Abstract:
A switch has a housing, a contact mechanism having a movable contact piece disposed in the housing, an operating element that operates the movable contact piece, a spring member of the contact mechanism that operates the movable contact piece to open and close a contact, and a regulating mechanism that suppresses vibration of the spring member arranged at a position contacting the spring member.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Technical Field 
         [0002]    The present invention relates to switches, and in particular, to a micro-switch capable of inhibiting the occurrence of resonance phenomenon and preventing false operation. 
         [0003]    2. Related Art 
         [0004]    Conventionally, the switch may be a brake lever interlocking switch including a switch case, a swing plate attached to the switch case to swing interlocking with the brake lever, a plurality of push rods that is attached to the switch case to push down with the swing plate and that has different distances from the center of rotation of the swing plate, and a switch means facing such push rods (see Japanese Unexamined Patent Publication No. 10-297364) 
       SUMMARY 
       [0005]    In the above-described switch, however, the amplitude of a spring  99  or a spring member increases by the vibration generated when opening and closing the contact or the impact force applied from the outside, and the resonance phenomenon tends to easily occur, as shown in  FIG. 8  thereof. When the resonance phenomenon occurs, not only does false operation occur, but the spring member easily breaks, the contact wears, and the contact lifespan becomes short. 
         [0006]    One or more embodiments of the present invention provides a switch capable of inhibiting the occurrence of the resonance phenomenon caused by the increase of the amplitude of the spring member and preventing false operation, and furthermore, preventing the breakage of the spring member and realizing long contact lifespan. 
         [0007]    In accordance with one or more embodiments of the present invention, there is provided a switch in which a movable contact piece of a contact mechanism arranged in a housing is operated with an operating element, and the movable contact piece is operated with a spring member of the contact mechanism to open and close a contact; wherein a regulating means for suppressing vibration of the spring member is arranged at a position of contacting the spring member. Especially, the regulating means may be arranged to be brought into contact with the spring member at time of resonance. 
         [0008]    According to one or more embodiments of the present invention, when the contact mechanism is operated with the operating element or when the impact force is applied from the outside, the spring member is not brought into contact with the regulating means if the spring member is not vibrating, whereas the spring member is brought into contact with the regulating means if the spring member is vibrating, particularly, if the spring member starts to vibrate. As a result, the regulating means shifts the timing to increase the amplitude of the spring member so that the amplitude of the spring member does not increase and the resonance phenomenon can be inhibited. Therefore, the false operation can be prevented, and furthermore, the breakage of the spring member can be prevented and the wear of the contact can be reduced so that a switch of longer contact lifespan can be realized. 
         [0009]    In one or more embodiments of the present invention, the spring member may be a coil member. 
         [0010]    Accordingly, a switch having a large degree of freedom of design can be realized since the elastic displacement amount of the coil spring is large. 
         [0011]    In one or more embodiments of the present invention, the spring member may be a plate spring integral with the movable contact piece. 
         [0012]    Accordingly, a switch with less number of components and number of assembly steps and with high productivity can be obtained. 
         [0013]    In one or more embodiments of the present invention, the spring member may be a plate spring of a separate body from the movable contact piece. 
         [0014]    Accordingly, a switch having a large degree of freedom of design can be realized by using the plate spring of a separate body. 
         [0015]    In one or more embodiments of the present invention, the regulating means may be a tongue piece cutout from a terminal of the contact mechanism. 
         [0016]    Accordingly, a switch with less number of components and number of assembly steps and with high productivity can be obtained. 
         [0017]    In one or more embodiments of the present invention, the regulating means may be a projection arranged in a projecting manner on the inner surface of the housing or a bulging portion bulging out from the inner surface of the housing. 
         [0018]    Accordingly, a switch with high productivity can be obtained by integrally molding the regulating means at the same time as the housing. 
