Patent Publication Number: US-6657139-B2

Title: Keyboard

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a keyboard for use as an input device of a computer and other similar devices and, more particularly, to a novel keyboard structure that achieves the low profile and the light weight. 
     FIG. 1 shows a conventional keyboard structure, which is identical with that proposed by the applicant of this application in Japanese Patent Application Laid-Open Gazette No. 288639/99 entitled “Keyboard Switch.” 
     A description will be given first, with reference to FIGS. 1 and 2, of the prior art example. The illustrated keyboard is composed of a keyboard substrate  11 , a membrane switch sheet  12 , a keyboard frame  14  and an actuator  15 . The substrate  11  and the frame  14  are each made of a metal sheet. The membrane switch sheet  12  is sandwiched between the substrate  11  and the frame  14  to provide rigidity in the membrane switch sheet  12  and hold it flat. 
     The membrane switch sheet  12  in this example is shown to be a laminated structure of formed a pattern sheet  12 - 1  and an insulating sheet  12 - 2 . On the top of the pattern sheet  12 - 1  there are deposited contact patterns  12 A and  12 B forming a switch  12 S and a wiring pattern (not shown) for detecting the conduction/nonconduction of electricity between the contact patterns  12 A and  12 B. In the insulating sheet  12 - 2  overlying the pattern sheet  12 - 1  there is made an opening  12 C through which the contact patterns  12 A and  12 B and their surrounding areas are exposed. The pattern sheet  12 - 1  and the insulating sheet  12 - 2  are sandwiched between the substrate  11  and the frame  14  with the exposed surface of the insulating sheet  12 - 2  held upward. 
     In the frame  14  there is also formed an opening  14 A at the position corresponding to the opening  12 C made in the membrane switch sheet  12 . Through these openings  14 A and  12 C a conduction part  18 C projecting downward from the actuator  15  makes contact with the contact patterns  12 A and  12 B to establish electric connections between them. 
     The actuator  15  in this example comprises pairs of first and second links  6 A and  6 B forming a pantographic lifting or support frame as depicted in FIG. 2A; a keytop  17  (see FIG. 2B) mounted atop the pair of links  6 A and  6 B; and a tactile-response collapsible rubber dome  18  which, upon depression of the keytop  17 , allows the conduction part  18 C to move down into contact with the contact patterns  12 A and  12 B and, upon removal of the downward force applied to the keytop  17 , restores the keytop  17  to the position of its top dead center. 
     The rubber dome  18  is composed of: a cylindrical portion  18 A of a relatively large diameter that encompasses the contact patterns  12 A and  12 B; and a dome portion  18 B with which the cylindrical portion  18 A is capped. On the ceiling of the dome portion  18 B there is protrusively provided the conduction part  18 C having a flat lower end face. When a downward force is applied to the roof of the dome portion  18 B through the keytop  17 , the dome portion  18 B becomes elastically deformed, bringing down the conduction part  18 C. Incidentally, when the dome portion  18 B is deformed to some extent, its reaction force sharply decreases due to its oilcan phenomenon, providing tactile feedback to the keytop  17  being depressed. 
     Reference numerals  14 B and  14 C respectively denote a pair of leg rotary shaft bearings and a pair of slide shaft bearings both formed by drawing the frame  14 . The pair of leg rotary shaft bearings  14 B rotatably receives leg rotary shafts  16 A that extend outwardly from the lower end portions of the second links  6 A at right angles thereto. The pair of leg slide shaft bearings  14 C receives leg slide shafts  16 A that similarly extend outwardly from the lower end portions of the second links  6 A at right angles thereto, the leg slide shafts  16 A being slidable parallel to the frame surface. Likewise, a pair of rotary bearings  17 A formed on the underside of the keytop  17  rotatably receives first coupling rod  16 C extending between top end portions of the pair of first links  6 B. And, a pair of slide bearings  17 B on the underside of the keytop  17  receives keytop support sliding shafts  16 D protrusively provided on the inner side surfaces of top end portions of the pair of first links  6 B, the sliding shafts  16 D being slidable parallel to the underside of the keytop  17 . The links  6 A and  6 B, the bearings  14 B,  14 C,  17 A and  17 B, and the keytop  17  constitute the pantographic support frame. 
