Patent Publication Number: US-9899162-B2

Title: Keyboard

Description:
FIELD OF THE INVENTION 
     The present invention relates to a keyboard, and more particularly to a keyboard with a mechanical key structure. 
     BACKGROUND OF THE INVENTION 
     Generally, the widely-used peripheral input device of a computer system includes for example a mouse, a keyboard, a trackball, or the like. Via the keyboard, characters or symbols can be directly inputted into the computer system. As a consequence, most users and most manufacturers of input devices pay much attention to the development of keyboards. As known, a keyboard with scissors-type connecting elements is one of the widely-used keyboards. 
     The key structure of a keyboard will be described as follows. The key structure comprises a scissors-type connecting element.  FIG. 1  is a schematic side cross-sectional view illustrating a key structure of a conventional keyboard. As shown in  FIG. 1 , the conventional key structure  1  comprises a keycap  11 , a scissors-type connecting element  12 , a rubbery elastomer  13 , a membrane switch circuit member  14  and a base plate  15 . The keycap  11 , the scissors-type connecting element  12 , the rubbery elastomer  13  and the membrane switch circuit member  14  are supported by the base plate  15 . The scissors-type connecting element  12  is used for connecting the base plate  15  and the keycap  11 . 
     The membrane switch circuit member  14  comprises plural key intersections (not shown). When one of the plural key intersections is triggered, a corresponding key signal is generated. The rubbery elastomer  13  is disposed on the membrane switch circuit member  14 . Each rubbery elastomer  13  is aligned with a corresponding key intersection. When the rubbery elastomer  13  is depressed, the rubbery elastomer  13  is subjected to deformation to push the corresponding key intersection of the membrane switch circuit member  14 . Consequently, the corresponding key signal is generated. 
     The scissors-type connecting element  12  is arranged between the base plate  15  and the keycap  11 , and the base plate  15  and the keycap  11  are connected with each other through the scissors-type connecting element  12 . The scissors-type connecting element  12  comprises a first frame  121  and a second frame  122 . A first end of the first frame  121  is connected with the keycap  11 . A second end of the first frame  121  is connected with the base plate  15 . The rubbery elastomer  13  is enclosed by the scissors-type connecting element  12 . Moreover, the first frame  121  comprises a first keycap post  1211  and a first base plate post  1212 . The first frame  121  is connected with the keycap  11  through the first keycap post  1211 . The first frame  121  is connected with the base plate  15  through the first base plate post  1212 . The second frame  122  is combined with the first frame  121 . A first end of the second frame  122  is connected with the base plate  15 . A second end of the second frame  122  is connected with the keycap  11 . Moreover, the second frame  122  comprises a second keycap post  1221  and a second base plate post  1222 . The second frame  122  is connected with the keycap  11  through the second keycap post  1221 . The second frame  122  is connected with the base plate  15  through the second base plate post  1222 . 
     The operations of the conventional key structure  1  in response to the depressing action of the user will be illustrated as follows. Please refer to  FIG. 1  again. When the keycap  11  is depressed, the keycap  11  is moved downwardly to push the scissors-type connecting element  12  in response to the depressing force. As the keycap  11  is moved downwardly relative to the base plate  15 , the keycap  11  pushes the corresponding rubbery elastomer  13 . At the same time, the rubbery elastomer  13  is subjected to deformation to push the membrane switch circuit member  14  and trigger the corresponding key intersection of the membrane switch circuit member  14 . Consequently, the membrane switch circuit member  14  generates a corresponding key signal. When the keycap  11  is no longer depressed by the user, no external force is applied to the keycap  11  and the rubbery elastomer  13  is no longer pushed by the keycap  11 . In response to the elasticity of the rubbery elastomer  13 , the rubbery elastomer  13  is restored to its original shape to provide an upward elastic restoring force. Consequently, the keycap  11  is returned to its original position where it is not depressed. 
     With increasing development of science and technology, a mechanical key structure is introduced into the market. The mechanical key structure can provide better tactile feel.  FIG. 2  is a schematic side cross-sectional view illustrating a conventional mechanical key structure. As shown in  FIG. 2 , the mechanical key structure  2  comprises a keycap (not shown), a pedestal  21 , an upper cover  22 , a push element  23 , a linkage element  24 , a first spring strip  25 , a second spring strip  26  and a circuit board (not shown). The circuit board is located outside the pedestal  21 . The pedestal  21  is covered by the upper cover  22 . The upper cover  22  has an opening  221 . The linkage element  24  is located at a middle region of the pedestal  21 . Moreover, the linkage element  24  is movable upwardly or downwardly relative to the pedestal  21 . The second spring strip  26  is partially disposed within the pedestal  21 , and arranged between the linkage element  24  and the first spring strip  25 . The push element  23  and the linkage element  24  are collaboratively disposed on the pedestal  21 . The push element  23  is penetrated through the opening  221  of the upper cover  22  and coupled with the keycap. Moreover, the first spring strip  25  and the second spring strip  26  are electrically connected with the circuit board. 
     Please refer to  FIG. 2  again. The linkage element  24  has a protrusion structure  241 . The protrusion structure  241  is extended from a sidewall of the linkage element  24  toward the first spring strip  25 . Moreover, the first spring strip  25  comprises a fixing part  251  and an elastic part  252 . The fixing part  251  is fixed on the pedestal  21 . The elastic part  252  is extended from the fixing part  251 . Moreover, the elastic part  252  is contacted with the protrusion structure  241  of the linkage element  24 . Consequently, the elastic part  252  is movable relative to the fixing part  251 . 
