Abstract:
A base plate for magnetic disk drives is provided that includes a hooked protrusion integrated therein between adjacent spindle motor coils. The cross-over wires that span between adjacent coils are secured by the hooked protrusions, thereby optimizing coil height and reducing manufacturing steps. The hook-like protrusions of one embodiment of the present invention are preferably stamped into the base plate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/632,382 filed Dec. 2, 2004, which is incorporated by reference in its entirety herein. 
    
    
     FIELD 
     The present invention relates to low-profile motors such as, for example, spindle motors for disk drives. 
     BACKGROUND 
     Micro drives are low profile miniature hard disk drives for portable applications, such as personal digital assistants, cell phones, music players, camera, digital recorders, etc. A micro drive includes the basic components of a conventional hard disk drive, but is much smaller. More particularly it includes rotatable media, i.e., one or more hard disks, a hub on which the one or more disks are mounted, a spindle affixed to a base plate and about which the hub and media rotate, and an electric motor to effectuate rotation of the hub and media. The electric motor typically comprises a rotor and a stator. The rotor may comprise one or more permanent magnets positioned about the hub, and the stator may comprise a plurality of fixed electromagnets disposed in a circular pattern proximate the permanent magnets on the hub or rotor. Controlling current flow through the electromagnets causes the hub and media to rotate. 
     The stator generally includes a circular member or yoke. Generally, a plurality of teeth extend inwardly from the circular portion of the yoke and are wrapped with wire to form individual electromagnets. However, the teeth can either extend inwardly or outwardly, depending on whether the motor is an interior or exterior stator type, as will be appreciated by one of skill in the art. Typically, an interior stator is employed in a 2.5″ and larger disk drive, wherein smaller form-factor drives employ an exterior stator because there is sufficient radial space for the windings. The yoke and teeth are normally a laminate, constructed from a number of layers of conductive material, although they may be a single core instead of a laminate. Each tooth has a distal and proximate end. The proximate end of each tooth is connected to the circular portion of the yoke and the distal end is opposite the proximate end and adjacent the permanent magnets mounted on the hub. Normally, disk drives use three phase electric motors and, therefore, the number of teeth is a multiple of the number three, e.g. 6, 9, 12 or more. Every third tooth is electrically connected or wired together to form each of the three phases. As outlined herein, every third tooth is wired together to form a single phase (i.e. a 9 slot, 12 pole ABC winding is described), but one skilled in the art will appreciate that other windings are possible depending on the number of poles and the number of slots provided. Thus, three separate wires would be used to individually control each phase of the motor. Coordinating the current flow through the independent wires coiled about the teeth of each phase controls the rotation of the rotor/hub. 
     Micro drives often utilize in-hub motors, meaning the rotor and stator are positioned inside the hub, or under-hub motors, meaning the stator is positioned underneath the rotor, in order to reduce the height of the motor and thereby reduce the overall height profile of the drive. Another way to reduce height is to alter the windings forming the coils on the stator teeth, which is very applicable with respect to smaller disk drives that must employ an exterior stator motor as described above. Normally, each tooth has multiple layers of windings. The totality of windings on a tooth comprises a coil. Thus, the stator height comprises the height of each tooth, plus two times the coil thickness. The height of each tooth comprises the plurality of conductive laminate layers forming each tooth, also referred to as the core of the electromagnet or a stator core. To alter the stator height, the diameter of the wire may be changed, the number of layers of windings may be changed and/or the height of the core may be changed. 
     The stator wires that form each coil generally enter and exit the coil at the proximate end of each tooth. This is because, as noted previously, the wires necessarily skip or cross over adjacent teeth in order to be wound in multiple phases. As should be appreciated, routing wires from the distal end of one tooth, either to the distal or proximate end of another tooth, while skipping over two intervening teeth, can cause problems. For example, the cross over wire(s) can interfere with the rotation of the hub, waste valuable space, and pose reliability and noise issues. Thus, in order to avoid interference with the hub, a stator coil will most always have an even number of winding layers in order for the wire to exit the tooth at the proximate end and not cross over any intervening coils. For example, the first layer is formed from the proximate end to the distal end of a tooth and the second layer of the winding is formed from the distal end to the proximate end. The wire will then be routed around the yoke perimeter to the next tooth that is in phase with the previously wound coil. Of course, there may be four or six or more winding layers and not just two. In this way, the wire does not interfere with the rotation of the rotor and, as noted, there will always be an even number of winding layers. 
