Abstract:
In an object detection method for a capacitive touchpad, at least one reference time interval is used to distinguish whether a variation of the sensed value on the touchpad is resulted from an operation of an object on the touchpad, actions such as an object touch down to the touchpad, an object lift from the touchpad and an object movement on the touchpad are then determined, and operations corresponding to various gestures are correctly detected.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is generally related to a detection method for a touchpad and, more specifically, to a noise resistive method for object detection on a capacitive touchpad.  
       BACKGROUND OF THE INVENTION  
       [0002]     Capacitive touchpad is an input device to control cursor movement by providing a smooth panel for user&#39;s finger or conductive object to touch or move thereon. Since capacitive touchpad is very thin, it can be designed into ultra-thin notebook, keyboard, digital player and other devices, and further, its non-mechanical design makes it very easy to be maintained.  
         [0003]      FIG. 1  is a cross-sectional view of a conventional two-dimensional capacitive touchpad  100 , which comprises a panel  102 , a Y-axis sensing layer  104 , an insulator layer  106 , an X-axis sensing layer  108 , and a bottom plate  110 . When a finger  112  touches on the panel  102 , the sensed value (in capacitance) on the touched position will have a variation, and the control circuit connected to the touchpad  100  can convert the capacitance on the touchpad  100  to a sensed value as shown in  FIG. 2 , by which the position where the finger  112  touches and the moving distance and the moving direction of the finger  112  can be determined. Conventionally, the sensed value on the touchpad  100  is used to determine if an object touches on the touchpad  100  by the way as shown in  FIG. 3 . When the sensed value is greater than a threshold th, it is determined that an object touches on the touchpad  100 , and on the contrary, when the sensed value is less than the threshold th, it is determined that the object leaves the touchpad  100  or no object touches on the touchpad  100 .  
         [0004]     However, the detection for the touchpad  100  might be interfered by noise resulted from wireless device such as mobile phone and others, and therefore, the touchpad  100  might misjudge that an object touches, taps, moves or practices any gesture thereon.  FIG. 4A  is an example showing a noise generated on the touchpad  100 , the noise will be converted to a sensed value by an analog-to-digital converter (ADC) as shown in  FIG. 4B , and finally, by a sampling process, it will become a waveform as shown in  FIG. 4C . The waveform of  FIG. 4C  is similar to one generated when two fingers touch on the touchpad  100  as shown in  FIG. 5 , and therefore, the noise exemplary shown in  FIG. 4A  could be misjudged to be an operation of two fingers touching on the touchpad  100 , thereby causing the touchpad  100  to have an operation that is not desired or predicted.  
         [0005]     Therefore, there is a need of a detection method for a touchpad that will avoid noise to interfere the operation of the touchpad.  
       SUMMARY OF THE INVENTION  
       [0006]     An object of the present invention is to provide an object detection method for a capacitive touchpad for preventing the operation of the touchpad from noise interference.  
         [0007]     In an object detection method for a capacitive touchpad, according to the present invention, at least one reference time interval is used to distinguish whether a variation of the sensed value on the touchpad is resulted from an operation of an object on the touchpad, actions such as an object touch down to the touchpad, an object lift from the touchpad and an object moving on the touchpad are then determined, and operations corresponding to various gestures are correctly detected.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]     These and other objects, features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which:  
         [0009]      FIG. 1  is a cross-sectional view of a conventional two-dimensional capacitive touchpad;  
         [0010]      FIG. 2  shows a relationship between the sensed value and the touched position of the touchpad shown in  FIG. 1 ;  
         [0011]      FIG. 3  shows a variation of the sensed value on the touchpad shown in  FIG. 1 ;  
         [0012]      FIG. 4A  shows an exemplary noise applied to the touchpad shown in  FIG. 1 ;  
         [0013]      FIG. 4B  shows the sensed value from the noise shown in  FIG. 4A  converted by an analog-to-digital converter;  
         [0014]      FIG. 4C  shows the waveform by sampling the sensed value shown in  FIG. 4B ;  
         [0015]      FIG. 5  shows a detected waveform of the sensed value when two fingers touch on the touchpad shown in  FIG. 1 ;  
         [0016]      FIG. 6  shows a variation of the sensed value on the touchpad shown in  FIG. 1  when the sensed value becomes greater than a down threshold;  
         [0017]      FIG. 7  shows a difference between two sensed values shown in  FIG. 6 ;  
         [0018]      FIG. 8  shows a detected signal;  
         [0019]      FIG. 9  shows a detected signal and a touch signal;  
         [0020]      FIG. 10  shows a variation of the sensed value on the touchpad shown in  FIG. 1  when the sensed value becomes less than a lift threshold;  
         [0021]      FIG. 11  shows a difference between two sensed values shown in  FIG. 10 ;  
         [0022]      FIG. 12  shows a detected signal;  
         [0023]      FIG. 13  shows a detected signal and a lift signal;  
         [0024]      FIG. 14  shows a variation of the sensed value on the touchpad shown in  FIG. 1  when an object moves from still to left side;  
         [0025]      FIG. 15  shows a difference between two sensed values shown in  FIG. 14 ;  
         [0026]      FIG. 16  shows a detected signal and a tap signal;  
         [0027]      FIG. 17  shows a detected signal and a drag signal; and  
         [0028]      FIG. 18  shows a detected signal and a double tap signal. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]     In a detection method for a capacitive touchpad according to the present invention, the noise resistive capability of the touchpad is enhanced without any improvement on the hardware detection circuit of the touchpad, and several gestures for operations on the touchpad can be distinguished by such method.  
