JPH0415487B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Purpose of the Invention [Field of Industrial Application] This invention provides a method for applying pressure to detect a pressurizing point where the concentrated load acts when a concentrated load acts on a flat plate. It concerns a point detector.

[Prior Art] A method conventionally used to detect the point of application of a concentrated load acting on a flat plate is to arrange a large number of electrodes, strain gauges, etc. in a matrix on the flat plate, and Pressure points were detected by comparing the magnitude of strain in each part of the flat plate detected by electrodes and strain gauges.

[Problems to be Solved by the Invention] However, in the conventional pressure point detector configured as described above, the number of strain gauges arranged in a matrix increases, making the structure of the detector complicated and , and prices are becoming more expensive.

This invention was made in view of the above circumstances, and has a small number of component parts, a simple structure,
Another object of the present invention is to provide a pressurization point detector that can reliably detect pressurization points.

(b) Structure of the Invention [Means for Solving the Problem] Corresponding to this object, the pressure point detector of the present invention includes a flat substrate made of a material having a piezoresistive effect, and a center plate of the substrate. 3 at an arbitrary distance from
and an electrode attached to a portion of the substrate to detect the amount of change in resistance due to displacement of each portion, and the electrode includes a circular inner electrode formed on one surface of the substrate and an outer side of the inner electrode. It is characterized by consisting of an annular outer electrode located on the surface and a common electrode formed on the other surface.

Hereinafter, details of the present invention will be explained with reference to the drawings showing one embodiment.

In FIGS. 1 and 2, 1 is a pressure point detector, and the pressure point detector 1 has a substrate 2. In FIG. The substrate 2 is made of a polymer material having rubber-like elasticity, such as ethylene vinyl acetate copolymer, as a base material, and a conductive substance such as carbon graphite, nickel, or aluminum mixed therein to form a plate-shaped composite material. It is. In this case, the change in electrical resistance of the substrate 2 made of a composite material with respect to external pressure is the third
The result will be as shown in the figure.

The substrate 2 has electrodes 3, 3 at arbitrary distances from the center.
a, 3b, and 3c are provided. As shown in FIG. 4, the electrodes 3 include an inner electrode 4 and an outer electrode 5 formed on the lower surface of the substrate 2, and a common electrode 6 formed on the upper surface of the substrate 2.

The inner electrode 4 is a circular electrode with radius r ₁ .
The outer electrode 5 is a circular electrode having an inner diameter of 2r ₂ , and the common electrode 6 is a circular electrode having approximately the same diameter as the outer diameter of the outer electrode 5 . The surface resistance of the substrate 2 is measured by keeping the inner electrode 4 and the common electrode 6 at the same potential and applying a voltage between the inner electrode 4 and the outer electrode 5. The volume electrical resistance of the substrate 2 can be measured by applying a voltage between the common electrode 6 and the inner electrode 4 while keeping them at the same potential. This makes it possible to know the relationship between the magnitude of the compressive force applied to the substrate 2 and the two types of electrical resistance.

Each of the electrodes 4, 5 and 6 is formed by depositing metal such as gold or aluminum on the surface of the substrate 2 using a vacuum deposition method. There are two types of metal vapor deposition methods used in this case. One is to place a mask in the shape of an electrode on the substrate 2 made of a polymer composite material, perform metal vacuum vapor deposition on top of the mask, and then This is a method in which the same type of vacuum evaporation is performed by flipping 2 over. Although this metal vapor deposition method requires alignment of the upper and lower vacuum vapor deposition locations, it has the advantage that the desired electrode pattern can be formed simultaneously with the vacuum vapor deposition. The second method is to form only electrode films on the upper and lower surfaces of the substrate 2 in the vacuum evaporation process,
Thereafter, an electrode pattern is formed by a method such as photoetching. This method is
The success or failure of a force sensor is determined by the level of technical proficiency in etching, but unlike the first method described above, this method has the feature of being able to form microelectrodes.

[Function] The function of the pressure point detector configured as described above is as follows.

First, the force detection effect at the installation position of the electrode 3 will be explained.

