Touch-panel device

The present application claims priority from Japanese applications JP 2009-098235 filed on Apr. 14, 2009 and JP 2009-196958 filed on Aug. 27, 2009, the contents of which are hereby incorporated by reference into these applications.

1. Field of the Invention

The present invention relates to a touch-panel device, and more particularly, to a technology of detecting a touched position in a projected capacitive type touch-panel device.

2. Description of the Related Art

A touch-panel device (also called touch screen) is a user interface device which includes an input device called touch pad and an output device formed of, for example, a flat panel display, in which the input device and the output device are integrally formed. The touch-panel device has a feature of an intuitive operation method in which an operation target displayed on a display is directly touched with a finger or the like, and is widely used for an information terminal device or the like.

There are various methods of implementing the touch-panel device, and one of those methods includes a projected capacitive type system. According to the projected capacitive type system, a plurality of electrodes are arranged on the touch panel, and a touched position is detected based on a change in electrostatic capacitance of the electrodes caused when a fingertip approaches the touch panel. The electrodes are formed of a material with high transmittance and arranged on the display panel, to thereby form a touch-panel device.

Accuracy of touched position detection may be referred to as a performance index of a touch panel as an input device. When an error between a position on the display panel actually touched by a user and a detected position is smaller, the accuracy is higher.

JP 2003-511799 A (hereinafter, referred to as Patent Document 1) discloses a method as an example of a technology of detecting a touched position with high accuracy in a projected capacitive type touch-panel device. According to the touched position detecting method, electrodes for detecting positions in an X direction and a Y direction are arranged in a pattern so as to allow a fingertip to touch a plurality of electrodes simultaneously when touching the display panel, to thereby determine the touched position with high accuracy.

Alternatively, JP 2008-269297 A (hereinafter, referred to as Patent Document 2) employs an electrode pattern in which electrodes for detecting positions in an X direction and a Y direction are formed on a single layer, to thereby reduce the manufacturing process.

However, the conventional touched position detecting method involves a problem that, in a case where a range (touched area) on the touch panel touched by a fingertip extends off an area (electrode area) where the electrodes are arranged, accuracy of touched position detection is reduced. In order to prevent such reduction in accuracy, an effective range for detecting a touched position needs to be limited to a certain range within the electrode area. Accordingly, even if the electrodes are arranged across the entire touch panel, a touched position falling on an area at the edge of the touch panel still may not be detected.

The present invention has been made in order to solve the above-mentioned problems, and therefore, it is an object of the present invention to provide a touch-panel device capable of detecting a touched position with high accuracy even when a touched area extends off an electrode area, to thereby form the entire electrode area as an effective range for detecting the touched position.

The present invention provides two kinds of solving means as follows.

According to first solving means, the touched area is assumed to be, for example, a circular in shape. A width in an X direction and a width in a Y direction of an area where the touched area in a circular shape and the electrode area overlap each other may be determined based on sensor measured values. When the width in the X direction and the width in the Y direction are different from each other, it is judged that the touched area extends off the electrode area, and a position of a center of the touched area in the circular shape is calculated as the touched position.

According to second solving means, in a case where a signal value of an electrode provided on the edge of the touch panel becomes largest, it is judged whether or not a periphery of the touch panel is touched. In a case where the periphery of the touch panel is touched, a weighted average is calculated in the touched position calculation process based on an electrode position parameter value which is different from the value employed in a case where the center of the touch panel is touched. A signal value of each of the electrodes is assigned a weight and the weight is varied in accordance with a touch size, to thereby correct a calculated position.

It should be noted that JP 10-020992 A (hereinafter, referred to as Patent Document 3) also discloses a method of detecting a touched position with high accuracy in a state where an electrode provided on the edge of the touch panel takes a largest signal value. However, in the method according to Patent Document 3, an electrode position adjacent to the electrode provided on the edge portion and an electrode position at anothe-r edge portion are selected, to thereby detect a touched position by using an approximate quadratic curve. Accordingly, this method is completely different from the method according to the present invention.

