Abstract:
A keyboard switch with an internal air escape network, such as a series of channels or through holes, for containing air or fluid escaping from the switching cavities when a key is depressed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims all rights of priority to Japanese Patent Application Serial No. 2003-175262, filed Jun. 19, 2003 (pending).  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to the switching mechanisms used in keyboards for various electronic devices, particularly personal notebook computers in which the keyboard is disposed above the inner circuitry.  
       DESCRIPTION OF THE RELATED ART  
       [0003]     The conventional mechanisms for converting a key-top pressing motion into a switching action of an electric contact, such as is found in a keyboard switch, generally include two types. The first utilizes a rubber cap connected to the key top, where the rubber cap is typically in the shape of an edgeless hat or cup. The second type utilizes a dome-like spring body serving as the key top. Additionally, either type of the described conventional types of keyboard switches may come in two distinct varieties. In the first, the contact system includes a membrane switch in which the upper and lower contacts are disposed opposite each other and separated by a spacer. In the second, a pair of fixed contacts provided on a substrate are bridged with a movable contact provided on the back side surface of the rubber cap or dome-like spring body. In these conventional examples of the keyboard switch, when the rubber cap or dome-like spring body is buckled or inverted by a key-top pressing motion, the air or other fluid inside the rubber cap or dome-like spring body is rapidly compressed. Such compression creates a counter force against the key-top pressing motion, thereby eventually creating chattering or bouncing of the contacts.  
         [0004]     Several solutions to the above identified problems were previously suggested in the industry. For example, it was suggested to link the inner space of the rubber cap of dome-like spring body with the atmosphere. Additionally, it was suggested to form inside the keyboard switch a space for air reservoir which communicates with the inner space of the rubber cap of the dome-like spring body. An example of a key switch having an air vent equivalent portion linking the inside of the rubber cap with the atmosphere is shown in Japanese Published Unexamined Patent Application 2001-100889 and Japanese Published Unexamined Patent Application H08-255530. An example of a key switch having a through hole, provided in a substrate having a pair of fixed contacts, and the inner space of the rubber cap (covering the pair of fixed contacts) communicating with the atmosphere directly behind the back surface of the substrate via the through hole is shown in Japanese Published Unexamined Patent Application 2000-243179.  
         [0005]     In above examples of the improved key switch structure, however, dust or water drops can penetrate from the upper surface of the keyboard into the inner space of the dome-like spring members or rubber caps accommodating electrodes therein. Therefore, though the configurations of these examples are effective in terms of adjusting pressure variations in the inner space, the electrodes are exposed to dust or water drops.  
         [0006]      FIG. 8  illustrates the configuration of a conventional dome switch (keyboard switch)  201 . A surface sheet  202  is provided with a movable electrode in the inner head portion (not shown in the figure) and with a plurality of projecting portions  207  having dome-like spring bodies. A spacer sheet  203 , positioned below the surface sheet  202 , includes a plurality of through holes  209  positioned correspondingly to the projecting portions  207  and slit-like air escape portions  210  connecting all through holes  209 . A flexible printed circuit (FPC)  204  located below the spacer sheet  203  is provided with a fixed electrode  211 , wiring, and an air escape opening  206 . A laminated adhesive sheet  205  is positioned below the FPC  204  and is provided with an air escape opening  212 . Air escape portions  210  and air escape openings  206  and  212  are linked together such that air escape portions  210  are open to the space below the adhesive sheet  205 . In this example, if a projecting portion  207  is inverted toward the FPC  204  by a push-down action, the air located inside the projecting portion  207  escapes to the space below the adhesive sheet  205  through the air escape portion  210  via the through hole  209  (see Japanese Published Unexamined Patent Application No. 2002-170457).  
         [0007]     In this conventional example, as shown in  FIG. 8 , an air escape structure includes through holes  209 , connected to the air escape opening  206  of the FPC  204  via the air escape portion  210 , and the air escape opening  212  of the adhesive sheet  205 . However, because the capacity of the air escape portion  210  is not sufficiently large, the air escape opening  206  is provided so as to match the size of the air escape portion  210 , and the air escape orifice  212  is provided so as to match the size of the air escape orifice  206 , the air located inside the projecting portions cannot move smoothly during push-down action of the projecting portions  207 . Particularly, when a plurality of projecting portions  207  are pushed down at the same time, the capacity of the air escape path is insufficient thus preventing adequate air escape. As a result, an undesirable effect on user&#39;s fingers can be produced during push-down action of the projecting portions  207 .  
         [0008]      FIG. 9  illustrates the configuration of a conventional keyboard switch using a rubber cap. An electrically insulating sheet  130  includes a holding plate  160  with a plurality of openings  160   a  and key tops  150  installed in the opening  160   a . Fixed electrodes  132 ,  133  and wiring are provided on the surface of the insulating sheet  130 . Through openings  130   f  are provided in the vicinity of fixed electrodes  132 ,  133 . Rubber caps  140  are pasted onto the insulating sheet  103  such that each rubber cap covers a pair of fixed electrodes  132 ,  133  and an opening  130   f . Each rubber cap  140  is provided with movable electrodes (not shown in the figures) positioned on the inner surface of the top portion. The electrically insulating sheet  130  is laminated with a spacer sheet  120 , provided with a plurality of elongated holes  122  opposing the rows of rubber caps  140  and having the same width as rubber caps  140 , and a base plate  110 . Openings  130   f  and elongated holes  122  are thus linked together. When the rubber cap  140  is pushed down by the push-down action of the key top  150 , the air located inside the rubber cap  140  is released into the elongated hole  122  via the opening  130   f  and absorbed in the space of the elongated hole  122 . (See Japanese Published Unexamined Patent Application No. 2002-279854).  
