JPS634601A - Ac driving method 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] (Industrial Application Field) The present invention relates to a means for electrically driving pressure-sensitive conductive rubber in order to detect pressing force or displacement as a change in electrical resistance value. .

[Prior art]

2. Description of the Related Art Conventionally, a rubber resistor in which a conductor such as graphite or metal is dispersed in rubber and whose resistance changes depending on the pressing force is known as a pressure-sensitive conductive rubber.

By selecting appropriate values for graphite particle diameter, dispersion density, etc., this pressure-sensitive conductive rubber has a resistance value of several hundred to several hundred when the load changes in the range of 50 to 300 g (approximately the force of pushing with a finger). is varied within the range of Ω, and the displacement at that time is several tens to
Since it can be adjusted to vary within a range of several 100 μm, it can be used as a load sensor, pressure sensor, sensor for displacement, deformation, etc. (-type strain gauge), and has excellent corrosion resistance and is inexpensive. The material has a rubber-like appearance and is easy to handle.

In order to use this pressure-sensitive conductive rubber as a sensor, it is easy to apply pressure or displacement by holding it between electrodes, or by providing an electrode on one side and a pressure-receiving plate on the other. It can be taken out as a change in resistance. Hereinafter, such a sensor will be referred to as a touch control switch (hereinafter abbreviated as TC3).

By the way, to drive this Te3 and detect the resistance, conventionally it was done by applying direct current, but as development progresses for robots, tactile sensors and other applications, there is a need for more precise detection. It is now possible to However, conventional Te3 has been found to have shortcomings in reproducibility, responsiveness to small changes, etc., and there is a question that there is a limit to its applicability.

Therefore, in order to explain the mechanism in which the resistance changes depending on the pressing force, the cross section of Te3 is enlarged and schematically shown in FIG. The Te3 has a basic structure in which both sides of the pressure-sensitive conductive rubber 1 are sandwiched between electrodes 4 and a pressure receiving plate 5 is provided on the outside thereof. When the force F is applied to the pressure-receiving plate 5 and presses the pressure-sensitive conductive rubber, the conductive particles 3 in a dispersed state approach each other and finally come into continuous contact with each other as shown by hatching in the figure. A portion is generated, and the electrodes 4 become electrically conductive.

Naturally, the proportion of the conductive particles 3 that are continuous between the electrodes increases as the pressing force F increases, and the resistance value decreases accordingly.The resistance value R of the pressure-sensitive conductive rubber 1 is as follows. It is known that the force F changes approximately in proportion to the -1,8 to -1,9 power.

The inventor conducted a detailed study on the behavior of the conductor 3 dispersed in the rubber layer 2, and found that when the magnitude of the force F is changed extremely slowly, the relationship between the force F and the resistance R is as shown in FIG. Strictly speaking, it changes in an irregular zigzag curve.

Furthermore, it was found that the zigzag shape had poor reproducibility. If conductive particles with a symmetrical shape are used, the resistance will drop all at once when the pressing force reaches a certain value, which is a so-called on-off switch operation, and the resistance value will gradually decrease as the pressing force increases. In order to achieve this, it is necessary to use irregularly shaped conductor particles, so the above characteristics can be said to be the essential characteristics of pressure-sensitive conductive rubber.

Therefore, when observing in detail the state in which irregularly shaped conductive particles with uneven surfaces are in contact with each other due to pressing force, it is observed that they are in contact in various ways depending on the situation. It is understood that this is because the conductor particles 3 dispersed within the continuous layer of rubber cause the contact state to fluctuate with slight changes in conditions and is difficult to maintain constant.

[Purpose of the invention]

The present invention has been made to improve the above-mentioned problems, and aims to provide a novel driving means for pressure-sensitive conductive rubber that can advantageously utilize the advantages of pressure-sensitive conductive rubber and overcome its drawbacks. The purpose is

[Structure of the invention]

The configuration of the present invention to achieve the above object is to apply a high-frequency alternating current of a predetermined frequency to a pressure-sensitive conductive rubber whose electrical resistance value changes in accordance with the pressing force, thereby changing the impedance of the pressure-sensitive conductive rubber. It is characterized by detection.

The high frequency used in carrying out the present invention is preferably approximately 100 cycles to approximately 10M cycles. Habo 1
If it is less than 00K cycles, the response characteristics due to the skin effect will change, and if it is more than 10M cycles, there is a risk of transmitting radio waves to the outside, which is not preferable.

When carrying out the present invention, high-frequency alternating current may be applied to the pressure-sensitive conductive rubber using either a high-frequency voltage or an electric current.

The present invention utilizes the skin effect of high-frequency current flowing through a conductor, and the interior of the pressure-sensitive conductive rubber to which high-frequency alternating current is applied mainly consists of the resistance of the conductor and a capacitor made of a rubber dielectric interposed between them. It can be seen that a complex circuit network is formed, and the present invention was completed by discovering that the impedance has an extremely stable value with respect to the pressing force.

