JPH09160711A - Tablet input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent misinput due to a hand touch, and detect the breakage of a tablet quickly and prevent secondary damage by connecting one electrodes of one resistance film to a power source side and then detecting abnormality of the tablet from variation of potential developed at the other electrode on the output side. SOLUTION: A timing generator 4 instructs for switching among an X measurement mode, a Y measurement mode, and a check mode. In the check mode, transistors(TR) 14B and 2 are turned on and a TR 16B is turned off to apply a voltage to a resistance film 10B of the Y axis while a detection resistance 1 is connected in series. Further, TRs 14A and 15A are turned off and a resistance film 10A of the X axis is connected to an AD converter 102. Here, if a hand touch is made to the tablet the resistance films 10A and 10B come into surface contact and decrease in resistance value and a detection voltage Vs inputted to the AD converter 102 varies. Therefore, binary data outputted from an output terminal 103 is compared to judge the hand touch.

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 in a portable information terminal or the like.

[0002]

2. Description of the Related Art A tablet input device is a functional block for handwriting input of data and commands using a dedicated pen or the like in a portable information terminal such as an electronic notebook.

The tablet input device is roughly classified into two types, that is, an electromagnetic induction type and a pressure sensitive resistive film type, but in the portable information terminal, the pressure sensitive resistive film type which is advantageous in cost is mainly used. ing.

FIG. 10 shows a block diagram of a conventional pressure-sensitive resistive film type tablet input device. In this FIG.
A tablet 100 is composed of an X-axis resistance film 10A and a Y-axis resistance film 10B. 11A, 1
2A is an electrode of the X-axis resistance film 10A, 11B and 12B are electrodes of the Y-axis resistance film 10B, and 101 is a contact resistance when the tablet is pointed by a pen.

FIG. 11 is a block diagram showing an actual image of the tablet 100. The tablet 100 has two electrodes 11A, 12A and 11B, 12 on opposite sides.
Two resistance films 10A and 10B having B attached thereto are prepared, and these resistance films 1 are provided so that these electrodes do not overlap.
0A and 10B are offset by 90 degrees and pasted together. Of the two resistance films 10A and 10B, a voltage is applied between the electrodes provided on the opposite sides of one resistance film, and the remaining resistance film measures the partial pressure at the indicated position X, It is possible to obtain the two-dimensional coordinates of Y.

The X-axis resistance film 10A has a positive power source 20 via a PNP transistor 14A connected to the electrode 11A.
It is connected to the. Further, the electrode 11B of the resistance film 10A is
It is connected to the NPN transistor 16A. This NP
The collector terminal of the N-transistor 16A is the AD converter 1
02 is connected to the input side.

Similarly, the Y-axis resistance film 10B is connected to the same positive power source 20 via the PNP transistor 14B connected to the electrode 11B, and the electrode 12B is connected to the NPN transistor 16B.
Similarly, the collector terminal of B is connected to the input side of the AD converter 102. The AD converter 102 is configured to convert the X-axis and Y-axis instruction potentials into binary data. 103 is its output terminal.

A timing generator 104 generates timing signals Xv, Xg, Yv, Yg. The timing signal Xv is input to the PNP transistor 14A via the base resistor 13A, and the timing signal Yv is input to the base resistor 1
3B is input to the PNP transistor 14B, the timing signal Xg is input to the NPN transistor 16A via the base resistor 15A, and the timing signal Yg is input to the PNP transistor 1 via the base resistor 15B.
6B is input.

The actual operation of the tablet input device of FIG. 10 will be described with reference to the timing chart of FIG. As shown, an X measurement mode for measuring the X axis and a Y measurement mode for measuring the Y axis are provided along the time axis direction, and the two-dimensional coordinates of X and Y are changed by alternately switching these modes. I will get it.