     In this example, the substrate  11  and the frame  24  are fixedly joined together by: forming bumps  11 A in the substrate  11  by stamping; inserting the bumps  11 A through through holes  12 D in the membrane switch sheet  12  into contact with the underside of the frame  14 ; and spot-welding the substrate  11  and the frame  14  at top surfaces or crests  19  of the bumps  11 A. That is, the bumps  11 A and the through holes  12 D are provided at plural places in the substrate  11  and in the membrane switch sheet  12 , respectively, so that the substrate  11  and the frame  14  are welded together at the plural places. 
     The above conventional keyboard uses an aluminum sheet for the substrate  11  and a stainless steel sheet for the frame  14 . Before the stainless steel sheet came into use as the frame  14 , a thick resin sheet had been used. The use of the thick resin sheet, however, inevitably increases the overall keyboard thickness. The use of the stainless steel sheet in place of the resin sheet permits reduction of the overall keyboard thickness. Because of its high specific gravity, however, the stainless steel sheet increases the overall weight of the keyboard. 
     Further reduction of the keyboard thickness and weight could be achieved by use of: a single-sheet keyboard structure in which the membrane switch sheet  12  is deposited all over the substrate  11  as of aluminum low in specific gravity and the actuator  15  is mounted directly on the top of the membrane switch sheet  12 ; or a two-sheet keyboard structure in which in which the membrane switch sheet  12  is sandwiched between the substrate  11  and the frame  14  both of which are thin aluminum sheets (for example, 0.2 to 0.3 mm thick). 
     The present inventor studied which of the one- and two-sheet keyboard structures would be mechanically stronger. The following is cross-sectional secondary moments I 1  and I 2  of aluminum sheets with a length b and thicknesses t 1 =0.6 mm and t 2 =0.5 mm, respectively, as depicted in FIGS. 3A and 3B and the cross-sectional secondary moment I 3  of a laminated member of two aluminum sheets with the length b and thicknesses t 3 =0.3 mm and t 4 =0.2 mm, respectively, as depicted in FIG.  3 C. 
     
       
           I   1 =( b /12)(0.6 3 )=0.018 b   
       
     
     
       
           I   2 =( b /12)(0.5 3 )=0.010 b   
       
     
     
       
           I   3 =( b /12)(0.8 3 −0.3 3 )=0.04 b   
       
     
     The cross-sectional secondary moment I 3  of the laminated structure is about twice larger than the cross-sectional secondary moment I 1  of the single-sheet structure of the thickness t 1 =0.6 mm and approximately four times larger than in the case of the single-sheet structure of the thickness t 2 =0.5 mm. 
     In the case of the two-sheet structure, although each sheet is as thin as around 0.2 to 0.3 mm, the cross-sectional secondary moment is I 3 =0.04b about twice larger than in the case of the single-sheet structure with t 1 =0.6 mm and about four times larger than in the case of the single-sheet structure with t 2 =0.5 mm. This suggests that the two-sheet structure is greater in rigidity than the single-sheet structures. Accordingly, the two-sheet keyboard structure will achieve the low profile and light weight. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a two-sheet-structured keyboard of great rigidity. 
