JP4208067B2 - Fiber optic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to an optical fiber sensor that is installed in a form such as buried in the soil and used to detect the amount of deformation, etc., and more particularly, the optical fiber is supported in a single row state, a double row state, or a parallel running state. It is related with the optical fiber sensor with which it was equipped.
Such an optical fiber sensor, for example, performs BOTDR (Brillouin Optical Time Domain Reflectometry), which measures the strain distribution in the longitudinal direction of the optical fiber using the Brillouin scattered light of the optical fiber, and so on. It is useful as a detection end).
[0002]
[Prior art]
As a technique for installing a long optical fiber at a monitoring target location in order to monitor environmental condition fluctuations such as landslides, the optical fiber is fixed in a state in which a longitudinal strain is applied (for example, see Patent Document 1). A structure in which the surface of a structure is covered with an aggregate-containing reaction-curable resin while applying tension to the optical fiber is known (for example, see Patent Document 2). None of these are used without being embedded, and a support that is manufactured separately from the monitoring object and extends over the measurement range (sensing section) is not employed. That is, in the former, an optical fiber is fixed to a pile provided for each fulcrum, and a support having two fulcrums separated in the longitudinal direction of the optical fiber is not introduced. In the latter, the optical fiber is covered and fixed to the structure over the entire measurement range, and a support having two fulcrum points separated from each other in the longitudinal direction of the optical fiber is not introduced. In either case, the optical fiber is stretched straight in the measurement range.
[0003]
On the other hand, as a technique to be used by being embedded in the soil or the like, an optical fiber is inserted into a flexible casing tube (strip material) and fixed with a filler (for example, see Patent Document 3), or a PVC pipe. Fixing the optical fiber in a tensioned state while joining the short fiber (strip material) with the optical fiber fixed to the outer periphery with a band or the like while adding the (strip material). Something is known (for example, see Patent Document 5). In these cases, a strip is used as a support having two or more fulcrums separated in the longitudinal direction of the optical fiber, and is embedded in a state where it extends over the measurement range. However, the optical fiber is stretched straight in the measurement range.
[0004]
FIG. 9 is a front view schematically showing such an optical fiber sensor vertically, where (a) shows a state immediately after embedding, and (b) shows a state after an assumed environmental fluctuation has occurred. ing.
This optical fiber sensor 20 (see FIG. 9A) is a combination of a support 21 made of strip material and four rows of optical fibers 10, and each of the optical fibers 10 has a longitudinal direction relative to the support 21. They are all mounted on the outer peripheral surface of the support 21. At the time of mounting, each optical fiber 10 is distributed to a place where the outer peripheral surface of the support 21 is divided into four equal parts in the circumferential direction, and a plurality of plural optical fibers 10 attached on the outer peripheral surface of the support 21 at a predetermined pitch that defines a sensing section. The fulcrum 22 is supported.
Such embedment of the optical fiber sensor 20 is performed by inserting the optical fiber sensor 20 into a hole excavated in the soil and then introducing a filler into the hole.
Then (see FIG. 9B), when a landslide or the like occurs and the optical fiber sensor 20 bends in accordance with the deformation of the soil, the concave optical fiber 10 contracts while the convex optical fiber 10 extends. Therefore, the degree and direction of variation can be detected based on the amount and difference of the distortions.
[0005]
[Patent Document 1]
JP 2001-296112 A (first page, FIG. 2-3)
[Patent Document 2]
JP 2002-131024 (Page 1-2, FIG. 1)
[Patent Document 3]
Japanese Patent Laid-Open No. 2-52222 (first page, FIG. 6)
[Patent Document 4]
JP-A-10-197298 (first page, FIG. 4)
[Patent Document 5]
JP 2002-54956 A (first page, FIG. 3)
[0006]
[Problems to be solved by the invention]
However, in such a conventional optical fiber sensor, it is assumed that fluctuations in environmental conditions occur in a state of being distributed over a plurality of sensing intervals. Therefore, local variations such as narrow fluctuations occurring in a single sensing interval are assumed. Since the deformation state is different with respect to general fluctuations, satisfactory measurement results are not always obtained. For example (see FIG. 9 (c)), when only a formation narrower than the single sensing section is displaced across the optical fiber sensor 20, the deformation mode of the support 21 is almost in the state of fixed beams at both ends. The optical fiber 10 is not easily deformed together with the body 21, and the optical fiber 10 is similarly deformed in any of the concaves and convexes so that there is almost no difference in distortion. The ability is also lost. For this reason, for example, when a steep fault is expected, a conventional optical fiber sensor is not sufficient.
