Patent Publication Number: US-7589292-B2

Title: Keypad with light guide layer, keypad assembly and portable terminal

Description:
CROSS RELATED APPLICATION 
     This application is a Divisional Application of U.S. Ser. No. 11/367,610 filed on Mar. 3, 2006, now U.S. Pat. No. 7,411,142 which claims the benefit of the earlier filing date of that patent application entitled “Keypad with Light Guide Layer, Keypad Assembly and Portable Terminal” filed in the Korean Intellectual Property Office on May 13, 2005, and assigned Serial No. 2005-40177, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a keypad with which a portable terminal or the like is provided, and more particularly to a keypad with a light guide layer, and a keypad assembly. 
     2. Description of the Related Art 
     A keypad used in a conventional portable terminal generally includes a plate-like elastic pad, a plurality of key buttons which are formed on a first side of the elastic pad, and each of which has characters (letters, numerals or symbols) printed on its upper surface, and a plurality of protrusions (or actuators) formed on a second side of the elastic pad, located opposite the first side. Also, it is normal for the portable terminal to have a plurality of light emitting devices (usually 15 to 20 in number) for backlighting the keypad. 
       FIG. 1  illustrates a sectional view of a keypad assembly of the prior art. The keypad assembly  100  includes a keypad  110 , a switch board  150  and a plurality of light emitting diodes (hereinafter referred to as “LED”)  170 . 
     The keypad  110  includes a plate-like elastic pad  120 , a plurality of key buttons  140  which are formed on a first side  122  of the elastic pad  120  and each of which has characters (letters, numerals or symbols) printed on its upper surface, and a plurality of protrusions  130  formed on a second side  124  of the elastic pad  120 , located opposite the first side  122 . Each protrusion  130  on the second side  124  of the elastic pad  120  is arranged in a position corresponding to a center of each key button  140 . A plurality of grooves  126  may be formed on the second side  124  of the elastic pad  120 . The grooves  126  are disposed around the respective protrusions  130  so as to avoid interferences between the light emitting diodes  170  and the protrusions  130 . 
     The switch board  150  has a plate-like printed circuit board (hereinafter referred to as “PCB”)  155  and a plurality of switches  160  formed on an upper surface, facing the keypad  110 , of the PCB  155 . Each switch  160  consists of an electrically conductive contact member  162  and an electrically conductive dome  164  completely covering the contact member  162 . 
     The plurality of light emitting diodes  170  are mounted on the upper surface of the PCB  155 , and are positioned such that each of them is covered with a corresponding groove  126  of the elastic pad  120 . 
     If a user pushes down any one key button  140 , a portion of the keypad  110 , located under the key button  140 , is deformed onto the switch board  150 , and, thus, a corresponding protrusion  130  belonging to the deformed portion of the keypad  110  presses a corresponding dome  164 . The pressed dome  164  comes into electrical contact with a corresponding contact member  162 . 
     For operating the switches  160 , each light emitting diode  170  may not be located under the corresponding key button  140 . Thus, light emitted from each light emitting diode  170  obliquely illuminates the corresponding key button  140  after passing through the elastic pad  120 . On this account, there is a problem in that the key button  140  is not uniformly illuminated. In other words, a central portion of each key button  140  is relatively darkly illuminated whereas edge portions of the key button  140  are relatively brightly illuminated. Also, even if a greater number of light emitting diodes are provided so as to uniformly and brightly illuminate the key buttons  140 , there occurs a further problem of large power consumption and high manufacturing cost. 
     To solve these problems, a method is proposed to use inorganic EL (Electro Luminance) for illuminating key buttons. However, the inorganic EL requires an additional inverter for converting DC current to AC current because AC power must be used for the inorganic EL, and electric noise and sound noise occurring in the inorganic EL must be settled beforehand. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve at least the above-mentioned problems occurring in the prior art and provides additional advantages, by providing a keypad, a keypad assembly and a portable terminal, which can realize uniform and bright illumination, small power consumption and low manufacturing cost. 
     In one embodiment, there is provided a keypad comprising a light guide layer into which light travels, at least one key button being disposed on an upper surface of the light guide layer, a lower elastic layer being disposed on a lower surface of the light guide layer, located opposite the upper surface, and at least one reflective pattern being formed on the light guide layer and partially reflecting the light traveling into the light guide layer toward the key button. 
