Abstract:
Provided is an instrument driving device which is capable of suppressing loss of synchronism caused by vibration and impact etc. The driving device ( 1 ) comprises: a magnet ( 2 ) which rotates; a driving gear ( 3 ) which is coaxial with the magnet ( 2 ); an output gear ( 5 ) which is driven by the magnet ( 2 ); a needle pointer shaft ( 6 ) which has a needle pointer ( 14 ) mounted thereon and also rotatably supports the output gear ( 5 ); a transmission gear ( 4 ) which transmits rotation of the driving gear ( 3 ) to the output gear ( 5 ); and a case ( 12 ) which accommodates parts of the magnet ( 2 ), the driving gear ( 3 ), the output gear ( 5 ), the transmission gear ( 4 ), and the needle pointer shaft ( 6 ), wherein a stopper ( 16 ) and a bearing part ( 12   c ) which rotatably supports the needle pointer shaft ( 6 ) are provided in the case ( 12 ), a protrusion ( 15 ) which makes contact with the stopper ( 16 ) is formed in the output gear ( 5 ), a contact point ( 12   d ) with which the needle pointer shaft ( 6 ) makes contact is formed in the bearing part ( 12   c ), and the end section ( 16   b ) at the protrusion ( 15 ) side of the stopper ( 16 ) is in the same position as the contact point ( 12   d ) in the axial direction of the needle pointer shaft ( 6 ).

Description:
DESCRIPTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to an instrument driving device, and more particularly, relates to an instrument driving device with a built-in stopper mechanism. 
         [0003]    2. Background Art 
         [0004]    There has been known a conventional instrument driving device disclosed in Patent Literature 1. In such an instrument driving device, a rotor including a magnet, which serves as a driving source by multipolar magnetization, and at least one reduction gear, which engages with the rotor, are built in a case, and a needle pointer is mounted on a needle point shaft which is mounted to the reduction gear and protrudes outside the case. As a structure for determining a zero point position, the instrument driving device includes the case provided with a stopper and the reduction gear provided with a protrusion. In addition, when the needle pointer is returned to a zero point, the instrument driving device stops the stopper member and the protrusion in a state (a zero point position) in which the stopper member and the protrusion come into contact with each other. In this case, the rotor is retained so as not to move by attraction to a magnetic member, such as a stator which is not shown, by magnetism. 
       CITATION LIST 
     Patent Literature 
       [0005]    [PTL 1] Japanese Unexamined Patent Application Publication No. 2001-327149 (particularly see  FIG. 3 ) 
       SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0006]    A problem that the invention is to solve will be described using schematic views of  FIGS. 6 to 8 . In the conventional instrument driving device, when an external force acts on the needle pointer or a needle pointer shaft  101  by a vibration, an impact, or the like and the needle pointer shaft  101  is inclined about a lower end thereof by an angle θ 1  in an arrow a direction, a reduction gear  102  is also inclined and a protrusion  103  provided in the reduction gear  102  is also inclined. Consequently, the protrusion  103  is displaced by a displacement x in an arrow b direction so as to overlap with a stopper  201 . 
         [0007]    The protrusion  103  tries to push the stopper  201  from the left to the right of  FIG. 7  by the displacement x in the arrow b direction. However, since the stopper  201  is provided in the case and is immovable, the protrusion  103  rotates about the needle pointer shaft  101  from the right to the left of  FIG. 8  by an angle θ 2  in an arrow c direction as a reaction. 
         [0008]    The reduction gear  102  engages with the rotor. The rotation of the rotor is decelerated to be transmitted to the reduction gear  102 , whereas the rotation of the reduction gear  102  is accelerated to be transmitted to the rotor. Accordingly, the rotation of the reduction gear  102  by the angle θ 2  is accelerated to be transmitted to the rotor. 
         [0009]    An angle of the rotor which rotates together with the rotation of the reduction gear  102  upsets the state in which the rotor is stably retained by the attraction to the stator, and the protrusion  103  is separated from the stopper  201  at a position coming into contact with the stopper  201 . That is, the state in which the rotor is stably retained by the attraction to the stator, for example, originally, the state in which the needle pointer indicates a “0” scale (not shown in the drawing) by the protrusion  103  coming into contact with the stopper  201  enters a failure state by receiving a vibration, an impact, or the like, and thus the protrusion  103  is separated from the stopper  201  and the needle pointer indicates a position different from the “0” scale (not shown in the drawing). Therefore, there was a problem that so-called a step-out state is reached. 
