Abstract:
A mounting system attaches head suspensions to actuator head mounting arms of a disc drive actuator. The mounting system includes head suspension mounting plates and features on both the head suspension mounting plates and on the actuator head mounting arms that facilitate snap-fitting or press-fitting of the mating components, as well as features that ensure both accurate alignment and maintenance of the position of the mounted head suspensions in and about the major orthogonal axes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 09/100,676, file on Jun. 19, 1998, now U.S. Pat. No. 6,052,260, issued Apr. 18, 2000, which claimed priority to provisional application No. 60/050,351, filed on Jun. 20, 1997. 
    
    
     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 an improved mounting system for attaching the head suspensions that support the read/write heads to the head mounting arms of the disc drive actuator. 
     BACKGROUND OF THE INVENTION 
     Disc drives of the type known a “Winchester” disc drives or hard disc drives are well known in the industry. Such disc drives 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 10,000 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 hydrodynamic 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 head suspensions or flexures. 
     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. An actuator housing is mounted to the pivot shaft by an arrangement of precision ball bearing assemblies, and 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. On the side of the actuator housing opposite to the coil, the actuator housing also typically includes a plurality of vertically aligned, radially extending actuator head mounting arms, to which the head suspensions mentioned above are mounted. 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 housing, with the attached head suspensions and head assemblies, in accordance with the well-known Lorentz relationship. As the actuator housing rotates, the heads are moved radially across the data tracks along an arcuate path. 
     The head suspensions mentioned above are typically formed from thin stainless steel foil. In order to provide a robust connection between the head suspension and the actuator head mounting arms, the attachment end of the head suspension is typically welded to a relatively thick mounting plate which includes features intended to cooperate with mating features on the actuator head mounting arms to attach the head suspensions to the actuator. 
     By far the most common head suspension mounting method in current use is swage mounting. Swage mounted head suspensions include mounting plates that are formed with a cylindrical swage boss. Typically, the entire array of head/suspension assemblies is placed in cooperative arrangement with the actuator head mounting arms, with the swage bosses of the head suspension mounting plates inserted into openings in the actuator head mounting arms. A swaging tool, consisting of a ball feature having a diameter slightly larger than the inner diameter of the swage bosses, is then passed through the entire vertically aligned stack of swage bosses, expanding the swage bosses into firm contact with the inner diameters of the openings in the actuator head mounting arms. Thus, swage mounting of the head/suspension assemblies is simple and economical for use in high volume manufacturing environments. 
     Swage mounting of head suspensions does, however, produce potential problems. Firstly, the plastic deformation of the swage bosses during the swaging process induces large mechanical stresses in the material of the mounting plates, and these mechanical stresses can lead to deformation of the planar portion of the mounting plates to which the thin head suspensions are welded. Such deformation can lead to uncontrolled variation in the pitch and roll static attitudes of the entire head suspension/head assembly, adversely affecting the data recording/recovery performance of the entire disc drive. 
     Secondly, since the swage mounting plates must be located on the upper and lower surfaces of the actuator head mounting arms, and since certain minimal vertical dimensions of the various components must be maintained to provide the necessary mounting strength, swage mounting dictates that the vertical spacing between the elements of the head/disc stack has a finite minimum. In order to provide the maximum amount of storage capacity in a disc drive, designers seek to incorporate the greatest number of heads and discs possible within industry-defined physical form factors, or, alternatively, to develop ever smaller form factors. Thus, swage mounting imposes limits on the number of heads and disc that can be fitted into a defined physical package, and may impose limits on the total storage capacity of the disc drive. 
     Finally, swage mounting, by definition mechanically deforms the associated components when it is performed. If, after assembly, a faulty component is discovered, it is first difficult to disassemble a swage mounted head suspension assembly without damaging other “good” components. Additionally, reinsertion of a replacement swage mounted head suspension into a head mounting arm that has already been stressed by a previous swaging operation may result in less than optimal mounting force, leading to undesirable variation in the finished product. 