The pressure-sensitive conductive rubber used in the present invention may be made of rubber such as silicone rubber as an elastic body, as disclosed in, for example, JP-A-49-114798 and JP-A-53-79937. It is made by dispersing conductive particles such as graphite particles and metal particles such as nickel.

According to the method of the present invention, (8) In the conventional DC application, the resistance value R to the pressing force F was proportional to the force F to the -1,8 to -1,9 power, but it can be changed over a wide range of the force F. Therefore, the impedance 2 changes linearly with respect to F with a negative slope.

With conventional direct current application, changes in resistance R had poor reproducibility in response to minute changes in F, but there is a big difference in that changes in impedance Z change smoothly, improving detection accuracy and reproducibility. (C) In conventional direct current application, the effects of creep and hysteresis phenomena were quite large, but with respect to impedance Z, the effects can be suppressed to less than half of the conventional effects. This characteristic is thought to be due to the fact that the elastic deformation of rubber is not a change in volume but a change in shape.

The present invention is characterized by the above points, and has made it possible to significantly improve the utility value of pressure-sensitive conductive rubber.

The waveform of the high frequency wave used in carrying out the present invention may be appropriately selected, such as a normal sine wave or a rectangular wave, taking into consideration the characteristics of the circuit to be used. It is preferable to cut off the DC component and apply only the AC component to the pressure-sensitive conductive rubber.

There is no particular restriction on the shape of the pressure-sensitive conductive rubber used in the present invention, but for example, a small piece of pressure-sensitive conductive rubber in the form of a sheet with a thickness of about several 11 mm is placed on an electrode with a lead wire attached, and then It has a structure with a pressure-receiving electrode attached to a lead wire, and the size of the small sensor is, for example, l cmφ or l crrr x l c.
A material with a thickness of about 0.5 mm can be used.

In addition, it is preferable that the grip force or tactile sensor of the hand robot has a matrix configuration, for example, several c.
Any suitable material, such as a m-square one, can be used.

〔Example〕

Hereinafter, the present invention will be described in detail by way of an embodiment with reference to the accompanying drawings.

FIG. 1 shows a block diagram of the basic configuration of a circuit that implements the method of the present invention. In the figure, the high frequency AC generated in the high frequency oscillation circuit 6 is passed through the TC3 after the DC component is canted by the coupling capacitor C1. The voltage is applied to the level detection circuit 7 included in the signal.

A high-frequency voltage or current corresponding to the impedance of the pressure-sensitive conductive rubber used here is extracted, detected by a detection circuit 8, and output as a DC signal from an output terminal 9 to a predetermined display circuit.

Using the above impedance detection circuit, the force F is 0.5
Using a pressure-sensitive conductive rubber having a resistance R of 0.5 Ω at kg/cnl, the relationship between frequency f, pressing force F, and impedance Z is shown in FIGS. 2 and 3.

Figure 2 shows the relationship between frequency f and impedance Z when pressing force F = 00. Below 100 cycles, impedance is approximately 10 regardless of frequency.
The impedance Z is constant at Ω, and over 100 cycles, the impedance Z decreases linearly with the logarithm of the frequency f, as shown in the figure. That is, the response characteristics of Te8 change after 100 cycles.

Figure 3 shows the relationship between force F and impedance Z when an alternating current with frequency f = IM cycle is applied.As shown in the figure, a linear relationship holds over a wide range, and at very low values the impedance The Z value exhibits a characteristic that rises rapidly.

In the figure, the relationship between resistance R and pressing force F is indicated by a dashed line. From these two curves it can be easily seen that the method according to the invention can utilize Te3 very advantageously as a sensor.

In the conventional detection means using direct current, a means was used in which a resistor with a low resistance value was inserted in parallel with Te3 in order to make the above-mentioned curve a straight line. This method has the disadvantage that it becomes a curve as shown by the dotted line in FIG. 3, and the range that can be approximated by a true straight line is narrow.

According to the research of the present inventor, Te3 is a member in which a dielectric material is sandwiched between electrodes, and its high frequency characteristics are extremely specific. That is, in a normal capacitor, the capacitance increases as the electrode spacing decreases, but since the conductor is dispersed inside Te3, the capacitor capacitance also decreases as the electrode spacing decreases.

Therefore, each of the above characteristics is true for Te3 as a high frequency element.
suggests that it is available.

Next, further explanation will be given using a specific example of a detection circuit that detects force.

First, FIGS. 4 and 5 are schematic explanatory diagrams of the detection unit used in this embodiment.

FIG. 4 is a side view of Te3 using a double-sided pressure receiving plate, and the same members as in FIG. 8 are given the same numbers and their explanations are omitted. Both ends of the pressure-receiving force Fi5 are supported by spacers 10, and when force F is applied to the pressure-receiving plate 5, the pressure-sensitive conductive rubber 1 is deformed to a position where this force F balances the elasticity of the pressure-receiving plate 5.

