Patent Publication Number: US-6906275-B2

Title: Movable contact unit, panel switch using the same and electronic equipment having the panel switch

Description:
FIELD OF THE INVENTION 
   The present invention relates to a movable contact unit having a plurality of push switches used in operation section of downsized electronic equipment such as cellular phone and the like, panel switch using the movable contact units and electronic equipment having the panel switch. 
   BACKGROUND OF THE INVENTION 
   Nowadays, along with the advance of performance and diversity of downsized electronic equipment such as cellular phones and the like, panel switch having a plurality of arranged push switches and mainly used in operation section of them is required to have high accuracy and usability as well as cheap prices. 
   A conventional movable contact unit for push switches used in operation section of downsized electronic equipment and a panel switch using the movable contact units are described with reference to FIG.  10  through FIG.  13 . Here, perpendicular scale in each drawing is drawn enlarged for easy understanding. 
     FIG. 10  shows a cross-sectional front view of a conventional movable contact unit,  FIG. 11  shows an exploded perspective view of the conventional movable contact unit. In  FIG. 11 , movable contact  1  formed from a resilient thin metal sheet has a dome shape and base sheet  2  formed from a flexible insulation substrate has a plurality of through holes  2 A in predetermined positions. Movable contact  1  is placed in each through hole  2 A of base sheet  2 . Cover sheet  3  formed from a flexible insulation substrate and coated with adhesive material  3 A on bottom surface is bonded on individual convex upper surface of movable contact  1  and is fixed on base sheet  2  to form a movable contact unit  4  having a plurality of push switches. 
     FIG. 12  shows a cross-sectional front view of a panel switch using an above mentioned conventional movable contact unit, and  FIG. 13  shows an exploded perspective view of the panel switch. In  FIG. 13 , stationary contact substrate  5  has a plurality of stationary contact  7  consisted of central stationary contact  7 A and peripheral stationary contact  7 B on predetermined positions of hard plate-like insulation board  6 . Peripheral edge of each movable contact  1  of movable contact unit  4  is placed on corresponding peripheral stationary contact  7 B such that convex bottom surface of movable contact  1  faces each central stationary contact  7 A, basing on small hole  5 A of substrate  5  and small hole  2 B of base sheet  2  for positioning, to form panel switch  8  having a plurality of arranged push switches. 
   Panel switch  8  mentioned above is mounted on an operation section of electronic equipment. When convex upper surface of a movable contact  1  is depressed by operation button (not shown) through cover sheet  3 , convex bottom surface of movable contact  1  performs resilient motion with a click feeling to connect central stationary contact. Then, central stationary contact  7 A of stationary contact substrate  5  and outside stationary contact  7 B are electrically coupled to make a push switch ON stage. Upon release of depression from operation button, a resilient restoring force of movable contact  1  acts to disconnect convex bottom surface from central stationary contact  7 A to return to push switch OFF stage as shown in FIG.  12 . 
   However, in above mentioned conventional movable contact unit  4  and panel switch using the movable contact unit, ingress of dust between movable contact unit  4  and stationary contact substrate  5  moves in between movable contact  1  and stationary contact  7  to cause problems of loose connection in push switch of panel switch, during use of electronic equipment incorporated with panel switch having a combination of movable contact unit  4  and stationary contact substrate  5 . 
   SUMMARY OF THE INVENTION 
   A movable contact unit disclosed in this invention comprises:
     (a) a base sheet formed from a flexible insulation substrate having a plurality of through holes in predetermined positions;   (b) a plurality of movable contacts placed freely in vertical motion in respective through holes of the base sheet;   (c) a cover sheet formed from a flexible insulation substrate and bonded on upper surface of the base sheet, using adhesive coated on bottom surface of the cover sheet, to hold respective movable contacts in predetermined positions in the through holes of the base sheet; and   (d) a weak adhesive layer applied on bottom surface of the base sheet except the through holes.   

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a cross-sectional front view of a movable contact unit used in a first preferred embodiment of the present invention. 
       FIG. 2  is an exploded perspective view of a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 3A  is a cross-sectional schematic view for a manufacturing method of a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 3B  is a cross-sectional schematic view for a forming method of a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 4  is a bottom view of a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 5  is a cross-sectional front view of a panel switch using a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 6  is an exploded perspective view of a panel switch using a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 7  is a partially cross-sectional front view of an electric equipment having a panel switch using a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 8  is a partially cross-sectional front view of another example of electric equipment having a panel switch used in the first preferred embodiment of the present invention. 
       FIG. 9  is an appearance view of a movable contact unit used in the first preferred embodiment of the present invention. 
