JP4010076B2 - Low interference touch panel device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a touch panel device for detecting a touch position of the finger panel, in which is disposed a uniform surface resistance facing the particularly effective area of the panel, passing a AC current to the finger through the panel The present invention relates to a touch panel device that detects the position.
[0002]
[Prior art]
Examples in the art include those shown in US Pat. No. 1,536,723, or those whose details are unclear but those shown in US Pat. No. 2,603,986 and US Pat. No. 1,881,208.
[0003]
[Problems to be solved by the invention]
Of the above-mentioned conventional ones, those that perform time-division signal measurement operations, or when analog multiplexers are used for simplification, miniaturization, cost reduction, and uniformity of parameters for each signal measurement. In the case of two pieces of measurement, when two or more of the same model are used simultaneously close to each other, the detection position is shaken due to mutual interference.
[0004]
[Means for Solving the Problems]
A panel having a uniform surface resistor disposed on an effective area for detecting a finger touch position is provided, and the surface resistor is constantly oscillated by a voltage so that an AC current is passed through the surface resistor to the finger at the time of touch. The AC current at a plurality of connection points between the panel and the signal processing unit or an AC voltage proportional to the AC current is measured in a time-sharing manner, and the finger touch position on the panel is determined based on the measured value. A touch panel device that is calculated from a ratio, and proposes a low-interference touch panel device in which the frequency error of the voltage oscillation is within 1 / (50T) [Hz], thereby reducing interference when using a plurality of devices nearby. It is.
[0005]
[Action]
As a first operation, the absolute value detection type AC signal level demodulation circuit is not affected by the phase change of the AC signal. As a second effect, by stopping all AC signal measurements for one position detection within a time when the total indwelling value flowing through the panel including the current due to interference can be regarded as constant, each signal level is terminated. If the ratio is not shifted, the calculated position will not shift. That is, the same effect is obtained by reducing the error of the vibration frequency of each panel and lowering the beat frequency due to interference.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention has a panel in which a uniform surface resistor is disposed facing an effective area on the principle of operation, and the surface resistor is constantly oscillated by voltage to touch the panel and to conduct electricity corresponding to the finger or the finger. An AC current is passed through the body through the panel, AC signals at a plurality of connection points between the panel and the signal processing unit are measured in a time-sharing manner, and the touch position on the panel is calculated from the ratio of these measured values. Although it is limited to the touch panel device, it is a one-dimensional position detection device or a two-dimensional position detection device.
[0007]
【Example】
Details of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram for explaining the main part of an apparatus according to an embodiment of the present invention and interference during simultaneous operation of two units. When the finger of the person 2 touches the surface of the panel unit 1 (hereinafter referred to as the panel 1), the position (X and Y coordinates on the surface of the panel 1) is detected. The panel 1 is provided with a surface resistor 3 having a uniform resistance value distribution, and a resistive electrode 4 is attached to the periphery thereof. The resistive electrode 4 has a low resistance, and the resistance value between both ends of each side is about 30 to 150Ω. The sheet resistance value of the sheet resistor 3 is about 1 kΩ / □. The finger contact surface of the surface resistor 3 includes an insulating layer and a method in which the finger and the surface resistor 3 are in direct contact. The present invention is applicable to both.
[0008]
Each apex (point A, B, C, D) of the resistive electrode is connected to each input (vibration voltage application circuit 6, 6, 6, 6) of the signal processing unit 7 by each connecting wire 5, 5, 5, 5. Electrically connected. The vibration voltage application circuits 6, 6, 6, and 6 transmit the current flowing through the points A, B, C, and D of the panel 1 to the analog multiplexer 8 (MUX) and connect the vibration voltage of the vibration voltage generator 9 to the connecting wire. Apply to 5, 5, 5, 5. Therefore, the surface resistor 3 is constantly oscillating with voltage.
