JPS61219844A - Force sensor - Google Patents

Abstract

PURPOSE:To make it possible to detect a wide range of force in an elastic range while reducing the cost and wt. of the titled sensor, by providing an electrode comprising a metal membrane obtained by metal vapor deposition to the front and back surfaces of a substrate made of a polymer composite material having piezoresistive effect. CONSTITUTION:A force sensor 1 has a substrate 2 and an electrode pair 10 consisting of electrodes 3, 4, 5 is mounted to both upper and lower surfaces of the substrate 2. The substrate 2 is formed by using a polymer material having rubbery elasticity, for example, an ethylene/vinyl acetate copolymer as a base material and mixing a conductive substance such as carbon, graphite, nickel or aluminum with said base material and forming the resulting mixture into a plate shape. The electrodes 4, 5, 6 are formed by vapor deposition and the electrodes 3, 5 are circular while the electrode 4 is annular. By applying voltage between the electrodes 5, 3 in such a state that the electrodes 5, 4 are held to the same potential, the volume electric resistance of the substrate 2 can be measured. By this method, the relation between the magnitude of compression force applied to the substrate 2 and electric resistance can be determined.

Description

Detailed Description of the Invention (a) Object of the Invention [Field of Industrial Application] This invention relates to a force sensor used to detect force.

[Prior Art] Generally, when detecting force, conventionally, a strain detection gauge is attached to one rod or a diaphragm to measure the force of one rod against external force.
To detect the opening, or when the diaphragm itself is made of 3i, impurities are diffused onto the surface of the St single crystal substrate to form a strain gauge, and the external force on the diaphragm surface is detected. In addition, capacitive pressure detectors have also been used as force sensors.

[Problems to be Solved by the Invention] However, in the case of a force sensor that combines a bar and a strain gauge, the strain affixing position and affixing method have a significant effect on the accuracy of the force sensor. Manufacturing was extremely time-consuming and required skill.

Moreover, there was a possibility that the strain gauge would peel off due to overload. In addition, in the case of a force sensor with a strain gauge formed on the surface of a silicon diaphragm, although it has good accuracy, it requires temperature compensation within that accuracy range, requires a large number of manufacturing steps, and is expensive. There was a problem. Furthermore, with regard to capacitive force detectors, there have been problems such as the output value fluctuating depending on the state of the dielectric material existing between the electrode plates and changes in the environment of the electrode plates.

The present invention was made in view of the above circumstances, and provides a force sensor that has a simple manufacturing process, is inexpensive, is lightweight, and is capable of detecting force over a wide range within the elastic range. The purpose is to

(b) Structure of the invention [Means for solving the problem] In response to this purpose, the force sensor of the present invention is formed by metal vapor deposition on the front and back surfaces of a substrate made of a polymer composite material having a piezoresistive effect. It is characterized by being provided with an electrode made of a thin metal film. - Hereinafter, details of the present invention will be explained with reference to the drawings without showing one embodiment.

In FIG. 1, 1 is a force sensor, and the force sensor 1 has a substrate 2, and is provided with an electrode pair 10 consisting of an electrode 3, an electrode 4, and an electrode 5 on both upper and lower surfaces of the substrate 2. The substrate 2 is made of a polymeric material having rubber-like elasticity, such as ethylene vinyl acetate copolymer, as a base material, and a conductive material such as carbon graphite, nickel, aluminum, etc., as a base material. A plate-shaped composite material is formed by mixing the iN9 substance. In this case, the change in electrical resistance of the substrate 2 made of a composite material with respect to external pressure is as shown in FIG.

An electrode 3 and an electrode 4 are formed on the lower surface of the substrate 2, and an electrode 5 is formed on the upper surface of the substrate 2.

Electrode 3 is a circular electrode with radius r1. The electrode 4 is a circular electrode having an inner diameter of 2r2, and the electrode 5 is a circular electrode having approximately the same diameter as the outer diameter of the electrode 4. Keeping electrode 3 and electrode 5 at the same potential, electrode 5 is kept at the same potential as electrode 3.
By applying a voltage between the electrode 3 and the electrode 3, the volume electrical resistance of the substrate 2 can be measured. 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 3.4 and 5 is formed by depositing a metal such as gold or aluminum onto the surface of the substrate 2 using a vacuum deposition method. There are two methods of metal evaporation 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 evaporation on top of it, 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 vacuum evaporation, in which only electrode films are formed on the upper and lower surfaces of the substrate 2, and then an electrode pattern is formed by photoetching. The success or failure of this method is determined by the technical skill level of the etching process, but unlike the first method described above, it has the feature of being able to form microelectrodes.

