JP4656141B2 - Touch panel drive circuit, coordinate input device - Google Patents

Description

  The present invention relates to a touch panel drive circuit that drives a touch panel that includes a pair of resistive films arranged in a superimposed manner, and a coordinate input device that detects the coordinates of contact points of both resistive films using the touch panel drive circuit.

  Conventionally, a coordinate input device that detects a coordinate of a contact point of both resistive films formed by pressing the touch panel using a resistive film type touch panel including a pair of resistive films arranged in a superimposed manner has been provided. Are known.

Here, FIG. 10 is a circuit diagram showing a configuration of a main part of a touch panel drive circuit 120 that drives this type of touch panel 110.
As shown in FIG. 10, the resistance films M1 and M2 constituting the touch panel 110 are formed in a rectangular shape, and the first electrode Di1 and the second electrode Di2 are formed at both ends of each resistance film Mi (i = 1, 2). ing.

  The first electrodes D11 and D21 of the resistance films M1 and M2 are connected to a positive power source (voltage VDD) via the switching transistors T1 and T4, respectively, and the second electrodes D12 and D2 of the resistance films M1 and M2 are connected. D22 is connected to the ground (GND) via switching transistors T2 and T3, respectively.

  The coordinate input device detects voltages (Vx, Vy) corresponding to the coordinates of the contact points of the resistance films M1 and M2 generated by pressing the touch panel 110 by driving the touch panel drive circuit 120 as follows. To do.

  That is, with the transistors T1 and T2 turned on and the transistors T3 and T4 turned off and a current is passed through the resistance film M1, the voltage Vx at the contact point with the resistance film M2 on the resistance film M1 is set to the resistance film M2. Detection is performed via the electrode D21 (or D22), and then the resistance film on the resistance film M2 is turned on with the transistors T1 and T2 turned off and the transistors T3 and T4 turned on and current is passed through the resistance film M2. The voltage Vy at the contact point with M1 is detected through the electrode D11 (or D12) of the resistance film M1.

  When the detection voltage (Vx, Vy) is converted into coordinates (X, Y) representing the position of the contact point, each electrode Dij (j = 1, 2) obtained when a current is passed through the resistance film Mi. The following conversion equations (1) and (2) are used as the voltage Vij (hereinafter referred to as reference voltage) Vij.

X = (Vx−V11) / (V12−V11) × (Xmax) (1)
Y = (Vy−V21) / (V22−V21) × (Ymax) (2)
However, as shown in FIG. 9A, the X coordinate corresponding to the reference voltage V11 corresponds to 0, the X coordinate corresponding to the reference voltage V12 corresponds to Xmax, the Y coordinate corresponding to the reference voltage V21 corresponds to 0, and the reference voltage V22. Let Ymax be the Y coordinate.

  By the way, the reference voltage Vij fluctuates due to factors such as the aging of the resistance films M1 and M2 and the circuit and the change of the use environment (for example, temperature). Therefore, in order to maintain detection accuracy, the reference voltage Vij The voltage Vij needs to be measured again (also called calibration).

  However, considering the case where such a coordinate input device is applied to, for example, a home electronic device, it is not desirable to perform calibration by manual operation because it forces the user to perform the operation.

  Therefore, in order to automatically execute calibration, output terminals for taking out voltages are provided to all the electrodes Dij of the resistance films M1 and M2, and an A / D converter is connected to each of them, so that any time A configuration in which the reference voltage Vij can be detected has been proposed (see, for example, Patent Document 1).

In particular, the device described in Patent Document 1 (hereinafter referred to as a conventional device) detects the reference voltages V11 and V12 when detecting the detection voltage Vx, and also detects the reference voltages V21 and V22 when detecting the detection voltage Vy. Every time one measurement is performed, all six voltages defining the above-described conversion equations (1) and (2) are acquired.
Japanese Patent No. 3072750

However, the conventional apparatus has a problem in that the circuit configuration becomes large because an output end and thus an A / D converter is provided for each electrode Dij.
Further, when the detection voltage Vx and the reference voltages V11 and V12 necessary for the conversion thereof are measured with different A / D converters when Vy and V21 and V22 necessary for the conversion are measured, A / D conversion is performed. There is also a problem that the detection accuracy deteriorates due to the influence of the offset voltage of the detector.

  Instead of providing an A / D converter for each electrode Dij, the number of A / D converters is selected by using a changeover switch that selectively switches the output from each electrode Dij and supplies it to the A / D converter. However, in this case, there is a problem that a large number of changeover switches are required and the configuration becomes large. In particular, in the conventional apparatus, since it becomes impossible to measure a plurality of voltages at the same time by reducing the number of A / D converters, there is a problem that the measurement time required for one measurement increases.

  Furthermore, in applications where the fluctuation of the reference voltage does not fluctuate significantly (for example, when applied to a device used in the home), measuring the reference voltage Vij each time only takes time. There was also a problem of being useless.

  In order to solve the above-described problems, the present invention provides a touch panel drive circuit for driving a touch panel that can reduce the number of A / D converters while minimizing the addition of the configuration and maintaining detection accuracy. It is another object of the present invention to provide a coordinate input device using the touch panel drive circuit.

  The touch panel drive circuit according to claim 1, which is an invention made to achieve the above object, includes a first resistor and a second resistor formed in a rectangular shape having a first electrode at one end and a second electrode at the other end. A touch panel in which the films are overlapped so that the arrangement directions of the first and second electrodes of each resistance film are orthogonal to each other is driven.

  The current supply circuit selectively allows a current to flow between the first and second electrodes of one of the first and second resistance films, and the output circuit is connected to the first electrode of the first resistance film. A first detection voltage that is a voltage and a second detection voltage that is a voltage of the first electrode of the second resistance film are detected.

Furthermore, in the present invention, the bypass switch is configured to conduct and block between the second electrodes of each resistance film.
In the touch panel drive circuit configured as described above, the voltage of the second electrode of the first resistive film can be detected via the first electrode of the second resistive film by conducting the bypass switch. The voltage of the second electrode of the second resistive film can be detected via the first electrode of the first resistive film.

