JP4366403B2 - Strain sensor and strain detection system - Google Patents

Description

  The present invention relates to a strain sensor and a strain detection system for detecting strain generated in a detected portion.

  In daily maintenance management of structures, visual inspection by visually observing the appearance is widely performed. Visual inspection is performed for the purpose of early detection of damage and deterioration of the structure and confirmation of the progress of deterioration, but damage such as cracking, floating, water leakage, subsidence, deformation, and discoloration occurs in the structure. Since it is often inspected after a certain amount of time, not immediately after it has been done, it is difficult to say that it is an essential maintenance.

  On the other hand, a strain sensor shown in FIG. 13 is conventionally known as a strain sensor for detecting strain generated in a structure (see, for example, Patent Document 1).

  A strain sensor 101 disclosed in Patent Document 1 is a portion obtained by fixing a part 102a in the middle of one optical fiber 102 to an object to be detected (object to be detected in a strain state) 110 and excluding the part 102a. 102 b is covered with a protective member 103, one end is connected to the light source 104, and the other end is connected to the light receiving unit 105. The optical fiber fixing portion 102 is fixed to the detected object 110 with an adhesive (not shown), and the portion of the detected object 110 where the optical fiber fixing portion 102 is fixed becomes the detected portion 110 a of the strain sensor 101.

  Further, in the strain sensor 101, when the detected object 110 is damaged at the detected part 110a, the optical fiber 102 is damaged at the optical fiber fixing part 102a, while the detected object 110 is a part other than the detected part 110a. The optical fiber 102 is formed so as not to be damaged at the optical fiber fixing portion 102 when it is damaged at 110b.

  According to the strain sensor 101, if the transmitted light cannot be detected by detecting the presence or absence of transmitted light from the light source 104 that has passed through the optical fiber 102, the damaged portion of the detected object 110 is detected. On the other hand, if the transmitted light can be detected by the detection unit 110a, it is determined that the damaged part of the detected object 110 is a part 110b other than the detected part 110a, or the detected object 110 is not damaged. The

However, when the strain sensor 101 is fixed to the detected object 110, the operator fixes the optical fiber fixing portion 102 to the detected object 110 while taking care not to damage the optical fiber 102. There is an inconvenience that the work of fixing the strain sensor 101 is complicated. In addition, since the magnitude of the strain detected by the strain sensor 101, that is, the magnitude of the strain that causes the optical fiber 102 to break, depends on the strength of the optical fiber 102, the strength of the adhesive, and the like. It is inconvenient that it is difficult to manage the desired value.
JP 2002-48676 A

  The present invention eliminates such inconvenience, can be easily fixed to a detected object to detect the strain state, and can easily manage the magnitude of the detected strain to a desired value. It is an object to provide a strain sensor and a strain detection system.

  In order to achieve such an object, a strain sensor of the present invention includes an optical fiber into which visible light is introduced, and a rigid tube that is extrapolated to the optical fiber so as to cover a part of the optical fiber. And the tube has an opening formed by cutting out a part of the peripheral wall portion of the inner peripheral surface and the outer peripheral surface of the optical fiber, and the opening portion is When the outer peripheral surface of the tube is fixed to the detected portion, the stress generated according to the strain generated in the detected portion is concentrated at the opening portion, and the strain exceeds a predetermined value. Further, the optical fiber is formed so as to be broken at the opening portion by the concentration of the stress. A to-be-detected part is a site | part which is going to detect a distortion state.

  In the strain sensor according to the present invention, when visible light is introduced from one end of the optical fiber in a state where the outer peripheral surface of the tube is fixed to the detected portion, the strain is not generated in the detected portion. Since the optical fiber is not broken, the visible light introduced into the optical fiber does not leak at the opening portion and reaches the other end from one end of the optical fiber.

  However, when a strain occurs in the detected portion, a part of the peripheral wall portion of the tube is cut out by the opening, and stress generated according to the strain concentrates on the opening of the tube. . In addition, since the inner peripheral surface of the tube and the outer peripheral surface of the optical fiber are bonded, the stress generated according to the strain is concentrated on the opening portion of the optical fiber. And if the distortion which arose in the said to-be-detected part exceeds predetermined value, the said optical fiber will fracture | rupture in this opening part location by the stress concentrated on the opening part location of this optical fiber. Due to this breakage, the visible light introduced into the optical fiber leaks outside from the opening portion and cannot reach the other end. At this time, when the strain sensor is viewed from the outside, light emission is confirmed at the opening portion of the optical fiber by visible light leaking from the opening portion to the outside. Then, by visually confirming this light emission from the outside of the strain sensor, it is possible to detect that a strain having a magnitude exceeding the predetermined value has occurred in the detected portion.

  Further, since the strain sensor only needs to be fixed to the detected object so that the outer peripheral surface of the tube is fixed to the detected portion, the operator can strain the optical fiber without damaging the optical fiber. The sensor can be easily fixed to the object to be detected. Furthermore, the strain sensor can easily manage the magnitude of strain detected by changing the size, shape, etc. of the opening of the tube, that is, the magnitude of strain at which the optical fiber breaks to a desired value. Can do.

  Therefore, according to the present invention, there is provided a strain sensor that can be easily fixed to an object to be detected for detecting a strain state and that can easily manage the magnitude of the detected strain to a desired value. Can be realized.

