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

Abstract

Provided are a fiber-optic pressure sensor and a fiber-optic pressure measuring instrument that are capable of achieving cost reduction and / or high sensitivity, and also achieving further highly accurate pressure measurement.　A fiber-optic pressure sensor 1 includes: an optical fiber 10; a cylindrical part 20 into which one end side t of the optical fiber 10 is inserted through one opening 23 thereof and fixed; a pressure sensitive part 30 which is provided with a reflection surface 33 disposed opposite to an end 11 at the one end side t of the optical fiber 10 and a pressure receiving surface 34 facing the other opening 24 of the cylindrical part 20 and facing away from the reflection surface 33 and which is movable in the cylindrical part 20 in the axis P direction; and an elastic body 40 which is interposed between the cylindrical part 20 and the pressure sensitive part 30 and which operates linearly due to a repulsive force acting in response to the movement of the pressure sensitive part 30 in a direction approaching the end 11 at the one end side t of the optical fiber 10. A fiber-optic pressure measuring instrument using the fiber-optic pressure sensor is also provided.

Description

Optical fiber type pressure sensor and optical fiber type pressure measuring instrument

[0001] The present invention relates to an optical fiber type pressure sensor and an optical fiber type pressure measuring instrument.

[0002] Conventionally, optical fiber type pressure sensors for measuring pressure inside fine tubes and 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 optically processed based on the optical path difference of reflected light of light emitted from an optical fiber. A force sensor that measures a pressure change by detecting and analyzing the pressure change is disclosed.

[0003] In the technique described in Patent Document 1, the movable range of the total reflection mirror moved by pressure is an extremely minute range due to the shape deformation of the diaphragm, which is on the order of the wavelength of light incident on the optical fiber. Therefore, a pressure change is detected and measured by monitoring a change 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, leading to increased cost of the entire apparatus. In addition, since pressure is measured by monitoring extremely minute positional movement through wavelength changes, it has been difficult to increase measurement sensitivity. Furthermore, the realization of even higher-precision pressure measurement has been desired.

[0005] Japanese Unexamined Patent Publication No. 2019-187646

[0006] Therefore, an object of the present invention is to provide an optical fiber type pressure sensor and an optical fiber type pressure measuring instrument that can achieve one or both of cost reduction and high sensitivity, and can also achieve even higher-precision pressure measurement.

[0007] The above objective is achieved by the present invention as follows. That is, the embodiments of the present invention are as follows: <1> An optical fiber pressure sensor for detecting pressure at one end of an optical fiber, comprising: an optical fiber; a cylindrical portion into which one end of the optical fiber is inserted and fixed from one opening; a pressure-sensitive portion having a reflective surface positioned opposite to the end of the optical fiber and a pressure-receiving surface facing away from the reflective surface and towards the other opening in the cylindrical portion, and being movable in the axial direction within the cylindrical portion; and an elastic body interposed between the cylindrical portion and the pressure-sensitive portion, which acts as a repulsive force against movement of the pressure-sensitive portion toward the end of the optical fiber and operates linearly.

[0008] <2> The optical fiber pressure sensor according to claim 1, wherein the elastic body operates linearly within a pressure range of 100 to 250 mmHg.

[0009] <3> The optical fiber pressure sensor according to <1>, wherein a pressing force is applied to the elastic body while no external pressure is applied to the pressure-receiving surface.

[0010] <4> The optical fiber pressure sensor according to <1>, wherein the elastic body is a spring.

[0011] <5> The optical fiber pressure sensor described in <3>, wherein the wire diameter of the spring is 0.1 mm or less and the number of turns is 15 or more.

[0012] <6> The optical fiber pressure sensor described in <4>, wherein the spring constant of the spring is 0.2 N / mm or less.

[0013] <7> An optical fiber pressure measuring instrument comprising: an optical fiber pressure sensor as described in <1>; 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.

