Patent Publication Number: US-7718910-B2

Title: Movable contact assembly and switch using the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to a movable contact assembly for configuring an input operation unit for various electronic apparatuses, and a switch including the movable contact assembly. 
     BACKGROUND OF THE INVENTION 
     Key switches having illuminating functions are often used in operating panels mounted to various electronic apparatuses, such as portable telephones and portable data terminals. Such illuminating functions are performed by directly illuminating keys with a light-emitting diode (LED) or by transmitting light from an LED through a light guide sheet. 
       FIG. 4  is a sectional view of switch  501  disclosed in Japanese Laid-Open Patent Publication No. 2007-53063. Central fixed contact  101  and peripheral fixed contact  102  are provided on an upper surface of circuit board  100 . Sheet  110  is attached to the upper surface of circuit board  100  with adhesive layer  111 . Sheet  110  has dome portion  120  protruding upwardly. Movable contact  130  having a dome shape is accommodated in dome portion  120 . A lower surface of the central portion of movable contact  130  faces central fixed contact  101  with a gap between contacts  101  and  130 . An outer edge of movable contact  130  is mounted onto peripheral fixed contact  102 . An upper surface of movable contact  130  is held on dome portion  120  of sheet  110  with adhesive layer  111 . 
     Sheet  110  is a light guide sheet that transmits light incident from a side edge surface, and illuminates the upper surface. 
     Light source  150  is mounted on circuit board  100 . Light source  150  includes light-emitting portion  151  facing the side edge surface of sheet  110  to cause light from light source  150  to enter in parallel with sheet  110  made of a light guide sheet. Transparent resin  160  collects light from light-emitting portion  151 , and introduces the light efficiently onto the side edge surface of sheet  110 . 
     An operation of conventional switch  501  will be described below. 
     As a pressing force is applied to movable contact  130  from above dome portion  120  of sheet  110 , the force reverses the dome shape of movable contact  130  when the force exceeds a predetermined level. Then, movable contact  130  contacts central fixed contact  101 , thereby connecting central fixed contact  101  electrically with peripheral fixed contact  102 . And, when the force is released, movable contact  130  returns to have its original dome shape shown in  FIG. 4 , thereby electrically disconnecting central fixed contact  101  from peripheral fixed contact  102 . 
     When light source  150  emits light, the light enters through the side edge surface of sheet  110 , the light guide sheet. The light is introduced into sheet  110  including dome portion  120 , and illuminates the upper surface of sheet  110 . Dome portion  120  covers movable contact  130  along the upper surface of movable contact  130 . A key made of light-transmissible material and having a mark, such as characters or symbols, may be provided on sheet  110 . This structure provides switch  501  which is operated easily even in the dark, in which the key is activated, and the mark is visibly recognized. 
     In switch  501 , sheet  110 , the light guide sheet, has a shape along the dome shape of movable contact  130 . The light guide sheet having the light entering the side edge surface thereof may preferably thick so as to accept the light easily. For example, the sheet may often have a thickness of about 0.2 mm. However, if sheet  110 , the light guide sheet, has the thickness of 0.2 mm, an excessive force is required due to a stress of sheet  110  when depressing movable contact  130 , accordingly preventing switch  501  from being activated easily. 
     SUMMARY OF THE INVENTION 
     A movable contact assembly includes a movable contact having a dome shape, a base sheet contacting an upper surface of the movable contact, a columnar portion provided on an upper surface of the base sheet, and a light guide sheet provided on an upper surface of the columnar portion. The light guide sheet has a light-receiving surface for introducing light into the light guide sheet, and allows the introduced light to be emitted from an upper surface of the light guide sheet. The base sheet includes a dome portion having a concave lower surface, and a flat portion connected with an outer edge of the dome portion. The columnar portion is positioned on the upper surface of the dome portion away from the outer edge of the dome portion of the base sheet. 
