JP2008134155A - Optical fiber strain gage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber strain gage for highly accurately detecting tension and bending force applied to an object to be measured by being welded on the object to be measured in addition to solving the problem of temperature compensation in a simple and inexpensive configuration. <P>SOLUTION: The optical fiber strain gage 100 is formed of: a gage base 10 for forming an air gap 13; continuously formed first groove parts 14A, 14B and second groove parts 15A, 15B; an optical fiber 11 fixed on both the groove parts; an FBG 111 formed on the optical fiber; first fixing parts 12A1, 12B1 extending in a direction orthogonal to both the groove parts for fixing the gage base 10 and an object to be measured; and second fixing parts 12A2, 12B2 extending in parallel to both the groove parts. Since a gage base 10 is fixed in two directions, the optical fiber strain gage is firmly fixed on the object to be measured to prevent it from being deformed out of a face, and detects the strain of the object to be measured generated by bending force or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical fiber strain gauge used for industrial process measurement, strain measurement in a linear motor car, power transmission line, generator, etc., measurement in a strong electromagnetic field noise environment, civil engineering-related measurement in a lightning strike environment, etc. The present invention relates to an optical fiber strain gauge using FBG [Fiber Bragg Grating].

  Conventionally, as one of optical fiber sensors such as an optical fiber strain gauge using FBG, the present applicant has proposed an optical fiber strain gauge having a compact configuration capable of solving the problem of temperature compensation (patent) Reference 1).

  The above optical fiber strain gauge is fixed to a measurement object by welding or the like, measures the measurement object using FBG, and has a linear expansion coefficient between the gauge base to which the optical fiber is attached and the measurement object. The temperature compensation is performed using the difference between the two. FBG uses an optical fiber Bragg diffraction grating in which the refractive index of the core of a single mode optical fiber for communication is periodically changed in the fiber axis direction as a detection element, and the refractive index of the incident light to the diffraction grating. This utilizes a phenomenon in which only a specific wavelength (Bragg wavelength) corresponding to the period is selectively reflected. In other words, when the strain is applied to the detection element, the period of the diffraction grating changes, and thus the wavelength of the reflected light is shifted. Therefore, the amount of strain applied from the shift amount of the wavelength can be measured. According to such an optical fiber type strain gauge, a compact optical fiber type strain gauge capable of temperature compensation can be obtained at low cost by using only one FBG.

JP 2001-94059 A

  The above-mentioned optical fiber strain gauge can be used even in a narrow portion because of its compact configuration, and can solve the temperature compensation problem, so that the temperature of the measurement object changes. Even in cases, it can be used. And this optical fiber type strain gauge can detect the distortion | strain of the measuring object which generate | occur | produced in the measuring object by tensile force etc. with high precision.

  However, when this optical fiber type strain gauge is fixed to the measurement object, it is fixed by welding the fixed part of the gauge base to the measurement object. This fixed part is provided only in the width direction of the gauge base. It was done. In addition, since the fixing portion and the groove for inserting the optical fiber are provided, the thick portion is reduced in the vicinity of the fixing portion of the gauge base. As a result, the out-of-plane rigidity of the gauge base is reduced as a result of the reduction of the thick-walled portion.Therefore, when bending force acts on the measurement object and distortion occurs, the gauge base is attached to the measurement object. There was a risk of plastic deformation out of plane when deforming together.

  If the gauge base is plastically deformed out of plane in this way, it will not return to its original state even after the load such as bending force is removed from the measurement object. If the gauge base does not return to its original position, the optical fiber strain gauge cannot accurately measure the strain generated in the measurement object. For this reason, this fiber optic strain gauge can be used to measure the strain of a measurement object to which a bending force or the like acts even though the measurement object to which a tensile force acts can detect the strain with high accuracy. There was a risk of a decrease in accuracy.

  Under such circumstances, the above-mentioned optical fiber strain gauge that can solve the problem of temperature compensation as described above and can detect strain with high accuracy can be used for measuring strain of a measurement object on which bending force or the like acts. There is a growing need for improvements to suit.

  The present invention has been made in view of the various problems as described above. The object of the present invention is to solve the problem of temperature compensation with a simple and low-cost configuration and to weld the measurement object. An object of the present invention is to provide an optical fiber strain gauge capable of detecting not only a tensile force applied to the measurement object but also a bending force with high accuracy.

  In order to solve the above-described problems, in the optical fiber strain gauge of the present invention, a gauge base in which a gap portion is formed, and a first and a first formed continuously on the one surface of the gauge base via the gap portion. Two grooves, an optical fiber fixed and extending in the first and second grooves, a sensing element comprising a Bragg diffraction grating formed in a portion of the optical fiber located in the gap, and the gauge base An optical fiber strain gauge having a fixing portion to which a fixing force is applied by fixing means for fixing a measurement object, wherein the fixing portion is in a direction perpendicular to the first groove and the second groove. The first fixed portion extending and the second fixed portion extending in parallel with the first groove and the second groove are characterized by being formed.

  This makes it possible to fix the gauge base in two directions, the width direction and the longitudinal direction. Therefore, with this optical fiber strain gauge, it is possible to prevent the gauge base from being firmly fixed to the measurement object and prevent deformation, and to detect the distortion of the measurement object caused by bending force or the like with high accuracy. be able to.

  Further, it is preferable that the second fixing portion is formed so as to extend in two directions from an end portion of the first fixing portion. As a result, the optical fiber strain gauge can be firmly fixed to the object to be measured, and the optical fiber strain gauge can be prevented from being deformed out of the plane by an external force. Further, the second fixing portion may be provided on both side portions of the gauge base. With this, in the gauge base including the first fixing portion and the second fixing portion, the first fixing portion and the second fixing portion are provided. However, since it is provided at a symmetrical position across the first groove and the second groove, it is possible to make it difficult to undergo deformation such as torsion.

  Further, the optical fiber strain gauge of the present invention is further divided and formed on the gauge base by stepped portions extending in a direction perpendicular to the axial direction of the optical fiber and the sensing element and formed on both sides of the gap. And a thin-walled portion located around the gap and a thick-walled portion having a thickness greater than that of the thin-walled portion. The optical fiber strain gauge according to the present invention further includes a constricted portion formed in the thin portion of the gauge base.

  As a result, the optical fiber strain gauge of the present invention has a thin portion and a constricted portion where deformation is noticeable, and a thick portion other than that. Therefore, the deformation of the sensing element comprising the Bragg diffraction grating is remarkable. It is possible to improve the detection sensitivity of the strain by disposing it in the portion appearing in.

  In the optical fiber strain gauge of the present invention, the gauge base is made of a material having a first linear expansion coefficient, and the optical fiber strain gauge is made of the material having a second linear expansion coefficient. It is more preferable that temperature compensation is performed using a difference between the first linear expansion coefficient and the second linear expansion coefficient, which is fixed to the object.

