Abstract:
Disclosed is an actuator that generates the reciprocating rotational motion of an electric toothbrush or similar without employing a drive transmission mechanism as a separate entity from a drive source. An actuator ( 100 ) includes a fixed body ( 110 ) comprising an outer yoke ( 140 ) having inner wall planes that respectively oppose the magnetic pole planes of unlike poles of a magnet ( 150 ) with a predetermined gap therebetween. A coil ( 122 ) is arranged to encircle the magnet ( 150 ) between the magnetic pole planes of the unlike poles of the magnet ( 150 ) and the inner wall planes of the outer yoke ( 140 ) that respectively oppose the magnetic pole planes of the unlike poles, and this coil ( 122 ) is movably supported as a movable body ( 120 ) by way of an elastic member ( 130 ) fastened to the fixed body ( 110 ). The reciprocating rotational motion of the movable body ( 120 ) is afforded by the supply of an alternating current of a frequency approximately equivalent to the resonant frequency of the movable body ( 120 ) from an alternating current supply ( 180 ) to the coil ( 122 ).

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to an actuator used in, for example, an electric toothbrush or an electric sonic wave toothbrush. 
       BACKGROUND ART  
       [0002]    Electric toothbrushes including electric sonic wave toothbrushes known heretofore include a bass brushing tooth brush places the brush in the part between the tooth and the gum at an angle (at an angle of approximately 45 degrees) and vibrates the brush to the right and left in back-and-forth linear motion, a rolling brushing toothbrush that rotates back and forth (forward and backward) over a predetermined angle range around a shaft and moves from the gum to the tooth rotating, and so on. 
         [0003]    The drive of toothbrushes like these involves many structures for converting the rotation of a rotating DC motor that rotates regularly around a shaft into back-and-forth linear motion or back-and-forth rotating motion, via a motion direction converting mechanism. Furthermore, besides these structures, a structure to move a toothbrush in back-and-forth linear motion by means of a linear drive actuator, and a structure to move a toothbrush in back-and-forth rotating motion by making a resonance vibrating mechanism apart from the drive source resonate by the vibration of an actuator, are known. 
         [0004]    With an electric toothbrush structured to move the brush part in back-and-forth linear motion by means of a linear drive actuator, as shown in patent literature 1, the linear actuator directly produces back-and-forth vibration in the axial direction of an output shaft that is directly connected with the brush part, and makes possible bass brushing. With this structure, there is little power loss due to a motion converting mechanism, and makes possible fast vibration. 
         [0005]    Furthermore, with an electric toothbrush of a structure having an actuator and resonance vibrating mechanism apart from the drive source, as shown in patent literature 2, a drive means with an electro magnet and permanent magnet vibrates the resonance vibrating mechanism having a lever arm. By this means, the lever arm that is coaxially connected with the brush part moves in swinging motion, making possible rolling brushing. 
       Citation List 
     Patent Literature 
     PTL 1  
       [0000]    
       
         Japanese Patent Application Laid-Open No. 2002-078310 
       
     
       PTL 2  
       [0000]    
       
         Japanese Patent Publication No. 3243529 
       
     
       SUMMARY OF INVENTION  
     Technical Problem 
       [0008]    Now, to make possible rolling brushing with an electric toothbrush and to make the handle part in which the drive part to drive a rolling brushing toothbrush is accommodated as thin as possible, there is a demand to miniaturize the toothbrush drive part. 
         [0009]    However, to realize rolling brushing using a regular motor that rotates around a shaft, apart from this motor, a motion direction converting mechanism to covert the rotation of this motor into back-and-forth rotating motion is necessary. Also, to realize rolling brushing using a linear drive actuator as shown in patent literature 1, apart from this linear drive actuator, a torque generating mechanism (drive source) is necessary. 
         [0010]    Also, the structure shown in patent literature 2 requires a drive source as well as a resonance vibrating mechanism apart from the drive source. 
         [0011]    Consequently, with conventional structures, if a motor or a linear drive actuator is used as a drive source of an electric toothbrush, it is necessary to secure a space for placing a drive source, and, in addition, a motion direction converting mechanism, a torque generating mechanism, or a resonance vibrating mechanism, apart from the drive source, and there is therefore problem that it is difficult to miniaturize the toothbrush. 
         [0012]    In addition, in the event a drive transmitting mechanism (e.g. motion direction converting mechanism) is provided apart from an actuator (e.g. motor) as a toothbrush drive part, there is a threat of producing noise in the drive transmitting mechanism and there is furthermore a threat that the drive transmitting mechanism suffers poor efficiency due to power loss, and it is necessary to take measures against these. 
         [0013]    In view of the above, it is an object of the present invention to provide a small actuator and electric toothbrush that can realize back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source. 
       Solution to Problem 
       [0014]    An actuator according to the present invention adopts a configuration having: a permanent magnet; an outer yoke that has inner wall parts that oppose magnetic pole planes of different poles in the permanent magnet a predetermined interval apart; a coil that is placed between the magnetic pole planes of different poles and the inner wall parts of opposing the magnetic pole planes of different poles and surrounds the permanent magnet; a movable body that has one of the permanent magnet and the coil; a fixed body that has the other one of the permanent magnet and the coil, and the outer yoke, and supports the movable body in a movable fashion via an elastic support part; and an alternating current supplying part that supplies an alternating current of substantially a same frequency as a resonance frequency of the movable body, to the coil. 
         [0015]    An actuator according to the present embodiment adopts a configuration having: a fixed body having a permanent magnet and an outer yoke which has inner wall planes opposing magnetic pole planes of different poles of the permanent magnet a certain interval apart; a movable body having a coil that is placed between the magnetic pole planes of different poles and the inner wall planes opposing the magnetic pole planes of different poles and that surrounds the permanent magnet, the movable body being supported in a movable fashion via an elastic support member attached to the fixed body; and an alternating current supplying part that supplies an alternating current of substantially the same frequency as a resonance frequency of the movable body, to the coil. 
         [0016]    An actuator according to the present invention has: a movable body that has a permanent magnet, an outer yoke that covers a coil that surrounds the permanent magnet and that has an inner periphery part that opposes the magnetic pole planes of the permanent magnet a certain interval apart, and an outer periphery part of the coil; a fixed body that supports the movable body in a movable fashion via an elastic support part; and an alternating current supplying part that supplies an alternating current of substantially the same frequency as a resonance frequency of the movable body, to the coil. 
         [0017]    An electric toothbrush according to the present invention adopts a configuration having: an actuator of the above configuration; and a toothbrush part that is coaxially coupled with the output shaft, at a head of the toothbrush part a hair bundle part being provided to be perpendicular to an axial direction. 
       Advantageous Effects of Invention 
       [0018]    According to the present invention, it is possible to achieve back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source, so that it is possible to miniaturize an actuator and electric toothbrush. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]      FIG. 1  is a perspective view showing an actuator according to the first embodiment of the present invention; 
           [0020]      FIG. 2  is a perspective view showing a state an outer yoke is removed from this actuator; 
           [0021]      FIG. 3  is a principal-part exploded perspective view of this actuator; 
           [0022]      FIG. 4  is a schematic cross-sectional view showing a principal-part configuration of this actuator; 
           [0023]      FIG. 5  is a schematic view for explaining operation of this actuator; 
           [0024]      FIG. 6  shows a cycle of alternating current supplied from an alternating current supplying part to a coil; 
           [0025]      FIG. 7  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to a second embodiment of the present invention; 
           [0026]      FIG. 8  shows a configuration of an actuator according to a third embodiment of the present invention; 
           [0027]      FIG. 9  is an exploded perspective view of this actuator; 
           [0028]      FIG. 10  is a schematic view for explaining operation of this actuator; 
           [0029]      FIG. 11  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to a fourth embodiment of the present invention; 
           [0030]      FIG. 12  is a perspective view showing an actuator according to a fifth embodiment of the present invention; 
           [0031]      FIG. 13  is a principal-part exploded perspective view of this actuator; 
           [0032]      FIG. 14  is a principal-part exploded perspective view of an actuator according to a sixth embodiment of the present invention; 
           [0033]      FIG. 15  shows an elastomer, which is a viscoelastic member used in this actuator; 
           [0034]      FIG. 16  is a perspective view showing an actuator according to a seventh embodiment of the present invention; 
           [0035]      FIG. 17  is a principal-part exploded perspective view of an actuator according to the seventh embodiment of the present invention; 
           [0036]      FIG. 18  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to the seventh embodiment of the present invention; 
           [0037]      FIG. 19  is a schematic view for explaining operation of an actuator according to the seventh embodiment of the present invention; 
           [0038]      FIG. 20  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to an eighth embodiment of the present invention; 
           [0039]      FIG. 21  is an outer view of a configuration of an actuator according to a ninth embodiment of the present invention; 
           [0040]      FIG. 22  is an exploded perspective view showing an actuator according to the ninth embodiment of the present invention; 
           [0041]      FIG. 23  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to the ninth embodiment of the present invention; 
           [0042]      FIG. 24  is a schematic view for explaining operation of an actuator according to the ninth embodiment of the present invention; 
           [0043]      FIG. 25  is a perspective view showing an actuator according to a tenth embodiment of the present invention; 
           [0044]      FIG. 26  is a principal-part exploded perspective view of an actuator according to the tenth embodiment of the present invention; and 
           [0045]      FIG. 27  is an exploded perspective view showing an actuator according to an eleventh embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0046]    Now, embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 
       First Embodiment 
       [0047]      FIG. 1  is a perspective view showing actuator  100  according to the first embodiment of the present invention, and  FIG. 2  is a perspective view showing a state an outer yoke is removed from this actuator  100 . Also,  FIG. 3  is a principal-part exploded perspective view of this actuator. 
         [0048]    Actuator  100  shown in  FIG. 1 through 3  has fixed body  110 , movable body  120  (see  FIG. 2 ), elastic members (elastic support parts)  130  (see  FIG. 2 ) that support movable body  120  on fixed body  110  in a movable fashion, and alternating current supplying part  180  (see  FIG. 3 ). 
         [0049]    As shown in  FIG. 1 , with this actuator  100 , when movable body  120  (see  FIG. 2 ) that is supported in fixed body  110  via elastic members  130  moves, back-and-forth rotating vibration transmission shaft (hereinafter referred to as “shaft”)  125 , which is the output shaft of movable body  120 , rotates in forward and backward directions (the directions of arrows in  FIG. 1 ) in a predetermined angle range, and outputs back-and-forth rotating vibration outside. 
         [0050]    As shown in  FIG. 3 , fixed body  110  has base plate  112 , support wall parts  114  and  116 , outer yoke  140 , and magnet  150  that is attached to outer yoke  140  via non-magnetic body (spacer)  160 . 
         [0051]    In fixed body  110 , base plate  112  forms a flat rectangular shape that is long in the direction in which shaft  125  extends, and is formed of a non-magnetic body here. Above a center area on the surface of base plate  112 , coil  170  of movable body  120  is placed, and outer yoke  140  having a U-shaped cross section (including the shape of a letter U placed sideways) is attached to base plate  112 , to cover this coil  170 . 
         [0052]    Furthermore, support wall parts  114  and  116  are erected from edge parts of base plate  112  that are spaced apart in the long direction. 
         [0053]    Support wall parts  114  and  116  have opening parts  114   a  and  116   a  in which shafts  125  and  126  of movable body  120  are inserted. Shaft  126  is inserted in opening part  114   a , and shaft  125  is inserted in opening part  116   a.    
         [0054]    Support wall parts  114  and  116  support movable body  120  in a movable fashion via elastic members  130 . That is to say, support wall parts  114  and  116  hold movable body  120  in a movable fashion via elastic members  130  in a state in which shafts  125  and  126  are inserted in opening parts  114   a  and  116   a . In a normal state, movable body  120  is supported virtually horizontally (that is, virtually parallel to base plate  112 ) by means of support wall parts  114  and  116  and elastic members  130 . Shafts  125  and  126  may also be loosely inserted in opening parts  114   a  and  116   a . Elastic members  130  will be described later in detail. 
         [0055]    Outer yoke  140  is placed between these support wall parts  114  and  116  to cover the main part of movable body  120 . 
         [0056]    Outer yoke  140  has a cross section approximately in the shape of a letter U that is placed sideways, and is formed by bending a flat magnetic body. Outer yoke  140  has yoke center part  141  of a flat rectangular shape, and mutually opposing sidewall parts  142  and  143  that hang from the side parts of yoke center part  141 . In this case, outer yoke  140  is attached to base plate  112  to cover coil  170  and coil holding part  124  of movable body  120 , and the tip parts of sidewall parts  142  and  143  are closed by base plate  112 . 
         [0057]    Outer yoke  140  constitutes a magnetic circuit with coil  170  of movable body  120  to be placed inside and magnet  150  that is attached in yoke center part  141  of outer yoke  140 . 
         [0058]      FIG. 4  is a schematic cross-sectional view showing a principal-part configuration of actuator  100 . 
         [0059]    As shown in  FIG. 4 , magnet (permanent magnet)  150  is placed in the center area on the back of yoke center part  141  of outer yoke  140 , via non-magnetic body  160 , such that air gaps G are formed between magnet  150  and opposing sidewall parts  142  and  143  of outer yoke  140 . 
         [0060]    Magnet  150  is provided to hang from yoke center part  141 , via non-magnetic body  160 , and different magnetic poles face the inner wall parts of sidewall parts  142  and  143 . 
         [0061]    That is to say, here, the S-pole end (S magnetic pole plane  150   a ) of magnet  150  faces the inner wall plane of sidewall part  142  of outer yoke  140 , and the N-pole side (N magnetic pole plane  150   b ) faces the inner wall plane of sidewall part  143  of outer yoke  140 . 
         [0062]    Furthermore, magnet  150  is a cuboid having a length to match the length of the extension direction of outer yoke  140 , and is attached in yoke center part  141 , via non-magnetic body  160  having the same outer shape, along the extension direction of yoke center part  141 . 
         [0063]    By this means, magnet  150  has virtually the same length as the length of the long direction of outer yoke  140 , and is placed in yoke center part  141  in a state the inner wall planes of opposing sidewall parts  142  and  143  all face planes of different magnetic poles. 
         [0064]    In air gaps G between magnet  150  and sidewall parts  142  and  143  of outer yoke  140 , coil  170  of movable body  120  is placed spaced apart from side wall planes (magnetic pole planes)  150   a  and  150   b  of magnet  150 , inner wall planes of sidewall parts  142  and  143 , and the back of yoke center part  141 . 
         [0065]    Coil  170  is a voice call here and is wound to surround the periphery of magnet  150 . To be more specific, in each air gap, coil  170  is wound in a direction perpendicular to the direction in which magnet  150  and sidewall parts  142  and  143  oppose each other. From alternating current supplying part  180 , an alternating current supply (AC voltage) is supplied as shown in  FIG. 3  and  FIG. 4 . 
         [0066]    This coil  170  is placed in coil holding part  124  and held, and coil holding part  124  is supported by fixed body  110  via elastic members  130 . 
         [0067]    As shown in  FIG. 2  and  FIG. 3 , this coil holding part  124  is formed in the shape of a letter C placed sideways on a side view, and has bottom plate part  124   a  on which coil  170  is placed, and front wall part  124   b  and rear wall part  124   c  that that erect from edge parts of bottom plate part  124   a  that are spaced apart along the long direction (that is, along the direction in which shaft  125  extends). 
         [0068]    This coil holding part  124  is formed of a non-magnetic body. In front wall part  124   b , shaft  125  is attached perpendicular, and, in rear wall part  124   c , shaft  126  is placed to be positioned coaxially with shaft  125 . That is to say, shaft  125  is placed approximately along the center of magnet  150 , approximately parallel to varying magnetic pole planes  150   a  and  150   b  of magnet  150  (see  FIG. 4 ). 
         [0069]    Thus, with coil holding part  124  and shafts  125  and  126 , coil  170  constitutes movable body  120  that is supported in a movable fashion, by means of support wall parts  114  and  116 . 
         [0070]    Elastic members  130  support movable body  120  in the area between opposing support wall parts  114  and  116  such that movable body  120  is able to move in the front, back, left and right directions, and also supports movable body  120  in twisting directions of magnet  150  and shaft  125 . 
         [0071]    Here, elastic members  130  are formed with flat, zigzag springs that project virtually horizontally in opposing directions in upper end areas of the opposing planes of support wall parts  114  and  116 . That is to say, elastic members  130  are each formed with a thin, band-shaped metallic plate of a zigzag shape that repeats, from its one end to the other end, extending in one width direction and returning in the other width direction, and elastic members  130  are each able to compress in a twisting direction if one end and the other end are fixed. 
         [0072]    Via elastic members  130  configured in this way, in the area surrounded by base plate  112  and outer yoke  140 , movable body  120  is supported by both support wall parts  114  and  116  of fixed body  110  to be able to move in twisting directions about the axis of shafts  125  and  126 . 
         [0073]    Incidentally, as shown in  FIG. 1  and  FIG. 2 , shaft  125  of movable body  120  is provided to project outward from support wall part  116  in the same direction as the direction of extension of outer yoke  140 . That is to say, in actuator  100 , shaft  125  is provided to project in a direction that is virtually perpendicular to the direction magnet  150  and sidewall parts  142  and  143  oppose each other. 
         [0074]    Shaft  125  is fixed in front wall part  124   b  of coil holding part  124  in this way, and, by this means, is attached to movable body  120  to be located on an axis to pass the center of gravity of movable body  120 . By this means shaft  125  is able to move in back-and-forth rotating vibration with coil  170  and coil holding part  124  constituting the main body of movable body  120 , and transmit this vibration outside. 
         [0075]    When actuator  100  is used for an electric toothbrush, a toothbrush part is coaxially coupled with shaft  125 , and, at the head of this toothbrush part, a hair bundle part is provided to be perpendicular to the axial direction. By this means the toothbrush part moves in the same motion as shaft  125 , that is, moves in rolling motion, which is back-and-forth rotating vibration. 
         [0076]    With actuator  100  of the present embodiment, assuming that the inertia of movable body  120  is J and the spring constant in a twisting direction is k sp , as compared with fixed body  110 , movable body  120  vibrates in a resonance frequency calculated based on equation 1 below: 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       1 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     f 
                     0 
                   
