Abstract:
There is provided a key switch structure including: a plate shaped key top; a link mechanism supporting the key top such that the key top can be depressed; a membrane sheet comprising a contact point portion; a back plate supporting the link mechanism and adhered to the membrane sheet; a plurality of holder members insert molded onto the back plate and supporting the link mechanism; and a resilient member provided between the key top and the membrane sheet, the resilient member being compressed by depressing of the key top and pressing the contact point portion to make a continuity.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2011-108063 filed on May 13, 2011, the disclosure of which is incorporated by reference herein. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a key switch structure, and in particular relates to a key switch structure employed in a keyboard where there is a strong demand for thinner models, for example in a portable personal computer or word processor. 
         [0004]    2. Related Art 
         [0005]    In keyboards employed in for example portable personal computers, configuration is made such that no matter where on the key top a key is depressed, the key top moves downwards without tilting, ensuring good operation characteristics. Existing key switch structures therefore have a link mechanism provided beneath the key top. Key switch structures exist with a link mechanism provided beneath the key top (see for example Japanese Patent No. 4341733). 
         [0006]    Such key switch structures are configured with a key top  210 , a first link member  220 , a second link member  230 , a holder  250 , a membrane  260 , a back plate  270 , and a resilient member  240 . 
         [0007]    As illustrated in  FIG. 9  and  FIG. 10 , the above key switch structure is a structure provided with a configuration in which the key top  210  descends whilst maintaining a horizontal state due to a link mechanism in which two link members  220 ,  230  are assembled together in an X-shape. 
         [0008]    A first support projection  224  on the first link member  220  is rotatably supported by rotation support members  214  at a rear side of the key top  210 , and first support projections  234  on the second link member  230  are similarly rotatably supported by rotation support members  254  on the holder  250 . Thus second support projections  222 ,  232  provided to the other respective ends of the link members are supported so as to be capable of sliding by slide support members  256 ,  212  provided to the holder  250  and the key top  210 , respectively. 
         [0009]    When the key top  210  has been depressed, the resilient member  240  deforms in a squashing direction, deforming towards the membrane  260 , whilst the link members assembled together in an X-shape cause the second support projections  222 ,  232  to slide. The key top  210  consequently descends whilst maintaining a horizontal state. 
         [0010]    A projection  252  provided to the holder  250  passes through a hole  262  in the membrane  260  and a hole  272  in the back plate  270 , and a leading end is positioned and fixed with respect to the back plate  270  using a method such as welding. 
         [0011]    However, when fabrication accuracy for the back plate  270  and the holder  250  is poor, and/or the accuracy when welding together the two components is poor, gaps can develop between the back plate  270  and the holder  250 . There is also the possibility of the second support projection  222  (slide section) of the first link member  220  moving up and down, namely in the key top depressing direction, giving rise to a wobbling sensation during depressing as the key top  210  is unable to maintain a horizontal state. 
         [0012]    If for the sake of convenience the holder  250  is formed as a single unified component including the rotatable support sections  254  and the slide support section  256 , and the resilient member  240  is disposed directly below the center of the key top  210 , there will inevitably be a thinned portion present in a portion of the link member due to the first link member  220  having a profile enclosed from the periphery by the holder  250 . Accordingly force is concentrated at this thinned portion when load is applied during depressing the key top  210 , giving rise to a wobbling sensation. 
         [0013]    Even in cases where the back plate  270  is provided with an up stand into which the second support projection  222  is fitted, when the fabrication accuracy is low the link member (the second support projection  222  and the first support projections  234 ) will give rise to a wobbling sensation due to not being disposed correctly. 
         [0014]    In the above structure disclosed in Japanese Patent No. 4341733, depending on the fabrication accuracy there is a concern that a sensation of insufficient rigidity during operation, referred to as a wobbling sensation, will be caused by lowering of the positional accuracy of the link member, or due to force being concentrated at thinned portions present in the link member. 
       SUMMARY 
       [0015]    In consideration of the above circumstances, an object of the present invention is to provide a key switch structure with excellent holder positional accuracy and a high rigidity of link members. 
         [0016]    To achieve the object, the present invention provides a key switch structure including: a plate shaped key top; a link mechanism supporting the key top such that the key top can be depressed; a membrane sheet including a contact point portion; a back plate supporting the link mechanism and adhered to the membrane sheet; plural holder members insert molded onto the back plate and supporting the link mechanism; and a resilient member provided between the key top and the membrane sheet, the resilient member being compressed by depressing of the key top and pressing the contact point portion to make a continuity. 
