JP2009025065A - Pressure sensor and distributed pressure sensor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact pressure sensor which can measure a micro pressure whose pressure level is in a degree of 1 kPa, can measure the varying pressure over a wide range of 1 kPa to 100 kPa, and is less apt to break, and to provide a distributed pressure sensor capable of measuring a pressure distribution with high density. <P>SOLUTION: A pair of elastic members 30 are jointed to both surfaces of a piezoelectric lamella 10, formed by stretching a polymer piezoelectric material, and a pressure-receivingplate 40 is jointed to an end face of the piezoelectric lamella 10. A micro varying pressure can be measured with high sensitivity, by making the surface area of the pressure plate 40 which is wider than the cross section of the end face of the piezoelectric lamella 10, and thereby allowing pressure received with the large pressure plate 40 to gather and act on the thin cut face of the piezoelectric lamella 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pressure sensor that detects minute fluctuating pressure of liquid, gas, or solid, and a distributed pressure sensor that detects pressure distribution. In particular, the present invention relates to a pressure sensor that is highly sensitive and that is difficult to break, and that can be manufactured with a small size of a pressure receiving surface, and a distributed pressure sensor in which a plurality of pressure sensors are arranged at high density.

  A conventional pressure sensor has a strain detection element such as a strain gauge attached to the back of a circular pressure plate that supports the periphery, and measures the bending strain when the pressure plate is bent out of the plane under pressure. There are many things to measure. Then, a piezoelectric material plate has been widely used as an integrated pressure receiving plate and strain gauge.

The piezoelectric material plate has the characteristic of sensitively outputting electrical signals due to the piezoelectric effect caused by the load, so that a force is applied from the vertical direction to the larger surface of the piezoelectric material plate to distort the piezoelectric material plate. Development of a sensor that detects a charge signal generated by measuring the pressure of a liquid, gas, or solid is progressing (for example, FIG. 1 and [0026] of Patent Document 1, FIG. 1 of Patent Document 2, and Patent Document 4). 3, FIG. 2 and [0018] of Patent Document 5, FIG. 1 and FIG. 2 of Patent Document 6, FIG. 1, FIG. 2, [0008] and [0009] of Patent Document 7, FIG. 9, FIG. 5 and [0009] of Patent Document 9, FIGS. 1 and 3 of Patent Document 10, FIGS. 1 and 4 of Patent Document 11, FIG. 1 of Patent Document 12, FIG. 1 and FIG. 3 of Patent Document 13, Patent (See FIG. 1 of reference 14).
JP 2006-340944 A JP 2006-226858 A JP 2006-194669 A JP 2006-38710 A JP 2005-221339 A JP 2005-147991 A Japanese Patent Laying-Open No. 2005-147983 JP 2002-148273 A JP-A-11-169592 JP-A-9-229729 JP-A-8-327416 Japanese Patent Laid-Open No. 4-127027 JP-A-2-268230 JP-A 64-54225

  In all of the above patent documents, pressure is measured from the direction perpendicular to the larger surface of the piezoelectric material plate, the pressure is measured by bending the piezoelectric material plate, and force is applied from the end surface of the piezoelectric material plate. There is no one that measures pressure by adding.

  The piezoelectric material plate is manufactured by stretching a piezoelectric material made of a polymer, and a large charge signal flows mainly when strained in the stretching direction. When a force is applied perpendicularly to the surface of the piezoelectric material plate as in the above-mentioned patent document, the force is transmitted concentrically, but only a part of the force that is distorted in the stretching direction from the force applied perpendicularly to the piezoelectric material plate surface . For this reason, only a part of the applied force only distorts the piezoelectric material plate. Therefore, there is a problem that the sensitivity is low and it is difficult to measure a minute pressure. And the amplification factor of an amplifier must be made very high, drift becomes large, and an accurate pressure cannot be detected.

  Furthermore, in order to measure a minute pressure with such a configuration, the piezoelectric material plate must be thin and have a large area. If the piezoelectric material plate is made thinner, the deflection becomes larger and a minute pressure can be detected. However, if the piezoelectric material plate is made thinner, if a minute pressure of about 1 kPa can be measured, the pressure sensor can easily be detected by the pressure exceeding the upper limit. There is a problem that it breaks. For example, a pressure sensor that measures a minute pressure of about 1 kPa breaks when a pressure of 10 kPa, which is approximately 10 times higher, is applied.

  In addition, if the area of the piezoelectric material plate is increased, the piezoelectric material plate is easily bent, so that even a minute pressure can be detected, but there is a problem that a small sensor cannot be manufactured. For this reason, most of the sensors for measuring micro pressure currently on the market are circular with a diameter of 9 mm or more.

  Under such circumstances, there is currently no small pressure sensor that can measure a minute pressure and has a wide allowable pressure range and is not easily broken.

  The problem to be solved by the present invention is to provide a small pressure sensor that can measure a minute pressure of a pressure level of 1 kPa and can measure a wide range of fluctuating pressures of 1 kPa to 100 kPa and is not easily broken. Another object of the present invention is to provide a distributed pressure sensor capable of measuring a pressure distribution with high density by arranging a plurality of pressure sensors in a straight line or two-dimensionally.

