JP2005345376A - Displacement measuring system and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure displacement in a structure, by performing measurement once later on, without acquiring the backward scattered light in real time, by always operating an expensive analyzer. <P>SOLUTION: A plastic optical fiber 11 is laid in advance in the structure 21. The signal light is made incident from one end of this laid plastic optical fiber 11. The backward scattered signal light is detected in response to plastic deformation caused in the plastic optical fiber 11. A displacement position and its displacement quantity are also measured by an OTDR device 12 based on the chronological changing trend in the quantity of the detected signal light. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a displacement measuring system and method for measuring a displacement caused by an earthquake or the like in a structure such as a tunnel or a building.

  Conventionally, when detecting a displacement generated in a structure such as a building or a tunnel due to an earthquake or the like, a method of electrically detecting the displacement using a strain gauge is generally used. However, in this method, as many wires as the number of sensors to be embedded are required, so it is not possible to reduce the cost, and it is necessary to continuously energize these electrical sensors and continue to record measured values. When a power failure occurs due to an earthquake, there is a problem that such a displacement cannot be detected.

  For this reason, a technique for measuring strain by embedding an optical fiber in a structure has been proposed particularly in recent years (see, for example, Non-Patent Documents 1 and 2). In this strain measurement technology, BOTDR (Brillouin Optical-fiber Time Domain Reflectometry) is used to allow signal light to enter from one end of the strain sensing optical fiber, and the backscattered light generated in the optical fiber at the same end. By observing, the generated distortion is measured.

  Further, in this strain measurement technique, it is possible to detect the strain applied to all points along the optical fiber by embedding one optical fiber in the structure in advance.

  However, the strain measurement technique using this optical fiber has a problem that even if an earthquake occurs, unless the backscattered light is acquired in real time, the associated strain cannot be identified.

  In this strain measurement, since a glass optical fiber is usually used, the strain is broken at a strain of about 5%. For this reason, when a large displacement occurs in the structure due to an earthquake or the like, the optical fiber itself breaks, and there is a problem that backscattered light corresponding to the displacement cannot be detected. .

Naruse, “Strain distribution sensing by BOTDR”, OPTRONICS (2000), No.3, pp.144-148 Hideo Iwaki “Current Status and Future of Optical Fiber Sensing in Construction Field”, 32nd Lightwave Sensing Technology Study Group, LST32-11, pp.79-84, Dec.2003

  Therefore, the present invention has been devised in view of the above-described problems, and the purpose thereof is to always operate an expensive analyzer without acquiring backscattered light in real time. It is intended to provide a displacement measuring system and method capable of measuring displacement in a structure by performing measurement only once after the fact, and in the case where a large displacement occurs in the structure. It is an object of the present invention to provide a displacement measuring system and method capable of measuring with high accuracy.

  In the present invention, in order to solve the above-described problem, a plastic optical fiber is laid in advance in a structure, and signal light is incident from one end of the laid plastic optical fiber, and plastic deformation generated in the plastic optical fiber is reduced. Accordingly, the backscattered signal light is detected, and further, the position of the displacement and the amount of the displacement are measured based on the temporal change tendency of the detected light amount of the signal light.

  That is, a displacement measuring system according to the present invention is a displacement measuring system for measuring the position and amount of displacement generated in a structure, and a plastic optical fiber previously laid in the structure and one end of the plastic optical fiber. In addition, the signal light is incident on the plastic optical fiber, and the backscattered signal light is detected according to the plastic deformation generated in the plastic optical fiber. A displacement measuring device for measuring the amount of displacement.

  Further, the displacement measuring method according to the present invention is a displacement measuring method for measuring the position of the displacement generated in the structure and the amount of the displacement. In the laying process, the plastic optical fiber is laid in advance in the structure, and the laying process. The signal light is incident from one end of the laid plastic optical fiber, and the backscattered signal light is detected according to the plastic deformation generated in the plastic optical fiber, and the detected signal light quantity tends to change over time. And a displacement measuring step for measuring the position of the displacement and the amount of the displacement.

  In the displacement measuring system and method according to the present invention, a plastic optical fiber is laid in advance in a structure, signal light is incident from one end of the laid plastic optical fiber, and in response to plastic deformation generated in the plastic optical fiber. Then, the back-scattered signal light is detected, and the position of the displacement and the amount of the displacement are measured based on the temporal change tendency of the detected light amount of the signal light.