[0009]
The human body 2 has a grounding effect on the AC component due to the grounding capacity and the like, but is not in a completely grounded state. Therefore, when the finger of the human body 2 touches the surface of the panel 1, an AC current flows to the finger of the human body 2 due to the capacitance between the finger and the surface resistor or by direct contact, and the surface resistor 3 Current distribution occurs. More current flows through the points A, B, C, and D to a place near the point touched by the finger of the human body 2. The touch position is calculated from the ratio of the current flowing through the points A, B, C, and D. At this time, since the human body 2 is not in a completely grounded state, an oscillating voltage of about 20 to 70% of the oscillating voltage of the surface resistor 3 is also generated in the human body 2.
[0010]
The oscillating voltage application circuits 6, 6, 6, and 6 pass a passing current to the circuit ground even when not selected by the analog multiplexer 8 (MUX), and always maintain the input characteristics at a constant condition. Otherwise, the current distribution of the surface resistor 3 fluctuates and it becomes very difficult to calculate the position with high accuracy. The AC signal current passing through the analog multiplexer 8 (MUX) is subjected to signal processing such as current / voltage conversion, band-pass filtering, and AC signal level demodulation, and applied to the A / D converter 10 (A / D). Is done. From each digitized data, the processor 11 (CPU) calculates the position on the surface of the panel 1 touched by the finger of the human body 2.
[0011]
Refer to Japanese Patent Application No. 10-321508 and others for more detailed actual circuit and grounding effect factors of the human body. In the case of the configuration of the panel 1 shown in FIG. 1, it is possible to perform simultaneous measurement instead of time division measurement by the analog multiplexer 8 (MUX), but in that case, a current / voltage conversion circuit, a bandpass filter circuit , Amplifying circuit, AC signal level demodulating circuit, level shift circuit, A / D converter, etc., all need 4 sets, and all these circuit parameters such as gain, phase rotation amount, settling time etc. are the same (Variation should be reduced to 1/500 or less). For the above reasons, not only the device shown in FIG. 1 but almost all devices in the present technical field perform time-division measurement.
[0012]
Regarding the present invention, there are the following three important points as the location conditions. The first point is voltage oscillation of the electrical components of the panel. The second point is that when a finger or a conductor that can be regarded as equivalent to a finger touches the panel surface, an AC current is passed outside the panel (to a finger or the like) through the touch point. The third point is that a uniform surface resistor is arranged facing the effective area for touch detection, and the current flowing there is measured at each point, and the current ratio (or voltage ratio proportional to the current). The touch position is calculated from Therefore, it does not depend on the magnitude of the current flowing through the finger or the like.
[0013]
Here, a case where two or more of the same model are used simultaneously close to each other will be described with reference to FIG. What has been described so far is the first touch panel device. The second touch panel device 14 is in the vicinity and is operated by the second human body 13 in the immediate vicinity of the first human body 2. There is an independent vibration voltage generator similar to the vibration voltage generator 9 in the second touch panel device 14 as well, and there is a slight variation between the frequencies. Therefore, there is a slight difference in the frequency of electrical vibration between the two panels.
[0014]
The second human body 13 has the vibration frequency component of the second touch panel device 14 for the reason described above (explained at the end of paragraph 0009). This is transmitted to the human body 2 via the inter-body capacitance 12 which is inevitably generated, and is also transmitted to the surface resistor 3 after all. The above phenomenon is particularly remarkable when the first human body 2 and the second human body 13 are operating their respective touch panel devices by tying their free hands.
[0015]
That is, the AC signal current flowing at the touch point of the surface resistor 3 is obtained by superimposing the AC signal current transmitted from another device and input on the original AC signal current by the self device. FIG. 4 shows a vector display of this state for easy understanding. Reference numeral 41 denotes an electric vibration phase (reference phase) of the panel 1 of the self apparatus. Reference numeral 43 is a vector display of the original AC signal by the self apparatus, and reference numeral 42 is a vector display of the AC signal transmitted from another apparatus. Since both signals have a frequency difference, the vector 42 rotates, and the locus of the tip of the combined vector is indicated by reference numeral 44 (circular). A composite AC signal represented by this composite vector flows to the touch point of the surface resistor 3. The phase angle varies from Φ1 (45) to Φ2 (46) as shown. FIG. 4 also shows that the phase of the vector 43 (original AC signal current by the self device) is usually advanced by about 70 to 80 degrees from the oscillation voltage phase of the panel 1.
