JP4868593B2 - Optical fiber sensor - Google Patents

Description

  The present invention relates to an optical fiber sensor, and more particularly to an optical fiber sensor that measures strain generated in a measurement object using an FBG optical fiber sensor (optical fiber grating).

  It occurs in the structure and machinery in order to grasp and diagnose the durability, fatigue, damage, life, etc. (hereinafter collectively referred to as soundness) of machinery such as buildings and bridges and equipment. Measurement of strain distribution and strain history (strain progress rate, maximum strain amount, change in dynamic characteristics, etc.) may be required. In general soundness monitoring in conventional structures, electrical strain gauges and acceleration sensors are attached to the required parts of the structure (for example, stress-concentrated parts such as steel welds and joints and reinforcing vertical brace materials). Measuring distortion. However, since electrical sensors such as strain gauges require various treatments such as electromagnetic noise and lightning countermeasures and rust prevention processing in the sensor part and transmission part, recently optical fiber sensors that do not require these are used. Research and development is underway with a focus on soundness monitoring. Optical fiber sensors use optical signals instead of electrical signals, are strong against electromagnetic noise, are explosion-proof, and are made of quartz glass, so there is no need for rust-proofing, and they have durability that can be used outdoors for a long time. Features suitable for health monitoring.

One of the optical fiber sensors used for soundness monitoring is an FBG (Fiber Bragg Grating) type optical fiber sensor (hereinafter sometimes referred to as an FBG sensor or an optical fiber grating). This is a grating in which the refractive index of the core portion of the optical fiber is periodically changed in the light traveling direction. Grating portion of the FBG sensor (detecting section) reflects only light of the wavelength near the Bragg wavelength lambda _B ((1) see formula) determined by the period d and the effective refractive index n ₀ of the refractive index change, other The light of the wavelength is transmitted as it is. From equation (1), it can be seen that when the refractive index n ₀ or the period d of the grating portion changes, the Bragg wavelength λ _B reflected from the grating portion also changes accordingly. For example, when an external force is applied to the grating portion of the FBG sensor and a strain ε is generated in the axial direction of the optical fiber, the grating portion expands and contracts accordingly, the period d changes, and the effective refractive index n ₀ also changes. . The shift amount Δλ _B1 of the Bragg wavelength λ _B caused by the change of the period d and the refractive index n ₀ is given by the equation (2). In the equation (2), ρ _c is a photoelastic coefficient, which is a coefficient representing a change in effective refractive index of the grating portion due to the strain ε. As can be seen from Equation (2), if the grating portion of the FBG sensor is fixed to the measurement target and the shift amount Δλ _B1 of the Bragg wavelength λ _B is detected, the measurement portion with the grating portion (detection portion) fixed is detected. The strain ε can be measured.

However, the grating portion of the FBG sensor is affected not only by an external force but also by a temperature change ΔT. This is because the period d and the effective refractive index n ₀ change with the temperature change ΔT. If both sides of equation (1) are partially differentiated by temperature, equation (3) is obtained as a shift amount Δλ _B2 of Bragg wavelength λ _B due to temperature change ΔT. Here, α and ζ are rates of change of the period d and the refractive index n ₀ accompanying the temperature change ΔT, respectively. The shift amount Δλ _fbg of the Bragg wavelength λ _B when the external force and the temperature change ΔT are simultaneously loaded on the grating part of the FBG sensor is the shift amount Δλ _B1 due to the influence of the external force and the shift amount Δλ _B2 due to the influence of the temperature change ΔT. (4). What is actually detected by the FBG sensor is the shift amount Δλ _fbg in the equation (4), and it is impossible to detect only the shift amount Δλ _B1 related to the strain ε. Therefore, in order to accurately measure the strain ε to be measured by the FBG sensor, a temperature compensation method for removing the shift amount Δλ _B2 due to the influence of the temperature change ΔT from the detected shift amount Δλ _fbg is necessary.

Conventionally, as a temperature compensation method in an optical fiber sensor, as shown in FIG. 9, a strain measurement FBG sensor 61 is fixed on a substrate 63 having the same linear expansion coefficient as that of the optical fiber, and the displacement is not constrained on the substrate 63. A method is proposed in which the temperature compensating FBG sensor 62 is fixed in such a relaxed state, and the strain ε is measured by the difference in the amount of shift of the Bragg wavelength detected by both the FBG sensors 61 and 62 (Patent Document 1). . Further, as shown in FIG. 10, in Patent Document 2, a first FBG sensor 61 and a second FBG sensor 62 are placed on one tension between a first holder 64 and a second holder 65 that are relatively movable in the X direction. Discloses a method of measuring the strain ε in the X direction based on the difference in the Bragg wavelength shift detected by the two FBG sensors 61, 62. Further, as shown in FIG. 11, Patent Document 3 fixes both ends of a strain measurement FBG sensor 61 to a measurement target 50 with mounting plates 67 and 68, and a temperature at a mounting plate 69 having a linear expansion coefficient equal to that of the measurement target 50. A method is disclosed in which only one end of the compensation FBG sensor 62 is fixed to the measurement object 50 and the strain ε is measured by the difference in the amount of shift of the Bragg wavelength detected by both the FBG sensors 61 and 62.
Japanese Patent No. 2983018 JP 2002-257520 A Japanese Patent No. 3711905

However, none of the temperature compensation methods disclosed in Patent Documents 1 to 3 can remove the influence of all temperature changes ΔT from the shift amount Δλ of the Bragg wavelength λ _B actually detected by the FBG sensor. There is a problem that 50 strain ε cannot be measured accurately. In general, as shown in FIG. 9, the FBG sensor is fixed to the surface of the measurement object 50 after being attached to a fixing plate such as a substrate 63 with an adhesive or the like. When the thermal expansion coefficient of the fixed plate is different from that of the FBG sensor, the expansion and contraction of the fixed plate accompanying the temperature change ΔT is transmitted to the FBG sensor, and the influence of the expansion and contraction of the fixed plate is reflected on the shift amount Δλ of the Bragg wavelength λ _B. When the thermal expansion coefficient of the measurement target 50 is different from that of the fixed plate, the expansion / contraction of the measurement target 50 due to the temperature change ΔT is transmitted to the FBG sensor via the fixed plate, and the measurement target is set to the shift amount Δλ of the Bragg wavelength λ _B. The effect of 50 stretches is reflected. Therefore, in order to perform temperature compensation of the shift amount Δλ actually detected by the FBG sensor, not only the influence (shift amount Δλ _{B2 in the} equation (3)) caused by the temperature change ΔT but also the FBG sensor. It is necessary to remove the influence of expansion due to the temperature change ΔT of the fixed plate and the measurement target.

Specifically, if the linear expansion coefficient α of the FBG sensor and the linear expansion coefficient β of the fixed plate are different, the FBG sensor is subjected to distortion (= (β−α) ΔT) due to the expansion and contraction of the fixed plate accompanying the temperature change ΔT. . The influence of the expansion and contraction of the fixed plate is the shift amount Δλ _B3 of the Bragg wavelength λ _{B in} the equation (11), and the shift amount Δλ _sensor due to the influence of the detected temperature change ΔT is the equation (12). Further, when the linear expansion coefficient β of the fixed plate and the linear expansion coefficient γ of the measurement target 50 are different, the FBG sensor is strained (= (γ−β) through the fixed plate due to the expansion and contraction of the measurement target 50 due to the temperature change ΔT. ) ΔT). The influence of the expansion / contraction of the measurement object 50 is the shift amount Δλ _B4 of the Bragg wavelength λ _{B in} the equation (13), and the shift amount Δλ _target due to the influence of the detected temperature change ΔT is the equation (14). In Equation (13), η is a strain magnification ratio, which indicates a ratio of an effective strain transmitted to the FBG sensor among strains generated in the fixed plate due to expansion / contraction of the measurement object 50, and is a coefficient determined by the structure of the fixed plate. It is. On the other hand, the strain ε of the measurement object 50 caused by the external force is also transmitted to the FBG sensor through the fixed plate, and the influence of the external force is expressed as a shift amount λ _{B5 in the} equation (15) using the strain magnification factor η. When the external force and the temperature change ΔT are simultaneously applied, the shift amount Δλ _{all of the} equation (16) is detected. In order to accurately measure the strain ε of the measurement object 50 with the FBG sensor, the shift amount Δλ _{target of the} equation (14) due to the influence of the temperature change ΔT is detected from the detected shift amount Δλ _{all of the} equation (16) [ie, Effect of expansion / contraction of FBG sensor itself due to temperature change ΔT (shift amount Δλ _{B2 in} equation (3)), influence of expansion / contraction of fixed plate (shift amount Δλ _{B3 in} equation (11)), and influence of expansion / contraction of measurement object ( All of the shift amount Δλ _B4 ) in equation (13) must be removed.

