Abstract:
Tactile-response collapsible or flip-over domes are provided which are each equipped with a dome part having a press part ( 74 ) for driving one of switch portions arranged in matrix form on a membrane switch sheet ( 20 ) and a flange part ( 73 ) around the lower end portion of the dome part. An embossed sheet ( 8 ), which has embossed cylindrical protrusions for holding the flange parts ( 73 ) of the domes from above, is provided on the membrane switch sheet.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a keyboard that drives a membrane switch by tactile-response collapsible or flip-over domes, and a method of making the keyboard. 
     A description will be given first, with reference to FIGS. 1 to  4 , of a prior art example. 
     In FIG. 1, reference numeral  10  denotes a keyboard substrate made of a metal sheet or sheet of synthetic resin that has the same mechanical strength as does the metal sheet. Reference numeral  13  denotes a keyboard frame made of a metal sheet or sheet of synthetic resin that has the same mechanical strength as does the metal sheet. The substrate  10  has bumps  11  arranged in matrix form. The substrate  10  and the frame  13  overlying it are welded, fused or bonded together through the bumps  11  to define therebetween a gap in which to house a membrane switch sheet  20  described later on. Incidentally, the substrate  10  and the frame  13  are coupled together in the final step of the manufacturing process of the keyboard switch. 
     The frame  13  has, as depicted in FIGS. 3A and 4, punched-out openings  31  each corresponding to one of switch portions  20 S of the membrane switch sheet  20  that are arranged in matrix form; hence, the openings  31  correspond to keytops  4 , too). The membrane switch sheet  20 , which is received in the gap defined by the substrate  10  and the frame  13 , is composed of a movable contact sheet  21 , a spacer  22  and a fixed contact sheet  23 . The spacer  22  has punched-out contact areas  221 . As depicted in FIG. 4, the movable contact sheet  21  has on the underside thereof a movable contact  211  and the fixed contact sheet  23  has on the top thereof a fixed contact  231  disposed opposite the movable contact  211 . The contact area  221 , the movable contact  211 , the fixed contact  231  and the keytop  4 , described later on, are positioned relative to one another to form the switch portion  20 S. A plurality of such switch portions  20 S are arranged in matrix form to provide the keyboard switch. 
     Reference numeral  4  denotes the keytop mentioned above. As shown in FIG. 1, the keytop  4  and the frame  13  are mechanically linked by a pantographic lifting or support frame  50  interposed therebetween. The pantographic support frame  50  has, as depicted in FIG. 2A, a first coupling rod  52 , a pair of first links  5  each connected at one end to one of opposite ends of the first coupling rod  52  at right angles thereto and extending therefrom substantially in parallel with the other, a second coupling rod  63 , and a pair of second links  6  each connected at one end to one of opposite ends of the second coupling rod  63  at right angles thereto and extending therefrom substantially in parallel with the other. The second links  6  are coupled together by a semicircular coupling portion  64  formed integrally therewith nearer their free ends than their centers so that an insertion hole  65  is defined by the coupling rod  63  and a semicircular coupling portion  64  for receiving a tactile-response collapsible dome. The first links  5  and the second links  6  are combined, with the outside surfaces of the latter intermediately of their ends held in contact with the inside surfaces of the central portions of the former intermediately of their ends. The first and second links  5  and  6  are connected centrally thereof by shafts  60  in a manner to be rotatable relative to each other as depicted in FIG.  1 . 
     The keytop  4  has, as shown in FIG. 2B, on the underside thereof along its two opposed sides rotary bearings  41  and slide bearings  42 . The coupling rod  52 , which serves also as a keytop support rotary shaft of the first links  5 , is rotatably received in the rotary bearings  41  of the keytop  4 , whereas keytop support sliding shafts  62  of the second links  6  are slidably received in the slide bearings  42 . As shown in FIGS. 1,  2 A,  2 B,  3 A and  3 B, leg slide shafts  51  of the first links  5  are slidably received in leg slide shaft bearings  32  formed by drawing the frame  13  in the vicinity of the switch portion  20 S, and leg rotary shafts  61  of the second links  6  are rotatably received in leg rotary shaft bearings  33  formed by drawing the frame  13 . 
