Abstract:
Techniques for detecting multiple touch points for touch screens are disclosed. A touch screen includes a first conductive layer and a second conductive layer, each conductive layer having a positive terminal and a negative terminal. Efficient operations of detecting multiple points on the touch screen are described using various voltage/currents differences from the positive and negative terminals of the first and second conductive layers.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the techniques for touch screens, and more particularly to techniques for detecting touch screen. 
         [0003]    2. Description of Related Art 
         [0004]    Touch screens are gradually becoming main means of inputting information to an electronic system. Techniques for detecting multiple touch points are more attractive in the touch screen fields. However, techniques for detecting multiple touch points are mostly implemented on an optical touch screen, which are too expensive for most customers. 
         [0005]      FIG. 1A  is a schematic diagram showing a conventional four-wire resistive touch screen with a single touch point thereon. The four-wire resistive touch screen includes an X conductive layer and a Y conductive layer. The X conductive layer has a positive terminal Xp and a negative terminal Xn at the ends thereof. The Y conductive layer has a positive terminal Yp and a negative terminal Yn at the ends thereof. The X conductive layer is physically separated from the Y conductive layer by a spacer. When a touch point P 1  with enough pressure appears on the resistive touch screen, the X conductive layer may contact with the Y conductive layer at the touching point P 1 .  FIG. 1B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 1A . 
         [0006]    Xplate denotes a total resistance of the X conductive layer from the negative terminal Xn to the positive terminal Xp. The touching point P 1  divides the total resistance Xplate into the resistances R 1  and R 3  proportionally as the X conductive layer has a uniform linear resistivity. Yplate denotes a total resistance of the Y conductive layer from the negative terminal YN to the positive terminal YP. The touch point P 1  divides the total resistance Yplate into the resistances R 4  and R 6  proportionally as the Y conductive layer has a uniform linear resistivity. Rz denotes a contact resistance between the X conductive layer and the Y conductive layer at the touch point P 1 . Thus, the x and y coordinates of the touch point P 1  may be located as long as the resistance values R 3  and R 6  are calculated. 
         [0007]    The terminal Yp is connected to a positive reference voltage VT, the terminal Yn is grounded, and the voltage value V 1  on the terminal Xp is measured. The voltage value V 1  satisfies a following formula: 
         [0000]    
       
         
           
             
               
                 V 
                  
                 
                     
                 
                  
                 1 
               
               VT 
             
             = 
             
               
                 
                   R 
                    
                   
                       
                   
                    
                   6 
                 
                 Yplate 
               
               . 
             
           
         
       
     
         [0008]    Similarly, the terminal Xp is connected to the positive reference voltage VT, the terminal Xn is grounded, and the voltage value V 3  on the terminal Yp is measured. The voltage value V 3  satisfies a following formula: 
         [0000]    
       
         
           
             
               
                 V 
                  
                 
                     
                 
                  
                 3 
               
               VT 
             
             = 
             
               
                 
                   R 
                    
                   
                       
                   
                    
                   3 
                 
                 Yplate 
               
               . 
             
           
         
       
     
         [0009]    The resistance values R 3  and R 6  are calculated according to the above two formulas. So, the coordinate of the touch point P 1  is located. However, the conventional four-wire resistive touch screen is mainly provided for detecting single touch point on the touch screen. If there are two or more touch points on the touch screen, it is very difficult to determine a relative motion tendency of the two or more touch points by calculating the coordinates of each touch point. 
         [0010]    Thus, improved techniques for method and device for detecting multiple touch points on a resistive touch screen are desired to overcome the above disadvantages. 
       SUMMARY OF THE INVENTION 
       [0011]    This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract or the title of this description may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
         [0012]    In general, the present invention is related to techniques for detecting multiple touch points for touch screen. The touch screen includes a first conductive layer and a second conductive layer, each conductive layer having a positive terminal and a negative terminal. The operation of detecting multiple points on the touch screen includes: coupling the positive terminal of the second conductive layer to a positive reference voltage, coupling the negative terminal of the second conductive layer to a negative reference voltage, sampling the positive terminal of the first conductive layer to obtain a series of first voltage samples V 1 ( i ), sampling the negative terminal of the first conductive layer to obtain a series of second voltage samples V 2 ( i ); coupling the positive terminal of the first conductive layer to the positive reference voltage, coupling the negative terminal of the first conductive layer to the negative reference voltage, sampling the positive terminal of the second conductive layer to obtain a series of third voltage samples V 3 ( i ), sampling the negative terminal of the second conductive layer to obtain a series of fourth voltage samples V 2 ( i ), wherein i is a sampling number; calculating a rotating parameter X(i) according to the first voltage samples V 1 ( i ), the second voltage samples V 2 ( i ), the third voltage samples V 3 ( i ) and the fourth voltage samples V 4 ( i ); determining a rotating direction of two touch points in the touch screen according to the rotating parameter X(i); and wherein the rotating parameter X(i) is a function of 
         [0000]    
       
         
           
             
               
                 Xplate 
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                 
               
               - 
               
                 Yplate 
                 
                   
                     V 
                      
                     
                         
                     
                      