According to the first solving means, a touched position may be detected with high accuracy even in a case where the touched area extends off the electrode area in one of the X direction and the Y direction.

According to the second solving means, a touched position may be detected with high accuracy by using an electrode for detecting a touched position in one direction, even in a case where the periphery of the touch panel is touched.

In the accompanying drawings:

FIG. 1 is a block diagram illustrating an entire configuration of a touch panel module according to a first embodiment of the present invention;

FIG. 2 is a cross-sectional view illustrating a cross-sectional structure of a touch panel;

FIG. 3 is a flow chart illustrating a procedure of a touched position detection process;

FIG. 4 is a diagram illustrating examples of sensor measured values in a case where a touched area extends off an electrode area;

FIG. 5 is a diagram illustrating how to calculate a touched position in the case where the touched area extends off the electrode area;

FIG. 6 is a block diagram illustrating an entire configuration of a touch panel module according to a second embodiment of the present invention;

FIG. 7 is a flow chart illustrating another procedure of the touched position detection process;

FIG. 8 is a diagram illustrating a case where a touched position falls on a center of the touch panel; and

FIG. 9 is a diagram illustrating a case where a touched position falls on a periphery of the touch panel.

In the following, exemplary embodiments of the present invention are described.

[First Embodiment]

FIG. 1 is a block diagram illustrating an entire configuration of a touch panel module (touch-panel device) employed in a first embodiment of the present invention. The touch panel module includes a touch panel 1 , an electrostatic capacitance detecting unit 2 , a control unit 3 , a storage unit 4 , and a bus connection signal line 5 . In the touch panel 1 , electrodes X 1 to X 5 and electrodes Y 1 to Y 5 serving as sensor terminals for detecting a touch by a user are formed in an electrode pattern. The electrostatic capacitance detecting unit 2 is connected to the electrodes X 1 to X 5 and the electrodes Y 1 to Y 5 , and measures electrostatic capacitance in each of the electrodes. The control unit 3 detects a touched position, based on the measured electrostatic capacitance, and notifies a host of the detection result via the bus connection signal line 5 . The storage unit 4 stores the following values as parameters and working data necessary in a touched position detection process to be performed by the control unit 3 . The parameters include a reference value 41 , a measured value 42 , and a difference value 43 , which are sequence data with an element count corresponding to a total count of the electrodes. In the first embodiment, the element count of the sequence is 10. A touch threshold value 44 , a conversion ratio 45 , an overlap width X 46 , and an overlap width Y 47 each are single numeric value data.

FIG. 2 is a cross-sectional view illustrating a cross-sectional structure of the touch panel 1 . In the touch panel 1 , an electrode layer Y, an insulating layer 12 , an electrode layer X, and a protective layer 11 are laminated in the stated order on a substrate layer 13 .

FIG. 3 is a flow chart illustrating a procedure of the touched position detection process.

FIG. 4 is a diagram illustrating examples of sensor measured values in a case where a touched area extends off an electrode area.

FIG. 5 is a diagram illustrating how to calculate a touched position in a case where the touched area extends off the electrode area.

In the following, with reference to the flow chart of FIG. 3 , a processing flow of detecting a touched position is described.

The following process is started when the touch panel module is turned on.

In Step S 1 , the control unit 3 initializes the reference value 41 . Specifically, the control unit 3 measures electrostatic capacitance in each of all the electrodes (electrodes X 1 to X 5 and electrodes Y 1 to Y 5 ), and stores the value thus determined as the reference value 41 of each of the electrodes. The reference value 41 corresponds to electrostatic capacitance determined for each of the electrodes when the touch panel 1 is not touched. It is assumed here that the touch panel 1 is not touched when the touch panel module is turned on.

In Step S 2 , the control unit 3 first measures electrostatic capacitance for each of all the electrodes, and stores the value thus determined as the measured value 42 for each of the electrodes. Further, the control unit 3 stores a value determined by the expression (1) below as the difference value 43 .

Difference value 43=Measured value 42−Reference value 41  (1)

It should be noted that in a case where a value determined by the expression (1) is negative, 0 is stored instead of the determined value, as the difference value 43 . The difference value 43 corresponds to electrostatic capacitance increased in each of the electrodes due to the touch on the touch panel 1 .

