Abstract:
A head gimbal assembly has a gimbal with a limiter formed from a sheet prior to attachment to the load beam structure. The limiter has a pair of flange extensions, each flange extension having an arm extension. The flange extensions and the arm extension are bent around a tip of the load beam to interleave the limiter around the load beam. The arm extensions have a narrower width than a width of the flange extensions, providing room for adjustment to the pitch and roll attitude of the system after assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority from provisional application Ser. No. 60/417,236, filed on Oct. 9, 2002, and entitled “HEAD GIMBAL ASSEMBLY HIGH PERFORMANCE SHOCK LIMITER”. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a disc drive assembly. In particular, the present application relates to a shock limiting suspension for a magnetic read-write head in a disc drive assembly. 
     Disc drives of systems are known which read data from a disc surface during operation of a disc drive. Typically, such disc drive systems include magnetic disc drives and optical disc drive systems. Generally, discs are rotated for operation of the disc drive via a spindle motor to position for reading data from or writing data to selected portions or tracks on the disc surface. 
     The read-write head generally includes an air bearing surface, which floats or flies above the disc surface in a known manner. Generally, the slider flies with a positive pitch angle at which the leading edge of the slider flies at a greater distance from the disc surface than the trailing edge via a suspension assembly, which includes a load beam and a gimbal. The slider is coupled to the load beam via a gimbal. The load beam applies a load force to the slider via a dimple. The dimple defines an access about which the slider pitches and rolls via the gimbal. The slider is preferably resilient in the pitch and roll direction to enable the slider to follow the topography of the disc based on the hydrodynamic lifting force caused by the disc rotation. 
     Generally, the gimbal permits the air bearing slider to pitch and roll as the slider flies above the disc surface. It is important to maintain the proximity of the slider relative to the disc surface during operation. In a typical disc drive, a magnetic transducer element is carried on the slider to write data to the disc surface. 
     Depending on the mass and stiffness of the suspension assembly, including the gimbal and the load beam, external vibration may excite the load beam and gimbal at a resonant frequency. Thus, the input motion or external vibration may be amplified substantially, causing unstable misalignment of the slider relative to the disc surface. Such misalignment may result in data loss and/or damage to the disc surface. 
     External vibration or excitation of the suspension assembly and slider may introduce varied motion of the slider and suspension assembly. Depending on the nature and frequency of the excitation force, the slider and suspension assembly may cause torsional mode motion, sway mode vibration and bending mode resonance. Torsional mode motion relates to rotation or twisting of the suspension assembly about an in-plane axes. Bending mode resonance essentially relates to up-down motion of the suspension assembly relative to the disc surface. Sway mode vibration relates to in-plane lateral motion and twisting. It is very important to limit resonance motion to assure stable fly characteristics for the slider. In particular, it is important to control the torsion and sway mode resonance, since they produce a transverse motion of the slider, causing head misalignment with respect to the data tracks of the disc surface. 
     Generally, the resonance frequency of the suspension assembly is related to the stiffiness or elasticity and the mass of the suspension system. Thus, it is desirable to design a suspension system, which limits the effect of sway mode and torsion mode resonance in the operating frequencies of the disc drive, while providing a suspension design which permits the slider to pitch and roll relative to the dimple. 
     Deflection limiters are beneficial for multiple reasons. During a shock event, such as dropping the disc drive or the lap top computer, the mass of the head can pull the gimbal away from the load beam if there is not deflection limiter. The shock event can induce stress in the gimbal. This stress may be enough to bend the gimbal and result in dimple separation and/or changes to the pitch and roll static angle (attitude) of the gimbal. A deflection limiter is designed to prevent separation of the gimbal by insuring that the deflection is not large enough to cause the stress to reach the gimbal&#39;s yield point, which could cause gimbal separation resulting in disc drive failure. 
     Such deflection limiters structures are broadly known. Generally, they are designed to either prevent excessive movement during shock events such as the jarring or dropping of a computer, or to prevent non-operational damage to the suspension-gimbal structure. 
     Generally, there are two ways in which to introduce a shock limiter to a disc drive structure: features are presented on the load beam to engage the gimbal and limit the excessive motion during shock events, or features are presented on the gimbal to engage the load beam to prevent excessive motion during a shock event. 
     In the field of suspension technology for magnetic disc drives, stainless steel is typically used as the support structure for the slider. A typical configuration consists of an etched gimbal ring, which is welded to the suspension load beam. A circuit is routed over or adjacent to the steel gimbal to provide an electrical connection to the slider. The assembly is cantilevered from the load beam and pre-loaded against a dimple, which protrudes from the load beam. For robustness, a hook is formed in the steel gimbal sheet and is interleaved through an opening in the load beam. This feature serves as the “limiter”. 
