Abstract:
The present invention relates to a stepping motor. The stepping motor comprises: a rotor having a cylindrical magnet with a plurality of N-S poles being radially magnetized and a shaft having one end coupled to the center of the magnet and rotationally supported by bearings; at least one coil wound into the shape of a rim with an air gap from a side of the magnet; and a stator shaped as a cylinder for receiving the coil, the stator having a cylindrical inner pole tooth with a proper diameter, the inner pole tooth being projected from one inner central face of the stator opposedly to the side of the magnet, and a plurality of outer pole teeth extendedly branched at the same interval and opposedly arranged with an air gap from the outer circumferential face of the magnet.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a stepping motor for performing rotational movement corresponding to pulse power, in particular, which enables downsizing of the stepping motor while ensuring stable output performance.  
           [0003]    2. Description of the Related Art  
           [0004]    In general, a stepping motor maintains a very large static torque in the stopped position compared to other motors while being rotated at a given angle without feedback for detecting the position of a shaft and stopping at a considerably high precision rate. Therefore, the stepping motor does not require a separate position-maintaining mechanism such as electromagnetic brake and the rotation speed thereof is proportional to pulse rate, and thus the stepping motor has a driving characteristic that it can be readily controlled.  
           [0005]    Due to such characteristics, the stepping motor is generally used in operations for precisely controlling mechanical movement, and in particular, widely used as a driving source of since it can be controlled digitally via pulse.  
           [0006]    For example, the stepping motor is used as a driving source for controlling the printing position of a print head, the pen position of an X-Y plotter or the head position of a floppy disk and various disk ROMs. Also, the stepping motor is used for precision control of various electronic instruments such as paper money counter, sewing machine, electric typewriter and facsimile.  
           [0007]    [0007]FIG. 1 is a schematic sectional view showing a stepping motor of the prior art, and FIG. 2 is a perspective view showing the stepping motor of the prior art. As shown in the drawings, the stepping motor is mainly comprised of a rotor and a stator.  
           [0008]    The rotor is constituted of a shaft s and a magnet m. The shaft s functioning as an output end having a predetermined length is inserted into bearings b coupled in central planes of the first and second cover plates c 1  and c 2  to be supported rotationally in a forward or reverse direction. In the outer circumferential face of one end of the shaft s, is provided the magnet m substantially shaped as a cylinder, which has a configuration that N and S poles are alternately magnetized in the outer circumferential face.  
           [0009]    Meanwhile, the magnet m is arranged opposite to the following coils  130  and  230  in the inner circumferential face of the stator with a predetermined air gap therefrom to generate a predetermined amount of electromagnetic force through the interaction.  
           [0010]    The stator is mainly comprised of the first and second yokes  110  and  210  which are arranged and coupled colinear, and the coils  130  and  230  are wound in the inner faces of the yokes  110  and  210 .  
           [0011]    In particular, the first yoke  110  has an inside bobbin  120  and the coil  130  wound around the outer face of the bobbin  120 . In the inner face of the rotor opposed to the magnet m, the yoke is alternately arranged to have a shape of tooth-type engagement.  
           [0012]    The second yoke  210 , as the first yoke  110 , is provided in the inner face with a bobbin  220  around which the coil  230  is wound. In the inner face of the foregoing rotor opposed to the magnet m, the yoke is alternately arranged to have a shape of tooth-type engagement.  
           [0013]    Meanwhile, the first and second stators  100  and  200 , when seen from the drawings, are so configured that the right and left faces are integrally fixed by the first and second cover plates c 1  and c 2  interposing bearings in the central face for rotationally supporting the shaft s.  
           [0014]    In the conventional stepping motor having the configuration as set forth above, when both of the coils  130  and  230  of the first and second stators  100  and  200  are externally applied with current, the coils  130  and  230 , the first and second yokes  110  and  210  and the magnetic poles of the magnet m undergo interaction to generate electromagnetic force, thereby causing the rotor having the magnet m and the shaft s to rotate about the first and second stators  100  and  200 .  
