Fiber optic pressure sensor and fiber optic pressure measurement instrument

Abstract

Provided are a fiber optic pressure sensor and a fiber optic pressure measurement instrument capable of suppressing the entry of a liquid or gas to be measured into a pressure-sensitive part.　A diaphragm mirror-type fiber optic pressure sensor 1 detects pressure on one end side t of an optical fiber 10 and comprises a pressure sensitive part 30 at an end part 11 on the one end side t. The fiber optic pressure sensor 1 also has a tip part sealed by means of a sealing member 50 composed of an expanding / contracting part 51 that is at least partially elastic. Also provided is a fiber optic pressure measurement instrument using the fiber optic pressure sensor 1.

Description

Fiber-optic pressure sensor and fiber-optic pressure measuring instrument

[0001] The present invention relates to a fiber-optic pressure sensor and a fiber-optic pressure measuring instrument.

[0002] Conventionally, fiber-optic pressure sensors for measuring pressure inside a fine tube or the like have been proposed. For example, in Patent Document 1, a diaphragm portion deflected by pressure serves as a pressure-receiving surface, and the movement of a total reflection mirror fixed to the pressure-receiving surface is used to optically detect the optical path difference of reflected light of light emitted from an optical fiber, and a force sensor that measures pressure change by analyzing the same is disclosed.

[0003] In the technology described in Patent Document 1, the movable range of the total reflection mirror that moves by pressure is an extremely small range resulting from the shape deformation of the diaphragm, and is on the order of the wavelength of light incident on the optical fiber. Therefore, pressure change is detected and measured by monitoring changes in the optical spectrum of the reflected light from the total reflection mirror with a spectrometer.

[0004] However, a system including a spectrometer that monitors wavelength changes of reflected light is complex and precise, which leads to high cost for the entire apparatus. Furthermore, since pressure is measured by monitoring extremely small positional movement via wavelength changes, it has been difficult to increase measurement sensitivity.

[0005] Regarding the usage environment of pressure sensors, for example, when attempting to measure internal pressure filled with liquid such as inside a blood vessel in a medical setting, it is desirable to prevent the liquid to be measured from entering around the pressure-sensitive part, which is a movable part that moves under external pressure. It is also desirable to prevent the gas to be measured from entering around the pressure-sensitive part even when measuring gas pressure. If the area around the pressure-sensitive part is filled with the liquid or gas to be measured, the pressure-sensitive part becomes independently suspended in the liquid or gas, and even if pressure is applied to the liquid or gas, the pressure is not transmitted to the pressure-sensitive part, which raises a concern that pressure cannot be detected.

[0006] Japanese Patent Application Laid-Open No. 2019-187646

[0007] Therefore, the present invention aims to provide an optical fiber pressure sensor and an optical fiber pressure measuring instrument that can suppress the ingress of the liquid or gas to be measured into the pressure-sensitive part.

[0008] The above objective is achieved by the present invention as described below. That is, the embodiments of the present invention are as follows.

[0009] <1> A diaphragm mirror type optical fiber pressure sensor that detects pressure at one end of an optical fiber and has a pressure-sensitive part at the tip of the said end, wherein the tip is sealed with a sealing member which is composed of an elastic expandable part that is at least a part of it.

[0010] <2>

[0011] The optical fiber pressure sensor according to <1>, wherein the material of the expandable portion is rubber. <3> The optical fiber pressure sensor according to <2>, comprising: an optical fiber; a cylindrical portion into which one end of the optical fiber is inserted and fixed from one opening; and an elastic body interposed between the cylindrical portion and the pressure-sensitive portion, wherein a repulsive force acts against the movement of the pressure-sensitive portion toward the end of the one end of the optical fiber, wherein the pressure-sensitive portion comprises a reflective surface positioned opposite to the end of the one end of the optical fiber, and a pressure-receiving surface facing away from the reflective surface and toward the other opening in the cylindrical portion, and is movable in the axial direction within the cylindrical portion, and the sealing member seals at least the gap between the cylindrical portion and the pressure-sensitive portion.

[0012] <4> The optical fiber pressure sensor according to <3>, wherein the sealing member is formed in the shape of a cap and covers the entire other opening in the cylindrical portion.

[0013] <5> The optical fiber pressure sensor according to <3>, wherein the material of the expandable portion is silicone rubber.

[0014] <6> The optical fiber pressure sensor according to <3>, wherein the expandable portion is tubular, the sealing member has a sealing portion that seals one end of the expandable portion, the cylindrical portion is inserted into the other end of the expandable portion and at least a part of it is in close contact with the outer surface of the cylindrical portion over its entire circumference, the sealing portion covers the entire other opening and is in contact with the pressure-sensitive portion, and the hardness of the sealing portion is higher than the hardness of the expandable portion.

