Abstract:
When plural types of key-switch bodies arranged on a keyboard base are fitted with the corresponding types of key-tops, fitting of an incorrect key-top on a key-switch is avoided. Each key-top has a key-top side assortment cord comprising a unique combination of convex portions and concave portions which is determined by the type thereof, and a housing of each key-switch body has a body side assortment cord comprising a unique combination of convex portions and concave portions engageable with the key-top side assortment cord in pairs. The key-tops can be fitted to the key-switch bodies only when the key-top side assortment cord is brought into engagement with the body side assortment cord.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keyboard apparatus in which fitting of an incorrect key-top on a key-switch body in the type of the key-top and fitting direction thereof is avoided when each key-top corresponding to each of plural kinds of the key-switch bodies arranged on a keyboard base is fitted thereto. 
     2. Description of the Related Art 
     On a keyboard base of a computer, a word processor, etc. numerous key-switches  100  . . . are arranged, as shown in FIG. 6 for example. To these key-switches  100  . . . are fitted key-tops for being pushed by a finger having various shapes in a top view thereof, such as roughly rectangular shapes, half-size shapes, crosswise shapes, odd size L-shapes, etc. Moreover, when taking only the half size shaped key-switch (referred to “a half key” below), as an example, there are subtle differences in the shapes thereof in accordance with arranged positions thereof, as shown by key-switches  100   a ,  100   b ,  100   c ,  100   d ,  100   e , and  100   f.    
     The key-switch generally comprises a key-top  110  and a key-switch body (referred to simply “a body” below)  120 , as shown in FIGS. 7A and 7B, as an example. The key-top  110  comprises a top plate  11  being pushed by a finger, a stem portion  12  extending below the top plate  11  through an axis “X” of the key-top  110 , a hook portion  13  disposed in the both sides of the stem portion  12  sandwiched therebetween, and a side wall  14  extending below the periphery of the top plate  11 . 
     The body  120  comprises a housing  21  accommodating the body  120 , a rubber spring  22  connected to the bottom end of the stem portion  12  having a shape of a bowl inverted on the surface, and a membrane switch  24  disposed underneath a pushing portion  23  of the rubber spring  22 , being formed below the center apex of the rubber spring  22 . In the housing  21  formed are a socket  25  into which the stem portion  12  is vertically slidably inserted, and a hook holding hole  26  with which the hook portion  13  engages so that the key-top  110  cannot be pulled out from the body  120 . 
     In order to fit the key-top  110  to the body  120 , the key-top  110  is oriented relative to the body  120  so that the hook portion  13  engages with the hook holding hole  26  relative to the axis “X”; the end of the stem portion  12  is inserted into the socket  25 ; and the key-top  110  may be only pushed downward in this state. At this time, the stem portion  12  is connected to the rubber spring  22  by fitting an annular portion  29  of the rubber spring  22  formed upward protrudingly from the center apex thereof into the end of the stem portion  12 ; simultaneously the end portion of the hook portion  13  is inserted into and brought into engagement with the hook holding hole  26  so as to be not pulled out therefrom; and fitting is completed. 
     In this key-switch, when the top plate  11  is pushed by a finger, the stem portion  12  slides downward in the socket  25  such that the end of the stem portion  12  pushes the rubber spring  22  downward to buckle it. Thereby, the membrane switch  24  is pushed by the pushing portion  23  so as to be brought into conduction. When the finger is separated from the top plate  11 , the key-top  110  returns to the original position thereof by a repulsion force of the rubber spring  22  to thereby turn the membrane switch  24  off. 
     When the keyboard is assembled, each key-switch body having a specific function is arranged at and assembled in the corresponding position of the keyboard in advance; each key-top corresponding to the body is fitted thereto; and a specific symbol such as an alphabet is printed afterward on the top plate surface of the key-top by a laser for example. 
     When key-tops having distinct different shapes and sizes are assembled, fitting thereof to each of corresponding bodies is comparatively easy due to easy recognition thereof. However, in order immediately to recognize key-tops having subtle differences in the shapes thereof, as half keys  100   a  to  100   f , to fit them to corresponding bodies, considerable attention is needed, such that key-tops of the different type are prone to be incorrectly fitted. Once the different type of key-top is incorrectly fitted, it cannot be pulled out because the hook portion  13  engages with the hook holding hole  26  as described above, resulting in decreasing productivity so that it is eliminated from the production line as a failed product, for example. 
     Even the same type of key-top generally has a shape being unsymmetrical between back and foreground sides of the keyboard surface, so that fitting of key-tops inverting back and foreground sides has been done. 
     SUMMARY OF THE INVENTION 
     The present invention solves the above-described problems. Accordingly, it is an object of the present invention to provide a keyboard apparatus in which incorrect fitting in types and fitting directions of key-tops is prevented when plural types of key-tops are fitted to corresponding types of key-switch bodies arranged on a keyboard base. 