         [0009]     As shown in  FIG. 9 , the capacity of the elongated hole  122  is sufficient to accommodate the air located inside one rubber cap  140 . However, the drawback of such a configuration is that when a plurality of key tops  150  are pushed down at the same time, the quantity of air that is moved by such a push-down action cannot be contained within the elongated holes. Thus, when a plurality of key tops  150  are pushed down at the same time, the air located inside this plurality of key tops  150  is discharged into elongated holes  122  via openings  130   f  and is partially accommodated within the inner space of elongated holes  122 . The air that is not accommodated is released from elongated holes  122  to the outside via individual ventilation holes  130   g . Ventilation holes  130   g  are formed as through holes in the vicinity of the outer side of rubber caps  140  in the electrically insulating sheet  130  and are linked to the elongated holes  122 . Thus, the inner space of rubber caps  140  is eventually linked to the outside space via the ventilation holes  130   g  and a completely sealed state of the key switch cannot be maintained. Moreover, the volume of air allowed to escape is limited by the small size of ventilation holes  130   g  reducing the flow rate of air and adversely affecting the process of keying on this keyboard.  
         [0010]     Further, in the example described above with respect to  FIG. 9 , ventilation openings  130   f  located inside rubber caps  140  are linked to the elongated hole  122  having a linear shape corresponding to the arrangement of key tops  150 . Therefore, only linear arrangement of the key tops, shown in  FIG. 11 ( a ), can be provided with the air escape structure described in  FIG. 9 , and non-linear key arrangements shown in FIGS.  11 ( b )- 11 ( d ) cannot be used.  
         [0011]      FIG. 11  illustrates the conventional key arrangement.  FIG. 11 ( b ) shows a cellular telephone comprising a keyboard for hand-held devices. In this example, the keys are arranged in three arcs drawn around an imaginary center located close to the origin point P corresponding to the base of the finger used to operate the keys (see Japanese Published Unexamined Patent Application No. H10-243075).  FIG. 11 ( c ) is a character input unit having a key arrangement with irregular disposition of the keys which is different from the linear disposition, shown in  FIG. 11 ( a ) (see Japanese Published Unexamined Patent Application No. H08-137592).  FIG. 11 ( d ) is an example showing a keyboard unit in which all keys are separated into the left and right groups and disposed so as to obtain a V-shape configuration. In this case, twisting of the hands or arms of the operator during keying is reduced and key operability is improved (see Japanese Published Unexamined Patent Application No. H11-085355). A similar key arrangement is well known in keyboards employing an ergonomic design. Non-linear key-arrangements shown in FIGS.  11 ( b )- 11 ( d ) cannot be utilized with the linear air escape structure shown in  FIG. 9 .  
         [0012]      FIG. 10  illustrates the configuration of a conventional membrane-type keyboard switch. The membrane keyboard switch shown in  FIG. 10 ( a ) is the water- and dust-resistant structure in which no openings are provided in the upper surface, although the caps do not protrude as in the example shown in  FIG. 8 . During the push-down action the air is located below the operational portion of the switch. Particularly, the spacer (also called a support) structure, supporting the upper sheet having electrodes and wiring, has an air release configuration similar to the conventional examples shown in  FIGS. 8 and 9 .  
         [0013]     The membrane keyboard switch has a three-layer structure of an upper sheet  301 , a lower sheet  302 , and a bracket  303 . An upper electrode  304  and an upper spacer  306  having a small surface area are arranged on the lower surface of the upper sheet  301  such that the upper spacer surrounds the upper electrode  304 . An annular opening is provided in the upper spacer  306  so as to form a substantially circular upper switch space  308  around the round upper electrode  304 . A narrow upper air release channel  312 , shown in  FIG. 10 ( b ), is formed in the substantially circular upper switch space  308 , and an upper air collecting space  310  having a large capacity is provided at the head of the upper air release channel  312 . A lower electrode  305  and a lower spacer  307 , that is partially different from the lower spacer  307  only in two sections, are arranged such that the lower spacer  307  surrounds the lower electrode  305  on the upper surface of the lower sheet  302  (as shown in  FIG. 10 ( a )).  
         [0014]     In the lower spacer  307 , an annular opening is provided so as to form a substantially circular lower switch space  309  surrounding the round lower electrode  305 . A lower air collecting space  311 , shown in  FIG. 10 ( b ), corresponding to the aforesaid upper air collecting space  310 , is provided at a certain distance away from the annular opening, and a narrow lower air release channel  313  is formed in the lower air collecting space  311 . The upper air release channel  312  and lower air release channel  313  are provided in positions facing the upper and lower air collecting spaces  310 ,  311  having the same shape. Sheets  301  and  302  are positioned such that the two spacers  306 ,  307  are joined while facing each other.  
         [0015]     With the configuration shown in  FIG. 10 ( b ),  10 ( c ), and  10 ( d ), a linking channel is formed between the lower switch space  309 , the upper switch space  308 , the upper air release channel  312 , the upper air collecting space  310 , the lower air collecting space  311 , the lower air release channel  313 , and, finally, the outside space  317 . In this example, because the upper and lower air release channels  312  and  313  have a small width and are provided separately above and below at the two ends of the air collecting spaces  310  and  311 , the air flow rate can be suppressed and the flow rate can be further reduced by the air collecting spaces, allowing dust that was admixed to the outer air to precipitate in the air collecting spaces  310  and  311 .  