         [0010]    The present invention has been made in view of the above-mentioned problem, and an object thereof is to provide an instrument driving device with which it is possible to suppress a step-out caused by a vibration, an impact, or the like. 
       Means for Solving the Problem 
       [0011]    An instrument driving device of the present invention includes a rotating magnet, a driving gear having the same axis as the magnet, an output gear driven by the magnet, a needle pointer shaft having a needle pointer mounted thereon and rotatably supports the output gear, a transmission gear that transmits rotation of the driving gear to the output gear, and a case that accommodates the magnet, the driving gear, the output gear, the transmission gear, and a portion of the needle pointer shaft, wherein
       the case is provided with a stopper and a bearing portion that rotatably supports the needle pointer shaft,   the output gear is provided with a protrusion that comes into contact with the stopper,   the bearing portion is provided with a contact point with which the needle pointer shaft comes into contact, and   an end at the protrusion side of the stopper is provided at the same position as the contact point in an axial direction of the needle pointer shaft.       
 
         [0016]    Furthermore, in the present invention, a contact portion having the contact point may have a sectional circular shape in an axial direction of the bearing portion. 
         [0017]    Furthermore, in the present invention, a contact portion having the contact point may have a spherical surface shape. 
         [0018]    Furthermore, in the present invention, an end of the needle pointer shaft may have a planar surface in a direction perpendicular to the axial direction of the needle pointer shaft. 
       Effect of the Invention 
       [0019]    According to the above-mentioned present invention, it is possible to provide an instrument driving device with which it is possible to suppress a step-out caused by a vibration, an impact, or the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    [ FIG. 1 ] A top view illustrating an instrument driving device according to an embodiment of the present invention. 
           [0021]    [ FIG. 2 ] A cross-sectional view taken along line A-A of  FIG. 1 . 
           [0022]    [ FIG. 3 ] A top view illustrating an instrument driving device from which an upper case is removed and of which a portion is cut, according to the embodiment. 
           [0023]    [ FIG. 4 ] A schematic view illustrating the principal portions of an instrument driving device when viewed from the top, according to the embodiment. 
           [0024]    [ FIG. 5 ] A front view illustrating an instrument device using an instrument driving device according to the embodiment. 
           [0025]    [ FIG. 6 ] A schematic view illustrating the principal portions of a conventional instrument driving device when viewed from the side. [ FIG. 7 ] A schematic view illustrating the principal portions of a conventional instrument driving device when viewed from the top. 
           [0026]    [ FIG. 8 ] A schematic view illustrating the principal portions of a conventional instrument driving device when viewed from the top. 
       
    
    
     MODES FOR CARRYING OUT THE INVENTION 
       [0027]    An instrument driving device  1  of the present embodiment is a stepping motor which is a kind of electric motor, and is used for an instrument device M including a needle pointer  14  and rotates the needle pointer  14 . 
         [0028]    The stepping motor  1  of the present embodiment includes a magnet  2 , a driving gear  3  which has the same axis as the magnet  2 , a transmission gear  4  which has a first gear  4   a  engaging with the driving gear  3  and a second gear  4   b  provided on the same axis as the first gear  4   a,  an output gear  5  which engages with the second gear  4   b  of the transmission gear  4 , two coils  9  which generate a rotating magnetic field to apply a rotational force to the magnet  2 , a first rotating shaft  10  which is a rotation center of the magnet  2 , a second rotating shaft  11  which is a rotation center of the transmission gear  4 , a needle pointer shaft  6  which is a rotation center of the output gear  5 , a retention magnet  18 , and a case  12  which accommodates the magnet  2 , the driving gear  3 , the transmission gear  4 , the output gear  5 , the needle pointer shaft  6 , the coils  9 , the first rotating shaft  10 , the second rotating shaft  11 , and the retention magnet  18 . 
         [0029]    The magnet  2  is made of a synthetic resin including a magnetic material which is referred to as a so-called plastic magnet. The magnet  2  has a doughnut shape which has a through hole at a circular center thereof. The driving gear  3  and the first rotating shaft  10  pass through the through hole. It is sufficient if the magnet  2  includes one or more each of an N-pole and an S-pole. In the present embodiment, the magnet  2  includes four magnetic poles in total of two N-poles and two S-poles, and the magnetic poles are provided so as to be radially uniform about a rotation axis of the magnet  2 . Accordingly, the magnetic poles are multipolar-magnetized on an outer peripheral surface of the magnet  2  along a rotational direction thereof using the first rotating shaft  10  as a central shaft. 
