JP2014025811A - Capacitance-coupled electrostatic sensor - Google Patents

Abstract

The present invention provides a capacitive coupling type sensor capable of accurately determining ON / OFF of a switch by increasing sensitivity and further greatly reducing the influence of external noise.
A current flowing between a plurality of switch electrodes and a conductive member is converted into a voltage by a current / voltage conversion circuit and a signal generated by an oscillator is synchronized by synchronous oscillation circuits. The converted sin signal and cos signal are converted. A multiplication circuit 19 that multiplies the sin signal and the cos signal is provided, and the output signal of the multiplication circuit 19 is stabilized by the low-pass filter circuit 21 and then converted into a DC signal, and the converted DC voltage is measured, Compare the threshold values stored in the arithmetic unit.
[Selection] Figure 6

Description

  The present invention relates to an input device using a capacitive coupling method as an input method.

  Conventionally, a capacitive coupling touch switch is known as an input device using the capacitive coupling method. The touch switch includes a panel switch and a control board. The panel switch has an electrode sheet printed with silver paste or ITO (indium tin oxide) as a switch electrode on the surface of a PET film that becomes an insulator, and an insulating base material that becomes an insulator such as acrylic, glass, and resin. Consists of those bonded with adhesive (double-sided tape, etc.). When a finger or hand approaches the switch electrode, a parallel plate capacitor is formed between the switch electrode and the finger or hand, and capacitance is generated. This change in capacitance is converted to a frequency by a C / F conversion circuit (a circuit that converts capacitance C to frequency F) formed by a capacitor C and a resistor R, and the frequency is converted into an input capture function (number of frequencies). Is replaced with digital data, and the on / off state of the touch switch is determined by arithmetic processing. When there are a plurality of switch electrodes, the switch electrodes are selected by a switching circuit provided for each switch electrode (see Patent Document 1).

The touch switch using the capacitive coupling method detects an area where the finger or hand can touch the switch electrode, and detects that the finger or hand approaches the switch electrode. It is a digital input device that detects on / off.
The switch electrode forms a touch switch by printing an electrically conductive material on the surface of the PET film by a screen printing method. Screen printing is a printing method that uses an squeegee (rubber spatula or metal spatula) to push out ink from the space between the yarns called the opening (screen plate) and form an image pattern. It is a method rooted in Japan as a traditional craft such as sushi and printing. Further, the thickness of the completed image pattern is the thickness of the screen plate used. Currently, screen printing has been established as an indispensable method in the electronics field, and screen printing is always used in the production of printed wiring boards, electronic components, flat panel displays, and automobile meters. It is known.

The switch electrode is printed by using silver paste (substance is silver) ink and ITO (indium oxide) (substance is tin) ink, which is a conductive material, on the surface of the PET film that becomes an insulator by screen printing. Forming a switch. The thickness of the screen plate for forming the switch electrode is 10 to 30 μm. Further, silver paste ink and ITO (indium tin oxide) ink, which are conductive materials, have high resistivity values, and have an area resistance of several Ω to several kΩ / cm 2.
Switch electrodes printed by the screen printing method have a printing speed determined by the moving speed of the squeegee, the viscosity of the ink, the expansion and contraction of the plate depending on the printing environment, and the size and thickness of the switch electrode for each printing are in units of several millimeters. It is said that it is difficult to make the variation in size and thickness zero by a difference of several μm. Therefore, the resistance value of the switch electrode for each printing is not constant, and it is difficult to suppress the variation in the resistance value for each printing to 0Ω.

  The frequency when a switch in which a switch electrode is formed on a PET film is used as an input area of the touch switch can be expressed by t = 0.7 × C × R by the capacitor C and the resistor R. The switch electrode has a resistance value of ΔR. The frequency of the switch electrode is generated as a frequency obtained by adding the resistance value ΔR of the switch electrode to the resistance R. The frequency t can be expressed by t = 0.7 × C × (R + ΔR).