     The keyboard according to the present invention comprises: 
     a membrane switch sheet having switch portions arranged thereon in matrix form and through holes made therein in correspondence to the arrangement of keys, each of said switch portions having a pair of contact patterns; 
     a keyboard frame formed by a thin sheet of aluminum that has openings made therein opposite said switch portions, said keyboard frame being laminated on the top of said membrane switch sheet to provide therein rigidity; 
     a keyboard substrate formed by a thin sheet of aluminum that has a plurality of trapezoidal bumps formed by stamping for engagement with said through holes, said keyboard substrate being laminated on the underside of said membrane switch sheet with said membrane switch sheet sandwiched therebetween, and said plurality of trapezoidal bumps being welded to said keyboard frame; and 
     an actuator mounted above each of said opening portions of said keyboard frame to make and break each of said switch portions in response to the depression of a keytop. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram, partly in section, depicting a prior art example; 
     FIG. 2A is a perspective view of a pantographic support frame used in the FIG. 2 example; 
     FIG. 2B is a perspective view of a keytop used in the FIG. 1 example; 
     FIG. 3A is sectional view of a reinforcement member using one plate of a certain thickness; 
     FIG. 3B is sectional view of a reinforcement member using one plate of another thickness; 
     FIG. 3C is sectional view of a reinforcement member using two plates of different thicknesses; 
     FIG. 4 is a sectional view taken on the line  4 — 4  in FIG. 5, for explaining an embodiment of the present invention; 
     FIG. 5 is an enlarged bottom view of the FIG. 4 embodiment; 
     FIG. 6 is an enlarged sectional view taken on the line  6 — 6  in FIG. 5; 
     FIG. 7 is an enlarged sectional view illustrating a modification of the cross-section along the line  4 — 4  in FIG. 5; 
     FIG. 8 is an enlarged bottom view of the keyboard structure according to the present invention, for explaining other structural features; 
     FIG. 9 is an enlarged sectional view taken on the line  9 — 9  in FIG. 8; 
     FIG. 10 is a sectional view showing a modification of the cross-section depicted in FIG. 9; and 
     FIG. 11 is a diagram, partly in section, illustrating another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will be given, with reference to FIGS. 4 to  7 , of an embodiment of the keyboard according to the present invention. FIG. 4 is a sectional view taken on the line  4 — 4  in FIG.  5 . The keyboard according to the present invention is provided with: the keyboard substrate  11  and the keyboard frame  14  between which the membrane switch sheet  12  for ON/OFF switching operation is sandwiched to provide rigidity in the membrane switch sheet  12  as described previously in respect of the FIG. 1 prior art example; and the actuators  15  each of which applies pressure through one of the openings  14 A (see FIG. 5) to the membrane switch sheet  12  to cause it to perform an ON/OFF switching operation. 
     In this embodiment, the substrate  11  and the frame  14  are both formed by aluminum thin sheets with a view to reducing the total weight of the keyboard structure. At the same time, to compensate for the decreased strength of the keyboard caused by the use of the thin aluminum sheets, through holes  12 E and  12 F are made in the membrane switch sheet  12  adjacent the substantially rectangular openings  14 A made in the frame  14 , and trapezoidal bumps or protrusions  11 B and  11 C are formed by stamping the substrate  11  in opposing relation to the through holes  12 E and  12 F. The trapezoidal bumps  11 B are square in plan configuration, whereas the bumps  11 C are elliptic in plan configuration. The heights of the trapezoidal bumps  11 B and  11 C are nearly equal to the thickness of the membrane switch sheet  12 . FIG. 5 is a view of the keyboard from its bottom side (from the substrate  11  side). FIG. 6 is a sectional view taken along the line  6 — 6  in FIG.  5 . Incidentally, the bump  11 A fitted in the through hole  12 D in FIG. 5 has the same configuration as that of the bump  11 A fitted in the through hole  12 D described previously with reference to FIG.  1 . 
     In FIG. 5, the direction of the line  6 — 6  will hereinafter be referred to as a row direction and the direction of the line  4 — 4  as an inter-row direction. The arrangement of the keytops  17  is indicated by the two-dot chain line. The openings  14 A are formed in plural rows in a staggered configuration in correspondence to the arrangement of the actuators  15 . The through holes  12 E are made in the membrane switch sheet  12  between adjacent openings  14 A in the same row, and the through holes  12 F are made in the membrane switch sheet  12  between adjacent rows of openings  14 A. Accordingly, the square trapezoidal bumps  11 B are fitted in the through holes  12 E formed between the openings  14 A arranged in the row direction, and the elliptic trapezoidal bumps  11 C and the circular trapezoidal bumps  11 A are formed between the rows of openings  14 A. 
     The trapezoidal bumps  11 B and  1 C are called trapezoidal since their top surfaces are formed flat. These trapezoidal bumps  11 B and  11 C are fitted in the through holes  12 E and  12 F made in the membrane switch sheet  12  with their flat top surfaces in contact with the back of the frame  14 , and the substrate  11  and the frame  14  are joined together by spot-welding them at one or more points of their contact portions. Reference numeral  21  denotes welded portions (by spot-welding that uses laser light, for instance). In the FIG. 5 embodiment the square trapezoidal bumps  11 B are each spot-welded at four corners to the frame  14 , whereas the elliptic trapezoidal bumps  11 C are each spot-welded at two points to the frame  14 . FIG. 7 shows the case where the bumps  11 C are each welded at one point. In this instance, it is desirable to provide sufficient strength at the welded joint by welding over a relatively wide area. Such a single-spot-welding scheme permits substantial reduction in the number of welded joints, hence decreasing the number of manufacturing steps involved. 
