JP2011163941A - Optical fiber sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect horizontal stresses, even when a body contacts the entire measurement area making up a contact surface with the body, and horizontal stresses are applied thereby. <P>SOLUTION: In FBG sensors 14A to 14D, a stress detection sensor part 16 is arranged so as to be internally included in a stress direction conversion part 18 in plan view. Gratings 26x, 26y are expanded and contracted by horizontal stress F<SB>H</SB>transmitted from the stress direction conversion part 18, whereas gratings 72x, 72y are arranged outside of the stress direction conversion part 18 in the measurement area 22. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical fiber sensor having an optical fiber in which gratings that reflect light of a specific wavelength are arranged.

  Conventionally, in an optical fiber sensor called an FBG (Fiber Bragg Grating) sensor in which a plurality of gratings (diffraction gratings) are provided in an optical fiber core embedded in a sheet body, when the stress from an object is received, Utilizing the phenomenon that the wavelength of the reflected light changes due to distortion in the grating, the shift amount of the wavelength of the reflected light (reflection wavelength) accompanying the generation of the distortion is detected, and the shift amount is detected based on the detected shift amount. Stress is detected (for example, refer to Patent Document 1).

JP 2002-71323 A

  In the optical fiber sensor of Patent Document 1, when an object comes into contact with a corresponding portion between two adjacent gratings in a measurement area that is a detection surface, and horizontal stress is applied from the object to the corresponding portion. In addition, one grating is stretched by the horizontal stress, and the other grating is compressed by the horizontal stress. As a result, the distortion amounts and the shift amounts of the reflected wavelengths of the two gratings have different sizes, and the position, size, and direction of the horizontal stress applied to the measurement area can be detected.

  However, when an object larger than the measurement area in plan view comes into contact with the entire measurement area and a horizontal stress is applied, all the gratings including the two gratings have the same structural change (distortion). Therefore, the difference in the distortion amount of each grating and the difference in the shift amount of the reflection wavelength are not clear differences enough to detect the horizontal stress, which makes it difficult to detect the horizontal stress. It was.

  The present invention has been made in view of the above problems, and even when the object is in contact with the entire area to be measured which is a contact surface with the object and the horizontal stress is applied, the horizontal stress can be detected. An object of the present invention is to provide an optical fiber sensor that can be used.

The optical fiber sensor according to the present invention is
A plurality of stress detection sensor units composed of optical fibers in which gratings that reflect light of a specific wavelength are arrayed, and a stress direction conversion unit that converts external stress into stress in the direction in which the gratings are arrayed and transmits the stress to each grating. Prepared,
Each of the stress detection sensor units and the stress direction conversion unit are disposed in a measurement area that receives the external stress,
The plurality of stress detection sensor units are arranged so as to be included in the stress direction conversion unit in a plan view, and a first stress detection sensor unit in which the grating expands and contracts by the stress transmitted from the stress direction conversion unit; And a second stress detection sensor unit disposed outside the stress direction conversion unit in the measurement area.

  According to the present invention, the first stress detection sensor unit is disposed so as to be included in the stress direction conversion unit, and the second stress detection sensor unit is disposed outside the stress direction conversion unit. Has been. Therefore, when a horizontal stress as an external stress is applied from the object to the area to be measured, the grating of the first stress detection sensor unit expands and contracts according to the horizontal stress, while the second stress Since the grating of the stress detection sensor unit is disposed outside the stress direction conversion unit, it exhibits expansion and contraction different from the grating of the first stress detection sensor unit.

  Accordingly, the amount of distortion of the grating and the amount of shift of the reflected wavelength are different between the grating of the first stress detection sensor unit and the grating of the second stress detection sensor unit. The difference in amount and the difference in shift amount are clear differences to the extent that the horizontal stress can be detected. As a result, even if the horizontal stress is applied to the entire area to be measured, the position, magnitude, and direction of the applied horizontal stress can be detected.

  As described above, according to the present invention, in the area to be measured, the first stress detection sensor unit is disposed so as to be included in the stress direction conversion unit, and the first stress detection sensor unit is disposed outside the stress direction conversion unit. By disposing the stress detection sensor unit 2, the horizontal stress can be detected even when the horizontal stress is applied when the object is in contact with the entire area to be measured which is a contact surface with the object. It becomes possible.

  Here, the optical fiber is disposed along the area to be measured so as to penetrate the stress direction conversion section, and the first stress detection sensor section includes a first grating disposed in the optical fiber. The second stress detection sensor unit may include a second grating disposed on the optical fiber.