Further, FIG. 5 is a side view of Te3 using a cantilever type pressure receiving plate, which is advantageous for detecting a small pressing force F.

FIG. 6 shows an example of a circuit actually used, and the oscillation circuit 6 uses a circuit in which a crystal oscillator 16 is connected in parallel with the resistor R1 of an amplifier 15 provided with a feedback resistor R1. . After cutting the DC component of the high frequency obtained by this oscillator 6 with a coupling capacitor C1, it is applied to a pressure level detection circuit 7 in which resistors R2 and Te3 are connected in series, and the partial voltage is sent to a detection circuit 8 via a coupling capacitor C2. Output. The detection circuit 8 includes two diodes D1 and D as shown in the figure.
2 and rectification using a resistor R3 and a capacitor C3, and the detected value converted to direct current is amplified by a direct current amplifier circuit composed of a comparator 17 and a feedback resistor R4, and then sent to an output terminal. 9
′ is output.

Figure 7 shows a circuit that outputs the difference between the pressing force and the set value by utilizing the property that the impedance of the pressure-sensitive conductive rubber to high frequencies changes linearly with the pressing force, and is characterized by the detection circuit 7'. It is.

That is, this detection circuit 7' includes a circuit for detecting the impedance of Te3 (hereinafter referred to as TC3 circuit) having the same configuration as the negative output circuit 7 and the detection circuit 8 in FIG.
A circuit for detecting the impedance of the variable resistor RV (hereinafter referred to as a circuit for detecting the impedance of the variable resistor RV) has the same configuration as above except that the variable resistor RV is used instead of e3, the polarity of the diodes D1 and D2 is reversed, and negative high frequency waves are detected. (referred to as a comparison circuit) are connected in parallel.

The oscillation circuit 6 of this embodiment has an RC
The high frequency wave oscillated by the oscillation circuit is amplified by the amplifier 18 and applied to the detection circuit 7'. In the detection circuit 7', the high frequency from the starting circuit is applied to the TCS circuit and the comparison circuit through coupling capacitors C1 and 01', respectively. The output from the TC3 circuit is the detected and rectified positive half wave of the high frequency corresponding to the impedance of Te8, which is output to resistor R8, and the output of the comparator circuit is output to variable resistor RV (after being adjusted to the set value, fixed resistor The negative half-wave of the high frequency corresponding to the impedance of (acting as) is detected and rectified and output to the resistors R and l.

Therefore, from the connection point between the resistor R6 and the resistor R,/ by these outputs, the sum (actually, subtraction) value of both outputs is obtained as a divided voltage and input to the comparator 17.

Therefore, it is possible to take out from the output terminal 9 an output in which the deviation value of the pressing force F from the constant level set by the variable resistor Rv maintains a linear relationship.

In the above explanation, the method of the present invention has been explained using an example of detecting pressing force, but the present invention is not limited to this, and the method is not limited to this.
It will be easily understood that it can be applied to detecting pressure, etc.

〔Effect of the invention〕

In the method of the present invention, when detecting the pressing force of the pressure-sensitive conductive rubber, a high frequency is applied and detected as an impedance value, so it is possible to directly extract the detected values of pressing force, displacement, etc. as a linear relationship. Furthermore, since detection accuracy and reproducibility have been improved and the effects of creep and hysteresis have been reduced, the field of application of pressure-sensitive conductive rubber can be far expanded compared to the past.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a basic circuit for carrying out the method of the present invention, Figures 2 and 3 are diagrams showing the high frequency characteristics of pressure-sensitive conductive rubber, and Figures 4 and 5 are examples of TCS. A side view, FIG. 6 is a circuit diagram of one embodiment, FIG. 7 is another circuit diagram, FIG. 8 is an explanatory diagram of the mechanism in which the pressure-sensitive conductive rubber has conductivity, and FIG. 9 is a diagram of the pressure-sensitive conductive rubber pressed. FIG. 3 is a diagram showing the relationship between pressure and resistance value. 1... Pressure-sensitive conductive rubber, 2... Rubber elastic body, 3...
Conductor particles, 4... electrode, 5... pressure receiving plate, 6...
Oscillation circuit, 8...Detection circuit, CI...Coupling capacitor, F...Press force, TCS...Touch control switch. Figure 1 Figure 4 Figure 5 Figure 6 Figure 7 Figure 7 Mouth Figure 8 Figure 9 Pressure force

Claims (1)

[Claims] AC driving of a pressure-sensitive conductive rubber, characterized in that high-frequency alternating current of a predetermined frequency is applied to a pressure-sensitive conductive rubber whose electrical resistance value changes in response to pressing force, and impedance of the pressure-sensitive conductive rubber is detected. Method.