  As a result, the displacement system and method to which the present invention is applied are structured by performing measurement once afterwards without acquiring backscattered light in real time by always operating an expensive analyzer. The displacement inside can be measured, and even when a large displacement occurs in the structure, it can be accurately measured.

  Hereinafter, as a best mode for carrying out the present invention, a displacement measuring system for measuring a displacement caused by an earthquake or the like in a structure will be described in detail with reference to the drawings.

  For example, as shown in FIG. 1, the displacement measuring system 1 includes a plastic optical fiber 11 laid in advance in a structure 21 such as a building, and an OTDR (Optical-fiber) connected to one end of the plastic optical fiber 11. Time Domain Reflectometry) device 12.

  The plastic optical fiber (POF) 11 uses PMMA (polymethyl methacrylate) as a base material, and can transmit light without breaking even when a tensile strain of nearly 100% is applied. The POF 11 is generally configured with a cladding outer diameter of 1 mm and a core diameter of 0.98 mm, and is covered with a jacket made of polyethylene or the like. By the way, this POF 11 has a larger transmission loss than a glass optical fiber. Therefore, the POF 11 is divided into about 100 m lengths, and an OTDR device 12 is sequentially connected to the end faces of the divided POFs 11 for measurement. May be performed.

  The OTDR device 12 allows signal light to enter from one end of the POF 11 and detects the signal light backscattered according to plastic deformation generated in the POF 11. The OTDR apparatus 12 measures the position of the displacement (strain ε) generated in the POF 11 and the amount of displacement (strain amount) based on the tendency of the detected amount of signal light to change over time.

  Incidentally, the OTDR device 12 may measure the position of the displacement and the amount of the displacement by measuring the number of photons of the detected signal light. In such a case, signal light having a wavelength of 650 nm, a pulse width of 5 ns, and an output of about 10 mW is emitted from the OTDR device 12, and the backscattered light is measured by a photo counter (not shown). The OTDR device 12 makes the signal light as the pulsed light enter the POF 11 many times, and records and integrates the photon time-series pulses each time.

  FIG. 2 shows the pulse train acquired for each of the signal lights # 1 to #n incident in the POF in time series. As shown in FIG. 2A, when a displacement occurs at the point H in the POF 11, the pulse train is density-modulated based on this displacement. When this is measured up to the signal light #n and the pulse frequency distribution is recorded with respect to time, a histogram having a peak at the point H can be formed as shown in FIG. It can be seen that the result of this histogram shows a similar tendency even when compared with the response of backscattered light detected by a normal OTDR as shown in FIG. In the OTDR device 12 capable of measuring the number of photons of such signal light, the spatial resolution corresponding to the time reading accuracy can be improved to about 10 mm.

  Next, a displacement measuring method by the displacement measuring system 1 to which the present invention is applied will be described.

  First, the POF 11 is laid in the structure 21 as an object whose displacement is measured by the displacement measuring system 1. About the installation place of POF11, it is set as the arbitrary places which want to measure a displacement according to the condition of the structure 21 and the construction method. Incidentally, when the POF 11 is laid, it may be arranged in a state in which an elastic strain or a plastic strain is applied in advance according to the laying location. The method of laying the POF 11 may be based on any method including the case of embedding the POF 11 in the structure 21 by using concrete or the like.

  Next, the displacement of the POF 11 laid in the structure 21 is measured by the OTDR device 12. This displacement measurement is performed when determining the degree of damage to the structure 21 after the occurrence of an earthquake or the like, or when diagnosing aging deterioration in the structure 21, and is performed after the laying of the POF 11 described above. It is common to do it.

  FIG. 3 shows the result of detecting the signal light incident on the POF 11 where the displacement has occurred by backscattering. When the time-dependent change in the response of the signal light corresponds to the distance D from the OTDR device 12 in the POF 11, as shown in FIG. 3, it is confirmed that a peak occurs at the distance D of 30 m. be able to. This peak occurs as a result of signal light being backscattered at a location where the distance D in the POF 11 is 30 m.

