Abstract:
A spindle clamp for supporting a disk includes a radial control member that is in contact with an opening through a jaw and that has a contour such that radial expansion of the jaw is induced during initial movement of the jaw toward a registration surface for seating the disk. However, the contour is such that further movement of the jaw toward the registration surface is an axial motion, rather than a combination of axial and radial motion. In one preferred embodiment, the jaw is unitary, but is configured to enable the radial expansion while having sufficient rigidity to reliably clamp a data disk seating on the registration surface. The jaw may include a lip which is configured to contact the major surface of the disk opposite to its contact with the registration surface.

Description:
TECHNICAL FIELD 
     The invention relates generally to spindle clamps for supporting and releasing a data disk and more particularly to securing a rigid disk for rotation about an axis. 
     BACKGROUND ART 
     Magnetic and optical data disks are used to store a large quantity of data. The information is stored on at least one major planar surface of the disk, allowing the information to be accessed when the disk is secured to a spindle clamp for high-speed rotation of the disk. Spindle clamps are also referred to as “disk clamps” and “disk chucks.” 
     In the quality control testing as well as the manufacturing of magnetic and optical data disks, rapid robotic removal of a tested disk from a spindle is followed by replacement with a disk to be tested or processed. A suitable spindle is described in U.S. Pat. No. 4,755,981 to Ekhoff. The spindle clamp of Ekhoff includes movable jaw segments which slide along a centrally positioned cone to expand the arrangement of jaw segments when a disk is to be clamped and to contract the arrangement when a disk is to be released. Thus, a collet-type mechanism is used to secure the disk at its central opening. The function of the spindle clamp is to secure the disk in a tightly concentric manner, while introducing minimal distortion or waviness to the precision planar surfaces of the disk. Because of the high volume of disks involved and the short period of processing time, it is important that this clamping/unclamping function occurs reliably and without any required secondary actions, such as attaching a removable cap with a screw. In the device described in the Ekhoff patent, the primary holding force is applied to the disk in a radial fashion as the three jaw segments slide downwardly along the cone under the influence of a spring located on the underside of the clamp. The movement of the jaw segments along the cone is controlled by connection to a cap, which consists of an axially extending post having an upper head. The stroke motion is applied to the post either pneumatically or mechanically. Slippage of the disk is controlled by the force that is applied as the jaw segments are wedged between the inside circumference of the disk and the cone along which the jaw segments slide. 
     The ability of a spindle clamp to secure a storage disk is limited by the processing tolerance to distortion introduced into the disk, as well as by the point of slippage of the jaw segments against the inner cone. This point of slippage is primarily affected by the level of lubrication which is introduced in order to control particle generation that would occur through wear processes. Another concern is that spindle clamps used in quality control and other such processing should be designed to handle disks with different configurations and thicknesses, without introducing distortions due to variations in contact between the jaw and the disk inside diameter and the resulting load concentrations. 
     SUMMARY OF THE INVENTION 
     A spindle clamp for supporting a disk in accordance with the invention includes a radial control member in contact with an axial opening of a jaw, with the radial control member having a contour such that radial expansion of the jaw is induced during initial movement of the jaw toward a registration surface for seating the disk, but further radial expansion is avoided in a final portion of the movement toward the registration surface. In one preferred embodiment, the jaw is “unitary,” but enables radial expansion while having sufficient rigidity to reliably clamp a data disk, such as a conventional magnetic or optical disk. While the jaw is unitary, it may be comprised of a number of portions which are connected to allow the radial expansion. As used herein, the term “unitary” is defined as designating a one-piece structure. Also in one preferred embodiment, the jaw includes a lip which is configured to contact the major planar surface of the disk opposite to the contact with the registration surface, thereby clamping the disk. 
     The jaw may be connected to a cap which is dimensioned to guide the disk into the desired orientation on the registration surface. The cap is coaxial to the unitary jaw and may include an axially symmetric arrangement of fingers. Thus, the spindle clamp may operate in either a vertical or horizontal spin axis. In an application having a vertical spin axis, the arrangement of fingers and gravitational force cooperate to ensure that the disk is in a desired orientation on the registration surface. On the other hand, in an application utilizing a horizontal spin axis, the compound motion of the jaw cooperates with the arrangement of fingers upon which the disk inside diameter rests. The unitary jaw includes slots which are aligned with the fingers to allow the jaw to expand and contract radially between a dimension exceeding a comparable dimension of the fingers and a dimension less than that of the fingers. 
     In order to control potential generation of particles which may adversely affect the data disk, the jaw is preferably formed of a hard plastic material, such as the engineering plastic PEEK (Polyaryletheretherketone). By forming the jaw as an integral structure capable of expanding radially but remaining rigid, dimensional stability is maintained in the radial and axial directions. The individual working elements of the jaw cannot be taken out of sequence or otherwise compromised. In a preferred embodiment, an elastomeric O-ring acts to bias the jaw into its collapsed condition. This ensures that the axial opening of the jaw remains in contact with the radial control member. 
