JP3772303B2 - Strain measuring device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention measures the amount of strain in an underground excavation well or hole, for example, by measuring the amount of strain in the length direction of an underground excavation well or pipe inserted along the bore using an FBG applied optical fiber strain sensor. In addition, with respect to measuring devices used to efficiently measure various amounts of distortion, particularly in narrow spaces, in various building structures, etc., the durability and measurement accuracy of the measuring device should be improved. With the goal.
[0002]
[Prior art]
When measuring the amount of strain in various structures, etc., the optical fiber is directly interposed between the fulcrum and the action point, and the degree of distortion is measured by measuring the amount of extension of the optical fiber accompanying the movement of the action point with an optical strain sensor. A measurement method that uses a device that can measure a minimum skewness by attaching it to the outer surface of a structure or the like has been already filed by the present applicants (Japanese Patent Application). 2000-204849).
[0003]
In the above-described invention, an optical fiber is directly interposed between a stationary fulcrum such as a ceiling or a suspension reference point and an action point movable with respect to the fulcrum, and the amount of extension of the optical fiber accompanying the movement of the action point is increased. The measurement is performed with an optical sensor, and the weight or strength of the object that causes the movement of the action point, and the inclination of the measurement surface and the change in crack width are measured with high accuracy as the degree of distortion.
[0004]
[Problems to be solved by the invention]
However, the above-described distortion measuring device is used in that an optical fiber is directly interposed between fulcrums and action points in use, and only the portions of the fulcrums and action points are pasted using an adhesive or the like. In addition, the optical fiber strain sensor and the optical fiber wiring connected thereto are exposed, and the exposed portion is easily damaged and has poor durability. Further, from the viewpoint of preventing such damage, in the actual construction site, a protective structure such as applying a resin coating to the above-described optical fiber strain sensor or optical fiber wiring or covering with a metal protector is often applied.
[0005]
For this reason, rigidity due to such a protective structure is added and the inherent rigidity of the object to be measured is increased. As a result, the accuracy in measuring the degree of distortion tends to be adversely affected. Not only that, it is inevitable that the structure of the strain measuring device is complicated and large, and since it is easily damaged, it requires sufficient attention for transportation and handling, and the cost of the measuring device is low. Soaring is inevitable.
[0006]
Therefore, the present inventor opened a pore of a certain depth in the plastic material, inserted an optical fiber strain sensor into the pore, and positioned at both ends in the length direction of the inserted optical fiber strain sensor. The two metal bodies, which are more rigid than the plastic material, are fixed to the plastic material integrally, and the two metal bodies are fixed to both ends of the measurement section of the measured part, and the plastic material is subjected to the strain stress received. A technique has been devised for measuring the amount of strain with the optical fiber strain sensor described above.
[0007]
The strain measurement method using such a plastic material is excellent in handleability and can measure the strain amount with high accuracy, but it requires considerable skill and difficulty in drilling holes in the plastic material. In addition, since plastic materials are hygroscopic and the material and volume change over time, causing deformation and distortion in the plastic itself, the reliability of the measurement results gradually becomes longer when used over a long period of time. In order to be lost, it is inevitable that a complicated and large-sized structure is inevitably required since a large moisture-proof protection structure is required to take a complete moisture-proof measure.
[0008]
[Means for Solving the Problems]
In the present invention, in the distortion measuring device using the FBG applied optical fiber strain sensor, a metal material is used instead of a plastic material as a measurement body, and the structure is simplified and the measurement accuracy is improved. The durability is remarkably improved and the cost is remarkably reduced. However, even if a metal material is used for the measurement body here, the amount of strain cannot be measured unless the elasticity is lower than that of the two rigid bodies fixed to the portion to be measured.