                   = 
                   
                     
                       1 
                       
                         2 
                          
                         π 
                       
                     
                      
                     
                       
                         
                           K 
                           sp 
                         
                         J 
                       
                     
                   
                 
               
               
                 
                   [ 
                   1 
                   ] 
                 
               
             
           
         
       
     
         [0077]    In actuator  100  of the present embodiment, an alternating current of substantially the same frequency as a resonance frequency f 0  of movable body  120  is supplied from alternating current supplying part  180  to coil  170 . By this means, it is possible to drive movable body  120  efficiently. 
         [0078]    As shown in  FIG. 4 , in fixed body  110  and movable body  120 , outer yoke  140 , magnet  150  and coil  170  form a magnetic circuit. 
         [0079]    Actuator  100  has a magnetic circuit where magnetic fluxes produced from magnet  150  (designated by outline arrows) pass an air gap where coil  170  is placed, sidewall part  143  of outer yoke  140 , yoke center part  141 , sidewall part  142  and the opposite air gap, in order, and reaches the opposite pole of magnet  150 . 
         [0080]    Movable body  120  of this actuator  100  is supported by a spring mass system structure supported by fixed body  110  via elastic members  130 . When an alternating current of the same frequency as resonance frequency f 0  of movable body  120  is supplied to coil  170 , movable body  120  is driven in a resonant state. The back-and-forth rotating vibration that is produced then is transmitted to shaft  125  of movable body  120 . 
         [0081]    Actuator  100  is driven based on the equation of motion represented by equation 2 below and based on the circuit equation represented by equation 3 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       2 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     J 
                      
                     
                       
                         
                            
                           2 
                         
                          
                         
                           θ 
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                       
                          
                         
                           t 
                           2 
                         
                       
                     
                   
                   = 
                   
                     
                       
                         K 
                         t 
                       
                        
                       
                         i 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       
                         K 
                         sp 
                       
                        
                       
                         θ 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       D 
                        
                       
                         
                            
                           
                             θ 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                     - 
                     
                       T 
                       Load 
                     
                   
                 
               
               
                 
                   [ 
                   2 
                   ] 
                 
               
             
           
         
       
       
         J: Inertia moment [Kgm2] 
         θ(t): Angle [rad] 
         K t : Torque constant [Nm/A] 
         i(t): Current [A] 
         K sp : Spring constant [Nm/rad] 
         D: Attenuation coefficient [Nm/(rad/s)] 
         T LOAD : Load torque [Nm] 
       
     
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       3 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     e 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       Ri 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                     + 
                     
                       L 
                        
                       
                         
                            
                           
                             i 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                     + 
                     
                       
                         K 
                         e 
                       
                        
                       
                         
                            
                           
                             θ 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   3 
                   ] 
                 
               
             
           
         
       
       
         e(t): Voltage [V] 
         R: Resistance [Ω] 
         L: Inductance [H] 
         K e : Counter electromotive force multiplier [V/(rad/s)] 
       
