JPH11338625A - Resistance film tablet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a correction value that is absorbable even against various change parameters in a conventional two-layer structure without bothering an operator by providing an intermediate terminal in the existing tablet structure. SOLUTION: When power is inputted to a device, voltage of intermediate terminal which is separately provided in X and Y coordinate resistance films of a resistance film type tablet which are overlapped on a displaying part and are used is measured at plural places before calculating a coordinate at the time of resistance film pressure owing to external pressure or in the cycle of a fixed time, the value is fetched as a reference voltage value of a coordinate shown by each intermediate terminal and an optional coordinate is calculated and decided based on the reference voltage value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistive film tablet which is used by being superimposed on a display unit in various information processing apparatuses, or a resistive film which requires accuracy of input coordinates without being superimposed on the display unit. It is about tablets.

[0002]

2. Description of the Related Art In the prior art, various methods such as an optical coordinate detection method, an electrostatic coupling method, an electromagnetic induction method and a resistive film method are used as a tablet method for selecting information displayed on a display unit with a pen. Used in processing equipment.

[0003] Of these methods, the resistive film method is the only coordinate input method that allows a user to select a display icon with a finger or select an ordinary sharp-edged member at the time of selecting coordinates, and to input figures and characters. Others require a dedicated stylus pen.

However, in the resistive film system, when calculating the coordinates of pressing with a finger or a pen from the structure, variations in the resistive film, resistance non-linearity at the end, variations in the lead-out electrodes, and applied voltage Changes in the temperature / humidity environment, and the aging of the resistive film due to the deterioration of the panel due to the frequency of pressing the panel forming the resistive film.
The value of the resistance value is constantly changing.

For this purpose, in Japanese Patent Publication No. Hei 5-31766, reference coordinates are displayed on a display unit, the operator presses the coordinates with a pen, and any other input coordinates are shifted. Is obtained in order to obtain a value for correcting.

Another method is disclosed in Japanese Patent Laid-Open No. 4-3851.
No. 2 discloses that the temporary coordinates before correction are displayed by pressing the pen at an arbitrary position, the pen is dragged to the displayed temporary coordinates, the pressing is stopped on the temporary coordinates, and the correction value is displayed. Have also been proposed.

There is a difference whether the display is first or the pen operation first, but in any case, the correction value is obtained by the operation of adjusting the pen to the reference point, and the subsequent coordinate correction is enabled.

On the other hand, automatic correction methods disclosed in Japanese Patent Application Laid-Open Nos. 9-44309 and 9-160772 have been proposed.

Japanese Patent Application Laid-Open No. 9-44309 discloses that a separate resistance (trimming resistance and reference resistance) is provided at the end of a resistive film to provide a correction value in a tablet unit. In the publication, a resistance film for automatic position correction is provided separately from a resistance film for touch position detection to obtain a correction value of a reference position.

Japanese Unexamined Patent Publication (Kokai) No. 4-182813 discloses a technique for generating an electrode other than the electrodes at both ends. This is to increase the accuracy of detection coordinates by dividing the resistive film electrode into a plurality of regions, and does not include the concept of coordinate correction of the present invention, and does not perform automatic correction.

[0011]

As described above, Japanese Unexamined Patent Publication No. 9-44309 discloses that different resistances (trimming resistances and reference resistances) are provided in a tablet so that environmental changes such as voltage changes and temperature changes can be achieved. Can absorb the variation of the resistive film in each manufacturing process, but the correction value with this separate resistor is fixed and absorbs the change over time when the tablet is used for a long term It is not possible.

Japanese Patent Application Laid-Open No. 9-160772 discloses that
By providing a resistive film for automatic position correction in addition to the resistive film for touch position detection, knowing the reference voltage at specific physical coordinates, environmental changes such as voltage changes and temperature changes, and variations in the resistive film during the manufacturing process , And the change with time when the tablet is used for a long period of time can be absorbed, but the tablet has a four-layer structure, and the tablet cannot be provided at low cost.

