Abstract:
In a movement detection method for multiple objects on a capacitive touchpad, the waveform of sensed values on the touchpad is monitored for its variation to determine respective movements of the objects on the touchpad, and various operational gestures are further determined exactly.

Description:
FIELD OF THE INVENTION 
     The present invention is generally related to a detection method for a touchpad and, more specifically, to a movement detection method for multiple objects on a capacitive touchpad. 
     BACKGROUND OF THE INVENTION 
     Capacitive touchpad is used as 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 a capacitive touchpad is very thin, it can be designed into an ultra-thin notebook, a keyboard, a digital player and other devices, and further, its non-mechanical design makes it very easy to be maintained. 
       FIG. 1  shows a cross-sectional view of a typical 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 on the touched position will have a variation, and the control circuit connected to the touchpad  100  can convert the capacitances on the touchpad  100  to the 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 from 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 value th, it is determined that an object touches on the touchpad  100 ; on the contrary, when the sensed value is less than the threshold value th, it is determined that the object leaves the touchpad  100  or no object touches on the touchpad  100 . 
     However, the way to operate programs or devices by detecting gestures of single object, such as touching down to a touchpad, leaving from a touchpad, and moving on a touchpad, could no longer fulfill users&#39; requirements in current electronic products. For this reason, there is a need to detect double or even more objects on a touchpad. Specifically, the actions of multiple objects operating on a touchpad can be defined as various gestures to vary the operations. 
     There have been proposed several detection methods for multiple objects touching on a touchpad. For example, in U.S. Pat. No. 5,825,352 issued to Stephen et al., the waveform of sensed values is detected to determine the object touching on a touchpad.  FIGS. 4A to 4D  show the waveforms of sensed values from a touchpad  001  in two directions in a conventional method. In  FIGS. 4A to 4D , X profile  002  is the distribution of the sensed values in the horizontal direction of the touchpad  001 , and Y profile  003  is the distribution of the sensed values in the vertical direction of the touchpad  001 . Each peak of the waveform in the X profile  002  represents an object touching on the touchpad  001 . For example, as shown in  FIG. 4A , the waveform in the X profile  002  has single peak  021 , and it means there is only one object  011  on the touchpad  001 . In  FIG. 4B , the waveform in the X profile  002  has two peaks  021  and  022 , and it means there are two objects  011  and  012  on the touchpad  001 . As shown in  FIG. 4C , if the waveform in the X profile  002  has three peaks  021 ,  022 , and  023 , it means there are three objects  011 ,  012 , and  013  on the touchpad  001 . By detecting the number of the objects on the touchpad  001 , various gestures could be identified. For instance, two objects moving on the touchpad  001  may be defined as a first gesture, and two objects leaving from the touchpad  001  within a reference time interval since their touching down to the touchpad  001  may be defined as a second gesture, and so on. By this way, practical gestures are increased and the operations become more simple and varied. 
     However, it cannot determine the respective movements of two or more objects by the foregoing method. For example, as shown in  FIG. 4B , two objects  011  and  012  touches on the touchpad  001 , resulting in the X profile  002  having two peaks  021  and  022  and the Y profile  002  having one peak  031 . Then, if the object  011  starts to move upward and the object  012  keeps still on the touchpad  001 , the X profile  002  still has two peaks  021  and  022 , while the Y profile  003  splits from one peak  031  to two peaks  031  and  032  as shown in  FIG. 4D . It becomes more difficult to determine which object on the touchpad  001  is the moved one. If the movement of respective object can be determined individually, more practical gestures can be defined, and more operations for a touchpad can be applied thereto. 
     Therefore, it is desired a method for detecting the movement of respective one among multiple objects on a capacitive touchpad. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a movement detection method for multiple objects on a capacitive touchpad, in order to determine respective movements of the multiple objects. 
     Another object of the present invention is to provide a detection method for multiple objects gesture on a capacitive touchpad. 
