Abstract:
A stator sub-assembly comprises: a coil bobbin which is composed of a cylinder having a winding of a magnet wire therearound, and a terminal block provided with terminal pins connected to lead wires of the winding and coupled stator yokes housing said coil bobbin therein and having a cutout for allowing the terminal block to protrude therethrough. The cutout has a width adapted to allow the terminal block to circumferentially shift rotationally about the center of an axial direction of the coil bobbin.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a stator sub-assembly, a stator assembly, a motor using the same, and a manufacturing method of the stator assembly.  
           [0003]    2. Description of the Related Art  
           [0004]    A stepping motor has been extensively used as a motor used for a rotating component and the like of an OA apparatus or an automobile. The stepping motor converts a digital electric input into a mechanical motion in response to electric signals and rotates stepwise by a fixed angle for each step, thus attaining a high accuracy in positioning. One type of such a stepping motor is a PM (permanent magnet) stepping motor using a permanent magnet in a rotor section thereof.  
           [0005]    A conventional PM stepping motor is provided with a stator assembly  100  as shown in FIG. 10. The stator assembly  100  comprises two stator subassemblies  101  and  101  attached back to back.  
           [0006]    [0006]FIG. 11 shows an exploded view of one of the two stator subassemblies  101  and  101 . The stator sub-assembly  101  comprises a cylindrical cup-shaped outer stator yoke  102 , an inner stator yoke  103  made of a ring-shaped steel plate and a winding  104 .  
           [0007]    The outer stator yoke  102  and the inner stator yoke  103  are formed such that after punching out their respective soft magnetic materials, their respective plurality of pole teeth  102   a  and  103   a  are intermeshed, with a gap. The winding  104  is formed by winding a magnet wire W around a flanged bobbin  105  made of plastic resin The flanged bobbin  105  includes a terminal block  107  protruding from its cylindrical flange substantially perpendicularly to its axial direction, and has a plurality of terminal pins  106  projecting from the terminal block  107  and fixed thereto. Lead wires of the winding  104  are hooked around the terminal pins and soldered. The terminal pins  106  are connected to a driving circuit of an apparatus on which the stepping motor is mounted.  
           [0008]    A cutout  102   b  is formed in the outer stator yoke  102  in order to allow the terminal block  107  protrude outward. Referring to FIG. 12, a width of the cutout  102   b  is set to be substantially equal to a width of the terminal block  107 , thereby securely fixing the winding  104  within coupled stator subassemblies  101  and  101 .  
           [0009]    The stator assembly  100  is formed such that the two stator subassemblies  101  and  101  each having the above-described structure are, for example, resin-molded with one another with their respective inner yokes in contact. Here, the two stator subassemblies  101  and  101  are coupled such that their respective plurality of pole teeth are misaligned by an optical electrical angle, for example, 90 degrees.  
           [0010]    However, when the stator assembly  100  is structured as described above, a displacement in a relative electrical angle between the two kinds of pole teeth has to be adjusted, causing a dislocation between the two terminal blocks opposite to each other to occur as shown in FIG. 11. Consequently, it is difficult or complicated to make a smooth electrical connection between the stepping motor provided with the above-described stator assembly  100  and an apparatus on which the stepping motor is mounted.  
           [0011]    For example, in case of connecting the terminal pins  106  with a flexible printed circuit (FPC)  109  having connection holes  108  as shown in FIG. 12, it is necessary to make such a special design as to boring rather big connection holes due to the dislocation between the two terminal blocks opposite to each other. However, enlarging the connection holes involves defects such as incomplete soldering, thereby diminishing the reliability of soldering.  
           [0012]    In brief, the conventional stator assembly  100  has a defect in that the dislocation between the two terminal blocks  107  and  107  opposite to each other can occur, causing the defects of the electrical connection between the motor having the stator assembly  100  and the apparatus on which the motor is mounted, eventually diminishing the manufacturing reliability of the stator assembly and the motor.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention has been made in the light of the above, and its object is to provide a stator sub-assembly, a stator assembly, and a motor which allow them to have their respective smooth electrical connections with an apparatus on which they are mounted and also to provide a method of manufacturing a highly-reliable stator.  
