JP3189756B2 - Optical fiber strain sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber strain sensor for measuring a strain of a structure using an optical fiber.

[0002]

2. Description of the Related Art Conventionally, as an optical fiber sensor for measuring the strain of a structure, Japanese Patent Application No. 8-261 by the present applicant has been proposed.
996. This optical fiber sensor will be described with reference to FIG. The optical fiber sensor 27 of FIG.
The solenoid 22 is formed by winding the optical fiber 21 for at least one turn and bonding a part or the entire circumference in the circumferential direction to the entire area in the axial direction and the solenoid 22 in contact with the inside of the solenoid 22 and in parallel with each other. An optical fiber sensor 27 comprising two formers 23 each having an elliptical shape and one end fixed to an object to be measured.
It is. The solenoid 22 is previously flattened in an elliptical shape by two formers 23 so as to cope with both tensile and compressive deformation.

[0003] The former 23 is made of a rubber base 2.
4, the lower end surface of the former 23 is exposed on the same plane as the bottom surface of the base 24, and has a shape that can be directly adhered to the object to be measured. Reference numeral 23a denotes an adhesion surface on which the former 23 is adhered to the measurement object. Further, the solenoid 22 and the former 23 are covered with a rubber cover 25 for protection. Former 23 is a solenoid 2
The portion provided with 2 is thin, and the portion adhered to the measurement object is formed thick so as to be sufficiently fixed to the measurement object. The deformation of the measurement object is fixed to the measurement object 2
It appears as a change in the distance between the formers of the book, and this change causes a change in the outer diameter shape of the solenoid, which corresponds to the amount of optical transmission loss of the optical fiber sensor 27. it can.

[0004]

However, the conventional optical fiber sensor shown in FIG. 3 has the following problems. First, in the conventional optical fiber sensor, since the constituent materials of the sensor except the optical fiber 21 and the former 23 are made of rubber, it is difficult to fix the optical fiber cable 26, and the rubber protective cover 25 is also buried underground. There is a disadvantage that strength is insufficient below. And the optical fiber sensor, it is necessary to adjust the distance between formers to configure a sensor having desired characteristics, such as the range of strain to be measured, the sensitivity, and the gauge length. There is no special mechanism for this adjustment.

In this type of optical fiber sensor, the solenoid 22 may fall out of the former 23 when a large bending deformation is applied. However, no countermeasure has been taken for this and there is room for improvement. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its main object to provide an optical fiber strain sensor which can easily measure the strain of a structure using an optical fiber. I do.

Another object of the present invention is to provide an optical fiber strain sensor which can easily measure the strain of a structure and can be used for a long period of time even in an outdoor or underground environment.

Another object of the present invention is to provide an optical fiber strain sensor capable of easily measuring the strain of a structure and adjusting the sensor to have a desired characteristic.

[0009]

Means for Solving the Problems The present invention has been made to achieve the above object, and the invention of claim 1 has the following features.
The optical fiber is wound at least one turn or more, and a part or the entire circumference in the circumferential direction is adhered over the entire area in the axial direction, and the solenoid is arranged in parallel with each other by contacting the inside of the solenoid, and the solenoid is made elliptical, and Fixing two formers connected to the object to be measured, a rigid base plate smaller than the object to be measured for fixing the former, a metal protective cover for protecting the solenoid and the former, and fixing the optical fiber cable. An optical fiber strain sensor having a pressing member. This optical fiber strain sensor has an optical fiber strain sensor in which a base plate is made of a material having a rigidity smaller than that of an object to be measured, for example, rubber, and a former and a pressing member of an optical fiber cable are made of metal, and a hybrid structure of rubber and metal is used. Therefore, the optical fiber strain sensor has a structure that is not affected by an external force applied to a portion other than the contact surface with the object to be measured.

The invention according to claim 2 has a former stand fixed to the object to be measured for coupling the object to be measured and the former, and a former arm attached to the former stand and having a former attached to the tip thereof. The optical fiber strain sensor according to claim 1, wherein the distance between the two formers is easily adjusted.