     For these and other reasons to be noted below, a need clearly exists for an alternative to swage mounting of the head suspension assemblies in a disc drive. 
     SUMMARY OF THE INVENTION 
     The present invention is an improved mounting system for attaching the head suspensions to the actuator mounting arms of a disc drive actuator. The mounting system of the invention includes novel features on both the head suspension mounting plates and on the actuator head mounting arms that facilitate snap-fitting or press-fitting of the mating components, as well as features that ensure accurate alignment of the mounted head suspensions in the major orthogonal axes. Several embodiments of the invention are disclosed. 
     It is an object of the invention to provide a mounting system for attaching head suspensions to actuator mounting arms in a disc drive. 
     It is another object of the invention to provide a head suspension mounting system that incorporates snap-fitting or press-fitting, and thus facilitates rework. 
     It is another object of the invention to provide a head suspension mounting system that includes features for orthogonally aligning the mounted head suspensions. 
     It is another object of the invention to provide a head suspension mounting system that minimizes the vertical, or Z-axis, height while maintaining adequate mechanical strength. 
     It is another object of the invention to provide a head suspension mounting system that is simple and economical to implement in a high volume manufacturing environment. 
     The manner in which the present invention achieves these objects, as well as other features, benefits and advantages of the invention, can best be understood by a review of the following Detailed Description of the invention, when read in conjunction with an examination of the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a typical prior art disc drive in which the present invention is particularly useful. 
     FIG. 2 is a simplified detail sectional elevation view of a typical prior art swage mounting system for head suspensions. 
     FIG. 3 is a simplified plan view of a first embodiment of the invention. 
     FIG. 4 is a simplified plan view showing a modification to the embodiment of FIG.  3 . 
     FIG. 5 is a simplified plan view showing a modification to the embodiment of FIG.  4 . 
     FIG. 6 is a simplified sectional elevation view, taken along line A—A of FIG. 3, showing one advantage of the present invention. 
     FIG. 7 is a plan view of a second embodiment of the present invention. 
     FIG. 8 is a sectional elevation view, taken along line B—B of FIG. 7, showing one aspect of the embodiment of FIG.  7 . 
     FIG. 9 is a sectional elevation view, taken along line C—C of FIG. 7, showing a second aspect of the embodiment of FIG.  7 . 
     FIG. 10 is a sectional elevation view, taken along line D—D of FIG. 7, showing a third aspect of the embodiment of FIG.  7 . 
     FIG. 11 is a perspective view of features on the actuator head mounting arm that are a part of the embodiment of FIG.  7 . 
     FIG. 12 is a perspective view of a mounting plate that makes up a part of the embodiment of FIG.  7 . 
     FIG. 13 is a perspective view showing two of the mounting plates of FIG. 12 in their assembled orientation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings and specifically to FIG. 1, shown is a typical disc drive  2  in which the present invention is particularly useful. The disc drive  2  includes a base member  4  to which all other components are directly or indirectly mounted and a top cover  6  (shown in partial cutaway) which, together with the base member  4 , forms a disc drive housing enclosing delicate internal components and isolating these components from external contaminants. 
     The disc drive includes a plurality of discs  8  which are mounted for rotation on a spindle motor shown generally at  10 . The discs  8  include on their surfaces a plurality of circular, concentric data tracks, the innermost and outermost of which are shown by dashed lines at  12 , on which data are recorded via an array of vertically aligned head assemblies (one of which is shown at  14 ). The head assemblies  14  are supported by head suspensions, or flexures  16 , which are attached to actuator head mounting arms  18 . The actuator head mounting arms  18  are integral to an actuator bearing housing  20  which is mounted, via an array of ball bearing assemblies (not designated), for rotation about a pivot shaft  22 . 