In the following, a description is given on the assumption that the difference values 43 are determined as illustrated in FIG. 4 . In FIG. 4 , a graph on the upper side of the touch panel 1 illustrates examples of the difference value 43 and the touch threshold value 44 determined for each of the electrodes X 1 to X 5 . The electrodes X 1 to X 5 are plotted along the horizontal axis, and the height of the bar graph corresponds to the difference value 43 . The difference values 43 of the electrodes X 1 and X 2 are equal to or larger than the touch threshold value 44 , while the difference values 43 of the electrodes X 3 to X 5 are smaller than the touch threshold value 44 . In FIG. 4 , a graph on the right side of the touch panel 1 illustrates examples of the difference value 43 and the touch threshold value 44 determined for each of the electrodes Y 1 to Y 5 . The electrodes Y 1 to Y 5 are plotted along the horizontal axis, and the height of the bar graph corresponds to the difference value 43 . The difference values 43 of the electrodes Y 2 to Y 4 are equal to or larger than the touch threshold value 44 , while the difference values 43 of the electrodes Y 1 and Y 5 are smaller than the touch threshold value 44 .

In Step S 3 , the control unit 3 judges whether or not the touch panel 1 is touched. Specifically, the control unit 3 compares, for each of all the electrodes, the difference value 43 with the touch threshold value 44 set in advance. In this case, when both the X and Y axes include at least one electrode which has the difference value 43 equal to or larger than the touch threshold value 44 , the control unit 3 judges that the touch panel 1 is touched, and proceeds to Step S 4 . When the above-mentioned condition is not satisfied, the control unit 3 judges that the touch panel 1 is not touched, and returns to Step S 2 . In the case illustrated in FIG. 4 , the difference values 43 of the electrodes X 1 and X 2 and the electrodes Y 2 to Y 4 are equal to or larger than the touch threshold value 44 , and therefore it is judged that the touch panel 1 is touched.

In Step S 4 , the control unit 3 stores values determined by the expressions (2) and (3) below as the overlap width X 46 and the overlap width Y 47 , respectively.

Overlap width X 46=MAX (Difference value 43 of Y axis)*Conversion ratio 45  (2)

Overlap width Y 47=MAX (Difference value 43 of X axis)*Conversion ratio 45  (3)

Here, the function MAX returns a largest value selected from a plurality of values. In FIG. 4 , the difference value 43 of the electrode X 1 is largest on the X axis while the difference value 43 of the electrode Y 3 is largest on the Y axis. The conversion ratio 45 is a preset value, so as to convert the difference value 43 into a length on the touch panel 1 . The overlap width X 46 and the overlap width Y 47 correspond to, as illustrated in FIG. 5 , the widths in the X direction and in the Y direction, respectively, of an area where an area touched (touched area) and an area where electrodes are arranged (electrode area 6 ) overlap each other on the touch panel 1 .

The reason why the overlap width X 46 may be determined by the expression (2) is as follows. As is understood from FIG. 4 , the electrode Y 3 overlaps the touched area with a largest width in the X direction, and hence a change in electrostatic capacitance is largest, with the result that the difference value 43 of the electrode Y 3 becomes largest as illustrated in the graph on the right side. The electrodes Y 2 and Y 4 overlap the touched area with a width in the X direction smaller than that of the electrode Y 3 , and hence a change in electrostatic capacitance is smaller than that of the electrode Y 3 , with the result that the difference values 43 of the electrodes Y 2 and Y 4 are smaller than the difference value 43 of the electrode Y 3 as illustrated in the graph on the right side. The electrodes Y 1 and Y 5 overlap the touched area with only a slight width in the X direction, and hence a change in electrostatic capacitance is very small, with the result that the difference values 43 of the electrodes Y 1 and Y 5 are very small as illustrated in the graph on the right side. The overlap width X 46 corresponds to a width in the X direction of the area where the touched area and the electrode area 6 overlap each other, and hence the overlap width X 46 is proportional to the width in the X direction with which the electrode Y 3 overlaps the touched area, the electrode Y 3 overlapping the touched area with a largest width in the X direction. Accordingly, the overlap width X 46 is proportional to the difference value 43 of the electrode Y 3 . Therefore, the overlap width X 46 may be determined by the expression (2). The conversion ratio 45 may be determined from experiment or the like.