           [0015]    Lately, as the precision instruments are downsized and thin-shaped, the stepping motor mounted to the precision instruments is also required to be slimmed. However, the conventional stepping motor comprises a number of components having diameters different from each other in the outer circumferential face about the shaft s, thereby restricting downsizing.  
           [0016]    For example, there is a method for downsizing the conventional stepping motor by reducing the diameters of the magnet m and the coils  130  and  230 . In this configuration, however, electromagnetic force of the magnet m and the coils  130  and  230  are lowered also, thereby lowering mutual electromagnetic force by a large margin. Therefore, as the motor is downsized, the output capacity is also lowered thereby restricting downsizing.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention has been devised to solve the foregoing problem relates to a stepping motor for performing rotational movement corresponding to pulse power, in particular, in which coils of yokes are arranged axially of a magnet, thereby enabling downsizing of the stepping motor while ensuring stable output performance.  
           [0018]    In accordance with an aspect of the invention to obtain the foregoing object, a stepping motor comprises: a rotor having a cylindrical magnet with a plurality of N-S poles being radially magnetized and a shaft having one end coupled to the center of the magnet and rotationally supported by bearings; at least one coil wound into the shape of a rim with an air gap from a side of the magnet; and a stator shaped as a cylinder for receiving the coil, the stator having a cylindrical inner pole tooth with a proper diameter, the inner pole tooth being projected from one inner central face of the stator opposedly to the side of the magnet, and a plurality of outer pole teeth extendedly branched at the same interval and opposedly arranged with an air gap from the outer circumferential face of the magnet.  
           [0019]    Preferably, the yoke comprises first and second yokes provided at axially both sides of the magnet, wherein the first and second yokes are opposed to each other.  
           [0020]    Preferably, the inner pole tooth and the outer pole teeth are energized into the N or S pole.  
           [0021]    Also, preferably, the first and second yokes are fixedly inserted into a cylinder-shaped housing.  
           [0022]    In accordance with another aspect of the invention to obtain the foregoing object, a stepping motor comprises: a cylindrical magnet with a plurality of N-S poles being radially magnetized; a shaft having one end coupled to the center of the magnet and rotationally supported by bearings; a pair of coils axially provided at both sides of the magnet, each of the coils being wound into the shape of a rim in the outer circumferential face of a cylinder-shaped bobbin; first and second yokes for receiving the coils therein and arranged concentrically at both sides of the magnet; cylindrical inner pole teeth projected from the inner central faces of the first and second yokes, each of the inner pole teeth having one side opposed to one side of the magnet with a proper interval and energized into N or S pole according to the direction of current applied to each of the coils; outer pole teeth integrally provided in the outer circumferential faces of the first and second yokes, extendedly branched into opposed directions to one another to be opposed with a proper air gap in the outer circumferential face of the magnet, and energized into N or S poles according to the direction of current applied to the coils; and a housing for being fixedly coupled with the outer circumferential edges of the first and second yokes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a schematic sectional view showing a stepping motor of the prior art;  
         [0024]    [0024]FIG. 2 is a perspective view showing a stepping motor of the prior art;  
         [0025]    [0025]FIG. 3 is a sectional view showing a stepping motor in accordance with the invention;  
         [0026]    [0026]FIG. 4 is an exploded perspective view showing a stepping motor in accordance with the invention;  
         [0027]    [0027]FIGS. 5 and 6 are conceptual views showing flux paths in a stepping motor in accordance with the invention; and  
         [0028]    [0028]FIG. 7 illustrates operations in accordance with the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    The following detailed description will present a preferred embodiment in reference to the accompanying drawings.  
         [0030]    [0030]FIG. 3 is a sectional view showing a stepping motor in accordance with the invention, and FIG. 4 is an exploded perspective view showing a stepping motor in accordance with the invention. As shown in the drawings, the stepping motor is mainly comprised of a rotor for driving rotation and a stator for maintaining a fixed state.  
