Abstract:
The performance of a leaf spring disc clamp can be enhanced by utilizing a roughly triangular shape for the center aperture. Such a disc clamp exhibits a substantially more uniform distribution of clamping force on the data disc and thereby reduces the deformation of the disc. It has further been determined that a stiffening rib located adjacent to the rim portion which contacts the data disc also leads to more uniform distribution of clamping force. Lastly, vibrations in a leaf spring disc clamp from external shocks or drive operation can be reduced utilizing a dampening ring of visco-elastic material. The dampening ring can be fastened to the surface of the disc clamp or placed within a rib on the disc clamp.

Description:
RELATED APPLICATIONS 
     This application claims priority of U.S. provisional application Ser. No. 60/158,840, filed Oct. 12, 1999. 
    
    
     FIELD OF THE INVENTION 
     This application relates generally to disc drives and more particularly to a clamping mechanism for retaining one or more data storage disc on a spin motor. 
     BACKGROUND OF THE INVENTION 
     Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are typically coated with a magnetizable medium and mounted on the hub of a spin motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by transducers (“heads”) mounted to an actuator assembly for movement of the heads relative to the discs. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate positioning of the head over the center of the desired track. 
     The heads are each mounted via flexures at the ends of actuator arms that project radially outward from the actuator body or “E” block. The actuator body typically pivots about a shaft mounted to the disc drive housing adjacent to the outer extreme of the discs. The pivot shaft is parallel to the axis of rotation of the spin motor and the discs, so that the heads move in a plane parallel to the surfaces of the discs. 
     Typically, such actuator assemblies employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor typically includes a flat coil mounted horizontally on the side of the actuator body opposite the actuator arms. The coil is immersed in a vertical magnetic field of a magnetic circuit comprising one or more permanent magnets and vertically spaced apart magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs. 
     Modern disc drives typically include one or more discs mounted to the spin motor. Spacers are used to provide the separation between discs necessary for the actuators arms to movably locate the heads in relation with the disc surfaces. The discs and spacers collectively form a disc stack assembly, or disc pack, that is mounted on the spin motor hub and held together with a leaf spring disc clamp. 
     Disc clamps can be either stamped or milled. While milled clamps are more rigid and less prone to deflecting the abutting disc surface, they are relatively expensive to produce. Consequently, stamped leaf spring disc clamps, which are substantially less expensive, have become popular. The clamp is typically a circular spring-steel, sheet metal structure having a central portion and a rib portion at or near the outside diameter of the clamp, with an annular rib formed in the rim portion of the clamp. The central portion of the leaf spring disc clamp has a partial aperture that is bent or deflected toward the center of the clamp, forming a leaf spring above the level of the annular rib, and includes a plurality of screw holes spaced symmetrically about the central portion of the clamp. The screws used to mount the disc clamp springingly bend and deflect the central portion of the clamp toward the upper surface of the motor spindle as the screws are tightened, thereby forcing the annular rib into firm contact with the uppermost disc surface and applying a clamping force to the disc stack. 
     This type of disc clamp is not without problems. The disc clamp is secured with a plurality of screws, typically 3, circumferentially spaced around the center of the clamp. The majority of the clamping force is exerted by the rib portion adjacent the screw locations, with a significantly reduced level of clamping force, and often no clamping force at all, exerted by the rib portion between the screw locations. This variation in clamping force can mechanically distort the discs in a phenomenon sometimes referred to as “potato chipping,” meaning that the portions of the disc nearest the clamp screws are displaced further than the portions of the disc between the screws. 
     Disc drives are subject to external shocks and must be designed to meet certain specified shock requirements. The non-uniform clamping force from current disc clamp design requires higher clamping forces to prevent disc slip from external shocks to the disc drive and the higher clamping forces increase the severity of “potato chipping.” 
     One solution to “potato chipping” is to increase the number of mounting screws used to secure the disc clamp to the spin motor hub. As more screws are used and are spaced closer together, the discrepancy in clamping force is reduced but not eliminated. A disadvantage of this approach is that the use of additional screws complicates the manufacturing and assembly process and increases costs. 
     Mechanical distortion of the disc surface can, in turn, lead to undesirable variations in the read/write signals detected and written by the heads of the disc drive. Since the heads will fly at varying heights around the circumference of the disc while attempting to follow a distorted disc, the signals used to read and write data on the discs may be inadequate to ensure reliable data storage and recovery. 