     When the keycap is depressed, the keycap is moved downwardly to push the push element  23 . Consequently, the linkage element  24  connected with the push element  23  is moved downwardly. As the linkage element  24  is moved downwardly, the protrusion structure  241  of the linkage element  24  is contacted with the elastic part  252  and moved downwardly along the elastic part  252 . While the linkage element  24  is quickly moved in response to the depressing force of the user, the linkage element  24  is quickly moved across the elastic part  252 , and the elastic part  252  is pushed by the protrusion structure  241  of the linkage element  24 . Consequently, the elastic part  252  is moved relative to the fixing part  251  to collide with the second spring strip  26 . Since the first spring strip  25  and the second spring strip  26  are contacted with each other, the circuit board outputs a corresponding key signal. Moreover, while the first spring strip  25  and the second spring strip  26  are contacted with each other, a click sound is generated. Due to the click sound, the user can feel the depressing feedback. 
     Since the mechanical key structure  2  generates the click sound to provide the feedback feel while the keycap is depressed, the mechanical key structure  2  is favored by some users. However, the conventional mechanical key structure  2  still has some drawbacks. For example, the first spring strip  25  and the second spring strip  26  have to be protruded out of the pedestal  21  in order to be electrically connected with the circuit board. If the first spring strip  25  and the second spring strip  26  are not electrically connected with the circuit board, the operation of the mechanical key structure  2  cannot generate the key signal. Moreover, the keyboard comprises plural mechanical key structures  2 . For assembling the keyboard, it is necessary to sequentially electrically connect the first spring strips  25  and the second spring strips  26  of the plural mechanical key structures  2  with the circuit board. In other words, the process of assembling the keyboard is time-consuming and labor-intensive, and thus the assembling cost is high. 
     Therefore, there is a need of providing a keyboard with reduced assembling cost. 
     SUMMARY OF THE INVENTION 
     The present invention provides a keyboard with reduced assembling cost. 
     In accordance with an aspect of the present invention, there is provided a keyboard. The keyboard includes a base plate, a pressure sensing layer, a first key structure and a second key structure. The pressure sensing layer is located over the base plate. The pressure sensing layer includes plural pressure sensing regions. Each of the plural pressure sensing regions is configured to receive a first force or a second force. The first key structure is located over the pressure sensing layer, and aligned with the corresponding pressure sensing region. When the corresponding pressure sensing region is pushed by the first key structure, the first key structure provides the first force or the second force to the corresponding pressure sensing region. The second key structure is arranged beside the first key structure, located over the pressure sensing layer, and aligned with the corresponding pressure sensing region. When the corresponding pressure sensing region is pushed by the second key structure, the second key structure provides the first force or the second force to the corresponding pressure sensing region. When the first key structure or the second key structure is depressed with the first force or the second force, the keyboard outputs a corresponding pressure sensing signal. 
     In an embodiment, the keyboard further includes a circuit board and a controlling unit. The circuit board is electrically connected with the pressure sensing layer. The controlling unit is disposed on the circuit board and electrically connected with the pressure sensing layer. A lookup table recording a relationship between the first force, the second force, a first travelling distance and a second travelling distance is previously stored in the controlling unit. The controlling unit acquires the first travelling distance according to the first force and outputs a first pressure sensing signal corresponding to the first travelling distance, or the controlling unit acquires the second travelling distance according to the second force, and outputs a second pressure sensing signal corresponding to the second travelling distance. 
     In an embodiment, when the controlling unit judges that the corresponding pressure sensing region receives the first force, the controlling unit acquires the first travelling distance corresponding to the first force according to the lookup table, and outputs the first pressure sensing signal. When the controlling unit judges that the corresponding pressure sensing region receives the second force, the controlling unit acquires the second travelling distance corresponding to the second force according to the lookup table, and outputs the second pressure sensing signal. 
     In an embodiment, the keyboard further includes a circuit board and a controlling unit. The circuit board is electrically connected with the pressure sensing layer. The controlling unit is disposed on the circuit board and electrically connected with the pressure sensing layer. The controlling unit outputs a first pressure sensing signal corresponding to the first force according to the first force, or the controlling unit outputs a second pressure sensing signal corresponding to the second force according to the second force. 
     From the above descriptions, the present invention provides the keyboard with the key structure. The key structure is equipped with the light-emitting element and the movable element that is made of a light-transmissible material. Consequently, the key structure has the illuminating function. Moreover, the keyboard has the pressure sensing layer. By means of the pressure sensing layer, the key structure of the keyboard generates different pressure sensing signals according to different magnitudes of the depressing force. Since the functions of the keyboard are increased, the drawbacks of the conventional technologies are overcome. Optionally, the key structure is equipped with the spring strip according to the requirements of the user. The key structure with the spring strip can provide the depressing feedback to the user. Moreover, the key structure without the spring strip has reduced volume, and thus the key structure is slim. Moreover, the pressure sensing layer of the keyboard comprises plural pressure sensing regions. The electrical traces of the plural pressure sensing regions are formed in the pressure sensing layer, and a single electrical connection part is located at a side of the pressure sensing layer. The pressure sensing layer is electrically connected with the circuit board through the electrical connection part. Consequently, the electrical connection between the pressure sensing layer and the circuit board is achieved. In comparison with the conventional technology, the assembling cost is reduced. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side cross-sectional view illustrating a key structure of a conventional keyboard; 
         FIG. 2  is a schematic side cross-sectional view illustrating a conventional mechanical key structure; 
         FIG. 3  is a schematic exploded view illustrating a portion of a keyboard according to a first embodiment of the present invention; 
         FIG. 4  is a schematic side cross-sectional view illustrating a portion of the keyboard according to the first embodiment of the present invention; 
         FIG. 5  is a plot illustrating the relationship between forces and travelling distances in a lookup table of the controlling unit of the keyboard according to the first embodiment of the present invention; 
         FIG. 6  is a schematic side cross-sectional view illustrating the first key structure of the keyboard according to the first embodiment of the present invention, in which the keycap is depressed; 
         FIG. 7  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a second embodiment of the present invention; 
         FIG. 8  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a third embodiment of the present invention; 
         FIG. 9  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a fourth embodiment of the present invention; 
         FIG. 10  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a fifth embodiment of the present invention; 
         FIG. 11  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a sixth embodiment of the present invention; and 
         FIG. 12  is a plot illustrating the relationship between forces and travelling distances in a lookup table of the controlling unit of the keyboard according to the sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For solving the drawbacks of the conventional technologies, the present invention provides a keyboard. 
