Patent Publication Number: US-8530768-B2

Title: Thin illuminated keyboard

Description:
FIELD OF THE INVENTION 
     The present invention relates to a thin illuminated keyboard and particularly to a thin illuminated keyboard to condense and project light to keycaps to improve illumination. 
     BACKGROUND OF THE INVENTION 
     In order to meet varying users&#39; requirements, illuminated keyboards that integrate lighting modules to generate illumination have been developed and introduced on the market to attract consumers and provide an extra feature to increase their purchase motivation. While emphasizing the illuminated function, many producers also endeavor to reduce total thickness of the keyboard module so that it can be widely adapted to notebook computers or desktop computers highlighting thin and light design. 
     Conventional thin illuminated keyboards, for instance, R.O.C. patent No. M352718 discloses an illuminated keyboard which comprises a key set unit, a thin film circuit board and a lighting unit. The thin film circuit board includes a thin film bottom layer, a thin film middle layer on the thin film bottom layer and a thin film top layer on the thin film middle layer. The thin film bottom layer has a top surface with a plurality of protrusive reflective light guide points formed thereon. Light emitted from the lighting unit is reflected and scattered upwards through the light guide points. R.O.C. patent No. M368835 discloses a light guide plate for illuminated keyboards. The light guide plate includes a transparent base plate and a circuit unit laid on the top surface of the transparent base plate with conduction contacts formed thereon. The transparent base plate has a plurality of light guide points formed on the bottom surface thereof to divide the bottom surface into a plurality of light guide zones. When light projects to a lateral side of the light guide plate, it is refracted upwards through the light guide points to generate illumination. 
     Moreover, R.O.C. publication No. 200945112 also discloses a similar structure about a keyboard equipped with a self-illuminated circuit board. It includes a key module and a circuit board. The circuit board has at least one base plate made of a flexible light guide material and laid with circuits and a light emitting portion. The circuit board receives light from the light emitting portion and projects the light upwards to the key module. 
     All the aforesaid conventional techniques include a base plate made of a light guide material and laid with circuits, and the circuit board and light guide plate are integrated into a single element to shrink the thickness and size of the keyboard. However, in their keyboard modules, light is guided to project to the upper side of the keyboard through the light guide points on the circuit board or other light guide structures. Such a light guide structure makes the light scatter outside from the circuit board, and is difficult to condense the light to the area where the light is needed. Moreover, users are difficult to identify the character symbol on each keycap in such a condition. The light cannot be used effectively, hence more light emitting elements has to be installed. As a result, total power consumption increases and a greater amount of heat is generated. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to provide an illuminated keyboard with a thinner structure to confine light in the interior of the keyboard and project the light to preset locations to solve the problem of light scattering occurred to the conventional thin illuminated keyboards. 
     To achieve the foregoing object, the present invention provides a thin illuminated keyboard which comprises at least one keycap, an upper light guide plate and a lower light guide plate. The upper and lower light guide plates are located beneath the keycap, and have respectively a first light guide layer and a second light guide layer opposing each other. The first light guide layer and second light guide layer have respectively a first circuit layer and a second circuit layer laid on the opposing surfaces thereof. The first circuit layer and second circuit layer are interposed by at least one circuit switch corresponding to the keycap and triggered by depression of the keycap to generate a command signal. The first and second light guide layers also have respectively a first mask layer and a second reflection layer on the sides opposite to the first and second circuit layers. The first mask layer and second reflection layer form an optical passage between them. The first mask layer includes at least one light penetration zone receiving light from the optical passage to allow the light to project to the keycap at a preset location of the light penetration zone. 
     The thin illuminated keyboard of the invention thus formed provides features as follows: first, the first and second circuit layers are respectively integrated with the first light guide layer and second light guide layer, hence can significantly reduce total thickness and size of the keyboard; second, with the optical passage formed between the first mask layer and second reflection layer, light scattering can be prevented to make use of the light more effective; moreover, the light penetration zone can confine the light to be emitted in a local area of the keycap to condense light projection. 
     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 fragmentary exploded view of a first embodiment of the thin illuminated keyboard of the invention. 
         FIG. 2A  is a sectional view of the first embodiment of the thin illuminated keyboard of the invention. 
         FIG. 2B  is a fragmentary enlarged view of the first embodiment according to  FIG. 2A . 
         FIG. 3  is a sectional view of a second embodiment of the thin illuminated keyboard of the invention. 
         FIG. 4  is a sectional view of a third embodiment of the thin illuminated keyboard of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Please refer to  FIGS. 1 and 2A  for a first embodiment of the thin illuminated keyboard of the invention. It comprises a keycap  10 , an upper light guide plate  20 , a lower light guide plate  30  and a partition plate  40  located between the upper light guide plate  20  and lower light guide plate  30 . The upper light guide plate  20  and lower light guide plate  30  have respectively a first light guide layer  21  and a second light guide layer  31  opposing each other. The first light guide layer  21 , second light guide layer  31  and partition plate  40  can be made of light guide material such as poly(methyl methacrylate), polycarbonate or the like. 