         [0017]    Due to being configured as described above, the present invention can provide a key switch structure with excellent holder positional accuracy and a high rigidity of link members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0019]      FIG. 1  is a side view illustrating a key switch structure according to a first exemplary embodiment of the present invention; 
           [0020]      FIG. 2  is an exploded perspective illustrating the key switch structure shown in  FIG. 1 ; 
           [0021]      FIG. 3  is an exploded perspective view illustrating the key switch structure shown in  FIG. 1 ; 
           [0022]      FIG. 4  is an exploded perspective view illustrating from the rear side the key switch structure shown in  FIG. 1 ; 
           [0023]      FIG. 5A  and  FIG. 5B  are an enlarged plan view and cross-section illustrating a portion of a key switch structure according to a second exemplary embodiment of the present invention; 
           [0024]      FIG. 6A  and  FIG. 6B  are an enlarged plan view and cross-section illustrating a portion of a key switch structure according to a third exemplary embodiment of the present invention; 
           [0025]      FIG. 7A  and  FIG. 7B  are an enlarged plan view and cross-section illustrating a portion of a key switch structure according to a fourth exemplary embodiment of the present invention; 
           [0026]      FIG. 8  is a cross-section illustrating a key switch structure according to a fifth exemplary embodiment of the present invention; 
           [0027]      FIG. 9  is a side view illustrating a related key switch structure; and 
           [0028]      FIG. 10  is an exploded perspective view illustrating a related key switch structure. 
       
    
    
     DETAILED DESCRIPTION 
     Exemplary Embodiments 
       [0029]    Explanation follows of exemplary embodiments of a key switch structure according to the present invention, with reference to the drawings.  FIG. 1  is a cross-section illustrating a first exemplary embodiment, and  FIG. 2  to  FIG. 4  are exploded perspective views illustrating the first exemplary embodiment. 
         [0030]    A key switch structure of the present exemplary embodiment is configured from a key top  110 , a first link member  120 , a second link member  130 , a resilient member  140 , a first holder  150 , a second holder  152 , a membrane sheet  160 , and a back plate  170 . 
         [0031]    The back plate  170  is a plate member formed from a material having a certain degree of hardness and rigidity, such as made from a metal or a hard resin, and the membrane sheet  160  is configured from two sheets printed with wiring patterns and disposed on either side of a spacer sheet, not shown in the drawings. Namely the membrane sheet  160  is a configuration of a top sheet and bottom sheet, not shown in the drawings, that have been stuck together, and is formed from a soft material adhered to the front face of the back plate  170 . 
         [0032]    As shown in  FIG. 1 , holes  172  are provided in the back plate  170 , and when the resin first holder  150  and second holder  152  are formed, the back plate  170  is placed in a mold with the holes already processed, and the resin first holder  150  and second holder  152  are molded to align with the positions of the holes  172 . By forming the resin first holder  150  and second holder  152  in the holes  172  in the back plate  170  using what is referred to as insert molding, a structure with high positional accuracy of the first holder  150  and the second holder  152  attachment is attained. 
         [0033]    As shown in  FIG. 1 , the holes  172  may be configured with a profile provided with a taper or step expanding at the rear side of the attachment face, rather than as simple straight-sided holes. In such cases, since resin is also filled into the expanded holes  172  during insert molding, flanges  156 ,  154  are formed to the first holder  150  and the second holder  152 , respectively. 
         [0034]    In other words, by configuring the holes  172  with profiles opened wider on the opposite side of the back plate  170  to the membrane sheet  160 , such as the holes  172  shown in  FIG. 1 , since the first holder  150  and the second holder  152  are formed integrated to the flanges  154 ,  156  and passing through the holes  172 , the configuration enables stronger fixing to be achieved than with a straight-sided hole profile. 
         [0035]    In a single unit holder  250  such as illustrated in the related examples in  FIG. 9  and  FIG. 10 , it is necessary to position the link members avoiding the periphery of the single unit holder  250  so as not to impinge on the single unit holder  250 , leading to a reduction in the degrees of freedom for design, and the occurrence of thinned portions in the members. However, by splitting the holder into the first holder  150  and the second holder  152 , the degrees of freedom in the profile and positions of each of the link members is increased. 