[0009]
Therefore, in the present invention, when using a metal material that is not much different in quality as compared with the two rigid bodies as a measuring body, the cross-sectional area is used as a means for making a difference between the two rigid bodies and the elastic surface. Decided to use a small metal tube. That is, specifically, two rigid bodies having fixing means for integrally fixing to the measurement site at both ends of the location where the amount of strain is to be measured are integrally interposed between the rigid bodies. A metal tube measuring body, and the FBG applied optical fiber strain sensor is filled in the metal tube with an adhesive filled in the metal tube toward the rigid body direction at both ends of the metal tube. The present invention relates to a strain amount measuring device that is integrally inserted.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the specific contents of the present invention will be described based on the embodiment shown in FIGS. 1 and 2. 1A and 1B are rigid bodies, and 3 is a metal pipe measurement integrally interposed between two rigid bodies 1A and 1B. Represents the body. As the rigid bodies 1A and 1B, those having a shape and a material that can be fixed stably at both ends of the measurement points in a certain section without being deformed are selected. For example, depending on the measurement location, when it is used for the purpose of measuring the amount of strain in the depth direction in a hole excavated in the ground, it is formed into a shape that is easy to insert into the hole (for example, a cylindrical shape) A material having a certain hardness such as iron (in some cases, high carbon steel or hardened carbon steel) or other metal is selected.
[0012]
Further, fixing means 2 for fixing the rigid bodies 1A and 1B integrally to the start and end portions of a fixed section for measuring the strain amount is attached. The fixing means 2 may be of various structures depending on the shape and structure of the location to be measured. For example, when the fixing means 2 is installed in the excavation hole H excavated in the ground E as shown in FIG. May be a donut-shaped spacer for integrally fixing the rigid bodies 1A and 1B to the inner wall surface of the pipe P inserted in the excavation hole H, and may be directed in the radial direction at equal circumferential intervals. It may be a plurality of bar-like ones that are protruded.
[0013]
A general-purpose metal pipe can be used for the metal pipe measuring body 3, and the inner diameter has a necessary and sufficient inner diameter for inserting the optical fiber strain sensor 4 described later, and together with the rigid bodies 1A and 1B described above. The metal tube measuring body 3 is selected to have a size and a length that do not hinder the insertion into the measurement location, and the metal pipe measuring body 3 is screwed between the two rigid bodies 1A and 1B or welded, The optical fiber strain sensor 4 is inserted inside by an adhesive and is inserted inside.
[0014]
That is, as shown in FIG. 2, the optical fiber strain sensor 4 is inserted into the metal tube measuring body 3 toward the rigid bodies 1A and 1B on both sides to be integrally connected. As the optical fiber strain sensor 4 used in the present embodiment, “FBG applied sensor” (Fiber Bragg Grating) is used.
[0015]
Further, the metal tube measuring body 3 in which the FBG applied optical fiber strain sensor 4 is inserted is filled with an adhesive 5, and the FBG applied optical fiber strain sensor 4 which has been solidified is inserted into the metal tube measuring body 3. Integrate. In addition, 4a and 4b have shown the optical fiber wiring connected to the above-mentioned FBG application optical fiber distortion sensor 4 pulled in in rigid body 1A * 1B.
[0016]
Furthermore, the adhesive 5 filled in the metal tube measuring body 3 is not suitable for a volatile material such as an instantaneous adhesive or a type that cures by reacting with moisture in the atmosphere. As the possible adhesive, it is sufficient that it has excellent filling properties in the metal tube measuring body 3 and is cured in the metal tube measuring body 3 and the volume reduction after curing is not as small as possible. An example of such an adhesive is an epoxy resin adhesive.
[0017]
In the configuration of the above-described embodiment, a measurement example when an FBG applied sensor is used as the optical fiber strain sensor 4 will be described. Light having a wide wavelength band is incident from one end of the optical fiber and reflected at the sensor unit. Light is captured at the same end as the incident. When distortion occurs in the sensor unit, the reflected wavelength is shifted, and the amount of distortion is calculated by measuring the degree of this shift. In this case, the occurrence of distortion means that the length has changed, and is accurately expressed as [length of change] / [original length].
[0018]
The above-described FBG applied sensor is obtained by changing the refractive index of the core portion of the optical fiber for every predetermined period, and has a characteristic of selectively reflecting only light of a specific wavelength called “Bragg wavelength”. Therefore, when an external force is applied and distortion occurs in the FBG applied sensor, the Bragg wavelength changes, and the amount of change in the Bragg wavelength is proportional to the degree of distortion. The FBG applied sensor detects the amount of change in the Bragg wavelength by using the relationship between the amount of change in the Bragg wavelength and the degree of distortion, and measures the inclination of the object in the FBG applied sensor as the degree of distortion. It is something that can be done.
