Abstract:
An apparatus, system, and method are disclosed for compensating for high-gain vibration modes resulting from asymmetrical traces in integrated lead suspensions in hard disk drives. A compensation member secures to an actuated arm opposite a mount plate securing a head gimbal assembly (HGA) to the arm. The compensation member includes an elastic portion primarily mirroring the elastic properties of asymmetrical elastic properties of conductive traces extending along the HGA and arm. The elastic portion secures to an inertial portion primarily mirroring inertial properties, such as center of mass and moment of inertia, of the HGA. The elastic portion may be formed as a strip of material attached at its end points to the inertial portion. The inertial portion may be formed as a flat plate secured to the actuated arm in a manner similar to the mount plate.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a means and method for reducing vibration in hard-disk drives and more particularly to apparatus, systems, and methods for reducing off-track vibration in disk drives having asymmetrical integrated lead suspensions. 
     2. Description of the Related Art 
     A typical hard-disk drive will include a stack of disks or “platters” mounted on a common spindle. The surfaces of the disks are typically coated with a material that is readily magnetized and demagnetized. A number of read/write heads may be positioned over the disks as the disks are spun to magnetize portions of the disks to write information thereon or detect the magnetized portions to read information therefrom. A plurality of read/write heads may be used to simultaneously read information from multiple rigid platters that are typically arranged in a vertical stack and rotated as a unit via the spindle. 
     Information may be stored in concentric circles or tracks on the surface of the disks. Thus, to access information stored on the hard drive, the read/write head must first be moved radially to the correct track where the information is stored. The greater the number of tracks, the greater the amount of data that may be stored on the hard-disk drive. However, increasing the density of the tracks decreases the distance between tracks. Therefore, in order to accommodate greater track densities it is important that a read/write head be positioned as accurately as possible in order to read data from, or write data to, the correct track. Aberrant motion caused by vibrations and other effects may interfere with precise positioning and must therefore be avoided. 
     The read/write heads are typically moved from one track to another by an actuator that is capable of very precise movements. A suspension may be interposed between the read/write heads and the actuator in order to provide a degree of flexibility, enabling the read/write heads to “float” on the surface of the disk on a very thin layer of air, or “air bearing,” as the disks spin at a very high speed relative to the read/write heads. The combination of suspension and read/write head is often referred to as the head-gimbal assembly (HGA). 
     The suspension may include a load beam, a mount plate, a hinge plate and a flexure. The suspension secures to an arm through the mount plate, or another similar member. The arm is typically rotated by a voice coil, or other actuating mechanism. The hinge plate secures to the mount plate and flexibly secures the load beam and flexure to the arm. The load beam is typically substantially rigid and extends a substantial distance over the disks. The vertical flexibility and gram load of a suspension are provided by the hinge plate. The flexure is typically flexible in the pitch and roll directions and together with the gram load of the hinge plate is primarily responsible for enabling flotation of the read/write heads. 
     Electrically conductive traces extend from the read/write head and along the flexure, mount plate, and load beam, in order to transport electrical signals from the read/write head to and from drive electronics. The drive electronics interpret signals from the read/write head in order to retrieve data or send the appropriate signals to the read/write head causing it to write information to the disks. In some hard-disk drive suspensions, the traces are integrated with the suspension in order to provide ease of manufacture and high data rate capability. Such suspensions are referred to as integrated lead suspensions (ILS). 
     A typical ILS has traces routed from the read/write head symmetrically along the centerline of the suspension until just ahead of the hinge plate. At this location the traces typically make a 90 degree turn and go along the lateral side of the load beam, hinge plate, and mount plate. This asymmetric routing of the traces on one side of the suspension can create off track motion of the read/write head at certain frequencies and conditions. 
     In a typical hard disk drive a read/write head and flexure is provided for each data-bearing surface of each disk. The suspensions are swaged onto arms which interleave with the platter stack creating a “comb” shaped structure. Arms corresponding to disks in the middle of the stack may have two suspension and read/write head assemblies secured thereto in order to read from the disks above and below. However, the arm corresponding to the uppermost and lowermost disk typically include only a single suspension and read/write head either because the top surface of the uppermost disk and the bottom surface of the lowermost disk are usually not used to store data or because there is no other disk below or above the uppermost and lowermost disks providing a data-bearing surface requiring a read/write head. 
     Experiments conducted by the inventor indicate that the asymmetric routing of the traces on integrated lead suspensions typically does not cause deleterious vibration of the HGAs corresponding to the middle disks, inasmuch as each arm has two suspensions and read/write head assemblies secured thereto, which are typically mirror images of one another. Experiments conducted by the inventor indicate that although the HGAs of the middle disks do have vibration modes caused by the asymmetrical traces, the vibration modes are out of phase with one another and cancel each other out. As previously stated, the uppermost and lowermost arms each have a single suspension and read/write head assembly secured thereto. Experiments conducted by the inventor indicate that for the uppermost and lowermost arms the harmful vibration modes are not cancelled out and high magnitude off-track vibrations can occur. 
