Abstract:
A damper for a data storage device having a viscoelastic material and a constraint material disposed on the viscoelastic material, the constraint material covers the sides of the viscoelastic material to reduce exposure of the viscoelastic material from debris in the surrounding environment.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of disk drives. More particularly, the invention relates to a damper for use in data storage applications. 
     2. Description of Related Art 
     A key component of any computer system is a device to store data. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations on the disc, and electrical circuitry that is used to write and read data to and from the disc. Coupled to the actuator is a head-gimbal assembly (HGA) that includes a head and metal suspension. The HGA&#39;s can be stacked together into a head-stack assembly (HSA), which is propelled across the disk surface by the actuator. The HSA may include a voice coil and a set of magnets. When electric current is passed through the voice coil, an electromagnetic field causes the voice coil to move, and in turn, the HSA moves across the disk surface. There are a variety of disc drives in use today, such as hard disc drives, zip drives, floppy disc drives. All utilize either rotary or linear actuators. 
     Magnetic heads read and write data on the surfaces of rotating disks that are co-axially mounted on a spindle motor. The magnetically-written “bits” of information are laid out in concentric circular “tracks” on the surfaces of the disks. The disks must rotate quickly so that the computer user does not have to wait long for a desired bit of information on the disk surface to become positioned under the head. In modern disk drives, data bits and tracks must be extremely narrow and closely spaced to achieve the high density of information per unit area of the disk surface that is desired. 
     The required small size and close spacing of information bits on the disk surface have consequences on the design of the disk drive device and its mechanical components. Because there is relative motion between the disk surface and the magnetic head due to the disk rotation and head actuation, any contact between the head and disk, due to mechanical shocks or vibration, can lead to tribological failure of the interface. Such tribological failure, known colloquially as a “head crash,” can damage the disk and head, and usually cause data loss. Vibration is particularly a serious problem when it occurs at or near the resonant frequencies of the disk drive components. 
     To reduce vibration problems in the disk drive assembly, several methods have been employed. One such method includes providing a damper on the actuator arm, head-gimbal assembly or head-stack assembly. Another method includes providing a damper disposed between adjacent load beams, as disclosed in U.S. Pat. No. 6,498,704. A further method includes interposing a damper between the outer surfaces of the hard disk drive assembly and the inner surface of a housing that contains the hard disk drive assembly, as disclosed in U.S. patent application Ser. No. 11/269,545. 
     Referring to  FIG. 1 , a typical prior art damper  9  may include a constraint material  11  and a viscoelastic layer  13 . The viscoelastic material  13  may be made of a viscoelastic polymer with a double sided pressure sensitive adhesive, while the constraint material  11  may be made of aluminum, steel, zinc, copper or ceramic. The viscoelastic layer  13  absorbs and reduces external shocks or vibrations, while the constraint material  11  provides sheer damping capabilities. The viscoelastic layer  13  may be disposed between a component of the hard disk drive and the constraint material  11 . Typically, a viscoelastic adhesive is used to couple the viscoelastic layer  13  to the constraint material  11 . This viscoelastic adhesive may squeeze-out or otherwise migrate during damping applications. Exposure of the viscoelastic adhesive to the hard disk drive assembly also tends to attract contamination, thereby creating a contaminated hard disk drive environment. 
     One method for reducing the exposure of the viscoelastic adhesive is to limit exposing the adhesive, by only exposing it at the edges  15 . As shown in  FIG. 2 , the viscoelastic adhesive is only exposed at the edge  15  where the viscoelastic layer  13  has the same width as the constraint material  11 . Another method for reducing exposure of the viscoelastic adhesive is by directing the cut edge of the constraint material  11  so that the burr height  19  will cover some fraction of the exposed edge of the viscoelastic layer  13 . 
       FIG. 3  shows an edge  17  of the viscoelastic layer  13  protected by a burr  19  of the constraint material  11 .  FIG. 4  shows a viscoelastic layer  13  that is not as wide as the constraint material  11 . The viscoelastic layer  13  is thereby set back and burr protected. 
     Since the cut edge burr  19  varies in height and the nominal height only covers a fraction of the exposed edge, the edge of the viscoelastic layer  13  still remains exposed and accessible to be mechanically dislodged and to be contaminated. With an increasing demand for improved dampers for use in data storage devices, there remains a need in the art for a damper that protects the viscoelastic layer from contamination. 
