JPS62208517A - Electric resistance characteristics correction circuit of pressure sensitive conductive rubber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a touch control switch (hereinafter referred to as TC3) that utilizes changes in electrical resistance due to compressive deformation of pressure-sensitive conductive rubber.
This relates to a characteristic correction circuit (abbreviated as ).

[Prior art]

Conventionally, a rubber resistor is known as a pressure-sensitive conductive rubber, which is constructed by dispersing a conductor such as graphite or metal in rubber so that its resistance changes depending on the pressing force.

By selecting appropriate values for the carbon particle diameter, dispersion density, etc., a load of 50 to 300 g (approximately pushing with a finger) shows a change of several hundred to several Ω, and in terms of displacement, it shows a change of several Ω. It can be adjusted to make a similar change in the range of 10 to several 100 μm.

Therefore, it can be used as a load sensor, pressure sensor, displacement, or deformation sensor (a kind of strain gauge), has excellent corrosion resistance, is inexpensive, has a rubber-like appearance, and is easy to handle (if it is held between electrodes, For example, if an electrode is placed on one side and a pressure receiving plate is placed on the other side, changes can be easily taken out.
3) can be configured.

However, the relationship between this resistance R and the force F is the relationship shown by Roe F-1, 11-1, 9, and the sensitivity changes depending on the magnitude of the force F, so it is not practical. is not fully utilized.

First, a typical configuration of Te3, which converts pressure-sensitive conductive rubber into electrical resistance change obtained by compressing and deforming it, is as shown in FIG. It has a structure in which a pressure-receiving side electrode 5 with a lead wire 4 attached thereon is placed on the attached electrode 3.

Hereinafter, Te3 shown in FIG. 7 will be expressed by the symbols shown in FIG. 8.

Figure 8 shows an example of a basic circuit configuration that has been generally considered in the past. Te3, which uses pressure-sensitive conductive rubber, is connected between the base of transistor Q and the -B power supply, and A resistor R1 is connected between the base and ground. Further, the base and collector of the transistor Q are connected to a 10B power supply through resistors Rz and Ri, respectively, and its emitter is grounded through a resistor R4, so that the output is taken out from the collector of the transistor Q. It has become. Note that the transistor Q mentioned above is a bipolar transistor. Figure 9 shows the output characteristics showing the relationship between the pressure applied to Te3 and the voltage obtained from the collector of transistor Q. As shown in the figure, when Q is operated at a linear operating point, the characteristics are not linear. It has a characteristic that is almost inversely proportional to the 1.8th power, and in the past, the range of use was the part D, where the change in resistance against changes in force was relatively gentle and the rate of change was more even.

In this way, when using Te3, conventionally, it has been used with its resistance value change characteristics as is, or with the variable range narrowed by a low resistance attached in parallel to Te3. There were times when it was convenient. Moreover, if a pressure-sensitive conductive rubber can be obtained that has a resistance change under a load of 50 to 100 g within the above-mentioned usage range, it will be possible to use it in a variety of ways, but it is difficult to produce it industrially stably. The situation is difficult.

[Purpose of the invention]

This invention was made in view of the above-mentioned problems, and its purpose is to convert the force applied to the pressure-sensitive conductive rubber into an amount of electricity by using the wide range of resistance inherent in the pressure-sensitive conductive rubber. It is an object of the present invention to provide a Te3 characteristic correction circuit that can fully utilize the change characteristics and realize a linear relationship when extracting the force applied to the pressure-sensitive conductive rubber as an electric quantity.

[Structure of the invention]

The configuration of the present invention for achieving the above object is such that a circuit is connected to the pressure-sensitive conductive rubber in a circuit that compresses and deforms the pressure-sensitive conductive rubber and converts a pressing force into an amount of electricity by utilizing a change in electrical resistance value. A circuit for correcting electric resistance characteristics of pressure-sensitive conductive rubber, characterized in that the electrode is connected to give a signal representing a change in electric resistance to the circuit, and a field effect transistor is provided for taking out the change in resistance as an output. It is.

That is, the present invention provides a field effect transistor (
Focusing on the fact that the drain current of a FET (hereinafter abbreviated as FET) is proportional to the square of the gate voltage, the resistance of the pressure-sensitive conductive rubber described above is approximately 1.8 to 1.
By canceling out the characteristic that is inversely proportional to the ninth power, the pressing force is converted into an amount of electricity that changes almost linearly.

Therefore, the pressure-sensitive conductive rubber is usually appropriately connected as a resistor to a circuit that applies voltage to the gate of the FET.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows the basic configuration of a circuit according to an embodiment of the present invention, and FIG. 2 shows the characteristics of an FET (field effect transistor).