         [0016]     In the example shown in  FIG. 10 , it is structurally self-evident that a configuration in which air escape portions or openings are provided in a sheet of flexible printed substrate comprising fixed electrodes and wiring cannot be employed. Problems associated with the structure described in this example are listed below. The structure facilitates a simple push-down action without a clicking action or a buckling action resulting in comparatively slow air movement during the action, incapacitating a rapid movement of the air in the course of the clicking or buckling action (such as described with respect to examples shown in  FIGS. 8 and 9  above). Employment of this conventional structure decreases the flow rate of the air moving from the switch spaces  308  and  309  to the external portion  317 , thus causing the stagnation of the air and making it inapplicable for executing the clicking or buckling action for which the air has to flow rapidly without a delay. Moreover, because the above-described linking channel has a complex structure, which is divided into the upper and lower spaces, the upper and lower spaces cannot be composed as one general space or support.  
       SUMMARY OF THE INVENTION  
       [0017]     It is an object of the present invention to resolve the above-described problems and to provide a keyboard switch in which a key arrangement can be other than a linear one, the structure is sealed, and fluctuations of the inner space of the protruding member occurring during operation are released inside the keyboard switch, while the operation feel is improved.  
         [0018]     The present invention provides a switching mechanism for use in keyboards for electronic devices that achieves an improved user feel over the prior art. The invention is carried out by providing a through hole in strategic locations of the mechanisms supporting the key switch so that air or other fluid contained in the space collapsed by operation of the key can escape smoothly either into other containment chambers or to the outside atmosphere. Less bucking, clicking and bouncing of the keys is produced by providing an air (or fluid) intake reservoir within the switch, along with a through hole or other channel network to connect the fluid reservoirs of adjoining switches, either with or without connecting to the outside atmosphere. The invention contemplates at least three embodiments—one involving a conventional keyboard switch utilizing a rubber cap, and another involving a conventional membrane switch utilizing a dome-like spring body. A third embodiment contemplates use of the aforesaid conventional membrane switch utilizing a dome-like spring body, along with a containment mechanism which prevents the air or fluid from escaping to the outside atmosphere. The third embodiment permits an airtight membrane keyboard with all of the benefits of the disclosed invention.  
         [0019]     The above aspects, advantages and features are of representative embodiments only. It should be understood that they are not to be considered limitations on the invention as defined by the claims. Additional features and advantages of the invention will become apparent in the following description, from the drawings, and from the claims.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0020]     The invention is illustrated by way of example and not limitation and the figures of the accompanying drawings in which like references denote like or corresponding parts, and in which:  
         [0021]      FIG. 1  provides side-view cutaway of the invention as incorporated into a conventional keyboard switch with a rubber cap.  
         [0022]      FIG. 2  demonstrates a sample fixed-electrode wiring used to incorporate the invention into a conventional keyboard switch with a rubber cap.  
         [0023]      FIG. 3  illustrates various configurations for different embodiments of the fixed-electrode region and protruding member supports.  
         [0024]      FIG. 4  illustrates the structures in which a guiding and supporting mechanism is incorporated onto a wiring.  
         [0025]      FIG. 5  illustrates a plate-like holder for locking the guiding and supporting mechanism.  
         [0026]      FIG. 6  demonstrates a side-view cutaway of the invention as incorporated into a dome-switch keyboard.  
         [0027]      FIG. 7  illustrates a fixed-electrode wiring used to incorporate the invention into a dome-switch keyboard.  
         [0028]      FIG. 8  provides an expanded view of the laminate layers used to incorporate the invention into a dome switch keyboard.  
         [0029]      FIG. 9  provides a structural view of the keyboard switch using a conventional rubber cap.  
         [0030]      FIG. 10  provides a structural view of the conventional membrane-type keyboard.  
         [0031]      FIG. 11  illustrates the conventional key arrangement for a variety of keyboard applications. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]     In accordance with the first embodiment of the present invention, the keyboard switch includes a rubber cap used as the protruding member, i.e., the collapsible and re-formable physical apparatus used to separate the electrical contacts which make up the switch.  FIG. 1  provides a cross-sectional view of the keyboard switch in accordance with the first embodiment of the present invention. The invention as incorporated into a conventional keyboard switch is illustrated. The keyboard switch includes a flat base plate  11  composed of a metal such as aluminum, a fixed electrode support  13 , a rubber cap support  14  placed onto the base plate  11 , a membrane sheet  12  arranged above the two supports  13  and  14 , a rubber cap (or elastic cap)  15  mounted on the membrane sheet  12 , a sheet-like holder  80  secured onto the membrane sheet  12  and having a rectangular opening for loosely inserting the rubber cap, a key top  16  driven by pushing down the rubber cap  15 , and a guiding and supporting mechanism  17  of an approximately X-like shape supporting the key top  16 . The lower portion of the supporting mechanism  17  is mounted on the sheet-like holder  80 , and its arms are pivotally connected to each other in their approximate center so as to conduct guidance for the vertical movement of the key top.  