[0015] <7> The optical fiber pressure sensor according to <6>, wherein the sealing portion is formed by curing an uncured material supplied to one end of the expandable portion.

[0016] <8> The optical fiber pressure sensor according to <6>, wherein the material of the sealing portion is a hard material.

[0017] <9> The optical fiber pressure sensor described in <6>, wherein the hardness of the expandable portion is 60 points or less on a Type A durometer compliant with JIS K 6253.

[0018] <10> The optical fiber pressure sensor according to <6>, wherein the thickness of the expandable portion is 0.1 mm or less.

[0019] <11> An optical fiber pressure measuring instrument comprising: an optical fiber pressure sensor as described in <3>; a light source that incidents light on the other end of the optical fiber; and a photodetector that measures the intensity of the reflected light when the light incident on the other end of the optical fiber and emitted from the one end of the optical fiber irradiates the reflective surface.

[0020] According to the present invention, it is possible to provide an optical fiber type pressure sensor and an optical fiber type pressure measuring instrument that can suppress the ingress of the liquid or gas to be measured into the pressure-sensitive part.

[0021] This is a cross-sectional view showing an optical fiber pressure sensor according to a first embodiment, which is an exemplary aspect of the present invention. This is an enlarged cross-sectional view of the main part of the sensor body in the optical fiber pressure sensor according to a first embodiment, which is an exemplary aspect of the present invention. This is a schematic diagram showing a pressure test being performed on an optical fiber pressure measuring instrument using the optical fiber pressure sensor according to the first embodiment. This is an enlarged cross-sectional view of the main part of the sensor body in the optical fiber pressure sensor according to a second embodiment, which is an exemplary aspect of the present invention. This is an enlarged cross-sectional view of the main part of the sensor body in the optical fiber pressure sensor according to a third embodiment, which is an exemplary aspect of the present invention.

[0022] Hereinafter, three exemplary embodiments of the present invention, specifically optical fiber pressure sensors and optical fiber pressure measuring devices, will be described with reference to the drawings. The following three embodiments are examples of diaphragm mirror type optical fiber pressure sensors that detect pressure at one end of an optical fiber and have a pressure-sensitive element at the tip of that end.

[0023] Furthermore, a "diaphragm mirror type" refers to a method of measuring pressure by using a pressure-sensitive unit equipped with a reflective surface positioned opposite one end of an optical fiber and a pressure-receiving surface facing away from the reflective surface, and measuring the distance between one end of the optical fiber and the reflective surface, which fluctuates depending on the pressure received by the pressure-receiving surface.

[0024] [First Embodiment] Figure 1 is a cross-sectional view showing an optical fiber pressure sensor according to the first embodiment. As shown in Figure 1, the optical fiber pressure sensor 1 according to the first embodiment (hereinafter sometimes simply referred to as "pressure sensor 1") includes an optical fiber 10 and a sensor body 100 attached to the tip of one end of the optical fiber 10.

[0025] Figure 2 is an enlarged cross-sectional view of the main part of the sensor body 100 in the pressure sensor 1. As shown in Figures 1 and 2, the sensor body 100 has a cylindrical part 20, a pressure-sensitive part 30, and an elastic spring 40. In Figures 1 and 2, the tip side of the pressure sensor 1 and the optical fiber 10 are indicated by arrow t, and the base end side is indicated by arrow b (the same applies in subsequent figures). Also in Figures 1 and 2, the central axis of the cylindrical part 20 and the pressure-sensitive part 30 is represented by a dashed line P (hereinafter referred to as "central axis P" or "axis P"). The pressure sensor 1 is a device that detects pressure at the sensor body 100 on one end side (tip side t) of the optical fiber 10.

[0026] The optical fiber 10 is generally made of a resin (plastic) or quartz material. In this embodiment, the optical fiber 10 is a single-core optical fiber consisting of a core located at the radial center and a cladding located on the outer circumference of the core. The relative refractive index difference between the core and the cladding of the optical fiber 10 is, for example, 0.1% or more and 11% or less.

[0027] In this embodiment, the cylindrical portion 20 consists of a cylindrical small-diameter portion 21 and a large-diameter portion 22, with the small-diameter portion 21 fitted and fixed into the large-diameter portion 22. One end (tip side t) of the optical fiber 10 is inserted into and fixed into the cylindrical portion 20 through one opening (the opening on the small-diameter portion 21 side) 23 of the cylindrical portion 20. Therefore, the inner diameter of the small-diameter portion 21 is approximately the same as the outer diameter of the optical fiber 10.

