JP2000221011A - Optical fiber type strain gage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate adjustment concerned in manufacture, enhance workability, cope with various samples with common simple constitution, and facilitate temperature compensation to provide high precision. SOLUTION: An optical fiber 11 and a reflection member 12 are opposed with a prescribed gap length G on a common axis to be fixed thick wall parts 13b, 13c of a base material 13. This optical fiber type strain gage is weldedly fixed to a sample by spot welding in plural points in a portion along the vicinity of the boundary line between the thick wall parts 13b, 13c of the base material 13 to be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber type strain gauge using an optical fiber for a strain detecting section, and more particularly to an optical fiber type strain gauge for improving a joining method of an optical fiber sensing section to a specimen and a temperature compensation. Related to strain gauges.

[0002]

2. Description of the Related Art Conventionally, as a strain gauge for measuring a strain such as a deformation of an object, a strain gauge using a metal foil whose electric characteristics, for example, electric resistance changes due to deformation, has been generally used. Such a resistor strain gauge made of a metal foil is used by attaching a metal foil to a base material and attaching a strain gauge formed with a strain gauge pattern to a specimen. A change in characteristics such as electric resistance of the strain gauge based on the strain generated in the specimen is detected by an electric circuit such as a bridge circuit, and the magnitude of the strain is measured. When strains in various directions occur in the test specimen, a plurality of strain gauges are attached in different directions, and the detected information is appropriately analyzed to determine the direction and magnitude of the strain generated in the test specimen. Can be measured.

A strain gauge using a metal foil has a thickness of several μm or less and has extremely low rigidity, so that the strain of the specimen is almost completely reduced even if the shearing force applied to the base material and the adhesive layer is small. It has the advantage of being transmitted. However, in such a resistor strain gauge made of a metal foil, since a measurement value is detected by a weak electric signal, a circuit portion from the strain gauge to the measurement circuit may be affected by electromagnetic induction or the like. Therefore, for example, when the specimen is in an environment where a strong electromagnetic field exists, or when the distance between the specimen and the measurement circuit is long, the measurement value may be inaccurate due to the influence of electromagnetic induction. There is
It was difficult to eliminate that effect.

Therefore, in recent years, an optical fiber type strain gauge which optically detects a strain using an optical fiber has been receiving attention as a strain gauge which is not affected by electromagnetic induction. This optical fiber type strain gauge
For example, one end of an optical fiber has a gap and faces a reflection surface formed on one end of a wire made of metal or the like. In such a configuration, the amount of reflected light that is transmitted from the other end of the optical fiber and reflected by the reflecting surface of the wire fluctuates based on the displacement (interval) of the gap due to strain. . The magnitude of the distortion is measured by detecting the amount of light reciprocating through the gap at the other end of the optical fiber. Here, the principle of the strain measurement will be described.
When there is a gap G (gap length = G) filled with a substance having a refractive index n between the end faces of the optical fibers, if the wavelength of the light is λ and the spot size (mode field diameter) at the exit end of the optical fiber is w, the light Coupling efficiency between fibers η
Is represented by Equation 1.

[0005]

(Equation 1)

Equation (1) is a formula when light is incident on an optical fiber from an optical fiber as shown in FIG. 8. When the light is re-entered on the same optical fiber using a mirror as shown in FIG. Assuming that the reflectance is 100%, the gap G is doubled.

[0007]

(Equation 2) Therefore, assuming that the intensity of the light emitted from the optical fiber is I ₀ , the relationship of the light intensity I _R re-incident from the mirror to the return optical fiber is as follows: coupling efficiency η = I _R / I ₀
It is represented by

[0008]

(Equation 3) That is, if the light intensity of the incident light to the optical fiber is kept constant, by measuring the light intensity of the return light,
The gap G can be measured.

[0009] The present applicant has previously disclosed in Japanese Patent Application Laid-Open No. 10-1419.
No. 23 has proposed an optical fiber type strain gauge. In the optical fiber type strain gauge disclosed in Japanese Patent Application Laid-Open No. H10-141923, as shown in FIG. 10, an optical fiber 1 has a light projecting unit and a light receiving unit coupled to one end. The other end of the optical fiber 1 is inserted through the opening at one end of the sleeve 2, and the end of the optical fiber 1 reaches the vicinity of the intermediate position of the sleeve 2. The optical fiber 1 is sealed. Reflective member 3
Is a stepped columnar member with a protruding wire portion 3a. A reflecting surface is formed at the tip of the wire portion 3a of the reflecting member 3. The base member 4 has an opening 4a having a shape substantially similar to the outer shape at the center of the rectangular plate. The sleeve 2 containing the optical fiber 1 and the reflecting member 3 are bonded and fixed to the base member 4 in advance. In the hollow portion of the sleeve 2, the reflecting surface at the distal end of the wire portion 3 a faces the distal end surface of the optical fiber 1 with a predetermined gap.

