Patent Publication Number: US-2003231432-A1

Title: Windage, shock and low mass conventional suspension design

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
     [0001] This application claims priority from U.S. Provisional Application Serial No. 60/389,816, filed Jun. 18, 2002 and entitled IMPROVED WINDAGE, SHOCK AND LOW MASS CONVENTIONAL SUSPENSION DESIGN. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] The present invention relates to data storage devices. In particular, the present invention relates to improving performance of suspension assemblies in data storage devices.  
       [0004] 2. Related Art  
       [0005] In data storage devices, data is typically stored in tracks on a memory medium. To access the data, the head is positioned within a track of the memory medium while the medium moves beneath the head.  
       [0006] In many storage devices, the head is positioned by an actuator assembly that includes a motor that rotates one or more actuator arms. Each actuator arm supports one or two suspensions that each support a head/gimbal assembly. Typically, a suspension includes three distinct areas: a base plate area that connects to the actuator arm, a spring area that provides a vertical spring force to bias the head toward the medium, and a load beam that extends from the spring area to the head/gimbal assembly. A spring force provided by the suspension is designed to allow the head to follow height variations on the surface of the medium without impacting the medium or moving too far away from the medium. Typically, it is desired that the spring area be more elastic or flexible than the remainder of the suspension. However, if the spring area or the remainder of the load beam is too elastic and compliant the load beam will tend to bend and resonate in response to windage induced forces.  
       [0007] Windage induced forces have become a particular concern as the performance of disc drives has increased. For example, many high performance drives run at 15 k RPM or higher, causing significant windage forces within the disc drive. Also, there is an increasingly higher number of bits being packed into every square inch of the disc drive surface, leading to a higher number of tracks per inch and a reduced track width. As a result, suspensions are more susceptible to slider off-track motion and other mechanical resonant vibrations that lead to reduced servo bandwidth and reduced track following capabilities of the disc drive.  
       [0008] In order to minimize slider off-track motion due to windage, the suspension design may be altered in such a way so as to achieve higher resonance frequencies without compromising on the performance requirements of the disc drive. An effective way to reduce slider off-track motion resulting from windage excitation is to increase the suspension resonant frequencies. Suspension resonance frequencies can be increased by, for example, reducing the length of the suspension, using a thicker sheet of material for the load beam and bend section, or reducing the effective bend length of the suspension. These options have inherent drawbacks and costs that may be significant enough to make them an undesirable option. For example, thicker suspension material is heavier and also deteriorates drive level shock and seek access time performance. Shorter and thicker suspensions usually have very high vertical stiffness that results in additional re-working of the head stack assembly process to achieve the desired gram load to the head/gimbal assembly.  
       [0009] Windage driven slider off-track motion may also result from the excitation of the electrical interconnect tail adjacent to the base plate area of the suspension. To minimize this excitation, the tail is usually attached to suspension tabs that extend from the base plate or load beam. However, attaching the interconnect tail to suspension tabs does not completely eliminate the problem as the suspension tabs are typically compliant and asymmetrical, and can translate the windage driven tail motion into slider off-track motion. As mentioned above, the problem of windage induced motion has become a more significant problem as the windage forces increase with increased rotation speeds of the storage medium.  
       SUMMARY OF THE INVENTION  
       [0010] A data storage device includes a head and a suspension assembly capable of supporting the head. The suspension assembly includes a base plate having a first base plate surface facing toward the storage medium, and a load beam having a length, a first load beam surface facing toward the storage medium, and a second load beam surface facing toward the first base plate surface. The second load beam surface is secured to the first base plate surface, and an interconnect of the storage device is secured to the first load beam surface along substantially the entire load beam length.  