     In another embodiment, there is provided a keypad assembly comprising a keypad including a light guide layer into which light travels, at least one key button being disposed on an upper surface of the light guide layer, a lower elastic layer being disposed on a lower surface of the light guide layer, located opposite the upper surface, and at least one reflective pattern being formed on the light guide layer and partially reflecting the light traveling into the light guide layer toward the key button, and a switch board being provided, on an upper surface thereof facing the keypad, with at least one switch, wherein as the key button is pushed down, a portion of keypad is deformed onto the switch to press the switch. 
     In another embodiment, there is provided a keypad assembly comprising a switch board being provided on an upper surface thereof with at least one switch, a keypad including a light guide layer having an upper surface, a lower surface and side surfaces, and at least one key button being disposed on the upper surface of the light guide layer while being positioned above the switch, at least one light emitting device being disposed adjacent to at least one of the side surfaces of the light guide layer, a lower elastic layer being disposed on a lower surface of the light guide layer, located opposite the upper surface, and at least one reflective pattern being formed on a portion of the upper or lower surface of light guide layer, located under the key button, and partially reflecting the light traveling into the light guide layer toward the key button. 
     In yet another embodiment, there is provided a portable terminal comprising, a keypad including a light guide layer into which light travels, at least one key button being disposed on an upper surface of the light guide layer, a lower elastic layer being disposed on a lower surface of the light guide layer, located opposite the upper surface, and at least one reflective pattern being formed on the light guide layer and partially reflecting the light traveling into the light guide layer toward the key button, and a switch board being provided, on an upper surface thereof facing the keypad, with at least one switch, wherein as the key button is pushed down, a portion of keypad is deformed onto the switch to press the switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a sectional view of a conventional keypad assembly; 
         FIG. 2  is a sectional view of a keypad assembly in accordance with a preferred embodiment of the present invention; 
         FIG. 3  is a plain view of the keypad assembly shown in  FIG. 2 ; 
         FIG. 4  is a sectional of a keypad in accordance with another preferred embodiment of the present invention; 
         FIG. 5  is a sectional view of a keypad in accordance with another yet preferred embodiment of the present invention; 
         FIG. 6A  is a sectional view of a ribbon optical fiber; and 
         FIG. 6B  is a sectional view of an optically transparent film. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the similar components are designated by similar reference numerals although they are illustrated in different drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may obscure the subject matter of the present invention. 
       FIG. 2  illustrates a sectional view of a keypad assembly in accordance with a preferred embodiment of the present invention, and  FIG. 3  illustrates the keypad assembly in a plain view. 
     The keypad assembly  200  includes a keypad  210 , a switch board  280  disposed apart from the keypad  210 , at least one light emitting device  320 , and a second PCB  310 . 
     The keypad  210  includes a light guide layer  220 , upper and lower elastic layers  230 ,  240 , a plurality of key buttons  270 , a plurality of protrusions  260 , and a plurality of reflective patterns  250 . In  FIG. 3 , the light guide layer  220  is shown by a dotted line. 
     The light guide layer  220  guides light coupled into it. The coupled light travels from one side to the other side of the light guide layer  220 . The light guide layer may include an optical fiber array consisting of a plurality of optical fibers which are arranged side by side in rows and each of which has a core and a cladding. Light coupled to the core of each optical fiber travels into the core by virtue of total reflection at an interface between the core and the cladding. A refractive index of the core is larger than that of the cladding. The light guide layer  220  has flexibility—i.e., a property of being easily bent—, so it is locally deformed toward the switch board  280  as the key button  270  is pushed down. A ribbon optical fiber consisting of a plurality of glass optical fibers or plastic optical fibers and a resin coating layer surrounding the glass optical fibers or the plastic optical fibers may be used as the optical fiber array. The light guide layer preferably has a thickness not greater than 0.5 millimeters (mm)(preferably within a range of 0.25 to 0.5 mm). 
     The light guide layer  220  may also include an optically transparent film having flexibility, and light coupled to the optically transparent film travels into the optically transparent film by virtue of total reflection at interfaces between the optically transparent film and the elastic layers  230 ,  240  external thereto. Otherwise, by adjusting refractive indices of the optically transparent film and upper and lower elastic layers  230 ,  240  and/or an incident angle of light, light coupled into the keypad  210  may travel into the keypad  210  by virtue of total reflections at interfaces between the upper and lower elastic layers  230 ,  240  and an air layer external thereto. 