     This type of limiter is relatively simple to incorporate into a Load/Unload mobile drive application due to the available material around the load point and slider necessary to support the lift tab feature at the distal end. However, incorporating such a limiter into a non-Load/Unload or a contact start stop (CSS) design becomes difficult because of a number of factors: material availability, resonance requirements, tolerance “stack-up”, slider bonding area, clearance for assembly processes, attitude adjustability, and robustness. 
     In non-Load/Unload and CSS designs, there is insufficient available material to incorporate the limiter engagement feature. Specifically, the load beam tip is narrow and the load point is typically coincident with the end of the beam, leaving little extra material from which to form the limiter engagement feature. 
     Resonance requirements of the head gimbal assembly dictate that the structural mass at the load arm tip must be minimized. Specifically, it is desirable to minimize the mass added to the structure. If mass must be added, it is desirable to keep the added mass as close as possible to the center line or axis of the structure in order to maintain the equilibrium or balance of the structural mass. By minimizing the mass and by keeping the added mass near the center line, the overall resonance performance of the structure is enhanced. 
     With respect to tolerance “stack up”, incorporation of a limiting feature internal to the load beam (such as the interleaved hook through an opening in the load beam) requires clearance for clamping, forming, and welding, and other steps of the fabrication and assembly processes. 
     Additionally, when the limiter is interleaved through an opening in the load beam, material must be removed from the load beam to provide the opening. This, in turn, impacts the resonance performance of the system as a whole. Additionally, removal of material from the gimbal/tongue area to provide the limiter structure necessarily reduces the size of the bonding area available for attaching the slider to the gimbal. 
     Finally, the various limiters in the prior art typically impose structural limitations on the disc drive structure, such as allowing clearance for gold ball bonding processes and limiting adjustability of the pitch and roll static attitude during assembly. 
     Therefore, it is desirable to have a robust shock limiter that maintains the narrow profile of the load beam and that adds little material in a balanced arrangement close to the center axis (center of mass) of the suspension. Moreover, it is desirable that the gimbal interleave with the load beam without requiring an opening in the load beam and without removing much material from the gimbal in the bonding area. Finally, it is desirable to have a robust shock limiter that maintains pitch and roll static attitude adjustability during assembly. 
     BRIEF SUMMARY OF THE INVENTION 
     A shock limiter for use with in a disc drive having rotatable discs is formed from a unitary piece of material integrally with the gimbal. The limiter has a pair of flange extensions arranged symmetrically relative to a longitudinal axis of the gimbal. Each flange extension has an arm extension, which can be interleaved around the attachment tip to limit movement of the gimbal relative to the load beam in a shock event. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a disc drive including an actuator assembly and a load beam of the prior art. 
         FIG. 2  is a perspective view of an actuation assembly in the prior art. 
         FIG. 3  is a perspective view of a prior art shock limiter positioned through an opening in the load beam. 
         FIG. 4  is a bottom view of another prior art shock limiter. 
         FIG. 5  is a top plan view of an interleaved shock limiter according to the present invention. 
         FIG. 6  is a bottom plan view of the interleaved shock limiter of the present invention. 
         FIG. 7  is a bottom plan view of the shock limiter prior to assembly. 
         FIGS. 8   a - 8   c  are bottom plan views of the limiter engagement element shown prior to bending, after the first bend is made and after the second bend is made, respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a prior art disc drive  10  including an actuation assembly for positioning a slider  12  over a track  14  of a disc  16 . Disc drive  10  includes a voice coil motor (VCM)  18  arranged to rotate an actuator arm  20  on a spindle around an axis  22 . A load beam  24  is connected to actuator arm  20  at a head mounting block  26 . A gimbal  28  is connected to an end of load beam  24  and slider  12  is attached to gimbal  28 . Slider  12  carries a transducing head (not shown in  FIG. 1 ) for reading and/or writing data on concentric tracks  14  of disc  16 . Disc  16  rotates around an axis  30 , producing a hydrodynamic layer of air that keeps the slider  12  aloft a small distance above the surface of disc  16 .  FIG. 1  shows a high capacity disc driving having multiple rotating discs  16 . The disc drive has an upper and lower actuation assembly, with the lower actuation assembly being shown in phantom. 
       FIG. 2  is a perspective view of a prior art actuation assembly  32  for positioning slider  12  over track  14  of disc  16 . Actuation assembly  32  includes an upper assembly  32 A and a lower assembly  32 B that are identical. Both the upper assembly  32 A and the lower assembly  32 B have actuator arm  20  with load beam  24  connected to the actuator arm  20  at head mounting block  26 . Gimbal  28  is connected to an end of load beam  24 , and slider  12  is attached to gimbal  28 . Slider  12  carried by upper assembly  32 A reads and writes data from an upper surface of disc  16 . Slider  12  located on lower assembly  32 B reads and writes data from the lower surface of disc  16 . 
