Optical Fiber Sensor

Abstract

To provide an optical fiber sensor which can be fixed comparatively easily to a comparatively large object to be measured such as a building, and can detect distortion in a comparatively wide range.SOLUTION: The optical fiber sensor includes a body 10 and a support 20 which are joined with a joining member 30. In the body 10, an optical fiber 14 fixed to first and second base members 11, 12 includes an FBG section 18 in which a Bragg wavelength varies with a distance between the first base member 11 and the second base member 12. A third base member 13 with the joining member 30 joined thereto is arranged so as to be moved with respect to the first and second base members 11, 12. The first base member 11 and the second base member 12 are joined with a first elastic body 15. The second base member 12 and the third base member 13 are joined with a second elastic body 16 having an elastic constant which is different from an elastic constant of the first elastic body 15. A guide member 17 regulates the second and third base members 12, 13 so as to move in a specific direction.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical fiber sensor equipped with an FBG (Fiber Bragg Grating), and in particular to an optical fiber sensor suitable for detecting distortions and the like of a relatively large measurement target such as a building. [Background technology]

[0002] Conventionally, optical fiber sensors using optical fibers equipped with FBGs have been used to detect strain and the like in structures such as buildings, bridges, and tunnels. This type of optical fiber sensor acquires the amount of strain and the like based on the Bragg wavelength of the FBG, which changes in response to deformation of the optical fiber. In addition, this type of optical fiber sensor is, for example, fixed by attaching the entire FBG portion of the optical fiber to the object to be measured with an adhesive or the like. Alternatively, the entire FBG portion is fixed to a base member such as metal, and the base member is then fixed by attaching to the object to be measured with an adhesive or the like. With such a fixing method, deformation of the object to be measured is directly or indirectly transferred to deformation of the FBG.

[0003] However, with a fixing method in which an FBG is directly attached to the object to be measured with adhesive or the like, the FBG is only a few centimeters long, so only local deformation of the object can be measured. In other words, when applied to a relatively large object to be measured, such as a building, it is difficult to measure strain over a relatively wide range (for example, a length of several tens of centimeters to several meters) with a single FBG. For this reason, a fixing method is adopted in which an optical fiber including an FBG is fixed over the entire length of a long base member that has a length similar to the measurement range, and the entire long base member is attached to the object to be measured. With this fixing method, deformation of the object to be measured over the entire area where the base member is attached can be transferred to deformation of the FBG.

[0004] On the other hand, Patent Document 1, listed below, discloses a configuration in which an FBG is formed in an optical fiber about 1 m long, and both ends of the optical fiber are fixed to an object to be measured. With this configuration, it is possible to measure the average deformation of the object to be measured over a 1-m-long portion over which the optical fiber is stretched.

[0005] As a technique related to the present invention, Patent Document 2 discloses a configuration in which an optical fiber on one side of an FBG formed on an optical fiber is directly fixed to an object to be measured, and the optical fiber on the other side is indirectly fixed to the object to be measured via a spring. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-039309 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-221615 Summary of the Invention [Problem to be solved by the invention]

[0007] Even when FBGs are directly attached with adhesive or the like, it is possible to obtain the deformation distribution of a relatively large area to be measured by attaching a large number of FBGs to that area. However, the task of directly attaching a large number of FBGs to the object to be measured requires a great deal of man-hours. Another problem is that the optical fiber sensor itself becomes more expensive because a large number of FBGs must be formed on the optical fiber.

[0008] Furthermore, in the fixing method in which a long base member to which an optical fiber including an FBG is attached is attached to the object to be measured, the shape of the long base member is fixed, so it is bulky to transport, and the task of attaching the long base member to the object to be measured is not easy. In addition, the longitudinal length of the base member is predetermined, so it cannot be adjusted on the work site. There are also challenges.

[0009] Furthermore, in the fixing methods disclosed in Patent Documents 1 and 2, it is necessary to fix one side to the object to be measured and then fix the other side to the object to be measured, which makes the fixing work very cumbersome. In particular, when applying pretension to FBGs to enable detection of strain in the compression direction, it is very difficult to apply pretension uniformly to all FBGs fixed to the object to be measured.

[0010] Furthermore, in a configuration in which a measurement object is fixed via a spring as disclosed in Patent Document 2, it is possible to reduce the amount of displacement transmitted to the FBG by the spring. However, FBGs have low rigidity and therefore have almost no spring properties, and unless the amount of displacement transmitted to the FBG is made extremely small, they will easily break. In other words, when applied to a relatively large arbitrary measurement area, it is extremely difficult to convert the amount of displacement of the measurement object into a range of displacements appropriate for the FBG and transmit it to the FBG.

