JP4730124B2 - Optical fiber deformation detection sensor - Google Patents

Description

  The present invention relates to an optical fiber deformation detection sensor using an optical fiber formed with a Bragg grating applied to intrusion detection.

  In general, as a method for detecting deformation of a material or a structure due to an external force, a method using an optical fiber on which a Bragg grating is formed is known. The Bragg grating is a grating (diffraction grating) having diffraction grating fringes whose refractive index periodically changes, and has a property of reflecting only light having a specific wavelength (Bragg wavelength) corresponding to the interval between the diffraction grating fringes. When the portion of the optical fiber where the Bragg grating is formed is deformed, the distance between the diffraction grating fringes is changed according to the deformation, so that the wavelength of the reflected light is changed. The deformation amount of the Bragg grating can be detected by detecting the wavelength change of the reflected light. Therefore, the amount of deformation of the structure due to external force can be detected by installing the optical fiber on which the Bragg grating is formed in close contact with the structure.

  As an intrusion detection system applying such an optical fiber deformation detection sensor using a Bragg grating, an optical fiber equipped with a Bragg grating is installed at the upper end of the fence in the site, and an intruder tries to get over the fence. A method of detecting the deformation of the fence with an optical fiber is known. About 40 Bragg gratings are formed at intervals in one optical fiber, and the respective Bragg grating forming portions are arranged at positions where the measurement object and the fence are deformed. Since the wavelength of the reflected light varies by changing the interval between the diffraction grating stripes of each Bragg grating, the position of the Bragg grating, that is, the intrusion position can be detected based on the wavelength of the reflected light (for example, Patent Document 1). reference).

  Further, as an optical fiber deformation detection sensor equipped with a Bragg grating used in such an intrusion detection system, a leaf spring that deforms according to the deformation amount of the measurement object due to an external force, and along the longitudinal direction of the leaf spring An optical fiber having a Bragg grating integrated and fixed is known. (For example, refer to Patent Document 2).

Japanese Patent Laying-Open No. 2005-32224 (page 3-4, FIG. 1) JP 2003-222507 A (page 2-3, FIG. 1)

  In an intrusion detection system using a conventional optical fiber, there are various measurement objects. Even when the measurement object is a fence, the measurement position is a fence-like part of a fence or a column, or the measurement object is other than a fence. An object whose deformation is measured, such as a door or a bag, is often different in material, shape, rigidity, and the like. That is, the amount of deformation at the position where the Bragg grating is arranged varies greatly depending on the position to be measured. However, the allowable range of the amount of change in the distance between the diffraction grating stripes of the Bragg grating is as small as several nanometers, and if an amount of deformation beyond that is applied to the optical fiber, the optical fiber is damaged or cut. Therefore, the deformation amount of the optical fiber needs to be within an allowable range of the change amount of the distance between the diffraction grating stripes of the Bragg grating corresponding to various deformation amounts at the position where the Bragg grating is arranged.

  In an optical fiber deformation detection sensor in which an optical fiber with a Bragg grating is integrated along the longitudinal direction of a conventional leaf spring, the amount of deformation of the object to be measured is within the allowable range of the change in the spacing of the diffraction grating stripes of the Bragg grating In order to fit within, it is necessary to convert the deformation amount of the leaf spring into a deformation amount within several nanometers with respect to the deformation amount at the position where each Bragg grating is arranged. The elastic modulus of the material is determined. However, in the intrusion detection system, there are various measurement object materials, shapes, rigidity, etc., so the range of deformation of the measurement object is wide, and this deformation amount is the amount of change in the diffraction grating fringe spacing of the Bragg grating. In order to be within the allowable range, it is necessary to change the shape of the leaf spring, the elastic modulus of the material, and the like according to the amount of deformation at each measurement position. Changing the shape of the leaf spring in accordance with the measurement position in this way is not only disadvantageous in terms of cost, but also changes or changes in the measurement object over time or changes in the measurement position, for example, deformation due to fence deterioration. Cost and maintenance, such as the need to replace the leaf spring in order to cope with changes in the amount of deformation of the measurement object that accompanies changes in the amount or renewal of the fence or change in the measurement position from the fence to the door There was an inspection problem.

  The present invention has been made to solve the above-described problems. The range of deformation of the measurement object is wide, and even if the amount of deformation at the position where each Bragg grating is arranged differs greatly, the same Since the amount of deformation can be measured accurately with the optical fiber deformation detection sensor of the configuration, there is no need to change the configuration of the optical fiber deformation detection sensor in accordance with the measurement position, and the measurement object changes with time. Even if the range of deformation changes, there is no need to change the configuration of the optical fiber deformation detection sensor. As a result, it is possible to provide an intrusion detection system that can be maintained and inspected at low cost.