           [0014]    In order to achieve the above object, according to a first aspect of the present invention, a stator sub-assembly comprises:  
           [0015]    a coil bobbin composed of a cylinder having a winding. of a magnet wire therearound, and a terminal block provided with terminal pins connected to lead wires of the winding; and  
           [0016]    coupled stator yokes housing the coil bobbin therein and having a cutout for allowing the terminal block to protrude therethrough, the cutout having a width adapted to allow the terminal block to circumferentially shift rotatably about a center of an axial direction of the coil bobbin.  
           [0017]    In the first aspect of the present invention, a first angle made by two radii connecting a center of the coupled stator yokes to both circumferential ends of the terminal block may be set to be smaller than a second angle made by two radii connecting the center of the coupled stator yokes to both circumferential ends of the cutout.  
           [0018]    In the first aspect of the present invention, the first angle may be set to be smaller than the second angle by an electrical angle of at least 10 degrees.  
           [0019]    According to a second aspect of the present invention, a stator assembly comprises two stator subassemblies, wherein  
           [0020]    the two stator subassemblies each comprise: a coil bobbin composed of a cylinder having a winding of a magnet wire therearound, and a terminal block provided with terminal pins connected to lead wires of the winding; and coupled stator yokes housing the bobbin therein and having a cutout for allowing the terminal block to protrude therethrough, the cutout having a width adapted to allow the terminal block to circumferentially shift rotationally about a center of an axial direction of the coil bobbin; and  
           [0021]    the two stator sub-assemblies are disposed such that respective terminal blocks of the two stator sub-assemblies abut on each other.  
           [0022]    In the second aspect of the present invention, a first angle made by two radii connecting a center of the coupled stator yokes to both circumferential ends of the terminal block may be set to be smaller than a second angle made by two radii connecting the center of the coupled stator yokes to both circumferential ends of the cutout.  
           [0023]    In the second aspect of the present invention, the first angle may be set to be smaller than the second angle by an electrical angle of at least 10 degrees.  
           [0024]    In the second aspect of the present invention, the respective terminal blocks of the two stator sub-assemblies may be positioned so as to be circumferentially overlapped each other.  
           [0025]    In the second aspect of the present invention, the terminal block may have a positioning mechanism.  
           [0026]    In the second aspect of the present invention, respective coupled stator yokes of the two stator sub-assemblies may be disposed such that respective pole teeth of the respective coupled stator yokes are misaligned relative to each other by a predetermined electrical angle.  
           [0027]    According to a third aspect of the present invention, a motor has a stator assembly according to the second aspect of the present invention.  
           [0028]    According to the fourth aspect of the present invention, a method of manufacturing a stator assembly includes two stator sub-assemblies each comprising: a coil bobbin composed of a cylinder having a winding of a magnet wire therearound and a terminal block provided with terminal pins connected to lead wires of the winding; and coupled stator yokes housing the coil bobbin therein and having a cutout for allowing the terminal block to protrude therethrough, the method comprising:  
           [0029]    a process in which the two stator sub-assemblies are superimposed back-to-back such that respective coupled stator yokes of the two stator sub-assemblies are disposed in a predetermined relative position, with respective terminal blocks of the two stator sub-assemblies abutting on each other; and  
           [0030]    a process in which the respective terminal blocks are positioned so as to be circumferentially overlapped with each other in a state of the respective coupled stator yokes being fixedly attached each other. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    These objects and other objects and advantages of the present invention will become more apparent upon reading of the following detailed description and the accompanying drawings in which:  
         [0032]    [0032]FIG. 1 shows a cross-sectional structure of a stepping motor according to an embodiment of the present invention;  
         [0033]    [0033]FIG. 2 shows a perspective view of a stator assembly shown in FIG. 1;  
         [0034]    [0034]FIG. 3 shows an exploded view of a stator subassembly shown in FIG. 2;  
         [0035]    [0035]FIG. 4 shows a partial illustration of a coupling state of an outer stator yoke and an inner stator yoke;  
         [0036]    [0036]FIG. 5 shows a sectional view of the stator assembly shown in FIG. 2 taken along an abutting contact surface of the two stator subassemblies with the outer stator yoke housed in a coil bobbin:  
         [0037]    FIGS.  6 A- 6 D show four methods of positioning a terminal block;  
         [0038]    [0038]FIG. 7 shows a side view of a stator assembly in a positioned state;  
         [0039]    [0039]FIG. 8 shows an FPC;  
         [0040]    [0040]FIG. 9 shows a perspective view of a conventional stator assembly;  
         [0041]    [0041]FIG. 10 shows an exploded view of the stator subassembly shown in FIG. 9;  
         [0042]    [0042]FIG. 11 shows a side view of the stator assembly shown in FIG. 9; and  
         [0043]    [0043]FIG. 12 shows a configuration of a conventional FPC. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]    Preferred embodiments of the present invention will hereinafter be explained with reference to the accompanying drawings.  