[0011] The present invention has been made in consideration of the problems with the conventional technology, and aims to provide an optical fiber sensor that can be relatively easily fixed to a relatively large object to be measured, such as a building, and that can detect deformation over a relatively wide range with a single FBG. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the present invention employs the following technical means. The optical fiber sensor according to the present invention comprises a main body, a support separate from the main body, and a connecting member. The main body and the support are fixed to the object to be measured. The connecting member connects the main body and the support without contacting the object to be measured. The main body comprises a first base member, a second base member, an optical fiber, a third base member, a first elastic body, a second elastic body, and a guide member. The second base member is arranged movably relative to the first base member. The optical fiber comprises an FBG (Fiber Bragg Grating) section whose Bragg wavelength varies depending on the distance between the first base member and the second base member, and is fixed to the first base member and the second base member. The third base member is arranged movably relative to the first base member and the second base member, and is connected to the connecting member. The first elastic body connects the first base member and the second base member. The second elastic body connects the second base member and the third base member. The guide member is arranged to support the second base member and the third base member. to the first base member Restricts movement to a specific direction. The first base member is fixed to the guide member, and the guide member is fixed to the object to be measured. Alternatively, a configuration can be adopted in which the guide member also serves as the first base member, and the guide member is fixed to the object to be measured.

[0013] The optical fiber sensor of the present invention can be installed on an object to be measured relatively easily, for example, by fixing the main body and support to the object to be measured and then connecting the main body and support with a connecting member. Furthermore, it is not bulky to transport, and the measurement range can be adjusted at the work site by changing the length of the connecting member. Furthermore, by adjusting the ratio of the elastic constants of the first elastic body and the second elastic body, the ratio between the displacement of the object to the displacement transmitted to the FBG unit can be very easily set, so that even a relatively wide measurement range can be appropriately detected as strain on the object to be measured between the main body and support.

[0014] In this optical fiber sensor, for example, a configuration can be adopted in which the portion of the optical fiber including the FBG portion is linearly arranged, and the guide member restricts the movement direction of the second base member and the third base member to the axial direction of the linearly arranged optical fiber. Also, a configuration can be adopted in which the first base member is fixed to the guide member, and the guide member is fixed to the object to be measured. Furthermore, a configuration can be adopted in which the first elastic body or the second elastic body is provided in a detachable state. Additionally, a configuration can be adopted in which the first base member, the second base member, the third base member, and the guide member are formed of plate-like members.

[0015] In the above configuration, the elastic constant of the first elastic body may be greater than the elastic constant of the second elastic body, or the elastic constant of the first elastic body may be smaller than the elastic constant of the second elastic body. [Effects of the Invention]

[0016] According to the present invention, it is possible to relatively easily install the device on a relatively large measurement object such as a building, and to appropriately detect deformation over a relatively wide range. Furthermore, it is not bulky when transported, and the measurement range can be adjusted at the work site. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a perspective view showing an example of the structure of an optical fiber sensor according to an embodiment of the present invention. [Figure 2] 2(a) and 2(b) are enlarged perspective views showing the vicinity of the support body and main body of the optical fiber sensor according to one embodiment of the present invention. [Figure 3] 3(a) and 3(b) are diagrams showing the main body of an optical fiber sensor according to one embodiment of the present invention. [Figure 4] 1 is a diagram showing an example of an optical fiber arrangement in a main body of an optical fiber sensor according to an embodiment of the present invention. [Figure 5]5A to 5C are diagrams illustrating the operation of the optical fiber sensor according to the embodiment of the present invention. [Figure 6] FIG. 2 is a schematic diagram showing an example of a reflected light spectrum of an optical fiber sensor according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Embodiments of the present invention will be described in more detail below with reference to the drawings. FIG. 1 is a perspective view showing an example of the structure of an optical fiber sensor according to this embodiment. The optical fiber sensor 1 according to the present invention includes a main body 10, a support 20 separate from the main body 10, and a connecting member 30 connecting the main body 10 and the support 20. The main body 10 and the support 20 are fixed to the object to be measured. The distance between the main body 10 and the support 20 on the object to be measured is set, for example, within a range of several tens of centimeters to several meters depending on the size of the area of ​​the object to be measured for strain. Fixing the main body 10 and the support 20 to the object to be measured can be performed using any known method appropriate for the material of the object, such as bolts or spot welding. Although not particularly limited, in this embodiment, the main body 10 and the support 20 are fixed to the object to be measured by bolts inserted into fixing through holes. In this case, threaded holes into which the bolts are threaded are provided at the fixing positions of the object to which the main body 10 and the support 20 are fixed.

[0019] Figures 2(a) and 2(b) are enlarged perspective views showing the vicinity of the support body 20 and the main body 10 in Figure 1. Figures 3(a) and 3(b) are diagrams showing an example of the structure of the main body 10 of the optical fiber sensor 1 in this embodiment. Figure 3(a) corresponds to a bottom view (viewed from the side fixed to the object to be measured), and Figure 3(b) corresponds to a plan view.

