JP2002062200A - Cable for sensing strain and strain measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure strain accurately by easily adjusting sensitivity to the strain of an optical fiber conductor by improving the structure of a cable for sensing strain. SOLUTION: With the cable for sensing strain, the optical fiber core wire 20 is arranged in a slot 14 and is intermittently fixed at junction parts 12a, 12a, etc., at both sides in the direction of conductor length near a grating part 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field related to a strain sensing cable and a strain measuring method used for measuring a local strain in a structure such as a building, a ship, an airplane, or the ground.

[0002]

2. Description of the Related Art Conventionally, it has been studied to measure (sense) a longitudinal strain using an optical fiber core wire in an optical fiber cable. A method is known. For example, in a sensing method using Rayleigh scattering, strain is detected from a loss value due to a state of applying a stress to an optical fiber core. However, the evaluation of distortion by this method is qualitative and cannot be quantitatively evaluated.

On the other hand, for example, in a sensing method using Brillouin scattering, distortion can be quantitatively evaluated by measuring a Brillouin shift amount with respect to an applied stress in an axial direction of an optical fiber core wire. However, there is a problem that the temperature resolution needs to be corrected, and the pulse resolution of the evaluation light source is limited, so that the distance resolution is limited.

Therefore, conventionally, in order to increase the distance resolution so as to be 1 m or less and to sense distortion in a minute section in detail, a high-strength fiber grating is disclosed in, for example, JP-A-11-218450. It is known to utilize a built-in optical fiber core. The high-strength characteristics required for such a fiber grating for strain sensing have been solved by an over-coating irradiation technique and a long hydrogen filling technique. Also, by using this high-strength fiber grating,
High-speed dynamic measurement of strain is also possible.

[0005]

By the way, in order to use an optical fiber cable as a strain sensing cable for measuring a strain application distribution in a minute section, an optical fiber core is fixed in the cable. It is required that this optical fiber core be sensitive to strain.

Further, since the maximum value of the distortion of the optical fiber core is, for example, about 5%, when the distortion of the object to be measured is relatively large, the distortion of the optical fiber core does not exceed the maximum value. When the distortion of the measurement target is relatively small, it is also required to adjust the sensitivity to the distortion of the optical fiber core according to the magnitude of the distortion of the measurement target so that the distortion of the optical fiber core becomes larger.

[0007] However, in order to satisfy the above-mentioned requirement of responding with high sensitivity to the distortion, the optical fiber core and the cable are integrally distorted by fixing the optical fiber at all the contact portions with the cable. With such a configuration, it is difficult to change the frictional force between the optical fiber core and the cable, so that it is difficult to adjust the sensitivity of the optical fiber core to distortion.

Further, when the optical fiber core wire and the cable are fixed at the place where the fiber grating is formed, a strain is generated in the grating portion before the strain measurement is caused by the fixation, and the strain is accurately measured. May not be possible.

The present invention has been made in view of the above points, and a main object of the present invention is to improve the structure of a strain sensing cable to easily adjust the sensitivity of an optical fiber core to distortion. Accordingly, it is possible to accurately measure distortion.

[0010]

In order to achieve the above-mentioned object, the present invention provides a strain sensing cable, comprising: placing an optical fiber core in a cable near the fiber grating forming portion of the core; It was fixed intermittently on both sides in the length direction.

More specifically, according to the first aspect of the present invention, a strain sensing body made of a long elastic body, and a surface of the strain sensing body,
A concave streak provided along the axis of the strain sensing element, and an optical fiber disposed in the concave streak and detecting at least distortion in the bending direction of the strain sensing element by the applied axial stretching strain. A cable for strain sensing, comprising: a core portion having a grating portion on which a high-strength fiber grating is formed; and A core wire fixing means for intermittently fixing both sides in the direction is provided.

According to the above configuration, the magnitude of the frictional force between the optical fiber core and the concave portion can be changed by changing the interval between the fixing positions. Can easily be adjusted.

