A MECHANISM FOR CLAMPING AND SPINNING A FLEXIBLE DISK

Abstract: A mechanism for clamping and spinning a flexible disk comprising a spindle (14) and a collet (16). The spindle (14) includes a guide hub (22) supported by two ball bearings (26) and (28) mounted on a fixed shaft (42). The guide hub (22) is a hollow cylinder and is rotated by a belt (92) driven by an electric motor. A precision bore (34), equal in diameter to the nominal diameter of the center hole in the flexible disk, is provided in the guide hub (22) as a reference surface for positioning the disk, and a surface (58) perpendicular to the axis of the spindle (14) is provided for clamping the disk. The collet (16) comprises two interlocking molded plastic parts, a finger ring (72) and a clamp hub (74), that are rotateable attached to a guide arm (20). The finger ring (72) includes several radially moveable fingers which form a conical camming surface (103) with a maximum diameter slightly larger than that of the guide hub bore. A surface (108) for clamping the flexible disk is provided on the clamp hub. An O-ring (76) is positioned between the finger and the clamp hub to provide a compliant stop for inward movement of the fingers.

Description: Specification - A MECHANISM FOR CLAMPING AND SPINNING A FLEXIBLE DISK BACKGROUND OF THE INVENTION Field of the Invention The present invention relates broadly to mag¬ netic recording/playback equipment and relates more specifically to an improved flexible disk drive including a mechanism for positioning, clamping, and spinning a flexible disk. Flexible disk recording media, or floppy disks as they are commonly known, are thin cir¬ cular disks of a plastic material such as polyes- ter coated with a magnetic material and are used for the storage of digital data in the form of magnetic patterns. The flexible disk is enclosed in a protective envelope with access holes for spinning the disk and for accessing the magnetic surface. In operation, the flexible disk is clamped to a rotating hub or spindle by a clam¬ ping mechanism and is rotated at a constant speed. Digital data is recorded on the flexible disk in concentric recording tracts by posi- SUBSTITUTE SHEET tio'ning a read/write head in contact with the spinning magnetic surface at the appropriate radial location and by electromagnetically exci¬ ting the write windings of the head thereby aligning the magnetic particles in the surface coating in patterns corresponding to the digital data. Playback of recorded data is accomplished by sensing the electromagnetic response of the read windings of the head. A trend toward higher data storage sensity has necessitated increasingly tighter tolerances on head positioning accuracy as well as recording track concentricity to allow closer intertrack spacing and, hence, more data storage per flexi- ble disk. The positioning of the recording tracks on a flexible disk are radially referenced to a high precision hole and the axis of the spinning mechanism must coincide. If not coinci¬ dent, the read/write head may access portions of several adjacent recording tracks as they oscillage by the head. Therefore, the proper registration and positioning of the flexible disk by the clamping mechanism is critical to reliable data storage. Clamping and spinning mechanisms used on disk drives of this type act to accurately center the TE SHEET flexible disk and to clamp it to a rotating hub or spindle. since flexible disks are removeable, a clamping mechanismd must be capable of unclamp- ing a disk to- allow removal, then centering and clamping a newly inserted disk. The rotating hub or spindle normally rotates continuously. The clamping and spinning mechanism must accelerate a newly inserted flexible disk to the rotational velocity of the hub or spindle prior to clamping it to the hub or spindle. Accordingly, the rota- tional inertia of the clamping and spinning mech¬ anism and the process by which it accelerates the flexible disk are important. The clamping and spinning mechanism must also precisely center the flexible disk with respect to the rotational axis of the hub or spindle. Although the center holes of flexible disks are precisely fabricated, vari¬ ations in the hole diameters may exist due to the thermal expansion characteristics of the plastic disk material. These variations are of such a magnitude that they must be considered and com¬ pensated for in disk drives with close intertrack spacing. Consequently, the clamping and spinning mechanism must provide for accurate centering of flexible disks having a range of center hole di- ameters. SUBSTITUTE SHEET Description of the Prior Art One type of clamping and spinning mechanism disclosed in the prior art included a conical surface portion of a