[0028] Furthermore, if the optical fiber 10 is thinner and it is difficult to make the inner diameter of the small-diameter portion 21 approximately the same as the outer diameter of the optical fiber 10, an auxiliary tubular portion having an inner diameter approximately the same as the outer diameter of the optical fiber 10 and an outer diameter approximately the same as the inner diameter of the small-diameter portion 21 may be interposed. That is, by fitting the auxiliary tubular portion into the small-diameter portion 21 and fitting the optical fiber 10 into the auxiliary tubular portion and fixing them as appropriate, one end (tip side) of the optical fiber 10 is inserted and fixed through one opening (opening on the small-diameter portion 21 side) 23 of the cylindrical portion 20.

[0029] The cylindrical portion 20 can be made of any material, such as stainless steel, aluminum, various resins, or glass. The material can also be varied depending on the part, for example, using stainless steel for the small diameter portion 21 and resin for the large diameter portion 22.

[0030] In this embodiment, the pressure-sensitive portion 30 is rod-shaped, having a cylindrical thin-diameter portion 31 and a cylindrical thick-diameter portion 32 coaxially with it. A stepped surface 35 is formed at the boundary between the thin-diameter portion 31 and the thick-diameter portion 32, protruding by the difference in diameter between the two portions and facing the base end side b. The pressure-sensitive portion 30 is a integrally molded part made of metal such as stainless steel. In the pressure-sensitive portion 30, the thick-diameter portion 32 is located within the large-diameter portion 22 of the cylindrical portion 20, and a part of the thin-diameter portion 31 is inserted into the small-diameter portion 21 of the cylindrical portion 20.

[0031] The pressure-sensitive portion 30 is movable within the cylindrical portion 20 in the axial direction (direction along the central axis P). The outer diameter of the large-diameter portion 32 of the pressure-sensitive portion 30 is approximately the same as the inner diameter of the large-diameter portion 22 of the cylindrical portion 20, and the outer diameter of the small-diameter portion 31 of the pressure-sensitive portion 30 is approximately the same as the inner diameter of the small-diameter portion 21 of the cylindrical portion 20. However, a small gap is provided between the large-diameter portion 32 of the pressure-sensitive portion 30 and the large-diameter portion 22 of the cylindrical portion 20, and between the small-diameter portion 31 of the pressure-sensitive portion 30 and the small-diameter portion 21 of the cylindrical portion 20, to the extent that the pressure-sensitive portion 30 can move freely within the cylindrical portion 20 in the axial direction (direction along the central axis P).

[0032] The pressure-sensitive section 30 has a mirror-like reflective surface 33 at one end (the base end b, the end on the narrow diameter section 31 side) and a pressure-receiving surface 34 at the other end (the tip end t, the end on the wide diameter section 32 side). The reflective surface 33 of the pressure-sensitive section 30 is positioned opposite the end 11 of one end (tip end t) of the optical fiber 10. The pressure-receiving surface 34 of the pressure-sensitive section 30 is facing away from the reflective surface 33 (back to back) and is facing the other opening 24 of the cylindrical section 20 (the opening on the wide diameter section 22 side).

[0033] The spring (elastic body) 40 is interposed between the cylindrical portion 20 and the pressure-sensitive portion 30. More specifically, the spring 40 is interposed between the end face 21t of the tip side t of the small diameter portion 21 located within the large diameter portion 22 and the stepped surface 35 of the pressure-sensitive portion 30, with the small diameter portion 31 of the pressure-sensitive portion 30 inserted into it. The spring 40 is configured such that a repulsive force from the spring 40 acts against the movement of the pressure-sensitive portion 30 in the direction (arrow b direction) towards the end 11 of one end (tip side t) of the optical fiber 10.

[0034] A cap-shaped sealing member 50 is placed over the tip end 26 of the cylindrical portion 20, covering the entire other opening 24 of the cylindrical portion 20. The sealing member 50 has an elastic, tubular expandable portion 51 and a sealing portion 52. One end of the expandable portion 51, the tip end t, is a narrowed stretched piece 53, and the sealing portion 52 seals the stretched piece 53. The large-diameter portion 22 of the cylindrical portion 20 is inserted into the other end of the expandable portion 51, the base end b, and at least a part of it is in close contact with the outer circumferential surface of the large-diameter portion 22 over its entire circumference.

[0035] On the other hand, the sealing portion 52 covers the entire other opening 24 in the cylindrical portion 20 and is in contact with the pressure-sensitive portion 30. Because the sealing portion 52 covers the entire other opening 24 in the cylindrical portion 20, and the expandable portion 51 is in close contact with the outer circumferential surface of the large-diameter portion 22 around its entire circumference, the other opening 24 in the cylindrical portion 20 is sealed from the outside, thereby sealing the gap 25 that occurs between the cylindrical portion 20 and the pressure-sensitive portion 30.