       FIG. 3  is a magnified perspective view of a prior art head gimbal assembly  34  with a shock limiter  36  positioned through an opening  38  in the load beam  24 . The location of the weld point  40  for attaching the gimbal  28  to the load beam  24  is shown in shadow. This prior art shock limiter  36  is positioned well behind the slider  12 , such that the inertial load on the gimbal  28  is acting away from the shock limiter  36  and from the weld point  40 . During a shock event particularly in the direction indicated by arrow (L), this shock limiter  36  may fail to limit the movement of the gimbal  28  and slider  12 . Specifically, the gimbal  28  is likely to bend due to the load disposed far away from the limiter, and the shock limiter  36  is likely to pull out of the opening  38 , thereby failing to limit the bending motion of the gimbal  28  and head  12 . 
       FIG. 4  illustrates a bottom view of an alternative embodiment of a prior art head gimbal assembly  34 , having a shock limiter  36  formed from the gimbal  28  and positioned through opening  38  in the load beam  24 . As shown, the slider  12  is positioned almost directly over the limiter  36 , thereby improving the performance of the limiter  36 ; however, to produce the limiter from the gimbal  28 , material must be removed from the gimbal  28 , directly in the bonding area under the slider  12 . This material removal necessarily weakens the bond between the gimbal  28  and the slider  12 , which may lead the slider  12  to separate from the gimbal  28  during a shock event. 
     The opening  38  shown in both  FIGS. 3 and 4  is formed by removal of material from the load beam  24 . In order to provide openings for interleaving the limiter through the load beam  24 , the load beam tip  48  must be made larger, thus compromising the resonance performance of the structure. 
       FIG. 5  illustrates a shock limiter configuration in a head gimbal assembly  42  according to the present invention, which is intended for disc drive applications, including Load/Unload and non-Load/Unload designs.  FIG. 5  illustrates a load beam  44  having a static-attitude dimple  46  and a load beam tip  48  with a dimple  50 . The gimbal  52  is attached to the load beam  44  via weld points  54 . The slider  12  (shown in shadow) is bonded to the gimbal  52 . A flex circuit  56  is shown attached to the gimbal  52 . Gimbal  52  has a limiter  58  having flange portions  60  and arm portions  62 . 
     As shown, the flange portions  60  of the limiter  58  are bent upward around the load beam tip  48 , and the arm portions  62  are bent toward one another over the load beam tip  48 . Both bends define angles relative to the planar surface of the gimbal  52 . In one embodiment, the angle of each bend approaches 90 degrees, relative to the surface of the gimbal  52 . In a preferred embodiment, the angles are approximately 80 degrees. When a shock event occurs, the event can induce stress in the gimbal  52 . The arm portions  62  prevent separation of the gimbal  52  from the load beam  44  by insuring that the deflection of the gimbal  52  is not large enough to cause the stress to reach the yield point of the attachment of the gimbal  52  resulting in damage. 
       FIG. 6  illustrates head/gimbal assembly  42  of  FIG. 5  from a bottom plan view.  FIG. 6  shows a load beam  44  connected to a gimbal  52  via weld points  54 . The location of the dimple  50  is shown (in phantom) on the tongue  64  of the gimbal  52  for clarity, though the dimple  50  would not be visible through the gimbal  52  in actuality. As shown, the limiter  58  has flange portions  60  with an arm portions  62  that are bent around the load beam tip  48  on both sides of the load beam tip  48 . 
     Generally, the length of the flange portions  60  and the arm portions  62  are limited by the width of the gimbal  52 . If the load beam  44  has rails extending along its length to reinforce the load beam  44 , the length of the arm portions  62  may be limited by the location of the end of the rails relative to the position of the gimbal  52 . Specifically, during assembly, the arm portions  62  are bent toward the dimple  50 , and there must be sufficient clearance between the arm portions  62  and the end of the rails so the arm portions  62  do not contact the rails during the bending process. 
     In  FIG. 7 , the gimbal  52  is shown prior to attachment to the load beam  44 . Specifically, the gimbal  52  may be machined, laser processed, etched or otherwise fabricated using any known technique. As shown, the gimbal  52  is flat with the shape of the limiter  58  cut out from the flat substrate of the gimbal  52 . 
