Abstract:
A keyboard key structure adopted for use on a larger sized key to provide users more effective depressing movements on the key includes two elastic domes to support a key cap in a non-depressed position. The two elastic domes are designed in an unsymmetrical fashion to equip with different compression displacements and flexibility and enable the key cap to move in one direction to reach a depressed position and complete signal input.

Description:
FIELD OF THE INVENTION 
     The invention relates to a key structure adopted for use on a larger size key, and particularly to a key that can generate an indicating light to achieve effective depressing movements and indicate current key conditions. 
     BACKGROUND OF THE INVENTION 
     A keyboard generally consists of a plurality of keys to serve as a communication interface to an electronic data processing apparatus (such as a computer). Keyboard structures are constantly evolving and new features and functions continuously added. For instance: 
     First, every key on the keyboard inputs a preset signal when depressed once and automatically returns to its original position when released. To make the return movement possible, the general approach is to install a spring under the key. Taking the keyboard of a personal computer as an example, every keyboard has more than one hundred keys, including numeral keys, character keys and function keys. Hence more than one hundred springs have to be installed. Such a design increases costs for the springs, and also increases assembly time. To resolve this problem, some producers have designed an elastic plate with elastic domes corresponding to key positions. The elastic plate is made from material such as rubber by integrated injection forming processes. The rubber has rich elasticity, thus the elastic domes may be used to replace the springs. Through integrated injection forming processes, production costs and assembly time can be greatly reduced. 
     Second, with a growing number of application software on the market, hot keys are added on the keyboards in addition to the numeral keys, character keys and function keys to facilitate user operations of the application software. For example, to link to networks used to require many steps. Now, through the design of the hot keys, linking to networks can be accomplished by a single push on a selected hot key. 
     Third, many keyboards have illumination design to enable users to operate easier in circumstances where ambient light is not sufficient. The light sources used are mostly light emitting diodes. Depending on illuminating methods, some illuminating keys adopt constant lighting while others adopt an on/off approach based on key operations. 
     The Hot keys mentioned above generally have a larger size than conventional keys. The elastic plate to provide elastic force for the Hot Keys should also have elastic domes of a larger size. While this can easily be done through injection forming process, the larger size of the elastic dome made from rubber causes reduced flexibility (the elastic dome becomes softer). As a result, return elasticity decreases. When using a single elastic dome to match a key of a larger size, because the elastic becomes softer, the depression location on the key of a user&#39;s finger can affect the compression direction of the elastic dome and result in ineffective depression. 
     Moreover, for illuminating keys, the light sources are generally located between the circuit board and elastic plate. To design keys that are turned on or off depending on key operations, the light sources must match key locations. However the elastic plate tends to obstruct light projection of the light sources and causes reduction of light intensity. U.S. Pat. No. 5,612,692 discloses a design for illuminating keys. The illuminating key includes a key cap and an elastic dome located under the key. That patent has a complex structure, and the light source is located on a position biased to the key. Only a small portion of the key is illuminated. Moreover, light generated by lighting elements has to pass through the media of the elastic dome and key cap. Thus the illuminating effect is undesirable. 
     The conventional techniques set forth above either have complex structures and designs for larger size or illuminating keys, cannot provide effective depression, or have complicated manufacturing processes and higher production costs. The higher costs and complicated production processes become huge disadvantages for the electronic industry, which has to wrestle with the challenges of continuous price reduction and increasing demands for shorter research and development cycles. Improved designs for keys to simplify production processes and reduce production costs are critical technical issues yet to be overcome. 
     SUMMARY OF THE INVENTION 
     The primary object of the invention is to provide a key structure for larger size and illuminating keys. 
     The key structure according to the invention consists of a key cap and two elastic domes. The key cap has a bottom rim which has two lugs located on two sides thereof The two elastic domes hold and support the lugs of the key cap in a non-depressed position. The two elastic domes have different compression displacements and flexibility to allow the cap to move in a selected direction to reach a depressed position and accomplish signal input. 
     The key structure according to the invention has a lighting element on the circuit board located between two elastic domes to allow light to directly project through the key cap without the obstruction of the elastic domes. 