[0036] The location where the expandable portion 51 adheres closely to the outer circumferential surface of the large-diameter portion 22 over its entire circumference is preferably near the end 54 of the base end b, which is the other end of the expandable portion 51. The adhesion between the expandable portion 51 and the large-diameter portion 22 may be achieved by elastic force, by bonding with an adhesive, by tightening by other means, by other means, or by a combination of these means. In this embodiment, the expandable portion 51 and the outer circumferential surface of the large-diameter portion 22 are adhered closely to each other over their entire circumference by bonding the end 54 of the expandable portion 51 and its vicinity with an adhesive 55. The adhesive 55 should be selected appropriately according to the material of the surface to be bonded, and if the material of the expandable portion 51 is silicone rubber, a silicone-based adhesive is preferred.

[0037] The material of the expandable portion 51 is not particularly limited as long as it is an elastic material such as silicone rubber, synthetic rubber, natural rubber, or elastomer, but it is preferably rubber, and it is especially preferable that it be silicone rubber, which has excellent stability and durability in various usage environments.

[0038] In this embodiment, an uncured material such as an adhesive sealant is supplied to the extended piece (part number 53 in Figure 2), which is one end of the expandable portion 51 extending from the tip end 26 of the cylindrical portion 20, and cured to form a sealed portion 52, thereby sealing the open end (tip end) of the expandable portion 51.

[0039] The term "uncured material" as used herein refers to a material that is liquid or gel-like in its uncured state and hardens when supplied to a desired location and subjected to a predetermined curing method. Examples of predetermined curing methods include leaving the material for a predetermined period of time (natural drying, room temperature curing), heating, and ultraviolet irradiation.

[0040] In this embodiment, a commercially available material used as an adhesive sealant is used as the uncured material. In this embodiment, it is preferable to use a silicone-based adhesive sealant that has good adhesion to silicone tubes as the adhesive sealant.

[0041] The pressure-receiving surface 34 of the pressure-sensitive unit 30 is in close contact with the sealing portion 52 of the sealing member 50, and is configured to be subjected to pressure under the influence of external atmospheric pressure or water pressure (or hydraulic pressure of a liquid other than water, as applicable).

[0042] The pressure-sensitive unit 30, which receives pressure via the sealing portion 52 of the sealing member 50, is hardly affected by the interposition of the sealing member 50 because the elastic expansion / contraction portion 51 has elasticity (expandability / contractibility), and moves in a direction approaching the end portion 11 on one end side (tip end side t) of the optical fiber 10 (direction of arrow b), acting to contract the spring 40.

[0043] The expansion / contraction portion 51 is required to have elasticity (expandability / contractibility) that allows it to flexibly expand and contract when the pressure-sensitive unit 30 moves in the direction of arrow b or arrow t in accordance with the magnitude of pressure applied to the pressure-receiving surface 34. On the other hand, the sealing portion 52 is required to have rigidity that transmits pressure received from the outside to the pressure-receiving surface 34 with as little attenuation as possible.

[0044] Therefore, in the sealing member 50, the hardness of the sealing portion 52 is preferably higher than the hardness of the expansion / contraction portion 51, and it is more preferable that the material of the sealing portion 52 is a hard material. In the case of the present embodiment where the sealing portion 52 is formed by curing an uncured material, the hardness of the cured product obtained by curing the uncured material is preferably higher than the hardness of the expansion / contraction portion 51, and it is more preferable that the cured product is a hard material.

[0045] The hardness of the expansion / contraction portion 51 is preferably 60 points or lower, and more preferably 20 points or lower, as measured with a type A durometer in accordance with Japanese Industrial Standard JIS K 6253. When the hardness of the expansion / contraction portion 51 is appropriately low, the sealing member 50 can be provided with elasticity (expandability / contractibility) that flexibly expands and contracts in accordance with the movement of the pressure-sensitive unit 30 in the direction of arrow b or arrow t. Note that the time from close contact of the pressure surface to reading the indicated value was set to 1 second or less.

[0046] The thickness of the stretchable portion 51 is preferably 0.1 mm or less, more preferably 0.05 mm or less. When the thickness of the stretchable portion 51 is appropriately thin, the sealing member 50 can be provided with elasticity (stretchability) that allows flexible stretching and contracting in accordance with the movement of the pressure-sensitive portion 30 in the direction of arrow b or arrow t. Regarding the shape of the sealing portion 52, it is preferably a flat plate shape with as high flatness as possible, so that pressure received from the outside can be transmitted to the pressure-receiving surface 34 as uniformly as possible.