According to a second aspect of the present invention, in the strain sensing cable according to the first aspect, the strain sensing element has a different bending stiffness in two directions orthogonal to each other on a plane perpendicular to the length direction. And the concave stripes
It is characterized by being provided offset to the side where the bending stiffness is reduced with respect to the center position of the strain sensing element.

According to the above configuration, it is possible to increase the distortion of the optical fiber core wire as compared with the case where the optical fiber core wire is arranged at the center position of the strain sensing element, and it is possible to increase the sensitivity of strain measurement. Further, since the magnitude of the strain of the optical fiber core with respect to the magnitude of the strain of the strain sensing element is uniquely determined, quantitative measurement of the strain can be accurately performed.

According to a third aspect of the present invention, in the strain sensing cable of the first or second aspect, the breaking load of the core wire fixing means is larger than the breaking load of the core wire.
As a result, it is possible to prevent the core wire fixing means from breaking before the core wire with an increase in the strain load applied to the cable, and to secure the strain measurement performance when the core wire is not broken. it can.

According to a fourth aspect of the present invention, in the strain sensing cable according to any one of the first to third aspects, the core wire fixing means is made of an adhesive. In the invention according to claim 5, the core wire fixing means comprises: a filling member which holds the core wire and is partially filled in the recessed portion so as to slightly protrude from the surface of the strain sensing element; And a joining member joined so as to fix the projecting portion of the filling member. In the invention according to claim 6, the core wire fixing means holds a part of the core wire so as to slightly protrude from the surface of the strain sensing body, and a filling member filled in the concave streak portion,
And a joining member joined so as to fix the protruding portion of the core wire to the surface of the strain sensing element. Further, in the invention according to claim 7, the core wire is housed in the concave ridge portion so that a part thereof slightly protrudes from the surface of the strain sensing element, and the core wire fixing means includes the core wire on the strain sensing element surface. It was made of a joining member joined so as to fix the protruding portion. According to these inventions, the configuration of the core wire fixing means suitable for measuring the strain can be embodied as a simple configuration.

According to an eighth aspect of the present invention, in the strain sensing cable according to any one of the first to seventh aspects, the core is a single-core type core made of one optical fiber. According to the ninth aspect of the present invention, the core is a multi-core tape-type core in which a plurality of optical fibers are arranged in parallel in the axial direction. According to the tenth aspect of the present invention, the cord is a cord-type cord covered with a protective layer. According to these inventions, a core wire desirable for strain measurement can be obtained.

According to an eleventh aspect of the present invention, there is provided a strain measuring method for measuring a strain using the strain sensing cable according to any one of the first to tenth aspects, wherein scattered light guided through a core in an optical fiber is provided. Distortion is measured based on at least one change amount of reflected light and transmitted light. Thus, the strain measurement method using the strain sensing cable of the present invention can be embodied.

[0019]

(Embodiment 1) Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a cross section perpendicular to the length direction of a strain sensing cable 10 according to the present embodiment, and FIG. 2 is a perspective view schematically showing the strain sensing cable 10.

As shown in FIG. 1, the strain sensing cable 10 includes a slot rod 15 made of a long elastic material such as polyethylene, and a tension member 16 and an optical fiber 20 inside the slot rod.

The slot rod 15 is bent in two directions perpendicular to each other on a plane perpendicular to its length (direction perpendicular to the plane of FIG. 1) (parallel to the plane of FIG. 1). The stiffness is different. More specifically, as shown in the figure, the cross section of the slot rod 15 is substantially elliptical, and the bending rigidity in the short axis direction of the short axis direction and the long axis direction orthogonal to each other is large. Is lower than. The cross-sectional shape of the slot rod 15 is not limited to a substantially elliptical shape, and may be a substantially elliptical shape or the like.

