Abstract:
A low-profile spindle motor for a disc drive data storage device includes a cylindrical sleeve which is used to mount the motor to a housing base using press-fitting or adhesive bonding, thus eliminating the vertical height required by screws, bolts or other prior art mounting mechanisms. The same cylindrical sleeve is used to mount the stator stack of the motor, and, on the inner surface of the cylindrical sleeve, to mount the ball bearing assemblies used to allow rotation of a central shaft and attached disc-mounting hub. In another aspect of the invention, ball bearing assemblies having a sealing element on only one side are used to allow greater separation between the ball bearing assemblies, while maintaining a low-profile motor. In yet another aspect of the invention, signals to drive the motor are directed to the stator windings via a printed circuit cable whose termination pads are disposed in the vertical space between adjacent stator windings.

Description:
This is a continuation of application Ser. No. 08/171,881, filed Dec. 21, 1993, now abandoned, which is a continuation of Ser. No. 07/962,427 filed Oct. 16, 1992, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to the field of rigid disc data storage devices, and more particularly, but not by way of limitation, to a low profile structure for a spindle motor used to rotate the discs on which data is stored. 
     2. Brief Description of the Prior Art 
     Disc drives of the type referred to as “Winchester” disc drives are well known in the industry. Such disc drives typically use one or more rigid discs coated with a magnetic medium for the storage of digital data. These discs are mounted for rotation at a constant speed on a brushless dc spindle motor whose speed is carefully controlled by digital electronics. 
     Demands of the market and advances in technology have lead to the reduction in the physical size of rigid disc drives from the original fourteen inch outside diameter (O.D.) discs to drives utilizing 2.5″, 1.8″ and 1.3″ O.D. discs, with inner diameters (I.D.) of 20 mm, 12 mm, and 10 mm, respectively. As the diameter of the discs themselves has been reduced, so too has the relative height of the disc drives. Current models of 2.5″ disc drives, for instance, have been introduced with overall heights of only 12.5 mm. 
     Such considerations have lead to the development of the present invention, which provides a spindle motor for such a low-profile disc drive. 
     SUMMARY OF THE INVENTION 
     The present invention defines a spindle motor which is of minimal vertical height, while still providing adequate “stiffness” to reliably rotate the discs in a disc drive data storage device. One aspect of the invention which contributes to the overall reduction in size is that the motor of the present invention is intended to be either press-fitted or adhesively bonded into an opening in the base member of the disc drive housing, thus eliminating the need for a mounting flange and screws, which would add to the vertical height if present. A second aspect of the invention is that the motor of the present invention is intended to make use of the maximum available portion of the overall disc drive height, to provide maximum spacing between a pair of ball bearings which allow the rotation of the discs, to cause maximum “stiffness” of the motor. This minimizes wobble or “non-repeatable run-out” (NRR) of the discs mounted to the motor. A third aspect of the invention involves the use of specially configured ball bearings, which have a seal on only one side of the bearing structure, thus contributing to an increase in the center-to-center spacing between the bearings, and adding to the stability of the motor. A fourth aspect of the invention pertains to the method used to connect externally generated motor drive signals to the ends of the motor stator windings, to further reduce overall motor height. A fifth aspect of the present invention provides a motor which is easy and inexpensive to manufacture due to a minimum number of parts which make up the motor. 
     It is an object of the present invention to provide a low-profile spindle motor for a disc drive data storage device. 
     It is another object of the present invention to provide a low-profile spindle motor for a disc drive data storage device which has adequate separation between the ball bearings to ensure reliable rotation of the discs. 
     It is another object of the present invention to provide a low-profile spindle motor for a disc drive data storage device which has a minimal number of parts to allow ease of assembly and reduced manufacturing costs. 
     It is another object of the present invention to provide a low-profile spindle motor for a disc drive data storage device which has favorable performance characteristics over a wide range of ambient operating temperatures. 
     These aspects of the motor of the present invention along with other features and benefits can best be understood by reading the following detailed description of the invention in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view with a partial cutaway which shows a disc drive data storage device in which the spindle motor of the present invention is particularly useful. 
     FIG. 2 is a sectional elevation view of a first embodiment of the spindle motor of the present invention. 
     FIG. 3 is a sectional elevation view of a preferred embodiment of the spindle motor of the present invention. 
     FIG. 4A is a bottom view of the stator and pcc sub-assembly of the spindle motor of the present invention. 