         [0019]    The projection or the bulging portion may be assembled after being molded separate from the housing rather than being integrally molded on the inner surface of the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1A ,  1 B, and  1 C are perspective views showing a switch according to a first embodiment of the present invention; 
           [0021]      FIG. 2  is an exploded perspective view of the switch shown in  FIG. 1B ; 
           [0022]      FIG. 3  is an exploded perspective view of the switch shown in  FIG. 1C ; 
           [0023]      FIGS. 4A and 4B  are perspective views showing a contact mechanism of the switch shown in  FIGS. 1A to 1C ; 
           [0024]      FIGS. 5A ,  5 B, and  5 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0025]      FIGS. 6A ,  6 B, and  6 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0026]      FIGS. 7A ,  7 B, and  7 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0027]      FIGS. 8A ,  8 B, and  8 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0028]      FIGS. 9A and 9B  are perspective views showing a switch according to a second embodiment of the present invention; 
           [0029]      FIG. 10  is an exploded perspective view of the switch shown in  FIG. 9A ; 
           [0030]      FIG. 11  is an exploded perspective view of the switch shown in  FIG. 9B ; 
           [0031]      FIGS. 12A and 12B  are perspective views showing a contact mechanism integrally molded with the base shown in  FIGS. 1A to 1C ; 
           [0032]      FIGS. 13A ,  13 B, and  13 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0033]      FIGS. 14A ,  14 B, and  14 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0034]      FIGS. 15A ,  15 B, and  15 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0035]      FIGS. 16A ,  16 B, and  16 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0036]      FIGS. 17A and 17B  are perspective views showing a switch according to a third embodiment of the present invention; 
           [0037]      FIG. 18  is an exploded perspective view of the switch shown in  FIG. 17A ; 
           [0038]      FIG. 19  is an exploded perspective view in which the switch shown in  FIG. 17B  is viewed from the lower side; 
           [0039]      FIGS. 20A and 20B  are perspective views showing a contact mechanism of the switch shown in  FIGS. 17A and 17B ; 
           [0040]      FIGS. 21A ,  21 B, and  21 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0041]      FIGS. 22A ,  22 B, and  22 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0042]      FIGS. 23A ,  23 B, and  23 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0043]      FIGS. 24A ,  24 B, and  24 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0044]      FIGS. 25A ,  25 B, and  25 C are perspective views showing a switch according to a fourth embodiment of the present invention; 
           [0045]      FIG. 26  is an exploded perspective view in which the switch shown in FIG.  25 A is viewed from the lower side; 
           [0046]      FIG. 27  is an exploded perspective view of the switch shown in  FIG. 25C ; 
           [0047]      FIGS. 28A and 28B  are perspective views showing a contact mechanism of the switch shown in  FIGS. 25A ,  25 B, and  25 C; 
           [0048]      FIGS. 29A ,  29 B, and  29 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0049]      FIGS. 30A ,  30 B, and  30 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0050]      FIGS. 31A ,  31 B, and  31 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; 
           [0051]      FIGS. 32A ,  32 B, and  32 C are a front view describing the operation process, a cross-sectional view cut at a position of removing only the side wall on the front surface side of the housing, and a cross-sectional view cut at a position of vertically dividing the operating element in half; and 
           [0052]      FIG. 33  is a graph showing the measurement result of the vibration experiment conducted on the first embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0053]    Hereinafter, embodiments of the present invention will be described with reference to the accompanied drawings  FIGS. 1A to 1C  to  FIGS. 32A to 32C . In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention. 
         [0054]    As shown in the accompanied drawings  FIGS. 1A to 1C  to  FIGS. 8A to 8C , a switch according to a first embodiment is configured by a housing  10 , an operating element  20  attached to the housing  10  through a rubber cap  25 , and a contact mechanism  30  assembled to a holder  31  incorporated in the housing  10  from the side and operated by the operating element  20 . 
         [0055]    As shown in  FIG. 1A , the housing  10  includes an attachment hole  11   b  at a side surface of a step portion  11   a  arranged on one side of a one side surface of a housing main body  11 , and has a positioning boss  11   c  arranged in a projecting manner on the other side. As shown in  FIG. 1B , the housing main body  11  includes a vertically long assembly opening  11   d  at the end face on the other side. Furthermore, the housing main body  11  has an operation hole  11   f  arranged between a pair of protection barriers  11   e ,  11   e  arranged in a projecting manner to the other side of the upper end face ( FIG. 2 ). 
