Abstract:
A method and apparatus for damping vibration in a flexible cable for use in a magnetic disk drive apparatus. The vibration damping mitigates resonant oscillation of the flexible cable which would otherwise cause tracking errors by forcing the actuator of the away from the desired data track on a magnetic disk. A layer vibration damping material and one or more electrical leads are enclosed within a surrounding electrical insulator, the damping material being completely enclosed, while the leads have selected portions exposed to allow electrical connection devices.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vibration damping in a hard disk drive device, and more particularly to a vibration damped flexible circuit for use in such a disk drive device. 
     2. Description of the Related Art 
     Moving magnetic storage devices, especially magnetic disk drives, are in prevalent use in computer systems, due in large part to their ability to inexpensively store large quantities of non-volatile data for quick access. Magnetic disk drives utilize at least one rotatable magnetic media disk having concentric data tracks defined for storing data, a magnetic recording head or transducer for reading data from and/or writing data to the various data tracks, a slider for supporting the transducer in close proximity to the data tracks typically in a flying mode above the storage media, a suspension assembly for resiliently supporting the slider and the transducer over the data tracks, and a positioning actuator coupled to the transducer/slider/suspension combination for moving the transducer across the media to the desired data track and maintaining the transducer over the data track center line during a read or write operation. The transducer is attached to or is formed integrally with the slider which supports the transducer above the data surface of the storage disk by a cushion of air, referred to as an air-bearing, generated by the rotating disk. 
     Alternatively, the transducer may operate in contact with the surface of the disk. Thus, the suspension provides desired slider loading and dimensional stability between the slider and an actuator arm which couples the transducer/slider suspension assembly to the actuator. The actuator positions the transducer over the correct track according to the data desired for a read operation or to the correct track for placement of the data during a write operation. The actuator is controlled to position the transducer over the desired data track by moving the transducer across the surface of the disk in a direction generally transverse to the data tracks. The actuator may include a single arm extending from a pivot point, or alternatively a plurality of arms arranged in a comb-like fashion extending from a pivot point. A rotary voice coil motor (VCM) is attached to the rear portion of the actuator arm or arms to power movement of the actuator over the disks. The term seek refers generally to the radial movement of the head or transducer to a specified track on the disk. 
     The VCM located at the rear portion of the actuator arm is comprised of a top plate spaced above a bottom plate with a magnet or pair of magnets therebetween. The VCM further includes an electrically conductive coil disposed within the rearward extension of the actuator arm and between the top and bottom plates, while overlying the magnet in a plane parallel to the magnet. In operation, current passes through the coil and interacts with the magnetic field of the magnet so as to rotate the actuator arm around its pivot and thus position the transducer as desired. 
     The magnetic media disk or disks in the disk drive are mounted to a spindle. The spindle is attached to a spindle motor, which rotates the spindle and the disks to provide read/write access to the various portions on the concentric tracks on the disks. One or more electrical conductors extend over the suspension assembly to electrically connect the read/write transducer to a read/write chip on the actuator arm. A multi-line flexible printed circuit cable (actuator flex cable) provides the electrical contact between the read/write chip and other circuitry located outside the disk drive housing. Inside the disk drive housing, the actuator flex cable connects to an electrical connector pin assembly, which in turn, through an opening or connector port in the housing, connects to the external electronics. 
     The actuator flex cable is a flexible circuit that carries electrical signal to and from the actuator. It is typically comprised of a plurality of electrical conductors encapsulated within an insulating material. The actuator flex cable provides electrical contact from the external electronics fixed to the disk drive housing to the actuator which is supported on bearings allowing radial motion of the actuator about its pivot point. The radial motion of the actuator allows the read/write transducers supported on suspensions fixed to the actuator to access data tracks on the disk surfaces located at any radial position from the inside diameter of the disk to the outside diameter of the disk. The preferred method of fixing the actuator flex cable between the electronics card on the fixed disk drive housing and the rotatable actuator is to form the actuator flex cable in a loop so that the actuator flex cable causes minimal constraint on the actuator rotation. The loop of the actuator flex cable connecting the actuator with the electronics card can vibrate during seeking of the actuator, introducing unwanted vibration modes to the actuator. Vibration (often referred to as random transient vibration) of the actuator during seek operations degrades settling performance of the disk drive. 