     This movable contact assembly provides a switch illuminating its upper surface and being activated easily with a preferable feeling. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is an exploded perspective view of a switch according to an exemplary embodiment of the present invention. 
         FIG. 1B  is an enlarged view of a light guide sheet of the switch according to the embodiment. 
         FIG. 2  is a sectional view of the switch according to the embodiment. 
         FIG. 3  is a sectional view of the switch according to the embodiment. 
         FIG. 4  is a sectional view of a conventional switch. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1A  is an exploded perspective view of switch  1001  according to an exemplary embodiment of the present invention. Plural keys  1  and  201  made of resin, such as polycarbonate, are provided on a primary surface of switch  1001 . Key sheet  2  made of elastic material, such as silicone rubber, is provided under key  1 . Keys  1  and  201  are adhered to key sheet  2  with an adhesive. Keys  1  and  201  and key sheet  2  may be made of the same material and may be formed unitarily with each other. 
     Lower surface  2 B of key sheet  2  is flat. Upper surface  3 A of light guide sheet  3  is situated on lower surface  2 B. Upper surface  3 A of light guide sheet  3  may be adhered to lower surface  2 B of key sheet  2  or may simply contact lower surface  2 B. Light source  51 , such as a light-emitting diode, is coupled to edge surface  3 P of light guide sheet  3 . Edge surface  3 P has light-receiving surface  3 Q for introducing light from light source  51  into light guide sheet  3 . 
     Light guide sheet  3  is made of transparent film made of material, such as acrylic resin, silicone resin, urethane resin, polycarbonate resin, or polyethylene terephthalate (PET) resin, having high light conductivity. 
       FIG. 1B  is an enlarged view of light guide sheet  3 . Portion  3 T of upper surface  3 A of light guide sheet  3  is a rough surface that scatters light entering from the light-receiving surface  3 Q and that efficiently emits the light from portion  3 T of the rough surface out of upper surface  3 A. The rough surface of portion  3 T of upper surface  3 A, the rough surface, may be formed, by, for example, screen-printing, a lot of dots  3 R made of transparent resin. In this case, the brightness of upper surface  3 A of light guide sheet  3  changes depending on the distance from light-receiving surface  3 Q. However, the brightness of upper surface  3 A can be substantially uniform by determining the diameters and density of dots  3 R appropriately. The light transmitting inside light guide sheet  3  scatters to illuminate keys  1  and  201  provided on upper surface  3 A. 
       FIG. 2  is a sectional view of switch  1001 . Base sheet  4  made of an insulating sheet is provided under light guide sheet  3 . Base sheet  4  includes base layer  54  situated on upper surface  4 A and adhesive layer  7  situated on lower surface  4 B. Movable contacts  8  and  208  are bonded to lower surface  4 B of base sheet  4  with adhesive layer  7 . Movable contacts  8  and  208  made of thin metal sheets have circular or elliptical outer edges  8 C and  208 C, respectively. Movable contact  8  protruding upward has a dome shape having convex upper surface  8 A and concave lower surface  8 B. Movable contact  208  protruding upward has a dome shape having convex upper surface  208 A and concave lower surface  208 B. Base sheet  4  includes dome portions  5  and  205  contacting movable contacts  8  and  208 , respectively, and flat portion  55  provided between dome portions  5  and  205 . Dome portions  5  and  205  have concave lower surfaces  5 B and  205 B along convex upper surfaces  8 A and  206 A of movable contacts  8  and  208 , respectively. Dome portions  5  and  205  have upper surfaces  5 A and  205 A and outer edges  5 C and  205 C, respectively. Flat portion  55  is connected with outer edges  5 C and  205 C of dome portions  5  and  205 , and has upper surface  55 A and flat lower surface  55 B. That is, upper surface  4 A of base sheet  4  includes upper surfaces  5 A and  205 A of dome portions  5  and  205 . Lower surface  4 B includes lower surfaces  5 B and  205 B of dome portions  5  and  205  and lower surface  55 B of flat portion  55 . Base sheet  4  having such configuration may be formed by embossing an insulating sheet. 
