Abstract:
A disc drive snubber for protection of a disc drive disc from mechanical shock, the snubber positioned to limit the deflection of the disc in the operational mode, the position of the disc snubber determined in response to user reported defects. The snubber, positioned beneath the disc in near proximity to the outer diameter of the disc, extends along about a 60 degree segment of the disc and is made of a FIPG material.

Description:
BACKGROUND 
     Disc drives are digital data storage devices that store and retrieve large amounts of user data in a fast and efficient manner. Data are magnetically recorded on the surfaces of one or more data storage discs affixed to a spindle motor for rotation at a constant high speed. 
     An array of vertically aligned data transducing heads are controllably positioned by an actuator to read data from and write data to tracks defined on the disc recording surfaces. An actuator motor rotates the actuator to move the heads across the disc surfaces. The heads are suspended from gimbal assemblies extending from arms of the rotary actuator assembly and include aerodynamic features that enable the heads to fly upon a fluid air bearing established by currents set in motion by the rotation of the discs. When the disc drive is deactivated, a shutdown operation is commenced wherein the heads are moved to a safe parking position before the discs come to a stop. 
     It is a continuing trend in the disc drive industry to provide disc drives with ever increasing data storage capacities using the same or smaller form factor (i.e., outside dimensions) for the drives. As a result, successive generations of drives are often provided with discs that are closer together, reducing disc to actuator arm clearances. At the same time, disc drives are being utilized in harsher environments, such as portable computers, requiring increases in the robustness of the drives to withstand ever greater external vibration and shock input levels. For example, a typical disc drive might be required to withstand up to 200 g mechanical shock. 
     Such mechanical shocks can cause significant deflection of the discs, leading to catastrophic damage to the disc media and heads. More particularly, disc to actuator arm contact can induce a shock wave large enough for referral to the gimbal assemblies and heads, causing the heads to flex off the landing zones as a result of the relatively flexible gimbal assemblies. The heads can thus achieve significant velocities in accelerating from and back toward the discs. When such velocities are sufficiently severe, damage can occur to the heads and the disc surfaces as the heads strike landing zones. Moreover, the corner of a tilted head can strike the disc surface, increasing probability of damage to the head or to the disc. 
     While prior art disc snubbers have limited deflection of disc drive discs, it has been observed that localized snubbers can be displaced upon application of a mechanical shock. In a relatively small computer such as a laptop, where space is limited, the added cost of assembly and installation of extra pieces can defeat the purpose of a low cost, space efficient computer. 
     Accordingly, there is a need for an improved approach to minimizing damage to a disc drive as a result of non-operational shock by limiting the ability of the discs to contact the arms and heads of an actuator of the disc drive. 
     SUMMARY 
     A disc drive assembly data storage device having a rotatable disc in an operational mode that has at least one disc snubber that is positioned to limit the deflection of the discs in the operational mode of the disc drive assembly data storage device, the position of the disc snubber being determined in response to user reported defects. The snubber is preferably positioned beneath and in near proximity to the outer diameter of the disc and extending along about a 60 degree segment of the disc. Preferably, the snubber is made of a flow in place gasket (FIPG) material. 
     In one preferred embodiment the disc drive has a cavity track, and the snubber is formed with a lower portion extending into the cavity track. 
     These and various other features and advantages which characterize the claimed invention will become apparent upon reading the following detailed description and upon reviewing the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a data storage device of the type in which preferred embodiments of the snubber of the present invention is particularly useful for the prevention of defects caused by mechanical shock. 
         FIG. 2  depicts a topple drop shock test. 
         FIG. 3  is a planar view in perspective of the base deck of the data storage device of  FIG. 1 . 
         FIG. 4  is a plan view of the base deck of  FIG. 3  showing a preferred location of the snubber. 
         FIG. 5  is a perspective view of the base deck showing the cavity track in which the snubber is formed. 
         FIG. 6  depicts the steps of a method of determining the characteristics and position of a snubber for prevention of user reported defects to a data storage device such as shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Accordingly, there is a need for an improved approach to minimizing damage to a disc drive as a result of non-operational shock by limiting the ability of the discs to contact the arms and heads of an actuator of the disc drive. 
