JPS5828635A - Pressure sensor - Google Patents

Abstract

PURPOSE:To improve the hysteresis of a pressure sensor, by providing two pressure-sensitive elements which are arranged into a slab shape with different characteristics to each other and distributing these pressure-sensitive elements concentrically by fitting a pressure-sensitive element into the hole provided to the other element. CONSTITUTION:Pressure-sensitive elements 11 and 12 comprise the conductive fibers such as the carbon fibers, etc. which are arranged into a flat plate shape so that the state of contact is varied among the fibers by the applied pressure and the resistance value is varied in relation to the change of the contact resistance and the current route. The element 11 is fitted into a circular hole 13 of the element 12, and these elements 11 and 12 are set concentrically to be stored into a casing 15 along with a pressure plate 14. The elements 11 and 12 are then held between a support plate 16 at the bottom of the casing 15 and the plate 14. In such constitution, no difference of output is virtually caused between the elements 11 and 12 to the same level of pressure. Thus the hysteresis is improved greatly 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 pressure sensitive elements whose resistance value changes in relation to changes in the contact state of the fibers in response to applied force.

Conventionally, as a pressure sensor using this type of pressure sensitive element, for example, there is a pressure sensor 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 denotes a pressure-sensitive element, which is 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 applied pressure in the thickness direction, the pressure sensitive element 1 generates stress and stress strain, and as a result, the contact resistance between the fibers and the current path change, resulting in a change in the resistance value of the pressure sensitive element 1. . 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-mentioned pressure sensor has no hysteria in the relationship between pressure and resistance value due to the mechanical properties of conductive fibers such as carbon fibers.

Therefore, the resolution of pressure detection is narrow and the applications are limited.

The present invention has been made in view of the above-mentioned circumstances regarding a pressure sensor using conductive fibers, and includes one of two pressure-sensitive elements each having different characteristics, each of which is formed by orienting conductive fibers such as carbon fibers in a flat plate shape. The other pressure sensing element is fitted into the hole provided in the hole and arranged concentrically, and is held between the support plate and the pressure plate, and the resistance value of these two pressure sensing elements is used to apply the pressure through the pressure transmitting member. It is an object of the present invention to provide a pressure sensor that improves the hysteresis that exists between pressure and resistance value by differentially combining two pressure-sensitive elements with different characteristics by detecting the pressure applied to the pressure plate. The purpose is

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

Figure 3! In this case, 11 and 12 are pressure sensitive elements similar to those shown in FIG. The conductive fibers are made of conductive fibers such as carbon fibers that are oriented in a flat plate shape so that the resistance value changes as a result of the change in resistance value.

The pressure-sensitive element 11 has a disk-like shape, and the pressure-sensitive element 12 has an annular shape with a hole 13 in the center having a diameter slightly larger than the diameter of the pressure-sensitive element 11. The pressure sensitive elements 11 and 12 have the same thickness.

Electrode plates 11a and llb are adhered to the upper and lower surfaces of the pressure sensitive element 11, respectively, and electrode plates 12a and 12b are adhered to the upper and lower surfaces of the pressure sensitive element 12, respectively.

The pressure sensitive element 11 is the hole 13 of the annular pressure sensitive element 12.
The two pressure sensitive elements 11 and 12 are arranged concentrically and accommodated in the casing 15 together with the pressure plate 14, and the It holds pressure sensitive elements 11 and 12.

Electrode plates 11a and 12 of the pressure sensitive elements 11 and 12
The electrode plates 11b and 12b are bonded to the pressure plate 14, and the electrode plates 11b and 12b are bonded to the support plate 16 of the casing 15, respectively.

The pressure plate 14 has an external pressure transmission member 17 protruding from the center of its upper surface through the hole 18 of the casing 15 so as to be freely retractable, while a compression spring 19 is compressed between the pressure plate 14 and the support plate 16 I am wearing it.

As described in Japanese Patent Application No. 56-67264, the compression spring 19 suppresses creep strain caused by the mechanical properties of the conductive fibers of the pressure sensitive elements 11 and 12, and expands the pressure measurement range. The above compression spring 1
The pressure plate 14 , which is urged away from the support plate 16 by the pressure transmitting member 17 , is pressed against a step 20 provided inside the casing 15 and has a limited range of motion against pressure applied from the outside through the pressure transmission member 17 . be done.

The pressure sensor described above is used by being incorporated into the circuit shown in FIG.

In Fig. 4, R1 and R2 are semi-fixed variable resistors, k
0□ and □2 are resistances representing pressure sensitive elements 11 and 12, respectively, and these variable resistors Rt.

R2, resistor R□, and '12 are connected to form each side of the bridge, respectively.

That is, the electrode plates 11b and 1 between the pressure sensitive elements 11 and 12
2b is connected to the ground, and a variable resistor of 0 is connected between the electrode plate 11a of the pressure-sensitive element 11 and the power source +■D, and 0 is connected between the electrode plate 12a of the pressure-sensitive element 12 and the power source +■D. A variable resistor R2 is connected between them.

The potential ■□ of the electrode plate 11a and the potential v of the electrode plate 12a
The potential difference of 12 (0, -2, 2) is amplified by a well-known subtraction amplifier consisting of an operational amplifier OA, resistors R3, R4, Rs, and 6.