         [0033]     The membrane sheet  12  is a flexible printed circuit (FPC) formed by screen printing, or by some other similar process, to create, an electrically conductive pattern of fixed electrodes  18  and wiring  19  consisting of an electrically conductive ink placed on a transparent base sheet having electrically insulating properties and composed of a resin film such as a polyester film. The electrically conductive pattern can be of a variety of shapes according to the entire shape and specification of the keyboard switch. The pattern is essentially made up of pairs of fixed electrodes of a variety of shapes and a wiring pattern connected thereto. If desired, wiring  19 , excluding the fixed electrodes  18 , may be covered with a resistant film (not illustrated) to prevent the electrically conductive pattern from being peeled off or broken by friction when the membrane sheet is stacked in the switch.  
         [0034]      FIG. 2  illustrates an example of a wiring pattern  19  used to electrically connect an assortment of fixed electrodes  18  distributed over the membrane sheet  12  in creating a key pattern for a keyboard. Each fixed electrode  18  is composed of a pair of electrodes in a bridge connection configuration that are paired in a row with the prescribed spacing. Any shape can be employed for the fixed electrodes  18 , provided that the shape thereof enables reliable bridge contact with the moveable electrode  22 . Especially preferred is a comb-like shape.  
         [0035]     As shown in  FIG. 1 , a support structure comprising the fixed electrode support  13  and the rubber cap support  14  is provided at the lower surface of the membrane sheet  12 . The support is preferably made from resin (or a similar material) and may be integrally molded with the membrane sheet  12  or formed as a separate body. When the support structure is formed as a separate body, it may be bonded to the membrane sheet  12  with an adhesive or formed by printing. The support structure is formed to have a very small prescribed thickness (as viewed in the lamination direction). The structure formed by supports  13  and  14  preferably supports the pairs of fixed electrodes  18  and a collar  20  of the rubber cap  15  from below the membrane sheet  12 . By being placed between the membrane sheet  12  and the base plate  11 , the same supporting structure forms a gap  21  (B) communicating via a ventilation hole  23  with the inner space  29 (A) of the rubber cap  15 . A variety of patterns can be used for the support structure, as shown in  FIG. 3 .  
         [0036]     Small ventilation holes  23  are formed in the membrane sheet  12  in the vicinity of the fixed electrodes  18  (preferably one hole per one pair). A plurality of ventilation holes  23  can be provided in one rubber cap  15  in order to absorb rapid changes in the air flow amount and to obtain good user-feel of pressing the rubber cap  15 .  
         [0037]     Space  21 (B) serves as a space for accommodating the changing air volume. It is linked to the space outside the keyboard switch.  
         [0038]      FIG. 3  illustrates the supports of various types suitable for supporting the protruding member in accordance with the present invention. (Even though the various supports illustrated in  FIG. 3  can also be used with other embodiments of the present invention, the explanation will only be conducted with respect to the first embodiment.)  
         [0039]     The main purpose of using the supports  13  and  14  is to bear the push-down load when the key top  16  is pushed down. More specifically, they support the fixed electrode  18  to which a load is applied via a movable electrode  22 , and the collar  20  to which a load is applied via the skirt portion  24  of the rubber cap  15 . Additionally, supports  13  and  14  define boundaries of space  21 (B) for accommodating the air or other fluid present inside the rubber cap  15  in the keyboard switch. The supports are formed to a predetermined height above the surface of the membrane sheet  12 .  
         [0040]      FIG. 3 ( a ) shows a type A support in which a round fixed electrode support  13  wider than the round fixed electrode region is formed in the center of a rectangular region. A straight channel  32 ,  33 ,  34 ,  35  is provided in the middle of each side of the rectangular region such that each straight channel extends perpendicularly to the side on which it is formed and to at least two other straight channels. A substantially circular channel  31  surrounds the fixed electrode support  13  and links together central openings of channels  32 ,  33 ,  34  and  35 , thus forming a cross-like structure centered in the substantially circular channel  31 . A through hole  23  is placed at each intersection between channels  32 ,  33 ,  34 , or  35  and the substantially circular channel  31 . Thus, four through holes  23  are formed along the channel  31 .  
         [0041]      FIG. 3 ( b ) shows a type B support in which the fixed electrode support  13  is omitted from the similar shape shown in  FIG. 3 ( a ).  
         [0042]      FIG. 3 ( c ) shows a type C support in which cross-like channels are formed by longitudinal linear ribs  36 ,  37 ,  38  and  39  and lateral linear ribs  41 ,  42 ,  43 , and  44  intersecting at 90° angles The fixed electrode support  13  (not shown in  FIG. 3 ( c )) is formed within the intersection area  45  where the longitudinal channels formed by linear ribs  36 ,  37 ,  38 ,  39  cross the lateral channels formed by linear ribs  41 ,  42 ,  43 ,  44 . A rubber cap support  14  (not shown in  FIG. 3 ( c )) may be formed within the radial portion of the shown structure, i.e. within the portion radially distanced from the center of the intersection zone  45  of the cross-like channels. The linear ribs, formed, for example, by multi-layer printing of resin, have a predetermined height and a linear shape in the side view and plane view, respectively.  
         [0043]      FIG. 3 ( d ) shows a type D support in which the linking channels shown in  FIG. 3 ( a ) are formed by raised ribs. More specifically, the type D support is configured of straight linear ribs  46 ,  48 ,  49 ,  51 ,  52 ,  54 ,  55 , and  57  linked to circular arc-like ribs  47 ,  50 ,  53 ,  56 . Raised ribs are preferably being formed by multi-layer printing of resin or by some other similar process. The rubber cap support  14  (not shown in  FIG. 3 ( d )) is preferably formed by the circular arc-like ribs  47 ,  50 ,  53 , and  56  and the straight linear ribs  46 ,  48 ,  49 ,  51 ,  52 ,  54 ,  55 , and  57  which preferably have a length somewhat greater than the width of the collar  20  (not shown in  FIG. 3 ( d )).  