Further, on the short-axis side surface (upper and lower sides in FIG. 1) of the slot rod 15, slots 14 as concave ridges formed along the axis of the slot rod 15 at a predetermined depth. 14 are provided. An optical fiber core 20 is disposed along the concave line in the one slot 14 (for example, the upper side in FIG. 1). 1 detects at least the distortion of the slot 14 in the bending direction
It is constituted by a single-core type core wire composed of two optical fibers.

That is, the optical fiber 20 is offset in the short axis direction with respect to the center position of the slot rod 15, that is, in the short axis direction, and substantially parallel to the length direction of the slot rod 15. The slot rod 15 is fixed so as to be distorted in accordance with the distortion of the slot rod 15. Further, the optical fiber core 20 has a plurality of types of fiber gratings 21 having different reflection characteristics (or transmission characteristics), and the grating portions 18 and 1 formed with high strength.
8, ...

On the other hand, the tension member 16 provided inside the slot rod 15 is made of, for example, iron or the like.
The cable 10 extends through the inside of the slot rod 15 along the longitudinal centerline of the cable 10 to protect the optical fiber 20 from damage such as when the cable 10 is laid.

Next, the optical fiber 20 will be described in detail with reference to FIGS. FIG. 4 schematically shows a cross section of the optical fiber 20 included in the strain sensing cable 10. FIG. 5 schematically shows an optical fiber portion of the optical fiber 20, and the optical fiber portion is a fiber grating 21.
Are written on the core 22 and a clad 23 formed around the core 22.

The grating 21 written (formed) on the core 22 of the optical fiber 20 has a refractive index of the core 2 along the axial direction having a period Λ (for example, 0.3 to 0.6 μm).
m) has a short-period refractive index modulation structure changed in m).
Light having a Bragg wavelength defined by the period Λ and the average refractive index of the core 21 is converted into the light of the grating 2.
1 will be selectively reflected. In the present specification, the Bragg wavelength may be referred to as a “reflection peak wavelength”.

As described above, since the Bragg wavelength changes depending on the period 、, when distortion occurs in the optical fiber 20 due to heat or external force, the period に お け る in the portion where the distortion occurs has no distortion. It will change (shift) from the value of the state. The magnitude of this change (shift amount)
Can be optically observed as a shift amount of the Bragg wavelength (reflection peak wavelength). In the optical fiber 20, a plurality of types of fiber gratings 21 having different reflection characteristics are formed at positions separated in the axial direction.
Therefore, by observing the shift amount in each fiber grating 21, the distortion amount at the position of each fiber grating 21 can be monitored. That is, by detecting the shift amount of the reflection peak wavelength generated due to the change in the physical state of each fiber grating, it becomes possible to sense distortions and the like at a plurality of locations generated on a long fiber.
That is, at least the strain in the bending direction of the slot rod 15 can be detected by the strain in the axial direction of the optical fiber core 20.

As a feature of the present invention, FIGS.
As shown in FIG. 1, the optical fiber 20 is disposed on the bottom surface 14a in the slot 14 of the strain sensing cable 10 along the axis of the slot rod 15. , Slot 14
Plate-shaped fixing structural material 1 having a width substantially equal to the width of
1 so that the slot 1 overlaps the optical fiber 20.
4 is filled. The fixing structural member 11 is made of, for example, a resin such as rubber or polyethylene. In this state, the thickness of the fixing structural material 11 is
1 and the diameter of the optical fiber 20 are slightly larger than the depth of the slot 14, and the upper part of the fixing structural material 11 is slightly above the surface of the slot rod 15. It is made to protrude outward.

The projecting portion of the fixing structural member 11 is formed by interposing a tape-like holding roll 12 made of, for example, resin on the surface of the slot rod 15 at an approximately equal pitch from the outside of the fixing structural member 11. They are joined by spirally winding. At this time, as shown in FIG. 3, bonding portions 12 a, 12 a which are bonding portions of the fixing structural material 11 and the surface of the slot rod 15 by the presser winding 12 are provided on both sides of the grating portion 18 in the core wire length direction. And the joining portions 12a, 12a on both sides thereof and the grating portion 18
Are substantially equal to each other.