     
         [0093]    That is to say, the inertia moment, rotation angle, torque constant, current, spring constant, attenuation coefficient, and load torque in actuator  100  can be changed as adequate in a range to satisfy equation 2, and the voltage, resistance, inductance, and counter electromotive force multiplier can be changed as adequate in a range to satisfy equation 3. 
         [0094]    Next, the operations of actuator  100  will be described in detail. 
         [0095]      FIG. 5  is a schematic view for explaining operation of actuator  100  according top the first embodiment. Although the flow of magnetic fluxes from magnet  150  is shown by outline arrows in  FIG. 5A , the same flow applies to  FIG. 5B  to  FIG. 5D , and illustration is omitted in  FIG. 5B  to  FIG. 5D . Also, although  FIG. 5A  shows alternating current supplying part  180  that supplies an AC voltage to coil  170 , the same applies to  FIG. 5B  to  FIG. 5D , and illustration is omitted in FIG.  5 B to  FIG. 5D . 
         [0096]    When an alternating current is supplied from alternating current supplying part  180  to coil  170 , thrusts F 1 , F 2 , F 3  and F 4  are produced in coil  170 , following Fleming&#39;s left hand rule. By this means, in movable body  120  that is attached to base plate  112  and support wall parts  114  and  116  via elastic members  130  in a movable fashion, a rotating force about an axial center at the center of rotation is produced. 
         [0097]    One operation cycle of actuator  100  will be described. 
         [0098]    When a current flows in coil  170  in the direction shown in  FIG. 5A  (a current to flow in this direction will be hereinafter referred to as “forward current”), upward thrust F 1  (directed toward outer yoke  140 ) is produced in part  170   b  of coil  170  opposing N-pole plane  150   b  of magnet  150 . Meanwhile, in part  170   a  of coil  170  opposing S pole plane  150   a  of magnet  150 , downward thrust F 2  (directed toward base plate  112 ) is produced. 
         [0099]    By this means, a rotating force is produced in movable body  120  that has coil  170  and that is supported by support wall parts  114  and  116  that erect from base plate  112  of fixed body  110  (see  FIG. 2  and  FIG. 3 ), via elastic members  130 . Movable body  120  moves anticlockwise to assume the position shown in  FIG. 4B  by thrusts F 1  and F 2  of coil  170 . 
         [0100]    In the state shown in  FIG. 5B , actuator  100  produces reaction forces, designated by arrows R 1  and R 2 , by the restoring force of elastic members  130  (see  FIG. 2  and  FIG. 3 ). From the state shown in  FIG. 5B  to the state shown in  FIG. 5D , a reverse current is supplied to coil  170  as compared with  FIG. 5A . By this means, from the state shown in  FIG. 5B  to the state shown in  FIG. 5C , movable body  120  rotates anticlockwise with respect to fixed body  110  by the reaction forces designated by arrows R 1  and R 2  and by the thrusts designated by arrows F 3  and F 4 . From the state shown in  FIG. 5C  to the state shown in  FIG. 5D , movable body  120  rotates anticlockwise with respect to fixed body  110  by the thrusts designated by arrows F 3  and F 4 . 
         [0101]    In the state shown in  FIG. 5D , actuator  100  produces reaction forces, designated by arrows R 3  and R 4 , by the restoring force of elastic members  130 . From the state shown in  FIG. 5D  to the state shown in  FIG. 5A , a forward current is supplied to coil  170 . By this means, from the state shown in  FIG. 5D  to the state shown in  FIG. 5A , movable body  120  rotates anticlockwise with respect to fixed body  110  by the reaction forces designated by arrows R 3  and R 4  and by the thrusts designated by arrows F 1  and F 2 . 
         [0102]    From the state shown in  FIG. 5A  to the state shown in  FIG. 5B , movable body  120  rotates anticlockwise with respect to fixed body  110  by the thrusts designated by arrows F  1  and F 2 . Although movable body  120  operates in back-and-forth rotating vibration about magnet  150 , but movable body  120  is also able to operate in the same way as shown in  FIG. 5  by thrusts F 1  to F 4 , without using the reaction force of elastic members  130 . 
         [0103]    Next, what alternating current is supplied to coil  170  of movable body  120  in each state shown in  FIG. 5  will be described briefly. 
         [0104]      FIG. 6  shows the cycle of alternating current supplied from alternating current supplying part  180  to coil  170  of movable body  120  in the actuator according to the present invention. 
         [0105]    The alternating current to flow in the coil may be a pulse wave of frequency f 0  as shown in  FIG. 6A  or may be a sine wave of frequency f 0  as shown in  FIG. 6B . 
         [0106]    In the state of  FIG. 5A , the forward current at time point t 1  shown in  FIG. 6  is supplied. In the state of  FIG. 5B , the direction of the current is switched as shown at time point t 2  in  FIG. 6 . In the state of  FIG. 5C , the reverse current at time point t 3  shown in  FIG. 6  is supplied. Also, in the state of  FIG. 5D , the direction of the current is switched as shown at time point t 4  in  FIG. 6 , and, in the state of  FIG. 5D , the forward current at time point t 5  shown in  FIG. 6  is supplied. This is one operation cycle, and, by repeating these operations, movable body  120  repeats the displacement operations shown in  FIG. 5A  to  FIG. 5D , and, by this means, produces back-and-forth rotating vibration. 
         [0107]    In actuator  100 , movable body  120  produces back-and-forth rotating motion (that is, back-and-forth rotating vibration), and this back-and-forth rotating vibration is sent outside via shaft  125 . When a toothbrush part is coupled with shaft  125  and a hair bundle part is provided to be perpendicular to the axial direction at the head of this toothbrush part, the toothbrush part moves in back-and-forth rotating vibration and makes possible rolling brushing. 
         [0108]    By this means, actuator  100  satisfies equations 2 and 3 and is driven by a resonance phenomenon using the resonance frequency represented by equation 1. By this means, in actuator  100 , the power to be consumed in a static state is only the loss due to load torque and the loss due to friction and the like, so that low power drive is possible—that is, it is possible to move movable body  120  in back-and-forth rotating vibration at low power consumption. As described above, with actuator  100  of the present embodiment, it is possible to realize back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source, and furthermore make possible back-and-forth rotating motion at low power consumption. 
         [0109]    Furthermore, with this actuator  100 , movable body  120  is driven using coil  170  which is a voice coil, so that a detent force, which is magnetic attraction, is not produced, and therefore excellent controllability is provided. To be more specific, the position of movable body  120  while stopped is secured at the center location by the restoring force of elastic members  130 , so that there is little power loss when the drive stops. 
         [0110]    Furthermore, movable body  120  is formed with coil  170  and coil holding part  124 , not including outer yoke  140 . Consequently, the scale of the inertia moment of movable body  120  does not depend on the outer shape and is determined based upon the shape of coil  170 . Coil  170  is placed inside outer yoke  140  and is unlikely to be a factor to increase the inertia. The increase of inertia moment due to change of the outer shape of actuator  100  is reduced, so that constraints are removed in terms of design, and it is therefore possible to improve the freedom of design with respect to actuator  100  itself. 
         [0111]    An electric toothbrush having actuator  100  provides the same advantage, so that it is possible to miniaturize the electric toothbrush itself. 
       Second Embodiment 
       [0112]    In the configuration of actuator  100  according to the first embodiment shown in  FIG. 1 through 6 , an actuator according to the second embodiment uses a magnetic base, instead of non-magnetic base plate  112 . Consequently, the other parts are the same as in actuator  100 , and their detailed descriptions will be omitted. 
         [0113]      FIG. 7  is a schematic cross-sectional view showing a principal-part configuration of actuator  100 A according to a second embodiment of the present invention. In  FIG. 7 , the flow of magnetic fluxes in a magnetic circuit by magnet  150  is shown by outline arrows. 
         [0114]    Based upon the configuration of actuator  100  according to the first embodiment, actuator  100 A is configured such that base plate  112  is made magnetic base plate  112 A and movable body  120  having coil  170  is surrounded by a magnetic body. On the inner side of coil  170  surrounded by outer yoke  140  and base plate  112 A, similar to the configuration of actuator  100 , magnet  150  that is attached to outer yoke  140  a certain gap apart is placed to direct its magnetic pole planes in a direction to cross the direction coil  170  is wound. These magnetic pole planes are placed to sandwich sidewall parts  142  and  143  of outer yoke  140  by coil. With this configuration, compared to actuator  100 , actuator  100 A forms two paths for magnetic fluxes by magnetic  150  in fixed body  110 . 
         [0115]    That is to say, as shown in  FIG. 7 , in the magnetic circuit of actuator  100 A, magnetic fluxes (shown by outline arrows) that are produced from magnet  150  reach sidewall part  143  of outer yoke  140  via an air gap where coil  170  is placed. Then, from sidewall part  143  of outer yoke  140 , the magnetic fluxes pass both yoke center part  141  and base plate  112 A on the opposite side of yoke center part  141 , and then arrive at sidewall part  143 . Magnetic fluxes passing sidewall part  142  pass the opposite air gap from sidewall part  142  and continue to the opposite pole of magnet  150 . The operation of movable body  120  in actuator  100 A is virtually the same as in actuator  100 , and so descriptions will be omitted here. 
         [0116]    By this means, similar to actuator  100 , actuator  100 A is able to realize back-and-forth rotating motion of a toothbrush and the like without using a drive transmitting mechanism apart from a drive source. In addition, in actuator  100 A, the magnetic saturation in the magnetic circuit is reduced, so that it is possible to increase the thrust of movable body  120  that is produced when an AC voltage is supplied from alternating current supplying part  180  to coil  170 . 
         [0117]    Compared to the configuration of actuator  100  according to the first embodiment, actuator  100 A of this second embodiment is able to increase the torque which coil  170  produces to move movable body  120  by 1.05 times. 
         [0118]    Furthermore, with this second embodiment, the outer periphery part of fixed body  110  accommodating movable body  120  in a movable fashion—that is, a magnetic circuit including magnet  150 —is formed with outer yoke  140 , which is a magnetic body, and base plate  112 A, which is a magnetic body. 
         [0119]    That is to say, by forming the outer surface of actuator  100 A using a magnetic body, in actuator  100 A, it is possible to prevent magnetic fluxes from leaking from the magnetic circuit including base plate  112 A, outer yoke  140 , magnet  150  and coil  170 . 
       Third Embodiment 
       [0120]      FIG. 8  shows a configuration of actuator  100 B according to a third embodiment of the present invention and shows a state in which outer yoke  140  is removed from base plate  112 B in actuator  100 B, and  FIG. 9  is an exploded perspective view of this actuator. Actuator  100 B basically has the same configuration as actuator  100  according to the first embodiment, shown in  FIG. 1 , and therefore parts in actuator  100 B that are the same as in actuator  100  will be assigned the same reference numerals and codes as in actuator  100  and their explanations will be omitted. 
         [0121]    Based upon the configuration of actuator  100  according to the first embodiment, in an actuator according to this third embodiment, magnet  150  is removed from outer yoke  140 , fixed on base plate  112  via a non-magnetic body (spacer), and movable body  120  is turned upside down and fixed on fixed body  110  to be able to move in twisting directions in back-and-forth rotating vibration. 
         [0122]    To be more specific, actuator  100 B has fixed body  110 B, movable body  120 B, elastic members  130  that support movable body  120 B on fixed body  110 B so as to be able to move in twisting directions about shaft  125  of movable body  120 B, and alternating current supplying part  180  (see  FIG. 9  and  FIG. 10 ). 
         [0123]    As shown in  FIG. 8  and  FIG. 9 , fixed body  110 B has base plate  112 B, magnet  150  that is placed on base plate  112 B via projection part  160 B of a non-magnetic body (spacer), and U-shaped outer yoke  140  that is attached to base plate  112 B to cover magnet  150 . 
         [0124]    In fixed body  110 B, flat, rectangular base plate  112 B is formed of a non-magnetic body, and magnet  150  is attached, via non-magnetic projection part  160 B that is formed to project upward in the center area on the surface. 
         [0125]    Magnet  150  is attached on non-magnetic projection part  160 B such that air gaps are formed between its differing magnetic pole planes and opposing sidewall parts  142  and  143  of outer yoke  140 . Like magnet  150  of the above embodiments, the magnetic pole planes of magnet  150  are spaced apart in a direction perpendicular to shaft  125  and oppose sidewall parts  142  and  143  of outer yoke  140 . 
