Abstract:
A low profile spindle motor for supporting and rotating media disk or disks of a hard disk drive includes a plurality of stator teeth, a winding layer which may be formed by printed circuit board or the like, and a rotor. The plurality of stator teeth are disposed in an annular region surrounding an axis of rotation of the motor, and have projected ends for increasing the tooth area facing a magnet ring of the rotor. The winding layer has a plurality of windings disposed surrounding the axis of rotation. Each winding is coupled to one of the plurality of stator teeth. The magnet ring is positioned radially spaced apart and coplanar with the annular region. The magnet ring has magnetic poles annularly distributed to generate magnetic fluxes along radial direction. Spindle motor formed according to the invention has a low profile, improved performance and manufacturability.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a permanent magnet synchronous spindle motor. In particular, it relates to a low profile spindle motor for use in data storage systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Permanent magnet synchronous motor may be used in a data storage system such as a hard disk drive to support and rotate one or more media disks. With the applications of hard disk drives being extended from computer systems to consumer products, in particular portable electronic devices such as portable audio visual players and digital video cameras, etc, the physical dimension of hard disk drives in these applications are demanded to be small compared to those for computer systems, and hence low profile and miniature hard disk drives are developed to meet these requirements. In the meantime, the requirements for storage capacity, data accuracy and data access speed keep increasing. Hard disk drives designers and manufacturers are facing continuous challenges in developing hard disk drives to meet these requirements. 
         [0003]    Difficulties have been arising in finding solutions to further reduce the physical dimension, in particular the thickness of hard disk drives, while maintaining or even improving the performance of hard disk drives. It is appreciated that one of the key factors which hinders thickness reduction of hard disk drives, lies in the stator structure of the spindle motor. 
         [0004]    Presently, spindle motors are configured with stator windings wounded on stator teeth, and oriented along radial directions of the spindle motor. A relatively large space between adjacent windings must be reserved, in order for the winding tooling to operate and winds the winding turns on the stator teeth. The windings may also have to be designed with more turns, or thick wire with few turns, for meeting the requirements from motor drive system. However, more winding turns, or thick wire, will result in greater dimension of winding ends, which will affect the thickness reduction of the spindle motor. 
         [0005]    What is needed is therefore a spindle motor for supporting and rotating media disk(s) of a hard disk drive, which has a structure and configuration to enable an improved manufacturability, reduced motor thickness while maintaining or even improving the performance. 
       SUMMARY OF INVENTION 
       [0006]    Embodiments of the present invention provide stator and winding structures and configurations for low profile permanent magnetic synchronous spindle motor for hard disk drives. 
         [0007]    According to one embodiment, there is provided a spindle motor in which the stator teeth and rotor magnet are radially and coplanarly disposed with respect to each other. A winding layer, such as that formed of a conductive layer of a Printed Circuit Board (PCB), a wiring layer of a wire-bonded substrate or the like, is provided, with its conductive layer forming stator windings in a plane or a two-dimensional area, and are axially oriented, i.e. with the winding center axis parallel to the axis of rotation of the spindle motor. 
         [0008]    According to another embodiment, there is provided a spindle motor in which the stator teeth are disposed in an annular region surrounding an axis of rotation of the motor. A plurality of windings are provided, each being coupled to one of the plurality of stator teeth. Each winding has its winding axis oriented parallel to the axis of rotation. A rotor of the spindle motor has a magnet positioned radially spaced apart and being coplanar with the annular region. The magnet has magnetic poles annularly distributed to generate magnetic fluxes along radial direction of the magnet. 
         [0009]    According to a further embodiment, a laminated stator ring is provided in a spindle motor. The laminated stator ring includes a first layer which forms the stator yoke, a dielectric substrate disposed on the first layer, and a conductive layer provided on the dielectric substrate. A plurality of windings are formed by the conductive layer. The laminated stator ring further includes a second layer which forms a plurality of stator teeth. Each of the stator teeth is coupled to one of the windings, with projected edges which increase the tooth area surrounding the permanent magnet ring. 
         [0010]    Embodiments of the present invention provide axially orientated stator windings in a two dimensional region. A magnetic flux passage or loop is formed to pass radially from the rotor magnet, guided by the stator teeth along radial direction, guided by winding core along axial direction, and guided by stator yoke along circumferential direction. With the solutions provide by embodiment the present invention, spindle motors may be provided with improved motor performance and manufacturability and significantly reduced thickness. 
