Abstract:
In a touched position detection method for a touch panel for detecting a touched position, based on measured values by a plurality of sensors, presence of a touch is determined when a measured value by a sensor exceeds a touch threshold. As a touch threshold, a value which cannot be attained due to a mere noise but can due to presence of a touch is set. With respect to sensors located in the vicinity of a sensor showing a high measured value, a higher weighted value is applied to modify a measured value in a touched position calculation process than that to be applied to other sensors.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese application JP2008-229236 filed on Sep. 8, 2008, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a touch panel, and in particular to a method for detecting a touched position on a projected capacitive static capacitance type touch panel. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, touch panels have become popular to be used as a user interface of a mobile device. 
         [0006]    As one type of a touch panel, a static capacitance type is available. This type has come to be used in a wider market as being superior in transmittance and durability, though having a noise problem to be addressed. A touch panel, as being adhesively attached to a display screen, is likely affected by noise due to a display driving circuit. Accordingly, problems may be caused due to noise, including erroneous detection of a touch when the touch panel is not touched at all, difference between a calculated touched position and an actual touched position, and so forth. 
         [0007]    As an example of a technique for reducing noise influence on a static capacitance type touch panel, Japanese Patent Laid-open Publication No. 2007-26065 discloses a touch detection method. According to this touch detection method, presence of a touch is determined when a measured value by a touch detection sensor is maintained equal to or larger than a predetermined threshold for a period longer than a predetermined period. This can avoid erroneous touch detection due to noise which appears only for a short period. 
         [0008]    However, the method disclosed in the above described Japanese Patent Laid-open Publication No. 2007-26065 has some problems. First, as elapse of a predetermined period of time after a touch begins is needed to detect a touch, detection of a quick touch by a user (instantaneous touch, or the like) may be failed. Second, there is a possibility that a calculated position be different from an actual touched position as noise influence is not taken into consideration in a touched position calculation process following touch detection. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention has been conceived in order to solve the above-described problems, and an object thereof is to provide a touch panel capable of detecting a touch in a short period and calculating a touched position with high accuracy, while preventing erroneous touch detection, under circumstances where noise will be caused. 
         [0010]    According to a touched position detection method for a touch panel according to the present invention, presence of a touch is determined when a measured value by a sensor exceeds a touch threshold. As a touch threshold, a value which cannot be attained due to a mere noise but can due to presence of a touch is set. With respect to sensors located in the vicinity of a sensor showing a high measured value, a higher weighted value is applied to modify a measured value in a touched position calculation process than that to be applied to other sensors. 
         [0011]    As presence or absence of a touch can be determined, based on a single measured value by a sensor, a quick operation by a user can be detected. Further, as a measured value by a sensor located near a touched position is made much of in calculation of a touched position, remarkable displacement of a calculated touched position from an actual touched position due to noise influence can be avoided. 
         [0012]    By implementing the touched position detection method according to the present invention through software process, it is possible to address a noise problem without increasing hardware cost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a block diagram showing a structure of a touch panel module; 
           [0014]      FIG. 2  is a cross sectional view showing a cross sectional structure of a touch panel; 
           [0015]      FIG. 3  is a flowchart of a procedure of a touched position detection process to be carried out by a control unit; 
           [0016]      FIG. 4  is a graph showing an example of a difference value for describing a touch detection process; 
           [0017]      FIG. 5  is a graph showing an example of a difference value for describing a touched position calculation process; 
           [0018]      FIG. 6  is a graph showing an example of a weighted value; 
           [0019]      FIG. 7  is a graph showing an example of an update process for updating a reference value; and 
           [0020]      FIG. 8  is a graph showing an example of an update process for updating a reference value. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    In the following, an embodiment for describing the present invention will be described. 
       Embodiment 1  
       [0022]      FIG. 1  is a block diagram showing a structure of a touch panel module used in this embodiment. The touch panel module comprises a touch panel  1 , a control unit  2 , a bus connection signal line  3 , and a storage unit  4 . In the touch panel  1 , electrode patterns (electrodes X 1  to X 5  and Y 1  to Y 5 ) which are sensor terminals for detecting a touch by a user are formed. The control unit  2  is connected to the electrodes X 1  to X 5  and Y 1  to Y 5 , and measures static capacitance of each electrode. The control unit  2  detects a touched position, based on the measured static capacitance, and notifies a host of the result via the bus connection signal line  3 . The storage unit  4  stores a parameter and working data necessary in a touched position detection process by the control unit  2 . The parameter comprises a touch threshold  41 , a near-peak range  42 , a near-peak offset value  43 , and a non-near-peak offset value  44 , each being a numeric value. The working data comprises a reference value  45 , a measured value  46 , a difference value  47 , and a weighted value  48 , each being an array of numeric values. The number of elements of each array is equal to the number of electrodes, which is ten in this embodiment. 
         [0023]      FIG. 2  is a cross sectional view showing a cross sectional structure of the touch panel  1 . The touch panel  1  has a structure in which an electrode layer Y, an insulation layer  12 , an electrode layer X, and a protection layer  11  are stacked in this order on a substrate layer  13  serving as a bottom surface. Note that by mounting the layers each formed using a transparent member on a flat display, a display having a touch panel can be formed. 
         [0024]      FIG. 3  is a flowchart showing a procedure of a touched position detection process to be carried out by the control unit  2 . 