         [0126]    Projection part  160 B is formed on base plate  112 B integrally and has the same outer shape as magnet  150 . Here, projection part  160 B is a cuboid to extend, with magnet  150 , in the long direction of base plate  112 B. Projection part  160 B places magnetic  150  apart from base plate  112 B, thereby securing an area to allow coil  170  of movable body  120 B located in the surroundings of magnet  150  to move in back-and-forth rotation about magnet  150 . 
         [0127]    Thus, movable body  120 B is placed on fixed body  110 B such that coil  170  and upper plane part  124   d  of coil holding part  124 B are placed over magnet  150  attached on projection part  160 B projecting from base plate  112 B. 
         [0128]    Movable body  120 B is placed in an air gap formed between opposing inner wall part planes of outer yoke  140  and magnet  150 , and is formed with coil  170  that surrounds magnet  150 , and coil holding part  124 B that holds coil  170 . 
         [0129]    In coil holding part  124 B where front wall part  124   b  and rear wall part  124   c  hang from edge parts of upper plane part  124   d  that are spaced part in the log direction, coil  170  is attached on the back of upper plane part  124   d.    
         [0130]    Coil holding part  124 B is attached to support wall parts  114  and  116  of fixed body  110 B, via elastic members  130 , to be able to move in twisting directions about shafts  125  and  126  provided perpendicular to the axial direction of coil  170 . Elastic members  130  are formed on support wall parts  114  and  116  integrally by means of insert molding. 
         [0131]    Similar to actuator  100  of the first embodiment and actuator  100 A of the second embodiment, an alternating current having approximately the same frequency as a resonance frequency is supplied to coil  170  from alternating current supplying part  180  that supplies an AC voltage. By this means, movable body  120 B, supported in fixed body  110 B by means of elastic members  130  to be able to move in twisting directions of shaft  125 , moves in back-and-forth rotating vibration by the thrust by coil  170  in fixed body  110 B. 
         [0132]      FIG. 10  is a schematic diagram for explaining the operation of actuator  100 B according to the third embodiment of the present invention. Although the flow of magnetic fluxes from magnet  150  is shown by outline arrows in  FIG. 10A , the same flow applies to  FIG. 10B  to  FIG. 10D , and illustration is omitted in  FIG. 10B  to  FIG. 10D . Also, although  FIG. 10A  shows alternating current supplying part  180  that supplies an AC voltage to coil  170 , the same applies to  FIG. 10B  to  FIG. 10-D , and illustration is omitted in  FIG. 10B  to  FIG. 10D . 
         [0133]    As shown in  FIG. 10A , actuator  100 B has a magnetic circuit where magnetic fluxes produced from magnet  150  (designated by outline arrows) pass air gap G where coil  170  is placed, sidewall part  143  of outer yoke  140 , yoke center part  141 , sidewall part  142  and the opposite air gap, in order, and reaches the opposite pole of magnet  150 . 
         [0134]    With actuator  100 B, when an alternating current is supplied from alternating current supplying part  180  to coil  170 , thrusts F 1 , F 2 , F 3  and F 4  are produced in coil  170 , following Fleming&#39;s left hand rule. By this means, a rotating force about an axial center being shaft  125 , which is the center of rotation, is produced in coil  170 , and, similar to the case of coil  170  of actuator  100  shown in  FIG. 5 , movable body  120  repeats the operations of  FIG. 10A ,  FIG. 10B ,  FIG. 10C , and  FIG. 10D , and produces back-and-forth rotating vibration. 
         [0135]    In this way, with actuator  100 B, magnet  150  is directly placed on projection part  160 B that is formed on non-magnetic base plate  112 B integrally, so that, compared to actuator  100  of the first embodiment, it is not necessary to use a separate non-magnetic body and it is therefore possible to reduce the number of parts and make actuator  100 B cost effective. 
         [0136]    Furthermore, upon assembly, magnet  150  is placed on projection part  160 B that projects from the surface of flat base plate  112 B, so that, compared to the case of placing magnet  150  in the denting interior of U-shaped outer yoke  140 , it is possible to perform positioning and assembling operations easily. Furthermore, although actuator  100 B places magnet  150  differently compared to actuator  100 , the magnetic circuit configuration is the same and the same effect as actuator  100  of the first embodiment can be provided. In particular, with actuator  100 B, it is possible to achieve back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source. 
       Fourth Embodiment 
       [0137]      FIG. 11  is a schematic cross-sectional view showing a principal-part configuration of actuator  100 C according to a fourth embodiment of the present invention, and also is a schematic cross sectional view showing configurations of a fixed body and movable body in actuator  100 C. In  FIG. 11 , the flow of magnetic fluxes in actuator  200 C is shown by outline arrows. 
         [0138]    Based upon the configuration of actuator  100 B shown in  FIG. 8  and  FIG. 9 , actuator  100 C according to this fourth embodiment has a configuration to replace non-magnetic base plate  112 B with magnetic base plate  112 C, and the other configurations are the same. 
         [0139]    That is to say, with actuator  100 C, magnet  150 , having differing magnetic poles that are horizontally apart, is placed in approximately the center area on the surface of magnetic base plate  112 C of a flat rectangular shape. U-shaped outer yoke  140  is placed on base plate  112 C to cover magnet  150 . Inner wall parts  142   a  and  143   a  of sidewall parts  142  and  143  of outer yoke  140  are placed to oppose different magnetic poles (S magnetic pole plane  150   a  and N magnetic pole plane  150   b ) of magnet  150  via air gaps G. 
         [0140]    In air gap G, coil  170  is placed to surround magnet  150 , and these coils  170  are held by coil holding parts  124 B. In this case, similar to the third embodiment, coil holding part  124 B inserts shafts  125  and  126  rotatably in opening parts  114   a  and  116   a  of support wall parts  114  and  116  (see  FIG. 9 ), and is held via elastic members  130  in a movable fashion. That is to say, movable body  120 C is attached to fixed body  110 C to be able to move in back-and-forth rotation vibration in twisting directions about shaft  125  (not shown). 
         [0141]    In actuator  100 C configured this way, magnetic fluxes to flow out from magnet  150  travel on two paths in fixed body  110 . 
         [0142]    That is to say, in actuator  100 C, magnetic fluxes (shown by outline arrows) that are produced from magnet  150  pass an air gap where coil  170  is placed, from N magnetic pole plane  150   b , passes base plate  112 C from sidewall part  143  from outer yoke  140 , passes yoke center part  141  of outer yoke  140  on the opposite side from base plate  112 C, and reaches sidewall part  142 . The magnetic fluxes then passes an air gap from side wall part  142 , and continue to S magnetic pole plane  150   a , which is the opposite pole of magnet  150 . Similar to actuator  100 B, an alternating current having approximately the same frequency as a resonance frequency is supplied to coil  170  from alternating current supplying part  180  that supplies an AC voltage. By this means, movable body  120 C, supported in fixed body  110 C by means of elastic members  130  to be able to move in twisting directions of shaft  125  (see  FIG. 9 ), moves in back-and-forth rotating vibration by the thrust by coil  170  in fixed body  110 C. The back-and-forth rotating vibration of movable body  120   c  in actuator  100 C is the same as actuator  100 , and its description will be omitted. 
         [0143]    Then, in addition to the working advantages of actuator  100 B, the magnetic circuit of actuator  100   c  can provide the same advantages as by actuator  100 A of the second embodiment. In addition, in actuator  100 C, magnetic saturation is reduced, so that it is possible to increase the thrust of movable body  120 C that is produced when an AC voltage is supplied from alternating current supplying part  180  to coil  170 . 
         [0144]    Furthermore, the outer periphery part of fixed body  110 V accommodating movable body  120 C in a movable fashion—that is, a magnetic circuit including magnet  150 —is formed with outer yoke  140 , which is a magnetic body, and base plate  112 C, which is a magnetic body. That is to say, by forming the outer surface of actuator  100 C using a magnet body, in actuator  100 C, it is possible to prevent magnetic fluxes from leaking from the magnetic circuit including base plate  112 C, outer yoke  140 , magnet  150  and coil  170 . 
       Fifth Embodiment 
       [0145]      FIG. 12  is a perspective view showing actuator  100 D according to a fifth embodiment of the present invention, and  FIG. 13  is a principal-part exploded perspective view of this actuator  100 D. Actuator  100 D basically has the same configuration as actuator  100  according to the first embodiment, shown in  FIG. 1 , and therefore parts in actuator  100 D that are the same as in actuator  100  will be assigned the same reference numerals and codes as in actuator  100  and their explanations will be omitted. 
         [0146]    Based upon actuator  100  shown in  FIG. 1 , actuator  100 D according to the fifth embodiment has a configuration in which shafts  125  and  126  are inserted through support wall parts  114  and  116  of fixed body  110  via bearing  190  and axially supported in a rotatable fashion, and the rest of the configurations are the same. 
         [0147]    That is to say, as shown in  FIG. 12  and  FIG. 13 , in actuator  100 D, shaft  125  which movable body  120  has is rotatably inserted in bearing  190  attached to opening part  116   a  of support wall part  116 . This shaft  125  transmits and outputs the movement/motion of movable body  120 , and functions as a bearing to axially support movable body  120  on fixed body  110 . 
         [0148]    Furthermore, shaft  126  that is placed coaxially with shaft  125  in movable body  120  and that projects in the opposite direction from shaft  125  is rotatably inserted in bearing  190  attached to opening part  114   a  of support wall part  114 . 
         [0149]    Consequently, with actuator  100 D, when an alternating current is supplied from alternating current supplying part  180  to coil  170 , movable body  120  having coil  170  moves in stable back-and-forth rotating vibration about an axial center of shaft  125  with respect to fixed body  110 . 
         [0150]    In this way, with actuator  100 D, movable body  120  is axially supported by support wall parts  114  and  116 , via shafts  125  and  126  inserted in bearing  190 , in a rotatable fashion, with freedom in the rotating direction and axial direction. Furthermore, in a state in which movement in the axial direction is constrained, movable body  120  is supported by support wall parts  114  and  116  via elastic members  130 . That is to say, movable body  120  uses an axial support structure using support wall parts  114  and  116 , shafts  125  and  126  and bearing  190 , and is supported in fixed body  110  by securing freedom in the direction of rotation, so that movable body  120  is structured to be strong against shock. 
         [0151]    Consequently, actuator  100 D is able to achieve the same advantages as by actuator  100 , and, in addition, move in stable back-and-forth rotating motion by fixing the axis of rotation of shafts  125  and  126 , so that it is possible to improve the robustness of the actuator itself against shock. 
         [0152]    Although with this embodiment bearing  190  is provided in support wall parts  114  and  116  in actuator  100  according to the first embodiment to support shafts  125  and  126  of movable body  120  in a rotatable fashion, this is by no means limiting, and other places in actuators  100 A,  100 B and  100 C according to the second to fourth embodiments are equally applicable and available for modification. 
       Sixth Embodiment 
       [0153]      FIG. 14  is a principal-part exploded perspective view of an actuator according to a sixth embodiment of the present invention and  FIG. 15  shows an elastomer, which is a viscoelastic member used in this actuator. Based upon actuator  100  according the first embodiments shown in  FIG. 14 , actuator  100 E shown in  FIG. 14  replaces the configuration of elastic member  130  and the rest of the configurations are the same. The same parts will be assigned the same reference numerals and codes and their explanations will be omitted. 
         [0154]    Based upon the configuration of actuator  100 , with actuator  100 E, a viscoelastic body which itself attenuates significantly (elastomer  197  here) is used instead of elastic members  130  (which are zigzag springs). 
         [0155]    As shown in  FIG. 15 , elastomer  197  has center part  197   a  having insertion opening  198  in which shafts  125  and  126  are inserted, and arm parts  197   b  that project from center part  197   a  in a direction perpendicular to the axial center of shaft  126  and shaft  125 . Elastomer  197  is a viscoelastic body and can be displaced by elastically defining center part  197   a  and arm parts  197   b.    