  As a result, temperature compensation is performed by utilizing the difference between the linear expansion coefficient of the gauge base material and the linear expansion coefficient of the measurement object, so that temperature compensation is possible even when only one sensing element comprising a Bragg diffraction grating is used. Thus, an optical fiber strain gauge having a compact configuration can be obtained at low cost.

  In addition, the optical fiber strain gauge of the present invention is more preferably used in a state where a tensile force is previously applied to the sensing element. As a result, there is no possibility that the sensing element will buckle due to compressive force or the like, and the compressive strain can be measured stably.

  According to the present invention, since an optical fiber strain gauge using a sensing element composed of a Bragg diffraction grating can be firmly fixed to a measurement object, it can be suitably used for a measurement object on which a bending force or the like acts. Is possible. In addition, strain measurement with temperature compensation can be performed by providing only one sensing element composed of a Bragg diffraction grating.

  Embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not limit the invention according to the claims, and all the combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent.

  FIG. 1 is a perspective view of an optical fiber strain gauge 100 according to an embodiment of the present invention, FIG. 2 is a diagram for explaining a gauge base 10 in the optical fiber strain gauge 100, and FIG. 1 is a diagram showing an optical fiber 11 in a strain gauge 100. FIG. First, the configuration of the optical fiber strain gauge 100 will be described with reference to FIG.

  As shown in FIG. 1, the optical fiber strain gauge 100 of this embodiment includes a gauge base 10 and an optical fiber 11. In the gauge base 10, an H-shaped gap 13 is formed in the center in the longitudinal direction over the width direction, and thick portions 18A and 18B are formed on both sides in the longitudinal direction across the gap 13. Is formed. The gauge base 10 has a thin rectangular parallelepiped shape as a whole.

  Further, steps 16A and 16B are formed at both boundary portions between the gap portion 13 and the thick portions 18A and 18B, and the surrounding portion forming the H-shaped gap portion 13 is a thick portion. The thin portion 17 is thinner than 18A and 18B. That is, the thin portion 17 and the thick portions 18A and 18B are partitioned by the steps 16A and 16B. And the thin part 17 has the constriction part 20 so that it may become line symmetrical about the centerline of the longitudinal direction of the gauge base 10 as a reference line.

  In addition, the thick portions 18A and 18B include the first groove portions 14A and 14B continuously through the gap portion 13 in the central portion in the width direction of the gauge base 10 and over the entire length direction of the gauge base 10. Second groove portions 15A and 15B that are narrower than the first groove portions 14A and 14B are formed. The optical fiber 11 is inserted and fixed in the first groove portions 14A and 14B and the second groove portions 15A and 15B. The thick portions 18A and 18B are formed with fixing portions 12A and 12B.

  Next, the detailed configuration of the gauge base 10 will be described with reference to FIG.

  2A is a plan view of the gauge base 10, FIG. 2B is a side view in the longitudinal direction, and FIG. 2C is a side view in the width direction. As described above, the gauge base 10 includes the fixing portions 12A and 12B, the gap portion 13, the first groove portions 14A and 14B, the second groove portions 15A and 15B, the steps 16A and 16B, the thin portion 17 and the thick portions 18A and 18B. , And a constricted portion 20 is formed.

  As shown in FIGS. 2A and 2B, the fixing portions 12 </ b> A and 12 </ b> B, which are characteristic portions of the present embodiment, are formed from the first groove portions 14 </ b> A and 14 </ b> B from the lateral side of the gauge base 10. , And the second groove portions 15A, 15B are formed two by two so as to be line symmetric with respect to the reference line. The fixing portions 12A and 12B are formed of two fixing portions, which are a first fixing portion 12A1 and 12B1 extending in the width direction of the gauge base 10 and a second fixing portion 12A2 and 12B2 extending in the longitudinal direction of the gauge base 10. The first fixing portions 12A1 and 12B1 and the second fixing portions 12A2 and 12B2 are thin so as to be easily fixed to the measurement object by welding.

  The second fixing portions 12A2 and 12B2 are formed on the side portions in the width direction of the gauge base 10, and the first fixing portions 12A1 and 12B1 are formed from the central portion in the longitudinal direction of the second fixing portions 12A2 and 12B2. The gauge base 10 is formed to extend toward the center. That is, the fixing portions 12A and 12B of the present embodiment are T-shaped, the portion of the T-shaped horizontal bar becomes the second fixing portion 12A2 and 12B2, and the portion of the T-shaped vertical bar is the first. The fixing portions 12A1 and 12B1 are formed.

  As shown in FIGS. 2A and 2C, the first groove portions 14A and 14B and the second groove portions 15A and 15B are symmetrical with respect to the center line in the width direction of the gauge base 10 as a reference line. The first groove portions 14A and 14B are formed from both longitudinal sides of the gauge base 10 to a position slightly beyond the center line of the first fixing portions 12A1 and 12B1, and the first groove portions 14A and 14B have gaps therebetween. Between the portion 13 is the second groove portions 15A and 15B.

  2 (a) and 2 (b), the constricted portion 20 is a recessed portion formed in the thin portion 17 from the both sides in the width direction of the gauge base 10 toward the inside. 18A and 18B are connected by a thin portion 17 in which the constricted portion 20 is formed. Therefore, since the rigidity of the gauge base 10 is reduced by the constricted portion 20, the constricted portion 20 is easily bent when an external force or the like acts on the gauge base 10.

  In the present embodiment, the dimensions of the gauge base 10 are as follows. That is, the total length l of the base 10 is 40 mm, the total width b of the gauge base 10 is 12 mm, the thickness d of the thick portions 18A and 18B is 0.6 mm, and the distance between the center lines of the first fixing portions 12A1 and 12B1 (gauge length ) L is 28 mm, the gap G between the gap portions 13 is 6 mm, the length 11 of the first fixing portions 12A1 and 12B1 is 5 mm, the width b1 of the first fixing portions 12A1 and 12B1 is 1 mm, and the length of the second fixing portions 12A2 and 12B2 The length l2 is 7 mm, the width b2 of the second fixing portions 12A2 and 12B2 is 1.5 mm, the width b3 of the first groove portions 14A and 14B is 0.5 mm, the width b4 of the second groove portions 15A and 15B is 0.13 mm, The depth d1 of the groove portions 14A and 14B and the second groove portions 15A and 15B is 0.3 mm, the width b5 of the thin portion 17 is 1 mm, and the thickness d2 of the thin portion 17 is 0.2 mm.

