Touch panel apparatus and position detection method using the touch panel apparatus

A touch panel apparatus includes a first substrate including a first conductive film, a second substrate including a second conductive film, a first terminal, a second terminal, a third terminal, and a fourth terminal respectively provided on the second substrate, and a controller. The controller calculates a potential difference between a measured potential and a reference potential of each of the first and second terminals with connecting the first and second terminals to the power source and the third and fourth terminals to the ground potential, and a potential difference between a measured potential and a reference potential of each of the third and fourth terminals with connecting the second and third terminals to the power source and the first and fourth terminals to the ground potential, determines a potential difference having a largest value, and calculates a relationship between two contact points based on the determined potential difference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-240426 filed on Nov. 27, 2014, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a technology for a touch panel and a position detection method using the touch panel.

BACKGROUND

A touch panel is an input device allowing data to be input directly onto a display The touch panel is used by being placed on a front surface of a display. The touch panel can be used for various purposes because the touch panel data can be input based on data that is visually recognized from a display.

A known resistive film type touch panel has a transparent conductive film formed on an upper electrode substrate and a transparent conductive film formed on a lower electrode substrate in a manner that the conductive films face each other. By exerting force to the upper electrode substrate, the conductive films contact each other to enable detection of the position at which force is exerted.

The resistive film type touch panel can be categorized into a four-wire type and a five-wire type. The four-wire type touch panel has X-axis electrodes arranged on one of the upper and lower electrode substrates and Y-axis electrodes arranged on the other one of the upper and lower electrode substrates (See Patent Document 1).

The five-wire type touch panel includes an electrode substrate that has both X-axis electrodes and Y-axis electrodes provided thereon and another electrode substrate that is used as a probe for measuring potential (See Patent Document 2).

Patent Document 3, for example, discloses a four-wire type touch panel that can detect multiple touched areas.Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-272722;Patent Document 2: Japanese Laid-Open Patent Publication No. 2008-293129Patent Document 3: Japanese Laid-Open Patent Publication No. 2009-176114

However, multi-touch cannot be easily detected with the five-wire type touch panel.

SUMMARY

According to an aspect of the invention, there is provided a touch panel apparatus including a first electrode substrate including a first conductive film, a second electrode substrate having four corners and including a second conductive film, a first power-feed terminal, a second power-feed terminal, a third power-feed terminal, and a fourth power-feed terminal respectively provided on the four corners, a controller, a first resistor that connects with the first power-feed terminal, a second resistor that connects with second power-feed terminal, a third resistor that connects with the second power-feed terminal, and a fourth resistor that connects with the third power-feed terminal. The controller calculates a first potential difference ΔV1Xbetween a potential of the first power-feed terminal and a first reference potential and a second potential difference ΔV2Xbetween a potential of the second power-feed terminal and a second reference potential in a state where the first power-feed terminal is connected to a power source potential via the first resistor, the second power-feed terminal is connected to the power source potential via the second resistor, and the third and fourth power-feed terminals are connected to a ground potential. The controller calculates a third potential difference ΔV2Ybetween a potential of the second power-feed terminal and a third reference potential and a fourth potential difference ΔV3Ybetween a potential of the third power-feed terminal and a fourth reference potential in a state where the second power-feed terminal is connected to the power source potential via the third resistor, the third power-feed terminal is connected to the power source potential via the fourth resistor, and the first and fourth power-feed terminals are connected to the ground potential. The controller selects at least a potential difference having a largest potential difference value among the first, second, third, and fourth potential differences ΔV1X, ΔV2X, ΔV2Y, and ΔV3Y. The controller calculates a positional relationship between two points where the first and second conductive films contact each other based on the selected potential difference having the largest potential difference value.

It is to be understood that both the foregoing general description and the followed detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described with reference to the accompanying drawings. In the following embodiments, like components/parts are denoted with like reference numerals and further description thereof may be omitted.

First Embodiment

A touch panel apparatus according to the first embodiment is described. The touch panel apparatus of this embodiment is a 5-wire touch panel including an upper electrode substrate10and a lower electrode substrate20. The touch panel apparatus can detect a multi-touch operation, or a gesture operation (pinching in, pinching out) that is used for increasing or reducing the size of an image displayed on a display for example.

As illustrated inFIG. 1, the touch panel apparatus also includes an amplifier70, and a controller80. The controller80includes a control part81, a coordinate detector82, a determination part83, a distance calculator84, a 2 point calculator85, a direction detector86, an AD (Analog-to-Digital) convertor87, and a storage88.

The control part81controls the entire touch panel apparatus. The amplifier70amplifies analog voltage data obtained from various potential measurement parts provided in the touch panel apparatus. The AD convertor87convertor87receives the analog voltage data from the amplifier70and converts the analog voltage data into digital voltage data. The amplifier70is provided so that potential can be measured even in a case where the resistance change rate is low when the touch panel100is operated. The storage part88stores various data.

The coordinate detector82detects the coordinates of a contact point, which is a point that the upper conductive film and the lower conductive film of the touch panel are contacted. The determination part83determines whether the contact point is one point or two points. The distance calculator84calculates the distance between two contact points. The 2 point calculator85calculates the coordinates of each of the two contact points. The direction detector86detects the direction in which the two contact points are arranged. The coordinate detector82, the determination part83, the distance calculator84, the 2 point calculator85, and the direction detector86each perform a process based the digital voltage data converted by the AD convertor87.

The controller80is, for example, a microprocessor. In this case, the function of each of the coordinate detector82coordinate detector82, the determination part83, the distance calculator84, the 2 point calculator85, and the direction detector86direction detector86can be implemented by the controller80that executes a program stored in the storage part88.

A touch panel200that is included in the touch panel apparatus is described in detail with reference toFIG. 2. A transparent conductive film11(e.g., ITO (Indium Tin Oxide)) is formed on a surface of the upper electrode substrate10. A transparent conductive film21(e.g., ITO) is formed on a surface of the lower electrode substrate20. The upper electrode substrate10and the lower electrode21are placed in a state facing each other.