  That is, according to the touch panel drive circuit of the present invention, only by providing a bypass switch, a dedicated output terminal for detecting the voltage of the second electrode (and thus an A / D converter or a changeover switch connected to the output terminal) ) Can be omitted, and the device configuration of the device that digitally processes the output of the touch panel drive circuit can be reduced in size.

  Note that the output circuit preferably includes an output selection switch that alternatively outputs one of the first detection voltage and the second detection voltage, as described in claim 2, for example.

In this case, it is possible to output the first detection voltage and the second detection voltage via a single output terminal, and hence A / D conversion by a single A / D converter.
Therefore, according to the present invention, not only the device configuration of the device that digitally processes the output of the touch panel drive circuit can be reduced in size, but also the voltage of the first electrode, the voltage of the second electrode for one resistive film, Since the detection voltage can be output via a single output terminal and A / D conversion can be performed using a single A / D converter connected thereto, the offset of the A / D converter It is possible to prevent a decrease in detection accuracy due to the influence of the above.

  The output circuit may include two output selection switches as described in claim 3. In this case, in addition to the effect of the second aspect, the voltage related to the first resistance film is output to the output of one output selection switch, and the voltage related to the second resistance film is output to the output of the other output selection switch. By controlling so, the processing for the output of the touch panel drive circuit can be simplified.

  That is, if it is known which voltage is output from which output selection switch, it is possible to determine which resistance film the voltage is, so that it is not necessary to separately add information to identify this, and the processing is simplified. Can be

  Next, the invention according to claim 4 is a coordinate input device configured using the touch panel drive circuit according to any one of claims 1 to 3, wherein a preset start condition is satisfied. The calibration measurement unit executes the first to fourth reference measurement controls.

  In the first reference measurement control, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes a current through the first resistance film, and the first detection voltage is detected via the output circuit. Thus, the first reference voltage representing the voltage of the first electrode of the first resistance film is detected.

In the second reference measurement control, the touch panel drive circuit is set so that the bypass switch is turned on and the current supply circuit passes a current through the first resistance film, and the second detection voltage is detected via the output circuit. The second reference voltage representing the voltage of the second electrode of the first resistive film is detected.

In the third reference measurement control, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes the current through the second resistive film, and the second detection voltage is detected via the output circuit. The third reference voltage, which is the voltage of the first electrode of the second resistance film, is detected.

In the fourth reference measurement control, the touch panel drive circuit is set so that the bypass switch is turned on and the current supply circuit passes the current through the second resistance film, and the first detection voltage is detected via the output circuit. The fourth reference voltage that is the voltage of the second electrode of the second resistive film is detected.

  Since the coordinate input device of the present invention configured as described above is configured by using the touch panel drive circuit according to any one of claims 1 to 3, the same effect as this can be obtained.

Furthermore, in the coordinate input device according to claim 5, when the contact detection circuit detects contact between the first resistance film and the second resistance film, the normal measurement means executes the first and second coordinate measurement controls. .
In the first coordinate measurement control, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes the current through the first resistance film, and the second detection voltage is detected via the output circuit. The first axial voltage corresponding to the position of the contact point with the second resistive film on the first resistive film is detected.

  In the second coordinate measurement control, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes a current through the second resistance film, and the first detection voltage is detected via the output circuit, A second axial voltage corresponding to the position of the contact point with the first resistive film on the second resistive film is detected.

  Then, the coordinate generation means is detected by the normal measurement means using a conversion formula that defines the correspondence between the first and second axis voltages and the position coordinates of the contact point using the first to fourth reference voltages. The position coordinates of the contact point are obtained from the first and second axis voltages.

  In the coordinate input device of the present invention configured as described above, the measurement of the first and second axis voltages is performed at a timing different from the measurement of the first to fourth reference voltages, and according to the operation of the touch panel. Since only the first and second axis voltages need be detected when obtaining the coordinates, the coordinates can be obtained quickly.

  Further, in the coordinate input device of the present invention, the calibration measuring means detects the detected first to fourth reference voltages when they are out of a predetermined allowable range, as described in claim 6. It is desirable that the result is discarded, and the coordinate generation means defines the conversion formula using the first to fourth reference voltages that have been normally detected last by the calibration measurement means.

In this case, when the detection results of the first to fourth reference voltages clearly show abnormal values, it is possible to reliably prevent the calculation of inaccurate coordinates using this.
Further, as described in claim 7, the temperature detection means for detecting the ambient temperature, the time measurement means for measuring time, and the detection results of the calibration measurement means correspond to the detection results of the temperature detection means and the time measurement means. And a history value storage means for storing the attached value as a history value, the coordinate generation means uses the temperature at which the first to fourth reference voltages are normally detected last and the temperature detection means. If the temperature difference from the detected current temperature exceeds the preset allowable temperature difference, the history value that has the smallest temperature difference from the current temperature among the history values stored in the history value storage means within the past fixed period You may comprise so that a conversion formula may be prescribed | regulated using a value.

  In other words, even if the detection results of the first to fourth reference voltages are abnormal, the conversion formula is defined using the history value that is normally detected at a temperature close to the current temperature. The accuracy of detection is not greatly deteriorated, and the reliability of detection can be maintained.

Embodiments of the present invention will be described below with reference to the drawings.
<Overall configuration>
FIG. 1 is a perspective view showing an external appearance of a multifunction machine in which a coordinate input device to which the present invention is applied is incorporated.

  The multi-function device 1 is a multi-function device (MFD: Multi Function Device) having a main body 1a integrally having a printer unit 2 at the bottom and a scanner unit 3 at the top, and a receiver 1b provided on a side surface of the main body 1a. It has a printer function, a scanner function, a copy function, a facsimile function, a telephone function, and the like. In the multifunction device 1, functions other than the printer function may be omitted, and for example, it may be configured as a single-function printer.

