Patent Publication Number: US-6215210-B1

Title: Motor, structure of stator of the motor and assembly method of the stator

Description:
This application is a divisional application of application No. 09/156,168 filed Sep. 17, 1998, now U.S. Pat. No. 6,049,147. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a motor, and in particular, relates to a structure of a stator thereof comprising a magnetic plate and a printed circuit board stacked together by calking and an assembly method of the stator. 
     2. Description of the Related Art 
     Presently, in a tape recorder and a video tape recorder, a capstan shaft is used in a combination of a pinch roller to transport a magnetic tape at a constant speed. The capstan shaft is driven at a constant speed by a motor. Recently, a direct drive method is employed, wherein the capstan shaft is directly connected to a rotor of a capstan motor. 
     In such a capstan motor as employing the direct drive method, the capstan motor generally comprises a rotor and a stator. The stator comprises a stator substrate having a magnetic plate made of a zinc steel sheet and a printed circuit board stacked together by calking, a bearing holder for rotatably supporting the capstan shaft through bearings and a stator core having windings and forming magnetic circuits, wherein the the stator core and the bearing holder are fixed to the stator substrate. The capstan shaft is integrally fixed to the rotor thereof. 
     SUMMARY OF THE INVENTION 
     Accordingly, a general object of the present invention is to provide a motor, a method of installing the motor, a structure of a stator of the motor and an assembly method of the stator. 
     A specific object of the present invention is to provide a stator structure of a motor, the stator structure comprising a stator substrate having a double-layer structure of a printed circuit board and a magnetic plate jointed together at a plurality of calking sections, wherein a centroid is determined with respect to the plurality of calking sections on the stator substrate, and defining a vacant area having no electric parts disposed nearby the centroid on the printed circuit board to allow the vacant area to be supported by a supporter of a calking jig. 
     Another and more specific object of the present invention is to provide an assembly method of a stator structure of a motor, the stator structure including a stator substrate having a double-layer structure of a printed circuit board and a magnetic plate jointed together at a plurality of calking sections, the method comprising steps of: determining a centroid with respect to the plurality of calking sections on the stator substrate; defining a vacant area without electric parts mounted nearby the centroid on the printed circuit board; calking the plurality of calking sections by using a calking jig having a plurality of calking pins for pressing the plurality of calking sections and having a retainer section for supporting the stator substrate, wherein the plurality of calking pins are disposed at positions agreeing to the plurality of calking sections provided on the printed circuit board and the retainer section is disposed facing a vicinity of the centroid so as to allow the retainer section to support the vacant area when the plurality of calking sections are calked by the plurality of the calking pins of the calking jig. 
     Other specific object of the present invention is to provide a motor composed of a rotor and a stator, the stator including a motor base, a printed circuit board stacked on a bottom of the motor base and a bearing holder mounted on the motor base and a magnetic core section having a plurality of stator coils, the rotor including a capstan shaft rotatably supported by the bearing holder through bearing means, a rotor yoke provided at an end of the capstan shaft, wherein the rotor is rotated by a mutual magnetic action between magnets provided on the rotor yoke and the plurality of the stator coils of the stator, wherein the bearing holder is provided with a flange protruding therefrom, the flange having motor base installation sections and core installation sections, and wherein the magnetic core section has a ring section provided with plural magnetic cores around an outer circumference thereof and has plural installation branches protruding radially toward a center of the ring section and respectively having installation portions connected respectively to the core installation sections of the flange, the plural installation branches defining cutout portions therebetween, and wherein the motor is assembled by causing the flange of the bearing holder to be interposed between the motor base and the plural installation branches together with the printed circuit board underneath, and ends of the stator coils are connected to respective terminal sections provided on the printed circuit board being partially exposed through the cutout portions defined between the plural installation branches of the ring section. 
     Other specific object of the present invention is to provide a method of installing a motor composed of a stator and a rotor, the stator including a motor base, a bearing holder mounted on the motor base and a magnetic core section having a plurality of stator coils, the rotor including a capstan shaft rotatably supported by the bearing holder through bearing means, a rotor yoke provided at an end of the capstan shaft, wherein the rotor is rotated by a mutual magnetic action between magnets provided on the rotor yoke and the plurality of the stator coils of the stator, wherein the bearing holder is provided with a flange protruding therefrom; the flange having motor base installation sections and core installation sections; and wherein the core section has a ring section provided with plural magnetic cores around an outer circumference thereof and plural installation branches protruding toward a center of the ring section and having respective installation portions connected respectively to the core installation sections of the flange, and wherein the motor is assembled by causing the flange of the bearing holder to be interposed between the motor base and the plural installation branches in such a manner that the motor base installation sections of the flange are exposed between the plural installation branches, and wherein a pinch roller of an apparatus is disposed on and pushed along a line toward the capstan shaft of the motor, wherein the line extends from one of the motor base installation sections to one of the plural installation branches. 
