Patent Publication Number: US-2010118560-A1

Title: Capacitance-type sensor

Description:
CLAIM OF PRIORITY 
     This application is a Continuation of International Application No. PCT/JP2008/063877 filed on Aug. 1, 2008, which claims benefit of the Japanese Patent Application No. 2007-205142 filed on Aug. 7, 2007, both of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a capacitance-type sensor integral with a light guide, the sensor having a sensor function and a light guide function. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publications Nos. 2006-164672 and 2007-068173 disclose techniques related to the present invention. 
     Japanese Unexamined Patent Application Publication No. 2006-164672 discloses an apparatus in which a capacitance-type sensor is attached to a light guide. In this apparatus, light emitted from light sources illuminates a mirror from the back side through the light guide. At the same time, the capacitance-type sensor detects a human body and turns on and off the light sources. Specifically, when a human body approaches the capacitance-type sensor, the sensor detects it and switches the operation mode of the light sources. Thus, the mirror is illuminated from the back side and the front side of the mirror is lit up brightly. 
     Japanese Unexamined Patent Application Publication No. 2007-068173 discloses a technique related to an electronic device including a light guide and having an illuminating function. In this electronic device, light emitting parts are inserted in their corresponding accommodating parts formed in the light guide. Light emitted from the light emitting parts propagates along the light guide and is guided by light guiding parts formed in a touch pad. Then, the light illuminates various touch keys on a main body. 
     The apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2006-164672 has a configuration in which the light guide and the capacitance-type sensor are produced separately. Therefore, it is difficult to reduce costs involved in manufacturing the apparatus. 
     Also, in the apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2006-164672, an electrode constituting the capacitance-type sensor has a planar shape. This poses no problem as long as a securing surface, such as a mirror, to which the capacitance-type sensor is secured is flat. However, if the securing surface is a curved surface, it is difficult to attach the capacitance-type sensor to the securing surface. That is, an unnecessary gap is created between the electrode surface and the curved surface. This reduces the capacitance of the capacitance-type sensor and makes it difficult to achieve high detection accuracy. 
     The present invention has been made to solve the problems described above. The present invention provides a capacitance-type sensor that makes it possible to reduce costs by reducing the number of components, and is capable of providing high detection accuracy. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the present invention, a capacitance-type sensor includes a light guide and a plurality of electrodes integrally formed on one surface of the light guide. The capacitance-type sensor detects a capacitance formed between an object approaching the other surface of the light guide and any of the electrodes. 
     Since the electrodes of the capacitance-type sensor are integrally formed on the light guide, it is possible to reduce manufacturing costs. At the same time, the capacitance-type sensor can be easily attached to the inside of an electronic device. 
     For example, the light guide may have a curved portion, and the electrodes may be formed on an inner surface of the curved portion. 
     Since this can prevent easy creation of an unnecessary gap (air space) between the electrodes and the curved portion of the light guide, it is possible to maintain high detection accuracy of the capacitance-type sensor. 
     It is preferable that the light guide be disposed on a substrate having a plurality of light sources thereon, and be positioned such that light emitted from the light sources enters the light guide. 
     With this configuration, light emitted from the light sources can be efficiently guided into the light guide. 
     It is preferable that the other surface of the light guide, the other surface not having the electrodes thereon, be provided with a resin layer to be in close contact with an outer case of an electronic device to which the light guide is to be attached. 
     This configuration ensures close contact between the light guide and the outer case and prevents an air space from being created therebetween. Thus, it is possible to prevent sensitivity of the capacitance-type sensor from being degraded, and prevent a loss of light caused by a difference in refractive index. 
     It is preferable that the resin layer contain a light diffusing agent or a fluorescent agent. 
     This makes it possible to diffuse light or the like and thus to prevent unevenness of light (formation of hot spots). Therefore, for example, it is possible to evenly illuminate the outer case. 