                     3 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     4 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    and Xplate is a total resistance of the first conductive layer, and Yplate is a total resistance of the second conductive layer. 
         [0013]    Thee are many features, benefits and advantages in the present invention which will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0015]      FIG. 1A  is a schematic diagram showing a resistive touch screen with a single touch point thereon; 
           [0016]      FIG. 1B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 1A ; 
           [0017]      FIG. 2A  is a schematic diagram showing the resistive touch screen with two touch points P 1  and P 2  thereon, wherein coordinates of the touch point P 1  is (x 1 ,y 1 ), coordinates of the touch point P 2  is (x 2 ,y 2 ), and a position relation of the touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &gt;y 1 ; 
           [0018]      FIG. 2B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 2A ; 
           [0019]      FIG. 3A  is a schematic diagram showing the resistive touch screen with two touch points P 1  and P 2  thereon, wherein the coordinates of the touch point P 1  is (x 1 ,y 1 ), the coordinates of the touch point P 2  is (x 2 ,y 2 ), and the position relation of the touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &lt;y 1 ; 
           [0020]      FIG. 3B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 3A ; 
           [0021]      FIG. 4  is a block diagram showing a touch screen detecting device according to one embodiment of the present invention; 
           [0022]      FIG. 5  is a flow chart showing a method for recognizing a motion tendency of two touch points on the resistive touch screen according to one embodiment of the present invention; 
           [0023]      FIG. 6A  is a flow chart showing a first embodiment of a method for recognizing a non-rotating motion of the two touch points on the resistive touch screen; 
           [0024]      FIG. 6B  is a schematic diagram showing a contraction of the two touch points located on a first diagonal of the resistive touch screen; 
           [0025]      FIG. 6C  is a schematic diagram showing an expansion of the two touch points located on a first diagonal of the resistive touch screen; 
           [0026]      FIG. 6D  is a schematic diagram showing the contraction of the two touch points located on a second diagonal of the resistive touch screen; 
           [0027]      FIG. 6E  is a schematic diagram showing the expansion of the two touch points located on a second diagonal of the resistive touch screen; 
           [0028]      FIG. 6F  is a flow chart showing a second embodiment of the method for recognizing the non-rotating motion of the two touch points on the resistive touch screen; 
           [0029]      FIG. 7A  is a flow chart showing a first embodiment of a method for recognizing a rotating motion of the two touch points on the resistive touch screen; 
           [0030]      FIG. 7B  is a diagram schematically showing a physical meaning of a rotating parameter used in the method shown in  FIG. 7A ; 
           [0031]      FIG. 7C  is an exemplary diagram schematically showing a counterclockwise rotation of the two touch points; 
           [0032]      FIG. 7D  is an exemplary diagram schematically showing a clockwise rotation of the two touch points; 
           [0033]      FIG. 7E  is another exemplary diagram schematically showing the clockwise rotation of the two touch points; 
           [0034]      FIG. 7F  is another exemplary diagram schematically showing the counterclockwise rotation of the two touch points; 
           [0035]      FIG. 7G  is a diagram schematically showing a physical meaning of a rotating parameter used in the method shown in  FIG. 7H ; 
           [0036]      FIG. 7H  is a flow chart showing a second embodiment of the method for recognizing the rotating motion of the two touch points on the resistive touch screen; and 
           [0037]      FIG. 8  is an exemplary flow chart illustrating the method for recognizing the motion tendency of the two touch points on the resistive touch screen according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of devices or systems contemplated in the present invention. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
         [0039]    Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams or the use of sequence numbers representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
         [0040]    Embodiments of the present invention are discussed herein with reference to  FIGS. 2-8 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes only as the invention extends beyond these limited embodiments. 
         [0041]      FIG. 4  is a block diagram showing a touch screen detecting device  200  according to one embodiment of the present invention. The device  200  can support not only single touch point detection but also motion tendency detection of two touch points. Referring to  FIG. 4 , the device  200  includes a resistive touch screen  220 , a selector  240 , an analog-to-digital converter (ADC)  260  and a micro processor  280 . 
         [0042]    The resistive touch screen  220  includes an X conductive layer (also referred as a first conductive layer) along an X-axis direction and a Y conductive layer (also referred as a second conductive layer) along a Y-axis direction. The X conductive layer has a positive terminal Xp and a negative terminal Xn at the respective ends thereof along the X-axis direction. The Y conductive layer has a positive terminal Yp and a negative terminal Yn at the respective ends thereof along the Y-axis direction. Each conductive layer has a uniform linear resistivity along the respective directions. In one embodiment, Xplate is provided to denote a total resistance of the X conductive layer and may be about 300Ω in general. Yplate is provided to denote a total resistance of the Y conductive layer and may be about 700Ω in general. The X conductive layer is physically separated from the Y conductive layer by a gap or a spacer. When one touch point with enough pressure appears on the resistive touch screen  220 , the X conductive layer contacts with the Y conductive layer at the touch point. 
         [0043]    The selector  240  includes a positive reference voltage (VT) selector  242 , a negative reference voltage (GND) selector  246  and a measuring terminal selector  244 . The positive reference voltage selector  242  is configured to select one of the terminal Yp and the terminal Xp to connect to a positive reference voltage VT. The negative reference voltage selector  246  is configured to select one of the terminal Yn and the terminal Xn to connect to a ground reference GND. The measuring terminal selector  244  is configured to select one of the terminals Yp, Yn, Xp, Xn as a measuring terminal. The ADC  260  is configured to sample an analog voltage on the measuring terminal of the selector  240  and convert the analog voltage into the digital voltage. 
         [0044]    The micro processor  280  is configured to receive the digital voltage samples and recognize a motion tendency of two touch point on the resistive touch screen depending on the digital voltage samples. In one embodiment, the voltage samples comprise a series of first voltage samples V 1 ( i ), a series of second voltage samples V 2 ( i ), a series of third voltage samples V 3 ( i ) and a series of fourth voltage samples V 4 ( i ). When the positive terminal Yp is coupled to the positive reference voltage VT and the negative terminal Yn is grounded, the first voltage samples V 1 ( i ) are obtained by sampling a voltage on the positive terminal Xp, and the second voltage samples V 2 ( i ) are obtained by sampling a voltage on the negative terminal Xn. When the positive terminal Xp is coupled to the positive reference voltage VT and the negative terminal Xn is grounded, the third voltage samples V 3 ( i ) are obtained by sampling a voltage on the positive terminal Yp, and the fourth voltage samples V 4 ( i ) are obtained by sampling a voltage on the negative terminal Yn. 