         [0044]      FIG. 3 ( e ) shows a type E support in which the rubber cap support  14  is formed by four ring segments  58 ,  59 ,  60 , and  61 . The width of the ring in the radial direction is somewhat larger than the collar width of the rubber cap. The overall shape of the type E support includes the fixed electrode support  13  located in the center of the ring, and the four ring segments  58 ,  59 ,  60 , and  61  are arranged concentrically around the support  13  such that a substantially circular channel  31  is formed around the support  13 . Channels  62 ,  63 ,  64 , and  65  formed between ring segments  61 ,  58 ,  59 , and  60  open into the substantially circular channel  31 .  
         [0045]      FIG. 3 ( f ) shows a type F support in which a plurality of straight ribs  66  are arranged in a ring-like pattern where the ribs are radiating away from the center. The channels are formed between the straight ribs. In this structure, the length of ribs  66  is preferably equal to the width of a ring segment shown in  FIG. 3 ( e ) and is somewhat longer than the collar width of the rubber cap. The rubber cap support  14  thus comprises the radiating straight ribs  66  arranged in the ring-like pattern.  
         [0046]     Examples of support configurations shown in FIGS.  3 ( a ),  3 ( b ),  3 ( c ),  3 ( e ), and  3 ( f ), employ both the fixed electrode support  13  and the rubber cap support  14 . Only the support configuration shown in  FIG. 3 ( d ) represents a specific example in which the fixed electrode support  13  is omitted and the fixed electrode is softly supported by the rubber cap support  14 .  
         [0047]     In the above-described examples of supports, ventilation holes  23  may be provided around the fixed electrode support  13  in at least four locations corresponding to channel sections, as in the example shown in  FIG. 3 ( a ). They may also be positioned in a ring-like pattern around the fixed electrode support  13  or along the substantially circular channel  31 . Ventilation holes  23  are linked to the space  21  (B) with at least four channels. Therefore, the location for providing the ventilation holes can be freely selected in at least four directions even if the key arrangement is somewhat changed. As a result, the problems conventionally associated with the key arrangements can be resolved.  
         [0048]     Thus, the presently provided configuration of the support makes it possible to form the channels linking the ventilation holes of the membrane sheet and the space  21 (B) located below the membrane sheet in a plurality of different locations. Therefore, channels for sufficient escape of the air can be ensured even if the key arrangement is somewhat changed.  
         [0049]     The rubber (or elastic) cap  15 , as shown in  FIG. 1 , is formed from an electrically insulated resin or rubber, such as a silicon rubber, so as to have a cap-like shape (in the form of an edgeless hat or cup). Rubber cap  15  is also formed integrally to have a downward-open cap-like shape having a tubular top portion  71  extending upward from the top portion of the cap. The skirt portion  24  extends downward from the perimeter of the tubular top portion  71 , and a thick collar  20  is provided in the extended position at the lower end portion of the skirt portion  24 . This rubber cap  15  offers s a push-down projection  72  formed integrally with the top portion on the inner side of the cap so as to protrude downward. A movable electrode  22  composed of an electrically insulating film is preferably formed by printing on the distal end of the push-down projection  72 .  
         [0050]     The rubber cap  15  is positioned so that the movable electrode  22  and fixed electrode  18  face each other, and the lower surface of the collar  20  is then securely bonded to the upper surface of the membrane sheet  12 .  
         [0051]     When the rubber cap is driven by being pushed down, the movable electrode  22  is bridge connected to the fixed electrode  18 . As for the movable electrode  22 , a cylindrical rod-like movable electrode composed of an electrically conductive rubber or the like may be employed instead of the electrically conductive film.  
         [0052]      FIG. 4  is an explanatory drawing illustrating a structure in which a guiding and supporting mechanism is provided on a wiring pattern.  FIG. 4 ( a ) is a plane view of the guiding and supporting mechanism.  FIG. 4 ( b ) shows a wiring pattern arranged around the fixed electrode on the membrane sheet.  FIG. 4 ( c ) is a plane view of the guiding and supporting mechanism mounted on the wiring pattern. The guiding and supporting mechanism ensures smooth and accurate movement of the key top in the vertical direction.  
         [0053]      FIG. 5  is an explanatory drawing of a plate-like holder for locking the guiding and supporting mechanism.  
         [0054]      FIG. 4 ( b ) shows the membrane sheet  12 , as viewed from the fixed electrode  18  side (surface side); the structural elements located on the back side surface are shown by the dotted lines. The fixed electrode  18 , having a pair of electrodes disposed opposite each other, and wiring  19 , extending from the fixed electrode  18 , are formed on the surface side of the membrane sheet  12 . A ventilation hole  23  penetrates through the membrane sheet  12  in the vicinity of the fixed electrode  18 . Collar portion  20  of the rubber cap is provided so as to cover the fixed electrode  18  and the ventilation hole  23 .  
         [0055]     The invention shown in  FIG. 4 ( b ) utilizes the type E support comprising four ring segments  58 ,  59 ,  60 , and  61 , shown by broken lines and formed so as to expand from the collar portion  20 . This support structure is provided on the back side surface of the membrane sheet  12  so as to support the collar portion  20  of the rubber cap. As a result, the fixed electrode  18  is covered over the entire surface area and reliably supported by the fixed electrode support  13 . Furthermore, the fixed electrode support  13  is provided over a surface area slightly larger than that of the fixed electrode  18 . As a result, the fixed electrode  18  is covered over the entire surface area and is reliably supported with the fixed electrode support  13 .  