A first power-feed terminal31, a second power-feed terminal32, a third power-feed terminal33, and a fourth power-feed terminal34are provided on one of four corners of the conductive film21, respectively. In this embodiment, the first power-feed terminal31, the second power-feed terminal32, the third power-feed terminal33, and the fourth power-feed terminal34are formed, so that a line connecting the first power-feed terminal31and the second power-feed terminal32and a line connecting the third power-feed terminal33and the fourth power-feed terminal are parallel to the Y-axis. Further, a line connecting the first power-feed terminal31and the fourth feed material34and line connecting the second feed material33and the third power-feed terminal39are parallel to the X-axis.

A first switch SW1is connected between the first power-feed terminal31and a first resistor R1serving as a voltage divider. The resistor R1is also connected to a power source Vcc. A second switch SW2is connected between the first power-feed terminal31and the power source Vcc. A third switch SW3is connected between the first power-feed terminal31and a ground potential (0V). A first measuring part AD1that is connected to the first power-feed terminal31measures the potential of the first power-feed terminal31.

It is to be noted that “measuring part AD1” is a term that collectively refers to the elements in the controller80functioning to measure the potential of the first power-feed terminal21. In this embodiment, the measuring part AD1includes the AD convertor87. The output of the first power-feed terminal31is input to the AD convertor87. The same also applies to the AD conversion parts AD2to AD4.

A fourth switch SW4is connected between the second power-feed terminal32and a second resistor R2serving as a voltage divider. The resistor R2is also connected to the power source Vcc. A fifth switch SW5is connected to the second power-feed terminal32and a third resistor R3serving as a voltage divider. The resistor R3is also connected to the power source Vcc. A sixth switch SW6is connected to the second power-feed terminal32and the power source Vcc. The measuring part AD2that is connected to the second power-feed terminal32measure the potential of the second power-feed terminal32.

A seventh switch SW7is connected between the third power-feed terminal33and a fourth resistor R4serving as a voltage divider. The resister R4is connected to the power source Vcc. An eighth switch SW8is connected to the third power-feed terminal33and the power source Vcc. A ninth switch SW9is connected to the third power-feed terminal33and a ground potential (0V). The third potential measurement part AD3that is connected to the third power-feed terminal AD3measures the potential of the third power-feed terminal AD3.

A tenth switch SW10is connected to the fourth power-feed terminal34and to a ground potential (0V).

A fifth resistor R5serving as a voltage divider is connected to the conductive film11and an eleventh switch SW11. The switch SW11is connected to a ground potential (0V). The measuring part AD4that is connected to the conductive film11measures the potential of the conductive film11.

The resistance value of the resistor R1and the resistance value of the resistor R2are the same. Similarly, the resistance value of the resistor R3and the resistance value of the resistor R4are the same.

<Detection of a Middle Point>

When detecting the X coordinate of a contact point with the touch panel200, the switch SW2, the switch SW6, the switch SW9, and the switch SW10are switched on whereas the switch SW1, the switch SW3, the switch SW4, the switch SW5, the switch SW7, the switch SW8, and the switch SW11are switched off as illustrated inFIG. 3, so that a potential distribution is generated on the conductive film21in the X-direction of the conductive film21and the measuring part AD4measures the potential.

When detecting the Y coordinate of a contact point with the touch panel200, the switch SW3, the switch SW6, the switch SW8, and the switch SW10are switched on whereas the switch SW1, the switch SW2, the switch SW4, the switch SW5, the switch SW7, the switch SW9, and the switch SW11are switched off as illustrated inFIG. 4, so that a potential distribution is generated on the conductive film21in the Y-direction of the conductive film21and the measuring part AD4measures the potential.

In a case where the contact point is one point, the detected X coordinate and Y coordinate represent the coordinates of the single contact point. In a case where the contact points are two points, the detected X coordinate and Y coordinate represent the coordinates of the middle point of the two points.

Next, the detection of two contact points is described. When detecting an operation performed on the touch panel apparatus where the contact points are two points, a potential distribution is generated on the conductive film21in the X direction and in the Y direction of the conductive film21. The following processes are performed after two points are detected.

When generating a potential distribution on the conductive film21in the X-direction of the conductive film21, the switch SW1, the switch SW4, the switch SW9, the switch SW10are switched on whereas the switch SW2, the switch SW3, the switch SW5, the switch SW6, the switch SW7, the switch SW8, and the switch SW11are switched off as illustrated inFIG. 5. The voltage Vcc is applied to the first power-feed terminal31and the second power-feed terminal32via the resistor R1and the resistor R2, respectively. The measuring part AD1and the measuring part AD2measure the potential in the state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21.

When generating a potential distribution on the conductive film21in the Y-direction of the conductive film21, the switch SW3, the switch SW5, the switch SW7, the switch SW10are switched on whereas the switch SW1, the switch SW2, the switch SW4, the switch SW6, the switch SW8, the switch SW9, and the switch SW11are switched off as illustrated inFIG. 6. The voltage Vcc is applied to the second power-feed terminal32and the third power-feed terminal33via the resistor R3and the resistor R4, respectively. In this state where the potential distribution is generated on the conductive film21, the measuring part AD2and the measuring part AD3measure the potential.

A gesture operation (pinch out/in operation) that is performed for, for example, increasing or reducing the size of an image displayed on a display is performed by widening or narrowing the distance between two contact points on the touch panel.

The positional relationship between two contact points on the touch panel200is described with reference to 4 patterns S1, S2, S3, and S4illustrated inFIG. 7. The pattern S1is a pattern in which two points are separated along the X-direction (horizontal direction). The pattern S2is a pattern in which two points are separated along a diagonal line extending from an upper left to a lower right. The pattern S3is a pattern in which two points are separated along the Y-direction (vertical direction). The pattern S4is a pattern in which two points are separated along a diagonal line extending from an upper right to a lower left.

FIGS. 8 to 11illustrate a relationship of a distance between two contact points and a potential difference ΔV between a measured potential and a reference potential. In this embodiment, the reference potential is a divided potential of the power-feed terminal measured when the touch panel200is in an untouched state. InFIGS. 8 to 11, “AD1(X)” indicates a potential difference between a divided potential of the first power-feed terminal31measured by the measuring part AD1and the reference potential of the first power-feed terminal31when the potential distribution is generated on the conductive film21in the X-direction of the conductive film21via the resistor R1and the resistor R2as illustrated inFIG. 5. “AD2(X)” indicates a potential difference between a potential of the second power-feed terminal32measured by the measuring part AD2and the reference potential of the second power-feed terminal32when the potential distribution is generated on the conductive film21in the X-direction of the conductive film21as illustrated inFIG. 5. Further, “AD2(Y)” indicates a potential difference between a potential of the second power-feed terminal32measured by the measuring part AD2and the reference potential of the second power-feed terminal32when the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21via the resistor R3and the resistor R4as illustrated inFIG. 6. “AD3(Y)” indicates a potential difference between a potential of the third power-feed terminal33measured by the measuring part AD3and the reference potential of the third power-feed terminal33when the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21as illustrated inFIG. 6.