     Power to drive the actuator bearing housing  20  in its rotation about the pivot shaft  22  is provided by a voice coil motor (VCM) shown generally at  24 . Electronic circuitry (partially shown at  26 , generally, and partially carried on a printed circuit board (not shown)) to control all aspects of the operation of the disc drive  2  is provided, with control signals to drive the VCM  24  as well as data signals to and from the heads  14 , carried between the electronic circuitry and the moving actuator assembly via a flexible printed circuit cable (PCC)  28 . 
     Turning now to FIG. 2, shown is a sectional elevation view of a typical prior art swage mounting system for head suspension assemblies. In the figure it can be seen that the head suspension ( 16  in FIG. 1) includes a spring member  30  and a relatively robust mounting plate  32  both commonly formed of stainless steel, and that the mounting plate  32  further includes a swage boss  34  which is inserted into an opening  36  in the actuator head mounting arm  18 . The figure also shows that a pair of mounting plates  32  is associated with each actuator head mounting arm  18 , with one of the swage bosses  34  inserted into the hole  36  on the top of the actuator head mounting arm  18 , and the other inserted from the bottom. The actuator body ( 20  in FIG. 1) and, therefore, the actuator head mounting arms  18  are commonly formed of aluminum or magnesium to minimize moving mass. 
     The swage boss  34  can also be seen to include a central opening  38 . After the base plates  32  of the head suspension assemblies have been positioned relative to the actuator head mounting arms  18  as shown in FIG. 2, a swaging tool (not shown) is passed through the central openings  38  in the swage bosses  34 . The swaging tool includes a ball member that is slightly larger than the diameter of the central opening  38  in the swage bosses  34 , and thus will cause plastic deformation of the swage bosses  34 , expanding them into intimate contact with the inner diameter of the openings  36  in the actuator head mounting arms  18 , all in a manner well known in the industry. 
     While the prior art swage mounting system just described is commonly used in the industry, it does have several drawbacks. Firstly, since the plate portion of the mounting plates  32  must lie in contact with the upper and lower surfaces of the actuator head mounting arms  18 , the necessary thickness of the mounting plates  32  is a limiting factor on the spacing of adjacent head mounting arms  18 , which leads to an attendant limitation on the spacing between adjacent heads and discs, and thus to limitations on the overall data storage capacity of a disc drive of a particular form factor, or, alternatively, serves as a limit on the vertical dimension of a desired new form factor. 
     Secondly, since the actuator head mounting arms  18  are typically formed as integral portions of a one-piece actuator body ( 20  in FIG.  1 ), the vertical spacing  40  between adjacent actuator head mounting arms  18  must provide not only for the thickness of the mounting plates  32  but for the vertical dimension of the swage bosses  34  as they are passed between adjacent actuator head mounting arms  18  and brought into alignment with the holes  36  in the actuator head mounting arms  18 . 
     A third drawback of the prior art swage mounting system of FIG. 2 is that the swaging operation produces different mechanical stresses on head suspension assemblies on the upper and lower surfaces of the actuator head mounting arms  18 . That is, as the swaging tool is passed through all of the swaging bosses  34  in the entire actuator assembly, in, for instance, the downward direction, the majority of the mechanical stresses applied by the swaging operation place the swage bosses  34  of assemblies on the upper surfaces of the head mounting arms  18  in tension, while the swage bosses  34  of assemblies on the lower surfaces are placed in compression. 
     This inequality in applied mechanical stresses can lead to unequal distortion of the base plates  32  on upper and lower surfaces of the actuator head mounting arms  18 , and associated uncontrolled variations in static roll and pitch attitudes applied to the head suspensions, which can in turn lead to undesirable variation in the forces applied to the heads carried on the head suspensions. 
     The present invention overcomes all of these disadvantages. 
     FIG. 2 also includes references to define two of the major orthogonal axes that will be referred to in the ensuing discussion. In the figure, it can be seen that the X-axis corresponds to the longitudinal length of the actuator head mounting arm  18 , as well as the longitudinal axis of the head suspension, while the Z-axis is shown to be the vertical axis. 