         [0056]     Referring to  FIG. 4 ( b ), the ventilation hole  23  located in the membrane sheet  12  extends to the substantially circular channel of the support structure on the outer side (as viewed in the radial direction) of the fixed electrode support  13  of the support so as to pass from the front surface to the back side surface of the sheet on the inner side of the inner periphery of the collar portion  20  in the rubber cap.  
         [0057]     Although the embodiment of the invention shown in  FIG. 4 ( b ) utilizes the type E support, other types of supports shown in  FIG. 3  may be used with similar advantages. Accordingly, additional explanation thereof is omitted as unnecessary.  
         [0058]     The guiding and supporting mechanism  17  shown in  FIG. 4 ( a ) is constructed by assembling a working frame  81  of an square-like shape, a working arm  82  of an approximately U-like shape and the two shaft portions  86  and  91  connected so as to obtain an approximately X-like shape. The working frame  81  comprises arms  89  having a shaft portion  91  in the intermediate part thereof and a linking beam  87  linked to arms  89  on both sides. Thus arms  89  form two sides of the square-like shape of the frame  81 . The frame also includes sliding pins  90  located at both sides of one end of the frame  81 . The working frame  82  comprises arms  84  constituting two side portions of the U-like bracket structure, connected to bearing pins  85  at the open side of the bracket structure. Shaft  86  is positioned in the intermediate portion of each arm  84 , and a beam  83  links arms  84  at the closed end of the U-shaped structure.  
         [0059]     As shown in  FIG. 1 , a plate-shaped holder  80  is provided on top of the membrane sheet  12  for locking the guiding and supporting mechanism  17 . Plate-shaped holder  80  comprises a flat support plate  73  provided with openings  75  and U-shape support frames  76  disposed inside the openings  75 , as shown in  FIG. 5  and  FIG. 1 . The support plate  73  is preferably made of a very thin metal sheet and has integrally formed therewith a plurality of raised tabs  74  that rise upward at an angle at the edges of the openings  75 . The support frame  76  is positioned and held in a constricted state between the raised tabs  74  and membrane sheet  12  by fitting the raised tabs  74  into fitting grooves  79  on both sides of the support frame  76 . The support frame  76  also has a pair of constricting and holding portions  77  formed on the inner side of both side portions of the frame  76  for supporting a pair of bearing pins  85  of the guiding and supporting mechanism  17 . Further, sliding steps  78  are formed in the support frame  76  for slidably guiding the pair of sliding pins  90 .  
         [0060]      FIG. 4 ( c ) illustrates a state in which the guiding and supporting mechanism  17  shown in  FIG. 4 ( a ) was placed on the wiring pattern shown in  FIG. 4 ( b ). In this embodiment, the guiding and supporting mechanism  17  is placed directly or, if necessary, via a resistant film on the membrane sheet  12  provided with a wiring pattern. Sliding pins  90  of the guiding and supporting mechanism  17  are slidably guided by the sliding steps  78  of the support frame  76  and the membrane sheet  12 , as shown in  FIG. 1 .  
         [0061]     In other words, the structure is such that the sliding pins  90  slide over the surface of the membrane sheet  12  where the wiring is located. Similarly, the bearing pins  85  of the guiding and supporting mechanism  17  are rotatably supported by the constricting and holding portions  77  of the support frame shown in  FIG. 5  and the membrane sheet  12 . In other words, the structure is such that the bearing pins  85  rotate over the surface of the membrane sheet  12  where the wiring is located. Here, as shown by the dotted line regions in  FIG. 4 ( c ), the contact regions, where the bearing pins  85  and sliding pins  90  are in contact with the membrane sheet  12 , are set outside the wiring region. The dotted line regions shown in  FIG. 4 ( c ) approximately represent the contact regions. These contact regions  101 ,  102 , and  103  are provided preferably outside the region of wiring  19  and outside the region where the collar  20  of the rubber cap is placed. At least the contact region  101 , where the sliding pins  90  are disposed, is to be provided outside the region of wiring  19  and outside the region where the collar  20  of the rubber cap is placed. As a result, the guiding and supporting mechanism  17  can be mounted on the membrane sheet  12  directly or via a resistant film, without introducing an insulating sheet.  
         [0062]     The key top  16  shown in  FIG. 1  is made of a synthetic resin such as an ABS resin, and characters are provided by gravure process or printing on the upper surface thereof. At the lower surface of the key top  16 , the holder  25  having a p-like shape shown in the figure is locked with a latch. The guiding and supporting mechanism  17  with an X-like arm structure of working frame  82  and working frame  81  rotatably supported around their central portion is provided between the key top  16  and the holder  25 . When the key top  16  is pushed down, the rubber cap  15  can be pressed uniformly in the up-down direction (vertical direction) via the guiding and supporting mechanism  17 .  
         [0063]     As described above, the guiding and supporting mechanism  17  comprises working frames  81  and  82 , and linking beams  83  and  87 . The linking beam  83  is guided and supported between the underneath surface of the key top  16  and the latch  26  of the holder  25 . The other linking beam  87  is sandwiched between the underneath surface of the key top  16 , the stopper  28 , and the latch  27  provided at the holder  25 .  