[0010]

As described above, the optical fiber type strain gauge has a great advantage in that it is not affected by electromagnetic induction as compared with the resistance type strain gauge using a metal foil. Due to the rigidity, the loss in strain transmission is large. Further, the optical fiber type strain gauge also has a problem due to viscoelastic behavior generated in the base material and the bonding portion due to the shear stress at the joint between the components. Further, there is a problem in workability at the time of joining, and it is not easy to obtain good characteristics. In addition, the measured value of the optical fiber type strain gauge fluctuates not only with strain but also with temperature, so that temperature compensation must be appropriately performed.

The optical fiber type strain gauge disclosed in Japanese Patent Application Laid-Open No. 10-141923 described above has a simple structure.
The loss of strain transmission is small, the workability related to bonding is relatively good, and high accuracy can be obtained, and high accuracy can be obtained even in an environment where temperature changes are remarkable. However, in the case of Japanese Patent Laid-Open No. 10-141923 described above,
When the material of the specimen 5 is different, the length dimension or the material of the reflecting member 3 including the wire portion 3a necessary for adjusting the temperature compensation is different. Therefore, in order to perform appropriate temperature compensation, it is necessary to change at least one of the length and the material of the reflecting member 3 including the wire portion 3a in accordance with the material of the specimen 5. It is required that the configuration be specialized for each material. For this reason, it is not possible to construct an optical fiber type strain gauge having versatility that can cope with various test specimen materials only by simple adjustment.

In the above-mentioned Japanese Patent Application Laid-Open No. Hei 10-141923, the optical fiber 1 is arranged in a small-diameter sleeve 2 and
When bonding the sleeve 2 and the reflecting member 3 to the base member 4, it is not easy to align the axis of the optical fiber 1 with the wire portion 3a of the reflecting member 3. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide easy adjustment in manufacturing and good workability, and to cope with various specimens with a common simple configuration. It is an object of the present invention to provide an optical fiber type strain gauge which can perform high accuracy. A second object of the present invention is to provide an optical fiber type strain gauge which has good workability particularly in assembling and adjusting at the time of manufacturing, and can easily withstand high temperatures.

A third object of the present invention is to provide an optical fiber type strain gauge which has good workability particularly in assembly and adjustment at the time of manufacturing. A fourth object of the present invention is to provide an optical fiber type strain gauge which has good workability particularly in attaching to a test sample and can obtain a high strain transmission rate in an attaching portion. A fifth object of the present invention is to provide an optical fiber type strain gauge having extremely good workability particularly in adjustment relating to temperature compensation during manufacturing.

[0014]

According to a first aspect of the present invention, there is provided an optical fiber strain gauge according to the present invention, comprising: an optical fiber having one end coupled to a light emitting and receiving part; A thin linear reflection member having a reflection surface formed at the tip of the optical fiber; a substantially plate-like shape; an opening formed by removing a central portion; and a predetermined parallel portion parallel to the plate-like plate surface. Only the portion along the central axis of the direction is bulged to one surface side of the plate to form a thick wall, and the thick portion is opposed to the inside of the opening along the central axis to have a predetermined size. While projecting, each tip of the optical fiber and the reflecting member is further projected from the projecting end face of the thick portion by a predetermined dimension,
In a state where the reflection surface of the reflection member is opposed to the other end surface of the optical fiber with a gap having a predetermined size, the optical fiber and the reflection member are embedded and fixedly supported in the thick portion, and And a base member which abuts the other surface of the plate on the specimen and is welded to the specimen at a boundary between the thick portion and the thin plate portion.

According to a second aspect of the present invention, in the optical fiber type strain gauge, the reflecting member includes a thin metal wire made of a metal. The optical fiber type strain gauge according to the present invention described in claim 3, wherein the base material is formed by forming a groove on the other surface side along the central axis in advance, and the optical fiber is formed in the groove. The optical fiber and the reflection member are fixed to the base material in a state where the reflection member is arranged.
The optical fiber type strain gauge according to the present invention described in claim 4 is characterized in that the base material is spot-welded to the specimen. The optical fiber strain gauge according to the present invention described in claim 5, wherein the reflecting member is
Taking into account the temperature dependence of the relative position with respect to the other end face of the optical fiber, the protruding end face of the thick portion of the base material so as to offset the temperature-dependent variation in the effective gauge length of the specimen. Is characterized in that a protruding dimension with respect to is set.

