Abstract:
A switch mechanism has a ratchet, two tappets, and two sensors. The ratchet has a plurality of sawteeth. The tappets are installed at two opposite sides of the ratchet. Each sensor is installed beside the ratchet for generating detecting signals. When the ratchet rotates clockwise, the sawteeth of the ratchet will push one tappet toward its corresponding sensor so as to generate corresponding clockwise detecting signals. When the ratchet rotates counterclockwise, the sawteeth of the ratchet will push the other tappet toward its corresponding sensor so as to generate corresponding counterclockwise detecting signals.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a switch mechanism, and more specifically to a switch mechanism that is used in a pointing device to decide a rotational direction of a wheel installed on the pointing device. 
     2. Description of the Prior Art 
     In computer systems, the use of a windowing operating system to browse, edit or otherwise manipulate data is commonplace. Distinct graphical areas termed windows are displayed on the monitor that is connected to the computer system. Documents are displayed within the confines of the window for perusal by a user. If a document is too large, then only a portion of the document is displayed inside the window. If the user desires to see off-window portions of the document, then a mouse is used to manipulate a scroll bar located on a side of the window to scroll the window, and hence bring the hidden portions of the document into view. For example, if the user desires to browse in a downward direction within the window, the user clicks on a downward arrow sign of the scroll bar (by way of the mouse), and the document will move upward by a predetermined unit, usually by a line of text. Similarly, if the user wants to browse in an upward direction, the user uses the mouse to click on an upward arrow sign of the scroll bar, and the document is scrolled downward. The above is a familiar ground to general computer users, and so nothing more need be said about it. 
     FIG. 1 is a perspective view of a mechanical mouse  10  with a wheel  14  according to a prior art. The mechanical mouse  10  comprises a housing  12 . The wheel  14  is installed in the housing  14 , and is capable of rotating clockwise and counterclockwise so as to control a scroll bar on a side of a window to move the scroll bar upward and downward, enabling the user to scroll the window and thus conveniently browse a document. When the user is perusing a portion of a document, the user may rotate the wheel  14  of the mouse  10  clockwise to activate the scroll bar to scroll the document upward. Alternatively, the user may rotate the wheel  14  counterclockwise to activate the scroll bar to scroll the document downward. This is a familiar convenience that is well-know in the art. 
     FIG. 2 is a perspective view of an inner portion of the mechanical mouse  10 . FIG. 3 is a top view of the inner portion of the mechanical mouse  10 . As shown in FIG.  2  and FIG. 3, the mechanical mouse  10  further comprises a substrate  16  installed inside the housing  12 , an support  20  installed on the substrate  16  having a notch  21 , a shaft  18  connected with the wheel  14  rotatably installed inside the notch  21  of the support  20 , a first light source  42  and a second light source  44  installed adjacent to the wheel  14  on two ends of the support  20 , and a first sensor  32  and a second sensor  34  installed on an opposite side of the wheel  14  at two ends of the upholder  20 . The wheel  14  has a rough surface  22 , and a plurality of narrow gaps  24  extend along a radial direction as measured from the center of the wheel  14 . The first light source  42  and the second light source  44  generate light  46  and light  48 , respectively. The first sensor  32  and the second sensor  34  are used to detect the light  46  and light  48  passing through the narrow gaps  24  respectively, and generate corresponding detecting signals. 