     In order to solve the above-described problems, in a keyboard apparatus according to the present invention, the key-top comprises a key-top side assortment cord formed of a combination of convex portions and concave portions which is determined by the type thereof, and the key-switch body comprises a body side assortment cord formed of a combination of convex portions and concave portions and which is brought into engagement with the key-top side assortment cord in pairs, wherein the key-top can be fitted to the key-switch body only when the key-top side assortment cord is brought into engagement with the body side assortment cord. 
     In this keyboard apparatus, the key-top can be fitted to the corresponding key-switch body only when the key-top side assortment cord formed of a combination of convex portions and concave portions which is determined by the type of the key-top is brought into engagement with the corresponding body side assortment cord in pairs. Accordingly, another type of key-top having a assortment cord which is not brought into engagement with the body side assortment cord cannot be fitted to the body, resulting in prevention of a mistake in which a different key-top is fitted wrong to the body. 
     In a keyboard apparatus according to the present invention, the key-top side assortment cord may be formed below a port on of a side wall of the key-top, and the body side assortment cord may be formed above a housing of the key-switch body. 
     Thereby key-top side and body-side assortment cords are easily formed and cannot be also in sight from outside, resulting in non-loss of design and appearance thereof. 
     In a keyboard apparatus according to the present invention, the key-top may further comprise a key-top side direction cord for defining the fitting direction disposed in a different position from that of the key-top side assortment cord having a convex portion or a concave portion, and the key-switch body may further comprise a body side direction cord disposed in the engaging position with the key-top side direction cord having a concave portion or a convex portion, and wherein the key-top can be fitted to the key-switch body only when the key-top side direction cord is brought into engagement with the body side direction cord. 
     Since the key-top can be fitted to the key-switch body only when the key-top side direction cord is brought into engagement with the body side direction cord, the key-top cannot be fitted in the inverted direction. 
     In a keyboard apparatus according to the present invention, the key-top side direction cord may be formed in the foreground position of the keyboard or the back position thereof. 
     Thereby the key-top side direction cord is easily formed and cannot be also in sight from outside, resulting in non-loss of design and appearance. Since the direction cord can be visually checked it can be used as a sign for checking the inserting direction of the key-top before insertion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a keyboard apparatus according to an embodiment of the present invention; 
     FIG. 2 is a sectional view of a key-switch according to the embodiment; 
     FIG. 3 is a side view of the key-switch shown in FIG. 2; 
     FIG. 4 shows assortment cord patterns used in the key-switch shown in FIG. 2; 
     FIG. 5 is a side view of a key-switch according to another embodiment of the present invention; 
     FIG. 6 is a plan view showing an example of a conventional keyboard apparatus; 
     FIG. 7A is a sectional view of an example of a conventional key-switch in its OFF (free) position; and 
     FIG. 7B is a sectional view of the example of the conventional key-switch in its ON (pushed down) position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to drawings, embodiments of the present invention will be described. Throughout the description below, like reference characters designate like portions having functions common to those of the conventional key-switch described with reference to FIG. 7, and description thereof will be abbreviated or simplified. 
     (First Embodiment) 
     FIG. 1 shows an example of a keyboard apparatus according to the present invention, on which numerous key-switches each having a different function are arranged. Among these key-switches, each of key-switches  1   a ,  1   b ,  1   c ,  1   d ,  1   e , and  1   f , called half-keys, has a different type of key-top. 
     Among these key-switches  1   a  to  1   f , the key-switch  1   a , for example, comprises a key-top  10  and a body  20  as shown in FIG.  2 . The key-top  10  comprises a stem portion  12  extending below the center portion of a rectangular top plate  11  with rounded corners thereof, a hook portion  13  disposed in the both sides of the stem portion  12  sandwiched therebetween, a side wall  14  extending below the periphery of the top plate  11 , and a key-top side assortment cord portion  15  extending further below a side wall  14   a  of the side wall  14  in the keyboard back side. 
     The body  20  comprises a housing  21  accommodating the body  20 , a rubber spring  22  connected to the bottom end of the stem portion  12  having a shape of a bowl inverted on the surface, and a membrane switch  24  disposed underneath a pushing portion  23  of the rubber spring  22 , being formed below the center apex of the rubber spring  22 . In the housing  21  formed are a socket  25  into which the stem portion  12  is vertically slidably inserted, a hook holding hole  26  with which the hook portion  13  engages so that the key-top  10  cannot be pulled out from the body  20 , and a body side assortment cord portion  27  extending upward from the bottom end of the housing in an opposing relationship with the key-top side assortment cord portion  15 . 
     As shown in FIG. 3, the key-top side assortment cord portion  15  is laterally divided into four sections forming bits  15 A,  15 B,  15 C, and  15 D, respectively. The bits in both end  15 A and  5 D form convex portions downward, while the intermediate bits  15 B and  15 C form concave portions. Thereby, a key-top side assortment cord is formed of a combination of the convex portions and the concave portions, which is determined by the type of key-top. 