  In the strain sensor of the present invention, the tube may include a diaphragm structure on a side of the opening. By changing the size, shape, etc. of the diaphragm structure, the magnitude of the strain detected by the strain sensor can be easily managed to a desired value.

  In the strain sensor of the present invention, the tube may have a flat surface on the outer peripheral surface, and the flat surface may be fixed to face the detected portion. The strain sensor is attached to the detected part by spot welding the pipe to the detected part on the flat surface or by bonding the pipe to the detected part with an adhesive applied to the flat surface. It can be easily and firmly fixed.

  The strain sensor according to the present invention further includes a flexible substrate that is fixed to the outer peripheral surface of the tube between each of both ends of the tube and the opening, and the tube passes through the substrate. It may be fixed to the detected part. The strain sensor is easily fixed to the detected portion by spot welding the substrate to the detected portion or by bonding the substrate to the detected portion with an adhesive applied to the substrate. be able to. Further, since the substrate is fixed to the outer peripheral surface of the tube between each end of the tube and the opening, it does not prevent the stress generated according to the strain from concentrating on the opening. .

  The substrate may have a plurality of through holes penetrating in the thickness direction. Thereby, when the adhesive is applied to the surface opposite to the surface fixed to the tube of the substrate and the strain sensor is adhered to the detected portion, the adhesive enters the through hole and adheres to the surface. Since the force increases, the strain sensor can be firmly fixed to the detected portion.

  Furthermore, the strain detection system of the present invention includes one or more strain sensors of the present invention and a visible light source that introduces visible light from one end of an optical fiber of the strain sensor.

  According to the strain detection system of the present invention, a strain detection system that can be easily fixed to an object to be detected in the field and that can easily manage the magnitude of the detected strain to a desired value is realized. Can do.

  Moreover, the distortion which arose in the several location of the to-be-detected object is detectable by fixing multiple the strain detection system of this invention to the to-be-detected object.

  Furthermore, the strain detection system of the present invention comprises a plurality of strain sensors of the present invention, one end of the optical fiber of each strain sensor is provided close to each other, and at least visible light from the one end of the optical fiber of each strain sensor. It is possible to introduce.

  According to the strain detection system of the present invention, the introduction of visible light to a plurality of strain sensors can be performed at one place where the one ends of the optical fibers are close to each other.

  In addition, the strain detection system of the present invention includes a plurality of strain sensors of the present invention, and one optical fiber is shared as an optical fiber of each of the strain sensors, and each strain sensor tube includes the one light. It is provided with an interval in the longitudinal direction of the fiber, and visible light can be introduced from one of both ends of the one optical fiber.

  According to the strain detection system of the present invention, since the one optical fiber is used as the optical fiber of the strain sensor, an inexpensive system can be realized.

  In this case, when visible light is introduced from one of both ends of the one optical fiber, if one optical fiber breaks at the opening portion of any one of the strain sensors, the fracture occurs. Visible light cannot be made to reach other strain sensors existing on the downstream side of the spot. In this case, the visible light can be made to reach the other strain sensor by introducing the visible light not from one end of the one optical fiber but from the other end.

  At this time, the one optical fiber may be extended so that both ends thereof are close to each other. In order to introduce visible light from the other end of the one optical fiber, a visible light source connected to one of the ends of the one optical fiber is connected to both ends of the one optical fiber. When switching to be connected to the other of the two, both ends of the one optical fiber are close to each other, so there is almost no need to change the installation location of the visible light source, simplifying the work at the site can do.

  In addition, the strain detection system of the present invention includes the strain sensor of the present invention, an optical coupler for branching that includes an input unit and a plurality of output units, and one end of the optical fiber of the strain sensor is connected to one output unit. An optical coupler for merging having a plurality of input units and an output unit, the other end of the optical fiber of the strain sensor being connected to one input unit, another output unit of the branching optical coupler, and the A plurality of sets each having a bypass optical fiber having both ends connected to the other input section of the confluence optical coupler, wherein the plurality of sets is the one of the two sets adjacent to each other. The output unit of the converging optical coupler and the input unit of the other set of branching optical couplers are connected in series by connecting with a connecting optical fiber, and the plurality of sets connected in series Of characterized by being capable introduce visible light from the input of the branching optical coupler set which exists at one end of the.

  The branching optical coupler is a part for branching one optical path into a plurality of optical paths, and the joining optical coupler is a part for joining a plurality of optical paths into one optical path.

  Visible light input to one set of branching optical couplers of the two adjacent sets is branched and output to a plurality of output units of the branching optical coupler. Visible light output from one output unit of the branching optical coupler reaches one input unit of the optical coupler of the one set of converging sensors via the optical fiber of the one set of strain sensors. On the other hand, the visible light output from the other output unit of the branching optical coupler reaches the other input unit of the merging optical coupler via the one bypass optical fiber. The visible lights that have reached the merging optical coupler are merged, and reach the input of the branching optical coupler of the other set of the two adjacent sets via the coupling optical fiber.

