Abstract:
Apparatus for back-lit illumination of key designation characters in a keypad has a plurality of individual translucent key cores arranged in a planar pattern, with a base membrane disposed between key cores and fitting around each key at least the outer ends of the key cores except for the key designation characters. An elastomeric, electroluminescent lamp (EEL) is held in assembly against the inner ends of the key cores so as to illuminate the designation characters when activated and deform locally when a key is depressed.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of keypad illumination and particularly, to the application of electroluminescent systems for this purpose.  
         BACKGROUND AND SUMMARY OF THE INVENTION  
         [0002]    Keypads are widely used to facilitate data and command input for variety of devices in the consumer electronics industries. These devices include cellular to telephones, personal organizers, hand-held computers, pagers, calculators and the like. The design of such keypads has been refined to provide good tactile feedback in light-weight, inexpensive sub-assemblies. When there is a potential for use under low ambient lighting it is desirable to provide integral keypad illumination for some devices. For example, keypad illumination can be particularly useful in cellular telephones and personal organizers. In the current state-of-the-art, such illumination is provided by an array of subminiature or surface mount LED lamps, nested in a minimal space between the keypad and the key contact panel. While such arrangements can be effective, power consumption and bulk pose inherent design challenges. Power consumption is sometimes addressed by inclusion of a power-on time limit. The bulk effect can be minimized by careful design, but most likely at the expense of uniform illumination. Thus, there are trade-offs and compromises that can impact both functionality and sales appeal of the product.  
           [0003]    Therefore, a first object of the present inventions is to provide apparatus that facilitates the illumination of keypads. A second object of the inventions is that this keypad illumination apparatus be in a compact, light-weight form that does not materially increase product bulk and/or weight. A third object of these inventions is to provide keypad illumination apparatus with a significantly reduced power requirement. Yet other objects are that this apparatus maintains good tactile feel and provides uniform light distribution.  
           [0004]    In a preferred embodiment of the present inventions apparatus for back-lit illumination of key designations in a keypad comprises a plurality of individual, translucent key cores. A base membrane disposed in a horizontal plane around and between key cores maintains the key pattern. A thin flexible, opaque film covers the upper surface of the base membrane and the key cores and is laser etched to expose characters for illumination on the key operating ends. In the alternative, the opaque film covering may be omitted and the characters may be opaque. An elastomeric, membrane-like electroluminescent lamp (EEL), as disclosed by Burrows in U.S. Pat. No. 5,856,030, is interposed between the keypad and the key contact panel where it is held in assembly against the horizontal lower surface of the base membrane and the lower, actuating ends of the keys, so as to illuminate the designation characters through the key cores when activated. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a cross-sectional view of a first preferred embodiment of the illuminated keys of the present inventions;  
         [0006]    [0006]FIG. 2 is a cross-sectional view of a second preferred embodiment of the illuminated keys of the present inventions; and  
         [0007]    [0007]FIG. 3 is a cross-sectional view of a third preferred embodiment of the illuminated keys of the present inventions.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]    The present inventions are described in the following by referring to drawings of examples of how the inventions can be made and used. In these drawings, reference characters are used throughout the views to indicate like or corresponding parts. The embodiments shown and described herein are exemplary. Many details are well known in the art, and as such are neither shown nor described.  
         [0009]    [0009]FIGS. 1, 2 and  3  show a cross-sectional view of three variations of a keypad assembly incorporating the present inventions, embodiments  100 ,  200  and  300 . In reference to these drawings, key assemblies  12 ,  14  and  16  respectively, each represent a plurality of keys. There is shown, in the manner well known to those skilled in the art, how the outer ends of these keys extend through holes  18 ,  20  and  22  respectively in keyboard  17 . Also well known is the manner in which inner end extensions  24 ,  26  and  28  respectively, deflect domes  30 ,  32  and  34  to provide selective electrical continuity with contacts  36 ,  38  and  40 .  
         [0010]    In FIG. 1, keys  12  can be made as part of a monolithic unit wherein key cores  42  and base membrane  44  are formed of an elastic, translucent material such as a silicone rubber compound or can be made as an assembly wherein elastic base membrane  46  includes a plurality of pockets  48  into which individual, translucent key cores  50  are fitted. In either case, base membrane  44  or  46  is fixedly mounted with respect to elastomeric electroluminescent lamp (EEL)  52 , either directly, or through the thickness of a spacer as described below in FIG. 3. EEL  52  is fixedly mounted atop a stack assembly comprising spacer board  54 , domed switch contact panel  56 , spacer board  58  and circuit board  60 . When key  12  is depressed, deflection of elastic base membrane  44  or  46  allows extension  24  to press against EEL  52  and in turn, by virtue of the elasticity of EEL  52 , to deflect dome  30  against contact  36 . The diameter of hole  62  in spacer board  54  is sufficient to allow the required deflection of EEL  52  for the fatigue cycle design life of the keypad, as does hole  64  in spacer board  58  for deflection of switch contact panel  56 .  