  The present invention includes a piezoelectric thin plate made of a piezoelectric material, and a pressure receiving plate disposed on an end surface of the piezoelectric thin plate and having an area larger than a cross-sectional area of the end surface of the piezoelectric thin plate, and the pressure received by the pressure receiving plate is It is characterized in that a minute pressure is detected in addition to being perpendicular to the end face of the piezoelectric thin plate.

  Further, the present invention provides an elastic member for sandwiching the piezoelectric thin plate, makes an elastic modulus of the elastic member smaller than an elastic modulus of the piezoelectric thin plate, and concentrates the force received by the pressure receiving plate on the piezoelectric thin plate. It is characterized by adding.

  Furthermore, the present invention is characterized in that the elastic modulus of the elastic member is 1/100 to 1/2000 of the elastic modulus of the piezoelectric thin plate.

  Furthermore, the present invention is characterized in that the elastic member is selected from natural rubber, synthetic rubber, silicon rubber, sponge rubber, sponge, foam rubber, or cork.

  Furthermore, the present invention is characterized in that the piezoelectric thin plate is formed by stretching a piezoelectric material, and the pressure receiving plate is disposed on an end surface in the stretching direction of the piezoelectric thin plate.

  Furthermore, the present invention is characterized in that the piezoelectric thin plate is made of a polymer piezoelectric material made of polyvinylidene fluoride or vinylidene cyanide.

  Furthermore, the present invention is characterized in that an area of the pressure receiving plate is 20 times or more an end surface area of the piezoelectric thin plate.

  Furthermore, the present invention is characterized in that a plurality of the piezoelectric thin plates are arranged in parallel.

  Furthermore, the present invention is characterized in that the piezoelectric thin plate and the elastic member are covered with a box having an opening surface on one surface, and the pressure receiving plate is directed to the opening surface.

  Furthermore, the present invention is characterized in that the pressure receiving plate is rectangular.

  Furthermore, the present invention is characterized in that the pressure receiving plate has a curved surface.

  Furthermore, the present invention is characterized in that a plurality of pressure sensors according to claim 10 are used, and the surfaces of the pressure receiving plates are aligned and adjacently arranged linearly or two-dimensionally.

  According to the present invention, the pressure receiving plate is installed on the end face of the piezoelectric thin plate, and the surface area of the pressure receiving plate is made larger than the area of the end face of the piezoelectric thin plate. A force is collected by a pressure plate having a large surface area, and this force is concentrated on a small end face of the piezoelectric thin plate to distort the piezoelectric thin plate. Therefore, the sensitivity is high and a minute pressure can be detected.

  Further, according to the present invention, since the elastic member is made of a material having a smaller elastic modulus than the piezoelectric thin plate, most of the force received by the pressure receiving plate is applied to the piezoelectric thin plate, not the elastic member. For this reason, most of the force received by the pressure receiving plate distorts the piezoelectric thin plate in the stretching direction, and a highly sensitive pressure sensor can be provided.

  Furthermore, according to the present invention, both surfaces of the piezoelectric thin plate are sandwiched between elastic members to suppress bending. Since the piezoelectric thin plate is distorted only in the stretching direction, the applied force and the amount of distortion are in a proportional relationship, so there is an advantage that there is no measurement error due to bending and that an accurate fluctuating pressure can be detected.

Furthermore, according to the present invention, the pressure is detected by applying a force in the extending direction of the piezoelectric thin plate. Since the piezoelectric thin plate mainly generates a charge signal according to the amount of strain in the stretching direction, the applied force directly distorts the piezoelectric thin plate in the stretching direction without waste, so that the piezoelectric thin plate is as small as 1 kPa (0.1 g / mm ² ). This has the advantage that it can be detected with high sensitivity even at a low pressure.

  Furthermore, according to the present invention, since both sides of the piezoelectric thin plate are sandwiched between elastic members, the piezoelectric thin plate is not broken and a high-pressure sensor is realized.

  Furthermore, according to the present invention, since the outside is covered with a box having high hardness such as metal, there is an advantage that a pressure sensor with increased strength can be provided.

  Further, since the plurality of piezoelectric thin plates are arranged, the pressure receiving plate does not tilt, and the force received by the pressure receiving plate is transmitted to the piezoelectric thin plate, so that the pressure can be detected with high sensitivity.

  Furthermore, according to the present invention, since a pressure can be detected with high sensitivity without using a large piezoelectric thin plate, a small pressure sensor can be provided.

  Furthermore, according to the present invention, since all are made of a solid material, there is an advantage that it is easy to handle and hard to break.

  Furthermore, the pressure receiving plate can be used in a desired shape such as a rectangle, and a distributed pressure sensor in which a plurality of pressure sensors having a rectangular pressure receiving plate are arranged adjacent to each other can be obtained. Thereby, since there is no gap between the pressure sensors, accurate pressure distribution measurement can be realized.

  Furthermore, since the pressure-receiving plate surface can be formed of a curved surface, the pressure can be measured even if the portion to be measured such as the bow has a shape other than the plane.