       [0011] In another aspect of the invention, a data storage device for storing and accessing data in tracks on a storage medium includes a head configured to read information from the storage medium and a suspension assembly arranged and configured to support the head. The suspension assembly includes a base plate having a width and a length, a first surface facing the storage medium, and a second surface facing away from the storage medium. The suspension assembly also includes a load beam having a proximal end and a distal end, a first surface facing the storage medium, and a second surface facing away from the storage medium with the proximal end of the load beam being secured to the base plate. The storage device also includes an interconnect extending between the distal end of the load beam and the base plate and physically oriented along the first surface of the load beam and the first surface of the base plate such that the orientation of the interconnect minimizes unstabilizing forces to the suspension assembly.  
       [0012] In a yet further aspect of the invention, a head suspension assembly for a disc drive having a storage medium includes a load beam and a base plate. The load beam includes a distal end and a proximal end, a first surface facing away from the storage medium, and a second surface facing toward the storage medium. The base plate includes a length and a width, a first surface facing away from the storage medium, and a second surface facing toward the storage medium. The second surface of the base plate is secured to the first surface of the load beam and the width of the base plate is wide enough to secure an interconnect of the disc drive to the first surface of the base plate.  
       [0013] These and various other features as well have advantages that characterize the present invention and will be apparent upon reading of the following detailed description and review of the associated drawings. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014]FIG. 1 is a top perspective view of a disc drive in which several discs have been removed to show various features of the disc drive in which embodiments of the present invention may be practiced.  
     [0015]FIG. 2A is a top perspective view of a suspension assembly under the prior art.  
     [0016]FIG. 2B is a top plan view of a suspension assembly under the prior art.  
     [0017]FIG. 2C is a bottom plan view of a suspension assembly under the prior art.  
     [0018]FIG. 3A is a top perspective view of one embodiment of a suspension assembly according to principles of the invention.  
     [0019]FIG. 3B is a top plan view of the embodiment shown in FIG. 3( a ).  
     [0020]FIG. 3C is a bottom plan view of the embodiment shown in FIG. 3( a ).  
     [0021]FIG. 3D is a side view of the embodiment that is shown in FIG. 3( a ). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0022]FIG. 1 is an asymmetric view of a disc drive  100  having structure in which principles of the present invention may be practiced. The disc drive  100  includes a base  102 , and a cover (not shown). Base  102  and the cover form a disc drive enclosure. Extending into base  102  is a spindle motor  106  to which several discs  110  are secured. Each disc  110  is generally angular in shape, with an inner edge  112  and an outer edge  114  circumscribing opposing disc surfaces  116  (of which only one is visible in the drawing) to which data can be stored for later retrieval. Base  102  provides a cavity or room for disc  110  to be seated in a substantially coaxial arrangement, with an inner wall  118  of the base running around outer edges  114  of disc  110 , substantially transverse to disc surfaces  116 .  
     [0023] On one side of a pivot  121 , an actuator assembly  120  includes a plurality of arms  122  to which are attached load beams or suspensions  124 . At the end of each suspension  124  is a slider  126  that carries the read/write devices (designated generally by  128 ). The present invention is equally applicable to sliders having different types of read/write devices, such as what is generally referred to as transducers, magneto resistive heads, giant magneto resistive heads, or tunneling magneto resistive heads. On another side of the pivot, actuator assembly  120  extends to support a voice coil  130  next to one or more magnets  132  fixed relative to base  102 . When energized, resultant electromagnetic forces on voice coil  130  cause actuator assembly  120  to rotate about pivot  121 , thereby bringing the read/write devices into various radio locations relative to disc surfaces  116 . It can be seen that, with spindle motor  106  rotating discs  110  for example, in a direction indicated by arrow  140 , and actuator assembly  120  moving read/write heads  128  in an arcuate path, as indicated by arrow  142 , across disc surfaces  116 , various locations on disc surfaces  116  can be accessed by the read/write heads for data recordation or retrieval.  
     [0024] As discs  110  are rotated, fluid or air adjacent to disc surfaces  110  is also brought into motion, generating air streams or flow currents in the disc drive enclosure. This airflow, or windage, create forces both in direction  140  in the plane of disc surfaces  116 , as well as a direction normal to the plane of disc  116 . There also may be various other windage-induced forces occurring throughout the cavity provided by base  102  and cover  104 .  