     FIG. 4 a  is a diagram of output signals of the two sensors  32  and  34  on a time axis when the wheel  14  of the prior art mechanical mouse  10  rotates clockwise. FIG. 4 b  is a diagram of output signals of the two sensors  32  and  34  on a time axis when the wheel  14  of the prior art mechanical mouse  10  rotates counterclockwise. FIG. 5 is a table contrasting output signals of the two sensors  32  and  34  with time when the wheel  14  of the mechanical mouse  10  rotates clockwise and counterclockwise as shown in FIG. 4   1   and FIG. 4 b.  When a user rotates the wheel  14 , the shaft  18  rotates inside the notch  21  of the support  20 . The narrow gaps  24  also rotate, following the wheel  14 . The number of narrow gaps  24  is carefully considered in the design of the wheel  14 , as are both the spacing between adjacent gaps  24  and the width of the gaps  24 . In a corresponding way, the positions of the first sensor  32 , the second sensor  34 , the first light source  42  and the second light source  44  are carefully selected. These carefully selected parameters enable differentiation of clockwise and counter-clockwise rotation of the wheel by waveform phase analysis of two optically detected signals. When the wheel  14  rotates clockwise and permits the light  46  generated by the first light source  42  to just pass through a narrow gap  24  to the first sensor  32 , the first sensor  32  will detect the light  46  and generate an output signal “1” (i.e., a high-potential signal). At the same time, the light  48  generated by the second light source  44  is blocked by the spacing between two narrow gaps  24 , and so the second sensor  34  is unable to detect the light  48  and generates an output signal “0” (i.e., a low-potential signal). Then, as the wheel  14  continues to rotate clockwise, the light  46  generated by the first light source  42  passes through the middle portion of the narrow gap  24 , continuing to arrive at the first sensor  32 . At the same time, the light  48  generated by the second light source  44  just passes through a narrow gap  24  and arrives at the second sensor  34 . Hence, the output signals generated by the first sensor  32  and the second sensor  34  are “1” and “1”, respectively. Continuing in this manner, it should be clear that the design of the narrow gaps  24  generates a phase discrepancy of 90 degrees between the output signal of the first sensor  32  and the second sensor  34 . As the wheel  14  continues to rotate clockwise, the output signals generated by the first sensor  32  and the second sensor  34  become “0” and “1”, respectively. As the wheel  14  rotates clockwise even more, the output signals generated by the first sensor  32  and the second sensor  34  change to “0” and “0”, respectively. 
     Although the wheel  14  is capable of vertical movement along the shaft  18  (i.e., that the wheel  14  is movable up-and-down while rotating inside the notch  21  of the support  20 ), such movement does not affect the result of the output signals of the corresponding first sensor  32  and the second sensor  34 . That is, the phase difference between the output signals of the first sensor  32  and the second sensor  34  remains 90 degrees. 
     As shown in FIG. 4 a , FIG. 4 b  and FIG. 5, when the wheel  14  rotates clockwise, if the output signal of the first sensor  32  is “0”, then the output signal of the second sensor  34  will be “1” inside a period t 1 . The output signal of the sensors  32  and  34  inside period t 1  may thus be though of as “01”. If the wheel  14  continues to rotate clockwise, the output signal of the sensors  32  and  34  inside period t 2  will be “00”. The output signal of the sensors  32  and  34  inside period t 3  is “10”. The output signal of the sensors  32  and  34  inside period t 4  is “11”. The output signals of the sensors  32  and  34  inside periods t 5  and t 6  are same as the output signals of the sensors  32  and  34  inside periods t 1  and t 2 , respectively. The output signals of the first sensor  32  and the second sensor  34  are thus periodic over four cycles. To determine whether the wheel  14  is rotating clockwise or counter-clockwise, one need only determine if the arrangement of the output signals of the sensors  32  and  34  changes from “01”, “00”, “10” to “11” in the proper sequence. For example, when the output signal of the sensors  32  and  34  changes from “00” to “10”, it is inferred that the wheel  14  is rotating clockwise. Similarly, when the wheel  14  rotates counterclockwise, the output signals of the first sensor  32  and the second sensor  34  also have four periods in a cycle. The output signal of the sensors  32  and  34  inside period t 1  is “00”. The output signal of the sensors  32  and  34  inside period t 2  is “01”. The output signal of the sensors  32  and  34  inside period t 3  is “11”. The output signal of the sensors  32  and  34  inside period t 4  is “10”. The output signals of the sensors  32  and  34  inside periods t 5  and t 6  are same as the output signals of the sensors  32  and  34  inside periods t 1  and t 2 , respectively. Therefore, to decide whether the wheel  14  is rotating counterclockwise, one simply determines if the arrangement of the output signals of the sensors  32  and  34  changes from “00”, “01”, “11” to “10” in order. For example, when the output signal of the sensors  32  and  34  changes from “10” to “00”, it is inferred that the wheel  14  is rotating counterclockwise. 
     FIG. 6 is a diagram of the output signals of the two sensors  32  and  34  versus time when the wheel  14  of the prior art mechanical mouse  10  rotates clockwise, wherein the width of one narrow gap  24  of the wheel  14  is too small. As shown in FIG. 6, the output signals of the sensors  32  and  34  inside periods t 8 , t 9  and t 10  are “11”, “01” and “00”, respectively. If the first sensor  32  receives light  46  that passes through a gap  24  having a gap width that is too small, the phase difference of the output signals of the wheel  14  detected by the sensors  32  and  34  will not be 90 degrees. The output signals of the sensors  32  and  34  inside periods t 11  and t 12  is “00” and “11” respectively. As the wheel  14  rotates continues its clockwise rotation, the output signal of the sensors  32  and  34  inside period t 13  becomes “01”. 