[0014] According to the present invention, it is possible to provide an optical fiber pressure sensor and an optical fiber pressure measuring instrument that can achieve either or both of the following: cost reduction and high sensitivity, as well as even higher precision pressure measurement.

[0015] This is a cross-sectional view showing an optical fiber pressure sensor according to an exemplary embodiment of the present invention. This is an enlarged cross-sectional view of the main part of the sensor body in an optical fiber pressure sensor according to an exemplary embodiment of the present invention. This is a graph showing the relationship between the amount of spring deflection and the pressure applied to the spring used in the embodiment. This is a schematic diagram showing a pressurization test being performed on an optical fiber pressure measuring instrument according to the embodiment. This is an enlarged cross-sectional view of the main part of the sensor body in an optical fiber pressure sensor according to a first modified example of the present invention. This is an enlarged cross-sectional view of the main part of the sensor body in an optical fiber pressure sensor according to a second modified example of the present invention. This is an enlarged cross-sectional view of the main part of the sensor body in an optical fiber pressure sensor according to a third modified example of the present invention.

[0016] Hereinafter, an optical fiber pressure sensor and an optical fiber pressure measuring instrument according to exemplary embodiments of the present invention will be specifically described with reference to the drawings.

[0017] [Embodiment] Figure 1 is a cross-sectional view showing an optical fiber pressure sensor according to an embodiment. As shown in Figure 1, the optical fiber pressure sensor 1 according to the embodiment (hereinafter sometimes simply referred to as "pressure sensor 1") has an optical fiber 10 and a sensor body 100 attached to the tip of one end of the optical fiber 10.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] 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).

[0026] 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.

[0027] A tube 60 is placed over the tip end t of the cylindrical portion 20. The tube 60 consists of a pipe-shaped pipe portion 61 and a sealing portion 62 that seals the tip end t of the pipe portion 61. The tube 60 is sealed with the pipe portion 61 in close contact with the outer surface of the large-diameter portion 22 of the cylindrical portion 20, and the sealing portion 62 covers the other opening 24. In other words, the tube 60 prevents moisture, solid matter, etc. from entering the inside of the sensor body 100.

[0028] The material of the tube 60 is not particularly limited as long as it is a rubber-elastic material such as silicone rubber, synthetic rubber, natural rubber, or elastomer, but it is especially preferable that it be a silicone rubber tube, which has excellent stability and durability in various usage environments. The pressure-receiving surface 34 of the pressure-sensitive part 30 is in close contact with the sealing part 62 of the tube 60, and is subjected to pressure by external atmospheric pressure or water pressure (or the liquid pressure of a liquid other than water) through the through hole 52, which will be described later.

[0029] The pressure-sensitive part 30, which receives pressure through the sealing portion 62 of the tube 60, 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 tube 60's presence) because the pipe portion 61 is flexible, thereby acting to contract the spring 40. Thus, although the pressure-receiving surface 34 of the pressure-sensitive part 30 receives external pressure through the sealing portion 62 of the tube 60, the pressure-receiving surface 34 is still indirectly subjected to external pressure, so the presence of the tube 60 will be omitted in the following explanation.

[0030] The tip end t of the cylindrical portion 20 is covered and fixed with a spring retainer 50 so as to enclose the entire tube 60. The spring retainer 50 has a cylindrical portion 56 whose inner diameter is approximately the same as the large-diameter portion 22 that covers the tube 60, and a protruding piece 51 provided at the tip end t of the cylindrical portion 56, which extends in an annular shape toward the center (towards the central axis P). A through hole 52 is formed at the tip end t of the sensor body portion 100, with an opening diameter narrowed by the amount of the annular protruding piece 51 compared to the inner diameter of the cylindrical portion 56. In other words, the tip end t of the sensor body portion 100 has a so-called aperture shape. The material of the spring retainer 50 can be metal, resin, etc., and there are no particular restrictions.

