Patent Publication Number: US-7897889-B2

Title: Movable contact element and switch using the same

Description:
FIELD OF THE INVENTION 
     The present invention relates to a movable contact used for operating various electronic apparatuses and a switch using the same. 
     BACKGROUND ART 
     Recently, light emitting diodes or EL elements are mounted in various electronic apparatuses, specifically mobile terminals such as mobile phones. The light emitting diodes or EL elements emit light so as to light an operation portion such that the operation or identification of pushbutton or display sheet is easily performed even when the surrounding is dark. Further, there is demand for a movable contact element and switch which are easy to use and are inexpensive. 
     Such a conventional movable contact element and switch using the same will be described with reference to  FIGS. 5 and 6 . In the drawings, the thicknesses of layers and regions are exaggerated for clarity.  FIG. 5  is a cross-sectional view of a conventional switch.  FIG. 6  is an exploded perspective view of essential parts of the switch. In  FIGS. 5 and 6 , film-shaped light guiding sheet  1 , which is optically transparent and has flexibility, has a light guiding layer  1 A whose top and bottom surfaces are interposed between upper protective layer  1 B and lower protective layer  1 C. A plurality of movable contacts  3 , which are formed in substantially a dome shape and are made of a conductive metal thin plate, are bonded to the bottom surface of light guiding sheet  1  through an adhesive (not shown). Light guiding layer  1 A above movable contact  3  has a plurality of light emitting portions  1 D formed in an irregular shape. In such a manner, movable contact element  4  is constructed. 
     Substrate  5  having a plurality of wiring patterns (not shown) formed on the top and bottom surfaces thereof has a plurality of fixed contacts  6  formed on the top surface thereof, the fixed contacts  6  being composed of circular central fixed contact  6 A and U-shaped outer fixed contacts  6 B surrounding central fixed contact  6 A. The outer circumference of movable contact  3  is placed on outer fixed contacts  6 B such that the center of the bottom surface of movable contact  3  faces central fixed contact  6 A with a predetermined space provided therebetween. A plurality of light emitting elements  7  composed of light emitting diodes and so on are mounted on substrate  5  in the right side of light guiding sheet  1  such that the light emitting surfaces thereof face the right side surface of light guiding layer  1 A of light guiding sheet  1 . Sheet-shaped operation body  8  made of insulating resin is composed of light transmitting portion  8 A and light shielding portion  8 B covering the top surface of light transmitting portion  8 A. On the top surface of a plurality of operation portions  8 C, a display portion  8 D is provided, through which light transmitting portion  8 A is exposed in a character or sign shape. Pressing portion  8 E projecting downward is abutted on the top surface of light guiding sheet  1  at the central portion of movable contact  3 . The conventional switch is constructed in the above-described manner. The switch constructed in such a manner is mounted on the operation surface of an electronic apparatus, central fixed contact  6 A or outer fixed contacts  6 B and light emitting elements  7  are connected to electronic circuits (not shown) of the apparatus through wiring patterns by a connector or lead lines (not shown). 
     In the above-described construction, when predetermined operation portion  8 C of operation body  8  is pressed downward, pressing portion  8 E provided on the bottom surface of operation portion  8 C presses the top surface of light guiding sheet  1 . Then, light guiding sheet  1  is bent to press the substantially dome-shaped central portion of movable contact  3 . When a predetermined pressing force is applied, movable contact  3  is elastically inverted downward with a click feeling such that the center of the bottom surface of movable contact  3  comes in contact with central fixed contact  6 A. Then, central fixed contact  6 A and outer fixed contacts  6 B are electrically connected through movable contact  3 . 
     When the pressing force applied to the operation portion  8 C is released, movable contact  3  is elastically inverted upward by an elastic restoring force, and the center of the bottom surface is separated from central fixed contact  6 A such that central fixed contact  6 A is electrically disconnected from outer fixed contacts  6 B. 
     Further, depending on the electrical connection and disconnection of fixed contact  6 , the switching of the respective functions in the apparatus is performed. Further, when a voltage is applied to light emitting element  7  from an electric circuit of the apparatus, light emitting element  7  emits light. The light is incident on light guiding layer  1 A from the right side surface of light guiding sheet  1  such that the entire body of light guiding layer  1 A is lighted. The light is reflected by light emitting portions  1 D within light guiding layer  1 A, which are formed in an irregular shape. Further, light emitting portions  1 D emit light. Then, the light passes through upper protective layer  1 B so as to light display portion  8 D of operation body  8  from the lower side. Therefore, even when the surrounding is dark, the display of characters or signs of operation portion  8 C can be recognized, which makes it easy to perform an operation. Further, as a prior art document relating to the invention, Japanese Patent Unexamined Publication No. 2006-318905 is known. 
