Abstract:
A disk clamp for clamping a plurality of disks within a disk drive has a single fastening hole located at its symmetrical center sized to pass the shaft of a screw having a head diameter larger than the fastening hole. The screw fastens the disk clamp to a motor hub supporting the plurality of disks. The disk clamp has a moat around the fastening hole, at a maximum diameter that is smaller than the head diameter of the head on the fastening screw. The moat may be circular, have spike trenches angled toward the fastening hole, or be spiral. The diameter of the spiral moat decreases in a clockwise or counterclockwise direction toward the fastening hole. The midsection of the disk which the screw head covers is biased at a negative angle toward the fastening hole forcing particles generated during assembly toward the fastening hole of the disk clamp.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to disk drives and more specifically, to a disk clamp for a disk drive that reduces debris migration onto the disk surface. 
     2. Description of Related Art 
     Work stations, personal computers and laptop computers require disk drives that provide a large amount of data storage within a minimal physical area. A disk drive typically includes one or more hard disks that are rotated at a constant high speed by a spindle motor. Generally, disk drives operate by positioning a transducer or read/write head over respective tracks on the disks. The information is written to and read from tracks on the disks through the use of an actuator assembly which rotates during a seek operation. The actuator is coupled to control electronics which control the positioning of the actuator and the read/write functions of the transducer. A typical actuator assembly includes a plurality of actuator arms which extend towards the disks with one or more flexures extending from each of the actuator arms. Mounted at the distal ends of each of the flexures is a head which acts as an air bearing enabling the head to fly in close proximity above the corresponding surface of the associated disk. The demand for increasing density of information stored on these disks is becoming greater and greater for a multitude of reasons. The increase of multi-user and multi-tasking operating system work stations which provide an operating environment requiring the transfer of large amounts of data to or from the hard disks, large application programs, the popularity of notebook and laptop computers and the continuing trend toward higher performance microprocessors all contribute to this end. The structural designs of these systems are also continually shrinking, requiring hard disk drives having high capacity storage capability while occupying a minimal amount of space within the system. 
     In order to accommodate these demands, there is a need for smaller hard disk drives which have increased storage capacity. To read this more densely stored information, engineers have decreased the gap fly height between the heads and the disks. Reducing the gap fly height leads to increased contact between a head and the data portion of the disk during operation of the disk drive. Nevertheless, there has been an industry wide push to reduce the height at which transducers are maintained over the disk surface without actually contacting the disk surface. 
     When a transducer flies over a rotating disk, the flying height tends to fluctuate slightly above and below a normal flying height because the disk surface itself is not flat. At lower flying heights the variation in the fly height may cause the transducer to contact the disk surface. This intermittent contact, if repeated, can damage the transducer or the disk and may cause drive failures. 
     In conventional disk drives, a stack of disks is provided on a cylindrical hub of a spindle motor. A disk clamp is provided on top of the stack of disks on the hub. The clamp has a larger radius than that of the hub so that the outer diameter of the clamp is in contact with the top disk. A plurality of screws, or a single screw, fit through holes located in the disk clamp. These screws (screw) are threaded into bores in the hub. When a screw is tightened, the force applied to the midsection of the disk clamp is transferred to the outer circumference of the disk clamp which contacts the disk surface. This force secures the disks to the spindle motor hub. The disks must be secured under considerable force in order to prevent any slippage of one or more disks in the presence of mechanical shocks. Even very slight slippage of a disk within a drive could result in mechanical misalignment of the transducer which could result in data transfer errors or failure. 
     The assembly of the disk clamp over the disk stack tends to generate minute particles which tend to disburse on the surface of the disks themselves. These small particles contribute to transducer contact with the disk surface, culminating in head crashes. The more fastening screws utilized to secure the disk clamp to the spindle motor, the more opportunity there is for the generation of these minute particles. 
     Accordingly, there is a need for a disk clamp that prevents dispersal of particles generated during assembly of the disk stack. The present invention provides a solution to this problem. 