[0019]
However, the rigid bodies 1A and 1B in which the metal pipe measuring body 3 is integrally interposed in the intermediate portion are inserted into the pipe P attached in the excavation hole H excavated in the underground E, and the excavation hole at the target depth is obtained. When the fixing means 2 is used to integrally fix the starting end portion and the terminal end portion of the portion where the strain of H is measured, the metal pipe measuring body 3 according to the degree of strain of the pipe P received by both the rigid bodies 1A and 1B. Deform. In this case, it is assumed that measurement preparation is performed by irradiating one end of an optical fiber connected to the optical fiber strain sensor 4 embedded in the metal tube measuring body 3 with a predetermined amount of light.
[0020]
Next, based on the principle diagram of FIG. 3 in which only the diameter of the portion of the metal tube measuring body 3 is sufficiently enlarged for convenience of explanation, the metal pipe measuring body is assumed in a portion where the pipe P is not distorted as a premise. 3 is not deformed, L = R = a. However, when the pipe P is distorted, the metal pipe measuring body 3 is deformed along the length direction of the pipe P, and the rigid bodies 1A and 1B are not deformed. Therefore, the rigid bodies 1A and 1B are clearly corresponding to the bending of the pipe P. A positional relationship with an angle is formed. In the metal pipe measuring body 3, contraction occurs on the inner side (R side) where the pipe P is bent, and expansion occurs on the outer side (L side) where the pipe P is bent. Therefore, in this case, R = a−b L = a + b. If the distance between the rigid bodies 1A and 1B = a, then b ′ at a position where the rigid body 1B is separated by a distance d in the direction perpendicular to the pipe P can be approximated as b ′ = d × tan c.
[0021]
From this, it can be seen that there is a correlation between the angle formed by the rigid bodies 1A and 1B and the amount of deformation of the metal tube measuring body 3 sandwiched between the rigid bodies 1A and 1B. Although it is difficult to directly obtain the angle c in FIG. 3, since the angle c can be obtained from the deformation amount of the metal pipe measuring body 3, finally the strain amount of the drill hole with respect to the pipe P, that is, the ground is measured. can do.
[0022]
【The invention's effect】
As described above, the present invention provides, as a strain amount measuring device, two rigid bodies having fixing means that are positioned at both ends of a portion where a strain amount is to be measured and each of which is integrally fixed to a measured location ; It consists of a metal tube measuring body that is integrally interposed between rigid bodies, and the metal tube measuring body is filled with adhesives in the metal tube and FBG applied optical fiber strain sensor toward the rigid body direction at both ends of the metal tube. Since it is solidified and inserted integrally with the metal tube, it simplifies the structure, maintains high accuracy of measurement, particularly improves durability, and significantly reduces costs. For example, the amount of strain in an underground excavation well or a hole can be measured, or various types of strain in various building structures and the like, particularly in a narrow space, can be efficiently measured.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a use state of a strain amount measuring apparatus according to an embodiment of the present invention.
2 is an enlarged cross-sectional view showing a central portion of a metal tube measuring body portion in FIG. 1;
FIG. 3 is a diagram for explaining the principle of measuring means using the FBG application sensor of the present invention.
[Explanation of symbols]
1A rigid body 1B rigid body 2 fixing means 3 metal tube measuring body 4 optical fiber strain sensor 5 adhesive

Claims (1)

Two rigid bodies that are positioned at both ends of the portion where the amount of strain is to be measured and have a fixing means for integrally fixing to the portion to be measured, and a metal pipe measuring body that is integrally interposed between the rigid bodies, The metal tube measuring body is inserted into the metal tube integrally with the FBG-applied optical fiber strain sensor in the direction of the rigid body at both ends of the metal tube, with the adhesive filled in the metal tube and solidified. A distortion amount measuring apparatus characterized by comprising:

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