retainer ring is increased during at least a portion of the time that the retainer ring is relatively advanced toward the retainer ring slot on the outer wall of the pivot bearing. In one embodiment, the retainer ring has a pair of ends that are spaced apart when the retainer ring is in a neutral or static state (e.g., in a non-distorted shape). The expansion of the retainer ring by the pivot bearing may include increasing the spacing between this pair of ends during at least a portion of the time that the retainer ring is being relatively advanced toward the retainer ring slot on the outer wall of the pivot bearing. Preferably the retainer ring is arcuately shaped between its pair of ends to enhance its interface with the outer wall of the pivot bearing. 
     One or more individual actuator arms may be disposed between the retainer ring and another appropriate stop associated with the pivot bearing in the case of the first aspect. This “second” stop may be in the form of another retainer ring, although typically it will be in the form of a flange that is part of the pivot bearing. In any case, biasing forces may be exerted on each actuator arm that is located between the retainer ring and the second stop associated with the pivot bearing. These biasing forces may compress the actuator arm (s) between the retainer ring and the second stop associated with the pivot bearing. Biasing forces may be provided by disposing one more springs or other appropriate biasing members (e.g., an elastomer), somewhere between the retainer ring and the second stop associated with the pivot bearing. A preferred biasing member is a Belleville spring. In one embodiment, such a Belleville spring is seated against the retainer ring and biases the actuator arm(s) toward the second stop associated with the pivot bearing. Such a Belleville spring can also be seated against the second stop associated with the pivot bearing to direct the actuator arm(s) toward the retainer ring. At least one Belleville spring could be disposed on each side of what may be characterized as an actuator arm stack so as to place the same in compression or in at least somewhat of a compressive state. 
     A second aspect of the present invention is directed to a disk drive head stack assembly. This head stack assembly generally includes at least one head/arm assembly that is mounted on a pivot bearing. This pivot bearing includes an inner bearing member and an outer bearing member that are able to rotate relative to each other. An outer wall or surface of the outer bearing member includes a section that is tapered between first and second locations along a length dimension of the outer wall of the pivot bearing. The outer bearing member is larger at the second location than at the first location, and the second location is disposed somewhere between the first location and a retainer ring slot that is formed on and disposed about at least a portion of an outer wall of the outer bearing member. A retainer ring is disposed in this retainer ring slot to retain each head/arm assembly of the head stack assembly between the retainer ring and a second stop associated with the outer bearing member. 
     Various refinements exist of the features noted in relation to the second aspect of the present invention. Further features may also be incorporated in the second aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The head stack assembly associated with the second aspect may include a single head/arm assembly. Multiple head/arm assemblies may be mounted on the pivot bearing in accordance with the second aspect of as well. Each head/arm assembly may include a rigid actuator arm, a flexible suspension, and a head (e.g., a slider and one or more transducers) that is appropriately mounted on the suspension. 
     The retainer ring slot associated with the pivot bearing of the second aspect may be annular. The retainer ring that is disposed within this retainer ring slot will typically extend about less than, an entire annular portion of the outer wall of the outer bearing member. For instance, the retainer ring may include a pair of ends that are disposed in spaced relation when the retainer ring is disposed within the retainer ring slot. Preferably the retainer ring is arcuately shaped between this pair of ends to enhance its interface with the outer wall of the pivot bearing within the retainer ring slot. Other configurations may be appropriate for the retainer ring. 
     The second stop associated with the outer bearing member of the pivot bearing utilized by the second aspect may be in the form of an annular flange that is part of the outer bearing member. However, the second stop could also be in the form of a second retainer ring that is disposed within a second retainer ring slot formed on the outer wall of the outer bearing member. 
     Biasing forces may be exerted on any head/arm assembly disposed between the retainer ring and the second stop associated with the pivot bearing in the case of the second aspect. These biasing forces may place any head/arm assembly located between the retainer ring and the second stop associated with the pivot bearing in compression or in at least somewhat of a compressive state. Biasing forces may be provided by disposing one more springs or other appropriate biasing members (e.g., an elastomer) somewhere between the retainer ring and the second stop associated with the pivot bearing. A preferred biasing member is a Belleville spring. In one embodiment, such a Belleville spring is seated against the retainer ring and biases each head/arm assembly toward the second stop associated with the pivot bearing. Such a Belleville spring can also be seated against the second stop associated with the pivot bearing to direct each head/arm assembly toward the retainer ring. At least one Belleville spring could be disposed on each side of what may be characterized as a head/arm assembly stack so as to place the same in at least somewhat of a compressive state. 
