Abstract:
A keyboard equipped with a backlight structure includes a keyboard portion, a bridge board and a base board located beneath the keyboard portion to form a light transmission space. The bridge board has a light channeling portion to channel light entering the light transmission space to the keyboard portion where light emission is desired to refract the light. The structure can be made at a lower cost and converge light to display the keyboard portion without illuminating the entire keyboard portion.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a keyboard equipped with a backlight structure and particularly to a keyboard that has a backlight structure below a keyboard portion to project light on the keyboard portion. 
   BACKGROUND OF THE INVENTION 
   Illuminated keyboards or backlit keyboards used in a low light or dark environment for desktop computers, laptop computers, notebook computers or Web TV sets are known in the art. Reference can be found in U.S. Pat. Nos. 6,284,988, 6,322,229, 6,199,996, 6,554,442 and 6,179,432, and R.O.C. patent publication Nos. 509955, 465777, 535385, 438035, 570235, 468833 and 516671. They mostly have a built-in luminous sheet to emit light to enable users to recognize the striking positions of the keyboard. 
   The aforesaid techniques have a common feature: the lighting element and the key cap are merely interposed by a trigger element and a moving mechanism. And the key cap, trigger element and moving mechanism are made from transparent material (some of them have opaque key caps with transparent character notations). The lighting element emits light from the entire sheet. The keyboard is illuminated evenly in a backlight fashion. Such a lighting mode creates problems in use, notably: 
   Illuminated keyboard mostly is used in a lower light or dark environment, such as on the airplane, in the car, and the like where luminance is not sufficient. With the entire keyboard illuminated, the total luminance is too strong and affects other people nearby. It the low light environment, user&#39;s visual recognition power decreases. In the occasion where the entire sheet is illuminated evenly, it is difficult for the user to recognize the individual notation on the key cap. Even if the character notation is made from opaque material, or the key cap is made from opaque material and the character notation is formed by transparent material, the light passes through between neighboring key caps and generates light interference and makes recognition difficult. For people who are not familiar the layout of character notations, striking mistakes frequently occur and erroneous output of instruction signals takes place. 
   SUMMARY OF THE INVENTION 
   Therefore the primary object of the present invention is to solve the aforesaid disadvantages. The present invention provides a backlight structure to converge light to the keyboard portion for illuminating without projecting light on the entire keyboard portion. The backlight structure of the invention includes a bridge board and a base board beneath the keyboard portion to form a light transmission space. Light entering the light transmission space passes through a light channeling portion located on the bridge board and in the light transmission space, and is directed to a corresponding location of the keyboard portion where light emission is desired to refract the light to the keyboard portion to emit light. Hence actual light emission scope on the keyboard portion is confined by the location and size of the light channeling portion. 
   Another object of the invention is to provide the light channeling portion and the bridge board that are made integrally by injection forming. The bridge board or the base board has a refraction surface to enhance the luminance of the lighting source. Hence a lower cost light source may be used to reduce the total cost of the backlight structure. 
   The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of the keyboard of the present invention. 
       FIG. 2  is a fragmentary exploded view of the keyboard of the present invention. 
       FIG. 3A  is a sectional view of the keyboard of the present invention. 
       FIG. 3B  is a fragmentary enlarged view according to  FIG. 3A . 
       FIG. 4  is a schematic view of another embodiment of the present invention. 
       FIGS. 5A and 5B  are schematic views of the light sources of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Please referring to  FIGS. 1 ,  2 ,  3 A and  3 B, the keyboard  10  equipped with a backlight structure according to the invention includes a keyboard portion  101  on a upper side that has a plurality of keys  11 . Each key  11  has a key cap  111  with a notation  1111  formed on the surface and a moving mechanism  112  coupling with the key  111  to allow the key  111  to be depressed for a selected displacement. In an embodiment, the moving mechanism  112  is a scissors type mechanism, and has another end coupling with a bridge board  12  to allow the keyboard portion  101  to be depressed relative to the bridge board  12  for a selected distance. There is a signal triggering means  13  beneath the keyboard portion  101 . The signal triggering means  13  includes a circuit board  131  and an actuation element  132  to be compressed by the keyboard portion  101  to trigger the circuit board  131  to output a signal. There is a base board  14  beneath the bridge board  12  spaced therefrom to form a light transmission space  20 . The bridge board  12  has at least one light channeling portion  121  directing towards the light transmission space  20  and corresponding to the keyboard portion  101  where light emission is desired (such as the notation  1111 ). The light channeling portion  121  receives light emitted from light sources  30   a  and  30   b  and entered the light transmission space  20 , and channels the light to the keyboard portion  101 . Thus forms the backlight structure of the keyboard  10 . 
   The light channeling portion  121  may be designed in a form according to the desired luminance of the keyboard portion  101 , such as a cylindrical strut shown in  FIG. 3B , or a polygon shown in  FIG. 4 . The light channeling portion  121  may further include a light sensitive member or light sensitive layer  123  to increase light absorption power or light refraction. In addition, the light channeling portion  121  has a light emission portion  122  on another end to converge or scatter light to the keyboard portion  101 . In the event that light converging is adopted, light is focused on the notation  1111  of the key cap  111 . The notation  1111  may be formed by carving or transparent to emit light for easy recognition. In the event that light scattering is adopted, the light is projected to the scope of the key cap  111 , and the key cap  111  is made from a transparent material. Either way, the light is projected to a single key cap  111 . The area between neighboring key caps  111  does not receive light. Thus total illumination of the entire body can be avoided, and striking of the key  11  can be performed accurately. Moreover, the light channeling portion  121  may be extended to the base board  14 . Aside from providing light refraction, it also can aid bracing of the bridge board  12  to achieve a firmer anchoring effect. 
   Referring to  FIGS. 5A and 5B , because of the invention provides the light transmission space  20 , the light sources  30   a  and  30   b  do not have to be formed in an entire sheet. As shown in  FIG. 5A , the light source  30   a  is located on the peripheral side of the keyboard portion  101 . Referring to  FIG. 5B , the emission light source  30   b  is located beneath the keyboard portion  101  and formed in a plate located in the light transmission space  20 . The light sources  30   a  and  30   b  further can be connected to a power supply switch  31  outside the keyboard  10 . To enhance reflection of the light sources  30   a  and  30   b  to increase the luminance in the light transmission space  20 , at least one refraction surface is formed on the bottom surface of the bridge board  12  and the surface of the base board  14  (if the circuit board  131  is located in the light transmission space  20 , at least one refraction surface is formed on the bottom surface of the bridge board  12  and the surface of the base board  14  located in the light transmission space  20 . If multiple actuation elements  132  are connected to a MYLAR sheet located in the light transmission space  20 , then at least one refraction surface is formed on the bottom surface of the bridge board  12  and the surface of the MYLAR sheet located in the light transmission space  20 ). Hence light emitted from the light sources  30   a  and  30   b  and entered the light transmission space  20  has a greater luminance through the refraction surface. If the light sources  30   a  and  30   b  already have a sufficient luminance, to avoid external light from interfering the light in the light transmission space  20  in the upward direction, the bottom surface of the bridge board  12  and the surface of the base board  14  in the light transmission space  20  may be formed in an opaque mask surface. Thereby the light sources  30   a  and  30   b  in the light transmission space  20  can project light only through the light channeling portion  121  to the keyboard portion  101  to emit light. 
   While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.