     In one preferred embodiment of the radial control member, its contour transitions from a conical surface to a cylindrical surface. During a clamping operation, the conical surface controls the initial operation of the jaw, which moves both axially and radially. For embodiments that include the lip, the radial expansion of the jaw places the lip beyond the inside diameter of the disk. Prior to the lip reaching the surface of the disk, control of the operation of the jaw is transitioned to the cylindrical surface, such that the jaw moves only in an axial direction to a clamping position in which the disk is secured in position. The invention accommodates various disk thicknesses with various disk chamfer configurations along the inside diameter, without compromise in performance. Whether actuated pneumatically or mechanically, the disk-release operation causes the jaw to move initially in an axial direction until a dimension somewhat greater than the greatest anticipated disk thickness, whereafter the conical surface allows the jaw to retract inside the confines of the cap. Thus, a seated disk can be removed and a second disk may be installed for subsequent disk processing. The cap preferably has a smooth lead-in which facilitates the disk placement by automation to the guide fingers of the cap. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a spindle clamp in accordance with one embodiment of the invention. 
         FIG. 2  is a perspective view of the assembled spindle clamp of  FIG. 1 . 
         FIG. 3  is a side cutaway view of the spindle clamp of  FIG. 1  shown in a clamped position. 
         FIG. 4  is a side view of the spindle clamp of  FIG. 3  shown in its unclamped position. 
         FIG. 5  is a perspective view of a unitary jaw in accordance with one embodiment of the invention. 
         FIG. 6  is a top view of the unitary jaw of  FIG. 5 . 
         FIG. 7  is a sectional view of the jaw of  FIG. 6 , taken along lines  7 - 7 . 
         FIG. 8  is a perspective view of the cap of  FIG. 1 . 
         FIG. 9  is a sectional view of the cap of  FIG. 8 . 
         FIGS. 10 and 11  illustrate an alternative embodiment of a unitary jaw in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1 and 2 , one embodiment of spindle clamp  10  in accordance with the invention is shown as including a rotational clamp body  12  having an upper registration surface  14  for seating a data disk. The clamp body may be mounted to an air-bearing spindle using the standard technique of inserting screws into an arrangement of screw holes  16 . The bottom of a clamp body is perpendicular to the axis of rotation of the air-bearing spindle and is accurate to at least 0.25 micron. 
     The lower portion of the clamp body  12  is formed of a metal, typically stainless steel or aluminum to which is attached a ceramic carbide portion that includes the registration surface  14 . The ceramic carbide registration surface is ground parallel to the bottom surface of the clamp body to within 0.25 micron, so as to control any possibility of axial run out of the disk while being processed. 
     Extending through the clamp body  12  is an axial shaft  18  which is internally threaded at both its upper end and its lower end. Referring now to  FIGS. 1-3 , at the lower end of the shaft, a screw  20  passes through a piston  22  and is threaded into the shaft. The piston is biased downwardly into the position shown in  FIG. 3  by a spring  24 . The piston acts as a spring carrier and locator, so that the spring exerts downward force sufficient to physically clamp a disk  28  against the registration surface  14 . 
     While the shaft  18  is biased by the spring  24  in the downward direction as viewed in  FIGS. 1-3 , the bias can be overcome by activation of a rubber diaphragm  26 . Thus, the piston may be manipulated pneumatically. Pressure applied by the diaphragm acts directly on the piston  22 . The piston is pushed upwardly ( FIG. 4 ) into dimensionally corresponding grooves within the interior of the clamp body to release the disk and allow insertion of a second disk before the diaphragm is deactivated. At the upper end of the axial shaft  18 , a unitary jaw  30  is captured between a C-clip  32  and a cap  34 . A screw  36  secures the cap and jaw to the shaft. Thus, manipulation of the piston  22  at the bottom end of the shaft moves the jaw and cap upwardly and downwardly. While the manipulation of the piston is described as being pneumatic, mechanical approaches may be substituted without diverging from the invention. 
     As will be described in detail below, the cap  34  is a unitary member in at least one preferred embodiment, but nevertheless allows radial expansion and retraction. From the clamping position shown in  FIG. 3 , the upward movement of the various components relative to the clamp body  12  is not accompanied by radial expansion or contraction of the jaw. However, in a second stage of operation of the jaw, retraction occurs. After the shaft  18  has moved upwardly by a dimension to ensure that the jaw is further away from the registration surface  14  then a distance greater than the thickest anticipated disk, further upward movement of the shaft triggers a compound operation in which the jaw moves upwardly and retracts inwardly. Preferably, the inward retraction is such that the radial dimension of the jaw is no greater than that of downwardly depending fingers  38  ( FIGS. 1 ,  8 , and  9 ) of the cap  34 . This allows the disk  28  to be removed and allows a substitute disk to be installed for disk processing. 
     The cap  34  includes a smooth lead-in surface  40  to facilitate disk placement by automation. Moreover, the combination of the fingers  38  is dimensioned to form a smooth guiding feature, so that the disk can be placed reliably on or near the registration surface  14 , by a robot or other feed system. In the unclamped position of  FIG. 4 , two of the fingers  38  of the cap are represented in phantom. The outer surfaces of the fingers are curved and the curvatures are dimensioned both individually and collectively to smoothly contact the inside diameter of a disk  28  as the disk is seated into the position shown in  FIG. 4 . 