  At this time, when the optical fiber of any one of the set strain sensors is broken, the visible light input to the optical coupler for branching of the set is merged through the bypass optical fiber of the set. A branch of a set that reaches the optical coupler for the optical fiber, reaches the optical coupler for branching of the other set of the two adjacent sets, and is adjacent to the set in which the optical fiber is broken through the optical fiber for connection The optical coupler is reached. As a result, the visible light can be made to reach another set of strain sensors existing on the downstream side of the set having the strain sensor in which the optical fiber is broken. Therefore, according to the strain detection system of the present invention, visible light can reach other strain sensors even when the optical fiber of any one of the strain sensors is broken.

  The strain detection system according to the present invention includes a plurality of strain sensors according to the present invention, a plurality of branching optical couplers having an input unit and a plurality of output units, and distributed visible light from the plurality of output units. Each of the output sections of the branching optical coupler is connected to an input section of each of the branching optical couplers by a connecting optical fiber. The strain sensor is connected to one end of an optical fiber of each strain sensor.

  In the strain detection system of the present invention, the visible light input to the light distribution and supply unit reaches the branching optical coupler from each output unit of the light distribution and supply unit via the connection optical fiber, and the branching is performed. It is introduced into the optical fiber of each strain sensor from each output portion of the optical coupler. At this time, the visible light that reaches one of the strain sensors does not pass through the optical fiber of the other strain sensor.

  Therefore, even when the optical fiber of any one of the strain sensors is broken, visible light can reach the optical fiber of another strain sensor. Further, by increasing the number of output units of the light distribution and supply means, the total number of strain sensors connected to the output unit via the branching optical coupler can be increased.

  The optical distribution and supply means is configured using, for example, one or more branching optical couplers.

  The strain detection system of the present invention includes a plurality of strain sensors of the present invention and an optical switch that selectively outputs input visible light from a plurality of output units, and the optical switch includes each output unit. One end of an optical fiber of each of the strain sensors is connected to each other.

  In the strain detection system of the present invention, the light input to the optical switch is selectively introduced into the optical fiber of the strain sensor connected to each output unit of the optical switch. At this time, the visible light that reaches one of the strain sensors does not pass through the optical fiber of the other strain sensor.

  Therefore, even when the optical fiber of any one of the strain sensors is broken, visible light can reach the optical fiber of the other strain sensor.

  Further, since the optical fiber of the strain sensor is directly connected to the optical switch, the connection work at the site is easy.

  In addition, by increasing the number of output units of the optical switch, the total number of strain sensors connected to the output unit can be increased.

  Further, the other end of the optical fiber of each strain sensor may be provided at a position visible from the outside. Strain can be detected by checking the presence or absence of light emission at the other end of the optical fiber instead of checking the presence or absence of light emission at the opening portion of the optical fiber. At this time, the presence or absence of light emission can be efficiently confirmed by concentrating the other ends of the optical fibers.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a system configuration diagram illustrating a configuration example of a strain detection system including the strain sensor according to the first embodiment. FIG. 2 is an explanatory view showing the configuration of the strain sensor of the first embodiment shown in FIG. 1, FIG. 2 (a) is a plan view, FIG. 2 (b) is a side view, and FIG. 2 (c) is AA. It is an expanded sectional view. FIG. 3 is an explanatory view showing the operation of the strain sensor of the first embodiment. FIG. 4 is an explanatory view showing a configuration of a modification of the strain sensor of the first embodiment shown in FIG. 1, FIG. 4 (a) is an explanatory view showing a first modification, and FIG. 4 (b) is a second modification. It is explanatory drawing which shows an example. 5A and 5B are explanatory views showing the configuration of the strain sensor of the second embodiment. FIG. 5A is a perspective view, FIG. 5B is a plan view, and FIG. 5C is a side view. FIG. 6 is an explanatory side view showing an example of the opening of the tube of the strain sensor of the present embodiment, and FIG. 7 is an explanatory plan view showing an example of the throttle structure of the tube of the strain sensor of the present embodiment. 8 to 10 are system configuration diagrams showing the strain detection system of the present embodiment. FIG. 11 is an explanatory view of attachment of the strain detection system of the present embodiment, and FIG. 12 is a system configuration diagram showing a modification of the strain detection system of the present embodiment.

  A strain detection system 1 shown in FIG. 1 includes a strain sensor 2 according to the first embodiment and a visible light source 3. The strain sensor 2 is fixed to a part of the detected object 4 which is a structure such as a bridge, a column, a beam, or a wall. The visible light source 3 may be provided near the strain sensor 2, may be provided at a location away from the strain sensor 2, or is provided only when inspecting for the presence or absence of strain. May be.

  The strain sensor 2 includes an optical fiber 5 connected at one end to a visible light source 3 and introduced with visible light, a tube 6 extrapolated to the optical fiber 5 so as to cover a part of the optical fiber 5, And a pair of substrates 7 and 7 fixed to the outer peripheral surface.

  The optical fiber 5 is a general communication optical fiber having a core diameter of 50 μm and a coating diameter of 250 μm, for example. One end of the optical fiber 5 is connected to the visible light source 3 via the connector 8, and the portion between the connector 8 and the tube 6 has a flexible synthetic resin having an outer diameter of 600 μm and an inner diameter of 400 μm, for example. It is covered with a protective tube 9 made of metal.