According to the present invention, by providing a middle terminal in the existing tablet structure, it is possible to obtain a correction value capable of absorbing various change parameters in the conventional two-layer structure without the need for the operator. The purpose is to make it possible.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the invention according to claim 1 has a middle terminal different from the two electrode terminals applied to the resistive film. The resistance film tablet is characterized in that a coordinate value is corrected by measuring an applied voltage between the middle terminal and another terminal.

According to a second aspect of the present invention, in the resistive tablet according to the first aspect, the middle terminal is provided at a specific position on a side surface different from the installation position of the two electrode terminals. It is a resistive tablet.

According to a third aspect of the present invention, there is provided the resistive tablet according to the first aspect, wherein the middle terminal is connected to an X terminal.
A resistance film tablet provided on each of the coordinate resistance film and the Y coordinate resistance film.

Further, according to a fourth aspect of the present invention, in the resistance film tablet according to the third aspect, the middle terminal is connected to an X terminal.
A resistance film tablet provided at a specific position at a fixed distance from four corners of a coordinate resistance film and at a specific position at a certain distance from four corners of a Y coordinate resistance film.

According to a fifth aspect of the present invention, a voltage is applied to two electrode terminals provided on a resistive film, and a voltage of each middle terminal is measured, whereby a reference voltage indicated by coordinates of the middle terminal is obtained. And calculating the coordinates indicated by the measured voltage when the resistive film is pressed by the external pressure.

According to a sixth aspect of the present invention, in the resistive tablet according to the fifth aspect, the measurement of the reference voltage is performed before calculating the coordinates indicated by the measured voltage when the resistive film is pressed by the external pressure. Is a resistive film tablet.

According to a seventh aspect of the present invention, there is provided the resistive tablet according to the fifth aspect, wherein the measurement of the reference voltage is performed when the apparatus is turned on.

According to an eighth aspect of the present invention, there is provided the resistive tablet according to the fifth aspect, wherein the measurement of the reference voltage is performed in a cycle of a predetermined time.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Note that the present invention is not limited by this.

FIG. 1 is a conceptual diagram of a display-integrated tablet according to the present invention, in which a display unit and a tablet are overlapped.

The LCD shows a liquid crystal as a display unit.
Denotes a lower resistance film of the tablet, and SR1 denotes an upper resistance film of the tablet.

Each of the upper and lower resistive films is formed in a sheet shape, and SR1 and SR2 are formed on each surface of the upper sheet (ST1) and the lower sheet (ST2) in FIG. 2 by a vapor deposition technique or the like.

FIG. 3 is a sectional view of this superposed structure.

In FIG. 3, a lower sheet (ST2) is provided on a liquid crystal display (LCD), and a lower resistive film (S2) is provided on the upper surface thereof.
R2) and terminal leads (L1, L5, L7,
L8, L9, L12) and the like, and a conductive vapor deposition surface (SP2) is provided thereon. An upper resistive film (SR1) and a terminal lead wire (L2, L2 in FIG. L3, L4, L6, L10, L11) so that the lower sheet ST2 can be disposed thereon.
Layered on.

At this time, the upper sheet (ST1) and the lower sheet (ST2) sandwich the particulate material (D) for securing a gap between the insulating sheets, and the ends are connected to the conductive adhesive (T). The upper sheet (ST
The structure is summarized in 1).

As a result, the upper resistance film (SR1) of the upper sheet (ST1) and the lower resistance film (SR) of the lower sheet (ST2) are formed.
2) is a liquid crystal (L) which is a display surface sandwiched between two resistive films.
CD) can be physically overlapped with the CD.

FIG. 2 is a diagram showing the details of the upper sheet (ST1) and the lower sheet (ST2). For the sake of explanation, the upper sheet (ST1) has a resistive film and lead lines formed on the back by vapor deposition molding as shown in the figure. The lower sheet (ST2) shows a state in which a resistive film and a lead wire as shown in the table are formed by vapor deposition.