     It is preferable that the light guide have a plurality of hooking portions for securing the light guide to the substrate, and that the substrate have a plurality of contacts in contact with their corresponding electrodes and a plurality of hooked portions hooked with their corresponding hooking portions. It is then preferable that when the hooking portions are hooked with their corresponding hooked portions, the contacts be connected to their corresponding electrodes and the light sources be positioned opposite their corresponding incident portions of the light guide. 
     With this configuration, the capacitance-type sensor integral with the light guide can be easily attached to the electronic device. Additionally, the light sources can be placed opposite their corresponding incident portions simultaneously with connecting the connectors to their corresponding connection electrodes. 
     According to an embodiment of the present invention, since the electrodes of the capacitance-type sensor are formed on the light guide, it is possible to reduce the number of components and manufacturing costs. 
     It has been conventionally difficult to form electrodes at a corner and a curved portion of a light guide. According to an embodiment of the present invention, however, electrodes can be formed at such portions of the light guide with high accuracy. It is thus possible to improve the degree of design freedom. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view partially illustrating a configuration of an electronic device including a capacitance-type sensor integral with a light guide, according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the capacitance-type sensor. 
         FIG. 3  is a perspective view of a substrate and the capacitance-type sensor as viewed from a direction different from that in  FIG. 2 . 
         FIG. 4A  and  FIG. 4B  are cross-sectional views of a connector connected to the capacitance-type sensor.  FIG. 4A  is a cross-sectional view illustrating a state in which the connector is brought into contact with the capacitance-type sensor.  FIG. 4B  is a cross-sectional view illustrating a state after the connector is connected to the capacitance-type sensor. 
         FIG. 5A  to  FIG. 5C  illustrate steps of manufacturing the capacitance-type sensor using an in-mold process. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a cross-sectional view partially illustrating a configuration of an electronic device including a capacitance-type sensor integral with a light guide, according to an embodiment of the present invention.  FIG. 2  is a perspective view of the capacitance-type sensor.  FIG. 3  is a perspective view of a substrate and the capacitance-type sensor as viewed from a direction different from that in  FIG. 2 .  FIG. 4A  and  FIG. 4B  are cross-sectional views of a connector connected to the capacitance-type sensor.  FIG. 4A  is a cross-sectional view illustrating a state in which the connector is brought into contact with the capacitance-type sensor.  FIG. 4B  is a cross-sectional view illustrating a state after the connector is connected to the capacitance-type sensor. Note that the illustration of an outer case is omitted in  FIG. 2  and  FIG. 3 . 
     Examples of the electronic device illustrated in  FIG. 1  include, but are not limited to, a mobile phone, an electronic dictionary, and a portable music player. A capacitance-type sensor  10  (hereinafter simply referred to as “sensor”) according to an embodiment of the present invention is attached to such an electronic device. 
     As illustrated in  FIG. 2  and  FIG. 3 , the sensor  10  has a light guide  11  serving as a base. The light guide  11  is made of transparent resin material, such as acryl or polycarbonate. A plurality of detection electrodes  12 , connection electrodes  13 , and wires  14  for connections between the detection electrodes  12  and their corresponding connection electrodes  13  are disposed on an inner surface  11 B of the light guide  11  (i.e., on a lower surface of the light guide  11  in the Z 2  direction of the drawings). The detection electrodes  12  are electrodes having a predetermined area. The detection electrodes  12  are provided for forming a capacitance between themselves and an object, such as a human body. 
     The detection electrodes  12 , the connection electrodes  13 , and the wires  14  are formed on the inner surface  11 B of the light guide  11 , in particular, on an inner surface of a curved portion  11 C of the light guide  11  by using, for example, an in-mold transfer process (described in detail below). The in-mold transfer process flexibly deals with a non-planar light guide, such as the light guide  11  of  FIG. 2 , and makes it possible to form detection electrodes on an uneven surface and a corner of the light guide with high accuracy. 
