Measurement system, measurement method, and analysis device

Abstract

Provided are a measurement system, a measurement method, and an analysis device that are capable of easily improving accuracy in measuring the shape of a linear structure. This measurement system for measuring the shape of a linear structure comprises a strain distribution measurement device 4 that, using a multicore optical fiber fixed along the extension direction of the linear structure, measures strain distributions that follow in the extension direction of the multicore optical fiber at two different timings or measures the difference between the strain distributions; and an analysis device 5 for calculating the shape of the multicore optical fiber using the difference between the strain distributions measured at two different timings and calculating the shape of the linear structure on the basis of the shape of the multicore optical fiber.

Description

Measurement system, measurement method, and analysis device

[0001] The present disclosure relates to a measurement system, a measurement method, and an analysis device.

[0002] There is a technology to measure the shape of a linear structure such as a pipeline by inserting a multi-core optical fiber (MCF) into the linear structure and measuring the shape of the MCF. However, when the MCF is inserted into the linear structure, a twist is inevitably applied to the MCF, which significantly affects the shape measurement accuracy.

[0003] Therefore, Non-Patent Documents 1 and 2 disclose a technique for applying a sufficiently large and known amount of twist to an MCF in advance and measuring the shape taking the amount of twist into consideration. Non-Patent Document 3 discloses a technique for suppressing the occurrence of twist.

[0004] Roger Duncan, 6 others, “High-accuracy fiber-optic shape sensing”, Proceedings of Spie, Vol.6530, 2007, p.65301S-1-p.65301S-11 Yong-Lae Park, 8 others, “Real-Time Estimation of 3-D Needle Shape and Deflection for MRI-Guided Interventions”, IEEE / ASME Transactions on Mechatronics, Vol.15, No.6, December 2010, p.906-p.915 Yoshiki Maeda and 9 others, “Shape sensing for large-scale line structures with multi-core fibers by using Brillouin OTDR”, OFS2020, T3.39, 2020

[0005] However, the method of pre-applying a sufficiently large, known amount of twist to the MCF requires a special twist application device in the MCF manufacturing process, which has a significant impact on yield and manufacturing costs, and has the problem that it is difficult to insert the MCF while maintaining the applied amount of twist.

[0006] The present disclosure has been made in consideration of the above circumstances, and aims to provide a measurement system, a measurement method, and an analysis device that can easily improve the accuracy of measuring the shape of linear structures.

[0007] A measurement system according to one aspect of the present disclosure is a measurement system for measuring a shape of a linear structure, and includes: a strain distribution measurement device that uses a multi-core optical fiber fixed along an extending direction of the linear structure to measure each strain distribution along the extending direction of the multi-core optical fiber at two different timings or a difference between the each strain distribution; and an analysis device that calculates the shape of the multi-core optical fiber using the difference between the strain distributions measured at the two different timings, and calculates the shape of the linear structure based on the shape of the multi-core optical fiber.

[0008] A measurement method according to one aspect of the present disclosure is a measurement method for measuring a shape of a linear structure, in which a strain distribution measurement device uses a multi-core optical fiber fixed along the extending direction of the linear structure to measure each strain distribution along the extending direction of the multi-core optical fiber at two different timings or a difference between the each strain distribution, and an analysis device calculates the shape of the multi-core optical fiber using the difference between the strain distributions measured at the two different timings, and calculates the shape of the linear structure based on the shape of the multi-core optical fiber.

[0009] An analysis device according to one aspect of the present disclosure includes: a receiving unit that receives strain distributions along the extension direction of a multi-core optical fiber at two different timings measured using the multi-core optical fiber fixed along the extension direction of the linear structure, or a difference between the strain distributions; and a computing unit that calculates a shape of the multi-core optical fiber using the difference between the strain distributions measured at the two different timings, and calculates a shape of the linear structure based on the shape of the multi-core optical fiber.

[0010] According to the present disclosure, it is possible to provide a measurement system, a measurement method, and an analysis device that can easily improve the accuracy of measuring the shape of a linear structure.