[0020] As shown in FIG. 2(a), in this embodiment, the support body 10 is composed of a substantially square plate-like member 21. Through holes 23, through which the above-mentioned fixing bolts 29 are inserted, are provided at the four corners of the plate-like member 21. Furthermore, a wall portion 22 is provided at one end (the end on the main body 10 side) of the plate-like member 21, standing in a direction perpendicular to the surface of the plate-like member 21. A turnbuckle 24 is connected to the wall portion 22, and a connecting member 30 is connected to a ring-shaped portion 24a provided at the end of the turnbuckle 24 on the main body 10 side. The connecting member 30 connects the main body 10 and the support body 20 without coming into contact with the object to be measured.

[0021] Although not particularly limited, in this embodiment, a stainless steel band is used as the connecting member 30 that connects the support body 20 and the main body 10. By adopting this, for example, the connecting member 30 can be transported in a rolled up state to eliminate bulkiness, and it becomes possible to arbitrarily set the distance between the support 20 and the main body 10 at the work site where the optical fiber sensor 1 is installed. Note that the connecting member 30 can be made of any material and have any shape as long as it can transmit the relative displacement between the support 20 and the main body 10 that occurs in response to strain occurring in the object to the FBG section of the main body 10.

[0022] As shown in Figures 2(b), 3(a), and 3(b), the main body 10 includes a first base member 11, a second base member 12, a third base member 13, a first elastic body 15, a second elastic body 16, and a guide member 17. The first base member 11, the second base member 12, and the third base member 13 are arranged on a first surface of the guide member 17. The main body 10 is fixed to the object to be measured with a second surface of the guide member 17 in contact with the object to be measured. In addition, as will be described later, the main body 10 includes an optical fiber 14 on which an FBG portion 18 is formed on the guide member 17 side of the first base member 11 and the second base member 12.

[0023] 2(b), 3(a), and 3(b), in this embodiment, the guide member 17 includes a plate-shaped member 60 and screws 65 and 66 that are threaded into screw holes 67 and 68 formed in the plate-shaped member 60 corresponding to the second base member 12 and the third base member 13. As will be described later, the guide member 17 has the function of restricting the movement directions of the second base member 12 and the third base member 13 in one axial direction.

[0024] The plate-like member 60 has a generally square base 61 and a generally rectangular extending portion 62 extending in one direction from the base 61. The four corners of the base 61 are provided with slotted through grooves 63 through which the above-mentioned fixing bolts 69 are inserted. In this example, the through grooves 63 are provided along the extending direction of the extending portion 62, so that when fixing the main body 10 to the object to be measured, the position along the extending direction can be adjusted. Furthermore, a tubular body 64 is provided at the end of the base 61 opposite the extending portion 62 for drawing the optical fiber 14 to the outside of the main body 10. Here, three tubular bodies 64 are arranged, and the optical fiber 14 is configured to be drawn to the outside through the central tubular body 64 and one of the other tubular bodies 64.

[0025] The first base member 11, the second base member 12, and the third base member 13 are arranged in this order from the base 61 side of the guide member 17 along the extension direction of the extension portion 62. In this example, the first base member 11, the second base member 12, and the third base member 13 are made of plate-like members having the same width as the width of the extension portion 62 in the short direction. The materials of the first base member 11, the second base member 12, and the third base member 13 are not particularly limited. Here, the first base member 11, the second base member 12, and the third base member 13 are made of stainless steel.

[0026] The first base member 11, the second base member 12, and the third base member 13 have wide portions 31, 41, 51 in parts thereof that are wider than the width in the short direction of the extension portion 62. The wide portions 31, 41, 51 function as connecting portions to which the first elastic body 15 that connects the first base member 11 and the second base member 12 is connected, and as connecting portions to which the second elastic body 16 that connects the second base member 12 and the third base member 13 is connected.

[0027] As will be described later, the optical fiber 14 having the FBG section 18 is fixed to each of the first base member 11 and the second base member 12 with the FBG section 18 arranged across the first base member 11 and the second base member 12. Therefore, in this embodiment, from the viewpoint of facilitating the fixing of the optical fiber 14, the first elastic body 15 is constituted by two meander-shaped elastic sections that connect the first base member 11 and the second base member 12 at both ends in the width direction, and the first base member 11, the second base member 12, and the first elastic body 15 are realized as a single member. Note that the first base member 11, the second base member 12, and the first elastic body 15 are configured as a single member. It is not essential that the first base member 11 and the second base member 12 are connected together, and they may be configured as separate members. The gap between the first base member 11 and the second base member 12 is approximately several millimeters, but for the sake of explanation, a relatively large gap is depicted in the drawings.