     SUMMARY OF THE INVENTION 
     A damper for a data storage device having a viscoelastic material and a constraint material disposed on the viscoelastic material. The constraint material is formed or coined to have an edge offset or a flanged edge for covering the sides of the viscoelastic material. This considerably reduces exposure of the viscoelastic material to debris. The viscoelastic material may be a viscoelastic polymer with a double sided, pressure sensitive adhesive. The constraint material may be made of aluminum, stainless steel, nickel-plated stainless steel, zinc, copper, ceramic, nickel, mylar or elastomeric material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The exact nature of this invention, as well as the objects and advantages thereof, will become readily apparent from consideration of the following specification in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein: 
         FIG. 1  is a perspective view of a prior art damper. 
         FIG. 2  is a cross-sectional view of a portion of a prior art damper with exposed viscoelastic adhesive edges. 
         FIG. 3  is a cross-sectional view of a portion of a prior art damper with burr protected viscoelastic adhesive edges. 
         FIG. 4  is a cross-sectional view of a portion of a prior art damper with a viscoelastic layer set back and burr protected. 
         FIG. 5  is a perspective view of a damper according to an embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of the damper of  FIG. 5  along line  6 - 6 . 
         FIG. 7  is a perspective view of a damper according to another embodiment of the present invention. 
         FIG. 8  is a cross-sectional view of the damper of  FIG. 7  along line  8 - 8 . 
         FIG. 9  is a flow chart depicting a method for fabricating a damper, of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 5  is a perspective view of a damper  21  for use in data storage applications, according to an embodiment of the present invention.  FIG. 6  is a cross-sectional view of the damper  21  of  FIG. 5  along line  6 - 6 . 
     Referring to  FIGS. 5 and 6 , the damper  21  includes a constraint material  23  and a viscoelastic layer  25 . The viscoelastic layer  25  absorbs and reduces external shocks or vibrations, while the constraint material  23  provides sheer damping capabilities. A viscoelastic adhesive may be used to couple the viscoelastic layer  25  to the constraint material  23 . The viscoelastic layer  25  may be formed of a viscoelastic polymer with a double sided pressure sensitive adhesive. The viscoelastic layer  25  may be adapted to maintain the constraint material  23  in position against a component of a data storage device. The constraint material  23  is preferably stainless steel, but may be formed of a non-magnetic materials, such as, aluminum, stainless steel, nickel-plated stainless steel, zinc, copper, nickel, mylar, ceramic material, viscoelastic or elastomeric material. The viscoelastic layer  25  and the constraint material  23  are selected so that the frequencies damped are in a desired range of interest. 
     As shown in  FIGS. 5 and 6 , the constraint material  23  is shaped with an edge offset  27  that encloses the viscoelastic layer  25 . The edge offset  27  extends a predetermined distance. A forming or coining technique, well known to persons skilled in the art, is used to accomplish this. The predetermined distance is sufficient to enclose the side  31  of the viscoelastic layer  25 . The coining technique used to shape the constraint material  23  creates a pocket  29  in the constraint material  23  with which the viscoelastic layer  25  is positioned, thereby enclosing the adhesive material. 
     By enclosing the adhesive on the viscoelastic layer  25 , less contamination or damage potential occurs. Contamination can only occur if debris entering into the inlet  29  between the inside walls of the edge offset  27  of the constraint material  23  and side  31  of the viscoelastic layer  25 . However, even if the viscoelastic layer  25  is contaminated, the shape of the enclosure of the constraint material  23  prevents subsequent mechanical dislodging of debris, thereby preventing contamination of the hard disk drive environment. Accordingly, the shape of the constraint material  23  forms a debris trap that limits debris from attaching to or detaching from the viscoelastic layer  25 . 
     Another advantage of the present invention is that the stiffness of the constraint material  23  increases due to the edge offset  27 . This stiffness increase may be used to tune the damper  21  for optimum performance. The stiffness increase may be used to develop smaller and/or less massive dampers  21  than those used in the prior art, while providing similar structural and functional benefits. 
       FIG. 7  is a perspective view of a damper  33  for use in data storage applications, according to another embodiment of the present invention.  FIG. 8  is a cross-sectional view of the damper  33  of  FIG. 7  along line  8 - 8 . 
     Referring to  FIGS. 7 and 8 , the damper  33  includes a constraint material  35  and a viscoelastic layer  37 . The viscoelastic layer  37  absorbs and reduces external shocks or vibrations, while the constraint material  35  provides sheer damping capabilities. The viscoelastic layer  37  and the constraint material  35  are selected so that the resultant damper  33  damps frequencies in a desired range. 