         [0011]    Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the inventive concept of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    These and other aspects and advantages of the present invention will be described in detail with reference to the accompanying drawings, in which: 
           [0013]      FIG. 1  is a perspective view of a spindle motor according to one embodiment of the present invention; 
           [0014]      FIG. 2  is a exploded partial perspective view of  FIG. 1 ; 
           [0015]      FIG. 3A  is a cross sectional front view of  FIG. 1 ; 
           [0016]      FIG. 3B  is a partially enlarged view of  FIG. 3A ; 
           [0017]      FIG. 3C  is a cross sectional front view of a spindle motor according to another embodiment of the present invention 
           [0018]      FIG. 4  is a perspective view showing an armature winding of a spindle motor shown in  FIG. 1 ; 
           [0019]      FIG. 5  is a perspective view showing a stator yoke of a spindle motor shown in  FIG. 1 ; 
           [0020]      FIG. 6A  is a perspective view showing a winding core of a spindle motor shown in  FIG. 1 ; 
           [0021]      FIG. 6B  is a perspective view of a stator tooth of a spindle motor shown in  FIG. 1 , with a winding core formed or assembled thereon; 
           [0022]      FIG. 6C  is a perspective view showing winding cores connected to a stator yoke a spindle motor; 
           [0023]      FIG. 7  is a perspective partial view of  FIG. 3A  showing magnetic flux passage; 
           [0024]      FIG. 8  is a perspective partial view of a spindle motor according to another embodiment of the present invention; 
           [0025]      FIG. 9  is a perspective view of a spindle motor according to a further embodiment of the present invention; 
           [0026]      FIG. 10  is a partially enlarged cross sectional view of  FIG. 9 ; 
           [0027]      FIG. 11  is a perspective view showing one exemplary single phase armature winding of a spindle motor shown in  FIG. 9 ; 
           [0028]      FIG. 12  is a perspective view showing a stator yoke of a spindle motor shown in  FIG. 9 ; 
           [0029]      FIG. 13A  is a perspective top view showing the outer layer of stator teeth of a spindle motor shown in  FIG. 9 ; 
           [0030]      FIG. 13B  is a perspective bottom view showing the outer layer of stator teeth of a spindle motor shown in  FIG. 9 ; 
           [0031]      FIG. 14A  is a perspective top view showing the inner layer of stator teeth of a spindle motor shown in  FIG. 9 ; 
           [0032]      FIG. 14B  is a perspective bottom view showing the inner layer of stator teeth of a spindle motor shown in  FIG. 9 ; 
           [0033]      FIG. 15  is a perspective partial view of  FIG. 9  showing magnetic flux passage; 
           [0034]      FIG. 16  is a partial cross sectional view showing a tooth pin configuration of a spindle motor according to another embodiment of the present invention. 
           [0035]      FIG. 17  is a partial cross sectional view showing a tooth pin configuration of a spindle motor according to yet another embodiment of the present invention. 
           [0036]      FIG. 18  is a partial cross sectional view showing a stator yoke pin configuration of a spindle motor according to still another embodiment of the present invention. 
           [0037]      FIG. 19  is a perspective partial view of a spindle motor according to a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0038]    As shown in  FIGS. 1 ,  2 ,  3 A and  3 B, a spindle motor  100  according to one embodiment of the present invention includes a stator  110  and a rotor  210  with a generally ring-shaped permanent magnet  220  which is disposed radially inside stator  110  and rotatable relative to stator  110  about an axis of rotation  102  of spindle motor  100 . Permanent magnet  220  has magnetic N and S poles  222 ,  224  configured to generate and receive magnetic fluxes  232 ,  234  along radial directions, i.e. perpendicular to axis of rotation  102  ( FIG. 2 ). 
         [0039]    Stator  110  has a first set of windings  120 , each being oriented with its winding axis  122  parallel to axis of rotation  102  ( FIGS. 3A ,  3 B). Stator  110  further includes a plurality of stator teeth  140 , and a stator yoke  150  positioned below stator teeth  140 . The plurality of windings  120  is positioned between the set of stator teeth and stator yoke  150 . A plurality of winding cores  160  are each placed between a corresponding stator tooth  140  and stator yoke  150 , and passing through the center hollow portion of a corresponding winding  120 . Each stator tooth  140  has a first end portion  142  adjacent to permanent magnet  220 , forming an annular gap  340  therebetween. End portion  142  may be projected along a direction parallel to the axis of rotation  102 , and with a height to accommodate the thickness of permanent magnet  220 . 