     SUMMARY OF THE INVENTION 
     The generation of debris particles during assembly of a disk pack in a disk drive is considerably ameliorated by trapping these particles in a moat formed into the disk clamp surrounding the fastening hole. The moat is covered by the head of the screw fastening the disk clamp to the motor hub. The moat keeps the debris generated during torque-down of the screw on the inside of the moat, between the moat and fastening hole. Various moat designs have been found to be effective. Besides a circular moat, a spike trench moat having trenches angled toward the fastening hole, or a spiral moat are effective in retaining debris under the head of the screw. Another preferred method of retaining debris under the head of the fastening screw biases the area surrounding the fastening hole (the midsection) at to a negative angle towards the fastening hole of the disk clamp. This negative angle of the midsection forces particles generated during assembly inward, toward the fastening hole, trapping the particles under the head of the fastening screw. 
    
    
     
       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  shows a top cut-away view of an assembly of a disk drive; 
         FIG. 2  shows a top cut-away view of the disk stack in a disk drive; 
         FIG. 3  is a cross-section of the disk clamp and drive motor hub assembly; 
         FIG. 4  is a perspective of a prior art disk clamp; 
         FIG. 5  is a top view of a disk clamp at the fastening hole, illustrating one embodiment of the invention; 
         FIG. 6  is a cross-section of the disk clamp at the fastening hole attached to the motor hub by a fastening screw; 
         FIG. 7  is a cross-section expanded view of one side of the fastening screw holding down the disk clamp; 
         FIG. 8  is a top view illustration of a disk clamp according to another preferred embodiment; 
         FIG. 9  is a top view illustration of a disk clamp according to yet another preferred embodiment; 
         FIG. 10  is a top view illustration of yet another preferred embodiment; 
         FIG. 11  is a cross-section of a disk clamp attached to a spindle motor hub by a single screw; 
         FIG. 12  is a cross-section expanded view of a disk clamp attached to a motor hub by a single screw showing an alternate preferred embodiment of the disk clamp; and 
         FIG. 13  is a cross-section expanded view of a disk clamp of  FIG. 12  being attached to a motor hub by a single screw showing the contact area between the screw head and the disk clamp. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  represents a cut-away top view of a disk drive  11  having one or more hard disks  13  with each of the hard disks having information written in a series of data tracks  16  thereon. The disk drive  11  utilizes at least one transducer  15  for reading and writing information to the hard disk  13 . The transducer  15  may be a conventional conductive element or may be a magneto-resistive element, for example. The transducer  15  is connected to an actuator arm  17 . The movements of the actuator arm  17  are controlled by a voice coil motor  21  to pivot about a pivot junction  19 . A control circuitry  23  is used to control the operation of the actuator arm  17  and other components (not shown) within the disk drive  11 . 
     During a seek operation, for example, the track position of the head  15  is moved across the surface of the disk  13 . The head  15  is connected to the actuator arm  17  by a flexure  51 . 
     The hard disk  13  may be a single disk or a stack of disks. The hard disk  13  is connected to a spindle motor (not shown) by a disk clamp  25 . According to the present invention, the disk clamp attaches the hard disk  13  to the hub of the spindle motor by a screw  29 . A plurality of holes  27  are located in the disk clamp  25  circumferentially spaced about the fastening screw  29 . 
     The disk clamp  25  affixes the hard disk  13  to the hub of the motor by the force exerted by the fastening screw  29 . During operation of the disk drive  11 , the hard disk  13  is rotated by the motor, and the actuator arm  17  moves the transducer  15  across the surface of the hard disk  13  transferring data between the transducer  15  and the hard disk  13 . 
     Referring to  FIGS. 2 ,  3  and  4 , a spindle motor (not shown) carries the generally cylindrical hub  35  which has a cylindrical bottom flange  39  and a cylindrical head  37  extending upward from the flange  39 . The head  37  defines a centrally located fastener bore  30 . The flange  39 , hub  35 , head  37  and fastener bore  30  are all preferably substantially concentric. It should be noted, however, that the hub may have many different configurations in accordance with the present invention. For example, the hub can include several circumferentially spaced fastener bores rather than a single centrally located fastener bore  30 . The disk pack assembly illustrated for the disk  13  includes an annular spacer  41  that is seated on the hub  35  so that it extends around the head  37  and rests on the flange  39 . It should be kept in mind that the present invention can be used without the spacer  41 . Also in an embodiment where the disk drive includes multiple disks  13 , a plurality of spacers  41  are used to separate each of the disks  13 . The disk  13  is in turn seated on the hub  35  so that it extends about the hub head  37  and rests on the spacer  41 . The disk  13  has a lower data surface  33  and an upper data surface  31 . 