         [0056]    As shown in  FIG. 2 , the operating element  20  is assembled to the operation hole  11   f  of the housing  10  so as to be movable up and down by fitting an annular edge of an opening  26  of the rubber cap  25  to an annular groove  21   a  formed on the upper side. A slip-out preventing projection  21   b  is projected to the side at the outer peripheral surface on the lower side of the operating element  20  ( FIG. 3 ). 
         [0057]    As shown in  FIG. 2 , the contact mechanism  30  has a common terminal  50  arranged between an always-opened fixed contact terminal  40  and an always-closed fixed contact terminal  45  assembled to the holder  31 . An always-opened fixed contact  40   a  and an always-closed fixed contact  45   a  are respectively arranged at one end of the always-opened fixed contact terminal  40  and the always-closed fixed contact terminal  45 . A movable contact piece  60 , a coil spring  70  serving as a spring member, and an operation piece  80  are assembled to the common terminal  50 . 
         [0058]    The holder  31  has an outer peripheral shape that can be inserted from an assembly opening  11   d  of the housing  10 , and has press-fit slits  32   a ,  32   b ,  32   c  alternately arranged in a zigzag manner on a vertical wall  32 . A pair of guide projections  32   d ,  32   d  is arranged on an inward surface of the vertical wall  32  to position regulate the operating element  20 , to be described later. 
         [0059]    The common terminal  50  has a pair of raised pieces  51 ,  51  formed by cutting and raising both side edges on one side. The raised piece  51  has a cutout  51   a  formed at the upper end and has a lock receiving portion  51   b  formed at the outward edge of the raised piece  51 . The common terminal  50  has a tongue piece  51   c  cut and raised between the raised pieces  51 . Furthermore, the common terminal  50  includes a lock hole  51   d  in the vicinity of the tongue piece  51   c.    
         [0060]    The tongue piece  51   c  prevents resonance of the coil spring  70  by bringing a bent portion formed by bending the distal end edge to the lower side into contact with the lower surface of the coil spring  70  to be described later. The bent portion may have a shape that not only point contacts the coil spring  70 , but also line contacts or area contacts thereto. In particular, if configured to line contact or area contact, the coil spring  70  can be reliably brought into contact with the bent portion even if the dimensional accuracy and the assembly accuracy of the components vary, so that the amplification of the amplitude of the coil spring  70  can be more reliably prevented. 
         [0061]    The movable contact piece  60  is a conductive plate spring having a substantially U-shape, where a movable contact  61   a  is arranged at one end and a lock portion  61   b  that becomes a supporting point of turn is formed at both ends on the other end side. The movable contact piece  60  also includes a lock hole  61   c  in the vicinity of the movable contact  61   a.    
         [0062]    The coil spring  70  has one end  71   a  lockable to the lock hole  61   c  of the movable contact piece  60  and the other end  71   b  lockable to the lock hole  51   d  of the common terminal  50 . 
         [0063]    The operation piece  80  has an engagement shaft portion  81   a  formed along the edge on one side, and a slip-out preventing projection  81   b  that engages the cutout  51   a  of the raised piece  51  arranged to project to the side at both side edges of the intermediate portion. The operation piece  80  has a lock receiving portion  81   d  arranged at a distal end of an arm portion  81   c  bent down from both side edges on the other side, and has the other end serving as an operation receiving portion  81   e.    
         [0064]    The assembly method of the switch according to the first embodiment will now be described. 
         [0065]    First, the one end  71   a  of the coil spring  70  shown in  FIG. 2  is locked to the lock hole  61   c  of the movable contact piece  60 , and the other end  71   b  is locked to the lock hole  51   d  of the common terminal  50 . As shown in  FIG. 4A  and  FIG. 4B , the slip-out preventing projection  81   b  of the operation piece  80  is engaged to the cutout  51   a  of the common terminal  50 , and thereafter the engagement shaft portion  81   a  of the operation piece  80  is engaged to the lock receiving portion  51   b  of the common terminal  50  and the lock portion  61   b  of the movable contact piece  60  is locked to lock receiving portion  81   d  formed in the arm portion  81   c . The movable contact piece  60  is thereby biased towards the lower side by the spring force of the coil spring  70 . 
