JPS6029972B2 - Pressure sensitive tablet device - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a tablet device using a pressure-sensitive resistor sheet, and particularly relates to a pressure-sensitive tablet device that can accurately detect a pressed position on a tablet. .

[Technical Background of the Invention] Conventionally, there is a type of information input device that uses a pressure sensitive resistor sheet to input information by utilizing a change in resistance at a pressed position.

FIG. 1 is a circuit diagram showing an example of its configuration. In the figure, a conductive layer 2 made of a metal sheet is formed on the upper surface of a pressure-sensitive resistor sheet 1 by vapor deposition, sputtering, etc.
Further, resistive plates 3 having uniform sheet resistance are laminated on the lower surface, and these constitute the tablet body. Figure 2 shows its laminated structure, and A in Figure 1.
-A cross-sectional view taken along arrows. Now, between the conductive layer 2 of the tablet body and the ground terminal, there is a power supply 4 for applying a driving voltage.
is connected, and a positive driving voltage is always applied to the conductive layer 2 by this power source 4.

On the other hand, on each side of the resistance plate 3, there are detection electrodes 5a, 5b, each having a plurality of diodes arranged and connected at equal intervals.
5c and 5d are provided. These detection electrodes 5a,
5b, 5c, and 5d direct current flowing from the power source 4 into the resistive plate 3 through the pressing positions of the conductive layer 2 and the pressure-sensitive resistor sheet (hereinafter referred to as pressure-sensitive sheet) 1 on each side of the resistive plate 3. This is for uniformly discharging water from the entire area. In addition,
The diode prevents the current that has once flowed out from flowing back into the resistor plate 3. Each of the detection electrodes 5a, 5b, 5c, and 5d has a detection resistor 6a'6.
After passing through b, 6c, 6d, the opposing electrodes 5a, 5
b, 5c, and 5d are connected in common, and then connected to one constant current source 8 via switches 7a and 7b. This constant current source 8 is connected to the power source 4 for applying the drive voltage.
This is to keep the output current constant. Further, each of the detection resistors 6a, 6b. Resistors 6b and 6 among 6c and 6d
c is an operational amplifier 9a for detecting the voltage drop.
, 9b are connected, and these operational amplifiers 9a, 9
The voltage value detected at b is sent to a sampling hold circuit (S
/H) is outputted via 10a and 10b. Note that the detection control circuit 11 includes each of the switches 7a,
7b alternately, the sampling and holding circuits 10a and 10b are made to perform a sampling and holding operation accordingly, and thereby the pressed position on the tablet body is detected separately in the X direction and the Y direction. belongs to. With such a configuration, when an arbitrary position on the tablet body is pressed with an indicator pen or the like, the resistance value of the pressure-sensitive sheet 1 at this pressed position decreases, resulting in a substantially short-circuited state.

Here, assuming that the switch 7a is closed by a control signal issued from the detection control circuit 11, the output current of the power source 4 is applied to the conductive layer 2 and the pressure-sensitive sheet 1 by the pressing operation with the indicator pen. It flows out from the detection electrodes 5a, 5b via the position and resistance plate 3, and then flows to the detection resistors 6a, 6b. And our detection resistor 6a
, 6b, the voltage drop across the resistor 6b is detected by the operational amplifier gb, and this detected value is sent to the sampling hold circuit 10.
It is held at b. Note that since the sum of the currents flowing through each of the detection resistors 6a and 6b is determined to be a constant value by the constant current source 8, the ratio of the currents flowing through each of the detection resistors 6a and 6b depends on the pressing position of the pressure-sensitive sheet 1. This corresponds to the resistance ratio of the corresponding resistance plate 3. Therefore, the value of the voltage drop across the detection resistor 6b detected by the operational amplifier 9b and held by the sampling and hold circuit 10b directly indicates the x-direction coordinate of the pressed position on the tablet body. When the X-direction coordinates of the pressed position are detected in this way, a control signal is output from the detection control circuit 11 and the switch 7a
Switch 7b is closed instead.