[0028] The first base member 11 is fixed to the guide member 17. Any known method can be used for fixing. Here, the first base member 11 is fixed to the guide member 17 by screws 32 inserted into through holes provided in the first base member 11 and screw holes 70 provided in the plate-like member 60 corresponding to the through holes.

[0029] The second base member 12 is disposed movably relative to the first base member 11. The movability is not particularly limited. Here, a through groove 42 is provided in the second base member 12 along the extending direction of the extending portion 62. The guide member 17 has a screw hole 67 formed at a position corresponding to the through groove 42, and a screw 65 that screws into the screw hole 67. The shaft diameter of the screw 65 is slightly narrower than the width of the corresponding through groove 42. The screw 65 and the screw hole 67 are not fastened to the second base member 12 when the optical fiber sensor 1 is in an operating state. In other words, the second base member 12 is slidable along the extending direction of the extending portion 62 and is held by the guide member 17 in a state where it is prevented from coming off from the guide member 17. In this example, the through groove 42 is provided at two locations at the end on the first base member 11 side and one location at the center in the width direction on the third base member 13 side. The through groove 42 at the end on the first base member 11 side is semicircular, and the through groove 42 at the center in the width direction on the third base member 13 side is elongated.

[0030] Similarly, the third base member 13 is disposed movably relative to the first base member 11 and the second base member 12. The movability is not particularly limited. Here, an elongated through groove 52 is provided in the third base member 13 along the extending direction of the extending portion 62. The guide member 17 has a screw hole 68 formed at a position corresponding to the through groove 52, and screws 66 (screws 66a and 66b) that screw into the screw hole 68. The axial diameter of the screw 66 is slightly narrower than the width of the corresponding through groove 52. The screws 66 and the screw holes 68 are not fastened to the third base member 13 when the optical fiber sensor 1 is in an operating state. In other words, the third base member 13 is slidable along the extending direction of the extending portion 62 and is held by the guide member 17 in a state where it is prevented from coming off the guide member 17. In this example, the through grooves 52 are provided at two locations in the width direction on the first base member 11 side from the center in the extension direction of the extending portion 62 of the third base member 13, and at one location in the center in the width direction on the connecting member 30 side. In this embodiment, the screw 66a and the screw hole 68 corresponding to the through groove 52 in the center in the width direction on the connecting member 30 side are designed so that the third base member 13 can be fixed to the plate-like member 60 when the screw 66a is fully tightened. This prevents the third base member 13 from moving during transportation or until the optical fiber sensor 1 is fixed to the object to be measured, and prevents the second base member 12 from moving in conjunction with the movement of the third base member 13. From the perspective of preventing the second base member 12 from moving, for example, a configuration may be adopted in which the screw 65 and the screw hole 67 corresponding to the through groove 42 in the center in the width direction on the third base member 13 side can fix the second base member 12 to the plate-like member 60 when the screw 65 is fully tightened.

[0031] Furthermore, the end portion of the third base member 13 on the tip side of the extending portion 62 protrudes outward beyond the extending portion 62. A through groove 53 is formed in the protruding portion along the width direction, and the above-mentioned connecting member 30 is connected to the through groove 53.

[0032] The first base member 11 and the second base member 12 are connected by a first elastic body 15, and the second base member 12 and the third base member 13 are connected by a second elastic body 16. In this embodiment, the first elastic body 15 has a larger elastic constant than the second elastic body 16. As described above, in this embodiment, the first elastic body 15 is formed as a meandering plate-like member integrally formed with the first base member 11 and the second base member 12. The second elastic body 16 is formed as a detachable helical spring. Any known configuration can be used for the detachable configuration. In this embodiment, the second elastic body 16 is detachably attached to the second base member 12 and the third base member 13 with bolts and nuts. This configuration allows the elastic constant (spring constant) of the second elastic body 16 to be selected arbitrarily, thereby allowing the ratio of the elastic constants of the first elastic body 15 and the second elastic body 16 to be adjusted arbitrarily. The first elastic body 15 generates a biasing force in a direction that brings the first base member 11 and the second base member 12 closer together when the gap between them widens. Similarly, the second elastic body 16 generates a biasing force in a direction that brings the second base member 12 and the third base member 13 closer together when the gap between them widens.

[0033] Next, the optical fiber 14 including the FBG portion 18 will be described. Fig. 4 is a bottom view (viewed from the guide member 17 side) showing the first base member 11, the second base member 12, and the first elastic body 15. The optical fiber 14 includes an FBG (Fiber Bragg Grating) portion 18 whose Bragg wavelength varies depending on the distance between the first base member 11 and the second base member 12.