     The constraint material  35  of  FIGS. 7 and 8  is shaped to have an edge offset  36  with a flange edge  39 . This shape encloses the viscoelastic layer  37 . The edge offset  36  with flanged edge  39  is fabricated to extend a predetermined distance using a well-known forming or coining technique. Preferably, the predetermined distance of the edge offset  36  is sufficient to cover the side  41  of the viscoelastic layer  37 . The fabrication process creates an inlet  43  in the constraint material  35  with which the viscoelastic layer  25  is positioned, enclosing the adhesive material. 
     By enclosing the adhesive on the viscoelastic layer  37 , less contamination or damage potential occurs. Contamination can only occur if debris enters the inlet  43  between the inside walls of the edge offset  36  and the side  41  of the viscoelastic layer  37 . Once the viscoelastic layer  37  is contaminated, the shape of the constraint material  35  prevents subsequent mechanical dislodging of debris thereby preventing contamination of the hard disk drive environment. Accordingly, the enclosure formed in the constraint material  35  forms a debris trap that limits debris from attaching to or detaching from the viscoelastic layer  37 . 
     One advantage of fabricating damper  33  is the relative ease in manufacture. It is easier to vertically cut side  40  of the flanged edge  39  for damper  33  rather than horizontally cut the edge offset  27  for damper  21 . Another advantage of damper  33  is the increased time for travel or migration of debris from the inlet  43  to side  40  of the flanged edge  39 . The debris must travel across the length of the flanged edge  39  before being exposed to the hard disk drive environment. 
     Another advantage of damper  33  is that the stiffness of the constraint material  35  increases due to the edge offset  36  and the flanged edge  39 . This stiffness increase may be used to tune the damper  33  for optimum performance. The stiffness increase may be used to develop smaller, less massive dampers  33  than those used in the prior art, while providing similar structural and functional benefits. 
     A method for fabricating the constraint material  35  for use in a data storage device is illustrated in  FIG. 9 . The viscoelastic layer  25  or  37  is prepared by cutting a viscoelastic tape into a desirable or predetermined shape, step  55 , and removing any excess tape, step  57 . The desirable or predetermined shape of the viscoelastic layer  25  or  37  may be any shape or size for achieving desirable damping characteristics in the data storage device. For example, the viscoelastic layer  25  or  37  may be used to provide damping to the voice coil of a head-stack assembly (not shown), and accordingly, the viscoelastic layer  25  or  27  is shaped to fit in the bobbin space between the voice coil. In another example, the viscoelastic layer  25  or  37  may be used to provide damping to an actuator arm, and accordingly, the viscoelastic layer  25  or  27  is shaped to substantially the same dimensions as the actuator arm or portions thereof. 
     The constraint material  23  or  35  is prepared by cutting and forming (or coining) a clean constraint material band, such as a stainless steel band, into the desired predetermined shape, step  59 . The fabricated constraint material  23 ,  35  is cleaned to remove any debris resulting from the fabrication process, step  61 . As can be appreciated from the aforementioned embodiments, the desirable shape of the constraint material  23  or  35  may include an offset edge  27  or an offset edge  36  with a flange edge  39  that forms a well  29 ,  43  in which the viscoelastic layer  25 ,  37  is positioned, enclosing any adhesive material from exposure to contamination. 
     Once the viscoelastic layer  25 ,  37  and the constraint material  23 ,  35  are shaped, they are joined together to form a damper  21  or  33 , step  63 . The viscoelastic layer  25 ,  37  and the constraint material  23 ,  35  may be joined by co-piloted joining. 
     In all of the above described embodiments, the intended use in a disk drive suggests suitable ranges for the physical properties of the dampers. The constraint material  23 ,  35  thickness typically ranges from as low as possible, on the order of about 0.0002″ to about 0.005″. The viscoelastic layer  25 ,  37  typically is within the same thickness range, although there is no requirement for the two to be of equal thickness for a particular implementation. In length, the dampers  21  or  33  may range from about 0.200″ up to about 2.000″ with a width, not necessarily constant along the length, ranging from about 0.100″ up to about 1.000″. In addition, more than one ply of constraint material  23 ,  35  and viscoelastic layer  25 ,  37  may be used, forming an arrangement that may be multi-level or constrained on both top and bottom.