Abstract:
A multiple objects detection method for a capacitive touchpad, through at least one preset time, whether it is noise and interference or an operation of object on touchpad is thus distinguished, actions such as object touches the touchpad, leaves the touchpad are then judged correctly, and different kinds of gesture operations are precisely detected.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is generally related to a detection method for capacitive touchpad, and more specifically, to a multiple objects detection method for resisting noise.  
       BACKGROUND OF THE INVENTION  
       [0002]     Capacitive touchpad is an input device for controlling cursor movement by providing smooth panel for finger to slide on it. Since capacitive touchpad is very thin, it can thus be designed into ultra-thin notebook, key board, digital player or other devices, besides, its non-mechanical design makes it very easy to be maintained.  
         [0003]      FIG. 1  is the prior art two dimensional capacitive touchpad  100 , comprising panel  102 , Y axis sensing layer  104 , insulated layer  106 , X axis sensing layer  108  and bottom board  110 . When finger  112  touches panel  102 , the sensed value (capacitance value) on the touched location will have a change, and the control circuit connected to touchpad  100  can convert the capacitance on the touchpad into sensed value, as shown in  FIG. 2 , in order to judge finger location, amount of movement and direction of movement. In the prior art technology, the detected sensed value is used to judge if the object touches capacitive touchpad  100 , this is as shown in  FIG. 3 , when sensed value is larger than critical value th, it means object touches touchpad  100 , on the contrary, when sensed value is smaller than critical value th, it means object leaves touchpad  100  or object is not on touchpad  100 .  
         [0004]     However, touchpad  100  might be interfered by signals from wireless device such as cellular phone, etc., and generate noise, therefore, touchpad  100  might misjudge that object is touching, clicking, moving or performing any gesture operation on it.  FIG. 4A  is an example showing noise generated on touchpad  100 , the noise is converted into sensed value through analog digital converter, as shown in  FIG. 4B , finally through a sampling process, the waveform as in  FIG. 4C  is obtained, this kind of waveform is similar to the waveform generated when two fingers touch touchpad  100 , as shown in  FIG. 5 , therefore, noise in  FIG. 4A  could be misjudged to be two fingers touching touchpad  100 , this could lead to wrong operation.  
         [0005]     Therefore, a detection method which can prevent interference from noise is highly expected.  
       SUMMARY OF THE INVENTION  
       [0006]     An object of the present invention is to provide a multiple objects detection method for capacitive touchpad which can prevent the interference from noise.  
         [0007]     According to the present invention, a multiple objects detection method for a capacitive touchpad is to set up at least a preset time to distinguish whether the sensed value change on touchpad is noise or operation of object on touchpad, actions such as object touches the touchpad, leaves the touchpad are then judged correctly, and different kinds of gesture operations are precisely 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 the two dimensional capacitive touchpad of the prior art;  
         [0010]      FIG. 2  is the relationship drawing between sensed quantity and location of the touchpad of  FIG. 1 ;  
         [0011]      FIG. 3  is the detected sensed quantity change when two fingers are touching touchpad;  
         [0012]      FIG. 4A  displays noise;  
         [0013]      FIG. 4B  is the sensed quantity obtained when noise in  FIG. 4A  is converted by analog digital converter;  
         [0014]      FIG. 4C  is the waveform after sampling  FIG. 4B ;  
         [0015]      FIG. 5  is the detected waveform when two fingers are touching touchpad;  
         [0016]      FIG. 6  is the detected sensed quantity change after sensed quantity is larger than the critical value th;  
         [0017]      FIG. 7  is the difference between two sensed quantities in  FIG. 6 ;  
         [0018]      FIG. 8  displays detected signal;  
         [0019]      FIG. 9  displays detected signal and touched signal;  
         [0020]      FIG. 10  is the detected sensed quantity change after sensed quantity is smaller than the critical value th;  
         [0021]      FIG. 11  is the difference between two sensed quantities in  FIG. 10 ;  
         [0022]      FIG. 12  displays detected signal;  
         [0023]      FIG. 13  displays detected signal and lift signal;  
         [0024]      FIG. 14  displays detected signal and single click signal;  
         [0025]      FIG. 15  displays detected signal and double click signal; and  
         [0026]      FIG. 16  displays detected signal and dragging signal. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]     The detection method of the present invention does not need the improvement on hardware detection circuit to enhance noise resisting capability, besides, it can distinguish several gestures.  
         [0000]     &lt;Detection for Verifying Multiple Objects Touch&gt; 
         [0028]      FIG. 6  displays the detected sensed value change after two peak values of sensed value are all larger than critical value th wherein curve  200  is detected sensed value at this time, curve  202  is detected sensed value at last time.  FIG. 7  is the difference of the two sensed values in  FIG. 6 ,  FIG. 8  shows detected signal  204 . Please refer to  FIGS. 6, 7  and  8 , in detecting the sensed value on touchpad, when the two peak values of sensed value detected is larger than critical value th, as shown in  FIG. 6 , detected signal  204  will turn from low level into high level, as shown in  FIG. 8 , then within time interval TDownDetect, sensed value on the touchpad is detected continuously, sensed value  202  detected last time is taken from sensed value  200  detected this time to get a sensed value difference value dV, as shown in  FIG. 7 , if the sensed value difference values dV obtained within time interval TDownDetect are all positive values, it means that two objects have touched touchpad. Wherein each peak value of sensed value is corresponded to one object, therefore, in other embodiment, if there are more than two objects touching the touchpad, the sensed values will be corresponded to more than two peak values.  