     As depicted in FIG. 3A, the width D 1  of the opening  31  between the leg slide shaft bearings  32  is smaller than the distance between the outermost ends of the leg slide shafts  51  but somewhat larger than the length of the connecting rod  52  so that the first links  5  and the rod  52  are allowed to pass through the opening  31 . Accordingly, when the pantographic support frame  50  is mounted on the frame  13  with the leg rotary and slide shafts  61  and  51  received in the leg rotary and slide shaft bearings  33  and  32 , respectively, in FIG. 4, the links  5  and  6  tilt toward the keytop  4  through the opening  31  and the keytop support rotary and slide shafts  52  and  62  engage the rotary and slide shaft bearings  41  and  42  on the underside of the keytop  4 , respectively. 
     A tactile-response collapsible or flip-over dome  7  (FIGS. 1 and 2A) is composed of a cylindrical part  71  firmly fitted on a projection  43  formed on the underside of the keytop  4  centrally thereof, a dome part  72 , a flange part  73  formed integrally with the lower end portion of the dome portion  72 , and a press part  74  formed integrally with the ceiling of the dome portion  72 . The dome  7  is made of rubber or elastic synthetic resin. The dome part  72  is elastically deformed by the cylindrical part  71  that is pressed down upon depression of the keytop  4 , but the flange part  73  is formed thick and hence is not much deformed. 
     The dome  7  lies between the underside of the keytop  4  and the movable contact sheet  21  of the membrane switch sheet  20  through the opening  31  of the frame  13  and the dome insertion hole  65 , holding the keytop  4  in its raised position. That is, if the dome  7  is not present, the pantographic support frame  50  is lowered and lies flat, but when the dome  7  is interposed between the underside of the keytop  4  and the movable contact sheet  21  of the membrane switch sheet  20 , the keytop is pushed up by the dome  7  and the pantographic support frame  50  is raised almost its full height. The dome  7  has its cylindrical portion  71  engaged with the projection  43  (FIG. 1) protrusively provided on the underside of the keytop  4  centrally thereof as mentioned previously. The lower end face of the flange  73  is adhesive bonded to the surface of the movable contact sheet  31  in the vicinity of the opening  31  as indicated by  73 . 
     Turning next to FIG. 4, the assembling of the keyboard will be described below. In FIG. 4 there are shown parts of only one key of the keyboard with their insides upward. 
     In the first place, keytops  4  with their undersides upward are arranged in matrix form on an assembly table (not shown) at intervals equal to those of the switch portions  20 S. Then, the frame  13  is placed face down on the assembly table with each opening  31  held in alignment with the corresponding keytop  4 . Then, the pantographic support frame  50  is placed with the keytop support slide shafts  62  engaged with the slide shaft bearings  42  and the coupling rod  52  also serving as the keytop support rotary shaft fitted in the slide shaft bearings  41 , while at the same time the leg slide shafts  51  of the first links  5  are fitted in the leg slide shaft bearings  32  and the leg rotary shaft  61  of the second links  5  is fitted in the leg rotary shaft bearings  33 . Then, the dome  7  with its cylindrical part  71  downward is inserted through the dome insertion hole  65  (FIG. 2A) and pressed to put the cylindrical part  71  on the projection  43  of the keytop  4 . Then, an adhesive is applied onto the lower end face of the flange  73  of the dome  7 . Then, the movable contact sheet  21  is placed on the frame  13  and the pantographic support frame  50  with the movable contact  11  upward opposite the dome  7 . The assembling process is stopped until the adhesive sets, after which the spacer  22  is placed on the movable contact sheet  21  with the contact area  221  held in opposing relation to the movable contact  211 . Then, the fixed contact sheet  23  is placed on the spacer  22  with the fixed contact  231  held opposite the contact area  221  of the spacer  22 . Thereafter, the fixed contact sheet  23  is placed on the substrate  10 , and the substrate  10  is welded to the frame  13  at the bumps  11  of the former. In this way, the keyboard is assembled. 
     Upon depression of the keytop  4 , the dome  7  deforms with a tactile response and the press part  74  presses down the movable contact  211  into contact with the fixed contact  231 . Upon releasing the pressure on the keytop  4 , the dome  7  flips over and returns to its initial position, raising the press portion and hence allowing the movable contact  211  to get out of contact with the fixed contact  231 . 