         [0040]    In the present embodiment, each of the stator teeth  140  is formed of a first layer  144  and a second layer  148 . First and second layers  144  and  148  may be fabricated by, for example, stamping, and assembled together to form a stator tooth  140 . The end portion  142  of first layer  144  may be bent or projected upwardly, and the end portion  146  of second layer  148  may be bent or projected downwardly. Bent or projected end portions  142  and  146  are dimensioned to accommodate the height of permanent magnet  220 . An advantage of forming the stator teeth with end portions  142  and  146  facing the permanent magnet is that, the effective magnetic interaction area between the permanent magnet and the stator teeth can be increased compared to that formed by stator teeth without the end portions  142  and  146 . The magnetic/mechanical energy conversion capability, and motor torque generation capability, can therefore be enhanced. In the meantime, the main area of stator teeth remains thin and this contributes to the reduction of overall thickness of the spindle motor. 
         [0041]    In the present embodiment, windings  120  may be formed by conductive circuitries of a printed circuit board (PCB). As shown in  FIG. 3B , the printed circuit board has a conductive layer  124  laminated on a dielectric substrate  126 . Windings  120  are formed of spiral circuits from the conductive layer  124  by PCB fabrication technology. Once the desired windings  120  are formed on the conductive layer  124 , the PCB may be sandwiched between stator teeth  140  and stator yoke  150  by, adhesion, soldering, pressing or the like, to form a laminated stator ring structure, as shown in  FIG. 3B . In an alternative embodiment, windings  120  may be formed by bonding conductive wires on a substrate. 
         [0042]    According to another embodiment, as shown in  FIG. 3C , there may be a second set of windings  127  formed by a second conductive layer  128  of the PCB. The second set of windings  127  may be electrically coupled to the first set of windings  120 . Depending on the requirements of the spindle motor, a multi-layer PCB may be provided, with three or more conductive layers, so as to form more sets of windings. Each set of the windings may connect with another set in series, or in parallel, to form the required multi phase armature windings of the motor. 
         [0043]    Spindle motors configured according to embodiments of the present invention advantageously form planar and axially oriented stator windings.  Manufacturing difficulties and limitations encountered in fabricating conventional spindle motor windings are successfully overcome. Because the windings are formed in a winding plane which is substantially a two dimensional area, the thickness of the windings are much reduced. Fabricating the windings from a PCB greatly improved the manufacturability, and increased the design freedom of the shape and patterns of the windings. 
         [0044]    For example, the winding may be formed by surrounding one or two core regions, as shown in  FIG. 4 . Depending the design requirements, more than one layers of windings may also be formed in a stator assembly, which can be conveniently implemented by the multi layer PCB fabrication technology. 
         [0045]    An added advantage is that, as the PCB may be laminated or adhered together with the stator teeth and stator yoke, both the strength and rigidity of the stator assembled is increased, which may also contribute to the overall performance improvement of the spindle motor. 
         [0046]    As shown in  FIG. 5 , stator yoke  150  is formed of a single piece of magnetically permeable material, with openings such as holes or slots  152  formed thereon for coupling to winding cores  160 . 
         [0047]      FIGS. 6A and 6B  show winding core structures which may be adopted in the embodiment shown in  FIG. 1 . Winding core  160  may be cylindrical or circular segment shaped, and formed separately, as shown in  FIG. 6A . Winding core  160  may be fabricated by forging, stamping, machining or metal injection molding, and assembled to a corresponding stator tooth  140 . In the example shown in  FIG. 6A , upon completion of the fabrication, the winding core  160  may be assembled to a stator tooth (not shown). Alternatively, each of the stator teeth  140  and a corresponding winding core may be formed of a single part ( FIG. 6B ) by, for example, injection molding or die casting. In an alternative embodiment, winding cores  160  may be formed integrately on, or connected to, stator yoke  150 , as shown in  FIG. 6C . 
         [0048]    Stator teeth  140 , winding core  160  and stator yoke  150  are made of ferrite magnetic material, and form a magnetic flux passage to allow magnetic flux generated by permanent magnet  210  to pass through and interact with stator windings. 
         [0049]    Magnetic flux passage along adjacent stator teeth  140   a  and  140   b  are taken as an example for illustration, as shown following the passage route indicated by outlined arrows in  FIG. 7 . 
