JP3004837B2 - Tablet input device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tablet input device used as a man-machine interface for small electronic devices, computers, and information terminals, and more particularly to an improvement of a resistive tablet input device. is there.

[0002]

2. Description of the Related Art FIG. 4 is a schematic block diagram showing an example of a tablet input device. In this tablet input device, XY coordinates are set on the tablet 1 and an input pen 2 is provided. When the switch of the pen 2 is turned on, the control unit 3 is activated.
The control unit 3 scans the XY coordinates on the tablet 1 and detects the coordinates (X ₁ , Y ₁ ) of the point pressed by the input pen 2.

FIG. 5 illustrates an example of a main part of a tablet input device as shown in FIG.
This input device has an upper resistance film F1 and a lower resistance film F2. An electrode E1 is provided at one end of the upper surface resistance film F1, and another electrode E2 is provided at the other end. A voltage is applied to these electrodes E1 and E2 when detecting X-axis coordinates. Similarly, an electrode E2 is provided at one end of the lower resistance film F2, and another electrode E4 is provided at the other end. A voltage is applied to these electrodes E3 and E4 when detecting the coordinates of the Y axis. It goes without saying that the X axis and the Y axis can be interchanged.

The transistors T1, T2, T3 and T4
Work as drivers for driving the electrodes E1, E2, E3 and E4, respectively. The remaining transistor T5
And T6 are electrode driving drivers used to confirm whether or not the pressing level of the input pen is appropriate.

FIG. 6 is a flowchart showing a procedure for detecting the XY coordinates of the input point in the tablet input device of FIG. First, in step S1, the transistors T2 and T5 are turned on, and all the remaining transistors T1, T3, T4 and T6 are turned off. In this state, in step S2, it is determined whether the pressing level of the input pen is appropriate for the X axis. If the pressing level of the input pen is insufficient, the process returns from step S2 to step S1. On the other hand, X of the input pen
If the pressure level on the shaft is appropriate, the process proceeds to step S3.

In step S3, the transistor T
1 and T2 are turned on, and all the remaining transistors T3, T4, T5 and T6 are turned off. In this state, in step S4, the voltage in the X-axis direction is read from the terminal X.

[0007] Thereafter, detection of a position on the Y axis is performed. That is, in step S5, the transistors T4 and T6 are turned on, and all the remaining transistors T1, T2, T3 and T5 are turned off.
In this state, in step S6, it is determined whether the pressing level of the input pen is sufficient with respect to the Y axis. If the input pen is not sufficiently pressed, the process proceeds from step S6 to step S6.
Return to 1. On the other hand, if the input pen pressing level is sufficient for the Y axis, the process proceeds to step S7.

In step S7, the transistor T3
And T4 are turned on, and all the remaining transistors T1, T2, T5 and T6 are turned off. In this state, in step S8, the voltage in the Y-axis direction is read from the terminal Y.

That is, the X coordinate of the position pressed by the input pen is determined by the voltage in the X axis direction read from the terminal X, and the coordinate in the Y axis direction is determined by the voltage in the Y axis direction read from the terminal Y. Is done. However, as understood from steps S2 and S6, in the conventional tablet input device, when the pen pressing force is insufficient with respect to either the X axis or the Y axis, the coordinate detection is not performed. Return to the first step. That is, when the pen pressing force is insufficient, it is determined that incorrect data has been input, and the data is discarded without being used for coordinate calculation.

[0010]

As described above, the conventional resistive tablet input device has a drawback that data cannot be input unless the pressing force of the user with the input pen has exceeded a predetermined pressure. . This is because, in a conventional tablet input device, after a voltage is applied to the resistance film of the axis to be measured (X or Y), the divided voltage at the point pressed by the input pen is read through the other measurement side resistance film. When the pressing force is small, the upper surface resistive film F
1 and the lower resistance film F2.

