Abstract:
The outer surface of the cartridge sleeve is provided with features which increase the frictional coefficient between the cartridge sleeve and a tolerance ring placed around the cartridge. The cartridge and ring are then press-fit into the actuator bore together. The increased friction between the cartridge and ring prevents slip between them, eliminating the need to increase compressive forces between the ring and the bore and bearing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/246,169, filed Nov. 6, 2000. 
    
    
     FIELD OF THE INVENTION 
     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 movement of disc drive actuators. 
     BACKGROUND OF THE INVENTION 
     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. 
     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. 
     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. These magnets are typically mounted to pole pieces which are held in positions vertically spaced from another by spacers at each of their ends. 
     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. 
     As explained above, the actuator assembly typically includes an actuator body that pivots about a pivot mechanism disposed in a medial portion thereof. The function of the pivot mechanism is crucial in meeting performance requirements associated with the positioning of the actuator assembly. A typical pivot mechanism has two ball bearings with a stationary shaft attached to an inner race and a sleeve attached to an outer race. The sleeve is also secured within a bore in the actuator body. The stationary shaft typically is attached to the base deck and the top cover of the disc drive. 
     Bearing cartridges have been mounted within actuator bores in a variety of ways. Some have simply press-fit the cartridge into the bore; others have formed the bore of the actuator of plastic in order to facilitate such press-fitting. Still others have provided screws in the actuator body which extend into the bore, either to serve as set screws pressing against the cartridge sleeve or to engage threads in the cartridge sleeve so as to pull the cartridge into tight contact with the bore. However, all of these methods present additional problems: simple press-fitting risks damage to both the bore and cartridge; plastic bores are subject to thermal expansion and contraction, as well as fatigue; and providing screws and their bores requires additional parts, manufacturing steps and costs. 
     One solution to these problems has been to provide a groove in the outer surface of the sleeve, and then positioning a tolerance ring within the groove. The tolerance ring is typically made of a compressible yet resilient piece of material such as a corrugated steel sheet. The bearing cartridge and tolerance ring assembly is then press-fit into the bore of the actuator body, the tolerance ring holding the cartridge in place within the bore while yielding enough so that neither the cartridge nor the bore is damaged as a result of the press-fitting operation. This method has proven largely satisfactory. 
     However, even this arrangement raises other problems. The bearing and tolerance ring are typically made of steel because of its high strength. The actuator bore&#39;s inner surface is typically made of aluminum because of its relatively low weight and cost. Aluminum is a much softer material than steel, so when the bearing cartridge and tolerance ring are pressed into the actuator bore, the steel corrugations tend to “bite” into the soft aluminum bore by mildly deforming the aluminum, resulting in a high level of friction between the ring and bore. Because the bearing cartridge is made of steel, however, there is little between the cartridge and ring to create friction between them. This greatly raises the risk of axial slippage between the bearing cartridge and the tolerance ring during shock events. In fact, tests have borne this out, indicating that slip between the ring and the cartridge occurs at about a mere 20% of the force required to cause slip between the ring and actuator bore. 
     In order to prevent slip between the cartridge and tolerance ring, then, it has generally been necessary to increase assembly forces to a very high degree. The result has been that slip between the cartridge and tolerance ring has been eliminated, by creating a tighter fit between the bore, ring and cartridge. The extremely tight fit has the added effects of making assembly more problematic, raising the risk of cartridge or actuator damage, and also results in frictional forces between the ring and bore far in excess of what is necessary to prevent slip between them. 
     What the prior art has been lacking is a bearing cartridge mounting arrangement which is easily assembled but which is resistant to slip when subject to axial forces. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an easily assembled bearing cartridge mounting arrangement. Prior to installing a bearing cartridge in an actuator bore, a tolerance ring is placed around the cartridge. The outer surface of the cartridge sleeve is provided with features which increase the frictional coefficient between the cartridge sleeve and the tolerance ring. The cartridge and ring are then press-fit into the actuator bore together. The increased friction between the cartridge and ring prevents slip between these two components, eliminating the need to increase compressive forces between the ring and the bore and bearing. Additional features and benefits will become apparent upon a review of the attached figures and the accompanying description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows an exploded view of a disc drive incorporating the bearing mounting assembly of the present invention. 
     FIG. 2 shows an exploded view of an actuator incorporating the bearing mounting assembly of the present invention. 
     FIG. 3 depicts a cross-sectional view of a bearing mounted within an actuator. 