In the temperature compensation method shown in FIG. 9, the shift amount Δλ _{all of the} equation (16) is detected by the strain measurement FBG sensor 61, and the shift amount Δλ _{B2 of the} equation (3) is detected by the temperature compensation FBG sensor 62. From the equation (16), the difference between the shift amounts of the FBG sensors 61 and 62 is Δλ _B3 + Δλ _B4 + Δλ _B5 . Since the linear expansion coefficient α of the FBG sensor is equal to the linear expansion coefficient β of the fixed plate (substrate 63), the shift amount Δλ _{B3 in} equation (11) is 0, but the temperature change ΔT is not limited to Δλ _B5 to be obtained. Since the dependent term Δλ _B4 (= λ _B η (1−ρ _c ) (γ−β) ΔT) remains, the influence of the temperature change ΔT cannot be removed (Equation (21)). In the method of FIG. 9, since the temperature compensating FBG sensor 62 is held in a loose hollow state, the temperature compensating FBG sensor 62 is easily deformed in accordance with externally applied vibrations, and is distorted during a long measurement period. The measurement accuracy of ε may be deteriorated.

Further, in the temperature compensation method shown in FIG. 10, when the first holder 64 and the second holder 65 move relative to each other, a reverse force is applied to the first FBG sensor 64 and the second FBG sensor 65. The sign of the influence of the strain ε due to the external force detected at 61 and 62 (the shift amount Δλ _{B5 in} equation (15)) is reversed. Further, the sign of the influence of the expansion / contraction of the measurement object 50 due to the temperature change ΔT (shift amount Δλ _{B4 in the} equation (13)) is also reversed. That is, the first FBG sensor 61 detects the shift amount Δλ _{all (+} ) in the equation (16), whereas the second FBG sensor 62 detects the shift amount Δλ _{all (−) in which} the signs of Δλ _B4 and Δλ _B5 are reversed. (= Δλ _B2 + Δλ _B3 −Δλ _B4 −Δλ _B5 ) is detected. Thus, the difference in shift amount of the two FBG sensors 61 and 62 becomes (22), also the temperature change section depends on _{ΔT 2Δλ B4 (= 2λ B η} (1-ρ c) (γ-β) ΔT) remains Therefore, it is impossible to extract only the component Δλ _B5 of the strain ε of the measurement target 50 to be obtained.

Further, in the temperature compensation method shown in FIG. 11, the linear expansion coefficient β of the fixed plate 69 of the temperature measuring FBG sensor 62 is made equal to the linear expansion coefficient γ of the measurement target 50, so that the fixed plate detected by the FBG sensor 62 is used. The effect of strain due to the expansion / contraction of the shift is the shift amount Δλ _B3 ′ in the equation (23). That is, the strain measurement FBG sensor 61 detects the shift amount Δλ _{all in the} equation (16), whereas the temperature compensation FBG sensor 62 has the shift amount Δλ _{B2 in the} equation (3) and ( A shift amount Δλ _sensor (= Δλ _B2 + Δλ _B3 ′) obtained by superimposing the shift amount Δλ _B3 ′ in equation (23) is detected. Therefore, the difference between the shift amounts of the two FBG sensors 61 and 62 is expressed by equation (24), which is also a term (= (η−1) λ _B (1−ρ _c ) (γ−β) ΔT) that depends on the temperature change ΔT. Therefore, the strain ε of the measurement object 50 cannot be measured with high accuracy. Further, since the temperature measurement module 62 has a cantilever structure, the temperature compensation FBG sensor 62 may be deformed during a long measurement period and the measurement accuracy may be deteriorated.

  The term (underlined part of equations (21), (22), and (24)) that depends on the temperature change ΔT described above is a major problem if it is a short-term strain measurement that can ignore the temperature change ΔT. However, it becomes a problem in the case of soundness monitoring that measures small strains of structures over a long period of time. Accordingly, an object of the present invention is to provide an optical fiber sensor that can remove only the strain by removing the influence of the temperature change ΔT that occurs in the FBG sensor.

  1 and 2 to 4, one embodiment of the optical fiber sensor according to the present invention has the same coefficient of thermal expansion β as that of the measurement target 50 and has one side on the surface of the measurement target 50. The first fixing body 10 and the second fixing body 20 that are fixed at a predetermined interval L1 (in the illustrated example, a predetermined interval L1 between the fixing members 6 and 6) are opposed to each other, and the fixing members 10 and 20 are bridged. A pair of optical fiber gratings 2 and 3 fixed to both the fixing members 10 and 20, extending to the second fixing member 20 side on the opposite side 11 of the first fixing member 10, and the opposite side 11. A first extending portion 12 having a part of a facing edge 13 that faces each other via a gap S is provided. The first extending portion 12 extends to the opposite side 21 of the second fixing body 20 toward the first fixing body 10 and within the gap S. A second extending portion 22 having a facing edge 23 facing the facing edge 13 of the first extending portion 12 with a predetermined gap L2 is provided in part, and an optical fiber grating 2; Is fixed on the line connecting the opposing edges 13 and 23 of the extending portions 12 and 22 of the fixing members 10 and 20, and the other of the optical fiber gratings 2 and 3 (FIG. In the example shown, the optical fiber grating 3) is fixed on a line connecting the opposite sides 11 and 21 other than the extending portions 12 and 22 of the fixing members 10 and 20.

  Preferably, the pair of optical fiber gratings 2 and 3 are fixed in parallel. More preferably, the second fixing body 20 side and the first fixing body 10 are respectively disposed on the opposite sides 11 and 21 other than the extending portions 12 and 22 of the first fixing body 10 and the second fixing body 20 as shown in the illustrated example. The first protrusion 17 and the second protrusion 27 are provided so as to protrude to the side and the front edges 18 and 28 face each other with a predetermined gap L3, and the other of the optical fiber gratings 2 and 3 (in the illustrated example, the optical fiber grating 3). ) Is fixed on the line connecting the leading edges 18 and 28 of the projecting portions 17 and 27. In this case, the predetermined gap L2 between the opposing edges 13 and 23 of the two extending portions 12 and 22 and the predetermined gap L3 between the tip edges 18 and 28 of the two protruding portions 17 and 27 can be made the same size.

  Desirably, as shown in FIG. 6 (A), the opposing edge bridge connecting the opposing edges 13 and 23 with rigidity smaller than the fixing bodies 10 and 20 between the opposing edges 13 and 23 of the extending portions 12 and 22. A portion 31 is provided, and a leading edge bridging portion 32 is provided between the leading edges 18 and 28 of the projecting portions 17 and 27 to connect the leading edges 18 and 28 with rigidity smaller than the fixing bodies 10 and 20. The opposing edge bridging portion 31 and the tip edge bridging portion 32 can have the same cross-sectional area. More preferably, the first fixing body 10 and the second fixing body 20, the opposing edge bridging portion 31 and the tip edge bridging portion 32 are integrally formed from a plate-like member having the same thermal expansion coefficient β as that of the measurement target 50. To do. Further, as shown in FIG. 4D, outer edge coupling portions 33 and 34 for connecting the outer edges of the first fixing body 10 and the second fixing body 20 to each other can be provided. In this case, the first fixing body 10 and the second fixing body 20 and the outer edge coupling portions 33 and 34 may be a frame 30 integrally formed from a plate-like member having the same thermal expansion coefficient β as that of the measurement target 50.

  Referring to the embodiment of FIG. 7, another aspect of the optical fiber sensor according to the present invention is that the upper-layer fixing bodies 10 and 20 and the lower-layer fixing bodies 15 and 25 having the same thermal expansion coefficient β as that of the measurement object 50 are used. A laminated body (10 + 15), (20 + 25), and a predetermined interval L1 (predetermined between fixing members 6 and 6 in the illustrated example) with each side of the upper layers 10 and 20 and the lower layers 15 and 25 facing the surface of the measurement target 50 A first laminated fixing body 19 and a second laminated fixing body 29 that are fixed at an interval L1), and a pair of optical fiber gratings 2 that are bridged between the laminated fixing bodies 19 and 29 and fixed to the fixing bodies 19 and 29; 3 extending to the opposite side 11 or 16 of the upper and lower one side layer (upper layer 10 or lower layer 15) of the first laminated fixing body 19 and facing the opposite side 11 or 16 A first extending portion 12 having a part of an opposing edge 13 facing through a gap S is provided, and the upper and lower one side layers of the second laminated fixing body 29 are provided. The upper layer 20 or the lower layer 25 extends to the side of the first laminated fixing body 10 on the opposite side 21 or 26 of the first laminated fixing body 19 on the side where the first extending portion 12 is provided, and is first in the gap S. 1 A second extending portion 22 having a portion facing an opposing edge 13 of the extending portion 12 at a predetermined gap L2 is provided, and one of the optical fiber gratings 2 and 3 (in the illustrated example, an optical fiber The grating 2) is fixed on a line connecting the opposing edges 13 and 23 of the extending portions 12 and 22, and the other one of the optical fiber gratings 2 and 3 (the optical fiber grating 3 in the illustrated example) is fixed to both the laminated fixing members 19, Fixed on the line connecting the opposite sides 16, 26 or 11, 21 of the other upper and lower 29 layers (lower layer 15, 25 or upper layer 10, 20 opposite to the layer provided with the extended portions 12, 22) It is.