Since a measuring circuit having a finite input impedance is used to read the divided voltage, when reading the divided voltage, a current flows through the voltage dividing point pressed by the pen. That is, this current flows into the measurement circuit through the contact resistance and the resistance film on the measurement side. At this time, if the resistance of the resistive film is sufficiently smaller than the contact resistance, the contact resistance can be ignored. However, if the contact resistance becomes 1/10 or more of the resistance of the resistive film, a large error is included in the read data. Will be.

Further, in the conventional tablet input device, the position coordinates are calculated from the voltage division value itself. T
4 must have small output impedance and their impedance must be stable. Therefore, a driver having a relatively large output impedance such as a C-MOS transistor cannot be used in the conventional tablet input device.

In view of the above-mentioned problems of the prior art, one object of the present invention is to provide a tablet input device capable of accurately reading input position data even when a pressing force of an input pen is small. is there.

Another object of the present invention is to provide a high-speed tablet input device in which all input data can be read so that the effective sampling speed is improved.

Still another object of the present invention is to provide a tablet input device capable of inputting information related to handwriting by detecting a pressing force of an input pen.

It is yet another object of the present invention to provide a tablet input device that can use a C-MOS driver having a relatively large output impedance.

[0017]

A tablet input device according to the present invention comprises first and second resistive films facing each other, a first electrode at one end of the first resistive film, a second electrode at the other end, a fourth electrode in the third electrode and the other end at one end of the second resistance film, first, second, third and fourth arbitrary one for low-level and two power voltage level different in high levels of the electrode Driver means for independently applying any one, and first and second electrodes in the first resistive film
With the low and high levels of
The divided voltage V ₁ at the input pressing point where the first and second resistive films are pressed.
And the voltages of the first and second electrodes are respectively
With the high level and the low level set,
A first voltage measuring means for measuring the voltage V ₂ and a second resistive film
In this case, the voltages of the third and fourth electrodes are low and high, respectively.
Measure the divided voltage V ₃ at the input pressing point with the level set
And the voltages of the third and fourth electrodes are
Voltage V ₄ at the input pressing point with the
Second voltage measuring means for measuring the divided voltage
Calculate the X coordinate of the input pressing point from V ₁ and V ₂ and calculate the divided voltage
Calculation for calculating the Y-coordinate of the input pressure point from V ₃ and V ₄
Means .

[0018]

In the tablet input device of the present invention, a low level is applied to any one of the first, second, third and fourth electrodes.
Driver means for applying any one of Le and two power voltage level different in high levels independently provided,
Voltage is applied twice to each resistive film in a different manner and
Dividing the voltage of the input pressing point is measured twice Runode can detect the input position coordinates from the proportional relationship without dividing voltages being influenced by the contact resistance between the upper and lower resistive films. That is, in the tablet input device according to the present invention, the input position coordinates can be accurately read regardless of the pressing force of the input point. Also, the value of the contact resistance can be obtained based on the proportional relationship between the divided voltages.

[0019]

FIG. 1 schematically shows a main part of a tablet input device according to an embodiment of the present invention. This tablet input device comprises an upper resistive film F1 and a lower resistive film F
2 is provided. An electrode E1 is provided at one end of the upper surface resistance film F1, and another electrode E2 is provided at the other end. Similarly, an electrode E3 is connected to one end of the lower resistance film F2.
Is provided, and another electrode E4 is provided at the other end.

The drivers D1, D2, D3 and D4 are:
They are connected to electrodes E1, E2, E3 and E4, respectively. As each of these drivers, a C-MOS tri-state type can be used.

FIG. 2 is a flowchart for explaining the operation of the tablet input device shown in FIG. First, in step S1, the driver D1 outputs L level (GND level: ground level) and the driver D2
Output an H level (V _CC level: power supply voltage level). On the other hand, the remaining drivers D3 and D4 are in a floating state. That is, the electrode E1 of the upper surface resistance film F1
Are fixed at the GND level, and the other electrode E2 is fixed at the V _CC level. In this state, in step S2,
The divided voltage V ₁ at the point where the tablet is pressed by the pen is read from the terminal X using an AD (analog-digital) converter (not shown).