FIG. 8is a graph illustrating the changes of the potential difference ΔV when the distance between two contact points is changed in the directions of pattern S1ofFIG. 7. In the case of the pattern S1, the potential difference ΔV increases as the distance between two contact points becomes wider in X-direction in “AD1(X)” and “AD2(X)” ofFIG. 8. On the other hand, because the distance between the two contact points in Y-direction is substantially0, the potential difference ΔV in each of “AD2(Y)” and “AD3(Y)” hardly changes (approximately 0V) even when the distance between the two contact points becomes wider in the X-direction. The potential difference AD1(X) and the potential difference AD2(X) have tend to change in a similar manner when the distance between the two contact points are widened.

FIG. 9is a graph illustrating the changes of the potential difference ΔY when the distance between two contact points is changed in the directions of pattern S2ofFIG. 7. In the case of the pattern S2, the distance between the two contact points changes in both the X-direction and the Y-direction. Because the pattern S2is positioned substantially on the line connecting the first power-feed terminal31and the third power-feed terminal33inFIG. 7, the potential difference measured by the measuring part AD1or the potential difference measured by the measuring part AD3changes in a more significant manner than the potential difference measured by the measuring part AD2when the distance between the two contact points is changed along the pattern S2. Therefore, when the distance between the two contact points becomes wider, the change of potential difference ΔV becomes larger in an order of AD2(Y), AD2(X), AD3(Y), and AD1(X) as illustrated inFIG. 9. More specifically, although each of the potential differences AD1(X) and AD3(Y) change in a more significant manner, each of the potential differences AD2(X) and AD2(Y) change in a less significant manner when the distance between the two contact points becomes wider.

FIG. 10is a graph illustrating the changes of the potential difference ΔV when the distance between two contact points is changed in the directions of pattern S3ofFIG. 7. In the case of the pattern S3, the potential difference ΔV increases as the distance between two contact points becomes wider in the Y-direction in “AD2(Y)” and “AD3(Y)” ofFIG. 10. On the other hand, because the distance between the two contact points in the X-direction is substantially0, the potential difference ΔV hardly changes (approximately 0V) even when the distance between the two contact points becomes wider in the direction along the pattern S3in “AD1(X)” and “AD2(X)”. The potential difference AD2(Y) and the potential difference AD3(Y) tend to change in a similar manner when the distance between the two contact points are widened.

FIG. 11is a graph illustrating the changes of the potential difference ΔV when the distance between two contact points is changed in the directions of pattern S4ofFIG. 7. In the case of the pattern S4, the change of potential difference ΔV becomes larger in an order of AD3(Y), AD1(X), AD2(Y), and AD2(X) as illustrated inFIG. 11. More specifically, each of the potential differences AD2(X) and AD2(Y) changes in a more significant manner, but each of the potential differences AD1(X) and AD3(Y) changes in a less significant manner when the distance between the two contact points becomes wider.

As illustrated inFIGS. 8 to 11, each of the potential differences AD1(X), AD2(X), AD2(Y), and AD3(Y) exhibit values corresponding to the distance between the two contact points in the X-direction and the distance between the two contact points in the Y-direction. Therefore, the distance between two contact points can be derived by referring to each value of the potential differences AD1(X), AD2(X), AD2(Y), and AD3(Y) when there are two contact points.

Next, the reason that the potential difference ΔV becomes larger as the distance between two contact points becomes greater is described with the example illustrated inFIG. 5in which the conductive film11on the upper side and the conductive film21on the lower side contact at two points in a state where potential distribution is generated on the conductive film21in the X-direction of the conductive film21via the resistor R1and the resistor R2.

In this state, the conductive film11and the conductive film12contact at two contact points A and B as illustrated inFIG. 12. Accordingly, a combined resistance of the resistance r1of the conductive film11and the resistance r2of the conductive film21being connected in parallel is generated between the contact point A and the contact point B. The value of the combined resistance between the contact point A and the contact point B becomes less than the resistance value of the resistor r2of the conductive film21and the resistance value of the resistor r1of the conductive film11.

In addition, the resistance of the touch panel200between the first power-feed terminal31and a power-feed terminal at the ground potential being serially connected to the combined resistance also decreases. Therefore, the divided potential measured by the measuring part AD1, (the voltage of the power source Vcc divided by the resistance of the touch panel200between the first power-feed terminal31and ground potential and the resistance of the first resistor R1) when two contact points exist becomes less than the divided potential that is measured by the measuring part AD1when the contact point is a single point.

Further, the resistance of the touch panel200between the first power-feed terminal31and the power-feed terminal at the ground potential decreases as the distance between the contact point A and the contact point B increases, because the proportion of the combined resistance relative to the resistance between the first power-feed terminal and the power-feed terminal at the ground potential increases. Accordingly, the potential measured by the measuring part AD1also decreases, and the potential difference ΔV measured when a distance between the contact point A and the contact point B is increasing becomes larger compared to the potential difference ΔV measured when the contact point A and the contact point B become closer toward each other.

Similarly, the resistance of the touch panel200between the second power-feed terminal32and the power-feed terminal at the ground potential (including the combined resistance) also decreases. Accordingly, the potential measured by the measuring part AD2, that is, the divided potential detected from the second power-feed terminal32(the voltage of the power source Vcc divided by the resistance of the touch panel200between the second power-feed terminal32and the ground potential and the resistance of the second resistor R2) decreases. Further, the resistance of the touch panel200between the second power-feed terminal32and the power-feed terminal at ground potential decreases as the distance between the contact point A and the contact point B increases. Accordingly, the potential measured by the measuring part AD2decreases, and the potential difference ΔV becomes larger compared to the potential difference ΔV measured when the contact point A and the contact point B become closer toward each other.