     Prior attempts to correct vibration in outer HGAs have used dummy members mirroring only the inertial properties of the flexure and read/write head assembly. None have provided a means for compensating for the dynamic interaction of the traces with the other components of the HGA. 
     In view of the foregoing, it is apparent that a need exists for an apparatus, method, and system for compensating for off-track vibration modes caused by asymmetric routing of traces in integrated lead suspension (ILS) head-gimbal assemblies (HGAs). Such an apparatus should be easily manufacturable. To that end, it would be an improvement in the art to provide an apparatus that is a single member easily securable to an actuator arm. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available hard-disk drives. Accordingly, the present invention has been developed to provide an apparatus, system, and method for reducing vibrations causing off-track motion of read/write heads in hard-disk drives having asymmetrically routed integrated lead suspensions. 
     The apparatus will typically be used in a storage system wherein information is stored on a number of rotating disks. A read/write head may be suspended over each disk in close proximity thereto and write information to or reads information from the disk. The read/write head may be mounted on a suspension extending between the disks. A suspension may mount to a stiff arm rotated by an actuator in order to selectively position the read/write head. 
     An asymmetrical conduction path carries signals to and from the read/write head. The conduction path may be asymmetrical with respect to the suspension. The asymmetrical configuration may include routing of the conduction path along one lateral side of portions of the suspension and arm. A compensation member may secure to the actuator arm and compensate for off-track vibrations caused by the asymmetrical conduction path. 
     The compensation member includes, in one embodiment, an elastic member compensating for elastic properties, such as bending modes or spring constants in shear or tension, of the asymmetrical conduction path. The elastic member may mirror the asymmetry of the asymmetrical conduction path. For example, the elastic portion may be positioned on the same lateral side as asymmetric portions of the asymmetrical conduction path. 
     In one embodiment, the elastic portion is a strip of material extending longitudinally along the side of the compensation member. The strip may be attached at its endpoints and define a void between itself and the remainder of the compensation member. 
     The compensation member may include an inertial portion primarily configured to mirror the inertial properties of the suspension and read/write head. The inertial portion may include a universal portion securing to the arm by a means substantially similar to that of the mount plate, such as swaging. The means of attachment can also be epoxy bonding, welding or other practical means of securement. The inertial portion may include a custom portion readily altered in the design phase to cause the inertial properties of the inertial portion to match different suspensions. In one embodiment, the custom portion is a tab extending longitudinally from the compensation portion. 
     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussion of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
     These features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is a schematic representation of one embodiment of a data storage system in accordance with the present invention; 
         FIG. 2  is a top view illustration of the system of  FIG. 1 ; 
         FIG. 3  is a perspective view illustration of an embodiment of a head gimbal assembly (HGA) and arm in accordance with the present invention; 
         FIG. 4  is a top view of one embodiment of an HGA and arm, in accordance with the present invention; 
         FIG. 5  is a frequency response plot representative of single and dual HGA arms; 
         FIG. 6  is a top view illustration of a compensation member, in accordance with the present invention; 
         FIG. 7 , is a perspective view illustration of a combined compensation member and HGA, in accordance with the present invention; and 
         FIG. 8 , is a frequency response plot representative of single HGA arms both with and without a compensation member. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention. 
       FIGS. 1 and 2  show schematic diagrams of one embodiment of a data storage system in which the present invention may be deployed, which is designated by the general reference number  10 . The system  10  may include a plurality of magnetic recording disks  12 . Each disk  12  may have a plurality of concentric data tracks. The disks  12  are typically mounted on a spindle motor shaft  14 , which may connect to a spindle motor  16 . The motor  16  is typically mounted to a chassis  18 . The disks  12 , spindle  14 , and motor  16  form a disk stack assembly  20 . 
     A plurality of read/write heads  30  may be positioned over the disks  12  such that at least one surface of each disk  12  has a corresponding head  30 . Each head  30  may attach to one of a plurality of suspensions  32 . Each suspension  32  may have a corresponding actuator arm  34 . Suspensions  32  are typically connected to a rotary actuator  36 . The actuator  36  moves the heads in a radial direction across disks  12 . The actuator  36  typically includes a rotating member  38  mounted to a rotating bearing  40 , a motor winding  42 , and motor magnets  44 . The actuator  36  is also mounted to chassis  18 . The heads  30 , suspension  32  and actuator  36  form an actuator assembly  46 . The disk stack assembly  20  and the actuator assembly  46  may be sealed in an enclosure  48  (shown by a dashed line), which provides protection from particulate contamination. 
