Abstract:
Method and apparatus for attenuating resonances in a flex circuit which interconnects a stationary element and a moveable element, such as a connector and a head stack assembly (HSA) in a data storage device. An intermediary portion of the flex circuit forms a dynamic loop between the stationary element and the moveable element. A damper member is attached to the flex circuit so as to continuously extend adjacent the stationary element and along less than an overall extent of the dynamic loop. The damper member attenuates resonances excited in the flex circuit during movement of the moveable element.

Description:
BACKGROUND 
       [0001]    Data storage devices store and retrieve large amounts of data in a fast and efficient manner. A disc drive is a type of data storage device that often includes one or more data storage discs spun by a spindle motor at a constant high rotational speed. 
         [0002]    Data storage and retrieval from the disc surfaces is effected by a rotary actuator assembly (sometimes referred to as a head stack assembly, or HSA). The HSA supports a number of data transducing heads that are controllably moved across the disc surfaces by an actuator motor (sometimes referred to as a voice coil motor, or VCM). 
         [0003]    The spindle motor and the HSA are typically mounted to a base deck that cooperates with a top cover to provide a protected interior environment for the discs and heads. A printed circuit cable (PCC) provides the requisite electrical communication paths between the HSA and a data storage device printed circuit board (PCB) mounted to the exterior of the base deck. The PCB supports communication and control electronics for operation and control of the device. 
         [0004]    The PCC includes a flex cable that has a flexible, laminated member that electrically isolates and supports a number of embedded electrical conductor paths along the length of the laminated member. Generally, one end of the flex cable is coupled to the PCB and the other end of the flex cable is coupled to the HSA. 
         [0005]    An intermediary portion of the flex cable can operate as a dynamic loop (slack loop) that provides strain relief while the HSA moves the heads radially in close proximity to the disc surfaces. In practice, the flex cable loop can often act like a spring, exerting bias forces on the HSA as the slider heads are moved to different radial positions with respect to the disc surfaces. Resonances in the flex cable can also be induced during seek operations when the HSA moves a selected head from an initial track to a destination track. Various embodiments of the present invention are generally directed to an apparatus and method for attenuating resonances in a flex circuit, such as in a data storage device. 
       SUMMARY 
       [0006]    In accordance with various embodiments, the flex circuit interconnects a stationary element and a moveable element, such as a connector and a head stack assembly (HSA). An intermediary portion of the flex circuit forms a dynamic loop between the stationary element and the moveable element. 
         [0007]    A damper member is attached to the flex circuit so as to continuously extend adjacent the stationary element and along less than an overall extent of the dynamic loop. The damper member attenuates resonances excited in the flex circuit during movement of the moveable element. 
         [0008]    These and various other features and advances which characterize various embodiments of the present invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an isometric view of a data storage device constructed in accordance with various embodiments of the present invention, wherein a cover member of the device has been removed in  FIG. 1  to reveal various components of interest. 
           [0010]      FIG. 2  is an elevational view of a portion of a printed circuit cable (PCC) of  FIG. 1  showing an attached damper member. 
           [0011]      FIG. 3  is a side view of the damper member in accordance with some embodiments. 
           [0012]      FIGS. 4A and 4B  are graphical illustrations of an exemplary reduction of deleterious resonant frequencies accomplished through the use of the damper member of  FIG. 2 . 
           [0013]      FIGS. 5 and 6  are graphical illustrations of corresponding exemplary reductions in unsafe seeks accomplished through the use of the damper member of  FIG. 2 . 
       
    
    