Find the frequency when there are four switch electrodes. When the switch switches of the switch electrodes are SW1 to SW4, the resistance values can be expressed as SW1 (resistance value: ΔR1), SW2 (resistance value: Δ2), SW3 (resistance value: Δ3), SW4 (resistance value: Δ4). The frequency of each switch electrode is SW1 frequency t = 0.7 × C × (R + ΔR1)
SW2 frequency t = 0.7 × C × (R + ΔR2)
SW3 frequency t = 0.7 × C × (R + ΔR3)
SW4 frequency t = 0.7 × C × (R + ΔR4)
It can be expressed as
Further, there is a variation in resistance value in units of several ohms to several tens of ohms for each screen printing. When the resistance value of variation is Δr, each frequency for each printing is SW1 frequency t = 0.7 × C × (R + Δ1 + Δr).
SW2 frequency t = 0.7 × C × (R + Δ2 + Δr)
SW3 frequency t = 0.7 × C × (R + Δ3 + Δr)
SW4 frequency t = 0.7 × C × (R + Δ4 + Δr)
It can be expressed as
In recent years, electronic circuits using digital technology have been widely used, and radio wave interference due to frequencies from low to high of digital signals is likely to occur.
For example, if you bring a radio receiver to the side of an appliance such as a TV, you will get noise and noise. This is because the radio receiver picks up the radio noise generated from the appliance.
In addition, when AC power is supplied to a radio receiver, noise may be mixed into the AC power line and picked up as power noise depending on the wiring of the household power supply. When an electric appliance such as a TV and a radio receiver are connected to the same AC power outlet, the radio receiver picks up the power noise generated from the connected electric appliance, and noise enters.
As countermeasures against the noise contamination in the living environment, there are countermeasures for preventing noise from being mixed into the device, or countermeasures for improving noise resistance so as not to cause a failure even when receiving noise. However, in the current situation, it is difficult to take measures against noise because it is not known what kind of noise is mixed in the living environment.
The method of converting the change in capacitance into a frequency by a C / F conversion circuit is to convert the change in capacitance into C
The frequency is converted into a frequency (t = 0.7 × C × (R + ΔR)) by the / F conversion circuit, and the change in the frequency is replaced with digital data by the input capture function. Since this system is operated using frequencies, the influence of mixing of frequencies, which are noises generated in the living environment, is unavoidable.

In addition, the frequency generated when a switch in which a switch electrode is printed on a PET film is used as a touch switch in a method of converting a change in capacitance into a frequency using a C / F conversion circuit. It turns out that it changes with the shape of.
On the other hand, in the literature 2 and the literature 3, there is a capacitance type sensor that avoids the influence of noise in a situation where the frequency of the noise generated in the living environment and the frequency of the signal to be detected cannot be distinguished. Proposed.

JP 2005/084982 A US Patent Application Publication No. 2007/0257890 JP 2011-008725 A

In Patent Document 1, the change in capacitance is converted to a frequency by a C / F conversion circuit, and the frequency obtained by the switch electrode is the same as the radio noise or supply power that is the same or close to the frequency obtained by the switch electrode. Alternatively, when power supply noise having a close frequency is mixed, the frequency generated by the C / F circuit and the noise frequency are synchronized with each other or interfere with each other, and even if a finger or a person approaches the switch electrode, The electric capacity is not changed, and a malfunction such as an inability to input occurs.
Since the frequency to be generated varies depending on the size of the switch electrode, the number of generated frequencies increases as the number of switch electrodes having different sizes increases. Therefore, the number of touch switches that malfunction due to radio wave noise or power supply noise that is the same as or close to the generated frequency increases. In the method of converting the change in capacitance into a frequency by the C / F conversion circuit, if the frequency of ± several tens of KHz is not separated from the frequency of the noise, it cannot escape from the noise and the range of malfunction due to the noise increases. Dealing with noise is very difficult.

  In addition, the change in capacitance is replaced with digital data using the C / F conversion circuit, and the frequency is replaced with digital data by the input capture function (function for counting the number of frequencies), and the on / off state of the touch switch is determined by arithmetic processing. ing. By counting the number of frequencies with the input capture function, the number of frequencies changes for each switch electrode, and it is very difficult to keep the operation speed constant and increase the speed.