  The multifunction device 1 is connected mainly to an external information device such as a computer or a communication line, and based on print data including image data and document data received via the external device and communication line, an image is recorded on a recording sheet. And record documents. Note that the multifunction device 1 is connected to a digital camera or the like, and records image data output from the digital camera or the like on a recording sheet or is loaded with various storage media such as a memory card and recorded on the storage medium. It is also possible to record image data or the like on a recording sheet.

  As shown in FIG. 1, the main body 1a has a wide and thin, generally rectangular parallelepiped outer shape whose width and depth are larger than the height. The scanner unit 3 located at the upper part of the main body 1a is provided below the document cover 3a provided as a top plate of the multifunction machine 1 so as to be freely opened and closed, and a platen on which a document to be read is placed. It consists of glass and an image sensor that optically reads a document placed on the platen glass, and is configured as a so-called flatbed scanner.

  An opening 4 is formed in the front of the printer unit 2 located at the lower part of the main body 1a, and a paper feed tray and a paper discharge tray are provided in two upper and lower stages inside the opening 4. In addition, a slot portion 5 in which various small memory cards as storage media can be loaded is provided above the opening 4.

  On the front side of the upper surface of the main body 1a, there are provided various operation buttons 7 and a display panel 8, and an operation panel 6 for operating the printer unit 2, the scanner unit 3, the receiver 1b, and the slot unit 5 is provided. In addition, the touch panel 11 which comprises the coordinate input device 10 (refer FIG. 3) mentioned later is provided in the surface of the display panel 8. FIG.

  For example, as shown in FIG. 2, the coordinate input device 10 detects the coordinates of the position touched by the user when a soft key is displayed on the display panel 8 together with an explanation about the operation procedure. Then, it is specified which soft key is operated.

<Coordinate input device>
FIG. 3 is a block diagram including a circuit diagram for explaining the configuration of the coordinate input device 10.
As shown in FIG. 3, the coordinate input device 10 includes a resistive film type touch panel 11 including a pair of resistive films M1 and M2 arranged in an overlapping manner, a touch panel drive circuit 20 that drives the touch panel 11, and a touch panel drive. The control unit 30 controls the operation of the circuit 20 and obtains the position coordinates indicating the position of the contact point where the two resistance films M1 and M2 are in contact with each other when pressed by the user based on the output from the touch panel drive circuit 20.

  The resistance films M1 and M2 constituting the touch panel 11 are formed in a rectangular shape, and a first electrode Di1 and a second electrode Di2 are formed on both ends of each resistance film Mi (i = 1, 2), respectively. .

<Touch panel drive circuit>
The touch panel drive circuit 20 includes switching transistors T1 and T4 connected between the first electrodes D11 and D21 of the resistance films M1 and M2 and a positive power supply (voltage VDD), and the first of the resistance films M1 and M2. The switching transistors T2 and T3 connected between the two electrodes D12 and D22 and the ground (GND), the voltage (first detection voltage in the present invention) of the first electrode D11 of the resistance film M1, and the resistance film M2 A pair of output circuits 21 and 22 each configured to selectively output one of the voltages of the first electrode D21 (second detection voltage in the present invention), and the second electrode D12 of the resistance film M1 A bypass switch SW3 that conducts / cuts off the second electrode D22 of the resistance film M2 is provided.

  In the following, the arrangement direction (vertical direction in the figure) of both electrodes D11 and D12 of the resistance film M1 is defined as the X-axis direction, and the arrangement direction of both electrodes D21 and D22 of the resistance film M2 (left and right direction in the figure). The Y-axis direction is assumed.

The output circuit 21 is used for detecting a voltage value necessary for calculating the X-axis coordinates, and the output circuit 22 is used for detecting a voltage value necessary for calculating the Y-axis coordinates.
The output circuit 21 receives the output from the output selection switch SW1 with high impedance, and alternatively outputs one of the voltages of the first electrodes D11 and D21 of the resistance films M1 and M2. A buffer 23 and a low-pass filter (LPF) 25 that removes unnecessary noise components from the output of the buffer 23 are provided.

On the other hand, the output circuit 22 includes an output selection switch SW 2, a buffer 24, and an LPF 26, similarly to the output circuit 21.
The output circuits 21 and 22 are connected to resistors 27 and 28 for pulling up the outputs of the switches SW1 and SW2 (that is, the inputs of the buffers 23 and 24) to the power supply voltage VDD, respectively. Note that the resistance values of the resistors 27 and 28 are set to a value (for example, 100 times or more) sufficiently larger than the resistance between the electrodes Di1 and Di2 of the resistance film Mi.

  The touch panel drive circuit 20 configured as described above has seven types of settings (contact detection setting, X axis detection setting, Y axis detection setting, first reference voltage detection setting, second reference voltage detection setting, 3 reference voltage detection setting, 4th reference voltage detection setting).

  Hereinafter, the settings of the transistors T1 to T4 are represented by {T1, T2, T3, T4}, and the settings of the switches SW1 to SW3 are represented by {SW1, SW2, SW3}. The first and second electrodes Dij are simply referred to as electrodes Dij.

<< Contact detection setting >>
In the contact detection setting, {T1, T2, T3, T4} = {off, on, off, off}, {SW1, SW2, SW3} = {D21 side,-, off}. However, {-} in the setting of the switches SW1 and SW2 indicates that either side may be connected.

As a result, the power supply voltage VDD is applied to the electrode D21 via the resistor 27 and the switch SW1.
Here, if the resistance films M1 and M2 are in a non-contact state (the touch panel 11 is not operated), since the transistor T3 is turned off, no current flows through the resistance film M2. The output of the output circuit 21 set on the side is held at the power supply voltage VDD.

  On the other hand, when the resistance films M1 and M2 are in a contact state (the touch panel 11 is operated), a current flows from the electrode D21 to the electrode D12 connected to the on-set transistor T2 via the contact point. The output of the electrode D21, and hence the output of the output circuit 21, drops below the power supply voltage VDD by the voltage drop at the resistor 27.