In the X measurement mode, Xv and Yg are set to L level and Yv and Xg are set to H level. As a result, the transistors 14A and 16A are turned on, and a voltage is applied across the X-axis resistance film 10A. Further, the transistors 14B and 16B are turned off, and the Y-axis resistance film 10B is in a high impedance state in which it is grounded by the input impedance of several hundred kΩ of the AD converter 102. When there is a pen instruction, the X-axis resistance film 10A and the Y-axis resistance film 10B come into contact with each other via the contact resistance 101. Resistive film 10
The resistance values of A, 10B and the contact resistance 101 are both AD.
Since it is much smaller than the input impedance of the converter 102, the divided potential corresponding to the indicated position on the X axis is input to the AD converter 102 via the contact resistance 101 and the Y axis resistance film 10B. . As a result, the binary data indicating the designated position on the X axis is output to the output terminal 1 of the AD converter 102.
03 is output.

In the Y measurement mode, conversely, Xv and Yg are set to H level and Yv and Xg are set to L level. Then, in the same operation as in the X measurement mode, binary data indicating the designated position of the Y axis is output to the output terminal 103 of the AD converter 102.

By repeating the above operation, two-dimensional coordinates of the X axis and the Y axis are obtained. In the above description, the pen instruction detection mode is omitted for simplicity.

[0013]

As described above, the conventional tablet input device is configured to apply a voltage to the resistance film of the shaft to be measured and obtain the indicated position from the resistance partial pressure. Therefore, if the user accidentally presses the tablet with his palm (hereinafter referred to as “touch”),
Since the X-axis resistance film 10A and the Y-axis resistance film 10B are in contact with each other over a wide range, incorrect data will be obtained. Particularly in the case of a portable information terminal, not only handwritten character data but also data in which a predetermined stroke called a gesture is assigned to a command is used as data from the tablet input device. For example, if this erroneous data is interpreted as a command to erase stored data such as an address book, the user will lose important data.

Further, in the above-mentioned conventional tablet input device, when the tablet is damaged due to an external load factor, particularly when the electrodes are short-circuited to each other, an excessive current flows and the power consumption is wasted, and the power consumption remains unchanged. If left unattended, there is a problem in that the battery may be damaged in the worst case.

The present invention solves the above-mentioned conventional problems, and can prevent erroneous input due to a touch on the tablet, and further, can promptly detect damage to the tablet to prevent secondary damage. It is intended to provide a tablet input device.

[0016]

In order to achieve this object, a tablet input device of the present invention has a structure in which electrodes between electrodes provided on opposite sides of one resistance film of two resistance films of X axis and Y axis. In a tablet input device in which a voltage is applied to one of the resistive films and the remaining resistive film measures the partial pressure at the indicated position, connect one electrode of either resistive film to the power supply side, and then It is configured to detect the abnormality of the tablet by the change in the potential appearing on the electrode.

According to this structure, when an abnormality occurs in the resistance film for some reason, the potential appearing on the other electrode changes accordingly. Therefore, the abnormality is detected by detecting the change in the potential. Is detected immediately.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the first embodiment of the present invention.
3 is a block diagram of the tablet input device according to the embodiment of FIG. Here, the same members as those in the conventional tablet input device shown in FIG. 10 are designated by the same reference numerals, and detailed description thereof will be omitted. In FIG. 1, the electrode 12B of the Y-axis resistance film 10B is the electrode 12B.
One terminal of the detection resistor 1 for measuring the potential of B is connected. The NPN transistor 2 controlled by the timing signal Yc is connected to the other terminal of the detection resistor 1. Reference numeral 3 is a base resistance of the NPN transistor 2. The timing signal Yc is the other timing signals Xv, Xg,
It is generated by the timing generator 4 like Yv and Yg. The NPN transistor 2 and the base resistor 3 as described above constitute a detection switch.

The operation of the apparatus shown in FIG. 1 will be described with reference to FIG. 2 which is a timing chart showing the operation of the apparatus. In FIG. 2, an X measurement mode for measuring the X axis and a Y measurement mode for measuring the Y axis are provided in the time axis direction, and these modes are alternately switched to obtain the two-dimensional coordinates of X and Y. It is similar to the conventional tablet input device shown in FIG. Here, in addition to this, there is a check mode. In X measurement mode and Y measurement mode,
Yc is set to L level. Therefore, since the transistor 2 is in the off state, the operation in the X measurement mode and the Y measurement mode is the same as that of the conventional example.