Further, in Patent Document 2, the capacitance at the intersection of at least one detection electrode and at least one drive electrode is measured at three different signal frequencies, and averaged or majority determined from the three measured values. Or, from the median, the true capacitance at the intersection was determined.
However, in the case where the two types of noise have the same frequency as two of the three frequencies being measured, there is a risk that a true capacitance may not be determined. Furthermore, when a model using the same frequency is in contact with the vicinity, there is a possibility that a malfunction may occur due to interference between the frequencies.

Similarly, in Patent Document 3, the true capacitance is determined by majority using one or more detection signal frequencies for one sensor. When the frequency of three or more detection signals is N, and the noise has the same frequency as that of a detection signal of a type equal to or less than N / 2, Patent Document 2 cannot determine a true capacitance. There is a risk of malfunction.
Similarly, in the method of detecting the electrostatic capacitance at the intersection of at least one detection electrode and at least one drive electrode, it is recommended that the distance between the detection electrode and the drive electrode be as small as possible. .5 mm to 1 mm or less is desirable. In addition, since the amount of shielding is determined by the size of the finger that shields the capacitive electric field, it is recommended that the detection electrode and the driving electrode fall within 5 mm × 5 mm to 12 mm × 12 mm. The narrow spacing reduces the diffusion of the capacitive electric field in the vertical direction, and the amount of interruption increases rapidly when the finger approaches. In addition, since the interval is narrow, the capacitive electric field is also large and is hardly affected by noise.

  The present invention is a touch switch in which a plurality of switch electrodes made of a conductive material are arranged on an insulator, the plurality of switch electrodes are provided in parallel to each other, and a conductive member is connected to each switch electrode, and the conductive member In order to measure the capacitance change between the plurality of switch electrodes, the current flowing between the plurality of switch electrodes and the conducting member is converted into a voltage by a current / voltage conversion circuit and generated by an oscillator. In order to convert the signal into a sin signal and a cos signal synchronized by the synchronous oscillation circuit and drive the switch electrode to which the sin signal is applied, wiring connected to the switch electrode and another switch electrode The wiring connected to is connected to the control unit, and the current / voltage converted voltage by the current / voltage conversion circuit is multiplied by the sin signal and the cos signal. A multiplication circuit, the sin signal and the cos signal are stabilized by a low-pass filter circuit and converted to a DC signal by the multiplication circuit, the converted DC voltage is measured, and the voltage and operation unit are measured. According to a first aspect of the present invention, there is provided a capacitive coupling type electrostatic sensor characterized by comparing ON and OFF of a switch by comparing stored threshold values. In the second aspect, the gap between the switch electrodes is hollow, and in the above capacitive coupling type electrostatic sensor, the third point is that the wiring leading to the switch electrode is drawn from the center of each switch electrode. In the above capacitive coupling type electrostatic sensor, the switch electrode is surrounded by an intermediate potential or ground. It is intended to.

  In the present invention, even in a capacitively coupled electrostatic sensor having a wide interval between switch electrodes, the switch electrodes are provided in parallel to each other, so that the sin signal and the cos signal having a phase difference of 90 degrees are output from the current / voltage conversion circuit. By multiplying by a multiplication circuit, only an AC signal having a true current value becomes a double AC frequency including a DC signal, and becomes a DC signal by passing through a low-pass filter. Even if the switch electrodes are connected, all the frequencies are higher than the frequency of the sin signal, and noise can be eliminated by passing the low-frequency filter with the AC signal having a high frequency. For this reason, even if a noise frequency other than the frequency of the sin signal is mixed into the switch electrode, a capacitance is accurately generated between the switch electrode and the finger and hand, and the on / off state of the touch switch can be detected. it can.

Electrode structure diagram. Electrode arrangement drawing. Finger, capacitive electrostatic field and electrode structure diagram. Capacitive electric field diagram viewed from the vertical direction. A plurality of capacitive electric field interference diagrams. Input device block diagram. Multiplication circuit waveform diagram. Input signal level and phase difference diagram. The relationship diagram of a finger and a switch electrode. Sine signal multiplication waveform diagram.

