JPH029701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a simple and highly accurate pressure sensor for relatively low pressures. Furthermore, the pressure sensor referred to herein is not a device for measuring pressure in an analog manner, but is a device that detects whether a predetermined pressure has been reached based on the presence or absence of electrical continuity between terminals.

Bourdon tubes, diaphragms, and the like are well-known devices for measuring pressure, but the sensor of the present invention can be made much smaller than these. Pressure sensors using semiconductors are known as small sensors, but they are for high pressure and are not suitable for low pressure areas.

The main object of the present invention is to detect pressure by using a method in which a large number of conductive thin wires having a length shorter than the thickness of an insulating rubber sheet are oriented in the thickness direction of the sheet when no pressure is applied; This depends on the presence or absence of electrical continuity between the facing conductors that sandwich the pressure-sensitive conductive rubber sheet that has been burnt out.

It is well known that rubbers containing conductive particles exhibit pressure-sensitive conductivity, and conductive rubbers with particularly high pressure sensitivity are commercially available, and the use of these as pressure sensors has already been proposed. There is. However, this type of pressure-sensitive conductive rubber has the problem that it is not necessarily suitable as a pressure sensor because it does not always exhibit the same conductivity under a constant pressure due to unavoidable lot-to-lot variations.

Regarding lot-to-lot variation, the same applies to the pressure-sensitive conductive rubber sheet containing conductive thin wires used in the present invention, but the unique points of this conductive rubber sheet are:
When two conductive wires are held together under a predetermined pressure and a sufficient current is passed between the conductors, the connected conductive thin wires become activated by burning, and below that pressure, they become completely non-conductive. However, the newly connected thin conductive wire retains its original activity under higher pressure, so this can be used to switch on and off very accurately at a predetermined pressure. This is what a pressure sensor can do.

FIG. 1 shows an example of a pressure sensor obtained by the present invention. 1 is a conductor that supports the pressure-sensitive conductive rubber, but there is also a true conductor 3 and an insulating substrate 2 that supports it.
This is a laminated structure with a laminate structure, which will be further explained later using FIG. 2. 4 is a circular section of a pressure-sensitive conductive rubber sheet, 5 is a flexible conductor that presses the pressure-sensitive conductive rubber under the pressure to be detected, 6 is a spacer, and 7 and 8 are insulating resin. A pair of molded casings connected by 8 lower screws to the container whose pressure is to be sensed. A part of the outer periphery of the casing 7 is cut out in order to fit the conductor 1 into the casing.

FIG. 2 is a plan view of the conductor 1 in FIG. 1. The true conductor 3 is divided into two parts with a gap in between, and each end forms a terminal, which is connected to a control device by soldering, a connector, or the like.

In the above example, the upper conductor was divided into two parts and used as electrical terminals, but it is of course possible to take electrical terminals from each of the upper and lower conductors without dividing the upper conductor.

Pressure-sensitive conductive rubber can be used that has undergone the aforementioned burnout treatment under a predetermined pressure, but after the sensor is assembled, it can be used by applying a predetermined pressure with a voltage applied between the terminals. Burnout treatment is preferable in order to obtain accurate operating pressure. It is even more reliable if both are used together.

The conductor that presses the pressure-sensitive conductive rubber under pressure may be a flexible sheet-like conductor as a whole, but it may be a composite of a conductor sheet and a flexible plastic sheet. Good too. If the substance to be pressure tested is a corrosive fluid, it can be used with a variety of substances by selecting a corrosion-resistant plastic sheet. When the substance to be pressure-tested is a fluid, at least the surface that comes into contact with the fluid is required to be flexible, but when directly receiving a load from a solid, flexibility is not necessarily required. Such an example is shown in FIG.

FIG. 3 shows a kind of tactile sensor, in which a conductor that presses pressure-sensitive conductive rubber 4 is integrated with a contact 5. The other configurations are almost the same as in FIG. 1.

As the pressure-sensitive conductive rubber, those described in JP-A-55-122306 can be used. As the material for the rubber matrix, silicone rubber, urethane rubber, thermoplastic polyester, etc. are preferably used, and among them, a matrix made of silicone rubber is preferable in terms of electrical properties, creep resistance, etc. The pressure-sensitive conductive rubber sheet can be made easily sensitive to small pressures by dividing it into several parts or punching small holes in it.

Factors for adjusting the sensitive pressure include the shape and material of the rubber sheet and the thin conductive wire, but the relationship between the thickness of the sheet and the length of the thin conductive wire is particularly important. An average length to thickness ratio between 1.0 and 0.7 is used. Even if this ratio is set to, for example, 0.90, there is actually a slight distribution around it, but by the time the predetermined set pressure is reached, thin wires that are already connected will be inactivated by being electrically burned out. can do. Although there is no particular restriction on the number of thin wires to be burnt out, it is preferable to adjust the ratio of average length to thickness in advance so that the number does not exceed the middle of the whole.