The invention according to claim 3 is characterized in that the two former stands fixed to the object to be measured are provided with tapping at the bottom thereof for fixing to the adjusting jig when adjusting the sensor. The optical fiber strain sensor according to claim 1, wherein the distance between the two formers is easily adjusted.

According to a fourth aspect of the present invention, there is provided an optical fiber strain sensor according to the first aspect, wherein the two formers fixed to the object to be measured are provided with optical fiber shift stoppers. This is an optical fiber strain sensor in which the solenoid does not fall out of the former even when a large bending deformation is applied.

The invention according to claim 5 is characterized in that after the adjustment of the sensor is completed, a fixing plate for fixing the distance between the two formers and removing it at the time of measurement is provided. The optical fiber strain sensor is an optical fiber sensor in which the distance between two formers can be easily adjusted.

According to a sixth aspect of the present invention, in the optical fiber strain sensor according to the first aspect, the sensor cable of the optical fiber is an optical fiber coated with a metal tube. This is an optical fiber strain sensor that protects the sensor cable for a long period of time in an environment.

According to a seventh aspect of the present invention, in the optical fiber strain sensor according to any one of the first to sixth aspects, a protective cover for covering the whole is attached, and the protective cover is provided in a gap between the optical fiber cable outlet. An optical fiber strain sensor characterized by being filled with resin, which can protect the sensor for a long period of time outdoors or in an underground environment.

According to the present invention, since the main structural members of the sensor other than the base plate are made of metal, the structure is not affected by an external force applied to portions other than the contact surface with the object to be measured. In an underground environment, a protective cover or a metal tube-coated optical fiber is used to protect the sensor for a long time. Also, in order to facilitate the adjustment of the distance between the two formers, the former has a two-part structure of a stand and an arm, and the former stand is provided with a tapping for fixing to an adjustment jig when adjusting the sensor. I have. After the sensor adjustment is completed, the distance between the two formers can be fixed by the fixing plate. In addition, since the two formers are provided with optical fiber slip stoppers, the solenoid does not fall out of the former even when a large bending deformation is applied.
Therefore, it is possible to stably measure the strain of a structure for a long period of time outdoors or in an underground environment. The elliptical shape referred to here means a substantially elliptical shape, and does not mean a mathematically exact ellipse.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical fiber strain sensor according to the present invention will be described with reference to the drawings.
1A and 1B are views showing an embodiment of the present invention, wherein FIG. 1A is a partially cutaway plan view, and FIG. 1B is an XY cross section having a partially cutout of FIG. FIG.

In FIG. 1, an optical fiber strain sensor 1
Reference numeral 0 denotes a solenoid 2 in which the optical fiber 1 is wound around the optical fiber 1 for at least one turn in a solenoid shape, and a rod-shaped 2 which is in contact with the inside of the solenoid 2 and is arranged in parallel in the axial direction.
The two formers 3 are fixed to the object 8 to be measured. Two Former 3
Are arranged at intervals slightly longer than the inner diameter of the original perfect circle in which the optical fiber 1 is wound in a solenoid shape, and the solenoid 2 becomes elliptical in a state where the solenoid 2 is supported by two formers 3. In addition, the shape of the solenoid 2 may be a long hole shape, and the elliptical shape means a substantially elliptical shape,
Obviously, this does not mean a mathematically exact ellipse.

First, referring to FIG. 1, a description will be given of strain measurement by the optical fiber strain sensor 10. The optical fiber strain sensor 10 can measure the strain of the measurement target 8 by directly or indirectly fixing the former 3 to the measurement target 8. When tensile deformation occurs in the measuring object 8, the distance between the two formers changes from the initial state L to (L + λt), and the curvature given to the solenoid 2 by the former 3 increases, so that the optical transmission loss increases. When compression deformation occurs in the measuring object 8, the distance between the two formers is changed from the initial state L to (L
−λc), and the curvature given to the solenoid 2 by the former 3 becomes smaller, so that the optical transmission loss becomes smaller. Here, λt and λc are displacement amounts. By measuring the optical transmission loss, the distortion of the measuring object 8 can be measured.