To compensate for the temperature of the force sensor 1, proceed as follows.

As shown in FIGS. 3 and 4, four electrode pairs 10a, 1
0b, 10c, and 10d are provided. In this case, the electrode 5 of each electrode pair is made common. Electrodes 10a and 10c are force sensor 1
The electrode pairs 10b and 106 are arranged symmetrically with respect to the center at a fixed distance apart, and the electrode pair 10b and 106 are arranged symmetrically with respect to the center at another fixed distance. By configuring the outputs of these four electrode pairs into a bridge circuit as shown in Figure 5,
Able to cope with temperature changes.

[Operation] The force detection operation in the force sensor 1 configured as described above is as follows.

Let h be the thickness of the base Ifi2, and let R be the volume resistance at that time. The specific resistance of the polymer composite material constituting the substrate 2 is ρ
Then, ρ at this time is p= ((π(r, 10r2) )/h) R-(1)
becomes. In equation (1), when a load is applied to the board 2 shown in Figure 1 from above, the respective values are ρ → ρ + Δρ, h
-+h→Δh1 r1→r1+Δr1, r2→r2+Δr2R−R+ΔR. Substituting this into equation (1) and rearranging it, (ΔR/
R)=(Δρ/ρ)+(Δh/h)−(2(Δr1+
r2) ) /(r → −r) ... (2) can be calculated. In equation (2), ΔR/R is a gauge factor that is generally referred to, and the resistance change under each load is determined. That is, Δh, Δr1Δr2 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.

Also, Δρ is 1Ω-C+a to 1000Ω-
This term comes from the gauge factor due to the use in the semiconducting region, which is relatively low as cm, and corresponds to the gauge change in the case of a conductive gauge.

An example of how to effectively utilize the force sensor 1 of the present invention is shown in FIG. That is, in the example shown in FIG. 6, a circular differential pressure detector 11 is constructed using the force sensor 1. The differential pressure detector 11 includes a closed container 12, and the internal space of the closed container 12 is divided into two chambers 13 and 14 with the force sensor 1 as a boundary. By applying pressure PO to the upper chamber 13, the pressure difference between the pressure Ps in the chamber 14 below the substrate 2 is applied to the substrate 2.
, and its output is derived from equation (2).

(c) Effects of the Invention The force sensor of this invention is constructed by simply forming a metal vapor deposited film on both sides of a substrate made of a composite material, so it is extremely easy to manufacture, and therefore the price can be kept low. can. There is no need to attach strain gauges, and the location and method of attaching strain gauges does not affect force detection accuracy.
Force sensors can be manufactured without requiring any skill. 1. The electrodes are formed from thin films formed by metal vapor deposition.
It has a strong adhesion force, does not peel off even under overload, and allows the device to be made smaller and lighter, and can be easily used for force detection in industrial robots and the like. Moreover, temperature compensation is easy, and force can be detected over a wide range within the elastic range of the substrate.

[Brief explanation of drawings]

FIG. 1 is an explanatory longitudinal cross-sectional view showing a force sensor, FIG. 2 is a graph showing changes in electrical resistance of a substrate with respect to external pressure, and FIG. 3 is an explanatory longitudinal cross-sectional view showing a force sensor according to another embodiment of the present invention. Fig. 4 is a plan view of the force sensor shown in Fig. 3, Fig. 5 is a circuit diagram showing a temperature compensation circuit, and Fig. 6 is a vertical cross-sectional view showing a differential pressure detector incorporating the force sensor. be. 1... Force sensor 2... Substrate 3... Electrode
4... Electrode 5... Electrode 10, 10a, 1
0b. 10c, 10d... Electrode pair Fig. 1 Fig. 2 Mr. 1, jL Yu-ihi Fig. 3 4 3 10b loa lo
dFigure 4Figure 5Figure 6

Claims (1)

[Claims] A force sensor comprising electrodes made of thin metal films formed by metal vapor deposition on the front and back surfaces of a substrate made of a polymer composite material having a piezoresistive effect.