     It has been observed that the majority of the disc defects occurring as a result of non-operational shock in certain disc drives are attributable to ramp disc contact, resulting in unacceptable head disc interference. In fact, studies have shown that 30 to 40 percent of such defects fall within this category of causation. Such defect rates have motivated the study of the failure cause of ramp disc contact, and the present invention provides solutions for such. 
     Ramp disc contact is defined as deflection of a disc edge in the Z axis (with the disc rotatable in the XY plane) so as to contact the ramp. Discs are especially susceptible to this type of deflection when the disc drive incurs free topple drop shock while the disc is in the operating mode. The points of contact can shed off ramp materials that tend to deposit on the outer edge of the disc in the form of a unique signature or footprint. The resulting ramp debris has a high tendency of being caught under the head slider during loading and unloading operations, and result in media defects and further head disc interference. 
     The embodiments of the present invention have demonstrated that ramp disc contact can be eliminated or greatly mitigated.  FIG. 1  provides a top plan view of a data storage device  100  constructed in accordance with preferred embodiments of the present invention. The data storage device  100  is preferably characterized as a disc drive which magnetically stores digital data. 
     The disc drive assembly  100  includes a housing  102  which defines an internal environment for the drive. The housing  102  has a base deck  104  and a top cover  106  (shown partially cutaway). A spindle motor  108  supported within the housing  102  rotates a number of magnetic recording discs  110  at a constant, high speed. A rotary actuator  112  controllably moves a corresponding number of data transducing heads  114  across recording surfaces of the discs  110  through application of current to a coil  116  of a voice coil motor (VCM)  118 . 
     The high speed rotation of the discs  110  in the operational mode generates fluidic currents generally denoted by arrow  119 , and the heads  114  are aerodynamically supported over the recording surfaces by fluidic currents established by rotation of the discs  110 . It is contemplated that the disc drive assembly  100  can include one or more discs  110 , and one head  114  for each side of each disc. 
     A flex circuit assembly  120  provides electrical communication paths between the actuator  112  and a printed circuit board assembly (PCBA) mounted to the underside of the base deck  104 . When the disc drive assembly  100  is in a non-operating mode, the heads  114  are brought to rest onto a load/unload ramp  122  supported by the base plate  104  near the outermost diameters of the discs  110 ; a latch  124  secures the actuator  112  in a parked position on the load/unload ramp  122 . Fasteners (not shown) extend through the top cover  106  and into receiving apertures (not shown) in the base deck  104  to secure the top cover  106  thereto. 
     Ramp disc contact causing potential head disc interference related defects were studied in certain hard disc drives.  FIG. 2  shows a diagrammatical representation of a simulated test of the result of the disc drive assembly  100  being tumbled onto a hard surface. The disc drive assembly  100  is supported by a surface  130  on a corner  132  of the housing  102  and is inclined at a 60 degree angle. The purpose of the simulation was to duplicate ramp disc contact to determine its contributing factor. 
     From the position of the disc drive assembly  100  depicted in  FIG. 2 , a series of disc drives  100 , without the benefit of being equipped with the present invention, were topple dropped from rest at 60° and allowed to come to rest on the surface  130  multiple times on each of the x- and y-axes. It was determined that if the cumulative impact shock level experienced by each drive from such multiple drops exceeds about 200 g&#39;s, the resultant damage would adequately set a base line from which the present invention could be evaluated. 
     After the drives  100  were subjected to the multiple topple drop test, the drives were disassembled and discs were analyzed using a Candela® disc laser scanning machine for inspection of the defects. (Candela is a registered trademark of KLA-Tencor Technologies Corporation of Milpitas, Calif.) The scans showed ramp disc contact markings on the disc edges and several particle scratches. These and other defect signatures provided clear footprints as to the source of the defects, thus marking same with that reported as field failures. 
     To ensure that the ramp disc contact was the result of the shock imparted during the topple drop tests described above, other possible causes, such as manufacturing processes, were evaluated on identical drives not submitted to the topple drop tests. This evaluation showed that the defect signatures were different, verifying that the defect signatures from the topple drop tests could be relied upon as a baseline representing field reported defects from externally generated shocks. 
     With these results at hand, it was undertaken to design a disc snubber that would minimize disc deflection of the type that causes ramp disc contact. As depicted in  FIG. 3 , several snubber locations  140 A through  140 F were designated on the base deck  104  and disposed radially at the outer edges of the discs (the discs are removed in  FIG. 3 ). At each of these locations a snubber pad  142  was adhered to the base plate. Each of the snubber pads was made of FIPG (flow in place gasket) material, the thickness of which being that as necessary to provide a clearance gap of approximately 0.020 inch (this gap dimension will be determined by the clearance necessary for free rotary movement of the discs  110  while preventing disc ramp contact upon deflection of the discs  110  to the degree determined by the topple drop tests above). 