     Columnar portions  6  and  206  having substantially circular columnar shapes are provided on upper surfaces  5 A and  205 A of dome portions  5  and  205  of base sheet  4 , respectively. Columnar portion  6  has upper surface  6 A and lower surface  6 B situated on upper surface  5 A away from outer edge  5 C of dome portion  5 . Columnar portion  206  has upper surface  206 A and lower surface  206 B situated on upper surface  205 A away from outer edge  205 C of dome portion  205 . Lower surface  6 B of columnar portion  6  is adhered to upper surface  5 A of dome portion  5 . Upper surface  6 A of columnar portion  6  is mounted on lower surface  3 B of light guide sheet  3 . Lower surface  206 B of columnar portion  206  is adhered to upper surface  205 A of dome portion  205  Upper surface  206 A of columnar portion  206  is mounted on upper surface  205 A of dome portion  205 . Light guide sheet  3  has a plate shape. That is, portions  3 C and  3 D of light guide sheet  3  located directly above dome portions  5  and  205  of base sheet  4  are flat. At least portion  3 E of light guide sheet  3  extending from portion  3 C to portion  3 D is flat. Light guide sheet  3  is supported with columnar portions  6  and  206  from beneath at portions  3 C and  3 D. Even before being adhered to lower surface  2 B of key sheet  2 , light guide sheet  3  is attached to base sheet  4  with columnar portions  6  and  206  while maintaining nearly horizontal orientation. Light guide sheet  3 , columnar portions  6  and  206 , movable contacts  8  and  208 , and base sheet  4  constitute movable contact assembly  1002 . As shown in  FIG. 3 , portions of light guide sheet  3  away from columnar portion  6  ( 206 ) may sag, however, it has little or no effect to the operation of the movable contact assembly and the function of the light guide sheet. 
     In movable contact assembly  1002  of switch  1001 , light guide sheet  3  is away from base sheet  4  via columnar portions  6  and  206 , and allows base sheet  4  to mainly have a function for holding movable contacts  8  and  208 , thus allowing base sheet  4  not to guide light. Hence, the thickness of base sheet  4  may be smaller than that of sheet  110  of conventional switch  501  shown in  FIG. 4 , and may be smaller than 0.2 mm, for example, 0.15 mm or preferably smaller than 0.1 mm. 
     Movable contact assembly  1002  is assembled with key sheet  2  and board  9 . As shown in  FIG. 2 , movable contact assembly  1002  is bonded to board  9  with adhesive layer  7  provided on lower surface  4 B of base sheet  4 . Fixed contacts  10 A,  10 B,  210 A, and  210 B are provided on upper surface  9 A of board  9 . Fixed contacts  10 A and  210 A face lower surfaces  8 B and  208 B of movable contacts  8  and  20 , respectively, by gaps between surfaces  10 A and  8 B and between  210 A and  208 A. Fixed contacts  10 B and  210 B contact outer edges  8 C and  208 C of movable contacts  8  and  208  mounted thereon. 
     An operation of switch  1001  will be described below. 
     Key  1  is pressed to apply a pressing force to key  1 , and key sheet  2  having elasticity accordingly sags partially, accordingly causing light guide sheet  3  to sag. Upon light guide sheet  3  sagging, the pressing force is transmitted to movable contact  8  through columnar portion  6 . Upon exceeding a predetermined level, the pressing force reverses the dome shape of movable contact  8  to cause upper surface  8 A and lower surface  8 B to be concave and convex, respectively. This operation allows lower surface  8 B of movable contact  8  to contact fixed contact  10 A, and connects fixed contact  10 A electrically with fixed contact  10 B, thus turning on the switch. The pressing force applied to key  1  is released, and key sheet  2  and base sheet  4  accordingly return to have their original shapes by their elastic force. The shape of movable contact  8  returns to its original shape, thus having convex upper surface  8 A and concave lower surface  8 B. Thereby, lower surface  8 B of movable contact  8  is removed from fixed contact  10 A, thus disconnecting fixed contact  10 A from fixed contact  10 B, thus turning off the switch. 