     DESCRIPTION 
       [0014]      FIG. 1  shows a data storage device  100  constructed in accordance with various embodiments of the present invention. While the data storage device  100  is characterized as a disc drive, such is merely exemplary and not limiting to the scope of the claimed subject matter. 
         [0015]    The device  100  includes a housing with a base  102 , a top cover (not shown) and a disc stack  104 , which is mounted on a spindle motor (not shown) by a disc clamp  106 . The disc stack  104  includes one or more individual data discs  108  mounted for rotation about a central axis  110 . Each disc  108  has at least one data surface, and for each disc data surface, the data storage device  100  has an associated disc head slider  112  and supported read/write, data transducer head (not separately numbered) for communication with the disc surface. 
         [0016]    As depicted in  FIG. 1 , each of the sliders  112  is supported by a flex arm  114  that in turn is attached to a suspension arm  116  of a head stack assembly (HSA)  118 . The HSA  118  shown in  FIG. 1  is of the type known as a rotary moving coil actuator and includes a voice coil motor (VCM)  120 . The VCM  120  rotates the HSA  118  and attached data transducer heads about a pivot shaft  122  to position the data transducer heads over a desired data track along an arcuate path  124 . The VCM  120  is driven by servo electronics of a controller on a printed circuit board (PCB)  125 , that is electrically accessed via a bulkhead connector  126 . 
         [0017]    A flexible printed circuit cable (PCC)  128 , also sometimes herein referred to as the flex circuit assembly, runs between the pivot housing of the HSA  118  and the connector  126 . A clamp  130  engages the proximal end of the flexible cable  128  and directs the PCC  128  to extend the medial portion  132  of the PCC  128  in the form of a slack loop, as shown. The other end of the PCC  128  attaches to the connector  126 . 
         [0018]    The slack loop formed by the PCC  128  provides mechanical isolation of the HSA  118  to allow rotary motion of the HSA  118  during accessing operations with minimal mechanical constraint. The loop of the PCC  128  can be subjected to vibration during data seeks, introducing unwanted random transient vibration modes (RTV) to the HSA. These RTV&#39;s degrade settling performance of the data storage device. Data storage device performance is measured by track-misregistration (TMR) caused by degradation of positioning control by data storage device component vibration, including the RTV&#39;s of the PCC  128 . Specifically, the PCC  128  can introduce modes of vibration during data seeks that have identified RTV modes in the frequency range from 300 Hz to 700 Hz, and the unwanted vibration modes of the PCC  128  can be attenuated by placement of damping material in contact with portions of the PCC loop. 
         [0019]    Turning to  FIG. 2 , shown therein is a connector pad  134  of the connector  126 , and the end portion  136  of the PCC  128  is attached thereto, with the electrical conductors of the PCC  128  providing electrical communication between the PCB (not shown) and the HSA  118  and thus to the data transducer heads. 
         [0020]    Adhered to the end portion  136  is a damper member  138 . In some embodiments, the damper member  138  is a constraint layer damper that is made of multiple layers of damping material. It should be noted that the damper member  138  spans along the PCC  128  where the same overlaps the connector pad  134 , and the damper member  138  extends beyond the end of the connector pad  134  to span for a determined distance along a portion of the slack loop, or medial portion  132 , of the PCC  128 . 
         [0021]    The damping material layers of the damper member  138  are selected to have similar stiffness, or flexibility, as that of the PCC  128 . As the slack loop (the medial portion  132 ) is flexed with movement of the HSA  118 , that portion of the damping material extending beyond the edge of the connector pad  134  is put into shear with a negligible bias force delivered from the damper to the medial portion  132 . This is accomplished by having the damper material span both a non-dynamic and a dynamic portion of the slack loop. 
         [0022]    The layers of damping material of the damper member  138  are preferably a viscous material that forms the middle layer of a constraint damping system. Basically, the viscous layers are put into shear when the PCC  128  bends, and vibration energy is dissipated in shearing the viscous material. The shearing occurs where the flex circuit (the PCC  128 ) exits the rigid connector pad  134  up to the extended end of the damper member  138 . This is the result of the damper member  138  straddling both a rigid member (the connector pad  134 ) and a flexible member (the slack loop of the PCC  128 ). One advantage of this configuration is that the location of the damper member  138  is achieved with negligible impact on the freedom of motion of the slack loop, resulting in lower bias forces upon the HSA  118 . 
         [0023]    The length, width and volume of the viscous material contained in the damper member  138  should be selected to provide the best compromise between the damping effect and the amount of bias force added to the slack loop. An exemplary construction of the damper member  138  is shown in  FIG. 3  to include a suitable flexible, plastic outer layer  140  and a compressible inner layer  142 . A suitable material for the outer layer  140  is a flexible film such as Kapton® film, a polyimide film marketed by the E.I. DuPont de Nemours and Company of Wilmington, Del. 
         [0024]    A suitable material for the inner layer  142  is 3M 242F02 adhesive, a thin  20  viscoelastic polymer available from vendors handling products of the 3M Company, St. Paul, Minn. The adhesive adheres upon contact, and is protected prior to use with a polyester liner (not shown) that is easily removed for applying the damper member  138  to the PCC  128 , as described. 
         [0025]      FIGS. 4A and 4B  demonstrate the effectiveness of the damper member  138 , with the data depicted in  FIG. 4A  representing performance of a device such as  100  without the damper  138  and the data depicted in  FIG. 4B  representing the performance of the device with the damper  138 . Both  FIGS.4A and 4B  show the frequency content that the HSA controller applies when the head arrives on a desired track. In  FIG. 4A , a prominent peak at 500 Hz is visible, indicating a problem of lengthy track settlement. It should be noted that this frequency varies from drive to drive, and the range noted in practice is between about 510 Hz and 600 Hz. In  FIG. 4B , the damper  138  is shown to have removed this frequency peak. These figures demonstrate the significant reduction of correction required at the 500 Hz level. 
         [0026]    This is further illustrated by  FIGS. 5 and 6  that depict another way to illustrate the efficacy of the various embodiments disclosed herein.  FIG. 5  generally depicts the device  100  without the damper  138  and the data depicted in  FIG. 6  representing the performance of a data drive with the damper  138 . In each, the horizontal axis is the length of seek along path  124  ( FIG. 1 ), and the vertical axis is the percentage of those seeks that lie outside an arrival time window within which it is safe for data write operations to commence. This safe window is required to prevent the writing head from erasing tracks adjacent to the desired track. 
         [0027]    It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. For example, the particular elements may vary depending on the particular application of the damping member without departing from the spirit and scope of the present invention. 
         [0028]    In addition, although the embodiments described herein are generally directed to a printed circuit cable in a disc drive data storage device, it will be appreciated by those skilled in the art that the damping member of the present invention can be used for other types of systems without departing from the spirit and scope of the claimed invention.