In the present invention, even in a capacitively coupled electrostatic sensor having a wide interval between switch electrodes, the switch electrodes are provided in parallel to each other, one of the parallel switch electrodes is referred to as a switch drive electrode, and the other is referred to as a switch receiving electrode. In each electrode group, a switch drive electrode of the switch drive electrode group to which a sin signal is applied, a drive conduction member for connecting the switch drive electrode, a current / voltage conversion circuit, and a switch reception electrode of the switch detection electrode group via the switch driving electrode A reception conducting member is connected, and a signal generated by an oscillator is oscillated by a synchronous transmission circuit to oscillate two signals, a sin signal and a cos signal having a phase difference of 90 degrees. One of the sin signals is an amplifier circuit and a switching circuit. The switch driving electrode is driven via, and connected to the resistor R of the current / voltage conversion circuit via the switch receiving electrode and the switching circuit. A capacitor is formed between the switch drive electrode of the switch drive electrode group having these wirings and the switch reception electrode of the switch reception electrode group to constitute one touch switch. At this time, if the switch drive electrode of the switch drive electrode group not connected by the switching circuit and the switch receive electrode of the switch receive electrode group are arranged at positions away from the switch electrode constituting the touch switch, It may be in an unconnected state. However, if it is in the vicinity, there is a possibility that the unconnected switch electrodes receive noise from disturbance and interfere with the switch electrodes constituting the touch switch. It is desirable to connect to an intermediate potential or ground.
One of the sin signals is connected to a multiplication circuit. The cos signal is connected to another multiplication circuit. The output of the current / voltage conversion circuit is connected to two multiplication circuits through an amplifier circuit and a bandpass filter circuit, and is multiplied by a sin signal and a cos signal, respectively. Only an AC signal having a true current value has a double AC frequency including a DC signal, and becomes a complete DC signal by passing through a low-pass filter circuit.
Noise other than the frequency of the sin signal and the cos signal mixed into the switch electrode group becomes an AC signal having a frequency higher than the frequency of the sin signal / cos signal by multiplication with the sin signal / cos signal. It can be eliminated by passing through a low-pass filter circuit sufficiently lower than the signal frequency.

Further, by controlling the frequency of the signal generated by the oscillator, the signal from the oscillator can be converted into a sin signal and a cos signal by the synchronous transmission circuit, and the frequency of the sin signal and the cos signal can be set. Since a bandpass filter can be provided to remove noise of harmonic components and low frequency components in the frequency band of the sin signal to be used, a bandpass filter corresponding to the frequency of the sin signal can be used. desirable.
Here, in the initialization state such as when the power is turned on, the sin signal in a state where the finger and hand are not in contact with the individual switch electrodes connected to the drive of the sin signal and the resistor R of the current / voltage conversion circuit. The vector value of the input signal is stored in the control device from the detection signal X obtained by multiplication with the detection signal Y obtained by multiplication with the cos signal. The vector value at this time is called an offset value, the sine signal side is called an Xoffset value, and the cos signal side is called a Yoffset value.
When measuring the state of the finger, hand, and switch electrode, the capacitance between the drive of the sin signal and the switch electrode connected to the resistor R of the current / voltage conversion circuit is measured, and the sin signal at that time The difference between the vector value and the offset value of the input signal from the detection signal Y obtained by multiplication of the detection signal X and the cos signal by multiplication with the equation root (square of (X−Xoffset) + square of (Y−Yoffset)) calculate.
If this calculated value is equal to or greater than the threshold, it is determined that the finger and hand are in contact with the vicinity of the switch electrode, and if it is equal to or less than the threshold, the finger and hand are separated from the switch electrode. Judged off. Furthermore, by providing another threshold value, two threshold values corresponding to the ON / OFF state of the switch electrode before the calculation can be used, and the hysteresis is controlled for the ON / OFF of the switch electrode with respect to the calculated value. It can also be done.
Similarly, other switch electrodes are also performed.