The same applies to a case where potential distribution is generated on the touch panel in the Y-direction of the touch panel200via resistors.

The divided potential detected from the first power-feed terminal31or the second power-feed terminal32when the contact point A and the contact point B are extremely close to each other becomes close to the divided voltage measured when the contact point is a single point, because the proportion of the combined resistance between two contact points relative to the resistance between the first or second power-feed terminal31,32and the power-feed terminal at the ground potential becomes extremely low when the contact point A and the contact point B are close to each other. Therefore, the potential difference ΔV measured by the measuring part AD1and the potential difference ΔV measured by the measuring part AD2may in some cases be approximately 0V when the two contact points are extremely close to each other.

Next, a method for detecting a position of a contact point of the touch panel apparatus of this embodiment is described with reference toFIG. 13. The position detection method of this embodiment is performed in a case of, for example, determining whether an operation such as pinch-out or pinch-in is performed. The processes described herein in connection with flow charts are implemented by the controller.

In Step S102, a touch-on detection process for detecting a touch operation on the touch panel200is conducted. The touch-on detection process is conducted by measuring the potential with the measuring part AD4in a state where the switch SW2, the switch SW6, the switch SW8, the switch SW11are switched on whereas the switch SW1, the switch SW3, the switch SW4, the switch SW5, the switch SW7, the switch SW9, and the switch SW10are switched off as illustrated inFIG. 14. In this state, the potential of each of the first power-feed terminal31, the second power-feed terminal32, and the third power-feed terminal33is Vcc.

When detecting a touch-on operation, two switches among the switch SW2, the switch SW6, and the switch SW8may be switched on to set the potential of two terminals among the first power-feed terminal31, the second power-feed terminal32, and the third power-feed terminal33to Vcc. Alternatively, one switch among the switch SW2, the switch SW6, and the terminal SW8may be switched on to set the potential of one terminal among the first power-feed terminal31, the second power-feed terminal32, and the third power-feed terminal33to Vcc.

Then, in Step S104, it is determined whether a touch-on operation is being performed. When a finger or a pen is contacting the touch panel200, the conductive film11and the conductive film12would be contacting each other. Accordingly, the potential in which the power source Vcc is divided by the resistance of the conductive film11and the resistor R5is detected by the measuring part AD4. Thus, when the potential is detected by the measuring part AD4, it is determined that a touch-on operation is performed on the touch panel200, in other words, a touch is detected, and the flow ofFIG. 13proceeds to Step S106. If no potential is detected by the measuring part AD4, it is determined that a touch is not detected, and the flow ofFIG. 13is ended.

In Step S106, a coordinate of the contact point is measured. In this case, a potential distribution is generated in the X-direction of the conductive film21to allow the measuring part AD4to measure the potential as illustrated inFIG. 3. Then, the coordinate detector82coordinate detector82detects the X-coordinate of the contact point based on the potential measured by the measuring part AD4.

Similarly, a potential distribution is generated on the conductive film21in the Y-direction of the conductive film21to allow the measuring part AD4to measure the potential as illustrated inFIG. 4. Then, the coordinate detector82coordinate detector82detects the Y-coordinate of the contact point based on the potential measured by the measuring part AD4. Thereby, the X coordinate and the Y coordinate of the contact point are detected. In a case where the contact point is one point, the detected X coordinate and the Y coordinate indicate the coordinates of the contact point. In a case where the contact point is two points, the detected X-coordinate and the Y-coordinate indicate the coordinates of the middle point of the two contact points.

Then, in Step S108, the maximum potential difference ΔVm is detected. The term “maximum potential difference ΔVm” refers to the highest value of voltage difference between a reference potential and the potential detected by each of the measuring parts AD1to AD3. The detection of the maximum potential difference ΔVm is described in further detail with reference to the below-described sub-routine.

Then, in Step S110, the determination part83determines whether the maximum potential difference ΔVm obtained in Step S108is greater than a threshold ΔVth. The threshold ΔVth is a criterion for determining whether the contact point on the touch panel200is one point or two points. In a case where the maximum potential difference ΔVm is less than the threshold ΔVth, the contact point is determined to be one point, and the flow ofFIG. 13proceeds to Step S112. In a case where the maximum potential difference ΔVm is greater than the threshold ΔVth, the contact point is determined to be two points, and the flow ofFIG. 13proceeds to Step S114.

When it is determined that the contact point is one point (S112), the coordinates detected in Step S106are output as the coordinates of the contact point.

On the other hand, in a case where the maximum potential difference ΔVm is determined to be greater than the threshold ΔVth in Step S110, the maximum potential difference ΔVm is measured once again in Step S114. When obtaining the maximum potential difference ΔVm in S114a potential distribution in the conductive film21is generated by connecting the switches under the same conditions as when the maximum potential difference ΔVm is obtained in S108, and the potential is measured by the measuring parts that have obtained the maximum potential difference ΔVm in Step S108. The maximum potential difference ΔVm is measured twice for detecting a gesture operation based on the information touched(?) on the touch panel200.

Then, in Step S116, it is determined whether the maximum potential difference ΔVm measured in S114is greater than the threshold ΔVth. In a case where the maximum potential difference ΔVm measured in S114is less than the threshold ΔVth, the measured potential is determined as an error, and the flow ofFIG. 13is ended. In a case where the maximum potential difference ΔVm measured in S114is greater than the threshold ΔVth, the contact point is determined to be two points, and the flow ofFIG. 13proceeds to Step S118.

Then, in Step S118, the distance between two contact points is calculated. The distance calculator84calculates the distance L between the two contact points by using the below-described Expression (1) or Expression (2) based on the maximum potential difference ΔVm. In Expression (1), “α1”, “β1”, and “γ1” are proportional coefficients. In Expression (2), “α2” and “β2” are proportional coefficients.

Alternatively, the distance L between two contact points may be calculated based on, for example, a graph illustrating the correlation between the maximum potential difference ΔM and the distance L as illustrated inFIG. 15. The graph ofFIG. 15, which corresponds to the graph ofFIG. 8by converting the vertical axis and the horizontal axis, is stored in, for example, the storage88.
L=α1×(ΔVm)2+β1×ΔVm+γ1<Expression (1)>
L=α2×√{square root over (ΔVm)}+β2×ΔVm<Expression (2)>

Then, in Step S120, coordinate data of the two contact points is output. The two point calculator85calculates the coordinate data of each of the two contact points based on the distance between the two contact points in the X-direction or the Y-direction obtained in Step S118and the coordinates detected in Step S106, and outputs the calculated coordinate data.