In this manner, the optical fiber 20 is
The lower surface 14a of the slot 14 and the fixing structural material 11 are fixed by the presser winding 12 via the fixing structural material 11.
And is fixed by the frictional force between them.

The breaking load of the fixing structural member 11 and the holding roll 12 is made larger than the breaking load of the optical fiber 20. That is, as the applied strain increases, the optical fiber 20 is broken earlier than the fixing structural material 11 and the presser winding 12, and the strain is measured until the optical fiber 20 breaks. I can do it. In addition, this fixing structural material 1
The breaking load of the holding wire 1 and the holding wire 12 is
It is sufficient if the breaking load is slightly larger than the breaking load of 0, and it is not necessary to make the breaking load sufficiently large.

The fixing structural member is a plate-shaped member that is continuous in the axial direction. However, the present invention is not limited to this, and the fixing structural member may be locally provided at a position corresponding to a fixing point on the core wire by the presser winding 12. Good. Also, at this time, it is not necessary to provide fixing structural members at all locations corresponding to the fixing points, and they may be provided at least partially.

Next, with reference to FIG. 6, the basic principle of measuring the strain distribution (or stress distribution) using the strain sensing cable 10 including the optical fiber 20 will be described.

The optical fiber core wire 20 included in the strain sensing cable 10 has n (n is an integer of 2 or more) fiber gratings FBG _{1 to} FBG _n .
In this example, the optical fiber 20 is coupled to a broadband light source 31 and a spectroscope 32 via a coupler 33.
The broadband light source 31, the spectroscope 32, and the coupler 33 constitute an optical measurement system 40. In the present embodiment, as described above, for example, a superluminescence diode light source (SLD light source) can be used as the broadband light source 31, and the spectroscope 32 has, for example, a resolution of 0.1 n.
m or less in the infrared wavelength region.

First, the broadband light (measuring light) emitted from the broadband light source 31 enters the optical fiber 20 through the coupler 33. This broadband light first enters the fiber grating FBG1. Of the incident broadband light, light having a reflection peak wavelength λ1 determined by the period Λ1 of the fiber grating FBG1 is selectively reflected to the left. The reflected light having the wavelength λ1 enters the spectroscope 32 via the coupler 33. Above the optical fiber 20, a transmitted light spectrum is schematically shown, and below the optical fiber 20, a reflected light spectrum is schematically shown.

Of the broadband light incident on the first fiber grating FBG1, the fiber grating FBG
The band component not reflected by 1 enters the next fiber grating FBG2. Here, similarly, the light having the reflection peak wavelength λ2 determined by the period Λ2 of the second fiber grating FBG2 is selectively reflected to the left, and the wavelength λ2
Is incident on the spectroscope 32 via the coupler 33.

In the configuration example shown in FIG. 6, the reflection peak wavelengths λ1 of the fiber gratings FBG1 to FBGn are set.
.Gamma.n increase as the distance from the incident end side of the optical fiber 20 increases.
G1 to FBGn have been produced. That is, λ1 <λ
The relationship of 2 <... λn _-1 <λn holds.

In this example, for example, when a stress is applied to the fiber grating FBG3 having the reflection peak wavelength λ3, the stress causes strain in the fiber, and as a result, the reflection peak wavelength of the FBG3 changes from λ3 to (λ3
+ Δλ). By measuring the wavelength shift amount Δλ, the amount of distortion at the position of the FBG 3 can be monitored, and the stress applied to the position of the FBG 3 can be measured. I explained about FBG3,
For FBG1 to FBGn, the strain and stress at each position can be measured in the same manner. Therefore, to increase the distance resolution, the distance d between the fiber gratings may be reduced, and to increase the number of measurement points, the optical fiber core 20 may be used.
In this case, the number of fiber gratings 21 (the number of set wavelengths) may be increased. Note that the relationship between the wavelength shift amount and the strain (or stress) may be measured and recorded in advance.