     The tapered section of the outer wall of the outer bearing member in the case of the second aspect may assume a variety of configurations that will function to increase the effective diameter of the retainer ring by its engagement with the outer wall of the outer bearing member as the retainer ring is relatively advanced toward the retainer ring slot. One embodiment of the tapered section utilizes a constant slope. The magnitude of this slope is at least about 0.1 in one embodiment, is at least about 0.2 in another embodiment, and is at least about 0.3 in yet another embodiment. Another related characterization of the tapered section is in terms of an expansion ratio. The “expansion ratio” is a ratio of the amount that the retainer ring expands by moving along the tapered section (e.g., “expansion” being in a direction that is perpendicular to a rotational axis of the pivot bearing), to the distance that the retainer ring has advanced along the tapered section in a direction that is perpendicular to the direction of the expansion (e.g., in a direction that is parallel with the rotational axis of the pivot bearing). This expansion ratio is at least about 0.2 in one embodiment, is at least about 0.4 in another embodiment, and is at least about 0.6 in yet another embodiment (e.g., twice the slope of the tapered section). 
     Another embodiment of the second aspect has the tapered section of the outer wall of the pivot bearing with an arcuate shape progressing from the first location to the second location. Any configuration may be utilized for the tapered section that will increase the effective diameter of the retainer ring by its engagement with the tapered section as the retainer ring is relatively advanced toward the retainer ring slot along the tapered section from the first location to the second location. 
     The retainer ring may be initially mounted on the tapered section of the pivot bearing without having to substantially increase the size thereof in the case of the second aspect. In one embodiment, the size of the retainer ring need not be increased at all to initially dispose the retainer ring on the tapered section of the pivot bearing and so as to be in interfacing relation therewith. No separate tooling is thereby required to initially position the retainer ring on the outer wall of the pivot bearing. Stated another way, the retainer ring may be manipulated solely by hand to dispose the retainer ring on the outer wall of the pivot bearing. Stated yet another way, the inner diameter of the retainer ring in an undeformed state is larger than an outer diameter of a portion of the tapered section of the pivot bearing on which the retainer ring may be initially disposed in one embodiment. Preferably the inner diameter of the retainer ring may be disposed on the tapered section (at the first location or somewhere between the first and second locations) without having to increase its inner diameter from an undeformed state of the retainer ring. However, it should be appreciated that an appropriate pliers could be used to initially increase the inner diameter of the retainer ring for installation on the tapered section of the pivot bearing for subsequent expansion by the transition section in accordance with the second aspect. 
     In one embodiment of the second aspect, the outer diameter of the tapered section, either at the first location or somewhere between the first and second locations, is the same as the inner diameter of the retainer ring in an undeformed or static state. Once the retainer ring is initially disposed on the tapered portion of the outer wall of the pivot bearing, the size of the retainer ring is increased by at least about 8% in one embodiment, and by at least about 10% in another embodiment, prior to being disposed within the retainer ring slot. Stated another way, the diameter of the tapered section at the second location is at least about 8% greater in one embodiment, and at least about 10% greater in another embodiment, than the diameter of the tapered section at the first location to provide for the desired expansion of the retainer ring. 
     In one embodiment of the second aspect, a cylindrical section of the outer wall is disposed between the retainer ring slot and the second location that defines the “large” end of the tapered section. Other configurations may be appropriate for any length of the outer wall that is disposed between the retainer ring slot and the second location that defines the “large” end of the tapered section. The second location defining the “large” end of the tapered section may also be disposed immediately adjacent to the retainer ring slot. 
     A third aspect of the present invention is directed to a disk drive head stack assembly. This head stack assembly generally includes at least one head/arm assembly that is mounted on a pivot bearing. This pivot bearing includes an inner bearing member and an outer bearing member that are able to rotate relative to each other. An outer wall or surface of at least a portion of the outer bearing member is in the form of a frustum. A first end of the frustum is smaller than a second end of the frustum, and this second end is located somewhere between the first end and a retainer ring slot that is formed on and disposed about at least a portion of an outer wall of the outer bearing member. A retainer ring is disposed in this retainer ring slot to retain each head/arm assembly of the head stack assembly between the retainer ring and a second stop associated with the outer bearing member. The various features discussed above in relation to the second aspect may be utilized by this third aspect, individually or in any combination. 