For example, when calculating the X-coordinates of the two contact points, the X-coordinates of one contact point is calculated by adding the X-coordinates detected in Step S106with half the value of the distance between the two contact points obtained in Step S118. The X-coordinates of the other contact point is calculated by subtracting half the value of the distance between the two contact points obtained in Step S118from the X-coordinates detected in Step S106. The Y-coordinates of the two contact points are assumed as the Y-coordinates detected in Step S106. Further, the coordinates of a middle point between the two contact points and the distance between the two contact points may be used as output data instead of the coordinates of the two contact points.

When calculating the Y-coordinates of the two contact points, the Y-coordinates of one contact point is calculated by adding the Y-coordinates detected in Step S106with half the value of the distance between the two contact points obtained in Step S118. The Y-coordinates of the other contact point is calculated by subtracting half the value of the distance between the two contact points obtained in Step S118from the Y-coordinates detected in Step S106. The X-coordinates of the two contact points are assumed as the X-coordinates detected in Step S106.

By performing the above-described process, the distance and coordinates of contact points can be obtained in a case where the contact point in the touch panel200is two points, and a multi-touch operation can be detected even a five-wire type touch panel is used.

By repeating the above-described process and observing the change of the distance between the two contact points, it can be determined whether the operation performed on the touch panel200is an operation of widening the distance between two contact points or an operation of narrowing the distance between two contact points. Accordingly, with the touch panel200of this embodiment, a pinch-out operation and a pinch-in operation can be detected.

Next, a sub-routine of Step S108for detecting the maximum potential difference is described with reference toFIG. 16.

First, in Step S202, a potential distribution is distributed on the conductive film21in the X direction of the conductive film21via the resistors R1, R2. As illustrated inFIG. 5, the switch SW1, the switch SW4, the switch SW9, and the switch SW10are switched on, and the switch SW2, the switch SW3, the switch SW5, the switch SW6, the switch SW7, and the switch SW8are switched off, so that a potential distribution is generated in X-direction via the resistors R1, R2. The switch SW11is switched off.

Then, in Step S204, the divided voltage at the second power-feed terminal32is measured by the measuring part AD2in a state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21. The potential measured in this state are referred to as a “measured potential AD1(X)”.

Then, in Step S206, the divided voltage at the second power-feed terminal32is measured by the measuring part AD2in a state where the potential distribution is generated in the X-direction. The potential measured in this state are referred to as a “measured potential AD2(X)”.

Then, in Step S208, a potential distribution is distributed on the conductive film21in Y direction of the conductive film21via the resistors R2, R4. As illustrated inFIG. 6, the switch SW3, the switch SW5, the switch SW7, and the switch SW10are switched on, and the switch SW1, the switch SW2, the switch SW4, the switch SW6, the switch SW8, and the SW9are switched off, so that a potential distribution is generated on the conductive film21in the Y-direction of the conductive film21via the resistors R3, R4. The switch SW11is also switched off.

Then, in Step S210, the divided voltage at the second power-feed terminal32is measured by the measuring part AD2in a state where the potential distribution is generated in Y-direction. The potential measured in this state are referred to as a “measured potential AD2(Y)”.

Then, in Step S212, the divided voltage at the third power-feed terminal33is measured by the measuring part AD3in the state where the potential distribution is generated in Y-direction. The potential measured in this state are referred to as a “measured potential AD3(Y)”.

Then, in Step S214, a potential difference ΔV1Xbetween the measured potential AD1(X) and a reference potential(=|measured potential AD1(X)−reference potential AD1(X)|) is calculated. The reference potential AD1(X) is a potential at the first power-feed terminal measured beforehand by the measuring part AD1in the state where potential distribution is generated on the conductive film21in the X direction of the conductive film21via a resistor while the touch panel is not touched.

Then, in Step S216, a potential difference ΔV2Xbetween the measured potential AD2(X) and a reference potential(=|measured potential AD2(X)−reference potential AD2(X)|) is calculated. The reference potential AD2(X) is a potential at the second power-feed terminal measured beforehand by the measuring part AD2in the state where potential distribution is generated in the Y-direction via a resistor while the touch panel is not touched.

Then, in Step S218, a potential difference ΔV2Ybetween the measured potential AD2(Y) and a reference potential(=|measured potential AD2(Y)−reference potential AD2(Y)|) is calculated. The reference potential of AD2(Y) is a potential at the second power-feed terminal measured beforehand by the measuring part AD2in the state where potential distribution is generated on the conductive film21in Y direction via a resistor while the touch panel is not touched.

Then, in Step S220, a potential difference ΔV3Ybetween the measured potential AD3(Y) and a reference potential(=|measured potential AD3(Y)−reference potential AD3(Y)|) is calculated. The reference potential AD3(Y) is a potential at the third power-feed terminal measured beforehand by the measuring part AD3in the state where potential distribution is generated on the conductive film21in the Y-direction of the conductive film21via a resistor while the touch panel is not touched.

Then, in Step S222, the largest potential difference among the potential differences ΔV1X, ΔV2X, ΔV2Y, and ΔV3Yis selected to be the maximum potential difference ΔVm. The direction that the voltage has been applied for obtaining the maximum potential difference ΔVm and the potential measuring part that was used to measure the potential corresponding to the maximum potential difference ΔVm are stored in the storage8

Next, a method for measuring reference potentials is described with reference toFIG. 17. The reference potentials are measured before conducting touch detection process with the touch panel200illustrated inFIG. 13, and stored in the storage88. The reference potentials AD1(X), AD2(X), AD2(Y), and AD3(Y) are measured and stored in the storage88.

First, in Step S252, a touch-on detection is performed. The touch-on detection is conducted by measuring the potential with the measuring part AD4in a state illustrated inFIG. 14. In this state, the potential of the conductive film21is Vcc.