[0016]

That is, the optical fiber strain gauge according to the first aspect of the present invention has an optical fiber having one end coupled to the light emitting and receiving portion and an outer diameter substantially equal to that of the optical fiber, and a reflecting surface formed at the tip. Having a thin line-shaped reflecting member, having a substantially plate shape, forming an opening by removing a central portion, and only a portion along a center axis line in a predetermined direction parallel to the plate-shaped plate surface. Forming a thick wall by swelling on one side of the plate,
The distal ends of the optical fiber and the reflecting member are provided at the protruding end face of the thick portion at the thick portion of the base material, the thick portion facing the inside of the opening along the central axis and protruding by a predetermined size. The optical fiber and the reflecting member are embedded and fixedly supported in a state where the reflecting surface of the reflecting member is opposed to the other end surface of the optical fiber with a gap of a predetermined size. Then, the other surface of the plate is brought into contact with the specimen, and the base material is welded to the specimen at the boundary between the thick portion and the thin plate portion for use.

According to such a configuration, it is easy to adjust the production such as the alignment between the optical fiber and the reflecting member, the workability is good, and the weldable metal can be used.
Various test specimens can be handled with a common simple configuration, and high accuracy can be obtained. In the optical fiber type strain gauge according to claim 2 of the present invention, the reflection member includes a thin metal wire made of metal. With such a configuration, workability in assembling and adjustment during manufacturing is particularly good, and the reflecting member can be fixed by embedding by so-called hot pressing or plating other than bonding, and high temperature resistance can be easily achieved.

According to a third aspect of the present invention, in the optical fiber type strain gauge, the base member is formed in advance by forming a groove on the other surface side along the central axis, and the light is provided in the groove. With the fiber and the reflecting member arranged, the optical fiber and the reflecting member are fixed to the base material. With such a configuration, workability particularly in assembly and adjustment during manufacturing is improved. In the optical fiber type strain gauge according to claim 4 of the present invention, the base material is spot-welded to the specimen. With such a configuration, particularly, the workability in attaching to the test specimen is good, and a high strain transmission rate can be obtained in the attaching portion.

According to a fifth aspect of the present invention, in the optical fiber type strain gauge, the reflection member is provided with respect to an effective gauge length of the specimen in consideration of temperature dependency of a relative position with respect to the other end surface of the optical fiber. The projecting dimension of the thick portion of the base material with respect to the projecting end face is set such that the temperature-dependent fluctuation is offset. With such a configuration, workability in design, machining, assembly, and adjustment relating to temperature compensation during manufacturing can be particularly improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical fiber type strain gage according to the present invention will be described in detail below based on embodiments with reference to the drawings. 1 to 5 show the configuration of an optical fiber type strain gauge according to one embodiment of the present invention. FIG. 1 is a schematic perspective view showing a principle configuration of an optical fiber type strain gauge, FIG. 2 is a top view thereof, FIG. 3 is a front view thereof, FIG. 4 is a left side view thereof, and FIG. It is a longitudinal cross-sectional view on the center axis. The optical fiber type strain gauge shown in FIGS. 1 to 5 includes an optical fiber 11, a reflecting member 12, and a base material 13.

The optical fiber 11 has, for example, an outer diameter of 130 μm.
This is a fiber made of silica (SiO ₂ ) or the like having a length of about m, and a light emitting part and a light receiving part (not shown in FIG. 1) are coupled to one end on the right side in FIG. The other end surface of the optical fiber 11, that is, the left end surface in the drawing is smooth mirror-polished in the case of the intensity changing type, and the semi-transmissive mirror surface is coated with, for example, Inconel in the case of the interference type. The reflecting member 12 is composed of a thin line member made of, for example, a metal, that is, a metal thin line, which is approximately the same outer diameter as the optical fiber 11, for example, an outer diameter of about 130 μm, and has an appropriate length. Has a reflecting surface that reflects light by, for example, performing mirror finishing and further performing gold sputtering.