     A fourth aspect of the present invention is directed to a disk drive head stack assembly. This head stack assembly generally includes at least one head/arm assembly that is mounted on a pivot bearing. This pivot bearing includes an inner bearing member and an outer bearing member that are able to rotate relative to each other. An outer wall or surface of the outer bearing member includes a retainer ring slot that is disposed about at least a portion of the outer wall. At least a portion of the outer wall is contoured to increase the diameter of a retainer ring that is engaged with the outer wall as the retainer ring is being relatively advanced toward the retainer ring slot. The retainer ring is disposed in this retainer ring slot to retain each head/arm assembly of the head stack assembly between the retainer ring and a second stop associated with the outer bearing member. The various features discussed above in relation to the second aspect may be utilized by this fourth aspect, individually or in any combination. 
     A fifth aspect associated with the present invention is directed to a disk drive head stack assembly. This head stack assembly generally includes at least one head/arm assembly that is mounted on a pivot bearing. This pivot bearing includes an inner bearing member and an outer bearing member that are able to rotate relative to each other. An outer wall or surface of the outer bearing member includes a retainer ring slot that is disposed about at least a portion of the outer wall. The outer wall has a first effective diameter at a first location and a second effective diameter at a second location that is spaced from the first location in the direction of a retainer ring slot that is formed about at least a portion of the outer wall. The first effective diameter is about equal to the effective diameter of a retainer ring in a neutral state or when no external forces are modifying its shape. Moreover, the second effective diameter is larger than the first effective diameter. The retainer ring is disposed in the retainer ring slot to retain each head/arm assembly of the head stack assembly between the retainer ring and a second stop associated with the outer bearing member. The various features discussed above in relation to the second aspect may be utilized by this fifth aspect, individually or in any combination. 
     A sixth aspect of the present invention generally relates to an actuator arm assembly for disk drives in which a stack of actuator arm assembly components are compressed together to maintain the same in a certain fixed positional relationship by as few as one spring, such as an annular spring washer(s) (e.g., more than one spring may be utilized). In this regard, the actuator arm assembly includes a pivot which is attachable to an encasement for the disk drive. Two stops of sorts are provided on the pivot (e.g., vertical stops in the case where the pivot is vertically disposed). One or more of the stops could be integrally formed with the pivot or separately attachable to the pivot. Appropriate “stops” would include flanges, retaining/snap rings, or the like. 
     A stack of actuator arm assembly components is disposed between the two noted stops and interfaces with a pivot shaft of the pivot. The stack includes at least one, and preferably no more than three, individual actuator arms, but could also include voice coil motor componentry or the like (e.g., an arm that carries the coil). Each actuator arm has a flexible load beam attached thereto which extends over a computer-readable storage medium disk (e.g., one for the disk “above” the arm and another for the disk “below” the arm). Information is read from the disk, written to the disk, or both, through a head(s) which is attached on typically that end portion of the load beam which is displaced from the typically rigid actuator arm. The noted stack of actuator arm assembly components is compressed together to register the arms to the intended location at least somewhere between the two noted stops to maintain the same in a fixed positional relationship through only one or more springs. 
     Various refinements exist of the features noted in relation to the sixth aspect of the present invention. Further features may also be incorporated in the sixth aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The noted pivot may be defined by a pivot bearing or cartridge bearing assembly which allows the actuator arm(s) to pivot/rotate relative to the encasement for the disk drive. One of the stops may be defined by the structure of this cartridge bearing assembly (e.g., a flange formed on an end portion thereof), while another of the stops may be defined by a retaining ring or the like which is detachably connected to the cartridge bearing assembly. In this case an annular groove, slot or the like may be formed about the pivot shaft for receipt of this retaining ring and against which the noted spring(s) may act to compress the actuator arm assembly stack. This simplifies the assembly procedure of the disk drive, and thereby reduces costs. Particulate amounts within the disk drive should also be reduced in relation to disk drives which use threaded connections to clamp the actuator arm assembly stack together. 
     Each actuator arm utilized by the sixth aspect may include an aperture through which the noted pivot shaft extends such that each actuator arm encircles the pivot shaft. Each actuator arm preferably includes a substantially planar surface in at least proximity to the pivot shaft to provide a suitable surface with radius of contact over which a frictional interface may be established with adjacent components in the stack through the axially-directed load provided by the noted spring(s). Preferably each actuator arm is of at least substantially uniform thickness. Minimizing the thickness of each actuator arm will also reduce inertial forces, which will in turn further reduces the potential for relative radial movement between components of the actuator arm assembly stack which is being maintained by the compressive forces of the spring(s). 