     Another problem encountered with the current disc clamps is the transfer of vibrations from the discs to the clamp. Current disc clamps do not dampen vibrations from shocks to the disc drive and the vibrations can resonate in the disc clamp or set it to “ringing.” This “ringing” then is transferred to the discs. Vibrations in the discs are an additional source of undesirable variations in the read/write signals detected and written by the heads. 
     Accordingly there is a need for a mechanism that would more evenly distribute the force applied to the disc surface from the disc clamp and also dampen vibrations in the disc clamp. 
     SUMMARY OF THE INVENTION 
     Against this backdrop the present invention has been developed. The performance of a disc clamp can be enhanced by utilizing a roughly triangular shape for the center aperture. Such a disc clamp exhibits a substantially more uniform distribution of clamping force and reduces the “potato chipping” of the disc. It has further been determined that a stiffening rib located adjacent to the rim portion which contacts the data disc also leads to more uniform distribution of clamping force. The invention has advantages over other mechanisms in that it does not require additional screws, other parts, or a significant change in the manufacturing process. 
     Accordingly, an aspect of the invention is found in utilizing a roughly triangular shaped central aperture in a disc clamp fastened with three screws to distribute the clamping force more uniformly on the disc. 
     Another aspect of the invention is providing a stiffening rib adjacent to the annular contract surface to increase the stiffness of the contact surface and more uniformly distribute the clamping force. 
     Yet another aspect of the invention is fastening a dampening ring to the disc clamp to reduce the amount of vibration in the disc clamp. 
     These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a disc drive incorporating a preferred embodiment of a disc clamp in accordance with the present invention showing the primary internal components. 
     FIG. 2 is an exploded view of an exemplary disc pack assembly utilizing a disc clamp in accordance with a preferred embodiment of the present invention. 
     FIG. 3 is a separate perspective view of a preferred embodiment of the disc clamp in accordance with the present invention. 
     FIG. 4 is a graphical representation of the clamping force distribution of the disc clamp shown in FIG.  3 . 
     FIG. 5 is a plan view of a preferred embodiment of a disc clamp in accordance with the present invention showing the optimal range of sizes of a central aperture. 
     FIG. 6 is a cross-sectional view of the disc clamp shown in FIG.  3 . 
     FIG. 7 is a cross-sectional view of another preferred embodiment of the present invention having a vibration dampening ring installed. 
    
    
     DETAILED DESCRIPTION 
     A disc drive  100  constructed in accordance with a preferred embodiment of the present invention is shown in FIG.  1 . The disc drive  100  includes a base  102  to which various components of the disc drive  100  are mounted. A top cover  104 , shown partially cut away, cooperates with the base  102  to form an internal, sealed environment for the disc drive in a conventional manner. The components include a spindle motor  106  that rotates one or more discs  108  at a constant high speed. Information is written to and read from tracks on the discs  108  through the use of an actuator assembly  110 , which rotates during a seek operation about a bearing shaft assembly  112  positioned adjacent the discs  108 . The actuator assembly  110  includes a plurality of actuator arms  114  which extend towards the discs  108 , with one or more flexures  116  extending from each of the actuator arms  114 . Mounted at the distal end of each of the flexures  116  is a head  118 , which includes an air bearing slider enabling the head  118  to fly in close proximity above the corresponding surface of the associated disc  108 . 
     During a seek operation, the track position of the heads  118  is controlled through the use of a voice coil motor (VCM)  124 , which typically includes a coil  126  attached to the actuator assembly  110 , as well as one or more permanent magnets  128  which establish a magnetic field in which the coil  126  is immersed. The controlled application of current to the coil  126  causes magnetic interaction between the permanent magnets  128  and the coil  126  so that the coil  126  moves in accordance with the well-known Lorentz relationship. As the coil  126  moves, the actuator assembly  110  pivots about the bearing shaft assembly  112 , and the heads  118  are caused to move across the surfaces of the discs  108 . 
     The spindle motor  106  is typically de-energized when the disc drive  100  is not in use for extended periods of time. The heads  118  are moved over park zones  120  near the inner diameter of the discs  108  when the drive motor is de-energized. The heads  118  are secured over the park zones  120  through the use of an actuator latch arrangement  122 , which prevents inadvertent rotation of the actuator assembly  110  when the heads are parked. 