Then, in Step S254, it is determined whether a touch-on operation is being performed. In a case where an object is contacting the touch panel200(touch-on), the potential in which the power source Vcc is divided by the resistance of the conductive film11and the fifth resistor R5is detected by the measuring part AD4. When the potential is detected by the measuring part AD4, it is determined that a touch-on operation is performed on the touch panel200, and the flow ofFIG. 17is ended. If no potential is detected by the measuring part AD4, the flow ofFIG. 17proceeds to Step S256.

In Step S256, a potential distribution is generated on the conductive film21in the X-direction of the conductive film21via the resistors R1, R2in the state illustrated inFIG. 5. The switch SW11is switched off. In the state of Step S256, conductive film11and the conductive film21are not in contact.

Then, in Step S258, the measuring part AD1measures a potential in a state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21. The potential measured by the measuring part AD1in this state is referred to as a reference potential AD1(X).

Then, in Step S260, the measuring part AD2measures a potential in the state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21. The potential measured by the measuring part AD2in this state is referred to as a reference potential AD2(X).

Then, in Step S262, a potential distribution is generated in the Y-direction via the resistors R3, R4in the state illustrated inFIG. 6. The switch SW11is switched off. In the state of Step S262, the conductive film11and the conductive film21are not in contact.

Then, in Step S264, the measuring part AD2measures a potential in the state where the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21. The potential measured by the measuring part AD2in this state is referred to as a reference potential AD2(Y).

Then, in Step S266, the measuring part AD3measures a potential in the state where the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21. The potential measured by the measuring part AD3in this state is referred to as a reference potential AD3(Y).

By performing the above-described processes, the reference potential of each power-feed terminal of the touch panel200is measured. Each of the measured reference potentials are stored in the storage88and used for calculating potential difference Δv.

With the touch panel apparatus according to the embodiment, the distance and coordinates of contact points of a multi-touch operation can be detected, so that a pinch-out operation and a pinch-in operation can be detected.

Second Embodiment

Next, a second embodiment of the present invention is described. A touch panel apparatus of this embodiment enables detection of a gesture operation other than the pinch-out operation and the pinch-in operation_that is performed, for example, when rotating an image displayed on a screen.

When focusing on the amount of change of potential differences ΔV illustrated inFIGS. 8-11, the combination of potential differences Δ causing significant change differs depending on the directions S1-S4illustrated inFIG. 7. This is because the distance between the positions of two contact points and the power-feed terminal is short. Because the resistance distribution of the ITO film that serves as the conductive film21is the same, the distance between two points being short is equivalent to the resistance value being small. In addition, a combined resistance generated between the two points has a resistance that is lower than other parts of the conductive film21. Therefore, electric current flows through a path having the smallest resistance, that is, a path between an electrode that is close to a depressed position of two points and the ground GND. In other words, the direction of two contact points can be defined according to the combination of an electrode having the largest potential difference and an electrode having the second largest potential difference.

For example, according to the pattern S1illustrated inFIG. 7, AD2(X) has the largest potential difference value and AD1(X) has the second largest potential difference value as illustrated inFIG. 8. Therefore, the combination of the largest potential difference and the second largest potential difference is AD2(X) and AD1(X) in the case of pattern S1.

According to the pattern S2illustrated inFIG. 7, AD1(X) has the largest potential difference value and AD3(Y) has the second largest potential difference value as illustrated inFIG. 9. Therefore, the combination of the largest potential difference and the second largest potential difference is AD1(X) and AD3(Y) in the case of pattern S2.

According to the pattern S3illustrated inFIG. 7, AD3(Y) has the largest potential difference value and AD2(Y) has the second largest potential difference value as illustrated inFIG. 10. Therefore, the combination of the largest potential difference and the second largest potential difference is AD3(Y) and AD2(Y) in the case of pattern S3.

According to the pattern S4illustrated inFIG. 7, AD2(X) has the largest potential difference value and AD2(Y) has the second largest potential difference value as illustrated inFIG. 11. Therefore, the combination of the largest potential difference and the second largest potential difference is AD2(X) and AD2(Y) in the case of pattern S4.

Accordingly, there is a correlation between the direction in which two contact points are arranged and the power-feed terminals having the largest potential difference and the second largest potential difference, and the combination of the largest potential difference and the second largest potential difference is different depending on each pattern S1-S4. Therefore, the positional relationship of two contact points, that is, the direction in which two contact points are arranged can be determined based on the combination of the largest potential difference and the second largest potential difference.

When the combination of the largest potential difference and second largest potential difference is AD2(X) and AD1(X), it can be determined that a pattern of the two contact points corresponds to the pattern S1in which two contact points are separated along the X-direction.

When the combination of the largest potential difference and the second largest potential difference is AD1(X) and AD3(Y), a pattern of the two contact points corresponds to the pattern S2in which two contact points are separated along a straight line from an upper left area to a lower right area.

When the combination of the largest potential difference and the second largest potential difference is AD3(Y) and AD2(Y), a pattern of the two contact points corresponds to the pattern S3in which two contact points are separated along the Y-direction.

When the combination of the largest potential difference and the second largest potential difference is AD2(X) and AD2(Y), a pattern of the two contact points corresponds to the pattern S4in which two contact points are separated along a straight line from an upper right area to a lower left area.

In a case where the touch panel200is contacted at two contact points, the two contact points may be arranged in a direction deviated from the directions corresponding to patterns S1to S4. However, even in this case, the direction of the two contact points can be determined based on the relationship between the largest potential difference and the second largest potential difference of each pattern S1to S4.

The touch panel according to this embodiment uses the combination of the largest and second largest potential differences to detect positions of two contact points.

The method for detecting a position in a touch panel of this embodiment is described with reference toFIG. 18.

First, a touch-on detection is performed in Step S302. The measuring part AD4measures a potential in a state illustrated inFIG. 14. The potential of each of the first power-feed terminal31, the second power-feed terminal32, and the third power-feed terminal33is Vcc in this state.

Then, in Step S304, it is determined whether a touch-on operation is being performed. When the potential is detected by the measuring part AD4, it is determined that a touch-on operation is performed on the touch panel200, and the flow ofFIG. 18proceeds to Step S306. If no potential is detected by the measuring part AD4, it is determined that a touch-on operation is not performed, and the flow ofFIG. 18is ended.