     With the structure in which the substrate  11  and the frame  14  are welded to each other at places between adjacent openings  14 A in each row and between the rows of openings  14 A, it is possible to firmly join the substrate  11  and the frame  14 , providing increased strength in the keyboard. In particular, the formation of the openings  14 A in the frame  14  decreases its strength around the openings  14 A, but the decrease in the strength of the frame  14  can be suppressed by welding it to the substrate  11  at the points adjoining the openings  14 A. This constitutes a major factor for succeeding in the production of a great-rigidity keyboard. 
     While the FIG. 4 embodiment has been described to use the pantograph structure for the actuator  15 , the present invention is not limited specifically to such a structure. As will be easily seen from the above, the present invention is applicable not only with the membrane switch sheet  12  of the two-sheet configuration in which the contact patterns  12 A and  12 B are exposed as depicted in FIG. 1 but also with a membrane switch sheet of a three-sheet configuration in which three insulating sheets are laminated so that the contact patterns are not exposed. 
     Turning next to FIGS. 8 and 9, another embodiment of the present invention will be described below. FIG. 9 is an enlarged sectional view taken along the line  9 — 9  in FIG.  8 . This embodiment uses aluminum thin sheets for the keyboard substrate  11  and the keyboard frame  14  to achieve weight reduction of the keyboard. Further, some of the trapezoidal bumps or protrusions  11 B formed by stamping the substrate  11  are not welded to the frame  14  in the through holes  12 E made in the membrane switch sheet  12 , but instead a pair of parallel rectangular lugs  14 D and  14 E are downturned from the frame  14  in the area just above each through hole  12 E, and inserted through a pair of parallel slits SL made in the top of the trapezoidal bump  11 B, then the lower ends of the downturned lugs  14 D and  14 E projecting beyond the underside of the bump  11 B are bent parallel thereto so that the lugs  14 E and  14 D are swaged to the bump  11 B. This is intended to provide increased rigidity in the substrate  11  and the frame  14  joined together. 
     It is desirable that the number of such swaged structures as shown in FIGS. 8 and 9 be in the range of 10 to 20% of the trapezoidal bumps  11 B, and the swaged structures are uniformly spread all over the keyboard. The swaged structures provide increased rigidity in the keyboard formed by the substrate  11 , the membrane switch sheet  12  and the frame  14 . Since the swaged structures afford rigidity particularly against bending about the direction perpendicular to the line  9 — 9  in FIG. 8, the rigidity of the keyboard can be further increased by uniformly arranging the pairs of lugs  14 D and  14 E so that the lugs  14 A and  14 E are bent at right angles to those in adjacent trapezoidal bumps  11 B. Furthermore, by selecting the thickness of the frame  14  to be equal to or smaller than the depth of a recess  11 F defined on the back side of the bump  11 B, the lugs  14 D and  14 E do not project beyond the underside of the plate  11  as shown in FIG.  9 —this enables the realization of a low-profile keyboard. 
     In the embodiments of FIGS. 8 and 9, the slits SL are made in each trapezoidal bump  11 B, and the lugs  14 D and  14 F downturned from the frame  14  are swaged thereto in the opening  14 E made therein. It is also possible, however, to employ such a structure as depicted in FIG. 10, in which the trapezoidal bumps  11 B in the substrate  11  and the openings  12 F in the membrane switch sheet  12  are not formed between some of adjacent openings  14 A and the openings  12 F but instead the lugs  14 D and  14 E are swaged to the substrate  11  after being inserted through slits SL made in the substrate  11  and the membrane switch sheet  12 . In this case, however, the bent portions of the lugs  14 A and  14 E project out beyond the back of the substrate  11 . 