     The disk pack assembly shown in  FIG. 3  includes a disk clamp  25 . Disk clamp  25  is shown separately in  FIG. 4 . Disk clamp  25  is centrally located on the upper surface  31  of the disk  13 . A rim  49  forms the periphery or outer diameter of the disk clamp  25 . A concentrically located fastening hole  45  in the disk clamp defines a centrally located space for insertion of a fastening screw  29 . 
     It should be kept in mind that multiple circumferentially spaced fastener holes  45  may be utilized to match up with multiple fastener bores  30  in the hub head  37 . The disk clamp  25  is preferably made of stainless steel, although it could be made of aluminum or materials or alloys having similar desired characteristics. 
     Fastening screw  29  extends through the fastener hole  45  of the disk clamp  25  and into the fastener bore  30  in the hub  35 . The fastening screw  29  engages the hub  35  and draws the central midsection  43  of the disk clamp  25  downward beyond its normal resting position, thereby creating stress and a constant downward pressure at the rim  49 . The rim  49  in turn applies a downward pressure on the upper surface  31  of disk  13 , thereby holding the disk  13  securely in place on the hub  35 . 
       FIG. 4  illustrates a prior art disk clamp  25 . A fastening hole  45  is centrally located within the disk clamp  25  which is preferably formed as a circular member. A plurality of through holes  27  are circumferentially located about the centrally located fastening hole  45  in the main portion of the disk clamp  25 . A midsection  43  surrounds the fastening hole  45  inside the balance holes  27 . Tooling holes  51 ,  53  are located in the body of the disk clamp between the midsection and outer diameter of the disk clamp. These holes may be utilized by a spanner type tool that is inserted during assembly to keep the disk clamp and spindle motor from turning as the screw attaching the disk clamp  25  is tightened. These holes are also utilized as a reference marker for locating a reference for placing weights in the weight holes  27 , to balance the disk pack after assembly. 
       FIG. 5  is a top view of a disk clamp according to a preferred embodiment of the present invention.  FIG. 5  shows the midsection area of the disk clamp  25 . Surrounding the fastening hole  45  is a moat  55  that may be etched, laser cut, or metal worked (coined) into the disk clamp. 
       FIG. 6  is a cross-sectional view of the disk clamp  25  of  FIG. 5  being held to the head  37  of the hub  39  (not shown). The fastening screw  29  has an internal fastening slot  57  which may be hexagonal, for example. The head on screw  29  overlaps the edges of the disk clamp  25  at the fastening hole  45 . Circumferentially located around the fastening hole  45  is the moat  55 . The moat  55  is located underneath the head of fastening screw  29  when the disk clamp is being held down by the screw  29 . 
       FIG. 7  illustrates more clearly the moat  55  located under the head of fastening screw  29  when the screw  29  is threaded into the hub  37 . 
     The moat  55  has a width measured at its mouth and a depth measured from the surface of disk clamp  25  to the deepest part of the moat. The moat preferably ranges in depth from 0.00068 inches to 0.00184 inches. The moat preferably varies in width from 0.00200 inches to 0.00427 inches. 
     The size of the moat must not be so large that it structurally impairs the disk clamp at this fastening point. Yet, the moat should be large enough to perform its function of maintaining debris formed as a result of tightening the screw  29  down over the surface of the disk clamp  25  in the area of the fastening hole  45  between the fastening hole and the moat trapped under the head of the bolt  29 . 
     Considerable experimentation by the inventors with the disk clamp utilizing the moat as described above, surprisingly revealed that debris within the disk drive on the surface of the hard disks was reduced while debris between the moat  35  and the edge of the disk clamp hole  45  was increased. 