       FIG. 3  is a schematic exploded view illustrating a portion of a keyboard according to a first embodiment of the present invention.  FIG. 4  is a schematic side cross-sectional view illustrating a portion of the keyboard according to the first embodiment of the present invention. As shown in  FIGS. 3 and 4 , the keyboard  3  comprises a base plate  31 , a pressure sensing layer  32 , a first key structure  33 , a second key structure  34 , a circuit board  35  and a controlling unit  36 . It is noted that the keyboard comprises plural key structures. For succinctness and clarification, only the first key structure  33  and the second key structure  34  are shown in the drawings. The pressure sensing layer  32  is located over the base plate  31 , and disposed on a top surface of the circuit board  35 . The pressure sensing layer  32  comprises plural pressure sensing regions  321 . Each pressure sensing region  321  is aligned with a corresponding key structure. When the pressure sensing region  321  is pushed by the corresponding key structure, the pressure sensing region  321  receives a first force or a second force. The first key structure  33  is located over the pressure sensing layer  32 . Moreover, the first key structure  33  is aligned with the corresponding pressure sensing region  321  of the pressure sensing layer  32 . When the pressure sensing region  321  is pushed by the first key structure  33  with the first force or the second force, the keyboard  3  generates a first pressure sensing signal or a second pressure sensing signal. Similarly, the second key structure  34  is arranged beside the first key structure  33  and located over the pressure sensing layer  32 . Moreover, the second key structure  34  is aligned with the corresponding pressure sensing region  321  of the pressure sensing layer  32 . When the corresponding pressure sensing region  321  is pushed by the second key structure  34  with the first force or the second force, the keyboard  3  generates the first pressure sensing signal or the second pressure sensing signal. 
     The circuit board  35  is electrically connected with the pressure sensing layer  32 . The controlling unit  36  is disposed on the circuit board  35  and electrically connected with the pressure sensing layer  32 . According to the magnitude of the force received by the pressure sensing layer  32 , the controlling unit  36  judges the travelling distance of the key structure and generates the corresponding pressure sensing signal. For example, the first key structure  33  is depressed by the user. When the magnitude of the force exerted on the first key structure  33  is acquired by the controlling unit  36  through the pressure sensing layer  32 , the controlling unit  36  judges the magnitude of the exerted force. If the exerted force is the first force, the controlling unit  36  acquires a first travelling distance corresponding to the first force and generates the first pressure sensing signal corresponding to the first travelling distance. If the exerted force is the second force, the controlling unit  36  acquires a second travelling distance corresponding to the second force and generates the second pressure sensing signal corresponding to the second travelling distance. The ways of judging the travelling distance of the key structure and generating the corresponding pressure sensing signal by the controlling unit  36  will be described later. In an embodiment, the circuit board  35  is a printed circuit board (PCB), and the controlling unit  36  is a firmware component that is disposed on the circuit board  35 . It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention. For example, in another embodiment, the controlling unit is a microprocessor that is disposed on the circuit board. 
     The inner components of the first key structure  33  will be described as follows. Please refer to  FIGS. 3 and 4  again. The first key structure  33  comprises a keycap  330 , a pedestal  331 , an upper cover  332 , a movable element  333 , a light-emitting element  334 , an elastic element  335  and an elastomer  336 . The pedestal  331  comprises a light-transmissible region  3311  and a pedestal opening  3312 . The light-transmissible region  3311  is formed in a lower portion of the pedestal  331 , and aligned with the light-emitting element  334 . The pedestal opening  3312  is also formed in the lower portion of the pedestal  331 . Moreover, the pedestal opening  3312  is arranged beside the light-transmissible region  3311 . The pedestal  331  is covered by the upper cover  332 . Moreover, the upper cover  332  has an upper cover opening  3321  corresponding to the movable element  333 . The keycap  330  is connected with a first end of the movable element  333  through the upper cover opening  3321 . The movable element  333  is installed on the pedestal  331 , and penetrated through the upper cover opening  3321  so as to be connected with the keycap  330 . When the movable element  333  is depressed by the user, the movable element  333  is moved relative to the pedestal  331 . The elastic element  335  is sheathed around the movable element  333 . The light-emitting element  334  is disposed on a top surface of the circuit board  35 , and located under the pedestal  331 . The light-emitting element  334  is electrically connected with the circuit board  35  to emit a light beam B. Moreover, the light-emitting element  334  emits the light beam B to the movable element  333 . The elastomer  336  is located near the movable element  333 . Moreover, when the elastomer  336  is pushed by the movable element  333 , the elastomer  336  is subjected to deformation and penetrated through the pedestal opening  3312 . Consequently, the corresponding pressure sensing region  321  is pressed by the elastomer  336 . 