If the pressure-sensitive sensor has the above configuration, the applied force applied to the protruding portion of the casing 15 of the pressure-transmitting member 17 is transmitted to the pressure-sensitive element 11.12 and the compression spring 19 through the stop plate 14.

For this reason, these pressure sensitive elements 11 and 12 and the compression spring 1
9 receives the above-mentioned applied force and generates stress as well as stress strain.

Stress strain generated in compression spring 21 and pressure sensitive elements 11 and 12
occurs in The stress strain is constant, and the sum of the stresses generated in the pressure sensitive elements 11 and 12 appears as the stress generated at the tip of the pressure transmitting member 17.

The stress strain of each pressure-sensitive element 11 and 12 is determined by the mechanical properties of these pressure-sensitive elements 11 and 12, and specifically determined by the firing temperature at the time of adult cow and the type of fiber raw material.

Therefore, when pressure is applied to the pressure-sensitive element 11, its resistance value changes along the curve 11 in the direction of arrow A0, as shown in FIG. When the applied force is removed, the resistance value of the pressure sensitive element 11 changes along the curve 1'H in the direction of arrow A; Therefore, a difference of Δ and □l occurs in the resistance value of the pressure sensitive element 11.

Similarly to the above, when the pressure sensitive element 12 is pressurized, its resistance value changes along the curve 12 in the direction of 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 ea in the direction of arrow A↓. For the same pressure P, there is a difference of Δ and □2 in the resistance value of the pressure sensitive element 12 between pressurization and depressurization.

However, in the circuit shown in Figure 4, the variable resistor
4. R2 makes the resistor □ and 12 (pressure sensitive element 1
1 and 12) respectively, and adjust the currents I0 and 12 flowing through ΔRu×11=Δ12× in the entire range of applied pressure.
I2, the electrode plate 11a of the pressure sensitive element 11
The potentials ■, □ and the potential of the electrode plate 12a of the pressure-sensitive element 12 ■□
For the same pressure P, the value of the potential difference (■11-■□2) of 2 is the same when pressurizing and when pressurizing, as follows.

That is, with respect to the above pressure P, when pressurizing, ■1l-v1
2=R11x11-R12x12, and when the pressure is removed, ■1l-v12"(R11+'R11)11"-(R1
2+ΔR12) 12 = Rt t X I t-R1
2X I 2.

Therefore, the output V of the operational term intermediate unit OA is obtained by amplifying the potential difference (Vt□-■□2). As shown in Figure 6, the third
Hysteresis can be almost eliminated with respect to the pressure applied to the pressure sensor shown in the figure.

The pressure sensor shown in FIG. 3 is used when measuring force or load applied to the pressure transmission member 17, but when measuring liquid pressure or gas pressure, etc., the pressure sensor shown in FIG. 7 is used. As shown in Fig. 3, the pressure sensor casing 1
A slit-like recess 3 is formed on the protruding end surface of the pressure transmitting member 17 of No. 5.
1, a diaphragm 32 is bonded to the open end surface of the recess 31, and the diaphragm 32 is bonded to the tip surface of the pressure transmitting member 17.

The present invention is not limited to the above-mentioned embodiments, and various configurations can be made within the scope of the gist of the present invention.

As is clear from the above detailed explanation, the present invention provides two pressure-sensitive elements having different characteristics each formed by orienting conductive fibers in a flat plate shape between a support plate and a pressure plate in a concentric manner. In addition, these two pressure-sensitive elements are differentially combined to cancel out the hysteresis of each pressure-sensitive element, so the difference in output for the same pressure applied to the pressure sensor is Hysteresis is almost completely eliminated, hysteresis is greatly improved, and the applications of pressure sensors are expanded.

[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 applied force and resistance value of the pressure sensor of FIG. 1, FIG. 3 is a sectional view showing the general structure of the pressure sensor according to the present invention, and FIG. A circuit diagram for pressure detection used in the pressure sensor; FIG. 5 is a characteristic diagram showing the relationship between the applied force and the resistance value of the two pressure sensing elements used in the pressure sensor shown in FIG. 3; 6 is an explanatory diagram of the output of the pressure detection circuit of FIG. 4, and FIG. 7 is a sectional view of a modification of FIG. 3. 11, 12...Pressure sensitive element (tta, xl, x2a
. 12b...electrode plate), 13...hole, 14...pressure plate, 15...casing, 16...support plate, 17...
...Pressure transmission member, 19...Compression spring, 31...Recess, 32...Diaphragm. Patent applicant: Sharp Co., Ltd. Agent: Patent attorney: Aobai Ao and two others Figure 1 Figure 2

Claims (1)

[Claims] (1) Two pressure-sensitive pieces with different characteristics that are oriented and formed 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. the pressure-sensitive elements are arranged concentrically by fitting the other pressure-sensitive element into a hole provided in one of the pressure-sensitive elements,
The two pressure-sensitive elements are held between the support plate and a pressure plate to which external pressure is applied from an external pressure transmission member, and a compression spring is compressed between the support plate and the pressure plate. A pressure sensor characterized in that pressure applied to a pressure transmission member is detected from a resistance value of a pressure sensitive element.