[0007]
For the inconvenience due to such a lack of deformation of the support, when using a support having a certain degree of rigidity, for example (see FIG. 10 (a)), a support made of a strip material thinner than conventional ones. 31 is used instead, and the filling material 32 is attached around the support 31 to maintain the thickness of the entire sensor, and the optical fiber 10 is embedded therein, so that the optical fiber 10 is arranged as in the conventional case. It is also possible to do. In this case, even when the support 31 is not deformed, the filling material 32 passes through both sides of the thin support 31 and easily moves and deforms. Therefore, the optical fiber 10 also closely follows local soil deformation and the like. Therefore, the detection sensitivity to the extent of fluctuation is increased. However, even in this optical fiber sensor 30, since the optical fiber 10 is similarly distorted on the concave side and the convex side (see FIGS. 10B and 10C), it is not possible to sufficiently detect the fluctuation direction.
[0008]
Therefore, the purpose of use is to be embedded in the location to be monitored, and the manufacturing mode in which the optical fiber is attached to a support that is more rigid than the monitored object so that it can be easily stored, transported, installed, etc. is maintained. Therefore, even if the environmental fluctuation of the monitoring target is local, not only can the degree of fluctuation be detected with high sensitivity, but also the ingenuity in the structure of the optical fiber sensor so that the fluctuation direction can be detected. It becomes a technical challenge.
This invention is made in order to solve such a subject, and it aims at implement | achieving the optical fiber sensor which can detect the local fluctuation | variation of installation objects, such as an embedding destination, well.
[0009]
[Means for Solving the Problems]
The gist of the solution means of the present invention created to solve such problems will be described with reference to the drawings. FIG. 1 shows the principle of the present invention, in which (a) is an end view / plan view of an optical fiber sensor, and (b) and (c) are longitudinal front views of an optical fiber sensor installation location.
[0010]
The purpose of the optical fiber sensor of the present invention is to bend the optical fiber 10 where local fluctuation is expected, and to use this curved portion for measurement. Therefore, in addition to the optical fiber 10, the optical fiber sensor 40 is also provided with a pair of fulcrums 42 for supporting it at two points (see FIG. 1A). The fulcrum 42 is attached to the fixing member 41 or the like for fixing.
When the optical fiber sensor 40 is installed on the soil 44 or the like to be monitored (see FIG. 1B), the fixing member 41 is disposed so that the fulcrum 42 comes to each end position of the sensing section 43 that is the measurement range. The optical fiber 10 is longer than the sensing section 43 and is bent in an arcuate shape, with the convex side of the center / intermediate portion facing the desired measurement direction.
[0011]
Then, when the soil etc. 44 is deformed and moved locally in the sensing section 43, the soil etc. 44 in that portion pushes the optical fiber 10, and a force F acts on the optical fiber 10. When the variation direction of the soil 44 coincides with the direction of the convex side of the optical fiber 10 (see FIG. 1C), the force F is applied to the optical fiber 10 to further deepen the curvature of the optical fiber 10. A longitudinal tensile force is applied.
On the other hand, although illustration is omitted, when the direction of change of the soil 44 or the like is perpendicular to the direction of the convex side of the optical fiber 10, the optical fiber 10 is laterally kept in its curved shape. Because it moves to, no external force is applied. Further, when the variation direction of the soil or the like 44 is opposite to the convex side of the optical fiber 10, the external force acts to shallow the curve or to distort the curve harmonically. The compression force tends to be applied to the optical fiber 10. In either case, no longitudinal tensile force is applied to the optical fiber 10.
[0012]
By installing the optical fiber 10 in such a curved manner, the optical fiber 10 can be faithfully deformed in accordance with environmental changes without being restricted by the deformability of the support or the like, and can be deformed to the convex side. Since it is strongly sensitive and causes large distortion, the detection sensitivity is improved. In addition, since the anisotropy corresponding to the bending direction is given to the detection characteristics, it is possible to detect a change in the desired direction without being restricted by the deformation mode of the support.
Therefore, according to the present invention, it is possible to detect the degree of fluctuation with high sensitivity even if the environmental fluctuation of the monitoring target is local, for the purpose of measuring the fluctuation state by installing an optical fiber sensor at the monitoring target position. can do.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
About the optical fiber sensor of this invention achieved by such a solution, a structure and an effect are demonstrated about several forms for the implementation.