  With reference to FIG.1 and FIG.2, schematic structure of the pressure sensor of this invention is demonstrated. FIG. 1 is a plan view (A) of a pressure sensor according to the present invention and a cross-sectional view (B) of an A-A ′ portion. FIG. 2 is a perspective view of the main part of the pressure sensor.

  As shown in FIGS. 1A, 1B, and 2, the pressure sensor has a surface area larger than the area of the end face of the piezoelectric thin plate 10 on the end face of the piezoelectric thin plate 10 with the electrode film 20 attached to the front and back surfaces. A pressure receiving plate 40 is arranged, and a pair of flexible elastic members 30 are joined in a form in which the electrode films 20 on both sides of the piezoelectric thin plate 10 are sandwiched.

  The pressure receiving plate 40 is joined to the entire one end surface (T1) of the elastic member 30 and the piezoelectric thin plate 10, and this is accommodated in a case 60 of a rigid member. The pressure receiving plate 40 protrudes slightly from the opening of the rigid member case 60 and is disposed on a plane parallel to the opening surface, and the other end surface (T2) of the elastic member 30 and the piezoelectric thin plate 10 is the bottom surface of the rigid member case 60. It is fixed to. Wirings (80A, 80B) are connected to the electrode film 20 via electrical terminals.

  The piezoelectric thin plate 10 measures a minute pressure fluctuation by concentrating the pressure received by the surface of the pressure receiving plate 40 on a small end surface of the piezoelectric thin plate 10. For this reason, since it is better that the cross-sectional area of the end face of the piezoelectric thin plate 10 is as small as possible, a thin one is preferably used, and one having a thickness of 20 μm to 200 μm is preferably used.

  In the present invention, the piezoelectric thin plate 10 formed by stretching a polymer piezoelectric material having a low elastic modulus, such as polyvinylidene fluoride or vinylidene cyanide, is preferably used because the charge signal is generated by the stretching strain of the piezoelectric thin plate 10. .

  Further, the pressure receiving plate 40 may be installed on the end surface of the piezoelectric thin plate 10 in the extending direction. The piezoelectric thin plate 10 made of a polymer piezoelectric material is usually uniaxially stretched (for example, 1) weighted stretching: a method in which a polymer piezoelectric material is stretched while being heated to a glass transition temperature. 2) Method using an automatic stretching machine: A method in which a polymer piezoelectric material is stretched by a motor while being heated to a glass transition temperature. 3) Vapor exposure stretching method: There is a method of manually stretching a polymer piezoelectric material while exposing it to boiling water vapor. ) And polarized by applying a high voltage. In this case, the piezoelectric thin plate 10 is mainly polarized in accordance with the amount of strain in the stretching direction and generates an electrical signal.

  A pair of electrode films 20 are provided on the front and back surfaces of the piezoelectric thin plate 10 by vapor deposition, sputtering, etc., and electrical terminals are attached to the electrode film 20 with conductive paint, caulking, etc., and wirings (80A, 80B) are connected to each. A commercially available piezoelectric film having electrode films attached to both sides may be used as it is.

  As the pair of flexible elastic members 30 to be joined in such a manner as to sandwich the electrode films 20 on both surfaces of the piezoelectric thin plate 10, those having a thickness of 0.5 mm to 10 mm and an elastic modulus smaller than that of the piezoelectric thin plate 10 are used.

  Since the elastic modulus of the elastic member is smaller than that of the piezoelectric thin plate, most of the force received by the pressure receiving plate is applied to the piezoelectric thin plate, and the expansion / contraction strain of the piezoelectric thin plate is promoted. Thereby, even if a minute force is applied to the pressure receiving plate, the force is efficiently applied to the piezoelectric thin plate, so that even a minute pressure can be detected.

  A flexible elastic member having a modulus of elasticity of 1/100 to 1/2000 of the piezoelectric thin plate 10 may be used, and examples of the elastic member 20 include natural rubber, synthetic rubber, silicon rubber, sponge rubber, sponge, and foam rubber. Various rubbers or rubber-based materials can be suitably used. You may use the material which bonded various rubber | gum and rubber-type material, or the material which bonded the cork board to various rubber | gum.

  When the elastic modulus of the elastic member 30 is very small, the elastic member 30 is likely to be deformed. In particular, when the elastic member 30 is deformed in a left-right imbalance, the piezoelectric thin plate 10 is bent, and there is a possibility that a charge signal proportional to the pressure cannot be output. In such a case, the elastic member 30 having a larger elastic modulus may be disposed on the side away from the piezoelectric thin plate 10, and the bending of the piezoelectric thin plate 10 due to the unequal deformation of the elastic member 30 can be suppressed, and the charge signal proportional to the pressure. Will be output.

  The pair of elastic members 30 are used with the same width, and the piezoelectric thin plate 10 is disposed substantially at the center. If the position of the piezoelectric thin plate 10 is the center, both the elastic members 30 are uniformly deformed, so that the pressure receiving plate 40 does not tilt and the pressure can be detected accurately.

  The electrodes 20 on the front and back surfaces of the piezoelectric thin plate 10 and the flexible elastic member 30 are integrated by bonding with an adhesive having an elastic modulus substantially equal to that of the flexible elastic member 30 after curing.