On the basis of this principle, at least one variation of scattered light, reflected light and transmitted light guided through the core 22 in the optical fiber 20 is converted into at least one of the wavelength and the time. Measure distortion based on

Next, a method for detecting a strain distribution (or stress distribution) using the strain sensing cable according to the present invention will be described with reference to FIGS. 7 (a) and 7 (b).
In this example, the above-described strain sensing cable 10 is buried in the road 72, and at this time, the cable 10
The slots 14 in which the optical fiber cores in which the fiber gratings 21 are written are housed in a unified manner so as to face either upward (toward the road) or downward. One end of the strain sensing cable 10 is connected to the monitoring device 71. The monitoring device 71 includes a configuration similar to that of the optical measurement system 40 in FIG. 5 inside. The strain sensing cable 10 has a large number of built-in fiber gratings, and each fiber grating has a slightly different reflection peak wavelength.

As shown in FIG. 7A, when automobiles 73 and 74 and the like are present on the road 72, the corresponding portion of the strain sensing cable 10 is distorted due to the influence.
Based on the principle described above, the monitoring device 71 can detect the axial strain distribution on the strain sensing cable 10.

As shown in FIG. 7B, the strain sensing cable 10 can be meanderingly embedded in a monitoring area having a two-dimensional spread, and the monitoring area shown in FIG. It is possible to detect which part has a certain amount of distortion.

According to the structure of the present embodiment, the magnitude of the frictional force between the optical fiber 20 and the bottom surface 14a of the slot 14 is changed by changing the distance between the joints 12a. Therefore, the sensitivity of the optical fiber 20 to the distortion can be easily adjusted.

That is, when the distortion of the object to be measured is smaller than the maximum measurable distortion of the core wire 20 and the degree of the change of the distortion is small, the distance between the joints 12a, 12a is reduced to reduce the optical fiber. The distortion of the measurement target can be measured in detail by increasing the sensitivity of the core wire 20. On the other hand, when the strain to be measured is larger than the maximum measurable strain of the optical fiber 20, the joint 1
By increasing the interval between 2a and 12a, the sensitivity of the optical fiber core wire 20 can be reduced, and the distortion of the measurement target can be measured with the optimum sensitivity that does not damage the core wire 20.

Further, by providing the optical fiber 20 at an offset from the center of the slot rod 15, distortion of the optical fiber 20 can be reduced as compared with the case where the optical fiber 20 is arranged at the center of the slot rod 15. It is possible to increase the sensitivity and increase the sensitivity of strain measurement.

Further, by setting the cross-sectional shape of the slot rod 15 to be substantially elliptical, the magnitude of the strain of the optical fiber core with respect to the magnitude of the strain of the strain sensing element is uniquely determined. Can be performed accurately.

In this embodiment, the description has been given of the road 72. However, the stress in a tunnel or a bridge can be similarly detected. In addition, even if stress or bending occurs in the optical fiber cable due to landslides,
It is also possible to remotely observe the state of the optical fiber cable without having to go to the location where the landslide has occurred.

Although the distortion varies depending on the temperature, if the relationship between the reflection peak of the optical fiber 20 and the temperature is measured and recorded in advance, the temperature can be corrected.

Then, the presser winding 1 in the present embodiment
2, the joint 12 a formed by the presser winding 12
May be fixed with an adhesive at the same position.
However, the breaking load at the time of curing the adhesive is set to be larger than the breaking load of the optical fiber 20. With this configuration, a similar effect can be obtained.

