JPH0497614A - Touch sensor device - Google Patents

Abstract

PURPOSE:To obtain a sure and stable output signal by using a differentiation circuit so as to detect only a change in the electromotive force of a piezoelectric element, thereby detecting a touch only when a touch is caused. CONSTITUTION:When the piezoelectric element 7 is touched, the output of the piezoelectric element 7 is extracted as a signal for only a change in an electromotive force by the differentiation circuit 12 and the signal is rectified by a diode 13 to input only the positive level of a change in the electromotive force to an integration circuit 16. The integration circuit 16 integrates a positive change in the electromotive force to obtain a stabilized voltage waveform and when the output exceeds a prescribed voltage, a comparator 26 outputs an output signal and only when the piezoelectric element 7 is touched, it is detected independently of a method of a touch or the difference of the touch methods. Thus, a sure and stable output signal is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a touch sensor device using piezoelectric elements such as piezoelectric ceramics.

2. Description of the Related Art In recent years, various touch sensor devices have been invented and put into practice, which output an output when touched by a human body. Some of these include those with contacts, those that use capacitance, and those that use pressure-sensitive elements whose impedance changes with pressure. Touch sensor devices are not necessarily perfect in terms of reliability such as lifespan or cost, and the most appropriate type of touch sensor device for the purpose of use is selected and used.

On the other hand, although the piezoelectric effect of a piezoelectric element that generates an electromotive force due to pressure has been used in many fields, there has been no example of its use as a touch sensor device.

The inventors have developed a touch sensor device that utilizes electromotive force due to the piezoelectric effect of a piezoelectric element. The configuration will be explained below.

As shown in the figure, the piezoelectric element 1 is used as a touch sensor, and one end is grounded.

The other end of the piezoelectric element 1 is input to a comparator circuit 5 consisting of an operational amplifier 'Q2 and a resistor 3.4, and is compared with a predetermined voltage set by the resistor 3.4. Note that 6 is a power source for a resistor 3.4 that sets the base voltage of the operational amplifier 2 and the comparator circuit 6.

In the above configuration, when the piezoelectric element 1 is touched in a tapping manner, an electromotive force as shown in FIG. 6 (-) is generated at both ends due to the piezoelectric effect. An electromotive force as shown in FIG. 6(a) is generated at both ends of 1. The output voltage waveform shown in FIG. 5(a) has a large peak voltage value but a small pulse width, that is, a high frequency component. On the other hand, the output voltage waveform shown in FIG. 6(a) has a large pulse width, that is, a low frequency component, but a small peak voltage value.

When the electromotive force of the piezoelectric element 1 is larger than the predetermined reference voltage set by the resistor 3.4, the output signal from the operational amplifier 2 is as shown in FIG. 6(b) and FIG. 6(b), respectively. Output. At this time, due to the resistance value of the resistor 3°4,
Since the reference voltage of the comparison circuit 5 can be set, desired detection sensitivity can be obtained.

Problems to be Solved by the Invention In such a touch sensor device, unless the electromotive force of the piezoelectric element 1 is input directly to the comparator circuit 5, stress is maintained on the piezoelectric element 1 due to a mounting defect or the like. If this occurs, unstable electromotive force may be generated and malfunction may occur. Furthermore, the detection output shape is not stable due to the touch method and individual differences, making reliable detection difficult, and there is a possibility of erroneous detection in response to noise coming in from outside.

Furthermore, if a severe impact is applied to the piezoelectric element 1 and an electromotive force is generated that may destroy the operational amplifier 2, an overvoltage will be applied to the input terminal of the operational amplifier 2, leading to destruction. At this time, the electromotive force generated by the piezoelectric element 1 outputs not only a positive voltage but also a negative voltage, and the negative voltage is applied to the operational amplifier 2. Therefore, using an operational amplifier with dual power supplies (positive and negative) requires power supplies on the positive and negative sides, which increases costs, and operational amplifiers that use a single power supply are susceptible to malfunction or destruction due to the negative voltage being applied. I will invite you.

Furthermore, although the characteristics of the piezoelectric element 1 change over time due to deterioration over time due to the application of a DC voltage, in the touch sensor device described above, the piezoelectric element 1 is directly connected to the input terminal of the operational amplifier 2. DC voltage continues to be applied to the piezoelectric element 1 due to leakage current from the input terminal 2.

