JPS5828634A - Pressure sensor - Google Patents

Abstract

PURPOSE:To increase greatly the hysteresis of a pressure sensor, by combining differentially two pressure-sensitive elements which are formed by orienting the conductive fibers into a flat plate shape with different characteristics to each other and offsetting the hysteresises of both pressure-sensitive elements. CONSTITUTION:As shown in the diagram, pressure-sensitive elements 11 and 12 are adhered to the upper and lower faces of an electrode plate 13 by means of a conductive adhesive. At the same time, an electrode plate 15 is adhered to the upper face of the element 11 to be opposite to the plate 13 by means of a conductive adhesive. The elements 11 and 12 laminated to each other with intervension of the plate 13 are stored into a casing 17 along with a pressure plate 16 to be held between a support plate 18 at the bottom of the casing 17 and the plate 16. The hysteresises of the elements 11 and 12 are offsett to each other by combining differentially these pressure-sensitive elements having different characteristics. Thus the hysteresis is greatly improved for a pressure sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensor that uses conductive fibers, such as carbon fibers, as a pressure-sensitive element, whose resistance value changes in relation to changes in the contact state of the fibers in response to applied force.

Conventionally, there is one example of a pressure sensor using this type of pressure sensitive element, which was proposed by the present applicant in Japanese Patent Application No. 56-67264 (title of the invention "Pressure Sensor").

The above-mentioned pressure sensor has a basic configuration as shown in a sectional view in FIG.

In FIG. 1, reference numeral 1 designates a pressure-sensitive element made by orienting and molding conductive fibers such as carbon fibers into a flat plate shape, and the fibers are intricately entangled with each other. 2a and 2b are electrode plates adhered to both sides of the pressure sensitive element 1.

In response to the applied pressure in the thickness direction, the pressure sensitive element 1 generates stress and stress strain, and the contact resistance between the fibers and the current path change accordingly, causing the pressure sensitive element 1 to
resistance value changes. Changes in resistance value are detected by electrode plates 2a and 2b.

The resistance value of the pressure sensor shown in FIG. 1 changes as shown in FIG. 2 with respect to applied pressure.

However, the above pressure sensor has hysteresis in the relationship between pressure and resistance value due to the mechanical properties of conductive fibers such as carbon fibers, and it is difficult to remove this hysteresis. there were.

The present invention has been made in view of the important issues regarding pressure sensors using conductive fibers, and the present invention is based on two pressure-sensitive sensors having different characteristics each formed by orienting conductive fibers such as returned fibers in a flat plate shape. By stacking elements and holding them between a support plate and a pressure plate, and detecting the pressure applied to the pressure plate through the pressure transmission member from the resistance value of these two pressure-sensitive elements, it is possible to detect two pressure-sensitive elements with different characteristics. It is an object of the present invention to provide a pressure sensor in which two pressure sensing elements are differentially combined to improve the hysteresis that exists between pressure and resistance value.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 8, reference numerals 11 and 12 are pressure sensitive elements similar to those in FIG. The conductive fibers are made of conductive fibers such as return fibers that are oriented in a flat plate shape so that the resistance value changes in relation to the applied pressure.

As shown in FIG. 4, the pressure-sensitive elements 11 and 12 are bonded to the upper and lower surfaces of the electrode plate 18 using a conductive adhesive, respectively, and the pressure-sensitive elements 11 and 12 are placed opposite to the electrode plate 13. An electrode plate 14 is attached to the upper surface of the pressure-sensitive element 12, and an electrode plate 15 is attached to the lower surface of the pressure-sensitive element 12 using a conductive adhesive.

As shown in FIG. 8, the pressure-sensitive elements 11 and 12 stacked with the electrode plate 13 in between are accommodated in the casing 17 together with the pressure plate 16, and the support plate 18 at the bottom of the casing 17 The pressure sensitive element 1 is placed between the pressure plate 16 and the pressure plate 16.
It holds 1 and 12.

The electrode plate 14 of the pressure sensitive element 11 is also connected to the pressure plate 16.

The electrode plates 15 of the pressure-sensitive element 12 are adhered to the support plates 18 of the casing 17, respectively.

The pressure plate 16 has an external pressure transmission member 19 protruding from the center of its upper surface through the hole 20 of the casing 17 so as to be freely retractable, and a compression spring 21 is compressed between the pressure plate 16 and the support plate 18. are doing.

As described in Japanese Patent Application No. 56-67264, the compression spring 21 is designed to suppress creep strain caused by the mechanical properties of the conductive fibers of the pressure-sensitive elements 11 and 12, and to widen the pressure measurement range. This is for the purpose of expanding the compression spring 2.
The pressure plate 16, which is urged to move away from the support plate 18 from 1 to 1, operates by being pressed against a step 22 provided inside the casing 17 against pressure applied from the outside through the pressure transmission member 19. Range is limited.

The pressure sensor is incorporated into the circuit of FIG.

In FIG. 5, R1 and R2 are semi-fixed variable resistors, R
11 and R12 are resistors representing pressure sensitive elements 11 and 12, respectively, and these variable resistors R and R2 and resistor R1
1 and R12 are connected to each side of the bridge.

That is, the electrode plate 18 between the pressure sensitive elements 11 and 12 is connected to the ground, and a variable resistor R1 is connected between the electrode plate 14 of the pressure sensitive element 11 and the power supply +VD, and the pressure sensitive element 12 is connected to the ground. A variable resistor R2 is connected between each electrode plate 15 and the power supply +VD.