It is also possible to propagate communication light to the optical fiber 20 and use the optical fiber 20 as a communication optical fiber. In this case, the communication light and
The measurement light having a wavelength band different from the communication wavelength band of the communication light is coupled to the optical fiber 20 by a coupler (for example, a WDM coupler) 33.
In this case, the strain distribution of the optical fiber can be measured in the live state without affecting the communication by the communication light.

(Embodiment 2) FIG. 8 shows Embodiment 2 of the present invention (in the following embodiments, the same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. In contrast to the structure in which one fixing structural material 11 is provided in the slot 14 of the strain sensing cable 10 according to the first embodiment, a plurality of fixing structural materials 11 and 1 are provided.
1,... Are provided.

That is, in this embodiment, the slot 14
From the bottom surface 14a side of the two fixing structural members 11, 1
1, an optical fiber core 20 and two fixing structural members 11,
11 are laminated so as to abut each other.

With such a configuration, the same effect as in the first embodiment can be obtained. And
In addition to this, when machining the depth of the slot 14, for example, it is difficult to obtain a desired depth that just fits the optical fiber 20 and one fixing structural material 11,
In addition, there is a problem that the cost increases if such processing is performed. However, by changing the number of laminated fixing structural members 11 to the slot rod 15 having the slot 14 of a predetermined depth, Thus, a desired strain sensing cable can be configured at low cost.

Further, the sensitivity to the distortion of the optical fiber core can be easily adjusted depending on the position in the stacking direction of the plurality of fixing structural members where the optical fiber core is held. That is, the sensitivity of the optical fiber can be increased as the fixing structural material is held closer to the upper side in the laminating direction (the surface side of the slot rod).

The number and thickness of the fixing structural members are not particularly limited. For example, a plurality of fixing members having a relatively small and uniform thickness may be laminated. By doing this,
The sensitivity of the optical fiber 20 can be adjusted more finely.

Further, the core wire may be fixed in the slot only by the presser winding without disposing the fixing structural material. That is, the optical fiber 20 is accommodated in the slot 14 so that a part thereof slightly protrudes from the surface of the slot rod 15, and the optical fiber 20 is joined so that the protruding portion of the core 20 is fixed by the presser winding 12. You may.

(Embodiment 3) FIG. 10 shows Embodiment 3 of the present invention, in which the form of the optical fiber core is changed from that of the strain sensing cable of Embodiment 2 to form a tape-shaped optical fiber core. (Tape type core wire) 50.

That is, as shown in FIG.
The tape-type core wire is provided with four optical fiber wires, the center lines of which are arranged in parallel on a straight line, and the periphery thereof is covered with a tape coating 52. These four optical fiber cores include an optical fiber core 20 for strain measurement and an optical fiber core 30 for other purposes such as communication. In this embodiment, a fiber grating is formed on the measurement core 20 in the same manner as in the above embodiments.

In this embodiment, the tape type core wire is 4
Although the core is used, the number of cores is not limited to this, and the thickness and the number of fixing structural members are not particularly limited.

(Embodiment 4) FIG. 9 shows Embodiment 4 of the present invention. In the strain sensing cable of Embodiment 2, the positional relationship between the optical fiber 20 and the fixing structural member 11 and the fixing The number of the structural materials 11 is changed.

That is, for example, three fixing structural members 11
Is filled over the bottom surface 14a of the slot 14, and the optical fiber 20 is placed thereon, and the optical fiber 20 is held by the fixing structural members 11. The projecting portion of the core wire 20 may be fixed to the surface of the slot rod 15 by the presser winding 12 while slightly projecting from the surface of the slot rod 15.

By doing so, the same effect as described above can be obtained, and the sensitivity of the cord 20 can be further increased. In the present embodiment, similarly, the thickness and the number of the fixing structural members are not particularly limited.

(Fifth Embodiment) FIG. 12 shows a fourth embodiment of the present invention, in which the form of the optical fiber core is changed to the cord-type core 54 in the strain sensing cable of the first embodiment. Things.