  Preferably, the pair of optical fiber gratings 2 and 3 are aligned in the vertical direction and fixed in parallel. If necessary, as shown in FIG. 7D, spacers 14 and 24 are provided between the upper layers 10 and 20 and the lower layers 15 and 25 of the first laminated fixing body 19 and the second laminated fixing body 29, respectively. Can do. More preferably, the opposite sides of the upper and lower other layers (the lower layers 15 and 25 or the upper layers 10 and 20 on the opposite side of the layer provided with the extending portions 12 and 22) of the first laminated fixing body 19 and the second laminated fixing body 29. The first and second protrusions 17 and 27 project toward the second laminated body 29 and the first laminated body 19 respectively at 16, 26 or 11, 21 and the front edges 18 and 28 face each other with a predetermined gap L3. And the other of the optical fiber gratings 2 and 3 (in the illustrated example, the optical fiber grating 3) is fixed on a line connecting the tip edges 18 and 28 of the projecting portions 17 and 27. In this case, the predetermined gap L2 between the opposing edges 13, 23 of the extending portions 12, 22 of the upper and lower one side layers (upper layers 10, 20 or lower layers 15, 25) and the upper and lower other layers (lower layers 15, 25 or The predetermined gap L3 between the tip edges 18 and 28 of the projecting portions 17 and 27 of the upper layers 10 and 20) can be the same size.

  Desirably, as shown in FIG. 8, the opposed edge bridging portion 31 connecting the opposed edges 13 and 23 with rigidity smaller than the laminated fixing members 19 and 29 between the opposed edges 13 and 23 of the extended portions 12 and 22. A leading edge bridging portion 32 is provided between the leading edges 18 and 28 of the projecting portions 17 and 27 so as to connect the leading edges 18 and 28 with rigidity smaller than both the laminated fixing members 19 and 29. In this case, as shown in FIGS. 2B and 2C, the upper and lower one side layers (upper layers 10 and 20 or lower layers 15 and 25) of the first laminated fixing body 19 and the second laminated fixing body 29 are opposed to each other. It is assumed that the bridging portion 31 is integrally formed from a plate-like member having the same coefficient of thermal expansion β as that of the measurement object 50, and the upper and lower other layers (lower layers 15, 25 or the lower layer 15) of the first laminated fixing body 19 and the second laminated fixing body 29. The upper layers 10 and 20) and the leading edge bridging portion 32 may be integrally formed from a plate-like member having the same coefficient of thermal expansion β as that of the measurement target 50.

  In addition, outer edge coupling portions 33 and 34 for connecting the outer edges of the upper and lower one side layers (upper layers 10 and 20 or lower layers 15 and 25) of the first laminated fixing body 19 and the second laminated fixing body 29 are provided. Outer edge coupling portions 33 and 34 that connect the outer edges of the upper and lower other layers (the lower layers 15 and 25 or the upper layers 10 and 20) of the fixing body 19 and the second laminated fixing body 29 can be provided. In this case, a frame body 36 in which upper and lower one side layers (upper layers 10 and 20 or lower layers 15 and 25) and outer edge coupling portions 33 and 34 are integrally formed from a plate-like member having the same thermal expansion coefficient β as that of the measurement target 50 or 35, a frame body 35 or 36 in which the other upper and lower layers (lower layer 15, 25 or upper layer 10, 20) and outer edge coupling portions 33, 34 are integrally formed from a plate-like member having the same coefficient of thermal expansion β as that of the measurement target 50. It is good.

  In the optical fiber sensor according to the present invention, the first fixing body 10 and the second fixing body 20 that are fixed at a predetermined interval L1 with the sides 11 and 21 facing each other on the surface of the measurement object 50 have the same thermal expansion as the measurement object 50, respectively. It is made of a material having a rate β, and is opposed to a part of the first extending portion 12 extending from the facing side 11 of the first fixing body 10 toward the second fixing body 20 with the facing side 11 interposed through a gap S. An edge 13 is formed, and an opposing edge of the first extending portion 12 is formed in a part of the second extending portion 22 extending from the facing side 21 of the second fixing member 20 toward the first fixing member 10 within the gap S. 13 is formed on a line connecting the opposing edges 13 and 23 of the extension parts 12 and 22 of the fixing members 10 and 20 to the other side. Since the FBG sensor 3 is fixed on a line connecting the opposing sides 11 and 21 other than the extending portions 12 and 22 of the fixing members 10 and 20, the following remarkable effects can be obtained.

(A) Since the pair of FBG sensors 2 and 3 are fixed to the measurement object 50 via the fixing members 10 and 20 having the same thermal expansion coefficient β as the measurement object 50, the Bragg wavelength detected by the FBG sensors 2 and 3 From the shift amount Δλ _{all of} λ _B (equation (16)), the influence of expansion / contraction of the measurement object 50 associated with the temperature change ΔT (shift amount Δλ _{B4 in} equation (13)) can be removed.
(B) Since the strain ε of the measurement object 50 due to external force is applied to both FBG sensors 2 and 3 in the opposite direction, the temperature change is obtained by calculating the difference between the shift amounts Δλ _all detected by the FBG sensors 2 and 3. Both the influence of the expansion / contraction of the FBG sensor itself due to ΔT (shift amount Δλ _{B2 in} equation (3)) and the influence of the expansion and contraction of the fixing members 10 and 20 (shift amount Δλ _{B3 in} equation (11)) are both removed. Only the shift amount of the strain ε (shift amount Δλ _{B5 in the} equation (15)) can be taken out, and the strain ε of the measurement target 50 can be measured with high accuracy.
(C) The ratio between the predetermined interval L1 of the fixing bodies 10 and 20 fixed to the measurement object 50 and the predetermined gap L2 of the opposing edges 13 and 23 of the fixing bodies 10 and 20 fixing the FBG sensor 2; The strain ε of the measurement object 50 can be detected at the required magnification η (= L1 / L2 and L1 / L3) by the ratio of the 27 leading edges 18 and 28 to the predetermined gap L3, depending on the application and location. Thus, the measurement sensitivity can be adjusted and the measurement accuracy of the strain ε can be improved.
(D) Further, the FBG sensor 3 is fixed on a line connecting the tip edges 18 and 28 of the projecting portions 17 and 27 provided on the opposite sides 11 and 21 of the fixing bodies 10 and 20, and the extending portion for fixing the FBG sensor 2 By setting the predetermined gap L2 of the opposing edges 13 and 23 of 12, 22 and the predetermined gap L3 of the leading edges 18 and 28 of the protrusions 17 and 27 for fixing the FBG sensor 3 to the same size, both FBG sensors 2, Thus, the magnification η of the strain ε detected in step 3 can be made uniform, the calculation for measuring the strain ε can be facilitated, and the strain measurement accuracy can be further improved.

(E) Strain measurement of the measurement target 50 that does not require parameters depending on the measurement target 50 such as the coefficient of thermal expansion is possible, so that it is a general-purpose optical fiber sensor that can be applied to strain measurement of various measurement targets 50 be able to.
(F) Since it is sufficient to fix the FBG sensors 2 and 3 to the fixing bodies 10 and 20 under the same conditions before or after fixing the fixing bodies 10 and 20 to the measurement object 50, the construction is simple and easy. Therefore, variation in installation quality hardly occurs, and stable strain measurement can be performed for a long time.
(G) Further, by making the fixing members 10 and 20 plate-like or plate-like frame members, the fixing members 10 and 20 can be easily processed and handled, and the fixing work for the measurement object 50 and the FBG sensor are performed. It is possible to further facilitate the fixing work of a few.
(H) A pair of laminated fixing bodies in which the fixing bodies are stacked in layers are fixed to face the surface of the measurement object 50, and the FBG sensor 2 and the FBG sensor 3 are respectively placed between the upper layer and the lower layer of the laminated fixing bodies. By aligning and fixing in the vertical direction, it is possible to bring the environments of both the FBG sensors 2 and 3 to the strain and temperature extremely close to each other, and further high-precision strain measurement can be expected.