     In an embodiment, the elastic element  335  is a helical spring, and the light-emitting element  334  is a light emitting diode (LED). Moreover, the light-transmissible region  3311  of the pedestal  31  is an opening or a light-transmissible structure that is made of a transparent material. Consequently, the light beam B can pass through the light-transmissible region  3311 . Moreover, each pressure sensing region  321  of the pressure sensing layer  32  has a perforation  322 . The light-emitting element  334  is inserted into the corresponding perforation  322  and disposed on the top surface of the circuit board  35 . 
     Please refer to  FIG. 4  again. The movable element  333  comprises a main body  3331 , a coupling part  3332 , a light guide post  3333  and an extension part  3334 . The coupling part  3332  is located at a first end of the main body  3331  and connected with the keycap  330 . The light guide post  3333  is located at a second end of the main body  3331 , and located near the light-emitting element  334 . The light guide post  3333  is used for guiding the light beam B to the keycap  330  through the coupling part  3332 . The extension part  3334  is extended externally from the main body  3331 , and aligned with the elastomer  336 . That is, the elastomer  336  is arranged beside the light guide post  3333 , and aligned with the pedestal opening  3312 . While the movable element  333  is moved relative to the pedestal  331 , the elastomer  336  is pushed by the extension part  3334 , and the elastomer  336  is subjected to deformation and penetrated through the pedestal opening  3312 . Consequently, the corresponding pressure sensing region  321  is pressed by the elastomer  336 . Moreover, the elastic element  335  is sheathed around the light guide post  3333  and contacted with the pedestal  331 . The elastic element  335  provides an elastic force to the movable element  333 . In response to the elastic force, the movable element  333  is moved upwardly relative to the pedestal  331 . 
     In this embodiment, the main body  3331 , the coupling part  3332 , the light guide post  3333  and the extension part  3334  are made of a light-transmissible material. Moreover, the light guide post  3333  is assembled with the lower portion of the main body  3331 , and the extension part  3334  is assembled with a sidewall of the main body  3331 . The inner components of the second key structure  34  are similar to those of the first key structure  33 , and are not redundantly described herein. 
     The operations of the controlling unit  36  will be described as follows.  FIG. 5  is a plot illustrating the relationship between forces and travelling distances in a lookup table of the controlling unit of the keyboard according to the first embodiment of the present invention. Please refer to  FIGS. 3, 4 and 5 . The lookup table S is previously stored in the controlling unit  36 . The relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is recorded in the lookup table S. In this context, the force in the lookup table S is the force detected by the pressure sensing region  321 , and the travelling distance in the lookup table S is the moving distance of the keycap  330  of the first key structure  33 . The curve as shown in  FIG. 5  indicates the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances. In the curve of  FIG. 5 , the horizontal axis indicates the magnitudes of the travelling distances in the lookup table S, and the vertical axis indicates the magnitudes of forces in the lookup table S. 
     Please refer to  FIG. 5  again. When the travelling distance is zero, the corresponding force is F 0 . That is, the keycap  330  is not moved in response to the exerted force F 0  on the first key structure  33 . The reason why the keycap  330  is not moved is that the force F 0  is balanced by the elastic force of the elastic element  335 . When the travelling distance is in the range between zero and T 1 , the exerted force is in the range between F 0  and F 1 . That is, the exerted force F 1  can overcome the elastic force and result in the moving distance T 1  of the keycap  330 . While the travelling distance of the keycap  330  is changed from zero to T 1 , the elastomer  336  is not subjected to deformation. When the travelling distance is in the range between T 1  and T 2 , the exerted force is in the range between F 1  and F 2 . That is, as the exerted force is gradually increased, the elastomer  336  is subjected to deformation and the keycap  330  is continuously moved in response to the deformation of the elastomer  336 . When the exerted force is increased to F 2 , the deformation of the elastomer  336  reaches the elastic limit. Under this circumstance, the moving distance of the keycap  330  is only T 2 . As the exerted force is increased to the magnitude larger than F 2 , the keycap  330  is no longer moved. The segment between the travelling distance T 1  and the travelling distance T 2  is nonlinear. 
     The operations of the first key structure  33  of the keyboard  3  in response to the depressing action of the user will be illustrated in more details as follows. Please refer to  FIGS. 3, 4, 5 and 6 .  FIG. 6  is a schematic side cross-sectional view illustrating the first key structure of the keyboard according to the first embodiment of the present invention, in which the keycap is depressed. While the keycap  330  of the first key structure  33  is depressed lightly, the keycap  330  is moved downwardly to push the movable element  333  in response to the light depressing force. As the keycap  330  is moved downwardly, the movable element  333  is moved downwardly relative to the pedestal  331 . While the movable element  333  is moved downwardly, the elastic element  353  is compressed by the main body  3331  of the movable element  333  and the keycap  330  is moved to generate a travelling distance (see  FIG. 6 ). Moreover, as the main body  3331  is moved downwardly, the extension part  3334  connected with the main body  3331  is correspondingly moved downwardly. Since the elastomer  336  is connected with the extension part  3334 , the elastomer  336  is penetrated through the pedestal opening  3312  to press the corresponding pressure sensing region  321  with a first force. After the pressure sensing region  321  receives the first force and senses the magnitude of the first force, the magnitude of the first force is transmitted from the pressure sensing region  321  to the controlling unit  36 . According to the magnitude of the first force (e.g., F 3 ) and the lookup table S, the controlling unit  36  acquires a first travelling distance T 3  corresponding to the first force F 3 . In addition, the controlling unit  36  generates the first pressure sensing signal corresponding to the first travelling distance T 3 . 