     Due to a flaw in a gap  24 , when the wheel  14  rotates from period t 10  to period t 11 , the output signal of the sensors  32  and  34  does not change, but remains “00”. The computer system thus determines that from period t 10  to period t 11 , the “the wheel  14  does not rotate”. When the wheel  14  rotates from period t 11  to period t 12 , the output signal of the sensors  32  and  34  changes from “00” to “11”. From FIG. 5 it is clear that the output signal of the sensors  32  and  34  never changes from “00” to “11”, regardless of whether the wheel  14  is rotating clockwise or counterclockwise. The computer system is thus unable to determine the rotational direction of the wheel  14 , which may cause the mouse  10  to behave erratically. A similar problem occurs with a counterclockwise rotation of the wheel  14 . As the rotational direction of the wheel  14  is determined by the order of the output signals of the two sensors  32  and  34 , if the width of a narrow gap  24  of the wheel  14  is too large or too small, incorrect output signals may easily occur, leading to an incorrect determination of the rotational direction of the wheel  14 . 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the present invention to provide a switch mechanism for use inside a pointing device that is capable of accurately determining the rotational direction of a wheel. 
     The present invention, briefly summarized, discloses a switch mechanism comprising a ratchet, two tappets, and two sensors. The ratchet has a plurality of sawteeth. The tappets are installed at two opposite sides of the ratchet. Each sensor is installed adjacent to the ratchet for generating detecting signals. When the ratchet rotates clockwise, the sawteeth of the ratchet will push one tappet toward its corresponding sensor so as to generate corresponding clockwise detecting signals. When the ratchet rotates counterclockwise, the sawteeth of the ratchet will push the other tappet toward its corresponding sensor so as to generate corresponding counterclockwise detecting signals. 
     It is an advantage that the switch mechanism of the present invention mouse is able to accurately determine the rotational direction of a wheel using a single detecting signal that is generated by either the first sensor or the second sensor. There is no need for two separate detecting signals. 
     These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a mechanical mouse with a wheel according to the prior art. 
     FIG. 2 is a perspective view of an inner portion of the mechanical mouse of FIG.  1 . 
     FIG. 3 is a top view of the inner portion of FIG.  2 . 
     FIG. 4 a  is a diagram of output signals of two sensors versus time when the wheel of the prior art mechanical mouse rotates clockwise. 
     FIG. 4 b  is a diagram of output signals of two sensors versus time when the wheel of the prior art mechanical mouse rotates counterclockwise. 
     FIG. 5 is a table contrasting output signals of two sensors with time when the wheel of the mechanical mouse rotates clockwise and counterclockwise. 
     FIG. 6 is a diagram of the output signals of two sensors versus time when a defective wheel of the prior art mechanical mouse rotates clockwise. 
     FIG. 7 is a perspective view of a mouse with a wheel according to the present invention. 
     FIG. 8 is a perspective view of an inner portion of the mouse of FIG.  7 . 
     FIG. 9 is a top view of the inner portion of FIG.  8 . 
     FIG. 10 is a side view of a switch mechanism of a mouse according to the present invention. 
     FIG. 11 is a diagram of a left half portion of a present invention switch mechanism when a ratchet rotates clockwise. 
     FIG. 12 is a diagram of a right half portion of a present invention switch mechanism when a ratchet rotates clockwise. 
    
    
     DETAILED DESCRIPTION 
     FIG. 7 is a perspective view of a mouse  50  with a wheel  54  according to the present invention. The mouse  50  comprises a housing  52 . An opening  53  is formed in the housing  52  and the wheel  54  is disposed inside the opening  53 . The mouse  50  presents the same method of operation for a user as the prior art mouse, and so requires no further discussion. 
     FIG. 8 is a perspective view of an inner portion of the mouse  50  shown in FIG.  7 . FIG. 9 is a top view of the inner portion shown in FIG.  8 . As shown in FIG.  8  and FIG. 9, the mouse  50  further comprises a substrate  56  disposed inside the housing  52 , a support  60  installed on the substrate  56 , a shaft  58  extending into the support  60  and connected to the wheel  54 , and a switch mechanism  70  installed on one side of the support  60 . The switch mechanism  70  is driven by the shaft  54  so as to have synchronous operation with the wheel  54 . 
