Abstract:
A hard disk assembly comprises a hub made of injection molded liquid crystal plastic, to which is mounted a magnetic disk by a twist-lock screw top. The expensive step of machining the critical hub component is avoided because sufficient accuracies can be achieved with the liquid crystal plastic when injection molded.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to computer memory and more specifically to removable hard disk cartridges and disk drives. 
     2. Description of the Prior Art 
     The popularity of personal computers is, in part, fueled by the ever decreasing costs of such systems. The component manufacturers which supply parts to the personal computer manufacturers are under increasing pressure to reduce their costs to keep up with the ever shrinking profit margins. The hard disk memory, such as fixed disk and removable disk, in a personal computer system represents a major cost included in such systems. 
     The manufacturers of hard disk drives have therefore been exploring ways to reduce their costs. A principal part of the cost of fabricating a hard disk drive, and/or removable cartridge, is the machining and assembly costs involved. When unit costs were much higher, the machining of various critical parts for hard disk memories seemed insignificant. Now, machining of metal parts represents a significant cost in disk drive and cartridge manufacturing. 
     Less expensive components and manufacturing methods are therefor critical to competitors in the personal computer and hard disk drive industries. 
     SUMMARY OF THE PRESENT INVENTION 
     It is therefore an object of the present invention to provide a hard disk cartridge that is inexpensive to manufacture. 
     It is an object of the present invention to provide hard disk cartridge that provides good performance. 
     Briefly, a hard disk assembly embodiment of the present invention comprises a hub made of injection molded liquid crystal plastic, to which is mounted a magnetic disk by a twist-lock screw top. 
     An advantage of the present invention is that a hard disk hub is provided that is inexpensive to manufacture. 
     Another advantage of the present invention is that a hard disk assembly is provided that is useful in a removable hard disk cartridge application. 
     A still further advantage of the present invention is that a cartridge disk is provided that permits automated manufacturing techniques to be used for mounting the disk to the hub. 
     Another advantage of the present invention is that a hard disk assembly is provided in which the expensive step of machining the critical hub component is avoided because acceptable finished component tolerances can be achieved with liquid crystal plastic when simply injection molded. 
     These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the drawing figures. 
    
    
     IN THE DRAWINGS 
     FIG. 1 is an exploded three-dimensional assembly diagram of a hard disk assembly embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of the hard disk assembly of FIG. 1 taken along the line  2 — 2  through the axis of rotation of the hard disk assembly; 
     FIGS. 3A,  3 B and  3 C, respectively, are a top view, a cross-sectional view taken along the line  3 B— 3 B of FIG. 3A and a bottom view of the screw top included in the hard disk assembly of FIG. 1; 
     FIGS. 4A and 4B, respectively, are a top view and a cross-sectional view taken along the line  4 B— 4 B of FIG. 4B of the plastic hub included in the hard disk assembly of FIG. 1; 
     FIG. 5 is a top view of the magnetic plate included in the hard disk assembly of FIG. 1; and 
     FIG. 6 is a perspective view of a hard disk cartridge that includes the hard disk assembly of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates a hard disk assembly embodiment of the present invention, referred to herein by the general reference numeral  10 . The hard disk assembly  10  comprises a plurality of guide teeth  11  on a screw top  12 , at least one recording surface  13  on a magnetic disk  14  with a center opening  15 , a plastic hub  16  with a drive gear  17 , a lip  18  and a set of locking teeth  19 , and a magnetic plate  20  with a plurality of sprocket holes  21  and a drive opening  22 . The screw top  12  and the hub  16  each comprise a liquid crystal plastic, e.g., such as is sold commercially under the trademark VECTRA A130, by Hoechst Chemicals (Germany). The recording surface  13  comprises a magnetic coating, such as ferrite oxide, for the recording of data with a magnetic read/write head in a disk drive that mates with the hard disk assembly  10 . 
     The fit of the magnetic disk  14  and especially the center opening  15  to the plastic hub  16  and its lip  18  must be precise so that wobble and runout when the disk  14  is rotated are controlled. Conventional metal hubs include a machining step in their fabrication. The plastic hub  16  is preferably injection-molded of liquid crystal plastic to five to ten micrometer accuracy using otherwise conventional fabrication techniques. With liquid crystal plastic material and a readily-attained five to ten micrometer molding accuracy, no subsequent machining is required to give good results. 
     FIG. 2 shows the screw top  12  and magnetic plate  20  in position for assembly to the plastic hub  16  with the disk  14  in between. In a typical implementation, the plastic hub  16  has a outside diameter “d” of approximately forty-five millimeters and a thickness “t” of 5.2 millimeters. The magnetic plate  20  allows a disk drive that receives the hard disk assembly  10  when mounted in a removable cartridge to seize and hold the hard disk assembly to a spindle and motor. The drive gear  17  is engaged to rotate the magnetic disk  14  during operation. The center opening  15  of the magnetic disk  14  fits around the plastic hub  16  tightly against the lip  18  and is locked down by the screw top  12  by action of a set of locking) teeth  24  that engage the matching set of locking teeth  19 , e.g., with a quarter-turn of the top  12  to the hub  16 . 
     The screw top is illustrated in FIGS. 3A,  3 B and  3 C. As shown in FIG. 3C, each locking tooth  24  on the screw top  12  may, for example, span an arc of 45°. 
     In FIGS. 4A and 4B, the hub  16  is illustrated as having a set of bosses  23 . The locking teeth  19  each span an arc of 45° with a space in between to accept the locking teeth  24  on the screw top  12 . During assembly, the locking teeth  24  are passed through the center opening  15  in the magnetic disk  14 , and twist-interlocked with the locking teeth  19  on the plastic hub  16 . 
     FIG. 5 shows the magnetic plate  20 . The holes  21  are beveled to mate easily with the bosses  23 . The holes  21 , may, for example, be distributed about the center axis at 60° increments at a circle diameter of approximately twenty-five millimeters. When inserted into the holes  21 , the bosses  23  provide a positive mechanical rotational lock between the plate  20  and the hub  16 . 
     FIG. 6 illustrates a removable hard disk cartridge  30  that contains the hard disk assembly  10  and keeps it clean and protects it from mechanical injury. A door  32  is used to open and give access to a set of read/write heads in a hard disk drive into which the cartridge  30  is inserted. A top case section  34  and a bottom case section  36 , which when combined enclose the hard disk assembly  10 , may be made of polycarbonate, as may the doors  32 . The doors  32  include a two-piece door mechanism for parting open the doors along a line parallel to the plane of the magnetic disk  10 . 
     Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.