FIG. 1 shows an embodiment of an optical fiber sensor 1 of the present invention attached to the surface of a measurement object 50. The illustrated optical fiber sensor 1 includes a first fixing body 10 and a second fixing body 20 made of the same material having the same thermal expansion coefficient β as the strain measurement object 50, and a pair that is fixed between the fixing bodies 10 and 20. FBG sensors 2 and 3 (grating portions of optical fibers 4 and 5). It is desirable that the thermal expansion coefficient β of each of the fixing bodies 10 and 20 is as close as possible to the thermal expansion coefficient γ of the measurement target 50, but the influence of expansion / contraction of the measurement target 50 on the assumed temperature change ΔT (( As long as the shift amount Δλ _B4 ) in the equation (13) is within an allowable range, the coefficient of thermal expansion of the measurement target 50 may be slightly different. For example, when measuring the strain ε of a metal-based measurement object 50 such as a steel frame or machinery, the fixing members 10 and 20 are made of the same metal material. When the concrete surface of the structure is to be measured 50, each of the fixing bodies 10 and 20 is made of carbon steel substantially equal to the thermal expansion coefficient γ of the concrete. However, since the thermal expansion coefficient γ of the concrete varies depending on the type and amount of the aggregate, carbon steel is used as a rule, but depending on the thermal expansion coefficient γ of the measurement object 50, each of the fixing bodies 10, 20 It is desirable to select or prepare the material.

  FIG. 2 shows a plan view and a cross-sectional view of the first fixing body 10 and the second fixing body 20 fixed on the surface of the measurement object 50. The first fixing body 10 and the second fixing body 20 in the illustrated example are each a fixing unit that fixes one side 11, 21 on the surface of the measurement object 50 so that the sides 11, 21 face each other, and a part of the opposing side 11, 21. The first extending portion 12 and the second extending portion 22 extending from the other side of the fixing members 20 and 10 to the fixing members 20 and 10 side, and the first protruding portion protruding toward the fixing members 20 and 10 from the other portions 11 and 21 thereof. 17 and a second projecting portion 27. In the illustrated example, the fixing members 10 and 20 are fixed on the surface of the measurement object 50 by an appropriate fixing member 6 (for example, a screw) inserted through the fixing hole 6a (see FIG. 6D) of each fixing portion. A predetermined distance L1 is set between the fixing members 6 and 6. However, the fixing bodies 10 and 20 may be fixed to the measurement object 50 by using an adhesive or welding. In that case, the interval between the parts fixed on the measurement object 50 of each fixing unit (for example, the opposite side 11, 21 intervals) may be set to the predetermined interval L1.

  The extending portion 12 of the first fixing body 10 in the illustrated example is provided with a protruding portion (or protruding portion) 12a that protrudes sideways in a part, and the opposing side 11 of the first fixing body 10 is formed by the protruding portion 12a. And an opposing edge 13 facing each other through a gap S. Further, the extended portion 22 of the second fixing member 20 has a protruding portion (or a protruding portion) that protrudes into the gap S between the opposite side 11 of the first fixing member 10 and the first extending portion 12 at a part thereof. ) 22a is provided, and the overhanging portion 22a forms an opposed edge 23 that faces the opposed edge 13 of the first extending portion 12 in the gap S with a predetermined gap L2 (see FIG. 5B). The protruding portion 17 of the first fixing body 10 and the protruding portion 27 of the second fixing body 20 protrude so that the respective leading edges 18 and 28 face each other with a predetermined gap L3 (see FIG. 4C). ).

  When the strain ε is generated in the measurement target 50 due to the external force in the X direction in FIG. 2, the strain ε is transmitted to the first fixing body 10 and the second fixing body 20, and the opposite edges 13 and 23 of the extending portions 12 and 22 are both. Displacements having different polarities are simultaneously generated in the gap L2 and the gap L3 between the leading edges 18 and 28 of the projecting portions 17 and 27. That is, when a load is applied to both the fixing members 10 and 20 so as to separate or approach each other according to the distortion deformation of the measurement target 50, the tip edges 18 and 28 of the projecting portions 17 and 27 are similarly separated from or approach each other. The opposing edges 13, 23 of the extending parts 12, 22 are moved so as to approach or separate from each other. For this reason, one FBG sensor 2 spanned over the opposing edges 13 and 23 of the extension parts 12 and 22 and both ends fixed, and the both ends are spanned over the tip edges 18 and 28 of the projecting parts 17 and 27. The other FBG sensor 3 is loaded with a tensile force and a compressive force, respectively. Each of the fixing members 10 and 20 is sufficiently larger in rigidity than the optical fibers 4 and 5 constituting the FBG sensors 2 and 3 so that the relative displacements of the opposing sides 11 and 12 are all concentrated on the FBG sensors 2 and 3. Is desirable.

  In the embodiment of FIG. 2, the fixing portions of the fixing members 10 and 20 are rectangular, and L-shaped extending portions 12 and 22 are provided on opposite sides 11 and 21 of the fixing portion so as to support one end and extend in a right angle direction. The edges on one end side of the projecting portions 12a, 22a at the other ends of the L-shaped extending portions 12, 22 are opposed to each other at a gap L2 to form opposing edges 13, 23. However, the shape of the extending portions 12 and 22 is not limited to the illustrated example, and any shape that causes deformation between the opposing edges 13 and 23 that has a polarity opposite to the deformation direction of the fixing members 10 and 20 can be selected. . For example, as shown in FIG. 3 (B), the extending portions 12 and 22 may be extended obliquely from the fixing members 10 and 20, and other than the ends of the extending portions 12 and 22 as shown in FIG. 3 (A). Overhang portions (or projections) 12a and 22a may be provided at the intermediate portion. Further, as shown in FIG. 5C, instead of the overhanging portions (or projections) 12a and 22a, the curved leading edges of the extending portions 12 and 22 are opposed to each other, and the leading edges are spaced from each other. It is good also as the opposing edges 13 and 23 which face in L2.

Further, the shape of the protrusions 17 and 27 is not limited to the I-shaped one that supports one end of each fixing body 10 and 20 and extends in a perpendicular direction as in the embodiment of FIG. It is possible to select an arbitrary shape such that deformation having the same polarity as that of the deformation direction occurs between the tip edges 18 and 28. Preferably, as shown in the drawing, the gap L3 between the leading edges 18 and 28 of the projecting portions 17 and 18 for fixing the FBG sensor 3 and the opposing edges 13 and 23 of the extending portions 12 and 22 for fixing the FBG sensor 2 are provided. The gap L2 has the same size, and the magnification rate η of distortion deformation of both the fixing members 10 and 20 is matched as will be described later. However, it is not an essential condition for the present invention that the gap L2 of the opposing edges 13 and 23 and the gap L3 of the tip edges 18 and 28 are the same size, as long as the sizes of the gap L2 and the gap L3 are respectively predetermined. The difference in the distortion magnification rate η can be corrected in the difference calculation of the shift amount Δλ _all of the FBG sensors 2 and 3 described later. Therefore, as shown in FIG. 3 (A), both or one of the protrusions 17 and 27 of the fixing members 10 and 20 are omitted, and the FBG sensor 3 is connected to the fixing members 10 and 20 other than the extending portions 12 and 22. It is also possible to cross and fix the opposite sides 11 and 21.

  In the embodiment of FIG. 2, the deformation due to the strain ε of the measuring object 50 generated between the opposing sides 11 and 21 of the fixing members 10 and 20 at the predetermined interval L1 is opposed to the predetermined gap L2 between the extending portions 12 and 22. It is detected as a deformation of the enlargement ratio η (= L1 / L2) by the FBG sensor 2 spanned between the edges 13 and 23, and is spanned between the leading edges 18 and 28 of the predetermined gap L3 between the two projecting portions 17 and 27. The FBG sensor 3 detects the deformation of the enlargement factor η (= L1 / L3). By detecting the strain ε of the measurement object 50 with the FBG sensors 2 and 3 in an enlarged manner, the detection sensitivity and detection accuracy of the strain ε can be increased. However, if the detection sensitivity is excessively increased, there is a risk that the FBG sensors 2 and 3 are cut. Therefore, it is desirable to appropriately adjust the strain expansion rate η according to the application and location.

  The strain expansion rate η in the FBG sensors 2 and 3 changes the ratio of the predetermined gap L2 of the facing edges 13 and 23 to the predetermined gap L1 of both the fixing members 10 and 20 or the ratio of the predetermined gap L3 of the tip edges 18 and 28. It is adjustable with. For example, as shown in FIG. 4A, the opposing directions of the opposing edges 13 and 23 of the extending portions 12 and 22 and the protruding portions 17 and the opposing sides 11 and 21 of the fixing members 10 and 20 are opposed to each other. , 27 by crossing the opposing directions of the tip edges 18 and 28 at an angle θ = 45 degrees, respectively, the strain magnification ratio η in the FBG sensors 2 and 3 can be reduced by 0.7 (= 1 / √2) times. it can. In addition, as shown in FIG. 5B, the extension portions 33 and 34 projecting toward the fixing members 20 and 10 are provided on the outer edges of the fixing members 10 and 20, and the extension portions 33 and 34 are provided with predetermined gaps L2 and L3. By fixing (screwing or the like) to the measurement object 50 with a smaller predetermined gap L1, the strain magnification rate η detected by the FBG sensors 2 and 3 can be made 1 or less. If the rigidity of the fixing members 10 and 20 is not sufficiently large compared to the optical fibers 4 and 5 constituting the FBG sensors 2 and 3, the strain ε of the measurement target 50 is concentrated only on both the FBG sensors 2 and 3. However, a part is relieved by the fixing members 10 and 20. If the degree of relaxation is k (<1), the deformation enlargement rate η detected by both the FBG sensors 2 and 3 is reduced by k times.