     One particularly desirable spring for this application in the case of the sixth aspect is a Belleville spring which is of an annular configuration and which is at least generally frustumly shaped (e.g., truncated cone). Sufficient axial loads may be generated by such a Belleville spring to maintain the components of the actuator arm assembly stack in the desired position during normal disk drive operations, including loads which exceed the inertial forces to which the actuator arm assembly is exposed during rotation of the same, as well as assembly and handling loads. This is believed to particularly be the case when no more than 3 actuator arms are included in the stack. However, preferably the spring is able to maintain the positional relationship between the various components of the stack when exposed to a crash stop impact or when exposed to other non-op shocks (e.g., via a dropping of the disk drive). 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of a disk drive. 
         FIG. 2  is a cutaway side view of the head/arm assembly stack and computer-readable storage medium disk from the disk drive of FIG.  1 . 
         FIG. 3  is an exploded, perspective view of the head/arm assembly stack from the disk drive of FIG.  1 . 
         FIGS. 4A-B  are perspective views of the head/arm assembly stack from the disk drive of  FIG. 1  in the assembled condition. 
         FIG. 5  is one embodiment of a Belleville spring which may be used in the head/arm assembly stack from the disk drive of FIG.  1 . 
         FIG. 6A  is a perspective view of another embodiment of a head/arm assembly that is mounted on another embodiment of a pivot bearing and that may be used in the disk drive of FIG.  1 . 
         FIG. 6B  is an exploded, perspective view of the head/arm assembly and pivot bearing of FIG.  6 A. 
         FIG. 7A  is a one perspective view of the pivot bearing used by the head/arm assembly of FIG.  6 A. 
         FIG. 7B  is a another perspective view of the pivot bearing used by the head/arm assembly of FIG.  6 A. 
         FIG. 7C  is an exploded, perspective view of the pivot bearing used by the head/arm assembly of FIG.  6 A. 
         FIG. 7D  is a cross-sectional view of the pivot bearing used by the head/arm assembly of FIG.  6 A. 
         FIG. 7E  is an enlarged view of a portion of the pivot bearing of FIG.  7 D. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described in relation to the accompanying drawings which at least assist in illustrating its various pertinent features.  FIG. 1  presents a disk drive  2  having a disk drive housing defined by a base plate  6  and a cover that is appropriately attached thereto (not shown). The disk drive  2  generally includes a disk  10  of an appropriate computer-readable storage medium and a head stack assembly  16  for reading information from and writing information to the disk  10 . The disk  10  is mounted on a rotatable spindle  14  for rotation by an appropriate motor (not shown) within an at least substantially horizontal reference plane. Typically the disk  10  will include a plurality of tracks which are concentrically disposed about the spindle  14  and which may be used to store information in discrete regions of the disk  10 . 
     The head stack assembly  16  includes a head/arm assembly stack  18 . Referring now to  FIG. 2-4B  as well, the stack  18  includes two individual and discrete actuator arms  22  (e.g., separate structures) which are individually mounted on an actuator arm pivot bearing or cartridge bearing assembly  30 . These actuator arms  22  are at least substantially rigid structures (i.e., little or no deflection during normal operations of the disk drive  2 ) and extend from the cartridge bearing assembly  30  to a location which is “over” opposing surfaces of the disk  10  in cantilevered fashion. Each actuator arm  22  includes a circular mounting aperture  26  through which a hub  34  of the cartridge bearing assembly  30  extends. At least those surfaces of the actuator arms  22  which are disposed about the mounting aperture  26  are of a substantially planar nature for enhancing the frictional interface between the various components of the stack  18 . However, in one embodiment the entirety of each actuator arm  22  is of substantially uniform thickness throughout its entire length. 
     Disposed on an end portion of each of the actuator arms  22  is a flexible load beam or suspension  38 . There is a head  42  (e.g., one or more transducers formed on/in a slider or slider body) mounted on typically an end portion of each of the load beams  38 . Each actuator arm  22  and its corresponding load beam  38  and head  42  may be characterized as a head/arm assembly  17 . In any case, preferably the heads  42  are capable of both reading information from and writing information to the corresponding surface of the disk  10 . However, both of these functions are not required for purposes of the present invention. The heads  42  may be disposed on the corresponding surface of the disk  10  prior to powering the disk drive  2  (e.g., of a contact start/type drive). Various lift mechanisms may be employed to displace the heads  42  from the disk  10  during the initial powering up stage of the disk drive  2 , although such is also not required for purposes of the present invention. The drive  2  may also be in the form of a dynamic load/unload configuration. In any case, during normal operations of the disk drive  2  each head  42  may be disposed at a certain fly height above the corresponding surface of the disk  10  which is determined by the rotational speed of the disk  10  (which generates an air cushion which biases the heads  42  away from the disk  10 ) and the flexure of the load beams  38  (which typically biases the heads  42  toward the corresponding disk  10 ). Contact or near contact recording technologies could also be utilized. 