[0034] As shown in FIG. 4 , the optical fiber 14 including the FBG section 18 is arranged across the first base member 11 and the second base member 12, with the optical fiber 14 on both sides of the FBG section 18 fixed to each of the first base member 11 and the second base member 12 with a fixing material 71 such as an adhesive. In this embodiment, grooves 33 and 43 with a depth slightly greater than the outer diameter of the optical fiber 14 are formed in the first base member 11 and the second base member 12 at positions where the optical fiber 14 will be arranged. In this embodiment, the groove 33 is composed of two parallel grooves, and the groove 43 is composed of a hairpin-shaped groove in which two parallel grooves corresponding to the groove 33 are connected by an arc. The optical fiber 14 is arranged on each of the first base member 11 and the second base member 12 while being accommodated in the grooves 33 and 43. The grooves 33 and 43 at the positions where the fixing material 71 will be arranged are formed wide, so that the fixing material 71 is also accommodated in the grooves 33 and 43. As described above, the optical fiber 14 is drawn out to the outside through the central tubular body 64 and one of the other tubular bodies 64 of the three tubular bodies 64 provided at the base 61 of the guide member 17.

[0035] 4, the portion of the optical fiber 14 including the FBG portion 18 is arranged linearly. The movement direction of the second base member 12, which is restricted by the guide member 17, is the axial direction of the linearly arranged optical fiber 14. Therefore, the movement direction of the third base member 13, which is restricted by the guide member 17, is also the axial direction of the linearly arranged optical fiber 14 (FBG portion 18).

[0036] In the above configuration, the first base member 11, the second base member 12, and the optical fiber 14 constitute a strain gauge, and when the second base member 12 moves relative to the first base member 11, the movement is output as a variation in the Bragg wavelength. The variation in the Bragg wavelength can be obtained by a conventional method using a measuring instrument connected to the end of the optical fiber 14.

[0037] The FBG section 18 reflects light of a wavelength defined by the Bragg wavelength. The FBG section 18 is composed of a plurality of diffraction gratings arranged at a predetermined interval in the core of the optical fiber 14, and the Bragg wavelength is proportional to the product of the refractive index of the optical fiber and the arrangement interval of the diffraction gratings. Therefore, when the FBG section 18 is pulled and the interval between the diffraction gratings increases, the wavelength of the light reflected by the FBG section 18 increases. In other words, the wavelength of the light reflected by the FBG section 18 varies depending on the interval between the second base member 12 and the first base member 11, and is greater when the second base member 12 is farther away from the first base member 11 than when the second base member 12 is closer to the first base member 11. The wavelength of the light becomes larger. In the drawing, the FBG section 18 (and the FBG section 19 described later) are represented by a black and white striped pattern for the sake of convenience.

[0038] Although not particularly limited, in this embodiment, the optical fiber 14 includes a temperature-compensating FBG section 19. As described above, the Bragg wavelength is determined by the refractive index of the optical fiber and the grating spacing of the diffraction grating. Therefore, the Bragg wavelength also varies due to fluctuations in the refractive index when the temperature changes and expansion and contraction of the optical fiber. As shown in FIG. 4, the temperature-compensating FBG section 19 is fixed to the first base member 11. In the optical fiber 14, the FBG section 19 and the FBG section 18 are formed adjacent to each other. Here, the Bragg wavelength of the FBG section 19 and the Bragg wavelength of the FBG section 18 are made different. This configuration can be realized, for example, by forming FBG sections having the same Bragg wavelength adjacent to each other on the same optical fiber 14, and by making the pretension applied to the FBG section 19 and the pretension applied to the FBG section 18 different when fixing the optical fiber 14 to the first base member 11 with a fixing material 71.

[0039] Although not particularly limited, in this embodiment, pretension is applied to the FBG unit 18 and the FBG unit 19 as follows. First, the optical fiber 14 is fixed to the first base member 11 and the second base member 12 by the fixing material 71. At this time, a desired pretension is applied to the FBG unit 19, and in this state, the optical fibers 14 on both sides of the FBG unit 19 are fixed to the first base member 11. Furthermore, the optical fibers 14 on both sides of the FBG unit 19 are fixed to the first base member 11 and the second base member 12 without pretension being applied to the FBG unit 18. Next, the first base member 11 and the second base member 12 to which the optical fibers 14 are fixed, and the third base member 13 are attached to the guide member 17. Furthermore, the second elastic body 16 is also connected to the second base member 12 and the third base member 13. At this time, the second base member 12 and the third base member 13 are in the slidable state described above. In this state, the third base member 13 is moved in a direction away from the second base member 12, and the desired pretension is applied to the FBG unit 18. In this state, the screw 66a is tightened to fix the third base member 13 to the guide member 17, and the state in which the desired pretension is applied to the FBG unit 18 is maintained.