         [0031]    The rotor is constituted of a shaft s and a magnet m, in which the shaft s, as shown in FIGS. 3 and 4, has a structure with one end inserted into the center of the first and second yokes  10  and  20  and axially supported by a plurality of bearings b 1  and b 2  to be rotated in a forward/reverse direction. In the outer circumference of the shaft s, the magnet m having magnetized N or S poles is arranged.  
         [0032]    The magnet m has a substantially cylindrical shape and a plurality of N and S poles are alternately magnetized in the outer circumference in a circumferential direction. The magnet m generates electromagnetic force through the interaction with the following coils  13  and  23 .  
         [0033]    The stator is mainly constituted of the first yoke  10  and the second yoke  20 . The first and second yokes  10  and  20  have a substantially cylindrical shape, and as shown in FIG. 3, are arranged concentrically at both sides interposing the magnet m with a predetermined interval of air gap.  
         [0034]    The first yoke  10  is shaped as substantially cylindrical, and has teeth-shaped outer pole teeth  11  in the outer circumferential face. The teeth-shaped outer pole teeth  11  surround the outer circumferential face of the magnet m, and have N or S polarity. In the central face inside the outer pole teeth  11 , is provided a cylinder-shaped inner pole tooth  15  which is opposed to the side of the magnet m.  
         [0035]    The outer pole teeth  11  and the inner pole tooth  15  have a predetermined interval of air gap in respect to the outer circumferential face and side of the magnet m. The outer pole teeth  11  of the invention are energized into the N or S poles, and branched at the same interval of 180 deg. The inner pole tooth  15  is generally shorter than the teeth-shaped outer pole teeth  11 , and energized into the N or S pole.  
         [0036]    Meanwhile, the first yoke  10  has a rim-shaped bobbin  12  in the inner face or the outer circumferential face of the inner pole tooth  15  and a coil  13  which is wound around the outer circumferential face of the bobbin  12 . The outside diameter of the bobbin  12  is slightly smaller than that of the outer pole teeth  11 . The diameter of a hole extending through the center of bobbin  12  is slightly larger than that of the inner pole tooth  15 .  
         [0037]    The first yoke  10  having the foregoing configuration is energized into the N or S pole through the conduction of the coil  13  provided in the inner face of the yoke  10 .  
         [0038]    The second yoke  20 , as the first yoke  10 , is provided with a cylinder-shaped inner pole tooth  25  and teeth-shaped outer pole teeth  21 . Between the inner pole tooth  25  and the outer pole teeth  21 , a rim-shaped bobbin  22  and a coil  23  are provided.  
         [0039]    The outer pole teeth  21  of the second yoke  20  are substantially cylindrical, and has the outer circumferential face having N or S polarity in the shaped of surrounding the outer circumferential face of the magnet m. The inner pole tooth  25  is in the central face inside the second yoke  20 , and arranged as opposed to the side of the magnet m.  
         [0040]    The outer pole teeth  21  and the inner pole tooth  25  have a predetermined interval of air gap in respect to the outer circumferential face and side of the magnet m, and energized through the conduction of the coil  23 .  
         [0041]    The first yoke  10  and the second yoke  20  are respectively energized into the N or S poles according to the direction of current applied to both of the coils  13  and  23 .  
         [0042]    In the stepping motor configured as set forth above, the cylindrical first and second yokes  10  and  20  are concentrically arranged with the predetermined air gap at both sides of the magnet m placed therebetween. In the inner faces of the first and second yoke  10  and  20 , are respectively provided the rim-shaped bobbins  12  and  22  around which coils  13  and  23  are wound. The first and second yokes  10  and  20  are respectively provided with the outer pole teeth  11  and  21 , which are extendedly branched toward each other to surround the magnet m with the predetermined air gap in the outer circumferential face of the magnet m. The outer pole teeth  11  and  21  are branched in plurality to form magnetic poles which are energized into the N or S poles. The cylindrical inner pole teeth  15  and  25  provided in the central faces inside the first and second yokes  10  and  20  have the diameters smaller than those of the outer pole teeth  11  and  21 . The lateral ends of the inner pole teeth  15  and  25  are opposed to each other at the sides of the magnet m with the predetermined air gap, and energized into the N or S pole.  