In order to protect the other end surface of the optical fiber 11 and the one end reflecting surface of the reflecting member 12,
The central portion may be covered with a cover or a coating material. The base member 13 is made of, for example, metal and has a substantially rectangular plate shape, a substantially rectangular opening 13a formed by removing a central portion, and a central axis line in a predetermined direction parallel to the plate-like plate surface. Only the portion along the line is bulged to one surface side of the plate to form the thick portions 13b and 13c, and the thick portions 13b and 13c are formed along the central axis in the opening 13a. And project toward the other side by a predetermined dimension. In order to form the base material 13, for example, a rectangular plate having a thickness of the thick portions 13b and 13c is prepared, and the opening 13a and the thin portion (the portions other than the thick portions 13b and 13c) are formed by etching. It may be formed.

On the other surface of the base member 13, on the back side of the thick portions 13b and 13c, the respective ends of the optical fiber 11 and the reflecting member 12 are attached along the central axis to the thick portions 13b and 13c. The optical fiber 11 and the reflection member are projected from the protruding end surfaces further by a predetermined size so as to be closer to each other, and the reflecting surface of the reflecting member 12 is opposed to the other end surface of the optical fiber with a gap of a predetermined size. The member 12 is embedded and fixedly supported in the thick portions 13b and 13c, respectively.

When the base material 13 is used, the other surface of the plate is brought into contact with a test piece made of metal in this case, and as shown in FIG.
For example, at a plurality of points 13p along the boundary portion between the welding portions 13w along the boundary portions with the portions 3b and 13c (see FIG. 6).
Is welded to the specimen by spot welding, and attached to the specimen.

When the optical fiber 11 and the reflecting member 12 are embedded, a groove having a substantially V-shaped or U-shaped cross section is formed in advance along the central axis of the base member 13 by etching or the like. Optical fiber 11 in groove
And the reflecting member 12 in a predetermined direction as described above,
It is arranged at a predetermined position and is buried by bonding with an adhesive. In embedding the optical fiber 11 and the reflecting member 12 in the groove of the base member 13, hot pressing, plating or silver brazing may be performed instead of bonding. Further, the portions where the optical fiber 11 is pulled out from the base material 13 (both ends in FIG. 2) are reinforced with a reinforcing material 13r such as an adhesive or a synthetic resin coating material (see FIGS. 2 and 3).

Next, the principle and operation of the optical fiber type strain gauge configured as described above will be described in detail. As described above, when using an optical fiber type strain gauge in which the optical fiber 11 and the reflecting member 12 are fixed to the base material 13 as described above, as shown in FIG. In a portion along the vicinity of the boundary between the thick portions 13b and 13c, the specimen (FIG. 10) is formed by spot welding at a plurality of points 13p.
5) is fixed to the specimen 5) by welding. For this reason, the strain transmission rate from the specimen in which the strain occurs to the optical fiber strain gauge should be sufficiently high. Here, the strain transmission rate is treated as 100%, and the strain transmission loss is not considered. In addition, the optical fiber type strain gauge having such a configuration includes the optical fiber 11 and the reflecting member 1 in advance.
If the 2 is fixed to the base material 13 with sufficiently high precision, it is only necessary to abut on the specimen and weld it when mounting on the specimen, and a special position adjustment at the time of welding is performed. Is unnecessary, and the workability is very good.

Next, with the optical fiber type strain gauge attached to the test piece, the deformation under the condition that the strain is applied to the test piece will be considered. in this case,
As shown in FIG. 6, the gauge length L is a dimension of the opening 13a in a direction along the central axis. The projecting dimension from the thin portions of the thick portions 13b and 13c of the base material 13 into the opening 13a is set to L _B (the thick portion 13b is also used for the thick portion 13b).
c is the same size), the projection size of the optical fiber 11 from the thick portion 13b toward the reflection member 12 is L _F , and the projection size of the reflection member 12 from the thick portion 13c toward the optical fiber 11 is L _M. G is the gap length between opposing end faces between the optical fiber 11 and the reflecting member 12. Further, the linear expansion coefficient of the optical fiber 11 will be described as α _F , the linear expansion coefficient of the reflection member 12 will be α _M , the linear expansion coefficient of the base material will be α _B , and the linear expansion coefficient of the specimen will be α. Assuming that the specimen to which the optical fiber type strain gauge is fixed by welding is extended by the amount of strain ε due to the load, the change ΔG of the gap length G due to the strain is expressed by the following equation (4).

[0028]

ΔG = (L _M + L _F + 2L _B + G) ε Therefore, L at this time is represented by Expression 5.

[0029]

Equation 5] _{L = (L M + L F} + 2L B + G) (1 + ε) Further, the effect of the gap length G due to a change in environmental temperature, discussed. That is, if the atmosphere around the specimen near the gauge attachment portion changes by ΔT ° C. and is completely transmitted to the optical fiber type strain gauge having the above-described structure, the following equation 6 is established.