         [0045]    Herein, i is a sampling number and i=1˜N, N is a positive integer in relation to a sampling time length and a sampling frequency. The voltage samples having the same sampling sequence number are sampled in the same sampling period. Similarly, the voltage samples having the different sampling sequence number are sampled in different sampling periods. For example, the micro processor  280  may receive a series of voltage samples: V 1 ( 1 ), V 2 ( 1 ), V 3 ( 1 ), V 4 ( 1 ), V 1 ( 2 ), V 2 ( 2 ), V 3 ( 2 ), V 4 ( 2 ), V 1  ( 3 ) . . . V 1 ( i ), V 2 ( i ), V 3 ( i ), V 4 ( i ). In another embodiment, only the first voltage samples V 1 ( i ) and the second voltage samples V 2 ( i ) are obtained in the some sampling periods. Two or four voltage samples with the same sampling number may be called as one sample or one sample point. 
         [0046]    Next, how to recognize the motion tendency of the two touch points on the resistive touch screen depending on the received voltage samples will be described hereafter in detail. Firstly, it requires to further explain a working principle of the resistive touch screen herein. 
         [0047]      FIG. 2A  is a schematic diagram showing the resistive touch screen with two touch points P 1  and P 2  thereon, wherein coordinates of the touch point P 1  is (x 1 ,y 1 ), coordinates of the touch point P 2  is (x 2 ,y 2 ), a position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &gt;y 1 . It is also called that the two touch points P 1  and P 2  locate on a first or principal diagonal of the touch screen for simplicity.  FIG. 2B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 2A . Referring to  FIG. 2B , the first voltage sample V 1  must be larger than the second voltage samples V 2 , namely V 1 −V 2 &gt;0, if the position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &gt;y 1  as shown in  FIG. 2A . Conversely, it is concluded that the position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &gt;y 1  if the first voltage sample V 1  is larger than the second voltage sample V 2 . Then, it is further concluded that a motion tendency of the two touch points P 1  and P 2  are contraction or expansion (both referred as a non-rotating motion) along the first diagonal of the touch screen if all the differences V 1 ( i )−V 2 ( i ) between the first voltage samples V 1 ( i ) and the second voltage samples V 2 ( i ) are larger than 0. 
         [0048]      FIG. 3A  is a schematic diagram showing the resistive touch screen with two touch points P 1  and P 2  thereon, wherein coordinates of the touch point P 1  is (x 1 ,y 1 ), coordinates of the touch point P 2  is (x 2 ,y 2 ), a position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &lt;y 1 . It is also called that the two touch points P 1  and P 2  locate on a second or secondary diagonal of the touch screen for simplicity.  FIG. 3B  is a circuit diagram showing an equivalent electrical circuit to the resistive touch screen shown in  FIG. 3A . Referring to  FIG. 3B , the first voltage sample V 1  must be less than the second voltage samples V 2 , namely V 1 −V 2 &lt;0, if the position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &lt;y 1  as shown in  FIG. 3A . Conversely, it is concluded that the position relation of the two touch points P 1  and P 2  satisfies x 2 &gt;x 1  and y 2 &lt;y 1  if the first voltage sample V 1  is less than the second voltage sample V 2 . Then, it is further concluded that the motion tendency of the two touch points P 1  and P 2  is contraction or expansion along the second diagonal of the touch screen if all the differences V 1 ( i )−V 2 ( i ) are less than 0. 
         [0049]    When the two touch points P 1  and P 2  on the resistive touch screen have the same y coordinate or the same x coordinate, the resistor R 5  or R 2  shown in  FIG. 2B  is equal to zero, whereby the first voltage sample V 1  is equal to the second voltage sample V 2 , namely V 1 −V 2 =0. Hence, it is concluded that the two touch points P 1  and P 2  are counterclockwise rotating or clockwise rotating (both referred as a rotating motion) if some differences V 1 ( i )−V 2 ( i ) are less than 0, and some differences V 1 ( i )−V 2 ( i ) are larger than 0. 
         [0050]      FIG. 5  is a flow chart showing a method  500  for recognizing a motion tendency of two touch points on the resistive touch screen according to one embodiment of the present invention. Referring to  FIG. 5 , the method  500  comprises the following operations. 
         [0051]    At  502 , a series of first voltage samples V 1 ( i ) are obtained by sampling the positive terminal Xp and a series of second voltage samples V 2 ( i ) are obtained by sampling the negative terminal Xn when the positive terminal Yp is coupled to the positive reference voltage VT and the negative terminal Yn is grounded. 
         [0052]    At  504 , differences V 1 ( i )−V 2 ( i ) between the first voltage samples V 1 ( i ) and the second voltage samples V 2 ( i ) are calculated. 
         [0053]    At  506 , it is determined whether some differences V 1 ( i )−V 2 ( i ) are larger than zero and some differences V 1 ( i )−V 2 ( i ) are less than zero. If yes, the process is taken to  510 , otherwise the process is taken to  508 . 
         [0054]    At  508 , it is concluded that the motion tendency of the two touch points P 1  and P 2  on the touch screen is contraction or expansion (both referred as the non-rotating motion). 
         [0055]    At  510 , it is concluded that the motion tendency of the two touch points P 1  and P 2  on the touch screen is counterclockwise rotation or clockwise rotation (both referred as the rotating motion). 
         [0056]    As a result, the general motion tendency of the two touch points on the touch screen is recognized depending on the received voltage samples V 1 ( i ) and V 2 ( i ). The method  500  shown in  FIG. 5  is a theoretical method to recognize the general motion tendency of the two touch points. Depending on implement, some modifications may be made to the method  500  because of the impact of various noises. For example, the operation of  506  is modified to determine whether the proportion of negative and positive of the differences V 1 ( i )−V 2 ( i ) is larger than a lower threshold (e.g. 5%) and less than a higher threshold (e.g. 95%). If yes, the process is taken to  510 , otherwise, the process is taken to  508 . 
         [0057]    In one embodiment, it requires to further determine that the motion tendency of the two touch points P 1  and P 2  on the touch screen is contraction or expansion after the general motion tendency of the two touch points on the touch screen is recognized as the non-rotating motion.  FIG. 6A  is a flow chart showing a first embodiment of a method for recognizing the non-rotating motion of the two touch points on the resistive touch screen. In order to fully understand the method, some knowledge for recognizing the non-rotating motion of the two touch points is described hereafter firstly. 
         [0058]    Referring to  FIG. 2B , the following formulas are deduced: 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       Iy 
                       * 
                       R 
                        