     FIG. 4B is a partial sectional view taken along line  4 A— 4 B of FIG.  4 A. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and in particular FIG. 1, shown is a disc drive  2  which includes a base member  4  and a top cover  5  which comprise the sealed housing to which all other elements of the disc drive are mounted. A disc  6  is mounted to a spindle motor (not shown) using a spring clamp  8  and a central screw  10 . A read/write head  12  is mounted via a flexure  14  to a head mounting arm  16  which is part of an actuator body  18 . The actuator body  18  is adapted for rotation about a pivot shaft  20  by a voice coil motor (VCM), shown generally at  22 . Electronic circuitry, shown partially at  24 , is used to direct power to the VCM  22  and transfer signals to and from the read/write heads  12  via a printed circuit cable (pcc)  26 . Motion of the actuator body  18  about the pivot shaft  20  causes the heads  12  to move across the discs  6  along arcuate path  28  to access data located in any one of a plurality of circular, concentric data tracks (not shown) on the disc surfaces. A second pcc  30  carries the drive pulses to rotate the spindle motor. This second pcc  30  connects to a plurality of pins  32  in a header which passes through the base member  4 , thus allowing external electronics (not shown) to control the spindle motor. 
     FIG. 2 shows a sectional elevation view of one embodiment of the spindle motor  34  of the present invention. In this and subsequent figures, the embodiment shown is for a spindle motor which supports a single data storage disc, although comparable advantages can be realized in spindle motors used to rotate multiple discs. Several components of the disc drive which are not actually a part of the motor  34  of the present invention are shown in FIG.  2 . For instance the base member  4 , top cover  5 , disc  6  and disc clamp  8  are shown as they relate to the motor  34 . The dimension designated he denotes the total height allocated to the disc drive assembly, or envelope height, and extends from the top surface of the top cover  5  to the lowermost point on the base member  4 . This envelope height, h e , is one of the defined design parameters, and, in a particular disc drive unit in which the motor of the present invention has been implemented, is 12.5 mm. Two additional vertical dimensions are noted on FIG.  2 . The dimension designated “m” is the height allowance for the mechanical components of the disc drive, such as the actuator, heads and discs, while the dimension designated “e” is the vertical space set aside for the electronic components of the disc drive, including a printed circuit board  36  and attached components  38 . 
     As a first aspect of the invention, the motor  34  of the present invention includes a cylindrical sleeve  40  which serves to perform a variety of functions. First, the lower portion of the sleeve  40  acts as a mounting mechanism for attaching the motor  34  to the base member  4 . This is accomplished by forming a complimentarily-shaped cylindrical opening  42  in the base member  4  into which the sleeve  40  can be either press-fitted or adhesively bonded. An opening  37  is also provided in the printed circuit board  36  to allow the passage of the sleeve  40  within the cylindrical opening  42 . A lower stop surface  46  serves to contact the upper surface of the base member  4  and control how far the sleeve  40  can protrude into the opening  42 . Such a scheme eliminates the mounting flange and fasteners commonly used to mount a spindle motor in a disc drive and thus serves to reduce the height of the motor  34 . An upper stop surface  48  acts as a support for a stack of stator laminations  50  which in turn support a plurality of stator windings  52 . This upper stop surface  48 , in conjunction with the outer surface  54  of the sleeve  40  above the upper stop surface  48 , serves to located the stator stack  50  both axially and radially. Commutated motor drive pulses are carried to the stator windings  52  via a printed circuit cable (pcc)  104 . The connection of the pcc  104  to the stator windings  52  is another inventive aspect of the motor  34  of the present invention and will be further discussed below. 
     On the inner surface  58  of the sleeve  40  is a stepped portion  60  which is used to axially located a pair of ball bearings  62   a ,  62   b  via contact with the outer races  64   a ,  64   b  of the ball bearings  62   a ,  62   b . The motor  34  further consists of a rotating shaft  66 , which includes a flange portion  68  near its upper end. This flange portion  68  serves as a contact surface for the inner races  70   a  of the upper ball bearing  62   a . Thus, when the sleeve  40 , ball bearings  62   a ,  62   b  and shaft  66  are press-fitted or adhesively bonded together, the axial and radial alignment of the shaft  66  relative to the sleeve  40  is defined, as is the preload of the ball bearings  62   a ,  62   b.    
     A hub member  72  is mounted to the top of the shaft  66 . This hub member  72  is used to mount the disc  6 , as well as to support a permanent magnet  74  which forms the rotor of the motor  34 . 
     A seal  76  is included at the bottom of the motor  34  to prevent the entrance of any outside contaminants into the motor  34 , which could then be possibly passed into the area of the heads (not shown) and disc  6 . The seal comprises a sheet-metal plate glued to the outer races  64   b  of lower bearings  62   b . This seal eliminates the need for a ferrofluid seal. 
     As a further contamination preventative, the air gap  78  between the cylindrical sleeve  40  and the shaft/hub subassembly  66 / 72  is intended to be as small as is reliably achievable using current mass production techniques. This will aid in isolating the delicate internal components of the disc drive from outside contaminants by creating a very small radially extending air gap portion between the lower surface of the flange portion  68  and the outer race  64   a  of the upper ball bearing assembly  62   a  and a second very small axially extending air gap portion between the outer extreme of the flange portion  68  and the inner surface  58  of the bearing sleeve  40 . Such convoluted air passageways are sometimes referred to as “labyrinth seals”. 