  Further, the gauge base 10 according to the present embodiment is configured such that the thick portions 18A and 18B, the first fixing portions 12A1 and 12B1, the second fixing portions 12A2 and 12B2, and the thin portion 17 are masked with a corrosion-resistant film. 13 is fabricated by etching with a strong corrosive liquid. Thereafter, the thick portions 18A and 18B are masked with a corrosion-resistant film, and the first fixing portions 12A1, 12B1, the second fixing portions 12A2, 12B2, and the thin portion 17 are etched with a strong corrosive liquid. Thereafter, the first groove portions 14A and 14B and the second groove portions 15A and 15B are produced by rolling with a rotary saw.

  In the present embodiment, the gauge base 10 is made of SUS304, which is an austenitic stainless steel. Austenitic stainless steel is characterized by excellent passivating effect of Cr and corrosion resistance by Ni, excellent workability and weldability, and high toughness at low temperatures.

  Note that the dimensions and materials of each part of the gauge base 10 are closely related to the temperature compensation of the optical fiber strain gauge 100 of the present embodiment. It will be described together with the description. Next, the optical fiber 11 of this embodiment will be described in detail with reference to FIG.

  3A is a side view of the optical fiber 11 used in the optical fiber strain gauge 100 of the present embodiment, and FIG. 3B is an α-α cross-sectional view of the optical fiber 11. FIG. 3C is a β-β cross-sectional view of the optical fiber 11. As shown in FIG. 3A, FIG. 3B, and FIG. 3C, the optical fiber 11 includes a fiber strand 11a and a first coating resin layer 11b that coats the fiber strand 11a. I have. Then, in a portion where the first coating resin layer 11b is not provided, a second coating resin layer 11c made of a resin having a smaller thickness and higher strength and moisture resistance than the first coating resin layer 11b is provided.

  Further, an FBG 111 (optical fiber black diffraction grating) as a sensing element is formed on a portion of the fiber strand 11a coated with the second coated resin layer 11c. This FBG 111 is an optical device in which the core portion 11d of the fiber strand 11a is formed in a diffraction grating shape by periodically changing the refractive index in the longitudinal direction of the optical fiber 11, and only an optical signal having a specific wavelength is received. It has the property of reflecting. Since the optical signal propagating through the optical fiber 11 is concentrated in the core portion 11d having a high refractive index in the fiber strand 11a, most of the optical signal propagating through the optical fiber 11 has a propagation loss. A small number of FBGs 111 are reached, some of the optical signals are transmitted through the FBG 111, and some of the optical signals are reflected by the FBG 111. Therefore, such an optical fiber 11 can be used as a sensing element having a highly accurate detection capability.

  Further, since the second coating resin layer 11c has higher strength and rigidity than the first coating resin layer 11b, the second coating resin layer 11c is subjected to shear deformation when strain is transmitted from the first coating resin layer 11b. Is kept low. Thereby, FBG111 covered with this 2nd coating resin layer 11c can detect a distortion | strain with high precision.

  In the optical fiber 11 of the present embodiment, the outer diameter is 250 μm, the fiber strand 11 a has a diameter of 125 μm, the core portion 11 d has a diameter of 5 to 10 μm, and the distance between the diffraction gratings of the FBG 111 is about 0.5 μm. The total length of the FBG 111 is 4 mm. The first coating resin layer 11b is UV resin, the second coating resin layer 11c is polyimide resin, the fiber strand 11a is quartz glass, and germanium having ultraviolet sensitivity is added to the core portion 11d. Then, the FBG 111 is formed by irradiating the core portion 11d with ultraviolet rays using the characteristics of germanium.

  In the optical fiber strain gauge 100 of the present embodiment configured by the gauge base 10 and the optical fiber 11 described above, the FBG 111 is disposed above the gap portion 13. A constricted portion 20 is formed in the thin portion 17 around the gap portion 13, and the gauge base 10 is bent from the vicinity of the constricted portion 20. That is, the FBG 111 is disposed in the most flexible part of the gauge base 10. Therefore, the optical fiber strain gauge 100 can transmit the strain of the measurement object to the FBG 111 with high accuracy, and the FBG 111 can detect the strain of the measurement object with high accuracy. .

  The optical fiber strain gauge 100 is configured to detect the strain when the strain of the measurement object is transmitted to the FBG 111 provided as a detection unit. Therefore, the optical fiber strain gauge 100 detects the strain. When performing, first, it is necessary to fix the optical fiber type strain gauge 100 to a measuring object (not shown). And when this optical fiber type strain gauge 100 is fixed to a measuring object, the inside of 1st adhering part 12A1, 12B1 and 2nd adhering part 12A2, 12B2 and a measuring object come to be welded. Yes.

  Thus, since 1st adhering part 12A1, 12B1 and 2nd adhering part 12A2, 12B2 are welded, the optical fiber type strain gauge 100 will expand and contract with a measuring object, and it is a fixed position. There will be no shift. Therefore, the strain of the measurement object is transmitted to the FBG 111 as the gauge base 10 expands and contracts together with the measurement object and the interval G of the gap 13 increases or decreases.

  Further, in the optical fiber strain gauge 100 of the present embodiment, when the gauge base 10 is fixed to a measurement object, a round bar shape of a spot welder is formed inside the first fixing portions 12A1 and 12B1 and the second fixing portions 12A2 and 12B2. This electrode is inserted, pressurized with this electrode and energized, and the contact point is heated and welded to fix to the measurement object. Therefore, a step is generated between the first fixing portions 12A1 and 12B1 and the second fixing portions 12A2 and 12B2, which are formed thinner than the thick portions 18A and 18B, and the thick portions 18A and 18B. Then, the optical fiber strain gauge 100 can be fixed to the measurement object simply by moving the electrode of the spot welder along the step. Simplification can be achieved.

  When detecting the strain with the optical fiber strain gauge 100 described above, a light source device (not shown) is connected to one end of the optical fiber 11 of the fixed optical fiber strain gauge 100 via an optical circulator (not shown). ) And a spectrum analyzer (not shown) to the optical circulator. Then, the light emitted from the light source device is sent to the FBG 111, reflected by the FBG 111, and the wavelength of the reflected light is measured by a spectrum analyzer, so that the optical fiber strain gauge 100 detects the strain.

  That is, when strain is transmitted to the FBG 111, the period of the diffraction grating in the FBG 111 changes, so that the wavelength of the reflected light is shifted. Therefore, the wavelength of the reflected light in a state where the strain is transmitted to the FBG 111 and the wavelength of the reflected light in a state where the strain is not transmitted to the FBG 111 are changed. By measuring this wavelength change with a spectrum analyzer, the optical fiber strain gauge 100 can detect the strain.

  Next, a method (temperature compensation) for excluding the influence of temperature change in the optical fiber strain gauge 100 will be described. First, the strain measurement principle and temperature effect in the FBG 111, which are preconditions for explaining the temperature compensation of the optical fiber strain gauge 100, will be described.

  The principle of strain measurement in the FBG 111 can be obtained from the following equation 1 for obtaining the wavelength of the optical signal reflected by the FBG 111.