  Accordingly, when the horizontal stress is applied to the area to be measured, the first grating expands and contracts due to the horizontal stress, and at the same time, the second grating expands and contracts. Can be performed efficiently.

  The stress direction conversion section includes a flat section extending along the measurement area, and a first stress transmission section bridged from the flat section to one end of the first grating in the optical fiber. And a second stress transmission portion bridged from the flat portion to the other end portion side of the first grating in the optical fiber.

  Thereby, the horizontal stress can be efficiently transmitted to the first grating.

  Further, if the second grating is disposed in the vicinity of the first stress transmission portion or in the vicinity of the second stress transmission portion in the optical fiber, the arrangement direction of the first grating, and the second Since the grating arrangement direction can be made substantially coincident, it is possible to distort the first grating and the second grating on the same axis when the horizontal stress is applied to the measurement area. It becomes. Therefore, it is possible to easily calculate the horizontal stress from the distortion amount and the reflection wavelength shift amount of the first grating and the second grating.

  In addition, a first optical fiber is disposed along the measurement area so as to penetrate the stress direction conversion portion, and penetrates the stress direction conversion portion and is orthogonal to the first optical fiber in plan view. The second optical fiber is disposed along the area to be measured, the first grating is disposed on the first optical fiber and the second optical fiber, and the first optical fiber and the second optical fiber are disposed on the first optical fiber and the second optical fiber, respectively. The second grating may be disposed on at least one of the two optical fibers.

  Thereby, for example, if the first optical fiber is arranged in the X direction along the measured area and the second optical fiber is arranged in the Y direction along the measured area, the horizontal stress is reduced. It is also possible to detect the components separately in the X direction and the Y direction.

  According to the present invention, in the area to be measured, the first stress detection sensor unit is disposed so as to be included in the stress direction conversion unit, and the second stress detection sensor unit is disposed outside the stress direction conversion unit. As a result, even when the object comes into contact with the entire area to be measured, which is a contact surface with the object, and a horizontal stress is applied, the horizontal stress can be detected.

It is a perspective view of the pressure sensor which has arrange | positioned the FBG sensor used as the premise of this embodiment in the sheet | seat body. It is a top view of the pressure sensor of FIG. It is a perspective view of the FBG sensor of FIG. It is a schematic explanatory drawing of the FBG sensor of FIG. It is explanatory drawing of the detection principle of the normal stress by the FBG sensor of FIGS. It is explanatory drawing of the FBG sensor of FIGS. 1-4 before horizontal stress is provided. It is explanatory drawing of the detection principle of the horizontal stress by the FBG sensor of FIG. It is a top view which shows the state which the object larger than the to-be-measured area which is a detection surface is contacting the pressure sensor of FIG.1 and FIG.2. It is explanatory drawing of the FBG sensor of FIG. 8 before a horizontal stress is provided. FIG. 10 is an explanatory diagram illustrating that the horizontal stress cannot be detected when the horizontal stress is applied to the measurement area in the state of FIGS. 8 and 9. It is a perspective view of the pressure sensor which has arrange | positioned the FBG sensor which concerns on this embodiment to the sheet | seat body. It is a top view of the pressure sensor of FIG. FIG. 13 is a plan view showing a state in which an object larger than the measurement area is in contact with the pressure sensor of FIGS. 11 and 12. It is explanatory drawing of the FBG sensor of FIG. 13 before a horizontal stress is provided. It is explanatory drawing of the detection principle of the horizontal stress by the FBG sensor of FIG. It is a graph which shows the output of the grating arrange | positioned outside the stress direction conversion part of FIGS. It is a top view which shows the modification of the pressure sensor of FIGS. It is a top view which shows the modification of the pressure sensor of FIGS. It is a top view which shows the modification of the pressure sensor of FIGS.

  A preferred embodiment of an optical fiber sensor according to the present invention will be described with reference to the drawings.

  First, prior to the description of the present embodiment, an outline of stress detection using an FBG sensor (Fiber Bragg Grating Sensor) as an optical fiber sensor which is a premise of the present embodiment will be described with reference to FIGS. .

  FIG. 1 is a perspective view of a pressure sensor 10 in which a plurality of FBG sensors 14 </ b> A to 14 </ b> D as a premise of the present embodiment are incorporated.

  In the pressure sensor 10, one optical fiber cable 20 is embedded along the surface direction (XY direction) of the sheet body 12 inside the flexible sheet body 12, and along the optical fiber cable 20. The plurality of FBG sensors 14A to 14D are arranged.