[0047] It should be noted that the pressure-receiving surface 34 of the pressure-sensitive portion 30 receives pressure from the outside via the sealing portion 52 of the sealing member 50. Although this reception is indirect, it remains unchanged that the pressure-receiving surface 34 receives pressure from the outside. Therefore, hereinafter, descriptions may be given by omitting the mention of the interposition of the sealing member 50 and using expressions such as "external pressure is applied to the pressure-receiving surface 34".

[0048] In the pressure sensor 1 according to the present embodiment, when no pressure is applied to the pressure-receiving surface 34, the reflective surface 33 of the pressure-sensitive portion 30 and the end portion 11 on one end side (tip side t) of the optical fiber 10 maintain a constant distance (gap). When the sensor main body 100 is placed in a pressurized environment, pressure is applied to the pressure-receiving surface 34 under external influence, the pressure-sensitive portion 30 moves in the direction of arrow b, and the reflective surface 33 of the pressure-sensitive portion 30 approaches the end portion 11 on one end side (tip side t) of the optical fiber. The distance (gap) between the reflective surface 33 and the end portion 11 decreases in inverse proportion to the magnitude of pressure received by the pressure-receiving surface 34 due to the action of the repulsive force of the spring 40.

[0049] The pressure sensor 1 according to the present embodiment as described above can be used as an optical fiber-type pressure measuring instrument when used together with a light source and a photodetector. FIG. 3 is a schematic configuration diagram showing a state where a pressure test is performed on the optical fiber-type pressure measuring instrument 60 according to the embodiment.

[0050] The optical fiber-type pressure measuring instrument 60 (hereinafter may be simply abbreviated as "pressure measuring instrument 60") performs measurement by inserting one end side of the optical fiber 10, to which the sensor main body 100 is attached at the end, into a fine tube to be measured (e.g., a blood vessel). FIG. 3 shows a state where one end side of the optical fiber 10 is inserted into a pressurizing chamber 71 in which the internal pressure is controlled by pressurization with a pressurizer 72.

[0051] As shown in Figure 3, the pressure measuring device 60 according to this embodiment includes an optical fiber type pressure sensor 1 according to this embodiment, a light source 62 that incidents light on the other end (base end b) of the optical fiber 10, an optical distributor 61 that distributes light in the middle of the optical fiber 10, and a photodetector 63 that receives the light distributed by the optical distributor 61 via the optical fiber 64 and measures its intensity.

[0052] The light source 62 generates visible light or laser light. When generating laser light, it has a semiconductor laser, and by passing electricity through the semiconductor laser, laser oscillation is caused and laser light is generated. The light source generates, for example, red to near-infrared laser light having a wavelength of 670 nm to 1600 nm.

[0053] The following explanation will be given with reference to Figures 1 and 2, along with Figure 3. The optical distributor 61 is a device that distributes the reflected light from the optical fiber 10 to the optical fiber 64 when the light emitted from the end 11 of one end (tip side t) of the optical fiber 10 is reflected by the reflective surface 33 and the reflected light is incident on the optical fiber 10 again. An optical fiber coupler or an optical circulator can be used as the optical distributor 61.

[0054] In the pressure measuring device 60, when light is irradiated from the light source 62, it enters the other end (base end b) of the optical fiber 10, passes through the optical fiber 10, and exits from the one end (tip end t) of the optical fiber 10. The reflective surface 33 of the pressure-sensitive part 30 faces the end 11 of the optical fiber 10, and the light emitted from the end 11 is reflected by the reflective surface 33 and returns to the end 11. The reflected light that has returned to the end 11 enters the optical fiber 10 again and travels towards the base end b. The reflected light is then distributed by the optical distributor 61, passes through the optical fiber 64 to the photodetector 63, and the intensity of the reflected light is measured.

[0055] When external pressure is applied to the pressure-receiving surface 34, and the gap between the reflective surface 33 and the end 11 becomes smaller, the total length of the light emitted from the light source 62 that is reflected by the reflective surface 33 and eventually reaches the photodetector 63 is shortened. By measuring the change in the light signal information due to this shortening of the total length (i.e., optical path difference) with the photodetector 63, the magnitude of the pressure received by the pressure-receiving surface 34 can be determined.

[0056] In the reflective surface (total reflection mirror 512) fixed to the diaphragm in the technology described in Patent Document 1, the movement due to the action of pressure is limited to the minute movement of the diaphragm, and the optical path difference is only a very small difference on the order of wavelength, less than 1 μm. Therefore, in order to read this optical path difference, it was necessary to detect and measure the pressure change by monitoring the change in the optical spectrum of the reflected light from the reflective surface with a spectrometer.

[0057] In this embodiment, the pressure-sensitive section 30, which has a reflective surface 33, can move relatively far in the direction of the central axis P, while being restricted by the repulsive force of the spring 40 and the sealing member 50. The movable stroke of the pressure-sensitive section 30 can range from tens of micrometers to hundreds of micrometers, depending on the design, so the optical path difference appears as a difference in light intensity. Therefore, in this embodiment, in order to read the optical path difference, the intensity of the reflected light can be measured by the photodetector 63.

