Abstract:
A disk drive comprising a rotor, to which a disk and a plurality of magnets are fixed, and an open-slot type integrally molded stator disposed about an outer periphery of the magnets, and wherein the stator comprises coils formed by etching metallic films on teeth. The invention may also be applied to a closed-slot type stator. With either type, it is possible to produce an opening that is equal to or smaller than the thickness of a coil wire and cogging torque is minimized.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a disk drive motor for rotating a disk or disks and to a disk storage device in which it is incorporated.  
           [0002]    Ordinarily, a stator of a spindle motor of a disk drive has an open-slot construction, in which slot intervals are larger in width than a conductive coil wire. A stator coil is formed in a wrapping system where a tool is inserted into a slot interval and a coil wire is wrapped around a tooth stator tooth coil forming section, or which uses a fitting system where a formed coil is fitted on a tooth. There is also a closed-slot construction described in Japanese Patent Laid-Open No. 54468/1994. A method of forming a coil in this closed-slot construction includes the wrapping system.  
           [0003]    In some cases, cogging torque is generated in a magnetic circuit of a disk drive that results in jerking or disrupted rotation. In particular, in attempting to reduce the disk diameter and or the overall shape of a disk and to produce a thin disk drive, it is necessary to increase magnetic forces to ensure the required torque. However, when a magnet producing large magnetic forces is used, for example, a Nd-Fe-B sintering magnet, an intense magnetic field can be generated but the cogging torque problem is also increased. To suppress such cogging torque, it is effective to decrease the radial gaps at the tooth tip ends to smoothly change the magnetic poles as in the above-mentioned prior art.  
           [0004]    In using a closed-slot construction, as described in the above-mentioned Japanese Patent Laid-Open No. 54468/1994, in which the tooth are caulked on a connecting part, the closed-slot construction can be fabricated but the increased number of parts causes problems such as increased assembling cost, degradation in durability at connections, increased thickness of the completed disk drive, or the like.  
           [0005]    In using an open-slot construction and a wrapping system in which the interval between adjacent tooth slits is decreased to the minimum thickness of a coil wire or less, the coil wire cannot be inserted into the slit, so the slit width must be enlarged by alteration to afford passage of the coil wire. When reworking is carried out to restore the original form, however, an accurate restoration is difficult, so that an area facing a rotor magnet is inevitably decreased. Since the tooth tip ends are opposed to a permanent magnet of a rotor to generate torque, torque is decreased when the area facing the rotor magnet is decreased.  
           [0006]    Moreover, since passage by enlarged pieces (minimum slit width) at the tooth tip ends is necessary when using the fitting system, alterations must be made in the same manner as above. That is, in both the closed-slot and open-slot construction, in which slot intervals are equal to or smaller in width than a coil wire, a coil has never been formed without reworking the tooth that constitute a stator core.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    An object of the invention is to make a disk drive, in which torque is not decreased even when using a closed-slot open-slot construction in which slot intervals are equal to or smaller in width than a coil wire. The above problems are solved by the following embodiments of the invention.  
           [0008]    In one aspect of the invention, a disk drive motor comprises a rotor to which a disk and a plurality of magnets are fixed, and an open-slot type integrally molded stator disposed about an outer periphery of magnets, with the stator comprising coils formed by etching metallic films on the teeth. In this manner, since the slot width can be decreased irrespective of the thickness of a conductive coil, it is possible to realize a disk drive motor with nominal cogging torque that is capable of smooth rotation.  
           [0009]    Further, when the minimum width of the slots is equal to or smaller than the minimum thickness of a coil wrapped around the stator, reduction in torque can be suppressed by using the above stator. In another aspect of the invention, a disk drive motor comprises a rotor, to which a disk and a plurality of magnets are fixed, and a stator provided with coils that are formed by etching metallic films on closed-slot type stator tooth disposed about an outer periphery of the magnets.  
           [0010]    Ordinarily, when using closed-slot type integrally molded teeth for a stator core, a coil conductor cannot be formed unless a special winding machine is used. With the above configuration, a stator coil can be formed without the use of any special winding machine. Moreover, since the slot width can be decreased irrespective of the thickness of a coil conductor, it is possible to realize a disk drive with small cogging torque and that is capable of smooth rotation.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a cross-sectional view showing an essential portion of a disk drive;  
         [0012]    [0012]FIG. 2 is a schematic view showing parts of a rotor and a stator in a disk drive motor as viewed from a direction of a rotating axis;  
         [0013]    [0013]FIG. 3 is a view showing an essential part of the structure of the disk drive motor taken along a cut plane c-c′ shown in FIG. 2;  
         [0014]    [0014]FIG. 4 is a view showing an essential part of the structure of the disk drive motor taken along a cut plane d-d′ shown in FIG. 2;  
         [0015]    [0015]FIG. 5 illustrates a procedure for forming a metal core substrate; and  
         [0016]    [0016]FIG. 6 is a graph showing the relationship between the spacing G about iron core piece tip ends and the cogging torque in motors with Nd-Fe-B bond magnets and Nd-Fe-B sintered magnets. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    [0017]FIG. 1 is a view showing a portion of a mounting structure of a disk drive according to the invention. A disk storage device  100  is constructed such that a space enclosed by a base  101 , a connector  170  and a cover  102  mounts therein a disk  103  having an outside diameter of 1 inch, a rotor  109  for driving the disk, and a stator, the storage device having the same outside dimension (43 mm×36 mm×3.3 mm) as that of a compact flash memory.  