  That is, the optical fiber cable 20 has an optical fiber (first optical fiber) 20x whose longitudinal direction is set to the X direction by meandering in the Y direction, and a longitudinal direction of the optical fiber cable 20 that is meandered to the Y direction. It is comprised from the optical fiber (2nd optical fiber) 20y made into the direction. In this case, the optical fiber 20x and the optical fiber 20y are arranged at different heights (see FIGS. 3 and 4), but the optical fiber 20x and the optical fiber 20y are orthogonal to each other in plan view (FIG. 2). FBG sensors 14A to 14D are provided at positions orthogonal to each other.

  Then, the sheet body 12 is formed by molding the optical fiber cable 20 and the FBG sensors 14A to 14D with a flexible material such as plastic or resin. The sheet body 12 is formed in order to fix the FBG sensors 14A to 14D inside the sheet body 12 and to protect the FBG sensors 14A to 14D from excessive stress or heat applied from the outside.

  1 and 2 show a case where four FBG sensors 14A to 14D are arranged and addressed in a 2 × 2 matrix, but the FBG sensor 14A embedded in the sheet body 12 is illustrated. The number of ~ 14D is not limited to four, and may be increased or decreased.

  1 to 4 illustrate the case where the optical fiber 20x is disposed below the optical fiber 20y, it is needless to say that the optical fiber 20x may be disposed above the optical fiber 20y. Furthermore, as shown in FIGS. 1 and 2, in the sheet body 12, the end of the optical fiber 20x is exposed to one side surface orthogonal to the X direction and the other one side surface orthogonal to the Y direction. Further, the end of the optical fiber 20y is exposed to the outside. These ends can receive light from the outside or can emit light from the optical fibers 20x and 20y.

  In the pressure sensor 10, the upper surface of the sheet body 12 in FIG. 1 is a measurement area (detection surface) 22 for detecting external stress.

  Here, the FBG sensors 14A to 14D will be described in detail with reference to FIGS.

  The stress direction conversion part 18 is arrange | positioned in the location where the optical fiber 20x and the optical fiber 20y orthogonally cross. In addition, in the orthogonal portion, a grating 26x is formed on the core 24x of the optical fiber 20x, and a grating 26y is formed on the core 24y of the optical fiber 20y, and one stress is generated by these gratings 26x and 26y. A detection sensor unit (first stress detection sensor unit) 16 is configured.

  That is, each of the FBG sensors 14A to 14D of the pressure sensor 10 includes one stress detection sensor unit 16 and one stress direction conversion unit 18. Further, as shown in FIG. 2, the stress detection sensor units 16 of the FBG sensors 14 </ b> A to 14 </ b> D are arranged so as to be included in the stress direction conversion unit 18 in plan view. Accordingly, the optical fibers 20x and 20y are arranged along the measurement area 22 so as to penetrate the respective stress direction changing portions 18 inside the sheet body 12. Note that all the gratings 26x and 26y have different grating intervals and reflection wavelengths.

  The stress direction conversion part 18 as a sensitive member with respect to the stress from the outside consists of elastic bodies, such as rubber | gum and resin. In this case, the stress direction conversion unit 18 includes a rectangular flat portion 28 extending in parallel with the sheet body 12 along the XY direction, and a grating 26x in the optical fiber 20x from two opposite sides of the flat portion 28. Of the grating 26y in the optical fiber 20y from two opposite sides of the flat portion 28 and two stress transmission portions 30x (first stress transmission portion and second stress transmission portion) bridged on both ends of the optical fiber It has two stress transmission parts 30y (the 1st stress transmission part and the 2nd stress transmission part) each bridged by the both ends.

  The two stress transmission portions 30x formed so as to face each other are connected to the flat portion 28 and inclined to the optical fiber 20x, and to the inclined portion 32x and to the outer peripheral surface of the optical fiber 20x. And a joint portion 34x surrounding a part of each. In this case, as shown in FIGS. 4 and 5, the angle formed between the flat portion 28 and the inclined portion 32x is set equal between the two stress transmission portions 30x, and the inclined portion 32x and the joint portion 34x Are also set equal to each other.

  On the other hand, the two stress transmission portions 30y formed so as to face each other are also connected to the flat portion 28 and inclined toward the optical fiber 20y, and the inclined portions 32y are connected to the flat portion 28, similarly to the stress transmission portion 30x. And a joining portion 34y that surrounds a part of the outer peripheral surface of the optical fiber 20y. Also, between the two stress transmission portions 30y, the angle formed by the flat portion 28 and the inclined portion 32y is set to be equal to each other, and the angle formed between the inclined portion 32y and the joint portion 34y is also set to be equal to each other.