[0011] FIG. 1 is a diagram showing the configuration of a measurement system according to this embodiment. FIG. 2 is a diagram showing examples of optical fibers and optical fiber cables. FIG. 3 is a diagram showing a method 1 for measuring the shape of a linear structure. FIG. 4 is a diagram showing a method 2 for measuring the shape of a linear structure. FIG. 5 is a diagram showing a method 1 for measuring the shape of an MCF and a linear structure. FIG. 6 is a diagram showing a method 2 for measuring the shape of an MCF and a linear structure. FIG. 7 is a diagram showing the positional relationship of cores, etc. FIG. 8 is a diagram showing the hardware configuration of an analysis device.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0013] [Summary of the Present Disclosure] The present disclosure relates to a method for measuring the shape of a linear structure by fixing an MCF to the linear structure and measuring the shape of the linear structure using the fixed MCF, or by using an MCF that has been fixed to the linear structure in advance.

[0014] In this way, by using an MCF fixed to a linear structure, special equipment or installation methods for suppressing or considering twisting are not required, and the shape of the linear structure can be easily measured using the MCF. In addition, there is no need to consider twisting that occurs when the MCF is inserted into the linear structure, and the accuracy of measuring the shape of the linear structure can be easily improved.

[0015] [Configuration of Measurement System] FIG. 1 is a diagram showing the configuration of a measurement system according to this embodiment.

[0016] The measurement system is a system for measuring the shape of a linear structure by using an optical fiber 1 fixed to the linear structure to be measured. A linear structure is, for example, a structure on which various cables such as those for electricity, gas, water, and communications are laid. Examples of such a linear structure include ducts, conduits, and tunnels installed on land, underground, on bridges, underwater, etc.

[0017] As shown in FIG. 1, the measurement system includes an optical fiber 1, an optical fiber cable 2, an optical switch 3, a strain distribution measuring device 4, and an analyzing device 5.

[0018] The optical fiber 1 is laid and fixed to the linear structure along the extending direction of the linear structure. Although the optical fiber 1 may be directly fixed to the linear structure, in this embodiment, the optical fiber 1 is laid and fixed to the linear structure via the optical fiber cable 2.

[0019] The optical fiber cable 2 is laid and fixed to the linear structure along the extending direction of the linear structure, and includes one or more optical fibers 1. The optical fiber cable 2 includes at least one MCF having multiple cores.

[0020] 2, the optical fiber 1 is, for example, an MCF 1a having four cores at the center and other than the center of the cross section, an MCF 1b having four cores in a square lattice pattern other than the center of the cross section, or a single-mode optical fiber 1c having one core at the center of the cross section. The MCF may or may not have a core at the center of the cross section.

[0021] As shown in FIG. 2, the optical fiber cable 2 has a rectangular shape in cross section with different vertical and horizontal lengths, and covers and fixes the entire sides of one or more optical fibers 1 including MCF.

[0022] In this way, the optical fiber cable 2 has different vertical and horizontal lengths in cross section, so that axial rotation of the optical fiber cable 2 is suppressed after the optical fiber cable 2 is installed and fixed to the linear structure. As a result, unintended twisting does not occur in the optical fiber 1, and there is no need to take this twisting into account in the analysis device 5, and no special device or installation method is required to take this twisting into account. As a result, it is possible to improve the accuracy of shape measurement.

[0023] 2, when multiple optical fibers 1 are mounted on one optical fiber cable 2, the multiple optical fibers 1a to 1c are arranged and fixed on the same straight line (in a row) in the cross section of the optical fiber cable 2. Of course, when the optical fibers are laid and fixed without using the optical fiber cable 2, the multiple optical fibers 1a to 1c are arranged and fixed on the same straight line (in a row) in the cross section of the linear structure.

[0024] In this way, since the multiple optical fibers 1 are arranged and fixed on the same straight line, after the optical fiber cable 2 is laid and fixed to the linear structure, no unintended twist occurs in the optical fibers 1, and no unique twists occur between the multiple optical fibers 1. As a result, it is possible to further improve the shape measurement accuracy.

[0025] The optical fiber cable 2 is, for example, a multi-core optical fiber (tape optical fiber) in which a plurality of optical fibers 1 are arranged in a horizontal row. A user may lay and fix the optical fiber cable 2 to a linear structure, or may use an optical fiber cable 2 that has been laid and fixed to a linear structure in advance.