     Rotation of the disk  10  may be used to vary the relative positioning between the disk  10  and the heads  42  at a particular data storage region of the disk  10 . Other data storage regions of the disk  10  are accessed by a pivoting of the head stack assembly  16  about the cartridge bearing assembly  30 . One appropriate rotational drive assembly of sorts is a voice coil motor  46  which is controlled by control electronics  62 . Part of the voice coil motor  46  is in the form of one or more stationary magnets (not shown). Another part of the voice coil motor  46  is the form of a coil which is incorporated in a coil/overmold assembly  50 . This coil/overmold assembly  50  is included in the head/arm assembly stack  18 . In this regard, the coil/overmold assembly  50  includes a mounting aperture  52  through which the hub  34  of the cartridge bearing assembly  30  extends. One of the actuator arms  22  is disposed above the coil/overmold assembly  50 , while the other of the actuator arms  22  is disposed below the coil/overmold assembly  50 . A central disposition of the coil/overmold assembly  50  (along/relative to the hub  34  of the cartridge bearing assembly  30 ) within the stack  18  is desired since the operative interface of sorts between the coil/overmold assembly  50  and the magnet of the voice coil motor  46  is what rotationally drives the head/arm assembly stack  18 . That is, preferably ½ of the stack  18  is on each side of the coil/overmold assembly  50  (e.g. above and below the coil/overmold assembly  50 ). 
     Pivotal motion of the head stack assembly stack  16  via the voice coil motor  46  moves the heads  42  to a different radial position on their corresponding disk  10  (e.g., to a different one of the concentrically disposed tracks formed on such disk  10 ). Simultaneous radial movement of all components of the head stack assembly  16  is preferred, as is the maintenance of the same relative radial positioning between each of the components of the stack  18  at all times and including during movement thereof. Any significant relative radial movement between any of the actuator arms  22 , or the coil/overmold assembly  50  for that matter, relative to the remainder of the head/arm assembly stack  18  may and likely will adversely affect the storage and/or retrieval of information to/from the disk  10 . “Slippage” between the components of the stack  18  could result in one of the actuator arms  22  moving say 5°, with the other of the actuator arms  22  moving say only 4°. This may be sufficient to dispose one of the heads  42  on the “wrong” track on the disk  10  or more generally at the “wrong” data storage address on the disk  10 . “Small” amounts of relative radial movement between the components of the head/arm assembly stack  18  should produce no degradation in performance of the disk drive  2 . An “intermediate” amount of relative radial movement between the components of the head/arm assembly stack  18  may produce some degradation in performance of the disk drive  2 . “Large” amounts of relative radial movement between the components of the head/arm assembly stack  18 , however, will likely result in the loss of data. The forces applied to the head/arm assembly stack  18  by one or more appropriate biasing members.(e.g., a Belleville spring  54 ) at least should alleviate those “large” amounts of relative radial movement which result in the subsequent loss of data. 
     Components of the head/arm assembly stack  18  are maintained in a fixed positional relationship relative to each other for simultaneous radial movement in the illustrated embodiment by an annular Belleville spring  54  which compresses the stack  18  together. As can be seen in  FIGS. 2 and 5 , the spring  54  has an at least generally frustumly-shaped profile. The Belleville spring  54  is mounted on the hub  34  of the cartridge bearing assembly  30  and exerts an at least generally axially-directed load on the head/arm assembly stack  18  to compress the same together and maintain its components in the desired fixed positional relationship. In this regard, the hub  34  of the cartridge bearing assembly  30  includes an annular, square/rectangularly-shaped slot  36  in which a retaining ring  58  or the like is disposed by “snapping” the same into position. Part of the Belleville spring  54  butts up against this retaining ring  58 . Another part of the Belleville spring  54  butts up against one of the actuator arms  22 . The other of the actuator arms  22  butts up against a flange  32  of the cartridge bearing assembly  30 . As such, the head/arm assembly stack  18  is compressed between the flange  32  and the retaining ring  58 , or more particularly the Belleville spring  54 . 