  As described above, since the optical fiber 20x is embedded at a position lower than the optical fiber 20y in the sheet body 12 (see FIGS. 1 to 4), the upper surface of the bonding portion 34x is the bonding portion. It is set at a position lower than the upper surface of 34y.

Next, the vertical stress F _P when the object 40 comes into contact with the measured area 22 of the sheet 12 and the vertical stress F _P (stress along the Z direction) is applied from the object 40 to the measured area 22. The detection of _P will be described with reference to FIG.

  Here, the contact area with the object 40 in the measurement area 22 is about the area corresponding to the FBG sensors 14A to 14D (the area of the projected image when the FBG sensors 14A to 14D are projected onto the measurement area 22). explain. In FIG. 5, illustration of the optical fiber 20y and the stress transmission unit 30y arranged along the Y direction is omitted for ease of explanation.

As shown in FIGS. 1 to 3, the shape of the stress direction changing portion 18 before the stress is applied is a substantially rotationally symmetric structure around the flat portion 28 (in FIG. 5, a symmetrical structure around the flat portion 28). because it is, the normal stress F _P along the Z direction to be measured area 22 is applied from the object 40, when the flat portion 28 is subjected to the vertical stress F _P, each stress transmission portion 30x, an ideal In particular, a stress F ′ (F ′ = F _P / 4) along the Z direction is applied.

That is, the four inclined portions from the sides of the flat portion 28 32x, since 32y extends respectively assigned the stress F'to one stress transmission portion 30x are ideally suited for use in normal stress F _P 1 / 4 the size of the F _P / 4.

The component (force) F ″ in the direction along the inclined portion 32x of the stress F ′ is F ″ = F′cos φ = if the angle between the Z direction (stress F ′) and the inclined portion 32x is φ. (F _P / 4) × cos φ.

In addition, since the angle formed between the force F ″ and the longitudinal direction (X direction) of the optical fiber 20x is (90 ° −φ), the force F ″ applied to the optical fiber 20x and the joint 34x is F ″ ″ = F ″ cos (90 ° −φ) = F′sinφ = (F _P / 4) × cosφ × sinφ.

By applying this force F ″ ″ to the optical fiber 20x, the grating 26x is distorted (expanded) in the X direction, and the lattice spacing of the grating 26x changes (increases). That is, since the FBG sensors 14A to 14D have a bilaterally symmetric structure, the same forces F '''' act on the left and right sides of the grating 26x in opposite directions, and as a result, the stress direction conversion unit 18 is not provided. However, the distortion amount of the grating 26x and the shift amount of the reflection wavelength can be increased. Therefore, the pressure sensor 10 and the FBG sensors 14A-14D, it can be easily detected (calculated) normal stress F _P based on the strain amount and the shift amount.

In FIG. 5, for ease of explanation, with respect to the vertical stress F _P, F', it is exaggerated for F'' and F'''. In FIG. 5, the case where the force F ″ ″ is applied to the grating 26x has been described. However, even when the force F ″ ″ is applied to the grating 26y, a large distortion is generated in the grating 26y in the same manner. , it is possible to increase the shift amount of the reflection wavelength, it is possible to normal stress F _P detected easily (calculated).

Next, the horizontal stress F _H when the object 50 comes into contact with the area to be measured 22 of the sheet body 12 and the horizontal stress F _H (stress along the X direction) is applied from the object 50 to the area to be measured 22. The detection of _H will be described with reference to FIGS.

  Here, the contact area with the object 50 in the area to be measured 22 is an area corresponding to a length shorter than the distance from the left end of the FBG sensor 14A (14B) to the right end of the FBG sensor 14C (14D). explain.

As shown in FIG. 6, the object 50 comes into contact with the portion between the FBG sensor 14A (14B) and the FBG sensor 14C (14D) in the measured area 22, and the horizontal stress F _H shown in FIG. When applied to the measurement area 22, the pressure sensor 10 has a shape deformed asymmetrically left and right by the horizontal stress F _{H as} a whole as compared to before stress application (the two-dot chain line in FIGS. 6 and 7). The shape shown by the solid line in FIG.

That is, the right stress transmission portion 30x of the FBG sensor 14A (14B) moves to the right in FIG. 7 due to the horizontal stress F _H , and the left stress transmission portion 30x of the FBG sensor 14C (14D) has the horizontal stress F _H. Moves to the right side of FIG.