  That is, when the touch panel drive circuit 20 is driven with the contact detection setting, it is possible to determine whether or not the touch panel 11 has been operated by monitoring the output voltage level of the output circuit 21.

<< X-axis detection setting >>
In the X axis detection setting, {T1, T2, T3, T4} = {on, on, off, off}, {SW1, SW2, SW3} = {D21 side,-, off}.

As a result, a current flows through the resistance film M1 via the transistors T1 and T2 set to ON and the electrodes D11 and D12.
If the resistance films M1 and M2 are in contact, the voltage at the contact point appears at the electrode D21. Therefore, the output of the output circuit 21 set on the electrode D21 side is the resistance film M1 (that is, the coordinate X). X-axis voltage Vx corresponding to the position of the contact point on the axis).

<< Y-axis detection setting >>
In the Y-axis detection setting, {T1, T2, T3, T4} = {off, off, on, on}, {SW1, SW2, SW3} = {−, D11 side, off}.

As a result, a current flows through the resistance film M2 via the transistors T3 and T4 set to ON and the electrodes D21 and D22.
Here, if the resistance films M1 and M2 are in contact, the voltage at the contact point appears at the electrode D11, and therefore the output of the output circuit 22 set on the electrode D11 side is the resistance film M2 (that is, the coordinate Y). Y-axis voltage Vy corresponding to the position of the contact point on the axis).

<< First reference voltage detection setting >>
In the first reference voltage detection setting, {T1, T2, T3, T4} = {on, on, off, off}, {SW1, SW2, SW3} = {D11 side,-, off}. That is, only the setting of the switch SW1 is different from the X-axis detection setting.

  As a result, a current flows through the resistance film M1 via the transistors T1 and T2 set to ON and the electrodes D11 and D12. The output voltage level of the output circuit 21 set on the electrode D11 side is the first reference voltage V11 which is the voltage of the electrode D11 when a current flows between the electrodes D11 and D12 (that is, the resistance film M1). Become.

<< Second reference voltage detection setting >>
In the second reference voltage detection setting, {T1, T2, T3, T4} = {on, on, off, off}, {SW1, SW2, SW3} = {D21 side,-, on}. That is, only the setting of the switches SW1 and SW3 is different from the first reference voltage detection setting.

  As a result, a current flows through the resistance film M1 via the transistors T1 and T2 set to ON and the electrodes D11 and D12. Further, the voltage of the electrode D12 appears on the electrode D21 via the switch SW3, the electrode D22, and the resistance film M2.

  Accordingly, the output voltage level of the output circuit 21 set on the electrode D12 side is the second reference voltage V12 that is the voltage of the electrode D12 when current flows between the electrodes D11 and D12 (that is, the resistance film M1). Become.

<< Third reference voltage detection setting >>
In the third reference voltage detection setting, {T1, T2, T3, T4} = {off, off, on, on}, {SW1, SW2, SW3} = {−, D21 side, off}. That is, only the setting of the switch SW2 is different from the Y-axis detection setting.

  As a result, a current flows through the resistance film M2 via the transistors T3 and T4 set to ON and the electrodes D21 and D22. The output voltage level of the output circuit 22 set on the electrode D21 side is the third reference voltage V21 that is the voltage of the electrode D21 when current flows between the electrodes D21 and D22 (that is, the resistance film M2). Become.

<< 4th reference voltage detection setting >>
In the fourth reference voltage detection setting, {T1, T2, T3, T4} = {off, off, on, on}, {SW1, SW2, SW3} = {−, D11 side, on}. That is, only the setting of the switches SW2 and SW3 is different from the third reference voltage detection setting.

  As a result, a current flows through the resistance film M2 via the transistors T3 and T4 set to ON and the electrodes D21 and D22. Further, the voltage of the electrode D22 appears at the electrode D11 via the switch SW3, the electrode D12, and the resistance film M1.

  Therefore, the output voltage level of the output circuit 22 set on the electrode D11 side is the fourth reference voltage V22 which is the voltage of the electrode D22 when current flows between the electrodes D21 and D22 (that is, the resistance film M2). Become.

<Control unit>
Next, the control unit 30 includes a two-channel A / D converter (ADC) in which an X-axis output circuit 21 is connected to one channel CH1 and a Y-axis output circuit 22 is connected to the other channel CH2. ) 31 and a control circuit 33 for generating a drive signal for driving the transistors T1 to T4 and the switches SW1 to SW3 constituting the touch panel drive circuit 20, and for taking in the output of the ADC 31 and storing it in the memory 35; An operation mode (normal measurement mode / calibration measurement mode / standby mode) is designated for the control circuit 33, and an operation on the touch panel 11 (based on the AD conversion data stored in the memory 35 by the control circuit 33) And a CPU 37 for executing a coordinate input process for obtaining coordinates representing a touched position.

  Further, the control unit 30 includes a temperature sensor 38 that detects the temperature around the touch panel 11 and the touch panel drive circuit 20, and a timer 39 for measuring time and date. Furthermore, at least a part of the memory 35 (hereinafter referred to as a non-volatile area) includes a non-volatile memory that can retain stored contents even when the power is turned off, or a memory that is backed up by an auxiliary power source or the like. The non-volatile area of the memory 35 includes calculation parameters used for calculating the coordinates X and Y (first to fourth reference voltages V11, V12, V21, V22 updated in S750 or S760 described later, and S820 described later. As shown in FIG. 8, the first to fourth reference voltages V11, V12, V21, and V22 obtained by the calibration process to be described later, as shown in FIG. 8, in addition to the coordinate offset values TXmin, TXmax, TYmin, TYmax) A history value table is stored that stores the measurement results associated with the measurement temperature, date and time, the determination result of the presence or absence of abnormality of the detected value (hereinafter, history values).

  In the description so far, the voltages supplied via the output circuits 21 and 22 of the touch panel drive circuit 20 are represented by Vij, Vx, and Vy. In the following description, the A / D converter 31 is used. The measurement data corresponding to these voltages after A / D conversion is also expressed using the same symbols.