As a result, the output current of the power source 4 is now reduced to the detection electrodes 5c, 5.
d flows to the detection resistors 6c and 6d, and the detection resistor 6
The voltage drop c is detected by the operational amplifier 9a as information indicating the Y-direction coordinate of the pressed position. In this way, the coordinates of the pressed position in the x direction and the y direction are detected. In this way, with the above configuration, the pressed position on the pressure-sensitive sheet, that is, the input information can be detected relatively easily compared to other tablet devices such as a capacitive type.

[Problems with background technology]

However, in the conventional device, the coordinates of the pressed position in the X direction and the Y direction are alternately detected by switching the switches 7a and 7b using one constant current source 8.

Therefore, the switches 7a and 7b and a circuit for controlling their switching are required, as well as sampling and holding circuits 10a and 10b for holding the detected values in the X direction and the Y direction. Therefore, the circuit configuration becomes complicated, which is not practical. In addition, since detection is performed while switching, unstable factors are likely to occur in the detected values, making it difficult to improve detection accuracy. [Object of the Invention] An object of the present invention is to provide a pressure-sensitive tablet device that can be realized with a simple configuration without using complicated circuits or controls, and can perform highly accurate and stable position detection. shall be.

[Summary of the invention]

In order to achieve the above object, the present invention sets the current flowing through the detection electrodes provided on each side of the tablet body to a constant value for each detection electrode, and selects the potential appearing on each detection electrode in this state. The pressed position on the tablet body is determined from the detection result.

In another aspect of the present invention, the current is made constant for each detection electrode, and the pressed position is determined from the potential of each electrode at that time.
The magnitude of the potential appearing on any electrode is monitored, and when this potential reaches a predetermined value set in advance, the pressed position information obtained at this time is taken as true information.

[Embodiments of the invention]

Figure 3 shows. This is a circuit configuration diagram of a pressure-sensitive tablet device according to an embodiment of the present invention, and the same parts as in FIG.

In the figure, constant current sources 22a, 22b,
22c and 22d are connected, and these constant current sources 22
each detection electrode 5a, 5 by a, 22b, 22c, 22d
The currents flowing out from b, 5c, and 5d are each made constant independently.

Also, between the detection electrodes 5a and 5b and between the detection electrodes 5c and 5d.
In between, there are subtracting circuits 21a and 21a each consisting of an operational amplifier.
21b is connected. These subtraction circuits 21a, 2
1b is for detecting the potential difference between the detection electrodes 5a and 5b and the potential difference between the detection electrodes 5c and 5d, respectively, and these potential differences are used as the coordinates of the pressed position on the tablet body in the x direction and the y direction. Output.
Furthermore, among the detection electrodes 5a, 5b, 5c, and 5d, the respective potentials appearing on the detection electrodes 5a and 5M are led to an addition circuit 23 using an operational amplifier, and are added in this circuit 23. ing. Note that this adder circuit 23 inverts the addition result and outputs it. The addition output of such an addition circuit 23 is sent to a comparison circuit 2 consisting of an operational amplifier.
It is guided by 4. This comparison circuit 24 compares the addition output of the addition circuit 23 with the output voltage (reference voltage) of the reference power supply 25, and when the output voltage is equal to or less than this reference voltage, the output becomes "H".
It emits a level detection timing signal CS.
This detection timing signal CS becomes a timing signal when recognizing potential difference information obtained by each of the subtraction circuits 21a and 21b in a pressed position recognition circuit (not shown).
By the way, the reference voltage is set as follows.

That is, the equivalent circuit of the device shown in FIG. 3 is shown in FIG. 4. In addition, Rv in the figure represents the resistance value of the pressure-sensitive sheet 1, and [,,,,r,2 and ``2,. The resistance value Rv of the pressure-sensitive sheet 1 changes as the amount of pressure increases, and becomes less sensitive when the amount of pressure is small. has a somewhat large value.In this way, when the resistance value Rv of the pressure sensitive sheet 1 is large,
The voltage V between the terminals of the constant current source 22a is V, =V-V.

-IRv-i,r,. become smaller and more obvious,
As a result, the constant current source 22a does not perform a constant current action.