     When the keycap  330  is no longer depressed by the user, no external force is applied to the keycap  330 . In response to the elasticity of the elastic element  335 , the compressed elastic element  335  is restored to its original shape to provide an elastic force to the movable element  333 . In response to the elastic force, the movable element  333  is moved upwardly relative to the pedestal  331  and returned to its original position where it is not depressed. 
     While the keycap  330  is depressed heavily, the actions of the first key structure  33  are similar to the above actions of lightly depressing the keycap  330 . In contrast, the pressure sensing region  321  receives a second force, and the magnitude of the second force is transmitted from the pressure sensing region  321  to the controlling unit  36 . According to the magnitude of the second force (e.g., F 2 ) and the lookup table S, the controlling unit  36  acquires a second travelling distance T 2  corresponding to the second force F 2 . In addition, the controlling unit  36  generates the second pressure sensing signal corresponding to the second travelling distance T 2 . 
     In the above embodiment, the first key structure  3  of the keyboard  3  is equipped with an elastomer  336 . The relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is recorded in the lookup table S. The lookup table S is previously stored in the controlling unit  36 . According to the lookup table S, the controlling unit  36  can acquire the travelling distance of the keycap  330  corresponding to the exerted force. Consequently, the function of sensing the multi-stage pressure can be achieved. Since different commands are executed by the keyboard  3  according to different pressure sensing signals, the functions of the first key structure  33  are increased. Moreover, the pressure sensing layer  32  of the keyboard  3  comprises the plural pressure sensing regions  321 . The electrical traces  323  of the plural pressure sensing regions  321  are formed in the pressure sensing layer  32 , and an electrical connection part  324  is located at a side of the pressure sensing layer  32 . The pressure sensing layer  32  is electrically connected with the circuit board  35  through the electrical connection part  324 . Consequently, the electrical connection between the pressure sensing layer  32  and the circuit board  35  is achieved. In comparison with the conventional technology, it is not necessary to sequentially electrically connect the key structures with the circuit board according to the present invention. In other words, the process of assembling the keyboard is time-saving, and the assembling cost is reduced. 
     The following three aspects should be specially described. Firstly, the keyboard  3  can be operated in different operation modes according to settings. For example, the keyboard  3  may be selectively in a travelling distance detection mode or a pressure detection mode through the settings of the controlling unit  36 . The operations of the keyboard  3  in the travelling distance detection mode are similar to those mentioned above. When the keyboard  3  is in the pressure detection mode through the settings of the controlling unit  36 , the controlling unit  36  directly outputs the pressure sensing signal corresponding to the magnitude of the received force. While the keycap  330  of the first key structure  33  is depressed lightly, the operations of the first key structure  33  are similar to the above lightly-depressing operations. After the magnitude of the first force is transmitted from the pressure sensing region  321  to the controlling unit  36 , the controlling unit  36  generates the first pressure sensing signal corresponding to the first force. While the keycap  330  of the first key structure  33  is depressed lightly, the operations of the first key structure  33  are similar to the above heavily-depressing operations. After the magnitude of the second force is transmitted from the pressure sensing region  321  to the controlling unit  36 , the controlling unit  36  generates the second pressure sensing signal corresponding to the second force. In an embodiment, the keyboard  3  further comprises a switching element (e.g., a button or a switch) to change the operation mode. That is, the keyboard  3  can be operated in different operation modes in order to comply with different requirements of the user. 
     Secondly, the keyboard  3  can be operated in a combined mode of the travelling distance detection mode and the pressure detection mode according to settings. For example, the operation mode of the keyboard  3  is determined according to the range of the travelling distance of the look-up table S of  FIG. 5 . According to the settings of the controlling unit  36 , the keyboard  3  is in the travelling distance detection mode when the travelling distance is in larger than or equal to zero and smaller than or equal to T 2 , and the keyboard  3  is in the pressure detection mode when the travelling distance is equal to T 2 . The operations of the keyboard  3  in the travelling distance detection mode are similar to those mentioned above. When the exerted force is increased to F 2 , the deformation of the elastomer  336  reaches the elastic limit. Under this circumstance, the keycap  330  is no longer moved, and the keyboard  3  enters the pressure detection mode according to the settings of the controlling unit  36 . Even if the exerted force is increased, the controlling unit  36  can still output the pressure sensing signal corresponding to the exerted force in the pressure detection mode. Consequently, the keyboard  3  of the present invention can provide more functions. 
     Thirdly, the first key structure  33  and the second key structure  34  of the keyboard  3  can be set as consecutive buttons, whose functions are similar to accelerator pedals in cars. For example, when the key structure corresponding to the down arrow is continuously depressed by the user, the scroll bar shown on the computer window (not shown) is moved downwardly. While the key structure is depressed lightly, the scroll bar is moved downwardly at a slower speed. While the key structure is depressed heavily, the speed of moving the scroll bar downwardly is gradually increased. In some embodiments, the function of the consecutive button is applied to the game software to increase the convenience of operating the keyboard. Consequently, the keyboard  3  of the present invention provides the function of the consecutive button to increase the operating convenience. 