     FIG. 4 shows a cross-sectional view of a tolerance ring sandwiched between a bearing cartridge and actuator bore. 
     FIG. 5 shows a cartridge with grooves formed in the sleeve. 
     FIG. 6 shows a cartridge with knurling formed in the sleeve. 
     FIG. 7 shows a cartridge with adhesive placed on the sleeve. 
     FIG. 8 shows a cartridge with resilient material placed on the sleeve. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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. The disc drive  100  includes a deck  110  to which all other components are directly or indirectly mounted and a top cover  120  which, together with the deck  110 , forms a disc drive housing which encloses delicate internal components and isolates these components from external contaminants. 
     The 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 bearing assembly  400  which includes a stationary pivot shaft  410  about which the actuator  300  rotates. 
     Power to drive the actuator  300  about the pivot shaft  410  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  are mounted to spaced pole pieces  350  which are fixed to the deck  110  and are further 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)  380 , which also transmits data signals to and from the heads  310 . 
     FIG. 2 shows a partially exploded, perspective view of an actuator  300  incorporating the bearing assembly of the present invention. The actuator  300  has a bore  370  formed therethrough which receivingly engages a bearing assembly. The bearing assembly is shown to include a bearing cartridge  400  and a tolerance ring  450  compressingly interposed between the bearing cartridge  400  and the bore  370  to retain the bearing cartridge  400  within the bore  370 . The cartridge  400  and the tolerance ring  450  are installed by first placing the tolerance ring  450  around the cartridge  400 , and then axially inserting the cartridge-ring assembly into the actuator bore  300 . 
     FIG. 3 shows a cross-sectional view of the actuator  300  with the bearing cartridge  400  and the tolerance ring  450  installed in actuator bore  370 . The cartridge  400  has a stationary pivot shaft  410  which has a threaded projection  415  at its lower end for secure mounting to the floor of deck  110 . The cartridge  400  also includes an outer sleeve  420  separated at upper and lower ends thereof by a pair of ball bearings  430 . The stationary shaft  410  may also include an upper threaded opening  440  to receive a fastener (not shown) for attachment of the stationary shaft  410  to the top cover  120 . It will be readily understood that the shaft  410  could be attached to the deck  110  and cover  120  by other means than those disclosed here without departing from the spirit of the present invention. In this manner it will be understood that the stationary shaft  410  is rigidly supported and the sleeve  420  is free to rotate about the stationary shaft  410 . The sleeve  420  of the bearing cartridge  400  forms an upper shoulder, a lower shoulder, and a groove of a reduced diameter between the shoulders. The tolerance ring  450  is seated in the groove before the bearing cartridge  400  is placed into the bore  370 . It should be understood that the width of ring  450  is actually shorter then the width of the groove for ease of assembly. 
     As can be seen in FIG. 2, the tolerance ring  450  is typically a split ring member which forms a cylindrical inner surface  460  and a cylindrical outer surface  470 , with a plurality of projecting corrugations  480  forming a corrugated surface on the outer surface  470 . Such tolerance rings are well-known, for a variety of purposes, and examples of such rings are those manufactured by USA Tolerance Ring. 
     It will be understood from FIG. 4 that the tolerance ring  450  is sandwiched between the groove of the sleeve  420  and the surface of the bore  370  of the actuator  300 . The sleeve  420  and tolerance ring  450  combine to provide an effective outer diameter that is greater than the diameter of bore  370 . As such, the sleeve  420  and tolerance ring  450  combination can be press fit into the bore  370 . The press-fit compresses the corrugations  480  as shown in FIG. 4 where the broken lines denote the shape of the corrugations  480  before insertion into the bore  370 . The compression imparted to the corrugations  480  of the tolerance ring  450  creates sufficient frictional resistance to retain the tolerance ring  450  within the bore  370 , preventing displacement of the tolerance ring  450  relative to the actuator in both the axial and radial directions. 
     The frictional resistance between the tolerance ring  450  and the actuator bore  370  is greater than that between the ring  450  and cartridge sleeve  420 . This is primarily because the corrugations  480  of the ring  450 , which are made of steel, actually “bite” into the softer aluminum from which the actuator bore  370  is formed. The bearing cartridge sleeve  420 , however, is made of steel, and much less frictional resistance is created between the machined surface of the sleeve  420  and the inner surface  460  of the tolerance ring  450 . It follows that even when the tolerance ring  450  is securely axially located within the bore  370 , slippage may occur nonetheless between the cartridge  400  and the tolerance ring  450  if measures are not taken to prevent it. It is for this reason that frictional elements are provided on the outer surface of the cartridge sleeve  420 . 