Next, the configuration of the present embodiment will be described in detail. In the sensor section of the optical fiber strain sensor 10, two former stands 3a are erected at predetermined intervals on a rubber base plate 4, and a former arm 3b is provided at the tip of each former stand 3a.
The solenoid 2 is supported by a former 3 provided at a tip end of a former arm 3b facing each other. The solenoid 2 is supported by a shift stopper 3c provided on the former 3. This sensor section is covered with a rubber cover 5.

The structure of the former part includes a former stand 3a which is a part to be fixed to the object 8 to be measured, and a former arm 3b having a former 3 on which the solenoid 2 is mounted and having a tip attached thereto. With such a structure, the distance between the two formers can be adjusted by adjusting the dimension of the former arm 3b. In particular, when the base plate 4 is made of a rubber material, the former stand 3a
Since it is difficult to accurately attach the former, the distance between the two formers can be adjusted by adjusting the former arm 3b. Further, the work of mounting the solenoid 2 is also facilitated.
Further, the two former stands 3a are tapped for fixing to the adjustment jig when the sensor is adjusted, and are formed with screw holes 3d. The two formers 3 are provided with stoppers 3c for the optical fiber 1, so that even when a large bending deformation is applied, the solenoids 2
Never get out of

A rubber cover 5 covers the solenoids 2 provided on the respective formers 3, and is further covered with metal protection covers 10a and 10b. A metal protection cover is provided adjacent to the protection cover 10b. 10c is arranged to cover the optical fiber cable. Protective cover 1
0a is fastened to the front block 6 by bolts 8a, and the protective covers 10b, 10c are pressed by metal pressing members 9a, 9b.
Has been concluded. Further, protective covers 10a to 10c
Is fixed to the protective covers 10a and 10c with the bolts 7. The rubber part and the metal part are integrally formed with a metal part during bonding or rubber molding. For example, a metal front block 6, a base plate 4, and a pressing member 9a
And the base plate 4 are integrally formed and joined.
After the adjustment of the sensor is completed, the distance between the two formers 3 can be fixed by fixing the fixing plate 11 to the protective covers 10a and 10c. When the optical fiber sensor is mounted on the measuring object 8, the fixing plate 11 is removed.

As described above, the base plate of the optical fiber strain sensor needs to be made of a material having a rigidity smaller than that of the measuring object 8 in order to follow the deformation of the measuring object 8. For example, if it is configured using a rubber material, it is possible to follow the deformation of pipelines such as steel pipes and resin pipes to be measured and the ground in which those pipelines are embedded. However, if the entire sensor is made of a rubber material, it is affected by an external force other than the deformation of the measuring object 8, for example, an earth pressure when used in an underground environment. Also, when attaching the optical fiber cable, there is no other suitable means for fixing to the rubber material other than bonding. Further, it is necessary to make the configuration such that the movement of the optical fiber cable is not transmitted to the solenoid 2, which is not suitable for attaching the optical fiber cable. Therefore, in the present embodiment, the base plate 4 is made of rubber, and the former 3, the pressing members 9a and 9b, the protective cover 10
By making a to 10c made of metal, the optical fiber strain sensor can be given rigidity and can follow the deformation of the measuring object 8.

The base plate may have a rigidity smaller than that of the object to be measured. When the object to be measured is a steel pipe, a base plate made of resin may be used.

The protective covers 10a and 10b are made of metal and are divided into two parts at the center of the two formers 3, so that the distance between the two formers is changed.
By moving the positions of the protective covers 10a and 10b to the left and right in accordance with the measurement conditions and the range of the measurement target 8, various measurement targets can be handled.