         [0000]     &lt;Detection for Verifying an Object Down&gt; 
         [0030]     In  FIG. 6 , it is shown a variation of the sensed value on the touchpad  100  shown in  FIG. 1  when the sensed value becomes greater than a down threshold th, in which curve  200  represents the sensed value at this time and curve  202  represents the sensed value at the last time.  FIG. 7  shows the difference between the sensed values  200  and  202  of  FIG. 6 , and  FIG. 8  shows a detected signal  204 . In a detection of the sensed value on the touchpad  100 , when the sensed value is detected greater than the down threshold th as shown in  FIG. 6 , the detected signal  204  will transit from low to high as shown in  FIG. 8 , and then, within a time interval T DownDetect , the sensed value on the touchpad  100  is continuously detected and the differential sensed value dV is calculated by subtracting each current sensed value  202  by the last sensed value  200  as shown in  FIG. 7 . If the differential sensed value dV within the time interval T DownDetect  maintains positive, it is determined that an object touches down to the touchpad  100 .  
         [0000]     &lt;Detection for Verifying a Touch Gesture&gt; 
         [0031]      FIG. 9  shows a detected signal  206  and a touch signal  208 . Once an object is determined to touch down to the touchpad  100 , the time duration that the object lasts on the touchpad  100  is counted. After the detection for verifying an object down confirms that the object indeed touches down to the touchpad  100 , if the object continuously stays on the touchpad  100  for a time duration equal to a reference time interval T Touch , the touch signal  208  is produced and a position information of the object is calculated and sent out.  
         [0000]     &lt;Detection for Verifying an Object Lift&gt; 
         [0032]      FIG. 10  shows a variation of the sensed value on the touchpad  100  shown in  FIG. 1  when the sensed value becomes less than a lift threshold th, in which curve  210  represents the sensed value at this time and curve  212  represents the sensed value at the last time,  FIG. 11  shows the difference between the sensed values  210  and  212  of  FIG. 10 , and  FIG. 12  shows a detected signal  214 . When an object has touched on the touchpad  100 , once the sensed value is detected less than the lift threshold th as shown in  FIG. 10 , the detected signal  214  will transit from high to low as shown in  FIG. 12 , and then, within a time interval T LiftDetect , the sensed value on the touchpad  100  is continuously detected and the differential sensed value dV is calculated by subtracting each current sensed value  210  by the last sensed value  212  as shown in  FIG. 11 . If the differential sensed value dV within the time interval T LiftDetect  maintains negative, it is determined that the object leaves from the touchpad  100 .  
         [0000]     &lt;Detection for Verifying a Lift Gesture&gt; 
         [0033]      FIG. 13  shows a detected signal  216  and a lift signal  218 . Once an object is detected to leave from the touchpad  100 , the time duration after the object leaves the touchpad  100  is counted. If the detection for verifying an object lift confirms that the object indeed leaves from the touchpad  100  and the object leaves the touchpad  100  for a time duration equal to a reference time interval T LiftGesture , the lift signal  218  is produced.  