     FIG. 3 shows a simplified plan view of a first embodiment of the present invention. The figure includes a mounting plate  50  to which the spring member  30  of the head suspension is welded, in that portion of the mounting plate  50  shown generally by numerical reference  52 . The mounting plate  50  also includes an arm mounting feature  54  which is substantially circular in plan. The invention presently contemplates that the mounting plate  50  would be formed of stainless steel, however, other suitable materials could be utilized without exceeding the envisioned scope of the invention. 
     The actuator head mounting arm  56  includes a truncated triangular opening  57  which forms a pair of contact fingers  58 . The circular arm mounting feature  54  and opening  57  are dimensioned such that the mounting plate  50  must be press-fitted into the opening  57 , resulting in contact at three points  60  about the diameter of the arm mounting feature  54  and contact at flat surfaces (not numerically designated) at the distal ends of the contact fingers  58 . As mentioned above, the actuator head mounting arm  56  would typically be formed of aluminum or magnesium, but the scope of the invention is envisioned to encompass the use of other suitable materials. 
     The figure also includes a reference that reiterates the X-axis as extending along the length of the actuator head mounting arm  56 , and defines the Y-axis as the lateral axis corresponding to the width of the actuator head mounting arm  56 . One of skill in the art will appreciate that the head suspension mounting system shown will act effectively to prevent relative motion between the head suspension and the actuator head mounting arm in both the X- and Y-axes, as well as preventing relative rotation of these elements about a pivot axis parallel to the Z-axis. 
     FIG. 4 is a plan view of a variation of the embodiment of FIG.  3 . In FIG. 4, the mounting plate  50  has the same form and serves the same functions as described above, and the actuator head mounting arm  56   a  has been modified by narrowing the base of one of the contact fingers  58   a  to provide a spring element  58   b.  The inclusion of the spring element  58   b  acts to reduce the spring rate of the contact finger  58   a,  and thus can be used as a designer option to control the mounting force applied by the actuator head mounting arm  56   a  to the mounting plate  50 . Such control may be desirable to prevent the application of excessive stress on system elements which could lead to the previously mentioned variations in static roll and pitch attitudes in the associated head suspension assembly. 
     FIG. 5 is a plan view of a second variation of the embodiment of FIG. 3, and is intended to show another apparatus for reducing localized mechanical stresses in the system components. In FIG. 5, the actuator head mounting arm  56   a  is of the same form and serves the same functions described above in the discussion of FIG. 4, but the actuator head mounting arm could also be the same as was described in relationship to FIG.  3 . 
     The mounting plate  50   a  of FIG. 5 has been modified to allow the inclusion of a polymeric member  62  between the modified arm mounting feature  54   a  of the mounting plate  50   a  and the associated contact features of the actuator head mounting arm  56   a.  When the elements shown in the figure are press-fitted together, the polymeric member  62  will deform more readily than the materials of the mounting plate  50   a  and actuator head mounting arm  56   a,  thus preventing the concentration of mechanical stresses in these components. 
     FIG. 6 is a simplified sectional elevation view, taken along line A—A of FIG. 3, of the head suspension mounting system embodiments described above in relation to FIGS. 3 through 5. FIG. 6 shows a pair of mounting plates  50  placed in a back-to-back relationship and mounted to an actuator head mounting arm  56 . From the figure it is apparent that the combined Z-axis height of the two mounting plates  50  is equal to the Z-axis height of the actuator head mounting arm  18 . This means that the Z-axis spacing of adjacent actuator head mounting arms  18  can be reduced in comparison to prior art swage mounting systems (see FIG.  2 ), or, alternatively, that the actuator head mounting arms  18  and mounting plates  50  could be made thicker and more robust. In fact, one of skill in the art will realize that the present invention allows much greater flexibility in selecting a desirable compromise between Z-axis spacing and component strength than was available with the prior art swage mounting system of FIG.  2 . 