         [0156]    Elastomer  197  is placed between support wall parts  116  and  114  and front wall part  124   b  and rear wall partl 24   c  of coil holding part  124 , and function as a spring. In elastomer  197 , projections on support walls part  116  and  114  and rear wall parts  124   b  and  124  are inserted and fit in holes  198   a  and  198   b  formed in locations shifted in the direction arm part  197   b  extends. 
         [0157]      FIG. 14  shows only projections  114   c  formed in support wall part  114  and projections  125   f  formed in front wall part  124   b , out of all projections to be inserted in holes  198   a  and  198   b  of elastomer  197 . Although not shown, similar projections to projections  114   c  of support wall part  114  are formed on support wall part  116 , and, likewise, similar projections to projections  125   f  of front wall part  124   b  are formed in rear wall part  124   c . Here, in arm parts  197   b  of elastomer  197 , projections of front and rear wall partl 24   b  and  124   c  are pressed and fit in holes  198   a  in locations near center part  197   a . Furthermore, projections of support wall parts  116  and  114  are pressed and fit in holes  198   b  in locations father from center part  197   a.    
         [0158]    Actuator  100 E thus has characteristics of the first embodiment and provides the same working advantages as by actuator  100 . In addition, by placing elastomer  197  between support wall parts  116  and  114  and front wall part  124   b  and rear wall part  124   c  of coil holding part  124 , and by pressing projections (only projections  114   c  and  125   f  are shown in  FIG. 13 ) in support wall parts  116  and  114 , front wall part  124   b  and rear wall part  124   c , into holes  198   a  and  198   b , actuator  100 E can be attached to both members. By this means, unlike cases where metallic springs such as zigzag springs and flat springs are used, complex processes of installation such as fastening of screws, bonding and insert molding are not necessary, and it is possible to allow elastomer  197  to function as a spring only by sandwiching elastomer  197  between movable body  120  and fixed body  110 , and it is therefore possible to improve the assembility of actuator  100  itself. 
         [0159]    Although with actuator  100 E movable body  120  is supported on fixed body  110 , using elastomer  197  instead of elastic member  130  according the first embodiment, to be able to move in twisting directions about the axis of shafts  125  and  126 , this is by no means limiting, and other places in actuators  100 A,  100 B and  100 C are equally applicable and available for modification. 
       Seventh Embodiment 
       [0160]      FIG. 16  is a perspective view showing actuator  100 F according to a seventh embodiment of the present invention, and  FIG. 17  is a principal-part exploded perspective view of this actuator  100 F. 
         [0161]    Actuator  100 F shown in  FIG. 16  and  FIG. 17  has fixed body  110 F, movable body  120 F, elastic members (elastic support parts)  130  that support movable body  120 F on fixed body  110 F in a movable fashion, and alternating current supplying part  180 . 
         [0162]    With this actuator  100 F, when movable body  120 F (see  FIG. 17 ) that is supported in fixed body  110 F via elastic members  130  moves, back-and-forth rotating vibration transmission shaft (hereinafter referred to as “shaft”)  125 , which is the output shaft of movable body  120 F (see  FIG. 17 ), rotates in forward and backward directions (the directions of arrows in  FIG. 16 ) in a predetermined angle range, and outputs back-and-forth rotating vibration outside. 
         [0163]    As shown in  FIG. 17 , fixed body  110 F has base plate  112 , support wall parts  114 A and  116 A, outer yoke  140 , and coil  170  that is attached to outer yoke  140 . Meanwhile, movable body  120 F has magnet (permanent magnet)  150 , magnet holding part  124 F that is supported by support wall parts  114 A and  116 A via elastic members  130  and that holds magnet  150 , and shafts  125  and  126 . 
         [0164]    In fixed body  110 F, in outer yoke  140 , magnet  150  of movable body  120 F is placed in an air gap the inner side of coil  170 . In actuator  100 F, by receiving as input an alternating current supply (AC voltage) from alternating current supplying part  180 , movable body  120 F is driven in a resonant state. 
         [0165]    To be more specific, in fixed body  110 F, base plate  112  forms a flat rectangular shape that is long in the direction in which shaft  125  of movable body  120 F extends, and is formed of a non-magnetic body here. 
         [0166]    Above the surface of base plate  112 , magnet  150  of movable body  120 F is placed, and outer yoke  140  having a U-shaped cross section (including the shape of a letter U placed sideways) is attached to base plate  112 , to cover this coil  170 . 
         [0167]    Furthermore, support wall parts  114 A and  116 A are erected from edge parts of base plate  112  that are spaced apart in the long direction. 
         [0168]    Support wall parts  114 A and  116 A have opening parts  114   a  and  116   a  in which shafts  125  and  126  of movable body  120 F are inserted. In a state in which shafts  126  and  125  are inserted rotatably in opening parts  114   a  and  116   a , respectively, support wall parts  114 A and  116 A support movable body  120 F rotatably via elastic members  130 . 
         [0169]    In a normal state, with elastic members  130 , support wall parts  114 A and  116 A hold movable body  120 F virtually horizontally (virtually parallel to base plate  112 ). Shafts  125  and  126  in may be inserted in opening parts  114   a  and  116   a  loosely. 
         [0170]    Elastic members  130  support movable body  120  in the area between opposing support wall parts  114 A and  116 A such that movable body  120 F is able to move in the front, back, left and right directions. 
         [0171]    Here, elastic members  130  are formed with flat, zigzag springs that project virtually horizontally in opposing directions in upper end areas of the opposing planes of support wall parts  114 A and  116 A. That is to say, elastic members  130  are each formed with a thin, band-shaped metallic plate of a zigzag shape that repeats, from its one end to the other end, extending in one width direction and returning in the other width direction, and elastic members  130  are each able to compress in a twisting direction if one end and the other end are fixed. 
         [0172]    One end of elastic members  130  configured in this way is attached to support wall parts  114 A and  116 A by insert molding and the other end is attached to magnet holding part  124 F that holds magnet  150 . By this means, in the area surrounded by base plate  112  and outer yoke  140 , support wall parts  114 A and  116 A support movable body  120 F, via elastic members  130 , to be able to move in twisting directions about the axis of shafts  125  and  126 . 
         [0173]      FIG. 18  is a schematic cross-sectional view showing a principal-part configuration of actuator  100 F according to the seventh embodiment of the present invention.  FIG. 18  shows the flow of magnetic fluxes, from magnet  150  as a magnetic circuit of actuator  100 F, with outline arrows. 
         [0174]    Outer yoke  140  has an approximately U-shaped cross section, and is formed by bending a flat magnetic body. Outer yoke  140  has yoke center part  141  of a flat rectangular shape, and mutually opposing sidewall parts  142  and  143  that hang from the side parts of yoke center part  141 . 
         [0175]    Outer yoke  140  here covers base plate  112  and support wall parts  114 A and  116 A from above, and covers magnet  150  and magnet holding part  124 F of movable body  120 F. The openings in the tip parts of sidewall parts  142  and  143  are closed by base plate  112 , and, with base plate  112  and support wall parts  114 A and  116 A, outer yoke  112 A forms a box shape to accommodate movable body  120 F. 
         [0176]    In inner wall parts  142   a  and  143   a  of opposing sidewall parts  142  and  143  of outer yoke  140 , coil  170  that is wound to surround the periphery of magnet  150  of movable body  120 F is fixed via air gaps. 
         [0177]    Coil  170  is a voice coil here, and is placed such that its outer diameter parts are fixed on inner wall planes  142   a  and  143   a  of side wall parts  142  and  143  of outer yoke  140 , and magnet  150  is placed on the inner side from the inner diameter parts, via air gaps from the inner periphery parts. That is to say, the inner periphery parts of coil  170  are placed to oppose the outer periphery planes of different poles of magnet  150  at a certain distance. 
         [0178]    Also, between side wall parts  142  and  143  of outer yoke  140 , coil  170  has a square cylindrical shape formed by winding a coil wire around an axis to extend in a direction virtually perpendicular to yoke center part  141  of outer yoke  140 , base plate  112  and shaft  125 . 
         [0179]    This coil  170  is attached on inner wall planes of outer yoke side wall parts  142  and  143  closer to yoke center part  141  and is placed in locations to face different magnetic poles of magnet  150  (magnetic pole planes  150   a  and  170   b ). 
         [0180]    Magnet (permanent magnet)  170 , which is placed on the inner side of coil  170  via air gaps, is a cuboid having magnetic pole planes  150   a  and  170   b  that are long in the direction in which outer yoke  1504  extends. Here, magnet  150  is held in a rotatable fashion in an air gap on the inner side of coil  170 , by means of magnet holding part  124 F held rotatably by support wall parts  114 A and  116 A via elastic members  130 . 
         [0181]    This magnet holding part  124 F is formed in the shape of a letter C placed sideways on a side view, and has bottom plate part  124   a  of a flat rectangular shape on which magnet  150  is placed, and front wall part  124   b  and rear wall part  124   c  that that erect from edge parts of bottom plate part  124   a  that are spaced apart along the long direction (that is, along the direction in which shaft  125  extends). 
         [0182]    This magnet holding part  124 F is formed of a non-magnetic body. In front wall part  124   b , shaft  125  is attached perpendicular, and, in rear wall partl 24   c , shaft  126  is placed to be positioned coaxially with shaft  125 . That is to say, shaft  125  is placed approximately along the center of magnet  150 , approximately parallel to varying magnetic pole planes  150   a  and  150   b  of magnet  150  (see  FIG. 19 ). 
         [0183]    Magnet holding part  124 F places magnet  150  apart from coil  170  and the back of yoke center part  141  of outer yoke  140 , and holds magnet  150  to be able to rotate in twisting direction about the axis of shafts  125  and  126 . In movable body  120 F, coil  170  is placed between front wall part  124   b  of magnet holding part  124 F and magnet  150  and between rear wall part  124   c  and magnet  150 , without making coil  170  touch these wall parts or magnet  150 , so that movable body  120 F is able to move on the inner side and outer side of coil  170 . 
         [0184]    Magnetic pole planes  150   a  and  150   b  of magnet  150 , held by magnet holding part  124 F, are placed to oppose, entirely, the inner wall planes of outer yoke sidewall parts  142  and  143  via coil  170 . 
         [0185]    Here, the S-pole end (S magnetic pole plane  150   a ) of magnet  150  faces the inner wall plane  142   a  of sidewall part  142  of outer yoke  140 , and the N-pole side (N magnetic pole plane  150   b ) faces the inner wall plane  143   a  of sidewall part  143  of outer yoke  140 . 
         [0186]    Incidentally, as shown in  FIG. 16  and  FIG. 17 , shaft  125  is provided to project outward from support wall part  116 A in the same direction as the direction of extension of outer yoke  140 . That is to say, in actuator  100 F, shaft  125  is provided to project in a direction that is virtually perpendicular to the direction magnet  150  and side wall parts  142  and  143  oppose each other over coil  170 . 
         [0187]    Shaft  125  is fixed in front wall part  124   b  of magnet holding part  124 F in this way, and, by this means, is attached to movable body  120 F to be located on an axis to pass the center of gravity of movable body  120 F. By this means shaft  125  is able to move in back-and-forth rotating vibration with magnet  150  and magnet holding part  124 F constituting the main body of movable body  120 F, and transmit this vibration outside. 
         [0188]    When actuator  100 F is used for an electric toothbrush, a toothbrush part is coaxially coupled with shaft  125 , and, at the head of this toothbrush part, a hair bundle part is provided to be perpendicular to the axial direction. By this means the toothbrush part moves in the same motion as shaft  125 , that is, moves in rolling motion, which is back-and-forth rotating vibration. 
         [0189]    With actuator  100 F of the present embodiment, assuming that the inertia of movable body  120 F is J and the spring constant in a twisting direction is k sp , as compared with fixed body  110 F, movable body  120 F vibrates in a resonance frequency calculated based on equation 1 below: 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       1 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     f 
                     0 
                   