  The tube 6 is a stainless steel rigid tube having an outer diameter of 1.2 mm, an inner diameter of 1.0 mm, and a length of 28 mm, for example. The optical fiber 5 is inserted into the tube 6 and disposed at the lowermost part of the inner peripheral surface of the tube 6. The tube 6 is filled with an adhesive 10 made of a transparent material that allows visible light to pass therethrough. The outer peripheral surface of the optical fiber 5 is bonded to the inner peripheral surface of the tube 6 by an adhesive 10.

  Further, the tube 6 has an opening 11 near the center in the longitudinal direction. As shown in FIG. 2C, the opening 11 is formed by cutting out, for example, a depth of 0.2 mm from the uppermost end of the outer peripheral surface of the tube 6 by a plane parallel to the substrate 7. The plan view shape of the opening 11 is a rectangular shape having a length of 8 mm and a width of 0.6 mm as shown in FIG. Moreover, the side view shape of the opening 11 is also a rectangular shape having a length of 8 mm and a depth of 0.2 mm as shown in FIG. When the inside of the tube 6 is viewed from the opening 11, the optical fiber 5 can be visually recognized through the adhesive 10.

  The pipe | tube 6 which has the opening part 11 is produced as follows, for example. First, the tube 6 not having the opening 11 is formed, and the optical fiber 5 is inserted through the tube 6 and disposed at the lowermost part of the inner peripheral surface of the tube 6. Next, the opening 11 is formed by cutting out the peripheral wall portion of the tube 6. Next, the adhesive 10 is poured into the tube 6 from the opening 11 in a state where both ends of the tube 6 are closed, and the tube 6 is filled. Next, air bubbles remaining in the adhesive 10 filled in the tube 6 are discharged by evacuation. The inside of the tube 6 is filled with the adhesive 10 by repeating the injection and vacuuming of the adhesive 10 a plurality of times. Finally, the adhesive 10 overflowing from the opening 11 is removed. Note that the optical fiber 5 may be inserted into the tube 6 after the opening 11 is formed in the tube 6.

  Each substrate 7 is a thin-film stainless steel plate having a thickness of 0.16 mm, for example, and has flexibility. Each substrate 7 has a length equal to the length from the end of the tube 6 to the end of the opening 11. The pair of substrates 7 and 7 are fixed to the outer peripheral surface of the tube 6 between each end of the tube 6 and the opening 11.

  The strain sensor 2 is fixed via the substrate 7 by spot welding the substrate 7 to a detected portion of the detected object 4 (a portion where the strain state is to be detected).

  The strain sensor 2 having the above-described configuration is configured so that when the strain generated in the detected portion of the detected object 4 exceeds a predetermined value by appropriately setting the size and shape of the opening 11, the opening The optical fiber 5 is formed to be broken by the stress concentrated at the 11 portions. This predetermined value is the minimum value of the strain necessary for the optical fiber 5 to break, and this is the size of the strain detected by the strain sensor 2. The strain sensor 2 of the first embodiment is formed such that the optical fiber 5 is broken when the strain of the detected portion is 5500 μm or more.

  As the visible light source 3, for example, an optical fiber conduction checker manufactured by NTT Advanced Technology Corporation can be used, and the visible light source 3 outputs red laser light (visible light).

  Next, the operation of the strain sensor 2 of the first embodiment configured as described above will be described. First, when the visible light source 3 is turned on, visible light from the visible light source 3 is introduced into the optical fiber 5 from one end. Since the optical fiber 5 is not broken in a state where the detection object 4 is not distorted, the visible light introduced into the optical fiber 5 reaches the other end without leaking at the eleven openings.

  Next, when a strain occurs in the detected portion of the detected object 4, the opening 11 of the tube 6 is notched so that the stress generated in the strain sensor 2 according to the strain is generated in the opening of the tube 6. Concentrate on 11 locations. Further, since the inner peripheral surface of the tube 6 and the outer peripheral surface of the optical fiber 5 are bonded, the stress generated according to this strain acts on the optical fiber 5. And if the distortion produced in the to-be-detected part of the to-be-detected object 4 exceeds 5500 micrometers, as shown in FIG. 3, the optical fiber 5 will be fractured | ruptured by the opening part 11 part with the stress which generate | occur | produced according to distortion. Due to this breakage, the visible light introduced into the optical fiber 5 leaks to the outside through the opening 11 and cannot reach the other end. When the strain sensor 2 is viewed from the outside, light emission 13 is confirmed at the 11 openings of the optical fiber 5 by visible light leaking from the 11 openings.

  By visually confirming the light emission 13, it is possible to detect that a strain having a magnitude of 5500 μ or more has occurred in the detected portion where the strain sensor 2 of the detected object 4 is fixed.

  According to the strain sensor 2, unlike the strain sensor 101 of the prior art, the optical fiber 5 is covered with the tube 6 and fixed to the detected object 4 via the substrate 7 fixed to the outer peripheral surface of the tube 6. Therefore, the operator can easily fix the strain sensor 2 to the detected object 4 without damaging the optical fiber 5. Furthermore, according to the strain sensor 2, the magnitude of the strain detected by changing the size, shape, etc. of the opening 11, that is, the magnitude of the strain at which the optical fiber 5 breaks can be easily managed to a desired value. be able to.

  The tube 6 and the substrate 7 of the strain sensor 2 are preferably made of a metal having excellent corrosion resistance, and examples include Inconel (registered trademark) in addition to stainless steel.