Here, when measuring noise with the same frequency as the sin signal mixed in the switch electrode, the offset value is the switch drive when all the wiring to be driven is unconnected or at a constant voltage such as an intermediate potential or ground. Since there is no signal from the electrode side, the offset value is set to zero. At the time of measurement, the vector value of the input signal is changed from the detection signal Y obtained by multiplication with the sin signal to the expression signal (the square of X + the square of Y) from the detection signal Y obtained by multiplication of the cosine signal. When the value is equal to or greater than the value for determining the presence or absence of mixing, it is determined that noise is mixed and the frequency of the signal from the oscillator is changed.
Then, at the time of initialization, whether or not noise is mixed is determined as described above to determine whether or not there is noise of the same frequency as the sin signal that drives the switch electrode. In the case of noise mixing, the signal frequency generated by the oscillator is changed, the signal from the oscillator is converted into a sin signal and a cos signal by the synchronous transmission circuit, the frequency of the sin signal and the cos signal is changed, and the noise is again generated. The presence or absence of contamination is determined. If it is determined that there is no noise, the switch electrode is measured and the touch switch is turned on / off.

  Hereinafter, the present invention will be described in detail by way of examples.

FIG. 1 shows an electrode structure diagram of the first embodiment.
The electrodes of the touch switch are a switch drive electrode 1 and a switch receiving electrode 2, which are formed by parallel straight lines. The length s is the same, and the thickness t is preferably 0.3 mm to 1 mm for a copper pattern on a substrate, and 0.5 mm to 1 mm for a silver paste or ITO on a film or glass. There is also the maximum dimension. Even if it is excessively thick, there is no merit in only increasing noise and using a large area. The switch drive electrode 1 is connected to the switching circuit 13 by the drive conducting member 3. The switch receiving electrode 2 is connected to the switching circuit 13 by the receiving conducting member 4. The length s and the distance d of the switch electrodes are preferably 5 mm or more in view of the size of the finger. The maximum value is determined by the noise resistance performance of the entire input device, the number and number of fingers used for input, the size of the hand, etc. The length is s if the number of fingers to be input is plural or input by hand. The distance d can be made larger. The drive conductive member 3 is drawn from the center of each electrode of the switch drive electrode 1 and the switch reception electrode 2.
FIG. 2 shows a layout of the electrodes.
FIG. 2A shows a single substrate 6 under the acrylic plate 5 having a thickness of 1 to 5 mm. On the substrate is a drive conducting member 3 connected to the switch drive electrode 1 on the left side, and on the right side. There is a reception conducting member 4 connected to the switch reception electrode 2.
FIG. 2-2 is the reverse of FIG. 2-1. There is a single substrate 6 on the acrylic plate 5 having a thickness of 1 to 5 mm. On the substrate 6, there is a drive conducting member 3 connected to the switch drive electrode 1 on the left side, and a switch receiving electrode on the right side. There is a reception conducting member 4 connected to 2.
In FIG. 2C, there are two substrates 6 under the acrylic plate 5 having a thickness of 1 to 5 mm. On the substrate 6, the drive conducting member 3 connected to the switch drive electrode 1 is connected to the left substrate 6. There is a reception conduction member 4 connected to the switch reception electrode 2 on the right side substrate 6. There is nothing between the left substrate 6 and the right substrate 6. That is, the space between the left substrate 6 and the right substrate 6 is a hollow structure. Further, the acrylic plate 5 may be hollow as well as between the left substrate 6 and the right substrate 6.
FIG. 2-4 is the reverse of FIG. 2-3. On the acrylic plate 5 having a thickness of 1 to 5 mm, there are two substrates 6. On the substrate 6, there is a driving conduction member 3 connected to the switch driving electrode 1 on the left substrate 6. There is a reception conducting member 4 connected to the switch reception electrode 2. There is nothing between the left substrate 6 and the right substrate 6. That is, the space between the left substrate 6 and the right substrate 6 is a hollow structure. Further, the acrylic plate 5 may be hollow as well as between the left substrate 6 and the right substrate 6.