  The pressure receiving plate 40 is a thin and rigid plate such as a metal plate, a resin plate, or a composite material plate. And since the received pressure plate 40 concentrates and applies the received force to the end surface of the piezoelectric thin plate 10, it is good to use a thing with a large surface area.

In the present invention, a small pressure sensor can be provided by reducing the surface area of the pressure receiving plate 40. For example, a side pressure of about 2 mm can be provided, and a 4 mm ² square pressure receiving plate 40 can be used as a small pressure sensor. In this case, if the thickness of the piezoelectric thin plate 10 to be used is 100 μm, the end face of the piezoelectric thin plate 10 is 0.2 mm ² , so the surface area of the pressure receiving plate 40 is 20 times that of the end face of the piezoelectric thin plate 10. If the surface area of the pressure receiving plate 40 is too small, no force can be collected on the end face of the piezoelectric thin plate 10, so that the pressure receiving plate 40 has an area of 20 times or more that of the end face of the piezoelectric thin plate 10. preferable.

  The pressure receiving plate 40 is used in the same shape as the shape of the integrated piezoelectric thin plate 10 and the end face (T1) of the elastic member 30, and the pressure receiving plate 40 is applied to one end face (T1) of the piezoelectric thin plate 10 and the elastic member 30 as a whole. Join.

  The pressure receiving plate 10 may be formed in various shapes such as a circle or a rectangle. If the pressure receiving plate 10 is rectangular, a plurality of pressure sensors can be adjacent to each other without a gap as will be described later, and distribution of water pressure or the like can be easily measured.

  The rigid member case 60 is made by processing a material such as metal or resin. An opening and a wiring hole that are slightly larger than the dimensions of the pressure receiving plate 40 are processed in the case 60, and the other parts around the case 60 are manufactured in a sealed form.

  The vicinity of the surface of the opening of the rigid member case 60 and the periphery of the piezoelectric thin plate 10 and the elastic member 30 are sealed by the seal member 90 over the entire periphery near the surface of the opening. Further, the wiring (80A, 80B) is pulled out of the rigid member case 60 through a wiring hole provided in a part of the rigid member case 60, and the drawn portion is sealed.

  The piezoelectric thin plate 10 and the elastic member 30 are housed in a rigid member case 60, and the piezoelectric thin plate 10 and the elastic member are placed in a state where the surface of the pressure receiving plate 40 slightly protrudes from the opening of the rigid member case 60 and is parallel to the opening surface. The other end surface (T2) of 30 is fixed to the bottom surface of the rigid member case 60 with an adhesive or the like.

  Next, the vicinity of the surface of the opening of the rigid member case 60 and the periphery of the piezoelectric thin plate 10 and the elastic member 30 are sealed and sealed with a sealing member 90 such as a thin rubber film over the entire periphery in substantially the same plane as the opening. . Further, after the wiring is pulled out of the case 60, the wiring hole is also sealed with a sealing member to be sealed.

  The pressure sensor configured as described above is used by fixing a part of the rigid member case 60 excluding the pressure receiving surface to an object. The fixing method may be bonding, fixing with an adhesive tape, screwing fixing, or the like.

  As described above, the pressure receiving plate 40 is disposed on the end face of the piezoelectric thin plate 10 so that force is applied from the direction in which the strength of the piezoelectric thin plate 10 is high, and the structure is supported by the elastic member 30 from both sides of the piezoelectric thin plate 10. For this reason, the sensor body is not broken, and the pressure sensor is excellent in strength. For the same reason, a wide allowable pressure measurement range is realized. Further, since it is covered with a case 60 made of a rigid member, the pressure sensor is further enhanced in strength.

  Next, the detection principle of the pressure of the pressure sensor of the present invention will be described with reference to FIGS.

  3 and 4 show a structure in which a pressure receiving plate 40 is joined to one end face of the piezoelectric thin plate 10 to which the electrode film of FIG. 1 is attached. FIG. 3 shows that the elastic member is not provided, and FIG. It shows what was provided. The direction of the pressure to be measured is the direction indicated by the arrows in FIGS.

  Since the thickness of the piezoelectric thin plate 10 is as thin as 20 μm to 200 μm, and the electrode film 20 has a nanometer thickness that hardly contributes to the bending rigidity, the bending rigidity of the piezoelectric thin plate 10 to which the electrode film 20 is attached is extremely small. For this reason, as shown in FIG. 3, when pressure is applied to the pressure receiving plate 40, the piezoelectric thin plate 10 is bent or bent in the lateral direction even when the pressure is very small, or when the length L of the piezoelectric thin plate 10 is long. As shown in FIG. 3B, buckling deformation occurs in the middle and an output signal proportional to the pressure cannot be obtained.

  Next, as shown in FIG. 4 (A), when a flexible elastic member 30 having a thickness of 0.5 mm to 10 mm is bonded to the front and back surfaces of the piezoelectric thin plate 10 with the electrode film 20 attached thereto, flexible elasticity is obtained. The elastic modulus of the member 30 is remarkably soft as 1/100 to 1/2000 of the elastic modulus of the piezoelectric thin plate 10, but the bending rigidity can be greatly increased by joining the flexible elastic member 30.