Then, in Step S306, a coordinate of the contact point is detected. When detecting the coordinates, a potential distribution is generated on the conductive film21in the X-direction of the conductive film21to allow the measuring part AD4measure the potential as illustrated inFIG. 3. Then, the coordinate detector82detects the X-coordinate of the contact point based on the potential measured by the measuring part AD4.

Similarly, a potential distribution is generated on the conductive film21in the Y-direction of the conductive film21to allow the measuring part AD4measure the potential as illustrated inFIG. 4. Then, the coordinate detector82detects the Y-coordinate of the contact point based on the potential measured by the measuring part AD4. Similar to the first embodiment, in a case where the contact point contacting the touch panel200is one point, the X and Y coordinates indicate the coordinates of the contact point, and in a case where the touch panel200is contacted at two points, the coordinates indicate the coordinates of the middle point of the two contact points.

Then, in Step S308, the maximum potential difference ΔVm is detected, and a sub-routine for detecting the maximum potential difference illustrated inFIG. 16is conducted.

Then, similar to the first embodiment, the determination part83determines whether the maximum potential difference ΔVm obtained in Step S308is greater than a threshold ΔVth in Step S310. When the maximum potential difference ΔVm is less than the threshold ΔVth, the contact point is determined to be one point, and the flow ofFIG. 18proceeds to Step S312. When the maximum potential difference A Vm is greater than the threshold ΔVth, the contact point is determined to be two points, and the flow ofFIG. 18proceeds to Step S314.

When it is determined that the contact point is one point, the coordinates detected in Step S306are output as the coordinates of the contact point in Step S312.

On the other hand, when it is determined that the contact point is two points, each measuring part measures a potential difference ΔV in Step S314, and the below-described sub-routine for measuring the potential difference ofFIG. 19is performed.

Then, in Step S316, a potential difference having the largest value among the potential differences ΔV1X, ΔV2X, ΔV2Yand ΔV3Yis assumed as the maximum potential difference ΔVm, and it is determined whether the maximum potential difference ΔVm is greater than the threshold ΔVth. If the maximum potential difference ΔVm is less than the threshold ΔVth, the measured potential is determined as an error, and the flow ofFIG. 18is ended. If the maximum potential difference ΔVm is greater than the threshold ΔVth, the contact point is determined to be two points, and the flow ofFIG. 18proceeds to Step S318.

Then, in Step S318, the direction in which the two contact points are arranged is detected. The direction detector86selects the potential difference having the largest value and the second largest value among the potential differences ΔV1X, ΔV2X, ΔV2Yand ΔV3Y, and determines the positional relationship between the two contact points, that is, direction of the two contact points, according to the combination of the selected potential differences. If the combination of the largest and second largest potential differences is ΔV1Xand ΔV2X, that is, AD1(X) and AD2(X), the two contact points correspond to the pattern S1.

When the combination of the largest and second largest potential differences is ΔV1Xand ΔV3Y, that is, AD1(X) and AD3(Y), the two contact points correspond to the pattern S2.

When the combination of the largest and second largest potential differences is ΔV2Yand ΔV3Y, that is, AD2(Y) and AD3(Y), the two contact points correspond to the pattern S3.

When the combination of the largest and second largest potential differences is ΔV2Xand ΔV2Y, that is, AD2(X) and AD2(Y), the two contact points correspond to the pattern S4.

Then, in Step S320, the distance between two points in the X direction, that is, the difference between the X-components of two contact points is calculated. The distance calculator84calculates the distance between two points in the X-direction by using, for example, the Expression (1) or Expression (2) based on the potential differences ΔV1X, ΔV2X. In the case of the pattern S1, the greater of the potential differences ΔV1X, ΔV2Xis used to calculate the distance between the two contact points in X-direction. In the case of the pattern S2or pattern S4, one of the potential differences ΔV1Xand ΔV2Xis used to calculate the distance between two contact points in X-direction.

Then, in Step S322, the distance between two contact points on the touch panel200in Y-direction is calculated. The distance calculator84calculates the distance between the two points contacting the touch panel200in Y-direction by using, for example, the Expression (1) or Expression (2) based on the potential differences ΔV2Y, ΔV3Y. For example, in the case of the pattern S3, the greater of the potential differences ΔV2Y, ΔV3Yis used to calculate the distance between the two contact points in Y-direction. In the case of the pattern S2or pattern S4, one of the potential differences ΔV2Yand ΔV3Yis used to calculate the distance between two contact points in Y-direction.

Then, in Step S324, coordinate data of the two contact points is output. In this embodiment, the two point calculator85calculates the coordinates of the two contact points based on the distance between two contact points in X-direction obtained in Step S320, the distance between two contact points in Y-direction obtained in Step S322, and the coordinates detected in Step S306. The two point calculator85outputs the calculated coordinates of the two points as coordinate data.

In a case where an arrangement of the two contact points corresponds to the pattern S1, the X-coordinates of one contact point is calculated by adding the X-coordinates detected in Step S306with half the value of the distance between two points in the X-direction obtained in Step S320whereas the X-coordinates of the other contact point is calculated by subtracting half the value of the distance between two points in the X-direction obtained in Step S320from the X-coordinates detected in Step S306. Thereby, the X coordinates of each of the two contact points are obtained. The Y-coordinates of the two contact points are assumed as the Y-coordinates detected in Step S306. The calculated coordinates of the two contact points are output as coordinate data.

In a case where an arrangement of the two contact points corresponds to the pattern S2, the X-coordinates of one contact point is calculated by adding the X-coordinates detected in Step S306with half the value of the distance between the X-components of the two points obtained in Step S320whereas the X-coordinates of the other contact point is calculated by subtracting half the value of the distance between the X-components of the two points obtained in Step S320from the X-coordinates detected in Step S306. Thereby, the X-coordinates of each of the two contact points are obtained. Further, the Y-coordinates of one contact point is calculated by adding the Y-coordinates detected in Step S306with half the value of the distance between the Y-components of the two points obtained in Step S322whereas the Y-coordinates of the other contact point is calculated by subtracting half the value of the distance between the Y-components of the two points obtained in Step S322from the Y-coordinates detected in Step S306. Thereby, the Y-coordinates of each of the two contact points are obtained. Because the pattern S2is a pattern in which the two contact points are separated along a diagonal line in the upper left and lower right directions, the coordinates of the two points can be identified based on the calculated coordinates of the two points. The calculated coordinates of the two contact points are output as coordinate data.