         [0011]    Application of power, preferably 50-200 VAC, to EEL  52  generates luminescence that impinges upon the inner ends of translucent key cores  42  or  50 . The outer ends of keys  12 , and preferably the entire outer surface, is covered with a thin opaque film  82 , too thin to show in cross section. The appropriate characters are laser etched on the end of each key  12 , as shown in FIG. 4, so that its translucent nature provides illumination. Alternatively, opaque characters may be printed on the outer end surface of the translucent keys.  
         [0012]    In FIG. 2, keys  14  are made as individual, translucent key cores  66  and adhesively bonded to EEL  52 . Bonding ring  68  is made on the inner end of key  66  to provide area for a competent bonded joint  69  and extension  26  is centrally located to align with dome  32 . Again, EEL  52  is fixedly mounted atop the stack assembly comprising spacer board  54 , domed switch contact panel  56 , spacer board  58  and circuit board  60 . When key  14  is depressed the elasticity of EEL  52  allows it to deflect against dome  32 , which is pushed against contact  38 . The diameter of hole  70  in spacer board  54  is larger than the previously described diameter of hole  62  because of the diameter of bonding ring  68 , so as to be sufficient to allow the required deflection of EEL  52  for 10 6  cycles without fatigue. As before, application of power to EEL  52  generates luminescence that impinges upon the inner end of translucent key cores  66 . The outer ends of key cores  66  and preferably their entire outer surface, is covered with a thin opaque film  82 , too thin to show in cross section. The appropriate characters are laser etched on the end of each key  14 , so that the character itself is illuminated by EEL  52 . Alternatively, opaque characters may be printed on the outer end surface of the translucent keys.  
         [0013]    In FIG. 3, keys  16  are made as an assembly wherein base membrane  72  is vacuum formed in a thin, clear polycarbonate or polyester sheet. Base membrane  72  includes a plurality of pockets  74  into which individual, translucent key cores  76  are fitted. Base membrane  72  is fixedly mounted with respect to EEL  52  through the thickness of a spacer  78 . EEL  52  is again fixedly mounted atop a stack assembly comprising spacer board  54 , domed switch contact panel  56 , spacer board  58  and circuit board  60 . When key  16  is depressed, base membrane  72  flexes, allowing extension  28  to press against EEL  52  and in turn, by virtue of the elasticity of EEL  52 , to deflect dome  34  against contact  40 . The diameter of hole  80  in spacer board  78  is sufficient to allow the required deflection of base member  72  for the fatigue cycle design life of the keypad, as does hole  64  in spacer board  58  for deflection of switch contact panel  56 .  
         [0014]    Application of power, to EEL  52  generates luminescence that impinges upon the inner end of translucent key cores and is transmitted through the clear material of pockets  74 . The outer ends of keys  16 , and preferably the entire outer surface of pockets  74 , is covered with a thin opaque film  82 , too thin to show in cross section. The appropriate characters are laser etched on the end of each key  16 , so that the character itself is illuminated by EEL  52 . Alternatively, opaque characters may be printed on the outer end surface of the keys.  
         [0015]    [0015]FIG. 4 shows the manner in which the outer ends of keys  12 ,  14  and  16  are covered with a thin, opaque film  82 , so that laser etching of the film exposes the appropriate characters  84  to the back lighting provided by EEL  52 . As described above, the process may be reversed by omitting opaque film  82  and making the characters  84  themselves opaque.  
         [0016]    The embodiments shown and described above are exemplary. It is not claimed that all of the details, parts, elements, or steps described and shown were invented herein. Even though many characteristics and advantages of the present inventions have been described in the drawings and accompanying text, the description is illustrative only. Changes may be made in the detail, especially in matters of shape, size, and arrangement of the parts within the scope and principles of the inventions. The descriptions above are not restrictive and do not point out what an infringement of this patent would be, but are to provide at least one explanation of how to use and make the inventions. The limits of the inventions and the bounds of the patent protection are measured by and defined in the following claims.