     Other objects and further features of the present invention will be apparent from the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view showing a calking jig; 
     FIG. 2 ( a ) is a plan view showing a structure of a stator in the related art; 
     FIG. 2 ( b ) is a side view showing the structure of the stator shown in FIG. 2 ( a ); 
     FIGS. 3 ( a ) to  3  ( c ) are schematic views for explaining a calking process; 
     FIG. 4 is a plan view showing a capstan motor for VTR (video tape recorder) employing a stator structure of a first embodiment in the present invention; 
     FIG. 5 is a side view showing the capstan motor shown in FIG. 4; 
     FIG. 6 is a plan view showing a surface for mounting electric parts on the capstan motor; 
     FIG. 7 is a plan view showing a stator structure of the first embodiment of the present invention; 
     FIG. 8 is a sectional view showing a brushless motor of a second embodiment of the present invention; 
     FIG. 9 is a plan view taken in the direction of an arrow  2  of the brushless motor shown in FIG. 8, wherein a rotor is removed from the brushless motor; and 
     FIG. 10 is a plan view showing the brushless motor shown in FIG. 9, wherein the calking centroid with respect to calking sections is depicted. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a side view showing a calking jig; 
     FIG. 2 ( a ) is a plan view showing a structure of a stator in the related art; 
     FIG. 2 ( b ) is a side view showing the structure of the stator shown in FIG. 2 ( a ); and 
     FIGS. 3 ( a ) to  3  ( c ) are schematic views for explaining a calking process. 
     Referring to FIGS. 2 ( a ) and  2 ( b ), a stator substrate  114  is formed by stacking a magnetic plate  108  made of a zinc steel sheet and a printed circuit board  107  on which a plurality of electric parts  106  are mounted. In the printed circuit board  107 , there are provided plural calking sections  101   a ,  101   b ,  101   c  and  101   d.    
     Upon calking a burring portion  115  of the calking sections  101   a ,  101   b ,  101   c  and  101   d , a calking jig  104  is used as shown FIG. 1, wherein a reference character  110  designates a calking pin and  109  a calking retainer for preventing the stator substrate  114  from being displaced when calked. 
     Referring to FIGS. 3 ( a ) to  3  ( c ) wherein an exemplary calking pin  110  and a burring portion  115  are depicted, the plural burring portions  115  of the calking sections  101   a ,  101   b ,  101   c ,  101   d  are calked by being pressed by the calking pins  110 , each provided in the calking jig  104  at a position corresponding to each of the positions of the burring portions  115  provided in the stator substrate  114 , while a vacant area  103  on the printed circuit board  107  where the electric parts  106  are not provided, is supported by being pressed by the retainer  109 . 
     Referring to FIGS.  2 ( a ) and  2 ( b ), a reference character  111  designates a flat circular area having a diameter of 20 mm of which a center corresponds to a centroid  105  (referred to as calking centroid) with respect to the calking sections  101   a ,  101   b ,  101   c  and  101   d . However, the flat circular area  111  is not supported by the calking retainer  109  because the some electric parts  106  are provided in the flat circular area  111 , thus, the calking retainer  109  is disposed to the vacant area  103 . 
     Generally, in the stator substrate  114  integrally made of the printed circuit board  107  and the magnetic plate  108  being calked, the degree of dimensional accuracy of the printed circuit board  107  is lower than that of the magnetic plate  108 . Thus, the printed circuit board  107  is apt to warp or buckle depending on the way of calking the burring portions  115 . 
     In the related art shown in FIGS.  2 ( a ) and  2 ( b ), the calking sections  101   a ,  101   d  could be calked in a high degree of dimensional accuracy, however, the calking sections  101   b ,  101   c  could not be done due to warping and buckling of the printed circuit board  107 , resulting in a hollow developed between the printed circuit board  107  and the magnetic plate  108 . As a result, there were problems of butting of the stator substrate  114  with the rotor  112  of the motor. 