     In the above-described conventional keyboard, respective cylindrical parts  71  of usually as many as several tens of domes  7  are each engaged with the projection  43  on the underside of the corresponding keytop  4  and the lower end face of the flange part  73  is adhesive bonded to the movable contact sheet  21  in the neighborhood of the opening  31 . The manufacture of this prior art example involves a step of adhesive bonding many domes  7  to the movable contact sheet  21 —this makes the manufacturing process complicated and time-consuming. That is, the dome  7  is shown on an enlarged scale for convenience of description, but in practice it is so small that the diameter of the flange part  73  is as small as less than 4 mm. Accordingly, the step of adhesive bonding a large number of such miniature domes  7  to the movable contact sheet  21  involves many exacting tasks and consumes much time. In addition, the bonding step requires time for setting of the adhesive, and the keyboard assembling is inevitably discontinued and hence is inefficient. 
     Further, since the number of domes  7  to be adhesive bonded to the movable contact sheet  21  is so large that it is impossible to ensure good bonding of all the domes; that is, there is a case where some of them are not properly bonded to the sheet  21 . Such improperly bonded domes need to be re-bonded after assembling of the keyboard, but this is very difficult to achieve. Incidentally, it is possible to avoid discontinuation of the assembling process by adhesive bonding the domes  7  on the surface of the movable contact sheet  21  prior to the start of the assembling. However, such a scheme also involves many exacting, time-consuming tasks, requires time for waiting for setting of the adhesive and suffers difficulties in re-bonding incorrectly bonded domes. 
     U.S. Pat. No. 5,967,298 discloses a keyboard free from such problems as mentioned above. In the U.S. patent a large diameter flange portion of the lower end portion of a dome is held on a substrate by a cylindrical member of a reduced diameter top end portion protrusively provided on the top of a flat frame, by which the dome is held on the substrate without using an adhesive. From its depicted configuration, it is estimated that the frame having formed integrally therewith the cylindrical member is formed by molding, though not mentioned specifically. In the case of forming the frame with such a cylindrical member by molding, it is difficult to make the thickness of the frame and the height of the cylindrical member small, inevitably making the keyboard thick. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a keyboard that is free from the necessity for adhesive bonding tactile-response collapsible domes to the keyboard frame and hence is readily assembled and thin, and a method of making such a keyboard. 
     The keyboard according to the present invention comprises: 
     a membrane switch sheet on which there are switch portions are arranged in matrix form; 
     tactile-response collapsible domes each provided with a dome part having therein a press part for driving the corresponding one of the switch portions and a flange part formed around the lower end portion of the dome part, the dome parts being formed of an elastic rubber material and disposed on the membrane switch sheet in correspondence to the respective switch portions; 
     an embossed sheet in which there are formed embossed cylindrical protrusions each for receiving the flange part of the corresponding dome, the top end portion of each embossed cylindrical protrusion being reduced in diameter for engagement with the top end portion of the corresponding flange part and the embossed sheet being placed on the membrane switch sheet; 
     pantographic support frames disposed on the embossed sheet astride the tactile-response collapsible domes; and 
     keytops each mounted on one of the pantographic support frames and elastically biased upward by the top of the underlying tactile-response collapsible dome. 
     The keyboard manufacturing method according to the present invention comprises the steps of: 
     (a) placing a frame, which has openings each corresponding to one of keytops and rotary shaft bearings and slide shaft bearings formed around each opening, on the keytops held upside down and arranged in matrix form; 
     (b) disposing pantographic support frames on the opening of the frame in correspondence to the keytops, engaging keytop support slide shafts and a keytop support rotary shaft of each of the pantographic support frames with slide shaft bearings and rotary shaft bearings formed on the underside of each keytop and engaging leg slide shafts and leg rotary shafts of the pantographic support frame with the slide shaft bearings and rotary shaft bearings of the frame; 
     (c) placing on the back of the frame an embossed sheet in which embossed cylindrical protrusions each having a reduced diameter end portion are formed in correspondence to the keytops so that the embossed cylindrical protrusions each lie at the center of one of the pantographic support frame; 
     (d) inserting the top of each tactile-response collapsible dome into one of the embossed cylindrical protrusions from the back of the embossed sheet; and 
     (e) placing a membrane switch sheet, on which switch portions are formed in matrix form in correspondence to the keytops, on the back of the embossed sheet and fixing the membrane switch sheet to the frame. 