<Normal measurement mode>
Here, the control executed by the control circuit 33 when the operation mode is set to the normal measurement mode will be described with reference to the flowchart shown in FIG.

  As shown in FIG. 4, the control circuit 33 set in the normal measurement mode first sets the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 to contact detection settings in S110, and in the subsequent S120, from the ADC 31. The A / D conversion data of the channel CH1, that is, the voltage VR of the electrode D21 is read.

  In S130, it is determined whether or not the read voltage VR is larger than a preset threshold value Vth. The threshold value Vth is the resistance value R1 of the resistor 27, the maximum value R2 of the total resistance of the resistance films M1 and M2, and the divided value of the power supply voltage VDD by the on-resistance R3 of the transistor T2 (VDD × (R2 + R3) / (R1 + R2 + R3) ) Is set to a larger value (for example, VDD / 2).

If it is determined in S130 that the voltage VR is equal to or higher than the threshold value Vth, the touch panel 11 is assumed not to be operated and the process proceeds to S220.
In S220, it is determined whether or not to continue this operation mode (here, the normal measurement mode). If not, the present control is terminated, and if continued, the process returns to S120. In this determination, for example, when the operation mode is switched to a mode other than the normal measurement mode, it is determined that the measurement is not continued.

On the other hand, when it is determined in S130 that the voltage VR is smaller than the threshold value Vth, it is assumed that the touch panel 11 is operated, and the process proceeds to S140.
In S140, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to X-axis detection. In subsequent S150, the A / D conversion data of the channel CH1, that is, the X-axis voltage Vx is read from the ADC 31 and stored in the memory. 35.

  In S150, A / D conversion data is continuously read a plurality of times (for example, 8 times), the average value of the remaining data from which the maximum value and the minimum value are removed is calculated, and the average value is used as measurement data. It may be stored in the memory 35 (the same applies to S170, S320, S340, S360, and S380 described later).

  In S160, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to detect the Y axis. In subsequent S170, the A / D conversion data of the channel CH2, that is, the Y axis voltage Vy is read from the ADC 31 to store the memory. 35.

  In S180, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to contact detection again. In subsequent S190, the A / D conversion data of the channel CH1, that is, the voltage VR of the electrode D21 is read from the ADC 31. In S200, it is determined whether or not the read voltage VR is equal to or higher than the threshold value Vth.

  When it is determined that the voltage VR is smaller than the threshold value Vth, the operation on the touch panel 11 is assumed to be continued, and the process returns to S190 and repeats S190 to S200 to stand by. On the other hand, if it is determined that the voltage VR is equal to or higher than the threshold value Vth, it is determined that the operation on the touch panel 11 has been released, and the process proceeds to S210.

In S210, the CPU 37 is notified that the measurement data, that is, the A / D conversion data of the X-axis voltage Vx and the Y-axis voltage Vy is stored in the memory 35, and the process returns to S120.
That is, when the control circuit 33 is operated in the normal measurement mode, the X-axis voltage Vx and the Y-axis voltage Vy are measured (A / D conversion) each time an operation on the touch panel 11 is performed, and the measurement data is stored in the memory 35. In addition to being stored, the CPU 37 is notified to that effect (with measurement data).

<Calibration measurement mode>
Next, the control executed by the control circuit 33 when the operation mode is set to the calibration measurement mode will be described with reference to the flowchart shown in FIG.

  As shown in FIG. 5, the control circuit 33 set in the calibration measurement mode first sets the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 to the first reference voltage detection setting in S310, and then continues to S320. Then, the A / D conversion data of the channel CH 1, that is, the first reference voltage V 11 is read from the ADC 31 and stored in the memory 35.

  In S330, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to the second reference voltage detection setting. In the subsequent S340, the A / D conversion data of the channel CH1, that is, the second reference voltage V12 is read from the ADC 31. And stored in the memory 35.

  In S350, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to the third reference voltage detection setting. In the subsequent S360, the A / D conversion data of the channel CH2, that is, the third reference voltage V21 is read from the ADC 31. And stored in the memory 35.

  In S370, the transistors T1 to T4 and the switches SW1 to SW3 of the touch panel drive circuit 20 are set to the fourth reference voltage detection setting. In the subsequent S380, the A / D conversion data of the channel CH2, that is, the fourth reference voltage V22 is read from the ADC 31. And stored in the memory 35.

  In S390, the CPU 37 is notified that the measurement of the first to fourth reference voltages V11, V12, V21, V22 is completed and the A / D conversion data as the measurement result is stored in the memory 35. End control.

  That is, when the control circuit 33 is operated in the calibration measurement mode, the first to fourth reference voltages V11, V12, V21, and V22 are automatically measured, and the measurement data is stored in the memory 35. (End of measurement) is notified to the CPU 37.

<Standby mode>
Next, the control executed by the control circuit 33 when the operation mode is set to the standby mode will be described with reference to the flowchart shown in FIG.

The control circuit 33 set to the standby mode operates in S910 to S930 in the same manner as S110 to S130 in the normal measurement mode, and waits until the touch panel 11 is operated.
When the touch panel 11 is operated and an affirmative determination is made in S930, the process proceeds to S940, the CPU 37 is notified that the touch panel 11 has been operated, and the present control is terminated.

<Coordinate input processing>
Next, coordinate input processing executed by the CPU 37 will be described with reference to the flowchart shown in FIG.

  Here, as shown in FIG. 9B, the size of the display area of the display panel 8 is smaller than the size of the detection area of the touch panel 11, and the display area of the display panel 8 is the detection area of the touch panel 11. It is assumed that both panels 8 and 11 are fixed so that they are arranged in the vicinity of the center and the X-axis direction and Y-axis direction of both regions exactly coincide.

Further, this process is started when the multifunction device 1 is powered on.
When this process is started, first, in S510, the first to fourth references necessary for setting conversion equations for converting the X-axis voltage Vx and Y-axis voltage Vy into coordinates X and Y representing the position where the touch panel 11 is operated. A calibration process (described later) for obtaining the voltages V11, V12, V21, and V22 (in some cases, offset values TXmin and TXmax of the X coordinate and offset values TYmin and TYmax of the Y coordinate) is executed.