         [0066]    Furthermore, the common terminal  50  shown in  FIG. 2  is press fit and positioned in the slit  32   a  of the holder  31 , and the always-closed fixed contact terminal  45 , the always-opened fixed contact terminal  40  are press fit to the slits  32   b ,  32   c , respectively. The movable contact  61   a  faces the always-closed fixed contact  45   a  and the always-opened fixed contact  40   a  so as to approach or separate thereto. 
         [0067]    After inserting the holder  31  from the opening  11   d  of the housing  10 , it is shielded with a resin mold. The opening edge on the lower side of the rubber cap  25  is fitted and thermally caulked to the opening edge of the operation hole  11   f  of the housing  10 , and then the operating element  20  is press fit from the opening  26  of the rubber cap  25  and the opening edge of the rubber cap  25  is elastically fitted and sealed to the annular groove  21   a  of the operating element  20 . 
         [0068]    The operation method of the switch will now be described. 
         [0069]    First, as shown in  FIGS. 5A to 5C , the operation receiving portion  81   e  of the operation piece  80  is biased to the upper side by the spring force of the coil spring  70  and the operating element  20  is also biased to the upper side in the no-load state. However, the operating element  20  does not slip out since the slip-out preventing projection  21   b  is locked to the top surface of the housing  10 . The movable contact  61   a  is brought into contact with the always-closed fixed contact  45   a  and separated from the always-opened fixed contact  40   a.    
         [0070]    As shown in  FIGS. 6A to 6C , when the operation receiving portion  81   e  of the operation piece  80  is pushed down with the operating element  20 , the engagement shaft portion  81   a  of the operation piece  80  turns with the lock receiving portion  51   b  of the raised piece  51  as the supporting point. When the lock receiving portion  81   d  of the operation piece  80  goes over the reference line (not shown) connecting both ends  71   a ,  71   b  of the coil spring  70 , the movable contact piece  60  is inverted and the movable contact  61   a  is switched from the always-closed fixed contact  45   a  to the always-opened fixed contact  40   a  ( FIGS. 7A to 7C ). Furthermore, when the operating element  20  is pushed down, the movable contact  61   a  is brought into contact with the always-opened fixed contact  40  at a predetermined contact pressure ( FIGS. 8A to 8C ). 
         [0071]    When the pushing force with respect to the operating element  20  is released, the movable contact piece  60  is turned in the reverse direction with the spring force of the coil spring  70 , and the operating element  20  is pushed to the upper side. Thus, the movable contact  61   a  is switched from the always-opened fixed contact  40   a  to the always-closed fixed contact  45   a  to return to the original position. The operating element  20  does not move out from the housing  10  since the slip-out preventing projection  21   b  locks to the top surface of the housing  10 . 
         [0072]    In the course of operation, the vibration occurs by the extension and contraction of the coil spring  70  when the movable contact piece  60  is turned, where the tongue piece  51   c  arranged on the common terminal  50  is brought into contact with the coil spring  70  thus shifting the timing of increasing the amplitude and preventing the resonance phenomenon. 
         [0073]    Similarly, the resonance phenomenon caused by the increase of the amplitude can be prevented even if an impact force is applied from the outside since the coil spring  70  is brought into contact with the tongue piece  51   c.    
         [0074]    As shown in  FIGS. 9A and 9B  to  FIGS. 16A to 16C , the switch according to a second embodiment is configured by the housing  10 , the operating element  20  attached to the housing  10 , and the contact mechanism  30  incorporated in the housing  10  and operated by the operating element  20 . 
         [0075]    As shown in  FIG. 10 , the housing  10  is configured by a base  12  in which the always-opened fixed contact terminal  40 , the always-closed fixed contact terminal  45 , and the common terminal  50  are insert molded, and a cover  13  having a planar shape that can be fitted to the base  12 . The contact mechanism  30  is configured by the always-opened fixed contact terminal  40 , the always-closed fixed contact terminal  45 , the common terminal  50 , and the movable contact piece  60 , to be described later. 