         [0036]    As shown in  FIG. 1 , a contact point portion  166  is provided to the interior of the membrane sheet  160 . The resilient member  140  is fixed above the contact point portion  166 , between the contact point portion and the key top  110 , for example using an adhesive. The resilient member  140  is formed with a substantially cap-shaped profile from a material such as rubber, and has a fitting hole  142  at the center of an upper portion. A contact depressing portion  144  is formed projecting towards the membrane sheet  160  at an internal face central portion of the resilient member  140 . 
         [0037]    The key top  110  moves towards the membrane sheet  160  (back plate  170 ) due to the key top  110  being depressed, whilst maintaining a parallel orientation to the membrane sheet  160  (back plate  170 ). A projection  118  provided to the rear face of the key top  110  and fitted into the fitting hole  142  accordingly presses the upper portion of the positioned and fixed resilient member  140 . The resilient member  140  accordingly undergoes compression deformation, and the internally formed contact depressing portion  144  contacts and presses the contact point portion  166  of the membrane sheet  160 . 
         [0038]    The contact point portion  166  has electrical contact points disposed at locations respectively facing each other on a top sheet and bottom sheet, not shown in the drawings, adhered to either side of a spacer sheet, not shown in the drawings, of the membrane sheet  160 . When the membrane sheet  160  is pressed in the thickness direction, the two electrical contact points provided facing each other on the top sheet and bottom sheet contact each other and are electrically connected, resulting in a closed switch state as a switch. 
         [0039]    When the depressing of the key top  110  is released, each configuration component returns to its original state due to the force of restitution (resilience) of the resilient member  140  and the membrane sheet  160 , the contact point portion  166  of the membrane sheet  160  separates, and the switch enters an open state as the electrical contact is broken. 
         [0040]    On the rear side of the key top  110  (the side facing the membrane sheet  160 ), rotation support members  112  are provided to rotatably support rotation shafts  124  provided to a first end of the first link member  120 . Slide support members  114  are also provided to support the slide projection  132  provided to a first end of the second link member  130  such that the slide projection  132  is capable of rotation and also parallel movement (motion) in a horizontal direction (a direction along the surface of the membrane sheet  160 ). 
         [0041]    The substantially rectangular frame profiled first link member  120  is provided with rotation shafts  128  that project towards the outside in the vicinity of the center of the two facing sides. Rotation shafts  124  are provided at the edge of one of the remaining two sides rotatably retained in rotation support members  112  provided to the rear side of the key top  110 . Slide projections  122  are provided at the edge of the other remaining side, supported by the second holders  152  integrally provided in the holes  172  in the back plate  170 , such that the slide projections  122  are capable of rotation and parallel movement (motion) in a horizontal direction. 
         [0042]    The first link member  120  is fitted so as to overlap along the same plane as the second link member  130 , forming a nested structure with the first link member  120  fitting inside the second link member  130 . The rotation shafts  128  of the first link member  120  fit into shaft holes  136  provided at facing positions on the second link member, assembled as shown in  FIG. 3  such that both members can rotate with the rotation shaft  128  acting as an axis. 
         [0043]    The membrane sheet  160  is adhered onto the back plate  170  with the first holders  150  and the second holders  152  respectively clear of holes  162 ,  164  formed to the membrane sheet  160  at positions aligned with the first holders  150  and the second holders  152 . 
         [0044]    Components such as the link members are assembled as follows. The rotation shafts  128  of the first link member  120  fit into the shaft holes  136  of the second link member  130 , such that the first link member  120  and the second link member  130  are assembled together in a rotatable X-shape. The rotation shafts  124  of the first link member  120  are inserted into the rotation support members  112  on the rear side of the key top  110  and the slide projections  132  of the second link member  130  are inserted into the slide support members  114  on the rear side of the key top  110  so as to be capable of rotation and also capable of parallel movement in a horizontal direction (a direction along the surface of the membrane sheet  160 ). 
         [0045]    The first link member  120  and the second link member  130  that are assembled in an X-shape are positioned by the first holders  150  and the second holders  152  insert molded in the holes  172  provided to the back plate  170 . Namely, the slide projections  122  provided to the first link member  120  are inserted into the second holders  152  and retained so as to be capable of both rotation and of parallel movement in a horizontal direction (a direction along the surface of the membrane sheet  160 ). 