[0031] In this embodiment, when no external pressure is applied to the pressure-receiving surface 34 (no load is acting in the direction of arrow b), the protruding piece 51, which is the contact part, contacts the pressure-receiving surface 34 and applies a pressing force to the spring 40. That is, when no external pressure is applied to the pressure-receiving surface 34, in other words, when no pressure is detected, the spring 40 is in a contracted state due to the applied pressing force. Then, when external pressure is applied to the pressure-receiving surface 34 and the pressure-sensitive part 30 tries to move in the direction toward the end 11 (direction of arrow b), the spring 40 contracts further and a repulsive force acts.

[0032] Figure 3 is a graph showing the relationship between the deflection amount of the spring used in this embodiment and the pressure applied to the spring. In the graph of Figure 3, the deflection amount is the length shortened when the compression spring is compressed. As shown in the graph of Figure 3, in an elastic body such as a spring, there is a nonlinear region A1 in which the magnitude of the pressure and the deflection amount do not show a proportional relationship when the deflection amount is small (pressure is small). As the deflection amount increases (pressure increases), it becomes a linear region A2 in which the magnitude of the pressure and the deflection amount show a linear relationship. If the deflection amount increases further (pressure increases), it becomes a nonlinear region A3 in which the magnitude of the pressure and the deflection amount do not show a proportional relationship again.

[0033] Therefore, in this embodiment, the protruding piece 51 applies an offset pressing force to the spring 40, causing the spring 40 to deflect to the extent that it is located in the linear region A2, beyond the nonlinear region A1, even when no pressure is applied to the pressure-receiving surface 34. That is, when pressure is applied to the pressure-receiving surface 34 and the spring 40 begins to deflect, the magnitude of the pressure and the amount of deflection show a linear relationship, and the spring 40 operates linearly. In other words, in this embodiment, the spring 40 is used in the linear region A2, where it operates linearly.

[0034] The nonlinear region A1 widens when there is a gap or play in the mounting portion between the spring 40 and the cylindrical portion 20 or the pressure-sensitive portion 30 (in this embodiment, the contact portion between the spring 40 and the end face 21t or the stepped surface 35), and hardly occurs when there is no gap or play. However, especially with an extremely small spring 40 like the one in this embodiment, even a small gap or play has a large influence on the ratio, and the nonlinear region A1 tends to become relatively wide. Therefore, as in this embodiment, it is effective to use the spring 40 in the linear region A2 where it operates linearly.

[0035] This section describes the case where the pressure applied to the pressure-receiving surface 34 of the pressure sensor 1 according to this embodiment is gradually increased. In this embodiment, even when external pressure is applied to the pressure-receiving surface 34, the pressure-sensitive part 30 does not move at first because the protruding piece 51 of the spring retainer 50 is applying pressure to the spring 40. At this stage, if the spring 40 is free, the pressure is operating nonlinearly, corresponding to the nonlinear region A1 in the graph of Figure 3.

[0036] When the pressure on the pressure-receiving surface 34 increases and exceeds the offset pressing force applied by the protruding piece 51 of the spring retainer 50, the pressure-sensitive part 30 begins to move toward the end 11 (in the direction of arrow b) while resisting the repulsive force of the spring 40. In other words, pressure measurement becomes possible from this point onward. At this stage, the pressure is such that the spring 40 is operating linearly, corresponding to the linear region A2 in the graph of Figure 3.

[0037] As the pressure on the pressure-receiving surface 34 increases further and exceeds a certain threshold, the spring 40 begins to become less able to contract. In other words, measuring the pressure becomes difficult from this point onward. At this stage, the spring 40 is again operating nonlinearly at this pressure, corresponding to the nonlinear region A3 in the graph of Figure 3.

[0038] In this embodiment, the spring 40 operates linearly by measuring the pressure within the range of the linear region A2. Therefore, with the pressure sensor 1 according to this embodiment, the pressure-sensitive part 30 moves linearly in response to the pressure received by the pressure-receiving surface 34, thus enabling high-precision pressure measurement.