         [0000]     &lt;Detection for Verifying an Object Moving&gt; 
         [0034]     The variation of an object on the touchpad  100  from still to move is verified to avoid noise or slight vibration of the object to cause a misjudgment on the object position which will result in the corresponding cursor to have wrong action.  FIG. 14  shows a variation of the sensed value on the touchpad  100  shown in  FIG. 1  when an object on the touchpad  100  moves from still to left, in which curve  220  represents the sensed value at this time and curve  222  represents the sensed value at the last time, and  FIG. 15  shows the difference between the sensed values  220  and  222  shown in  FIG. 14 . After an object is verified to touch on the touchpad  100 , the sensed value on the touchpad  100  is continuously detected and the differential sensed value dV is calculated by subtracting each current sensed value  220  by the last sensed value  222 . Within a time interval T Movingdetect , if the left side of the object is detected to have the differential sensed value dV in an increasing trend and the right side of the object is detected to have the differential sensed value dV in a decreasing trend as shown in  FIGS. 14 and 15 , the object is determined to move from still to left. On the contrary, within the reference time interval T Movingdetect l , if the left side of the object is detected to have the differential sensed value dV in a decreasing trend and the right side of the object is detected to have the differential sensed value dV in an increasing trend, the object is determined to move from still to right.  
         [0000]     &lt;Detection for a Moving Gesture&gt; 
         [0035]     If an object is detected to move on the touchpad  100  first time and the detection for verifying an object moving confirms that the object indeed moves on the touchpad  100 , a position information of the object is calculated and sent out. Thereafter, if the object is detected to move on the touchpad  100  again within a time interval shorter than a reference time interval T Moving , the position information of the object is calculated and sent out once more.  
         [0000]     &lt;Detection for a Tap Gesture&gt; 
         [0036]      FIG. 16  shows a detected signal  224  and a tap signal  226 . In response to an object touching down to the touchpad  100 , the detected signal  224  transits from low to high and then the time duration that the object lasts on the touchpad  100  is counted. If the detection for verifying an object down confirms that the object indeed touches down to the touchpad  100  and the object is further detected to leave from the touchpad  100  before a reference time interval T TapDown  is reached, the detected signal  224  transits from high to low, and the time duration after the object leaves the touchpad  100  is counted. If the detection for verifying an object lift confirms that the object indeed leaves the touchpad  100  and the object leaves the touchpad  100  for a time duration equal to a reference time interval T TapLift , the tap signal  226  is produced, and the tap position information is calculated and sent out.  
         [0000]     &lt;Detection for a Drag Gesture&gt; 
         [0037]      FIG. 17  shows a detected signal  228  and a drag signal  230 . When an object is detected to touch down to the touchpad  100  first time, the detected signal  228  transits from low to high and then the time duration that the object lasts on the touchpad  100  is counted. If the detection for verifying an object down confirms that the object indeed touches down to the touchpad  100  and the object is further detected to leave from the touchpad  100  before a reference time interval T TapDown  is reached, the detected signal  224  transits from high to low, and the time duration after the object leaves the touchpad  100  is counted. If the detection for verifying an object lift confirms that the object indeed leaves the touchpad  100  and the touchpad  100  is detected to be touched again before a reference time interval T TapLift  is reached, the detected signal  228  transits again from low to high, and the time duration that the object lasts on the touchpad  100  is counted again. If the detection for verifying an object down confirms that the object indeed touches down to the touchpad  100  and the object lasts on the touchpad  100  this second time for a time period equal to a reference time interval T DragDown , the drag signal  230  is produced and the position information of the object is calculated and sent out.  
         [0000]     &lt;Detection for a Double Tap Gesture&gt; 
         [0038]      FIG. 18  shows a detected signal  232  and a double tap signal  234 . When the touchpad  100  is touched by an object first time, the detected signal  232  transits from low to high and then the time duration that the object lasts on the touchpad  100  is counted. After the detection for verifying an object down confirms that the object indeed touches down to the touchpad  100 , if the object leaves the touchpad  100  before a reference time interval T TapDown , the detected signal  232  transits from high to low and the time duration after the object leaves the touchpad  100  is counted. If the detection for verifying an object lift confirms that the object indeed leaves from the touchpad  100  and the touchpad  100  is touched again before the time duration that the object leaves the touchpad  100  reaches a reference time interval T TapLift , the detected signal  232  transits again from low to high, and the time duration that the object lasts on the touchpad  100  in this second touch is counted. If the detection for verifying an object down confirms that the touchpad  100  is indeed touched by an object again, and the object leaves from the touchpad  100  again before the time duration that the object lasts on the touchpad  100  in the second touch reaches a reference time interval T DragDown , the detected signal  232  transits from high to low again. If the detection for verifying an object lift confirms that the object indeed leaves the touchpad  100  again, the double tap signal  234  is produced and a position information of the object is calculated and sent out.  
         [0039]     In the above embodiments, by monitoring the variation of the sensed value on the touchpad  100  and the various time durations that an object lasts on the touchpad  100  or leaves the touchpad  100 , the various operations on the touchpad  100  are distinguished correctly, and the misjudgments due to noise interference are avoided.  
         [0040]     While the present invention has been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and scope thereof as string forth in the appended claims.