     [0025] FIGS.  2 A-C are perspective, front, and back views, respectively, of a suspension assembly  200  of the prior art. Assembly  200  includes a head  202 , a load beam  204 , and a base plate  206  mounted with a boss (not shown). Load beam  204  includes a rigid portion  210 , a gimbal portion  212 , a base portion  214  and a bend portion  216 . Gimbal portion  212  supports head  202  via a connection at dimple point  218  of gimbal portion  212 . Base portion  214  of load beam  204  is sandwiched between base plate  206  and a support arm of the disc drive assembly.  
     [0026] Base plate  206  has a length and a width  220 ,  222 , respectively, that is comparable to a length and width  224 ,  226  of base portion  214  of load beam  204 . Length  220  of base plate  206  in the direction of head  202  determines in part a suspension bend length  228  that is measured between an end  207  (see FIG. 2C) of base plate  206  and dimple point  218  of gimbal portion  212 . Assembly  200  also includes a suspension length  230  that extends from a center axis of a boss hole  232  of base plate  206  to dimple point  218 .  
     [0027] Width  222  of base plate  206  and width  226  of base portion  214  of load beam  204  are configured to provide sufficient structure adjacent boss aperture  232  to support of load beam  204  and head  202 , while being no wider than is necessary so as to keep the weight and mass of the suspension assembly at a minimum. Widths  222 ,  226  are typically sized to match a width of the disc drive assembly support arm at the boss connecting point. Known suspension assemblies have not disclosed a way to increase widths  222 ,  226  beyond the width of the disc drive assembly support arm without significantly increasing the weight of the suspension assembly and compromising suspension assembly performance.  
     [0028] Assembly  200  also includes an interconnect  208  having a gimbal portion  240 , a load beam portion  242 , and a base portion  244 . Gimbal portion  240  is electrically connected with read/write transducers that are mounted on head  202 . Gimbal portion  240  is typically compliant and free floating in order to permit the necessary flexibility of head  202  relative to load beam  204 . Typically, load beam portion  242  extends along a longitudinal axis of load beam  204 . Base portion  244  typically extends along a side of base plate  206  and base portion  214  of load beam  204  and is connected to front and rear load beam tabs  234 ,  236  that extend from load beam  204 .  
     [0029] As discussed above, load beam tabs  234 ,  236  are typically simple extensions of load beam  204  and are thus made from the same relatively compliant material having the same thickness as load beam  204 . As a result of this configuration, load beam tabs  234 ,  236  are subject to bending and torsion forces that may occur from windage within the disc drive assembly, especially when flex circuit  208  is mounted to load beam tabs  234 ,  236 . Thus, as the windage forces increase, particularly as RPMs of the storage medium increase, interconnects secured to assembly  200  via load beam tabs  234 ,  236 , subject the assembly  200  to significant forces that typically increase off track motion of head  202 .  
     [0030] FIGS.  3 A-D provide perspective, top, bottom and side views, respectively, of a example suspension assembly  300  of the invention. Assembly  300  includes a head  302 , a load beam  304 , a base plate  306  and an interconnect  308 . Load beam  304  includes a rigid portion  310 , a gimbal portion  312  supporting head  302 , a base portion secured to base plate  306 , and a flexible portion or bend section  316 . Although load beam  304  is shown in FIGS.  3 A-D as a planer member without a bend formed therein, load beam  304  is typically bent at bend section  316  so as to provide a preload bend force that is applied between head  302  and the memory medium of the disc drive assembly.  