         [0030]    The driving gear  3  is made of a synthetic resin without magnetism. The driving gear  3  is provided on the same axis as the magnet  2  and rotates together with the rotation of the magnet  2 . In addition, the first rotating shaft  10  passes through the driving gear  3 . 
         [0031]    The transmission gear  4  is made of a synthetic resin without magnetism, and is integrally provided with the first gear  4   a  and the second gear  4   b.  The first gear  4   a  engages with the driving gear  3 . In addition, the second gear  4   b  engages with the output gear  5 . In addition, the transmission gear  4  is provided with the second rotating shaft  11  which is a rotation center. 
         [0032]    Similarly to the driving gear  3  and the transmission gear  4 , the output gear  5  is also made of a synthetic resin without magnetism, and engages with the second gear  4   b  of the transmission gear  4 . The output gear  5  is provided with the needle pointer shaft  6  which is a rotation center. 
         [0033]    In  FIG. 2 , a protrusion  15  is integrally provided on a lower side surface of the output gear  5 . The protrusion  15  includes a contact portion  15   a  which comes into contact with a stopper  16  provided in the case  12  to be described later. The protrusion  15  stops the rotation of the needle pointer shaft  6  at a predetermined position and determines a rotation range of the needle pointer shaft  6 , by coming into contact with the stopper  16 . 
         [0034]    In the present embodiment, a speed reduction mechanism including the driving gear  3 , the transmission gear  4 , and the output gear  5  is provided, and decelerates the rotation of the magnet  2  to transmit the decelerated rotation of the magnet  2  to the output gear  5 . 
         [0035]    The needle pointer shaft  6  is axially supported to be rotatable by the case  12 , and a portion of the needle pointer shaft  6  protrudes to the outside. Furthermore, an end  6   a  of the needle pointer shaft  6  has a planar surface in a direction perpendicular to the axial direction of the needle pointer shaft  6 . 
         [0036]    Each of the coils  9  is to wind a metal wire such as copper having conductivity around a bobbin  9   a  made of a synthetic resin. The coil  9  is connected to a control unit (not shown) through terminals  9   b  provided at the bobbin  9   a.    
         [0037]    The bobbin  9   a  is a cylinder formed with a through hole having a sectional rectangular shape. The coil  9  is arranged on a periphery of the magnet  2 , and a portion of a disk surface of the magnet  2  faces an inner peripheral surface of the through hole in the state in which a portion of the magnet  2  is penetrated into the through hole of the bobbin  9   a.    
         [0038]    By respectively inputting driving wave patterns, which are output from the control unit, to the two coils  9 , the rotating magnetic field is generated at the magnet  2 , and the rotational force is applied to the magnet  2 . Consequently, the rotation of the magnet  2  is transmitted to the needle pointer shaft  6  to drive the needle pointer shaft  6 . 
         [0039]    The case  12  is made of a synthetic resin without magnetism, and divided into upper and lower portions. The case  12  divided into the upper and lower portions is fixed by hooking a lock claw  12   a  provided at each of the upper and lower portions of the case  12 . 
         [0040]    The case  12  rotatably supports the first rotating shaft  10 , the second rotating shaft  11 , and the needle pointer shaft  6 . Particularly, in order to rotatably support the needle pointer shaft  6 , the case  12  includes an upper bearing portion  12   b  indicative of the middle of the needle pointer shaft  6  and a lower bearing portion  12   c  to rotatably support the end  6   a  of the needle pointer shaft  6 . 
         [0041]    The upper bearing portion  12   b  is a through hole, and the lower bearing portion  12   c  is a recessed concave portion. The bottom of the lower bearing portion  12   c  comes into contact with the needle pointer shaft  6 , and includes a contact portion  12   e  having a contact point  12   d  which is a support point where the needle pointer shaft  6  is inclined. 
         [0042]    The contact portion  12   e  having the contact point  12   d  has a sectional circular shape in the axial direction of the lower bearing portion  12   c.  Furthermore, in the present embodiment, the contact portion  12   e  having the contact point  12   d  has a spherical surface shape. The case  12  is integrally provided with the stopper  16  which comes into contact with the protrusion  15  provided on the output gear  5 . 
         [0043]    The stopper  16  is a protruding three-dimensional object, and includes a contact portion  16   a  which comes into contact with the protrusion  15 . In the present embodiment, the contact portion  15   a  of the protrusion  15  comes into contact with the contact portion  16   b  of the stopper  16 . 