[0014]
[First Embodiment]
The optical fiber sensor according to the first embodiment of the present invention, as described in claim 1 at the beginning of the application, is an optical fiber including an optical fiber for observing changes in environmental conditions and a support that supports the optical fiber in the longitudinal direction. The fiber sensor is characterized by providing a sensing section having the following structure. That is, the sensing section is a measurement range that spans two points set at an interval in the longitudinal direction of the optical fiber. In this sensing section, the optical fiber is attached to the support using the two points as fulcrums. The portion supported and sandwiched between the two points has a deformable form having a curved portion. The support body extends at least over the two points.
[0015]
In this case, by bending the optical fiber in the sensing section, it is possible to obtain the above-mentioned advantage that the degree of fluctuation to the convex side can be detected with high sensitivity even when the fluctuation of the buried portion is local, The length of the sensing section and the degree of bending of the optical fiber are established in advance by supporting the optical fiber at the both ends of the sensing section while maintaining the bendability / deformability of the optical fiber. In addition, since it can be handled with a support that is at least more rigid than the optical fiber, it can be easily stored, transported and installed.
In this way, the purpose of use is to be embedded and used in the location to be monitored, and the manufacturing mode in which the optical fiber is attached to a support that is more rigid than the monitored object so that storage, transportation, installation, etc. can be performed easily. In addition, even when the environmental fluctuation of the monitoring target is local, not only the degree of fluctuation can be detected with high sensitivity, but also the fluctuation direction can be detected.
[0016]
[Second Embodiment]
A second embodiment of the present invention is the optical fiber sensor of the first embodiment described above, as described in claim 2 at the beginning of the application, in which the optical fibers are arranged in double rows. In addition, each of the optical fibers in each row is preferably provided with the sensing zone, that is, the sensing zone having the above-described structure, in a double row state. Further, the double-row arrangement of the optical fibers is made in a state where the convex sides of the curved portions related to the optical fibers in each row are oriented in mutually independent directions, that is, in a state where the directions of the curved portions are different. That's it.
As a result, the variation state can be detected for a plurality of directions. Alternatively, the direction of fluctuation can be detected more accurately.
[0017]
[Third Embodiment]
A third embodiment of the present invention is the optical fiber sensor of the first and second embodiments described above, as defined in claim 3 at the beginning of the application, wherein the sensing section is on the longitudinal direction of the optical fiber. A plurality are provided in series. That is, the sensing sections are connected in series along the optical fiber.
Thereby, a wide range can be monitored.
[0018]
[Fourth Embodiment]
A fourth embodiment of the present invention is the optical fiber sensor according to any one of the first to third embodiments described above, as defined in claim 4 at the beginning of the application, and is located at both ends of the sensing section. In addition to being supported by the support at two points, the optical fiber is supported not by the support but by a filling material at a portion sandwiched between the two points. is there. Specifically, when the envelope or envelope of the optical fiber is closed or substantially closed, the internal space with respect to the virtual space including the envelope, or the envelope or envelope of the optical fiber is When not closed, the inner space of the optical fiber including the support and the virtual space including the envelope or envelope surface thereof close to the closed state is filled with the following filling material. It is that. That is, a material that is more easily deformed than the support is used for the filling material, for example, a soft material, a material with a low elastic modulus, a material with a low elastic limit, etc. are used, and the internal space is an internal space. It is a solid body capable of transmitting strain over a wide range.
In this case, the initial bending state and bending shape of the optical fiber are defined and determined by the filling material at the time of manufacture, so that the subsequent embedding operation and the like can be performed easily and accurately.
[0019]
[Fifth Embodiment]
A fifth embodiment of the present invention is the optical fiber sensor according to the fourth embodiment as described in claim 5 at the beginning of the application, wherein the solid body is a flexible membrane directly or together with inclusions. It is wrapped in the body.
Thereby, it can prevent that a filling material peels from the sensing mechanism comprised with an optical fiber or a support body.
[0020]
[Sixth Embodiment]
The sixth embodiment of the present invention is an optical fiber sensor according to the third to fifth embodiments described above, as described in claim 6 at the beginning of the application, and is configured in a long shape that can be folded in the crossover section. It is a thing. Specifically, the support is constituted by using a plurality of finite lengths, and one or two or more sensing sections are arranged for each of the finite lengths. Each corresponding finite length portion is a rod-shaped collective sensor, and a plurality of the collective sensors are connected in the longitudinal direction of the optical fiber so as to share the optical fiber, and a section spans between adjacent collective sensors in this series. In this transition section, the optical fiber is free from the support.
Thereby, since it becomes possible to fold an optical fiber sensor as needed, storage and transportation also become easy about a long optical fiber sensor.