Note that the resistance film (SR1) and the electrodes (XA, XB, X1, X1) written in the upper sheet (ST1) of FIG.
X2, X3, X4) and lead lines (L2, L3, L
4, L6, L10, L11) should be written with broken lines,
It is described with a solid line for easy viewing.

In FIG. 2, XA and XB are upper resistive films (SR
In the electrode terminal 1), X1, X2, X3, and X4 are middle terminals of the present invention.

Each of the middle terminals is provided with a lead line for measuring the potential at the physical position, and is combined with the lead lines of the preceding electrode terminals in one place.

Further, YA and YB are electrode terminals of the lower resistance film (SR2), and Y1, Y2, Y3 and Y4 are middle terminals of the present invention.

Each of the middle terminals is provided with a lead line for measuring the potential at the physical position, and is combined with the lead line of the preceding electrode terminal in one place.

These lead lines are put together on one sheet by the conductive adhesive (T) shown in FIG. 3 and connected to the tablet control circuit of the information processing apparatus through a connector.

Usually, a glass sheet or the like may be used for the lower sheet in these figures because of the strength.

Referring again to FIG. 1, the display-integrated tablet of the present invention will be described in detail. The upper resistive film (SR1) is provided with electrodes XA and XB and middle terminals X1, X2, X3 and X4. XA and XB are linearly formed with conductive members at both ends of the resistive film, respectively, and are led out as electrodes XA and XB. The middle terminals X1, X2, X3 and X4 have dimensions LX1 and LX2 physically determined from the ends of these electrodes. , LX3, LX4.

Similarly, an electrode Y is formed on the lower resistance film (SR2).
A, YB and middle terminals Y1, Y2, Y3, Y4 are provided,
The electrodes YA and YB are linearly (band-like) formed of conductive members at both ends of the resistive film, and are drawn out as the electrodes YA and YB.
The middle terminals Y1, Y2, Y3, Y4 are provided at positions of dimensions LY1, LY2, LY3, LY4 which are physically determined from the ends of these electrodes.

The position of the middle terminal is physically determined by the broken line positions XL1, XL2, YL1, and YL2 if the accuracy of the overlapping position of the tablet with respect to the display unit can be ensured even from the viewpoint of the display unit (LCD).

Accurately superimposing the display unit and the tablet unit does not cause any problem with the current technology, and the physical positions of the middle terminals of the upper sheet (SR1) and the lower sheet (SR2) can be accurately viewed from the display surface. Good placement is possible.

This physical position is directly treated as one of the two-dimensional coordinates of the display surface or the two-dimensional coordinates of the tablet.

Now, a typical case where the point P of the tablet is pressed with a pen will be described.
1. The resistance of RX2 appears at both ends of the point P, and RY1, RX2 on the lower sheet through the contact resistance (RS) between the upper and lower sheets.
This results in the resistance of RY2 being configured.

Next, a state in which the coordinates of the display surface or the tablet surface are detected in this state will be described.

FIG. 4 is a conventional diagram for detecting the X coordinate, and FIG. 5 is a conventional diagram for detecting the Y coordinate.

In FIG. 4, the power supply voltage (VP) is applied to the XA terminal of the upper sheet, and the ground voltage (GND) is connected to XB. Then, the YA terminal on the lower sheet is connected to the input of the A / D converter, and the YB terminal is opened.

By doing so, from the position of the middle point P of the schematic resistors RX1 and RX2 generated between the electrodes of the resistive film of the upper sheet, through the contact resistance (RS) of the upper sheet and the lower sheet, and through the RY1 of the lower sheet The potential at the point P can be measured from the terminal YA.

For the Y coordinate, the power supply voltage (VP) is applied to the YA terminal of the lower sheet, and the ground voltage (GN) is applied to YB.
D) is connected. Then, connect the XA terminal on the upper sheet to A / D
Connect to the input of the converter and leave the XB terminal open.