[0040] In this configuration, when the refractive index of the optical fiber 14 fluctuates and expands due to a temperature change, the Bragg wavelength of the FBG unit 18 for detecting the change in the distance between the second base member 12 and the first base member 11 and the Bragg wavelength of the temperature-compensating FBG unit 19 both shift in an increasing direction. On the other hand, when only the distance between the second base member 12 and the first base member 11 fluctuates, only the Bragg wavelength of the FBG unit 18 shifts, and no change occurs in the temperature-compensating FBG unit 19, so the Bragg wavelength of the FBG unit 19 does not fluctuate. In other words, the Bragg wavelength of the FBG unit 18 is subject to a wavelength shift in response to temperature change and a wavelength shift in response to the change in the distance between the second base member 12 and the first base member 11, which are superimposed on each other, and the Bragg wavelength of the FBG unit 19 is subject to only a wavelength shift in response to temperature change. Therefore, temperature compensation can be achieved by measuring the amount of shift in the Bragg wavelength of the FBG unit 18 and the amount of shift in the Bragg wavelength of the FBG unit 19.

[0041] Next, the operation of the optical fiber sensor 1 according to this embodiment will be described. Fig. 5 is an explanatory diagram showing the operation of the optical fiber sensor 1. For the sake of explanation, Fig. 5 only shows the first base member 11, the second base member 12, the third base member 13, the first elastic body 15, and the second elastic body 16. In the optical fiber sensor 1, the ratio between the elastic constant of the first elastic body 15 and the elastic constant of the second elastic body 16 can be changed as appropriate depending on the application.

[0042] As described above, in this embodiment, the elastic constant of the first elastic body 15 is greater than the elastic constant of the second elastic body 16. For the sake of explanation, it is assumed here that the elastic constant of the first elastic body 15 is greater than the elastic constant of the second elastic body 16. Assume that the ratio of the elastic constant of the second elastic body 16 to the elastic constant of the first elastic body 16 is 10 times the elastic constant of the second elastic body 16. When a tensile force is applied by the connecting member 30, in this example, the elongation amount Y of the second elastic body 16 becomes 10 times the elongation amount X of the first elastic body 15. For example, if the elongation amount Y of the second elastic body 16 is 100 micrometers when a tensile force is applied by the connecting member 30, the elongation amount X of the first elastic body 15 becomes 10 micrometers. Therefore, with this configuration, the displacement amount of the third base member 13 caused by the tensile force applied to the connecting member 30 can be reduced to within a range appropriate for measurement by the FBG unit 18 in accordance with the ratio of the elastic constant of the first elastic body 15 to the elastic constant of the second elastic body 16. As a result, the range (dynamic range) of the displacement amount of the third base member 13 that can be measured by the FBG unit 18 can be increased.

[0043] Furthermore, in this configuration, the magnitude of the pretension applied to the FBG unit 18 to detect strain in the compression direction, etc., can also be adjusted by the position of the third base member 13. As described above, in the optical fiber sensor 1, pretension is applied to the FBG unit 18 by moving the third base member 13 toward the connecting member 30. That is, the magnitude of the pretension applied to the FBG unit 18 (the amount of extension of the FBG unit 18) can be confirmed by the amount of displacement of the third base member 13 toward the connecting member 30 from the position of the third base member 13 when no tensile force is acting on the second elastic body 16 in the direction toward the connecting member 30. For example, if the elastic constant of the first elastic body 15 is 100 times the elastic constant of the second elastic body 16, a displacement amount that is 1 / 100 of the amount of displacement of the third base member 13 toward the connecting member 30 will be applied to the FBG unit 18. In this way, when the elastic constant of the first elastic body 15 is relatively large compared to the elastic constant of the second elastic body 16, it is also possible to visually check the magnitude of the pretension applied to the FBG unit 18. Therefore, it is possible to apply a desired pretension to the FBG unit 18 very easily. Note that the third base member 13 is fixed with the screws 66a in a pretensioned state, and the optical fiber sensor 1 is fixed to the object to be measured in this state; by releasing the fixing of the third base member 13 with the screws 66a after connecting the connecting member 30, it becomes possible to measure strain in a state in which the pretension is applied to the FBG unit 18.

[0044] FIG. 6 is a schematic diagram showing an example of the spectrum of reflected light (hereinafter referred to as the reflected light spectrum) when wide-bandwidth light including the Bragg wavelengths of the FBG sections 18 and 19 is incident on the optical fiber 14 in the optical fiber sensor 1. FIG. 6 is a schematic diagram showing fluctuations in the peak wavelength in the reflected light spectrum when strain occurs in the object to be measured between the main body 10 and the support 20 at a constant temperature. In FIG. 6, the horizontal axis corresponds to the wavelength of the reflected light, and the vertical axis corresponds to the intensity of the reflected light. In FIG. 6, the reflected light spectrum before fluctuations is shown by a dashed line.