[0058] According to this embodiment, because the stroke of the pressure-sensitive part 30 due to pressure changes is large, the pressure can be measured by measuring the intensity of the reflected light with the photodetector 63. This allows for a simpler device compared to a complex and precise system that includes a spectrometer to monitor the wavelength change of the reflected light, thus achieving lower costs. Furthermore, because the stroke of the pressure-sensitive part 30 due to pressure changes is large, the pressure-sensitive part 30 moves linearly with the pressure change, allowing for precise measurement and achieving high sensitivity. Of course, it is also possible to achieve further cost reduction by making the configuration simpler at the expense of high sensitivity, or to achieve even higher sensitivity by making the structure more sophisticated at the expense of low cost.

[0059] Furthermore, according to this embodiment, since the sealing portion 52 covers the entire other opening 24 in the cylindrical portion 20, and the expandable portion 51 is in close contact with the outer circumferential surface of the large-diameter portion 22 around its entire circumference, the other opening 24 in the cylindrical portion 20 is sealed from the outside, and the gap 25 between the cylindrical portion 20 and the pressure-sensitive portion 30 is sealed. As a result, the ingress of the liquid or gas to be measured into the pressure-sensitive portion 30 can be suppressed.

[0060] Furthermore, according to this embodiment, the pressure-sensitive part 30, which receives pressure through the sealing portion 52 of the sealing member 50, moves in a direction (arrow b direction) toward the end 11 of one end (tip side t) of the optical fiber 10 (without being significantly affected by the presence of the sealing member 50, because the expandable portion 51 is elastic (expandable) and acts to contract the spring 40. Therefore, the pressure measurement accuracy is high.

[0061] [Second Embodiment] Figure 4 is an enlarged cross-sectional view of the main part of the sensor body 200 in the optical fiber pressure sensor according to the second embodiment. Since the overall configuration of the optical fiber pressure sensor according to this embodiment is the same as that of the first embodiment, the reference numerals in Figure 1 should be read as the reference numerals in Figure 4 (especially the reference numerals in the 200 series).

[0062] Furthermore, the only difference in this embodiment from the first embodiment is the sealing member 250; all other components are the same as in the first embodiment. Therefore, in this embodiment, the description will focus on the configurations characteristic of this embodiment, and components with the same configuration and function as in the first embodiment will be denoted by the same reference numerals as in Figure 2 showing the first embodiment, and their detailed descriptions will be omitted.

[0063] In the sensor body 200 according to this embodiment, the configuration of the sealing member 250 differs from that of the sealing member 50 in the first embodiment. Specifically, as shown in Figure 4, the sealing member 250 has no narrowing of the diameter of the end portion 256 at the tip side t, which is one end of the expandable portion 251, and a sealing portion 252 made of a metal material such as stainless steel is fixed to the end portion 256 with an adhesive 255.

[0064] As described in the first embodiment, the sealing portion 252 preferably has a higher hardness than the expandable portion 251, and it is more preferable that the sealing portion 252 is made of a hard material, but the sealing portion 252 being made of a metal satisfies this condition. The sealing portion 252 may be made of metals other than stainless steel, such as aluminum, copper, or gold, or any hard material such as ceramics or various resins can be substituted. However, it is preferable to use stainless steel, which has excellent stability and durability in various usage environments.

[0065] According to this embodiment, the sealing portion 252 covers the entire other opening 24 in the cylindrical portion 20, while the expandable portion 251 is in close contact with the outer circumferential surface of the large-diameter portion 22 around its entire circumference. As a result, the other opening 24 in the cylindrical portion 20 is sealed from the outside, and the gap 25 between the cylindrical portion 20 and the pressure-sensitive portion 30 is sealed. Therefore, it is possible to suppress the ingress of the liquid or gas to be measured into the pressure-sensitive portion 30.

[0066] Furthermore, according to this embodiment, the pressure-sensitive part 30, which receives pressure through the sealing portion 252 of the sealing member 250, moves in a direction (arrow b direction) toward the end 11 of one end (tip side t) of the optical fiber 10 (without being significantly affected by the presence of the sealing member 250, because the expandable portion 251 is elastic (expandable), and acts to contract the spring 40. Therefore, the accuracy of pressure measurement is high. In particular, in this embodiment, since the material of the sealing portion 252 is a hard material, the external pressure can be transmitted to the pressure-receiving surface 34 with almost no attenuation, thus further increasing the accuracy of pressure measurement. Other functions and effects in this embodiment are the same as in the first embodiment.