ここで、数１の各変数は、λ_Ｂ：ブラッグ波長、ｎ_ｅｆｆ：光ファイバの実効屈折率、Λ：回折格子の間隔、である。

Here, each variable of Formula 1 is λ _B : Bragg wavelength, n _eff : effective refractive index of the optical fiber, and Λ: spacing of the diffraction grating.

  When strain is applied to the FBG 111, the Bragg wavelength also changes because the spacing of the diffraction grating changes, and the effective refractive index also depends on the strain. Therefore, the shift amount of the Bragg wavelength is derived from Equation 1 as follows.

次にこの数２を数１で割り、数３のように値を整理する。

Next, the number 2 is divided by the number 1, and the values are arranged as in the number 3.

ここで、数３の各値を数４と置き換えることにより、数５を導く。

Here, Equation 5 is derived by replacing each value of Equation 3 with Equation 4.

ここで、数５の各変数は、Δλ_Ｂ：ファイバの軸方向負荷ひずみによるブラッグ波長の波長シフト量、Ｐ_ρ：光弾性係数（ひずみによる屈折率変化の寄与を表す係数）、ε_Ｚ：ファイバの軸方向の負荷ひずみ、である。そして、この数５から、光ファイバのひずみ感度は、数６のように求められる。

Here, each variable of Equation 5 is: Δλ _B : wavelength shift amount of Bragg wavelength due to axial load strain of fiber, P _ρ : photoelastic coefficient (coefficient representing the refractive index change due to strain), ε _Z : fiber Load strain in the axial direction. From this equation 5, the strain sensitivity of the optical fiber is obtained as in equation 6.

本実施形態の光ファイバ１１は、ブラッグ波長が１５５０ｎｍであるので、数６の各変数に値を代入すると、ひずみ感度は、約１．２ｐｍ／μεとなる。

Since the optical fiber 11 of the present embodiment has a Bragg wavelength of 1550 nm, the strain sensitivity is approximately 1.2 pm / με when a value is substituted for each variable of Equation 6.

  The temperature influence in the FBG 111 can be obtained from the above equation 1 for obtaining the wavelength of the optical signal reflected by the FBG 111. When a temperature change is given to the FBG 111, the Bragg wavelength also changes because the effective refractive index changes. Further, since the glass of the optical fiber is also thermally expanded, the distance between the diffraction gratings is changed accordingly. Therefore, the shift amount of the Bragg wavelength is derived from Equation 1 as follows.

ここで、数７の各値を数８と置き換えることにより、数９を導く。

Here, Equation 9 is derived by replacing each value of Equation 7 with Equation 8.

ここで、数９の各変数は、Δλ_Ｂ：温度変化によるブラッグ波長シフト量、ζ：屈折率温度係数、α：光ファイバの線膨張係数である。そして、この数９から、光ファイバの温度感度は、数１０のように求められる。

Here, each variable in Equation 9 is Δλ _B : Bragg wavelength shift amount due to temperature change, ζ: refractive index temperature coefficient, and α: linear expansion coefficient of the optical fiber. From this equation 9, the temperature sensitivity of the optical fiber is obtained as in equation 10.

本実施形態の光ファイバ１１は、ブラッグ波長が１５５０ｎｍであるとき、実験値として数１０の温度感度は、約９．５ｐｍ／℃が得られる。このように、ＦＢＧではひずみ測定を行う際には、温度影響を無視することができないので、温度影響を補正する温度補償を行う必要がある。次に、温度補償の基本構造について、図４を用いて説明する。

In the optical fiber 11 of the present embodiment, when the Bragg wavelength is 1550 nm, the temperature sensitivity of several tens as an experimental value is about 9.5 pm / ° C. As described above, in the FBG, when the strain is measured, the temperature influence cannot be ignored. Therefore, it is necessary to perform temperature compensation for correcting the temperature influence. Next, the basic structure of temperature compensation will be described with reference to FIG.

FIG. 4 is a diagram for explaining a basic gauge base 1 which is a basic structure of temperature compensation according to the present embodiment. The basic gauge base 1 is a base gauge 10 of the optical fiber type strain gauge 100 in which the second fixing portions 12A2 and 12B2 and the thin portion 17 are not formed. The first groove portion 4, the second groove portion 5, and the thick portion 8 are provided, and are fixed to a strain body (not shown) by the fixing portion 2. In addition, it is possible to detect strain by inserting and fixing an optical fiber formed with FBG in the first groove portion 4 and the second groove portion 5. In the basic gauge base 1, when FBG temperature compensation is performed, it is necessary to compensate for the temperature effect of Δλ _B /ΔT=9.5 pm / ° C.

  Therefore, as a method adopted in the basic gauge base 1, temperature compensation is performed by applying strain to the FBG that changes in wavelength by −9.5 pm as the temperature increases by 1 ° C. using the linear expansion coefficient of the material. There is a way to do it. −9.5 pm / ° C. is −7.92 με / ° C. in terms of strain. That is, temperature compensation is possible by providing a structure that applies a compressive strain of 7.92 με to the FBG as the temperature rises by 1 ° C. In the basic gauge base 1, a specific dimension value can be obtained by Equation 11 for obtaining a change amount of the gap G of the gap 3 with respect to a temperature change of ΔT.

ＦＢＧが厚肉部８に予め張力を与えた状態で固定されている場合、温度補償に必要なひずみ（ε）は、数１２から求められる。ここで、Ｌｇは、基本構造におけるゲージ長（熱膨張及びひずみ伝達の基準寸法）である。

When the FBG is fixed in a state where tension is applied to the thick portion 8 in advance, the strain (ε) necessary for temperature compensation is obtained from Equation 12. Here, Lg is a gauge length (a reference dimension for thermal expansion and strain transmission) in the basic structure.

ここで、基本型ゲージベース１では、空隙部３の間隔Ｇ＝６ｍｍ、起歪体（本実施形態では、析出硬化系ステンレス鋼であるＳＵＳ６３０を使用）の線膨張係数α_ｅ＝１０．７×１０^−６、基本型ゲージベース１（材質：ＳＵＳ３０４）の線膨張係数α_ｂ＝１６．４×１０^−６、ＦＢＧ１１１の線膨張係数α_ＦＢＧ＝０．５５×１０^−６、温度補償を行うために必要なひずみε＝７．９２μｍとなり、この値と数１２から、ゲージ長Ｌｇは、２５ｍｍと算出される。

Here, in the basic gauge base 1, the gap G of the gap 3 is 6 mm, and the linear expansion coefficient α _e = 10.7 × of the strain generating body (in this embodiment, SUS630, which is precipitation hardening stainless steel). 10 ⁻⁶ , basic type gauge base 1 (material: SUS304) linear expansion coefficient α _b = 16.4 × 10 ⁻⁶ , _FBG 111 linear expansion coefficient α _FBG = 0.55 × 10 ⁻⁶ , for temperature compensation The strain ε = 7.92 μm required for this is calculated, and from this value and Equation 12, the gauge length Lg is calculated to be 25 mm.