         [0018]    A stationary shaft  105  is fixed to base  101  by a fixing screw  106 . A hub  104  is rotatably supported on stationary shaft  105  by bearings  107 ,  108 . Disk  103  is fixed to hub  104  by a ring  112  and a nut  113 . An annular-shaped permanent magnet  110  is fitted onto an upper surface of hub  104 . A metal core substrate  200  and wirings formed on the front and back sides of the metal core substrate function as a wiring substrate mounting thereon parts such as a stator, ICs etc. The wiring substrate is fixed at four corners thereof to projections (not shown) of base  101 . A circuit layer is formed on metal core substrate  200  to electrically connect an IC  150  and chip parts  151  by soldering or gold wires, and mounts on an end thereof a connector  170  formed with a plurality of signal pins through-which external electric signals are received from and transmitted to disk storage device  100 .  
         [0019]    To prevent particles entering from outside of disk storage device  100  from adhering to surfaces of disk  103 , a sealing resin  171  is applied on the connector  170  to be heated and cured, thereby plugging through-holes formed in connector  170 . A magnetic shielding plate  160  is provided between metal core substrate  200  and disk  103  to be fixed and mounted to a surface of metal core substrate  200 . The shielding plate shuts off magnetism generated from the metal core substrate thereby inhibiting influences on disk  103 .  
         [0020]    [0020]FIG. 2 is a schematic view showing parts of rotor  109  and stator in the disk drive motor as viewed from the direction of a rotating axis. Annular-shaped permanent magnet  110  constitutes a rotor  109 , and is divided circumferentially into a desired number of poles, for example, twelve or sixteen poles, to be magnetized. The direction of magnetization is radial as indicated by N poles and S poles in the figure.  
         [0021]    Metal core substrate  200  includes a teeth connection  201 , teeth coil forming portions  204 , teeth tip ends  205 , wirings  202 , and through holes  203 . The teeth connection  201  is a laminated plate composed of thin sheets of a soft magnetic material, for example, silicon iron, and constructed to result in minimal motor iron loss. The teeth coil forming portions  204  and teeth tip ends  205  are constructed in the same manner as the teeth connection, the teeth tip ends  205  being opposed to annular-shaped permanent magnet  110  with a radial gap  206  therebetween. The teeth coil forming portions  204  comprise the number of teeth, usually 18 or 24 i.e. 1.5 times the number of poles of the annular-shaped permanent magnet  110 .  
         [0022]    Wirings  202  are formed on the front and back surfaces of the teeth connection  201  and teeth coil forming portions  204  with insulating layers therebetween. The wirings on the teeth connection  201  constitute an electronic circuit capable of mounting thereon electronic parts and are connected to the wirings on the teeth coil forming portions  204 . The wirings on the front and back surfaces of the teeth coil forming portions  204  are connected to each other at through-holes  203  in a resin disposed between the teeth coil forming portions  204  and adjacent teeth coil forming portions, thus providing a winding structure, which wraps the teeth coil forming portions  204 . Thus the electronic parts mounted on the teeth connection  201  control an electric current flowing through the wirings to thereby control a magnetic field generated about the annular-shaped permanent magnet  110  to produce torque for rotating rotor  109 .  
         [0023]    G denotes the spacing between adjacent teeth tip ends  205 . When the spacing G is decreased or the teeth tip ends  205  are shaped to connect to one another, a part of lines of magnetic force inside the teeth tip ends is permitted to flow to adjacent teeth tip ends  205  whereby the magnetic forces with which annular-shaped permanent magnet  110  and the teeth tip ends  205  attract each other are decreased, and so the cogging torque is decreased.  
         [0024]    [0024]FIG. 3 shows a cross-sectional view of an essential part of the disk drive motor structure taken along a cut plane c-c′ in FIG. 2. Metal core substrate  200  is composed of two-layered front surface wirings  208 , two-layered back surface wirings  209 , teeth coil forming portions  204 , the through-holes  203 , and insulating layer  207 . The embodiment provides a winding construction in which the wirings are wound two times around the teeth coil forming portions  204 . When the wiring layer is made further multi-layered in the process of forming metal core substrate  200 , the windings may be further increased.  
         [0025]    [0025]FIG. 4 shows a part of the disk drive motor structure taken along a cut plane d-d′ in FIG. 2. The teeth connection  201  is constructed such that four thin sheets formed from silicon iron and having a thickness of about 0.1 mm are stacked on one another in the teeth coil forming portions  204  and have a total thickness t 1  of about 0.4 mm. In addition, two thin sheets are applied on the front and back surfaces of iron core piece tip ends  205 , respectively, and a total thickness t 2  amounts to about 0.8 mm. Thus, by increasing the thickness of iron core piece tip ends  205 , magnetic flux from annular-shaped permanent magnet  110  can be efficiently caught to ensure torque, and by forming the tooth coil forming portions  204  in areas other than the iron core piece tip ends to make the same thin sheets?], making the stator thin can be achieved.  