  Further, the strain sensor 2 is fixed to the detected object 4 by spot welding the substrate 7, but is opposite to the surface fixed to the tube 6 of the substrate 7 instead of spot welding. Alternatively, an adhesive (not shown) may be applied to the surface, and the strain sensor 2 may be adhered to the object 4 to be fixed. At this time, the substrate 7 preferably has a plurality of through holes 14 penetrating in the thickness direction as shown in FIG. As a result, the adhesive enters the through hole 14 and the adhesive force increases, so that the strain sensor 2 can be firmly fixed to the detected portion 4.

  Further, although the strain sensor 2 has the tube 6 fixed to the detected object 4 via the substrate 7, the tube 6 may be fixed directly to the detected object 4. At this time, it is preferable to fix the strain sensor 2 so that the opening 11 of the tube 6 is in a direction opposite to the detected object 4 so that the optical fiber 5 can be visually recognized from the outside of the strain sensor 2. As described above, when the tube 6 is directly fixed to the detected object 4, the surface of the tube 6 facing the detected object 4 (surface fixed to the detected object 4) is a flat surface. Is preferred. For example, as shown in FIG. 4B, in the case of the tube 6 having a semicircular cross-sectional shape, the surface facing the object to be detected 4 is flat compared to the case of the circular tube 6. Since it is a surface, spot welding to the detected object 4 on this surface and adhesion to the detected object 4 by the adhesive applied to this surface are easy, and the tube 6 is firmly attached to the detected object 4. Can be fixed.

  Furthermore, by changing the size of the opening 11 of the strain sensor 2, the size of the strain detected by the strain sensor 2 can be easily managed to a desired value.

  For example, the strain sensor 20 of the second embodiment shown in FIG. 5 is obtained by changing the size of the opening 11 of the strain sensor 2 of the first embodiment. The opening 11 of the strain sensor 20 is formed by cutting out the upper half of the outer peripheral surface of the tube 6 by a plane parallel to the substrate 7, that is, a depth of 0.6 mm from the uppermost end of the outer peripheral surface of the tube 6. The planar view shape of the part 11 is a rectangular shape having a length of 1.5 mm and a width of 1 mm as shown in FIG. By forming in this way, the magnitude of the strain detected by the strain sensor 20 of the second embodiment is 2400 μm.

  Further, by changing the size and shape of the opening 11 of the tube 6 or providing a diaphragm structure in the vicinity of the opening 11 of the tube 6, the magnitude of the strain detected by the strain sensors 2 and 20 can be reduced. It is also possible to manage.

  For example, as shown in FIG. 6 (a), when the side surface is cut out in a rectangular shape as in FIG. 1, the opening depth D of the opening 11 is increased and the opening length L is decreased. As a result, the stress is easily concentrated at the 11 positions of the opening of the tube 6, and the magnitude of the strain to be detected is reduced. Further, as shown in FIG. 6B, the opening 11 may be cut out in a semicircular shape in a side view. In this case, increasing the opening radius R of the opening 11 makes it easier for stress to concentrate on the opening 11 of the tube 6. Further, for example, as shown in FIG. 6C, the side surface shape may be cut into a triangular shape. In this case, by increasing the opening depth D of the opening 11 and decreasing the opening length L, stress is easily concentrated on the opening 11 of the tube 6. In the actual machine, considering the ease of processing, the opening 11 preferably has the shape of FIG.

  Further, for example, as shown in FIG. 7A, a planar semi-circular diaphragm structure (recessed portion) 15 may be provided on the side of the opening 11 of the tube 6. In this case, increasing the aperture radius R of the aperture structure 15 makes it easier for stress to concentrate on the opening 11 of the tube 6. Further, for example, a planar diaphragm structure 15 may be provided as shown in FIG. 7B, or a planar diaphragm structure 15 may be provided, for example, as shown in FIG. 7C. . In this case, by increasing the aperture width W of the aperture structure 15 and decreasing the aperture length L, stress is easily concentrated on the opening 11 of the tube 6. In the actual machine, the diaphragm structure 15 preferably has the shape shown in FIG.

  Next, an example of a system that detects strains of a plurality of detected parts using a plurality of strain sensors will be described.

  First, FIG. 8A shows a plurality of strain detection systems 1 shown in FIG. Visible light sources 3 of each strain detection system 1 are arranged close to each other and can be operated at one place. The optical fibers 5 of each strain detection system 1 are formed so as to have different lengths, and each strain sensor 2 can be fixed to each detected portion.

  At this time, the visible light source 3 may be detachably connected to one end of the optical fiber 5 of the strain sensor 2, and one visible light source 3 may be provided in each strain detection system 1 in order. By doing in this way, introduction of visible light to a plurality of strain sensors 2 can be carried out by one visible light source 3.

  Further, at this time, one end of the optical fiber 5 of the strain sensor 2 of each strain detection system 1 is disposed close to each other, and one visible light source 3 is disposed at the close position, and visible from one end of each optical fiber 5. Light may be introduced. By doing in this way, introduction of visible light to a plurality of strain sensors 2 can be performed at one place where one ends of optical fibers 5 of each strain sensor 2 are close to each other.

  Moreover, the strain detection system 30 shown in FIG. 8B includes a plurality of strain sensors 2a to 2c, and a single optical fiber 5 is shared as the optical fibers of the strain sensors 2a to 2c. The tubes of the strain sensors 2a to 2c are provided at intervals in the longitudinal direction of the single optical fiber 5. The visible light source 3 is detachably connected to one end of one optical fiber 5 and can also be connected to the other end of one optical fiber 5 as necessary.