[0045] As shown in FIG. 6 , the reflected light spectrum of the optical fiber sensor 1 before the change has peaks at the Bragg wavelength λ1 of the FBG unit 18 and the Bragg wavelength λ2 of the FBG unit 19. When strain occurs in the object to be measured between the main body 10 and the support 20 in a direction that widens the gap between the main body 10 and the support 20 while the temperature is constant, a displacement amount corresponding to the ratio of the elastic constant of the first elastic body 15 to the elastic constant of the second elastic body 16 is transmitted to the FBG unit 18, as described above. As a result, the Bragg wavelength of the FBG unit 18 shifts in an increasing direction. Since the Bragg wavelength of the temperature-compensating FBG unit 19 does not change, it can be understood that temperature compensation is not necessary (the temperature does not change). In this embodiment, the displacement amount due to the distortion of the object to be measured can be converted to a value within an appropriate range of displacement and transmitted to the FBG unit 18, thereby enabling the displacement due to the distortion of the object to be measured between the main body 10 and the support 20 to be appropriately measured. As is well known, the amount of displacement imparted to the FBG unit 18 can be calculated from the amount of change in the Bragg wavelength λ1 of the FBG unit 18. Therefore, the amount of displacement caused by the distortion of the object to be measured between the main body 10 and the support 20 can be calculated based on the amount of displacement of the FBG section 18 and the ratio of the elastic constant of the first elastic body 15 to the elastic constant of the second elastic body 16.

[0046] It is also possible to employ a configuration in which the elastic constant of the first elastic body 15 is smaller than the elastic constant of the second elastic body 16. For the sake of explanation, it is assumed here that the elastic constant of the first elastic body 15 is half the elastic constant of the second elastic body 16. When a tensile force is applied by the connecting member 30, in this example, the elongation amount Y of the second elastic body 16 becomes half the elongation amount X of the first elastic body 15. For example, if the elongation amount Y of the second elastic body 16 is 5 micrometers when a tensile force is applied by the connecting member 30, the elongation amount X of the first elastic body 15 becomes 10 micrometers. Therefore, with this configuration, the displacement amount of the third base member 13 caused by the tensile force applied to the connecting member 30 can be increased within a range appropriate for measurement by the FBG section 18 according to the ratio of the elastic constant of the first elastic body 15 to the elastic constant of the second elastic body 16. As a result, the displacement amount of the third base member 13 can be detected with high sensitivity.

[0047] When fixing the optical fiber sensor 1 described above to an object to be measured, the following procedure can be adopted, for example. First, the main body 10 and the support body 20 are fixed to the object to be measured. At this time, as described above, movement of the third base member 13 is prohibited by the screw 66a. In this state, the through groove 53 of the main body 10 and the annular portion 24a of the turnbuckle 24 of the support body 20 are set to face each other along the movement direction of the third base member 13.

[0048] Next, the connecting member 30 is attached to the through groove 53 of the main body 10, and the connecting member 30 is attached to the annular portion 24a of the turnbuckle 24 of the support body 20. Thereafter, the turnbuckle 24 is tightened to remove slack from the connecting member 30. Once the removal of slack from the connecting member 30 is complete, the fixation of the third base member 13 by the screw 66a is released. This puts the optical fiber sensor 1 in a state where it can measure strain between the main body 10 and the support body 20. Note that if the object to be measured is a building installed outdoors, it is preferable to install a cover or the like to cover the main body 10 to prevent dust and the like from entering the main body 10.

[0049] As described above, according to the present invention, the main body 10 and the support 20 are fixed to the object to be measured, and then the main body 10 and the support 20 are connected by the connecting member 30. This configuration allows for relatively easy installation even on relatively large objects to be measured, such as buildings. Furthermore, the device is not bulky during transportation, and the distance between the main body 10 and the support 20, which is the measurement range, can be adjusted at the work site. Furthermore, by adjusting the ratio of the elastic constants of the first elastic body 15 and the second elastic body 16, the ratio between the displacement of the object to be measured between the main body 10 and the support 20 and the displacement transmitted to the FBG unit 18 can be set very easily. Therefore, the displacement transmitted to the FBG unit 18 can be appropriately set depending on the material of the object to be measured and the size of the measurement range.

[0050] It should be noted that the above-described embodiments do not limit the technical scope of the present invention, and various modifications and applications other than those already described are possible within the scope of the present invention. For example, in the above-described embodiments, as a particularly preferred form, the FBG portion 18 of the optical fiber 14 is arranged linearly, and the second base member 12 and the third base member 13 move along the axial direction of the FBG portion 18. However, as long as the movement direction of the second base member 12 and the third base member 13 is a specific direction, it is not essential that the axial direction of the FBG portion 18 and the movement direction of the second base member 12 and the third base member 13 coincide with each other.