     Referring to FIGS. 1,  3  ( a ) to ( c ) and  4  to  7 , the detailed description of the present invention is given of a motor of a first embodiment according to the present invention, wherein like parts are designated with like reference characters in the prior art, and the detailed description is omitted here. 
     FIG. 4 is a plan view showing a capstan motor for VTR (video tape recorder) employing a stator structure of a first embodiment in the present invention; 
     FIG. 5 is a side view showing the capstan motor shown in FIG. 4; 
     FIG. 6 is a plan view showing a surface for mounting electric parts in the capstan motor: and 
     FIG. 7 is a plan view showing a stator structure of the first embodiment in the present invention. 
     Referring to FIGS. 4 and 5, a capstan motor for a VTR of a first embodiment is composed of 24 slots and 16 magnetic poles. Around an outre circumference of a rotor  112 , there are provided magnetic sensors  113  of MR elements. A stator substrate  114  has a double-layer structure of a printed circuit board  107  and a zinc steel sheet (as the magnetic plate)  108 , which are integrally jointed at four calking sections  101   a ,  101   b ,  101   c ,  101   d.    
     Upon calking, a calking centroid (center of gravity)  105  with respect to the calking sections  101   a ,  101   b ,  101   c ,  101   d  is determined on the stator substrate  104  by calculating as mentioned hereinafter referring to FIG.  7 . 
     On the printed circuit board  107 , there is defined a flat circular section  111  of a diameter of 5 to 20 mm having a center corresponding to the calking centroid  105  mentioned above, and the electric parts  106  are not provided on the flat circular section  111 . 
     Referring to FIG. 1, the calking pins  110  of the calking jig  104  are disposed to butt the calking sections  101   a ,  101   b ,  101   c ,  101   d  of the stator substrate  114 . The calking retainer  109  of the calking jig  104  has a flat surface at an distal end thereof and is disposed to face the flat circular section  111  having its center corresponding to the calking centroid  105  to allow the printed circuit board  107  to be supported. 
     As shown in FIG.  3 ( a ), the plural burring portions  115  are formed as parts of the zinc steel sheet  108  so as to slightly protrude from the printed circuit board  107 . The calking pins  110  of the calking jig  104  are disposed to face the burring portions  115 . As shown in FIG.  3 ( b ), the burring portions  115  are pressed from a printed circuit board side by the calking pins  110 , resulting in that the burring portions  115  are calked, as shown in FIG. 3 ( c ). In this case, calking is made by causing the stator substrate  114  to be supported by the calking retainer  109 . Thus, it is possible to integrally joint the printed circuit board  107  and the zinc steel sheet  108  together in a high degree of dimensional accuracy. 
     As mentioned above, the plural calking sections  101   a ,  101   b ,  101   c ,  101   d  are simultaneously calked by causing the stator substrate  114  to be supported by the calking retainer  109  at the calking centroid  105  of the calking sections  101   a ,  101   b ,  101   c ,  101   d  and pressing thereof simultaneously by 4 of the calking pins  110 . Thus, it is possible to prevent the warp, buckling and rising of the printed circuit board  107  from developing. 
     Next, the description is given of how to determine the calking centroid  105 . 
     When a position of the calking section  101   a  is made to be the origin: (0, 0), a distance (mm) from the origin to each of the calking sections  101   b ,  101   c ,  101   d  is expressed in (x, y) coordinates, for instance, as follows. 
     the calking section  101   b : (43.5, 14.0) 
     the calking section  101   c : (45.6, 60.4) 
     the calking section  101   d : (1.3, 56.5) 
     Thus, when the calking centroid  105  is represented by coordinates (x,y), the x coordinate and the y coordinate are represented as follows. 
     
       
           x= ¼(0+43.5+45.6+1.3)=22.6, and  
       
     
     
       
           y= ¼(0+14.0+60.4+56.5)=32.73. 
       
     
     Accordingly, the position of the calking centroid  105  can be determined as (x,y) =(22.6, 32.6). As mentioned in the foregoing, on the flat circular area  111  having a diameter of 20 mm having the center corresponding to the calking centroid  105 , any electric parts  106  are not provided. The diameter of the calking retainer  109  is slightly made smaller than that of the flat circular area  111 . Thus, there is no contact of the calking retainer  109  with the electric parts  106 , resulting in efficient holding of the printed circuit board  107 . 