The reason why the overlap width Y 47 may be determined by the expression (3) is as follows. As is understood from FIG. 4 , the electrode X 1 overlaps the touched area with a largest width in the Y direction, and hence a change in electrostatic capacitance is largest, with the result that the difference value 43 of the electrode X 1 becomes largest as illustrated in the graph on the upper side. The electrode X 2 overlaps the touched area with a width in the Y direction smaller than that of the electrode X 1 , and hence a change in electrostatic capacitance is smaller than that of the electrode X 1 , with the result that the difference value 43 of the electrode X 2 is smaller than the difference value 43 of the electrode X 1 as illustrated in the graph on the upper side. The electrode X 3 overlaps the touched area with only a slight width in the Y direction, and hence a change in electrostatic capacitance is very small, with the result that the difference value 43 of the electrode X 3 is very small as illustrated in the graph on the upper side. The electrodes X 4 and X 5 do not overlap the touched area with a width in the Y direction, and hence no change in electrostatic capacitance is caused, with the result that the difference values 43 of the electrodes X 4 and X 5 are 0 as illustrated in the graph on the upper side. The overlap width Y 47 corresponds to a width in the Y direction of the area where the touched area and the electrode area 6 overlap each other, and hence the overlap width Y 47 is proportional to the width in the Y direction with which the electrode X 1 overlaps the touched area, the electrode X 1 overlapping the touched area with a largest width in the Y direction. Accordingly, the overlap width Y 47 is proportional to the difference value 43 of the electrode X 1 . Therefore, the overlap width Y 47 may be determined by the expression (3). The conversion ratio 45 may be determined from experiment or the like.

In Step S 5 , the control unit 3 compares the values of the overlap width X 46 and the overlap width Y 47 with each other. When the difference between the values is smaller than a predetermined threshold value, the control unit 3 judges that the entire touched area falls within the electrode area 6 , and proceeds to Step S 6 . Otherwise, the control unit 3 proceeds to Step S 7 .

In Step S 6 , the control unit 3 determines a touched position based on the difference value 43 . Specifically, the control unit 3 determines, for each of the X axis and the Y axis, a weighted average assuming that the difference value 43 of each of the electrodes is a weight wi and the positions of the electrodes are xi and yi. In other words, the control unit 3 performs calculations of the expressions (4) and (5) below.

Touched position ( X coordinate)=Σ( wi*xi )/Σ( wi )  (4)

Touched position ( Y coordinate)=Σ( wi*yi )/Σ( wi )  (5)

In the manner as described above, one cycle of the touched position detection process performed in the case where the touched area does not extend off the electrode area 6 is completed, and the control unit 3 returns to Step S 2 .

In Step S 7 , the control unit 3 assumes that the touched area is circular in shape, and calculates the center position of the circle as the touched position. Here, as illustrated in FIG. 5 , it is assumed that the touched area extends off the electrode area 6 in the X direction. In this case, the X coordinate of the touched position is determined by the expression (6) below.

Touched position ( X coordinate)=Overlap width X 46−Overlap width Y 47/2  (6)

In FIG. 5 , X and R correspond to the X coordinate and the overlap width Y 47 / 2 , respectively. The Y coordinate may be determined by the expression (5) which is adopted in the case where the touched area does not extend off the electrode area 6 . Alternatively, in a case where the touched area extends off the electrode area 6 in the Y direction, X and Y may be replaced with each other in the calculation method described above, so as to determine the touched position similarly.

In the manner as described above, one cycle of the touched position detection process performed in the case where the touched area extends off the electrode area 6 is completed, and the control unit 3 returns to Step S 2 .