[0067] [Third Embodiment] Figure 5 is an enlarged cross-sectional view of the main part of the sensor body 300 in the optical fiber pressure sensor according to the third embodiment. Since the overall configuration of the optical fiber pressure sensor according to this embodiment is the same as that of the first embodiment, the reference numerals in Figure 1 should be read as the reference numerals in Figure 4 (especially the reference numerals in the 300 series).

[0068] Furthermore, the only components in this embodiment that differ from the first embodiment are the sealing member 350 and the pressure-sensitive part 330; all other components are the same as in the first embodiment. Therefore, in this embodiment, the explanation will focus on the components that are characteristic of this embodiment, and components that have the same configuration and function as in the first embodiment will be denoted by the same reference numerals as in Figure 2 showing the first embodiment, and their detailed explanation will be omitted.

[0069] In the sensor body 300 according to this embodiment, the configuration of the sealing member 350 differs from that of the sealing member 50 in the first embodiment. Specifically, as shown in Figure 5, firstly, the length of the large diameter portion 32 in the pressure-sensitive portion 330 in the longitudinal direction (arrow bt direction) is longer than the same length in the pressure-sensitive portion 30 of the first embodiment.

[0070] Furthermore, the sealing member 350 does not have a narrowed diameter at the tip end 356, which is one end of the expandable portion 351. The area from this end 356 to its vicinity is in close contact with the outer circumferential surface of the large-diameter portion 32 via the adhesive sealing layer 357. In other words, the sealing member 350 in this embodiment is not cap-shaped, but rather has a cylindrical expandable portion 351 with a slightly thicker adhesive sealing layer 357 formed on the inner circumferential surface from the end 356 to its vicinity. The adhesive sealing layer 357 can suitably use the adhesive sealant used as the uncured material in the first embodiment.

[0071] According to this embodiment, the adhesive sealing layer 357 seals the entire circumference between the expandable portion 251 and the outer circumferential surface of the large-diameter portion 32 of the pressure-sensitive portion 330, while the expandable portion 251 is in close contact with the outer circumferential surface of the large-diameter portion 22. As a result, the other opening 24 of the cylindrical portion 20 is sealed from the outside, and the gap 25 between the cylindrical portion 20 and the pressure-sensitive portion 330 is sealed. Therefore, it is possible to suppress the ingress of the liquid or gas to be measured into most areas of the small-diameter portion 31 and the large-diameter portion 332 of the pressure-sensitive portion 330.

[0072] Although the pressure-receiving surface 34 and a portion of the large-diameter portion 332 are in contact with the liquid or gas being measured, the entire area surrounding the pressure-sensitive part 330 is not filled with gas. Therefore, the pressure-sensitive part 330 does not float independently within the liquid or gas. Consequently, the pressure received by the pressure-receiving surface 34 causes the pressure-sensitive part 330 to move toward the end 11 of one end (tip side t) of the optical fiber 10 (in the direction of arrow b), thereby contracting the spring 40.

[0073] Furthermore, according to this embodiment, the pressure received by the pressure-receiving surface 34 exposed to the outside causes the pressure-sensitive part 30 to move in a direction (arrow b direction) toward the end 11 of one end (tip side t) of the optical fiber 10, without being significantly affected by the presence of the sealing member 50, and thus contracting the spring 40. As a result, the accuracy of pressure measurement is high. In particular, in this embodiment, the pressure-receiving surface 34 exposed to the outside directly receives the pressure and acts on the pressure-sensitive part 330, resulting in even higher accuracy of pressure measurement. Other functions and effects in this embodiment are the same as in the first embodiment.

[0074] The three embodiments described above are merely examples of typical forms of the present invention, and the present invention is not limited to these embodiments. For example, in the above embodiments, an example using a spring (40) as the elastic body is given, but the present invention is not limited thereto, and any elastic member can be used without particular restriction. As for other elastic members, there are no particular restrictions as long as the material has rubber elasticity, but a silicone rubber tube, which has excellent stability and durability in various usage environments, can be given as a suitable example.

[0075] Furthermore, while the above three embodiments describe examples in which the cylindrical portion is formed from two members, a small-diameter portion and a large-diameter portion, the present invention is not limited thereto. The small-diameter portion and the large-diameter portion may be formed by integral molding, or the outer diameter may be a constant diameter.