FIG. 3 shows a finger, a capacitive electric field, and an electrode structure diagram.
There are two electrodes under a 1-5 mm-thick acrylic plate or the like with a sufficient interval between the index books, one being the switch drive electrode and the other being the switch receiving electrode. A capacitive electric field is generated between the two electrodes and is represented by a plurality of curves. FIGS. 3A to 3C show a state where the capacitive electric field is cut off when the finger falls from the upper side to the lower side.
If the finger is sufficiently above, the capacitive electric field is not affected at all as shown in FIG.
When the finger falls to the center, the capacitive electric field starts to be cut off by the finger as shown in FIG. 3-2.
When the finger comes down, the capacitive electric field on the acrylic plate is sufficiently blocked by the finger as shown in FIG.
Also, as shown in FIG. 3-4, when the finger is at the left corner between the electrodes, when the finger is at the center as shown in FIG. 3-5, and when the finger is at the right corner as shown in FIG. 3-6. There is no difference in the amount of capacitive electric field that is blocked.
FIG. 4 shows a capacitive electric field diagram viewed from the vertical direction.
A capacitive electric field is generated between and around the switch driving electrode 1 and the switch receiving electrode 2. In particular, many capacitive electric fields 7 are large between the electrodes, indicating that there is little capacitive electric field coming out of both electrodes from the side surfaces of both electrodes. However, the capacitive electric field is blocked by placing a finger or the like close to the electrode.
FIG. 5 shows a diagram in which a plurality of capacitive electric fields interfere.
FIG. 5A shows that the capacitive fields of the two touch switches interfere with each other and the input ranges partially overlap.
FIG. 5B shows that when the set of individual switch electrodes is guarded by a neutral potential or ground, the capacitive electric field does not interfere and the input ranges do not overlap.

FIG. 6 is a configuration diagram in the case of measuring on / off of a touch switch that is an input device according to the first embodiment. First, the control device 24 incorporates a ROM and a working memory in which a program and constants (for example, a threshold value) are incorporated. A signal is output to a sin signal synchronous transmission circuit 10 and a cos signal synchronous transmission circuit 11 that convert a signal from the oscillator 9 into a sin signal and a cos signal. Amplifying circuit 12 that receives and amplifies the sin signal and supplies it to the switch driving electrode, switching control circuit 23 for controlling switching circuit 13 for selecting switch driving electrode 1 of switch electrode group 14, and receiving the sin signal from the switch receiving electrode The switch control circuit 23 for controlling the switch circuit 13 for selecting the switch receiving electrode 2 of the switch electrode group 14 to be performed, and the sin signal synchronization from the signal from the transmitter 9 corresponding to the frequency band of the sin signal from the band pass filter circuit 18. The sin signal of the oscillation circuit and the cos signal of the cos signal synchronous oscillation circuit are input to the multiplication circuit 19. The A / D conversion circuit 22 that converts the signal through the low-pass filter 21 into digital data, the cos signal from the synchronous transmission circuits 10 and 11 and the sin signal through the band-pass filter circuit 18 are multiplied, and the low-pass An A / D conversion circuit 22 that converts a signal that has passed through the filter 21 into digital data, and two A / D conversion digital data are calculated, and touch switch on / off information is obtained from each touch switch I / O. The external I / F 25 that outputs as
Here, in this embodiment, a case where four touch switches are provided will be described as an example. The touch switch is configured by a pair of the switch drive electrode 1 and the switch reception electrode 2 of the switch electrode SW1 of the switch electrode 15 forming the capacitor. Similarly, the touch switch SW2 includes the switch drive electrode 1 and the switch reception electrode 2. The touch switch SW3 is composed of a pair of the switch drive electrode 1 and the switch reception electrode 2, and the touch switch SW4 is composed of a pair of the switch drive electrode 1 and the switch reception electrode 2.