In the above description, it is assumed that the touched area is circular in shape. However, the first embodiment may be applied to any other case as long as the touched position may be calculated based on the overlap width X 46 and the overlap width Y 47 . That is, a width in the X direction and a width in the Y direction of an area where the touched area and the electrode area overlap each other may be determined, and a position of the center of the touched area may be determined based on the width in the X direction and the width in the Y direction thus determined, to thereby calculate the position of the center thus determined as the touched position. The touched area may be assumed to be in an arbitrary shape. For example, the touched area may be assumed to be circular or oval in shape. Alternatively, the touched area may be assumed to be in a shape which has a constant ratio of a width thereof in the X direction to a width thereof in the Y direction (for example, in a square or rectangular shape, or in a square or rectangular shape having rounded corners). Still alternatively, the touched area may be in a shape determined from experiment or the like.

[Second Embodiment]

Next, a second embodiment of the present invention is described. In the following, constituent elements that have been already described in the first embodiment are denoted by the same reference symbols, and the description thereof is omitted.

FIG. 6 is a block diagram illustrating an entire configuration of a touch panel module according to the second embodiment. Unlike the storage unit 4 of the first embodiment, the storage unit 4 of the second embodiment stores a touch size 48 and a weighting value 49 , in addition to the reference value 41 , the measured value 42 , the difference value 43 , and the touch threshold value 44 described above. The touch size 48 is a single numerical data. The weighting value 49 is a single or a plurality of numerical data.

FIG. 7 is a flow chart illustrating a procedure of a touched position detection process.

FIG. 8 is a diagram illustrating a case where a touched position falls on a center of the touch panel.

FIG. 9 is a diagram illustrating a case where a touched position falls on a periphery of the touch panel.

In the following, with reference to the flow chart of FIG. 7 , a processing flow of detecting a touched position is described. The following process is started when the touch panel module is turned on.

The processing in Steps S 11 to S 13 is similarly performed as in Steps S 1 to S 3 of the first embodiment, and therefore the description thereof is omitted.

In Step S 14 , the control unit 3 determines a total of the difference values 43 of all the electrodes, that is, the electrodes X 1 to X 5 and the electrodes Y 1 to Y 5 , and stores the determined value as the touch size 48 . The touch size 48 assumes a value proportional to the size of the touched area, and is notified to the host as an index indicating a strength of the touch, together with the touched position to be detected in the following steps. The reason why the touch size (value proportional to the size of the touched area) is determined based on the total of the difference values 43 of all the electrodes is as follows. For example, in FIG. 8 , the difference value 43 of the electrode X 1 is proportional to the size of the area where the electrode X 1 and the touched area overlap each other, the difference value 43 of the electrode X 2 is proportional to the size of the area where the electrode X 2 and the touched area overlap each other, the difference value 43 of the electrode X 3 is proportional to the size of the area where the electrode X 3 and the touched area overlap each other, the difference value 43 of the electrode X 4 is proportional to the size of the area where the electrode X 4 and the touched area overlap each other, and the difference value 43 of the electrode X 5 is proportional to the size of the area where the electrode X 5 and the touched area overlap each other. The same applies to the electrodes Y 1 to Y 5 . Accordingly, the difference values of all the electrodes may be summed, to thereby determine the touch size (value corresponding to the size of the touched area). In the second embodiment, the touch size is determined in the manner as described above. However, the touch size may be determined by any other method.

In the following, a procedure of detecting a touched position in the X direction is described. A touched position in the Y direction may also be determined by a similar procedure.

In Step S 15 , the control unit 3 judges whether or not the detected touch falls on a periphery of the touch panel 1 . Specifically, when any of the electrodes provided on the edge of the touch panel 1 , that is, the electrode X 1 or X 5 has the difference value 43 which is largest, the control unit 3 judges that the touch falls on the periphery of the touch panel 1 , and proceeds to Step S 17 . In a case where the above-mentioned condition is not satisfied, the control unit 3 judges that the touch does not fall on the periphery of the touch panel 1 (the touch falls on the center of the touch panel), and proceeds to Step S 16 . For example, in a state as illustrated in FIG. 8 , the electrode X 2 , which is not provided on the edge of the touch panel 1 , has the difference value 43 which is largest, and hence it is judged that the touch does not fall on the periphery of the touchpanel 1 . In a state as illustrated in FIG. 9 , the electrode X 1 , which is provided on the edge of the touch panel 1 , has the difference value 43 which is largest, and hence it is judged that the touch falls on the periphery of the touch panel 1 .