     Key  201  is pressed to apply a pressing force to key  201 , and key sheet  202  having elasticity accordingly sags partially, accordingly causing light guide sheet  3  to sag. Upon light guide sheet  3  sagging, the pressing force is transmitted to movable contact  208  through columnar portion  206 . Upon exceeding a predetermined level, the pressing force reverses the dome shape of movable contact  208  to cause upper surface  208 A and lower surface  208 B to be concave and convex, respectively. This operation allows lower surface  208 B of movable contact  208  to contact fixed contact  210 A, and connects fixed contact  210 A electrically with fixed contact  210 B, thus turning on the switch. The pressing force applied to key  201  is released, and key sheet  202  and base sheet  4  accordingly return to have their original shapes by their elastic force. The shape of movable contact  208  returns to its original shape, thus having convex upper surface  208 A and concave lower surface  208 B. Thereby, lower surface  208 B of movable contact  208  is removed from fixed contact  210 A, thus disconnecting fixed contact  210 A from fixed contact  210 B, thus turning off the switch. 
     Base sheet  4  covers movable contacts  8  and  208 , hence greatly influencing the reversing of the shapes of movable contacts  8  and  208  due to their elastic deformation. As described above, in switch  1001  in accordance with the embodiment, base sheet  4  can be thinner than conventional sheet  110  shown in  FIG. 4 , accordingly preventing base sheet  4  from affecting the reversing of the shapes of movable contacts  8  and  208 . Light guide sheet  3  needs to have a predetermined thickness in order to allow light to transmit therein. As shown in  FIGS. 2 and 3 , light guide sheet  3  has a flat shape or a shape sagging gently. This configuration allows light to easily transmit inside light guide sheet  3 , hence allowing light guide sheet  3  to be thin. The pressing forces are applied to movable contacts  8  and  208  via columnar portions  6  and  206  located away from outer edges  8 C and  208 C, respectively, and are efficiently transmitted to the centers of movable contacts  8  and  208 , hence reversing the shapes of movable contacts  8  and  208  easily. Columnar portions  6  and  206  contact light guide sheet  3  and base sheet  4  even while keys  1  and  201  are not depressed, an operator feels reaction force via a finger simultaneously upon having the finger pressing of keys  1  and  201 . Hence, the operator can activate switch  1001  with a preferable operation feeling. Columnar portion  6  and  206  are located at the center of movable contacts  8  and  208  away from outer edges  8 C and  208 C of movable contacts  8  and  208 , respectively. This structure allows central portions of upper surfaces  8 A and  208 A of movable contacts  8  and  208  to be pressed, but prevents outer edges  8 C and  208 C from being pressed. Hence, even if the centers of keys  1  and  201  are slightly misaligned from the centers of movable contacts  8  and  208 , the operator can activate switch  1001  with a preferable feeling. 
     Columnar portions  6  and  206 , light guide sheet  3 , and base sheet  4  may be made of resin material unitarily with each other to constitute a module. This structure stably positions columnar portions  6  and  206 , light guide sheet  3 , and base sheet  4 . Columnar portions  6  and  206  may not necessarily be bonded to both of light guide sheet  3  and base sheet  4 , but may preferably be bonded to base sheet  4 . 
     A functional layer for preventing leakage of light from light guide sheet  3  may be provided on lower surface  3 B of light guide sheet  3 . This layer allows strong light to be emitted from upper surface  3 A, accordingly illuminating keys  1  and  201  located above upper surface  3 A of light guide sheet  3  brightly. 
     In switch  1001 , movable switch  8  ( 208 ) and fixed contacts  10 A and  10 B ( 210 A and  210 B) constitute switch contact section. The switch contact section of the switch in accordance with the embodiment is not limited to this. A switch contact section that operates covered with base sheet  4  provides the same effects.