[0021]
[Seventh Embodiment]
A seventh embodiment of the present invention is the optical fiber sensor according to any one of the first to sixth embodiments described above, as recited in claim 7 at the beginning of the application, wherein the optical fiber is a metal sheath. It is covered and tension is applied from the sheath body.
Thereby, protection and tension | tensile_strength provision can be achieved simultaneously. It should be noted that by providing the optical fiber with a strain of elongation in advance by tension, not only the convex side but also the concave side can be detected clearly and distinctly.
[0022]
About the optical fiber sensor of this invention achieved with such a solution or embodiment, the concrete form for implementing this is demonstrated by the following 1st-6th Example.
The first example shown in FIG. 2 embodies the first embodiment described above, and the second example shown in FIGS. 3 and 4 differs from the second to third embodiments described above. The third example of FIG. 5 and the fourth example of FIG. 6 both embody the fourth to fifth embodiments described above and are shown in FIG. The fifth example embodies the above-described sixth embodiment, and the sixth example illustrated in FIG. 8 embodies the above-described seventh embodiment.
[0023]
[First embodiment]
A specific configuration of the optical fiber sensor according to the first embodiment of the present invention will be described with reference to the drawings. 2A is an end view / plan view of the optical fiber sensor, and FIG. 2B is a longitudinal front view thereof.
[0024]
This optical fiber sensor 50 has one optical fiber 10 as a measurement terminal and two fulcrums 42 and one for supporting it in order to observe soil distortion (environmental condition fluctuation) with BOTDR. The support body 51 is provided.
For the optical fiber 10, for example, known ones described in Patent Documents 1 to 5 are sufficient, but other optical fibers may be used as long as they are suitable for measurement purposes. Its typical diameter is 2 mm. The length is appropriately selected according to the measurement location, and may be several meters or several kilometers.
[0025]
Since the support body 51 supports the optical fiber 10 in the longitudinal direction and is embedded in the soil 44, a rigid strip material that does not easily corrode is suitable. For example, a straight tube material made of aluminum or stainless steel is used.
As long as the optical fiber 10 can be locally fixed at the fulcrum 42, the support 51 may be a known one described in Patent Documents 1 to 5, or may be one using other fasteners or clamping tools. The two fulcrums 42 are set on the support 51 with a predetermined interval. The predetermined interval coincides with and corresponds to the section length of the sensing section 43 which is a range to be measured.
[0026]
When the optical fiber 10 is mounted on the support 51 and the optical fiber sensor 50 is assembled, the optical fiber 10 is fixed to the support 51 at two points using the fulcrum 42. An optical fiber having a length obtained by adding a surplus length for bending to the section length is charged between the fulcrums 42. As a result, the optical fiber 10 is supported by the support body 51 with the two points set at intervals in the longitudinal direction as fulcrums 42, and a deformable form having a curved portion at a portion sandwiched between the two points. It will be a thing. Further, the sensing section 43 has such a structure.
[0027]
The use mode and operation of the optical fiber sensor 50 of the first embodiment will be described with reference to the drawings. 2 (b) and 2 (c) are longitudinal front views of the optical fiber sensor embedding location, (b) shows a state immediately after embedding, and (c) shows a state after environmental change.
[0028]
In this example (see FIG. 2 (b)), since the optical fiber sensor 50 is installed vertically, first, a vertical hole 52 is excavated in the soil 44, the optical fiber sensor 50 is inserted therein, and then the hole 52 is inserted into the soil. The optical fiber sensor 50 is embedded by filling with a filler or the like.
At that time, if necessary, if necessary, using an appropriate tool or auxiliary tool, the optical fiber 10 in the sensing section 43 is bent into an arcuate shape, and the convex side of the optical fiber 10 is predicted to be a local variation of the soil 44. (Look to the right in the figure).
[0029]
When there is a possibility that the support body 51 may be deformed or moved following local variation of the soil 44 in the sensing section 43, the fixing member 41 is installed outside the sensing section 43, and the support body is thus supported. It is desirable to fix 51 ends. The fixing member 41 may be a manufactured product such as a metal plank or a concrete block, or may be a diverted rock or the like. The rigidity of the support body 51 is high and / or the support body 51 protrudes sufficiently outside the sensing section 43, and the support body 51 does not deform or move greatly due to local fluctuation of the soil 44 within the sensing section 43. In such a case, the fixing member 41 is not necessary.
[0030]
The optical fiber 10 extending from the sensing section 43 in the soil 44 reaches the ground using the hollow of the support 51 or the like, and is connected to the BOTDR measurement device 12. The measuring device 12 and the measuring method thereof may be known ones mentioned in Patent Documents 1 to 5, for example.