     Sufficient axial loads are generated by the Belleville spring  54  so as to establish a frictional interface between adjacent components of the stack  18  which is greater than the inertial forces to which the head/arm assembly stack  18  is exposed during normal disk drive operations, as well as those which may be encountered during assembly and handling. That is, the normal forces exerted on the components of the head/arm assembly stack  18  by the Belleville spring  54  generate frictional forces between interfacing components of the stack  18  which exceeds the inertial forces exerted on the stack  18  during normal operations of the disk drive  2 , as well as during assembly and handling, and preferably even when the head/arm assembly stack  18  engages a crash stop (not shown) or when the disk drive  2  is exposed to other reasonable non-op shocks (e.g., due to a dropping of the disk drive  2 ). Frictional forces between adjacent components of the stack  18  (e.g., those forces which are required to initiate relative radial movement) which are in excess of the inertial forces to which the disk drive  2  is normally exposed means that there should be no relative movement between components of the stack  18 . Although other spring washers may be appropriate, use of the Belleville spring  54  is preferred due to its ability to generate rather significant axial loads within relatively small spaces, as well and the uniformity of the axial load provided by the Belleville spring  54  (e.g., about its circumference). 
     A number of factors contribute to the ability of the disk drive  2  to use the Belleville spring  54  to compress the head/arm assembly stack  18  together in a manner so as to allow no relative radial movement between individual components thereof. Initially is the amount of axial load applied by the Belleville spring  54 . In the case where two actuator arms  22  are included in the stack  18 , an axially load of about 50 pounds is preferred. Moreover and as noted, interfacing components of the stack  18  preferably mate along at least substantially planar surfaces. Minimizing the diameter of the hub  34  of the cartridge bearing assembly  30  and maximizing the width of the annular extent of the components of the stack  18  about the hub  34  may be implemented to allow for use of a Belleville spring  54  with a smaller inner diameter and a larger outer diameter for generating increased axial forces which would then require a larger force to induce relative radial movement between components of the stack  18 . 
     Another embodiment of a head stack assembly that may be utilized by the disk drive  2  of  FIG. 1  is illustrated in  FIGS. 6A-B  and is identified by reference numeral  66 . This head stack assembly  66  includes a single head/arm assembly  74 . Multiple head/arm assemblies  74  could be utilized by the head stack assembly  66  as well (not shown). The head/arm assembly  74  includes a rigid actuator arm  78 . A mounting aperture  82  extends through the entire thickness of the actuator arm  78  to allow the same to be mounted on a pivot bearing or cartridge bearing assembly  118  using a retainer ring or clip  102 . The actuator arm  78  is able to pivot or rotate relative to the disk drive housing, and more specifically relative to its corresponding disk, via the pivot bearing  118 . The actuator arm  78  is also appropriately configured for receiving a coil  90  used by the drive&#39;s voice coil motor. The coil  90  thereby also moves relative to the disk drive housing via the pivot bearing  118 , simultaneously along with the actuator arm  78 . 
     The head/arm assembly  74  further includes a typically flexible load beam or suspension  94  that is appropriately mounted on the actuator arm  78  (e.g., staked). A head  98  is mounted on the suspension  94  and includes a slider/slider body and one or more appropriate transducers (e.g., to read and/or write information to/from the corresponding data storage disk). Signals to/from the head  98  are provided by a flex cable  70  having a plurality of traces formed thereon (not shown). 
     Further details regarding the pivot bearing  118  are illustrated in  FIGS. 7A-E  in addition to  FIGS. 6A-B  noted above. The pivot bearing  118  generally includes a shaft or inner bearing member  146  and a sleeve or outer bearing member  122  that may rotate relative to each other by an upper bearing  138  and a lower bearing  142  that are disposed therebetween. The upper bearing  138  and lower bearing  142  may be of any appropriate type/configuration. A threaded bore  148  is included on the shaft  146  at one end thereof. This threaded bore  148  receives a threaded stud that extends up from the base plate of the disk drive housing. The opposite end of the shaft  146  includes a slot  150  than may be used to mount the shaft  146  on this threaded stud by rotating the shaft  146  relative to the base plate, to in turn thread the shaft  146  onto this stud. A hubcap  154  is press fit onto the end of the shaft  146  having the slot  150 . 