  In addition, the value calculated | required by Formula 12 transmits 100% of the distortion | strain of a measurement object to the basic type gauge base 1 on a junction part (not shown), and the distortion | strain of a basic type gauge base 1 is 100% to an optical fiber. It is a value calculated as being transmitted. Therefore, when this method is employed in the optical fiber strain gauge 100 of the present embodiment, in actual design, the transmission efficiency between each member is measured or FEM (finite) based on the value calculated by Equation 11. What is necessary is just to obtain | require an optimal shape by calculating | requiring by the element method etc. and considering those strain transmission efficiencies.

  In the optical fiber type strain gauge 100 of the present embodiment, the first fixing portion 12A1, 12B1, the second fixing portion 12A2, 12B2, and the first fixing result as a result of calculation by the finite element method based on the material characteristics of the gauge base 10 The distance (center distance) L between the center lines of the portions 12A1 and 12B1 was 28 mm. This is because the second fixing portions 12A2 and 12B2 are provided in addition to the first fixing portions 12A1 and 12B1, and therefore the distance L between fixing of the optical fiber strain gauge 100 of the present embodiment is the basic structure. It becomes longer than the gauge length Lg.

  Specifically, the gauge length Lg is a portion connecting the end portion from the gap portion 13 of the second fixing portions 12A2 and 12B2 and the substantially middle portion between the center lines of the first fixing portions 12A1 and 12B1. Therefore, although the size of the gauge base 10 is slightly larger than that of the basic gauge base 1, the optical fiber strain gauge 100 of the present embodiment has a structure configured based on the above-described formula. Therefore, it is possible to reduce the influence due to the temperature change.

  That is, when heat is applied to the optical fiber 11 due to an increase in temperature, the optical fiber 11 is thermally expanded, the period of the diffraction grating in the FBG 111 is increased, and the refractive index of the FBG 111 is changed. Cause a shift. However, the thick portions 18A and 18B also extend along with it, and the gap G of the gap portion 13 decreases accordingly.

  As a result, even if the optical fiber 11 undergoes thermal expansion and refractive index change due to temperature changes, and the wavelength of the reflected light shifts accordingly, the gap G of the gap 13 is contracted by thermal expansion, and the optical fiber 11 is physically compressed. Accordingly, in the optical fiber 11, the shift in the wavelength of the reflected light is offset by the extension of the thick portions 18A and 18B. Therefore, the optical fiber type strain gauge 100 can realize the optical fiber type strain gauge 100 with little temperature influence.

  In the optical fiber strain gauge 100 of the present embodiment, the fixing portions 12A and 12B of the present embodiment are T-shaped. However, as an embodiment of the present invention, the fixing portion 12A is not a T-shape. , 12B may be L-shaped. In that case, since the distance L between fixations changes, next, the change of the shape of fixation part 12A, 12B and the distance L between fixations is demonstrated using FIG.

  FIG. 5 is a view for explaining the relationship between the shape of the fixed portion, the distance L between fixed portions, and the gauge length Lg in the basic structure, and FIG. 5 (a) is a view showing the basic type gauge base 1. FIG. 5B is a view showing the gauge base 10 of the optical fiber strain gauge 100 of the present embodiment, and FIG. 5C is an optical fiber strain gauge 1000 of the second embodiment of the present invention. FIG. 5D is a diagram showing the gauge base 2010 of the optical fiber strain gauge 2000 according to the third embodiment of the present invention.

As shown in FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D, in the optical fiber strain gauges 100, 1000, and 2000, the second fixing portions 12A2, 12B2, 1012A2, Since 1012B2, 2012A2, and 2012B2 are provided, the distances L, L ₁₀₀₀ , and L ₂₀₀₀ between the fixations are longer than the gauge length Lg of the basic gauge base 1.

Further, the distances L, L ₁₀₀₀ , and L ₂₀₀₀ between the fixings change according to the shapes of the fixing parts 12A, 12B, 1012A, 1012B, 2012A, and 2012B. For example, when the fixing portions 12A and 12B are T-shaped like the optical fiber strain gauge 100, the fixing distance L is slightly longer than the gauge length Lg of the basic gauge base 1, whereas The fixing distance L ₁₀₀₀ of the optical fiber strain gauge 1000 of the second embodiment in which the fixing portions 1012A and 1012B are L-shaped is longer than the fixing distance L of the optical fiber strain gauge 100.

Further, in the optical fiber strain gauge 2000 of the third embodiment in which the fixing portions 2012A and 2012B are formed in an L shape and the bottom portion of the L shape is formed in the vicinity of the first groove portions 2014A and 2014B, a position that is a starting point of strain transmission. However, since it becomes the front-end | tip part of 2nd adhering part 2012A2 and 2012B2 which forms an L-shaped lower stick, gauge length Lg will become the space | interval of the front-end | tip part of 2nd adhering part 2012A2 and 2012B2. Therefore, in the optical fiber type strain gauge 2000 of the third embodiment, the distance between fixations L ₂₀₀₀ is longer than the distance between fixations L and L ₁₀₀₀ of the optical fiber type strain gauges 100 and 1000 of other embodiments.

  Therefore, as an embodiment of the present invention, the second fixing portions 12A2 and 12B2 are provided on the side portions of the gauge base 10, and the shape of the fixing portions 12A and 12B is a T-shape. It can be said that the gauge 100 is the most preferable form in terms of the size of the gauge base 10. Next, the fixing strength of the optical fiber strain gauge 100 of this embodiment will be described with reference to FIGS.

  FIG. 6 is a diagram for explaining a difference in fixing strength between the optical fiber strain gauge 100 of the present embodiment and a conventional optical fiber strain gauge 200 as a comparative example, and FIG. 7 is an optical fiber strain gauge. It is a figure for demonstrating the difference of an out-of-plane deformation in 100 and the conventional optical fiber type strain gauge 200. FIG.

  6A is a perspective view of the vicinity of the fixing portion 212A of the conventional optical fiber strain gauge 200, and FIG. 6B is the vicinity of the fixing portion 212A of the conventional optical fiber strain gauge 200. It is a top view. 6C is a perspective view of the vicinity of the fixing portion 12A of the optical fiber strain gauge 100 of the present embodiment, and FIG. 6D is a first view of the optical fiber strain gauge 100 of the present embodiment. FIG. 6 is a plan view of the vicinity of a fixing portion 12A1 and a second fixing portion 12A2. 7A is a diagram showing out-of-plane deformation when a force F is applied to the conventional optical fiber strain gauge 200, and FIG. 7B is a diagram illustrating the force applied to the optical fiber strain gauge 100. FIG. It is a figure which shows an out-of-plane deformation | transformation at the time of adding F.