         [0050]    A magnetic flux generated from an N pole of permanent magnet  220  passes across annular gap  340  along radial direction, and into a first stator tooth  140   a.  Guided by first winding core  160   a,  the magnetic flux turns downwardly along axial direction, and passes through first winding core  160   a.  When reaching stator yoke  150 , the magnetic flux turns along circumferential direction, and further turns along axial direction upwardly upon reaching an adjacent winding core  160   b . The magnetic flux is then guided by the adjacent stator tooth  140   b,  and turns radially back to an S pole of permanent magnet  220 . 
         [0051]    With a stator assembly configured as per the above illustrations, a spindle motor according to embodiments of the present invention achieved a low profile or thinner stator than conventional spindle motors. With stator windings axially orientated, the spacing reserved between stator windings for fabrication tooling necessary for conventional spindle motors is successfully eliminated. This allows for an increased winding density and winding space utilization, in a spindle motor, hence the power output of the spindle motor can be increased. 
         [0052]    As shown in  FIG. 8 , a spindle motor  400  according to a further embodiment of the present invention includes a stator  410  and a rotor  510 . Similar structures of stator teeth, axially-oriented windings and stator yoke are provided, which enable a spindle motor with much reduced thickness than that of the conventional spindle motors. The present embodiment varies from that shown in  FIG. 1  in that, rotor  510  has a ring-shaped permanent magnet  620 , and the stator  410  has a plurality of stator teeth  440  disposed inside the permanent magnet  620 . A spindle motor with outer rotor configuration can thus be formed. 
         [0053]    As shown in  FIGS. 9 , and  10 , a spindle motor  1100  according to an alternative embodiment of the present invention includes a stator  1110  and a rotor  1210  with a generally ring-shaped permanent magnet  1220  which is disposed radially inside stator  1110  and rotatable relative to stator  1110  about an axis of rotation  1102  of spindle motor  1100 . 
         [0054]    The present embodiment varies from that shown in  FIG. 1  in that, instead of providing winding cores of a cylindrical shape, formed separately and assembled onto a corresponding stator tooth, the outer end portion of each of the stator teeth  1140  may be bent downwardly along axial direction, forming a winding core portion  1162  which passes through windings  1120 . An advantage of the present embodiment is that, the winding cores may be formed in one manufacturing process step during forming the stator parts  1144  and  1148  by, for example, stamping. 
         [0055]    In the present embodiment, as shown in further detail in  FIGS. 11A ,  11 B,  12 A and  12 B, each of the stator teeth  1140  is formed of an outer layer  1140   a  and inner layer  1140   b.  Outer and inner layers  1140   a  and  1140   b  may be fabricated by, for example, stamping, and assembled together to form a stator tooth  1140 . The first end portion  1142  of outer layer  1140   a  may be bent or projected upwardly, and that of inner layer  1140   b  may be bent or projected downwardly. Bent or projected end portions  1142   a  and  1142   b  are dimensioned to accommodate the height of permanent magnet  1220 . An advantage of forming the stator teeth with end portions  1142   a  and  1142   b  facing the permanent magnet is that, the effective magnetic interaction area between the permanent magnet and the stator teeth can be increased compared to that formed by stator teeth without the bent or projected end portions  1142   a  and  1142   b.  The magnetic/mechanical energy conversion capability, and motor torque generation capability, can therefore be enhanced. In the meantime, the main area of stator teeth remains thin and this contributes to the reduction of overall thickness of the spindle motor stator at the stator teeth body area. Bent or projected end portions  1144  and  1148  form winding cores  1162 . 
         [0056]    As shown in  FIG. 13 , the windings  1120  may be formed by surrounding one or more winding core holes  1127 . Depending on the design requirements, more than one layers of windings may also be formed in a stator assembly, which can be conveniently implemented by the multi layer PCB fabrication technology. 
         [0057]    An added advantage is that, as the PCB may be laminated or adhered together with the stator teeth and stator yoke, both the strength and rigidity of the stator assembled can be increased, which may also contribute to the overall performance improvement of the spindle motor. 
         [0058]    As shown in  FIG. 14 , stator yoke  1150  may be formed of a single piece of magnetically permeable material, with openings such as holes or slots  1152  formed thereon, each for coupling to a winding core  1162 . 
         [0059]    Stator teeth  1140  and stator yoke  1150  are made of ferrite magnetic material, and form a magnetic flux passage to allow magnetic flux generated by permanent magnet  1220  to pass through and interact with stator windings. 