     The upper elastic layer  230  is attached onto an upper surface of the light guide layer  220  and has a plate-like shape. There is no limitation on the plate-like shape, and the upper elastic layer  230  may have any plate-like shape including a rectangular plate and so forth. Since the upper elastic layer  230  has elasticity, it returns the key button  270  to an original position after the key button  270  is pushed down. That is, the upper elastic layer  230  itself has a restoring force by which it restores its original shape, so it returns the key button  270  to its original position after the key button  270  is operated. The upper and lower elastic layers  230 ,  240  are made of material having low hardness, a high elastic strain, a high elastic restoring force and high optical transparency so as to provide a good click feeling, to suppress interference phenomena between the key buttons  270 , and not to cause permanent deformation in repetitive operation, and are preferably made of polyurethane, silicone or the like. 
     The plurality of key buttons  270  are formed on an upper surface of the upper elastic layer  230 , and letters, numerals and/or symbols are printed on upper surfaces of the key buttons  270 . The key buttons  270  may be made of the same material as or of different material from that of the upper elastic layer  230  while forming a one-piece component with the upper elastic layer  230 , or may be made of materials such as polycarbonate or acryl-based resin and then be attached onto the upper surface of the upper elastic layer  230 . Each key button  230  may be formed in any shape, for example, in the shape of a cylinder, an elliptic cylinder or the like. 
     The lower elastic layer  240  is attached onto a lower surface of the light guide layer  220 , and has a plate-like shape. There is no limitation on the type of the plate-like shape, and the lower elastic layer  240  may have any plate-like shape including a rectangular plate and so forth. Since the lower elastic layer  240  has elasticity, it cooperates with the upper elastic layer  230  to return the key button  270  to its original position after the key button  270  is pushed down. 
     If the light guide layer  220  has a thickness of 0.2 mm or less (e.g., within a range of 0.1 to 0.125 mm), then only the lower elastic layer  240  may be used while the upper elastic layer  230  is removed. That is, of the upper and lower elastic layers  230 ,  240  functioning to provide the keypad  210  with a restoring force, the upper elastic layer  230  may be removed when the light guide layer  220  is thin enough to be provided with a sufficient resilient force by only the lower elastic layer  240 . 
     The plurality of protrusions  260  are formed on a lower surface of the lower elastic layer  240 . The protrusions  260  may be made of the same material as or of different material from that of the lower elastic layer  240  while forming a one-piece component with the lower elastic layer  240 , or may be made of materials such as polycarbonate or acryl-based resin and then be attached onto the lower surface of the lower elastic layer  240 . Each protrusion  260  may be formed in any shape, for example, in the shape of a truncated cone, a trapezoidal hexahedron or the like. Each protrusion  260  is aligned under the corresponding key button  270  (in a widthwise direction of the keypad assembly  200  or in a direction perpendicular to an upper surface of a first PCB  290 ). The size and the shape of each protrusion  260  may be determined in consideration of the size of a dome  305  provided on the switch board  280 . For example, when a dome having a width (or diameter) of 5 mm is used, the protrusion may have a width of 2 mm and a thickness of 0.2 to 0.3 mm. 
     The plurality of reflective patterns  250  are formed on the lower surface of the light guide layer  220 , and each of them reflects a portion of the light, traveling into the light guide layer  220 , toward the corresponding key button  270 . Each reflective pattern  250  is locally formed on the lower surface of the light guide layer  220 , and is interposed between the light guide layer  220  and the lower elastic layer  240 . Light traveling into the light guide layer  220  by virtue of total reflection is incident to the reflective pattern  250  and is diffuse-reflected toward the key button  270 . Since most of the diffuse-reflected light does not satisfy a total reflection condition (that is, an incident angle is smaller than a threshold angle), the light is transmitted through the key button  270  to exit out of the key button  270 . Also, light passing by the reflective pattern  250  without being diffuse-reflected, and a part of the diffuse-reflected light, continue to travel through the light guide layer  220  while satisfying the total reflection condition, thereby contributing to the illumination of the other key buttons. In other words, the reflective pattern  250  causes diffuse reflection such that only a part of the incident light is used for illuminating the corresponding key button  270  and the remaining part of the incident light contributes to illuminating the other key buttons. The reflective patterns  250  enable uniform illumination of the key buttons  270  through diffuse reflection in random directions. Preferably, the reflective patterns  250  may be formed by scratching, lasing, forming, printing or the like. When the light guide layer  220  includes an optical fiber array, the reflective patterns  250  extend from a lower surface of the optical fiber array to core surfaces. 