As shown in Figure 1, this circuit converts the signal from Te3 into FE
The processing is performed using a T element, and Te3 is connected between the gate of the FET and the -B power supply. FE
A resistor R3 is connected between the gate and drain of T, and its drain is connected to a 10B power supply, while the FET
The source of the FET is grounded through a resistor R8, and the output is obtained from the source of the FET. Note that the relationship between the drain and the source can be reversed. That is, I
When converting the force applied to the C5 pressure-sensitive conductive rubber into an electrical quantity using its resistance change, use an FET as described above and set the output to 1° or ■. , R.

As shown by the arrow in FIG. 2, which shows the characteristics of the FET, O-v due to the change in resistance of IC3.

, V, and -O, and the bias can be changed in two directions. If the above ■2 is -2■, then the drain current is ■.

, is expressed as ros father (V-(-2))'', and the range between (-2V) and O is the range in which FETs are normally used. The relationship between the two is approximately a straight line within the range of l, and the curved portion within the broken line circle in the figure changes depending on how the bias is applied.

The linear relationship is not perfect, and as mentioned above, the degree of force separation (sensitivity) is reversed depending on whether IC3 is changed from the side or from the OV side.

Here, IC3 will be specifically explained below.

The resistance change characteristics of the pressure-sensitive conductive rubber used must not change drastically with pressure, but must change continuously.
Moreover, the range of the pressing force normally applied, for example, weak finger force (the range of change in resistance value between when pressed and when pressed strongly) is 1
It is desirable that the value be more than 100 digits. Therefore, pressure-sensitive conductive rubber has an on-off resistance change, that is, when it is not pressed, it has a high resistance value (at least IMΩ or more, for example, IO
MΩ), and is usually made into a conductor (
For example, there is a material with a characteristic of 1Ω or less), but a material with such a characteristic value is not preferable.

As a method for obtaining such a pressure-sensitive conductive rubber, known means are used, for example, using a silicone rubber elastic body as the elastic body, for example, as disclosed in JP-A-53-79937, artificial It can be produced by mixing and dispersing graphite particles in rubber, or by using fine nickel powder as disclosed in JP-A-49-114798.

The IC 3 shown in FIG. 7 can be modified in various ways; for example, in FIG. The width of the sheets 10 is 1/2 or less, and they are arranged so as not to touch each other, and the pressure-sensitive conductive rubber sheet 4 is placed on top of them,
Furthermore, IC3 may be obtained by placing a metal foil thereon. In this case, the metal foil is the pressure-sensitive conductive rubber sheet 1
This is because the current flowing inside the metal foil is made to flow only in the vertical direction, and the current flows in the horizontal direction inside the metal foil.

In addition, for the preparation of pressure-sensitive conductive rubber sheets, 150~
95 parts by weight of 200 meshes of artificial graphite were added to 100 parts by weight of RTV silicone rubber (manufactured by GE, USA) and cured according to a conventional method to form a pressure-sensitive conductive rubber with a thickness of 0.5 t.
It was made into a rubber sheet of m.

The IC 3 shown in FIG. 1 may have a structure in which a pressure-sensitive conductive rubber is held between two upper and lower electrodes, or may have a structure as described above.

By extracting an output using an FET as in the configuration shown in FIG. 1, it is possible to convert the force or displacement applied to the pressure-sensitive conductive rubber into a substantially straight line as shown in FIG. In other words, since FETs have high input impedance,
It is possible to make full use of the wide range of resistance change characteristics that IC3 originally has, and it is possible to correct the characteristics so that the pressure vs. output signal is almost linear.

FIG. 3 is an example of a practical circuit showing a specific example of an actual usage state. The control amplifier for TC8 using this FET includes IC3, FET, and IC. The IC is a general operational amplifier, and one input of the operational amplifier IC is connected to the drain of the FET, and is also connected to the output via a resistor R7. Further, a bias is applied to the other input of the operational amplifier IC.

A capacitor C and a resistor R are connected between the FET gate and ground.
6 is inserted, and a resistor R3 is connected between its gate and the -B power supply. The above capacitor C is
This is mainly to remove noise and maintain circuit stability, etc., which occur because the carbon particles in the pressure-sensitive conductive rubber are in discontinuous contact with each other (microscopically).

R9 is used for bias.