     On the other hand, the body side assortment cord portion  27  opposing the key-top side assortment cord portion  15  is lateraLly divided into four sections forming bits  27 A,  27 B,  27 C, and  27 D, respectively. The bits in both end  27 A and  27 D are to be concave portions while the intermediate bits  27 B and  27 C are to be convex portions to form a body side assortment cord formed of a combination of the convex portions and the concave portions, which mates with the key-top side assortment cord. 
     When fitting the key-top  10  to the body  20 , first the end of the stem portion  12  is inserted into the socket  25  and the key-top  10  will be pushed downward in this state. At this time, the convex bits  15 A and  15 D of the key-top side assortment cord portion  15  are inserted into the concave bits  27 A and  27 D of the body side assortment cord portion  27 , respectively, while the convex bits  27 B and  27 C of the body side assortment cord portion  27  are inserted into the concave bits  15 B and  15 C of the key-top side assortment cord portion  15 , respectively. Therefore, the key-top side assortment cord mates with the body side assortment cord. These assortment cords do not interfere with insertion of the key-top  10 . Accordingly, the fitting is completed when the key-top  10  is pushed down until the hook portion  13  is inserted into the hook holding hole  26 . 
     The above is a description with respect to the key-switch  1   a . Like in the key-switch  1   a,  in both of the key-top side and the body side, other key-switches  1   b ,  1   c ,  1   d ,  1   e , and  1   f  have assortment cord portions, each portion being divided into four bits to form a combination of convex and concave portions. The assortment cord portion of one side is mated with that of another side. As shown in FIG. 4, each of these assortment cord portions is given an assortment cord which has a specifically different cord pattern in accordance with the type of the key-switch. 
     As it is apparent from FIG. 4 that if the key-top for the key-switch  1   b  is intended to fit wrong to the key-switch  1   a , for example, it cannot be inserted because the bits of the “B” place of the assortment cord are both convex and are urged in contact with each other. Likewise, the key-tops of key-switches  1   c  to  1   f  cannot be also fitted to the body of the key-switch  1   a  because any of bits of the “B” or “C” places of the assortment cord is convex. The situation is also the sam with respect to other key-switches  1   b  to  1   f.    
     In this manner, only when the key-top side assortment cord portion is mated with the body side assortment cord portion, a key-top can be fitted to each respective body, and the key-top cannot be inserted into the body otherwise. This results in preventing a mistake that a different type key-top is incorrectly fitted. 
     (Second Embodiment) 
     As shown in FIG. 5, a key-switch  2   a  according to another embodiment of the present invention is the same as the key-switch  1   a  of the first embodiment except for having a direction lord portion  16  which extends further below a side wall  14   b  of a key-top  30  in the keyboard foreground side. The key-switch  2   a  can be substituted for the key-switch  1   a  to be arranged in a keyboard apparatus according to the present invention. 
     In the key-switch  2   a , the configuration of a body  20  is the same as that of the key-switch  1   a  according to the first embodiment, and there is nothing in a housing  21  just underneath the direction cord portion  16 , which does not interfere the downward movement of the key-top  30 . That is, this portion can be regarded as a concave portion forming a body side direction cord portion  28 . On the other hand, when the key-top  30  is inserted in the inverted direction into the body  20 , the direction cord portion  16  formed in the side wall  14   b  of the key-top  30  is to be urged in contact with a convex portion of the body side direction cord portion  28  formed in the housing in the back side of the keyboard. 
     This key-top  30  can be fitted to the body  20  depending only on an engagement relationship between the assortment cords, as long as it is correctly inserted in back and foreground directions. However, when the key-top  30  is inversely inserted in back and foreground directions, regardless of an engagement relationship between the assortment cords, the direction cord portion  16  is urged in contact with a convex portion of a body side assortment cord portion  27  so as not to be inserted. Thereby, the key-top can be prevented from being inversely fitted to the body by mistake. 
     Since the direction cord portion  16  is simply formed as an extension of the side wall  14   b  in the foreground side of the keyboard and cannot be also in sight from outside, it is easily formed without loss of design and appearance thereof. Furthermore, since the direction cord portion  16  is formed in the foreground side of the key-top, when the key-top is fitted to the body, discrimination between back and foreground directions can be achieved by a visual check before insertion, resulting in preventing a fitting mistake in advance. 
     In the first or second embodiment, although the assortment cord portion and the direction cord portion are formed in a plate shape, they are not particularly limited to the shape. For example, the convex portion may be formed in a pin shape. Although it is preferable that the assortment cord portion be formed in the back side of the key-switch while the direction cord portion be formed in the foreground side, the layout is not particularly limited. The number of bits (divided sections) of the assortment cord depends on t he number of types of the key-top. It is needless to say that the cord patterns thereof be not limited to those in the above-described embodiments. 
     In the keyboard apparatus according to the present invention, since the key-top can be fitted to the body only when the key-top side assortment cord is mated with the body side assortment cord, a mistake that a different type of key-top is wrong fitted to a specific type of body can be prevented. When the key-switch has the direction cord as well as the assortment cord, a mistake that the key-top is fitted in a wrong direction can be also prevented.