     Needless to say, it is possible to optionally determine a size of the flat circular area  111  where the electric parts  106  are not provided, and the size of the diameter of the calking retainer  109  in accordance with the number of the calking sections  101  and the size of the printed circuit board  107 . 
     As mentioned in the foregoing, according to the stator structure of the present invention, the stator substrate has a double-layer structure of the printed circuit board and the zinc steel sheet, and they are calked together at the four calking sections. At that time, the calking centroid is determined from the four calking sections. The electric parts are not provided within the flat circular area having a diameter of 20 mm of which a center corresponds to the calking centroid. Upon calking, the calking sections located around the outer circumference of the flat circular area are calked by causing the flat circular area to be held with the calking retainer. Thus, each of the calking sections in the printed circuit board is equally pressed with the calking pins, resulting in a prevention of the warp and rising of the printed circuit board. 
     According to the stator structure of the present invention, it is possible to prevent the warp and rising of the printed circuit board. Thereby, the stator substrate is securely made to be a flat plate, resulting in no contact of the stator substrate with the rotor and no vibration in a hollow developed between the printed circuit board and the magnetic plate due to the warp and rising of the printed circuit board. 
     Further, according to a method of the present invention that the electric parts are not provided on the flat circular area of which center corresponds to the calking centroid, it does not need an additional cost particularly because the printed circuit board can be designed or formed by the ordinary method. 
     Next, the description is given of a second embodiment of a brushless motor of the present invention referring to FIGS. 8 to  10 . 
     FIG. 8 is a sectional view showing a brushless motor of a second embodiment of the present invention; 
     FIG. 9 is a plan view taken in the direction of an arrow  2  of the brushless motor shown in FIG. 8, wherein a rotor is removed from the brushless motor; and 
     FIG. 10 is a plan view showing the brushless motor shown in FIG. 9, wherein the calking centroid with respect to calking sections is depicted. 
     As shown in FIG. 8, a brushless motor  1  of a second embodiment of the present invention generally comprises a rotor  10  and a stator  20 . The rotor  10  comprises a rotor yoke  11 , a capstan shaft  12  provided at a center of the rotor yoke  11 , driving magnets  13  provided around an internal circumference of the rotor yoke  11 , frequency generating magnets (referred to as FG magnets)  14  and a pulley  15  provided at a center of the rotor yoke  11  for driving external devices and a retainer  16  provided at a middle of the capstan shaft  12 . 
     A stator  20  comprises a motor base  21 , a printed circuit board  22  stacked at a bottom of the motor base  21 , a bearing holder  23  having a cylindrical section  23   a  and a flange  24 , and a stator coil assembly  25 . The cylindrical section  23   a  of the bearing holder  23  penetrates through both the printed circuit board  22  and the motor base  21 . Both the printed circuit board  22  and the motor base  21  are mounted on an upper surface of the flange  24 , and the stator coil assembly  25  is mounted on a lower surface of the flange  24 . 
     Reference character  21   a  designates a protruding section provided in the motor base  21  for contacting with electric parts,  27   a  and  27   b  oilless bearings for rotatably supporting the capstan shaft  12 ,  28  a screw for installing the bearing holder  23 ,  29  a thrust cup interposed between the bearing holder  23  and the retainer  16 , P a pinch roller to drive a tape with the capstan shaft  12 . 
     Referring to FIG. 9, on the printed circuit board  22  there are mounted a magnetic resistance element (referred to as MR element)  32  and IC (integrated circuit)  33 , and connecting sections  34  are formed. 
     The stator coil assembly  25  comprises a ring core  36  and stator coils  37  wound around the ring core  36 . 
     Specifically, the ring core  36  comprises protruding poles  36   a  for winding plural stator coils  37 , a ring section  36   b  for connecting internal circumference of the protruding poles  36   a . The ring section  36   b  has three installation branches  36   c  extending toward a center of the ring section  36   b  for attachment. Further, a reference character  36   d  designates mounting holes,  36   e  protruding portions for calking,  36   f ,  36   g  calking portions. 
     Distal ends  37   a  of each of the stator coils  37  are connected to the connecting sections  34 ,  34  so as to electrically connect the printed circuit board  22 . 
     Further, a reference character  24   a  designates motor base installation sections provided in the flange  24 , and  24   b  core installation sections provided in the flange  24 . 