                   = 
                   
                     
                       1 
                       
                         2 
                          
                         π 
                       
                     
                      
                     
                       
                         
                           K 
                           sp 
                         
                         J 
                       
                     
                   
                 
               
               
                 
                   [ 
                   4 
                   ] 
                 
               
             
           
         
       
     
         [0190]    In actuator  100 F of the present embodiment, an alternating current of substantially the same frequency as a resonance frequency f 0  of movable body  120 F is supplied from alternating current supplying part  180  to coil  170 . By this means, it is possible to drive movable body  120 F efficiently. 
         [0191]    As shown in  FIG. 18 , in fixed body  110 F and movable body  120 F, outer yoke  140 , magnet  150  and coil  170  form a magnetic circuit. 
         [0192]    To be more specific, actuator  100  has a magnetic circuit where magnetic fluxes produced from magnet  150  (designated by outline arrows) pass an air gap where coil  170  is placed, sidewall part  143  of outer yoke  140 , yoke center part  141 , sidewall part  142  and the opposite air gap, in order, and reaches the opposite pole of magnet  150 . 
         [0193]    Movable body  120 F of this actuator  100 F is supported by a spring mass system structure supported by fixed body  110 F via elastic members  130  (see  FIG. 16  and  FIG. 17 ). When an alternating current of the same frequency as resonance frequency f 0  of movable body  120 F is supplied to coil  170 , movable body  120 F is driven in a resonant state. The back-and-forth rotating vibration that is produced then is transmitted to shaft  125  of movable body  120 F. 
         [0194]    Actuator  100 F is driven based on the equation of motion represented by equation 2 below and based on the circuit equation represented by equation 3 below. 
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       2 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     J 
                      
                     
                       
                         
                            
                           2 
                         
                          
                         
                           θ 
                            
                           
                             ( 
                             t 
                             ) 
                           
                         
                       
                       
                          
                         
                           t 
                           2 
                         
                       
                     
                   
                   = 
                   
                     
                       
                         K 
                         t 
                       
                        
                       
                         i 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       
                         K 
                         sp 
                       
                        
                       
                         θ 
                          
                         
                           ( 
                           t 
                           ) 
                         
                       
                     
                     - 
                     
                       D 
                        
                       
                         
                            
                           
                             θ 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                     - 
                     
                       T 
                       Load 
                     
                   
                 
               
               
                 
                   [ 
                   5 
                   ] 
                 
               
             
           
         
       
       
         J: Inertia moment [Kgm2] 
         θ(t): Angle [rad] 
         K t : Torque constant [Nm/A] 
         i(t): Current [A] 
         K sp : Spring constant [Nm/rad] 
         D: Attenuation coefficient [Nm/(rad/s)] 
         T LOAD : Load torque [Nm] 
       
     
         [0000]    
       
         
           
             
               
                 
                   
                     ( 
                     
                       Equation 
                        
                       
                           
                       
                        
                       3 
                     
                     ) 
                   
                    
                   
                       
                   
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     e 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                   
                     
                       Ri 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                     + 
                     
                       L 
                        
                       
                         
                            
                           
                             i 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                     + 
                     
                       
                         K 
                         e 
                       
                        
                       
                         
                            
                           
                             θ 
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                         
                         
                            
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   6 
                   ] 
                 
               
             
           
         
       
       
         e(t): Voltage [V] 
         R: Resistance [Ω] 
         L: Inductance [H] 
         K e : Counter electromotive force multiplier [V/(rad/s)] 
       