     In the conventional movable contact and the switch using the same, light from light emitting element  7  is distributed on the entire portion of light guiding layer  1 A of light guiding sheet  1  such that the plurality of display portions  8 D of operation portion  8  are lighted. However, light emitting portions  1 D distant from light emitting element  7  become so dark that unevenness occurs in the lighting. To reduce the unevenness and perform uniform lighting, a large number of lighting elements  7  need to be disposed around light guiding sheet  1 . Then, the construction of the switch becomes complicated, and the price thereof increases. 
     SUMMARY OF THE INVENTION 
     An advantage of the present invention is that it provides a movable contact element which has a predetermined space formed between a lower sheet having a bottom surface to which a substantially dome-shaped movable contact made of a conductive thin metal plate is bonded and an optically-reflexive upper sheet disposed above the lower sheet. Further, light transmitting portions are provided in the upper sheet above the movable contact. When a switch is formed, light from a light emitting element is vertically reflected in the space between the upper sheet and the lower sheet both of which have light reflection properties, and lighting is performed through the light transmitting portions. Therefore, uniform lighting without unevenness can be performed by one or two light emitting elements. That is, it is possible to obtain a movable contact element whose construction is simple and the price is low. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a switch according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of essential parts of the switch according to the embodiment of the invention; 
         FIG. 3  is a cross-sectional view of a movable contact element of the switch according to the embodiment of the invention; 
         FIG. 4  is an expanded cross-sectional view of the switch according to the embodiment of the invention; 
         FIG. 5  is a cross-sectional view of a conventional switch; and 
         FIG. 6  is an exploded perspective view of essential parts of the conventional switch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will now be described with reference to  FIGS. 1 to 4 . In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Further, like reference numerals will be attached to the same components as those described in Background Art, and the detailed descriptions thereof will be omitted. 
     Embodiment 
       FIG. 1  is a cross-sectional view of a switch according to an embodiment of the invention.  FIG. 2  is an exploded perspective view of essential parts of the switch. In  FIGS. 1 and 2 , optically-transparent lower sheet  11  composed of polyethylene terephthalate or polycarbonate is formed in a film shape with a thickness of about 5 to 200 μm, preferably, about 25 to 100 μm. On the bottom surface of lower sheet  11 , light reflection layer  11 A obtained by dispersing scale-shaped aluminum or silver into transparent resin such as polyester or epoxy is printed with a thickness of about 0.1 to 10 μm. Movable contact  3  is made of a conductive thin metal plate, such as a copper alloy or silver, which is formed in substantially a dome shape. The plurality of movable contacts  3  are bonded to the bottom surface of lower sheet  11  through an adhesive (not shown) such as acrylic resin, silicon, or butyl rubber. On the top surface of lower sheet  11  above movable contact  3 , light diffusion layer  11 B obtained by dispersing white pigment or hollow glass beads into transparent resin is printed. 
     Similar to lower sheet  11 , optically-transparent upper sheet  12  has light reflection layer  12 A printed on the top surface thereof. On the top surface of lower sheet  11 , a plurality of dot spacers  13  composed of polyester or epoxy are formed at the outer circumference of movable contact  3  such that upper sheet  12  is disposed above lower sheet  11  with a space of about 10 to 200 μm formed therebetween. 
     Light reflection layer  12 A of upper sheet  12  above movable contact  3  has a plurality of hole-shaped light transmitting portions  12 B formed therein, light transmitting portions  12 B being spaced at a distance of about 0.5 mm from each other and having a diameter of about 0.1 to 0.5 mm. 
     In the vicinity of light transmitting portions  12 B, upper sheet  12  is swollen upward, while the thickness thereof is maintained as it is. A portion of lower sheet  11  corresponding to the swollen portion of upper sheet  12  is swollen upward, while the thickness thereof is maintained as it is. In such a manner, movable contact element  14  is constructed. 