         [0060]    Magnetic flux passage along adjacent stator teeth  1140   a  and  1140   b  are taken as an example for illustration, as shown following the passage route indicated by arrows in  FIG. 15 . 
         [0061]    A magnetic flux generated from an N pole of permanent magnet  1220 , depicted by line  1341  in  FIG. 15 , passes across annular gap  1340  along radial direction, and into a first stator tooth  1161  via bent or projected edge portion  1161   a . Guided by the first tooth body  1161   b , the magnetic flux turns downwardly along axial direction, and passes through the first tooth pin  1161   c  (which serves as a winding core). When reaching stator yoke  1150 , the magnetic flux turns along circumferential direction, and further turns along axial direction upwardly upon reaching an adjacent tooth pin  1162   c  (which also serves as a winding core). The magnetic flux is then guided by the adjacent stator tooth body  1162   b  and edge portion  1162   a,  and turns radially back to an S pole of permanent magnet  1220 . 
         [0062]    With a stator assembly configured as per the above illustrations, a spindle motor according to embodiments of the present invention achieved a low profile or thinner stator than conventional spindle motors. With stator windings axially orientated, the spacing reserved between stator windings for fabrication tooling necessary for conventional spindle motors is successfully eliminated. This allows for an increased winding density and winding space utilization. 
         [0063]    Providing the stator tooth with two layers, the center of permanent magnet ring can be configured higher than the winding layer. The two layers can also form the upwardly bent or projected edge  1142   a  and downwardly edge bent or projected  1142   b,  and these edge portions can increase the tooth surface area surrounding the magnet. Another benefit in using the two-layer stator tooth structure is that, the eddy current in the stator tooth body can be greatly reduced, and the core loss can also be greatly reduced. 
         [0064]      FIG. 16  shows a yoke structure which may be adopted in the embodiment shown in  FIG. 1  or  FIG. 9 . The yoke has a set of projections  1153   a,  each of which may be positioned in a corresponding hole  1127 . The projections  1153   a  together with inner and outer stator tooth pin  1144  and  1148  form a winding core to allow magnetic flux to pass through. Projections  1153   a  can increase the contacting area between the yoke  1150  and the stator tooth  1140 , therefore the magnetic flux is easier to pass through the stator tooth  1140  to yoke  1150 . The projections  153   a  can also increase the mechanical strength of the stator. 
         [0065]      FIG. 17  shows another yoke structure which may be adopted in the embodiment shown in  FIG. 1  or  FIG. 9 . The yoke  1150  has first set of projections  1153   a  and second set of projections  1153   b,  forming a set of projection-pairs. Each projection-pair may be positioned in a hole  127 . The projection-pairs  1153   a ,  1153   b  together with inner and outer stator tooth pine  1144  and  148  form a winding core to allow magnetic flux to pass through. These projection-pairs can further increase the contacting area between the yoke  1150  and the stator tooth  1140 , therefore the magnetic flux is more easier to pass through the stator tooth  1140  to yoke  1150 . The projections  1153   a  and  1153   b  can further increase the mechanical strength of the stator. 
         [0066]      FIG. 18  shows another yoke structure which may be adopted in the embodiment shown in  FIG. 1  or  FIG. 9 . The yoke  1150  has a set of projections  1153   a,  each of which may be positioned through a corresponding hole  1127 , and to coupled to a corresponding stator tooth  1140  directly. Projections  1153   a  now form winding cores to allow magnetic flux to pass through. It would be appreciated according to this yoke structure, that some or all the stator teeth  1140  need not be formed with bent or projected ends for being positioned in the holes  1127 . 
         [0067]    As shown in  FIG. 19 , a spindle motor  1400  according to a further embodiment of the present invention includes a rotor yoke  1410  and permanent magnet  1420 . Similar structures of stator teeth, axially-oriented windings and stator yoke are provided, which enable a spindle motor with much reduced thickness than that of the conventional spindle motors. The present embodiment varies from that shown in  FIG. 9  in that, a plurality of teeth  1440  are disposed inside the permanent magnet  1420 . A spindle motor with outer rotor configuration can thus be formed. 
         [0068]    Although embodiments of the present invention have been illustrated in conjunction with the accompanying drawings and described in the foregoing detailed description, it should be appreciated that the invention is not limited to the embodiments disclosed, and is capable of numerous rearrangements, modifications, alternatives and substitutions without departing from the spirit of the invention as set forth and recited by the following claims.