                       
                           
                       
                        
                       6 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           5 
                         
                         R 
                       
                       * 
                       Rz 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       Iy 
                       * 
                       R 
                        
                       
                           
                       
                        
                       6 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           5 
                         
                         R 
                       
                       * 
                       
                         ( 
                         
                           
                             Rz 
                              
                             
                                 
                             
                              
                             2 
                           
                           + 
                           
                             R 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0059]    Wherein R=Rz 1 +Rz 2 +R 2 +R 5 , 
         [0060]    Iy=VT/(R 4 +R 6 +Rb), 
         [0061]    Rb=R 5 //(Rz 1 +Rz 2 +R 2 ), Iy is a current flowing through the Y conductive layer. 
         [0062]    Depending on the formulas (1) and (2), the difference between the first voltage sample V 1  and the second voltage sample V 2  is: 
         [0000]    
       
         
           
             
               
                 
                     
                   
                     
                       
                         
                           
                             
                               V 
                                
                               
                                   
                               
                                
                               1 
                             
                             - 
                             
                               V 
                                
                               
                                   
                               
                                
                               2 
                             
                           
                           = 
                             
                            
                           
                             VT 
                              
                             
                               Rb 
                               
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                                 + 
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   6 
                                 
                                 + 
                                 Rb 
                               
                             
                              
                             
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                                 + 
                                 
                                   Rz 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                                 + 
                                 
                                   Rz 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                            
                           
                             VT 
                              
                             
                               1 
                               
                                 
                                   
                                     Yplate 
                                     - 
                                     
                                       R 
                                        
                                       
                                           
                                       
                                        
                                       5 
                                     
                                   
                                   Rb 
                                 
                                 + 
                                 1 
                               
                             
                              
                             
                               1 
                               
                                 
                                   
                                     
                                       Rz 
                                        
                                       
                                           
                                       
                                        
                                       1 
                                     
                                     + 
                                     
                                       Rz 
                                        
                                       
                                           
                                       
                                        