This constant current action causes the resistance value Rv to decrease as the amount of pressure applied to the pressure-sensitive sheet 1 increases, and as a result, the voltage V between the terminals of the constant current source 22a increases to a value as shown in FIG. ■It will start when the above is reached. On the other hand, when the amount of pressure applied to the pressure-sensitive sheet 1 is small and the resistance value is large, the output voltage V2 of the adder circuit 23 consisting of an inverting amplifier is in a saturated state.

This output voltage V2 decreases as shown in FIG. 5 as the amount of pressure applied to the pressure sensitive sheet 1 increases. In other words,
Changes in the output voltage V2 of the adder circuit 23 approximately correspond to changes in the voltage V between the terminals of the constant current source 22a. In addition,
This mutual relationship is the same for constant current sources 22b, 22c, and 22d. Therefore, the constant current source 22a,
The output voltage y2 of the adder circuit 23 corresponding to the amount of pressure applied to the pressure sensitive sheet necessary for 22b, 22c, and 22d to perform a sufficient constant current action may be set as the reference voltage (Vs in FIG. 5).

Next, the operation of the apparatus configured as above will be explained.

When an arbitrary point on the tablet body is pressed with an indicator pen or the like, the resistance value of the pressure-sensitive sheet 1 at this pressing position decreases, and as a result, the output current of the power source 4 increases due to the pressure of the conductive layer 2 and the pressure-sensitive sheet 1. Position, resistance plate 3 and each detection electrode 5
each constant current source 22 via a, 5b, 5c, 5d, respectively.
a, 22b, 22c, and 22d. That is, current flows through all the detection electrodes 5a, 5b, 5c, and 5d simultaneously. And each of these detection electrodes 5a, 5b, 5c, 5
If the amount of pressure applied to the pressure sensitive sheet 1 is greater than or equal to a certain level, the current flowing through the constant current sources 22a, 22b, 22c, 2
2d. On the other hand, when the resistance value of the pressure sensitive sheet 1 decreases as described above, the detection electrodes 5a,
5b and detection power 5c, 5d, each detection electrode 5a,
Since the current flowing through 5b, 5c, 5d is constant, the resistance values r, . , r, 2, et al., , the corresponding potentials already appear.

These potentials are introduced into the subtraction circuit 21a for the detection electrodes 5a and 5b, and the subtraction circuit 21b for the detection electrodes 5c and 5d.
The difference is found between 1a and 21b. At this time, the potential differences V3 and V4 output from each subtraction circuit 21a and 21b are V3:i, (r, Ikko, .)V4=i2(r2-
It is expressed as Ko2,).

However, rl=rll+r12 r2 ni r21 ten r22 It is.

Further, the potential difference V3, V4 is the sixth voltage difference depending on the pressing position.
As shown in the figure, -i, r, (1 i2r2) to 10 i, r,
(10i2r2). Therefore, each of the potential differences V3 and V4 corresponds to the coordinates in the X direction and the Y direction on the tablet body, so the potential difference V3
, V4 can be used as the pressing position. Further, the respective potentials of the detection electrodes 5a and 5b are added by an adding circuit 23, and compared with a reference voltage Vs by a comparing circuit 24. Then, when the addition output V2 of the addition circuit 23 becomes lower than the reference voltage Vs, that is, each constant current source 22a, 22b, 22
When the amount of pressure applied to the pressure-sensitive sheet reaches a value that allows stable constant current action of c and 22d, the comparator circuit 24 outputs "H".
"Level detection timing signal CS is generated. As a result, the position recognition circuit (not shown) does not recognize the potential difference values output from each subtraction circuit 21a, 21b before the generation of the detection timing signal CS. The potential difference value at the time when the detection timing signal CS is generated is recognized as the true position detection information.In this way, in the device of this embodiment, each of the detection electrodes 6a, 5b, 5c, 5d A constant current source 22a,
22b, 22c, and 22d, and in this state, the detection electrodes 5a, 5b and the detection electrodes 5c, 5d
Since the electric potential difference of each is detected and this is used as the coordinate information of the hair position, it is possible to detect the coordinate information of each direction simultaneously without having to separate the detection period in the x direction and the Y direction as in conventional devices. .