For this reason, the detection sensitivity not only changes over time and requires readjustment, but also may become undetectable.

In this way, the electromotive force due to the piezoelectric effect of piezoelectric elements such as piezoelectric ceramics varies by tens of mV depending on the touch intensity.
The electromotive force output waveform had variable polarity and frequency components due to the touch method and individual differences, making the output signal extremely unstable. Therefore, it is extremely difficult to obtain a stable output signal, and it is also difficult to maintain detection sensitivity.

The present invention is intended to solve this problem, and aims to obtain a reliable and stable output signal by using a wide range of electromotive force, in which the frequency and polarity of the output from the piezoelectric element are not determined depending on the method of touching the piezoelectric element, the difference in the frequency, and the polarity. It is said that

Means for Solving the Problems In order to achieve the above object, the present invention includes a piezoelectric element, a differentiating circuit that inputs the electromotive force of the piezoelectric element, a diode that rectifies the output of the differentiating circuit, and a diode that rectifies the output of the differentiating circuit. an integrating circuit that inputs a rectified signal; and a comparing circuit that compares the output of the integrating circuit with a predetermined voltage, and the comparing circuit outputs an output when the piezoelectric element mentioned above is touched. is used as a means of solving problems.

The present invention uses the above-mentioned problem-solving means to extract only the variation from the electromotive force generated by the piezoelectric element into a differentiator circuit, rectify it with a diode, and stabilize it with an integrator circuit, so that its output remains within a predetermined level. When the voltage exceeds the voltage value, the comparison circuit outputs an output signal, and only when the piezoelectric element is touched, it can be output regardless of the touch method or difference.

Example An embodiment of the present invention will be described below with reference to FIG.

As shown in the figure, the piezoelectric element 7 is used as a touch sensor, and a resistor 8 and a capacitor 9 are connected to both ends thereof, and one end is grounded. The other end of the piezoelectric element 7 is connected to an input I7 to a differentiating circuit 12 consisting of a capacitor 10 and a resistor 11. The output of this differentiating circuit 12 is input to the anode of a diode 13, and the cathode of the diode 13 is connected to the input of an integrating circuit 16 consisting of a resistor 14 and a capacitor 15.

The cathode of a Zener diode 17 is connected to the output of the integrating circuit 16, and the anode is grounded.

Further, a resistor 18 is connected in parallel with the Zener diode 17. Operational amplifier 19 constitutes an amplifier circuit 22 having a predetermined gain determined by resistors 20 and 21.

The output of the operational amplifier 19 is connected to the operational amplifier 23 and the resistor 24.2.
The voltage is input to a comparator circuit 26 consisting of 5, and is compared with a predetermined voltage set by resistors 24 and 25. Note that 2 is the power supply for the operational amplifier 19.23 and the resistor 24.25 that sets the reference voltage of the comparison circuit 26.

To explain the operation in the above configuration, first, when you tap the piezoelectric element 7, an electromotive force as shown in FIG. 2(a) is generated at both ends due to the piezoelectric effect, and when you touch the piezoelectric element 7, At both ends of the piezoelectric element 7 are shown
An electromotive force as shown in a) is generated.

The output voltage waveform shown in FIG. 2(a) has a large peak voltage value but a small pulse width, that is, a high frequency component.

On the other hand, the output voltage waveform shown in FIG. 3(a) has a large pulse width, that is, a low frequency component, but a small peak voltage value.

The output of this piezoelectric element 7 is determined by a differentiating circuit 12 as shown in FIG.
) and FIG. 3 (i3), only the change in electromotive force is extracted as a signal. By rectifying this signal with a diode 13, only the positive side of the change in electromotive force is transferred to the integrating circuit 1.
6 is input. As shown in FIGS. 2(C) and 3(C), the integrating circuit 16 integrates the positive side change in the electromotive force to form a stabilized voltage waveform, and inputs the output to the operational amplifier 19. The input signal is amplified with a gain set by resistors 20 and 21. The output waveform of the operational amplifier 19 is the same as the input waveform, the only difference being the magnitude depending on the voltage ratio, and is shown in FIGS. 2(C) and 3(C). Operational amplifier 19
When the output of the operational amplifier 23 is larger than the predetermined voltage set by the resistor 24.
d) and output as shown in FIG. 3(d).