FIG. 5 shows a concrete block diagram of the timing generator 4 for instructing mode switching, and FIG. 6 shows its timing chart. The timing generator 4 includes a synchronous 2-bit counter 41, an OR gate 42 and an inverter 4
And 3. By applying a clock as shown in FIG. 6 to the clock input terminal 40, outputs Q0 and Q1 are generated in the counter 41, and the output terminals 44, 45, 46 and 4 are generated.
7 and 48 include Yg, Yc, Xv, Xg, and Yv, respectively.
Generates the control signal of.

In check mode, Yv, Yg and X
g is set to L level, Xv is set to H level, and Yc is set to H level. Thereby, the transistor 14B
And the transistor 2 is on, and the transistor 1
Since 6B is turned off, a voltage is applied to the Y-axis resistance film 10B in the form of the detection resistor 1 connected in series. Further, the transistors 14A and 16A are turned off, and the X-axis resistance film 10A is in a high impedance state in which it is grounded by the input impedance of several hundred kΩ of the AD converter 102.

Therefore, in the check mode, if the power supply voltage is Vc, the resistance value of the Y-axis resistance film 10B is Rt, the resistance value of the detection resistor 1 is Rs, and the saturation voltage between the emitter and collector of the transistor 14B and the transistor 2 is Vcesat. ,
The terminal potential of the detection resistor 1, that is, the detection voltage Vs input to the AD converter 102 is represented by Expression (1).

Vs = (Vc−2 × Vcesat) × Rs / (Rt + Rs) (1) In the formula (1), if the transistors 14 B and 2 having a low emitter-collector saturation voltage are selected, the formula (1 It can be approximated as in 2).

Vs = Vc × Rs / (Rt + Rs) (2)

In the following description, the emitter-collector saturation voltage is ignored for simplicity. Here, consider a case where the user holds the tablet as shown in FIG. Then, since the Y-axis resistance film 10B and the X-axis resistance film 10A are in surface contact with each other, the resistance value of the contacted portion is reduced. Let us assume that the X-axis resistance film 10A and the Y-axis resistance film 10B have the same resistance value Rt, and consider the equivalent circuit shown in FIG. Then, when all the surfaces are in contact with each other, the X-axis resistance film 10A and the Y-axis resistance film 10B are equivalently combined in parallel, and the detection voltage Vs input to the AD converter 102 is expressed by the formula (3). Like

Vs = Vc × Rs / (Rt / 2 + Rs) (3)

That is, the detection voltage Vs input to the AD converter 102 changes from the value represented by the equation (2) to the value represented by the equation (3) when the user holds the tablet. Therefore, by comparing the binary data output from the output terminal 103 of the AD converter 102 with predetermined binary data, for example, by comparing the size of the binary data using a magnitude comparator or the like,
It can be determined whether or not a touch has occurred. Specifically, when the value is larger than the value represented by the expression (2), it is determined that the touch has occurred. CPU connected to the latter stage of the AD converter 102
When the touch is generated, the XY coordinate data from the tablet input device is invalid and is ignored.

FIG. 7 shows a timing chart of the above operation. Here, in the time from t1 to t2 when the touch is generated, the detection voltage input to the AD converter 102 has a large value shown in Expression (3). Therefore, the XY coordinate data during this period is invalid and is ignored.

Next, consider a case where the tablet 100 is damaged due to some cause. For example, when the Y-axis resistance film 10B is disconnected, the detection voltage V input to the AD converter 102 is detected.
s becomes like Formula (4).

Vs = GND (4) GND represents the ground potential.

On the contrary, the electrodes 11B and 1 of the Y-axis resistance film 10B are
When 2B and 2B are short-circuited, the detection voltage Vs input to the AD converter 102 is as shown in Expression (5). Vs = Vc (5) Vc represents a power supply potential.

That is, when the tablet 100 is damaged, the detection voltage Vs input to the AD converter 102 is
The value represented by the equation (2) changes to the value represented by the equation (4) or the equation (5). Therefore, as in the case where the user touches the tablet, by comparing the binary data output from the output terminal 103 of the AD converter 102 with predetermined binary data, it is possible to determine whether or not the tablet 100 is damaged. . When the tablet is damaged, the CPU connected to the subsequent stage of the AD converter 102 takes measures such as stopping the power supply to the tablet input device and notifying the user of the fact.