[0026] It is preferable that there are a plurality of MCFs, because the analysis device 5 can improve the accuracy of shape measurement by using the results of the analyses of the MCFs.

[0027] Furthermore, the cladding diameter of the MCF is preferably 125±1 μm, because this allows the use of existing optical fiber ribbons and optical fiber cable structures.

[0028] The number of cores in the MCF is preferably four or more, including three cores for shape measurement and one core for communication. Although two cores for shape measurement may be sufficient, three or more cores are preferable to obtain a certain degree of shape measurement accuracy.

[0029] Furthermore, it is preferable that the multiple optical fibers 1 include both an MCF and a single-mode optical fiber with one core at the center of the cross section. This is because the shape analysis accuracy can be improved by using the differential strain obtained from the single-mode optical fiber as the axial strain and correcting the axial strain obtained from the measured strain of the MCF in the analysis device 5 using this strain axis.

[0030] The user may lay and fix the optical fiber 1 to the linear structure, or may use the optical fiber 1 that has been laid and fixed to the linear structure in advance.

[0031] Continuing with reference to FIG. 1, the components of the measurement system will be described.

[0032] The optical switch 3 is a device that is connected to one end of one or more optical fibers 1 and selects one of the optical fibers 1 .

[0033] The strain distribution measuring device 4 is connected to the optical switch 3 and measures the strain distribution of the optical fiber 1 selected by the optical switch 3. The strain distribution measuring device 4 is, for example, a Brillouin Optical Time Domain Reflectometer (B-OTDR) or an Optical Frequency Domain Reflectometry (OFDR).

[0034] For example, the strain distribution measuring device 4 measures the strain distribution along the extension direction of an optical fiber 1 (MCF, single-mode optical fiber, etc.) selected by an optical switch 3 in an optical fiber cable 2 laid and fixed to a linear structure along the extension direction of the linear structure.

[0035] For example, the strain distribution measuring device 4 uses an optical fiber 1 selected by an optical switch 3 to measure the difference in strain distribution along the extension direction of the optical fiber 1 based on the cross-correlation of the spectra of each Rayleigh scattered light measured at two different times.

[0036] When a strain distribution measuring device 4 having the same number of measurement channels as the optical fiber 1 to be measured is used, the optical switch 3 is not necessary.

[0037] The analysis device 5 is connected to the strain distribution measuring device 4 and includes a receiving unit 51 that receives strain distribution data or a difference in strain distribution data from the strain distribution measuring device 4, and a calculation unit 52 that calculates the shape of the linear structure using the strain distribution data or the difference in strain distribution data.

[0038] For example, the analysis device 5 calculates the difference between each piece of strain distribution data measured at two different times by the strain distribution measuring device 4, calculates the shape of the MCF using the difference in strain distribution data, and calculates the shape of the linear structure based on the shape of the MCF.

[0039] For example, the analysis device 5 calculates the shape of the MCF using the difference in strain distribution data based on the cross-correlation of the spectra of each Rayleigh scattered light measured at two different times by the strain distribution measurement device 4, and calculates the shape of the linear structure based on the shape of the MCF.

[0040] For example, the analysis device 5 calculates the shape of the linear structure using the strain distribution of the MCF and the strain distribution of the single-mode optical fiber.

[0041] [Method for Measuring the Shape of a Linear Structure] (Method for Measuring Shape 1) First, a case where the strain distribution measuring device 4 measures strain distribution data will be described.

[0042] FIG. 3 is a diagram showing a method 1 for measuring the shape of a linear structural object.

[0043] Step S101: The user manually or by using an arbitrary introduction device lays and fixes the optical fiber cable 2 including one or more optical fibers 1 including MCF to the linear structure along the extending direction of the linear structure. Step S101 does not need to be performed if an optical fiber cable 2 already installed on the linear structure is used.

[0044] Step S102: The strain distribution measuring device 4 uses the MCF of the optical fiber cable 2 laid and fixed to the linear structure to measure the strain distribution along the extension direction of the MCF at a first timing when the shape of the optical fiber cable 2 is in a known state. The strain distribution measuring device 4 then sets the measured strain distribution as a reference strain distribution in a reference state. The reference state refers to a state when the shape of the optical fiber cable 2 is known, such as when the optical fiber cable 2 is laid and fixed.