         [0064]     The operation of the keyboard switch will be explained with respect to  FIG. 1 . First, when the key top  16  is pushed in the downward direction, the top portion of the rubber cap  15  is pressed down via the guiding and supporting mechanism  17 , the skirt portion  24  of the rubber cap  15  deforms and buckles, and this buckling action produces a clicking feel in the rubber cap  15 . Accompanying this, the sliding electrode  22  forms a bridge contact with the first and second fixed electrodes  18 , the first and second fixed electrodes  18  then become electrically connected, and a switch-on state is assumed. At this time, following the deformation of the rubber cap  15 , the air present inside the rubber cap  15  is released through the ventilation hole  23  into the space  21  (B) located between the membrane sheet  12  and base plate  11  and is accommodated within this space  21  (B) or partially released to the outside space.  
         [0065]     In the space  21 (B) bounded by the membrane sheet  12  and the base plate  11 , the portion outside the fixed electrode support  13  and the rubber cap support  14  that take a surface area region somewhat larger than that where the electrode and the collar portion  20  of the rubber cap  15  are located, serves as a space for absorbing the changing air volume. However, the space  21  (B) is also linked to the space outside the keyboard switch. Therefore, it has a much larger capacity than the volume of the elongated hole described in Japanese Published Unexamined Patent Application No. 2002-279854.  
         [0066]     For this reason, even when a plurality of key tops  16  are pushed down at the same time, the air present inside the plurality of rubber caps  15  will be released into the space  21 (B) through the ventilation holes  23  present inside the respective rubber caps, and fluctuations of air pressure will be absorbed inside the space  21  (B). The air present inside the space  21  (B) will be further released into the outside space at the head thereof. Thus, when one or a plurality of key tops  16  are pushed down, the air present inside the rubber caps  15  is sufficiently released into the space  21 (B) and the outside space through the ventilation holes  23 . Therefore, the pleasant buckling user-feel of rubber caps  15  can be maintained.  
         [0067]     If the push-down pressure applied to the key top  16  is then released from the switch-on state, the buckled rubber cap  15  will restore the original cap-like shape under the effect of its own elastic forces, the bridge contact state of the pair of fixed electrodes  18  will be switched to OFF, and the key top  16  will be pushed up and returned to the original position.  
         [0068]     In this process, the inside of the rubber cap  15  that had a small volume and had a small amount of air therein due to preceding buckling deformation takes up the air from the space  21 (B) and the outside space via the ventilation hole  23  and restores the original cap shape. As a result, the space  29 (A) bounded by the rubber cap  15  and the membrane sheet  12  and the large-capacity space  21  (B) that is linked to the outside space are linked via the ventilation hole  23 .  
         [0069]     Because spaces  29 (A) and  21  (B) are linked via the ventilation hole  23 , even if a large quantity of air moves under the inversion action of the projection, the fluctuations of air flow can be fully accommodated since the space  21 (B) has a large capacity and the linking channels do not have a sealed structure. Furthermore, the space  21  (B) is open to the outer space. As a result, a sealed structure that is dustproof and waterproof can be obtained without losing the melodic feel (buckling feel, clicking feel) of the key tops  16 .  
         [0070]     Additionally, as shown in  FIG. 3 ( c ), for example, the supports in accordance with the present invention can have at least four channel sections around the fixed electrode support  13 . Ventilation holes  23  can be provided within these channels and linked to the sealed space  21  (B) along at least four channels. Therefore, even if the key arrangement is somewhat changed, the location for providing the ventilation hole can be freely selected in at least four directions. As a result, the conventional problems associated with key arrangement can be resolved.  
         [0071]     The second embodiment of the present invention, in which the protruding member is composed of a surface sheet comprising a projecting portion and a spacer sheet, will be described below with respect to  FIG. 6 .  FIG. 6  is a cross sectional view of the keyboard switch of the second embodiment of the present invention. A projecting portion  94  executes a return action and an open-close action, a skirt portion  95  and a spacer sheet  93  enable the projecting portion  94  to realize an invertible stroke and also have a function of supporting the projecting portion  94  on the membrane sheet  12 . Therefore, from the standpoint of functions, the two components employed in the second embodiment, that is, the front sheet  92 , composed of the projecting portion  94  and the skirt portion  95 , and the spacer sheet  93  are equivalent to the rubber cap of the first embodiment. Thus, they are included in the same concept of a protruding member.  
         [0072]     Because of its shape, the keyboard switch in accordance with the present invention, as shown in  FIG. 6 , is also called a dome switch. This switch preferably includes the surface sheet  92 , spacer sheet  93 , membrane sheet  12 , and base plate  11 . Sheets  92 ,  93 ,  12  and base plate  11  are secured with an adhesive. The surface sheet  92  has elasticity and comprises a plurality of projecting portions  94  formed at the predetermined distance from each other via skirt portions  95  serving to support the projecting portions. Each projecting portion  94  is formed to have a dome-like shape that protrudes at the outer surface side and can be inverted at the inner surface side. The movable electrode  22  is provided on the inner surface of each projecting portion  94 . The surface sheet  92  is a sheet-like member preferably made from a synthetic resin such as polyethylene terephthalate (PET), and projecting portions can be formed therein by hot pressing. The electrode is formed by printing from carbon or through some other similar process.  