       FIG. 3  is a cross-sectional view of the movable contact element. As shown in  FIG. 3 , film-shaped separator  15  composed of polyethylene terephthalate or paper is bonded to the bottom surface of lower sheet  11  in movable contact element  14 , and the bottom surface of movable contact  3  is covered by separator  15 . Therefore, storage and transport are performed in such a manner that dust and oil does not adhere to movable contact  3 . 
     In  FIG. 1 , substrate  5  is formed of a film which is composed of polyethylene terephthalate or polycarbonate, or is formed of a plate which is composed of paper phenol or glass-containing epoxy. Substrate  5  has a plurality of wiring patterns (not shown) formed on the top and bottom surfaces thereof, the wiring patterns being composed of copper. Further, substrate  5  has a plurality of fixed contacts  6  provided thereon, fixed contacts  6  being composed of substantially circular central fixed contact  6 A and U-shaped outer fixed contacts  6 B surrounding central fixed contact  6 A. Fixed contacts  6  are composed of copper or carbon. On the top surface of substrate  5 , movable contact element  14  from which separator  15  is peeled off is loaded in such a manner that the outer circumference of each movable contact  3  is placed on outer fixed contacts  6 B. Further, movable contact element  14  is bonded in such a manner that the center of the bottom surface thereof faces central fixed contact  6 A with a predetermined space provided therebetween. Light emitting element  7  such as a light emitting diode or the like is mounted on substrate  5  in the right side of movable contact element  14 , and is disposed in such a manner that the light emitting surface thereof faces the space between upper and lower sheets  12  and  11 . Sheet-shaped operation body  8  made of insulating resin is composed of light transmitting portion  8 A and light shielding portion  8 B covering the top surface of light transmitting portion  8 A. On the top surface of a plurality of operation portions  8 C, display portion  8 D through which light transmitting portion  8 A is exposed in a character or sign shape is provided. Further, pressing portion  8 E projecting downward is abutted on the top surface of upper sheet  12  in the center of movable contact  3 . The switch is constructed in the above-described manner. 
     The switch constructed in such a manner is mounted on the operation surface of an electronic apparatus, and central fixed contact  6 A or outer fixed contacts  6 B and light emitting element  7  are connected to electric circuits (not shown) of the electronic apparatus through the wiring patterns by a connector or lead lines (not shown). 
     In above-described construction, when predetermined operation portion  8 C of operation body  8  is pressed downward, pressing portion  8 E formed on the bottom surface of operation portion  8 C presses the top surface of upper sheet  12 . Then, upper and lower sheets  12  and  11  are bent to press the substantially dome-shaped central portion of movable contact  3 . When a predetermined pressing force is applied, movable contact  3  is elastically inverted downward with a click feeling such that the center of the bottom surface of movable contact  3  comes in contact with central fixed contact  6 A. Then, central fixed contact  6 A and outer fixed contacts  6 B are electrically connected through movable contact  3 . 
     When the pressing force applied to the operation portion  8 C is released, movable contact  3  is elastically inverted upward by an elastic restoring force, and the center of the bottom surface thereof is separated from central fixed contact  6 A such that central fixed contact  6 A and outer fixed contacts  6 B are electrically disconnected. 
     Depending on the electrical connection and disconnection of fixed contact  6 , the switching of the respective functions of the apparatus is performed. Further, when a voltage is applied to light emitting element  7  from an electric circuit of the apparatus, light emitting element  7  emits light. The light is incident on the space between upper and lower sheets  12  and  11  of movable contact element  14 .  FIG. 4  is an expanded cross-sectional view of the switch when the light is incident on the space. As shown in  FIG. 4 , the light propagates straight in the space. Alternately, the light propagates through the space while being reflected by light reflection layer  11 A provided on the bottom surface of lower sheet  11  or light reflection layer  12 A provided on the top surface of upper sheet  12 . 
     As the lights are irregularly reflected by light diffusion layer  11 B, the lights are further diffused so as to be emitted from the plurality of hole-shaped light transmitting portions  12 B. Then, display portion  8 D of operation body  8  is lighted by the lights from the lower side. Therefore, even when the surrounding is dark, the display of characters or signs on operation portion  8 C can be recognized, which makes it easy to perform an operation. 
     Since upper and lower sheets  12  and  11  are swollen upward in the vicinity of light transmitting portion  12 B, light easily collides with lower sheet  11  at corresponding light transmitting portion  12 B. Therefore, the light colliding with lower sheet  11  is more effectively emitted upward from light transmitting portion  12 B. 