  Desirably, each of the fixing members 10 and 20 has a plate shape in which the fixing portion, the extending portions 12 and 22 and the projecting portions 17 and 27 are arranged on the same plane as in the illustrated example. Such plate-like fixing bodies 10 and 20 can be manufactured relatively easily and inexpensively by, for example, integral molding such as punching. Further, the one side surface of the fixing bodies 10 and 20 can be reliably fixed to the measurement object 50 and the FBG sensors 2 and 3 can be fixed to the opposite surface, and the fixing work to the measurement object 50 and the FBG sensors 2 and 3 can be fixed. Can be fixed easily. However, the fixing members 10 and 20 are not limited to planar ones. For example, as shown in FIG. 1B, when the fixing members 10 and 20 are installed on the surface of the measurement object 50 intersecting at a right angle or a specific angle, 12, 22 and the protrusions 17 and 27 can be bent or curved with respect to the fixing portion.

  As shown in FIGS. 2D and 2E, the fixing members 10 and 20 are provided with spacers that support the extended portions 12 and 22 and the protruding portions 17 and 27 away from the surface of the measurement target 50. (Legs) 14, 24 can be included. For example, as shown in FIG. 1B, when the optical fiber sensor 1 of the present invention is attached to a cracked part or a joint part 51a of a measurement object 50 such as a concrete structure, or the optical fiber sensor 1 is fixed to an uneven surface that is not smooth. In this case, it is effective that the extended portions 12 and 22 and the protruding portions 17 and 27 are floated from the surface of the measurement object 50 and fixed by the spacer 14. In the illustrated example, the heights of the spacers 14 of the fixing members 10 and 20 are the same. However, when fixing across uneven surfaces having different heights, the heights of the spacers 14 of the fixing members 10 and 20 are different. It is also effective. In addition, when the spacers 14 and 24 are easily deformed as shown in FIG. 2E, a part of the strain ε of the measurement object 50 is alleviated by the deformation of the spacers 14 and 24, and therefore detected by the FBG sensors 2 and 3. The enlargement factor η of the deformation to be reduced will decrease.

  The FBG sensors 2 and 3 can be fixed to the surfaces of the extending portions 12 and 22 of the fixing bodies 10 and 20 or the surfaces of the protruding portions 17 and 27 by an adhesive, a connecting screw, welding, and the like, respectively. When the surfaces of the fixing members 10 and 20 are smooth and it is difficult to position the FBG sensors 2 and 3, as shown in FIG. 5A, the surfaces of the extending portions 12 and 22 or the protruding portions 17 and 27. A positioning groove 41 for causing the optical fibers 4 and 5 at both ends of the FBG sensors 2 and 3 to be aligned may be formed on the surface (see also FIG. 5B). The positioning groove 41 has a width and a depth that do not significantly affect the rigidity of the extended portions 12 and 22 or the protruding portions 17 and 27. By forming the positioning groove 41, the adhesive strength between the fixing members 10 and 20 and the FBG sensors 2 and 3 can be increased. In order to further increase the adhesive strength, as shown in FIG. 4C, an FBG sensor 2 fitted in the positioning groove 41 using a pressing member (block or the like) 42 having the same thermal expansion coefficient as that of the fixing members 10 and 20, 3 may be fixed by the pressing member 42. In the illustrated example, the pressing member 42 is fixed by the adhesive 43, but it can also be fixed by a screw or the like.

  Desirably, as shown in FIG. 5D, a pretension adjuster 45 is provided on each of the surfaces of the extending portions 12 and 22 and the surfaces of the protrusions 17 and 27 of the fixing members 10 and 20, respectively. The FBG sensors 2 and 3 are fixed to the fixing members 10 and 20 by 45. The embodiment of FIG. 2 is a system in which the FBG sensors 2 and 3 that are elastic bodies themselves are stretched over the gaps L2 and L3 to apply compression and tension. The FBG sensors 2 and 3 are fixed to the surfaces of the extended portions 12 and 22 and the surfaces of the projecting portions 17 and 27 in a state in which a tensile force is applied in advance (pre-tensioned state) so that strain can be detected stably. It is desirable to do. The pretension adjusting tool 45 in the illustrated example has a long hole in the direction of the arrow, and the extension parts 12 and 22 and the projecting parts 17 and 27 below the long hole have, for example, screw holes formed therein. The pretension strength applied to the FBG sensors 2 and 3 can be adjusted by moving the adjuster 45 in the direction of the arrow. In the illustrated example, the first fixing body 10 and the second fixing body 20 are separated from each other, and it may be difficult to bridge the FBG sensors 2 and 3 between them. The removable outer edge coupling portions 33 and 34 (see FIG. 6D) that can temporarily fix the distance L1 between the opposing sides 11 and 12 of the fixing members 10 and 20 can be used.

  Further, when the strain ε generation direction (for example, the X direction in FIG. 2) of the measurement target 50 can be estimated, an external force is applied between the FBG sensors 2 and 3 between the fixing members 10 and 20 as shown in the illustrated example. It is desirable to cross in the direction and fix in parallel. By matching the direction of the FBG sensors 2 and 3 with the direction in which the external force is applied, the detection sensitivity (distortion conversion efficiency) of the strain ε of the measurement target 50 detected by the FBG sensors 2 and 3 can be maximized. Further, in the vicinity of the opposing edges 13 and 23 serving as the ends of the extending portions 12 and 22 for fixing the FBG sensors 2 and 3 and the tip edges 18 and 28 serving as the ends of the projecting portions 17 and 27, Concentration of stress can be avoided. Further, the opposing edges 13 and 23 of the extending parts 12 and 22 and the leading edges 18 and 28 of the protruding parts 17 and 27 are arranged so that the FBG sensors 2 and 3 have an environment (atmosphere) having substantially the same strain and temperature. Is preferably an adjacent neighborhood.

  Next, with reference to FIG.1 and FIG.2, the distortion measuring method by the optical fiber sensor 1 of this invention is demonstrated. In the illustrated optical fiber sensor 1, the FBG sensors 2 and 3 are fixed between the opposing edges 13 and 23 of the fixing bodies 10 and 20 and the tip edges 18 and 28, respectively, and then the fixing bodies are fixed. The fixing portions 10 and 20 are fixed to the surface of the measurement object 50 together with the FBG sensors 2 and 3 and installed. For example, if a sensor unit or module in which the fixing members 10 and 20 are fixed to the pair of FBG sensors 2 and 3 is manufactured in advance at a factory or the like, the installation work of the optical fiber sensor 1 can be facilitated. Adjustment of the pretension of each FBG sensor 2, 3 can be performed at the stage of manufacturing the sensor unit or module at the factory. However, it is also possible to fix the FBG sensors 2 and 3 between the fixing bodies 10 and 20 after fixing the fixing bodies 10 and 20 to the surface of the measurement object 50. In this case, for example, the pretension of the FBG sensors 2 and 3 is adjusted at the installation site by the pretension adjuster 45 shown in FIG.

The optical fiber sensor 1 of the present invention can fix the two FBG sensors 2 and 3 on the fixing members 10 and 20 under the same conditions (for example, the same adhesive or its dry state). Accordingly, there is a feature that the fixing quality of the two FBG sensors 2 and 3 is less likely to vary than the conventional optical fiber sensor (Patent Document 1 or the like) in which the fixing methods of the two FBG sensors 2 and 3 are different. Each of the FBG sensors 2 and 3 transmits a broadband optical signal and measures the shift amount Δλ of the Bragg wavelength λ _B generated in the grating unit, and the shift amount Δλ of both the FBG sensors 2 and 3. A strain amount calculation device 8 that calculates the strain ε of the measurement target 50 by obtaining the difference is connected.

Instead of using the two optical fibers 4 and 5, two FBG sensors (grating portions) 2 and 3 formed on one optical fiber wired as in the illustrated example are connected to the fixing body 10, It is also possible to cross over 20 and fix. In this case, if the FBG sensors 2 and 3 having different black wavelengths are prepared, the shift amount Δλ of each sensor 2 and 3 can be easily known by the strain measuring device 7 and the strain amount calculating device 8. Alternatively, even if the Bragg wavelengths of the FBG sensors 2 and 3 are the same, the reflected light wavelength λ _B and the time delay t thereof identify the reflected light from the FBG sensors 2 and 3, and each sensor 2 3 shift amount Δλ can be known. Further, for example, as shown in FIG. 1B, a plurality of optical fiber sensors 1 connected in series by optical fibers are arranged along a measurement object 50 (for example, a brace material, a seismic wall, etc. in which stress concentration of a structure is assumed). It is also possible to measure the strain ε at a plurality of sites on the measurement target 50 with the single strain measuring device 7 and the strain amount calculating device 8.