Table 1 shows changes in the detection voltage Vs input to the AD converter 102 described above. As can be seen from Table 1, in the means for comparing the binary data output from the output terminal 103 of the AD converter 102 with the predetermined binary data, by having a plurality of predetermined binary data, it is possible to prevent the touch and the tablet from being damaged. It is also possible to distinguish between.

[0034]

[Table 1]

As described above, when the touch is generated, the XY coordinate data from the tablet input device is invalid and is ignored. Therefore, it is possible to prevent a malfunction due to a hand, and it is possible to operate extremely stably. In addition, even if the tablet is damaged, by taking measures such as stopping the power supply to the tablet input device or notifying the user of that fact, excessive current will flow to the tablet, resulting in wasted power consumption and battery consumption. It is possible to provide a tablet input device with extremely high reliability without being damaged.

Next, a second embodiment of the present invention will be described with reference to the drawings. That is, in the above-described first embodiment, since the AD converter 102 is used to check for a finger touch, tablet damage, and the like, FIG.
It is necessary to energize the AD converter 102 even during the period of the check mode shown in (4), and relatively large power is consumed accordingly.

FIG. 8 is a block diagram showing a tablet input device according to the second embodiment of the present invention. Where 5
Is an operational amplifier, the positive input terminal of which is connected to the terminal of the detection resistor 1, that is, the electrode 12B of the Y-axis resistance film 10B. The negative input terminal of the operational amplifier 5 is connected to the voltage dividing resistors 6 and 7. Reference numeral 8 is an output terminal for the detection output of the operational amplifier 5.

In the second embodiment, the detection voltage Vs is not input to the AD converter 102 for processing, but the detection voltage Vs is composed of the operational amplifier 5 and the resistors 6 and 7. It is converted into a binary signal by the analog comparator. The operation of the other parts is the same as that of the first embodiment.

In the device of FIG. 8, the resistance value R6 of the resistor 6 is set as shown in equation (6), and the resistance value R7 of the resistor 7 is set as shown in equation (7). R6 = Rs ... (6) R7 = Rt / 2 ... (7) As a result, the negative input potential Vm of the operational amplifier 5 becomes the value shown in the equation (8).

Vm = Vc × Rs / (Rt / 2 + Rs) (8) Therefore, when the detection voltage Vs input to the AD converter 102 is smaller than the value shown in Expression (8), the operational amplifier 5 is used. The output terminal 8 of is at L level, and conversely when it is high, at H level. Expression (8) is the same as Expression (3) shown above.
When the tablet is damaged and short-circuited, or when the user touches the tablet, the output terminal 8 of the operational amplifier 5 becomes H level. Further, in a normal state, the detection voltage Vs has the value shown in the equation (2) shown above and smaller than the value shown in the equation (8), so that the output terminal 8 becomes the L level. That is, by monitoring the output terminal 8, it can be determined whether the tablet input device is operating normally.

As a result, the AD converter 102 does not need to be energized in the check mode. FIG. 9 shows an AD converter 1
3 is a timing chart showing the energized state of No. 02. FIG.
As shown in FIG. 5, the control of energization to the AD converter 102 can be easily realized by controlling the regulator (not shown) that supplies power to the AD converter 102 using the timing signal Yc.

Further, by connecting a plurality of similar analog comparators in which the values of the resistors 6 and 7 are adjusted in parallel,
As in the case of the first embodiment, it is possible to distinguish the damage and the touch of the tablet.

As described above, according to the second embodiment, in the check mode, the operational amplifier 5 and the resistors 6 and 7 are used.
Since the output of the analog comparator configured by is used, it is not necessary to energize the AD converter 102, and it is possible to detect a touch on the tablet or damage to the tablet with extremely low power consumption.

In all the above embodiments, the Y-axis resistance film 10B has been described as an example.
Regarding the X-axis resistance film 10A, the transistor 2 forming the detection switch, the base resistance 3, the operational amplifier 5 forming the analog comparator, and the resistors 6 and 7 are similarly formed on the X-axis resistance film 10A side. Also has the same effect.

In all of the above embodiments, the transistor is used as an example of the detection switch,
The same effect can be obtained by using a CMOS analog switch or a relay.