[0045] Step S103: The strain distribution measuring device 4 remeasures the strain distribution along the extension direction of the MCF at a second timing, which is after a certain time has elapsed (e.g., one year) or after a predetermined event has occurred (e.g., after an earthquake has occurred). Thereafter, the analysis device 5 calculates the shape of the MCF using the difference between the reference strain distribution measured in step S102 and the strain distribution remeasured in step S103, and calculates the shape of the linear structure 100 based on the shape of the MCF.

[0046] (Shape Measuring Method 2) Next, a case where the strain distribution measuring device 4 measures the difference in strain distribution data will be described.

[0047] FIG. 4 is a diagram showing a method 2 for measuring the shape of a linear structural object.

[0048] Step S201: This is the same as step S101 described above.

[0049] Step S202: The strain distribution measuring device 4 uses the MCF of the optical fiber cable 2 laid and fixed to the linear structure to measure the difference in strain distribution along the extension direction of the MCF based on the cross-correlation of the spectra of the Rayleigh scattered light measured at a first timing when the shape of the optical fiber cable 2 is in a known state and at a second timing after a certain time has passed or after a specified event has occurred.

[0050] Step S203: The analysis device 5 calculates the shape of the MCF using the difference in the strain distribution measured in step S202, and calculates the shape of the linear structural object 100 based on the shape of the MCF.

[0051] [Methods for Measuring the Shape of MCF and Linear Structure] Methods 1 and 2 for measuring the shape of MCF and linear structure will be described with reference to FIGS. 5 and 6. FIG.

[0052] (Shape measurement method 1) First, the shape measurement method 1 of the MCF and linear structural object will be described with reference to Fig. 5. Fig. 5 is a diagram showing the shape measurement method 1 of the MCF and linear structural object.

[0053] This method is performed in steps S102 and S103 of Fig. 3, and can be repeatedly performed at regular intervals. In this method, the MCF has no core at the center of the cross section, but has four cores arranged in a square lattice pattern other than the center of the cross section. The four cores are arranged in a square lattice pattern at approximately equal intervals on the same circumference at approximately the same distance from the center of the cross section of the cladding.

[0054] Step S301: The strain distribution measurement device 4 measures the strain distribution characteristics (strain at each point along the extension direction) of each core of the MCF in a predetermined state (for example, the reference state of step S102). If necessary, the strain distribution measurement device 4 measures the strain distribution characteristics of each core of another optical fiber. This allows the analysis device 5 to obtain strain distribution data along the extension direction of each core in the reference shape.

[0055] Step S302: The strain distribution measurement device 4 measures the strain distribution characteristics (strain at each point along the extension direction) of each core of the MCF in an arbitrary state (for example, at the time of step S103). If the accuracy required for shape analysis cannot be obtained, the strain distribution measurement device 4 measures the strain distribution characteristics of another optical fiber. This allows the analysis device 5 to obtain strain distribution data along the extension direction of each core when the shape is unknown.

[0056] Step S303: The analysis device 5 calculates the differential strain between the strain distribution data for the reference shape acquired in step S301 and the strain distribution data for the unknown shape acquired in step S302.

[0057] Here, each core C of the MCF ｉ (i = 1 to 4) differential distortion ε ｉ is the bending strain ε of the MCF due to bending ｂ and the axial strain ε in the extension direction of the MCF ａ However, the axial strain ε ａ is constant within the MCF, so that each core C ｉ Therefore, each core C ｉ The differential distortion ε ｉ is expressed by the formula (1).

[0058] ε ｉ = ε ｂ，ｉ +ε ａ ...(1) Meanwhile, each core C ｉ Bending strain ε ｂ，ｉ is expressed by equation (2).

[0059] ε ｂ，ｉ =r ｉ κ cos(α ｉ +β) ... (2) As shown in FIG. ｉ is the center C of the cross section Ｃ From each core Cｉ is the straight-line distance to α ｉ is Core C ｉ and the center of the cross section C Ｃ and the line connecting the core C ｉ The adjacent core C and the center C of the cross section Ｃ κ is the curvature of the MCF1, and the angle between the line connecting the cores C ｉ β is the bending angle applied to the MCF2, and each core C ｉ is a common value.