     FIPG material is readily available, lends itself to predictable manufacturing, and is thermally and chemically stable. Most importantly, because of the elasticity of FIPG material, it does not disintegrate easily when contacted by the spinning discs  110  upon deflection of same. One acceptable FIPG material is QAN TX-09 epoxy available from SJP Sealing Technology (S) Pte. Ltd of Singapore. The FIPG material, once dispensed in position, is oven air cured. 
     With the snubbers installed at the locations  140 A-F in  FIG. 3 , several of the disc drives  100  were assembled and those disc drives were subjected to the topple drop tests described above with respect to  FIG. 2 . After the drives  100  were subjected to the multiple topple drop test, the drives were disassembled and the discs were analyzed in the manner described above using the Candela® disc laser scanning machine for inspection of the defects. 
     These experiments showed that, when the disc drive assemblies  100  were equipped with the snubbers  142  and submitted to the 60 degree semi-constraint topple drop shock test depicted in  FIG. 2 , no evidence of ramp disk contact was found. These shock drop tests were repeated with various locations of multiple and single base plate mounted snubbers  142 , and it was found that adequate protection of the disc drive assembly  100  could be achieved using a single snubber  142  as shown in  FIG. 4 . Shown in this figure is the base plate  104  having formed thereon a single snubber  142  that is disposed at the outer edge of the disc  110  (not shown in  FIG. 4 ) and having an effective length to support the outer edge along about a 60 degree segment of the disc circumference. 
     The location of this 60 degree segment is not believed to be critical, and the location where the snubber  142  is to be installed can be selected from those physical locations on the base plate  104  where adequate space is available. In the disc drive assembly  100  as shown, the snubber  142  is conveniently located in a corner of the base plate  104  where a re-circulation filter will be located; in other disc drive layouts, this location may or may not be optimum. It should be noted that the present invention is not restricted to a single disc hard disc drive, as the deflection of the discs noted herein is that of the entire disc pack, since the discs are all mounted on the spindle motor and act like a homogenous body and deflect together. Thus, dampening deflection of the bottom disc is imparted to the entire disc pack. 
     The thickness dimension of the snubber  142  can readily be adjusted, and the thickness will usually be established at a dimension so that the desired gap will occur between the bottom disc and the top surface of the snubber  142  at the outer disc diameter near the load/unload ramp. 
       FIG. 5  is another view of the base plate  104  in which the snubber  142  is shown lifted above the surface of the base plate. A cavity track  148  has been formed in the base plate to form a retention track for the snubber  142 , which will be formed along the length of the cavity track  148 . With the lower portion of the snubber  142  filling the cavity track  148 , the snubber  142  will be more securely affixed to the base plate  104 . 
       FIG. 6  depicts the preferred embodiment of the present invention in which a test routine  150  is shown. The initial step  152  is to determine the types of disc defects that are being experienced and reported from field users of the disc drives. The next step  154  is to design a test that will replicate the defect history in a lab setting. This design phase will include analyzing test imparted defects to identify the defect signature and assure that it comports with the defect signatures of disc drives that are corrupted in field usage. Once this has been achieved, the next step  156  is to install a prospective protective snubber at a potential location that will prevent the defect. The test disc drive, at step  158 , is subjected to the test to determine whether the user reported defect has been prevented by the snubber. If no at  162 , step  158  is repeated with a snubber at another potential location, and steps  156  and  158  are repeated until at  162  the result is positive, that is, the user reported defect is prevented. 
     Once an acceptable location or locations have been determined by the test routine  150  of  FIG. 6 , various sizes of snubbers can be determined by repeating steps  154  through  158  until an optimum snubber is determined. 
     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 snubber assembly without departing from the spirit and scope of the present invention. 
     In addition, although the embodiments described herein are directed to the prevention of defects for a disc drive data storage device, it will be appreciated by those skilled in the art that the defect determination and prevention taught herein can be used for other types of data storage devices, including optical drives and magneto-optical drives, without departing from the spirit and scope of the claimed invention.