The bending stiffness in the thickness direction is calculated as the product of the elastic modulus of the object and the cross-sectional second moment in the thickness direction. When the cross section of the object is rectangular, the cross-sectional secondary moment in the thickness direction is calculated as (object width) × (object thickness) ³ × 1/12.

FIG. 4 (B) shows a BB ′ cross section of FIG. 4 (A). Here, the elastic modulus E ₁ of the piezoelectric thin plate to which the electrode film 20 is attached is 3000 MPa, the thickness h ₁ is 0.1 mm, When the width B (perpendicular to the drawing sheet) is 10 mm, the bending stiffness E ₁ I _{1 of} the piezoelectric thin plate 10 with electrodes (where I ₁ is the secondary cross-section in the thickness direction of the piezoelectric thin plate 10 with the electrode film) Moment) is E ₁ I ₁ = E ₁ × Bh ₁ ³ /12=2.5 MPa · mm ⁴ .

On the other hand, when a flexible elastic member 30 having an elastic modulus E ₂ of 1 MPa and a thickness h ₂ of 2 mm is bonded to both surfaces of the piezoelectric thin plate 10 to which the electrode film 20 is attached, E ₁ I ₁ + E ₂ I a ^{_{2 = 2.5MPa · mm 4 + 57.4MPa}} · mm 4 = 59.9MPa · mm 4 becomes.

  That is, it can be seen that even if the flexible elastic member 30 is much smaller than the elastic modulus of the piezoelectric thin plate 10, the bending rigidity is greatly increased. As a result, when pressure is applied to the pressure receiving plate 40, the piezoelectric thin plate 10 does not bend or buckle in the lateral direction. As a result, the piezoelectric thin plate 10 only contracts in accordance with the force applied to the pressure receiving plate 40, and an electrical signal corresponding to the amount of strain due to contraction can be generated. Therefore, the fluctuating pressure proportional to the magnitude of the pressure is accurately detected with high sensitivity.

  Next, with reference to FIG. 5, a description will be given of detecting a minute pressure by concentrating the force received by the pressure receiving plate, which is a feature of the present invention, on the end face of the piezoelectric thin plate. FIG. 5 is an exploded perspective view for explaining the relationship among the areas of the pressure receiving plate, the end face of the piezoelectric thin plate, and the elastic member.

  When pressure acts on the surface of the pressure receiving plate 40, a compressive force acts on the piezoelectric thin plate 10 and the flexible elastic member 30, and the piezoelectric thin plate 10 with the electrode film 20 and the flexible elastic member 30 are moved in the length direction by ΔL. Shrink. At this time, the magnitude of the electric charge Q generated in the piezoelectric thin plate 10 is proportional to the total sum of the compressive strains generated in the length L direction of the piezoelectric thin plate 10.

Now, the surface area of the pressure receiving plate 40 S ^(mm 2), the working pressure W (Mpa), the cross-sectional area of the piezoelectric sheet 10 carrying thereon an electrode _{S 1,} the cross-sectional area of the right and left flexible resilient member and _{S 2,} respectively Then, the compressive strain ε of the piezoelectric thin plate 10 is ε = ΔL / L = WS / (2S ₂ E ₂ + S ₁ E ₁ ). However, S = 2S ₂ + S ₁ .

The piezoelectric thin plate 10 to which the electrode film 20 is attached at this time shares S ₁ E ₁ / (2S ₂ E ₂ + S ₁ E ₁ ) of the total pressure, and the flexible elastic member 30 is 2S ₂ E ₂ / ( 2S ₂ E ₂ + S ₁ E ₁ ).

For example, E ₁ = 3000 MPa, S ₁ = h ₁ × B = 0.1 mm × 10 mm = 1 mm ² , E ₂ = 1 MPa, S ₂ = h ₂ × B = 2 mm × 10 mm = 20 mm ² used in the above example, Considering the case of S = 2S ₂ + S ₁ = 41 mm ² , the piezoelectric thin plate 10 provided with the electrode film 20 will share the pressure of about 98.7%, and the flexible elastic member 30 will share the pressure of about 1.3%. . That is, the piezoelectric thin plate 10 shares most of the pressure.

  As described above, the pressure sensor of the present invention uses a piezoelectric thin plate having a much smaller elastic modulus than that of a metal material (the elastic modulus of the piezoelectric thin plate is, for example, about 1/70 of that of a stainless steel plate) for pressure detection. The structure is such that pressure acts on the cut surface of the thin piezoelectric thin plate 10 without causing out-of-plane bending or buckling of the plate 10. That is, most of the force applied to the pressure receiving plate 40 having a large surface area is concentrated and transmitted to the end surface of the piezoelectric thin plate 10 having a small cross-sectional area. The force applied perpendicularly to the end face of the piezoelectric thin plate 10 acts so as to cause distortion in the extending direction in which the piezoelectric thin plate 10 generates the most electric charge. As a result, even if the pressure fluctuates, a large strain is generated in the entire piezoelectric thin plate 10 and a large charge Q proportional to the total sum of the strains generated in the piezoelectric thin plate 10 is generated to realize a highly sensitive pressure measurement. Yes.