In this case, the horizontal stress F is applied to the joint portion between the joint portion 34x of the right stress transmission portion 30x and the optical fiber 20x, and the joint portion between the joint portion 34x of the left stress transmission portion 30x and the optical fiber 20x. _{Since H} is transmitted, the horizontal stress F _H applied to the grating 26x of the FBG sensor 14A (14B) becomes a force for extending the lattice interval of the grating 26x, while the grating of the FBG sensor 14C (14D). The horizontal stress F _H applied to 26x becomes a force for compressing the lattice spacing of the grating 26x.

Therefore, when the horizontal stress F _H is applied to each grating 26x, each grating 26x is distorted by an amount different from each other along the X direction, so that the lattice spacing is also changed by an amount different from each other. As a result, the reflection of each grating 26x The shift amounts of the wavelengths are different from each other. Accordingly, the horizontal stress F _H can be calculated based on the difference in the shift amount of the reflection wavelength in each grating 26x before and after the application of the horizontal stress F _H.

6 and 7 have been described with respect to the case where the horizontal stress F _H is applied along the X direction, but the horizontal stress F _H is applied similarly when the horizontal stress F _H is applied along the Y direction. Of course, the stress F _H can be detected.

  In addition, as described above, the strain amount of the gratings 26x and 26y when the force along the arrangement direction (X direction and Y direction) of the gratings 26x and 26y is applied, the shift amount of the reflected wavelength, the normal stress and Since the detection of the horizontal stress is disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-276127, detailed description thereof is omitted.

Next, as shown in FIG. 8, when an object 60 larger than the area to be measured 22 is in contact with the area to be measured 22 in plan view and a horizontal stress F _H is applied from the object 60 to the area to be measured 22. Will be described with reference to FIGS.

In this case, since the object 60 is in contact with the entire area to be measured 22 (see FIGS. 8 and 9), a horizontal stress F _H is applied from the object 60 to the area to be measured 22 as shown in FIG. The pressure sensor 10 is generally deformed in the direction in which the horizontal stress F _H is applied (shown by the solid line in FIG. 10) as compared with that before the stress application (the two-dot chain line in FIGS. 9 and 10). Shape).

That is, each stress transmission portion 30x of the FBG sensor 14A~14D moves to the right in FIG. 10 by the horizontal stress F _H. In this case, the horizontal stress F _H is transmitted to the joint portion between the joint portion 34x of each stress transmission portion 30x and the optical fiber 20x. As a result, the horizontal stress F _H is applied to the gratings 26x of the FBG sensors 14A to 14D, respectively, causing the same structural change to expand and contract.

Here, changes in the lattice spacing of each grating 26x due to the application of the horizontal stress F _H , that is, changes in each joint 34x are a, b, c, and d. Further, the lattice spacing of the grating 26x of the FBG sensor 14A (14B) before application of the horizontal stress F _H is Δ _0, and the lattice spacing of the grating 26x of the FBG sensor 14C (14D) is Δ ₀ ′. Furthermore, the number of grids each grating 26x is N, the effective refractive index of the core 24x and n _eff.

In this case, before and after the application of the horizontal stress F _H , the reflection wavelength shift amount Δλ in the grating 26x of the FBG sensor 14A (14B) is expressed by the following equation (1), while the FBG sensor 14C (14D) ) Of the reflection wavelength in the grating 26x is expressed by the following equation (2).
Δλ = 2 × n _eff × {Δ ₀ + ( _ba ) / N} (1)
Δλ = 2 × n _eff × {Δ ₀ ′ + (dc) / N} (2)

As described above, since each grating 26x undergoes the same structural change due to the application of the horizontal stress F _H , changes in the lattice spacing (changes in each joint 34x) a, b, c, and d are as follows: 3) The amounts are the same as each other.
a = b = c = d (3)

Therefore, when the expression (3) is substituted into the expressions (1) and (2), the expression (1) is transformed into the expression (4), and the expression (2) is transformed into the expression (5). Is done.
Δλ = 2 × n _eff × {Δ ₀ + ( _ba ) / N}
= 2 × n _eff × Δ ₀ (4)
Δλ = 2 × n _eff × {Δ ₀ ′ + (dc) / N}
= 2 × n _eff × Δ ₀ ′ (5)

n _eff , Δ _0, and Δ ₀ ′ are preset values. If the lattice intervals Δ ₀ , Δ ₀ ′ are set to values close to each other, the difference in shift amount cannot be increased.

