JP2002005759A - Strain sensor using optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a strain sensor using an optical fiber capable of holding sufficient strength while securing the deformation detecting precision of a measured position. SOLUTION: An optical fiber coated fiber 11 is directly covered with a thin metal pipe 12, and the thin metal pipe 12 and the optical fiber coated fiber 11 are integrally deformed by the friction between them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an optical fiber which is suitably used for continuously monitoring a landslide, a ground deformation, a displacement of an artificial structure such as a building, a bridge or a tunnel. It relates to a strain sensor.

[0002]

2. Description of the Related Art Conventionally, a strain sensor using an optical fiber of this type utilizes the characteristic that when a strain is applied to an optical fiber core, the Brillouin scattering frequency of the optical fiber core shifts, and the strain sensor uses this characteristic. The position and the amount of distortion are measured.

Conventionally, as shown in FIG. 4, an optical fiber core 3 formed by coating the surface of an optical fiber 1 with a protective material 2 made of silicon and nylon is directly applied to a location to be measured. The method of sticking is adopted.

However, such a conventional method has a problem that the strength of the optical fiber core 3 is not sufficient.

Therefore, as shown in FIG. 5, the optical fiber core 3 is covered with a cushioning material 4 formed of aramid yarn or the like, and the cushioning material 4 is further covered with PV.
The strain sensor 6 is formed by covering with the covering material 5 formed of C or the like, or as shown in FIG.
The optical fiber core 3 is inserted into a large-diameter metal tube 7, and a gap 8 between the optical fiber core 3 and the metal tube 7 is filled with a filler 8 to form a strain sensor 9. Thus, it has been attempted to reinforce these strain sensors 6 and 9.

[0006]

However, even in such a method, the following problems still remain to be improved.

That is, in the strain sensors 6 and 9 reinforced as described above, the deformation of the measurement target is first performed on the coating material 5 and the metal tube 7 located on the outermost layer. The light is transmitted to the optical fiber core 3 via the buffer material 4 and the filler 8, and causes distortion in the optical fiber core 3.
At this time, the deformation of the cushioning material 4 and the filler 8 causes a displacement between the coating material 5 and the metal tube 7 and the optical fiber core wire 3, and as a result, the accuracy of distortion detection decreases. It is.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and has been made in consideration of a distortion using an optical fiber that can maintain sufficient strength while ensuring accuracy in detecting deformation of a measured portion. It is intended to provide a sensor.

[0009]

According to a first aspect of the present invention, there is provided a strain sensor using an optical fiber in which an optical fiber core is directly covered with a thin metal tube to achieve the above-mentioned object. The thin metal tube and the optical fiber core are integrally deformed by friction between them. In the strain sensor using the optical fiber according to claim 2 of the present invention, the inner diameter of the thin metal tube according to claim 1 is larger than the outer diameter of the optical fiber core.
It is characterized in that it is set within a range of ± 10%.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. In FIG.
Numeral 0 indicates a strain sensor using an optical fiber according to the present embodiment (hereinafter, abbreviated as a strain sensor). The strain sensor 10 is obtained by directly covering an optical fiber core 11 with a thin metal tube 12. The thin metal tube 12 and the optical fiber core 11 are integrally deformed by friction between them.

More specifically, the inner diameter of the thin metal tube 12 is ± 10% of the outer diameter of the optical fiber core wire 11.
%, And by setting within this range, the loss of the optical fiber core 11 does not increase,
Sufficient friction between the optical fiber core 11 and the thin metal tube 12 can be obtained.

The thickness of the thin metal tube 12 is set in accordance with the mechanical characteristics required for the strain sensor 10, and is appropriately set in the range of, for example, 0.05 mm to 0.2 mm. .

The method for coating the thin metal tube 12 on the optical fiber core 11 is as follows.
Into a seamless structure, and inserting the optical fiber core 11 slightly from one end of the thin metal tube 12 by press-fitting, or forming the optical fiber core 11 while bending a flat metal plate. After wrapping, a method of covering the optical fiber core 11 by connecting the butted portions of the metal plates by welding or the like may be used.

The thus constructed strain sensor 10 according to the present embodiment is installed by being buried inside the wall of the artificial structure 13 as shown in FIG. 3, for example, and installed outside. By being connected to the BOTDR 14 which is a distortion / distortion position detector, the state is set such that distortion can be detected.

As shown in FIG. 3, when the artificial structure 13 is deformed in a direction corresponding to a point P in a direction indicated by an arrow in FIG. 10 is distorted,
The position and the distortion are detected by the BOTDR 14.

Since the optical fiber core 11 is covered with the thin metal tube 12, the strength of the strain sensor 10 is ensured, and the internal optical fiber core 11 is not damaged. In addition, since the friction between the optical fiber core 11 and the thin metal tube 12 is appropriately set, the loss of the optical fiber core 11 is suppressed, and the distortion generated in the thin metal tube 12 is reduced. , Is accurately transmitted to the optical fiber core 11, and as a result, the deformation amount of the artificial structure 13 is detected with high accuracy.

In order to verify the detection accuracy, the length of the strain sensor 10 is set to 30 m, and a force of 3
% Of elongation, the strain of the optical fiber core 11 was measured, and the results are shown in FIG. As is clear from FIG. 2, the position and the amount of distortion are detected with high accuracy for the forcibly applied distortion.

As described above, according to the strain sensor 10 according to the present embodiment, the optical fiber core 11 is directly covered with the thin metal tube 12, and a predetermined friction is generated between them. Accordingly, the position at which the distortion occurs and the amount of distortion can be detected with high accuracy while the strength of the distortion sensor 10 is sufficiently ensured.

The various shapes, dimensions, and the like of the components shown in the above embodiment are merely examples, and can be variously changed based on design requirements and the like.

[0020]

As described above, according to the strain sensor using the optical fiber of the present invention, the optical fiber core is directly covered with the thin metal tube, and a predetermined friction is generated between them. With this configuration, it is possible to detect the position where the distortion occurs and the amount of distortion with high accuracy while sufficiently securing the strength of the distortion sensor.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a main part showing an embodiment of the present invention.

FIG. 2 is a distortion-distance diagram showing distortion detection results according to an embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a main part showing a state in which one embodiment of the present invention is mounted on an object to be measured.

FIG. 4 is a longitudinal sectional view showing one conventional example.

FIG. 5 is a longitudinal sectional view showing another conventional example.

FIG. 6 is a longitudinal sectional view showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber 2 Protective material 3 Optical fiber core wire 4 Buffer material 5 Coating material 6 Strain sensor 7 Metal tube 8 Filler 9 Strain sensor 10 Strain sensor 11 Optical fiber core wire 12 Thin metal tube 13 Artificial structure 14 BOTDR

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroshi Keiruma 1-2-1 Shibaura, Minato-ku, Tokyo F-term in OCC Corporation (reference) 2H050 AD06 BB26S BC11 BD06

Claims (2)

[Claims] 1. An optical fiber core wire is directly covered with a thin metal tube, and the thin metal tube and the optical fiber core wire are integrally deformed by friction between the two. A strain sensor using an optical fiber. 2. The optical fiber according to claim 1, wherein an inner diameter of the thin metal tube is set within a range of ± 10% with respect to an outer diameter of the optical fiber core. Strain sensor.