  As shown in FIGS. 6A and 6B, in the conventional optical fiber strain gauge 200, the gauge base 210 includes a fixing portion 212A extending in the width direction of the gauge base 210 and a measurement object (not shown). ) And are fixed by welding. Therefore, the thick portion in the width direction near the fixing portion 212A of the gauge base 210 is only a portion where the thin fixing portion 212A and the first groove portion 214A for inserting the optical fiber 11 are not provided. .

  Accordingly, as shown in FIGS. 6A and 7A, when the force F that deforms the gauge base 210 out of the plane acts on the gauge base 210, the gauge base 210 is fixed. Since only a few thick portions near the portion 212A are provided, the out-of-plane rigidity is lowered and the out-of-plane deformation is easily caused. Therefore, in the conventional optical fiber strain gauge 200, when the strain based on the bending deformation or the like of the measurement object is measured, the gauge base 210 is plastically deformed out of the plane, and the measurement object is subjected to a load such as a bending force. There is a possibility that even after being removed, it may not return to its original shape while being deformed. If the gauge base 210 does not return to its original position, the optical fiber strain gauge 200 cannot faithfully measure the strain generated in the measurement object.

  On the other hand, in the optical fiber type strain gauge 100 of the present embodiment, as shown in FIGS. 6C and 6D, the gauge base 10 has a first fixing portion 12A1 extending in the width direction of the gauge base 10. The second fixing portion 12A2 extending in the longitudinal direction of the gauge base 10 and a measurement object (not shown) are fixed by welding. Therefore, the thick fixing portion in the width direction near the first fixing portion 12A1 of the gauge base 10 inserts the first fixing portion 12A1 and the optical fiber 11 that are thin like the conventional optical fiber strain gauge 200. Only the portion where the first groove portion 14A is not provided.

  However, the optical fiber strain gauge 100 is further fixed to the longitudinal direction of the gauge base 10 by welding by the second fixing portion 12A2. Therefore, the second fixing portion 12A2 exerts a fixing force in the longitudinal direction on the gauge base 10, and the weld toe portion is also thick. Therefore, as shown in FIGS. 6C and 7B, when a force F that deforms the gauge base 10 out of the plane acts on the gauge base 10, the gauge base 10 Since the rigidity is increased by the fixing portion 12A2, out-of-plane deformation is difficult. Therefore, in the optical fiber strain gauge 100, it is possible to prevent the phenomenon that the gauge base 10 is deformed out of plane and cannot be restored when measuring the strain based on the bending deformation or the like of the measurement object. Detection accuracy can be improved.

  Further, in FIG. 7, in the conventional optical fiber strain gauge 200, deformation starts to occur from the fixing portions 212A and 212B, but in the optical fiber strain gauge 100 of the present embodiment, the gap portions of the second fixing portions 12A2 and 12B2 Deformation will start from the vicinity of the 13th weld stop. For this reason, in the conventional optical fiber strain gauge 200, deformation starts to occur in a portion where the thick portion is small, whereas in the optical fiber strain gauge 100, deformation starts at a location where the thick portion is large. Therefore, the deformation amount of the gauge base 10 can be reduced.

Because of the above-described effects, the optical fiber strain gauge 100 has high rigidity against out-of-plane deformation. Therefore, hysteresis, NL (nonlinearity), repeatability due to plastic deformation or non-linear contact occurring in the welded portion. It is possible to improve sensor characteristics such as.
Next, the usage example of the optical fiber type strain gauge 100 of this embodiment is demonstrated using FIG. 8, FIG.

  FIG. 8 is a diagram showing a displacement meter 300 using the optical fiber strain gauge 100 of the present embodiment. 8A is a sectional view of the displacement meter 300 as viewed from above, FIG. 8B is a sectional view of the displacement meter 300 as viewed from the side, and FIG. 8C is an optical fiber strain. It is the figure which expanded the part to which the gauge 100 is attached.

  As shown in FIGS. 8A, 8B, and 8C, the displacement meter 300 includes a main body 301, a strain generating portion 302, a cover 303, a shaft 304, a loading shaft 305, a spherical seat 306, a guide. A pipe 307, an end bush 308, an initial value adjusting nut 309, a tension spring 310, a mounting bolt 311, a connector 312, an optical cable 313, and the like are provided.

  The main body 301 is provided with a space 301a, and a strain generating portion 302 is disposed in the space 301a. The strain generating portion 302 is a U-shaped member, one end is fixed to the main body 301 by a mounting bolt 311, and the other end is connected to the loading shaft 305 and the spherical seat 306. In addition, an elliptical gap is provided in the intermediate portion of the strain generating portion 302, and the optical fiber strain gauge 100 of the present embodiment is attached to the portion where the gap is provided.

  In addition, a tension spring 310 is connected to the loading shaft 305, and the other end of the tension spring 310 is connected to a shaft 304 protruding outward from the main body 301. Further, the shaft 304 is protected by a guide pipe 307 attached to the main body 301, and an end bush 308 is provided at the tip of the guide pipe 307 so that the shaft 304 penetrates. Further, an initial value adjusting nut 309 is provided in the vicinity of the end bush 308, and the position of the tip portion of the shaft 304 can be adjusted by the initial value adjusting nut 309.

  Two connectors 312 are attached to the opposite side of the main body 301 where the guide pipe 307 is attached, and an optical cable 313 for protecting the optical fiber 11 is connected to each connector 312. Then, the optical fiber 11 is inserted from the optical cable 313 into the space 301 a and fixed to the optical fiber strain gauge 100. Then, the cover 303 is attached to the main body 301, and the space 301a is sealed.

  Such a displacement meter 300 connects an object to be measured to the shaft 304, transmits the displacement of the object to be measured to the strain generating portion 302 via the tension spring 310 and the loading shaft 305, and bends and deforms the strain generating portion 302. Then, the strain generated by this bending is transmitted to the optical fiber strain gauge 100 to detect the strain. The strain generating portion 302 is provided with an elliptical void portion, and since this portion has the lowest rigidity, the strain is generated most in the void portion. For this reason, the optical fiber strain gauge 100 attached to the gap can detect the strain of the strain generating portion 302 with high accuracy. Next, a process of attaching the optical fiber strain gauge 100 to the displacement meter 300 will be described with reference to FIG.

  FIG. 9 is a diagram for explaining a process for attaching the optical fiber strain gauge 100 to the strain generating section 302 of the displacement meter 300. Here, FIG. 9A is a view of the strain generating portion 302 as viewed from above, and FIG. 9B is a view of the strain generating portion 302 as viewed from the side.

  As shown in FIGS. 9A and 9B, when the optical fiber strain gauge 100 is attached to the strain generating portion 302, the strain generating portion 302 is attached to the mounting jig 400 for work. The mounting jig 400 includes a strain generating part presser 401, a pulley holder 402, a fiber presser 403, and a pulley 404.