     There exists a gap  66  between the arm portions  62  and the tongue  64  of the gimbal  52  on both sides of the limiter  58 , after the gimbal  52  is attached to the load beam  44 . Typically, gaps  56  have a minimum length of 2.5 mils. These gaps  56  provide a range of adjustability for head-media spacing and for adjusting the attitude of the slider  12  during the assembly process. In other words, the gimbal  52  can be adjusted even after arm portions  62  of the limiter  58  are extended around the load beam tip  48  by shifting the gimbal  52  relative to the load beam tip  48 . This adjustability was not available with prior art “snap fit” limiters where the limiter elements snapped through the body of the load beam. 
     As shown, the limiter  58 , including the flange portions  60  and the arm portions  62  are cut out from within the existing profile of the gimbal  52 , such that no additional material must be added to the gimbal  52  to provide the limiter  58 . Moreover, the footprint of the load beam  44  can be made smaller than the prior art interleaved assemblies because no opening  38  is provided in the substrate of the load beam  44 . Since no such openings are required, the load beam tip  48  can be kept narrow without sacrificing attachment surfaces for bonding or welding the gimbal  52  to the load beam  44 . In this manner, the flat footprint of the gimbal  52  is minimized without sacrificing performance. More importantly, no change is required to the load beam  40  in order to implement the limiter  58  of the present invention. Since no additional material is added to the load beam  40 , resonance performance is maintained. Moreover, since the material is removed from the gimbal  52  symmetrically to provide the limiter  58 , the overall assembly  38  experiences negligible change in mass. While a change in mass would effect resonance characteristics of the assembly and lower the performance of the system, the invention can be implemented without adversely effecting performance or resonance. 
       FIGS. 8   a - 8   c  illustrate the limiter  58  with the flange portions  60  and arm portions  62  in various positions.  FIG. 8a  shows the limiter  58  in a flat position. The limiter  58  has flange portions  60  and arm portions  62 , and the location of the dimple  42  is shown for clarity. As shown, each arm portion  62  defines the gap  56 . Additionally, the flange fold line  68  and the arm fold line  70  are illustrated as dotted lines. 
     In  FIG. 8   b , the limiter  58  is partially bent along the flange fold line  68 . As shown from a bottom view, the flange portion  60  extends downward and the arm portion  62  remains in the same plane as the surface of the flange portion  60 . 
     In  FIG. 8   c , the limiter  58  is shown in the fully assembled position, where the flange portion  60  is bent along the flange fold line  68 , and the arm portion  62  is bent along the arm fold line  70 . In this fully assembled position, when the limiter  58  is attached to the load beam  44 , the arm portions  62  extend around the load beam tip  48  as shown in  FIGS. 3 and 4 . 
     The gimbal  52  with the limiter  58  is formed from a unitary piece of substrate material, which may be a printed circuit board, metal, or any other material. The gimbal  52  may be formed from the same or different material from the load beam  44 . 
     Generally, after the gimbal  52  is fabricated with the limiter  58 , the gimbal  52  is welded to the load beam  44  at weld points  54 . Then, the flange portions  60  and the arm portions  62  are bent around the load beam tip  48  to complete the assembly of the shock limiter  58 . 
     The structure  38  described herein, including the limiter  58 , generally requires few if any adjustments to the controller corresponding to mass changes in the system. Additionally, the limiter structure  58  has negligible impact on the tolerances or clearances (assembly or operational) of the disc drive system. Finally, the gaps  66  provided by the arm portions  62  allow for some adjustability of the attitude of the slider  12 , limited by the size of the gap  66 . This allows for adjustment of the gimbal  52  in line with the dimple  46 . 
     In the present invention, the limiter  58  is located close to the load point and the center of mass of the slider, which increases the frequency response of the system. Additionally, by designing the limiter  58  to be located close to the load point (dimple  50 ), the limiter  58  is made more effective in limiting damage than prior art shock limiters. Moreover, the gap  66  is designed to maximize adjustability during assembly. Furthermore, the load beam tip  48  can be minimized because no internal load beam  44  features are required, such as slots, forms and the like, in order to implement the limiter  58 . Finally, the arrangement of the weld points  54  relative to the limiter  58  allows for more effective control of the gimbal  52  during a shock event, preventing damage. 
     Additionally, the invention minimizes the loss of the slider bonding area between the slider  12  and the tongue  64 . Deflection under acceleration loading in a shock event does not degrade the engagement of the slider  12  and the tongue  64 . 
     By positioning the slider  12  adjacent the shock limiter  58 , not only are the structural resonances of the system as a whole improved, but the moment arm caused by the load of the slider  12  on the gimbal  52  is at the center of mass, allowing the shock limiter  58  to function properly. Finally, the limiter  58  introduces little interference with ball bond and SA adjust processes. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.