                                       2 
                                     
                                   
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 + 
                                 1 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0063]    It can be seen that the difference V 1 −V 2  between the first voltage sample V 1  and the second voltage sample V 2  increases with the increase of the resistor R 5  or R 2 . Hence, it is concluded that the two touch points are expanding on the touch screen if the difference the first voltage sample V 1  and the second voltage sample V 2  tends to increase. On the contrary, it is concluded that the two touch points are contracting on the touch screen if the difference the first voltage sample V 1  and the second voltage sample V 2  tends to decrease. 
         [0064]    Similarly, the difference V 1 −V 2  decreases with the increase of the resistor R 5  or R 2  since the difference V 1 −V 2  shown in  FIG. 3B  is negative. Hence, it is concluded that the two touch points are expanding on the touch screen if an absolute value |V 1 −V 2 | tends to increase. On the contrary, it is concluded that the two touch points are contracting on the touch screen if the absolute value |V 1 −V 2 | tends to decrease. 
         [0065]    Referring to  FIG. 6A , the method  600  in the first embodiment comprises the following operations. 
         [0066]    At  602 , it is determined whether the differences V 1 ( i )−V 2 ( i ) are larger than zero. If yes, the process  600  is taken to  604 , otherwise, the differences V 1 ( i )−V 2 ( i ) are less than zero, the process  600  is taken to  610 . 
         [0067]    At  604 , it is determined whether the differences V 1 ( i )−V 2 ( i ) tend to increase. If yes, the process  600  is taken to  606 , where it is determined that the motion tendency of the two touch points is expansion in the first diagonal of the touch screen (as shown in  FIG. 6C ); otherwise, the differences V 1 ( i )−V 2 ( i ) tend to decrease, the process  600  is taken to  608 , where it is determined that the motion tendency of the two touch points is contraction in the first diagonal of the touch screen (as shown in  FIG. 6B ). 
         [0068]    At  610 , it is determined whether the differences V 1 ( i )−V 2 ( i ) tend to increase. If yes, the process  600  is taken to  612 , where it is determined that the motion tendency of the two touch points is contraction in the second diagonal of the touch screen (as shown in  FIG. 6D ); otherwise, the differences V 1 ( i )−V 2 ( i ) tend to decrease, the process  600  is taken to  614 , where it is determined that the motion tendency of the two touch points is expansion in the second diagonal of the touch screen (as shown in  FIG. 6E ). 
         [0069]      FIG. 6F  is a flow chart showing a second embodiment of the method for recognizing the non-rotating motion of the two touch points on the resistive touch screen. Referring to  FIG. 6F , the method  650  in the second embodiment comprises the following operations. 
         [0070]    At  622 , it is determined whether absolute values |V 1 ( i )−V 2 ( i )| of the differences V 1 ( i )−V 2 ( i ) tend to increase. If yes, the process  650  is taken to  624 , otherwise, the absolute values |V 1 ( i )−V 2 ( i )| tend to decrease, the process  650  is taken to  626 . 
         [0071]    At  624 , it is determined that the motion tendency of the two touch points on the touch screen is expansion (as shown in  FIG. 6C  and  FIG. 6E ). 
         [0072]    At  626 , it is determined that the motion tendency of the two touch points on the touch screen is contraction (as shown in  FIG. 6B  and  FIG. 6D ). 
         [0073]    As described above, it not requires to calculate the coordinates of the two touch points or the distance between the two touch points, only require to calculate the difference between the first voltage samples V( i ) and the second voltage samples V( i ), thereby reducing complexity and computation of the present invention. Additionally, even if a few of voltage samples V( i ) and V 2 ( i ) may result in some error conclusions because of the impact of noise or other facts, but the overall conclusion will still be correct since a series of voltage samples V( i ) and V 2 ( i ) are sampled continuously in the present invention. 
         [0074]    In one embodiment, it also requires to further determine that the motion tendency of the two touch points P 1  and P 2  on the touch screen is counterclockwise rotation or clockwise rotation after the general motion tendency of the two touch points on the touch screen is recognized as the rotating motion.  FIG. 7A  is a flow chart showing a first embodiment of a method for recognizing a rotating motion of the two touch points on the resistive touch screen. In order to fully understand the method, some knowledge for recognizing the rotating motion of the two touch points is described hereafter firstly. 
         [0075]    As described above, the following formulas are deduced by referring to  FIG. 2B : 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                   
                   = 
                   
                     
                       Iy 
                       * 
                       R 
                        
                       
                           
                       
                        
                       6 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           5 
                         
                         R 
                       
                       * 
                       R 
                        
                       
                           
                       
                        
                       z 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                   
                   = 
                   
                     
                       Iy 
                       * 
                       R 
                        
                       
                           
                       
                        
                       6 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           5 
                         
                         R 
                       
                       * 
                       
                         ( 
                         
                           
                             Rz 
                              
                             
                                 
                             
                              
                             2 
                           
                           + 
                           
                             R 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0076]    Wherein R=R 1 +R 2 +R 2 +R 5 , 
         [0077]    Iy=VT/(R 4 +R 6 +Rb 1 ), 
         [0078]    Rb 1 =R 5 //(Rz 1 +Rz 2 +R 2 ), Iy is a current flowing through the Y conductive layer. 
         [0079]    Similarly, the following formulas are got by referring to  FIG. 2B : 
         [0000]    
       
         
           
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     4 
                   
                   = 
                   
                     
                       Ix 
                       * 
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                         
                         R 
                       
                       * 
                       Rz 
                        
                       
                           
                       
                        
                       2 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
             
               
                 
                   
                     V 
                      
                     
                         
                     
                      
                     3 
                   
                   = 
                   
                     
                       Ix 
                       * 
                       R 
                        
                       
                           
                       
                        
                       3 
                     
                     + 
                     
                       Iy 
                       * 
                       
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                         
                         R 
                       
                       * 
                       
                         ( 
                         
                           
                             Rz 
                              
                             
                                 
                             
                              
                             2 
                           
                           + 
                           
                             R 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
         [0080]    Wherein R=R 1 +R 2 +R 2 +R 5 , 
         [0081]    Ix=VT/(R 1 +R 3 +Rb 2 ), 
         [0082]    Rb 2 =R 2 //(Rz 1 +Rz 2 +R 5 ), Ix is a current flowing through the X conductive layer 
         [0083]    Depending on the formulas (1) and (2), the difference between the first voltage sample V 1  and the second voltage sample V 2  is: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             V 
                              