     At this time, the light from light emitting element  7  does not propagate through a film such as polyethylene terephthalate or a layer such as polyester resin whose refractive index is high, but propagates straight in the space between upper and lower sheets  12  and  11 , that is, in the air whose refractive index is low. Alternately, the light propagates while being reflected in a vertical direction by light reflection layer  11 A or  12 A. Therefore, the degradation of brightness is small. In other words, the absorption of light is so small that the light can propagate a long way without any loss. Therefore, display portion  8 D located at a place separated from light emitting element  7  can be brightly lighted without unevenness. 
     In this embodiment, the space is formed between upper and lower sheets  12  and  11  with a light reflection property, and light from light emitting element  7  is reflected in the space. Further, the reflected light is guided upward from light transmitting portion  12 B. Therefore, uniform lighting without unevenness can be performed with respect to the plurality of display portions  8 D by a simple unit using one or two light emitting elements  7 . 
     Further, although lower sheet  11  is replaced with a typical optically-transparent sheet with no reflection film, light is reflected by the sheet to some degree. As described above, however, light reflection layer  11 A is provided on the bottom surface of lower sheet  11 , and both upper and lower sheets  12  and  11  are formed to have a light reflection property. Then, it is possible to perform brighter lighting without unevenness. 
     As shown in  FIG. 2 , light transmitting portions  12 B with a small number of holes are provided at a place close to light emitting element  7 , and light transmitting portions  12 C with a large number of holes are provided at a place which is separated from light emitting element  7  and in which light becomes weak. Therefore, the area of the light transmitting portion from which light is emitted, that is, the brightness of lighting can be varied, so that the plurality of display portions  8 D of operation body  8  can be lighted at uniform brightness without unevenness. 
     Further, when the end portions of lower sheet  11  and upper sheet  12  excluding the places on which light from light emitting element  7  is incident are bonded and sealed by an adhesive or thermal compression bonding, the light can be prevented from leaking to the outside. Therefore, it is possible to perform brighter and more uniform lighting. 
     In this embodiment, the predetermined space is formed between lower sheet  11  to which substantially dome-shaped movable contact  3  made of a conductive thin metal plate is bonded and light-reflecting upper sheet  12  disposed above lower sheet  11 . Further, light transmitting portions  12 B are provided in upper sheet  12  above movable contact  3 . Accordingly, light from light emitting element  7  propagates through the space between upper and lower sheets  12  and  11  with a light reflection property while being reflected in a vertical direction, and lighting is performed through light transmitting portions  12 B. Therefore, the lighting can be performed by one or two light emitting elements without unevenness. Simultaneously, it is possible to obtain an inexpensive movable contact element with a simple structure and a switch using the movable contact element. 
     In this embodiment, it has been described that light reflection layers  11 A and  12 A are printed on the bottom surface of lower sheet  11  and the top surface of upper sheet  12 , respectively. However, although the respective sheets are plated with aluminum, silver, or copper such that upper and lower sheets  12  and  11  has a light reflection property, the embodiment of the invention can be implemented. When light reflection layer  11 A or  12 A is provided by the plating, a light reflection layer may be formed on the top surface of lower sheet  11  or the bottom surface of upper sheet  12 , reverse to the above-described construction. In this case, since the respective sheets also have a light reflection property, it is possible to obtain the same operation and effect. 
     Instead of light reflection layer  11 A or  12 A, white pigment or dye may be dispersed into lower or upper sheet  11  or  12  such that lower or upper sheet  11  or  12  has a light reflection property, even though brightness is reduced. 
     In the above embodiment, it has been described that the plurality of dot spacers  13  are provided on the top surface of lower sheet  11  at the outer circumference of movable contact  3  such that the predetermined space is formed between lower sheet  11  and upper sheet  12 . However, although the plurality of dot spacers  13  is provided on the bottom surface of upper sheet  12 , the embodiment of the invention can be implemented. Further, the plurality of dot spacers  13  may be formed on the top surface of lower sheet  11  or the bottom surface of upper sheet  12  above movable contact  3  such that a space is provided therebetween. 
     The movable contact element and the switch using the same according to the invention can perform uniform lighting without unevenness and can be utilized for operating various electronic apparatuses with simple arrangement. Further, the movable contact element and the switch can be manufactured at a low cost.