     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. The drawings are only to serve for reference and illustrative purposes, and are not intended to limit the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of the invention, partly cut away; 
     FIG. 2 is a sectional view of the invention; 
     FIGS. 3A and 3B are schematic views of the invention in various operating conditions; and 
     FIG. 4 is a schematic view of an embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, the key structure of the invention is located on a keyboard  20 . The keyboard  20  includes an upper casing  21 , a plurality of keys (only one key  10  is shown in the drawings), an elastic plate  22 , a membrane circuit board  23  and a lower casing  24 . The upper casing  21  has an aperture  211  for the key  10  to pass through and extend outside for users to depress with a finger. The elastic plate  22  is made from a flexible material such as rubber by injection forming processes to keep the key  10  extending outside the aperture  211  in a non-depressed position, and to provide a returning elastic force when the key  10  is depressed (will be discussed later). The membrane circuit board  23  has connecting circuits (not shown in the drawings) and electric contacts  231 . Every key  10  corresponds to one electric contact. When the key  10  is depressed, it connects the electric contact  231  of the circuit board  23  to output a preset signal. 
     The key  10  according to the invention includes a key cap  11 , a first elastic dome  12  and a second elastic dome  13 . The key cap  11  is located in the aperture  211  of the upper casing  21 , and has a bottom rim that has a pair of lugs  111  and  112  located on two sides thereof. The lugs  111  and  112  are retained by the edges of the aperture  211  to prevent the key cap  11  from escaping from the aperture  211 . 
     The first elastic dome  12  and second elastic dome  13  are integrally formed with the elastic plate  22  by injection forming processes, and correspond respectively to the lugs  111  and  112  of the key cap  11 . The first elastic dome  12  includes a first supporting section  121  and a first elastic section  122 . The first supporting section  121  has a diameter d 1  and a height h 1 , and the first elastic section  122  has a height h 2 . The second elastic dome  13  has the same height h as the first elastic dome  12 , and includes a second supporting section  131  and a second elastic section  132 . The second supporting section  131  has a diameter d 2  and a height h 3 , and the second elastic section  132  has a height h 4 , wherein d 1 &gt;d 2 , and h 2 &gt;h 4 . That is, the diameter of the bottom rim of the first elastic dome  12  is greater than that of the second elastic dome  13 , and the height of the first elastic section  122  of the first elastic dome  12  is greater than that of the second elastic section  132  of the second elastic dome  13 . Hence the second elastic dome  13  has greater flexibility than the first elastic dome  12 . In terms of depression effect, the first elastic dome  12  is softer while the second elastic dome  13  is harder. In addition, the first elastic dome  12  has a longer compression displacement (h 2 ) than that (h 4 ) of the second elastic dome  13 . 
     Referring to FIGS. 2,  3 A and  3 B, in normal conditions, the first elastic dome  12  and the second elastic dome  13  jointly support the key cap  11  in a non-depressed position (as shown in FIG.  2 ). When there is a force applied to the key cap  11 , the key cap  11  is moved downwards. The first and second elastic sections  122  and  132  of the first and second elastic domes  12 ,  13  are pressed downwards. As the compression displacement (h 4 ) of the second elastic dome  13  is shorter than that (h 2 ) of the first elastic dome  12 , the second elastic section  132  of the second elastic dome  13  is completely compressed first and cannot be moved downwards further (as shown in FIG. 3A) while the first elastic dome  12  is being moved downwards continuously. That is, the key cap  11  is continuously moved downwards in the direction of the first elastic dome  12  until the first elastic dome  12  touches the electric contact  231  and reaches the depressed position of the key cap  11  to output a preset signal. When the depression force on the key cap  11  is released, the first elastic dome  12  and the second elastic dome  13  return to their original conditions, and the key cap  11  returns to the non-depressed position. 
     When adopting the key structure of the invention to keys of larger sizes, the design of different compression displacements and different flexibility of the first elastic dome  12  and second elastic dome  13  allow depression movements to shift in one direction and to make depression movement more effective for completing signal output. 
     While the embodiment set forth above is adopted for keys of larger sizes, it may be adopted equally well for illuminating keys and can generate a better illuminating effect. As shown in FIG. 4, to achieve the object of illumination, the key  10  further includes a circuit board  25 , which has a lighting element  26  located on a position corresponding to the key cap  11 . The lighting element may be a light emitting diode or other light emitting elements. As the key cap  11  is jointly supported by the first elastic dome  12  and the second elastic dome  13 , the elastic plate  22  may have an opening  221  formed between the first elastic dome  12  and the second elastic dome  13  to allow light generated by the lighting element  26  to pass through. The key cap  11  may be made from transparent material. When the key cap  11  is depressed and electric connection is established, the light element  26  immediately emits light to indicate current conditions. When the depression force is released from the key cap  11 , the light element  26  is turned off. Hence through the design of the first elastic dome  12  and second elastic dome  13  set forth above, light generated by the lighting element  26  can directly pass through the key cap  11  without being obstructed, and thus achieve an optimum illuminating effect. 
     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.