Assuming that the gap L2 between the opposing edges 13 and 23 of both the fixing members 10 and 20 of the optical fiber sensor 1 and the gap L3 between the tip edges 18 and 28 have the same size (same strain magnification η), the optical fiber sensor 1 When the external force and the temperature change ΔT are simultaneously applied to the FBG sensor 3 fixed between the tip edges 18 and 28, the shift amount Δλ _{all (+)} of the Bragg wavelength λ _{B in} the equation (31 ₎ is The distortion measuring device 7 detects the shift amount Δλ _{all (−)} of the Bragg wavelength λ _B of the equation (32) generated in the FBG sensor 2 that is detected by the strain measuring device 7 and fixed between the opposing edges 13 and 23. . Further, in the distortion amount calculation device 8, the difference between the shift amounts Δλ of the Bragg wavelength λ _B detected by both the FBG sensors 2 and 3 is calculated by the equation (33).

In the equation (33), the influence of the temperature change ΔT having the same polarity in both the FBG sensors 2 and 3, that is, the influence of the expansion and contraction of the sensor itself due to the temperature change ΔT (the shift amount Δλ _{B2 in the} equation (3)) The effect of 20 expansion / contraction (shift amount Δλ _{B3 in} equation (11)) is offset. Further, in the equation (33), since the thermal expansion coefficient β (see the equations (11) and (13)) of both the fixing bodies 10 and 20 is equal to the thermal expansion coefficient γ of the measurement object 50, the measurement accompanying the temperature change ΔT The influence of the expansion / contraction of the object 50 (shift amount Δλ _{B4 in the} equation (13)) is also removed. That is, _{all the} shift amount Δλ _target (Equation (14)) due to the influence of the temperature change ΔT is compensated from the shift amount Δλ _all of the Bragg wavelength λ _B detected by the FBG sensors 2 and 3 by the difference calculation of the equation (33). Only the shift amount of the strain ε of the measurement object 50 (shift amount Δλ _{B5 in the} equation (15)) can be extracted. When the strain ε in the Y direction in FIG. 2 is generated in the measurement object 50, the shift amount of the strain ε detected by both the FBG sensors 2 and 3 (the shift amount Δλ _{B5 in} equation (15)) is equal. The influence of the strain ε in the Y direction can be removed by the difference calculation of the equation (33), and only the strain ε in the X direction can be obtained with high accuracy.

Therefore, in the strain amount calculation device 8, both the fixing members 10,... Are calculated from the shift amount Δλ of the equation (33) and the strain expansion rate η of the gap L3 between the leading edges 18 and 28 (or the gap L2 between the opposed edges 13 and 23). It is possible to accurately measure the strain ε of the measurement object 50 at the predetermined interval L1 of 20. The Bragg wavelength λ _B and the photoelastic coefficient ρ _c in the equation (33) can be stored in advance in the memory of the strain amount calculation device 8, for example. When the gap L2 between the opposing edges 13 and 23 of the fixing bodies 10 and 20 and the gap L3 between the tip edges 18 and 28 have different sizes ₍ the distortion expansion ratio η ₍ Δλ _{all (−) in} the equation (31)) ₊₎ And (32) where Δλ _{all (-)} is different from the strain expansion ratio η _(-) ), the equation (33) shows 2Δλ _B5 = (η ₍₊₎ + η _(-) ) · λ _B ( 1−ρ _c ) ε, and therefore, the difference calculation result of Equation (33) may be corrected with the distortion expansion rate (η ₍₊₎ + η ₍₋₎ ).

  Further, the equation (33) obtained from the optical fiber sensor 1 of the present invention depends on the measurement target 50 such as the thermal expansion coefficient γ like the underlined portions of the conventional equations (21), (22), and (24). Therefore, general-purpose strain measurement independent of the shape and structure of the measurement target 50 is possible. Furthermore, according to the optical fiber sensor 1 of the present invention, it is possible to adjust the measurement sensitivity of the optical fiber sensor 1 by adjusting the strain magnification ratio η, and the external force in the equations (31) and (32). The influence of the strain ε can be enlarged compared to the influence of the temperature change ΔT. By expanding the influence of the external force, the temperature compensation performance can be maintained at a predetermined level or higher even when the temperature compensation performance varies due to the difference in the installation location and method of the sensor 1. Note that adding Equation (31) and Equation (32) yields Equation (34), which can eliminate the effect of strain ε due to external force and leave only the shift amount due to temperature change ΔT. For this reason, if the optical fiber sensor 1 of this invention is used, it is also possible to know the temperature change in the installation environment of the sensor 1. FIG.

  Thus, it is possible to provide the “optical fiber sensor capable of removing only the strain by removing the influence of the temperature change ΔT generated in the FBG sensor”, which is an object of the present invention.

  FIG. 6 shows that the opposing edges 13 and 23 are connected between the opposing edges 13 and 23 of the extending portions 12 and 22 of the first fixing body 10 and the second fixing body 20 with rigidity smaller than the fixing bodies 10 and 20. An opposing edge bridging portion 31 is provided, and a leading edge bridging portion 32 is provided between the leading edges 18 and 28 of both projecting portions 17 and 27 to connect the two leading edges 18 and 28 with rigidity smaller than both the fixing members 10 and 20. The Example of the optical fiber sensor 1 of this invention is shown. Each of the bridging portions 31 and 32 is also made of a material having the same coefficient of thermal expansion β as that of the strain measurement target 50 as in the case of the fixing members 10 and 20. In the illustrated example, the FBG sensors 2 and 3 can be fixed to the surfaces of the bridging portions 31 and 32 with an adhesive or the like, and the deformation of the fixing members 10 and 20 is caused to the FBG sensors 2 and 3 via the bridging portions 31 and 32. Since transmission is performed, it is optional whether the FBG sensors 2 and 3 are fixed in a state where a tensile force (pretension) is applied in advance. If necessary, as in the case of FIG. 5 (A), positioning grooves 41 may be provided on the surfaces of the bridging portions 31 and 32 so that the optical fibers 4 and 5 constituting the FBG sensors 2 and 3 are aligned. .

  It is desirable that the bridging portions 31 and 32 have the same cross-sectional area so that the relationship of load P-strain ε is the same. For example, as shown in FIG. 6 (B) and FIG. 6 (C), the bridging portion 31 has a small cross-sectional area that is narrow and thin so that the bridge portion 31 is more easily deformed than the extending portions 12 and 22 at both ends. The bridging portion 32 is a rod-shaped portion having a small cross-sectional area that is narrower and thinner than the protrusions 17 and 27 at both ends thereof so that it can be deformed more easily. More preferably, as described above, the length L2 of the bridging portion 31 (the gap L2 between the facing edges 13 and 23) and the length L3 of the bridging portion 32 (the gap L3 between the tip edges 18 and 28) are matched. By making the rigidity of both the bridging portions 31 and 32 equal and smaller than both the fixing members 10 and 20, the relative displacement of the opposing sides 11 and 12 can be concentrated on the both bridging portions 31 and 32. However, when the rigidity of both bridge portions 31 and 32 is small, a part of the strain ε of the measurement object 50 is relaxed by the bridge portions 31 and 32, and the FBG sensors 2 and 3 depend on the relaxation degree k (<1). The magnification rate η of the detected deformation is reduced. Further, the optical fiber sensor 1 needs to be used within a range where both the bridging portions 31 and 32 are not buckled.

  Further, as shown in FIG. 6D, the fixing members 10 and 20 and the bridging portions 31 and 32 are integrally formed from a plate-like member having the same thermal expansion coefficient β as that of the measurement target 50 by punching or the like. Can be. By integrally forming both the fixing members 10 and 20 and the two bridging portions 31 and 32, it is possible to further facilitate the fixing operation to the measurement object 50 and the fixing operation of the FBG sensors 2 and 3. Further, in the illustrated example, the outer edges of the fixing bodies 10 and 20 are connected to each other by the outer edge coupling portions 33 and 34 made of the same thermal expansion coefficient β as that of the strain measurement target 50, and both the fixing bodies 10 and 20 and both the bridging portions 31 and The whole 32 and the outer edge coupling portions 33 and 34 are formed as an integrally formed frame 30. If the rigidity of the bridging portions 31 and 32 is small, it may be possible that both the fixing members 10 and 20 are deformed at the time of work, but it is difficult to deform the frame 30 by providing the outer edge coupling portions 33 and 34. Therefore, further improvement in efficiency of the fixing work and the fixing work can be expected. It should be noted that the outer edge coupling portions 33 and 34 can be removed from the frame 30 and the outer edge coupling portions 33 and 34 are removed from the frame 30 after the fixing work to the measurement object 50 and the fixing work of the FBG sensors 2 and 3 are completed. It can be reused.