FIG. 6 is a circuit diagram of a pressure measuring device using the pressure sensor of the present invention. The piezoelectric thin plate is modeled by a capacitance C ₁ of the current source and the piezoelectric thin plate itself. A pressure sensor is a pressure measuring device, a capacitor capacitance C ₂ is 10nF~1μF connected in parallel to the pressure sensor wire, the input resistance R ₀ for amplifying a signal of the pressure sensor via the capacitor 10MΩ or The voltage amplifier 700 described above and a voltage recorder 800 for measuring and recording a signal from the voltage amplifier 700 are configured.

  In the case of a distributed pressure sensor, which will be described later, it is composed of capacitors as many as the number of sensors, a voltage amplifier 700 having the required number of channels, and a voltage recorder 800 having the required number of channels. The capacitor and the voltage amplifier 700 may be manufactured integrally, and the voltage recorder 800 can be replaced with a personal computer via an A / D converter.

When pressure acts on the pressure sensor and the piezoelectric thin plate is distorted, a current i = dQ / dt proportional to the time differentiation of the charge Q generated in the piezoelectric thin plate flows from the wiring connected to the piezoelectric thin plate. The signal proportional to dQ / dt is integrated by passing the capacitor C ₂ connected in parallel through a capacitor of 10 nF to 1 μF and the input resistance R ₀ of the voltage amplifier, and the terminal voltage of the input resistance portion of the voltage amplifier 700 is , And becomes proportional to the charge Q, that is, the magnitude of the pressure. Since the electric charge Q generated in the piezoelectric thin plate is small when the pressure is very small, it is preferable to use the voltage amplifier 700 having an amplification factor of 50 to 1000 times.

  FIG. 7 is a plan view (A) showing a schematic configuration of a pressure sensor in which a plurality of piezoelectric thin plates are arranged in parallel with respect to one pressure receiving plate, and a cross-sectional view taken along line CC ′ in FIG. 7 (A). is there. Two pairs of piezoelectric thin plates 10A, 10B and two elastic members 30 arranged on the same plane, and a pressure receiving plate 40 bonded to the entire one end surface orthogonal to the surfaces of the piezoelectric thin plates 10A, 10B and the elastic member 30; The piezoelectric thin plates 10 </ b> A and 10 </ b> B and a rigid member case 60 that houses the entire elastic member 30 are configured.

  The pressure receiving plate 40 is disposed at a position slightly protruding from the opening of the rigid member case 60 and parallel to the opening surface, and the other pair of piezoelectric thin plates 10A and 10B and the other end surface of the elastic member 30 are entirely disposed on the rigid member case. Fix to the bottom of 60. Next, the vicinity of the surface of the opening of the rigid member case 60 and the periphery of the piezoelectric thin plates 10 </ b> A and 10 </ b> B and the elastic member 30 are sealed by the seal member 90 in the vicinity of the surface of the opening. Further, wiring (81A, 81B, 82A, 82B) is drawn out of the case 60 of the rigid member through a wiring hole provided in a part of the case 60 of the rigid member, and the drawn portion is sealed.

  Since the pressure sensor of FIG. 7 measures a signal proportional to the pressure acting on the pressure receiving plate 40 by the sum of the output signals of the two piezoelectric thin plates 10A, 10B, the wiring 81A on the positive electrode side of the piezoelectric thin plate 10A The wiring 82A on the positive electrode side of the piezoelectric thin plate 10B is connected, and the wiring 81B on the negative electrode side of the piezoelectric thin plate 10A and the wiring 82B on the negative electrode side of the piezoelectric thin plate 10B are connected, and the sum of output signals of the two piezoelectric thin plates 10A and 10B. To measure. The connecting position may be outside the rigid member case 60 or inside the case 60.

  The pressure sensor configured as shown in FIG. 7 can increase the surface area of the pressure receiving plate 40. It should be noted that the two pairs of integrated piezoelectric thin plates 10A and 10B and the elastic member 30 may be arranged close to each other or spaced apart. Moreover, it is also possible to adopt a configuration in which three or more identical piezoelectric thin plates 10 and elastic members 30 are arranged in a plane, and the pressure receiving plate is joined to cover the whole.

  Thus, when a plurality of piezoelectric thin plates are arranged, the pressure receiving plate does not tilt due to deformation of one elastic member, and the bending of the piezoelectric thin plate can be suppressed, so that the pressure can be detected with high sensitivity.

  With reference to FIG. 8, the outline of the pressure sensor when the surface of the pressure receiving plate is a curved surface will be described. FIG. 8A shows a cross section of the pressure sensor, and FIG. The pressure receiving plate 40 of the pressure sensor shown in FIG. 7 is replaced with a pressure receiving plate 41 having a curved surface. In the present invention, since force is not applied to the surface of the piezoelectric thin plate from the vertical direction as in the prior art, a pressure receiving plate 41 having a convexly raised surface can be provided instead of the flat pressure receiving plate. Then, by making the surface of the pressure receiving plate 41 a curved surface, it is also used for pressure measurement of a curved surface portion such as the tip of an aircraft wing or the bow of a ship that could not be measured so far as shown in FIG. be able to.