     There have been attempts in the prior art to minimize the affects of flex cable vibration on the actuator or head carriage assembly positioning. For example, U.S. Pat. No. 5,907,452 issued to Kan discloses attaching a damper at one end of the flex cable, the damper being a component external to and separate from the flex cable. Those skilled in the art will appreciate that the additional components added by the prior art necessarily increase the cost and complexity of such device, and in some cases increase the risk that the added components may become dislodged resulting in a catastrophic failure of the disk drive. In addition such a device only provides damping to a portion of the flex cable. Therefore, there remains a need for a means for effectively damping vibration in a flexible cable of a disk drive device, while minimizing the use of addition components. Such a device would preferably make use of existing manufacturing techniques as much as possible. 
     SUMMARY OF THE INVENTION 
     The present invention provides a vibration damped, flexible cable for use in a magnetic data recording device such as a hard disk drive. The flexible cable includes one or more electrical leads and a layer of vibration damping material both surrounded by an electrical insulator. 
     The vibration damping material can be disposed adjacent to the leads, being sandwiched between the leads and the insulation layer. Since the damping layer is disposed within the insulation of the flex cable, there is no risk of the damping material coming loose from the flex cable. Other problems, such as outgassing and debris accumulation are also avoided. In addition, the present invention allows great flexibility in the amount and placement of damping material within the flex cable, such that essentially the entire flex cable can be damped with such material if desired. Preferably, the damping material covers an area of at least ⅓ the area of the flexible cable. Also, the shape of the flexible cable can vary along its length according to performance requirements. For example, the width along a lateral direction or thickness in a height direction can vary in order to place more damping material at locations that require greater vibration damping. 
     The electrical leads can be formed of a metal such as copper and the damping material can comprise, for example, ISD130™ made by 3M Corporation. The insulator can be constructed of a flexible electrical insulator such as Kapton™. In one possible embodiment, a second layer of damping material can be included, for example on the side of the leads opposite that of the first insulation layer. 
     The flex cable of the present invention can be constructed using existing manufacturing techniques. The leads can be applied onto a first layer of insulating material. Then, the vibration damping layer can be deposited onto the leads. A second layer of insulating material can then be applied over the first insulation layer, leads and vibration damping material. The application of heat and pressure can be used to bond the materials together, encasing the leads and the damping material within the surrounding insulation. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings, wherein: 
         FIG. 1 , is a perspective view of a disk drive according to an embodiment of the invention, shown with a removed cover in order to depict components therein; 
         FIG. 2  is a plan view of a disk drive according to an embodiment of the present invention; 
         FIG. 3  is a plan view of a flexible cable according to an embodiment of the invention shown with an upper portion of its insulation layer removed in order to illustrate components therein; 
         FIG. 4  is a cross sectional view taken along line  4 - 4  of  FIG. 3 , shown enlarged and rotated 90 degrees counterclockwise; 
         FIGS. 5   a  and  5   b  are exploded cross section views of components used to construct a flex cable according to the present invention; 
         FIGS. 6   a  and  6   b  are flow charts illustrating a method of making the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to  FIG. 1 , a disk drive apparatus, generally referred to as  100  includes a housing  102  and a lid  104 , which is shown removed in order to describe various component within the housing  102 . The disk drive  100  includes one or more magnetic disks  106  on the surface of which digital data can be stored as magnetic signals formed along concentric tracks. In a preferred embodiment, both sides of the disk  106  would have such data stored thereon, and those skilled in the art will recognize that any number of such disks  106  may be included in the disk drive  100 . 
     The disks  106  are mounted to a spindle  108 , which is connected with a spindle motor (not shown), which rotates the disk  106  within the housing  102 . An actuator assembly  110  includes an actuator arm  112 , integrally connected with an E-block, or comb  114 , and a suspension assembly  116 . The suspension assembly  116  includes a slider/transducer assembly  118  at its distal end and for movement across the surface of the disk  106 . While only one suspension assembly  116  is shown, those skilled in the art will appreciate that the disk drive  100  would include a suspension  116  for each side of each disk  106 . 