     One of skill in the art will also note that, should it be desirable to bring the spring members  30  of the head suspensions into closer relationship, that this can be readily accomplished with the head suspension mounting system of the present invention by simply stepping down and reducing the thickness of that portion of the mounting plate  50  (shown generally by numerical reference  52  in FIG. 3) to which the spring member  30  of the head suspension is welded. Indeed, the spring members  30  attached to one actuator head mounting arm  56  can be brought into direct contact by simply welding the spring members  30  to the opposite side of the mounting plates  50  to that shown in FIG. 6, should such be desirable. 
     From the foregoing discussion, it will be apparent to those of skill in the art that the embodiments of the present invention just described obviate the disadvantages described above of the prior art swage mounting system of FIG.  2 . That is, the present invention allows for closer Z-axis spacing of major disc drive components—thus facilitating either greater overall storage capacity or smaller form factors—and serves to prevent the concentration of excessive mechanical stresses in head suspension components that could lead to unacceptable variations in the static roll and pitch attitudes in the head suspensions. 
     All of the embodiments described to this point rely on the frictional force provided by the press-fitting of the mounting elements to maintain the Z-axis position of the head assemblies in relationship to the actuator head mounting arm. While this is adequate for current generations of disc drive products, future generations are expected to adhere to increasingly large mechanical shock specifications which may dictate the inclusion of positive restraint in the Z-axis. An alternative embodiment of the invention, to be described below, provides such positive Z-axis positional control. 
     FIG. 7 shows a simplified plan view of an alternative embodiment of the invention. In FIG. 7, the mounting plate  70  includes a suspension attachment portion, shown generally at  72 , to which the spring member  74  of the head suspension assembly is welded, typically in a symmetrical pattern of weld points, such as those designated with numerical reference  76 . The arm mounting portion of the mounting plate  70  is a tab portion  78  which is narrower at its base than at its proximal end. A cooperatively shaped opening (not designated) in the actuator head mounting arm  79  acts in concert with the tab portion  78  of the mounting plate  70  to constrain the system components in the X- and Y-axes, as will be apparent to one of skill in the art. 
     FIG. 9 also shows shows the contact fingers  80  of the actuator head mounting arm and shows that the tab portions  78  of the mounting plates include Z-axis registration features  90  which interact with cooperative features (not designated) in the contact fingers  80  to positively establish the Z-axis position of the mounting plates relative to the actuator head mounting arm. 
     FIG. 7 also shows that the actuator head mounting arm  79  includes a pair of contact fingers  80  created by the inclusion of the mounting opening in the actuator head mounting arm. One of the contact fingers  80  is shown with an optional notch  82  to provide control of the mounting force should such control be desired. 
     Other aspects of the embodiment of FIG. 7 can best be seen in FIGS. 8 through 13. 
     FIG. 8 is a sectional elevation view, taken along line B—B of FIG. 7, and shows two mounting plates  70  in back-to-back contact. As can be seen in the Figure, the contact surfaces of the mounting plates  70  include a plurality of elevation step features  84  (also shown as dashed lines in FIG. 7) which interact to stabilize the relationship between the two mounting plates  70  when a mounting force is applied to the mounting plate  70  in the direction of arrows  86  by the contact fingers ( 80  in FIG. 7) of the actuator head mounting arm ( 79  in FIG.  7 ). While the Figure shows two step features  84 , the scope of the present invention is envisioned to encompass the possibility of a single step, or a greater number of steps. 
     As was discussed in regard to the previously described embodiments of FIGS. 3 through 6, the invention envisions that the combined height  88  of the two mounting plates  70  will be substantially the same as the thickness of the actuator head mounting arm, providing the same benefits as described in the embodiments of FIGS. 3 through 6. 
     FIG. 9 is a sectional elevation view, taken along line C—C of FIG. 7, and shows another aspect of the embodiment of FIG.  7 . 