     In a movement detection method for multiple objects on a capacitive touchpad, according to the present invention, variation in the sensed values of respective object on the touchpad is discriminated to determine the movement of respective object on the touchpad for exactly detecting various gesture operations. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       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: 
         FIG. 1  shows a cross-sectional view of a typical two-dimensional capacitive touchpad; 
         FIG. 2  shows a relationship between the sensed values and the touched position of the touchpad shown in  FIG. 1 ; 
         FIG. 3  shows a variation of the sensed values from the touchpad shown in  FIG. 1 ; 
         FIG. 4A  shows the sensed values in two directions on a touchpad when one object touches the touchpad; 
         FIG. 4B  shows the sensed values in two directions on a touchpad when two objects touch the touchpad; 
         FIG. 4C  shows the sensed values in two directions on a touchpad when three objects touch the touchpad; 
         FIG. 4D  shows the sensed values in two directions on a touchpad when four objects touch the touchpad; 
         FIG. 5  shows a waveform of sensed value from a touchpad when two objects touch the touchpad in an embodiment of the present invention; 
         FIG. 6A  shows two regions defined by a method in an embodiment of the present invention; 
         FIG. 6B  shows two regions defined by a method in an embodiment of the present invention; 
         FIG. 7A  shows a waveform variation of the sensed values in an embodiment of the present invention; 
         FIG. 7B  shows the variation in the sensed values shown in  FIG. 7A ; 
         FIG. 8A  shows a waveform variation of the sensed values in an embodiment of the present invention; 
         FIG. 8B  shows the variation in the sensed values shown in  FIG. 8A ; 
         FIG. 9A  shows a waveform variation of the sensed values in an embodiment of the present invention; 
         FIG. 9B  shows the variation in the sensed values shown in  FIG. 9A ; 
         FIG. 10A  shows a waveform variation of the sensed values in an embodiment of the present invention; 
         FIG. 10B  shows the variation in the sensed values shown in  FIG. 10A ; 
         FIG. 11A  shows a detection of the displacement of a peak in the waveform of sensed values in an embodiment of the present invention; 
         FIG. 11B  shows a detection of the displacement of a peak in the waveform of sensed values in an embodiment of the present invention; 
         FIG. 12A  shows a detection of the displacement of the center of mass of a region in the waveform of sensed values in an embodiment of the present invention; 
         FIG. 12B  shows a detection of the displacement of the center of mass of a region in the waveform of sensed values in an embodiment of the present invention; 
         FIG. 13A  shows a diagram of two digital signals having an object moving on a touchpad in an embodiment of the present invention; and 
         FIG. 13B  shows a diagram of two digital signals having an object moving on a touchpad in an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a method for multiple objects detection on a capacitive touchpad, according to the present invention, the objects can be detected touching down to the touchpad, staying on the touchpad, and moving on the touchpad, and several gestures for operations on the touchpad can be distinguished by such method without any improvement or modification to the hardware detection circuit of the touchpad. 
     &lt;Determination of Respective Movement of Multiple Objects&gt; 
       FIG. 5  shows a waveform of sensed values scanned by the sensor of a touchpad  001  when two objects  120  and  122  touch the touchpad  001 . In the X profile  004 , two peaks  125  and  130  will be identified in the waveform corresponding to the objects  120  and  122 , respectively. If both the peaks  125  and  130  have sensed values greater than a threshold value x, it is determined that there are indeed two objects  120  and  122  touching the touchpad  001 . As shown in  FIGS. 6A and 6B , the waveform will be divided into a region  126  corresponding to the object  120  and a region  131  corresponding to the object  122 . In an embodiment, a valley  128  between the peaks  125  and  130  is further identified, and the regions  126  and  131  are so defined that they have the sensed values greater than a threshold value x 2 . As shown in  FIG. 6A , the valley  128  is at the position where the sensed value is lower than the threshold value x 2 , and thus the regions  126  and  131  will be separated from one another. Alternatively, as shown in  FIG. 6B , if the sensed value at the valley  128  is also greater than the threshold value x 2 , the valley  128  will be the dividing point or boundary that divides the waveform to specify the regions  126  and  131 . 