         [0046]    The rotation shafts  134  provided to the second link member  130  are inserted into the first holders  150  and retained so as to be capable of rotation. 
         [0047]    Consequently, when the key top  110  is depressed, the rotatably supported rotation shafts  124 ,  134  only rotate at these locations, without a change in horizontal position with respect to the back plate  170 . However, as the key top  110  is depressed the slide projections  122 ,  132  also move horizontally, above the membrane sheet  160  and at the rear side of the key top  110 . 
         [0048]    When this occurs, were the positioning accuracy of the second holders  152  to be poor, for example if the second holders  152  were to lift up from the membrane sheet  160 , there would be a possibility that the movement direction of the sliding projections  122  would cause a deviation in the depressing direction of the key top  110 , giving rise to a wobbling sensation. 
         [0049]    However, in the present invention, due to the second holders  152  being insert molded and integrated to the high rigidity back plate  170 , causes of poor positioning accuracy are reduced and a configuration capable of reducing any wobbling sensation is achieved. Since the first holders  150  are also insert molded to the back plate  170 , a configuration with excellent positioning accuracy with respect to the second holders  152  is achieved. 
         [0050]    As the first holders  150  and the second holders  152  are insert molded as respective independent components to the back plate  170 , and as the space the first link member  120  needs to keep clear of is small, the member can be made with ample thickness. Therefore, a configuration can be achieved capable of reducing a wobbling sensation arising from concentration of force when the key top  110  is depressed. 
       Second Exemplary Embodiment 
       [0051]      FIG. 5A  is a plan view illustrating an enlarged portion of a key switch structure according to a second exemplary embodiment, and  FIG. 5B  is a cross-section of the location indicated. 
         [0052]    A key switch structure of a second exemplary embodiment is configured including projection portions  174  formed by embossing centered on the holes  172  provided on the back plate  170 . 
         [0053]    Specifically, by providing the projection portions  174  centered on the holes  172  in the back plate  170  as projections towards the key top  110  side, the resin first holders  150  and second holders  152  are insert molded above the projection portion  174 . The resin for molding the first holders  150  and the second holders  152  consequently also fills spaces  176  formed inside the projection portions  174 . 
         [0054]    The insert molded resin first holders  150  and second holders  152  are consequently fixed so as to be integrated through the holes  172  to the resin of flange portions formed filling the spaces  176 . 
         [0055]    Namely, in the present exemplary embodiment, in contrast to the flanges  154 ,  156  formed in the first exemplary embodiment illustrated in  FIG. 1 , the volume of the spaces  176  is not limited by the thickness of the back plate  170 . 
         [0056]    Therefore, a configuration is achieved allowing larger resin flanges to be formed than the flanges  154 ,  156  of the first exemplary embodiment. 
         [0057]    In the plan view shown in  FIG. 5 , each of the projection portions  174  is configured as a cylindrical column, however there is no limitation thereto and projection portions  174  may be provided configured in various plan view shapes, such as a triangular column or quadrilateral column, and configuration may also be made such that plural holes  172  are provided to a single projection portion  174 . 
       Third Exemplary Embodiment 
       [0058]      FIG. 6A  is a plan view illustrating an enlarged portion of a key switch structure according to a third exemplary embodiment, and  FIG. 6B  is a cross-section of the indicated location. 
         [0059]    A key switch structure of a third exemplary embodiment is configured including enlarged portions  172 B formed by counter sinking centered on the holes  172  provided on the back plate  170 . 
         [0060]    Specifically, by providing the enlarged portions  172 B to the back plate  170  centered on the holes  172  with a hole diameter that enlarges on the reverse face to the side on which the first holders  150  and the second holders  152  are attached, the resin first holders  150  and second holders  152  are insert molded and integrated to flanges  154 ,  156  formed in the enlarged portions  172 B. 
         [0061]    Namely, in the present exemplary embodiment, compared to the flanges  154 ,  156  formed in the first exemplary embodiment illustrated in  FIG. 1 , by forming the enlarged portions  172 B by counter sinking a configuration is achieved allowing larger resin flanges  154 ,  156  to be formed. The thickness of the back plate  170  may be set thicker in order to accommodate the size of the enlarged portions  172 B. 
       Fourth Exemplary Embodiment 
       [0062]      FIG. 7A  is a plan view illustrating an enlarged portion of a key switch structure according to a fourth exemplary embodiment, and  FIG. 7B  is a cross-section of the indicated location. 