Let h be the thickness of the substrate 2, and let R be the volume resistance at that time. If the specific resistance of the polymer composite material constituting the substrate 2 is ρ, then ρ=[{π(r ₁ +r ₂ )}/h]R (1). In equation (1), when a load is applied from above to the board 2 shown in Figure 1, the respective values are ρ → ρ + Δρ, h → h + Δh, r ₁ → r ₁ + Δr ₁ , r ₂ → r ₂ + Δr ₂ R →R+ΔR. Substituting this into equation (1) and rearranging it, (ΔR/R) = (Δρ/ρ) + (Δh/h) −{2(Δr ₁ + r ₂ )}/(r ₁ + r ₂ ) ……(2 ) can be calculated. In equation (2), ΔR/R is the gauge factor that is generally referred to, and the resistance change under each load is determined. That is, Δh, Δr ₁ , and Δr ₂ are due to changes in the shape of the polymer composite material due to the load, and are terms corresponding to gauge changes in a generally known metal gauge.

In addition, Δρ is 1Ω-cm to 1000Ω when the pressure point detector 1 is
This term comes from the gauge factor due to use in the semiconducting region, which is relatively low at -cm, and corresponds to the gauge change in the case of semiconductor gauges.

Next, the principle of pressure point detection in the detector 1 will be explained.

As shown in FIG. 5, electrodes are placed at three points a, b, and c on the sensor plane (X-Z plane), and the coordinates of the pressurizing point P are determined from this. the length from a to p
Let R _A be the length from b to P, R _B be the length from c to P, and R _c be the length from c to P.

From the equation of a circle, the equation for radius R _A centered at a (r _a cosθ _a・ra sinθ _a ) is (x− _{r a cosθ a} ) ² + (Z− r _a sinθ _a ) ² = R _A ² … ...(3) The equation for the radius R _B centered on a b (r _b cosθ _b , r _b sinθ _b ) is (x−r _b cosθ _b ) ² + (Z−r _b sinθ _b ) ² = R _B ² ...(4) The equation of the radius R _C centered at c (r _c cosθ _c , r _c sinθ _c ) is (x−r _c cosθ _c ) ² + (Z−r _c sinθ _c ) ² = R _C ² ...(5) From equation (3), x ² + Z ² −2 (xr _a cosθ _a +Zr _a sinθ _a ) + r _a ² −R _A ² = 0 ...(6) From equation (4), x ² + Z ² −2(xr _b cosθ _b +Zr _b sinθ _b )+r _b ² −R _B ² =0 ...(7) From equation (5), x ² +Z ² −2(xr _c cosθ _c +Zr _c sinθ _c )+r _c ² -R _C ² =0 ...(8) For simplicity, as shown in Figure 6, θ _a = 0°, θ _b = 120°, θ _c = 240° r _a = r _b = _c = When considered as r, r _a cosθ _a = r r _a sinθ _a = 0 r _b cosθ _b = −0.5r r _b sinθ _b = 0.866r r _c cosθ _c = −0.5r r _c sinθ _c = 0.866r. Equations (6), (7), and ( ^{8 )} are derived from ^these as follows: x ² +Z ² −2rx+r ² −R _A ² =0 ……(6 ₎ ^′ (7)′ x ² +Z ² +rx+1.732rZ+r ² −R _C ² =0 ……(8)′.

(6)′−(7)′ is −3rx+1.732rZ=R _A ² −R _B ² …(9) (7)′−(8)′ is Z=(R _B ² −R _C ² )/− 3.464r ……(10), and substituting equation (10) into equation (9), x=(−R _B ² −R _C ² +R _C ² )/6r ……(11) (10), (11) From the formula, the coordinates (x, y) of the pressurizing point P are (x, y) = [{(-R _A ² - R _B ² + R _C ² )/6r}, {(R _C ² - R ^B ₂ )/ 3.464rZ}] ...(12)

FIG. 6 shows the arrangement of electrodes for establishing equation (12).

If the sensor is a uniform infinite plate, the amount of displacement at each electrode portion is proportional to the distance from each electrode to the pressurizing point.

Here, the resistance values of the various electrode parts under no load and under pressure are determined. Each electrode has a fourth
Assume that the structure is formed as shown in the figure.

There is an inner electrode 4 with a radius r ₁ inside the outer electrode 5 with an inner diameter 2r ₂ , and the resistance at no load between these two electrodes is
R _X becomes R _X = (C/L)ρ _SO , where L≒2π(r ₁
+r ₂ ), ρ _SO surface resistivity under no load, C represents r ₂ −r ₁ at the distance between both electrodes.