     The stages of operation of the jaw  30  are determined by the contour of a “radial control member”  42  that projects upwardly from the clamp body  12 . As best seen in  FIG. 1 , this radial control member includes an upper truncated conical surface  44  and a lower cylindrical surface  46 . With respect to both surfaces, the slope determines the radial expansion and retraction of the jaw  30 , so that the cylindrical surface is associated with an absence of expansion or contraction of the jaw. While the cylindrical and sloped surfaces provide benefits relative to other configurations which dictate the compound motions of the jaw, other possibilities may be available. 
       FIG. 3  is the clamping position of the jaw  30 , since the jaw is fully lowered to the position in which contact is made with the disk. In comparison,  FIG. 4  shows the unclamped position in which the disk is available for removal. 
     One embodiment of the unitary jaw is shown in more detail in  FIGS. 5 ,  6 , and  7 . The jaw is manufactured of a durable engineering plastic (such as PEEK) compatible with end-user process acceptability. While the jaw is cylindrical in nature, it is slotted in such a way that radial expansion and contraction are allowed. A first series of slots extend outwardly from the inside diameter of the jaw, but do not reach the outside diameter. In comparison, a second series of slots extend from the outside diameter, but flexible integral connections  52  maintain the single-piece integrity of the material. Furthermore, there is an angled slot  54  ( FIG. 7 ) into which an elastomeric O-ring  56  is inserted, so as to act as a hoop spring. The use of the O-ring causes the jaw to collapse or reduce its outside diameter when the jaw is allowed to relax. In use, the radial size of the jaw is determined by its contact with the radial control member  42  of  FIGS. 1 ,  3 , and  4 . 
     In addition to the first and second series of slots  48  and  50  of the jaw  30 , there is a series of radial slots  58  extending from the outside diameter of the jaw to allow the passage of the fingers  38  of the cap  34  of  FIGS. 8 and 9 . The number of slots  58  corresponds to the number of fingers. In the illustrated embodiment, there are six slots and six fingers. The provision of these slots  58  allows the jaw to collapse to a state in which the radial dimension of the jaw does not exceed the radial dimension defined by the arrangement of fingers, so that the fingers may be used to guide disks onto and off the spindle clamp when the jaw is in its collapsed state. 
     Another embodiment of the unitary jaw is shown in  FIGS. 10 and 11 . Again, an elastomeric O-ring  56  biases the jaw into its collapsed condition, but strategically located slots allow expansion and retraction. Functionally equivalent features of this embodiment and the previously described embodiment have shared reference numerals. 
     Another significant feature of the jaw  30  is the lip  60  which is best seen in  FIG. 7 . The function of the lip is to apply pressure to the surface of the disk being clamped.  FIG. 3  shows the disk  28  captured between the lower surface of the lip  60  and the registration surface  14  of the clamp body  12 . As the jaw  30  expands during the initial operation of downward movement of the jaw along a radial control member  42 , the lip extends beyond the fingers of the cap  34 . After the jaw reaches its transition position, the motion of the lip is purely axial until contact is made with the disk. 
     The cap  34  is best seen in  FIGS. 1 ,  8 , and  9 . The cap is directly attached to the axial shaft  18  which is connected to the piston  22  so as to act in unison under the influence of either the spring  24  or pneumatic pressure applied via the diaphragm  26 . The jaw  30  is sandwiched between the C-clip  32  and the underside of the cap  34 . As a result of connection to the cap and the inclusion of the slots  58  that accommodate the fingers  38  of the cap, the jaw will move axially with the cap but is free to move radially. When the spindle clamp is in a clamping condition with respect to a disk, a pneumatic unclamp command causes the cap to move upwardly, causing the jaw to move axially. Initially, the jaw is in contact with the cylindrical surface  46 , so that motion of the jaw is restricted to axial movement. After a minimal movement upward, equal or slightly greater than the distance necessary to accommodate the thickest disk anticipated to be clamped, the jaw reaches the transition position of  FIG. 4  and starts to move inwardly as further axial movement occurs. When the outside diameter of the lip is less than the inside diameter of the disk, the disk can be removed. 
     A subsequent disk can then be inserted onto the spindle clamp  10 . The lead-in surface  40  ( FIG. 3 ) of the cap accommodates robotic placement of the disk. Additionally, the spacing of the fingers  38  and the curvature of each finger are designed to properly position the disk. The presence of the fingers is particularly significant where the spindle clamp is operated with the spin access other than a vertical spin access. For example, in a horizontal application, the disk inside diameter rests upon the curved surfaces of the fingers, so that the disk is properly positioned when the jaw is initiated into its compound motions. After the initial radial expansion, the final motion of the jaw is purely axial, allowing the lip  60  of the jaw to clamp the disk in position against the registration surface  14 . 
     While selected embodiments of the axial force spindle clamp are illustrated, other embodiments are available. For example, the actuation of the motion may be mechanical rather than pneumatic. Also, the jaw  30  may be biased into a release condition, rather than the clamping position accomplished by the spring  24 . The spindle clamp may be used with various data disks, including magnetic disks and optical disks.