         [0000]     &lt;Detection for Verifying Multiple Objects Touch Gesture&gt; 
         [0029]      FIG. 9  shows detected signal  206  and touch signal  208 . After detecting at least two objects touch touchpad, it will start counting the staying time of the at least two objects on touchpad, when the above-mentioned “A detection method for verifying multiple objects touch” has been confirmed and objects have touched touchpad, calculate the number of objects touching touchpad, if the at least two objects stay continuously on touchpad with a time greater than a preset time T Touch , send out multiple objects touch signal  208  and calculate locations of the at least two objects and sends out location signals. Wherein the multiple objects touch signal  208  can include information of object number.  
         [0000]     &lt;Detection for Verifying Multiple Objects Leaving&gt; 
         [0030]      FIG. 10  shows detected sensed value change after two peak values of sensed values are smaller than critical value th, wherein curve  210  is sensed value detected at this time, curve  212  is sensed value detected last time.  FIG. 11  is the difference value between two sensed values measured in  FIG. 10 .  FIG. 12  shows detected signal  214 . Please refer to  FIGS. 10, 11  and  12 , after object has touched touchpad, once at least one peak value of the two peak values of the detected sensed values is smaller than critical value th, in this embodiment, two peak values of the sensed values are all smaller than critical value, as shown in  FIG. 10 , detected signal  214  will change from high level to low level, as shown in  FIG. 12 , then within time interval T LiftDetect , the detected sensed value is detected continuously, sensed value detected in the last time  212  is taken from sensed value detected each time  210  to get a sensed value difference value dV, as shown in  FIG. 11 , if the sensed value difference values dV obtained within time interval T LiftDetect  are all negative values, it means that at least one object of the two objects has left touchpad.  
         [0000]     &lt;Detection for Verifying Multiple Objects Lift Gesture&gt; 
         [0031]      FIG. 13  shows detected signal  216  and lift signal  218 . After object touches touchpad, once at least one object leaving touchpad is detected, start to calculate the leaving time of the at least one object leaving touchpad, and calculate number of objects left on the touchpad, if there is still object left on touchpad, calculate its location and send out location signal, if it meets the above-mentioned “A detection method for verifying multiple objects leaving” and the leaving time is greater than a preset time of T LiftGesture , send out lift signal  218 . Similarly, the lift signal  208  can include information of object number.  
         [0000]     &lt;Detection for Multiple Objects Tap Gesture&gt; 
         [0032]      FIG. 14  shows detected signal  220  and single click signal  222 . When at least two objects touching touchpad are detected, detected signal  220  will change from low level to high level, as shown in  FIG. 14 , then calculate the touching time for the object touching the touchpad and calculate the number of object, when “A detection method for verifying multiple objects touching” is confirmed and met, and if all objects leaving the touchpad are detected when the touching time is smaller than a preset time T TapDown , then detected signal  220  will change from high level to low level, again calculate the leaving time of the object leaving the touchpad, if it meets “A detection method for verifying multiple object leaving” and the leaving time is larger than a preset time of T TapLift , send out a single click signal  222 , in the mean time, calculate the single click locations of the at least two objects and send out location signals.  
         [0000]     &lt;Detection for Multiple Objects Double Tap&gt; 
         [0033]      FIG. 15  shows detected signal  224  and dragging signal  226 . When the first time at least two objects touch touchpad is detected, detected signal  224  will change from low level to high level, as shown in  FIG. 15 , then calculate first touching time of object touching the touchpad and calculate the number of objects, make sure it meets “A detection method for verifying multiple objects touching” and under the condition the object number is not changed, meanwhile, all the objects leaving the touchpad is detected when the first touching time is smaller than preset time T TapDown , then detected signal  224  will change from high level to low level, further calculate the leaving time of at least two objects leaving the touchpad, make sure it meets “A detection method for verifying multiple objects leaving”, meanwhile, all the objects touching the touchpad for the second time are detected again when the leaving time is smaller than preset time T TapLift , then detected signal  224  will change again from low level to high level, then calculate second touching time when the touchpad is touched for the second time, make sure it meets “A detection method for verifying multiple objects touching” and under the condition the object number is not changed, meanwhile, all the objects again leave the touchpad is detected once more if the second touching time is smaller than a preset time T DragDown , then detected signal  224  will change from high level to low level, make sure it meets “A detection method for verifying multiple objects leaving”, then send out double click signal  226 , in the mean time, calculate the locations of the at least two objects and send out location signals.  
         [0000]     &lt;Detection for Multiple Objects Drag Gesture&gt; 
         [0034]      FIG. 16  shows detected signal  228  and dragging signal  230 . When the first time at least two objects touch touchpad is detected, detected signal  228  will change from low level to high level, as shown in  FIG. 16 , then calculate first touching time of the at least two objects touching the touchpad and calculate object number wherein object number must be greater than or equal to 2, make sure it meets “A detection method for verifying multiple objects touching” and under the condition the object number is not changed, meanwhile, at least one object of the at least two objects leaving the touchpad is detected when the first touching time is larger than preset time T TapDown , then detected signal  228  will change from high level to low level, further calculate the leaving time of the object leaving the touchpad, make sure it meets “A detection method for verifying multiple objects leaving” and the number of objects left on the touchpad, then send out dragging signal  230  and, in the same time, calculate location of the object and send out location signal.  
         [0035]     In each of the above-mentioned embodiments, through a comparison between sensed value change and a preset time, we can verify all kinds operation on touchpad, misjudgment due to interference from noise can thus be prevented.  
         [0036]     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.