                             
                                 
                             
                              
                             1 
                           
                           - 
                           
                             V 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         = 
                           
                          
                         
                           VT 
                            
                           
                             Rb 
                             
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                               + 
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 6 
                               
                               + 
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 b 
                               
                             
                           
                            
                           
                             
                               R 
                                
                               
                                   
                               
                                
                               2 
                             
                             
                               
                                 R 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                               + 
                               
                                 Rz 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               + 
                               
                                 Rz 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           VT 
                            
                           
                             1 
                             
                               
                                 
                                   Yplate 
                                   - 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     5 
                                   
                                 
                                 Rb 
                               
                               + 
                               1 
                             
                           
                            
                           
                             1 
                             
                               
                                 
                                   
                                     Rz 
                                      
                                     
                                         
                                     
                                      
                                     1 
                                   
                                   + 
                                   
                                     Rz 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 
                                   R 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                               + 
                               1 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0084]    Depending on the formulas (4) and (5), the difference between the first voltage sample V 3  and the second voltage sample V 4  is: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       3 
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       4 
                     
                   
                   = 
                   
                     
                       Ix 
                        
                       
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                           * 
                           R 
                            
                           
                               
                           
                            
                           5 
                         
                         R 
                       
                     
                     = 
                     
                       
                         VT 
                         * 
                         R 
                          
                         
                             
                         
                          
                         2 
                         * 
                         R 
                          
                         
                             
                         
                          
                         5 
                       
                       
                         
                           R 
                           * 
                           Xplate 
                         
                         - 
                         
                           R 
                            
                           
                               
                           
                            
                           2 
                           * 
                           R 
                            
                           
                               
                           
                            
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
         [0085]    The following formula is set depending on the formulas (3) and (6): 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         X 
                         = 
                           
                          
                         
                           
                             Xplate 
                             
                               
                                 V 
                                  
                                 
                                     
                                 
                                  
                                 1 
                               
                               - 
                               
                                 V 
                                  
                                 
                                     
                                 
                                  
                                 2 
                               
                             
                           
                           - 
                           
                             Yplate 
                             
                               
                                 V 
                                  
                                 
                                     
                                 
                                  
                                 3 
                               
                               - 
                               
                                 V 
                                  
                                 
                                     
                                 
                                  
                                 4 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             
                               Yplate 
                               * 
                               R 
                                
                               
                                   
                               
                                
                               2 
                               * 
                               R 
                                
                               
                                   
                               
                                
                               2 
                             
                             - 
                             
                               Xplate 
                               * 
                               R 
                                
                               
                                   
                               
                                
                               5 
                               * 
                               R 
                                
                               
                                   
                               
                                
                               5 
                             
                           
                           
                             VT 
                             * 
                             R 
                              
                             
                                 
                             
                              
                             2 
                             * 
                             R 
                              
                             
                                 
                             
                              
                             5 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           
                             1 
                             VT 
                           
                            
                           
                             ( 
                             
                               
                                 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     5 
                                   
                                 
                                 * 
                                 Yplate 
                               
                               - 
                               
                                 
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     5 
                                   
                                   
                                     R 
                                      
                                     
                                         
                                     
                                      
                                     2 
                                   
                                 
                                 * 
                                 Xplate 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
         [0086]    Referring to  FIGS. 2A and 2B , it can be seen that the resistance value of the resistor R 2  indicates a distance value between the two touch points P 1  and P 2  along the X-axis direction, and the resistance value of the resistor R 5  indicates a distance value between the two touch points P 1  and P 2  along the Y-axis direction. 
         [0087]    Therefore, if the two touch points locate on the first diagonal as shown in  FIG. 2A , the following conclusions can be obtained according to the formula (7): when a connection line of the two touch points infinitely approximate to a horizontal line (in parallel with the X-axis), the resistance value of the resistor R 2  is far larger than that of the resistor R 5 , so the value of X is infinite; when the connection line of the two touch points infinitely approximate to a vertical line (in parallel with the Y-axis), the resistance value of the resistor R 2  is far less than that of the resistor R 5 , so the value of the X is infinitesimal. 
         [0088]    Similarly, if the two touch points locate on the second diagonal as shown in  FIG. 3A , the following conclusions can be obtained according to the formula (7) since a sign bit of the difference V 1 −V 2  shown in  FIG. 3A  is opposite to that of the difference V 1 −V 2  shown in  FIG. 2A : when the connection line of the two touch points infinitely approximate to the horizontal line, the resistance value of the resistor R 2  is far larger than that of the resistor R 5 , so the value of X is infinitesimal; when the connection line of the two touch points infinitely approximate to the vertical line, the resistance value of the resistor R 2  is far less than that of the resistor R 5 , so the value of the X is infinite. 
         [0089]    Hence, X is referred as a rotating parameter in the present invention.  FIG. 7G  schematically shows a physical meaning of the rotating parameter X, wherein P close to the horizontal dot line indicates that the rotating parameter X is positive when the two touch points on the first diagonal approximate to the horizontal dot line, N close to the horizontal dot line indicates that the rotating parameter X is negative when the two touch points on the second diagonal approximate to the horizontal dot line, P close to the vertical dot line indicates that the rotating parameter X is positive when the two touch points on the second diagonal approximate to the vertical dot line, and N close to the vertical dot line indicates that the rotating parameter X is negative when the two touch points on the first diagonal approximate to the horizontal dot line. 
         [0090]    In another embodiment, a modified rotating parameter X′ may be provided, wherein 
         [0000]    
       