rotating spindle and an annular array of fingers that pushed the flexible disk axially along the conical surface and over an edge. Once past the edge, the flexible disk was centered by a cylinderical surface and clamped to a radial surface by the fingers. Draw- backs to this approach included the precision machining required and the lack of compensation for varying center hold diameters. Examples of this design are found in U> S> Patent 3,898,814 issued Augsut 12, 1975 to Albert S. Chou, Yang Hu Tong, Harold C. Medley,and Warren C. Dalziel entitled "Mechanisms for Claming and Driving a Flexible disc", and in U. S. Patent 4,077,236 issued March 7, 1978 to Warren L. Dalziel enti¬ tled "Apparatus Having Inwardly Biased Fingers Hingedly Attached to a Hub for Clamping and Dri¬ ving a Flexible Disc." A variation of the above described clamping and spinning mechanism util¬ ized a hub with a bore concentric to the hub axis and an axially moveable cone and cylinder for centering a flexible disk. This mechanism had no SUBSTITUTE SHEET provision for gently accelerating the disk to speed thus aldlowing scuffing of the disk. It additionally suffered from the drawbacks of the previously described clamping mechanisms. An example of this design may be found in U. S. Pat¬ ent 3,678,481 issued July 18, 1972k to Warren L. Dalziel, Jay B. Nilson, and Donald L. Wartner entitled "Data Storage Apparatus Employing a Single Magnetic Disk." Other examples of prior art clamping and spinning mechanisms are found in U> S> Patent 3,609,722 issued September 28, 1971 to George E. Zenzefilis entitled "Center Sealing Data Disc Cassette and Processing Machine" and U. S. Patent 3,936,879 issued February 3, 1976 to Kenneth Allan Gustafson entitled "Cartridge Type Plaint (sic) Disc Apparatus." What is needed, therefore, is a mechanism for use with a disk drive that precisely positions and spins a flexible disk. What is also needed is a mechanism that precisely centers flexible disks having center hole diameters with standard tolerances. What is additionally needed is a mechanism for clamping and spinning a flexible disk that gradually accelerates the disk to operating speed to minimize damage to the disk. What is further needed is a mechanism that accur- SUBSTITUTE SHEET ately positions and spins a flexible disk while minimizing the need for precise and costly machined parts. SUMMARY OF THE PRESENT INVENTION A primary object of the present invention is to provide a mechanism for clamping and spinning a flexible disk which is capable of providing accurate alignment of the disk with respect to the spin axis. Another object of the present invention is to provide a mechanism for sequentially positioning a flexible disk with respect to a rotating spindle then accelerating and clamping the disk to the spindle. A further object of the present invention is to provide a collet with low rotational inertia for centering an accelerating a flexible disk for clamping to a rotating spindle. An additional object of the present invention is to provide a collet fabricated by the process of plastic molding. Still another object of the present invention is to provide a collet assembly that snaps to¬ gether. These and other objects, which will herein- SUBSTITUTE SHEET after become apparent, are accomplished in ac¬ cordance with the illustrated preferred embodi¬ ment of the present invention by providing a mechanism, utilized with a disk drive, for clamp- ing and spinning a flexible disk comprising a spindle and a collet. The spindle includes a guide hub supported by two ball bearings mounted on a fixed shaft that is attached to the frame of the disk drive. The guide hub is a hollow cylin- 0 der and is driven in rotation by an electric motor through a belt drive. A precision bore equal in diameter to the nominal diameter of the center hole in the flexible disk, is provided in the guide hub as a reference .surface for posi- 5 tioning the disk, and a surface perpendicular to the axis of the spindle is provided for clamping the disk. The collet comprises two interlocking molded plastic parts, a finger ring and a clamp hub, that are rotatebly attached to a guide arm by a ball bearing and a shoulder screw. The finger ring includes several radially moveable fingers which form a concical camming surface with a maximum diameter slightly larger than that of the guide hub bore. A surface for clamping the flexible disk is provided on the clamp hub. • An O-ring is positioned between the finger ring SUBSTITUTE SHEET OMPI and the clamp hub to provide a compliant stop for inward movement of the fingers. In operation, the guide arm moves the collet toward the rotating spindle and into contact ini- tially with the center hole of the flexible. As the collet and