     Another drawback of prior art cross-over wire interconnection schemes is that they compel the use of additional hardware. For example, some prior art stators include routing or retainer tabs interconnected to or interleaved within the layers of the stator yoke. The retainer tabs or hooks provide a location around the yoke for engaging and retaining the cross-over wires. This is an acceptable way to retain the cross-over wires in a predetermined location, however, additional complexity is added to the spindle motor which increases costs. Moreover, positioning the retaining tabs on the stator yoke, typically between adjacent teeth, promotes and reinforces the disadvantage that the start and finish of each stator coil still must be located at the proximate end of each tooth near the stator yoke thereby compelling an even number of coil winding layers. 
     While exiting wires at the proximate end of each stator tooth may simplify the routing of cross-over wires, it can also create other, unrelated limitations. As should be appreciated, to optimally design a disk drive the electric motor should also be optimized. This includes optimizing the characteristics of the stator. In the particular circumstances of a particular motor used in a particular design, it is not always desired simply to maximize the number of windings. For example, it may be desired to increase or decrease the number of laminate layers comprising each stator core, or to utilize an odd number of layers of windings rather than an even number, depending upon the wire diameter or gauge preferably selected for use in the drive. Changing one of these parameters can require changes to one or more of the others to maintain an optimized design. Thus, for small form factor electronic devices, the motor design must accommodate these factors while simultaneously seeking to decrease the height of the motor. Nonetheless, as noted above, in current drives it is more likely that the stator cores will have an even number of winding layers to avoid the problems created by cross-over wiring. As a result, it may not be possible both to optimize the motor and decrease its height. Trade offs may need to be made, such as sacrificing optimum performance to meet height restrictions caused by the number of layers of windings and/or the number of laminate layers, or sacrificing height to meet motor design objectives. The coil may have one less winding layer or one more winding layer than desired. If an additional winding is used, the stator height, and the overall drive height, will increase. If one less layer of windings is used, performance may be negatively affected, as might also be the case with an additional layer, and internal space may be unused and wasted. 
     Thus, it is a long felt need in the field of micro-drive production to provide a system that allows for an improved cross-over wire retainment strategy thereby providing the ability to decrease the height or thickness of the micro-drive while optimizing the characteristics of the motor for a particular end use application of the disk drive. The following disclosure describes an improved method of routing the cross-over wires between stator teeth that includes the addition of retaining tabs integrated into the base plate of the housing. 
     SUMMARY OF THE INVENTION 
     It is one aspect of the present invention to provide a support structure, utilized within a hard disk drive, with a plurality of stator wire retaining tabs. More specifically, one embodiment of the present invention includes a support structure that includes integral pairs of retaining tabs disposed between adjacent stator teeth, with one tab positioned radially inward of the other. For example, one tab is positioned adjacent the distal end and the other positioned adjacent the proximate end of the stator teeth. The retaining tabs provide locations for routing and restraining cross-over wires, thereby eliminating the requirement of having both the beginning and the end of a coil winding layer start at the proximate end of each stator tooth. This arrangement allows the winding layers to begin and/or end at either the proximate or distal end of each tooth. In turn, this arrangement conserves, or potentially reduces, stator height and potentially permits a reduction in disk drive size. It further allows greater flexibility to optimize the characteristics of the spindle motor. 
     One embodiment of the present invention employs radially disposed inner and outer retaining tabs that are generally opposed metal tabs preferably stamped into the support structure. The tabs are bent to form hook-like members or left in place if not needed. Accordingly, when winding a stator tooth, the cross-over wire may exit the distal end of a tooth and be routed through one or more retaining tabs on the support structure as needed, and then to the next appropriate tooth for winding. Cross-over wires exiting the proximate end of the tooth, near the stator yoke, may be routed through the radially outward tabs and along the stator yoke. Alternatively, cross-over wires that enter or exit from the distal portion of the tooth may be routed through the radially inward facing tabs and are directed around inappropriate teeth along the distal ends of the teeth or along the stator yoke. These retaining tabs also may be used in combination with tabs disposed on the stator yoke. 