  In S520, the operation mode of the control circuit 33 is set to the normal measurement mode, and in subsequent S530, it is determined whether or not a notification with measurement data (notification in S210) is received from the control circuit 33. The process proceeds to S540.

  In S540, the measurement data Vx, Vy stored in the memory 35 and the calculation parameters (first to fourth reference voltages V11, V12, Vs) obtained in the calibration process S510 and stored in the nonvolatile area of the memory 35 are calculated. Based on V21, V22 and the offset values TXmin, TXmax, TYmin, TYmax), the coordinates of the position touched on the touch panel 11 (and thus the display panel 8) are calculated using the following equations (3) and (4). To do.

X = [(Vx−V11) / (V12−V11) × (TXmax−TXmin)] + TXmin (3)
Y = [(Vy−V21) / (V22−V21) × (TYmax−TYmin)] + TYmin (4)
In subsequent S550, the calculated result is transferred to the display control process of the display panel 8 which is separately executed, and the process returns to S520.

  As shown in FIG. 9B, the first to fourth reference voltages V11, V12, V21, and V22 represent voltages detected when the end of the detection area of the touch panel 11 becomes a contact point. The offset values TXmin, TXmax, TYmin, and TYmax represent the X and Y coordinates corresponding to the reference voltages V11, V12, V21, and V22 according to the coordinate system of the display panel 8.

  On the other hand, if it is determined in S530 that the measurement data is not received from the control circuit 33, it is determined in S560 whether or not the sleep condition is satisfied. If the sleep condition is not satisfied, the process proceeds to S530. Returning, if the sleep condition is satisfied, the process proceeds to S570.

Specifically, it is assumed that the sleep condition is satisfied when an input to the device 1 including an operation on the operation panel 6 is not continuously performed for a predetermined time or more.
In S570, the operation mode of the control circuit 33 is set to the standby mode. In the subsequent S580, the process waits until the sleep release condition is satisfied. When the sleep release condition is satisfied, the process returns to S510. The sleep release condition includes at least an operation of the touch panel 11, that is, a case where a notification is received from the control circuit 33 operating in the standby mode.

  In other words, in this process, calibration is executed only when the apparatus is activated and when the apparatus returns from the sleep state, and the measurement for coordinate calculation is repeatedly executed after the calibration is completed.

<Calibration process>
Next, the calibration process executed in S510 will be described with reference to the flowchart shown in FIG.

  In this process, first, in S710, the operation mode of the control circuit 33 is set to the calibration measurement mode, and in the subsequent S720, the process waits until a measurement end notification (notification in S390) is received from the control circuit 33.

  When the measurement end notification is received from the control circuit 33, the current temperature is obtained from the temperature sensor 38 and the current date and time are obtained from the timer 39 in S730. Then, in S740, the measurement result stored in the memory 35 by the control circuit 33. Whether or not (first to fourth reference voltages V11, V12, V21, V22) is a normal value is determined by whether each reference voltage Vij is a value within a preset allowable range. To do. At this time, the determination result is stored in the history value table (see FIG. 8) together with the current temperature and the current date and time acquired in S730.

  If it is determined in S740 that all the measurement results are normal values, the process proceeds to S750, and the calculation parameters (first to fourth reference voltages V11, V12, (V21, V22) is updated with the measurement result, and the process proceeds to S770.

  On the other hand, if it is determined in S740 that any one of the measurement results has an abnormal value, the calculation stored in the non-volatile area of the memory 35 based on the history value stored in the history value table. The parameters for use (first to fourth reference voltages V11, V12, V21, V22) are updated, and the process proceeds to S770.

  Specifically, from the history values stored in the history value table, the newest history value whose determination result is normal is extracted, the detected temperature of the extracted history value, and the current value acquired in S730 If the temperature difference from the temperature is within a preset allowable temperature difference, the extracted history value is used as the update value.

  If the above temperature difference exceeds the allowable temperature difference, a history value having the smallest temperature difference from the current temperature is extracted from the history values stored in the history value table within the past certain period. The newly extracted history value is used as the update value.

In S770, it is determined whether or not manual calibration is to be performed. If not, the process is terminated. If it is to be performed, the process proceeds to S780.
Note that the manual calibration is performed, for example, when a special operation defined in advance is applied immediately after the power is turned on. The special operation may be applied via the operation panel 6, or a dedicated switch or the like may be provided separately.

  In S780, the operation mode of the control circuit 33 is set to the normal measurement mode, and the reference coordinates (Xa, Ya), (Xa, Yb), (Xb, Ya), (Xb, Yb) are displayed on the display panel 8. Is displayed, and the user touches the four points, so that four measurement data (X-axis voltage, Y-axis voltage) Vxa, Vya, Vb corresponding to the coordinate values Xa, Ya, Xb, Yb, Vxb and Vyb are acquired.

  However, Xa, Xb, Ya, Yb are known values having a relationship of Xa <Xb, Ya <Yb. For example, the lower limit value of the X coordinate given to the display area of the reference coordinate display panel 8 is 0. , Upper limit value: Xmax, lower limit value of Y coordinate: 0, upper limit value: Ymax (see FIG. 9B).

  In subsequent S790, based on the measurement data Vxa, Vya, Vxb, Vyb acquired in S780 and the first to fourth reference voltages V11, V12, V21, V22 updated in S750 or S760, the following (5) to ( 8) The X coordinate offset values TXmin and TXmax and the Y coordinate offset values TYmin and TYmax are calculated using the equation (8).