  FIG. 9 shows an embodiment of a distributed pressure sensor in which five pressure sensors are arranged and integrated on a straight line. Since the pressure sensor of the present invention can be manufactured by making the pressure receiving plate into a rectangular shape, a distributed pressure sensor can be easily configured by arranging a plurality of pressure sensors at high density and integrating them. For example, as shown in FIG. 9, if five cases of rigid members are aligned with the height of the pressure receiving plate 40 and integrated in a row, the pressure distribution at five consecutively arranged locations can be measured.

  In the conventional circular pressure receiving plate, for example, in the distribution pressure measurement of fluid, turbulent flow or the like is caused by the fluid entering the gap, and the accurate distribution pressure cannot be measured. On the other hand, since the present invention is a distributed pressure sensor in which pressure sensors are closely arranged without a gap, turbulent flow or the like does not occur, and an accurate distributed pressure can be measured.

  The pressure sensor shown in FIG. 10 was produced, and it was verified using a weight whether or not the pressure according to the applied force could be detected. Piezoelectric thin plates 10A and 10B made of polyvinylidene fluoride having a thickness of 80 μm having electrode films 20 deposited on both sides with aluminum were used. The piezoelectric thin plates 10A and 10B were sandwiched between first flexible elastic members 30 made of silicon rubber having a rubber hardness of 50 and a thickness of 1 mm. These were arranged in parallel, and a second flexible elastic member 31 made of a cork plate having a thickness of about 1 mm was bonded to the outside. The piezoelectric thin plate 10 and the elastic member 30 have a length L of 18 mm and a width B (perpendicular to the paper surface) of 6 mm. As the pressure receiving plate 40, an aluminum plate having a thickness of 0.5 mm was used. The surface area of the pressure receiving plate 40 is 6 mm × 6 mm. The case 60 of the rigid member was manufactured by processing an aluminum plate. In this way, two pressure sensors of the same size were created and verified.

Various weights were placed on the pressure receiving plate of the pressure sensor to detect voltage signals. A capacitor having a capacitance C2 of ₂₀₀ nF was used for the pressure measuring device, and a signal conditioner CDV-700A (Kyowa Denko) having an input resistance of 10 MΩ or more was used for the voltage amplifier. As a voltage recorder, Omniace RA1300 (NEC Sanei) was used. The amplification factor of the voltage amplifier is 80 times.

The result is shown in FIG. As can be seen from the figure, the weight load and the output voltage are proportional to each other in any pressure sensor. Therefore, it can be confirmed that the fluctuating pressure corresponding to the applied load can be accurately detected. Since a light weight of 5 g can be detected, a minute pressure of about 1.3 kPa (0.13 g / mm ² ) can be detected, and it can be confirmed that the sensitivity is good.

  Next, the pressure sensor shown in FIG. 12 was created, and the fluctuating pressure of water was measured using a water tank. A piezoelectric thin plate made of polyvinylidene fluoride having a thickness of 80 μm having electrode films 20 deposited on both sides with aluminum was used. A first flexible elastic member 30 made of silicon rubber having a rubber hardness of 50 and a thickness of 1 mm is bonded to the flexible elastic member, and a second flexible elastic member made of a cork plate having a thickness of 1.3 mm is attached to the outside thereof. The member 31 was bonded and used. The piezoelectric thin plate 10, the first elastic member 30, and the second elastic member 31 have a length L of 7 mm and a width B (perpendicular to the paper surface) of 10 mm. The pressure receiving plate 43 was an aluminum plate having a thickness of 0.5 mm, and the surface area was 5 mm × 10 mm.

  FIG. 13 shows the apparatus used to measure the fluctuating pressure of the wave. The pressure sensor 500 is installed at the boundary between the side wall and the bottom surface of a 50 cm long and 30 cm wide water tank, and water is supplied to a depth of about 5 cm. It is a figure explaining the experiment which put and rocked the water tank.

The pressure measuring device, the electrostatic capacitance _{C 2} is using capacitors 600 of 100 nF, the input resistance to the voltage amplifier 700 using 10MΩ or more signal conditioners CDV-700A (Kyowa Electronic Instruments). As the voltage recorder 800, Omniace RA1300 (NEC Sanei) was used. The amplification factor of the voltage amplifier is 200 times.

  FIG. 14 shows an example of a waveform when the wave is shaken slowly four times so that the wave hits the sensor and then finally greatly shaken once. The horizontal axis represents time and the vertical axis represents the voltage measured by the voltage recorder. The figure also shows an enlarged view of the waveform (the portion surrounded by the wavy line in FIG. 14A) when it was last violently hit. As can be seen from FIG. 14, four small peaks and one large peak can be detected, and the pressure waveform when a wave hits can be measured.

  For example, in tankers, sloshing occurs due to waves, etc., but in order to prevent crude oil leaks due to sloshing, a pressure sensor is installed on the wall of the crude oil chamber to detect sloshing and control so that crude oil can be transported safely. Yes. In this invention, since the wave which hits a wall surface can be measured with high sensitivity as mentioned above, it is suitable also for the use in a place with a pressure fluctuation without interruption, such as a ship.