flexible disk continue to move toward the rotating spindle, the disk is centered on the conical camming surface of the finger ring. Contact between the conical camming surface and the front edge of the guide hub bore as the collet mates with the hub causes the fingers of the collet to radially retract as the collet and flexible disk are acceleraterd by the rotating spindle. Further movement of the collet toward the rotating spindle clamps the flexible disk between the clamp hub and the guide hub. One advantage of the present invention is that it provides a collet with low rotational inertia that cooperates with a rotating spindle for accurately positioning and spinning a flex¬ ible disk. An additional advantage of the present invention is that it provides a mechanism for clamping and spinning a flexible disk that is low in cost and easy to assemble. Other objects and advantages of the present invention will be apparent to those skilled in SUBSTITUTE SHEET the art after having read the following detailed description of the preferred embodiment with ref¬ erence to the several figures of the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an exploded perspective view of a clamping and spinning mechanism, according to the present invention, used for centering, clamping, and rotating a flexible disk. Figure 2 is a sectional view of the clamping and spinning mechanism of Figure 1, taken along the line 2, 3-2,3 of Figure 1, illustrating the relative positioning of the elements of the clam¬ ping and spinning mechanism when in a disk load¬ ing position. Figure 3 is a sectional view of the clamping and spinning mechanism of Figure 1, taken along the line 2,3-2,3 of Figure 1, illustrating the relative positioning of the elements of the clam¬ ping and spinning mechanism when in a disk clamp¬ ing position. DESCRIPTION OF THE PREFERRED EMBODIMENT In reference now to Figure 1, there is shown a mechanism 10 for clamping and spinning a flex¬ ible disk 12 (shown in Figures 2 and 3) com¬ prising a spindle 14 and a collet 16. In general, the collet 16 acts to position and clamp the SUBSTITUTE SHEET O flexible disk 12 to the spindle 14 which rotates to spin the disk. A disk drive frame 18 provides an attachment point for the spindle 14. A swing arm 20, pivotably attached to the disk drive frame 18, provides a corresponding attachment point for the collet 16. Specifically, the spindle 14 comprises a guide hub 22 and its mounting structure and also comprises means for rotating the guide hub about a spindle axis 24. The means for rotating the guide hub 22 will later be described in detail. The guide hub 22 is free to rotate about the spindle axis 24 on two hub ball bearings 26 and 28. Two outer races 30 and 32 of the hub ball bearings 26 and 28 are pressed into one end of the cylindrical guide hub 22 in a cylindrical bore 34 and are separated by a spacer 36. Two inner races 38 and 40 of the hub ball bearings 26 and 28 are laterally positioned by a fixed shaft 42 that is pressed into a mounting hole 44 through a boss 46 on the surface of the disk drive frame 18. The inner ball bearing races 38 and 40 are axially captured betwee nthe boss 46 and a washer 48 that is secured to the end of the fixed shaft 42 by a screw 50 that passes through a clearance hole 52 in the washer and into a tapped SUBSTITUTE SHEET hole 54 in the fixed shaft. The axis of the guide hub 22, the ball bearings 26 and 28 and the fixed shaft 42 are all coincident with the spindle axis 24. Thus the guide hub 22, with its cylindrical bore 34 and a cylindrical exterior surface 56, is adapted for rotation about the spindle axis 24 with the bore and the exterior surface forming surfaces concentric to the spindle axis. A first disk clamping surface 58, perpendicular to the spindle axis 24, is formed on the end of the guide hub 22 away from the ball bearings 26 and 28. Its use will be described later. The collet 16 includes a pin 60 that extends through a mounting hole 62, washer 61 and snap- ring 63, and attaches a collet ball bearing 64 and a compression coil spring 66 to the swing arm 20. The compression coil spring 66 biases the collet ball bearing 64 toward a head 68 of the pin 60. By compressing the coil spring 66, the coil spring 66,the collet ball bearing can move axially along a collet axis 70, which is coinci¬ dent with the axis of the pin 60, toward the swing arm 20. A finger ring 72 and a clamp hub 74, with an 0-ring 76 positioned therebetween, are attached to the collet ball bearing 64. The clamp hub 74 is generally disk shaped and in- UBSTITUTE SHEET eludes several axial protrusions 78, each of which has a shoulder 80 that collectively form a flange 82 on the collet ball bearing 64, axially positions the clamp hkub 74. The finger