  Visible light is introduced into one optical fiber 5 from one end and reaches each of the strain sensors 2a to 2c. When the visible light source 3 is connected to the other end of the single optical fiber 5, the visible light is introduced into the single optical fiber 5 from the other end and reaches the strain sensors 2c to 2a.

  According to the strain detection system 30, since the single optical fiber 5 is used as the optical fiber of each of the strain sensors 2a to 2c, an inexpensive system can be realized.

  In this case, in a state where visible light is introduced from one end of one optical fiber 5, one optical fiber 5 is formed at 11 openings of any one strain sensor 2 (for example, strain sensor 2a). When rupture occurs, it becomes impossible to make visible light reach other strain sensors 2 (for example, strain sensors 2b and 2c) existing downstream from the broken portion. In this case, the visible light source 3 is moved to the vicinity of the other end of the single optical fiber 5 (the position of the one-dot chain line in the figure), and the other end of the single optical fiber 5 is connected to the visible light source 3. By introducing visible light from the other end of one optical fiber 5, it becomes possible to make visible light reach the other strain sensors 2 (strain sensors 2b, 2c).

  Further, the strain detection system 40 shown in FIG. 8C extends so that both ends of one optical fiber 5 of the strain detection system 30 are close to each other. The visible light source 3 introduces visible light from one end of one optical fiber 5. When one optical fiber 5 is broken at an opening 11 of any strain sensor 2 (for example, strain sensor 2a) and the other end of one optical fiber 5 is to be connected to the visible light source 3, Since both ends of the optical fiber 5 are close to each other, it is not necessary to change the installation location of the visible light source 3 and the work at the site can be simplified.

  Furthermore, the strain detection system 50 shown in FIG. 9 includes the strain sensor 2, the input unit 51, and a plurality of output units 52, and one end of the optical fiber 5 of the strain sensor 2 is connected to one output unit 52a. An optical coupler 53, a plurality of input sections 54 and an output section 55, and a merging optical coupler 56 in which the other end of the optical fiber 5 of the strain sensor 2 is connected to one input section 54a, and a branching optical coupler A plurality of sets 58 each including a bypass optical fiber 57 having both ends connected to the other output portion 52b of 53 and the other input portion 54b of the converging optical coupler 56 are provided. The branching optical coupler 53 is a part for branching one optical path into a plurality of optical paths, and the joining optical coupler 56 is a part for joining a plurality of optical paths into one optical path.

  Each set 58a to 58c includes the output unit 55 of the converging optical coupler 56 of one set 58 (for example, 58a) of two sets 58 (for example, the set 58a and the set 58b) adjacent to each other, and the other set 58. The input unit 51 of the branching optical coupler 53 (for example, 58b) is connected in series by being connected by a connecting optical fiber 59.

  The introduction optical fiber 60 connected to the visible light source 3 is connected to the input part 51 of the branching optical coupler 53 of the set 58 (for example, 58a) existing on one end side of the plurality of sets 58 connected in series. Has been.

  Visible light from the visible light source 3 is input to the branching optical coupler 53 of the set 58a existing on one end side of the plurality of sets 58 via the introduction optical fiber 60, and is output from one output unit 52a. The light branches into visible light and visible light output from the other output unit 58b. Visible light output from one output unit 58 a reaches one input unit 54 a of the merging optical coupler 56 via the optical fiber 5 of the strain sensor 2. On the other hand, the visible light output from the other output unit 58 b reaches the other input unit 54 b of the converging optical coupler 56 via the bypass optical fiber 57. The respective visible lights that have reached the joining optical coupler 56 join together and are input to the branching optical coupler 53 of the set 58b adjacent to the set 58a through the connecting optical fiber 59.

  Next, the visible light input to the branching optical coupler 53 of the set 58b reaches the converging optical coupler 56 in the same manner as the set 58a, and passes through the coupling optical fiber 59 to the adjacent set 58b. The signal is input to the branching optical coupler 53.

  Next, the visible light input to the branching optical coupler 53 of the set 58c reaches the converging optical coupler 56 in the same manner as the set 58a.

  At this time, for example, when the optical fiber 5a of the strain sensor 2a of the set 58a is broken, the visible light input to the branching optical coupler 53 of the set 58a is set via the bypass optical fiber 57 of the set 58a. It reaches the converging optical coupler 56 of 58a, and reaches the branching optical coupler 53 of the set 58b adjacent to the set 58a via the connecting optical fiber 59. As a result, visible light can be made to reach the strain sensors 2b and 2c of the other sets 58b and 58c existing on the downstream side of the set 58a having the strain sensor 2a in which the optical fiber 5a is broken. Therefore, according to the strain detection system 50, even when the optical fiber 5 of one of the strain sensors 2 is broken, visible light can reach the other strain sensors 2.

  10A includes a plurality of strain sensors 2a to 2d, a plurality of branching optical couplers 53a and 53b having an input unit 51 and a plurality of output units 52a and 52b, and an input unit 71. Light distribution supply means 73 for distributing and supplying visible light input from the plurality of output units 72a and 72b. Here, one optical coupler for branching is used as the optical distribution and supply means 73. However, depending on the number of strain sensors 2, one in which another branching optical coupler is connected to each output portion of the branching optical coupler via a coupling optical fiber may be used. Instead, an optical switch described later may be used.