Next, in step S3, the driver D1
Output the V _CC level, and the driver D2 outputs the GND level. That is, contrary to the case of step S1, the electrode E
1 is fixed at the _Vcc level, and the other electrode E2 is fixed at the GND level. In this state, in step S4, using the AD converter, reading the divided voltage V ₂ points tablet is pushed from the terminal X by the input pen.
Next, in step S5, the position of the pressure point by the input pen from the obtained ratio of divided voltage values V ₁ and V ₂ are computed. In step S5, as described later,
The contact resistance value can also be calculated using the result of the proportional calculation of the divided voltage.

Similarly, for the Y axis, in step S6, the driver D3 outputs L level and the driver D4
Output the H level. On the other hand, the drivers D1 and D2 are brought into a floating state. That is, the lower resistance film F2
Electrode E3 is fixed at the GND level, and the other electrode E4
_Are fixed at the V _CC level. In this state, step S7
In using the AD converter, reading a voltage divided value V ₃ from the terminal Y.

Next, in step S8, the driver D
3 outputs an H level, and the driver D4 outputs an L level. That is, the electrode E3 is fixed at the V _CC level, and the other electrode E4 is fixed at the GND level. In this state, in step S9, the voltage division value V ₄
Is read. Then, in step S10, the ratio of voltage division V ₃ and V _4, Y coordinates of the point where the input pen is pressed is calculated. Also, in step 10,
The contact resistance value can be calculated as in the case of the X axis.

Thereafter, in step S11, it is determined whether or not the obtained XY coordinates are within a specified area. If the obtained data is out of the specified area, the data is discarded as invalid data, and the process returns to S1. On the other hand, if the obtained data is valid within the specified area, the X and Y coordinate values are determined in step S12.

Referring to FIG. 3, a description will be given of a method of calculating position coordinates using the above-described divided voltage ratio. In FIG. 3, resistors R1 and R2 represent output resistances of drivers D1 and D2, respectively. The resistance (R3 + R4) indicates the resistance value of the upper surface resistance film F1 to which a voltage is applied.
That is, the point P between the resistors R3 and R4 represents a point pressed by the input pen.

On the other hand, the resistance R5 represents the contact resistance between the upper resistance film F1 and the lower resistance film F2 at the point pressed by the input pen. The resistance R6 is the lower resistance film F2.
The resistance value from the point pressed by the upper input pen to the terminal X is shown. The resistance R7 represents the input impedance of the measurement circuit (AD converter in this embodiment).

In such a situation, the voltage at the X terminal represents the divided voltage. Divided voltages V ₁ when the resistor R1 is connected to the GND level, and a resistor R2 to V _CC level is expressed by the following equation.

V ₁ = V _CC (R1 + R3) R7 / (R5 +
R6 + R7) (R1 + R2 + R3 + R4) Similarly, connect the resistor R1 to the _Vcc level and connect the resistor R2 to the G level.
Divided voltage V ₂ when connected to the ND level is expressed by the following equation.

V ₂ = V _CC (R2 + R4) R7 / (R5 +
R6 + R7) (R1 + R2 + R3 + R4) Therefore, the following proportional relationship is obtained.

V ₁ : V ₂ = (R1 + R3) :( R2 + R4) By the way, since the resistors R1, R2 and (R3 + R4) are known values, the values of the resistors R3 and R4 are obtained. Here, it can be understood that the proportional relationship between the divided voltages is independent of the contact resistance R5. However, it is necessary that the input impedance R7 of the measuring device is sufficiently larger than the resistance (R3 + R4) of the resistive film.