  FIG. 4 shows the relationship of the signal light response to the tensile strain applied to the POF 11. As shown in FIG. 4, as the tensile load to be applied to the POF 11 is increased, the tensile strain increases, and the response of the signal light gradually increases accordingly. Incidentally, when the POF 11 is only elastically deformed by the tensile load applied to the POF 11, the distortion is eliminated by removing the load, and the response of the signal light is reduced accordingly. However, when the POF 11 is plastically deformed due to the tensile load applied to the POF 11, even if the load is removed, the plastic strain remains, so that the response of the signal light returns to the original as shown by the dotted line in FIG. Will disappear.

  The plastic strain generated in the POF 11 remains semipermanently once the plastic deformation has occurred. Therefore, by laying this POF 11 in the structure 21, for example, as shown in FIG. 5 (a), the plastic deformation caused in the structure 21 due to the earthquake that occurred at the time t1 is post-mortem at the time t2. Can be detected. On the other hand, when a general glass optical fiber is laid in the structure 21 as an alternative to the POF 11, the optical fiber itself is broken by the earthquake that occurred at time t1. For this reason, even if signal light is incident on the optical fiber at time t2, backscattered light corresponding to the displacement cannot be detected as shown in FIG.

  That is, in the present invention, paying attention to the fact that the plastic strain remaining in the POF 11 causes a so-called memory effect that causes the optical characteristic change of the POF 11 to remain and also maintains the response of the signal light thereto. The position and amount of displacement generated in the structure 21 are measured afterwards. As a result, in the displacement measurement system 1 to which the present invention is applied, the expensive analysis device is always operated to acquire the backscattered light in real time, and the measurement is performed only once afterwards in the structure 21. It is possible to measure the displacement.

  In addition, since the displacement measuring system 1 uses plastic (PMMA) as a base material, it only plastically deforms even when a larger load is applied thereto. It will not break. For this reason, the present invention is useful particularly when a large earthquake occurs in that a large load is applied to the POF 11 and can be stored as a plastic deformation applied to the POF 11.

  The above-described memory effect is often expressed by a sensor or the like that must be supplied with power. However, in the displacement measurement system 1 to which the present invention is applied, such an effect can be expressed with no power source, which is large. Even when a power failure or the like occurs in the event of an earthquake or the like, displacement measurement can be performed without being affected by this. In particular, when a power failure occurs, it is extremely difficult to always operate the analyzer, but in the present invention having the above-described configuration, it is possible to leave the plastic deformation generated in the POF 11 semipermanently. Therefore, after the power transmission and distribution function in the city is fully restored after the earthquake, it is possible to measure this after the fact. In addition, by measuring the number of photons of the signal light, the resolution of displacement measurement in the structure 21 can be further improved.

  In the displacement measuring system 1 to which the present invention is applied, the amount of displacement generated in the structure 21 can also be measured. For example, when a 100 m POF 11 is wound around a round bar about 40 m away from the light source of the OTDR device 12, the profile of the signal light to be detected is the diameter d of the round bar as shown in FIG. There will be differences between them. Here, as shown in FIG. 6B for the signal light profile, when the peak portion is separated into the reflection amount and the loss amount, both the reflection amount and the loss amount decrease as the diameter d of the round bar increases. Will do. Since the distortion amount applied to the POF 11 depends on the size of the diameter d of the round bar, the reflection amount and the loss amount at the peak portion of the signal light change according to the distortion applied to the POF 11.

  In the displacement measurement system 1 to which the present invention is applied, when the plastic deformation of the POF 11 laid on the structure 21 is detected by analyzing the change tendency of the light amount of the signal light in advance, the light amount of the signal light is detected. By identifying the amount of reflection and the amount of loss at the peak portion, it is possible to more accurately determine the position and amount of displacement based on the plastic deformation.

  Incidentally, the signal light to be detected is reflected in accordance with each of the displacement modes such as tensile deformation and torsional deformation applied to the POF 11 and lateral pressure and temperature rise applied to the POF 11 in addition to the bending deformation described above. The profile tendency including the amount of loss is different. FIG. 7 shows a profile of signal light detected when a side pressure is applied to the POF 11, when torsional deformation is applied, and when tensile deformation is applied.