         [0073]     The spacer sheet  93  is a flexible sheet-like member preferably made from a resin such as polyethylene terephthalate (PET), and functions as a member for ensuring the stroke size of the projecting portion  94 . A plurality of fixed electrodes  18  and wiring  19  are provided on the membrane sheet  12  composed of a flexible printed circuit (FPC) or the like, and having a ventilation through hole  23  provided in the vicinity of the fixed electrode  18 .  
         [0074]     Fixed electrode support  13  is provided opposing the fixed electrode  18  between the membrane sheet  12  and the base plate  11 . The protruding member support  96  is provided to match the skirt portion  95  and the compatible spacer sheet  93 .  
         [0075]     The membrane sheet  12  and the base plate  11  are constructed with tight seal (except for the ventilation hole  23 ) by a switch case not shown. As a result, the space  97 , bounded by the surface sheet  92 , spacer sheet  93 , and membrane sheet  12 ; and the large-volume space  21  (B), bounded by the membrane sheet  12 , base plate  11 , protruding member support  96  provided with a linking channel, and fixed electrode support  13 , are linked via the ventilation hole  23 . The protruding member support  96  has a structure identical to that of the rubber cap support in the first embodiment illustrated by  FIG. 3 .  
         [0076]     Because the space  97  and the large-volume space  21  (B) are linked via the ventilation hole  23 , even if a large amount of air is moved by the inversion action of the projecting portion  94  the fluctuations of flow rate can be sufficiently accommodated because space  21 (B) has an adequately large capacity. Furthermore, because space  21 (B) is open to the outside space, the movement of air is greatly facilitated. As a result, a sealed structure that is dustproof and waterproof can be obtained without losing the melodic feel (buckling feel, clicking feel) of the key tops.  
         [0077]      FIG. 7 , a structural view of the third embodiment of the present invention, provides a lower surface view of the membrane sheet (plane view of the back side surface).  FIG. 7 ( b ) is a cross-sectional view of a rectangular region (represented by dotted lines) shown by C-C′ in  FIG. 7 ( a ), which is a cross-sectional view of the space from the back side surface of the membrane sheet (structural components located on the front surface side are omitted) to the base plate.  
         [0078]     In the third embodiment shown in  FIG. 7 , the structure from the membrane sheet to the base plate that was employed in the first embodiment and second embodiment is a completely sealed structure, except for the ventilation hole. A partition wall  100  surrounding the surface of the membrane sheet  12  and base plate  11  is provided at either of the opposing surfaces thereof, and a sealed space having no holes except for the ventilation hole  23  is bounded by the membrane sheet  12 , base plate  11 , and partition wall  100 .  
         [0079]     In the structure shown in FIGS.  7 ( a ) and  7 ( b ), a plurality of electrode supports  13  and protruding member supports  96  or rubber cap supports  14  are provided on the back side surface of the membrane sheet  12 , and the partition wall  100  which continuously surrounds the back side surface is provided so as to surround those components. The partition wall  100  is formed as a multilayer coating layer or adhesive layer mainly composed of a resin material so as to have the predetermined height, or as an antenna layer for wireless communication from an electrically conductive material such as electrically conductive ink. The partition wall  100  can have any shape in the plane view thereof, provided that it can surround the electrode support, protruding member support, and rubber cap support.  
         [0080]     The large-volume space  21 (B) bounded by the membrane sheet  12 , base plate  11 , and partition wall  100  is linked to the space  29 (A) bounded by the rubber cap and membrane sheet  12 , for example, only by the ventilation hole  23 . As a result, a sealed space can be composed by the two spaces.  
         [0081]     The effect of the present invention is described hereinbelow in greater detail. Because the space  29 (A), bounded by the rubber cap and membrane sheet, and the large-volume space  21 (B), bounded by the membrane sheet, base plate, protruding member support provided with a linking channel, and fixed electrode support, are linked via the ventilation hole; even if a large amount of air is moved by the inversion action of the projecting portion, the fluctuations in flow rate can be sufficiently absorbed because the space  21 (B) has a large capacity and is linked to the outside. As a result, a sealed structure that is dustproof and waterproof can be obtained without losing the melodic feel (buckling feel, clicking feel) of the key tops. Furthermore, if a partition wall surrounding the surface of the membrane sheet and base plate is provided at either of the opposing surfaces thereof, it is possible to obtain a sealed space having no holes except for the ventilation hole, this sealed space being bounded by the membrane sheet, base plate, and partition wall.  
         [0082]     As described above, the support structure can have at least four channel sections surrounding the fixed electrode support  13 . Additionally, a ring-shaped ventilation hole  23  can be provided in the vicinity of the four channels and linked to the sealed space  29 (A) with at least four channels. Therefore, even if the key arrangement is somewhat changed, the location for providing the ventilation hole can be freely selected in at least four directions. As a result, the problems conventionally associated with key arrangement can be resolved. In other words, the supports are constructed so that the channels linked to the space  21  (B) below the membrane sheet and the ventilation hole of the membrane sheet can be provided in a plurality of different locations. Channels can be selected such that the air can sufficiently escape even if the key arrangement is somewhat changed.  
         [0083]     For the convenience of the reader, the above description has focused on a representative sample of all possible embodiments, a sample that teaches the principles of the invention and conveys the best mode contemplated for carrying it out. The description has not attempted to exhaustively enumerate all possible variations. Other undescribed variations or modifications may be possible. For example, where multiple alternative embodiments are described, in many cases it will be possible to combine elements of different embodiments, or to combine elements of the embodiments described here with other modifications or variations that are not expressly described. Many of those undescribed variations, modifications and variations are within the literal scope of the following claims, and others are equivalent.