TXmin = Xa − {(Vxa−V11) / (Vxb−Vxa) × (Xb−Xa)} (5)
TXman = Xb + {(V12−Vxb) / (Vxb−Vxa) × (Xb−Xa)} (6)
TYmin = Ya − {(Vya−V21) / (Vyb−Vya) × (Yb−Ya)} (7)
TYman = Yb + {(V22−Vyb) / (Vyb−Vya) × (Yb−Ya)} (8)
In S800, a confirmation point representing known confirmation coordinates (for example, either the center coordinates of the display panel 8 or the reference coordinates) is displayed on the display panel 8, and the user touches the confirmation point. The X-axis voltage Vx and the Y-axis voltage Vy corresponding to the confirmation point are acquired.

  In S810, the first to fourth reference voltages V11, V12, V21, and V22 (that is, calculation parameters) updated in the previous S750 or S760, and the offset values TXmin, TXmax, TYmin, TYmax calculated in the previous S790. The coordinate (X, Y) is calculated based on the X-axis voltage Vx and the Y-axis voltage Vy acquired in S800 using the above-described conversion equations (3) and (4) defined by It is determined whether or not the error with respect to the confirmation coordinates is within a preset allowable error.

  If the error is larger than the allowable error, the offset value calculated in S790 is discarded and the process returns to S780, and manual calibration (S780 to S810) is performed again. For example, the process proceeds to S820, and the calculation parameters (offset values TXmin, TXmax, TYmin, TYmax) stored in the non-volatile area of the memory 35 are updated by the calculated value in S790, and this process is terminated.

<Effect>
As described above, in the coordinate input device 10, the touch panel drive circuit 20 includes the switch SW3 for conducting / cutting off the electrodes D12 and D22 of the resistance films M1 and M2, and switches the voltage of the electrode D12 of the resistance film M1 to the switch. SW3, electrode D22, resistive film M2, and electrode D21 can be detected, and the voltage of electrode D22 of resistive film M2 can be detected through switch SW3, electrode D12, resistive film M1, and electrode D11. Yes.

Therefore, according to the coordinate input device 10, it is not necessary to provide a dedicated output circuit or A / D converter in order to detect the voltages of the electrodes D12 and D22, and the configuration of the device can be simplified.
Further, the coordinate input device 10 includes two output circuits 21 and 22 that alternatively output the voltages of the electrodes D11 and D21, and the reference voltage V11, which is necessary for calculating the X coordinate via the one output circuit 21. V12 and X-axis voltage Vx are detected, and reference voltages V21 and V22 and Y-axis voltage Vy necessary for calculating the Y-coordinate are detected via the other output circuit 22, and each of them is detected by the A / D converter 31. Detection is performed on different channels.

  Therefore, according to the coordinate input device 10, even if each channel of the output circuits 21 and 22 and the A / D converter 31 has a different offset, the influence is canceled in the process of calculating the coordinates. Therefore, the coordinates can be obtained with high accuracy.

  In the coordinate input device 10, the measurement (calibration) of the reference voltage Vij is performed when the device is turned on or when the device returns from the sleep state, and the touch panel 11 is operated during the subsequent operation in the normal measurement mode. Sometimes, only the measurement of the X-axis voltage Vx and the Y-axis voltage Vy is performed.

  That is, the coordinate input device 10 built in a device used indoors, such as the multifunction machine 1, etc., changes so much that the error of the reference voltage Vij cannot be ignored due to a rapid temperature change during use. This is because the possibility of performing calibration is extremely low and it is not necessary to perform calibration every time the touch panel 11 is operated.

  Therefore, according to the coordinate input device 10, each time the touch panel 11 is operated, the coordinates X and Y are compared with the conventional device that measures not only the X-axis voltage Vx and the Y-axis voltage Vy but also the reference voltage Vij. The amount of processing required for the calculation can be reduced, and the time required for the processing can also be shortened.

Further, according to the coordinate input device 10, when any one of the measured reference voltages Vij is not within the preset allowable range, the detected temperature is selected from the history values as past measurement results. If there is no latest history value in which the temperature difference between the current temperature and the current temperature is less than or equal to the allowable temperature, or if there is no history value in which the temperature difference is less than or equal to the allowable temperature, the history value stored in the past certain period Since the reference voltage Vij is updated with the history value having the smallest temperature difference, it is possible to prevent the low-precision coordinates X and Y from being calculated by the abnormal reference voltage Vij.
[Other Embodiments]
In the above embodiment, the two output circuits 21 and 22 are provided, and the voltages Vx, V11, and V12 used for calculating the X-axis coordinate X and the voltages Vy, V21, and V22 used for calculating the Y-axis coordinate Y, The A / D converter 31 is supplied to different channels via the output circuits 21 and 22 to perform A / D conversion. However, the output circuit 22 is omitted, and these are converted into A / D converters. You may comprise so that A / D conversion may be carried out by one channel of D converter 31. FIG.

  In the above embodiment, the offset values TXmin, TXmax, TYmin, TYmax used in the conversion formula are obtained by manual calibration. However, as shown in FIG. 9A, the detection area size of the touch panel 11 and the display on the display panel 8 are displayed. If the region sizes match, these offset values are known (TXmin = 0, TXmax = Xmax, TYmin = 0, TYmax = Ymax), and therefore the processing of S770 to S820 may be omitted. Good. In this case, formulas (5) to (8) are not necessary, and formulas (1) and (2) can be used instead of formulas (3) and (4).

  In addition to these formulas, for example, when there is a case where the detection area of the touch panel 11 and the display area of the display panel 8 may cause a shift in which the directions of the X axis and the Y axis do not coincide, A calculation formula may be used.

  In the above-described embodiment, the conditions for executing the calibration are the time when the power is turned on and the time when the device returns from the sleep state. However, the present invention is not limited to this. It is also possible to use a command from

  In the above embodiment, the electrodes D11 and D21 and the positive power source are connected / disconnected by the transistors T1 and T4, and the electrodes D12 and D22 and the ground are connected / disconnected by the transistors T2 and T3. In place of the transistor pair, for example, a switch of one input and three outputs is used to connect a power supply or ground to the input side, and one of the output side is left unconnected, and the remaining two outputs are electrodes D11, D21 or D12 , D22 may be connected.