That is, the cord type core wire 54 of this embodiment
As shown in an enlarged view in FIG. 12, the single-core type core wire 20 of the first embodiment is further provided with a protective layer 56 made of, for example, vinyl chloride.
It is what was covered with. With this configuration, the same effect as in the first embodiment can be obtained.

(Embodiment 6) FIG. 13 shows Embodiment 5 of the present invention. In the strain sensing cable of Embodiment 1, the slot rod 15 and the fixing structural material 11 are fixed by the presser winding 12. In contrast, for example, it is fixed by a holding member 13 made of a resin such as polyethylene.

That is, also in this embodiment, the joining portion of the fixing structural material 11 by the holding member 13 is the same as in the first embodiment, and is fixed so that the grating portion is interposed therebetween. Only the core wire 20 of the slot rod 15 and the side on which the fixing structural material 11 is provided are fixed in a wavy manner. With such a configuration, the same effect as in the first embodiment can be obtained.

[0067]

As described above, according to the first aspect of the present invention, there is provided a strain sensor made of a long elastic body, and a concave strip provided on the surface of the strain sensor along the axis of the strain sensor. A strain sensing cable including a portion and a core wire made of an optical fiber that is disposed in the concave streak portion and detects at least strain in the bending direction of the strain sensing body by applied axial stretching strain, The core has a grating portion on which a high-strength fiber grating is formed, and is provided with a core fixing means for intermittently fixing the core in the concave streak on both sides in the core length direction near the grating. By changing the spacing between the fixed positions,
The sensitivity to the distortion of the optical fiber can be easily adjusted.

According to the second aspect of the present invention, the distortion sensing element is
In a plane perpendicular to the length direction, bending stiffness in two directions perpendicular to each other is different,
The concave streak is offset from the center position of the strain sensing element on the side where bending stiffness is reduced, so that the strain measurement is better than when the optical fiber core is located at the center position of the strain sensing element. Sensitivity can be improved. Further, quantitative measurement of distortion can be accurately performed.

According to the third aspect of the present invention, the breaking load of the core wire fixing means is made larger than the breaking load of the core wire, so that the core wire fixing means is moved ahead of the core wire with an increase in the applied load. Can be prevented from breaking, and the strain can be reliably measured until the core wire breaks.

According to a fourth aspect of the present invention, the core fixing means is made of an adhesive, and according to the fifth aspect of the present invention, the core fixing means is provided for holding the core and a part of the strain sensing element. 7. A filling member filled in the concave streak so as to slightly protrude from the surface of the strain sensing element, and a joining member joined so as to fix the projecting portion of the filling member to the surface of the strain sensing element, and According to the invention, the core wire fixing means is held so that a part of the core wire slightly protrudes from the surface of the strain sensing element, and the filling member filled in the concave ridge portion and the projection of the core wire on the surface of the strain sensing element. And a joining member joined so as to fix the portion. Further, according to the invention of claim 7, the cord is inserted into the recessed portion such that a part thereof slightly protrudes from the surface of the strain sensing element. The means for accommodating and fixing the core wire is provided on the surface of the strain sensing element. By so consisting bonded joint member so as to fix the projecting portion of the core wire, it is possible to obtain a structure suitable core fixing means as a simple structure for measurement of strain.

According to the tenth aspect, the first aspect is provided.
As a strain measurement method for measuring strain by using any one of the strain sensing cables according to any one of (1) to (9), a strain is measured based on at least one variation of scattered light, reflected light, and transmitted light guided through a core in an optical fiber. Is measured, the strain measuring method using the strain sensing cable of the present invention can be embodied.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a strain sensing cable according to a first embodiment.

FIG. 2 is a perspective view schematically showing a strain sensing cable according to Embodiment 1.

FIG. 3 is a plan view schematically showing a strain sensing cable according to the first embodiment.

FIG. 4 is a cross-sectional view showing an optical fiber core housed in a strain sensing cable.