[0030]

(Equation 6) Therefore, the change ΔG of the gap length G is expressed by Expression 7.

[0031]

Equation 7] _{ΔG = ΔL-2ΔL B -ΔL M} -ΔL F = {Lα- (2L B α B + L M α M + L F α F)} ΔT Next, change of the gap length G of Strain and temperature changes Consider. Based on the results of Equations 4 to 7, the change ΔG of the gap length G when a change due to both strain and temperature is applied to the test piece is expressed by Equation 8.

[0032]

Equation 8] _{ΔG = (L M + L F} + 2L B + G) ε + {(L M +
_{L F + 2L B + G)} (1 + ε) α- (L M α M + L F α F +2
L _B α _B)} ΔT In this case, conditions for the the influence of temperature "0" are as few 9.

[0033]

Equation 9] _{0 = {(L M + L} F + 2L B + G) (1 + ε) α-
(L _M α _M + L _F α _F +2 L _B α _B )｝ ΔT Here, if the generated strain ε is sufficiently small, it is expressed by the following equation (10) as εα ≒ 0.

[0034]

[Number 10] _{0 = L M (α M -α} ) + L F (α F -α) + 2L
_B (α _B −α) −Gα The dimensions of each part and the material of the reflecting member 12 may be determined according to the material of the specimen based on the equation (10). That is, when determining the size, for example, if those fabricating a strain gauge for specimens of linear expansion coefficient alpha, the linear expansion coefficient alpha _F of the optical fiber has already been determined, the characteristics of the light intensity variation , And the gap length G is constant. Also, in terms of design, in order to make the base material 13 common, dimensions related to the base material 13, that is, the gauge length L and the thick portions 13 b and 1
Projection dimension L _B to 3c of the opening 13a should preferably be constant. Therefore, Expression 11 is obtained. At this time, the linear expansion coefficient α _B of the base material 13 and the reflection member 1
2 of projection dimension L _M, and the linear expansion coefficient of the reflecting member 12 alpha _M
(And the protrusion dimension L _F of the optical fiber 11) have not been determined yet.

[0035]

[Equation 11]

Thereafter, the material of the base material 13 is determined in consideration of the weldability between the base material 13 and the test piece.
Determines the third linear expansion coefficient alpha _B, further, it determines the projecting dimension of the reflecting member 12 L _M and the linear expansion coefficient alpha _M according to the equation 11. Next, a specific calculation example in the case where the above-described optical fiber type strain gauge is configured according to the material of the specimen will be described. (1) Strain gauge for ordinary steel material In order to constitute the above-mentioned optical fiber type strain gauge when using ordinary steel material as a specimen, an optical fiber 11 is used.
Linear expansion coefficient alpha _F of projection dimension L _B of the thick portions 13b and 13c of the opening 13a of the base member 13, a gauge length L, the gap length G, and the linear expansion coefficient of the specimen alpha, follows each Set as follows.

The ^{_{α F = 0.5 × 10 -6 /}} ℃, L B = 1mm, L = 5mm, G = 0.05mm, α = 11.7 × 10 -6 / ℃, and the material of the base member 13 With the coefficient of linear expansion α _B = 16.
As SUS304 stainless steel of 2 × 10 ⁻⁶ / ° C.,
When obtaining the projection dimension L _M of the reflecting member 12 by the number 11 as described above, the number 13 is obtained from equation (12).

[0038]

(Equation 12)

[0039]

(Equation 13)Therefore, as the reflection member 12, the linear expansion coefficient α_M
= 11.7 × 10^-6/ 14 ° C, the number 14
And the number of projections of the reflecting member 12 as L _Mand
Projection dimension L of optical fiber 11_FIs required.

[0040]

## EQU14 ## L _M = 2.2 mm

[0041]

L _F = 0.750 mm (2) Strain gauge for stainless steel SUS630 material In order to constitute the above-mentioned optical fiber type strain gauge when stainless steel SUS630 material is used as a test piece, the wire of the optical fiber 11 is required. expansion coefficient alpha _F, projection dimension L _B of the thick portions 13b and 13c of the opening 13a of the base member 13, a gauge length L, the gap length G, and the linear expansion coefficient of the specimen alpha, respectively, as follows Set.