[0039] In practice, a safety margin is reserved, and the protrusion piece 51 applies a relatively large offset pressing force to the spring 40 such that the amount of deflection D2 is larger than the amount of deflection D1 at which the region switches from the non-linear region A1 to the linear region A2 in the graph of FIG. 3. Similarly, a corresponding device-based measure is separately implemented (such as providing a means for restricting the movement of the pressure-sensitive part 30 to prevent the spring 40 from deflecting beyond the measurement limit, or setting an upper measurement limit as the device specification) such that the measurement limit is reached at a deflection amount D3 smaller than the deflection amount D4 at which the region switches from the linear region A2 to the non-linear region A3 in the graph of FIG. 3. Therefore, as shown in the graph of FIG. 3, the range of deflection of the spring 40 during use is a measurement region A2' that is narrower than the linear region A2.

[0040] For medical applications of blood pressure measurement, the spring 40 as an elastic body preferably performs linear operation within a working pressure range of 100 to 250 mmHg.

[0041] Whether the spring 40 is performing linear operation can be checked in the following manner. First, for a spring, the deflection ratio can be defined by the following formula (1), and generally the range where the deflection ratio is 20 to 80% is regarded as the linear operation region.

[0042] Deflection ratio (%) = 100×δ / (Lf−Hs) …Formula (1) In the above formula (1), δ represents the amount of deflection (mm), Lf represents the free length of the spring (mm), and Hs represents the solid height of the spring, respectively. The solid height refers to the overall length of the compression coil spring when adjacent coils of the spring are in close contact with each other.

[0043] Furthermore, the amount of deflection δ can be calculated by the following formula (2). δ = P / k …Formula (2) In the above formula (2), P represents the load applied to the spring (N), and k represents the spring constant (N / mm), respectively.

[0044] Especially in medical applications, between blood pressure BP (mmHg) and P (N), with the area of the pressure receiving surface being S (mm ２ ), there is a relationship as shown in the following formula (3). BP = 0.000133×P / S …Formula (3)

[0045] Since the present invention is used in an ultrafine optical fiber pressure sensor, the wire diameter of the spring 40 is preferably 0.1 mm or less, and more preferably 0.08 mm or less. On the other hand, there is no lower limit to the wire diameter as long as the spring functions as such. However, if the wire diameter is too small, there is a concern that the function and performance as an elastic body will deteriorate. Therefore, the wire diameter of the spring 40 is preferably 0.03 mm or more, and more preferably 0.05 mm or more.

[0046] Furthermore, the number of turns of the spring 40 is preferably 15 turns or more, and more preferably 20 turns or more. If the number of turns of the spring 40 is too small, the measurable expansion / contraction region (i.e., the linear region A2) becomes narrow, resulting in a narrowed measurement range. On the other hand, there is no upper limit to the number of turns as long as the spring functions as such. However, if the number of turns is too large, there is a concern that the spring will deform when pressed. Therefore, the number of turns of the spring 40 is preferably 50 turns or less, and more preferably 40 turns or less.

[0047] Furthermore, the spring constant of the spring 40 is preferably 0.2 N / mm or less, and more preferably 0.1 N / mm or less. A high-sensitivity pressure sensor can be obtained by keeping the spring constant low. On the other hand, there is no lower limit to the spring constant as long as the spring functions as such. However, if the spring constant is too low, the measurement range becomes narrow. Therefore, the spring constant is preferably 0.01 N / mm or more, and more preferably 0.05 N / mm or more.