       FIGS. 8 and 9  illustrate alternative embodiments of the moat described above. Rather than a continuous moat circumferentially surrounding a fastening hole, a plurality of trenches  65 ,  75  angled towards the center of the fastening hole surround the fastening hole  45 . Each of the trenches  65  are angled towards the center of the fastening hole so that particles that are being generated by tightening of the screw onto the disk clamp  60  are moved inward and fall into one of the multiple moats  65 . The angle at which the trenches  65 ,  75  are placed may vary. The trenches may be curved in a clockwise direction or counterclockwise direction, depending on the threading direction of the screw so that the tightening of the screw is in a direction that moves particles being generated into the trenches  65 ,  75 . 
       FIG. 9  shows a disk clamp  71  wherein the trenches  75  have smooth tops  73 . These smooth tops eliminate scraping on the bottom of the screw head, thereby reducing the number of particles generated. The number of trenches  65 ,  75  used in the embodiments shown in  FIGS. 8 and 9  preferably vary between 4 to 12, depending on the material used for the disk clamp and the tightening force required. The depth and width of the trenches  65 ,  75  of  FIGS. 8 and 9  are comparable in size to the circumferential trench  55  shown in  FIGS. 5 and 6 . 
     Referring now to  FIG. 10 , a disk clamp  79  is shown having a fastening hole  81  with a spiral moat  83  surrounding the fastening hole  81 . The spiral moat does not have a constant radial distance from center, as does the circumferential moat of  FIG. 5 . Rather, it decreases to the center, in a clockwise or counterclockwise direction, depending on the direction the fastening screw threads to tighten down the disk clamp. 
     The diameter of the outermost portion of the spiral moat, the spike trenches, and the circumferential moat, described above, is always less than the head diameter of the fastening screw. 
       FIGS. 11 ,  12  and  13  illustrate an alternate embodiment of the present invention which is also designed to maintain particles generated during assembly trapped under the head of the fastening screw  29 . As shown in  FIG. 11 , a disk clamp  25  having a fastening hole  45  within which is located a fastening screw  29  that threads into the hub  35  by way of a fastener bore  30  in hub  35 . The disk clamp  25  has a midsection  87  surrounding the fastening hole  45 . 
     Standard practice in the prior art is to bias this midsection  87  so that when the head of the fastening screw  29  compresses the midsection  87  of the disk clamp to the hub  35 , the midsection  87  will flatten. 
     Offset angles are also used in other parts of a disk clamp. As taught in U.S. Pat. No. 7,209,320, the outside diameter of the disk clamp, at the disk to hub contact area has an offset angle that slopes downward from an inside to outside of the disk clamp contact point. The application of pressure during clamping will thus provide a more flat uniform contact area along the clamp surface. The prior art does not contemplate biasing the midsection of the disk clamp as proposed by the present invention or even recognize the reasons for doing so. 
     Contrary to this general wisdom, the present invention biases the midsection  87  around fastening hole  45  of the disk clamp  25  in a negative downward direction between 0 and −3.5 degrees. This negative angle is more clearly shown in  FIGS. 12 and 13 . The midsection  87  of the clamping disk  25  is angled downward when it is fastened by the head of the fastening screw  29 . By biasing the midsection downward in this manner, the particles generated during threading of the screw  29  into the hub  35  are forced inward, towards the fastening hole  45 . The inventors believe that the negative angle contributes to this movement of particles. Initial contact between the head of fastening screw  29  and the midsection  87  of the disk clamp is at the outside diameter of the screw head, cutting off any movement of particles past this initial contact point. 
     Experimentation by the inventors has found that considerably more particles are trapped under the head of the fastening screw  29  when the midsection  87  of the disk clamp is biased at a negative angle than as compared to a disk clamp that is biased positively in an upward direction, or a disk clamp that is flat. 
     It should be understood that the foregoing disclosure describes only the preferred embodiments of the invention. Various modifications may be made therein without departing from the spirit and scope of the invention as set forth in the claims to provide a disk clamp that traps debris particles generated during assembly of the disk pack in a disk drive. The particles are trapped underneath the head of the fastening screw.