By doing so, from the position of the middle point P of the schematic resistors RY1 and RY2 generated between the electrodes of the resistive film of the lower sheet, through the contact resistance (RS) of the upper sheet and the lower sheet, and through the RX1 of the upper sheet. The potential at the point P can be measured from the terminal of the XA.

From the X coordinate and the Y coordinate corresponding to the potential at the point P, VXP and VYP, the coordinates (XP,
YP).

In this coordinate detection, the resistive films of the upper sheet and the lower sheet are accurately determined only when the resistive films are stable as viewed from the ends of the lead lines.

Since the resistance film has a low value of 400 ohm to 900 ohm, each coordinate in the manufacturing process is actually caused by a variation in contact between the lead portions of the lead lines and a variation in which the resistance film is not uniformly formed. The detection voltage is different from the value.

Further, the detection voltage for each coordinate value is different even when the tablet is in use, due to the fluctuation of conditions due to the applied voltage and the environmental temperature and the temporal change of the resistance film caused when the resistance film is used for a long time. .

For this reason, in the conventional product, a correction operation is always required when the display coordinates and the tablet coordinates are different according to the techniques of Japanese Patent Publication No. Hei 5-31766 and Japanese Patent Laid-Open Publication No. Hei 4-38512. Was.

FIG. 6 is a view schematically showing the X-coordinate detection explanatory diagram of FIG. 4, which schematically shows the cause of the resistance value variation in the manufacturing process and the resistance value variation during long-term use.

In FIG. 6, RXA is the resistance outside the resistive film that appears between the power supply terminal and the resistive film, such as the contact resistance at the electrode terminal XA, and RXB is the contact resistance between GND and the like, such as the contact resistance at the electrode terminal XB. RY
A is a resistance outside the resistive film which appears between the A / D converter and the contact resistance at the electrode terminal YAB.
r4 and r7 are the basic resistance values of RX1, RX2 and RY1, r2, r5 and r8 are the element resistance values due to the factors that greatly change the basic resistance values, and r3 and r
6, r9 are element resistance values due to factors that change the basic resistance value to a small value.

Normally, these change due to a change in applied voltage, a change in temperature, and a change with time in the resistance film.

The contact resistance RS is disclosed in Japanese Unexamined Patent Publication No. 6-3247.
As disclosed in Japanese Patent Application Laid-Open No. 87-87, there is a solution for measuring by a different circuit or the like, and it is possible to determine that the pressure is effective only when the pressing resistance is small and invalid when the pressure is large. Since the value which becomes a problem as compared with the input impedance of can be an invalid value, it is treated as a solved problem in the present invention.

Here, even if r8, r9, and RYA constituting RY1 change, the change ratio is several percent of r7, which is much smaller than the input impedance of the A / D converter and has no influence on the coordinate determination. But r
2, r3, r5, r6 and RXA, RXB directly affect the change of the applied voltage to the intermediate potential P between VP and GND.

For this purpose, the detected potential at a fixed coordinate on the display surface is measured as disclosed in Japanese Patent Publication No. Hei 5-31766 and Japanese Patent Laid-Open Publication No. Hei 4-38512, and the value is used as a correction value to determine the potential of other coordinates. You need to decide.

The present invention solves this problem by using X1, X2, X3, X4 and Y1, Y2, Y3, Y4 as shown in FIG.
The present invention is to provide a means for knowing the voltage at the physical reference coordinate position without having to press the tablet again with the pen by measuring the voltage at the middle terminal.

FIG. 7 shows a schematic diagram of the detection of the middle terminal voltage of the present invention.

FIG. 7 shows a state where the middle terminal X1 of the upper sheet is measured.

In FIG. 7, when a voltage is applied to the application electrodes XA and XB of the upper resistance film (RS1) by VP and GND, contact resistances RXA and RXB around the electrode terminals are generated.
In addition, the internal resistance value of the resistive film also depends on the applied voltage, temperature,
And RX due to the change in the resistance value of the resistance film due to aging.
1, RX2 is constantly changed due to a change factor as shown in FIG.