Therefore, in the FBG sensors 14A to 14D and the pressure sensor 10 incorporating these, which are the premise of the present embodiment, the horizontal stress F _H applied to the entire area to be measured 22 is converted into two adjacent FBG sensors 14A (14B) and 14C. It is difficult to detect at (14D).

  Next, the pressure sensor 70 (the FBG sensors 14A to 14D) according to the present embodiment for solving such a problem will be described with reference to FIGS.

  In the description of the pressure sensor 70, the same components as those of the pressure sensor 10 described in FIGS. 1 to 10 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In each of the FBG sensors 14A to 14D, the pressure sensor 70 according to the present embodiment includes a second stress detection sensor unit and a grating 72x as a second grating on the optical fibers 20x and 20y outside the stress direction conversion unit 18. It differs from the pressure sensor 10 which is the premise of the present embodiment in that 72y is arranged.

  That is, in the pressure sensor 70 of FIGS. 11 and 12, the FBG sensors 14A to 14D each have one stress detection sensor unit 16, one stress direction conversion unit 18, and two gratings 72x and 72y.

  The gratings 72x and 72y are arranged in the vicinity of the joint portions 34x and 34y facing the side surface of the sheet body 12 in the sheet body 12. Further, in plan view, the grating 72x arranged outside the stress direction conversion unit 18 and the grating 26x arranged so as to be included in the stress direction conversion unit 18 are arranged substantially coaxially, The grating 72y arranged outside the stress direction conversion unit 18 and the grating 26y arranged so as to be included in the stress direction conversion unit 18 are also arranged substantially coaxially.

Incidentally, in the pressure sensor 70 according to this embodiment, the detection principle and the normal stress F _P, the detection principle of the horizontal stress F _H applied from the small object 50 than the measurement area 22 in a plan view, the pressure sensor 10 Same as the case.

Therefore, here, the detection of the horizontal stress F _{H applied} to the measurement area 22 from the object 60 larger than the measurement area 22 in plan view will be described with reference to FIGS.

When the horizontal stress F _H is applied from the object 60 to the measurement area 22 along the X direction, as in the case of the pressure sensor 10 (see FIGS. 8 to 10), the pressure sensor 70 The shape is deformed in the application direction (X direction) of the horizontal stress F _H (deformation from the state shown by the two-dot chain line in FIG. 15 to the shape shown by the solid line in FIG. 15).

That is, each stress transmission part 30x moves to the right side of FIG. 15 by the horizontal stress F _H. This case, the joint portion between the joint portion 34x and the optical fiber 20x of each stress transmission portion 30x, since horizontal stress F _H are transmitted respectively, the grating 26x of the FBG sensor 14A-14D, the horizontal stress F _H Each takes the same structural change and expands and contracts.

On the other hand, the grating 72x disposed on the left side of the FBG sensors 14A and 14B causes the horizontal stress F _{H due} to the rightward movement of the joint portion between the left joint portion 34x and the optical fiber 20x of the FBG sensors 14A and 14B. Acts as a tensile force. As a result, the grating 72x, by such horizontal stress F _H, distorted as the lattice spacing is expanded.

Here, if the lattice spacing of the grating 72x before the horizontal stress F _H is applied is Δ _{0 ″} , the reflection wavelength shift amount Δλ at the grating 72x before and after the application of the horizontal stress F _H is as follows: 6) It is represented by the formula.
Δλ = 2 × n _eff × (Δ _{0 ″} + a) (6)

As described above, since the change (a) in the grating spacing of the grating 72x is included in the expression (6), the reflection wavelength shift amount Δλ at the grating 72x is expressed by the expression (4) or (5). By calculating the difference from the reflected wavelength shift amount Δλ at the grating 26x, the difference in the shift amount Δλ is sufficiently larger than the pressure sensor 10 so that the horizontal stress F _H can be detected. As a result, the horizontal stress F _H can be easily detected based on the difference.

In the above description, as shown in FIG. 15, when the horizontal stress F _H is applied to the area to be measured 22 along the + X direction, the reflection wavelength shift amount Δλ of the left grating 72x is used to The case where the stress F _H is detected has been described.

On the contrary, when the horizontal stress F _H is applied to the -X direction (the direction from the right side of FIG. 15 to the left), the right side of the grating 72x horizontal stress F _H using a shift amount Δλ of the reflected wavelength of May be detected. In this case, the change in the lattice spacing in equation (6) may be replaced from “a” to “d”.