         [0076]    The base  12  has the always-opened fixed contact terminal  40  and the always-closed fixed contact terminal  45  projected from the upper surface, where the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a  are respectively arranged at the upper end, the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a  being faced to each other. The base has a pair of projection pieces  52 ,  52  of the common terminal  50  projecting out at the upper surface, where lock receiving portions  52   a ,  52   b  are arranged at the outer side edge of the projection pieces  52 ,  52 . Furthermore, the base  12  has an engagement nail portion  12   a  formed on both side surfaces facing each other. 
         [0077]    The cover  13  has a recessed area  13   b  for attaching the operation lever (not shown) formed in the vicinity of the operation hole  13   a  formed at the upper surface. The cover  13  has an engagement hole  13   c  formed at the corner on the lower side of the opposing side surface. Moreover, as shown in  FIG. 11 , the cover  13  has a projection  13   d  for position regulating a plate spring  72 , to be described later, arranged in a projecting manner at the top surface. 
         [0078]    As shown in  FIG. 10 , the movable contact piece  60  configuring the contact mechanism  30  is formed by performing press work on a conductive plate spring material, where a movable contact  62   a  is arranged on the end on the near side, and a fit-in hole  62   b  is formed on the far side. Furthermore, an arcuate plate spring  72  performed with bending work is cut out between the movable contact  62   a  and the fit-in hole  62   b . A lock portion  72   a  is arranged at the free end of the plate spring  72 . 
         [0079]    The operating element  20  has a planar shape that can be fitted to the operation hole  13   a  of the cover  13 , and has a pair of slip-out preventing projections  22   a ,  22   a  arranged in a projecting manner to the side at the lower end. 
         [0080]    The assembly method according to one or more embodiments of the present invention will now be described. 
         [0081]    First, as shown in  FIG. 10 , an inner side edge of the fit-in hole  62   b  of the movable contact piece  60  is locked to the lock receiving portion  52   a  of the projection piece  52  on one side projecting out from the base  12 , and the lock portion  72   a  of the plate spring  72  is locked to the lock receiving portion  52   b  of the projection piece  52  on the other side. The movable contact  62   a  is thus positioned between the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a , and is biased to the upper side ( FIGS. 12A ,  12 B). 
         [0082]    The cover  13  in which the operating element  20  is assembled to the operation hole  13   a  is fitted into the base  12 , and the engagement nail portion  12   a  of the base  12  is engaged and integrated with the engagement hole  13   c  of the cover  13 . The lower end of the operating element  20  shown in  FIG. 11  is thereby brought into contact with the movable contact piece  60 , and the projection  13   d  can be brought into contact with the plate spring  72  of the movable contact piece  60 . 
         [0083]    The operation method of the switch according one or more embodiments of the present invention will now be described. 
         [0084]    As shown in  FIGS. 13A to 13C , the movable contact  62   a  is brought into contact with the always-closed fixed contact  45  at a predetermined contact pressure by the spring force of the plate spring  72  of the movable contact piece  60  when the operating element  20  is in the no-load state. 
         [0085]    As shown in  FIGS. 14A to 14C  and  FIGS. 15A to 15C , the movable contact piece  60  bends when the operating element  20  is pushed down. When the lower end of the operating element  20  goes over the reference line (not shown) connecting the lock receiving portions  52   a ,  52   b  of the projection pieces  52 ,  52 , the movable contact piece  60  is inverted with the lock receiving portion  52   a  as a supporting point by the spring force of the plate spring  72  ( FIGS. 16A to 16C ). The movable contact  62   a  is thereby switched from the always-closed fixed contact  45   a  to the always-opened fixed contact  40   a , and the movable contact  62   a  is brought into contact with the always-opened fixed contact  40  at a predetermined contact pressure by further pushing in the operating element  20 . 
         [0086]    When the load of the operating element  20  is released, the movable contact piece  60  is inverted by the spring force of the plate spring  72 , and the movable contact  62   a  is switched from the always-opened fixed contact  40   a  to the always-closed fixed contact  45   a  to return to the original state. 
         [0087]    The plate spring  72  elastically deforms and vibrates when the movable contact piece  60  is turned, but the position regulating projection  13   d  of the cover  13  is brought into contact with the plate spring  72  thus shifting the timing of increasing the amplitude and preventing the resonance phenomenon. 