         [0044]    An end  16   b  at the protrusion  15  side of the stopper  16 , that is, a height of the stopper  16  is the same position as the contact point  12   d  in the axial direction of the needle pointer shaft  6 , as indicated by the dotted line in  FIG. 2 . 
         [0045]    The retention magnet  18  is made of a synthetic resin including a magnetic material which is referred to as so-called a plastic magnet, and has a columnar shape. The retention magnet  18  is provided in the vicinity of an outer periphery of the magnet  2 . The retention magnet  18  retains a stationary state using a magnetic force when the magnet  2  is static. The instrument driving device  1  of the present embodiment includes the retention magnet  18 , as a substitute for the stator which, when the magnet  2  is static, suppresses the rotation of the magnet  2  to carry out a retention function and is made of a magnetic material, similarly to the conventional instrument driving device. 
         [0046]    In the present embodiment, the retention magnet  18  includes one each of an N-pole and an S-pole. In the present embodiment, the S-pole side is arranged to be directed toward the magnet  2  side. 
         [0047]    In the present embodiment, in the state in which the protrusion  15  of the output gear  5  comes into contact with the stopper  16  of the case  12 , a relation between the magnet  2  and the retention magnet  18  corresponds to the state in which the S-pole  51  of the magnet  2  is repelled against the S-pole of the retention magnet  18  and the N-pole N 2  of the magnet  2  is attracted to the S-pole of the retention magnet  18 . In such a state, a force rotating in an arrow d direction is applied to the magnet  2 . The force rotating in the arrow d direction which is applied to the magnet  2  is stably retained in the state in which a force in an arrow e direction is applied to the transmission gear  4 , a force in an arrow f direction is applied to the output gear  5 , and the protrusion  15  of the output gear  5  comes into contact with the stopper  16 . 
         [0048]    According to the above configuration, the magnet  2  is stably retained in the stationary state by the magnetic force of the retention magnet  18 . 
         [0049]      FIG. 5  shows that the stepping motor  1  is used for the instrument device M. The instrument device M of the present embodiment indicates a vehicle speed using the needle pointer  14 . 
         [0050]    The needle pointer  14  is mounted on the needle pointer shaft  6 . The needle pointer  14  is provided at the back thereof with a display board  17  which includes an index portion  17 a such as a scale or a character indicated by the needle pointer  14 . The needle pointer  14  is stopped at a predetermined position, or a position indicative of “0” of the vehicle speed in the present embodiment, by the protrusion  15  and the stopper  16  provided in the stepping motor  1 . 
         [0051]    The result of the above configuration is that even when an external force such as a vibration or an impact acts on the needle pointer  14  or the needle pointer shaft  6  and thus the needle pointer shaft  6  is inclined about the end  6   a  of the needle pointer shaft  6  and the protrusion  15  provided on the output gear  5  is inclined, since the contact point  12   d  provided in the bearing portion  12   c  and the end  16   b  at the protrusion  15  side of the stopper  16  are arranged at the same position relative to the axial direction of the needle pointer shaft  6 , there is no case where the displacement of the protrusion  15 , resulting from the inclination, will not overlap the stopper  16 , and as a consequence, it is possible to prevent the protrusion  15  from rotating around the needle pointer shaft  6 . Accordingly, it is possible to suppress the rotation of the needle pointer shaft  6  due to a vibration, an impact, or the like, so that it is possible to suppress the rotation of the magnet  2  connected by the transmission gear  4  and the like, resulting in the suppression of a state referred to as so-called a step-out in which the needle pointer  14  indicates a position different from a “0” scale. 
       INDUSTRIAL APPLICABILITY 
       [0052]    The present invention is available for an instrument driving device including a reduction mechanism. 
       DESCRIPTION OF REFERENCE NUMERALS 
       [0053]      1  Instrument driving device (stepping motor) 
         [0054]      2  Magnet 
         [0055]      3  Driving gear 
         [0056]      4  Transmission gear 
         [0057]      5  Output gear 
         [0058]      6  Needle pointer shaft 
         [0059]      12  Case 
         [0060]      12   c  Lower bearing portion 
         [0061]      12   d  Contact point 
         [0062]      12   e  Contact portion 
         [0063]      14  Needle pointer 
         [0064]      15  Protrusion 
         [0065]      15   a  Contact portion 
         [0066]      16  Stopper 
         [0067]      16   a  Contact portion 
         [0068]      16   b  End 
         [0069]      18  Retention magnet 
         [0070]    M Instrument device