The feature of the circuit with the above configuration is that the FET is used as a variable resistance element, and the voltage gain of the operational amplifier IC (
GAIN) is determined by the resistance value between R7 and the FET drain-source D-3, so the FET gate voltage is initially set to V.
When the resistance value of TC3 decreases due to pressure, the voltage moves in the 10 direction due to the division ratio with R, and FE
The resistance value between the drain and source of T becomes low, and the GAIN of the operational amplifier IC increases depending on the ratio with R7.

Therefore, one of the input terminals of the operational amplifier IC (
If we give a certain bias to the positive side here,
The output voltage will change depending on the transmission characteristics of the FET.

An example of an actual usage condition is the configuration described above, and the output characteristics are almost linear as shown in Figure 4. Therefore, when converting the force applied to the pressure-sensitive conductive rubber into an electrical quantity, the characteristics must be corrected. can be used.

FIG. 5 shows a TCS control I by applying this invention.
FIG. 2 is a circuit configuration diagram when a hybrid type TC with analog output is configured as C.

In addition, in Fig. 6, TC3 is connected to the 8th bin P 8 = 11th bin pH in Fig. 5, and the output is F at the 1st bin P1.
It shows experimental results when measuring the -Vout characteristics, as well as experimental results when applying a voltage between the same pin P8 and pH and looking at the transmission characteristics of the loop of the IC. Note that the measurement results shown in FIG. 6 were measured with a short circuit between the 7th pin P7 and the 9th pin P9.

The circuit configuration of this hybrid IC for TC3 consists of two blocks: a voltage amplification section and an open circuit configuration.It can be applied to various sensors as a general control IC for TC3, and can also be used as an amplifier for musical instrument sensors (PC sensors). can.

ICI and IC are dual type 4 respectively.
558 and 1/2 was used for amplification. IC
1 constitutes a voltage amplification circuit, and GAIN is R, (1
It is determined by the resistance value between the drain and source of the FET (23 to -30).The resistance value between this drain and source can be varied by the GAIN bias voltage, and in this configuration, Rz (33 to Ω ) and R4 (12QKΩ) -
It is set to about 2V, and this terminal is installed as a +
If a bias is applied to the side, a maximum GAIN of 20 dB can be obtained. This GAIN curve is proportional to the transmission characteristic (approximately squared) of the FET, and when combined with the TC5 curve (inversely proportional to approximately the 1.8th power), a nearly linear output could be obtained.

Note that IC2 is configured so that it can be used not only as a constant current source but also as an emitter follower of an output circuit.

This invention can be used in various devices and has a wide range of applications.To give an example of its application, it can accurately detect pressures up to about 50 cm of water head, so it can be used as a pressure sensor, or it can be used normally with a finger. Pressure to press (50~
It can detect small forces such as those activated by a force of about 500g (approximately 500g), and can detect displacements of about μm, so it can be used as a strain gauge, and can be applied to various fields such as home appliances and industrial equipment. can.

〔Effect of the invention〕

This invention relates to a circuit that converts a force applied to a pressure-sensitive conductive rubber into an amount of electricity, which is connected to the circuit so as to give a signal representing a change in resistance of the pressure-sensitive conductive rubber, and outputs the change in resistance. Since the FET to be taken out is provided, the input impedance is high, so the wide range of resistance change characteristics that pressure-sensitive conductive rubber has can be fully utilized, and the correspondence between pressure and output signal is almost linear. Therefore, it has the effect of being easy to use in various devices.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of this invention, FIG. 2 is a diagram showing characteristics of the FET, FIG. 3 is a diagram showing an example of a practical circuit of this invention, and FIG. 4 is a diagram showing an example of the practical circuit of this invention. Figure 5 is a circuit configuration diagram of a hybrid IC for TC3 to which this invention is applied, Figure 6 is a characteristic diagram for the configuration of Figure 5, and Figure 7 is used for each example. FIG. 8 is a circuit diagram showing a conventional circuit configuration, and FIG. 9 is a diagram showing output characteristics in the case of FIG. 8. Te3...touch control switch, FET...
・Field effect transistor, R1-R5...
・Resistance, C...Capacitor, 1...Variable resistor, 2
, 3... Electrode, 4... Pressure-sensitive conductive rubber. Figure 1 Figure 2 (VGS) Figure 3 Figure 4 Figure 5 Figure 6 F-(kg)VGS-(V)

Claims (1)

[Claims] In a circuit that converts a pressing force into an electrical quantity by using a change in resistance value when a pressure-sensitive conductive rubber is compressed and deformed, an electrode connected to the pressure-sensitive conductive rubber gives a signal representing a change in resistance to the circuit. What is claimed is: 1. A circuit for correcting electrical resistance characteristics of pressure-sensitive conductive rubber, characterized in that it is connected as shown in FIG.