The oscillation frequency output from the oscillator 9 is set by the CPU of the control device 24, and the signal output from the oscillator is converted into a 90-degree phase difference between the sine signal and the cos signal from the two synchronous transmission circuits 10 and 11 and output. . Then, the sine signal is selected by the amplifier circuit 12 by selecting lines for driving the switch electrodes SW1 to SW4 of the four switch electrode groups 14 of the touch switches SW1 to SW4 and connected by the switching circuit 13. The switch drive electrode SW1 selected by the switching circuit 13 by the voltage of the sin signal amplified by the amplifier circuit 12 via any one of the switches SW1 to SW4 of the switch electrode group 14 selected by controlling the switching control circuit 23 from the control device 24. The current flowing through the resistor R is converted into a voltage by the current / voltage conversion circuit 16 through the switch reception electrode 2 of the switch electrode 14 paired with .about.4 and transmitted to the amplification circuit 17.
At this time, the switch electrodes that are not connected are made unconnected by controlling the switching circuit 13 by the switching control circuit 23 according to an instruction from the control device 24. Further, the currents i1 to i4 via the switch electrodes of the touch switches SW1 to SW4 are converted into voltages E1 to E4 by passing through the resistor R, and are amplified by the amplifier circuit 17. Then, the signal output from the oscillator 9 by controlling the switching control circuit 23 passes through the band-pass filter of the band-pass filter circuit 18 corresponding to the band of the sine signal to be generated, and other than the pass band at the frequency of the sine signal. Cut the frequency.
The frequencies output via the switching circuit 13 by the bandpass filter of the bandpass filter circuit 18 are respectively input to the Y side of the two multiplication circuits 19. A sin signal and a cos signal are input to the X side of the two multiplication circuits 19. By passing through each multiplication circuit 19, the result of each multiplication circuit 19 is amplified by the amplification circuit 20, and in the low-pass filter 21 that passes a very low frequency band, the noise signal is eliminated and the DC signal is taken out. Each DC signal is converted into digital data by the A / D converter 22 and input to the control device 24. The control device 24 obtains digital data by sequentially controlling the switching circuit 13 by the switching control circuit 23 in the order of the touch switch SW1, the touch switch SW3, the touch switch SW3, and the touch switch SW4.

FIG. 7 shows a waveform diagram of the multiplication circuit 19 when the on / off state of the touch switch according to the first embodiment is measured. The sin signal 10 or the cos signal 11 is input to the X input of the multiplication circuit 19. One side of the resistor R is connected to the ground. On the opposite side, as shown in FIG. 6, the sin signal that has passed through the amplifier circuit 17 and the band-pass filter circuit 18 is connected to the switch receiving electrode 2 constituting the touch switch via the switching circuit 13.
For example, when a human finger or the like approaches the touch switch SW1 of the connected switch electrode group 14, the current i1 flowing through the switch reception electrode 2 is capacitive from the switch drive electrode 1 to the switch reception electrode 2 by the finger or the like. The electric field is shielded, the current flows through the person and changes, and the potential difference E1 changes at both ends of the resistor R. By inputting this to Y of the multiplication circuit 19, the input signals of X and Y are multiplied, and only the AC signal of the true current value becomes a double AC frequency including the DC signal. It passes through and becomes a DC signal. Even if noise, which is another frequency component, is mixed in the electrodes constituting the touch switch SW1, all noise frequencies are multiplied by the sin signal / cos signal to become an AC signal having a frequency higher than that of the sin signal / cos signal. This can be eliminated by passing the low-pass filter 21 sufficiently lower than the frequency of the sin signal / cos signal. In this way, it is possible to grasp that a human finger or the like is approaching the touch switch.

FIG. 8 shows the input signal level and phase difference diagram of the present invention. The input signal multiplied by the sin signal in the multiplication circuit 19 of FIG. 7 becomes a detection signal by sin, and the input signal multiplied by the cos signal becomes a detection signal by cos. Here, in a state of initialization such as when the power is turned on, a finger, a hand, or the like is placed on the switch drive electrode 1 of the switch electrode group 14 constituting the touch switches SW1 to SW4 and the touch switch of the switch receiving electrode group 2 to be paired. Measurement is performed via the A / D converter 22 from the detection signal X obtained by multiplication with the sin signal and the detection signal Y obtained by multiplication with the sin signal, and the measured value is used as a vector value. The vector value when the power is turned on is called an offset value. Then, the sin signal side of the offset value is the Xoffset value, and the cos signal side is the Yoffset value. When the measurement is performed, the difference between the input signal vector value and the offset value from the detection signal X obtained by multiplication with the sin signal at that time and the detection signal Y obtained by multiplication of the cos signal, the equation route ((X-Xoffset) Squared + (Y-Yoffset) square). The phase difference is obtained from the formula arctangent ((X-Xoffset) / (Y-Yoffset)).
Obtaining and using the vector value and phase difference of the input signal is a very effective means for detecting position coordinates and the like that require accuracy.