The ^{_{α F = 0.5 × 10 -6 /}} ℃, L B = 1mm, L = 5mm, G = 0.05mm, α = 10.3 × 10 -6 / ℃, and the material of the base member 13 With the coefficient of linear expansion α _B = 16.
As SUS304 stainless steel of 2 × 10 ⁻⁶ / ° C.,
When the protruding dimension L _M of the reflecting member 12 is obtained by the above-described Expression 11, Expression 17 from Expression 16 is obtained. You.

[0043]

(Equation 16)

[0044]

[Equation 17]

Therefore, as the reflecting member 12, a wire made of ordinary steel or the like is used.
Expansion coefficient α_M= 11.7 × 10^-6Use material of / ° C
18 and 19, the projected dimension of the reflecting member 12
Law L _MAnd the projection length L of the optical fiber 11_FIs required
You.

[0046]

[Expression 18] L _M = 1.57 mm

[0047]

Equation 19 L _F = 1.38 mm, as described above, the optical fiber type strain gage according to the present invention, openings 12a from the thick portion 13b and 13c of the base member 13 during manufacture even when the specimen is different Only by changing the protruding length of the optical fiber 11 and the reflecting member 12 to the right side, appropriate temperature compensation can be performed.
Incidentally, the temperature compensation type in the optical fiber type strain gauge disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 10-141923 describes that, as shown in FIG.
₀ , the bonding dimension of the reflecting member 3 to the base member 4 is L ₁ , the bonding dimension of the capillary tube portion, that is, the sleeve 2 to the base member 4 is L ₂ , the length of the reflecting member 3 is L _1w , Expansion coefficient C _host and linear expansion coefficient C of the reflecting member 3
Assuming that the linear expansion coefficient of the optical fiber 1 can be ignored (= 0) as the _wire , it is expressed by Equation 20.

[0048]

(Equation 20) That is, the length L _1w of the reflecting member 3 is expressed by Expression 21.

[0049]

(Equation 21)Therefore, the above-described strain gauge for ordinary steel is constituted.
The linear expansion coefficient C of the specimen_host= 11.7 × 10^-6
/ ° C, adhesion dimension L of reflective member 3 to base material 4 ₁= 4m
m, adhesion dimension L of the sleeve 2 to the base material 4_Two= 4mm
And opening dimension L of base material 4₀= 5 mm, the temperature of Equation 21
By substituting into the degree compensation equation, Equation 22 is obtained.

[0050]

(Equation 22) Therefore, as the reflecting member 3, the linear expansion coefficient α _M =
When a material of 11.7 × 10 ⁻⁶ / ° C. is used, the length L _1w of the reflecting member 3 is obtained as _Expression 23.

[0051]

L _1w = 11 mm Also, when the above-described strain gauge for stainless steel SUS630 is formed, the coefficient of linear expansion of the specimen C _host = 1
0.3 × 10 ^-6 / ℃, bonding dimension L ₁ = 4 mm to the base material 4 of the reflecting member 3, the adhesion dimension L ₂ = 4 mm to the base material 4 of the sleeve 2, and the opening size of the base member 4 L ₀ = 5mm
Is substituted into the temperature compensation equation of Equation 21 to obtain Equation 24.

[0052]

(Equation 24) Therefore, as the reflecting member 3, the linear expansion coefficient α _M =
When a material of 11.7 × 10 ⁻⁶ / ° C. is used, the length L _1w of the reflecting member 3 is obtained as _Expression 25.

[0053]

L _1w = 9.92 mm The advantages of the above-described optical fiber strain gauge according to the embodiment of the present invention can be summarized as follows. (a) Even if the material of the specimen changes, the adjustment for temperature compensation can be performed only by adjusting the protrusion size of the reflection member 12 and the optical fiber 11, and the parts can be shared, and the manufacturing can be performed. Is easy and workability is good. (b) Since it is fixed to the test piece by welding, higher stability can be realized as compared with ordinary bonding and the like, and the strain transmission rate is considered to be 100, so the opening 13
An accurate gauge length L corresponding to the length of a is obtained,
Therefore, according to the above-described optical fiber strain gauge according to the present invention, adjustment relating to manufacturing is easy and workability is good, and it is possible to cope with various specimens with a common simple configuration. , High accuracy can be obtained.

FIG. 7 schematically shows an example of the configuration of a light intensity type strain measuring system using the optical fiber type strain gauge according to the above-described embodiment of the present invention. This can be applied in substantially the same manner as described above. The measurement system shown in FIG. 7 includes an optical fiber type strain gauge 101, a 2 × 2 coupler 102, a light emitting element 103, a first light receiving element 104, and a second light receiving element 105 similar to those shown in FIG. ing.