The contact resistance R5 can be obtained as follows. Since the value of the resistors R3 and R4 by a proportional calculation of the above-mentioned divided voltage is obtained, the voltage V _P at the pressing point of the input pen can be expressed by the following equation in the case of FIG. 3 (A).

V _P = V _CC V ₁ / (V ₁ + V ₂ ) The relationship between the divided voltages V ₁ and V _P at this time is expressed by the following equation.

V _P -V ₁ = V ₁ (R5 + R6) / R7 Here, assuming that the resistance R7 is sufficiently larger than the resistance R6, the resistance R5 is obtained by the following equation.

[0035] _{R5 = R7 (V P -V 1} ) / V 1 be Y also similar calculation in the calculation for the coordinate may be made it will be readily understood.

[0036]

As described above, according to the present invention, it is possible to provide a tablet input device capable of accurately detecting the XY coordinates of the pressed point regardless of the pressing force of the input pen.

Further, according to the present invention, since all data input to the tablet can be read, a tablet input device having a high effective sampling speed of input position data can be provided.

Further, according to the present invention, it is possible to provide a tablet input device capable of obtaining a contact resistance depending on a pen pressing force. That is, since the input tablet device according to the present invention can detect the pressing force of the pen, the input tablet device can represent the thickness of the line depending on the writing pressure, and can obtain information about the handwriting that is close to the feeling of using a normal writing instrument. Can be.

Furthermore, in the tablet input device according to the present invention, it is sufficient that the impedance of the driver is sufficiently smaller than that of the resistive film, so that a relatively large output impedance such as a C-MOS driver which cannot be used conventionally can be used. A driver having the same can also be used.

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically illustrating a main part of a tablet input device according to an embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of the tablet input device of FIG. 1;

FIG. 3 is a circuit diagram for explaining details of calculation in the flowchart of FIG. 2;

FIG. 4 is a block diagram schematically illustrating a tablet-type input device.

FIG. 5 is a circuit diagram showing an example of a main part of a conventional tablet input device.

FIG. 6 is a flowchart illustrating an operation of the tablet input device of FIG. 5;

[Explanation of symbols]

 Reference Signs List 1 tablet 2 pen 3 control unit F1, F2 resistive film E1, E2, E3, E4 electrode D1, D2, D3, D4 driver

────────────────────────────────────────────────── (5) Continuation of the front page (56) References JP-A-2-287815 (JP, A) JP-A-3-59712 (JP, A) JP-A-63-308630 (JP, A) JP-A 5- 53716 (JP, A) JP-A-5-46306 (JP, A) JP-A-4-352219 (JP, A) JP-A-1-133125 (JP, A) JP-A-58-94074 (JP, A) JP-A-5-173696 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G06F 3/00-3/03

Claims (1)

(57) [Claims] 1. A first and a second resistive film facing each other, a first electrode at one end of the first resistive film, a second electrode at the other end, a third electrode at one end of the second resistive film, A fourth electrode at the other end, and any one of the first, second, third, and fourth electrodes
And driver means for applying any one of the low and high level different from two power pressure levels independently, the voltage of the first and second electrodes in the first resistive film
The first and the second in the state of being set to the low level and the high level, respectively.
Measuring a divided voltage V ₁ of the input pressing point of pressing the second resistive film
And the voltages of the first and second electrodes are respectively
With the high level and the low level set, the input pressing point
First voltage measuring means for measuring the divided voltage V _2, and the voltage of the third and fourth electrodes in the second resistive film is
With the low level and high level respectively,
The divided voltage V ₃ at the pressure point is measured and the third and fourth voltages are measured.
Electrode voltage is set to high level and low level respectively.
Second conductive measuring the divided voltage V ₄ of the input pressure point in state
A pressure measuring means, said measured divided from the voltage V ₁ and V ₂ of the input pressure point
Calculates the X coordinate and the input from the dividing voltage V ₃ and V ₄
A tablet input device comprising: a calculating unit for calculating a Y coordinate of the pressed point .