  7 and 8 show a first laminated fixing body 19 in which an upper layer fixing body 10 and a lower layer fixing body 15 having the same thermal expansion coefficient β as the measurement object 50 are laminated, and an upper layer fixing body 20 having the same thermal expansion coefficient β. And the second laminated fixing body 29 in which the lower layer fixing body 25 is laminated, and one FBG sensor 2 is bridged between the upper fixing bodies 10 and 20 between the two laminated fixing bodies 19 and 29 and fixed. An embodiment of the optical fiber sensor 1 of the present invention in which the FBG sensor 3 is fixed between the lower-layer fixing bodies 15 and 25 between the laminated fixing bodies 19 and 29 is shown. In the above-described embodiment shown in FIGS. 1 to 6, the FBG sensors 2 and 3 are fixed to the surface of the measurement object 50 so as to be separated in the horizontal direction. There may be some differences. On the other hand, in the embodiment of FIG. 7, both the FBG sensors 2 and 3 can be aligned and fixed in the vertical direction, and the strain and temperature environments for the FBG sensors 2 and 3 can be made substantially coincident.

  The upper fixing members 10 and 20 of the laminated fixing members 19 and 29 in FIG. 7A are provided with a fixing unit that fixes one side 11 and 21 on the surface of the measurement object 50 at a predetermined interval L1, and the opposite side 11 thereof. , 21 includes a first extending portion 12 and a second extending portion 22 extending to the laminated fixing members 29 and 19 side. In the illustrated example, a fixing member 6 (for example, a screw or the like) is inserted into the fixing hole 6a aligned with each of the laminated fixing members 19 and 29 to fix the fixing members 19 and 29 to the surface of the measurement target 50, and the fixing member. Although the interval between 6 and 6 is the predetermined interval L1, each laminated fixing body 19 and 29 is fixed to the measurement object 50 by an adhesive or welding or the like, and the interval between the parts fixed to the measurement object 50 (for example, the opposite side 11). , 21) may be the predetermined interval L1.

  A protruding portion 12a that protrudes to the side is provided in a part of the extended portion 12 of the upper-layer fixing body 10, and the opposing edge 13 that faces the opposing side 11 of the first fixing body 10 via the gap S by the protruding portion 12a. Form. In addition, a protruding portion (or protruding portion) 22 a that protrudes in the gap S between the opposite side 11 of the first fixing body 10 and the first extending portion 12 is provided in a part of the extending portion 22 of the upper layer fixing body 20. The overhanging portion 22a forms an opposing edge 23 that faces the opposing edge 13 of the first extending portion 12 in the gap S with a predetermined gap L2 (see FIG. 5C). The shape of the extending portions 12 and 22 is not limited to the L-shape as shown in the example. As described above, the deformation of the polarity opposite to the deformation direction of the upper fixing members 10 and 20 is caused between the opposing edges 13 and 23. It can be made into an arbitrary shape that occurs in the above.

  Further, the lower-layer fixing members 15 and 25 of the laminated fixing members 19 and 29 in FIG. 7A include a fixing unit that fixes one side 16 and 26 on the surface of the measurement object 50 at a predetermined interval L1, and the opposite sides thereof. The first projecting portion 17 and the second projecting portion 27 projecting from the side surfaces 16 and 26 to the laminated fixing bodies 29 and 19 side. The protruding portion 17 and the protruding portion 27 are protruded so that the respective leading edges 18 and 28 face each other with a predetermined gap L3 (see FIG. 5B). The shape of the protrusions 17 and 27 is not limited to an I-shape as in the embodiment. As described above, the deformation having the same polarity as the deformation direction of the lower layer fixing bodies 15 and 25 is caused between the leading edges 18 and 28. It can have any shape that results. However, as described with reference to FIG. 3A, both or one of the lower-layer fixing members 15 and 25 or the protruding portions 17 and 27 can be omitted, and the FBG sensor 3 is connected to the lower-layer fixing members 15 and 25. Alternatively, it may be fixed over the opposite sides 16 and 26. The lower layer fixing members 15 and 25 are fixed to the upper layer fixing members 10 and 20 with an adhesive or the like so that the laminated fixing members 19 and 29 are integrally deformed.

  As shown in FIG. 7 (D), the FBG sensor 2 is connected to the opposite edges 13 of the extension portions 12 and 22 of the upper-layer fixing bodies 10 and 20 so that the external forces applied to the pair of FBG sensors 2 and 3 have different polarities. 23, the other FBG sensor 3 is fixed over the tip edges 18, 28 of the protrusions 17, 27 of the lower layer fixing bodies 15, 25. As can be seen from the figure, the upper fixing members 10 and 20 and the lower fixing members 15 and 25 of the laminated fixing members 19 and 29 are plate-shaped, and the FBG sensors 2 and 3 are vertically aligned and fixed. , The strain and temperature environments of the FBG sensors 2 and 3 can be very close. Preferably, the gap L2 between the opposing edges 13 and 23 of the upper layer for fixing the FBG sensor 2 and the lower layer for fixing the FBG sensor 3 so that the magnifications η of the strain ε detected by the FBG sensors 2 and 3 coincide with each other. The gap L3 between the leading edges 18 and 28 is made the same size. If necessary, spacers 14 and 24 are provided between the upper layer 10 and the lower layer 15 of the first laminated fixing body 19 and between the upper layer 20 and the lower layer 25 of the second laminated fixing body 29, respectively. The interval may be adjusted appropriately. The spacers 14 and 24 are fixed with an adhesive or the like between the upper layer fixing members 10 and 20 and the lower layer fixing members 15 and 25 so that the laminated fixing members 19 and 29 are integrally deformed. As shown in FIG. 2D, spacers (leg portions) 14 and 24 for supporting the laminated fixing members 19 and 29 apart from the surface of the measurement target 50 can be included below the lower fixing members 15 and 25. is there.

  Preferably, as shown in FIG. 8, the opposing edges 13, 23 are set between the opposing edges 13, 23 of the extended portions 12, 22 of the upper-layer fixing bodies 10, 20 with rigidity smaller than that of the upper-layer fixing bodies 10, 20. Connecting opposite edge bridging part 31 is provided, and both leading edges 18, 28 are connected between the leading edges 18, 28 of the protrusions 17, 27 of the lower fixing bodies 15, 25 with rigidity smaller than that of the lower fixing bodies 15, 25. The leading edge bridging portion 32 is provided, and the FBG sensors 2 and 3 are fixed to the surfaces of the bridging portions 31 and 32 with an adhesive or the like. As described above with reference to FIG. 6, the bridging portions 31 and 32 can have the same cross-sectional area so that the relationship of the load P-strain ε is the same, and the width and the thickness are small so that the strain is easily deformed. It can be a bar with a small cross-sectional area.

  More preferably, as shown in FIGS. 8B and 8C, the upper-layer fixing members 10 and 20 and the bridging portion 31 are punched from a plate-like member having the same coefficient of thermal expansion β as that of the measurement target 50. The lower frame body 35 is integrally formed from a plate-like member having the same coefficient of thermal expansion β as that of the measurement target 50, and the lower layer fixing bodies 15 and 25 and the bridge portion 32 are integrally formed. By using the upper frame 36 and the lower frame 35, it is possible to facilitate the fixing work to the measurement object 50 and the fixing work of the FBG sensors 2 and 3. As shown in FIG. 6C, the upper frame 36 includes outer edge coupling portions 33 and 34 that couple the outer edges of the upper fixing members 10 and 20 to each other, and the lower frame 35 has the outer edges of the upper fixing members 10 and 20. It is also possible to make the frame bodies 35 and 36 difficult to be deformed by including the outer edge coupling portions 33 and 34 that couple each other.

Also in the optical fiber sensor 1 of FIGS. 7 and 8, when an external force and a temperature change ΔT are simultaneously loaded, the shift amount of the Bragg wavelength λ _B in the FBG sensor 3 fixed between the lower layer fixing bodies 15 and 25. Δλ _{all (+)} (Equation (31)) is detected, and the shift amount Δλ _{all (-)} (Equation (32) ₎ of the Bragg wavelength λ _B is detected in the FBG sensor 2 fixed between the upper-layer fixing bodies 10 and 20. since the, by calculating the difference between the shift amount Δλ of the Bragg wavelength lambda _B detected by both FBG sensors 2 ((33)), the Bragg wavelength lambda _B detected by the FBG sensors 2 _{All the} shift amount Δλ _target (Equation (14)) due to the influence of the temperature change ΔT is removed from the shift amount Δλ _all, and only the shift amount of the strain ε of the measurement target 50 (shift amount Δλ _{B5 in} Equation (15)) is taken out. it can. In addition, since the strain and temperature environments for the FBG sensors 2 and 3 can be made substantially the same, even if there are variations in the installation location and method, the effect of the temperature change ΔT can be assured by calculating the difference of equation (33). It can be removed, and an improvement in strain measurement accuracy of the measurement object 50 can be expected. In the illustrated example, as described above, the upper-layer fixing members 10 and 20 are provided with the extending portions 12 and 22 that cause deformation of the opposite polarity, and the lower-layer fixing members 15 and 25 are provided with the protruding portions 17 and 27 that cause deformation of the same polarity. However, the same measurement is possible when the upper fixing members 10 and 20 are provided with the protruding portions 17 and 27 and the lower fixing members 15 and 25 are provided with the extending portions 12 and 22.