[0016]
Similarly, there is interference from the first device to the second device 14 and they interfere with each other. The influence of these interferences in the conventional apparatus on each AC signal measurement will be described. FIG. 5 shows the combined current (total panel current) flowing through the touch point of the surface resistor 3 in the time domain. The horizontal axis is time (t), and the vertical axis is the positive envelope (envelope) of the combined current (total panel current). When there is interference from another machine, the magnitude of this combined current changes in a sine wave shape as indicated by reference numeral 50, and the frequency (beat frequency) of the change is the vibration voltage generator of each of the two devices. Is equal to the absolute value of the difference in frequency.
[0017]
In the example of FIG. 1, the current values flowing through the four points (A, B, C, D) of the panel 1 are measured in a time-sharing manner, and the coordinates of one point flowing out and inflow from the surface resistor 3 to the outside. ) Is calculated. The time required for all measurements for points A, B, C, and D is T. The magnitude of the touch point current (total panel current) when the current value is measured for point A is the length indicated by reference numeral 51, and reference numerals 52, 53 are also provided for points B, C, and D, respectively. , 54. As described above, the magnitude of the AC current flowing into and out of the panel 1 fluctuates during the measurement for detecting the position once (during T). The main principle of time-sharing measurement is that the total panel current is constant during T. As shown in FIG. 5, when the magnitude of the total current to be used as a reference changes, the ratio of the AC currents at points A, B, C, and D measured in a time-sharing manner also changes, and the calculation result changes. . Furthermore, not only the magnitude of the AC signal but also the phase varies greatly.
[0018]
FIG. 5 shows two actual devices using a touch panel having a configuration shown as a panel 1 having a vibration voltage generator using a ceramic resonator, which is used as a clock for most of the present devices. This is a record of the operation. The electrical vibration frequency of the panel of the device is 20 kHz or more, and in the embodiment shown in FIG. 1, it is 460 kHz. When measuring the level of the AC signal, it is demodulated (converted to DC) and applied to the A / D converter. is doing. The reason is that it is very difficult to measure the level with high accuracy of about 0.1% with the AC signal as it is.
[0019]
FIG. 6 shows an AC signal demodulating circuit used in many present devices. The main part is an analog switch (analog gate) 60. The gate ON / OFF signal is a fixed phase control signal synchronized with the input AC signal. The averaging resistor 61 and the averaging capacitor 62 output the average value of the input AC signal voltage within the gate ON time. Even if a multiplier is used, an equivalent function is obtained. Even with such a simple demodulation circuit, the linearity is very excellent, and it is easy to obtain the ratio of each AC signal level with high accuracy.
[0020]
The influence of the phase change of the demodulation circuit of FIG. 6 will be described with reference to FIG. The gate ON time 74 is fixed in accordance with the positive side section of the original AC signal 70 by the self apparatus. Ideally, the waveform 70 is averaged from t1 to t2, and a demodulation (detection average) level 72 based on the original signal is output. However, when the phase angle of the composite vector shown in FIG. 4 is the minimum (Φ1) 45, the AC signal waveform 71 shown in FIG. 7 is obtained, and the demodulation (detection average) level 73 is averaged from t3 to t4 within the gate ON time 74. Output. Although the AC signals 70 and 71 have substantially the same amplitude, the output levels are greatly changed. It has been found that this is the influence of the phase change in the circuit of FIG. 6 when there is an interference input signal from another device.