This prepares for strain measurement.
[0031]
And (refer to FIG. 2 (c)), when the local variation occurs in the soil 44 at the sensing section 43 (in the figure, the intermediate layer portion is shifted from the left to the right), the support at the sensing section 43 thereby 51 and the optical fiber 10 are pushed, but the elongated support body 51 fixed at both ends hardly deforms, and the changing soil 44 moves through both sides of the support body 51, so that the fulcrum 42 The position of is almost fixed and does not move. Therefore, the thrust F by the changing soil 44 is efficiently applied to the curved portion of the optical fiber 10. The optical fiber 10 between the fulcrums 42 is stretched by this force F, and the amount of extension strain is optically detected by the measuring device 12.
Thus, in the optical fiber sensor 50, even when the variation of the monitored soil 44 is local, the variation can be accurately detected.
[0032]
[Second embodiment]
A specific configuration of the second embodiment of the optical fiber sensor of the present invention will be described with reference to the drawings. 3A is an end view / front view of the optical fiber sensor, and FIG. 3B is a side view thereof.
The optical fiber sensor 50 is different from the above-described optical fiber sensor 40 in that a plurality of sensing sections 43 are connected in series.
[0033]
The number of sensing sections 43 is appropriately set according to the length of the measurement range, and the support 51 and the optical fiber 10 are longer than the section length. If it is sufficient to measure the fluctuation in only one direction, the convex side of the curved portion of the optical fiber 10 may be aligned in the same direction when viewed from the support body 51. The convex side of the curved portion of the optical fiber 10 is directed alternately on the basis of the series of sensing sections 43 and to the opposite side on the basis of the support 51 so that measurement can be performed. Further, the optical fiber 10 remains in a single row, and the fulcrum 42 is shared by the adjacent sensing sections 43. Here, as a numerical example, the typical value of the diameter A of the support 51 is 2 mm to 10 mm, the amplitude B related to the bending of the optical fiber 10 is 5 mm to 50 mm, and the width C of the sensing section is about 1 m, but exceeds that. Those below and below are appropriately adopted depending on the measurement situation.
[0034]
The use mode and operation of the optical fiber sensor 50 of the second embodiment will be described with reference to the drawings. 3 (c) is a perspective view of the sandwich type filling material, FIG. 3 (d) is a side view of the assembled optical fiber sensor and the filling material, and FIG. 3 (e) is a longitudinal side view of the buried portion.
[0035]
In this case, prior to embedding the optical fiber sensor 50, an operation of wrapping the optical fiber sensor 50 with a set of filling materials 54 + 56 is performed. Filling material 54 + 56 (see FIG. 3 (c)) is formed by dividing a round bar made of a material that is easy to handle, such as clay cake and foamed rubber, and easily deforms into two shapes to form the filling materials 54 and 56. Accordingly, the groove 55 is carved at a position corresponding to the axial center in the divided surface of the one filling material 54.
[0036]
The optical fiber sensor 50 is placed on the split surface of the filling material 54 while the support 51 is placed in such a groove 55, the shape of the curved portion of the optical fiber 10 is adjusted, and then the filling material 56 is overlapped. When the filling materials 54 and 56 are joined by pressure bonding or other means (see FIG. 3D), the optical fiber sensor 50 is sandwiched between the filling materials 54 + 56, and the sensing section 43 of the required structure is moved in the longitudinal direction of the optical fiber 10. A state where a plurality of lines are connected to each other is established.
[0037]
In such an optical fiber sensor 50, the required structure of each sensing section 43 is maintained unless the shape of the filling material 54 + 56 is largely changed, so that the burying work can be performed easily and accurately. And (refer FIG.3 (e)), if the optical fiber sensor 50 is embed | buried in the soil 44 with the filling material 54 + 56, in any sensing area 43, the local fluctuation | variation of the soil 44 toward the convex side of the curved part of the optical fiber 10 will be carried out. This is mediated by local variation of the filling material 54 + 56 that occurs following this, and is detected with high sensitivity. In the example shown in the figure, the optical fiber sensor 50 is installed horizontally to detect the vertical movement of the soil 44. However, the installation direction is not limited, and is determined according to the direction of fluctuation to be measured. It is done.
[0038]
In the modification shown in FIG. 4A, two optical fibers 10 are shifted by a half wavelength to form a double row, and distortion can be measured in both sensing and reciprocating directions in any sensing section 43. It is like that.