     It is another aspect of the present invention to provide a method of securing cross-over wires that omits the need for additional hardware. Here, the retaining tabs are located on the support structure and not on the stator yoke, thereby eliminating the need for customized tab members or plastic clips disposed on the yoke. Thus, complexity of the system and manufacturing costs are significantly reduced. 
     It is still yet another aspect of the present invention to provide an optimized spindle motor that includes integral retaining tabs as shown and described herein which allows for odd or even number of stator coil layers, i.e. a more optimized design. This design permits optimizing the electro-magnetic characteristics of the motor. The ability to wrap the laminates in an even or an odd number further allows for a more efficient use of the allocated or available interior space of the disk drive housing. That is, the space traditionally required to return the winding to the yoke for routing to the next stator tooth is eliminated, thereby allowing the size of the micro drive to be decreased or the space allocated for the return wire to be taken up by a better designed motor, including a thicker laminate and/or larger or smaller diameter wires as the optimized design dictates. Optimizing the motor characteristics also increases battery life. 
     In another embodiment of the invention, only one retaining tab is positioned between adjacent stator teeth. Alternatively, two or more tabs may be positioned between adjacent teeth, and arranged in different configurations. For example, the tabs could be positioned at the same radial location relative to the spindle. They could also be laterally offset relative to each other. Persons of skill in the art will appreciate that the design characteristics of the stator can influence the location of the retainer tabs. Moreover, it should also be appreciated that the tabs may comprise one or more separate component pieces and do no need to be an integral part of the base plate or housing structure supporting the motor. 
     In a further embodiment of the present invention, the support structure is the base plate of a hard disk drive. 
     The Summary of the Invention is neither intended nor should it be construed as being representative of the full extent and scope of the present invention. The present invention is set forth in various levels of detail in the Summary of the Invention as well as in the attached drawings and the detailed description of the invention, and no limitation as to the scope of the present invention is intended by either the inclusion or non inclusion of elements, components, etc. in the Summary of the Invention. Additional aspects of the present invention will become more readily apparent from the Detailed Description, particularly, together with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and together with the general description of the invention given above and the detailed description of the drawings given below, serve to explain the principles of these inventions. 
         FIG. 1  is a top plan view of an electrical motor of the prior art that utilizes plastic retainer clips to secure cross-over wires; 
         FIG. 2A  is a top plan view of the laminations used in the electrical motor of the prior art; 
         FIG. 2B  is a cross sectional view of the embodiment shown in  FIG. 2A , taken along line  2 B- 2 B, wherein laminates with an inner profile are shown that are adapted to receive cross-over wires; 
         FIG. 3  is a schematic of the method of winding wires around a stator portion of an electrical motor; 
         FIG. 4  is a stator portion of an electrical motor interconnected to a base plate of the present invention showing inner and outer retaining tabs; 
         FIG. 5  is a partial perspective view of a laminate and coil combination of one embodiment of the present invention showing the retainer clips securing the cross-over wire; 
         FIG. 6  is a partial perspective view showing the stator portion of the electrical motor of the present invention; 
         FIG. 7  is a perspective view similar to that shown in  FIG. 6  with emphasis directed to the inward and outward retaining tabs; 
         FIG. 8  is a perspective view showing one wire routing method of the present invention; 
         FIG. 9  is a perspective view showing another wire routing method of the present invention; 
         FIG. 10  is a perspective view of the base plate showing the retaining tabs wherein the stator portion of the assembly is removed for clarity; and 
         FIG. 11  is a perspective view of yet another embodiment of the base plate. 
     
    
    
     It should be understood that the drawings are not necessarily to scale. In certain instances, details that are not necessary for an understanding of the invention or that render other details difficult to perceive may have been omitted. It should be understood, of course, that the invention is not necessarily limited to the particular embodiments illustrated herein. 