     The disk drive  100  further includes an amplifier circuit chip  120 . The amplifier chip  120  cooperates with the slider/transducer assembly  118  to read data from or write data to the disks  106 . A flexible printed circuit member or actuator flex cable  122  carries signals between the amplifier chip  120  and a connector pin assembly (not shown) attached to the disk housing  102 , which interfaces with the external signal processing electronics. The actuator flex cable  122  leading from the amplifier chip  120  is attached to an arm electronics (AE) bracket  124  which directs the actuator flex cable  122  to a connector port for connection to a connector pin assembly (not shown). 
     The actuator assembly  110  is mounted on a pivot bearing  126  for pivotal movement about a pivot point  128 , and functions to position the transducer  118  over selected data tracks on the disk  106 . The actuator assembly  110  includes a voice coil motor assembly  130 , which comprises a bottom plate (not shown), a magnet (not shown) a top plate  132 , and a coil  134  ( FIG. 2 ). Current passing through the actuator coil interacts with the magnetic field of the magnet to rotate the E-block  114 , and suspension assembly about the pivot point  128 , to thereby position the transducer  118  as desired over the disk  106 . 
     With reference now to  FIG. 2 , a plan view of the disk drive illustrates the location of the actuator assembly  110  relative to the disk  106  and housing  102 . The pivotal motion of the actuator assembly  110  and suspension assembly  116  across the surface  149  of the disk  106  is indicated by arrow  136 . The motion of the actuator  110  is limited by contact between stops  138 ,  140 , and rearward extensions or VCM coil support arms  142 ,  144 . Conductive coil leads  146  provide electrical connection of the VCM coil  134  to the actuator flex cable  122  near to the amplifier chip  120 . The limits of the actuator assembly rotation define the inner diameter (ID) track  151  and the outer diameter track  153  on the disk surface  149  that may be accessed by the slider transducer assembly  118 . 
     The actuator flex cable  122  is fixed to the actuator assembly  110  at a J-shaped fixture (J-block)  148 , which provides support for the actuator flex cable  122 , and directs the cable to form a self supported arc or loop between the actuator assembly  110  and the AE bracket  124 . The loop formed by the flex cable  122  provides mechanical isolation for the actuator assembly  110  allowing rotary motion of the actuator assembly  118  during operation of the disk drive  100  with minimal mechanical constraint. 
     Disk drive performance as measured by track misregistration (TMR) is degraded by vibration of components within the disk drive. In particular, movement of the actuator arm  112  over a selected track can set up oscillations in the flex cable  122  due to inertial and elastic (spring) properties of the flex cable itself. These oscillations can be torsional as well as lateral, as indicated by arrows  150  and  152  respectively and act to force the actuator arm  112  away from its intended position over the desired track. 
     With reference to  FIGS. 3 and 4 , which show plan and sectional views of a flex cable  122  according to a preferred embodiment of the present invention, a vibration damping material integrated within the flex cable minimizes the previously described problems associated with resonant oscillation of the flex cable  122 . The flex cable as illustrated in  FIG. 3  is shown extended flat and with an upper portion of its insulation layer removed in order to illustrate the components therein. The flex cable  122  of the present invention includes a plurality of conductive lines or leads  154  and a layer of vibration damping material  156  formed adjacent to the leads  154 . Both the leads  154  and vibration damping material layers  156  are encased within a flexible electrically insulating material  158 , with selected end portions of the leads being exposed to form contact pads  157  to allow for electrical contact with the amplifier circuit chip  120  and the connector pin assembly. For purposes of clarity, the flexible cable  122  is shown as having four electrical leads  154 , however, those skilled in the art will appreciate that the flexible cable  122  would likely include many more such leads. The damping material layers  156  can be formed in many different shapes and sizes within the cable  122 , as necessitated by design requirements. Preferably, however, the damping material covers an area at least ⅓ the area of the flexible cable  122  when viewed from above as in  FIG. 3 . More preferably, the damping material covers an area that is at least ½ the area of the flexible cable  122 . The damping material  156  could also be configured to be wider or thicker in areas where more damping is required and narrower or thinner elsewhere. 