  First, the gauge base 10 of the optical fiber type strain gauge 100 is fixed to the portion of the strain generating portion 302 where the gap portion is provided by welding the first fixing portions 12A1, 12B1 and the second fixing portions 12A2, 12B2. To do. Then, the strain generating portion 302 is fixed to the strain generating portion presser 401 using a fixing bolt 405.

  Next, the optical fiber 11 is fixed to the fiber holder 403, the optical fiber 11 is inserted into the first groove portions 14 A and 14 B, and the second groove portions 15 A and 15 B, and the optical fiber 11 is further extended to the pulley 404. Then, the optical fiber 11 is suspended from the pulley 404, and a weight 406 is attached to the suspended optical fiber 11. As a result, a tension is applied to the optical fiber 11, and the optical fiber 11 is applied to the first groove portions 14A and 14B and the second groove portions 15A and 15B of the gauge base 10 with the tension applied in advance. Fix by letting in. Through the above steps, the optical fiber strain gauge 100 of the present embodiment is attached to the strain generating portion 302, and the strain generating portion 302 is attached to the main body 301 as shown in FIG.

  In this embodiment, in order to accelerate the curing of the adhesive, the rod heater 408 attached to the heater fixing base 407 can be attached to the lower portion of the strain generating portion 302 of the mounting jig 400. ing. In this embodiment, since the gap G of the gap 13 is 6 mm with respect to the total length of the FBG 111 of 4 mm, it is relatively easy to dispose the FBG 111 above the gap 13. Workability at the time can be improved. Next, the results of the performance test of the displacement meter 300 will be described with reference to FIGS.

  10 is a diagram showing the load characteristics of the displacement meter 300, FIG. 11 is a diagram showing the nonlinearity of the displacement meter 300, FIG. 12 is a diagram showing the hysteresis of the displacement meter 300, and FIG. 13 is a thermostatic chamber (chamber). FIG. 14 is a diagram showing the amount of change in the measured value in the displacement meter 300 when the displacement meter 300 is inserted and the temperature in the tank is changed, and FIG.

  In this performance test, three types of tests were performed on the displacement meter 300. In the first test, displacement is repeatedly applied to the displacement meter 300 three times at 10-point steps, and measurement is performed. The results are shown in FIG. 10, FIG. 11, and FIG. The second test is a state in which a displacement is applied to the displacement meter 300, the displacement meter 300 is placed in a thermostatic chamber (chamber), and the temperature of the displacement meter 300 changes when the temperature in the chamber is changed. FIG. 13 shows the result. The third test is to examine the stability in a state where a certain displacement is applied to the displacement meter 300, and the result is shown in FIG.

  In the first test, a displacement of 0 mm to 40 mm is given to the displacement meter 300, the value detected every 4 mm is recorded, and this is repeated three times. In the first test, the load characteristic of the displacement meter 300 of the present embodiment was substantially linear as shown in FIG. The straight line in FIG. 10 is a straight line drawn based on the approximate values of all data, and the equation of this straight line is y = 0.0661x + 1545. The test results in FIGS. 11 and 12 are graphed with the straight line of the load characteristic as a reference. As shown in FIGS. 11 and 12, the detected value of the displacement meter 300 shows that the fluctuation of the non-linearity value is within the range of 0% RO to −1% RO as compared with the straight line of the load characteristic. It was stored in. Also in the hysteresis, the fluctuation of the value was within the range of 0% RO to -1% RO. Therefore, with this displacement meter 300, even if a load is repeatedly applied to the optical fiber strain gauge 100 being used, it becomes possible to maintain detection accuracy, and even when repeated detection is performed, highly accurate detection is possible. It turns out that it can be done.

  In the second test, the displacement meter 300 was placed in a thermostatic chamber (chamber), and the temperature in the thermostatic chamber (chamber) was set to -20 ° C by 20 ° C for 27 hours every 3 hours, with a displacement of 20 mm. The change in the detected value in the displacement meter during that time was recorded in the range from 1 to 60 ° C. In the second test, the temperature of 80 ° C. was changed during 27 hours, and the fluctuation of the value detected by the displacement meter was within the range of 0% RO to 1% RO. Thereby, in this displacement meter 300, the optical fiber type strain gauge 100 to be used is temperature-compensated, and it can be seen that temperature compensation is possible in the temperature range of −20 ° C. to 60 ° C.

  In the third test, a state in which a certain displacement is applied to the displacement meter is continued for 960 hours, and a change in a detected value in the displacement meter during that time is recorded. In the third test, even when 960 hours had passed, the fluctuation in the detected value was almost constant after that, with the initial fluctuation of 0.5% RO only occurring. Thus, it can be seen that the optical fiber strain gauge 100 can perform stable measurement even when a load is applied for a long time.

  As described above, in the optical fiber strain gauge 100 of the present embodiment, the gauge base 10 is fixed in the two directions of the width direction and the longitudinal direction by the first fixing portions 12A1 and 12B1 and the second fixing portions 12A2 and 12B2. It becomes possible to do. Therefore, in this optical fiber type strain gauge 100, the gauge base 10 can be firmly fixed to the object to be measured, so that it can be prevented from being deformed out of the plane. It can be detected with high accuracy. And although it is the optical fiber type strain gauge 100 using FBG111, the strain measurement which compensated temperature by one FBG111 is possible without providing FBG111 for temperature compensation. It is also possible to measure strain with high accuracy.

  The embodiment of the present invention is not limited to the above-described one, and the groove portion 14 and the fixing portion 12A are selected depending on the use environment for measuring strain, the material of the gauge base 10 and the optical fiber 11, and the like. , 12B, the position where the constricted portion 20 is formed may be changed. For example, as long as the temperature compensation of the FBG 111 can be performed, the groove portion 14, the fixing portions 12 </ b> A and 12 </ b> B, and the constricted portion 20 do not have to be line symmetric with respect to the respective reference lines. The dimensions L, G, etc. may not be the numerical values of the present embodiment.

  In the present embodiment, the fixing portions 12A and 12B are formed to be T-shaped by the first fixing portions 12A1 and 12B1 and the second fixing portions 12A2 and 12B2. The shape is not limited to this, and for example, the second fixing portion may be an L-shape formed so as to extend only from the end portion of the first fixing portion to the gap portion side. The same operation and effect as 100 can be achieved.

  Further, in this embodiment, the material of the gauge base 10 is SUS304, which is austenitic stainless steel. However, the material of the gauge base of the present invention is not limited to this, and FBG temperature compensation is possible. Any material having a possible linear expansion coefficient may be used.

  In addition, various forms can be adopted for welding for fixing the gauge base 10 and the object to be measured. In addition to spot welding of this embodiment, laser welding, and only pressure welding such as gas pressure welding can be used. First, it is possible to fix both by various fusion welding techniques.