     Therefore, during formation of the detection electrodes  12  on the light guide  11 , it is possible to prevent creation of an unnecessary gap (air space) between the lower surface  11 B or curved portion  11 C of the light guide  11  and the detection electrodes  12 . Thus, a capacitance formed by the detection electrodes  12  can be stabilized. 
     The sensor  10  is attached to the inside of an outer case  20  covering the electronic device. 
     With the sensor  10  attached to the inside, the outer case  20  may be fitted into a case of another electronic device. 
     A plurality of slits (not shown) for illumination are formed in a surface of the outer case  20 . The slits are formed by partially removing an outer coating of the outer case  20 . In the light guide  11 , illuminating parts (not shown) formed on a rough surface are located at positions corresponding to the slits. 
     As illustrated in  FIG. 3 , the electronic device has a substrate  30 . When the sensor  10  and the outer case  20  are attached to the electronic device, the light guide  11  is positioned opposite the substrate  30 . 
     The substrate  30  is provided with a plurality of light sources  31  and a connector  40 . The light sources  31  are preferably, but are not limited to, semiconductor optical elements, such as light-emitting diodes (LEDs). 
     The light sources  31  are disposed opposite one end face of the light guide  11  constituting the sensor  10 . That is, one end  11 D (see  FIG. 1 ) of the light guide  11  (i.e., an edge of the curved portion  11 C) is opposite the substrate  30 . The light sources  31  are disposed on the substrate  30  at positions opposite the end  11 D of the light guide  11 . As illustrated in  FIG. 3 , the one end face of the light guide  11  is provided with recessed incident portions  11   a . The light sources  31  are disposed inside their corresponding incident portions  11   a  and face them. The one end face of the light guide  11 , the one end face being provided with the incident portions  11   a , has hooking portions  11   b , at both ends in the Y direction. The hooking portions  11   b  protruding in the Z 2  direction are integral with the light guide  11 . The substrate  30  has hooking holes (hooked portions)  32  at positions opposite the hooking portions  11   b.    
     As illustrated in  FIG. 3 , the connector  40  is disposed near the center of the substrate  30 . As illustrated in  FIG. 4A  and  FIG. 4B , the connector  40  has a plurality of elastic contacts  41  formed by bending leaf springs and an insulating holding case  42  that accommodates the elastic contacts  41 . The elastic contacts  41  are spaced at predetermined intervals in the Y direction, so that adjacent elastic contacts  41  are insulated from each other. The elastic contacts  41  are elastically deformable at their ends in the Z direction. 
     As illustrated in  FIG. 1 , the light guide  11  has a resin layer  16  thereon in an area opposite the outer case  20 . The resin layer  16  allows a lower surface  20 A of the outer case  20  and an upper surface  11 A of the light guide  11  to be tightly secured to each other. This can prevent creation of an unnecessary gap (air space) between the lower surface  20 A of the outer case  20  and the upper surface  11 A of the light guide  11  and thus can stabilize the capacitance. 
     Light emitted from the light sources  31  enters the light guide  11  from the incident portions  11  a and propagates through the inside of the light guide  11 . Then, the light is output from the illuminating parts (not shown) of the light guide  11  and the slits (not shown) of the outer case  20  to the outside of the electronic device. Thus, the slits of the outer case  20  are brightly illuminated, so that the operator can see the illumination. 
     It is preferable that the refractive index of the resin layer  16  be greater than that of the light guide  11 . This can improve propagation efficiency of light that propagates inside the light guide  11 . 
     The resin layer  16  may contain light diffusing material or fluorescent material. This makes it possible to diffuse light or produce fluorescence in the resin layer  16  on the surface of the light guide  11 , and thus to prevent unevenness of light (formation of hot spots). That is, it is possible to provide uniform illumination. 