         [0043]    In the first and second stators  10  and  20  configured as set forth above, when the coils  13  and  23  are applied with current, the outer pole teeth  11  and  21  and the inner pole teeth  15  and  25  are energized to form flux paths in a region designated with “A” in FIG. 3.  
         [0044]    [0044]FIGS. 5 and 6 are conceptual views showing flux paths in a stepping motor in accordance with the invention, in which the first and second yokes  10  and  20  generate the flux paths through the conduction of the coils  13  and  23  as shown in the drawings.  
         [0045]    Therefore, in the stepping motor having the foregoing configuration, when the coils  13  and  23  of the first and second yokes  10  and  20  are applied with current, the outer pole teeth  11  and  21  and the inner pole teeth  15  and  25  of the first yokes  10  and  20  are energized. Under this condition, the flux paths are generated as shown with full lines due to leakage fluxes of the ends of the poles  15  and  25  opposed to the magnets m. As a result, electromagnetic force is generated between the coils  13  and  23  and the first and second yokes  10  and  20 , thereby causing the rotor to rotate about the stator.  
         [0046]    Meanwhile, the unexplained reference numerals b 1  and b 2  designate bearings b 1  and b 2  which are inserted into the central faces of the first and second yokes  10  and  20 . The bearings b 1  and b 2  axially support the shaft s to be rotated in forward and reverse directions. The reference numeral h designates a cylindrical housing which is coupled to the outer circumferential edges of the first and second yokes  10  and  20  to fix the same.  
         [0047]    The following description will present the operation of the stepping motor configured as above in accordance to the invention in reference to FIG. 7.  
         [0048]    When the coils  13  and  23  are applied with current in one direction in (a) and (e) states, the outer pole teeth  11  of the first yoke  10  are energized into the N pole and the inner pole tooth  15  into the S pole. On the other hand, the outer pole teeth  21  of the second yoke  20  are energized into the N pole and the inner pole tooth  25  into the S pole. The magnet m acting as the rotor is rotated counterclockwise for about 45 deg. to obtain (b) and (f) states.  
         [0049]    When the direction of current to the coil  13  of the first yoke  10 , the outer pole teeth  11  of the first yoke  10  are energized into the S pole and the inner pole tooth  15  into the N pole, but the outer pole teeth  21  and the inner pole tooth  25  of the second yoke  20  maintain the energized states of the N pole and the S pole. Then, the magnet m as the rotor is rotated counterclockwise for about 45 deg. from the (a) and (e) states to (c) and (g) states.  
         [0050]    When the direction of current of the coil  23  applied to the second coil  20  is reversed in the (c) and (g) states, the outer pole teeth  21  of the second yoke  20  are energized into the S pole and the inner pole tooth  25  into the N pole. At this time, the outer pole teeth  11  and the inner pole tooth  15  of the first yoke  10  maintain the energized states of the S pole and the S pole. As a result, the magnet m as the rotor is rotated counterclockwise from the (c) and (g) states for about 45 deg., and shown as (d) and (a) states.  
         [0051]    As the conducting directions of the coils  13  and  23  of the first and second yokes  10  and  20  are changed in sequence, the magnet m as the rotor can be rotated for a predetermined angle.  
         [0052]    Although the preferred embodiment of the present invention have been disclosed for illustrative purposes, the scope of the invention is not restricted to the embodiment but can be adequately varied in the category of the same spirit. For example, the shape and structure of the each component disclosed in the embodiment of the invention can be modified in implementation.  
         [0053]    In the stepping motor of the invention having the configuration and operation as set forth above, the coils are arranged axially at both sides of the magnet while the one ends of the yokes having the coils are opposedly extended in the outer circumferential face of the magnet to form the poles, thereby reducing the entire thickness of the motor while ensuring stable output performance.  
         [0054]    In particular, such a configuration further increases the degree of freedom in design due to downsizing of the motor.