     A flex assembly  130  provides the requisite electrical connection paths for the actuator assembly  110  while allowing pivotal movement of the actuator assembly  110  during operation. The flex assembly  130  includes a printed circuit board  132  to which head wires (not shown) are connected; the head wires being routed along the actuator arms  114  and the flexures  116  to the heads  118 . The printed circuit board  132  typically includes circuitry for controlling the write currents applied to the heads  118  during a write operation and a preamplifier for amplifying read signals generated by the heads  118  during a read operation. The flex assembly  130  terminates at a flex bracket  134  for communication through the base deck  102  to a disc drive printed circuit board (not shown) mounted to the bottom side of the disc drive  100 . 
     The discs  108  are secured to the hub  230  of a spin motor  106  in spaced-apart fashion. As illustrated in FIG. 2, three discs  108  are alternatively stacked together with spacers  220  that provide the vertical spacing necessary for actuator assembly function (described hereinafter). The stacked set of discs  108  and spacers  220  are mounted to the spin motor  106  via the disc clamp  210 . The typical disc clamp  210  is disc shaped having an outer rim portion, a sheet metal body, and a central spring portion forming a leaf-spring type disc clamp. Any combination of discs  108  and spacers  220 , along with a disc clamp  210 , can be referred to as a disc assembly or disc pack. Preferably, three mounting screws (not shown) are used to secure disc clamp the  210  to the spin motor hub  230  using threaded bores  222  in the hub  230 . 
     FIG. 2 shows the disc clamp  210  according to a preferred embodiment of the present invention. The disc clamp  210  has a bowed central leaf spring portion  218  that has a triangular central aperture  216 . The clamp  210  also has an annular rim portion  240  having an annular contact rib  330  and a concentric annular stiffening portion  332  adjacent to the rib (better seen in the sectional views of FIGS.  6  and  7 ). As described hereinafter, the annular rib  330  preferably provides the contact surface between the disc clamp  210  and the upper surface of the uppermost disc  108 . The adjacent stiffening portion  332  is a concentric rib  334  adjacent to the annular contact rib  330 . 
     The disc clamp  210 , as shown in FIG. 3, is a generally circular disc shaped body having a central portion  218  and a peripheral annular rim portion  240  forming an annular rib  330  and a concentric annular stiffening portion  332  adjacent to the rib  330 . The central portion  218  has a triangular central aperture  216  therethrough and screw mounting holes  212  equidistantly spaced around the central aperture  216  of the disc clamp  210 . The screw mounting holes  212  each receives a screw (not shown) to fasten the disc clamp  210  to the hub  230  of the spin motor  106 . The disc clamp  210  further includes a corner  214  between every two adjacent screw-mounting holes  212  within the central portion  218  of the disc clamp  210 . Each of the corners  214  of the central aperture  216  is rounded. 
     The triangular shape of the central aperture  216  enhances the equalization of the clamping force exerted by the annular rib  330  against the disc  108 , which reduces “potato chipping” of the disc  108 , i.e. the disc clamp  210  reduces the distortion of the disc  108  due to clamping forces. A graphical representation of the results of a computer model of the distribution of clamping force of a disc clamp  210  with a triangular shaped central aperture  216  is shown in FIG.  4 . The magnitude of the clamping force about the annular rib  330  is shown by the height of peaks superimposed on the view of the disc clamp  210 . The higher the peak, the greater the clamping force at that of the annular ring  330 . FIG. 4 shows that the triangular shape of the central aperture  216  performs the equalizing function in two ways. First, the triangular shaped aperture  216  more uniformly distributes the clamping force about the annular contact rib  330  than a typical disc clamp. Second, because the clamping force is more uniformly distributed, the disc clamp  210  reduces the amount of clamping force necessary to prevent disc  108  slip and meet a specified shock requirement. This, in turn, further reduces the force applied to the disc  108  and further reduces disc distortion attributable to the clamp  210 . 
     Computer modeling further determined the optimum operable range of for the triangular shaped aperture  216 . For a disc clamp  210  of typical size (i.e. outer diameter of 1.22 inches and an engagement surface or contact diameter of 1.125 inches), an optimum range for the triangular shaped aperture  216  diameter is from 0.7 to 0.78 inches as measured from a corner of the aperture, through the center of the disc clamp  210 , to farthest edge of the opposite screw mounting hole  212  as shown in FIG.  5 . Within the optimal range, the model indicates that a diameter is 0.77 inches achieves the most substantially uniform distribution of clamping force. 