The optical fiber type strain gauge 101 is shown in FIG.
Has the same configuration as the optical fiber type strain gauge shown in FIG. The 2 × 2 coupler 102 has first to fourth ports P
1 to P4, and splits and outputs the light input from the first port P1 to the second and third ports P2 and P3 at an intensity ratio of 50% / 50%. The 2 × 2 coupler 102 converts the light input from the third port P3 into a fourth light.
To the port P4.

The light emitting element 103 is connected to the first port P1 of the 2 × 2 coupler 102 via the optical fiber 111. Note that the second port P2 of the 2 × 2 coupler 102
Is coupled to the optical fiber type strain gauge 101 via an optical fiber 112. The first light receiving element 104
It is coupled to a fourth port P4 of the 2 × 2 coupler 102 via an optical fiber 114. Second light receiving element 104
Is coupled to the third port P3 of the 2 × 2 coupler 102 via the optical fiber 113. In such a configuration, light emitted from the light emitting element 103 is
11, the first port P1 of the 2 × 2 coupler 102
It is led to. In the 2 × 2 coupler 102, the first port P
The light incident on 1 is split at an intensity ratio of 50% / 50%, and the light is directed toward the second port P2 and the light traveling toward the third port P3, respectively.

An optical fiber type strain gauge 101 serving as a sensor section from the second port P 2 via an optical fiber 112.
Is emitted from the tip of the optical fiber 11 of the optical fiber type strain gauge 101, is reflected by the tip reflecting surface of the reflecting member 12, and returns to the same optical fiber 112 again. The light returning to the optical fiber 112 passes through the 2 × 2 coupler 102 and passes through the fourth port P4 to the optical fiber 1
The light is guided to the first light-receiving element 104 via. 2x2
Light emitted from the third port P3 of the coupler 102 returns to the second light receiving element 105 through the optical fiber 113. 2x
When the optical fiber type strain gauge 101 is installed in a place where the magnetic fiber or the electromagnetic field is affected, the two couplers 102 are secured at a distance by the optical fiber cable 112 and in a place where the magnetic field and the electromagnetic field are not affected. Be placed.

One of the lights emitted from the light emitting element 103 and branched by the 2 × 2 coupler 102 is supplied to the second port P
2 to the optical fiber type strain gauge 101,
The light is reflected by the reflection member 12 and returns to the 2 × 2 coupler 102. The reflected light returning from the optical fiber type strain gauge 101 to the second port P2 of the 2 × 2 coupler 102 is guided to the first light receiving element 104 via the fourth port P4 and used as signal light. 2 × emitted from the light emitting element 103
The other of the lights split by the two couplers 102 is guided to the second light receiving element 105 via the third port P3 and used as reference light. The optical signals detected by the first and second light receiving elements 104 and 105 are subjected to predetermined signal analysis processing, and are subjected to an optical fiber type strain gauge 101.
The change in the gap G, which is the strain detected by the above, is calculated.

In such a configuration, as described above, the optical fiber type strain gauge 101 can obtain an accurate strain measurement value, and is itself subjected to appropriate temperature compensation. Therefore, high-precision strain measurement that cannot be obtained with a conventional optical fiber strain gauge can be performed. The present invention is not limited to the above-described embodiment, but can be implemented with various modifications within the scope of the gist.

[0060]

As described above, according to the first aspect of the present invention, there is provided an optical fiber having one end coupled to a light emitting and receiving part and a thin line-shaped reflecting member having a reflecting surface formed at the tip. Has a substantially plate-like shape, has an opening formed by removing a central portion thereof, and has only one portion along a central axis in a predetermined direction parallel to the plate-like plate surface, one surface of the plate-like shape. The optical fiber and the reflection are formed on the thick portion of the base material, which is formed so as to bulge to the side and has a large thickness, and the thick portions are opposed to each other in the opening along the central axis and are protruded by a predetermined size. In a state in which each end of the member is further protruded by a predetermined dimension from the protruding end face of the thick portion, and the reflecting surface of the reflecting member faces the other end face of the optical fiber with a gap having a predetermined dimension, the light The fiber and the reflecting member are embedded and fixedly supported. A configuration in which the base material is welded to the specimen at the boundary between the thick part and the thin plate-shaped part in contact with the specimen, such as alignment of an optical fiber and a reflection member, etc. It is easy to adjust for manufacturing and good in workability, as long as it is a weldable metal, it can respond to various specimens with a common simple configuration,
An optical fiber strain gauge capable of obtaining high accuracy can be provided.