     A controller unit  50  typically provides overall control to the system  10 . The controller unit  50  may contain a central processing unit (CPU), memory unit and other digital circuitry. The controller  50  may connect to an actuator control/drive unit  56  which in turn is connected to the actuator  36 . This allows the controller  50  to control the movement of the heads  30  over the disks  12 . The controller  50  may be connected to a read/write channel  58  which in turn connects to the heads  30 . This enables the controller  50  to send and receive data from the disks  12 . The controller  50  may connect to a spindle control/drive unit  60  which in turn is connected to spindle motor  16 . This enables the controller  50  to control the rotation of the disks  12 . A host system  70 , which is typically a computer system, may connect to the controller unit  50 . The system  70  may send digital data to controller  50  to be stored on disks  12 , or may request the digital data be read from disks  12  and sent to the system  70 . The basic operation of DASD units is well known in the art and is described in more detail in “Magnetic Recording Handbook”, C. Dennis Mee and Eric D. Daniel, McGraw Hill Book Company, 1990. 
     Referring to  FIGS. 3 and 4 , the depicted combination of a head  30  and suspension  32  form a head gimbal assembly (HGA)  80 . In some embodiments, the head  30  mounts to the suspension  32  by means of a flexure  82 . The flexure  82  may be substantially flexible and provide for gimbaled mounting of the head  30  to the suspension  32 . Notwithstanding the need for flexibility, it may be unnecessary, or impracticable, to have a flexure  82  spanning the entire distance from the head  30  to the actuator  36  (See  FIG. 2 ). Accordingly, an arm  34  may extend from the actuator  36  and connect to the flexure  82 . In some embodiments, a mount plate  86  secures the HGA  80  to the arm  34 . A hinge plate  83  may secure to the mount plate  86  and the flexure  82  and provide for substantially hinged securement of the flexure  82  to the plate  86 . In some embodiments a load beam  84  may secure to the hinge plate  83  and provide a support for the flexure  82 . The mount plate  86  may secure to the arm  34  by a variety of means. In the illustrated embodiment, a swage hole  88  is provided in the mount plate to facilitate swaging of the mount plate  86  to the arm  34 . 
     Arms  34  corresponding to disks  12  in the middle of the disk stack assembly  20  may have two HGAs  80  secured thereto (hereinafter a “dual head arm  34 ”), with the heads  30  positioned between disks  12  during operation. Some embodiments may include two arms  34  each having a single flexure  82  and head  30  assembly secured thereto. The two arms  84  may secure to the actuator  36  by means of stacking. The arms  34  corresponding to the outermost disks  12  may include a single HGA  80  (hereinafter a “single head arm  34 ”), inasmuch as there is not additional surface above or below the uppermost and lowermost disks, respectively, that requires an additional HGA  80 . 
     Traces  92 , also referred to as electrical lines  92  or leads  92 , may carry electrical signals from the head  30 . Traces  92  may be made of a highly conductive metal such as copper or gold. The traces  92  may be asymmetric with respect to the HGA  80 . In the illustrated embodiment, the trace  92  includes both a symmetric portion  94  and an asymmetric portion  96 . The symmetric portion  94  may extend down the center of the flexure  82  to a position proximate the hinge plate  83 . The asymmetric portion  96  may then extend along the lateral side of the mount plate  86  and arm  34 . Each head  30  has a corresponding set of traces  92 . Accordingly, a dual head arm  34  will have two sets of traces  92  for two HGAs  80  mounted on both the top and bottom of the arm  34 , which will each be substantially the mirror images of each other. 
       FIG. 5  is a frequency-response plot of a dual head arm  34  and a single head arm  34  with the horizontal axis  100  representing frequency and the vertical axis  102  representing the magnitude of the response of the HGA  80 . It is clear that plot  104 , corresponding to a single head arm  34  has high-magnitude resonance peaks  106   a  and  106   b  in lower frequency ranges. In the illustrated embodiment, the peaks  106   a  and  106   b  occur respectively at approximately 11 kHz and 14 kHz. It will also be observed, that the peaks  106   a  and  106   b  do not occur in plot  108  corresponding to a dual head arm  34 . 