  Next, a description will be given of an experiment conducted by making a prototype of a sensor having substantially the same configuration as the pressure sensor shown in FIG. The configuration of the pressure sensor is such that the thickness of the second flexible elastic member 31 is 0.65 mm, the length L is 20 mm, the width B (perpendicular to the paper surface) is 8 mm, and the thickness is 7 mm. The surface area of the pressure receiving plate 40 is 8 mm × 7 mm.

The experiment was performed in the same manner as in Example 2 using the apparatus shown in FIG. As the pressure measuring device, a capacitor having a capacitance C2 of ₂₀₀ nF was used, and the same voltage amplifier and voltage recorder as those in Example 1 were used. The amplification factor of the voltage amplifier was 80 times.

  FIG. 15A shows an example of the experimental results with the horizontal axis representing time and the vertical axis representing the voltage measured by the voltage recorder. In the figure, positive pressure is shown on the negative side. From FIG. 15A, it can be seen that four small peaks and one large peak are detected, and the pressure waveform when the wave hits can be measured.

  FIG. 15B shows an enlarged view of a waveform (a portion surrounded by a wavy line in FIG. 15A) when a small wave hits. In FIG. 15B, since a plurality of smaller peaks inherent in the peak of a small wave are also detected, it was demonstrated that even a minute fluctuation pressure can be detected with high sensitivity.

It is the top view and sectional drawing which show schematic structure of the pressure sensor of this invention. It is a perspective view which shows schematic structure of the principal part of the pressure sensor of this invention. It is sectional drawing explaining the deformation | transformation state of the pressure sensor of this invention. It is sectional drawing explaining the deformation | transformation state of the pressure sensor of this invention. It is a disassembled perspective view explaining the output signal of the pressure sensor of this invention. It is a circuit diagram explaining the structure of the pressure measuring apparatus using the pressure sensor of this invention. It is the top view and sectional drawing which show schematic structure of the pressure sensor of the other form of this invention. It is the top view and sectional drawing which show schematic structure of the pressure sensor of the other form of this invention. It is a perspective view explaining one Example of the distributed pressure sensor of this invention. It is sectional drawing which shows schematic structure of the pressure sensor used for the Example of this invention. It is a graph which shows the measurement result of the pressure sensor of the present invention. It is sectional drawing which shows schematic structure of the pressure sensor used for the Example of this invention. It is sectional drawing which shows the apparatus used for the Example of this invention. It is a graph which shows the measurement result of the fluctuation | variation water pressure by the pressure sensor of this invention. It is a graph which shows the measurement result of the fluctuation | variation water pressure by the pressure sensor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piezoelectric thin plate 10A Piezoelectric thin plate 10B Piezoelectric thin plate 20 Electrode film | membrane 30, 31 Elastic member 40, 41 Pressure receiving plate 60 Case 80A, 80B Wiring 81A, 81B Wiring 82A, 82B Wiring 90 Seal member 700 Voltage amplifier 800 Voltage recorder

Claims (12)

A piezoelectric thin plate made of a piezoelectric material;
A pressure receiving plate disposed on an end surface of the piezoelectric thin plate, and having a larger area than a cross-sectional area of the end surface of the piezoelectric thin plate;
A pressure sensor for detecting a minute pressure by applying a pressure received by the pressure receiving plate perpendicularly to an end face of the piezoelectric thin plate.   An elastic member for sandwiching the piezoelectric thin plate is provided, the elastic modulus of the elastic member is made smaller than the elastic modulus of the piezoelectric thin plate, and the force received by the pressure receiving plate is concentrated and applied to the piezoelectric thin plate. The pressure sensor according to claim 1.   The pressure sensor according to claim 2, wherein the elastic modulus of the elastic member is 1/100 to 1/2000 of the elastic modulus of the piezoelectric thin plate.   The pressure sensor according to claim 2, wherein the elastic member is selected from natural rubber, synthetic rubber, silicon rubber, sponge rubber, sponge, foam rubber, or cork.   The pressure sensor according to claim 2, wherein the piezoelectric thin plate is formed by stretching a piezoelectric material, and the pressure receiving plate is disposed on an end surface of the piezoelectric thin plate in a stretching direction.   6. The pressure sensor according to claim 5, wherein the piezoelectric thin plate is made of a polymer piezoelectric material made of polyvinylidene fluoride or vinylidene cyanide.   The pressure sensor according to claim 2, wherein an area of the pressure receiving plate is 20 times or more an end surface area of the piezoelectric thin plate.   The pressure sensor according to claim 2, wherein a plurality of the piezoelectric thin plates are arranged in parallel.   The pressure sensor according to claim 2, wherein the piezoelectric thin plate and the elastic member are covered with a box having an opening surface on one surface, and the pressure receiving plate faces the opening surface.   The pressure sensor according to claim 2, wherein the pressure receiving plate has a rectangular shape.   The pressure sensor according to claim 2, wherein a surface of the pressure receiving plate is a curved surface.   A distributed pressure sensor using a plurality of pressure sensors according to claim 10, wherein the pressure receiving plates are aligned and arranged adjacent to each other in a linear or two-dimensional manner.

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