In order to burn out unnecessary conductive wires, it is preferable to gradually increase the voltage while the voltage is being applied, rather than applying the voltage after reaching the set pressure, since this does not require a large current. Regarding the point at which the burnout treatment is performed, it is preferable to complete the burnout process when the sheet has a large area before being cut into small pieces to be incorporated into a pressure sensor. Methods for burning out large sheets include running them between two energized rollers, sandwiching them between two energized metal sheets, and running them through a roller, or passing them through a rubber bag. Methods such as applying liquid pressure can be applied.

There are various combinations of casing size, shape, and material. In the example shown in Figure 1, an insulator is used as the casing material, but depending on the shape and material of the other parts, metal can also be used as long as the terminals used to detect continuity are not shorted. .

Example 1 (1) Preparation of pressure-sensitive conductive rubber sheet Magnetic stainless steel fibers with a thickness of 12 μm were cut to obtain a large number of short fibers with an average fiber length of 830 μm and a standard deviation of 8 μm. This is mixed with a low-temperature curing silicone rubber stock solution, sandwiched between two polyester sheets in a sandwich pattern with spacers placed around the periphery so that the liquid thickness is 900μ, and then sandwiched between two glass plates. held. After curing the rubber by holding it at 60℃ for 60 minutes with a magnetic field of 1500 Gauss applied in the thickness direction of the sheet, further
After curing at 100°C for 60 minutes, the rubber sheet was taken out. In the rubber sheet, short fibers are oriented in the thickness direction of the sheet, approximately 9 fibers/mm ² are arranged at approximately equal intervals.
existed at a density of

The above rubber sheet was sandwiched over a polyimide film with copper foil attached to one side, and this was placed on a glass plate, and a rubber roller was applied from above while a voltage of 10 V was applied between the two copper foils. Thereafter, a disk with a diameter of 8 mm was cut out from the rubber sheet.

(2) Assembling the pressure sensor The pressure sensor shown in Figure 1 was constructed.

In the figure, the spacer 6 is made from an epoxy glass laminate, has a thickness of 0.80 mm, and an inner diameter of 8.5 mm.
mm, and the outer diameter was 14 mm. The conductor 5 on the pressure receiving side is
A 30μ thick copper foil is pasted on the top surface of a 100μ thick polyimide film, and the outer diameter of the film is 14mm and the outer diameter of the copper foil part is 12mm. The conductor 1 on the back side is made of a 1.6 mm thick epoxy glass laminate with a 30 μ thick copper foil pasted on the bottom surface, and the outer diameter of the laminate at the disc part is 14 mm.
The outer diameter of the copper foil part is 12 mm, and the copper foil is divided into two parts with a gap of 0.5 mm.

(3) Adjusting the pressure sensitive level The assembled pressure sensor was connected to the Chitsuso pressure pipe, and the pressure was increased while measuring the resistance between the terminals.
Conduction occurred when 1.2Kg/cm ² was reached. Once the pressure was lowered, a voltage of 10V was applied between the terminals and the pressure was gradually increased to 1.5Kg/cm ² . During this period, 22 intermittent currents were detected. After reducing the pressure again, measure the resistance between the terminals while approx.
Pressure and depressurization of 1.0Kg/cm ² to 2.0Kg/cm ² were repeated in cycles of seconds, and the pressure at the time when the terminals were turned on and off was measured, and all were 1.5±0.1Kg/cm ²
It has been confirmed that the device can turn on and off at pressures of

[Brief explanation of drawings]

Figure 1 shows one of the pressure sensors obtained by the present invention.
FIG. 3 is a cross-sectional view showing an example. FIG. 2 is a plan view of the conductive plate 1 in FIG. 1. Figure 3 can be called a tactile sensor that is applied when the load to be detected is not a fluid but a contact pressure from a solid.
This is a type of pressure sensor obtained by the present invention.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a pressure sensor consisting of at least the following ○A to ○C, which applies a voltage between conductors stacked facing each other in a pressure load state to connect thin conductive wires in a connected state. A method for manufacturing a pressure sensor characterized by burning out it. ○B When no pressure is applied in an insulating rubber sheet, a large number of conductive thin wires having a length shorter than the thickness of the rubber sheet are oriented in the thickness direction of the rubber sheet, and the conductive wires are oriented in the thickness direction of the rubber sheet. A pressure-sensitive conductive rubber sheet made of thin wires that have been burnt out (B) A conductor that adheres to and presses the conductive rubber sheet (A) under the pressure to be sensed (C) On the back side of the conductive rubber sheet A conductor that is in close contact with and supports this, and that at least a part or all of it overlaps with the conductor marked with ○○.