The potential Vll of the electrode plate 14 and the potential V12 of the electrode plate 15
'2) Potential difference (Vll - V12) C. It is amplified by a well-known subtraction amplifier consisting of an operational amplifier OA and resistors RB, R4, R5 and R6.

When the pressure sensor has the above configuration, the applied force applied to the protruding portion of the casing 17 of the pressure transmission member 19 is transmitted to the pressure sensing element 11.12 and the compression spring 21 through the pressure plate 16.

For this reason, these pressure sensitive elements 11, 12 and compression springs 2
1 generates stress upon receiving the above-mentioned applied force, and also causes stress strain.

Stress strain generated in compression spring 21 and pressure sensitive elements 11 and 12
The stress and strain caused by the pressure sensitive elements 11 and 12 are of the same magnitude, and the pressure sensitive elements 11 and 12 are laminated together.

Although the stress generated is the same, the stress strain of each is determined by the mechanical properties of the pressure sensitive elements 11 and 12.

Therefore, when the tS pressure element 11 is pressurized, its resistance value changes along the curve j1 in the direction of the arrow A1, as shown in FIG.
However, when the force applied to the pressure sensitive element 11 is removed, the resistance value of the pressure sensitive element 11 changes as follows.
A curved line in the direction of arrow A'1! 1, and a difference of ΔR11 occurs in the resistance value of the pressure sensitive element 11 for the same pressure P during pressurization and depressurization.

Similarly to the above, when the pressure sensitive element 12 is pressurized, its resistance value changes along the curve j2 in the direction of the arrow A2, as shown in FIG.
On the other hand, when the force applied to the pressure sensitive element 12 is removed, the resistance value of the pressure sensitive element 12 changes along the curve ze in the direction of arrow A/, and During pressurization and depressurization, the resistance value of the pressure sensitive element 12 changes by Δ for the same pressure PK.
A difference in R12 occurs.

However, in the circuit of FIG.
, R2, resistors R11 and R12 (pressure sensitive element 11
and 12], respectively, by adjusting the currents 11 and I2 flowing through them, and ΔR11×work1=ΔR12 over the entire range of applied pressure.
X I2 , the potential Vll of the electrode plate 14 of the pressure sensitive element 11 and the potential V of the electrode plate 15 of the pressure sensitive element 12
The value of the potential difference (Vll - V12) of 12 mm is the same for the same pressure P during pressurization and depressurization, as in the first order.

That is, when pressurizing with respect to the above pressure P.

Vll - V12 = R11X II - R12X
I2, when the pressure is removed.

Vll −V12 = (R11+ΔR11) II
(R12+ΔR12) l2=R11X II −
It becomes R12XI2.

Therefore, the output V of the operational amplifier OA amplifies the potential difference (vtt - V12). As shown in FIG. 7, it is possible to almost eliminate hysteresis with respect to the pressure applied to the pressure sensor shown in FIG.

Note that the pressure sensor shown in FIG.
'It is used when measuring the force or load applied to the material 19, but when measuring liquid pressure or gas pressure, etc., the casing 17 of the pressure sensor shown in FIG. The pressure transmitting member 19 is provided with four mercury-shaped parts 81 on the protruding end surface, a diaphragm 82 is bonded to the open end surface of the recess 81, and the diaphragm 32 is bonded to the tip surface of the pressure transmitting member 19. be able to.

The present invention is not limited to the above embodiments.

Various configurations can be made within the scope of the invention.

As is clear from the above detailed explanation, the present invention is directed to a method of differentially combining two pressure-sensitive elements having different characteristics each made of conductive fibers oriented in the form of a flat plate. Since the existing hysteresis is canceled out, there is almost no difference in output for the same pressure applied to the pressure sensor, and the hysteresis of the pressure sensor can be greatly improved.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the basic configuration of a conventional pressure sensor.
2 is a characteristic diagram showing the relationship between the applied force and the resistance value of the pressure sensor shown in FIG. 1, FIG. 8 is a sectional view showing the general structure of the pressure sensor according to the present invention, and FIG. A cross-sectional view of a pressure-sensitive element used in a pressure sensor, Figure 5 is a circuit diagram for pressure detection used in the pressure sensor in Figure 8, and Figure 6 is a cross-sectional diagram of the pressure sensing element used in the pressure sensor in Figure 3. Characteristic diagrams showing the relationship between the applied force and the resistance value with respect to the applied force of the pressure-sensitive element, FIG. 7 is an explanatory diagram of the output of the pressure detection circuit of FIG. 5, and FIG.
FIG. 7 is a cross-sectional view of a modification of the figure. 11%12...Pressure sensitive element, 18.14.15...Electrode plate, 16...Pressure plate, 17...Casing, 18
...Support plate, 19...Pressure transmission member, 81...Recess, 82...Diaphragm. Patent applicant: Sharp Co., Ltd. Agent: Patent attorney: Aobai Ao and 2 others Figure 1 Figure 2

Claims (1)

[Claims] (1) Made of conductive fibers such as carbon fibers that are oriented in a flat plate shape so that the contact state between the fibers changes depending on the applied pressure, and the resistance value changes in relation to the change in contact resistance and current path. Two pressure-sensitive elements having different characteristics are provided, and these pressure-sensitive elements are stacked and held between a support plate thereof and a pressure plate to which external pressure is applied from an external pressure transmission member, and A pressure sensor characterized in that a compression spring is installed between the pressure plate and the pressure plate, and the pressure applied to the pressure transmission member is detected from the resistance values of the two pressure sensing elements.