According to the optical fiber type strain gauge of the second aspect of the present invention, since the reflecting member includes a thin metal wire made of metal, workability in assembling and adjusting at the time of manufacturing is particularly good, and the reflecting member Can be fixed by embedding by so-called hot pressing or plating other than bonding, and high temperature resistance can be easily achieved. Claim 3 of the present invention
According to the optical fiber type strain gauge according to the above, the base material is formed in advance by forming a groove on the other surface side along the central axis, and the optical fiber and the reflecting member are arranged in the groove. By fixing the optical fiber and the reflecting member to the base material, workability in assembling and adjusting at the time of manufacturing is particularly good.

According to the optical fiber type strain gauge of the fourth aspect of the present invention, since the base material is spot-welded to the specimen, workability particularly in attaching to the specimen is good, and , It is also possible to obtain a high strain transmission rate. According to the optical fiber type strain gauge according to claim 5 of the present invention, the reflection member is set at a temperature with respect to the effective gauge length of the specimen in consideration of the temperature dependence of a relative position with respect to the other end surface of the optical fiber. By setting a protrusion dimension with respect to a protrusion end face of the thick portion of the base material so as to cancel the dependent fluctuation,
In particular, it is possible to improve the workability in adjustment relating to temperature compensation during manufacturing.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of an optical fiber type strain gauge according to an embodiment of the present invention.

FIG. 2 is a top view schematically showing a configuration of the optical fiber type strain gauge of FIG.

FIG. 3 is a front view schematically showing a configuration of the optical fiber type strain gauge of FIG.

FIG. 4 is a left side view schematically showing a configuration of the optical fiber type strain gauge of FIG.

FIG. 5 is a longitudinal sectional view schematically showing a configuration of the optical fiber type strain gauge of FIG.

FIG. 6 is a schematic diagram for explaining the operation of the optical fiber type strain gauge of FIG.

FIG. 7 is a block diagram schematically showing a configuration of a measurement system using the optical fiber strain gauge according to the embodiment of the present invention.

FIG. 8 is a schematic diagram for explaining the principle of an optical fiber type strain gauge.

FIG. 9 is a schematic diagram for explaining the principle of an optical fiber type strain gauge.

FIG. 10 is a cross-sectional view schematically showing another example of the configuration of the conventional optical fiber strain gauge.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Reflecting member 13 Base material 13a Opening 13b Thick part 13c Thick part 13w Weld part 13r Reinforcement material 13p Spot welding 101 Optical fiber type strain gauge 102 2 × 2 coupler 103 Light emitting element 104 First light receiving element 105 Second light receiving element 111, 112, 113, 114 Optical fiber P1, P2, P3, P4 Port

Claims (5)

[Claims] 1. An optical fiber having one end coupled to a light emitting and receiving part, a thin wire-shaped reflecting member having a reflecting surface formed at the tip of the optical fiber, and a substantially plate-shaped member having a central portion cut off. Forming an opening, and only a portion along a central axis in a predetermined direction parallel to the plate-shaped plate surface is bulged toward one surface side of the plate shape to form a thick wall; The thick portion is opposed to the inside of the opening along the central axis so as to protrude by a predetermined size, and each end of the optical fiber and the reflecting member is further protruded by a predetermined size from the protruding end face of the thick portion, and the reflection In a state where the reflection surface of the member is opposed to the other end surface of the optical fiber with a gap having a predetermined size, the optical fiber and the reflection member are embedded and fixedly supported in the thick portion, and the plate-shaped member is provided. Contact the other surface of the specimen with the thick part and the thin part. Fiber optic strain gauge characterized by comprising a base material to be welded to the specimen at a boundary portion of the plate-like portion. 2. The optical fiber type strain gauge according to claim 1, wherein the reflection member includes a thin metal wire made of metal. 3. The base member has a groove formed in advance on the other surface side along the central axis, and the optical fiber and the reflecting member are arranged in the groove in a state where the optical fiber and the reflecting member are arranged in the groove. The optical fiber type strain gauge according to claim 1, wherein a reflecting member is fixed to the base material. 4. The optical fiber strain gauge according to claim 1, wherein the base material is spot-welded to the specimen. 5. The reflection member according to claim 1, wherein a temperature-dependent variation in an effective gauge length of the specimen is offset in consideration of a temperature dependence of a relative position with respect to the other end surface of the optical fiber. 5. A projecting dimension of the thick portion of the base material with respect to a projecting end face thereof is set.
The optical fiber strain gauge according to any one of the above.