     FIG. 10 is a side view of an inner portion of the switch mechanism  70  according to the present invention. As shown in FIG. 10, the switch mechanism  70  comprises a ratchet  72  having a plurality of sawteeth  73 , a first tappet  74  installed on one side of the ratchet  72 , a second tappet  76  installed on another side of the ratchet  72 , a positioning plate  80  disposed on the substrate  56  between second ends of the first tappet  74  and the second tappet  76 , a first sensor  82  installed on one side of the positioning plate  80  adjacent to the first tappet  74 , a second sensor  84  installed on another side of the positioning plate  80  adjacent to the second tappet  76 , a first inner elastic piece  92  disposed between the first tappet  74  and the first sensor  82 , a first outer elastic piece  94  disposed on an outer side of the first tappet  74 , a second inner elastic piece  96  disposed between the second tappet  76  and the second sensor  84 , and a second outer elastic piece  98  disposed on an outer side of the second tappet  76 . The first sensor  82  and the second sensor  84  generate corresponding detecting signals, respectively. When the ratchet  72  rotates, the sawteeth  73  of the ratchet  72  push the first tappet  74  and the second tappet  76  so as to cause the first sensor  82  or the second sensor  84  to generate the detecting signals. When the first sensor  82  generates detecting signals, the second sensor  84  will not generate detecting signals. Conversely, when the second sensor  84  generates detecting signals, the first sensor  82  will not generate detecting signals. 
     The ratchet  72  is connected with the wheel  54  by the shaft  58 , and so the rotational speed and rotational direction of the ratchet  72  matches those of the wheel  54 . Of course, the shaft  58  may be replaced by a gear set, and in this case the rotational speed (and even direction) of the ratchet  72  may differ from that of the wheel  54 . Nevertheless, in either case the rotational speed and direction of the ratchet  72  corresponds to those of the wheel  54  in a known way, and so may be thought of as equivalent. Such an alternative design is thus within the bounds of the present invention. 
     FIG. 11 is a diagram of a left half portion of the present invention switch mechanism  70  when the ratchet  72  rotates clockwise. FIG. 12 is a diagram of a right half portion of the present invention switch mechanism  70  when the ratchet  72  rotates clockwise. As shown in FIG.  11  and FIG. 12, when the ratchet  72  rotates clockwise and pushes the first end  74   a  of the first tappet  74 , the first tappet  74  rotates counterclockwise so as to cause the second end of  74   b  the first tappet  74  to push the first inner elastic piece  92 . Therefore, the first inner elastic piece  92  is pushed away from an initial position and triggers the first sensor  82 . The first sensor  82  thus generates the detecting signal. At the same time, the ratchet  72  will also push the second tappet  76 , causing the second tappet  76  to push against the second outer elastic piece  98 , pushing the second outer elastic piece  98  away from an initial position. The second inner elastic piece  96  does not trigger the second sensor  84 , and so the second sensor  84  does not generate a detecting signal. 
     As the first end  74   a  of the first tappet  74  and the first end  76   a  of the second tappet  76  continue to move across the sawtooth  73 , the first inner elastic piece  92  elastically pushes against the second end  74   b  of the first tappet  74  and returns to its initial position. Similarly, the second outer elastic piece  98  elastically pushes the second end  76   b  of the second tappet  76  and returns to its initial position. Because the second inner elastic piece  96  does not trigger the second sensor  84 , the second sensor  84  does not generate any detecting signal. 
     With the continuous clockwise rotation of the ratchet  72 , the first sensor  82  will repetitively generate detecting signals, whereas the second sensor  84  will generate no detecting signal. Thus, when the first sensor  82  generates a detecting signal, it can be inferred that the wheel  54  is rotating clockwise. Of course, it should be clear from the symmetry of the switch mechanism  70  that counter-clockwise rotations will cause the second inner elastic piece  96  to make contact with the second sensor  84  and thus generate a signal, while the first inner elastic piece  92  will make no contact with the first sensor  82  and hence generate no corresponding signal. Consequently, signals from the second sensor  84  are inferred as counter-clockwise rotations of the wheel  54 . The rotational angle covered by the wheel  54  may be inferred from the number of detecting signals generated. 
     Of course, the switch mechanism  70  of the present invention may also be used in trackballs, joy sticks and other such pointing devices or input devices. 
     In contrast to the prior art, the switch mechanism  70  of the present invention mouse  50  determines the rotational direction of the wheel  54  according to a single detecting signal that is generated by either the first sensor  82  or the second sensor  84 . There is no need to compare two detecting signals to each other. Therefore, even if the spacing interval between adjacent sawteeth  73  of the ratchet  72  is not precise, the mouse  50  still correctly determines the rotational direction of the wheel  54 . 
     The above disclosure is not intended as limiting. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.