       FIG. 10  is a cross-sectional front view of a conventional movable contact unit. 
       FIG. 11  is an exploded perspective view of a conventional movable contact unit. 
       FIG. 12  is a cross-sectional front view of a panel switch using a conventional movable contact unit. 
       FIG. 13  is an exploded perspective view of a panel switch using a conventional movable contact unit. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention is described by following preferred embodiments with reference to FIG.  1  through FIG.  9 . Here, perpendicular scale in each drawing is drawn enlarged for easy understanding and the similar configuration described in the conventional art have the same reference marks and the detailed descriptions thereof are simplified. 
   First Preferred Embodiment 
     FIG. 1  is a cross-sectional front view of a movable contact unit used in the first preferred embodiment of the present invention and  FIG. 2  is an exploded perspective view of the movable contact unit. 
   In  FIG. 2 , movable contact  1  formed from a resilient thin metal sheet has a round dome shape and base sheet  2  formed from a flexible insulation substrate has a plurality of through holes  2 A in predetermined positions. Movable contacts  1  are placed freely in vertical motion in respective through holes  2 A of base sheet  2 . Cover sheet  3  formed from a flexible insulation substrate and coated with adhesive material  3 A on bottom surface is bonded on individual convex upper surface of movable contact  1  to secure movable contact  1  on upper surface of base sheet  2 . 
   The above mentioned configuration is the same as conventional art but movable contact unit  10  used in the first preferred embodiment for panel switch having a plurality of push switches is provided with weak adhesive layer  9  on bottom surface of base sheet  2  except through holes  2 A. 
   A manufacturing method of movable contact unit  10  having weak adhesive layer  9  is described with reference to cross-sectional view shown in FIG.  3 . 
   First, whole bottom surface of flexible insulation substrate  11  of base sheet  2  is coated with a weak adhesive material to form weak adhesive layer  9  on the surface as shown in FIG.  3 A. 
   In addition, a combination of flexible insulation substrate  11  and second flexible insulation substrate  12 , thinner than flexible insulation substrate  11 , bonded under weak adhesive layer  9  is die-punched to provide a plurality of through holes  2 A in predetermined positions. 
   After the above processing, movable contacts  1  are placed on every through hole  2 A from upper side of flexible insulation substrate  11 , corresponds to base sheet  2  as shown in FIG.  3 B. 
   Then, cover sheet  3  formed from a flexible insulation substrate and coated with adhesive material  3 A on bottom surface is bonded on individual convex upper surface of movable contact  1  to hold movable contact  1 , then cover sheet  3  is fixed on upper surface of base sheet  2 . 
   Finally, second flexible insulation substrate  12  is peeled off from bottom surface of weak adhesive layer  9  to form a movable contact unit  10  having weak adhesive layer  9 . 
   Here, weak adhesive material coated on bottom surface of flexible insulation substrate  11  contains a higher ratio of hardener to base resin compared with ordinary adhesive materials. Moreover, coating thickness of 5 to 10 □m for weak adhesive layer  9  is approx. one third of typical adhesive coating thickness. Bonded substrate can be peeled off easily without any damage on the surface, as peeling-off strength from weak adhesive layer  9  formed as mentioned above is of the order of approx. 100 gf/25 mm that is about one tenth for typical adhesives. 
   In addition, in above mentioned manufacturing method, through holes  2 A provided on base sheet  2  are punched out in larger size than outer diameter of round dome shaped movable contact  1  as shown in a bottom view of movable contact unit in FIG.  4 . 
   Movable contact  1  is fixed by cover sheet  3  to keep a certain gap around movable contact  1  from inside diameter of through hole  2 A, correspond to weak adhesive layer  9  (shown in hatching in the drawing). 
   Consequently, movable contact unit  10  can perform with an acceptable click feeling by depressing operation, as weak adhesive layer  9  does not influence round dome shaped movable contact  1 . 
   Moreover, cover sheet  3  may not be applied individually as mentioned above, but can be a single sheet for fixing a plurality of neighboring movable contacts all together. 
   Additionally, if weak adhesive layer  9  is applied keeping a certain gap left from circumference of through hole  2 A, adhesive layer  9  affects on movable contact  1  far less than conventional art. 
     FIG. 5  is a cross-sectional front view of a panel switch using above mentioned movable contact unit  10 , and  FIG. 6  is an exploded perspective view of the panel switch. In  FIG. 6 , stationary contact substrate  5  has a plurality of stationary contact  7  consisted of central stationary contact  7 A and peripheral stationary contact  7 B on predetermined positions of hard plate-like insulation board  6 : that is similar to conventional art. 