     The switch board  280  includes a first PCB  290  and a dome sheet  300 . 
     The first PCB  290  has a plurality of electrically conductive contact members  295  formed on its upper surface and a plurality of domes  305  covering the electrically conductive contact members  295 . Each pair of the contact member  295  and the corresponding dome  305  constitutes a switch  295 ,  305 . The switch  295 ,  305  is aligned under the corresponding protrusion  260 . 
     The dome sheet  300  is attached to the upper surface of the first PCB  290 , and is provided with the plurality of electrically conductive domes  305  having a hemispherical shape. Each dome  305  completely covers the corresponding contact member  295 . 
     When a user pushes down any one key button  270 , a portion of the keypad  210 , located under the key button  270 , is deformed onto the switch board  280 , and thus a corresponding protrusion  260  belonging to the deformed portion of the keypad  210  presses a corresponding dome  305 . The pressed dome  305  comes in electrical contact with a corresponding contact member  295 . 
     The second PCB  310  is attached to an edge portion of the lower surface of the lower elastic layer  240 , and at least one light emitting device  320  is mounted on an upper surface of the second PCB  310  while its light emitting surface faces a side surface of the light guide layer  220 . Light exiting from the light emitting device  320  is coupled into the light guide layer  220  through the side surface of the light guide layer  220 . An ordinary flexible PCB (FPCB) may be used as the second PCB  310 , and an ordinary light emitting diode may be used as the light emitting device  320 . 
       FIG. 4  illustrates a sectional view of a keypad in accordance with another embodiment of the present invention. The keypad  210 ′ according to this embodiment has a construction in which the upper elastic layer  230  is removed from the keypad  210  shown in  FIG. 2 . The key buttons  270  are attached on the upper surface of the light guide layer  220 . Light traveling into the light guide layer  220  by virtue of total reflection is incident to the reflective pattern  250  and is diffuse-reflected toward the key button  270 . Since most of the diffuse-reflected light does not satisfy a total reflection condition (that is, an incident angle is smaller than a threshold angle), the light is transmitted through the key button  270  to exit out of the key button  270 . Also, light passing by the reflective pattern  250  without being diffuse-reflected, and a part of the diffuse-reflected light, continue to travel through the light guide layer  220  while satisfying the total reflection condition, thereby contributing to the illumination of the other key buttons. 
       FIG. 5  illustrates a sectional view of a keypad in accordance with another yet embodiment of the present invention. The keypad  210 ″ according to this embodiment has a construction in which a reflective pattern is positioned differently from that of the keypad  210 ′ shown in  FIG. 4 . A light guide layer  220 ′ is made of an optically transparent film having flexibility, and light coupled into the keypad  210 ″ travels into the keypad  210 ″ by virtue of total reflections at interfaces between the light guide layer  220 ′ and the lower elastic layer  240  and an air layer external thereto. The reflective pattern  250 ′ consists of a central portion  252  formed on an upper surface of the protrusion  260  and an edge portion  254  formed around the protrusion  260 . Light traveling into the keypad  210 ″ by virtue of total reflection is incident to the reflective pattern  250 ′ and is diffuse-reflected toward the key button  270 . Since most of the diffuse-reflected light does not satisfy a total reflection condition (that is, an incident angle is smaller than a threshold angle), the light is transmitted through the key button  270  to exit out of the key button  270 . Also, light passing by the reflective pattern  250 ′ without being diffuse-reflected, and a part of the diffuse-reflected light, continue to travel through the keypad  210 ″ while satisfying the total reflection condition, thereby contributing to the illumination of the other key buttons. 
     As described above, a keypad and a keypad assembly according to the present invention have an advantage in that they can uniformly and brightly illuminate the key buttons by means of elastic layers, which have elasticity, and a light guide layer, which has flexibility, provided between key buttons and protrusions. Also, since the keypad and the keypad assembly have the light guide layer, it is possible to reduce the number of necessary light emitting devices, power consumption and manufacturing cost. 
     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.