         [0045]    In the following preferred embodiments, a PM stepping motor using a permanent magnet and used as a rotating component or the like of an OA apparatus or an automobile will be discussed as an example.  
         [0046]    [0046]FIG. 1 shows a cross-sectional structure of a stepping motor  1  generally comprising a stator assembly  12  and a rotor assembly  13 .  
         [0047]    Referring to FIG. 2, the stator assembly  12  is formed such that two stator subassemblies  14  and  14  are superimposed back to back. As shown in an exploded view of FIG. 3, the stator subassembly  14  comprises an outer stator yoke  15 , an inner stator yoke  16 , a coil bobbin  17  and a cover ring  18 .  
         [0048]    The outer stator yoke  15  constitutes a periphery and top surface of the stator subassembly  14 , and is made of a cup-shaped, cylindrical soft magnetic steel plate, and has a plurality of first pole teeth  15   a  formed along its an inner circumference and bent up, and has a cutout  15   b  formed in its outer circumferential wall. The first pole teeth  15   a  are formed by bending the soft magnetic steel plate, and are set to be equidistant from one another at a predetermined electrical angle.  
         [0049]    A cutout  1   5   b  is formed in a side wall of the outer stator yoke  15  and is adapted to allow a terminal block  20  of a coil bobbin  17  to protrude therefrom. The terminal block  20  will be later described in detail. The outer stator yoke  15  also has a positioning notch  15   c.    
         [0050]    The inner stator yoke  16  is made of a soft magnetic steel plate or the like and is a ring-shaped plate whose outer diameter is substantially equal to an inner diameter of the outer stator yoke  15 . The inner and outer stator yokes are arranged such that they are substantially concentric with each other, and the inner stator yoke  16  is accommodated in an open space of the outer stator yoke  15  in such a manner as to constitute a bottom surface of the stator subassembly  14 .  
         [0051]    An inner circumference of the inner stator yoke  16  has the same diameter as that of the outer stator yoke  15 . A plurality of second pole teeth  16   a  are formed on an inner circumferential side of the inner stator yoke  16 , by bending the soft magnetic steel plate, and are set to be equidistant one another at a predetermined electrical angle.  
         [0052]    The first and second pole teeth  15   a  and  16   a  are intermeshed with a gap in a state that the outer and inner stator yokes  15  and  16  are properly positioned and coupled. FIG. 4 shows a partial illustration of that coupling state.  
         [0053]    Referring back to FIG. 3, a chamfered edge  16   b  is formed, by cutting off a plano-convex portion from a ring-shaped circumferential portion of the inner stator yoke  16 . And, the chamfered edge  16   b  has a substantially rectangular surface and it is close to a terminal block  20  of the coil bobbin  17 .  
         [0054]    A positioning projection  16   c  is formed at a point on the opposite to the chamfered edge  16   b  on a circumferential side portion of the inner stator yoke  16 . The positioning projection  16   c  is adapted to engage with a positioning notch  15   c  of the outer stator yoke  15 , so that the outer and inner stator yokes  15  and  16  are positioned correctly and securely and coupled with each other.  
         [0055]    The coil bobbin  17  is made of, for example, a plastic material and consists of a bobbin body  19  and the terminal block  20 .  
         [0056]    The bobbin body  19  is substantially cylindrical with its cross-section in a shape of a letter H, and it has a magnet wire W wound therearound in many turns. The many turns of the magnet wire W wound around the bobbin body  19  make a coil.  
         [0057]    The bobbin body  19  is disposed around the first and second pole teeth  15   a  and  16   a  such that it is concentric with the outer and inner stator yokes  15  and  16 .  
         [0058]    The terminal block  20  is formed continuously from an inner flange in such a manner as to protrude outward with a predetermined width for predetermined length so as to be shaped substantially rectangular. The terminal block  20  protrudes, with a predetermined width, outwardly from the bobbin body  19 , and it is substantially rectangular. The terminal block  20  has a certain thickness for housing terminal pins in the axial direction of the bobbin body  19 . With the inner stator yoke  16  received in the coil bobbin  16 , the chamfered edge  16   b  of the inner stator yoke  16  is shaped to fit an elevated portion of the terminal block  20 , thereby functioning as a means for positioning the terminal block  20  to slackly engage therewith.  