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1-3 , a stator portion  4  of a prior art electric motor is shown that includes a stator yoke  6  interconnected to a plurality, radially inwardly extending stator teeth  8 . Each tooth has a proximate end  10  wherein the tooth joins the stator yoke  6 , and a distal or free end  12  opposite the proximate end. As shown in  FIGS. 2A and 2B , the yoke  6  and teeth  8  consist of a plurality of stacked laminates. The laminates comprise an electrically conductive material, such as iron or compounds including iron, to assist in the formation of an electromagnet. Together, the laminates  14  of each tooth comprise a core. As shown in  FIG. 1 , each tooth  8  is wound by a wire  16 . The stator shown is part of a three-phase motor such that every third tooth is wrapped with the same wire, one skilled in the art will appreciate that embodiments of the present invention described herein are equally applicable for any stator winding scheme. (See,  FIG. 3 .) Thus, a current flowing through the stator portion  4  of the electric motor will activate groups of three teeth  8  in series to force a permanent magnet  18  operably interconnected to a rotor or hub  20  to rotate, e.g., a three-phase motor. Cross-over wires  22  interconnect one tooth to the next within each phase of the stator. Typically, in a disk drive, the stator yoke  6  fits in a raised ring  24  formed in the base plate  26 . 
     In prior art systems, such as is shown in  FIGS. 1-3 , cross-over wires enter and exit each tooth  8  from the proximate end  10 , adjacent the stator yoke  6 , thereby placing them in a location for routing to the next appropriate stator tooth  8 . However, routing the wires in this way creates motor design issues involving the back electromotive force (EMF) generated by the permanent magnet  18  on the various coils. EMF is the rate change of magnetic flux of the permanent magnet times the number of turns in the stator coil. More turns in the coil creates a greater back EMF. If the back EMF is too large or too small, motor performance will be negatively affected. An optimum motor design for a fixed disk drive height may call for an odd number of winding layers, but such a design will also position the cross-over portion  22  of wire  16  at the distal end of the tooth  8 . Therefore, an additional winding layer is typically added to return the wire to the proximate end of the tooth. As a result, the performance of the motor is negatively altered since, for example, a smaller wire must be used for the tooth to fit into the same volume. Alternatively, the wire  16  may simply be directly returned to the proximate end  10  of the tooth and not wrapped around the core, which is an inefficient use of space. In either instance, a valuable portion of the overall height envelope is used to accommodate the diameter of the additional wire layer. Accordingly, the stator height, including the coil, is increased by one or two wire diameters. In addition, the height of the disk drive as a whole may be increased. 
     Referring specifically now to  FIGS. 2A and 2B , a more concise view of the individual laminates  14  employed by the stator portion  4  of the electric motor is shown. The teeth may have a T-shaped profile with the distal end of the conducting material comprising cross-member  28  that provides for intimate electro-magnetic communication with the permanent magnet  18  interconnected to the rotor and/or hub  20  of a disk drive which rotates in the space  40 . One prior art method of retaining the cross-over wires  22  is shown in detail. More specifically, at least one of the laminates  14 , i.e. the third laminate  30 , includes a portion that is curled to form a hook  32 . The hooks  32  are used to secure cross-over wires  22  between adjacent teeth  8  of the spindle motor  4 . The drawback of this method of securing the cross-over wires is that customized laminates  14  are needed, thereby increasing the cost and complexity to manufacture the same. As is also illustrated, the hooks  32  are restricted in location to positions around the yoke  6 . This limits the manner in which wire  16  may be routed among the teeth  8 . 