         
           
             
               X 
               ′ 
             
             = 
             
               
                 Xplate 
                 
                    
                   
                     
                       V 
                        
                       
                           
                       
                        
                       1 
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       2 
                     
                   
                    
                 
               
               - 
               
                 Yplate 
                 
                    
                   
                     
                       V 
                        
                       
                           
                       
                        
                       3 
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       4 
                     
                   
                    
                 
               
             
           
         
       
     
         [0091]    The modification to the rotating parameter has no effect on the above conclusions when the two touch points locate on the first diagonal as shown in  FIG. 2A . however, the modification to the rotating parameter may lead to reversed conclusions when the two touch points locate on the first diagonal as shown in  FIG. 3A . the reversed conclusions comprises: when the connection line of the two touch points infinitely approximate to the horizontal line, the value of X′ is infinite; when the connection line of the two touch points infinitely approximate to the vertical line, the value of the X′ is infinitesimal.  FIG. 7B  schematically shows a physical meaning of the modified rotating parameter X′. 
         [0092]    Referring to  FIG. 7A , the method  700  in the first embodiment comprises the following operations. 
         [0093]    At  702 , it is determined whether the differences V 1 ( i )−V 2 ( i ) are from positive to negative. If yes, the process  700  is taken to  704 ; otherwise, the differences V 1 ( i )−V 2 ( i ) are from negative to positive, the process  700  is taken to  710 . An exemplary method to determine whether the differences V 1 ( i )−V 2 ( i ) are from positive to negative comprises: 
         [0000]      setting  d ( k )= V 1( k )− V 2( k ),  k ε i;    
         [0094]    if d(k)d(k+1)&lt;0, d(k)&gt;0 and d(k+1)&lt;0, determining that the differences V 1 ( i )−V 2 ( i ) are from positive to negative, wherein k, k+1, k+2, k−1 etc. are adjacent touch samples where the difference V 1 ( i )−V 2 ( i ) equal to zero; 
         [0095]    if d(k)d(k+1)&lt;0, d(k)&lt;0 and d(k+1)&gt;0, determining that the differences V 1 ( i )−V 2 ( i ) are from negative to positive. 
         [0096]    At  704 , it is determined whether the modified rotating parameters X′( i ) of adjacent touch samples where the difference V 1 ( i )−V 2 ( i ) equal to zero are larger than zero, wherein 
         [0000]    
       
         
           
             
               
                 X 
                 ′ 
               
                
               
                 ( 
                 i 
                 ) 
               
             
             = 
             
               
                 Xplate 
                 
                    
                   
                     
                       V 
                        
                       
                           
                       
                        
                       1 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       2 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                   
                    
                 
               
               - 
               
                 
                   Yplate 
                   
                     [ 
                     
                       
                         V 
                          
                         
                             
                         
                          
                         3 
                          
                         
                           ( 
                           i 
                           ) 
                         
                       
                       - 
                       
                         V 
                          
                         
                             
                         
                          
                         4 
                          
                         
                           ( 
                           i 
                           ) 
                         
                       
                     
                     ] 
                   
                 
                 . 
               
             
           
         
       
     
         [0097]    If yes, the process  700  is taken to  706 , where it is determined that the two touch points counterclockwise rotate (as shown in  FIG. 7C ); otherwise, the process  700  is taken to  708 , where it is determined that the two touch points clockwise rotate (as shown in  FIG. 7D ). 
         [0098]    At  710 , it is determined whether the modified rotating parameters X′( i ) of adjacent touch samples where the differences V 1 ( i )−V 2 ( i ) equal to zero are larger than zero. 
         [0099]    If yes, the process  700  is taken to  712 , where it is determined that the two touch points clockwise rotate (as shown in  FIG. 7E ); otherwise, the process  700  is taken to  714 , where it is determined that the two touch points clockwise rotate (as shown in  FIG. 7F ). 
         [0100]      FIG. 7H  is a flow chart showing a second embodiment of the method  750  for recognizing the rotating motion of the two touch points on the resistive touch screen. Referring to  FIG. 7H , the method  750  in the second embodiment comprises the following operations. 
         [0101]    At  722 , it is determined whether the rotating parameters X(i) of adjacent touch samples after the differences V 1 ( i )−V 2 ( i ) equal to zero are larger than zero, wherein 
         [0000]    
       
         
           
             
               X 
                
               
                 ( 
                 i 
                 ) 
               
             
             = 
             
               
                 Xplate 
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                 
               
               - 
               
                 
                   Yplate 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       3 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       4 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                   
                 
                 . 
               