[0051] In addition, in the above-described embodiment, only the second elastic body 16 is configured to be detachable, but a configuration may be adopted in which the first elastic body 15 is also detachable, or a configuration in which neither the first elastic body 15 nor the second elastic body 16 is detachable. In a configuration in which the first elastic body 15 is detachable, the first base member 11 and the guide member 17 do not need to be separate members, and a configuration in which the guide member 17 also serves as the first base member 11 can be adopted. Furthermore, in the above-described embodiment, the optical fiber 14 is configured to include an FBG section 19 for temperature compensation, but the optical fiber 1 It is not essential that the optical fiber 4 includes the FBG section 19 for temperature compensation.

[0052] Furthermore, in the above embodiment, a configuration has been described in which pretension is applied to the FBG unit 18 by moving the third base member 13. However, it is also possible to employ a configuration in which the FBG unit 18, to which a desired pretension has been applied, is attached to the guide member 17. Specifically, for example, the following procedure can be employed. A desired pretension is applied to the FBG unit 18 in a state in which a jig or the like is used to fix the distance between the first base member 11 and the second base member 12 to a predetermined distance. In this state, the optical fibers 14 on both sides of the FBG unit 18 are fixed to the first base member 11 and the second base member 12. Then, with the distance between the first base member 11 and the second base member 12 fixed by the jig, the first base member 11 and the second base member 12 are attached to the guide member 17.

[0053] In addition, the physical shape and material of each of the above-mentioned elements, such as the first base member 11, the second base member 12, the third base member 13, the first elastic body 15, the second elastic body 16, and the guide member 17, can be changed as desired within the scope of the effects of the present invention. [Industrial Applicability]

[0054] According to the present invention, the optical fiber sensor can be attached relatively easily to a relatively large object to be measured such as a building, and can detect deformation over a relatively wide range with one FBG, making it useful as an optical fiber sensor. [Explanation of symbols]

[0055] 1. Optical fiber sensor 10 Main Unit 11 First base member 12 second base member 13 Third base member 14 Optical Fiber 15 First Elastic Body 16 Second Elastic Body 17 Guide member 18 FBG section 19 FBG section (for temperature compensation) 20 Support 30 Connecting member

Claims

1. a main body and a support body separate from the main body that are fixed to the object to be measured; and a connecting member that connects the main body and the support body without contacting the object to be measured, The body comprises: a first base member; a second base member disposed movably relative to the first base member; an optical fiber fixed to the first base member and the second base member, the optical fiber including an FBG (Fiber Bragg Grating) portion whose Bragg wavelength varies depending on the distance between the first base member and the second base member; a third base member that is movably disposed relative to the first base member and the second base member and to which the connecting member is connected; a first elastic body connecting the first base member and the second base member; a second elastic body connecting the second base member and the third base member; a guide member that restricts the movement direction of the second base member and the third base member relative to the first base member to a specific direction; Equipped with The optical fiber sensor has the first base member fixed to the guide member, and the guide member fixed to the object to be measured.

2. a main body and a support body separate from the main body that are fixed to the object to be measured; and a connecting member that connects the main body and the support body without contacting the object to be measured, The body comprises: a first base member; a second base member disposed movably relative to the first base member; an optical fiber fixed to the first base member and the second base member, the optical fiber including an FBG (Fiber Bragg Grating) portion whose Bragg wavelength varies depending on the distance between the first base member and the second base member; a third base member that is movably disposed relative to the first base member and the second base member and to which the connecting member is connected; a first elastic body connecting the first base member and the second base member; a second elastic body connecting the second base member and the third base member; a guide member that restricts the movement direction of the second base member and the third base member relative to the first base member to a specific direction; Equipped with The optical fiber sensor has a guide member that also serves as the first base member, and the guide member is fixed to the object to be measured.

3. 3. The optical fiber sensor according to claim 1, wherein a portion of the optical fiber including the FBG portion is linearly arranged, and the guide member restricts the movement direction of the second base member and the third base member to an axial direction of the linearly arranged optical fiber.

4. 4. The optical fiber sensor according to claim 1, wherein the first elastic body or the second elastic body is provided in a detachable state.

5. 5. The optical fiber sensor according to claim 1, wherein the first base member, the second base member, the third base member, and the guide member are formed of plate-like members.

6. 6. The optical fiber sensor according to claim 1, wherein the elastic constant of the first elastic body is greater than the elastic constant of the second elastic body.

7. 6. The optical fiber sensor according to claim 1, wherein the elastic constant of the first elastic body is smaller than the elastic constant of the second elastic body.

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