In Step S 16 , the control unit 3 determines, as a coordinate calculation process performed for a touch falling on the center of the touch panel 1 , the touched position based on the difference value 43 of each of the electrodes. Specifically, the control unit 3 determines a weighted average assuming that the difference value 43 of each of the electrodes is a weight wi and the position of each of the electrodes is xi. In other words, the control unit 3 performs a calculation of the expression (7) below.

Touched position=Σ( wi*xi )/Σ( wi )  (7)

Here, the electrode position xi corresponds to a coordinate value of the center of each of the electrodes. In the state as illustrated in FIG. 8 , the electrodes X 1 to X 5 respectively have the electrode positions xi of 0.5, 1.5, 2.5, 3.5, and 4.5 in the stated order. In the manner as described above, one cycle of the touched position detection process is completed, and the control unit 3 returns to Step S 12 .

In Step S 17 , the control unit 3 determines, as a coordinate calculation process performed for a touch falling on the periphery of the touch panel 1 , the touched position based on the largest difference value 43 of an electrode and the difference value 43 of another electrode next to the electrode (two electrodes provided on the edge of the touch panel 1 ). Specifically, the control unit 3 performs the calculation of the expression (7), as in Step S 16 , based on the two electrodes provided on the edge of the touch panel 1 . The calculation performed in Step S 17 is different from Step S 16 in that the electrode positions xi, that is, parameter values of a sensor position, are defined as coordinate values of the outer edges of the two electrodes. In the state as illustrated in FIG. 9 , the position of the electrode X 1 is defined as 0, and the position of the electrode X 2 is defined as 2. The expression (8) below is calculated in this case, which is determined by substituting 0 and 2 into the electrode positions x 1 and x 2 for the two electrodes provided on the edge of the touch panel 1 in the expression (7).

Touched position=2 *w 2/( w 1 +w 2)  (8)

In the expression (8), the coordinate values (x 1 =0 and x 2 =2) of the outer edges of two electrodes are selected as the electrode positions so that the touched position may be calculated as 0 (edge of the touch panel 1 ) when the difference value 43 is measured only for the electrode X 1 while the touched position may be calculated as 1 (midpoint between the electrode X 1 and the electrode X 2 ) when the difference values 43 of the electrode X 1 and the electrode X 2 are equal to each other, that is, w 1 =w 2 . For example, in FIG. 9 , when the difference value w 1 of the electrode X 1 is 1 and the difference value w 2 of the electrode X 2 is 0.4, the touched position is calculated as 0.57 by using the expression (8) when x 1 =0 and x 2 =2 according to the second embodiment. On the other hand, the touched position is calculated as 0.79 by using the expression (7) which is based on the position coordinates of the centers of two electrodes provided on the edge of the touch panel 1 (x 1 =0.5 and x 2 =1.5). As is apparent from FIG. 9 , the actual touched position is closer to the touched position of 0.57 calculated according to the second embodiment than to the touched position of 0.79 calculated based on the position coordinates of the centers of the electrodes.

In the manner as described above, one cycle of the touched position detection process is completed, and the control unit 3 returns to Step S 12 .

As described above, in Step S 15 , it is judged that the touch falls on the periphery of the touch panel 1 under the condition that the difference value 43 of an electrode provided on the edge of the touch panel 1 is largest. However, another condition may also be employed. For example, the judgment may be made under a condition that a total of the difference values 43 of an electrode provided on the edge of the touch panel 1 and of a predetermined number of electrodes adjacent to the electrode is larger than a total of the difference values 43 of the rest of the electrodes.