     FIG. 11 illustrates another embodiment of the keyboard according to the present invention. In this embodiment the keyboard substrate  11  and the keyboard frame  14  are both formed by aluminum thin sheets so as to reduce the thickness and weight of the keyboard, and with a view to providing increased rigidity in the keyboard, the marginal portion of the frame  14  is downturned at right angles to form a bent portion  14 F. In this instance, by extending the bent portion  14 F as long as possible along the entire thickness of the substrate  11 , the strength of the bent portion  14 F is maximized to provide greater rigidity of the frame  14 . With the bent portion  14 F all around the frame  14 , it is possible to increase the rigidity of the frame  14  and hence provide a keyboard of increased rigidity accordingly. 
     In each of the embodiments described above, the use of aluminum thin sheets for the key board substrate  11  and the keyboard frame  14  permits reduction of the thickness of the keyboard with the substrate  11 , the membrane switch sheet  12  and the frame  14  laminated. Incidentally, by using a 0.2 mm thick aluminum sheet for the substrate  11 , a 0.3 mm thick aluminum sheet for the frame  14  and a 0.3 mm thick membrane sheet, the total thickness of the keyboard can be made as small as 0.8 mm. 
     In addition, the use of the thin aluminum sheet for the frame  14  permits reduction of the keyboard weight by approximately 20 to 30% as compared with a keyboard using a stainless steel plate. 
     Besides, even if the frame  14  is formed by an aluminum thin sheet with a view to weight reduction, the rigidity of the keyboard can be increased as described above by an arbitrary combination of: 
     (a) the structure in which the top surfaces of the trapezoidal bumps or protrusions  11 B and  11 C are spot-welded at one or more points to the back of the frame  14 ; 
     (b) the structure in which the frame  14  and the substrate  11  are joined together by swaging the lugs  14 D and  14 E to the substrate  11 ; and 
     (c) the structure in which the marginal portion of the frame  14  is downturned to form the bent portion  14 . 
     Accordingly, the present invention provides lightweight, low-profile and highly rigid keyboard, and hence the invention is of great utility when employed in practice. 
     Moreover, by performing the spot-welding step after joining the frame  14  and the substrate  11  by swaging the lugs  14 D and  14 E to the substrate  11 , the positioning of the membrane switch sheet  12  and the substrate  11  relative to each other is completed with the swaging step—this allows ease in the subsequent spot-welding step. 
     EFFECT OF THE INVENTION 
     As described above, the keyboard according to the present invention using aluminum for the keyboard frame  14  can be made lightweight as compared with a keyboard using a frame made of stainless steel. In particular, by making through holes in the membrane switch sheet at plural positions, then inserting through the through holes trapezoidal bumps formed by stamping of the substrate, and then welding the bumps to the frame, the substrate and the frame can be firmly joined together to provide great rigidity. This enables the realization of a lightweight, great-rigidity keyboard. 
     With the welded point between adjacent openings in the row direction or between rows of the openings made in the frame, it is possible to reinforce strength-decreased portions of the frame between the openings. This provides increased strength of the frame and hence further increases the strength of the laminated substrate and frame structure. 
     Furthermore, the top surfaces of the trapezoidal bumps or protrusions formed by stamping the frame are disposed in surface-to-surface contact relationship with the frame and the surface-contact portion is spot-welded at one or more points, by which the substrate and the frame can be held parallel to each other. The spot-welding at plural points enables the substrate and the frame to be firmly jointed together. The spot-welding does not deform the surrounding portion, in particular, the frame that is ultimately used as the keyboard surface; therefore, a high-quality keyboard can be obtained. 
     With the structure in which the lugs extended from the frame are projected out onto the underside of the trapezoidal bump through the through holes in the membrane switch sheet and the substrate and the projected end portions of the lugs are bent along the underside of the substrate to swage thereto the frame, the substrate and the frame can be joined together more firmly. In addition, bending the lugs provides increased rigidity in the direction perpendicular to that in which the lugs are bent. This ensures fabrication of a lightweight but great-rigidity keyboard. 
     Moreover, since the lugs bent on the back of the substrate are received in the recess defined by the underside of the trapezoidal bump, the lugs do not project out beyond the back of the keyboard substrate. Accordingly, the lug swaging structure does not constitute an obstacle to the realization of a low-profile keyboard. 
     Besides, the bent portion downturned from the keyboard frame all around it provides increased rigidity in the entire frame structure, thereby preventing the keyboard from bending or deformation.