[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 part 30 and the end 11 on one end side (tip end 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, which is affected by the outside through the through-hole 52 and the tube 60, the pressure-sensitive part 30 moves in the direction of arrow b, and the reflective surface 33 of the pressure-sensitive part 30 approaches the end 11 on one end side (tip end side t) of the optical fiber. The distance (gap) between the reflective surface 33 and the end 11 decreases in inverse proportion to the magnitude of the 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 this 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. Figure 4 is a schematic diagram showing a pressurization test being performed on the optical fiber type pressure measuring instrument 70 according to this embodiment.

[0050] The optical fiber pressure measuring instrument 70 (hereinafter sometimes simply referred to as "pressure measuring instrument 70") measures pressure by inserting one end of an optical fiber 10, to which a sensor body 100 is attached, into a minute tube (for example, a blood vessel) to be measured. Figure 4 shows the state in which one end of the optical fiber 10 is inserted into a pressurized chamber 81, where the internal pressure is controlled by pressurizer 82.

[0051] As shown in Figure 4, the pressure measuring device 70 according to this embodiment includes an optical fiber type pressure sensor 1 according to this embodiment, a light source 72 that incidents light on the other end (base end b) of the optical fiber 10, an optical distributor 71 that distributes light in the middle of the optical fiber 10, and a photodetector 73 that receives the light distributed by the optical distributor 71 via the optical fiber 74 and measures its intensity.

[0052] The light source 72 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 4. The optical distributor 71 is a device that distributes the reflected light from the optical fiber 10 to the optical fiber 74 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 71.

[0054] In the pressure measuring device 70, when light is irradiated from the light source 72, 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 71, passes through the optical fiber 74 to the photodetector 73, 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 72 that is reflected by the reflective surface 33 and eventually reaches the photodetector 73 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 73, the magnitude of the pressure received by the pressure-receiving surface 34 can be determined.

[0056] At this time, if the coefficient of determination when linearly approximating the detected reflected light intensity and the reference value measured simultaneously by a general pressure sensor is 0.8 or higher, the spring can be considered to be operating linearly. For example, in medical applications, it is preferable to have a linear relationship in the blood pressure range of 100 to 250 mmHg.

[0057] 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.

[0058] In this embodiment, the pressure-sensitive section 30, equipped with a reflective surface 33, can move relatively large in the direction of the central axis P, while being restricted by the repulsive force of the spring 40 and the protruding piece 51. 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 73.

[0059] 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 73. 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.

[0060] Furthermore, according to this embodiment, since the spring 40 is configured to detect pressure in the linear region A2 where it operates linearly, the pressure-sensitive part 30 moves linearly in response to the pressure received by the pressure-receiving surface 34, thus enabling highly accurate measurement.

[0061] [Modifications] Three modified examples of the above-described embodiment, in which the structure of the sensor body 100 differs, will be illustrated with reference to the drawings. In each of the following modifications, only a part of the configuration differs from the above embodiment, and the rest is the same as the above embodiment. Therefore, in each modification, the characteristic configuration will be described, and components that have the same configuration and function as the above embodiment will be denoted by the same reference numerals as in Figures 1 and 2 showing the above embodiment, and their detailed description will be omitted.

[0062] (First Modified Example) Figure 5 is an enlarged cross-sectional view of the main part of the sensor body 200 in the optical fiber pressure sensor according to the first modified example. In the sensor body 200 according to this modified example, the shape of the spring retainer 50a (particularly the protruding piece 51a that makes contact) is different from that of the spring retainer 50 of the embodiment. That is, as shown in Figure 5, the shape of the protruding piece 51a provided at the tip end t of the spring retainer 50a is not annular like the protruding piece 51 of the embodiment, but is claw-shaped with a part of the circumferential direction extending toward the center (towards the central axis P). Therefore, only the claw-shaped protruding piece 51a protrudes from the through hole 52a, and the through hole 52a has an area that is almost the same as the circular cross-section of the cylindrical portion 56a.