     Referring to FIG. 10, the brushless motor  1  of the second embodiment has the same stator structure as that of the first embodiment in the present invention. 
     As explained for the first embodiment of the present invention, in the stator structure of the second embodiment of the present invention, the stator substrate  114  has a double-layer structure of the printed circuit board  22  and the motor base  21  made of a zinc steel sheet, and they are calked together at the four calking sections  101   a ,  101   b ,  101   c ,  101   d . At that time, the calking centroid  105  is determined from the four calking sections  101   a ,  101   b ,  101   c ,  101   d . The electric parts are not provided within the flat circular area  111  having a diameter of 20 mm of which center agrees to the calking centroid  105 . Upon calking, the calking sections  101   a ,  101   b ,  101   c ,  101   d  located around the outer circumference of the flat circular area  111  are calked by causing the flat circular area  111  to be held with the calking retainer  109  of the calking jig  104  shown in FIG.  1 . Thus, each of the calking sections  101   a ,  101   b ,  101   c ,  101   d  in the printed circuit board  22  is equally pressed with the calking pins  110  of the calking jig  104 , resulting in a prevention of the warp and rising of the printed circuit board  22 . 
     Next, the description is given of the structural features and the effectiveness thereof in the present invention. 
     In the ring section  36   b , there are defined fan-shaped cutouts C between the installation branches  36   c ,  36   c  so that the printed circuit board  22  is partially exposed. The connecting sections  34  are formed on the exposed parts of the printed circuit board  22 . Accordingly, it is possible to directly connect the distal ends  37   a  of the stator coils  37  to the connecting sections  34 , this enables an effective assembly of the brushless motor and a reliable brushless motor. 
     The ring section  36   b  of the ring core  36  is provided with the three installation branches  36   c  radially at an equal angular interval protruding toward the center direction of the ring section  36   b , and the flange  24  is provided with the motor base installation sections  24   a  positioned at an equal angular distance from the adjacent installation branches  36   c  and on a same circumference as that of the core installation section  24   b . When the brushless motor  1  is assembled, the motor base  21  and the printed circuit board  22  are mounted together on the flange  24  at the motor base installation section  24   a  and the ring core  36  is mounted on the flange  24  at the core installation section  24   b  with the screws  28 . Accordingly, upon installing the ring core  36  and the bearing holder  23  in the motor base  21 , the installing positions of the ring core  36  and the motor base  21  can be optionally selected in a circumferential direction of the ring section  36   b . This feature enables an easy assembly of the brushless motor  1 . 
     Further, in order not to reduce a sectional area of magnetic circuit due to a provision of the calking portion  36   g  the protruding portions  36   e  for calking are formed to protrude from the ring section  36   b  in a semicircular shape toward the center of the ring section  36   b , resulting in no variations of magnetic resistance values between the magnetic circuits relative to the protruding poles  36   a  close to the calking portions  36   g  and the magnetic circuits of the protruding poles  36   a  remote from the calking portions  36   g . Thus, it is possible to prevent the variation of the magnetic characteristics in the magnetic circuit of the stator  20 , resulting in a reduction of unevenness of torque developed by the brushless motor  1 . 
     Upon applying the brushless motor  1  to a device, a pressing direction shown with an arrow A of a pinch roller P is determined along a line L extended from one of the motor base installation section  24   a  to one of the installation branches  36   c . Accordingly, it is possible to prevent an overall inclination of the brushless motor  1  when the capstan shaft  12  is pushed in the direction shown with the arrow A along the line L by the pinch roller P. 
     According to the present invention, the motor is assembled by causing the flange of the bearing holder to be interposed between the motor base and the plural installation branches together with the printed circuit board underneath, and ends of the stator coils are connected to respective terminal sections provided on the printed circuit board being partially exposed through the cutout portions defined between the plural installation branches of the ring section. Thus, upon installing the ring core and the bearing holder to the motor base, the installing positions of the ring core and the motor can be optionally decided in a circumferential direction of the ring section. This feature enables an easy assembly of the motor. 
     Further, according to the present invention, a pinch roller of an apparatus is vertically pushed to the capstan shaft of the motor in a direction along a line extended from the capstan shaft to one of the plural branch sections. 
     Thereby, the inclination of the capstan shaft of the motor caused by the pushing force exerted from the pinch roller is effectively prevented.