[0021]
As a first means for solving the problem, an absolute value detection type AC signal level demodulating circuit irrelevant to the phase change of the AC signal is used. An example is shown in FIG. The poor linearity of the diode is compensated by an operational amplifier. Only at the negative peak of the input AC signal, the diode 21 is turned on, and the absolute value holding capacitor 29 is charged to a voltage symmetrical with respect to the voltage source 27. During other times, the diode 22 becomes conductive, the diode 21 is reverse-biased, and the absolute value holding capacitor 29 is not charged any more. The resistor 28 has an effect of limiting the instantaneous current, causing the operational amplifier 20 to operate stably, and suppressing noise slightly. For the roles and constants of other elements, refer to the description of the reference numerals as a reference example.
[0022]
There is something to note here. Since the operational amplifier 20 serves as a switching control that turns on the diode 21 for a moment in the negative peak of the input waveform, it needs to operate at high speed and with high accuracy. In the case of the AC signal frequency of 460 kHz of the apparatus shown in FIG. 1, an operational amplifier having f _T of 50 MHz or more and SR of 50 V / μs or more is required. If it was less than that, it was impossible to calculate the touch position on the panel with an accuracy of 0.2% or less.
[0023]
Another example is shown in FIG. Instead of an operational amplifier, an inverter / linear amplifier 31 having an amplification degree (value of K) of about 30 is used. At the time of the negative peak of the input AC signal, the absolute value holding capacitor 39 is charged to a voltage symmetric with respect to the center voltage of the dynamic range of the inverter / linear amplifier 31. Although the voltage accuracy between the input and output is not so great, the linearity is within the required range, so the ratio of each AC voltage level can be calculated with high accuracy.
[0024]
By using these absolute value detection type AC signal level demodulation circuits, the amount of shake in calculation of the touch position due to interference from other devices has been reduced to about ½. Further, a second means for reducing the amount of blur due to interference will be described. In FIG. 5, it is sufficient that the beat frequency is low enough that it can be considered that there is no change in the envelope 50 during the measurement time T required for one position detection. Since the touch position is calculated from the ratio of each AC signal level, the magnitude of the total current flowing through the panel 1 is irrelevant. It suffices if the signal S / N ratio is sufficient.
[0025]
As a result of the experiment, it was found that if the cycle of the beat component 50 is 25 times or more of T, the range is acceptable for finger touch position detection. That is,
25T ≦ 1 / | f1-f2 |
Here, f1 is the electric vibration frequency of the panel of the self device, and f2 is the electric vibration frequency of the panel of the other device. The most reliable is to create a master frequency and supply it to all nearby devices with electrical wires. However, this is inconvenient when moving the device.
[0026]
In order to satisfy Equation 1, the frequency error of the electric vibration of the self device (and other devices) is
| F1-fr | ≦ 1 / (50T) [Equation 2]
You can see that. Here, fr is the design reference frequency, and the unit of Equation 2 is [Hz]. In the case of the apparatus shown in FIG. 1, T is 0.01 seconds, fr is 460 kHz, and frequency accuracy of 4 ppm or less is required. Therefore, a stabilized power supply is supplied to the temperature-compensated crystal oscillation circuit. Achieved.
[0027]
Even when the second means alone is used, if there is an insulating layer on the surface of the panel 1 shown in FIG. 1, the calculated blur range of the touch position is practically satisfactory even if the two operators 2 and 13 join hands. When the first and second means are used in combination, the calculated position blur range that does not hinder the above-described conditions even in a direct contact touch panel device without an insulating layer on the surface of the panel 1 is obtained.
[0028]
When three or more units are used in the vicinity, the vector display shown in FIG. 4 is a combination of three or more signals, but both the first unit and the second unit have two units. Has the same effect as time. Various methods of electrical connection between the surface resistor of the touch panel and the signal processing unit have been proposed, but all of those having the location conditions described in paragraph 001 12 have the same phenomenon. The above description applies not only to the two-dimensional panel but also to the one-dimensional panel.