In the modification shown in FIG. 4B, one long optical fiber 10 is folded back to form a double row. In this example, the optical fiber 10 is folded back at the support 51. In the example of FIG. 4A, the optical fiber 10 intersects with the support 51. Bidirectional measurement is possible.
The modification shown in FIG. 4C employs two sets of the two rows of optical fibers 10 in FIG. 4B and shifts them by ¼ half wavelength to make a total of four rows. As a result of the section 43 being shifted by half and multiplexed, the dead zone at the end of the sensing section 43 is eliminated.
[0039]
The modified example shown in FIG. 4 (d) also employs two sets of the two rows of optical fibers 10 in FIG. 4 (b). In this case, the support body 51 is not displaced in the longitudinal direction. One of the shafts is rotated by 90 °, and is in an orthogonal state in end view. Thus, in the optical fiber sensor 50, the curved portions of the optical fibers 10 in each row are oriented on the convex side in mutually independent orientations.
In this case, since the optical fiber 10 is arranged in all directions with the support 51 as the center, the component in each arrangement direction is detected by the optical fiber 10 in the corresponding direction with respect to the variation amount of the soil 44. Therefore, a change in an arbitrary direction orthogonal to the support 51 is detected by an operation such as calculating the vector sum thereof.
[0040]
[Third embodiment]
The optical fiber sensor 60 of the present invention whose manufacturing process is shown in FIG. 5 is different from the optical fiber sensor 50 described above in that a filling material 61 and a film body 62 are assembled in advance. Here, a specific example of the above-described optical fiber sensor 50 based on the modification of FIG. 4D will be described.
[0041]
In this case, first (see FIG. 5A), the fulcrum 42 is attached to the support 51 at a predetermined pitch corresponding to the sensing section 43, and then (see FIG. 5B), leaving the fulcrum 42. A filling material 61 such as clay is attached around the support 51, and the filling material 61 is made thinner as it is closer to the fulcrum 42 and thicker as it is farther from the fulcrum 42. At that time, it is easy to arrange the shape if it is axisymmetric with the support 51 as the central axis. When the filling material 61 has a spindle shape with a bulge, the optical fiber 10 is stacked thereon (see FIG. 5C), and the optical fiber 10 is locked to the support 51 at the fulcrum 42. The optical fiber 10 is extended along the surface of the filling material 61 while taking care not to loosen the optical fiber 10. In this way, the optical fiber 10 is mounted from the four sides of the support 51 in the end view. Then (see FIG. 5 (d)), a flexible film body 62 having an appropriate diameter selected from commercially available thin heat-shrinkable tubes is covered, and the film is heated and shrunk with a drier or the like to be placed on the filling material 61. Adhere closely.
[0042]
Thereby, the undesired drying and peeling of the filling material 61 are prevented. In addition, the optical fiber 10 is sandwiched and protected by the filling material 61 and the film body 62 and at the same time has a deformable curved portion required in the sensing section 43. Further, in each sensing section 43, the optical fiber sensor 60 is capable of transmitting strain in the inner space formed by the envelope 61 and the envelope surface of the optical fiber 10 and the support 51 with the filling material 61. Become a solid entity.
Such an optical fiber sensor 60 can be stored for a long time in a factory or the like until the filling material 61 is mounted. In addition, there is almost no risk of damage during storage or transportation. Because it is possible, practical value is high.
[0043]
[Fourth embodiment]
The optical fiber sensor of the present invention whose manufacturing process is shown in FIG. 6 is different from that of the third embodiment described above in that a filling material 63 is also added outside the envelope / envelope surface of the optical fiber 10. Is a point.
That is, the optical fiber sensor 60 is the same as described above until the optical fiber 10 is stretched on the support material 51 with the filling material 61 (see FIGS. 5C and 6A). ), Instead of directly wrapping it with the film body 62, a filling material 63 is added to the outer peripheral portion to form a round bar (see FIG. 6 (b)), and then the film body 62 is covered (see FIG. 6 (c)), This is finished by heat shrinking (see FIG. 6D).
[0044]
The material of the filling material 63 may be the same as or different from the filling material 61 as long as it is similar to the soil 44 and can transmit the strain of the soil 44 well.
In this case, in addition to taking over the effects of the third embodiment described above, the shape of the cross-section perpendicular to the longitudinal direction becomes uniform, and it fits well with the round hole that is the general shape of the embedding destination. Construction becomes even easier.
[0045]
[Fifth embodiment]
The specific configuration of the fifth embodiment of the optical fiber sensor of the present invention will be described with reference to the drawings. 7A and 7B are side perspective views of the optical fiber sensor 70, where FIG. 7A is a developed state and FIG. 7B is a folded state.