ring 72 includes several axial tabs 84 each of which has a hook 86 facing radially inward. These axial tabs 84 interlace among the axial protrusions 78 of the clamp hub 74 with the hooks 86 encircling the flange 82 of the collet ball bearing 62 to axially locate the finger ring 72. In this manner, the finger ring 72 and the clamp hub 74, with the 0-ring posi¬ tioned therebetween are attached to the collet ball bearing 64 for rotation about and transla- tion along the collet axis 70. The finger ring 72 also includes several fingers 88 forming a generally conical shape with each finger having a bump 90 formed on the inner surface thereof. The finger ring 72 and the clamp hub 74 are preferably molded plastic pieces for economy and light weight. 0-ring 76 is made of a low creep silicon pastic, such as silastic, and provides a resilient back-up for urging the fingers 88 out¬ wardly. Note that since the shaft diameter of pin 60 is substantially less than the diameter of hole 62, the collet assembly is more or less SUBSTITUTE SHEET "free floating" relative to arm 20, with its freedom being restrained only by the size of hole 62 and the stiffness of spring 66. In reference now to Figure 2, the remainder of the structure of the mechanism 10 will now be described. The spindle 14 includes a drive belt 92 that is wrapped around the cylindrical exterior surface 56 of the guide hub 22 and is driven by an electric motor (not shown) in a conventional manner to rotate the guide hub about the spindle axis 24. Attachment of the swing arm 20 to the disk drive frame and a pivot pin 96 through the pivot and the swing arm. The 0-ring 76 is posi¬ tioned in a groove 98 in the clamp hub 74 and pushes on the bump 90 on each finger 88 to move the finger outward causing a tip 100 of each finger to contact the clamp hub at surface 102. The fingers 88 of the finger ring 72 form a camming surface 103 of conical shape used in cen- tering the flexible disk. The collet bearing 64 has an inner race 104 located by the shoulder bolt 60 and an outer race 106 upond which the finger ring 72 and clampk hub 74 are mounted. The flange 64 of the collet bearing 64 is captured between the shoulders 80 of the clamp hub 74 and the hooks 86 of the finger ring 72. SUBSTITUTE SHEET OMPI The clamp hub 74 also includes a second disk clamping surface 108, opposite the first clamping surface 58 of the guide hub 22. Having described in detail the structure of the mechanism 10 for clamping and driving a flex¬ ible disk 12, the operation of the mechanism will now be explained. In Figure 2, the mechanism 10 is shown in a loading position with the swing arm 20 and collet 16 spaced apart from the flexible disk 12 and the spindle 14 . The flexible disk 12 includes a protective envelope 110 with a cen¬ tral access hole 112 therein, exposing the disk and a center hole 114. The flexible disk 12 is positioned at the loading position by a frame or guide (not shown) that is well known in lthe art. While the mechanism 10 is in the loading position the flexible disk 12 may be removed and replaced. At the loading position, the collet 16 is stationary while the spindle 14, or more specifi- cally, the guide hub 22 is rotating. The mechanism 10 remains at the loading posi¬ tion until the flexible disk 12 is positioned at approximately the proper position and the swing arm is lowered to begin the aligning and clamping sequence. Initially, the camming surface 103 of the finger ring 72 contacts the inside of the SUBSTITUTE SHEET center hole 114 of the flexible disk 12. The di¬ ameter of the camming surface 103 at the tips 100 at this position is slightly greater than the di¬ ameter of the center hole 114 which equals that of the guide hub bore 34. After contact with the flexible disk 12, the collet 16 continues to move toward the rotating guide hub 22, and the flexible disk moves laterally to center the center hole 114 on the conical camming surface 103. The collet 16 continues to move toward the spindle 14 carrying the flexible disk with it. As the collet 16 approaches the spindle 14, the camming surface 103 enters the hub bore 34. The flexible disk 12 touches the first clamping sur- face 58, the fingers 88 of the finger ring 72 begin to compress the 0-ring 76 and to retract to the smaller diameter of the guide hub bore 34. By so retracting the tips 100 of the fingers 88 act radially outward on the center hole 114 to center it on the guide hub 22. When the collet 16 and the flexible disk 12 contact the rotating guide hub 22, they begin to accelerate to the ro¬ tational velocity of the spindle 14. The collet 16 continues to move toward the spindle 14 until it reaches the clamping position ' shown in Figure 3. The flexible disk 12 is cen¬ tered on the rotating