   Peripheral edge of each movable contact  1  of movable contact unit  4  is placed on corresponding peripheral stationary contact  7 B such that convex bottom surface of movable contact  1  faces each central stationary contact  7 A with a certain gap. 
   Basing on small hole  5 A of substrate  5  and small hole  2 B of base sheet  2  for positioning, movable contact unit  10  is stacked on stationary contact substrate  5  and is bonded together using weak adhesive layer  9  applied on bottom surface of base sheet  2  of movable contact unit  10  to form panel switch  13  having a plurality of arranged push switches. 
   Namely, operation of panel switch  13  to depress convex upper surface of round dome shaped movable contact  1  through cover sheet  3  is the same as conventional art, but ingress of dust between base sheet  2  and stationary contact substrate  5  is prevented, as bottom surface of base sheet  2  of movable contact unit  10  and stationary contact substrate  5  is bonded together using weak adhesive layer  9 . 
   In addition, even if ingress of dust between the two occurred, dust can not move further, which contributes to little occurrence of loose connection of push switch, and movable contact  1  performs a steady resilient action, as a steady positioning of each movable contact  1  and corresponding each stationary contact  7  is maintained. 
   Moreover, weak adhesive layer  9  to bond movable contact unit  10  with stationary contact substrate  5  together has a weak peeling-off strength as afore-mentioned, the same as conventional art without any weak adhesive layer  9 , in case of, for example, combination change of movable contact unit  10  and stationary contact substrate  5 , if necessary, movable contact unit  10  can be peeled off easily from bonded stationary contact substrate without any damage and both can be reused. 
   Next,  FIG. 7  is a partially cross-sectional front view of a downsized electric equipment having a panel switch used in the first preferred embodiment. 
   As shown in  FIG. 7 , a plurality of operation buttons  14  formed from resilient insulation material and capable of free vertical motion exposes from upper housing  15 A, which performs as an operation section of the electric equipment. A panel switch is fixed on fixing member  16  placed surroundings of a plurality of operation button  14  using double-faced member  17 . Convex upper surface of each movable contact  1  of movable contact unit  10  touches bottom portion of each operation button  14  through cover sheet  3   
   Additionally, bonded stationary contact substrate  5  using weak adhesive layer  9  applied on bottom surface of base sheet  2  of movable contact unit  10  plays also a role of circuit board  18  for the electric equipment held in bottom side housing  15 B. Namely, central stationary contact  7 A and peripheral stationary contact  7 B of each stationary contact  7  are mounted on upper surface of circuit board  18  directly. 
   Electric equipment with above configuration performs with steady operation condition and with little occurrence of loose connection in push switches of operation section due to a good dust-proof property as well as low machine profile and cheep prices. Moreover, movable contact unit  10  can be peeled off easily from circuit board  18  which acts as stationary contact substrate, together with weak adhesive layer  9 , to exchange operation button  14  or fixing member  16  for a modification of operation section design of electronic equipment. 
   Second Preferred Embodiment 
     FIG. 8  is a partially cross-sectional front view of a downsized electric equipment having a panel switch used in the second preferred embodiment of the present invention. As shown in  FIG. 8 , the electric equipment comprises LCD (liquid crystal display) unit  20  exposed from upper side housing  19 A, light guide  21  secured on bottom surface of the housing, and display section  23  having light source  22  disposed at surrounding sides of the display section. Transparent protective lens  24  is mounted on upper surface of LCD display unit  20 . 
   In addition, extension section  26 A extended from base sheet  26  of movable contact unit  25  of the panel switch is provided at the bottom surface side of light guide  21 , and is bonded on circuit board  28  of the electric equipment with weak adhesive layer  27  coated on bottom surface, to mount the extension section such that contacts bottom surface of light guide  21 . 
   Movable contact unit  25  has an extended section of a predetermined length in one end of base sheet  26  consisted of whitish flexible insulation substrate with weak adhesive layer  27  coated on bottom surface as shown in an appearance view in FIG.  9 . Extension section  26 A is bonded flatly on plate-like circuit board  28  to act a light reflector for light guide  21 . 
   The invention thus contributes a development of electronic equipment having brighter and steadier display section  23  with cheaper cost prices. 
   According to the above, as the bottom surface of base sheet of movable contact unit is bonded stationary contact substrate using weak adhesive layer, not only the ingress of dust between movable contact unit and stationary contact substrate is prevented but the dust, even if entered, is difficult to move further, which contributes to little occurrence of loose connection of push switch and to keep a steady positioning of each movable contact and corresponding each stationary contact. 
   Moreover, the movable contact unit has an advantageous capability of peeling movable contact unit off from bonded stationary contact substrate easily and without any damage.