         [0059]    As explained in detail later, the slack engagement means that the coil bobbin  17  and the inner stator yoke  16  can rotate stepwise to a certain extent in their circumferential direction,  
         [0060]    A height of a lower elevation of the terminal block  20  is set to be substantially equal to a thickness of the inner stator yoke  16 . With the chamfered edge  16   b  of the inner stator yoke  16  slackly engaging with the terminal block  20 , the terminal block  20  shares substantially the same plane (one surface of the stator subassembly  14 ) with the inner stator yoke  16 .  
         [0061]    The terminal block  20  has an external sidewall substantially perpendicular to the axial direction of the bobbin body  19  and two terminal pins  21  and  21  each being a bar-like piece made of a conductive metal are fixed to the external sidewall of the in such a manner as to be erected substantially perpendicular to thereto.  
         [0062]    Both ends of the magnet wire W wound around the bobbin body  19 , that is, lead-out wires each extend on a top major surface terminal block  20 , reach the terminal pins  21  and  21 , and are caught and soldered thereon.  
         [0063]    The terminal pins  21  are adapted to be inserted into connection holes or the like in a PCB (printed circuit board) or an FPC (flexible printed circuit), so that electricity can be supplied to the magnet wire W via the terminal pins  21 , thus generating magnetic flux from the coil bobbin.  
         [0064]    [0064]FIG. 5 shows a sectional view of the stator assembly shown in FIG. 2 taken along an abutting contact surface of the two stator subassemblies  14  and  14  with the outer stator yoke housed in a coil bobbin.  
         [0065]    An angle φ made by two radii connecting a center of the outer stator yoke with two points on a minor arc of the terminal block to be housed in the cutout  15   b  is set to be smaller than an angle θ of the cutout  15   b . For example, the angle θ is set at  44  degrees of mechanical angle and the angle φ 40 degrees of mechanical angle. Most favorably, the angle φ is set to be smaller than the angle θ by an electrical angle of 10 degrees or more.  
         [0066]    As to the motor of the present invention, since a number of its magnetic poles is six, 360/6 degrees of mechanical angle is equivalent to 360 degrees of electrical angle. Therefore, since the most favorable angle φ depends on a number of magnetic poles of the concerned motor, it is preferable to use its electrical angle.  
         [0067]    Consequently, by setting the angle φ of the terminal block  20  to be smaller than the angle θ of the cutout  15   b , a gap is generated between the terminal block  20  and inner walls of the cutout  15   b , with the terminal block  20  protruding from the cutout  15   b . Therefore, as the coil bobbin moves, the terminal block  20  can move at a predetermined angle, that is, an angle produced by the generated gap, in a circumferential direction of the coil bobbin  17 .  
         [0068]    The terminal block  20  capable of rotating in the circumferential direction of the coil bobbin  17  eliminates a dislocation between the two terminal blocks  20  and  20  with the two stator yokes  15  and  16  superimposed at their respective predetermined positions in an assembly process of the stator assembly  12 , which will be mentioned in detail later.  
         [0069]    Referring back to FIG. 3, the cover ring  18  is made of an elastic material such as a plastic material which is a cylindrical material having its predetermined width and thickness. A diameter of the cover ring  18  is equal to or shorter than that of the coil bobbin  17  formed of wiring of the magnet wire W. The cover ring  18  has a slit  18   a  at an end of its circumference, and the slit  18   a  is adapted such that the cover ring  18  can easily cover the coil bobbin with the use of an elasticity thereof.  
         [0070]    The width of the cover ring  18  is set to be the same as or a little shorter than a distance between inner sides of the two flanges of the coil bobbin. Consequently, the cover ring  18  press-fitted in the coil bobbin  17  is adapted to cover and protect wirings of a magnet wire W.  
         [0071]    Referring back to FIGS. 1 and 2, the stator assembly  12  in the stepping motor  11  is formed such that the two stator subassemblies  14  and  14  each with the above-described structure are superimposed back to back with their respective terminal blocks  20  and  20  adjacent to each other. The two stator subassemblies  14  and  14  are resin-molded with each other, which will be described in detail later.  