It is explanatory drawing of an example of the optical fiber sensor of this invention using a pair of fixing body. It is the top view and sectional drawing of the optical fiber sensor of FIG. It is explanatory drawing of another example of the optical fiber sensor using a pair of fixing body. It is explanatory drawing of another example of the optical fiber sensor using a pair of fixing body. It is explanatory drawing of the method of fixing an optical fiber grating to a fixing body. It is explanatory drawing of an example of the optical fiber sensor using the frame which connected a pair of fixing body by the bridge | crosslinking part. It is explanatory drawing of an example of the optical fiber sensor using a pair of laminated fixing body. It is explanatory drawing of another example of the optical fiber sensor using a pair of laminated fixing body. It is explanatory drawing of an example of the sensor using the conventional optical fiber grating. It is explanatory drawing of another example of the sensor using the conventional optical fiber grating. It is explanatory drawing of another example of the sensor using the conventional optical fiber grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber sensor 2, 3 ... Optical fiber grating (FBG sensor)
4, 5 ... Optical fiber 6 ... Fixing member 6a ... Fixing hole 7 ... Strain measuring instrument 8 ... Strain amount calculation device (computer)
9 ... Memory
10: First fixing body (upper fixing body) 11 ... Opposite side
12 ... 1st extension part 13 ... Opposite edge
14 ... Spacer 15 ... Lower layer fixing body
16 ... Opposite side 17 ... First protrusion
18 ... Edge edge 19 ... First laminated fixing body
20 ... Second fixing body (upper fixing body) 21 ... Opposite side
22 ... Second extension 23 ... Opposing edge
24… Spacer 25… Lower layer fixing body
26 ... Opposite side 27 ... Second protrusion
28 ... tip edge 29 ... second laminated fixing body
30 ... Frame 31 ... Bridged part of opposite edge
32 ... Bridge at the tip edge 33 ... Outer edge part
34 ... Outer edge (outer edge joint) 35 ... Lower frame
36… Upper frame
41 ... Positioning groove 42 ... Presser member
43… Adhesive 45… Pretension adjuster
50 ... Measurement target 51 ... Steel column
52 ... Steel beam 51a ... Crack or joint
61 ... FBG sensor 62 ... FBG sensor
63 ... Substrate 64 ... Holder
64a, 64b ... holding part 65 ... holding tool
65a, 65b ... Holding part 66, 67, 68 ... Mounting plate

Claims (19)

A first fixing body and a second fixing body, each having the same thermal expansion coefficient as the measurement target and having one side opposed to the surface of the measurement target and fixing at a predetermined interval, are bridged between the two fixing bodies. A pair of optical fiber gratings fixed to the fixing body is provided, and an opposing edge extending to the second fixing body side and facing the opposing side through a gap is formed in part on the opposing side of the first fixing body. A first extending portion that extends toward the first fixing member on the opposite side of the second fixing member and faces the opposing edge of the first extending portion within a predetermined gap within the gap. A second extending portion is provided, one of the optical fiber gratings is fixed on a line connecting opposite edges of the extending portions of the fixing members, and the other of the optical fiber gratings is extended of the fixing members. An optical fiber sensor fixed on a line connecting opposite sides other than . 2. The optical fiber sensor according to claim 1, wherein the pair of optical fiber gratings are fixed in parallel.   3. The optical fiber sensor according to claim 1, wherein the first fixing body and the second fixing body are protruded toward the second fixing body side and the first fixing body side at opposite sides other than the extending portions, and the leading edges thereof are mutually spaced by a predetermined gap. An optical fiber sensor in which a first projecting portion and a second projecting portion facing each other are provided, and the other of the optical fiber grating is fixed on a line connecting the end edges of both projecting portions.   4. The optical fiber sensor according to claim 3, wherein the predetermined gap between the opposing edges of the two extending portions and the predetermined gap between the leading end edges of the two protruding portions are made the same size. 5. The optical fiber sensor according to claim 3, wherein a facing edge bridging portion that connects both facing edges with a rigidity smaller than that of the both fixing members is provided between the facing edges of the both extending portions, and between the front end edges of the projecting portions. An optical fiber sensor provided with a leading edge bridging portion that connects both leading edges with rigidity smaller than the two fixing members. 6. The optical fiber sensor according to claim 5, wherein the opposed edge bridging portion and the tip edge bridging portion have the same cross-sectional area. 7. The optical fiber sensor according to claim 5, wherein the first fixing body, the second fixing body, the opposed edge bridging portion, and the leading edge bridging portion are integrally formed from a plate-like member having the same thermal expansion coefficient as the measurement target. An optical fiber sensor. 8. The optical fiber sensor according to claim 1, further comprising an outer edge coupling portion that connects outer edges of the first fixing body and the second fixing body to each other. 9. The optical fiber sensor according to claim 8, wherein the first fixing body, the second fixing body, and the outer edge coupling portion are integrally formed from a plate-like member having the same thermal expansion coefficient as that of the measurement target. . 9. The optical fiber sensor according to claim 8, wherein the outer edge coupling portion can be removed. A first laminate fixing body, which is a laminate of an upper layer fixing body and a lower layer fixing body each having the same thermal expansion coefficient as the measurement object, and is fixed at a predetermined interval with each side of the upper layer and the lower layer facing each other on the surface of the measurement object And a second laminated fixing body, and a pair of optical fiber gratings that are bridged between the two laminated fixing bodies and fixed to the two fixing bodies, and opposite sides of the upper and lower one side layers of the first laminated fixing body Provided with a first extending portion formed in a part of a facing edge extending to the second laminated fixing body and facing the opposite side through a gap, and opposed to the upper and lower one side layers of the second laminated fixing body. A second extending portion formed on a side of the first laminated fixing member and having a facing edge formed in a part of the gap facing the facing edge of the first extending portion within a predetermined gap; One side of the cable is fixed on the line connecting the opposite edges of the two extension parts. And, an optical fiber sensor formed of a fixed other of said optical fiber grating on a line connecting the opposite sides of the upper and lower the other side layers of both stacked fuser. 12. The optical fiber sensor according to claim 11, wherein the pair of optical fiber gratings are aligned in the vertical direction and fixed in parallel. 13. The optical fiber sensor according to claim 11, wherein a spacer is provided between an upper layer and a lower layer of the first laminated fixing body and the second laminated fixing body.   14. The optical fiber sensor according to claim 11, wherein the first laminated fixing body and the second laminated fixing body are protruded toward the second laminated body side and the first laminated body side on opposite sides of the upper and lower other layers, respectively, and a leading edge. Is provided with a first protrusion and a second protrusion facing each other with a predetermined gap, and the other of the optical fiber grating is fixed on a line connecting the leading edges of the protrusions. 15. The optical fiber sensor according to claim 14, wherein a facing edge bridging portion is provided between the facing edges of the two extending portions to connect the facing edges with rigidity smaller than that of the laminated fixing bodies, and between the leading edges of the projecting portions. An optical fiber sensor provided with a leading edge bridging portion that couples both leading edges with less rigidity than the two laminated fixing members. 16. The optical fiber sensor according to claim 15, wherein the upper and lower one side layers of the first laminated fixing body and the second laminated fixing body and the opposite edge bridging portion are integrally formed from a plate-like member having the same thermal expansion coefficient as that of the measurement object. An optical fiber sensor in which the upper and lower other layers of the first laminated fixing body and the second laminated fixing body and the leading edge bridging portion are integrally molded from a plate-like member having the same coefficient of thermal expansion as the measurement object. . 17. The optical fiber sensor according to claim 11, wherein an outer edge coupling portion that connects outer edges of upper and lower one side layers of the first laminated fixing body and the second laminated fixing body, and the first laminated fixing body, An optical fiber sensor provided with an outer edge coupling portion that interconnects outer edges of the upper and lower other layers of the second laminated fixing body. 18. The optical fiber sensor according to claim 17, wherein the upper and lower one side layers and the outer edge coupling portion of the first laminated fixing body and the second laminated fixing body are integrally formed from a plate-like member having the same thermal expansion coefficient as the measurement target. And an optical fiber sensor formed as a frame body in which the upper and lower other layers of the first laminated fixing body and the second laminated fixing body and the outer edge coupling portion are integrally formed from a plate-like member having the same thermal expansion coefficient as the measurement target. 18. The optical fiber sensor according to claim 17, wherein the outer edge coupling portion can be removed.

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