         [0025]      FIG. 4  is a graph showing an example of the difference value  45  for describing a touch detection process. 
         [0026]      FIG. 5  is a graph showing an example of the difference value  45  for describing a touched position calculation process. 
         [0027]      FIG. 6  is a graph showing an example of the weighted value  48 . 
         [0028]      FIG. 7  is a graph showing an example of an update process for updating the reference value  45 . 
         [0029]      FIG. 8  is a graph showing an example of an update process for updating the reference value  45 . 
         [0030]    In the following, a flow of a process for detecting a touched position will be described, based on the flowchart shown in  FIG. 3 . Here, touched position detection in the X axis, utilizing the electrode X 1  to X 5  will be mainly described. A similar process to that for the X axis detection may be carried out for touched position detection in the Y axis, utilizing the electrodes Y 1  to Y 5 . 
         [0031]    When power supply for the touch panel module is turned on, the following process begins. 
         [0032]    At step S 1 , the control unit  2  initializes the reference value  45 . Specifically, static capacitance of each of the electrodes X 1  to X 5  is measured, and stored as a reference value  45  of the electrode. It is assumed here that the touch panel  1  is not touched when the power supply is turned on. 
         [0033]    At step S 2 , the control unit  2  measures static capacitance of each of the electrodes X 1  to X 5 , and stores a measured value as a measured value  46  of the electrode. Thereafter, a value obtained by the expression (1) below is stored as a difference value  47 . 
         [0000]      difference value b  47 =measured value 46−reference value 45   (1) 
         [0000]    Note that for a negative difference value  47 , 0 is stored instead of the obtained value. 
         [0034]    In the following, an example with the difference values  47  obtained being those shown in  FIG. 4  will be described. 
         [0035]    At step S 3 , the control unit  2  determines whether or not the touch panel  1  is touched. Specifically, whether or not a difference value  47  of a respective electrode X 1  to X 5  is equal to or more than a predetermined touch threshold  4  is determined. When a difference value  47  of at least one electrode is equal to or larger than the touch threshold  41 , presence of a touch is determined, and the process proceeds to step S 4 . Meanwhile, when this condition is not satisfied, absence of a touch is determined, and the process proceeds to step S 7 . With the case shown in  FIG. 4 , as the difference value  47  of the electrode X 3  is larger than the touch threshold  41 , presence of a touch is determined. 
         [0036]    At step S 4 , the control unit  2  determines a near-peak electrode. Specifically, difference values  47  of the electrodes X 1  to X 5  are compared to one another to define the one having the highest difference value  47  as a peak electrode. In the case shown in  FIG. 4 , the electrode X 3  is defined as a peak electrode. Thereafter, the n number of electrodes located on the right and left respective sides of the peak electrode as the center are defined as near-peak electrodes, with n being a predetermined parameter (a near-peak range  42 ). It is assumed that n is 1 (n=1) in this embodiment. Accordingly, the electrodes X 2  to X 4  are defined as near-peak electrodes, as shown in  FIG. 5 . 
         [0037]    At step S 5 , the control unit  2  obtains a weighted value  48  for a respective electrode X 1  to X 5 . For a near-peak electrode defined at S 4 , a value obtained by the expression (2) is stored as a weighted value  48 ; for other electrodes, a value obtained by the expression (3) is stored as a weighted value  48 . 
         [0000]      weighted value 48=difference value 47−near-peak offset value 43   (2) 
         [0000]      weighted value 48=difference value 47−non-near-peak offset value 44   (3) 
         [0000]    Note that for a negative weighted value  48  obtained by the expression (2) or (3), 0 is stored instead of the obtained value. 
         [0038]    It should be noted that the near-peak offset value  43  and the non-near-peak offset value  44  are predetermined parameters having the relationship expressed by the expression (4) below. 
         [0000]      near-peak offset value 43&lt;non-near-peak offset value 44   (4) 
         [0000]    The shadowed portions of the bars representative of the difference values  47  shown in  FIG. 5  correspond to weighted values  48 , and the portions corresponding to the weighted values  48  are separately shown in the form of a graph in  FIG. 6 . 
         [0039]    At step S 6 , the control unit  2  calculates a touched position. That is, a calculation process is carried out, based on the positions of the respective electrodes in the touch panel  1  and the weighted values  48  calculated at step S 5 .  FIG. 6  shows an example of a calculated touched position (between the electrode X 2  and the electrode X 3 ). 
         [0040]    At step S 7 , the control unit  2  updates the reference values  45  of the respective electrodes. Specifically, a calculation process is carried out, based on the current reference value  45  and the measured value  46  stored at step S 2 . Various methods are available for the calculation process. In the example shown in  FIG. 7 , a reference value  45  follows with delay a shifting measured value  46 . This method, however, has a problem that, during a period with a touch detected, the signal level of the difference value  47  gradually decreases. This will deteriorate accuracy of touched position detection. To address the phenomenon, the following process is carried out in this embodiment. Specifically, when a touch is not detected at step S 3 , reference values  45  of all electrodes are updated. When a touch is detected, on the other hand, a reference value  45  of only an electrode other than a near-peak electrode is updated, while that of a near-peak electrode is not ( FIG. 8 ). 
         [0041]    With the above, one cycle of a touched position detection process is completed, with the process thereafter returning to step S 2 . 
         [0042]    While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.