         [0026]    Reference d in FIGS. 3 and 4 denotes the wiring thickness of front surface wiring  208  or back surface wiring  209 , of which the wire conductor is of a minimum thickness. In a motor construction, in which a conventional winding is wrapped around teeth coil forming portions  204 , coils can be inserted about the teeth coil forming portions by enlarging the spacing G shown in FIG. 2 as compared to the winding thickness d. An advantage of the invention is that the coils, iron core pieces and wiring substrate can be formed as a unit, so that there is no need enlarge the spacing G as compared to the winding thickness d, and the spacing G may be made equal to or smaller than the winding thickness d. Further, the spacing G=0, that is, a configuration in which the teeth tip ends  205  are connected to one another, is also possible.  
         [0027]    [0027]FIG. 5 shows a procedure for forming metal core substrate  200 .  
         [0028]    (a) Teeth connection  201 , teeth coil forming portions  204  and the teeth tip ends  205  are prepared as metal core materials, all of which are formed from silicon iron having minimal iron loss and a thickness of about 0.1 mm.  
         [0029]    (b) The teeth tip ends are shaped by chemical etching and four magnetic metal sheets are laminated with an adhesive.  
         [0030]    (c) A RCC (Resin Coated Copper), being copper foil and coated beforehand on one side thereof with a resin adhesive layer, is applied on the front and back surfaces of teeth connection  201 , teeth coil forming portions  204  and teeth tip ends  205 .  
         [0031]    (d) A drill or laser is used to form through-holes  203  extending through the core materials of the metal substrate.  
         [0032]    (e) The inner walls of through-holes  203  are then copper plated.  
         [0033]    (f) By etching the copper foil, circuit patterns  202  in an X-direction are formed on the front and back surfaces of the substrate. At this time, wirings on flat portions of coils surrounding the teeth coil forming portions  204  are simultaneously formed.  
         [0034]    (g) The RCC is further laminated on the front and back surfaces, and circuit patterns  202  in a Y-direction are formed by etching in the same manner as the above. Here, second layer wirings are formed on the flat portions of coils surrounding teeth coil forming portions  204 . Through-holes connecting with the first layer through-holes and wirings are formed, and the interior of the through-holes are then copper plated.  
         [0035]    (h) A solder resist layer is formed to prevent dispersion of solder for soldered parts.  
         [0036]    (i) After solder is supplied by printing, a chip mounter is used to mount the IC  150  and the chip parts  151  and the parts are soldered in a reflow furnace. At this time, a connector is also mounted.  
         [0037]    According to the above procedure, formation of the metal core substrate and mounting of parts are completed, and resin  171  is used to seal the side of the connector as shown in FIG. 1. After mounting disk  103  on hub  104 , fixing screw  106  is used to fix rotor part  109  including bearings  107 ,  108  to base  101 . Thereafter, metal core substrate  200  mounting thereon magnetic shielding plate  160  is fixed to projections (not shown) formed at four corners of the base  101 . Finally, cover  102  is mounted and the disk storage device is completed.  
         [0038]    [0038]FIG. 6 shows a graph, in which an axis of abscissa represents a spacing G about teeth tip ends  205  and an axis of ordinates represents cogging torque. L 1  indicates a cogging torque of a motor including conventional Nd-Fe-B bond magnets. L 2  indicates a cogging torque of a motor including Nd-Fe-B sintered magnets having a higher performance. With L 1 , motor rotation is possible even in the range of G=0.1 to 0.15 mm since the cogging torque is not in excess of torque (=0.067 mNm) at the time of rated rotation (@3600 rpm). In contrast, with L 2  the cogging torque amounts to about three times that with L 1 , and is in excess of torque (=0.067 mNm) at the time of rated rotation (@3600 rpm) when in the range of G=0.05 mm or more, and therefore motor rotation becomes impossible, so that the spacing must be within the range of G=0.04 mm or less.  
         [0039]    With that motor construction, in which a conventional winding is wrapped around teeth coil forming portions  204 , the coil has a diameter of about 0.06 to 0.07 mm and so cannot be inserted about the teeth coil forming portions  204  when the spacing is in the range of G=0.04 mm or less. While coil formation is possible provided that the winding has a diameter of 0.04 mm or less, coil resistance is increased leading to an increase in energy loss due to current.  
         [0040]    According to the invention, the storage device can be created in principle even when the thickness of the wiring is equal to or smaller than the spacing G, so that spacing in the range of G=0.04 mm or less can be produced. Accordingly, reduction in cogging torque is made possible with the Nd-Fe-B sintered magnet, which is higher in performance than conventional magnets, and the design of a thin motor with high torque becomes possible.  
         [0041]    According to the above embodiment, the stator coil is formed without the use. of slit openings, so slit intervals can be small. In particular, it is possible to fabricate both closed slots and open slots in which an opening is equal to or smaller than a thickness of a coil wire.