In a case where the two points contacting the touch panel200corresponds to the pattern S3, the Y-coordinates of one contact point is calculated by adding the Y-coordinates detected in Step S306with half the value of the distance between the Y-components of the two points obtained in Step S322whereas the Y-coordinates of the other contact point is calculated by subtracting half the value of the distance between the Y-components of the two points obtained in Step S322from the Y-coordinates detected in Step S306. Thereby, the Y-coordinates of each of the two contact points are obtained. The X-coordinates of the two contact points are assumed as the X-coordinates detected in Step S306. The calculated coordinates of the two contact points are output as coordinate data.

In a case where the two points contacting the touch panel200corresponds to the pattern S4, the X-coordinates of one contact point is calculated by adding the X-coordinates detected in Step S306with half the value of the distance between the X-components of the two points obtained in Step S320whereas the X-coordinates of the other contact point is calculated by subtracting half the value of the distance between the X-components of the two points obtained in Step S320from the X-coordinates detected in Step S306. Thereby, the X-coordinates of each of the two contact points are obtained. Further, the Y-coordinates of one contact point is calculated by adding the Y-coordinates detected in Step S306with half the value of the distance between the Y-components of the two points obtained in Step S322whereas the Y-coordinates of the other contact point is calculated by subtracting half the value of the distance between the Y-components of the two points obtained in Step S322from the Y-coordinates detected in Step S306. Thereby, the Y-coordinates of each of the two contact points are obtained. Because the pattern S4is a pattern in which the two points contacting the touch panel200are separated along a diagonal line in the upper right and lower left directions, the coordinates of the two points can be identified based on the calculated coordinates of the two points. The calculated coordinates of the two contact points are output as coordinate data.

By performing a process of this embodiment, the coordinates of two contact points and the direction in which the two contact points are arranged can be determined. Further, by repeating the above-described steps and determining the direction in which the two contact points are arranged and determining the change of the distance between the two points, it can be determined whether the operation performed on the touch panel200is a pinch-in/pinch-out operation or a gesture operation such as for rotating an image on a display.

With the touch panel apparatus according to the second embodiment, the coordinates of each of the two contact points can be detected, not only can a multi-touch operation be detected, but also a gesture operation such as reducing, increasing, or rotating of an image can be detected with the two points contacting the touch panel200.

Two contact points move in a clockwise direction when the patterns of the positional relationship between the two contact points shifts in an order of pattern S1→S2→S3→S4→S1. In this case, a gesture operation in a clockwise rotation can be detected by determining such change of the pattern of the two contact points. Further, two contact points move in a counter-clockwise direction when the patterns of the positional relationship between the two contact points shifts in an order of pattern S1→S4→S3→S2→S1. In this case, a gesture operation in a counter-clockwise rotation can be detected by determining the changes of each of the patterns (pattern S1→S2→S3→S4→S1and pattern S1→S4→S3→S2→S1) of the two points.

In a case where the pattern S1changes to the pattern S2or the pattern S2changes to the pattern S1, the potential difference AD1(X) maintains to have a large value. In a case where the pattern S2changes to the pattern S3or the pattern S3changes to the pattern S2, the potential difference AD3(Y) maintains to have a large value.

In a case where the pattern S4changes to the pattern S1or the pattern S1changes to the pattern S4, the potential difference AD2(X) maintains to have a large value.

Next, a sub-routine of S314for detecting the potential difference is described with reference toFIG. 19.

First, in Step S402, a potential distribution is distributed in the X direction via the resistors R1, R2as illustrated inFIG. 5. The switch SW11is switched off.

Then, in Step S404, a potential is measured by the measuring part AD1in a state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21. The potential measured in this state are referred to as a “measured potential AD1(X)”.

Then, in Step S406, a potential is measured by the measuring part AD2in a state where the potential distribution is generated on the conductive film21in the X-direction of the conductive film21. The potential measured in this state are referred to as a “measured potential AD2(X)”.

Then, in Step S408, a potential distribution is generated on the conductive film21in the Y-direction of the conductive film21via resistors R3, R4as illustrated inFIG. 6. The switch SW11is switched off.

Then, in Step S410, a potential is measured by the measuring part AD2in a state where the potential distribution is generated in the Y-direction. The potential measured in this state are referred to as a “measured potential AD2(Y)”.

Then, in Step S412, a potential is measured by the measuring part AD3in the state where the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21. The potential measured in this state are referred to as a “measured potential AD3(Y)”.

Then, in Step S414, a potential difference ΔV1Xbetween the measured potential AD1(X) and a reference potential(=|measured potential AD1(X)−reference potential AD1(X)|) is calculated and stored in the storage. The reference potential AD1(X) is a potential measured beforehand by the measuring part AD1in the state where potential distribution is generated on the conductive film21in the X direction of the conductive film21while the touch panel is not touched.

Then, in Step S416, a potential difference ΔV2Xbetween the measured potential AD2(X) and a reference potential(=|measured potential AD2(X)−reference potential AD2(X)|) is calculated and stored in the storage. The reference potential AD2(X) is a potential measured beforehand by the measuring part AD2in the state where potential distribution is generated on the conductive film21in the Y-direction of the conductive film21.

Then, in Step S418, a potential difference ΔV2Ybetween the measured potential AD2(Y) and a reference potential(=|measured potential AD2(Y)−reference potential AD2(Y)|) is calculated. The reference potential AD2(Y) is a potential measured beforehand by the measuring part AD2in the state where the potential distribution is generated on the conductive film21in the Y direction of the conductive film21.

Then, in Step S420, a potential difference ΔV3Ybetween the measured potential AD3(Y) and a reference potential(=|measured potential AD3(Y)−reference potential AD3(Y)|) is calculated and stored in the storage. The reference potential AD3(Y) is a potential measured beforehand by the measuring part AD3in the state where the potential distribution is generated on the conductive film21in the Y-direction of the conductive film21.

With this embodiment, a gesture operation such as rotation can be detected by determining the changes of the positional relationship between two contact points. Further, with this embodiment, detection of a multi-touch operation and detection of various gesture operations such as rotation with two contact points contacting can be achieved because the coordinates of each of the contact two points can be detected.

Other aspects of the second embodiment are substantially the same as the aspects described in the first embodiment.