     As shown in  FIG. 1 , the first light guide layer  21  and second light guide layer  31  have respectively a first circuit layer  22  and a second circuit layer  32  laid on the opposing surfaces thereof. The first circuit layer  22  and second circuit layer  32  are interposed by at least one circuit switch  25  corresponding to the keycap  10 . The partition plate  40  has an opening corresponding to the circuit switch  25  to allow the first circuit layer  22  and second circuit layer  32  to contact with each other to be conducted through the opening. 
     The invention also has a bottom plate  50  located at the bottom of the lower light guide plate  30  and a driven mechanism  60  bridging the bottom plate  50  and keycap  10 . The driven mechanism  60  includes an elastic element  61  providing a returning force for the keycap  10  so that the keycap  10  can be moved reciprocally against the bottom plate  50  when a user depresses the keycap  10 . Through the aforesaid reciprocal movement of the keycap  10 , the elastic element  61  presses the first circuit layer  22  to form electrical connection with the second circuit layer  32  to trigger the circuit switch  25  to generate a command signal. 
     Also referring to  FIG. 2B , the first light guide layer  21  also has a first reflection layer  23  and a first mask layer  24  in this order on one side opposite to the first circuit layer  22 . The second light guide layer  31  has a second reflection layer  33  and a second mask layer  34  in this order on one side opposite to the second circuit layer  32 . The first mask layer  24  has at least one light penetration zone  241 . The first and second reflection layers  23  and  33  can be formed by coating, such as coating reflective ink on the first and second light guide layers  21  and  31 . The first and second mask layers  24  and  34  can also be formed by coating, such as coating dark-colored ink or shading ink on the first and second reflection layers  23  and  33 . The areas of the first reflection layer  23  and the first mask layer  24  corresponding to the keycap  10  are not coated to form the light penetration zone  241  to allow light to pass through. 
     The first mask layer  24  and second reflection layer  33  form an optical passage between them so that light can transmit through the optical passage among the upper light guide plate  20 , lower light guide plate  30  and partition plate  40 . The second mask layer  34  also can prevent the light from passing through the second reflection layer  33  to scatter downwards. The first reflection layer  23  allows the light scattering upwards to reflect to the optical passage to enhance light usage. Thus, the light is confined among the upper light guide plate  20 , lower light guide plate  30  and partition plate  40  without scattering. Meanwhile, the light penetration zone  241  receives the light from the optical passage and condenses and projects the light to the keycap  10  at a preset location of the light penetration zone  241 . 
     In the first embodiment shown in  FIGS. 1 and 2A , the upper light guide plate  20 , lower light guide plate  30  and partition plate  40  receive the light from a light emitting unit  70  which is located at a lateral side of the upper light guide plate  20 , lower light guide plate  30  and partition plate  40  to form light transmission between them. The light emitting unit  70  can select an electroluminescent light emitting element, an LED or other light emitting element according to actual requirements.  FIG. 3  depicts a second embodiment which differs from the first embodiment by forming a coaxial hole  35  passing through the partition plate  40 , lower light guide plate  30  and bottom plate  50  to form a housing space between the upper light guide plate  20  and bottom plate  50 . The light emitting unit  70  is fastened to the upper light guide plate  20  through surface-mount technology and held in the housing space, thereby to form optical transmission and conduction with the first light guide layer  21 . In this embodiment, a reflection plate  80  is provided below the bottom plate  50  to reflect the light projecting downwards in the housing space from the light emitting unit  70  back to the first light guide layer  21 , second light guide layer  31  and partition plate  40 . 
       FIG. 4  illustrates a third embodiment in which the upper light guide plate  20  includes a top plate  26  and a lateral portion  27  that can be formed by bending the upper light guide plate  20  to a right angle. The upper light guide plate  20  and lateral portion  27  form a holding space to hold the partition plate  40  and lower light guide plate  30 . In this embodiment, the lateral portion  27  is formed at one side of the top plate  26 . In practice, the lateral portion  27  can be formed at two sides of the top plate  26  or at the edges thereof. Through the first mask layer  24  formed on the lateral portion  27 , the light scattered from the lateral sides of the upper light guide plate  20 , lower light guide plate  30  and partition plate  40  is blocked and reflected by the first reflection layer  23 . 
     As a conclusion, the thin illuminated keyboard of the invention mainly utilizes the first and second light guide layers covered by the first and second reflection layers to reflect the light between the first and second light guide layers. Moreover, the first and second reflection layers respectively have the first and second mask layers formed thereon and an optical passage is formed between the first mask layer and second reflection layer to prevent the light from scattering through the first and second light guide layers. In addition, the light penetration zone is positioned to mate the keycap, thus the light can be condensed and project to the keycap. Furthermore, the light emitting unit is located in the housing space between the upper light guide plate and bottom plate to further shrink the total size of the keyboard. Moreover, with the first and second circuit layers integrally formed on the first and second light guide plates, no additional space is needed to hold the light guide elements and circuit elements in separate manner, hence the total structure of the thin illuminated keyboard can be made thinner and lighter. It provides a significant improvement over the conventional techniques. 
     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.