     Another aspect of the invention is described below with reference to the cross-sectional view of the disc clamp  210  in FIG.  6 . The annular rim portion  240  of the disc clamp  210  has a stiffening portion  332 . The stiffening portion  332  has a stiffening rib  334  adjacent and interior to the contact rib  330 . The stiffening rib  334  serves the purpose of increasing the stiffness of the contact rib  330 , thus further reducing non-uniform distribution of the clamping force while in contact with the disc  108 . 
     A third aspect of the invention is shown in cross-sectional view of the disc clamp  210  presented in FIG. 7. A dampening ring  400  of visco-elastic material is contained within or beneath the stiffening rib  334 . The dampening ring  400  serves the purpose of dissipating vibrational energy in the disc clamp  210  from external shocks to the disc drive  100  or from disc drive operation. The dampening ring  400  eliminates “ringing” in the disc clamp  210  by dampening vibrations of frequencies including the disc clamp&#39;s resonant harmonics. FIG. 7 shows a toroidal, or O-ring shaped, dampening ring  400  having a circular cross section. However, any appropriate cross sectional shape may be used. 
     In summary, a preferred embodiment of the invention may be viewed as a disc clamp (such as  216 ) for fastening a data disc (such as  108 ) to a disc spin motor hub (such as  230 ). The disc clamp (such as  210 ) has a generally circular disc shaped body having a concentric central portion (such as  218 ) and an annular rim portion (such as  240 ). The central portion (such as  218 ) defines a generally triangular central aperture (such as  216 ) therethrough and has spaced apertures (such as  212 ) around the central aperture (such as  216 ) for mounting the disc clamp (such as  210 ) to a spin motor hub (such as  230 ). The rim portion (such as  240 ) forms an annular contact rib (such as  330 ) through which a distributed clamping force is applied to the data disc (such as  108 ). 
     Preferably, the disc clamp (such as  210 ) has three spaced apertures (such as  212 ) around the central aperture (such as  216 ). In a preferred embodiment, the triangular central aperture (such as  216 ) generally has the shape of an equilateral triangle wherein the corners of the central aperture (such as  216 ) are curved and have a radius substantially equal to that of the radius of the disc clamp (such as  210 ). The disc clamp (such as  210 ) has an outer diameter of 1.22 inches, an engagement surface or annular contact rib (such as  330 ) diameter of 1.125 inches, and a triangular shaped aperture (such as  216 ) diameter between 0.7 to 0.78 inches and preferably 0.77 inches as measured from a corner of the aperture, through the center of the disc, to farthest edge of the opposite screw mounting hole (such as  212 ). 
     The invention also may be viewed as a disc clamp (such as  210 ) having a generally circular disc shaped body having an annular rim portion (such as  240 ) having an annular contact rib (such as  330 ), a concentric annular stiffening portion (such as  332 ) adjacent to the rib (such as  330 ), and a central portion (such as  218 ). Preferably, the stiffening portion (such as  332 ) forms a second annular rib (such as  334 ) stiffening the rim portion (such as  240 ). In a preferred embodiment the central portion (such as  218 ) has a central aperture (such as  216 ) therethrough that is substantially triangular shaped and three spaced apertures (such as  212 ) around the central aperture (such as  216 ) each for receiving one of three fasteners. 
     Alternatively, the invention also may be viewed as a disc clamp (such as  210 ) having a generally circular disc shaped body having an annular rim portion (such as  240 ) and a central portion (such as  218 ), wherein a dampening ring (such as  400 ) is fixed to the annular rim portion (such as  240 ) to dampen vibrations in the disc clamp (such as  210 ). Preferably, the dampening ring (such as  400 ) is toroidally shaped, made of a visco-elastic material and is positioned against the stiffening portion (such as  240 ) to adsorb vibrations in the disc clamp (such as  210 ). In the preferred embodiment, the dampening ring (such as  400 ) is fixedly held within a stiffening rib (such as  334 ) in the rim portion (such as  240 ) of the disc clamp (such as  210 ). 
     It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. For example, in alternative embodiments the dampening ring  400  can contact the surface of the disc  108  or may be placed within the contact rib  330  rather than the stiffening rib  334 . The dampening ring  400  may be fixed in place by any means including, but not limited to, adhesive, press fitting or molding it in place. The corners  214  of the triangular central aperture  216  can be utilized as spanner slots to assist in placement and mounting of the disc clamp  210  to the spindle motor  106 . The stiffening rib  334  or an addition stiffening rib  334  may be located exterior to the annular contact rib  330 . Numerous other changes may also be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.