     Materials used for vibration damping should exhibit large viscous losses in response to deformation. As will be appreciated by those skilled in the art, these losses are typically quantified in terms of a dynamic loss modulus. The vibration damping material  156  used in the flexible cable  122  of the present invention is preferably a material having a nominal dynamic loss modulus of 50% to 110%. Several materials are available for use as a vibration damping material  156 . Preferably, the vibration damping material is ISD130™, produced by 3M™ Corporation. Alternatively, ISD110™ or ISD112™, also produced by 3M Corporation can be used, as well as equivalent materials produced by ANATROL™ Corporation. While the vibration damping layer  156  is shown as being formed along one side of the leads  154 , it could be formed on either side or on both sides of the leads  154  depending on design considerations such as cost and vibration damping requirements. The electrical leads can be formed of many electrically conductive materials, and in the preferred embodiment they are formed of copper. The material chosen to construct the insulation layer  158  can be selected from among many flexible, electrically insulating materials, and in the preferred embodiment is KAPTON™. 
     With reference now to  FIGS. 5 and 6 , a method of constructing a flex cable  122  of the present invention will be described. Prior art flex cables are constructed by sandwiching a plurality of electrical leads between two electrically insulating films and applying heat and pressure to bond the insulating films to one another and to the leads. Advantageously, the flex cable of the present invention can be constructed in much the same way as prior art flex cables, allowing the use of existing tooling and processes. In a step  602 , a first electrically insulating film  160  is formed. Then, in a step  604  the leads  154  are applied to the first insulating film layer  160 . In a step  164 , the vibration damping material  156  is applied to the leads  154  and the first film  160 . Thereafter, in a step  608  a second layer of insulating film  162  is applied onto the first film  160 , leads  154  and damping material  156 . In steps  610  and  612 , heat and pressure are applied to the flex cable  122  to bond the layers together, encasing the leads  154  and damping material  156  within the insulating material as illustrated in  FIG. 3 . Steps  610  and  612  may be conducted simultaneously or separately depending on the type of bonding performed. Alternatively, with the use of certain adhesives, the heating step may be eliminated and bonding may be achieved by the application of pressure alone. 
     As will be appreciated by those skilled in the art, encasing the damping material within the insulating material  158  provides several advantages over a design having a damper externally attached to the flex cable. For example, existing damping materials are sticky materials and as such would tend to collect debris if attached externally. In addition, encasing the damping material within the insulation  158  of the flex cable assures that the damping material will not detach from the flex cable  122 . A detached damper being loose with in the disk drive  100 , would not only eliminate any advantageous damping effect, but would likely lead to a catastrophic failure of the drive  100 . Also, since the flex cable of the present invention can be manufactured with minimal deviation from existing manufacturing methods it can be easily and inexpensively manufactured. Furthermore, encasing the damping material  156  within the insulating material  158  eliminates any problems associated with outgassing of the damping material over time. 
     With reference to  FIG. 4   b , a possible alternate embodiment of the invention is described. A flexible cable  164  according to this embodiment includes first and second damping layers  156 ,  166 , sandwiching the electrical leads  154  therebetween. The first and second damping layers  156 ,  166  and the electrical leads  154  are sandwiched between the first and second insulating layers  162 ,  160 . With reference to  FIGS. 5   b  and  6   b  a method for constructing a flexible cable  164  according to this alternate embodiment of the invention includes, in a step  602 , providing a first insulation film  162 . Thereafter, in a step  603  a first vibration damping layer  156  is applied. Then, in a step  604 , the electrical leads  154  are applied. Then, in a step  606 , a second layer of vibration damping material  606  is applied. In a step  608 , the second insulation layer  160  is applied. Then, in steps  610  and  612 , heat and pressure are applied to bond the previously described elements together. 
     While the preferred embodiments of the present invention have been illustrated herein in detail, it should be apparent that modifications and adaptations to those embodiments may occur to those skilled in the art without departing from the scope of the present invention, which is to be limited only as set forth in the following claims.