         [0072]    Major surfaces not in contact with each other of the two superimposed stator subassemblies  14  and  14  are fixed, by projection welding or the like, to a first and second flanges  23  and  24 , which have been already formed each by punching out a stainless steel plate.  
         [0073]    The rotor assembly  13  comprises a shaft  26  press-fitted in a metallic holder  25 , bearings  27  and  27  fixed by caulking or the like to the fist and second flanges  23  and  24  and rotatably holding the shaft  26 , and a magnet  28  disposed around an outer circumferential wall of the holder  25 . The magnet  28  is fixed by bonding or insertion molding such that it is concentric with the shaft  26  and is also concentric with and faces both the pole teeth  15   a  and  16   a  with a slight air gap. The magnet  28  is magnetized on its circumferential surface along the circumferential direction with a plurality of alternating N- and S-poles having a preset width. When a predetermined pulse driving voltage is applied on the windings in the stator assembly  12 , the first pole teeth  15   a  are magnetized, for example, with S-pole. Consequently, N-poles in the surface of the magnet  28  are drawn toward the first pole teeth  15   a . In this manner, the rotor  13  moves by a predetermined angle.  
         [0074]    How to assemble the stepping motor with the above-described structure will be hereinafter explained. The shaft  26  is forcibly inserted into the holder  25 , and the magnet  28  is fixed around the holder  25 , constituting the rotor assembly  13 .  
         [0075]    The stator assembly  12  is structured as described below. The coil bobbin  17  is formed by winding a magnet wire W around the bobbin body  19 . A diameter, a number of turns, a length, etc. of the magnet wire W depend on applications of the stepping motor  11 . The cover ring  18  covers the coil bobbin  17 . The stator subassembly  14  is formed such that the inner and outer stator yokes  16  and  15  are coupled together in such a manner as to sandwich the coil bobbin  17  covered by the cover ring  18 . Here, the terminal block  20  of the coil bobbin  17 , the cutout  15   b  of the outer stator yoke  15  and the chamfered edge  16   b  are disposed in such a manner as to mate with one another.  
         [0076]    Then, using a predetermined holding jig, the two stator subassemblies  14  and  14  are correctly positioned such that their respective inner stator yokes  16  and  16  abut back to back. Alternatively, the holding jig may be used so as to directly hold each component of the two stator subassemblies  14  and  14  in their respective assembly sequence.  
         [0077]    The two stator subassemblies  14  and  14  are superimposed such that the pole teeth of their respective stator yokes  15  and  16  are misaligned, each having an optimum difference in an electrical angle, for example, of 90 degrees.  
         [0078]    With the above-described structure of the two stator subassemblies  14  and  14 , their respective terminal blocks  20  and  20  have to be fittingly positioned with respect to one another. For example, there are several mechanisms for achieving the fitting positioning of the coil blocks  20  and  20  as shown in FIGS.  6 A- 6 D.  
         [0079]    [0079]FIG. 6A shows a first mechanism in that positioning through-holes  20   a  and  20   a  for each of the terminal blocks  20  and  20  are bored therein in a direction substantially perpendicular to main surfaces thereof (an axial direction of the cylindrical coil bobbin  17 ). The positioning is carried out by inserting one positioning pin  30  into both the positioning through-holes  20   a  and  20   a.    
         [0080]    [0080]FIG. 6B shows a second mechanism in that positioning grooves  20   b  and  20   b  are cut in opposing surfaces of the two terminal blocks  20  and  20  in their protruding direction, placing the positioning grooves  20   b  and  20   b  at substantially a center of each coil block. The positioning is carried out by placing the one positioning pin  30  along both the positioning grooves with the two stator subassemblies  14  and  14  superimposed back to back.  
         [0081]    When using the positioning mechanisms shown in FIGS. 6A and 6B, the positioning pin  30  is removed after, for example, the terminal pins  21  have been connected to a circuit board such as an FPC, which will be explained later in detail.  
         [0082]    [0082]FIG. 6C shows a third mechanism in that either a V-shaped protuberance  20   c  or a V-shaped groove  20   d  in cross-section to mate with one another is formed on an opposing surface of each of the terminal blocks  20  and  20 . The positioning is carried out by mating the protuberance  20   c  with the groove  20   d.    
         [0083]    [0083]FIG. 6D shows a fourth mechanism in that a positioning jig is used for fittingly positioning the terminal blocks  20  and  20  by aligning sidewalls on the same side of the terminal blocks  20  and  20 .  