     Experiments conducted by the inventor have shown that the peaks  106   a  and  106   b  correspond to bending modes in the suspension  32  that are coupled with the bending modes of the arm  34 . Inasmuch as the traces  92  secure to both the suspension  32  and the arm  34 , the traces  92  affect the coupled bending modes. In particular, because the traces  92  extend along the lateral side of the arm  34 , the traces  92  create a lateral pull on the arm  34 , which corresponds to off-track motion of the read/write head  30 . The lateral pull of the traces  92  may be present in both single head arms  34  and dual head arms  34 . However, the absence of the peaks  106   a ,  106   b  in the plot  108  corresponding to a dual head arm  34  indicates that the problematic modes are out of phase with one another and cancel one another out. 
     Referring to  FIGS. 6 and 7 , a compensation member  120  may be secured to a single head arm  34  in order to cancel the problematic high-gain modes. The compensation member  120  may include an inertial portion  122  and an elastic portion  124 , or trace portion  124 . The inertial portion  122  may substantially mirror one or more inertial properties of the HGA  80 , such as mass, center of mass, and moment of inertia about one or more axes. The elastic portion  124  may substantially mirror the bending modes of the traces  92 , in particular the asymmetric lateral pull of the traces  92 . Although the elastic portion  124  primarily compensates for the bending modes of the traces  92 , it nevertheless has mass and the inertial properties that, when combined with the inertial properties of the inertial portion  122 , may mirror the inertial properties of the HGA  80 . 
     Depending on the application, the compensation member  120  may compensate for one or both of inertial properties of an HGA  80 . For example, in some embodiments, only the elastic properties of the elastic portion  124  will mirror the asymmetric elastic properties of the traces  92  whereas the inertial portion  122  does not substantially mirror inertial properties of the HGA  80 . 
     The compensation member  120  may secure to the arm  34  in a position corresponding to the mount plate  86 . That is, the same position that the mount plate  86  would have occupied in a dual head arm  34 . In some embodiments, the compensation member  120  may have a universal portion  126  having a configuration to facilitate securement to the arm  34  in the same manner as the mount plate  86 . A universal portion  126  may facilitate the use of the same arm  34  and the same assembly methods and machines for both the compensation member  120  and the mount plate  86 . In some embodiments, the universal portion  126  may include a swage hole  128 , and like structures, to facilitate swaged securement to the arm  34  in a manner similar to the mount plate  86 . 
     Certain embodiments of the inertial portion  122  may include a custom portion  130  to facilitate design of a compensation member  120  for a particular HGA  80 . In the illustrated embodiment, the custom portion  130  is embodied as a tab  132 . The tab  132  may be adjusted in size without requiring a change in the universal portion  126  of the compensation member  120 . 
     An elastic portion  124  may be embodied as a strip  134  extending longitudinally along a lateral side of the compensation member  120  corresponding to the lateral side of the load beam  84  along which the trace  92  extends. The thickness, width, and length of the strip may be selected to match the elastic effect of the trace  92 . The strip  134  may be secured at its end points  136   a ,  136   b  to the compensation member  120 . The strip  134  may be spaced apart from the compensation member  120  by a distance  138 . Separation from the compensation member  120  may facilitate independent stretching and bending of the elastic portion  124  in order to mimic the independent elastic properties of the traces  92  with respect to the HGA  80  and arm  34 . 
     The elastic portion  124  has mass, and as such contributes to the inertial properties of the compensation member  120 . Furthermore, the inertial portion  122  has elastic properties and therefore contributes to the elastic properties of the compensation member  120 . Nevertheless, the elastic portion  124  primarily mirrors the elastic and mass properties of the traces  92 , whereas the inertial portion  122  primarily mirrors the inertial properties of the HGA  80 . 
     In the illustrated embodiment the inertial portion  122  and elastic portion  124  are formed monolithically. In some embodiments, the inertial portion  122  and elastic portion  124  may be formed from a thin plate of uniform thickness. Alternatively, the inertial portion  122  and elastic portion  124  may be separate members made of the same or different materials and secured to one another by means of solder, glue, welds, or like securement means. Use of different materials may enable more refined mirroring of the properties of the suspension  32  and traces  92 . 
     Although the depicted suspension  32  includes a mount plate  86 , flexure  82 , hinge plate  83 , and load beam  84 , various other configurations are possible. Accordingly, a compensation member  120  may include an inertial portion  122  and elastic portion  124  corresponding to the inertial and asymmetric elastic properties of these alternative configurations. The strip  134  likewise may have different widths, thicknesses, and lengths to correspond to different configurations of traces  92 . 
       FIG. 8  is a frequency response plot  140  of a single head arm  34  having a compensation member  120  secured to the top of arm  34  and a frequency plot  142  of a single head arm  34  without a compensation member  120 . It is clear that the compensation member  120  reduces the magnitude of the peaks  144   a  and  144   b  as compared to the peaks  146   a  and  146   b  of the uncompensated single head arm  34 . Accordingly, off-track motion attributable to asymmetric vibration is reduced. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.