  The optical fiber strain gauge of the present invention is used for disaster prevention of public civil engineering such as tunnel fall, collapse, landslide, etc., life prediction and equipment diagnosis of large structures such as bridges, plant equipment, lifelines (buried gas conduits, etc.) It can be widely applied to applications such as for long-distance measurement systems.

It is a perspective view of the optical fiber type strain gauge 100 of this embodiment. 2A and 2B are views for explaining a gauge base 10 of the optical fiber strain gauge 100 of FIG. 1, FIG. 2A is a plan view of the gauge base 10, and FIG. 2B is a side view in the longitudinal direction; FIG. 2C is a side view in the width direction. FIGS. 3A and 3B are explanatory views of the optical fiber 11 of the optical fiber strain gauge 100 of FIG. 1, FIG. 3A is a view of the optical fiber 11 viewed from the side, and FIG. -Α sectional view and FIG. 3C are β-β sectional views of the optical fiber 11. It is a figure for demonstrating the basic type gauge base 1 used as the basic structure of the temperature compensation of this embodiment. It is a figure for demonstrating the relationship between the shape of an adhering part, and a gauge length, Fig.5 (a) is a figure which shows the basic type gauge base 1, FIG.5 (b) is an optical fiber type | formula of this embodiment. FIG. 5C is a diagram showing the gauge base 10 of the strain gauge 100, and FIG. 5C is a diagram showing the gauge base 1010 of the optical fiber strain gauge 1000 according to the second embodiment of the present invention, and FIG. These are figures which show the gauge base 2010 of the optical fiber type strain gauge 2000 of 3rd Embodiment in this invention. FIG. 6 is a diagram for explaining the fixing strength between the optical fiber strain gauge 100 of FIG. 1 and the conventional optical fiber strain gauge 200. FIG. 6A is a perspective view of the vicinity of the fixing portion 212A of the optical fiber strain gauge 200. 6B is a plan view of the vicinity of the fixing portion 212A of the optical fiber strain gauge 200, and FIG. 6C is a perspective view of the vicinity of the fixing portion 12A of the optical fiber strain gauge 100. FIG. 6D is a plan view of the vicinity of the first fixing portion 12A1 and the second fixing portion 12A2 of the optical fiber strain gauge 100. FIG. 7A is a diagram for explaining the strength against out-of-plane deformation of the optical fiber strain gauge 100 of FIG. 1 and the conventional optical fiber strain gauge 200, and FIG. 7A shows a force F applied to the optical fiber strain gauge 200. FIG. 7B is a diagram showing out-of-plane deformation when force F is applied to the optical fiber strain gauge 100. FIG. FIG. 8A is a view showing a displacement meter 300 using the optical fiber strain gauge 100 of FIG. 1, FIG. 8A is a cross-sectional view of the displacement meter 300 viewed from above, and FIG. FIG. 8C is a cross-sectional view seen from the side, and is an enlarged view of a portion where the optical fiber strain gauge 100 is attached. FIG. 9 is a diagram for explaining a process when the optical fiber type strain gauge 100 is mounted on the strain generating section 302 of the displacement meter 300 in FIG. 8, and FIG. 9A is a view of the strain generating section 302 as viewed from above. FIG. 9B is a view of the strain generating portion 302 as seen from the side. It is a figure which shows the load characteristic of the displacement meter 300 of FIG. It is a figure which shows the non-linearity of the displacement meter 300 of FIG. It is a figure which shows the hysteresis of the displacement meter 300 of FIG. It is a figure which shows the variation | change_quantity of the fluctuation | variation of the measured value in the displacement meter 300 at the time of changing the temperature inside the thermostat (chamber) of FIG. It is a figure which shows stability of the displacement meter 300 of FIG.

Explanation of symbols

1 Basic gauge base,
2 fixing part,
3 voids,
4 first groove,
5 second groove,
8 Thick part,
10 gauge base,
11 Optical fiber,
11a Fiber strand,
11b 1st coating resin layer,
11c 2nd coating resin layer,
11d core part,
12A, 12B fixing part,
12A1, 12B1 first fixing part,
12A2, 12B2 second fixing part,
13 voids,
14A, 14B first groove,
15A, 15B second groove,
16A, 16B steps,
17 Thin part,
18A, 18B Thick part,
20 Constriction,
100 fiber optic strain gauge,
111 FBG (fiber Bragg grating),
200 Conventional fiber optic strain gauge,
300 Displacement meter,
301 body,
301a space,
302 strain generating portion,
303 cover,
304 shaft,
305 loading shaft,
306 spherical seat,
307 guide pipe,
308 End bush,
309 Initial value adjustment nut,
310 tension spring,
311 mounting bolts,
312 connector,
313 optical cable,
400 mounting jig,
401 Strain holding part presser,
402 pulley holder,
403 Fiber retainer,
404 pulley,
405 fixing bolts,
406 weights,
407 heater fixing base,
408 Bar heater,
1000 Second optical fiber strain gauge,
2000 Third optical fiber strain gauge,

Claims (7)

A gauge base in which a void is formed;
First and second grooves continuously formed on one surface of the gauge base via the gap,
An optical fiber fixed and extending in the first and second grooves;
A sensing element comprising a Bragg diffraction grating formed in a portion located in the gap of the optical fiber;
An optical fiber strain gauge having a fixing portion to which a fixing force is applied by a fixing means for fixing the gauge base and the measurement object,
The fixing portion is
It is formed by a first fixing portion extending in a direction orthogonal to the first groove and the second groove, and a second fixing portion extending in parallel with the first groove and the second groove. An optical fiber strain gauge.   2. The optical fiber strain gauge according to claim 1, wherein the second fixing portion is formed so as to extend in two directions from an end portion of the first fixing portion.   3. The optical fiber strain gauge according to claim 1, wherein the second fixing portion is provided on both sides of the gauge base.   4. The optical fiber strain gauge according to claim 1, further comprising a step formed in the gauge base by stepped portions extending in a direction orthogonal to the axial direction of the optical fiber and the sensing element and formed on both sides of the gap. An optical fiber strain gauge having a thin portion formed and positioned around the gap portion and a thick portion thicker than the thin portion.   5. The optical fiber strain gauge according to claim 4, further comprising a constricted portion formed in the thin portion of the gauge base.   6. The optical fiber strain gauge according to claim 1, wherein the gauge base is made of a material having a first linear expansion coefficient, and the optical fiber strain gauge is made of a material having a second linear expansion coefficient. An optical fiber strain gauge, which is fixed to the measurement object and performs temperature compensation using a difference between the first linear expansion coefficient and the second linear expansion coefficient.   7. The optical fiber strain gauge according to claim 1, wherein the optical fiber strain gauge is used in a state in which a tensile force is applied to the sensing element in advance.

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