         [0084]    [0084]FIG. 7 shows a side view of the two stator subassemblies  14  and  14  properly positioned using any one of the above-described four positioning mechanisms. Even if a displacement in relative angle between the notches  15   b  and  15   b  of the stator subassemblies  14  and  14  occurs, any one of the four positioning mechanisms can serve to eliminate the displacement in relative angle.  
         [0085]    After that, with the outer and inner stator yokes  15  and  16  and the terminal block  20  properly positioned, the two stator subassemblies  14  and  14  are resin-molded integrally with one another to thereby form the stator assembly  12 .  
         [0086]    Then, the second flange  24  having one bearing  27  fixed, by welding or the like, thereto is fixed to one main surface of the stator assembly  12 . And, the rotor assembly  13  is housed in an inner surface of the ring-shaped stator assembly  12  such that one end of the shaft  26  extends through the bearings  27  and  27 . And, the first flange  23  having the other bearing  27  fixed thereto is disposed such that the other end of the shaft  26  extends through the one bearing  27 , and then the other main surface of the stator assembly  12  is fixed, by welding or the like, to the first flange  23 , thereby to complete the stepping motor  11  in this embodiment.  
         [0087]    The stepping motor  11  assembled by the above-described method is to be mounted on an apparatus such as a measuring instrument. An electrical connection between the stepping motor  11  and an apparatus on which it is mounted is made via a circuit board, for example, an FPC (flexible printed circuit)  32  having four connection holes  33  as shown in FIG. 8. Alternatively, the stepping motor  11  may be connected to a rigid circuit board not having flexibility, unlike the FPC  32 .  
         [0088]    Four terminal pins  21  projected on the two terminal blocks  20  and  20  are each inserted into the four connection holes  33  in the FPC and soldered therein. As described above, after the outer and inner stator yokes  15  and  15  are positioned relative to one another, the two terminal blocks  20  and  20  are again correctly positioned through adjustment to thereby eliminate their relative dislocation.  
         [0089]    Therefore, it is not necessary to do any additional thing such as setting a diameter of each of the connection holes  33  to be relatively long so as to eliminate the dislocation of the terminal pins  21 . Consequently, the above-described mechanisms do not involve any difficulty or complication such as inability of smooth soldering between the connection holes  33  and the terminal pins  21  due to the long diameter of each of the connection holes  33 , thereby achieving an easy and highly-reliable electrical connection.  
         [0090]    In brief, in this embodiment, the terminal block  20  can rotate by a predetermined angle as the bobbin  17  moves together with the terminal block projecting from the cutout  15   b.    
         [0091]    Consequently, this embodiment can eliminate the dislocation between the two terminal blocks  20  and  20  and  20  with the outer stator yokes  15  and  16  fixed at a predetermined relative location in a process of assembling the stator assembly  12 .  
         [0092]    Therefore, for example, it becomes easier to solder the terminal pins  21  to the FPC  32 , achieving a highly-reliable and stable electrical connection between the stepping motor and the apparatus on which it is mounted.  
         [0093]    The present invention is not limited to the above-described embodiment, and alternatively there may be any other variations and applications.  
         [0094]    In the above-described embodiment, the terminal block  20  projects in such a manner as to project with a predetermined width in a direction substantially perpendicular to an axial direction of the bobbin  17 . However, a shape of the terminal block  20  is not limited to the above-described example, and alternatively it may be any shape as long as it is possible to connect a magnet wire to the terminal pins  21 , which in turn is connected to an external electrode. For example, it may be structured such that a width of a potion horizontally overlapping the outer stator yoke  15  is narrower than the width of the other portion (the protruding portion).  
         [0095]    In the above-described embodiment, the PM stepping motor is used as an example for explanation. However, the present invention can also be applied to the other stepping motors and any other motor using a bobbin having a magnet wire wound therearound, such as spindle motors and servo motors.  
         [0096]    Various embodiments and changes may be made thereunto without departing from the broad spirit and scope of the invention. The above-described embodiments are intended to illustrate the present invention, not to limit the scope of the present invention. The scope of the present invention is shown by the attached claims rather than the embodiments. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention  
         [0097]    This application is based on Japanese Patent Application No. 2002-257199 filed on Sep. 2, 2002 and Japanese Patent Application No. 2003-118825 filed on Apr. 23, 2003, and including specification, claims, drawings and summary. The disclosure of the above Japanese Patent Application is incorporated herein by reference in its entirety.