FIG. 9 shows the relationship between the finger and the switch electrode.
FIG. 9A shows a case where the finger is far away from the electrodes constituting the touch switch. Even if the human finger 26 is farther than the distance between the switch drive electrode 1 and the switch receiving electrode 2 constituting the touch switch, a capacitance is generated between the finger 26 and the switch drive electrode 1. However, since the capacitance is so small that the current Δi hardly flows from the switch drive electrode 1 to the ground via the finger, the sin signal current i supplied is directly transmitted to the switch receiving electrode 2. Since the voltage levels of the signals are approximately the same, the signal that has passed through the multiplication circuit 19 with the subsequent sin and cos signals does not change.

  FIG. 9-2 shows a case where the finger approaches or comes into contact with the switch electrode constituting the touch switch. Capacitance is generated between the human finger and the switch drive electrode 1 constituting the touch switch and the finger 26, and the current Δi flows to the ground through the finger and loses the current Δi. The signal voltage is reduced. Subsequent signals passing through the multiplication circuit 19 with the sin and cos signals become smaller.

  A human finger measures in advance the currents i1 to i4 when the finger is not touching the switch electrodes SW1 to SW4 of the switch electrode group 14 constituting the touch switch, and the currents Δi1 to 4 when the finger touches the touch switch By setting the thresholds 1 to 4 to be in an on state, the touch switch operates.

  FIG. 10 shows a sin signal multiplication waveform diagram. Multiplying a · sin α and b · sin α yields (a · sin α) · (b · sin α) = (a · b / 2) − (a · b · cos 2α) / 2, where only a · b / 2. Where added, there is a cos signal that is half the frequency doubled. If this calculation result passes through the low-pass filter 21 having a sufficiently low value, the cos signal becomes 0, and only a · b / 2 constants are obtained. Even if a noise frequency other than the frequency of a · sin α is mixed according to this equation, the noise frequency is cut and the influence of the noise frequency is eliminated.

DESCRIPTION OF SYMBOLS 1 Switch drive electrode 2 Switch receiving electrode 3 Drive conduction member 4 Reception conduction member 5 Acrylic board 6 Substrate 7 Capacitive electric field 8 Guard electrode 9 Oscillator 10 sin signal synchronous oscillation circuit 11 cos signal synchronous oscillation circuit 12 amplifier circuit 13 switching circuit 14 switch Electrode group 15 Switch electrode 16 Current / voltage conversion circuit 17 Amplification circuit 18 Band pass filter circuit 19 Multiplication circuit 20 Amplification circuit 21 Low pass filter circuit 22 A / D converter 23 Switching control circuit 24 Controller 25 External I / F
26 fingers

Claims (4)

A touch switch in which a plurality of switch electrodes made of a conductive material are arranged on an insulator, the plurality of switch electrodes are provided in parallel to each other, and a conductive member is connected to each switch electrode, the conductive member and the plurality of switch electrodes In order to measure the capacitance change between, the current flowing between the plurality of switch electrodes and the conducting member is converted into a voltage by a current / voltage conversion circuit,
A signal generated by the oscillator is converted into a sin signal synchronized with a synchronous oscillation circuit and a cos signal, and a wiring connected to the switch electrode is connected to drive the switch electrode to which the sin signal is applied. A wiring circuit connected to another switch electrode is connected to the control unit, and a multiplication circuit is provided for multiplying the current-voltage converted voltage by the current-voltage conversion circuit, the sin signal and the cos signal, The multiplier circuit stabilizes the sin signal and the cos signal by a low-pass filter circuit, converts the signal to a DC signal, measures the converted DC voltage, and calculates the threshold value stored in the voltage and the calculation unit. A capacitive coupling type electrostatic sensor characterized by determining whether the switch is ON or OFF by comparing.   2. The capacitive coupling type electrostatic sensor according to claim 1, wherein a space between the switch driving electrode and the switch receiving electrode is hollow.   2. The capacitive coupling type electrostatic sensor according to claim 1, wherein the drive conduction member reaching the switch drive electrode and the switch reception electrode is drawn from the center of the switch reception electrode. Capacitive coupling type electrostatic sensor. 2. The capacitive coupling type electrostatic sensor according to claim 1, wherein the switch driving electrode and the switch receiving electrode are surrounded by an intermediate potential or ground.

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