Further, as shown in FIG. 2, the optical fiber strain sensor of this embodiment is provided with a protective cover 12 for removing the fixing plate and covering the whole, and the top plate 12a of the protective cover 12 is made of metal. The side plate 12b is made of rubber to have rigidity necessary for protecting the optical fiber strain sensor 10 and flexibility for following the deformation of the measurement object 8. Further, a waterproof treatment can be performed by filling a gap such as an outlet 13 of the optical fiber cable covered with the metal coating tube 1a with a filler such as an elastic silicone resin. Increases durability when buried outdoors or underground.

The optical fiber cable is a metal clad tube 1.
This is a metal tube-coated optical fiber that is completely waterproof and is resistant to external forces. Needless to say, this optical fiber cable can be wired outdoors or buried underground.

[0028]

As described above, the present invention has the following effects. According to the present invention, the main structural members of the sensor other than the base plate are made of metal, so that the structure is not affected by an external force applied to a portion other than the adhesion surface. The use of the metal tube-coated optical fiber has an advantage that stable strain measurement can be performed over a long period of time even in an outdoor or underground environment.

Further, according to the present invention, the structure of the former portion has a structure of a former stand and an arm, and the former stand is subjected to tapping for fixing to an adjustment jig of the sensor. Since the distance between the two formers can be fixed after the adjustment, there is an advantage that the sensor having desired characteristics can be easily adjusted.

According to the present invention, since the two formers are provided with the stoppers for the optical fibers, the solenoids do not fall out of the former even when a large bending deformation is applied. There is an advantage that an optical fiber strain sensor having good durability can be provided.

[Brief description of the drawings]

1A and 1B show an embodiment of an optical fiber strain sensor according to the present invention, wherein FIG. 1A is a partially cutaway plan view thereof, and FIG. 1B is an XY sectional view having the partially cutout portion.

FIG. 2 is a perspective view showing one shape in which a protective cover is provided on the optical fiber strain sensor of the present invention.

FIG. 3 is a diagram showing an example of a conventional optical fiber strain sensor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical fiber 1a metal cladding tube 2 solenoid 3 former 3a former stand 3b former arm 3c stopper 4 base plate 5 rubber protective cover 6 front block 7 bolt 8a-8d bolt 9a, 9b pressing member 10 optical fiber strain sensor 10a, 10b 10c Metal protective cover 11 Fixing plate 12 Overall protective cover 12a Top plate 12b Side plate 13 Outlet for optical fiber cable

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01B 11/00-11/30 102 G01L 1/24 G02B 6/00

Claims (7)

(57) [Claims] 1. A solenoid in which an optical fiber is wound at least one turn or more, and a part or the entire circumference of the solenoid is adhered over the entire area in the axial direction, and a solenoid is arranged in parallel with each other by contacting the inside of the solenoid. Two formers having an elliptical shape and connected to the object to be measured,
An optical fiber strain sensor comprising: a base plate having a rigidity smaller than a measurement object for fixing the former; a metal protective cover for protecting the solenoid and the former; and a pressing member for fixing the optical fiber cable. . 2. A form stand comprising: a former stand fixed to a measuring object to connect the measuring object to the former; and a former arm attached to the former stand and having a former attached to a tip thereof. 2. The optical fiber strain sensor according to 1. 3. The optical fiber strain sensor according to claim 1, wherein the two former stands are provided with tap processing at their bottom portions for fixing the former to an adjusting jig when adjusting the sensor. 4. The optical fiber sensor according to claim 1, wherein the two formers are provided with optical fiber shift stoppers. 5. The optical fiber strain sensor according to claim 1, further comprising a fixing plate for fixing the distance between the two formers after the adjustment of the sensor and removing the former at the time of measurement. 6. The optical fiber strain sensor according to claim 1, wherein the optical fiber sensor cable is a metal tube coated optical fiber. 7. The optical fiber strain sensor according to claim 1, wherein a protective cover for covering the whole is attached, and a resin is filled in a gap between the optical fiber cable outlet of the protective cover. Optical fiber strain sensor.