     
         [0206]    That is to say, the inertia moment, rotation angle, torque constant, current, spring constant, attenuation coefficient, and load torque in actuator  100 F can be changed as adequate in a range to satisfy equation 2, and the voltage, resistance, inductance, and counter electromotive force multiplier can be changed as adequate in a range to satisfy equation 3. 
         [0207]    Next, the operations of actuator  100 F will be described in detail. 
         [0208]      FIG. 19  is a schematic view for explaining operation of actuator  100 F according top the seventh embodiment. Although the flow of magnetic fluxes from magnet  150  is shown by outline arrows in  FIG. 19A , the same flow applies to  FIG. 19B  to  FIG. 19D , and illustration is omitted in  FIG. 19B  to  FIG. 19D . Also, although FIG.  19 A shows alternating current supplying part  180  that supplies an AC voltage to coil  170 , the same applies to  FIG. 19B  to  FIG. 19D , and illustration is omitted in  FIG. 19B  to  FIG. 19D . 
         [0209]    When an alternating current is supplied from alternating current supplying part  180  to coil  170 , thrusts F 1 , F 2 , F 3  and F 4  are produced in coil  170 , following Fleming&#39;s left hand rule. By this means, in movable body  120 F that is attached to base plate  112  and support wall parts  114 A and  116 A via elastic members  130  in a movable fashion, a rotating force about an axial center at the center of rotation is produced. 
         [0210]    One operation cycle of actuator  100 F will be described. 
         [0211]    When a current flows in coil  170  in the direction shown in  FIG. 19A  (a current to flow in this direction will be hereinafter referred to as “forward current”), downward thrust F 1  (directed toward base plate  112 ) is produced in part  170   b  of coil  170  opposing N-pole plane  150   b  of magnet  150 . Meanwhile, in part  170   a  of coil  170  opposing S pole plane  150   a  of magnet  150 , upward thrust F 2  (directed toward yoke center part  141  of outer yoke  140 ) is produced. 
         [0212]    By this means, a rotating force is produced in movable body  120 F that has magnet  150  and that is supported by support wall parts  114  and  116  that erect from base plate  112  of fixed body  110 F (see  FIG. 2  and  FIG. 3 ), via elastic members  130 . In movable body  120 F, thrusts R 1  and R 2  work on magnet  150  as reaction forces to thrusts F 1  and F 2  of coil  170 . By this means, movable body  120 F moves anticlockwise to assume the position shown in  FIG. 19B . 
         [0213]    With actuator  100 F shown in  FIG. 19B , a reaction force to place movable body  120 F in the state of  FIG. 19A  by the restoring force of elastic members  130  (see  FIG. 17  and  FIG. 18 ), is produced. From the state shown in  FIG. 19B  to the state shown in  FIG. 19D , a reverse current is supplied to coil  170  as compared with  FIG. 19A . By this means, from the state shown in  FIG. 19B  to the state shown in  FIG. 19C , movable body  120 F rotates anticlockwise with respect to fixed body  110 F, by the reaction force of elastic members  130  and thrusts R 3  and R 4  produced as reaction forces to the thrusts designated by arrows F 3  and F 4 . From the state shown in  FIG. 19C  to the state shown in  FIG. 19D , movable body  120 F rotates anticlockwise with respect to fixed body  110 F by the thrusts that work upon magnet  150 , designated by arrows F 3  and F 4 . 
         [0214]    With actuator  100 F shown in  FIG. 19D , a reaction force to place movable body  120 F in the state of  FIG. 19A  by the restoring force of elastic members  130  is produced. From the state shown in  FIG. 19D , passing the state shown in  FIG. 19A , to the state shown in  FIG. 19B , a forward current is supplied to coil  170 . By this means, from the state shown in  FIG. 19D  to the state shown in  FIG. 19A , movable body  120 F rotates anticlockwise with respect to fixed body  110 F, by the reaction force of elastic members  130  and by thrusts R 1  and R 2  which are produced as reaction forces to the thrusts designated by arrows F 1  and F 2  and which work upon magnet  150 . 
         [0215]    From the state shown in  FIG. 19A  to the state shown in  FIG. 19B , movable body  120 F rotates anticlockwise with respect to fixed body  110 F by the thrusts designated by arrows R 1  and R 2 . Although movable body  120 F moves in back-and-forth rotating motion, on the inner side of coil  170 , approximately about the extending center axis of magnet  150 , it is equally possible to operate movable body  120 F in the same way as shown in  FIG. 19 , by thrusts R 1  to R 4 , without using the reaction force of magnetic member  130 . 
         [0216]    Next, what alternating current is supplied to coil  170  of movable body  120 F in each state shown in  FIG. 19  will be described briefly. 
         [0217]    The alternating current to flow in the coil may be a pulse wave of frequency f 0  as shown in  FIG. 6A  or may be a sine wave of frequency f 0  as shown in  FIG. 6B . 
         [0218]    In the state of  FIG. 19A , the forward current at time point t 1  shown in  FIG. 6  is supplied. In the state of  FIG. 19B , the direction of the current is switched as shown at time point t 2  in  FIG. 6 . In the state of  FIG. 19C , the reverse current at time point t 3  shown in  FIG. 6  is supplied. Also, in the state of  FIG. 19D , the direction of the current is switched as shown at time point t 4  in  FIG. 6 , and, in the state of  FIG. 19D , the forward current at time point t 5  shown in  FIG. 6  is supplied. This is one operation cycle, and, by repeating these operations, movable body  120 F repeats the displacement operations shown in  FIG. 19A  to  FIG. 19D , and, by this means, produces back-and-forth rotating vibration. 
         [0219]    In actuator  100 F, movable body  120 F produces back-and-forth rotating motion (that is, back-and-forth rotating vibration), and this back-and-forth rotating vibration is sent outside via shaft  125 . When a toothbrush part is coupled with shaft  125  and a hair bundle part is provided to be perpendicular to the axial direction at the head of this toothbrush part, the toothbrush part moves in back-and-forth rotating vibration and makes possible rolling brushing. 
         [0220]    By this means, actuator  100 F satisfies equations 2 and 3 and is driven by a resonance phenomenon using the resonance frequency represented by equation 1. By this means, in actuator  100 F, the power to be consumed in a static state by resonance drive is only the loss due to load torque and the loss due to friction and the like, so that low power drive is possible—that is, it is possible to move movable body  120 F in back-and-forth rotating vibration at low power consumption. As described above, with actuator  100 F of the present embodiment, it is possible to realize back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source, and furthermore make possible back-and-forth rotating motion at low power consumption. 
         [0221]    Furthermore, movable body  120 F is formed with magnet  150  and magnet holding part  124 F, without using large-sized components like outer yoke  140 . Consequently, the scale of the inertia moment of movable body  120 F does not depend on the outer shape and can be determined based upon the shape of magnet  150 . Furthermore, given that magnet  150  is placed such that its center of gravity is located near shaft  125 , which is the output shaft of movable body  120 F, and, to be more specific, approximately on the axis of shaft  125 , so that magnet  150  is unlikely to be a factor to increase the inertia. The increase of inertia moment due to change of the outer shape of actuator  100 F is reduced, so that constraints are removed in terms of design, and it is therefore possible to improve the freedom of design with respect to actuator  100 F itself. 
         [0222]    An electric toothbrush having actuator  100 F provides the same advantage, so that it is possible to miniaturize the electric toothbrush itself. 
         [0223]    Also, although with the configuration of actuator  100 F according to the seventh embodiment base plate  112  is a non-magnetic body, this is by no means limiting, and it is equally possible to use a magnetic body. This configuration will be explained now with reference to  FIG. 20 . 
       Eighth Embodiment 
       [0224]      FIG. 20  is a schematic cross-sectional view showing a principal-part configuration of an actuator according to an eighth embodiment of the present invention.  FIG. 20  shows the flow of magnetic fluxes, from magnet  150  as a magnetic circuit of actuator  100 F, with outline arrows. 
         [0225]    Actuator  100 G shown in  FIG. 20  replaces non-magnetic base plate  112  in the configuration of actuator  100 F with magnetic base plate  112 G. Consequently, the other parts of actuator  100 G are the same as in actuator  100 F, and their detailed descriptions will be omitted. 
         [0226]    Fixed body  110 G of actuator  100 G has coil  170  that is placed to surround the periphery of magnet  150  of movable body  120 F via an air gap, outer yoke  140 , which is a magnetic body to fix the outer periphery parts of coil  170  to opposing inner wall planes  142   a  and  143   a , and base plate  11 G, which is a magnetic body. 
         [0227]    That is to say, with actuator  100 G, magnet  150  and magnet holding part  124 F of movable body  120 F (only bottom plate part  124   a  is shown in  FIG. 20 ) are surrounded by outer yoke  140  and base plate  112 G, which are magnetic bodies. Magnet  150  is placed on the inner side of base plate  112 G and on the inner side of coil  170  such that, similar to the configuration of actuator  100 F, magnetic pole planes  150   a  and  150   b  are directed toward side wall parts  142  and  143  of outer yoke  140 , at a certain distance, in a direction perpendicular to the direction coil  170  is wound. 
         [0228]    With this configuration, compared to actuator  100 F, actuator  100 G forms two paths for magnetic fluxes by magnet  150  in fixed body  110 G. 
         [0229]    That is to say, as shown in  FIG. 20 , in the magnetic circuit of actuator  100 G, magnetic fluxes (shown by outline arrows) that are produced from magnet  150  reach sidewall part  143  of outer yoke  140 , from magnetic pole plane  150   b , passing an air gap where coil  170  is placed. Next, from sidewall part  143 , the magnetic fluxes pass both yoke center part  141  and base plate  112 G on the opposite side from yoke center part  141 , and then arrive at sidewall part  143 . Magnetic fluxes pass sidewall part  142  and the opposite air gap in order, and continue to the opposite pole of magnet  150  (magnetic pole plane  150   a ). The operation of movable body  120  in actuator  100 G is virtually the same as in actuator  100 F, and so descriptions will be omitted here.  FIG. 20  shows thrusts F 1  and F 2  that are produced when a forward current is applied, and thrusts R 1  and R 2  of magnet  150 , which are reaction forces to these. When thrusts R 1  and R 2  are produced, movable body  120 F moves in the directions of thrusts R 1  and R 2 . When the direction of current changes, reverse thrusts to F 1  and F 2  work on coil  170 , and, by this means, opposite thrusts to R 1  and R 2  work on magnet  150 , and, consequently, movable body  120 F moves in directions designated by reverse thrusts to R 1  and R 2 . By repeating these, similar to the seventh embodiment, actuator  100 G moves mobile body  120 F in back-and-forth rotating vibration. 
         [0230]    As described above, with actuator  100 G of this eight embodiment, it is possible to achieve similar or the same working effects as actuator  100 F such as realizing back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source. In addition, with actuator  100 G, the magnetic saturation in the magnetic circuit is reduced, so that it is possible to increase the thrust of movable body  120 F that is produced when an AC voltage is supplied from alternating current supplying part  180  to coil  170 . 
         [0231]    Compared to the configuration of actuator  100 F according to the seventh embodiment, actuator  100 G is able to increase the torque which coil  170  produces to move movable body  120 F by 1.25 times. 
         [0232]    Furthermore, with this second embodiment, the outer periphery part of fixed body  110 F accommodating movable body  120 F in a movable fashion—that is, a magnetic circuit—is formed with outer yoke  140 , which is a magnetic body, and base plate  112 G, which is a magnetic body. 
         [0233]    That is to say, by forming the outer surface of actuator  100 G using a magnetic body, in actuator  100 G, it is possible to prevent magnetic fluxes from leaking from the magnetic circuit including base plate  112 G, outer yoke  140 , magnet  150  and coil  170 . 
       Ninth Embodiment 
       [0234]    To briefly summarize an actuator according to a ninth embodiment, based upon the configuration of actuator  100 F (see  FIG. 17  and  FIG. 18 ), coil  170  is removed from outer yoke  140 , fixed on base plate  112  via a non-magnetic body (spacer), and movable body  120 F is turned upside down and fixed on fixed body  110 F to be able to move in twisting directions in back-and-forth rotating vibration via non-magnetic members  130 . 
         [0235]      FIG. 21  is an outer view of actuator  100 H according to a ninth embodiment of the present invention,  FIG. 22  is an exploded perspective view of this actuator  100 H, and  FIG. 23  is a schematic cross-sectional view showing a principal-part configuration of this actuator  100 H. This actuator  100 H basically has the same configuration as actuator  100 F according to the seventh embodiment, shown in  FIG. 16 , and therefore parts in actuator  100 H that are the same as in actuator  100 F will be assigned the same reference numerals and codes as in actuator  100 F and their explanations will be omitted. 
         [0236]    As shown in  FIG. 21  to  FIG. 23 , actuator  100 H has fixed body  110 H that has outer yoke  140 , base plate  112 H, coil  170  and support wall parts  114 B and  116 B, movable body  120 H that has magnet  150  placed on the inner side (the inner periphery part) of coil  170  via an air gap, elastic members  130  that support movable body  120 H on fixed body  110 H such that movable body  120 H is able to rotate back and forth in twisting directions about shaft  125  of movable body  120 H, and alternating current supplying part  180  (see  FIG. 22  and  FIG. 23 ). 
         [0237]    In fixed body  110 H, base plate  112 H has base plate main body  1121  formed of a non-magnetic body of a flat rectangular shape. At edge parts on the surface of this base plate main body  1121 , that are spaced apart along the long direction, positioning projection parts  1122 , and  1123  that project upward and that fit in recesses formed in the lower planes of support wall parts  114 B and  116 B are provided. Support wall parts  114 B and  116 B are provided to erect from the places in base plate main body  1121  where support wall parts  114 B and  116 B are positioned via positioning projection parts  1122  and  1123 . 
         [0238]    Furthermore, in the center area on the surface of base plate main body  1121 , annular fitting channel part  1124  is formed. This annular fitting channel part  1124  is formed to match the shape of coil  170 , has an inner diameter to match the inner diameter of the cylindrical part of coil  170 , and provides a channel having a slightly greater width that the thickness of the cylindrical part of coil  170 . Coil  170  is provided to be positioned in annular fitting channel part  1124 . 