         [0088]    Similarly, the resonance phenomenon caused by the increase of the amplitude can be prevented even if an impact force is applied from the outside since the plate spring  72  is brought into contact with the projection  13   d  of the cover  13 . In particular, the slip-out of the movable contact piece  60  can be prevented even if horizontal oscillation is applied since the distal end of the projection  13   d  is fitted to the movable contact piece  60 . 
         [0089]    As shown in  FIGS. 17A and 17B  to  FIGS. 24A to 24C , a switch according to a third embodiment has the contact mechanism  30  incorporated in the housing  10  formed by the base  14  and the cover  15 , and has the contact mechanism  30  operable with the operating element  20  assembled to the housing  10 . 
         [0090]    As shown in  FIG. 18 , the base  14  includes an operation hole  14   a  for assembling the operating element  20 , and includes an attachment hole  14   b  for assembling an operation lever (not shown) in the vicinity of the operation hole  14   a . The base  10  includes slits  14   c ,  14   d ,  14   e  to which the common terminal  50 , the always-closed fixed contact terminal  45 , and the always-opened fixed contact terminal  40  can be press fit from the side. The base  10  includes a pair of attachment holes  14   f ,  14   g , and a rivet hole  14   e  is formed between the attachment holes  14   f ,  14   g . The base  10  has a projection  14   i  arranged in a projecting manner at the top surface. 
         [0091]    As shown in  FIG. 19 , the cover  15  has a side surface shape that can be fitted to the base  14 , where fit-in bosses  15   a ,  15   b  are arranged at positions corresponding to the attachment holes  14   f ,  14   f , and a rivet hole  15   c  is also formed. 
         [0092]    As shown in  FIG. 18 , the contact mechanism  30  includes the always-opened fixed contact terminal  40  and the always-closed fixed contact terminal  45  respectively including the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a  at the upper end, and the common terminal  50  for assembling the movable contact piece  60  and a curved plate spring  73 . 
         [0093]    The common terminal  50  is formed with lock receiving portions  53   a ,  53   b  on the outward surface of a pair of projection pieces  53 ,  53  formed by bending through press working. 
         [0094]    The movable contact piece  60  includes a movable contact  63   a  at one end and is formed with a pair of play-fit holes  63   b ,  63   c  by punching out a conductive plate spring. 
         [0095]    The plate spring  73  is formed by curving a band-shaped spring material through press working, where one end  73   a  and the other end  73   b  can be locked. 
         [0096]    The assembly method according to the third embodiment will now be described. 
         [0097]    First, as shown in  FIG. 18 , the inner side edge of the play-fit hole  63   a  formed in the movable contact piece  60  is locked to the lock receiving portion  53   a  formed at the projection piece  53  of the common terminal  50 , one end  73   a  of the plate spring  73  is locked to the lock receiving portion  53   b  formed at the projection piece  53 , and the other end  73   b  of the plate spring  73  is locked to the inner side edge of the play-fit hole  63   c  (see  FIGS. 20A ,  20 B). The common terminal  50  is then press fit and positioned in the slit  14   c  of the base  14  shown in  FIG. 18 , and the always-closed fixed contact terminal  45  and the always-opened fixed contact terminal  40  are respectively press fit and positioned in the slits  14   d ,  14   e . The movable contact  63   a  is thus positioned between the always-closed fixed contact  45   a  and the always-opened fixed contact  40   a , and is biased to the upper side. Thereafter, the operating element  20  is fitted into the operation hole  14   a  of the base  14 , and then the positioning bosses  15   a ,  15   b  of the cover  15  are inserted to the attachment holes  14   f ,  14   g  of the base  14  shown in  FIG. 19 . The rivet  15   d  is then inserted and caulked in the rivet holes  14   h ,  15   c , whereby the assembly task is completed. 
         [0098]    The operation method of the switch according to the third embodiment will now be described. 
         [0099]    As shown in  FIGS. 21A to 21C , if the operating element  20  is in the no-load state, the movable contact  63   a  is brought into contact with the always-closed fixed contact  45   a  at a predetermined contact pressure by the spring force of the plate spring  73  assembled to the movable contact piece  60 . 