     [0031] Base plate  306  has a length  320  and a width  322 , and base portion  314  has a length  324  and a width  326  that are comparable to length and width  320 ,  322 . Width  322  includes a width  351  of first and second base plate shelves  350 ,  352 . Width  326  of base portion  314  also includes a width  355  of first and second load beam shelves  354 ,  356 . Widths  351 ,  355  represent the distance the base plate  306  and base portion  314  extend beyond the width of a support arm of the disc drive assembly, which typically corresponds to the width of base plate  226  and load beam base portion  214  shown in the prior art of FIGS.  2 A-C. The additional width of the shelves  350 ,  352 ,  354 ,  356  beyond the width of the support arm provide a mounting surface to which the interconnect  308  may extend along and be secured to without interfering with required clearances around boss aperture  332  or interfere with the connection of suspension assembly  300  to the support arm.  
     [0032] Interconnect  308  includes a gimbal portion  340 , a load beam portion  342  and a base portion  344 . Gimbal portion  340  is electrically connected with head  302 . Gimbal portion  340  is typically compliant to permit free pivotal movement of head  302  about dimple point  318 . Load beam portion  342  extends along a longitudinal axis of rigid portion  310  of load beam  304 . Preferably, load beam portion  342  is secured at various points along the length of rigid portion  310  while remaining compliant through at least a portion of the flexible portion  316  of load beam  304  to allow unrestricted bending of flexible portion  316 . At a point near flexible portion  316 , load beam portion  342  transitions to a side of base portion  314  so as to extend along load beam shelf  356  and base plate shelf  352 . Because assembly  300  includes a reverse load beam orientation, that is, load beam  306  being mounted on the memory medium side of base plate  306  so as to sandwich base plate  306  between load beam portion  314  and the support arm of the disc drive assembly, interconnect  308  is able to extend smoothly and without an interruption in surface structure along load beam  304  from gimbal portion  312  to base portion  314 .  
     [0033] Although interconnect  308  may not be continuously connected to load beam  304  along an entire length of load beam  304  from gimbal portion  312  to a proximal end  315  (see FIG. 3C) due to aperture  362  and other functional considerations, interconnect  308  may be considered to be secured to load beam  304  along substantially the entire load beam length.  
     [0034] In alternative embodiments that do not include a reverse load beam orientation, interconnect  308  may extend along load beam  304  from gimbal portion  312  through flexible portion  316 , and then transition to a surface of base plate  306  that is facing the memory medium of disc drive assembly. In yet further embodiments, load beam  304  does not include first and second load beam shelves  354 ,  356 , thus requiring the base portion  344  of interconnect  308  to be secured directly to the first or second base plate shelf  350 ,  352  as interconnect  308  extends along length  324 ,  320  of load beam  304  and base plate  306 , respectively. In yet further embodiments, base portion  344  of interconnect  308  may extend along the first base plate shelf  350  and the first load beam shelf  354 .  
     [0035] Base plate  306  may also include an extension  333  that extends in the direction of head  302 . Extension  333  may provide additional support to load beam  304  at the transition point between base portion  314  and flexible portion  316 . Extension  333  may provide a reduction in the suspension bend length  328  as compared to the suspension bend length  228  shown in FIG. 2C of the prior art. As discussed earlier, a shorter suspension bend length increases the resonant frequencies of a suspension. The additional stiffness inherent with a shorter suspension bend length may be compensated for by making the flexible portion of the suspension load beam more compliant by either removing additional material by increasing the size of an aperture formed in the flexible portion (such as aperture  362  formed in flexible portion  314 ), or by reducing the thickness of the load beam either in the flexible portion  316  alone, or throughout load beam  304 .  
     [0036] Preferably, the thickness of the sheet material used for load beam  304  is reduced as compared to the thickness of material used for load beam  204  in known load beams. A thinner material for load beam  304  (given the same type of material) reduces the overall weight of the load beam, which may both provide additional compliance in flexible portion  314  and compensate for the added weight from load beam shelves  354 ,  356 . Known load beams typically require a sheet material having a thickness of between 0.002-0.004 inches. Load beam  304  preferably requires a sheet material having a thickness less than 0.002 inches and most preferably a thickness of 0.0015 inches of stainless steel material. As a result, the net mass of the load beam  304  is about equal to or less than the mass of load beam  204  of the prior art.  