             
           
         
       
     
         [0102]    If yes, the process  750  is taken to  724 , otherwise, the process  750  is taken to  726 . In one embodiment, setting d(k)=V 1 (k)−V 2 (k), k ε i; if d(k)d(k+1)&lt;0, k+1, k+2, k+3 etc. are determined as the adjacent touch samples after the difference V 1 ( i )−V 2 ( i ) equal to zero. At  724 , it is determined that the two touch points clockwise rotate (as shown in  FIG. 7E  and  FIG. 7D ). At  726 , it is determined that the two touch points counterclockwise rotate (as shown in  FIG. 7C  and  FIG. 7F ). 
         [0103]    A third embodiment (not shown) of the method for recognizing the rotating motion of the two touch points may be provided by modifying the second embodiment shown in  FIG. 7H . It is determined whether the rotating parameters X(i) of adjacent touch samples before the differences V 1 ( i )−V 2 ( i ) equal to zero are larger than zero. If yes, it is determined that the two touch points counterclockwise rotate; otherwise, it is determined that it is determined that the two touch points clockwise rotate. 
         [0104]    A fourth embodiment of the method for recognizing the rotating motion of the two touch points may be provided. In the fourth embodiment, the rotating parameters X(i) are detected all the time. If it is detected that the rotating parameters X(i) change from a larger positive number to a smaller negative number suddenly, it is concluded that the two touch points counterclockwise rotate. If it is detected that the rotating parameters X(i) change from a smaller negative number to a larger positive number suddenly, it is concluded that the two touch points clockwise rotate. Additionally, ordinary peoples in the art may provide other embodiments to recognize the rotating motion of the two touch points according to the rotating parameters X(i). 
         [0105]    Furthermore, a rotating angel of the two touch points is determined by counting times of the differences V 1 ( i )−V 2 ( i ) passing though zero. Provided that d( i )=V 1 ( i )−V 2 ( i ), if d(i)d(i+1)&lt;0, it indicates that the differences V 1 ( i )−V 2 ( i ) passing though zero one times. If the times is 1, the rotating angel is determined as 90 degree. If the times is 2, the rotating angel is determined as 180 degree. 
         [0106]    For further understanding the present invention, an exemplary application of the present invention is described hereafter.  FIG. 8  is an exemplary flow chart illustrating the method  800  for recognizing the motion tendency of the two touch points on the resistive touch screen according to one embodiment of the present invention. Referring to  FIG. 8 , the method  800  comprises the following operations. 
         [0107]    At  802 , a series of first voltage samples V 1 ( i ) are obtained by sampling the positive terminal Xp and a series of second voltage samples V 2 ( i ) are obtained by sampling the negative terminal Xn when the positive terminal Yp is coupled to the positive reference voltage VT and the negative terminal Yn is grounded. 
         [0108]    At  804 , differences V 1 ( i )−V 2 ( i ) between the first voltage samples V 1 ( i ) and the second voltage samples V 2 ( i ) are calculated. 
         [0109]    At  805 , the number N of touch samples with an absolute value of the difference V 1 ( i )−V 2 ( i ) thereof larger than a first threshold THR 1  is counted. The first threshold THR 1  is a positive value near to zero. 
         [0110]    At  806 , it is determined whether the number N is larger than a predefined number threshold T. If yes, the process  800  is taken to  810 , otherwise, the process is taken to  808 , where it is concluded that the touch screen has a singe touch point thereon. 
         [0111]    At  810 , it is determined whether all the difference V 1 ( i )−V 2 ( i ) is larger than a second threshold THR 2  or all the difference V 1 ( i )−V 2 ( i ) is less than a third threshold THR 3 . If yes, the process  800  is taken to  812 ; otherwise, the process  800  is taken to  820 . The second threshold THR 2  is less than or equal to 0, the third threshold THR 3  is larger than or equal to 0. The first threshold and the second threshold are set to eliminate some interference. 
         [0112]    At  812 , a first average value AVE 1  of the differences V 1 ( i )−V 2 ( i ) of the first half of touch simples is computed and a second average value AVE 2  of the differences V 1 ( i )−V 2 ( i ) of the second half of touch simples is computed. 
         [0113]    At  814 , it is determined that an absolute value |AVE 1 | of the first average value is larger than the absolute value |AVE 2 | of the second average value. If yes, it indicates that the absolute value |V 1 ( i )−V 2 ( i )| tends to decrease, the process  800  is taken to  816 , where it is concluded that the two touch points are contracting on the touch screen; otherwise, it indicates that the absolute value |V 1 ( i )−V 2 ( i )| tends to increase, the process  800  is taken to  818 , where it is concluded that the two touch points are expanding on the touch screen. 
         [0114]    At  820 , it is determined whether the rotating parameters X(i) of adjacent touch samples after the differences V 1 ( i )−V 2 ( i ) equal to zero are larger than zero, wherein 
         [0000]    
       
         
           
             
               X 
                
               
                 ( 
                 i 
                 ) 
               
             
             = 
             
               
                 Xplate 
                 
                   
                     V 
                      
                     
                         
                     
                      
                     1 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                   - 
                   
                     V 
                      
                     
                         
                     
                      
                     2 
                      
                     
                       ( 
                       i 
                       ) 
                     
                   
                 
               
               - 
               
                 
                   Yplate 
                   
                     
                       V 
                        
                       
                           
                       
                        
                       3 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                     - 
                     
                       V 
                        
                       
                           
                       
                        
                       4 
                        
                       
                         ( 
                         i 
                         ) 
                       
                     
                   
                 
                 . 
               
             
           
         
       
     
         [0115]    If yes, the process  800  is taken to  822 , otherwise, the process  800  is taken to  824 . At  822 , it is determined that the two touch points clockwise rotate. At  824 , it is determined that the two touch points counterclockwise rotate. 
         [0116]    The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.