     FIG. 3 shows a sectional view of a preferred embodiment of the spindle motor  80  of the present invention. While the motor  80  of FIG. 3 is very similar to the motor  34  of FIG. 2, the motor  80  of FIG. 3 includes an integrated hub/shaft  82  formed of a single piece of material. This reduces the parts count and thus provides a motor which is less expensive and easier to assemble. A second major difference between the motor  80  of FIG.  3  and the motor  34  of FIG. 2 can be seen by comparing the pair of ball bearings  84   a ,  84   b  and the cylindrical sleeve  86  with similar components in FIG.  2 . 
     The ball bearings  62   a ,  62   b  of FIG. 2 include a pair of seals  85  on both the upper and lower sides of the ball bearings  62   a ,  62   b , while the ball bearings  84   a ,  84   b  of the motor  80  of FIG. 3 are specially made ball bearings with a sealing element  88  on only a single side of the ball bearings  84   a ,  84   b . Including a sealing element  88  on the top surface of the upper ball bearing  84   a  and on the bottom surface of the lower ball bearing  84   b  provides the same effective sealing against particles generated in the ball bearings  84   a ,  84   b  themselves as does the double seal configuration of FIG. 2, and also provides a significant advantage over the double seal configuration. As can be seen by comparing FIGS. 2 and 3, the single seal bearings  84   a ,  84   b  have a much smaller vertical dimension. This allows the stepped portion  90  on the inner surface of the cylindrical sleeve  86  to be larger, separating the ball bearings  84   a ,  84   b  by a greater distance and contributing to an increase in the “stiffness” of the motor  80 . Any particles generated within the ball bearings  84   a ,  84   b  are still confined within the sealed area defined by the integrated hub/shaft  82 , the cylindrical sleeve  86  and the sealing elements  88 . 
     Yet another aspect of the invention which contributes significantly to the reduction in the height of the motor can best be seen by examining FIGS. 4A and 4B. FIG. 4A is a bottom plan view of a stator subassembly  92 , while FIG. 4B is a sectional view of the stator subassembly  92  taken along the line “ 4 B— 4 B” of FIG.  4 A. As can be seen, the stator subassembly  92  consists of a stack of stator laminations  94  which include a circular central opening  96  dimensioned to fit over the outside of the cylindrical sleeve ( 86  in FIG. 3) and a plurality of radially extending T-shaped stator poles  98 , one of which is shown in its entirety with dashed line  100 . Each of these stator poles  98  carries a stator winding  102   a - 102   d  comprised of a number of turns of wire. FIG. 4B shows one of these stator windings  102   a  in section and another stator winding  102   b  in elevation view, while shaded areas  102   c  and  102   d  show the general extent of an adjacent pair of stator windings in plan view. A flexible printed circuit cable (pcc)  104  is used to carry commutated DC drive pulses to the stator windings  102  via a plurality of signal traces  106 . FIG. 4A shows that this example motor includes nine stator poles  98 , but this is for example only and the present invention is in no way limited by the number of stator poles, number of electrical phases or other motor specifics. Each of the signal traces  106  ends in a solder pad  108   a-d  which is used to connect the signal traces  106  to the ends of the stator windings  102   a-c . In the example motor of FIG. 4A, there are four signal traces  106  and a comparable number of solder pads  108   a-d . Such a combination could be used, for instance, in a three-phase, star configured motor, with one of the pads serving as a common point for one end of all three phase windings, while the other three pads connect to the opposite end of each individual phase winding. 
     The inventive aspect under discussion can be understood by examining the pair of adjacent stator windings  102   c ,  102   d  in FIG.  4 A. As this plan view shows, a vertically extending gap  110  is formed between each such pair of adjacent stator windings. The signal traces  106  and solder pads  108   a-d  on the pcc  104  are located on the top side of the pcc  104 , i.e., on the side of the pcc  104  closest to the stator stack  94  and stator windings  102   a - 102   d . In order to bring the pcc  104  into the closest possible contact with the stator stack  94 , the solder pads  108   a-d  are each located in the vertically extending gap  110  between adjacent pairs of stator windings  102   a-d . The advantage of this approach is best seen in FIG. 4B which shows the end  112  of the stator winding  102   b  connected to solder pad  108   d . Since the solder pad  108   d  lies in the vertically extending gap  110  between adjacent stator windings, it can occupy the same vertical space as the stator winding  102   b . If the solder pad  108   d  were not aligned with the vertically extending gap  110 , or if the solder pad  108   d  were located on the other side of the pcc  104 , a significantly taller structure would, of necessity, be formed. 
     It will be clear that the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those inherent therein. While a presently preferred embodiment has been described for purposes of this disclosure, numerous changes may be made which will readily suggest themselves to those skilled in the art and which are encompassed in the spirit of the invention disclosed and as defined in the appended claims.