  In the above embodiment, the output circuits 21 and 22 (switches SW1 and SW2) are connected to the electrodes D11 and D21, and the switch SW3 is connected between the electrodes D12 and D22. The switch SW3 may be connected between the electrodes D11 and D21 and connected to the electrodes D12 and D22. However, in this case, the resistors 27 and 28 may be connected to the ground GND instead of the power supply VDD.

  In the above embodiment, one end of the resistors 27 and 28 is directly connected to the power source VDD. However, when the drop in the detection voltage due to the influence of the resistors 27 and 28 cannot be ignored, the resistors 27 and 28 are connected to the power source via the switch. The switch may be connected to VDD, and these switches may be turned on and used only when contact is detected.

The perspective view which shows the external appearance of the multifunctional device with which the coordinate input device was integrated. Explanatory drawing which shows the example of a display of a display panel. The block diagram containing the circuit diagram which shows the structure of a coordinate input device. The flowchart which shows the content of the control which a control circuit performs at the time of normal measurement mode. The flowchart which shows the content of the control which a control circuit performs at the time of a calibration measurement mode. The flowchart which shows the content of the coordinate input process which CPU performs. The flowchart which shows the content of the calibration process. Explanatory drawing which shows the content of a history value table. Explanatory drawing which shows the relationship between the detection area of a touch panel, its detection value, the display area of a display panel, and its coordinate. The circuit diagram which shows the structure of the conventional touch panel drive circuit. The flowchart which shows the content of the control which a control circuit performs at the time of standby mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... MFP 1a ... Main body 1b ... Receiver 2 ... Printer part 3 ... Scanner part 3a ... Document cover 4 ... Opening 5 ... Slot part 6 ... Operation panel 8 ... Display panel 10 ... Coordinate input device 11 ... Touch panel 20 ... Touch panel drive circuit 21, 22 ... Output circuit 23, 24 ... Buffer 25, 26 ... Low pass filter (LPF) 27, 28 ... Resistor 30 ... Control unit 31 ... A / D converter 33 ... Control circuit 35 ... Memory 37 ... CPU 38 ... Temperature sensor 39 ... Timers for timing M1, M2 ... Resistive film SW1, SW2 ... Output selection switch SW3 ... Bypass switch T1-T4 ... Transistor

Claims (7)

First and second resistance films formed in a rectangular shape having a first electrode at one end and a second electrode at the other end are arranged such that the arrangement directions of the first and second electrodes of each resistance film are orthogonal to each other. A touch panel driving circuit for driving a touch panel formed by overlapping,
A current supply circuit for selectively passing a current between the first and second electrodes of any one of the first and second resistance films;
An output circuit for detecting a first detection voltage that is a voltage of the first electrode of the first resistance film and a second detection voltage that is a voltage of the first electrode of the second resistance film;
A bypass switch for conducting and blocking between the second electrodes of the resistive films;
A touch panel drive circuit comprising: The output circuit is
The touch panel drive circuit according to claim 1, further comprising an output selection switch that alternatively outputs one of the first detection voltage and the second detection voltage.   The touch panel drive circuit according to claim 2, wherein the output circuit includes two output selection switches. The touch panel drive circuit according to any one of claims 1 to 3,
When a preset start condition is satisfied, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes a current through the first resistance film, and the output circuit A first reference measurement control for detecting a first reference voltage representing a voltage of the first electrode of the first resistive film by detecting a first detection voltage; and the bypass switch is turned on and the current supply circuit is The voltage of the second electrode of the first resistive film is set by detecting the second detection voltage through the output circuit by setting the touch panel drive circuit so that a current flows through the first resistive film. And a second reference measurement control for detecting a second reference voltage representing the setting, and the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes a current through the second resistance film. Te, by detecting the second detection voltage through the output circuit, and a third reference measurement control for detecting the third reference voltage is the voltage of the first electrode of the second resistive film, the bypass switch There turned on and the current supply circuit is set to the touch panel drive circuit to flow a current to the second resistive film, by detecting the first detection voltage through the output circuit, the second Calibration measurement means for executing a fourth reference measurement control for detecting a fourth reference voltage which is a voltage of the second electrode of the resistance film;
A coordinate input device comprising:
A contact detection circuit for detecting contact between the first resistance film and the second resistance film;
When the contact detection circuit detects a contact, the touch panel drive circuit is set so that the bypass switch is turned off and the current supply circuit passes a current through the first resistance film, and the first circuit is connected via the output circuit. A first coordinate measurement control for detecting a first axis voltage corresponding to a position of a contact point with the second resistance film on the first resistance film by detecting two detection voltages; and the bypass switch Is turned off and the current supply circuit sets the touch panel drive circuit so that a current flows through the second resistance film, and detects the first detection voltage via the output circuit, whereby the second resistance is detected. Normal measurement means for executing second coordinate measurement control for detecting a second axis voltage corresponding to the position of the contact point with the first resistive film on the film;
The first detected by the normal measurement means using a conversion formula that defines the correspondence between the first and second axis voltages and the position coordinates of the contact point using the first to fourth reference voltages. Coordinate generating means for determining the position coordinates of the contact point from the first and second axis voltages;
The coordinate input device according to claim 4, further comprising: The calibration measurement unit discards the detection result when the detected first to fourth reference voltages are out of a predetermined allowable range,
The coordinate generating means, coordinates according to 請 Motomeko 5 you characterized by defining the transformation formula used last successfully detected the first to fourth reference voltage at the calibration measurement means Input device.
Temperature detecting means for detecting the ambient temperature;
A time measuring means for measuring time;
A history value storage means for storing, as a history value, a result of detection by the calibration measurement means, which corresponds to a detection result of the temperature detection means and the time measurement means;
With
The coordinate generation unit is configured to obtain an allowable temperature difference in which a temperature difference between a temperature at which the first to fourth reference voltages are normally detected last time and a current temperature detected by the temperature detection unit is set in advance. When exceeding, the conversion formula is defined using the history value having the smallest temperature difference from the current temperature among the history values stored in the history value storage means within the past certain period. The coordinate input device according to claim 6.