     FIG. 9 is a sectional through the tab portions  78  of the mounting plates and shows that the step features  84  extend through the tab portions  78  of the mounting plates and act as described above in the description of FIG.  8 . 
     FIG. 9 also shows the contact fingers  80  of the actuator head mounting arm and shows that the tab portions  78  of the mounting plates include Z-axis registration features  90  which interact with cooperative features (not designated) in the contact fingers  80  to positively establish the Z-axis position of the mounting plates relative to the actuator head mounting arm. 
     FIG. 10 is a sectional side elevation view, taken along line D—D of FIG. 7, and also shows that the proximal end of the tab portions  78  of the mounting plates also include the Z-axis registration features  90  which engage cooperative features (not designated) in the actuator head mounting arm  79  and also shown by dashed lines in FIG.  7 . 
     Thus, once the pair of head mounting plates is longitudinally pressed into the opening in the actuator head mounting arm, the spring action of the contact fmgers  80  acts to firmly engage the head mounting plates in the X-, Y-, Z- and rotational axes. 
     The specific form of the components comprising the embodiment of FIG. 7 can perhaps best be seen in FIGS. 11 through 13. 
     FIG. 11 is a perspective view of the distal end of the actuator head mounting arm  79  and shows the contact fingers  80  which interact with the tab portion ( 78  in FIG. 7) to provide the mounting force of the head suspension mounting system of the present invention. FIG. 11 also shows the optional notch  82  associated with one of the contact fingers  80  to provide a thinned spring region  92  should such controllability of the spring force be desired. 
     When a pair of contacting head mounting plates ( 70  in FIG. 7) are pressed into the opening in the distal end of the actuator head mounting arm  79 , in the direction of arrow  94 , the contact fingers  80  rotate outwardly, in the general direction indicated by arrow  96 . When the paired mounting plates are totally seated within the opening in the distal end of the actuator head mounting arm  79 , the contact fingers  80  return to their original position, locking the head mounting plates in position. 
     FIG. 11 also shows a notch feature  98  which will engage the Z-axis registration features ( 90  in FIGS. 9 and 10) to positively establish the Z-axis position of the head mounting plates. 
     FIG. 12 is a perspective view of the head mounting plate  70  which can be seen to include the suspension attachment portion  72  and the tab portion  78 , the functions of which have been previously described. The figure also shows the step features  84  that define the varying thickness of the head mounting plate  70 . The example head mounting plate  70  shown in FIG. 12 envisions that the thickness of the head mounting plate  70  in the region of the suspension attachment portion  72  is substantially one-half of the desired overall thickness of a mated pair of the mounting plates  70 , and that the step features  84  extend only from the attachment end of the head mounting plates  70  to the suspension attachment portion  72 . However, the step features  84  could also extend throughout the entire length of the paired mounting plates  70 . 
     In FIG. 12, the Z-axis registration feature  90  can be seen to  10  extend from the proximal end of the tab portion around to the side of the tab portion  78 . 
     FIG. 13 is a perspective view showing a pair of the mounting plates  70  arranged in back-to-back contact. It will be noted that the Z-axis registration features  90  of the head mounting plates are brought into a coplanar relationship for engagement with the notch feature ( 98  in FIG. 11) to lock the mounting plates together in the Z-axis, as well as to establish the Zaxis position of the mounting plates  70  relative to the actuator head mounting arm. 
     It will now be apparent to one of skill in the art that a sectional view of the mounting features of the embodiment of FIGS. 7 through 13 would be very similar to that shown in FIG. 6 for the embodiments of FIGS. 3 through 5, with the additional benefit of the Z-axis registration features discussed above. 
     From the foregoing, it is apparent that the present invention is particularly well suited and well adapted to achieve the objects set forth hereinabove, as well as possessing other advantages inherent therein. While a particular combination of components and materials have been disclosed with regard to the presently preferred embodiments, certain variations and modifications may be suggested to one of skill in the art upon reading this disclosure. Therefore, the scope of the present invention should be considered to be limited only by the following claims.