         [0239]    Base plate  112 H is provided such that outer yoke  140  having a U-shaped cross section covers the surface of base plate  112 H and support wall parts  114 B and  116 B from above in a state in which sidewall parts  142  and  143  contact the outer periphery part of coil  170  on base plate  112 H. 
         [0240]    On the inner side of coil  170  provided in base plate  112 H—that is, in the inner part—magnet  150  provided via an air gap. 
         [0241]    In the area surrounded by outer yoke  140  and base plate  112 H, magnet  150  is held by magnet holding part  124 H supported in a rotatable fashion on the inner side of coil  170 , via elastic members  130  in support wall parts  114 B and  116 B. 
         [0242]    Magnet  150  is held by magnet holding part  124 H in a location apart from base plate  112 H and yoke center part  141  such that different magnetic pole planes  150   a  and  150   b  of magnet  150  face coil  170  via an air gap. 
         [0243]    Magnet holding part  124 H has upper plane part  124   d  that is fixed on the upper plane of magnet  150 , and front wall part  124   b  and rear wall part  124   c  that hang from edge parts of upper plane part  124   d  (front and rear edge parts) that are spaced part in the long direction of upper plane part  124   d . Magnet holding part  124 H is provided perpendicular to front wall part  124   b  and rear wall part  124   c  and inserts shafts  125  and  126 , which are provided along the position of the center of gravity of magnet  150 , in opening parts  114   a  and  116   a  of support wall parts  114 B and  116 B of fixed body  110 H. Furthermore, magnet holding part  124 H is provided in support wall parts  114 B and  116 B to be able to move via elastic members  130 . By this means, magnet  150  and magnet holding part  124 H are provided on the inner side of coil  170  placed in the periphery of magnet  150  so as to be capable of back-and-forth rotation in twisting directions about shafts  125  and  126 . Similar to the seventh embodiment, elastic members  130  are provided in support wall parts  114 B and  116 B. To be more specific, elastic members  130  are provided in inner lower side parts of support wall parts  114 B and  116 B (formed similar to support wall parts  114 A and  116 A), integrally, by means of insert molding. 
         [0244]    Similar to actuator  100 F of the seventh embodiment and actuator  100 G of the eighth embodiment, an alternating current having approximately the same frequency as a resonance frequency is supplied to coil  170  from alternating current supplying part  180  that supplies an AC voltage. By this means, mobile body  120 H that is supported on fixed body  110 H by elastic members  130  to be able to move in twisting directions of shaft  125 , moves in back-and-forth rotation vibration, in fixed body  110 H, by a reaction force that is produced in magnet  150  by the thrusts of coil  170 . 
         [0245]      FIG. 24  is schematic diagram showing operation of actuator  100 H according to the ninth embodiment of the present invention. Although the flow of magnetic fluxes from magnet  150  is shown by outline arrows in  FIG. 24A , the same flow applies to  FIG. 24B  to  FIG. 24D , and illustration is omitted in  FIG. 24B  to  FIG. 24D . Furthermore,  FIG. 24A  illustrates alternating current supplying part  180  that supplies an AC voltage to coil  170 , and, although the same flow of magnetic fluxes as in  FIG. 24A  is produced in  FIG. 24B  to  FIG. 24D , this is not illustrated for ease of explanation. 
         [0246]    As shown in  FIG. 24A , in actuator  100 H, a magnetic circuit is formed in which magnetic fluxes produced from magnet  150  (designated by outline arrows) pass, from magnetic pole plane  150   b , air gap G, coil  170 , side wall parts  143  of outer yoke  140 , yoke center part  141 , side wall parts  142 , an the opposite air gap, in order, and reach the opposite pole of magnet  150  (magnetic pole plane  150   a ). 
         [0247]    In actuator  100 H, when an alternating current is supplied from alternating current supplying part  180  to coil  170 , thrusts designated by arrows F 1 , F 2 , F 3  and F 4  in the drawing are produced in coil  170 , following Fleming&#39;s left hand rule. In response to this, rotating forces (thrusts R 1  to R 4 ) about an axial center being shaft  125 , which is the center of rotation, are produced in magnet  150 , and, similar to the case of mobile body  120 F of actuator  100 F shown in  FIG. 19 , movable body  120 F repeats the operations of  FIG. 24A ,  FIG. 24B ,  FIG. 24C , and  FIG. 24D , and produces back-and-forth rotating vibration. 
         [0248]    Actuator  100 H thus has the same working effects as actuator  100 F. In addition, with this actuator  100 H, upon assembly, coil  170  is attached to base plate  112 H. Furthermore, upon assembly, coil  170  is placed on the surface of flat base plate  112 H, so that, compared to the case of placing coil  170  in the denting interior of U-shaped outer yoke  140 , it is possible to perform installation easily. 
         [0249]    In this case, coil  170  is attached to be positioned in annular fitting channel part  1124  formed on the surface of base plate  112 H, so that it is possible to install coil  170  in a location positioned in base plate  112 H. 
         [0250]    Generally, coil  170  is made by winding a coil wire around a jig that defines the inner diameter of the coil, it is difficult to accurately control the outer diameter dimension of resulting coil  170 . Consequently, when coil  170  is provided inside outer yoke  140 , it is necessary to attach the outer periphery part of coil  170  to outer yoke  140 , so that accurate control is required upon making of coil  170  and this is burdensome. 
         [0251]    By contrast with this, with the present embodiment, in base plate  112 H, coil  170  is directly placed in annular fitting channel part  1124  where the inner diameter is defined, it is possible to determine the position of installation by the inner periphery part of coil  170 . Consequently, with actuator  100 H, it is possible to improve the assembility and reduce the work load. 
         [0252]    Although, actuator  100 H places, for example, coil  170  differently compared to actuator  100 F, the magnetic circuit configuration is the same, and it is therefore possible to achieve the same working effects as by actuator  100 F of the seventh embodiment. Especially, with actuator  100 H of the present embodiment, it is possible to realize back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source. 
         [0253]    Also, although with the configuration of actuator  100 H base plate  112 H is a non-magnetic body, this is by no means limiting, and it is equally possible to make base plate  112 H a magnetic body. In this case, similar to the eighth embodiment, the path of magnetic fluxes in fixed body  110 H passes, from one side wall part  143 , yoke center part  141  and base plate  112 H, in order, and reaches side wall part  142  on the other side, and therefore it is possible to provide the same advantage as by the second embodiment. 
       Tenth Embodiment 
       [0254]      FIG. 25  is a perspective view showing actuator  100 J according to a tenth embodiment of the present invention, and  FIG. 26  is a principal-part exploded perspective view of this actuator  100 J. This actuator  100 J basically has the same configuration as actuator  100 F according to the seventh embodiment, shown in  FIG. 16 , and therefore parts in actuator  100 J that are the same as in actuator  100 F will be assigned the same reference numerals and codes as in actuator  100 F and their explanations will be omitted. 
         [0255]    Based upon actuator  100 F shown in  FIG. 16 , actuator  100 J according to the tenth embodiment has a configuration in which shafts  125  and  126  are inserted through support wall parts  114 A and  116 A of fixed body  110 F via bearing  190  and axially supported in a rotatable fashion, and the rest of the configurations are the same. 
         [0256]    That is to say, as shown in  FIG. 25  and  FIG. 26 , in actuator  100 J, shaft  125  which movable body  120 F has is rotatably inserted in bearing  190  attached to opening part  116   a  of support wall part  116 A. This shaft  125  transmits and outputs the movement/motion of movable body  120 F, and functions as a bearing to axially support movable body  120 F on fixed body  110 F. 
         [0257]    Furthermore, shaft  126  that is placed coaxially with shaft  125  in movable body  120 F and that projects in the opposite direction from shaft  125  is rotatably inserted in bearing  190  attached to opening part  114   a  of support wall part  114 A. 
         [0258]    Consequently, with actuator  100 J, when an alternating current is supplied from alternating current supplying part  180  to coil  170 , movable body  120 F having coil  170  moves in stable back-and-forth rotating vibration about an axial center of shaft  125  with respect to fixed body  110 F. 
         [0259]    In this way, with actuator  100 J, movable body  120 F is axially supported by support wall parts  114 A and  116 A, via shafts  125  and  126  inserted in bearing  190 , in a rotatable fashion, with freedom in the rotating direction and axial direction. Furthermore, in a state in which movement in the axial direction is constrained, movable body  120 F is supported by support wall parts  114 A and  116 A via elastic members  130 . That is to say, movable body  120 F uses an axial support structure using support wall parts  114 A and  116 A, shafts  125  and  126  and bearing  190 , and is supported in fixed body  110 F by securing freedom in the direction of rotation, so that movable body  120 F is structured to be strong against shock. 
         [0260]    Consequently, actuator  100 J is able to achieve the same advantages as by actuator  100 F, and, in addition, move in stable back-and-forth rotating motion by fixing the axis of rotation of shafts  125  and  126 , so that it is possible to improve the robustness of the actuator itself against shock. 
         [0261]    Although with this embodiment bearing  190  is provided in support wall parts  114 A and  116 A in actuator  100 F according to the seventh embodiment to support shafts  125  and  126  of movable body  120 F in a rotatable fashion, this is by no means limiting, and, for example, it is equally possible to provide bearing  190  in support wall parts  114 A,  114 B,  116 A and  116 B of actuator  100 G and actuator  100 H of the eighth and ninth embodiments and support shafts  125  and  126  of movable body  120 F in a rotatable fashion. 
       Eleventh Embodiment 
       [0262]      FIG. 27  is an exploded perspective view showing actuator  100 K according to an eleventh embodiment of the present invention. Based upon actuator  100 F according the seventh embodiment shown in  FIG. 16  to  FIG. 19 , actuator  100 K shown in  FIG. 27  replaces the configuration of elastic members  130 , and the rest of the configurations are the same. The same parts will be assigned the same reference numerals and codes and their explanations will be omitted. 
         [0263]    Based upon the configuration of actuator  100 F, with actuator  100 K, a viscoelastic body which itself attenuates significantly (here, elastomer  197  for actuator  200 E according to the sixth embodiment, as shown in  FIG. 15 ) is used instead of elastic members  130  (which are zigzag springs). 
         [0264]    Elastomer  197  (see  FIG. 27  and  FIG. 15 ) is the same as that of the sixth embodiment, and, placed between support wall parts  116 A and  114 A and front wall part  124   b  and rear wall partl 24   c  of coil holding part  124 F, functions as a spring. In elastomer  197 , projections  114   c ,  116   c ,  124   f  and  124   g  formed in support walls parts  116 A and  114 A and rear wall parts  124   b  and  124   c  are inserted and fit in holes  198   a  and  198   b  formed in locations shifted in the direction arm part  197   b  extends. 
         [0265]    Here, in arm parts  197   b  of elastomer  197 , projections  124   f  and  124   g  of front and rear wall parts  124   b  and  124   c  are pressed and fit in holes  198   a  in locations near center part  197   a . Furthermore, projections  116   c  and  114   c  of support wall parts  116 A and  114 A are pressed and fit in holes  198   b  in locations father from center part  197   a.    
         [0266]    Actuator  100 K thus has characteristics of the seventh embodiment and provides the same working advantages as by actuator  100 F. In addition, by placing elastomer  197  between support wall parts  116 A and  114 A and front wall part  124   b  and rear wall part  124   c  of magnet holding part  124 F, and by pressing projections  114   c ,  116   c ,  124   f  and  124   g  of support wall parts  116 A and  114 A, front wall part  124   b  and rear wall part  124   c , into holes  198   a  and  198   b , actuator  100 K can be attached to both members (that is, support wall parts and front and rear wall parts). By this means, unlike cases where metallic springs such as zigzag springs and flat springs are used, complex processes of installation such as fastening of screws, bonding and insert molding are not necessary, and it is possible to allow elastomer  197  to function as a spring only by sandwiching elastomer  197  between movable body  120 F and fixed body  110 F, and it is therefore possible to improve the assembility of actuator  100 K itself. 
         [0267]    Instead of elastic members  130  of actuators  100 G and  100 H, elastomer  197  for actuator  100 K may support movable body  120 F on fixed body  110 F such that movable body  120 F is able to move in twisting directions about the axis of shafts  125  and  126 . 
         [0268]    Various changes can be made to the present invention without departing from the spirit of the present invention, and such changes are certainly within the scope of the present invention. 
         [0269]    The disclosures of Japanese Patent Application No. 2008-282360, filed on Oct. 31, 2008, and Japanese Patent Application No. 2008-282361, filed on Oct. 31, 2008, including the specifications, drawings, and abstracts, are incorporated herein by reference in their entirety. 
       INDUSTRIAL APPLICABILITY  
       [0270]    An actuator according to the present invention provides an advantage of realizing back-and-forth rotating motion of an electric toothbrush or the like without using a drive transmitting mechanism apart from a drive source and allowing miniaturization of an electric toothbrush or the like, and therefore is suitable for use as an actuator that is used for an electric toothbrush or the like to produce back-and-forth rotating vibration. 
       REFERENCE SIGNS LIST  
       [0000]    
       
           100 ,  100 A,  100 B,  100 C,  100 D,  100 E,  100 F,  100 G,  100 H,  100 J,  100 K 
         Actuator 
           110 ,  110 A,  110 B,  110 C,  110 F,  110 G,  110 H Fixed body 
           112 ,  112 A,  112 B,  112 C,  112 G,  112 H Base plate 
           114 ,  116 ,  114 A,  114 B,  116 A,  116 B Support wall part 
           120 ,  120 B,  120 C,  120 F,  120 H Movable body 
           124 ,  124 B Coil holding part 
           124 F,  124 H Magnet holding part 
           124   b  Front wall part 
           124   c  Rear wall part 
           125 ,  126  Shaft 
           130  Elastic member 
           140  Outer yoke 
           141  Yoke center part (center part) 
           142 ,  143  Sidewall part 
           142   a ,  143   a  Inner wall part 
           150  Magnet (permanent magnet) 
           150   a ,  150   b  Magnetic pole plane 
           160 ,  160 C Non-magnetic body 
           160 B Projection 
           170  Coil 
           180  Alternating current supplying part 
           190  Bearing 
           197  Elastomer