     Referring now to  FIGS. 4 and 5 , a stator  4  of one embodiment of the present invention is shown. A base plate  26  includes ridge  24  to accommodate the stator. The stator comprises a yoke  6 , including nine teeth  8  extending inwardly from the yoke. The individual teeth have a proximate end  10  connected to the yoke  6  and a distal end  12 . Each tooth further comprises a number of laminate layers  14 , although the core could also be a single, solid piece of material, depending upon the desired characteristics of the motor design. Disposed between each adjacent tooth  8  are a pair of retainer tabs. In the preferred embodiment, there is a radially inner retainer tab  50  and a radially outer retainer tab  52 . Only one wire  16  for one phase of the motor is shown, while the remaining two wires have been omitted for clarity. As best illustrated in  FIG. 5 , the wire  16  is routed starting from the proximate side  10  of a tooth  8  and wrapped around the tooth to yield a coil with an odd number of winding layers  30 . In particular, the cross-over wire  22  exits the tooth at the distal end  12 . The cross-over wire  22  is then routed to the next appropriate tooth  8   n+1  in the phase with tooth  8 , wherein the cross-over wire  22  is secured by the inner retainer tab  50  and the outer retaining tab  52 . The wire may then be routed along the stator yoke  6  to the next appropriate tooth  8   n+2  and so on, until the wire exits the stator. Thus, the requirement of bringing the cross-over wire  22  from the distal end  10  of the tooth to the proximate end  12  of the tooth  8  for purposes of routing the wire to the next tooth is eliminated, and a more optimized method of winding stator teeth  8  is provided that permits more efficient use of the space available and permits optimization of the motor. 
     It should be appreciated that although two tabs are shown, it is within the scope of the present invention to provide a single tab or more than two tabs. The tabs may also be placed side by side at the same radial position or in any other configuration that contributes to optimizing the motor design. The tabs are also shown in a deployed state. As an alternative, the tabs may be deployed only as needed or stamped only as needed such as pursuant to a motor design. 
     Referring now to  FIGS. 6 and 7 , a more detailed view of one embodiment of the present invention is shown that utilizes inner retaining tabs  50  and outer retaining tabs  52 . Here it is evident that the retaining tabs may be integrated directly into the base plate  26  by stamping, for example. It is also apparent from the figures that the tabs may be cut from the base plate and bent into place only when needed to support the routing of the wire. Alternatively, all of the tabs may be bent into place wherein only the required tabs are used. One skilled in the art will appreciate that any combination of bending or not bending the retaining tabs into place may be employed without departing from the scope of the invention since deploying extra tabs as shown does not affect the characteristics of the electric motor. It should also be appreciated that the retaining tabs may be made as a separate piece affixed to the base plate rather than formed as an integral part of the base plate. 
     Referring now to  FIG. 8 , wire routing methods that may be used with the embodiments of the present invention is shown. With reference to  FIG. 8 , the wire routing may entail the cross-over wire  22  being directed from the distal end  12  of one tooth  8  to the distal end  12  of the next appropriate tooth  8   n+1  via a path defined by the inner retaining tabs  50 . This configuration omits the requirement of rerouting the cross-over wires  22  back to the stator yoke  6 . 
     With reference to  FIG. 9 , a more traditional method of routing the cross-over wires  22  is shown wherein the wire  16  initially wraps around tooth  8 , then interconnects to the inner retaining clip  50  and then is fed to the outer retaining clip  52  and back to the yoke  6 . The wire is then fed around the stator yoke and looped around an inner retaining tab  50  and back to the yoke. The wire is then similarly looped around another inner tab  52  and routed to the next appropriate tooth  8   n+1 . Alternatively, the cross-over wire  22  may be wound in a figure eight formation around opposing tabs thereby maintaining stiffness in the wire. This is shown in  FIG. 9  in routing the cross-over wire from tooth  8   n+1  to tooth  8   +2 . It should be appreciated by one skilled in the art that the retaining tabs may secure wires from different sets of three phases of the motor, since the interactions between currents flowing through the wires does not appreciably affect the performance of the system. 
     Referring now to  FIGS. 10 and 11 , support structures  28  of some embodiments of the present invention are shown. Here, it is illustrated how the retaining tabs may be integrated directly into the generally metallic support structure by stamping. It should be appreciated, as noted previously, that the support structure may be the base plate of a disk drive, or a separate structure inserted into a disk drive housing. In addition, the same tool that is used to stamp the tabs into the base plates may also be used to bend them inwardly and outwardly as required. The design of  FIG. 10  includes a separate stamping for each tab  50  and  52 , while the embodiment of  FIG. 11  shows a single stamping for each pair of tabs. 
     While various embodiments of the present invention have been described in detail, it is apparent that modifications and alterations of those embodiments will occur to those skilled in the art. However, it is to be expressly understood that such modifications and alterations are within the scope and spirit of the present invention, as set forth in the following claims.