[0076] Furthermore, in the three embodiments described above, each optical fiber pressure sensor is given as an example, comprising a cylindrical portion into which one end of an optical fiber is inserted and fixed through one opening, and an elastic body interposed between the cylindrical portion and the pressure-sensitive portion, which exerts a repulsive force against the movement of the pressure-sensitive portion toward the end of the optical fiber at one end, wherein the pressure-sensitive portion comprises a reflective surface positioned opposite to the end of the optical fiber at one end, and a pressure-receiving surface facing away from the reflective surface and toward the other opening in the cylindrical portion, and is movable axially within the cylindrical portion, but the present invention is not limited thereto. The present invention can be applied to various types of diaphragm mirror type optical fiber pressure sensors. In the case of a diaphragm mirror type optical fiber pressure sensor that detects pressure at one end of an optical fiber and has a pressure-sensitive portion at the tip of that end, the present invention can be applied by sealing the tip with a sealing member composed of an expandable portion that is at least partly elastic.

[0077] Furthermore, those skilled in the art can implement the present invention in various modifications without departing from the core principles, in accordance with conventionally known knowledge. Such modifications, insofar as they still possess the configuration of the optical fiber pressure sensor and optical fiber pressure measuring instrument of the present invention, are of course included within the scope of the present invention.

[0078] Optical fiber pressure sensors and optical fiber pressure measuring instruments can be used in various fields to measure pressure inside small tubes and other narrow spaces. For example, in medical settings, they can be used inside blood vessels to measure blood pressure. They can also be used in a wide range of other fields, such as infrastructure (e.g., pressure measurement inside sewer pipes) and geotechnical engineering.

[0079] 1: Pressure sensor (optical fiber pressure sensor) 10, 64: Optical fiber 11: End (end on one side) 12: End (end on the other side) 20: Cylindrical part 21: Small diameter part 22: Large diameter part 23: One opening 24: The other opening 25: Gap 26: End 30: Pressure-sensitive part 31: Small diameter part 32: Large diameter part 33: Reflective surface 34: Pressure-receiving surface 35: Stepped surface 40: Spring (elastic body) 50, 250, 350: Sealing member 51, 251, 351: Expandable part 52, 252: Sealing part 53: Stretched piece 54, 254, 354: End 55, 255: Adhesive 60: Optical fiber pressure measuring instrument 61: Optical distributor 62: Light source 63: Photodetector 71: Pressurization chamber 72: Pressurizer 100, 200, 300: Sensor body; 256, 356: End portion; 357: Adhesive sealing layer

Claims

1. A diaphragm mirror type optical fiber pressure sensor that detects pressure at one end of an optical fiber and has a pressure-sensitive element at the tip of the said end, wherein the tip is sealed with a sealing member which is composed of an elastic expandable portion, at least a part of which is elastic.

2. The optical fiber pressure sensor according to claim 1, wherein the material of the expandable portion is rubber.

3. An optical fiber pressure sensor according to claim 2, comprising: an optical fiber; a cylindrical portion into which one end of the optical fiber is inserted and fixed through one opening; and an elastic body interposed between the cylindrical portion and the pressure-sensitive portion, wherein a repulsive force acts against the movement of the pressure-sensitive portion toward the end of the optical fiber at one end, the pressure-sensitive portion comprising a reflective surface positioned opposite to the end of the optical fiber at one end, and a pressure-receiving surface facing away from the reflective surface and toward the other opening in the cylindrical portion, and being movable in the axial direction within the cylindrical portion, and the sealing member sealing at least the gap between the cylindrical portion and the pressure-sensitive portion.

4. The optical fiber pressure sensor according to claim 3, wherein the sealing member is formed in the shape of a cap and covers the entire other opening in the cylindrical portion.

5. The optical fiber pressure sensor according to claim 3, wherein the material of the expandable portion is silicone rubber.

6. The optical fiber pressure sensor according to claim 3, wherein the expandable portion is tubular, the sealing member has a sealing portion that seals one end of the expandable portion, the cylindrical portion is inserted into the other end of the expandable portion and at least a part of it is in close contact with the outer surface of the cylindrical portion over its entire circumference, the sealing portion covers the entire other opening and is in contact with the pressure-sensitive portion, and the hardness of the sealing portion is higher than the hardness of the expandable portion.

7. The optical fiber pressure sensor according to claim 6, wherein the sealing portion is formed by curing an uncured material supplied to one end of the expandable portion.

8. The optical fiber pressure sensor according to claim 6, wherein the material of the sealing portion is a hard material.

9. The optical fiber pressure sensor according to claim 6, wherein the hardness of the expandable portion is 60 points or less on a Type A durometer compliant with JIS K 6253.

10. The optical fiber pressure sensor according to claim 6, wherein the thickness of the expandable portion is 0.1 mm or less.

11. An optical fiber pressure measuring instrument comprising: an optical fiber pressure sensor according to claim 3; a light source that incidents light on the other end of the optical fiber; and a photodetector that measures the intensity of the reflected light when the light incident on the other end of the optical fiber and emitted from the one end of the optical fiber is irradiated onto the reflective surface.

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