guide hub 22 by the finger STITUTE SHEET _OMPI ring 72 and is clamped to the rotating guide hub between the first and second disk clamping sur¬ faces 58 and 108. The compression coil spring 66 provides the- clamping force and acts through the collet ball bearing 64 and the clamp hub 74 to force the second disk clamping surface 108 against the flexible disk 12 and the first disk clamping surface 58. In this fashion, disk posi¬ tioning, clamping, and spinning are accomplished. As will be clear to those skilled in the art, modifications and changes may be made to the dis¬ closed embodiment without departing from the in¬ ventive concepts thereof. The above description is intended as illustrative and informative but not limiting in scope. Accordingly, it is inten¬ ded that the following claims be interpreted to cover all modifiations that reasonably fall within the scope of the invention. SUBSTITUTE SHEET

Claims: CLAIMS What is claimed is: 1. A mechanism for clamping and spinning a flexible disk having a center hole therethrough, comprising: a frame; a hub coupled to said frame and rotat¬ able about a first axis and ha-ving an open bore substantially equal in diameter to that of said center hole and concentric to said first axis and also having a first disk clamping surface perpen¬ dicular to said first axis and adjacent to said open bore; hub rotation means coupled to said hub for rotating said hub about said first axis? a collet moveably coupled to said frame and operable for rotation about a second axis and disposed on the opposite side of said flexible disk from said hub, said collet comprising a finger ring having radially resilient fingers forming a conical camming surface for centering said flexible disk and also comprising a clamping hub having a disk clamping surface perpendicular to said axis for clamping said flexible disk; and SUBSTITUTE SHEET collet positioning means coupled to said frame and said collet for moving said collet between a loading position out of contact with said second axis coincident with said first axis and having said flexible disk clamped between said first and second disk clamping surfaces and having said fingers contacting said open bore of said hub. 2. A mechanism as recited in claim 1 wherein said conical camming surface has a maximum diame¬ ter greater than that of said open bore of said hub when said collet is at said loading position and wherein said radially resilient fingers of said finger ring are deflected radially inward by said bore as said collet moves twoard said clamping position. 3. A mechanism as recited in claim 2 further comprising biasing means coupled to said finger ring for biasing said radially resilient fngers in a radially outward directon, while permitting said radially resilient fingers to be contracted radially inward when said collet is at said clamping position. 4. A mechanism as recited in claim 3 wherein said biasing means is a ring of elastomeic SUBSTITUTE SHEET material acting between said radially resilient fingers of said finger ring and said clamping hub. 5. A mechanism as recited in claim 1 wherein said collet positioning means comprises an arm pivotably attached to said frame having said collet rotatably mounted thereon, and means coupled to said arm for pivoting said arm to move said collet between said loading and said clamp- ing positions. 6. A mechanism as recited in claim 5 wherein said collet positioning means further comprises a compression spring acting to bias said collet away from said arm and toward said hub to provide a clamping force between said first and second disk clamping surfaces when said collet is at said clamping position. 7. A mechanism as recited in claim 1 wherein said hub is cylindrical in shape about said first axis and wherein said hub rotation means comprises a continuous belt wrapped around and in contact with the cylindrical exterior of said hub and also comprising means coupled to said belt for driving said belt to rotate said hub. 8. A mechanism as recited in claim 1 wherein SUBSTITUTE SHEET said finger ring and said clamping hubk are fab¬ ricated from a plastic material so as to minimize the rotational inertia of said collet. 9. A mechanism as recited in claim 1 wherein said collet includes a ball bearing race with a flange and wherein said clamping hub includes a shoulder to axially locate said ball bearing and wherein said finger ring inlcudes locking tabs that encircle said flange to hold said ball bear- ing against said shoulder thereby permitting said collet to be snapped together for assembly. SUBSTITUTE SHEET

Inventors: THOMPSON HERBERT E, THOMPSON, HERBERT, E.
Applicants: DRIVETEC INC, DRIVETEC, INC.
Application year: 1983
Main classification: G11B5
IPC codes: G11B17, G11B19