[0060] In this example, since there are four cores, a set of simultaneous equations with four unknowns is obtained for the equation (1) into which the equation (2) is substituted. ｉ The differential distortion ε ｉ and the center C of the cross section Ｃ From each core C ｉ Straight-line distance r to ｉ and the angle α between adjacent cores ｉ and are substituted into equation (1). Then, the analysis device 5 calculates the axial strain ε ａ Taking advantage of the fact that the curvature κ and the bending angle β do not depend on any of the cores, the curvature κ and the bending angle β are solved by an analytical method such as regression analysis.

[0061] Step S304: The analysis device 5 uses the Frenet-Serret integral formula to derive position vectors for each point where strain was measured from the curvature κ and bending angle β obtained in step S303. By continuously obtaining position vectors from the measurement start point, it is possible to determine the direction and extent of deformation at each point in the extension direction of the MCF, and to obtain the three-dimensional shape over the entire length of the MCF and the shape change from the reference state.

[0062] Thereafter, the analysis device 5 calculates the shape and shape change of the linear structural object based on the three-dimensional shape and shape change of the MCF. For example, the analysis device 5 outputs the three-dimensional shape and shape change of the MCF as the calculation result of the shape and shape change of the linear structural object. At this time, the analysis device 5 may utilize a map or the like on which the position information of the linear structural object is written.

[0063] (Shape Measuring Method 2) Next, the shape measuring method 2 of the MCF and linear structural object will be described with reference to Fig. 6. Fig. 6 is a diagram showing the shape measuring method 2 of the MCF and linear structural object.

[0064] When the strain distribution measuring device 4 measures the difference in strain distribution based on the cross-correlation between the spectra of Rayleigh scattered light measured at two different times, the shape of the MCF and linear structure can be measured in a similar manner using the method shown in Figure 6.

[0065] Step S401: The strain distribution measuring device 4 measures the spectrum of Rayleigh scattered light from each core of the MCF in a predetermined state (reference shape).

[0066] Step S402: The strain distribution measuring device 4 measures the spectrum of Rayleigh scattered light from each core of the MCF in an arbitrary state (unknown shape).

[0067] Step S403: The strain distribution measuring device 4 measures the difference in strain distribution based on the cross-correlation between the spectrum of Rayleigh scattered light for the reference shape acquired in step S401 and the spectrum of Rayleigh scattered light for the unknown shape acquired in step S402.

[0068] Step S404: The analysis device 5 calculates the shape of the MCF using the difference in strain distribution (differential strain) measured in step S403, and calculates the shape of the linear structural object 100 based on the shape of the MCF.

[0069] (Modification 1) A supplementary explanation will be given for the case where an MCF having a core at the center of the cross section is used.

[0070] In this case, the measured strain of the central core is not affected by bending, so the central core C ｉ The equation (1) relating to ε ｉ = ε ａ This becomes:

[0071] In this case, the analysis device 5 calculates the differential strain between the measured strain in the reference shape and the measured strain in the unknown shape in the central core as the axial strain ε ａ ', and the differential strain in the non-central core ε ｉ From the axial strain ε ａThe position vector is derived by solving the simultaneous equations of equation (1) from which ' is subtracted.

[0072] (Modification 2) In the case where a single-mode optical fiber having one core at the center of the cross section is included in addition to the MCF, the analysis device 5 calculates the differential strain obtained from the single-mode optical fiber as the axial strain ε ａ '' and the axial strain ε ａ The axial strain ε obtained from the measured strain of the MCF using ａ This makes it possible to improve the accuracy of shape measurement.

[0073] [Effects] According to this embodiment, the shape of a linear structure is measured using an MCF fixed to the linear structure, so there is no need for special equipment or installation methods to suppress or take twisting into account, and the shape of a linear structure can be easily measured non-destructively and remotely using an MCF. In addition, there is no need to take into account twisting that occurs when the MCF is inserted into the linear structure, so the accuracy of measuring the shape of the linear structure can be easily improved.

[0074] Furthermore, according to this embodiment, the MCF of the optical fiber cable 2 is used, which has different vertical and horizontal lengths in cross section, thereby suppressing axial rotation of the optical fiber cable 2. As a result, unintended twisting does not occur in the MCF, and there is no need to consider this twisting in the analysis device 5, and special devices or installation methods for considering this twisting are not required. As a result, it is possible to further improve the shape measurement accuracy.