The connection resistance RT at the middle terminal of X1 is A
Since the impedance is much smaller than the impedance of the / D converter, it can be ignored, and the position of X1 appears as the divided potential of the combined resistance of RXA and RX1 and the combined resistance of RX2 and RXB.

Since the physical position of X1 is determined by LX1 and LX12 + LX2, it is possible to determine the reference voltage at the determined physical position.

Similarly, it is possible to know the reference voltage of the middle terminal of each of X2, X3, and X4.

The lower resistance film (RS2) has Y1, Y2,
The reference voltage of each physical position of Y3 and Y4 can be similarly determined.

In FIG. 1, X1 and X3, X2 and X4, Y1
The reason for measuring the voltage across Y3 and Y3 and between Y2 and Y4 is that there is a possibility that the change in resistance value is different at both ends.
It is needless to say that having a larger number of these middle terminals results in having a larger reference voltage, which can improve the coordinate accuracy of the tablet.

Next, with reference to FIG. 8, when the reference voltage at the peripheral reference position of the tablet is determined, how the coordinates of the middle point when the tablet is pressed with a pen or a finger is determined will be described.

In the tablet of the present invention, the middle terminals X1, X2, X3, X4, and Y are located at positions physically determined as the middle terminals.
1, Y2, Y3, and Y3 are arranged as described in the above description.

FIG. 8 illustrates the middle terminal on the coordinate plane.

In FIG. 8, the detection reference voltage in the present invention at the physical coordinate position of each middle terminal is X1 = VX
1, X2 = VX2, X3 = VX3, X4 = VX4, Y1
= VY1, Y2 = VY2, Y3 = VY3, Y4 = VY4
Is detected. It is also assumed that the voltage of VIN is measured from the lower point P pressed by a pen or a finger.

The exact coordinates of the point P in this case can be obtained as described below. In the description, the physical distance between the terminals of X1, X2 and X3, X4 is XT, and the X width is XT.
M is assumed. The physical distance between the terminals Y1, Y2 and Y3, Y4 is YT, and the Y width is YM.

At this time, XP1 is (VX1−VIN) / XP1 = (VX1−VX2) / X
The relationship of T has come.

From this, XP1 = ((VX1-VIN) × XT) / (VX1-V
X2) Similarly, XP2 = ((VX3-VIN) × XT) / (VX3-V
X4) YP1 = ((VY1-VIN) × YT) / (VY1-V
Y2) YP2 = ((VY3-VIN) × YT) / (VY3-V
Y4) holds, and the coordinates of four points XP1, XP2, YP1, and YP2 can be determined.

As a result, since the coordinates of the point P, XP and YP are the intersections of the two line segments in FIG. 9, XP = ((XP1-XP2) / YM) + XP1 YP = ((YP1-YP2) / XM) + YP1, and the coordinates of the point P, XP and YP can be easily calculated.

Next, the coordinate correction timing in the display-integrated tablet device will be described.

FIG. 10 is a system configuration diagram of the display-integrated tablet device.

In FIG. 10, reference numeral 10-1 denotes a CPU for controlling the apparatus. A ROM 10-2 stores a control program of this apparatus and font information. The RAM 10-3 is a section for storing information that changes in the apparatus, and stores the input document information when the apparatus is a document processing apparatus. 10-4 is a power supply unit of the present apparatus. 10-5 is a power-on switch. A display control unit 10-8 controls the display unit 10-9. 10-5 is a tablet control unit,
It is a portion for controlling input information from the tablet 0-7, and corresponds to the terminal connection control to the A / D converter of the tablet and the A / D converter, which correspond to the coordinate detection of the present invention.

The display section 10-9 and the tablet 10-7 are superposed and integrated.