Therefore, R _X becomes R _X = {(r ₂ − r ₁ )/(r ₁ + r ₂ )π}ρ _SO .

Under these conditions, the voltage _VX generated when a constant current is passed through the electrodes 4 and 5 from a constant current source is R _X =・R _X = {(r ₂ − r ₁ ) / (r ₁ + r ₂ ) }ρ _SO・ ...(13) Next, consider the time of pressurization. When the shapes of the electrodes change by Δr ₁ and Δr ₂ and ρ _SO changes by Δρ due to pressurization, the resistance R at that time is R=[{(r ₂ +Δr ₂ )−(r, −Δr ₁ )}/{(r ₁ +
Δr ₁ + r ₂ + Δr ₂ )π}]×(ρ _SO +Δρ)……(14).

As above, the voltage V _p generated when a constant current flows is V _p =・R _X = [{(r ₂ + Δr ₂ ) − (r ₁ − Δr ₁ )}/{
(r ₁ + Δr ₁ + r ₂ + Δr ₂ ) π}] × (ρ _SO + Δρ)・…
...(15) Equation (15) - Equation (13) can be considered to be the voltage generated due to so-called pressurization. If the distance between the electrode and the pressurizing point is M, then M∝(V _p −V _R )...(16) This M is related to the values of R _A , R _B , and R _C in equation (12). In actual detection, equation (12) can be calculated by calculating the value of M in advance through calibration. The method is as follows.

The value of M is determined when constant pressure is applied while changing the distance n from one electrode (FIG. 7).

In the case of actual detection, the value of n is determined from the value of M of this calibration curve, and the value is used as is in equation (12).
By substituting the values of R _A , R _B , and R _C , the desired pressurizing point can be calculated.

Until now, we have assumed that the sensor material is a uniform, infinite plate. In reality, there are no infinite plates. The actual sensor structure is shown below.

As shown in FIGS. 8 and 9, the pressure point detector is a circular plate whose periphery is fixed. In the mechanical analysis of the pressure point detector, if it is assumed that the substrate 2 is a thin film, SP Tiemoshienko's theory can be directly applied here. (In general, this theory can be applied if the substrate material is a Si-based diaphragm shape.) However, when the thickness of the sensor is an issue, this theory is not applied and the conventional Δr is calculated using finite elements. have to ask.

That is, by finding each Δr when pressurizing at an arbitrary location using the finite element method, M
The value and n will be corrected.

In the present invention, an inner electrode and an outer electrode are used as the electrodes 3, but the shape of the electrodes is not limited thereto. That is,
Any configuration may be used as long as Δr can be changed by pressurization.

(c) Effects of the invention As is clear from the above explanation, in this invention, by using three sets of sensors that can detect resistance changes due to pressurization, it is possible to detect the pressurized point acting on the substrate. Therefore, a pressure point detector with a simple structure and low cost can be obtained.

[Brief explanation of drawings]

Figure 1 is a plan view showing the pressure point detector, Figure 2 is a plan view showing the pressure point detector;
The figure is a cross-sectional view of the A-A section in Figure 1, Figure 3 is a graph showing the change in electrical resistance of the substrate with respect to external pressure, Figure 4 is a longitudinal cross-sectional view showing this electrode, and Figure 5 is a diagram showing the pressure point detection. FIG. 6 is a plan view showing an example of electrode arrangement; FIG. 7 is a graph showing the value of M when constant pressure is applied while changing the distance n; FIG.
The figure is a longitudinal cross-sectional view showing how the pressurizing point detector is used, and FIG. 9 is a plan view showing how the pressurizing point detector is used. 1... Pressure point detector, 2... Substrate, 3, 3a,
3b, 3c...electrode, 4...inner electrode, 5...outer electrode, 6...common electrode.

Claims (1)

[Claims] 1. A flat substrate made of a material having a piezoresistive effect, and 3.
and an electrode attached to a portion of the substrate to detect the amount of change in resistance due to displacement of each portion, and the electrode includes a circular inner electrode formed on one surface of the substrate and an outer side of the inner electrode. 1. A pressure point detector comprising an annular outer electrode located on the surface and a common electrode formed on the other surface.