Due to the resistance values of resistor 20.21 and resistor 24.25,
Since the gain of the amplifier circuit 22 and the reference voltage of the comparison circuit 26 can be set, desired detection sensitivity can be freely obtained.

Since the differentiating circuit 12 outputs only the change in the electromotive force generated by the piezoelectric element, it outputs only when the piezoelectric element 7 is touched, and stress may be applied to the piezoelectric element 7 due to a mounting defect or the like. Even if the condition is maintained, the output will not drop and there will be no malfunction.

Further, since changes in the electromotive force are integrated and stabilized by the integrating circuit 16 and then amplified and compared, detection can be performed reliably regardless of the manner of touch or individual differences. Furthermore, since the integrating circuit 1e also operates as a no-cut filter, noise entering from outside is also blocked by this portion.

If a severe impact is applied to the piezoelectric element 7, the operational amplifier 1
Even if an electromotive force that might destroy the operational amplifier 19 is generated, the input voltage of the operational amplifier 19 is limited by the Zener diode 17, so the damage will not occur.

In addition, since the differentiating circuit 12 outputs only the change in the electromotive force generated by the piezoelectric element T, it outputs not only the positive side voltage but also the negative side voltage, but since the negative side voltage is cut off by the diode 13, the calculation No negative voltage is applied to the amplifier 19 either. Therefore, even in the case of an operational amplifier used with a single power supply, malfunction or destruction due to application of a negative voltage can be prevented.

Furthermore, although the characteristics of the piezoelectric element 7 change over time due to deterioration over time due to the application of a DC voltage, the capacitor 1o of the differentiating circuit 12 insulates the piezoelectric element 7 from a DC perspective, and the resistor 8
Since the voltage is absorbed by the switch, there is no deterioration, and since it does not have contacts like a switch, it has high reliability over a long life.

Effects of the Invention As is clear from the above embodiments, according to the present invention, there is provided a differentiating circuit into which the electromotive force of the piezoelectric element is input, a diode which rectifies the output of the differentiating circuit, and a signal rectified by the diode is input. Since it is equipped with an integrating circuit and a comparison circuit that compares the output of the integrating circuit with a predetermined voltage, a reliable and stable output signal can be obtained over a wide range of electromotive force with undefined frequency and polarity output by the piezoelectric element. In particular, since the differential circuit detects only the change in the electromotive force of the piezoelectric element, it can be detected only when it is touched.
There is no malfunction due to continuous stress being applied to the piezoelectric element, and reliability is extremely high.Also, since changes in electromotive force are stabilized by an integrating circuit, the output of the electromotive force of the piezoelectric element depends on the touch method and individual differences. Since detection is possible without being affected by the polarity or frequency components of the waveform, reliability can be extremely high.Furthermore, the diode protects the circuit of the operational amplifier and prevents malfunctions, increasing reliability.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a touch sensor device according to an embodiment of the present invention, and Figs. 2 (,) to (d) are voltage waveform diagrams of main parts when a piezoelectric element of the same touch sensor device is touched in a tapping manner. , Figures 3(,) to (d) are voltage waveform diagrams of main parts when the same piezoelectric element is touched, respectively, Figure 4 is a circuit diagram of the touch sensor device previously developed by the present inventors,
Figures 5 (a) and (b) are voltage waveform diagrams of the main parts when the piezoelectric element of the same touch sensor device is touched in a tapping manner, respectively, and Figures 6 (, ) and (b) are diagrams of the voltage waveforms of the main parts when the piezoelectric element of the same touch sensor device is touched. FIG. 4 is a diagram of main voltage waveforms when touched. 7... Piezoelectric element, 12... Differential circuit,
13... Diode, 16... Integrating circuit, 26... Comparing circuit. Name of agent: Patent attorney Shigetaka Awano and 1 other person.
Pentatom differential 1M path - diode - Integrator circuit Ichipikaku circuit Figure 2 Figure 1 Figure 2 Figure 2

Claims (1)

[Claims] a piezoelectric element, a differentiating circuit that inputs the electromotive force of the piezoelectric element, a diode that rectifies the output of the differentiating circuit, and an integrating circuit that inputs the signal rectified by the diode;
A touch sensor device comprising: a comparison circuit that compares the output of the integration circuit with a predetermined voltage, the comparison circuit outputting an output when the piezoelectric element is touched.