         [0063]    A key switch structure of a fourth exemplary embodiment is configured with a projection portion  174  formed by drawing centered on the holes  172  provided to the back plate  170 . 
         [0064]    Specifically, by providing the projection portions  174  centered on the holes  172  to the back plate  170  as projections towards the key top  110  side, the resin first holders  150  and second holders  152  are insert molded above the projection portions  174 . The resin for molding the first holders  150  and the second holders  152  consequently also fills the spaces  176  formed inside the projection portions  174 . 
         [0065]    The first holders  150  and the second holders  152 , which are insert molded resin, are consequently fixed and integrated through the holes  172  to the resin of the flange portions formed filling the spaces  176 . 
         [0066]    Namely, in the present exemplary embodiment, in contrast to the flanges  154 ,  156  formed in the first exemplary embodiment illustrated in  FIG. 1 , the volume of the spaces  176  is not limited by the thickness of the back plate  170 , achieving a configuration allowing larger resin flanges to be formed than the flanges  154 ,  156  of the first exemplary embodiment. 
         [0067]    As the projection portions  174  are shaped by drawing, a configuration is achieved in which concentration of stress in the flanges is not liable to occur, as the locations of corners and sharp angles in the spaces  176  can be reduced compared with forming by embossing or machining. 
         [0068]    In the plan view of  FIG. 7A , the projection portion  174  has a semi-spherical shape, however there is no limitation thereto and the projection portions  174  may be configured with various profiles such as a trapezoid shape, or a pyramid shape. Configuration may also be made such that a single projection portion  174  is provided with plural holes  172 . 
       Fifth Exemplary Embodiment 
       [0069]      FIG. 8  is a cross-section illustrating a portion of a key switch structure according to a fifth exemplary embodiment. 
         [0070]    A key switch structure of a fifth exemplary embodiment is configured by insert molding first holders  150  and second holders  152  from opaque resin onto a back plate  170  formed from a light transmitting material such as a transparent resin. 
         [0071]    A light source  180  such as an LED is embedded in the back plate  170 , and electrically connected to the membrane sheet  160  so as to emit light when supplied with electricity. The light source  180  illuminates the key top  110  from the back plate  170  side with the transparent back plate  170  serving as a light guiding member. More preferably the membrane sheet  160  and the resilient member  140  are also formed as light guiding members formed from transparent materials. 
         [0072]    As shown in  FIG. 8 , the key top  110  is provided with transparent illumination windows  190  in a structure transmitting even more light from the light source  180  through the back plate  170  to illuminate the key top  110 . The light from the light source  180  accordingly passes through illumination windows  190  and can be seen from above the key top  110 . 
         [0073]    The first holders  150  and the second holders  152  here are insert molded to the transparent back plate  170  using opaque resin. A configuration is thereby achieved capable of preventing a reduction in light intensity due to the light emitted from the light source  180  being scattered by the first holders  150  and the second holders  152 . 
       Sixth Exemplary Embodiment 
       [0074]    A key switch structure of a sixth exemplary embodiment is configured with plural projection portions as projections formed in an array projecting to the key top  110  side on the transparent back plate  170  of the fifth exemplary embodiment. 
         [0075]    By arraying projection portions on the transparent back plate  170  the projection portions reflect light guided from the light source  180  so as to appear as light emitting dots from the key top  110  side. 
         [0076]    That is to say, by reflecting light from the light source  180  the array of projection portions on the transparent back plate  170  illuminate the key top  110  from the inside. A configuration is consequently achieved enabling an increased light intensity to be transmitted through the illumination windows  190 . 
         [0077]    Note that the projection portions provided to the back plate  170  may be pre-formed on the transparent resin sheet forming the back plate  170 , may be provided at the same time as the first holders  150  and the second holders  152  during insert molding, or may be provided anew after insert molding. 
         [0078]    Conclusion 
         [0079]    Examples of exemplary embodiments of the present invention have been described above, however the present invention is not limited by any of the above exemplary embodiments, and obviously various embodiments can be implemented within a range not departing from the spirit of the invention. For example, the present invention relates to a key switch structure, however the present invention is also applicable to other structures of movable components employing link members. 
         [0080]    Namely the present invention is applicable where link members are retained above a plate shaped member, and is applicable to various structures as fixing structures for fixing link members to a plate shaped member.