[0075] Furthermore, according to this embodiment, since the multiple optical fibers 1 are arranged and fixed on the same straight line, there is no unintended twist in the optical fibers 1, and no inherent twist that differs between the multiple optical fibers 1. As a result, it is possible to further improve the shape measurement accuracy.

[0076] Furthermore, according to this embodiment, since the cladding diameter of the MCF is 125±1 μm, it is possible to utilize existing optical fiber ribbons and optical fiber cable structures, which makes it easier to measure the shape of linear structures.

[0077] Furthermore, according to this embodiment, the MCF has four or more cores, and therefore can be used not only for shape measurement but also for communication purposes.

[0078] Furthermore, according to this embodiment, the shape of a linear structure is calculated using the strain distribution of the MCF and the strain distribution of the single-mode optical fiber, so that the shape measurement accuracy can be further improved.

[0079] [Others] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present disclosure.

[0080] The analysis device 5 of this embodiment described above can be realized, for example, using a general-purpose computer system including a CPU 901, a memory 902, a storage 903, a communication device 904, an input device 905, and an output device 906, as shown in FIG. 8.

[0081] The memory 902 and the storage 903 are storage devices. In the computer system, the CPU 901 executes a predetermined program loaded onto the memory 902, thereby realizing each function of the analysis device 5.

[0082] The analysis device 5 may be implemented by one computer, or by multiple computers, or may be a virtual machine implemented on a computer.

[0083] The program for the analysis device 5 can be stored in a computer-readable recording medium such as a HDD, SSD, USB memory, CD, or DVD. The computer-readable recording medium is, for example, a non-transitory recording medium. The program for the analysis device 5 can also be distributed via a communication network.

[0084] REFERENCE SIGNS LIST 1, 1a, 1b, 1c Optical fiber 2 Optical fiber cable 3 Optical switch 4 Strain distribution measuring device 5 Analysis device 51 Receiving unit 52 Calculation unit 901 CPU 902 Memory 903 Storage 904 Communication device 905 Input device 906 Output device

Claims

1. A measurement system for measuring a shape of a linear structure, comprising: a strain distribution measurement device for measuring each strain distribution along the extending direction of the multi-core optical fiber at two different timings or a difference between each strain distribution, using a multi-core optical fiber fixed along the extending direction of the linear structure; and an analysis device for calculating the shape of the multi-core optical fiber using the difference between each strain distribution measured at the two different timings, and for calculating the shape of the linear structure based on the shape of the multi-core optical fiber.

2. The measurement system according to claim 1, wherein the multi-core optical fiber is provided in an optical fiber cable fixed along the extension direction of the linear structure and having different vertical and horizontal lengths in cross section.

3. The measurement system according to claim 1, wherein the multi-core optical fiber has a cladding diameter of 125±1 μm and a number of cores of four or more.

4. The measurement system according to claim 1, wherein the strain distribution measuring device measures the strain distribution along the extension direction of the single mode optical fiber using a single mode optical fiber fixed along the extension direction of the linear structure and having one core at the center of its cross section, and the analysis device calculates the shape of the linear structure using the strain distribution of the multi-core optical fiber and the strain distribution of the single mode optical fiber.

5. A measurement method for measuring a shape of a linear structure, comprising: a strain distribution measurement device measures each strain distribution along the extending direction of the multi-core optical fiber at two different timings or a difference between each strain distribution, using a multi-core optical fiber fixed along the extending direction of the linear structure; an analysis device calculates the shape of the multi-core optical fiber using the difference between each strain distribution measured at the two different timings, and calculates the shape of the linear structure based on the shape of the multi-core optical fiber.

6. An analysis device comprising: a receiving unit that receives each strain distribution along the extending direction of a multi-core optical fiber at two different timings measured using a multi-core optical fiber fixed along the extending direction of the linear structure, or a difference between the each strain distribution, and a calculation unit that calculates a shape of the multi-core optical fiber using the difference between the each strain distribution measured at the two different timings, and calculates a shape of the linear structure based on the shape of the multi-core optical fiber.

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