     The present invention further provides a second embodiment, which is distinguished from the first embodiment.  FIG. 7  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a second embodiment of the present invention. As shown in  FIG. 7 , the keyboard  4  comprises a base plate  41 , a pressure sensing layer  42 , a first key structure  43 , a second key structure  44 , a circuit board  45  and a controlling unit  46 . The pressure sensing layer  42  comprises plural pressure sensing regions  421 . A lookup table S (see  FIG. 5 ) recording the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is previously stored in the controlling unit  46 . The first key structure  43  comprises a keycap (not shown), a pedestal  431 , an upper cover  432 , a movable element  433 , a light-emitting element  434 , an elastic element  435  and an elastomer  436 . The pedestal  431  comprises a light-transmissible region  4311  and a pedestal opening  4312 . Moreover, the upper cover  432  has an upper cover opening  4321  corresponding to the movable element  433 . The structures and functions of the components of the keyboard  4  which are identical to those of the first embodiment are not redundantly described herein. In comparison with the first embodiment, the position of the pressure sensing layer  42  of the keyboard  4  of this embodiment is distinguished. 
     Please refer to  FIG. 7 . The pressure sensing layer  42  is disposed on the base plate  41 , and located near a bottom surface of the circuit board  45 . The circuit board  45  comprises plural circuit board openings  451 . Each circuit board opening  451  is aligned with the pedestal opening  4312  and the elastomer  436  of the corresponding key structure (e.g., the first key structure  43 ). While the keycap is depressed and the movable element  433  is correspondingly moved downwardly, the elastomer  436  connected with the movable element  433  is subjected to deformation and penetrated through the pedestal opening  4312  and the circuit board opening  451  sequentially. Consequently, the corresponding pressure sensing region  421  is pressed by the elastomer  436 . In other words, the pressure sensing layer  42  of this embodiment is located under the circuit board  45 . 
     The present invention further provides a third embodiment, which is distinguished from the above embodiments.  FIG. 8  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a third embodiment of the present invention. As shown in  FIG. 8 , the keyboard  5  comprises a base plate  51 , a pressure sensing layer  52 , a first key structure  53 , a second key structure  54 , a circuit board  55  and a controlling unit  56 . The pressure sensing layer  52  comprises plural pressure sensing regions  521 . A lookup table S (see  FIG. 5 ) recording the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is previously stored in the controlling unit  56 . The first key structure  53  comprises a keycap (not shown), a pedestal  531 , an upper cover  532 , a movable element  533 , a light-emitting element  534 , an elastic element  535 , an elastomer  536  and a spring strip  537 . The pedestal  531  comprises a light-transmissible region  5311  and a pedestal opening  5312 . Moreover, the upper cover  532  has an upper cover opening  5321  corresponding to the movable element  533 . The structures and functions of the components of the keyboard  5  which are identical to those of the above embodiments are not redundantly described herein. In comparison with the above embodiments, the first key structure  53  of this embodiment is distinguished. 
     The components of the first key structure  53  will be described as follows. In comparison with the first key structure  53  of the first embodiment, the first key structure  53  of this embodiment has the following three distinguished aspects. Firstly, the first key structure  33  further comprises the spring strip  537 . Secondly, the structure of the movable element  533  is distinguished. Thirdly, the installation of the elastomer  536  is distinguished. Please refer to  FIG. 8 . The spring strip  537  is installed on the pedestal  531  and arranged beside a first side of the movable element  533 . The movable element  533  comprises a main body  5331 , a coupling part  5332 , a light guide post  5333 , an extension part  5334  and a push part  5335 . The coupling part  5332  is located at a first end of the main body  5331  and connected with the keycap. The light guide post  5333  is located at a second end of the main body  5331 , and located near the light-emitting element  534 . The extension part  5334  is extended externally from the main body  5331 , and arranged beside a second side of the light guide post  5333 . Moreover, the extension part  5334  is aligned with the elastomer  536 . The push part  5334  is extended externally from the main body  5331  and located near the spring strip  537 . While the movable element  533  is moved relative to the pedestal  531 , the push part  5334  is contacted with the spring strip  537 . Consequently, the spring strip  537  is correspondingly swung to collide with the push part  5335 . Meanwhile, a sound is generated. 
     In this embodiment, the coupling part  5332 , the light guide post  5333 , the extension part  5334  and the push part  5335  are integrally formed with the main body  5331 . Moreover, the main body  5331 , the coupling part  5332  and the light guide post  5333  are made of a light-transmissible material. In this embodiment, the light guide post  5333  is integrally formed with the main body  5331 . In another embodiment, the light guide post  5333  is assembled with the lower portion of the main body  5331 . 
     In this embodiment, the elastomer  536  is installed on the pedestal  531 , and inserted into the pedestal opening  5312 . Moreover, the elastomer  536  is not connected with the extension part  5334 . That is, the elastomer  536  has a shape of an inverted cone. While the movable element  533  is moved relative to the pedestal  531 , the extension part  5334  is moved with the main body  5331  to push the elastomer  536 . The elastomer  536  is subjected to deformation and penetrated through the pedestal opening  5312 . Consequently, the corresponding pressure sensing region  521  is pressed by the elastomer  536 . 