     The sleeve  122  is configured to facilitate the mounting of the head/arm assembly  74  on the pivot bearing  118 . In this regard, an outer wall or surface  124  of the sleeve  122  includes what may be characterized as a tapered section  126 . One end  128   b  of this tapered section  126  has a smaller effective diameter than an opposite end  128   a  of this same tapered section  126 . In one embodiment, the tapered section  126  is frustumly-shaped or contoured in the form of a truncated cone. Stated another way, the tapered section  126  has a constant slope progressing from the end  128   b  to the end  128   a . Preferably the magnitude of this slope is at least about 0.1 in one embodiment, is at least about 0.2 in another embodiment, and is at least about 0.3 in yet another embodiment. The rate at which the retainer ring  102  is expanded by engagement with and movement relative to the pivot bearing  118  may be dictated by physical space limitations (e.g., the distance that the retainer ring  102  may advance along the rotational axis  119  to be expanded may be limited by space restrictions). Generally, a more gradual expansion of the retainer ring  102  is preferred. 
     Another related characterization of the tapered section  126  is in terms of the above-noted expansion ratio. The “expansion ratio” in relation to the pivot bearing  118  is a ratio of the amount that the retainer ring  102  expands by moving along the tapered section  126  (e.g., “expansion” being in a direction that is perpendicular to the rotational axis  119  of the pivot bearing  118 ), to the distance that the retainer ring  102  has advanced along the tapered section  126  in a direction that is perpendicular to the direction of the expansion (e.g., in a direction that is parallel with the rotational axis  119  of the pivot bearing  118 ). The expansion ratio of the tapered section  126  is at least about 0.2 in one embodiment, is at least about 0.4 in another embodiment, and is at least about 0.6 in yet another embodiment (e.g., twice the slope of the transition section  126 ). Other configurations of the outer wall  124  may be appropriate for expanding the retainer ring  102  as it is advanced relative to the pivot bearing  118  for disposition within the retainer ring slot  130 . For instance, the tapered section  126  could have at least somewhat of an arcuate shape/profile progressing between its ends  128   a ,  128   b  (not shown). 
     The end  128   a  of the tapered section  124  will typically be disposed at least generally adjacent to a retainer ring slot  130  formed on the outer wall  124  of the sleeve  122  . A portion of the outer wall  124  may be parallel with the pivot axis of the pivot bearing  118  between the end  128   a  and the retainer ring slot  130  (e.g., a cylindrical section). The end  128   a  could also be disposed immediately adjacent to the retainer ring slot  130 . The outer diameter of the retainer ring slot  130  is less than the outer diameter of the end  128   a  of the tapered section  126  in the illustrated embodiment. The retainer ring  102  is advanced along the tapered section  126 , which increases its effective diameter, so as to be able to be disposed in this retainer ring slot  130 . This retains the head/arm assembly  74  between the clip  102  and a flange  134  that is spaced from the retainer ring slot  130  and that is part of the sleeve  122 . An actuator arm protrusion  132  may be included on the sleeve  122  as well for interfacing with the actuator arm  78  (e.g., to locate the same relative to the pivot bearing  118 ). 
     It should be appreciated that the sleeve  122  of the pivot bearing  118  could be configured to accommodate multiple actuator arms  78  between the retainer ring  102  and the flange  134 . One or more biasing members (e.g., a Belleville spring  54 ) also could be utilized to maintain the actuator arm(s)  78  in compression between the retainer ring  102  and the flange  134 . For instance, a Belleville spring  54  could be disposed with its smaller diameter end disposed against the flange  134  and its larger diameter end engaged with an actuator arm  78 , a Belleville spring  54  could be disposed with its smaller diameter end disposed against the retainer ring  102  with its larger diameter end engaged with an actuator arm  78 , or both. This would then function to apply a compressive force to all head/arm assemblies  74  that are disposed or located between the retainer ring  102  and the flange  134 . All head/arm assemblies  74  could be biased toward the flange  134  or toward the retainer ring  102 . Another option would be to bias at least one head/arm assembly  74  away from the flange  134  and to bias at least one head/arm assembly away from the retainer ring  102  (e.g., in the case where a Belleville spring  54  is disposed between the flange  134  and a stack of head/arm assemblies  74 , and where another Belleville spring  54  is disposed between the retainer ring  102  and the stack of head/arm assemblies  74 ). 
     The configuration of the pivot bearing  118  significantly enhances the manner in which one or more head/arm assemblies numeral  74  may be mounted on the pivot bearing  118 . Consider the case where the head stack assembly includes a single head/arm assembly  74  as shown in  FIGS. 6-B . The head/arm assembly  74  would be disposed on the pivot bearing  118  so that it engaged or butted up against the flange  134  (e.g., the pivot bearing  118  extends through the mounting aperture  82  that extends through the actuator arm  78  of the head/arm assembly  74 ). The retainer ring  102  would then be disposed adjacent to the end  128   b  of the tapered section  126  of the sleeve  122 . The effective inner diameter of the retainer ring  102  is preferably at least generally the same as or possibly slightly larger than the effective outer diameter of the end  128   b . Preferably little to no expansion of the retainer ring  102  is required to initially position the same on the tapered section  126  at the end  128   b.    