         [0100]    As shown in  FIGS. 22A to 22C , the movable contact piece  60  bends when the operating element  20  is pushed down. When the reference line (not shown) connecting the lock receiving portion  53   a  of the projection piece  53  and the other end  73   b  of the plate spring  73  goes over the lock receiving portion  53   b  of the projection piece  53 , the movable contact piece  60  inverts with the lock receiving portion  53   a  as the supporting point by the spring force of the plate spring  73  ( FIGS. 23A to 23C ). Therefore, the movable contact  63   a  switches from the always-closed fixed contact  45   a  to the always-opened fixed contact  40   a , and when the operating element  20  is further pushed in, the movable contact  63   a  is brought into contact with the always-opened fixed contact  40   a  at a predetermined contact pressure ( FIGS. 24A to 24C ). 
         [0101]    When the load of the operating element  20  is released, the movable contact piece  60  is inverted by the spring force of the plate spring  73 , and the movable contact  63   a  is switched from the always-opened fixed contact  40   a  to the always-closed fixed contact  45   a  to return to the original state. 
         [0102]    The plate spring  73  elastically deforms and vibrates when the movable contact piece  60  is turned, but the plate spring  73  is brought into contact with the projection  14   i  arranged on the base  14  thus shifting the timing of increasing the amplitude and preventing the resonance phenomenon. 
         [0103]    Similarly, the resonance phenomenon can be prevented even if an impact force is applied from the outside since the plate spring  73  is brought into contact with the projection  14   i  of the cover  15 . 
         [0104]    As shown in  FIGS. 25A to 25C  to  FIGS. 32A to 32C , a switch according to a fourth embodiment has the contact mechanism  30  assembled in the housing  10  formed by a base  16  and a cover  17 , by which contact mechanism  30  can be operated with the operating element  20  assembled to the housing  10 . 
         [0105]    As shown in  FIGS. 25A to 25C , the base  16  includes an operation hole  16   a  for assembling the operating element  20  at the upper surface, and a recess  16   b  for assembling an operation lever (not shown). As shown in  FIG. 26 , the base  16  includes slits  16   c ,  16   d ,  16   e  to which the common terminal  50 , the always-opened fixed contact terminal  40 , and the always-closed fixed contact terminal  45  can be press fit from the side. Furthermore, base  16  has attachment holes  16   f ,  16   g  formed at the opposing corners. A projection  16   h  is arranged between the operation hole  16   a  and the attachment hole  16   g  ( FIG. 27 ). 
         [0106]    The cover  17  has a side surface shape capable of being fitted into the base  16 , and includes press-fit bosses  17   a ,  17   b  at positions corresponding to the attachment holes  16   f ,  16   g.    
         [0107]    As shown in  FIG. 26 , the contact mechanism  30  includes the common terminal  50  for assembling the movable contact piece  60 , the plate spring  74 , and the operation piece  84 , and the always-opened fixed contact terminal  40  and the always-closed fixed contact terminal  45  having the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a  arranged at one end. 
         [0108]    The common terminal  50  is formed to a step-form through press working, and includes lock receiving portions  54   a ,  54   b  including through-holes at the corners. 
         [0109]    The movable contact piece  60  includes a movable contact  64   a  at one end by punching out a conductive plate spring and is formed with reinforcement ribs  64   b ,  65   b  by bending and raising both side edges. A pair of lock nails  64   c ,  64   c  is bent and raised at the opening edge in the vicinity of the movable contact  64   a  of the opening edge of the movable contact piece  60 . 
         [0110]    The plate spring  74  is formed by curving a band-shaped spring material through press working, where one end  74   a  and the other end  74   b  have a lockable shape. 
         [0111]    As shown in  FIG. 27 , the operation piece  84  is bent to a substantially L-shape, where a lock portion  84   a  is formed at the distal end of the horizontal portion, an operation receiving portion  84   b  is formed at the upper end of the vertical portion, and a lock receiving portion  84   c  is formed at the outward surface. 
         [0112]    The assembly method according to the fourth embodiment will now be described. 