     The operations of the first key structure  53  of the keyboard  5  in response to the depressing action of the user will be illustrated as follows. While the keycap is depressed lightly, the keycap is moved downwardly to push the movable element  533  in response to the light depressing force. As the keycap is moved downwardly, the movable element  533  is moved downwardly relative to the pedestal  51 . As the movable element  533  is moved downwardly, the elastic element  535  is compressed by the main body  5331  of the movable element  533  and the keycap is moved to generate a travelling distance. Moreover, as the main body  5331  is moved downwardly, the extension part  5334  connected with the main body  5331  is correspondingly moved downwardly. Consequently, the elastomer  536  that is inserted in the pedestal opening  5312  is penetrated through the pedestal opening  5312  to press the corresponding pressure sensing region  521  with a first force. After the pressure sensing region  521  receives the first force and senses the magnitude of the first force, the magnitude of the first force is transmitted from the pressure sensing region  521  to the controlling unit  56 . According to the similar operating principle of the first embodiment, the controlling unit  56  acquires a first travelling distance corresponding to the first force. In addition, the controlling unit  56  generates the first pressure sensing signal corresponding to the first travelling distance. 
     Moreover, while the movable element  533  is moved downwardly, the push part  5335  is correspondingly moved downwardly to push the spring strip  537 . In response to the elasticity of the spring strip  537 , the spring strip  537  is correspondingly swung to collide with the push part  5335 . Consequently, a sound is generated. When the keycap is no longer depressed by the user, no external force is applied to the keycap. In response to the elasticity of the elastic element  535 , the compressed elastic element  535  is restored to its original shape to provide an elastic force to the movable element  533 . In response to the elastic force, the movable element  533  is moved upwardly relative to the pedestal  531  and returned to its original position where it is not depressed. The operations of heavily depressing the keycap are similar to those of lightly depressing the keycap, and are not redundantly described herein. 
     As mentioned above, the keyboard  5  of this embodiment is further equipped with the spring strip  537  and the push part  5335 . While the keycap is depressed, the spring strip  537  and the push part  5335  of the first key structure  53  are activated to generate a sound. Consequently, the user can feel the depressing feedback. 
     The present invention further provides a fourth embodiment, which is distinguished from the above embodiments.  FIG. 9  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a fourth embodiment of the present invention. As shown in  FIG. 9 , the keyboard  6  comprises a base plate  61 , a pressure sensing layer  62 , a first key structure  63 , a second key structure  64 , a circuit board  65  and a controlling unit  66 . The pressure sensing layer  62  comprises plural pressure sensing regions  621 . A lookup table S (see  FIG. 5 ) recording the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is previously stored in the controlling unit  66 . The first key structure  63  comprises a keycap (not shown), a pedestal  631 , an upper cover  632 , a movable element  633 , a light-emitting element  634 , an elastic element  635 , an elastomer  636  and a spring strip  637 . The pedestal  631  comprises a light-transmissible region  6311  and a pedestal opening  6312 . Moreover, the upper cover  632  has an upper cover opening  6321  corresponding to the movable element  633 . The structures and functions of the components of the keyboard  6  which are identical to those of the third embodiment are not redundantly described herein. In comparison with the third embodiment, the position of the pressure sensing layer  62  of this embodiment is distinguished. 
     Please refer to  FIG. 9 . The pressure sensing layer  62  is disposed on the base plate  61 , and located near a bottom surface of the circuit board  65 . The circuit board  65  comprises plural circuit board openings  651 . Each circuit board opening  651  is aligned with the pedestal opening  6312  and the elastomer  636  of the corresponding key structure (e.g., the first key structure  63 ). While the keycap is depressed and the movable element  633  is correspondingly moved downwardly, the extension part connected with the main body is correspondingly moved downwardly. Consequently, the elastomer  636  that is inserted in the pedestal opening  6312  is penetrated through the pedestal opening  6312  and the circuit board opening  651  to press the corresponding pressure sensing region  621 . For complying with the position of the pressure sensing layer  62 , the elastomer  636  of this embodiment is longer than the elastomer  536  of the third embodiment. In other words, the pressure sensing layer  62  of this embodiment is located under the circuit board  65 . 
     The present invention further provides a fifth embodiment, which is distinguished from the above embodiments.  FIG. 10  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a fifth embodiment of the present invention. As shown in  FIG. 10 , the keyboard  7  comprises a base plate  71 , a pressure sensing layer  72 , a first key structure  73 , a second key structure  74 , a circuit board  75  and a controlling unit  76 . The pressure sensing layer  72  comprises plural pressure sensing regions  721 . A lookup table S (see  FIG. 5 ) recording the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is previously stored in the controlling unit  76 . The first key structure  73  comprises a keycap (not shown), a pedestal  731 , an upper cover  732 , a movable element  733 , a light-emitting element  734 , an elastic element  735  and an elastomer  736 . The pedestal  731  comprises a light-transmissible region  7311  and a pedestal opening  7312 . Moreover, the upper cover  732  has an upper cover opening  7321  corresponding to the movable element  733 . The movable element  733  comprises a main body  7331 , a coupling part  7332 , a light guide post  7333  and an extension part  7334 . The structures and functions of the components of the keyboard  7  which are identical to those of the first embodiment are not redundantly described herein. In comparison with the first embodiments, the installation of the elastomer  736  is distinguished. 
     As shown in  FIG. 10 , the elastomer  736  of the first key structure  73  is disposed on the corresponding pressure sensing region  721 , and inserted into the pedestal opening  7312 . That is, the elastomer  736  has a shape of an upright cone. While the movable element  733  is moved relative to the pedestal  731 , the extension part  7334  is penetrated through the pedestal opening  7312  to push the elastomer  736 . The elastomer  736  is subjected to deformation, and thus the corresponding pressure sensing region  721  is pressed by the elastomer  736 . 
     In the embodiment, the pressure sensing layer  72  of the keyboard  7  is disposed on the top surface of the circuit board  75 . It is noted that numerous modifications and alterations may be made while retaining the teachings of the invention. For example, in another embodiment, the pressure sensing layer is disposed on the base plate and located near the bottom surface of the circuit board. 