     The ends  106   a ,  106   b  of the retainer ring  102  would be separated by an open space  114  of a first magnitude when the retainer ring  102  is disposed on the tapered section  126  proximate to the end  128   b . An arcuate section  110  of the retainer ring  102  is located between these ends  106   a ,  106   b . The retainer ring  102  may then be advanced along the tapered section  126 . There are multiple characterizations of this motion. One is that the retainer ring  102  is moved axially relative to the pivot bearing  118 . Another characterization is that the retainer ring  102  is moved at least generally parallel with a rotational axis  119  of the pivot bearing  118  (FIG.  6 B). Yet another characterization is that the retainer ring  102  is moved concentrically relative to the pivot bearing  118 . Relative movement of the noted type is all that is required between the retainer ring  102  and the pivot bearing  118 . 
     The above-noted relative movement between the retainer ring  102  and the pivot bearing  118  to advance the retainer ring  102  along the tapered section  126 , while in continued engagement therewith, increases the effective diameter of the retainer ring  102  or expands the size of the retainer ring  102 . Another way to characterize the response of the retainer ring  102  is that the magnitude of the open space  114  between its ends  106   a ,  106   b  increases during this movement of the retainer ring  102  relative to the sleeve  122  and that is in the direction of the retainer ring slot  130 . 
     The retainer ring  102  will be at its maximum diameter when it is disposed at the end  128   b  of the tapered section  126 . The retainer ring  102  has a certain amount of resilience or elasticity. Further movement of the retainer ring  102  toward the flange  134  will cause the retainer ring  102  to “snap” into the retainer ring slot  130 . The spring properties or elasticity of the retainer ring  102  causes this movement and also forcibly retains the same within the retainer ring slot  130 . That is, preferably the retainer ring  102  exerts an active, inwardly directed force on the sleeve  102 . Disposing the retainer ring  102  within the retainer ring slot  130  further fixes the position of the actuator arm  78  relative to the sleeve  122  of the pivot bearing  118 . That is, there should be little to no relative rotational movement between the actuator arm  78  and the sleeve  122  of the pivot bearing  118  during normal disk drive operations. 
     Summarizing the foregoing, the retainer ring  102  may be initially mounted on the tapered section  126  of the pivot bearing  118  without having to substantially increase the size thereof. In one embodiment, the size of the retainer ring  102  need not be increased at all to initially dispose the retainer ring  102  on the tapered section  126  of the outer wall  124  of the pivot bearing  118  and so as to be in interfacing relation therewith (e.g., the inner diameter of the retainer ring  102  in an undeformed state is at least as great as an outer diameter of a portion of the tapered section  126 ). No separate tooling is required to initially position the retainer ring  102  on the tapered section  126  of the outer wall  124  of the pivot bearing  118  in the preferred case. Stated another way, the retainer ring  102  may be manipulated solely by hand to initially dispose the retainer ring  102  on the tapered section  126  outer wall  124  of the pivot bearing  118 . In one embodiment, the outer diameter of the tapered section  126 , either at the end  128   b  or somewhere between the ends  128   b ,  128   a , is less than the inner diameter of the retainer ring  102  in an undeformed or static state. Preferably this is the maximum diameter encountered by the retainer ring  102  when initially disposing the same on the outer wall  124  of the pivot bearing  118 . Once the retainer ring  102  is initially disposed on the outer wall  124  of the pivot bearing  118 , the size of the retainer ring  102  is increased by at least about 8% prior to being disposed within the retainer ring slot  130  in one embodiment, and is increased by at least about 10% prior to being disposed within the retainer ring slot  130  in another embodiment,. Stated another way, the diameter of the tapered section  126  at its end  128   a  is at least about 8% greater than the diameter of the tapered section  126  at its end  128   b  to provide for the desired expansion of the retainer ring  102  in one embodiment, and is at least about 10% greater in another embodiment. This will then generate sufficient forces within the retainer ring  102  so as to apply sufficient forces against the outer wall  124  of the pivot bearing  118  when the retainer ring  102  is disposed within the retainer ring slot  130 . Once in the retainer ring slot  130 , the inner diameter of the retainer ring  102  is at least about 4% larger than when in its undeformed state. 
     The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.