The optical fiber sensor 70 is different from the optical fiber sensor 60 described above in that it can be folded.
That is, in the optical fiber sensor 70, when the above-described optical fiber sensor 60 is elongated, the collective sensors 71 and the crossing sections 72 are alternately arranged and connected in series so that the handling such as storage and transportation can be easily performed. It can be folded by remodeling it to a state.
[0046]
Specifically (see FIG. 7A), for each of the collective sensors 71, a support body 51 of a finite length is used, and some sensing sections 43 are partially formed in the same manner as the optical fiber sensor 60 described above. Arrange it and finish it into a rod-shaped body. However, the optical fiber 10 is shared by the plural collective sensors 71 without being divided in the longitudinal direction in order to connect the plural collective sensors 71 in a row in a row in the longitudinal direction. In addition, between the adjacent collective sensors 71 in the series, this is a transition section 72 without the support body 51. In this transition section 72, the optical fiber 10 having a length that can be bent by 180 ° or more without being damaged, Secure in a free state.
[0047]
Desirably, a free length that can be wound many times is secured, and a plurality of times and many times of winding are performed, and the optical fiber 10 is formed in a coil shape as shown in the cross section 72. . Further, in the crossing section 72, it is preferable to wrap the optical fiber 10 with a flexible cover 73 to protect the optical fiber 10 in a free state and to prevent the winding from being unwound. Although illustration is omitted, a flexible tube may be provided inside the optical fiber 10 instead of or in addition to the cover 73, and they may be movable in the axial direction. As a numerical example, the length of the collective sensor 71 is 2 m to 10 m, the section length of the transition section 72 is 100 mm to 600 mm, the free length of the optical fiber 10 in the transition section 72 is 1500 mm to 3000 mm, and the optical fiber 10 in the transition section 72. The number of wrinkles is from 5 to 10 times, and those exceeding and below are appropriately employed.
[0048]
In this case, by making the optical fiber 10 free from the support body 51 in the crossover section 72, the optical fiber sensor 70 can be easily folded in a compact manner or extended by bending and extending in the crossover section 72.
Such a long optical fiber sensor is stored and transported after being assembled at the factory in a folded state so as not to be bulky (see FIG. 7B), and is stretched into a single rod at the site. It is embedded in the soil 44 (see FIG. 7A), and then connected to the measuring device 12 for use.
Thus, the optical fiber sensor 70 can be easily stored, transported and installed despite being long.
[0049]
[Sixth embodiment]
A specific configuration of the sixth embodiment of the optical fiber sensor of the present invention will be described with reference to the drawings. 8A and 8B are cross-sectional views of the optical fiber, and FIG. 8C is an external view of the optical fiber.
This optical fiber sensor is different from the optical fiber sensors 50, 60, 70 described above in that the optical fiber 10 is covered with a sheath body 11.
[0050]
The sheath body 11 is a thin tube made of stainless steel, and the optical fiber 10 is accommodated in a hollow for protecting the optical fiber 10 and applying tension (see FIG. 8A), and tension is applied to the optical fiber 10. In this state, “caulking” is performed at predetermined pitches (see FIGS. 8B and 8C), so that the tension of the optical fiber 10 and the reaction force of the sheath body 11 are constantly maintained. The sheath body 11 has an outer diameter of 2 mm, a wall thickness of 0.2 mm, and a “caulking” pitch of 1000 mm. These are typical values, and the design is appropriately changed according to the application purpose.
[0051]
In this case, tension is preliminarily applied to the optical fiber 10 using the sheath body 11. The tension is applied only when necessary according to the measurement purpose. In general, in the strain measurement, the optical fiber 10 is extended by, for example, 0.5%. By doing so, not only elongation but also shrinkage can be measured.
Therefore, when the bending portion of the optical fiber 10 in the sensing section 43 is pushed to the convex side to cause elongation distortion, it can be detected as described above, and in addition, the bending section in the same or overlapping sensing section 43 can be detected. As for the optical fiber 10 and the sheath body 11 installed with the convex side of the optical fiber 10 facing the opposite side, the curved portion is pushed to the concave side to cause the sheath body 11 to be contracted and distorted. Since the pre-distortion is reduced, the combined detection capacity almost doubles.
[0052]
[Others]
In each of the above-described embodiments, soil distortion is cited as a specific example of environmental condition variation to be monitored, and embedding is cited as an installation form of the sensor. However, the use of the sensor of the present invention is limited to this. It is not necessary to monitor the deformation of concrete structures such as breakwaters, dams, and embankments by embedding or pasting them (such as the sensors shown in Figs. 4 (a) to (c)) or monitoring the icing behavior of lakes underwater. It is sufficient to use conditions that affect the optical state of the installed optical fiber cable, such as immersing and observing.