[0063] Similar to the protruding piece 51 in the embodiment, this protruding piece 51a contacts the pressure-receiving surface 34 and applies a pressing force to the spring 40 when no external pressure is applied to the pressure-receiving surface 34 (no load is acting in the direction of arrow b). In other words, when no external pressure is applied to the pressure-receiving surface 34, or in other words, when no pressure is detected, the spring 40 is in a contracted state due to the applied pressing force. The significance and concept of this offset pressing force are the same as in the embodiment.

[0064] In this modified example, the spring 40 operates linearly by measuring the pressure within the linear region A2 shown in the graph of Figure 3. Therefore, with the pressure sensor according to this modified example using the sensor body 200, the pressure-sensitive part 30 moves linearly in response to the pressure received by the pressure-receiving surface 34, thus enabling high-precision pressure measurement.

[0065] (Second Modification) Figure 6 is an enlarged cross-sectional view of the main part of the sensor body 300 in the optical fiber pressure sensor according to the second modification. In the sensor body 300 according to this modification, the shape of the spring retainer 50b is different from the spring retainer 50 of the embodiment and the spring retainer 50a of the first modification. That is, as shown in Figure 6, the contact portion provided at the tip end t of the spring retainer 50b is not a protruding piece such as a protruding piece 51 or protruding piece 51a, but a mesh 51b that covers the entire other opening 24 of the cylindrical portion 20. Therefore, the mesh 51b that exists over the entire opening at the tip end t of the cylindrical portion 56a is a through hole 52b.

[0066] Similar to the protruding piece 51 in the embodiment, this mesh 51b contacts the pressure-receiving surface 34 and applies a pressing force to the spring 40 when no external pressure is applied to the pressure-receiving surface 34 (no load is acting in the direction of arrow b). In other words, when no external pressure is applied to the pressure-receiving surface 34, or in other words, when no pressure is detected, the spring 40 is in a contracted state due to the applied pressing force. The significance and concept of this offset pressing force are the same as in the embodiment.

[0067] In this modified example, the spring 40 operates linearly by measuring the pressure within the linear region A2 shown in the graph of Figure 3. Therefore, with the pressure sensor according to this modified example using the sensor body 300, the pressure-sensitive part 30 moves linearly in response to the pressure received by the pressure-receiving surface 34, thus enabling high-precision pressure measurement.

[0068] (Third Modification) Figure 7 is an enlarged cross-sectional view of the main part of the sensor body 400 in the optical fiber pressure sensor according to the third modification. In the sensor body 400 according to this modification, the shape of the spring retainer 50c is different from the spring retainer 50 of the embodiment and the spring retainers 50a and 50b of the first and second modifications.

[0069] In this modified example, a protruding piece 51c, having the same shape as the protruding piece 51a in the second modified example, is provided on the spring retainer 50c as a contact portion. However, in this modified example, the protruding piece 51c is not provided on the tip end t of the spring retainer 50c, but on the inner circumferential surface of the peripheral wall 54 extending from the cylindrical portion 56c of the spring retainer 50c toward the tip end t. Furthermore, the peripheral wall 54 of the spring retainer 50c extends further in the direction of arrow t from the position where the protruding piece 51c is provided, and the tip end t of the spring retainer 50c is closed by the top plate 53. Therefore, in the sensor body 400 according to this modified example, there is no through hole on the side in the direction of arrow t. As described above, the pressure-receiving surface 34 of the pressure-sensitive part 30 does not need to have through holes in opposing positions, and it is sufficient that it is configured to receive the pressure of the external environment.

[0070] In this modified example, there is a gap between the pressure-receiving surface 34 and the top plate 53, and the area enclosed by the pressure-receiving surface 34, the top plate 53, and the peripheral wall 54 forms a semi-closed space 55. A part of the peripheral wall 54 in the semi-closed space 55 is open, forming a through hole 52c. The semi-closed space 55 is at the same pressure as the outside through the through hole 52c. Therefore, in this modified example, as in the embodiment and other modified examples, the pressure-receiving surface 34 is subjected to the same pressure as the environment in which the sensor body 300 is located.