     One embodiment of the present invention is illustrated in FIGS. 2,  3  and  5 , in which circumferential horizontal grooves  422  are provided in the outer surface of the cartridge sleeve  420 . Machining these grooves  422  creates edges and recesses which effectively “bite” into the inner surface  460  of the tolerance ring  450 , reducing the likelihood of slippage therebetween without unnecessarily increasing the frictional resistance between the ring  450  and the actuator bore  370 . Because the outer surface of the cartridge sleeve  420  is typically turned to precise specifications anyway, the grooves  422  can machined at the same time. This is advantageous in that manufacturing costs are not significantly increased by providing grooves  422  in the sleeve  420 . Grooves  422  are also easily inspected to ensure they are in conformance with tolerances and specifications. The horizontal orientation of the grooves  422  is particularly effective in preventing axial slippage between the cartridge  400  and sleeve  450 . 
     FIG. 6 shows another embodiment of the invention in which the outer surface of the sleeve  420  is knurled  424 . Again, knurling  424  provides a large number of edges and recesses which allow the sleeve  420  to “bite” into the inner surface  460  of the tolerance ring  450 . Knurling  424  has the added advantage of effectively preventing rotational slippage in addition to axial slippage. While rotational slippage is far less likely than axial slippage, given that cartridge sleeve  420  is free to rotate about pivot shaft  410 , it is conceivable that in some applications a severe rotational shock event might cause rotational slippage in the absence of frictional elements  424 . 
     FIG. 7 shows another embodiment of the invention in which the outer surface of the sleeve  420  is provided with adhesive  426 . Adhesive  426  provides a sticky surface on the cartridge sleeve  420  to which the tolerance ring  450  may bond, so as to prevent both axial and rotational slippage between the ring  450  and sleeve  420 . 
     FIG. 8 shows yet another embodiment of the invention in which the outer surface of the sleeve  420  is provided with a layer of resilient material  428 . The resilient material  428  may be rubber, plastic, or any other similar material that provides a soft surface into which the inner surface  460  of the tolerance ring  450  may “bite”, so as to prevent both axial and rotational slippage between the ring  450  and sleeve  420 . 
     Of course, it should be understood that a bearing cartridge mounting arrangement may differ from the example described above without departing from the spirit of the claimed invention. For example, while frictional elements are discussed above with respect to a corrugated tolerance ring, they could of course be used with other mounting systems in which enhanced friction with respect to the bearing cartridge is desirable. Moreover, other friction-enhancing methods could be provided in lieu of or in combination with those discussed above. For example, bead blasting, sanding, or other methods could be use to provide a rough surface in order to increase friction. 
     Alternatively stated, a first contemplated embodiment of the invention is an mounting assembly for an actuator  300  including a bearing cartridge  400  having a shaft  410  and a sleeve  420  rotatable about the shaft  410 . The cartridge  400  is configured to be positioned in a bore  370  within the actuator  300 . The assembly further includes a retention element  450  configured to be positioned between the sleeve  420  and a surface of the bore  370 . The assembly further includes at least one feature positioned between the shaft  410  and the retention element  450  configured to prevent relative movement between the sleeve  420  and the retention element  450 . Optionally, the retention element  450  may be a corrugated sheet  450 . As another option, the movement preventing feature may be a groove  422  in the sleeve  420 . As yet a further option, the movement preventing feature may be a plurality of grooves  422  extending about a periphery of the sleeve  420 . As another option, the movement preventing feature may be adhesive material  426  located on the sleeve  420 . 
     Alternately characterized, a second comtemplated embodiment of the invention is a disc drive  100  having a housing  110 , an actuator  300  having a bore  370  therein, and a bearing cartridge  400  fixed to the housing  110  and positioned within the actuator bore  370 . The cartridge has an axis of rotation. A resilient element  450  is positioned between the cartridge  400  and a surface of the bore  370 . The disc drive further includes at least one frictional element associated with the cartridge  400  and contacting the resilient element  450  so as to prevent all axial movement of the actuator  300  relative to the cartridge  400 . Optionally, the resilient element  450  may be a tolerance ring. As another option, the frictional element may be a knurled projection  424  located on the sleeve. As yet another option, the frictional element may be a resilient member  428  affixed to the sleeve. 
     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.