     In the keyboard and its manufacturing method according to the present invention, the embossed sheet need not always be used, but instead the embossed cylindrical protrusions may be formed in the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram, partly in section, showing a prior art example; 
     FIG. 2A is a perspective view of a pantographic support frame used in the FIG. 1 example; 
     FIG. 2B is a perspective view of a keytop in the FIG. 1 example; 
     FIG. 3A is a plan view of a frame; 
     FIG. 3B is its side view; 
     FIG. 4 is a diagram for explaining the assembling of the prior art example; 
     FIG. 5 is a diagram, partly in section, illustrating a keyboard according to an embodiment of the present invention; 
     FIG. 6 is a perspective view of an embossed sheet; 
     FIG. 7 is a diagram illustrating a sequence of steps involved in assembling the keyboard of the FIG. 5 embodiment; 
     FIG. 8 is an enlarged perspective view of a pantographic support frame used in another embodiment of the present invention; and 
     FIG. 9 is a diagram depicting a sequence of steps involved in assembling the keyboard of the FIG. 8 embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 5 illustrates in section an embodiment of the present invention, and FIG. 6 shows an embossed sheet  8  used in the FIG. 5 embodiment. In the embodiment the parts corresponding to those in the prior art example are identified by the same reference numerals. The keytop  4 , the pantographic support frame  50 , the frame  13  and the membrane switch sheet  20  are identical in construction with those described previously with respect to FIGS. 1 to  4 , and hence their detailed description will not be repeated. The present invention resides in that the embossed sheet  8  is interposed between the frame  13  and the membrane switch sheet  20  in the prior art example described previously. Accordingly, the prior art example will always be referred to in the following description of the present invention. 
     The embossed sheet  8  is formed by a metal sheet or film of hard synthetic resin such as polyethylene terephthalate and having a thickness of, for example, 50 to 100 μm. Reference numeral  81  denotes cylindrical protrusions having their open top end portions reduced in diameter. The cylindrical protrusions  81  are formed and arranged in matrix form by embossing the sheet  8  in correspondence to the switch portions  20 S. That is, the open top portion of each embossed cylindrical protrusions  81  is slightly reduced in diameter by being drawn in conformity with the flange part  73  protrusively provided on the lower end portion of dome  7 . 
     The flange portion  73  of the dome  7  is fitted in the embossed cylindrical protrusion  81  with the marginal edge of the reduced diameter open top of the latter resting on a stepped portion between a dome portion  72  and the flange portion  73 , whereby the dome  7  is fixed. The embossed sheet  8  is interposed between the frame  13  and the membrane switch sheet  20 . The dome  7  has its cylindrical and dome portions  71  and  72  projected out from the reduced diameter open top of the embossed cylindrical protrusion  81  and inserted through the dome insertion hole  65  of the pantographic support frame  50  with the cylindrical portion  71  engaged with the projection  43  on the underside of the pantographic support frame  4 . With the keyboard assembled in this way, the flange portion  73  of the dome  7  is engaged with and held by the embossed cylindrical protrusion  81  from above, and hence it is firmly retained between the keytop  4  and the membrane switch sheet  20 . 
     A description will be given, with reference to FIG. 7, of assembling the keyboard according to the present invention. 
     In the first place, keytops  4  with top faces downward are arranged in matrix form at the same intervals as those of the switch portions  20 S arranged in matrix form on an assembly table. 
     Next, the frame  13  is placed facedown on the assembly table with the openings  31  held in alignment with the keytops  4 , respectively. 
     Next, the pantographic support frame  50  is placed on the frame  13  with the keytop support slide shaft  62  fitted in the slide bearing  42 , the coupling rod  52 , which is the keytop support rotary shaft, fitted in the rotary bearing  41 , the leg slide shafts  51  of the first links  5  fitted in the leg slide bearings  32 , and the leg rotary shafts  61  of the second links  6  fitted in the leg rotary bearings  33 . 