[0053]
【The invention's effect】
As is clear from the above description, in the optical fiber sensor of the present invention, since the optical fiber is bent in the sensing section, the detection sensitivity especially on the convex side is improved. There is an advantageous effect that an optical fiber sensor capable of detecting fluctuations can be realized.
[Brief description of the drawings]
FIG. 1 shows the principle of the present invention, in which (a) is an end view / plan view of an optical fiber sensor, and (b) and (c) are longitudinal front views of an optical fiber sensor embedded portion.
2A is an end view / plan view of an optical fiber sensor according to the first embodiment of the present invention, and FIGS. 2B and 2C are longitudinal front views of an optical fiber sensor embedded portion.
3A is an end view / front view of an optical fiber sensor according to a second embodiment of the present invention, FIG. 3B is a side view thereof, FIG. 3C is a perspective view of a sandwich type filling material, FIG. Is a side view of the assembled optical fiber sensor and filling material, and (e) is a longitudinal side view of the buried portion.
4A to 4D each show a modified example of the second embodiment, in which the left side is an end view / front view of the optical fiber sensor, and the right side is a side view. FIG.
FIG. 5 shows a manufacturing process for the third embodiment of the optical fiber sensor of the present invention, and in each of (a) to (d), the left side is an end view / front view, and the right side is a side view.
FIG. 6 shows the manufacturing process of the fourth embodiment of the optical fiber sensor of the present invention, and in each of (a) to (d), the left side is an end view / front view, and the right side is a side view.
7A and 7B are side perspective views of a fifth embodiment of the optical fiber sensor of the present invention, where FIG. 7A is a developed state and FIG. 7B is a folded state.
8A and 8B are cross-sectional views of an optical fiber according to a sixth embodiment of the optical fiber sensor of the present invention, and FIG. 8C is an external view of the optical fiber.
9A and 9C are front views of a conventional optical fiber sensor.
FIG. 10 is a longitudinal front view of the optical fiber sensor in all of the improvement proposals (a) to (c).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Optical fiber, 11 ... Sheath body, 12 ... Measuring apparatus,
20 ... optical fiber sensor, 21 ... support, 22 ... fulcrum,
30 ... Optical fiber sensor, 31 ... Support, 32 ... Filling material,
40 ... optical fiber sensor, 41 ... fixing member, 42 ... fulcrum,
43 ... Sensing section, 44 ... Soil,
50 ... Optical fiber sensor, 51 ... Support, 52 ... Hole,
54 ... Filling material, 55 ... Groove, 56 ... Filling material,
60 ... Optical fiber sensor, 61 ... Filling material, 62 ... Film body, 63 ... Filling material,
70: optical fiber sensor, 71: collective sensor,
72: Crossing section, 73 ... Cover

Claims (6)

An optical fiber sensor comprising an optical fiber for observing fluctuations in environmental conditions and a support that supports the optical fiber in the longitudinal direction,
The optical fiber is supported by the support with two points set at intervals in the longitudinal direction as a fulcrum, and has a deformable configuration having a curved portion at a portion sandwiched between the two points. It has a sensing section ,
The optical fibers are arranged in double rows, and the sensing section is provided for each row of optical fibers, and the convex portions of the curved portions of the optical fibers in each row are oriented in mutually independent orientations. An optical fiber sensor characterized by comprising: The optical fiber sensor according to claim 1, wherein a plurality of the sensing sections are provided continuously in the longitudinal direction of the optical fiber. In the sensing section, the inner space of the envelope or the envelope surface of the optical fiber or of the optical fiber and the support is buried with a filling material, and is a solid body capable of transmitting strain over the inside. The optical fiber sensor according to claim 1 or 2, wherein The optical fiber sensor according to claim 3, wherein the solid body is wrapped with a flexible film body. 5. The optical fiber sensor according to claim 2 , wherein a plurality of finite lengths are used for the support, and one or two or more sensing sections are provided for each of the supports. As a sensor, a plurality of the collective sensors are connected in the longitudinal direction of the optical fiber so as to share the optical fiber, and the optical fiber is freely separated from the support in a transition section between adjacent collective sensors in this series. Accordingly, the optical fiber sensor is configured in a long shape that can be folded in the crossing section. The optical fiber sensor according to any one of claims 1 to 5, wherein the optical fiber is covered with a metal sheath so as to be tensioned from the sheath.

Images