As described above, in Step S 17 , two electrodes provided on the edge of the touch panel 1 are referred to. However, it is also conceivable to adopt a method in which three or more electrodes are referred to. Further, the electrode positions xi are defined as outer edges of two electrodes when calculating a weighted average. However, the electrode positions xi may be defined differently. The number of electrodes to be referred to and the electrode position xi may be determined depending on the matters of design, such as an assumed size of the touched area or an assumed width of the electrodes.

In the above, the second embodiment of the present invention has been specifically described. It should be noted that the touch-panel device according to the second embodiment has a feature in that the parameter values (x 1 and x 2 in the embodiment described above) for the sensor position to be used in the coordinate calculation process when the touch falls on the periphery of the touch panel 1 is different from those employed when the touch falls on the center of the touch panel 1 .

[Third Embodiment]

Next, a third embodiment of the present invention is described. In the third embodiment, the expression for calculating coordinates in Step S 17 of the second embodiment is modified.

In the third embodiment, in the case where the touch falls on the periphery of the touch panel 1 , each of the electrodes, which is referred to when calculating coordinates, is assigned a weight in order to reduce a deviation (error) of the calculated touched position from the actual touched position. There may be various methods of assigning weights to the electrodes. As one example, there may be employed a method in which, in the expression (7), the difference value 43 (wi) of each of the electrodes may be multiplied by a predetermined weighting coefficient ai, which is expressed by the expression (9) below.

Touched position=Σ( ai*wi*xi )/Σ( ai*wi )  (9)

In the expression (9), similarly to the second embodiment, the electrode positions xi of the two electrodes provided on the edge of the touch panel 1 are defined by coordinate values of the outer edges of the two electrodes, that is, x 1 =0 and x 2 =2, which is expressed by the expression (10) below.

Touched position=2 *a 2 *w 2/( a 1 *w 1 +a 2 *w 2)  (10)

The values of a 1 and a 2 are predetermined, and stored as the weighting value 49 . The values of a 1 and a 2 may be determined from experiment or the like.

As another example, there may be employed a method in which the difference value 43 (w 2 ) of the electrode X 2 is assigned a weight based on the expression (8) so as to calculate the expression (11) below.

Touched position=(1 +a )* w 2/( w 1 +a*w 2)  (11)

Here, the value a is predetermined, and stored as the weighting value 49 . The coefficient in the numerator is defined as 1+a so that the touched position may be calculated as 1 (midpoint between the electrodes X 1 and X 2 ) when the difference values 43 of the electrodes X 1 and X 2 are equal to each other, that is, w 1 =w 2 . The value a (weighting value 49 ) may be determined from experiment or the like.

[Fourth Embodiment]

Next, a fourth embodiment of the present invention is described. In the fourth embodiment, the third embodiment is modified.

In the third embodiment, each of the electrodes is assigned a weight based on a preset constant. However, an appropriate amount of the weight may not be fixed, and may vary depending on the strength of the touch. In the fourth embodiment, a variable is employed as the weighting value, which is varied in accordance with the touch size 48 . There may be various methods to change the weighting value. For example, in the expression (11), the weighting value 49 may be changed in accordance with the touch size 48 . A predetermined function may be used to determine the weighting value 49 . When the function is a linear function of the touch size 48 , the expression (12) below may be determined.

Weighting value 49 =b *Touch size 48 +c   (12)

Here, the values b and c are predetermined. The values b and c may be determined from experiment or the like.

In the embodiments described above, the left side of the touch panel 1 is illustrated by way of example. However, a touched position on the periphery on the right side, the upper side, or the lower side of the touch panel 1 may similarly be calculated with high accuracy.

In the first embodiment, the touched position is detected by using both electrodes in the X direction and the Y direction, and hence the touched position may be detected with high accuracy in the periphery of the touch panel 1 in one of the X direction and Y direction, that is, the periphery of the touch panel 1 which does not include the corners of the touch panel 1 . On the other hand, in the second to fourth embodiments, the touched position is detected by using the electrodes in only one direction (one of the X direction and the Y direction), and hence the touched position may be detected with high accuracy in the periphery of the touch panel 1 which includes the corners.

It should be noted that the present invention is not limited to the embodiments described above, and may be subjected to various modifications without departing from the gist of the present invention.

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.