     The present invention further provides a sixth embodiment, which is distinguished from the above embodiments.  FIG. 11  is a schematic side cross-sectional view illustrating a portion of a keyboard according to a sixth embodiment of the present invention.  FIG. 12  is a plot illustrating the relationship between forces and travelling distances in a lookup table of the controlling unit of the keyboard according to the sixth embodiment of the present invention. In this embodiment, the keyboard  8  comprises a base plate  81 , a pressure sensing layer  82 , a first key structure  83 , a second key structure  84 , a circuit board  85  and a controlling unit  86 . The pressure sensing layer  82  comprises plural pressure sensing regions  821 . A lookup table S* (see  FIG. 12 ) recording the relationship between the magnitudes of plural forces and the magnitudes of plural travelling distances is previously stored in the controlling unit  86 . The first key structure  83  comprises a keycap (not shown), a pedestal  831 , an upper cover  832 , a movable element  833 , a light-emitting element  834  and an elastic element  835 . The pedestal  831  comprises a light-transmissible region  8311  and a pedestal opening  8312 . Moreover, the upper cover  832  has an upper cover opening  8321  corresponding to the movable element  833 . The movable element  833  comprises a main body  8331 , a coupling part  8332 , a light guide post  8333  and an extension part  8334 . The structures and functions of the components of the keyboard  8  which are identical to those of the first embodiment are not redundantly described herein. In comparison with the first embodiment, the first key structure  83  of the keyboard  8  of this embodiment is not equipped with the elastomer. 
     As shown in  FIG. 11 , the first key structure  83  is not equipped with the elastomer. The extension part  8334  of the first key structure  83  is longer than the extension part  8334  of the first embodiment. Consequently, while the movable element  833  is moved downwardly, the extension part  8334  is contacted with the corresponding pressure sensing region  821 . The structures of the other components of the first key structure  83  are similar to those of the first key structure  33  of the first embodiment, and are not redundantly described herein. 
     Since the first key structure  83  is not equipped with the elastomer, the contents of the look-up table S* in the controlling unit  86  are different from the contents of the look-up table S of  FIG. 5 . In the curve of  FIG. 12 , the horizontal axis indicates the magnitudes of the travelling distances in the lookup table S*, and the vertical axis indicates the magnitudes of forces in the lookup table S*. Moreover, the curve of force versus travelling distance as shown in  FIG. 12  is different from that of  FIG. 5 . 
     Please refer to  FIG. 12  again. When the travelling distance is zero, the corresponding force is F 0 . That is, the keycap is not moved in response to the exerted force F 0  on the first key structure  83 . The reason why the keycap is not moved is that the force F 0  is balanced by the elastic force of the elastic element  835 . When the travelling distance is in the range between zero and T 1 , the exerted force is in the range between F 0  and F 1 . That is, the exerted force F 1  can overcome the elastic force and result in the moving distance T 1  of the keycap. When the travelling distance is in the range between T 1  and T 4 , the exerted force is in the range between F 1  and F 4 . That is, as the exerted force is gradually increased, the keycap is continuously moved in response to the exerted force. When the exerted force is increased to F 4 , the moving distance of the keycap is only T 4 . As the exerted force is increased to the magnitude larger than F 4 , the keycap is no longer moved. The segment between the travelling distance  0  and the travelling distance T 4  is linear. Moreover, the look-up table S or the look-up table S* may be selected according to the practical requirements. 
     In an embodiment, the keyboard of the present invention has both of an illuminating function and a pressure sensing function. For example, when the keycap is depressed lightly, the circuit board outputs the corresponding first pressure sensing signal. According to the first pressure sensing signal, the light-emitting element is controlled to generate a light beam with a first lighting effect. Whereas, when the keycap is depressed heavily, the circuit board outputs the corresponding second pressure sensing signal. According to the second pressure sensing signal, the light-emitting element is controlled to generate a light beam with a second lighting effect. For example, the light beam with the first lighting effect is a slow flickering light, and the light beam with the second lighting effect is a fast flickering light. According to the lighting effect, the user can recognize whether a lightly depressed function or a heavily depressed function is enabled. It is noted that the cooperative functions of the key structure are not restricted to the illuminating function and the pressure sensing function. 
     From the above descriptions, the present invention provides the keyboard with the key structure. The key structure is equipped with the light-emitting element and the movable element that is made of a light-transmissible material. Consequently, the key structure has the illuminating function. Moreover, the keyboard has the pressure sensing layer. By means of the pressure sensing layer, the key structure of the keyboard generates different pressure sensing signals according to different magnitudes of the depressing force. Since the functions of the keyboard are increased, the drawbacks of the conventional technologies are overcome. Optionally, the key structure is equipped with the spring strip according to the requirements of the user. The key structure with the spring strip can provide the depressing feedback to the user. Moreover, the key structure without the spring strip has reduced volume, and thus the key structure is slim. 
     Moreover, the pressure sensing layer of the keyboard comprises plural pressure sensing regions. The electrical traces of the plural pressure sensing regions are formed in the pressure sensing layer, and a single electrical connection part is located at a side of the pressure sensing layer. The pressure sensing layer is electrically connected with the circuit board through the electrical connection part. Consequently, the electrical connection between the pressure sensing layer and the circuit board is achieved. In comparison with the conventional technology, it is not necessary to sequentially electrically connect the key structures with the circuit board according to the present invention. Consequently, the assembling cost is reduced. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all modifications and similar structures.