     [0037] Base plate  306  also preferably uses a sheet material having a thickness less than the thickness of material used for base plate  206  of the prior art in order to compensate for the additional width of base plate shelves  350 ,  352  and length extension  307 . The thickness of known base plate material is greater than 0.0059 inches, while the thickness of base plate  306  is less than about 0.005 inches, and most preferably about 0.0049 inches thick stainless steel. An additional way to reduce the mass or weight of base plate  306  is to remove some of the base plate material with an aperture  360  in an area of base plate  306  that has less supporting functionality.  
     [0038] Base plate  206  of the prior art shown in FIGS.  2 A-C is approximately square-shaped having a length and width dimension of 0.2×0.2 inches with boss aperture  232  positioned approximately in the center of the square. Base plate  306  includes an additional 0.03 inches in added width for each of the base plate shelves  350 ,  352  for a total of 0.06 inches additional width over width  222  of base plate  206 . Base plate  306  also includes an additional 0.06 inches in length over length  220  of base plate  206  due to extension  332 . In order to maintain the same form factor when assembling suspension  300  as compared to the form factor standard in the art, boss aperture  332  is positioned off center (in a direction away from head  302 ) on the approximately square-shaped base plate  306 . Because of the additional length of extension  333 , suspension bend length  328  can be shortened relative to suspension bend length  228  shown in FIG. 2C.  
     [0039] When assembling base plate  306 , load beam  304  and interconnect  308  together, base plate  306  is first secured, typically with an adhesive or welding, to base portion  314  of bend section  304 . Interconnect  308  may be secured to load beam  304  and base plate  306  in a variety of different ways including, but not limited to, adhesives, welding, and thermal bonding. Base portion  344  of interconnect  308  may be laser welded to base portion  314  and base plate  306  at locations  370 ,  371 ,  372  and multiple other locations along the length of the interconnect. Laser welding is a known method of precisely securing multiple layers together.  
     [0040] One advantage of the reverse load beam orientation shown in FIGS.  3 A-D is that the load beam is closer to the memory medium of the disc drive assembly. As a result of the closeness of the load beam to the memory medium, less of a bend is required in the flexible portion of the load beam in order to provide the required pre-load forces between head  302  and the memory medium, as compared to a traditional load beam orientations. Less of a bend in the flexible portion may result in reduced amounts of buckling of the load beam and an increase in lateral stiffening of the load beam as compared to load beams with a greater bend in the flexible portion.  
     [0041] Interconnect  308  of assembly  300  is preferably arranged in such a way relative to base plate  306  and bend section  304  so as to be hidden from a top plan view (see FIG. 3B). As the surface area of interconnect  308  that is unsupported by a section of base plate is reduced to a minimum, assembly  300  becomes less susceptible to windage forces in the plane direction of the memory medium and from windage forces in a normal direction to the memory medium. A suspension assembly that is less susceptible to windage forces may result in improved disc drive performance.  
     [0042] Although the above description has focused on an interconnect that is formed from a flex circuit, interconnect  308  may be replaced by any number of designs or configurations that extend from the head  302  to a location proximal to base plate  306 . For example, interconnect  308  may be a twisted pair of wires, or as mentioned above, electrical leads embossed directly on the surface of load beam  304  and base plate  306 .  
     [0043] The present invention may provide numerous advantages as compared to known suspension assemblies, in particular the prior art shown in FIGS.  2 A-C. For example, suspension  300  provides the lowest measured windage induced slider off-track motion among known conventional suspension designs. Suspension  300  also provides the highest measured first bending frequency, the highest measured first torsion frequency, and the highest measured sway frequency among all known conventional, single state suspension designs. The load beam of suspension  300  makes use of the thinnest load beam sheet material and the thinnest base plate sheet material among all known conventional suspension designs, thus reducing the assembly mass. Suspension  300  also provides the highest head slap threshold among known conventional conventional, single stages suspension designs. Consequently, the present invention provides improvements and advantages over the prior art.  
     [0044] The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.