       FIGS. 7A to 8B  illustrate waveform variations when the object  120  of  FIG. 5  moves on the touchpad  001  in two opposite directions. In an embodiment, the touchpad  001  of  FIG. 5  is scanned each reference time interval.  FIG. 7A  shows the sensed values at this time scanning and the previous time scanning, and  FIG. 7B  shows the variation dV in the sensed values between these two scanning. In  FIG. 7A , curves  140  and  150  represent the waveforms of sensed values corresponding to the regions  126  and  131 , respectively, at the previous time scanning, and curves  142  and  152  represent the waveforms of sensed values corresponding to the regions  126  and  131 , respectively, at this time scanning. As shown in  FIG. 7B , the absolute value of the variation dV corresponding to the region  126  is greater than a threshold value th 1 , and it is thus determined that the object  120  moves on the touchpad  001 . Further, as shown in  FIGS. 7A and 7B , the sensed values corresponding to the region  126  have a trend of increasing in a direction, leftward in this embodiment, and decreasing in the opposite direction, rightward in this embodiment, it indicates that the object  120  of  FIG. 5  has a displacement to the left.  FIGS. 8A and 8B  show the case that the object  120  moves on the touchpad  001  rightward. 
     Contrarily,  FIGS. 9A to 10B  illustrate the sensed values and their variations in the case that the object  122  moves on the touchpad  001  and the object  120  is standstill. By using the same determining method in the above description,  FIGS. 9A and 9B  represent the case that the object  122  moving leftward, since the absolute value of the variation dV in the region  131  is greater than the threshold value th 2  and the sensed values corresponding to the region  131  have a trend of increasing at the left side and decreasing at the right side. Similarly,  FIGS. 10A and 10B  represent the case that the object  122  has a displacement to the right. 
     In another embodiment, the displacements of the peaks or the centers of mass of the regions  126  and  131  may be used to determine whether or not the objects  120  and  122  move on the touchpad  001 .  FIGS. 11A and 11B  show the waveforms of sensed values on the touchpad  001  of  FIG. 5 , in either of which the peak of the waveform has a displacement d at two times scanning spaced with a reference time interval therebetween. In  FIG. 11A , if the displacement d of the peak  125  in the region  126  between the waveforms  140  and  142  is greater than a threshold value th 1 , it is determined that the object  120  moves on the touchpad  001 . Likewise, as shown in  FIG. 11B , if the displacement d of the peak  130  in the region  131  between the waveforms  150  and  152  is greater than another threshold value th 2 , it is determined that the object  122  moves on the touchpad  001 . 
     As shown in  FIGS. 12A and 12B , the sensed values on the touchpad  001  of  FIG. 5  is detected twice with a reference time interval, and the displacements d of the centers of mass of the regions  126  and  131  are calculated. The center of mass refers to the center of the total sensed quantity caused by object touching on the touchpad  001 , and it is usually close to but not necessarily at the peak. In  FIG. 12A , if the displacement d of the center of mass of the region  126  between two scannings is greater than a threshold value th 1 , it is determined that the object  120  moves on the touchpad  001 . In  FIG. 12B , if the displacement d of the center of mass of the region  131  between two scannings is greater than another threshold value th 2 , it is determined that the object  122  moves on the touchpad  001 . 
     By using the above illustrated methods, it is determined that the object moves on the touchpad whatever the direction the object moves to. Thereafter, depending on the requirements of the specific applications, it may be produced the corresponding signal, such as including the position information of the object. 
     &lt;Detection for Multiple Objects Moving Gesture&gt; 
       FIGS. 13A and 13B  show two digital signals  202  and  204  produced by a touchpad  001  using the above methods. As usual, the sensed values on the touchpad  001  are detected, and if two objects  120  and  122  are detected touching on the touchpad  001 , it is further determined whether either of the objects  120  and  122  moves on the touchpad  001  by the above-mentioned method for determining respective movements of the objects  120  and  122 . If it is determined that the object  120  moves on the touchpad  001 , the digital signal  202  is produced as shown in  FIG. 13A . If it is determined that the object  122  moves on the touchpad  001 , the digital signal  204  is produced as shown in  FIG. 13B . The digital signals  202  and  204  may comprise the information corresponding to the displacements d of the moving object during a reference time interval, or including the absolute coordinate, the relative coordinate, or the variation in the sensed values of the moving object. 
     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.