Reference numeral 10-10 denotes a timer circuit for generating the automatic correction timing according to the present invention.
It gives information for control by interrupting the PU. 1
Reference numeral 0-9 denotes a pen for pressing the tablet, which can be performed with a finger.

FIG. 11 is a flowchart for explaining the measurement of the reference voltage according to the present invention when the power is turned on.

In FIG. 11, when the power is turned on in S11-1, X1, X2, X3, X4 and Y1,
The terminal potentials of Y2, Y3 and Y4 are measured.

The details have been described with reference to FIG.
From 14-1 to S14-8, the potential of each middle terminal is shown in FIG.
Measured with the circuit configuration of

Then, VX1, VX2, VX3,
The middle terminal potential of VX4, VY1, VY2, VY3, VY4 is measured, and the reference value is determined in S11-3.

When the top is pressed in S11-4, the input voltage is measured by the circuits in FIGS. 4 and 5 in S11-5, and S1 is calculated by the calculation corresponding to the above-described explanation in FIG.
The pressed coordinates are calculated in 1-6. Then, an event corresponding to the pressed coordinate is executed in S11-7, and the process proceeds to S11-7.
Until the power is turned off at -8, the process returns to S11-4, and processes corresponding to these pen inputs are executed.

FIG. 12 shows this reference value setting as shown in FIG.
It is a flowchart figure managed by the timer of -10, and resetting periodically.

In FIG. 12, when the power is turned on in S12-1 and the value of the timer is set in S12-2,
At 12-5, a timer interrupt is periodically generated. Each time, the potential of the middle terminal is measured at S12-3.
At -4, a reference value is set. This makes it possible to absorb the fluctuation of the reference value in the information processing device that is turned on for a long time, and after measuring the input voltage of the coordinates at the pen input in S12-6 in S12-7, the process proceeds to S1-7.
In 2-8, it is possible to calculate the coordinates with the reference value having a small error. Then, an event process is performed in S12-9. Since this operation is performed periodically until the power is turned off in S12-10, it is possible to always manage the input coordinates of the tablet with an accurate reference value.

FIG. 13 shows another embodiment of the method of measuring the reference value. Each time a pen input is performed in S13-1, the potential of the middle terminal is measured in S13-2, and the reference is measured in S13-3. A value is set, then the input voltage is measured in S13-4, coordinates are calculated in S13-5, and event processing is performed in S13-6.

For this reason, the processing time for pen input is shown in FIG.
Since the length is longer than 2, the accuracy of the coordinates is better than that of the method of FIG. 12, but the speed of pen input coordinate recognition becomes slow, which is not preferable in the case of inputting the locus of a pen on a tablet.

Therefore, FIG. 11 and FIG.
2. The methods of FIG. 13 are used in combination.

In the correction of the tablet, there is also a parallax correction generated from the display unit and the thickness of the tablet. However, since the correction value can be physically predicted for the parallax correction, when the input coordinates are calculated from the reference value. This becomes possible by adding this predicted value as an adjustment value.

As described above, with the tablet having the middle terminal of the present invention, the reference value to be corrected at the timing programmed on the device side is obtained without correcting the newly displayed reference point with the pen. It is possible to automatically extract the correct reference value and correct the coordinates without burdening the operator even if the resistance film of the tablet changes over time or changes in applied voltage / environmental temperature occur frequently. In addition, operability is greatly improved.

[0095]

According to the first to eighth aspects of the present invention, the tablet can be manufactured by changing the print pattern of the signal lead line without changing the conventional manufacturing process. It can be produced and has high mass productivity.

In addition, in the case of incorporating into an information processing apparatus, a switching circuit of a signal line for detecting a voltage to each middle terminal is required. It can be included, and does not lead to a significant cost increase.

Further, since the variation of the measured value of the resistance film with respect to the pressing point of each tablet in the manufacturing process can be similarly measured at the middle terminal of the present invention, a simple correction calculation can be performed. In addition, even with the lapse of time, the same measurement can be performed with the middle terminal.