     The permittivity e of the resin layer  16  is preferably at least one, and more preferably, three or more. In the sensor  10 , when a part of a human body (object), such as an operator&#39;s fingertip, approaches or comes into contact with the surface of the outer case  20 , a capacitance is formed between the part of the human body and any of the detection electrodes  12 . By detecting a change in capacitance with a detecting unit (not shown), the operating state of the operator can be detected. Therefore, when the resin layer  16  is made of material having high permittivity e, a large capacitance can be obtained. This makes it possible to stabilize the detecting operation of the sensor  10 . 
     As illustrated in  FIG. 3 , the sensor  10  is hooked and secured onto the substrate  30  by inserting the hooking portions  11   b  of the light guide  11  into their corresponding hooking holes  32  of the substrate  30 . 
     Thus, the incident portions  11   a  face their corresponding light sources  31 . At the same time, the connection electrodes  13  on the inner surface  11 B of the light guide  11  come into contact with their corresponding elastic contacts  41  of the connector  40 , as illustrated in  FIG. 4A . 
     When the sensor  10  is further pressed, the hooking portions l lb of the light guide  11  are hooked with their corresponding hooking holes  32 . The elastic contacts  41  are compressed and significantly elastically deformed in the holding case  42 . Since a force that presses back the connection electrodes  13  in the Z 1  direction is applied from the elastic contacts  41 , the elastic contacts  41  and their corresponding connection electrodes  13  are electrically connected to each other. 
     Thus, in the capacitance-type sensor  10  integral with the light guide  11  according to an embodiment of the present invention, the light guide  11  can be shaped to fit the outer case  20  that affects the exterior design. Additionally, the detection electrodes  12  can be freely formed on the light guide  11 . That is, it has been conventionally difficult to form detection electrodes on a curved portion of a light guide, but according to an embodiment of the present invention, the detection electrodes  12  can be formed on the curved portion  11 C etc. with high accuracy. Therefore, the light guide  11  can be shaped to fit the outer case  20 . It is thus possible to prevent the shape of the light guide  11  from affecting the design of the outer case  20 . 
     Next, a method for manufacturing the capacitance-type sensor  10  integral with the light guide  11  using the in-mold process will be described. 
       FIG. 5A  to  FIG. 5C  illustrate steps of manufacturing the capacitance-type sensor  10  integral with the light guide  11  using the in-mold process. 
     In the first step illustrated in  FIG. 5A , various electrodes  52  (including the detection electrodes  12 , the connection electrodes  13 , and the wires  14 ) are formed on a peel-off sheet  51 , such as a polyethylene terephthalate (PET) film, using a screen printing method or the like. 
     In the second step illustrated in  FIG. 5B , the peel-off sheet  51  having the various electrodes  52  thereon is sandwiched by a mold (not shown) for forming the light guide  11  on the peel-off sheet  51 . Then, transparent resin material is fed into the mold for injection molding. While the light guide  11  is being injection-molded, the electrodes  52  are transferred to the surface of the light guide  11 , so that the light guide  11  and the electrodes  52  are formed integrally. 
     When the material of the light guide  11  is thermoplastic resin, which is converted into a liquid by applying heat thereto, the thermoplastic resin is subjected to high temperature and pressure in the mold. In this case, since the electrodes  52  are appropriately shaped to fit the mold, it is possible to prevent creation of an air space between the completed light guide  11  and the electrodes  52  in the surface of the light guide  11 . 
     In the third step illustrated in  FIG. 5C , the peel-off sheet  51  is peeled off. Thus, the light guide  11  having the various electrodes  52  therein is completed. 
     As described above, according to an embodiment of the present invention, the electrodes  52  can be formed anywhere in the light guide  11  with high accuracy. 
     In the first step described above, the electrodes  52  may be formed on both sides of a PET film in which through holes are formed in advance, so that the electrodes  52  formed on one side and the other side are electrically connected to each other via the through holes. In this case, in the second step, if the light guide  11  is injection-molded on one side of the PET film, it is not necessary to carry out the third step in which the PET film is peeled off. This means that the light guide  11  can be used without removing the PET film.