  For example, as shown in FIG. 7A, when the lateral pressure is applied to the POF 11 as 143, 301, and 372 kgf, the reflection amount approaches 0 and only the loss amount is generated. Further, as shown in FIG. 7B, when the POF 11 is deformed so that the torsion angle is 0, 900, and 1440 deg, a signal in which the loss amount at the peak portion is larger than the reflection amount. A light profile can be obtained. As shown in FIG. 7C, when tensile deformation is applied to the POF 11 so that the distortion amount is 0, 50, 70%, the signal light has a shape in which the reflection amount at the peak portion is larger than the loss amount. Can be obtained.

  By referring to the profile including the reflection amount and the loss amount at the peak portion analyzed in advance, when the back scattered light from the POF 11 to be actually measured is detected, the mode of the displacement is identified in more detail. It is also possible to do.

  For example, when discriminating between bending deformation and a side pressure load, if the amount of reflection of the signal light is 0, it can be determined that the side pressure is loaded. Further, when determining either bending deformation or torsional deformation, since the profiles are similar to each other, it cannot be easily determined, but the change tendency of the amount of signal light with respect to the distance D is somewhat between the two. Because they are different, it is possible to make a determination based on these differences. When discriminating between the bending deformation and the torsional deformation, if the loss amount is larger than the reflection amount, it can be discriminated as the bending deformation. Further, when determining either the side pressure load or the torsional deformation, it can be determined that the side pressure is loaded if the amount of reflection of the signal light is zero. Further, when determining either the side pressure load or the tensile deformation, it can be determined that the side pressure is loaded if the reflection amount of the signal light is zero. Further, when determining either torsional deformation or tensile deformation, it can be determined that tensile deformation is applied if the loss amount is larger than the reflection amount.

  In addition, as an embodiment of the displacement measurement system 1 described above, the case where the POF 11 is laid on a structure such as a building has been described as an example. However, the present invention is not limited to such a case, and includes a house. Of course, it can be applied to displacement measurement of small buildings, gas pipes, water pipes, etc. and health monitoring of roads, slopes, bridges, etc.

It is a figure which shows the structure of the displacement measuring system to which this invention is applied. It is a figure which shows the pulse train acquired about each signal light # 1- # n which injected into POF in time series. It is a figure which shows the result of having backscattered the signal light which injected into POF which the displacement produced, and having detected it with the OTDR apparatus. It is a figure which shows the relationship of the response of the signal light with respect to the tensile distortion added to POF. It is a figure for demonstrating about the case where the plastic deformation which arose in the structure by the earthquake which generate | occur | produced at the time t1 is detected afterwards. It is a figure which shows the reflection profile of POF wound around the round bar. It is a figure which shows the profile of the signal light in each deformation | transformation mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Displacement measurement system, 11 Plastic optical fiber (POF), 12 OTDR apparatus, 21 Structure

Claims (6)

In a displacement measurement system for measuring the position of displacement generated in a structure and the amount of displacement,
A plastic optical fiber previously laid in the structure;
The signal light is incident from one end of the plastic optical fiber, the signal light backscattered according to the plastic deformation generated in the plastic optical fiber is detected, and the change in the light amount of the detected signal light over time is detected. A displacement measuring system comprising: a displacement measuring device that measures the position of the displacement and the amount of displacement based on the tendency. The displacement measuring system according to claim 1, wherein the displacement measuring device measures the position and the amount of the displacement by measuring the number of photons of the detected signal light. The displacement measuring system according to claim 1, wherein the displacement measuring device identifies the displacement mode based on the detected amount of the signal light. In a displacement measuring method for measuring the position of a displacement generated in a structure and the amount of the displacement,
A laying step of laying a plastic optical fiber in the structure in advance;
The signal light is incident from one end of the plastic optical fiber laid in the laying step, the signal light backscattered according to the plastic deformation generated in the plastic optical fiber is detected, and the detected signal light A displacement measuring method comprising: a displacement measuring step of measuring the position of the displacement and the amount of displacement based on a change tendency of the amount of light with time. The displacement measuring method according to claim 4, wherein, in the displacement measuring step, the position of the displacement and the amount of the displacement are measured by measuring the number of photons of the detected signal light. The displacement measuring method according to claim 4, wherein, in the displacement measuring step, the displacement mode is identified based on the detected light amount of the signal light.

Images