[0071] The protruding piece 51c, like the protruding piece 51 in the embodiment, contacts the pressure-receiving surface 34 and applies a pressing force to the spring 40 when no external pressure is applied to the pressure-receiving surface 34 (no load is acting in the direction of arrow b). In other words, when no external pressure is applied to the pressure-receiving surface 34, or in other words, when no pressure is detected, the spring 40 is in a contracted state due to the applied pressing force. The significance and concept of this offset pressing force are the same as in the embodiment.

[0072] In this modified example, the spring 40 operates linearly by measuring the pressure within the linear region A2 shown in the graph of Figure 3. Therefore, with the pressure sensor according to this modified example using the sensor body 400, the pressure-sensitive part 30 moves linearly in response to the pressure received by the pressure-receiving surface 34, thus enabling high-precision pressure measurement.

[0073] The embodiments and three modifications described above are merely examples of typical forms of the present invention, and the present invention is not limited to the above embodiments or modifications. For example, in the above embodiments and modifications, examples are given in which the cylindrical portion and the spring retainer are made of separate members, but the present invention is not limited thereto, and the protruding piece, mesh, etc. may be integrally molded with the cylindrical portion.

[0074] Furthermore, while the above embodiments and modifications use a spring (40) as the elastic body, the present invention is not limited thereto, and any elastic member can be used without particular restriction. Other members can also be used if they are elastic, as they exhibit the properties of nonlinear regions A1, A3 and linear region A2 shown in the graph of Figure 3, and the present invention can be applied in the same way as with a spring. Other elastic members can be any material with 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 embodiments and modifications 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, 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.

[0077] 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.

[0078] 1: Pressure sensor (optical fiber pressure sensor) 10, 74: 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 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, 50a, 50b, 50c: Spring retainer 51, 51a, 51c: Projecting piece (contact part) 51b: Mesh (contact part) 52, 52a, 52b, 52c: Through hole 53: Top plate 54: Peripheral wall 55: Semi-closed space 56, 56a, 56b, 56c: Cylindrical part 60: Tube 61: Pipe part 62: Sealing section 70: Optical fiber pressure measuring device 71: Optical distributor 72: Light source 73: Photodetector 81: Pressurization chamber 82: Pressurizer 100, 200, 300, 400: Sensor body

Claims

An optical fiber pressure sensor that detects pressure at one end of an optical fiber, The optical fiber and, A cylindrical portion into which one end of the optical fiber is inserted and fixed through one opening, A pressure-sensitive part is provided, which has a reflective surface positioned opposite to one end of the optical fiber, and a pressure-receiving surface facing away from the reflective surface and towards the other opening in the cylindrical part, and is movable in the axial direction within the cylindrical part, An elastic body interposed between the cylindrical portion and the pressure-sensitive portion, which acts as a repulsive force against the movement of the pressure-sensitive portion toward one end of the optical fiber and exhibits linear motion, A fiber optic pressure sensor having the following features. 　 The optical fiber pressure sensor according to claim 1, wherein the elastic body operates linearly within a pressure range of 100 to 250 mmHg. 　 The optical fiber pressure sensor according to claim 1, wherein a pressing force is applied to the elastic body while no external pressure is applied to the pressure-receiving surface. 　 The optical fiber pressure sensor according to claim 1, wherein the elastic body is a spring. 　 The optical fiber pressure sensor according to claim 4, wherein the wire diameter of the spring is 0.1 mm or less and the number of turns is 15 or more. 　 The optical fiber pressure sensor according to claim 4, wherein the spring constant of the spring is 0.2 N / mm or less. 　 The optical fiber pressure sensor according to claim 1, A light source is incident on the other end of the optical fiber, A photodetector measures the intensity of the reflected light when light is incident on the other end of the optical fiber and emitted from the one end of the optical fiber, A fiber optic pressure measuring instrument.

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