         [0113]    First, as shown in  FIG. 26 , the lock portion  84   a  of the operation piece  84  is locked to the lock receiving portion  54   a  arranged at the corner of the common terminal  50  from the lower side, and the inner side edge of the movable contact piece  60  is locked to the lock receiving portion  84   c  of the operation piece  84 . Furthermore, one end  74   a  of the plate spring  74  is locked to the lock nail portions  64   c ,  64   c  of the movable contact piece  60  and one end  74   b  of the plate spring  74  is locked to the lock receiving portion  54   b  arranged at the corner of the common terminal  50  (see  FIGS. 28A and 28B ). The common terminal  50  is then press fit to the slit  16   c  of the base  16  shown in  FIG. 26  for positioning, and the always-opened fixed contact terminal  40  and the always-closed fixed contact terminal  45  are respectively press fit to the slits  16   d ,  16   e  for positioning. The movable contact  64   a  is thus positioned between the always-opened fixed contact  40   a  and the always-closed fixed contact  45   a , and is biased to the upper side. The operating element  20  is then fitted into and positioned in the operation hole  16   a  of the base  16 , and thereafter, the positioning bosses  17   a ,  17   b  of the cover  17  are press fit and integrated to the operation holes  16   f ,  16   g  of the base  16  to complete the assembly task. 
         [0114]    The operation method of the switch according to the fourth embodiment will now be described. 
         [0115]    As shown in  FIGS. 29A to 29C , if the operating element  20  is in the no-load state, the movable contact  64   a  is brought into contact with the always-closed fixed contact  45   a  at a predetermined contact pressure by the spring force of the plate spring  74  assembled to the movable contact piece  60 . 
         [0116]    As shown in  FIGS. 30A to 30C , when the operating element  20  is pushed down to push down the operation receiving portion  84   b  of the operation piece  84 , the operation piece  84  turns with the lock portion  84   a  as the supporting point and the movable contact piece  60  lowers. When the reference line (not shown) connecting the lock receiving portion  84   c  of the operation piece  84  and the one end  74   a  of the plate spring  74  goes over the other end  74   b  of the plate spring  74 , the movable contact piece  60  inverts with the lock receiving portion  84   c  of the operation piece  84  as the supporting point by the spring force of the plate spring  74  ( FIGS. 31A to 31C ). Therefore, the movable contact  64   a  switches from the always-closed fixed contact  45   a  to the always-opened fixed contact  40   a . When the operating element  20  is further pushed in, the movable contact  64   a  is brought into contact with the always-opened fixed contact  40   a  at a predetermined contact pressure ( FIGS. 32A to 32C ). 
         [0117]    When the load of the operating element  20  is released, the movable contact piece  60  is inverted by the spring force of the plate spring  74 , and the movable contact  64   a  is switched from the always-opened fixed contact  40   a  to the always-closed fixed contact  45   a  to return to the original state. 
         [0118]    The plate spring  74  elastically deforms and vibrates when the movable contact piece  60  turns, but the projection  16   h  arranged on the base  16  is brought into contact with the plate spring  74  thus shifting the timing of increasing the amplitude and preventing the resonance phenomenon. 
         [0119]    Similarly, the resonance phenomenon can be prevented even if an impact force is applied from the outside since the plate spring  74  is brought into contact with the projection  16   h.    
       Example 
       [0120]    The resonance experiment was conducted using samples of the switches according to the first and second embodiments as an example. The resonance experiment was similarly conducted under the same condition using a sample of a switch in which the tongue piece is not arranged as a comparative example. The measurement results are shown in the graph of  FIG. 33 . 
         [0121]    As shown in  FIG. 33A , the resonance phenomenon did not occur in the coil spring in the example in which the tongue piece is arranged. 
         [0122]    As apparent from  FIG. 33B , the coil spring greatly vibrates and resonates in the comparative example in which the tongue piece is not arranged. Thus, it tends to easily break with increase in the number of stress oscillations and the lifespan also becomes shorter even if the stress amplitude width is within the elastic region. It is also recognized that the movable contact piece and the movable contact also vibrate with the resonance phenomenon of the coil spring. 
         [0123]    According to the above experimental results, the false operation can be prevented and the lifespan can be extended by having the tongue piece inhibit the occurrence of the resonance phenomenon. 
         [0124]    The switch according to the present invention is not limited to the above, and application may, obviously, be made on other micro-switches. 
         [0125]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.