FIG. 16 is a graph showing the relationship between the horizontal stress F _H and the reflection wavelength shift amount Δλ of each of the right and left gratings 72x in FIG. When a horizontal stress F _H (positive horizontal stress) along the + X direction is applied, the reflection wavelength shift amount Δλ at the left grating 72x increases, while the horizontal stress F along the −X direction increases. _{When H} (horizontal stress in the negative direction) is applied, it can be easily understood that the reflection wavelength shift amount Δλ at the right grating 72x increases.

As described with reference to FIG. 5, when the normal stress _FP is applied to the measurement area 22, in the stress direction conversion unit 18, the left and right stress transmission units 30 x cause different structural changes with respect to the flat portion 28. As a result, the lattice spacing of the grating 26x changes, but the influence of this structural change does not reach the gratings 72x arranged outside the stress direction changing portion 18. Accordingly, the pressure sensor 70, even normal stress F _P is applied to the measurement area 22, the lattice spacing of the gratings 72x does not change (no reaction).

In the above description, the case where the horizontal stress F _H is detected using the grating 72x arranged along the X direction has been described, but the case where the horizontal stress F _H is applied along the Y direction is described. However, like the grating 72x, the reflection wavelength shift amount Δλ shown in the equation (6) also occurs in each grating 72y, so that the horizontal stress F _H can be easily detected.

Furthermore, even when a horizontal stress F _H is applied in an arbitrary direction along the measured area 22, the components in the X direction and the component in the Y direction are detected using the gratings 72 x and 72 y described above. Thus, the horizontal stress F _H can be detected separately for each component.

  Further, the present embodiment is not limited to the configurations of FIGS. 11 to 16, and the configurations of FIGS. 17 to 19 can also be adopted.

  In FIG. 17, four gratings 72 x and 72 y are arranged inside the sheet body 12. Specifically, the two gratings 72x and 72y are respectively disposed between the side surface of the sheet body 12 and the joint portions 34x and 34y. Further, with respect to the remaining two gratings 72x and 72y, one grating 72x is disposed along the X direction in the curved portion of the optical fiber cable 20 between the two joint portions 34x and in the vicinity of the side surface of the sheet body 12. The other grating 72y is arranged along the Y direction at a location close to the side surface of the sheet body 12 in the curved portion of the optical fiber cable 20 between the two joining portions 34y.

Thereby, when the horizontal stress F _H is applied along the X direction, the horizontal stress F _H is detected using the reflection wavelength shift amount Δλ of at least one of the two gratings 72x, On the other hand, when the horizontal stress F _H is applied along the Y direction, if the horizontal stress F _H is detected using the shift amount Δλ of the reflection wavelength of at least one grating 72 y out of the two gratings 72 y. Good. Accordingly, the horizontal stress F _H can be efficiently detected using a smaller number of gratings 72x and 72y.

Further, in FIG. 18, nine FBG sensors 14 </ b> A to 14 </ b> I are arranged in a matrix shape inside the sheet body 12, and all the joint portions 34 x and 34 y facing each side surface of the sheet body 12, Gratings 72x and 72y are arranged between the two. As a result, the distribution of the horizontal stress F _H applied to the area to be measured 22 can be accurately detected.

Further, in FIG. 19, nine FBG sensors 14 </ b> A to 14 </ b> I are arranged in a matrix shape inside the sheet body 12, two gratings 72 x are arranged coaxially, and two gratings 72 y are also arranged coaxially. . Even in this case, the horizontal stress F _H can be efficiently detected using a smaller number of gratings 72x and 72y.

As described above, according to the pressure sensor 70 according to the present embodiment and the FBG sensors 14A to 14I that constitute the pressure sensor 70, the stress detection sensor unit (first (Stress detection sensor section) 16 is disposed, and second stress detection sensor sections and gratings 72x and 72y as second gratings are disposed outside the stress direction conversion section 18. Therefore, when a horizontal stress F _H as an external stress is applied from the object 60 to the area to be measured 22, the gratings 26 x and 26 y of the stress detection sensor unit 16 correspond to the horizontal stress F _H at the stress direction conversion unit 18. On the other hand, since the gratings 72x and 72y are disposed outside the stress direction changing portion 18, they show different expansion and contraction from the gratings 26x and 26y.

Thereby, between the gratings 26x, 26y and the gratings 72x, 72y, the distortion amounts of the gratings 26x, 26y, 72x, 72y and the reflection wavelength shift amount Δλ are different from each other. The difference of the shift amount Δλ is a clear difference that can detect the horizontal stress F _H. As a result, even if the horizontal stress F _H is applied to the entire area to be measured 22, the position, size and direction of the applied horizontal stress F _H can be detected.