     Next, the embossed sheet  8  is assembled with the frame  13  and the pantographic support frame  50  with each embossed cylindrical protrusion  81  held downward and received in the dome insertion hole  65 . 
     Next, the dome  7  with the cylindrical portion  71  downward is inserted through the embossed cylindrical protrusion  81  and the dome insertion hole  65  and the cylindrical portion  71  is engaged with the projection  43  of the keytop  4 . 
     Next, the movable contact sheet  21  is placed on the embossed sheet  8  with the movable contacts  211  upward in correspondence to the embossed cylindrical protrusions  81 . 
     Next, the spacer  22  is placed on the embossed sheet  8  with each contact area  221  opposite the corresponding movable contact  211 . 
     Finally, the substrate  10  is placed on the fixed contact sheet  23 , and is welded to the frame  13  at the bumps  11  to form a one-piece structure. In this way, the keyboard is assembled. 
     While in the above the embossed sheet  8  has been described to underlie the frame  13 , it is also possible to form embossed cylindrical protrusions  81  in the frame  13 , dispensing with the embossed sheet  8 . FIG. 8 depicts an example of the pantographic support frame  50  in such a case and FIG. 9 shows a sequence of steps involved in assembling the keyboard. As depicted in FIGS. 8 and 9, the links  6  of the pantographic support frame  50  are not coupled together by the semicircular coupling portion  64  shown in FIG. 2A, and hence they form a U-shaped structure as a whole. 
     A support piece  81 B is extended inwardly from the marginal edge of the opening  31  intermediate between the opposed slide shaft bearings  32 , and the support piece  81 B has in its tip end portion the embossed cylindrical protrusion  81  lying at the center of the opening  31 . The width of the support piece  81 B is smaller than the distance between innermost end faces of the opposed slide shafts  62 . Accordingly, when the shafts  51  and  62  of the pantographic support frame are fitted in the bearings  32  and  33 , respectively, the links  5  and  6  tilt toward the keytop  4  through the opening  31  and the shafts  52  and  62  are engaged with the bearings  41  and  42 , respectively. 
     Thus, the formation of the embossed cylindrical protrusions  81  in the frame  13  avoids the necessity for using the embossed sheet, and hence prevents an increase in the number of parts used. 
     EFFECT OF THE INVENTION 
     As described above, according to the present invention, by using the embossed sheet  8  having formed therein the embossed cylindrical protrusions  81  with reduced diameter open ends for holding the flange portions  73  of the domes  7  from above, the domes  7  can be incorporated and held in position very easily in the keyboard assembling process. In the embossed sheet  8  such as a synthetic resin film or metal sheet, there are arranged in matrix form the embossed cylindrical protrusions  81  with reduced diameter open ends in correspondence to the switch portions  20 S. The embossed sheet  8  can be made as thin as 50 to 100 μm, and consequently the keyboard can be made thin. Alternatively, the embossed cylindrical protrusions may be formed in the frame  13 . By inserting each dome  7  through the embossed cylindrical protrusion  81  and the flange part  73  of the dome  7  is held between the reduced diameter open end of the embossed cylindrical protrusion  81  and the frame  13 , the dome  7  cannot readily get out of the embossed cylindrical protrusion  81  with the reduced diameter open end. 
     In the assembling of the keyboard, the cylindrical part  71  of each dome  7 , held downward, is inserted through the embossed cylindrical protrusion  81  of the reduced diameter open end and the dome insertion hole  65  and is engaged with the projection  43  of the keytop  4 , by which the dome  7  is positioned in correspondence to the switch portion  20 S. This can easily be carried out using a known transfer/positioning device that attracts and transfers parts at one time. Accordingly, the number of assembling steps and the time therefor can be reduced as compared with those in the prior art in which a large number of small domes are adhesive bonded to the movable contact sheet. 
     When a defective dome  7  is found in the assembled keyboard, it is taken out by pressing the dome part  72  in its radial direction with a thin metal pin from outside, and a non-defective dome  7  is elastically deformed and pressed into the embossed cylindrical protrusion  81  from above. 
     By forming the embossed cylindrical protrusions  81  in the frame  13 , the number of parts used can be reduced accordingly. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.