[0046]

As described above, according to the tablet input device of the present invention, one electrode of one of the two resistance films of the X-axis and the Y-axis is connected to the power source side. Since the tablet's abnormality is detected by the change in the potential appearing on the other electrode on the output side, the potential appearing on the other electrode will fluctuate accordingly if an abnormality occurs in the resistance film for some reason. By detecting the fluctuation of this potential, the occurrence of abnormality can be immediately detected.

Therefore, for example, when a hand is generated, it is assumed that the XY coordinate data from the tablet input device is invalid, and by ignoring it, a malfunction due to the hand can be prevented in advance, and an extremely stable operation is possible. In addition, even if the tablet is damaged, by taking measures such as stopping power supply to the tablet input device and notifying the user of that fact, excessive current will flow to the tablet and power consumption will be wasted. It is possible to provide a highly reliable tablet input device which can prevent the battery from being damaged and the battery from being damaged.

Further, the tablet input device of the present invention comprises an operational amplifier for comparing the terminal potential of the detection resistor with a predetermined potential, and an AD converter for converting the divided voltage at the indicated position into binary data. Since the power supply to the AD converter is cut off when is running, the power supply to the AD converter is not required in the check mode, and therefore the detection of the touch on the tablet or damage to the tablet is extremely low. It can be realized with power consumption.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a tablet input device according to a first embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the tablet input device shown in FIG.

FIG. 3 is a diagram illustrating the occurrence of a touch.

FIG. 4 is a diagram illustrating a change in resistance value when a touch is generated in the tablet of FIG.

5 is a block diagram showing a configuration of the timing generator of FIG. 1. FIG.

FIG. 6 is a timing chart showing the operation of the timing generator shown in FIG.

7 is a detection voltage V in the tablet input device of FIG.
It is a timing chart which shows change of s.

FIG. 8 is a block diagram showing a configuration of a tablet input device according to a second embodiment of the present invention.

9 is a timing chart showing an energized state of the AD converter of the tablet input device in FIG.

FIG. 10 is a block diagram showing a configuration of a conventional tablet input device.

11 is a perspective view showing the structure of the pressure-sensitive resistance film type tablet shown in FIG.

12 is a timing chart showing the operation of the tablet input device shown in FIG.

[Explanation of symbols]

 1 Detection Resistor 2 NPN Transistor 4 Timing Generator 5 Operational Amplifier 6 Voltage Dividing Resistor 7 Voltage Dividing Resistor 10A Resistive Film 11A Resistive Film 100 Tablet 102 AD Converter

Claims (7)

[Claims] 1. A voltage is applied between electrodes provided on opposite sides of one resistance film of two resistance films of the X-axis and the Y-axis, and the remaining position of the resistance film is divided by the other resistance film. A tablet input device that measures pressure, configured to detect abnormalities in the tablet by connecting one electrode of one of the resistive films to the power supply side and then changing the potential appearing on the other electrode on the output side. A tablet input device characterized in that 2. A detection resistor having one terminal connected to an electrode of one of the resistance films which is not connected to the power supply side, a detection switch connected to the other terminal of the detection resistor, and the detection device described above. A timing generation circuit for controlling opening and closing of the switch, and when the detection switch is controlled to be in an ON state by the timing generation circuit, a series circuit is formed by the power source, the resistance film, and the detection resistor, and the detection resistor is formed. The tablet input device according to claim 1, wherein the tablet input device is configured to detect an abnormality of the tablet based on a change in the terminal potential of the tablet input device. 3. The tablet input device according to claim 2, further comprising an operational amplifier that compares the terminal potential of the detection resistor with a predetermined potential. 4. An AD converter for converting the partial pressure at the indicated position into binary data, which is configured to cut off energization to the AD converter when the operational amplifier is in operation. The tablet input device according to claim 3, wherein 5. An AD converter for converting the partial pressure at the indicated position into binary data is provided, and the AD converter is configured to convert the terminal potential of the detection resistor into binary data. The tablet input device according to claim 2. 6. The tablet input device according to claim 5, further comprising a comparator for comparing the output of the AD converter with predetermined binary data. 7. The tablet input device according to claim 2, wherein the detection switch is composed of a transistor.