This eliminates the need for switches, sampling and holding circuits, and circuits for controlling these, thereby simplifying the configuration. In addition, since detection can be performed in stable conditions such as current without dividing the detection period,
Detection accuracy can be improved. Furthermore, in this embodiment, when the sum of the potentials appearing on the detection electrodes 5a and 5b becomes the reference voltage Vs, the output voltages of the subtraction circuits 21a and 21b are recognized as true position detection information. Therefore, position detection information can be obtained in a state where each constant current source is sufficiently performing a constant current action, and as a result, detection accuracy and stability can be further improved. Furthermore, in this embodiment, the pressed position is detected by determining the potential difference between the opposing electrodes 5a, 5b and 5c, 5d. In comparison, the voltage drop due to the resistance value Rv of the pressure sensitive sheet 1 and the voltage drop V due to the diode. can be canceled out, and as a result, detection accuracy can be further improved. Note that the present invention is not limited to the above embodiments. For example, the direction of the current flowing through the detection electrode may be set in the opposite direction. In addition, various modifications may be made to the configurations of the detection electrodes, the arithmetic circuit for determining the pressed position from the potential, the detection control circuit, etc. without departing from the gist of the present invention. [Effects of the Invention] As described in detail above, the present invention stabilizes the current flowing through the detection electrodes using a constant current source for each detection electrode, and in this state, the pressure on the tablet body is determined from the potential appearing on each detection electrode. It detects the position, and in addition, monitors the magnitude of the potential appearing on the detection electrode, and recognizes the pressed position information obtained when this potential reaches a preset value as true information. It was designed to do so.

Therefore, according to the present invention, it is possible to provide a pressure-sensitive tablet device that can be realized with a simple configuration without using complicated circuits or controls, and can perform highly accurate and stable position detection.

[Brief explanation of the drawing]

Figures 1 and 2 show the configuration of the pressure-sensitive tablet device in the sub-chamber; Figure 1 is its circuit configuration diagram;
The figure is a cross-sectional view taken along line A-A in FIG. 1, and FIGS. 3 to 6 show an embodiment of the present invention, and FIG.
FIG. 4 is an equivalent circuit diagram of the device shown in FIG. 3, and FIGS. 5 and 6 are voltage waveform diagrams used to explain the operation of the device shown in FIG. 3. 1... Pressure sensitive sheet, 2... Conductive layer, 3... Resistance plate, 4. ．． ．． Power supply for applying driving voltage, 5a, 5b, 5c,
5d...detection electrode, 21a, 21b...subtraction circuit,
22a, 22b, 22c, 22d...constant current source, 23
...Addition circuit, 24...Comparison circuit, 25...Reference power supply. Figure 1 Figure 2 Figure 3 Figure 5 Figure 4 Figure 6

Claims (1)

[Scope of Claims] 1. A tablet main body having a pressure-sensitive resistor sheet having a conductive layer formed on one side and a resistor layer formed on the other side, and a tablet main body having a pressure-sensitive resistor sheet formed with a conductive layer on one side and a resistor layer formed on the other side; a driving voltage applying circuit that applies a driving voltage between the sensing electrodes and the conductive layer; and a current flowing through each of the sensing electrodes by applying the driving voltage to a constant value for each electrode. 1. A pressure-sensitive tablet device comprising: a constant current source circuit; and an arithmetic circuit that detects a pressed position of the tablet body from the potential appearing on each of the detection electrodes. 2. A tablet main body having a pressure-sensitive resistor sheet having a conductive layer formed on one side and a ladder layer formed on the other side, a detection electrode provided on each side of the resistor layer, and a drive voltage application circuit that applies a drive voltage between the detection electrode and the conductive layer; and a constant current source circuit that makes the current flowing through each of the detection electrodes constant for each electrode by applying the drive voltage. , an arithmetic circuit that detects the pressed position of the tablet main body from the potential appearing on each of the detection electrodes; and a calculation circuit that monitors the magnitude of the potential appearing on the detection electrode and when this potential reaches a predetermined value set in advance. and a detection control circuit for determining the detection result obtained by the arithmetic circuit as a true pressed position.