  The input unit 71 of the light distribution and supply means 73 is connected to the visible light source 3 by an introduction optical fiber 60. On the other hand, the output units 72 a and 72 b of the light distribution and supply means 73 are connected to the input units 51 of the branching optical couplers 53 a and 53 b by a connecting optical fiber 59. The output unit 72a of each branching optical coupler 53a, 53b is connected to one end of the optical fiber 5a, 5b of each strain sensor 2a, 2b, and the output unit 72b of each branching optical coupler 53a, 53b is connected to each strain sensor 2c. , 2d are connected to one end of the optical fibers 5c, 5d.

  The visible light input from the visible light source 3 to the light distribution and supply means 73 is branched and output from the output units 72a and 72b, and input to the branching optical couplers 53a and 53b. Visible light input to the branching optical couplers 53a and 53b branches and reaches the strain sensors 2a to 2d via the optical fibers 5a to 5d. At this time, visible light reaching each strain sensor 2 (for example, strain sensor 2a) does not pass through optical fibers 5 (for example, optical fibers 5b to 5d) of other strain sensors 2 (for example, strain sensors 2b to 2d). .

  Therefore, even when the optical fiber 5 of one of the strain sensors 2 (for example, the optical fiber 5a of the strain sensor 2a) is broken, visible light can reach the other strain sensors 2 (for example, the strain sensors 2b to 2d). .

  Further, the configuration of the optical distribution and supply means 73 is changed to increase the number of output units 72. For example, by using an optical switch having ten output units as the optical distribution and supply unit 73, an optical coupler for branching is used in the output unit 72. It is possible to easily increase the total number of strain sensors 2 connected via the.

  10B includes a plurality of strain sensors 2a to 2d, and an optical switch 83 that selectively outputs visible light input from the input unit 81 from the plurality of output units 82a to 82d. Is provided.

  The input unit 83 of the optical switch 83 is connected to the visible light source 3 by the introduction optical fiber 60. On the other hand, each output part 82 and 82b of the optical switch 83 is connected to one end of the optical fibers 5a to 5d of the strain sensors 2a to 2d.

  The visible light input from the visible light source 3 to the optical switch 83 is branched and output from the output units 82a to 82d, and reaches the strain sensors 2a to 2d via the optical fibers 5a to 5d. At this time, visible light reaching each strain sensor 2 (for example, strain sensor 2a) does not pass through optical fibers 5 (for example, optical fibers 5b to 5d) of other strain sensors 2 (for example, strain sensors 2b to 2d). .

  Therefore, even when the optical fiber 5 of one of the strain sensors 2 (for example, the optical fiber 5a of the strain sensor 2a) is broken, the visible light reaches the other strain sensors 2 (for example, the strain sensors 2b to 2d) and the strain is reduced. Can be detected.

  Further, since the optical fiber 5 of the strain sensor 2 and the visible light source 3 are directly connected to the optical switch 83, connection work at the site is easy. Moreover, although the optical switch 83 which has the four output parts 82a-82d is used in the figure, the number of the strain sensors 2 to connect can be increased by using an optical switch with many output parts.

  The above strain detection systems 1, 30, 40, 50, 70, and 80 can be used for crack management in the bridge 90 as shown in FIG. Here, a case where the strain detection system 70 is used will be described. First, before inspecting the distortion, a plurality of branching optical couplers 53a to 53c are fixed to the upper part of the bridge beam 91, and the branching optical couplers 53b, 53c is connected. Further, a plurality of strain sensors 2a to 2d are fixed in a place where the distortion of the main girder 92 is likely to occur, for example, in the vicinity of the welded portion, and the optical fiber 5 of each of the strain sensors 2a to 2d Connect to output. It is desirable that a plurality of strain sensors 2 be fixed in the expected crack direction. Next, when inspecting the presence or absence of distortion, the visible light source 3 is provided below the bridge beam 91, the visible light source 3 and the branching optical coupler 53a are connected by the introducing optical fiber 60, and visible light is introduced. At this time, by observing the strain sensors 2a to 2d from the outside and confirming the presence or absence of light emission at the openings of the optical fibers 5a to 5d, a predetermined value is applied to the detected portions of the strain sensors 2a to 2d. It is possible to detect that a strain exceeding the magnitude has occurred.

  Moreover, it is also possible to detect a strain at a location that cannot be observed from the outside, such as the inside of a wall, using the strain detection systems 1, 70, 80 described above. Here, a case where the strain detection system 70 is used will be described. As shown in FIG. 12, the strain sensors 2a to 2d are fixed to the detected part in advance, and the other ends of the optical fibers 5a to 5d are led out from the outside, for example, outside the wall. deep. Then, instead of confirming the presence or absence of light emission at the openings of each of the optical fibers 2a to 2d, the strain can be detected by confirming the presence or absence of light emission at the other end of each of the optical fibers 2a to 2d. . At this time, the presence or absence of light emission can be efficiently confirmed by concentrating the other ends of the optical fibers 5a to 5d.