FIG. 5 is a view schematically showing an optical fiber core on which a fiber grating is formed.

FIG. 6 is a configuration diagram for explaining a distortion amount measurement method according to the first embodiment.

FIG. 7 is a diagram illustrating an example in which a strain sensing cable is embedded in a road, and an example in which two-dimensional measurement is performed.

FIG. 8 is a partial cross-sectional view illustrating a main part of a strain sensing cable according to a second embodiment.

FIG. 9 is a partial cross-sectional view illustrating a main part of a strain sensing cable according to a fourth embodiment.

FIG. 10 is a partial cross-sectional view illustrating a main part of a strain sensing cable according to a third embodiment.

FIG. 11 is a cross-sectional view schematically showing a tape-type core wire.

FIG. 12 is a cross-sectional view schematically showing a cord type core wire.

FIG. 13 is a perspective view schematically showing a strain sensing cable according to Embodiment 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Strain sensing cable 11 Structural material for fixing (core wire fixing means) 12 Holding coil (core wire fixing means) 13 Holding member (core wire fixing means) 14 Slot (concave strip) 15 Slot rod (strain sensing element) 18 Grating section 20 Optical fiber core wire, single core type core wire (core wire) 21 Fiber grating 50 Tape type core wire (core wire) 54 Cord type core wire (core wire) 56 Protective layer

Claims (11)

[Claims] 1. A strain sensor made of a long elastic body, a concave portion provided on a surface of the strain sensor along an axis of the strain sensor, and disposed in the concave portion, A core wire made of an optical fiber for detecting at least a strain in a bending direction of the strain sensing body by an applied axial stretching strain, wherein the core wire is formed with a high-strength fiber grating. A strain sensing cable, comprising: a grating portion; and a core fixing means for intermittently fixing the core wire in the concave streak portion on both sides in the core length direction near the grating portion. 2. The strain sensing cable according to claim 1, wherein the strain sensing body has different bending stiffnesses in two directions orthogonal to each other in a plane perpendicular to the length direction. Is provided at a position offset from the center position of the strain sensing element on the side where the bending rigidity is reduced. 3. The strain sensing cable according to claim 1, wherein a breaking load of the core fixing means is larger than a breaking load of the core. 4. The strain sensing cable according to claim 1, wherein the core fixing means is made of an adhesive. 5. The strain sensing cable according to any one of claims 1 to 3, wherein the core wire fixing means holds the core wire and partially extends in the concave strip so as to slightly protrude from the surface of the strain sensing body. A strain sensing cable, comprising: a filled filling member; and a joining member joined to a surface of the strain sensing element so as to fix a protruding portion of the filling member. 6. The strain sensing cable according to any one of claims 1 to 3, wherein the core wire fixing means holds a part of the core wire so as to slightly protrude from the surface of the strain sensing element, and holds the core wire in the concave strip portion. A strain sensing cable, comprising: a filled filling member; and a joining member joined to fix a protruding portion of the core wire to a surface of the strain sensing body. 7. The strain sensing cable according to any one of claims 1 to 3, wherein a part of the core wire is housed in a concave portion so as to slightly protrude from the surface of the strain sensing body, and the core wire is fixed. The strain sensing cable comprises a joining member joined so as to fix the protruding portion of the core wire to the surface of the strain sensing body. 8. The strain sensing cable according to claim 1, wherein the core is a single-core type core made of one optical fiber. 9. The strain sensing cable according to any one of claims 1 to 7, wherein the core is a multi-core tape-type core in which a plurality of optical fibers are arranged in parallel in the axial direction. Cable for strain sensing. 10. The strain sensing cable according to claim 1, wherein the core is a cord-type core coated with a protective layer. 11. A strain measuring method for measuring strain using the strain sensing cable according to claim 1, wherein the scattered light, reflected light, and transmitted light guided through a core in an optical fiber. Measuring a strain based on at least one variation of the strain measurement method.