[0029]
【The invention's effect】
Even if two or more units are used simultaneously in the vicinity, the detection blur of the touch position is within a range that does not hinder, and the reliability / reliability of the device is improved.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory view of a main structure of an apparatus according to an embodiment of the present invention and interference when two units are operating.
FIG. 2 shows an example of an absolute value detection type AC signal level demodulating circuit using an operational amplifier.
FIG. 3 shows an example of an absolute value detection type AC signal level demodulation circuit using an inverting amplifier (inverter / linear amplifier).
FIG. 4 is a vector display diagram of an original AC signal and an AC signal input by interference from another device.
FIG. 5 is an envelope waveform diagram (beat waveform diagram) of a current at a touch point due to the presence of an AC signal that causes interference input.
FIG. 6 is a circuit example of AC signal demodulation (AC / DC conversion for level detection) used in many current devices.
FIG. 7 is a diagram showing the influence of a phase change in a conventional fixed-phase synchronous demodulation circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Panel part 2 1st human body 3 Surface resistor 4 Resistive electrode 5 surrounding a surface resistor Connection electric wire 6 Vibration voltage application circuit 7 Signal processing part 8 Analog multiplexer 9 Vibration voltage generator 10 A / D converter 11 Processor 12 Human body capacitance 13 Second human body 14 Second touch panel device 20 Operational amplifier 21 Diode (for example, HSM88)
22 Diode (eg HSM88)
23 Feedback resistance (eg 22 kΩ)
24 Stabilizing capacitor (eg 2pF)
25 Input resistance (eg 22kΩ)
26 coupling capacitors (eg 1000 pF)
27 DC bias voltage source (eg 1.2V)
28 Instantaneous current limiting resistor (eg 220Ω)
29 Absolute value holding capacitor (eg 1000 pF)
30 Discharge resistance (eg 150 kΩ)
31 Inverter / Linear Amplifier 32 Diode (eg HSM88)
33 Diode (eg HSM88)
34 Feedback resistance (eg 22 kΩ)
35 Stabilizing capacitor (eg 2pF)
36 Input resistance (eg 22kΩ)
37 coupling capacitors (eg 1000 pF)
38 Instantaneous current limiting resistor (eg 220Ω)
39 Absolute value holding capacitor (eg 1000pF)
40 Discharge resistance (eg 150 kΩ)
41 Electric vibration phase (reference phase) of self-device panel
42 Vector display of AC signal transmitted from another device 43 Vector display of original AC signal by own device 44 Trajectory 45 of composite vector tip 45 Minimum (advance) phase angle of composite vector 46 Maximum (advance) phase of composite vector Angle 50 Touch point current positive envelope 51 Touch point current magnitude when measuring point A current 52 Touch point current magnitude when measuring point B current 53 Measuring point C current The magnitude of the touch point current when the D point current is measured 54 The magnitude of the touch point current when the D point current is measured 60 Analog switch (analog gate)
61 Averaging resistor 62 Averaging capacitor 70 Original AC signal 71 by own device Signal 72 when φ1 phase angle of combined AC signal of AC signal transmitted from other device and AC signal of own device Demodulation by original signal (Detection average) Level 73 Demodulation (detection average) at φ1 level 74 Measurement time required for position detection for gate ON time T1

Claims (1)

A panel having a uniform surface resistor disposed facing an effective area for detecting a finger touch position is provided, and the surface resistor is constantly oscillated by a voltage so that an AC current is applied to the finger at the time of touch via the surface resistor. The AC current at a plurality of connection points between the panel and the signal processing unit or an AC voltage proportional to the AC current is measured in a time-sharing manner, and the finger touch position on the panel is determined based on the measured value. A low-interference touch panel, characterized in that the frequency error of the voltage oscillation is within 1 / (50T) [Hz], thereby reducing interference when using a plurality of devices in the vicinity. apparatus.

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