A system configuration figure showing an example of 1 composition of a strain sensing system provided with a strain sensor of a 1st embodiment. Explanatory drawing which shows the structure of the strain sensor of 1st Embodiment shown in FIG. Explanatory drawing which shows the action | operation of the strain sensor of 1st Embodiment. Explanatory drawing which shows the structure of the modification of the strain sensor of 1st Embodiment shown in FIG. Explanatory drawing which shows the structure of the strain sensor of 2nd Embodiment. Explanatory side view showing an example of the opening of the tube of the strain sensor of the present embodiment Explanatory top view which shows the example of the aperture | diaphragm | squeeze structure of the pipe | tube of the strain sensor of this embodiment. The system block diagram which shows the distortion | strain detection system of this embodiment. The system block diagram which shows the distortion | strain detection system of this embodiment. The system block diagram which shows the distortion | strain detection system of this embodiment. Installation explanatory drawing of the distortion | strain detection system of this embodiment. The system block diagram which shows the modification of the distortion | strain detection system of this embodiment. Explanatory drawing which shows the strain sensor of a prior art.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,30,40,50,70,80 ... Strain detection system, 2,20 ... Strain sensor, 3 ... Visible light source, 5 ... Optical fiber, One optical fiber, 6 ... Tube, 7 ... Substrate, 11 ... Opening 13: Light emission, 14 ... Through hole, 15 ... Aperture structure, 51 ... Input part of branching optical coupler, 52 ... Output part of branching optical coupler, 53 ... Optical coupler for branching, 54 ... Optical coupler for merging An input unit, 55: an output unit of an optical coupler for confluence, 56: an optical coupler for confluence, 72: an output unit of an optical distribution supply unit, 73: an optical distribution supply unit, 82: an output unit of an optical switch, 83: an optical switch.

Claims (13)

An optical fiber into which visible light is introduced;
A rigid tube extrapolated to the optical fiber so as to cover a part of the optical fiber,
The tube has an opening formed by cutting out a part of the peripheral wall portion thereof while the inner peripheral surface thereof is bonded to the outer peripheral surface of the optical fiber.
The opening portion concentrates stress generated according to the strain generated in the detected portion in the state where the outer peripheral surface of the tube is fixed to the detected portion, and the strain is predetermined. When the value is exceeded, the strain sensor is formed so as to break the optical fiber at the opening portion due to the concentration of the stress. The strain sensor according to claim 1,
The strain sensor according to claim 1, wherein the tube includes a diaphragm structure on a side of the opening. The strain sensor according to claim 1 or 2,
The strain sensor according to claim 1, wherein the tube has a flat surface on the outer peripheral surface, and is fixed with the flat surface facing the detected portion. In the strain sensor according to any one of claims 1 to 3,
Furthermore, the substrate is fixed to the outer peripheral surface of the tube between each of both ends of the tube and the opening, and has a flexible substrate,
The strain sensor is characterized in that the tube is fixed to the detected part via the substrate. The strain sensor according to claim 4,
The strain sensor has a plurality of through holes penetrating in a thickness direction.   A strain comprising one or more strain sensors according to any one of claims 1 to 5, and a visible light source for introducing visible light from one end of an optical fiber of the strain sensor. Detection system. A plurality of strain sensors according to any one of claims 1 to 5,
One end of each strain sensor optical fiber is provided close to each other,
Visible light can be introduced from at least one end of the optical fiber of each strain sensor. A plurality of strain sensors according to any one of claims 1 to 5,
As an optical fiber for each of the strain sensors, one optical fiber is shared,
Each strain sensor tube is provided with an interval in the longitudinal direction of the one optical fiber,
A strain detection system characterized in that visible light can be introduced from one of both ends of the one optical fiber.   9. The strain detection system according to claim 8, wherein the one optical fiber is extended so that both ends thereof are close to each other. The strain sensor according to any one of claims 1 to 5, an input unit, and a plurality of output units, wherein one end of an optical fiber of the strain sensor is connected to one output unit. An optical coupler for branching, an optical coupler for merging having a plurality of input units and output units, and the other end of the optical fiber of the strain sensor connected to the one input unit; and other optical couplers for branching A plurality of sets each having one output unit and a bypass optical fiber each having both ends connected to the other input unit of the merging optical coupler,
In the plurality of sets, the output unit of the optical coupler for merging of one set of two sets adjacent to each other and the input unit of the optical coupler for branching of the other set are connected by a coupling optical fiber. Connected in series by
A strain detection system characterized in that visible light can be introduced from an input section of the branching optical coupler of a set existing on one end side of the plurality of sets connected in series. A plurality of the strain sensors according to any one of claims 1 to 5, a plurality of branching optical couplers having an input unit and a plurality of output units, and a plurality of outputs of input visible light A light distribution and supply means for distributing and supplying from the unit,
Each output part of the optical distribution supply means is connected to an input part of each branching optical coupler by a connecting optical fiber,
Each output part of the branching optical coupler is connected to one end of an optical fiber of each strain sensor. A plurality of strain sensors according to any one of claims 1 to 5, and an optical switch that selectively outputs input visible light from a plurality of output units,
In the optical switch, one end of an optical fiber of each strain sensor is connected to each output unit. The strain detection system according to claim 6, 11 or 12,
2. The strain detection system according to claim 1, wherein the other end of the optical fiber of each strain sensor is provided at a position visible from the outside.

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