As described above, according to the present embodiment, the stress detection sensor unit 16 is arranged in the area to be measured 22 so as to be included in the stress direction conversion unit 18, and the gratings 72 x and 72 y are disposed outside the stress direction conversion unit 18. by placing the, even if the horizontal stresses F _H in contact with said object 60 across the measurement area 22 which is a contact surface with the object 60 has been applied, it is possible to detect the horizontal stress F _H Become.

Further, since the optical fibers 20x and 20y are arranged along the measured area 22 so as to penetrate the stress direction changing portion 18, the horizontal stress F _H is applied to the measured area 22 when the horizontal stress F _H is applied. Since the gratings 26x and 26y expand and contract due to F _H , and the gratings 72x and 72y expand and contract, the horizontal stress F _H can be detected efficiently.

The stress direction conversion unit 18 includes a flat portion 28 extending along the measurement area 22 and a stress transmission portion 30x bridged from the flat portion 28 to both ends of the gratings 26x and 26y in the optical fibers 20x and 20y. , 30y, the horizontal stress F _H can be efficiently transmitted to the gratings 26x, 26y.

Furthermore, if the gratings 72x and 72y are arranged in the vicinity of the joints 34x and 34y of the stress transmission parts 30x and 30y in the optical fiber cable 20, the arrangement direction of the gratings 26x and 26y and the arrangement direction of the gratings 72x and 72y are substantially omitted. Therefore, when the horizontal stress F _H is applied to the measurement area 22, the gratings 26x and 26y and the gratings 72x and 72y can be distorted on the same axis. Accordingly, it is possible to easily calculate the horizontal stress F _H from the distortion amount of each grating 26x, 26y, 72x, 72y and the reflection wavelength shift amount Δλ.

Further, in the stress direction conversion unit 18, the optical fibers 20 x and 20 y are orthogonal to each other in plan view, and the gratings 26 x and 26 y are disposed at the orthogonal positions, and the gratings 72 x and 72 y are optical fibers outside the stress direction conversion unit 18. Since they are arranged at 20x and 20y, respectively, it becomes possible to detect the horizontal stress F _H by separating it into components in the X direction and the Y direction.

  Note that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 10, 70 ... Pressure sensor 12 ... Sheet | seat body 14A-14I ... FBG sensor 16 ... Stress detection sensor part 18 ... Stress direction conversion part 20x, 20y ... Optical fiber 22 ... Area to be measured 26x, 26y, 72x, 72y ... Grating 28 ... Flat part 30x, 30y ... Stress transmission part 32x, 32y ... Inclined part 34x, 34y ... Joint part 40, 50, 60 ... Object

Claims (5)

A plurality of stress detection sensor units composed of optical fibers in which gratings that reflect light of a specific wavelength are arrayed, and a stress direction conversion unit that converts external stress into stress in the direction in which the gratings are arrayed and transmits the stress to each grating. Prepared,
Each of the stress detection sensor units and the stress direction conversion unit are disposed in a measurement area that receives the external stress,
The plurality of stress detection sensor units are:
A first stress detection sensor unit which is arranged so as to be included in the stress direction conversion unit in plan view and in which the grating expands and contracts due to the stress transmitted from the stress direction conversion unit;
A second stress detection sensor unit disposed outside the stress direction conversion unit in the measurement area;
An optical fiber sensor. The sensor according to claim 1, wherein
The optical fiber is disposed along the area to be measured so as to penetrate the stress direction changing portion,
The first stress detection sensor unit includes a first grating disposed in the optical fiber, and the second stress detection sensor unit includes a second grating disposed in the optical fiber. An optical fiber sensor. The sensor according to claim 2, wherein
The stress direction conversion portion includes a flat portion extending along the measurement area, a first stress transmission portion bridged from the flat portion to one end portion side of the first grating in the optical fiber, An optical fiber sensor comprising: a second stress transmission portion bridged from the flat portion to the other end portion side of the first grating in the optical fiber. The sensor according to claim 3, wherein
The optical fiber sensor, wherein the second grating is disposed in the vicinity of the first stress transmission part or in the vicinity of the second stress transmission part in the optical fiber. The sensor according to any one of claims 2 to 4,
A first optical fiber is disposed along the area to be measured so as to penetrate the stress direction changing portion;
A second optical fiber is disposed along the measured area so as to pass through the stress direction converter and to be orthogonal to the first optical fiber in plan view.
The first grating is disposed in each of the first optical fiber and the second optical fiber,
The optical fiber sensor, wherein the second grating is disposed in at least one of the first optical fiber and the second optical fiber.

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