In particular, the temporal change of the local resistance value due to the physical deformation of the resistive film at the specific pressing coordinates is periodically calculated because the target coordinates are calculated to be located on the coordinate lines at both ends of the resistive film. By measuring the terminal, the latest correction value can be secured, and the coordinate detection error can be absorbed.

That is, it is expected that the existing technology will greatly improve the specifications.

The improvement of the specification here means that the coordinate correction operation by the conventional operator is automatically performed, so that the operation becomes completely unnecessary, and the operator does not need to be aware of the necessity of the coordinate correction. On the other hand, information can be input to the tablet using a pen or finger.

The automatic acquisition of the reference value is performed when the power is turned on, when the timing is periodic, and when the coordinates are input. It is possible to flexibly obtain a correction value even in a place where there is a large change in environment, and it is possible to always provide the apparatus with improved accuracy in inputting coordinates.

[Brief description of the drawings]

FIG. 1 is a conceptual view of a tablet according to the present invention.

FIG. 2 is a detailed view of the tablet sheet of the present invention.

FIG. 3 is a sectional view of a tablet.

FIG. 4 is an X-coordinate detection circuit diagram.

FIG. 5 is a Y-coordinate detection circuit diagram.

FIG. 6 is a schematic diagram of a coordinate detection factor.

FIG. 7 is a schematic diagram of a middle terminal voltage detection.

FIG. 8 is an explanatory diagram of a middle terminal potential of the present invention.

FIG. 9 is an explanatory diagram of coordinates of a pressing point according to the present invention.

FIG. 10 is a configuration diagram of a loading system of the present invention.

FIG. 11 is a flowchart for setting a reference value when power is turned on.

FIG. 12 is a flowchart for setting a reference value by a periodic timer.

FIG. 13 is a flowchart for setting a reference value each time a pen is input.

FIG. 14 is an explanatory flowchart of middle terminal potential measurement.

[Explanation of symbols]

 ST1 Upper sheet of tablet ST2 Lower sheet of tablet SR1 Upper resistive film SR2 Lower resistive film XA X coordinate electrode XB X coordinate electrode YA Y coordinate electrode YB Y coordinate electrode X1 Middle terminal of upper resistive film X2 Middle terminal of upper resistive film X3 Middle terminal of resistance film X4 Middle terminal of upper resistance film Y1 Middle terminal of lower resistance film Y2 Middle terminal of lower resistance film Y3 Middle terminal of lower resistance film Y4 Middle terminal of lower resistance film

Claims (8)

[Claims] 1. A method according to claim 1, further comprising a middle terminal different from the two electrode terminals applied to the resistive film, and correcting a coordinate value by measuring a voltage applied between the middle terminal and another terminal. Resistive tablet. 2. The resistive tablet according to claim 1, wherein the middle terminal is provided at a specific position on a side surface different from a position where the two electrode terminals are installed. 3. The resistive tablet according to claim 1, wherein said middle terminal is provided on each of an X coordinate resistive film and a Y coordinate resistive film. 4. The resistive tablet according to claim 3, wherein the middle terminal is located at a specific position at a fixed distance from four corners of the X coordinate resistive film and at a specific position at a constant distance from the four corners of the Y coordinate resistive film. A resistive film tablet, characterized in that it is provided in a tablet. 5. A voltage is applied to two electrode terminals provided on the resistance film, and a voltage of each middle terminal is measured to determine a reference voltage indicated by the coordinates of the middle terminal. A resistive film tablet for calculating coordinates indicated by a time-dependent measured voltage. 6. The resistive tablet according to claim 5, wherein the reference voltage is measured before calculating coordinates indicated by the measured voltage when the resistive film is pressed by an external pressure. 7. The resistive tablet according to claim 5, wherein the measurement of the reference voltage is performed when the power of the device is turned on. 8. The resistive tablet according to claim 5, wherein the measurement of the reference voltage is performed in a cycle of a predetermined time.