An optical fiber deformation detection sensor according to the present invention has a uniform cross section with a rotation axis in the longitudinal direction, and is attached to a measurement object at an arbitrary angle around the rotation axis in the longitudinal direction, and a part excluding both ends. a plurality of elongated structures notch a low rigidity are formed than the other part, the forming part of the Bragg grating in the notch portion of the elongated structures are arranged so as to be in close contact with, said plurality those with an optical fiber disposed in the longitudinal direction of the long structure, connected to an end of the optical fiber, and an optical measuring instrument having the function of measuring the wavelength distribution of the reflected light from the Bragg grating It is.

  In the present invention, a cutout portion having a lower rigidity than the other portions is provided in a part of the long structure having a uniform cross-sectional shape except for both ends, and the formation part of the Bragg grating is in close contact with the cutout part. The installed optical fiber can be attached, and this long structure can be arbitrarily rotated about the rotation axis in the longitudinal direction and attached to the measurement object for deformation detection, so the amount of deformation at the position where the Bragg grating is placed can be reduced. Accordingly, the notch is deformed and converted into a change in the interval between the diffraction grating stripes of the Bragg grating, and the amount of deformation of the measurement object can be detected. Furthermore, even if the deformation amount at the position where each Bragg grating is arranged is greatly different, by attaching the long structure to the measurement object at an arbitrary angle, the notch portion of the measurement object is deformed. Since the amount of deformation can be adjusted, the amount of deformation of the notch can be adjusted so as to be within an allowable range of the amount of change in the spacing between the diffraction grating stripes of the Bragg grating.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram of an optical fiber deformation detection sensor 1 according to Embodiment 1 for carrying out the present invention. In FIG. 1, a notch 3 is provided at a substantially central portion of a long structure 2 having an L-shaped cross section, and an optical fiber 4 is disposed in close contact with the longitudinal direction of the long structure. A Bragg grating 5 is formed at a position corresponding to the notch 3 of the optical fiber 4. FIG. 2 is a schematic diagram of an intrusion detection system using the optical fiber deformation detection sensor 1 in the present embodiment. In FIG. 2, the optical fiber deformation detection sensors 1 are respectively attached to the upper portions of a plurality of frames 7 above the fence 6 via a pair of spacers 8 so that the central portion of the long structure can be deformed downward. ing. Each optical fiber deformation detection sensor 1 is connected by a single optical fiber, and a Bragg grating is formed at a position corresponding to the notch of each optical fiber detection sensor. The intervals between the diffraction grating fringes of the Bragg gratings are different so that the Bragg wavelengths of the Bragg gratings are different. An optical measuring instrument 9 is connected to the end of the optical fiber 4 common to a plurality of optical fiber deformation detection sensors.

  FIG. 3 is a perspective view of the optical fiber deformation detection sensor in the present embodiment. The cross section of the long structure 2 is L-shaped, and a part of the long structure 2 in the vertical direction is cut away to provide a cutout portion 3. The optical fiber 4 is disposed in close contact with the bottom surface of the long structure 2. In the intrusion detection system shown in FIG. 2, the lower surface of the bottom surface of the long structure 2 shown in FIG. 3 is arranged on the frame 7 via the spacer 8.

  Next, the operation in this embodiment will be described. In FIG. 2, light from a light source provided inside the optical measuring instrument 9 is incident on the optical fiber 4. The light propagating through the optical fiber 4 reaches a plurality of optical fiber deformation detection sensors 1. In the Bragg grating formed in each optical fiber deformation detection sensor 1, only light of a specific wavelength is reflected, and the reflected light returns to the optical measuring instrument 9. Since the Bragg wavelength of each Bragg grating is different, when the wavelength distribution of the reflected light is measured by the optical measuring instrument 9, the peak of the reflected light corresponding to each Bragg grating is observed.

  In FIG. 3, when a load 10 is applied to the long structure 2 as indicated by an arrow, the portion where the cutout portion 3 of the long structure 2 is formed has lower rigidity than the other portions. Stress concentrates on the portion 3 and the amount of deformation becomes larger than the other portions. Since the optical fiber 4 arranged in close contact with the notch 3 is formed with a Bragg grating 5, the optical fiber 4 is deformed according to the deformation amount of the notch 3, so that the optical fiber 4 is deformed. The interval between the diffraction grating fringes changes. As a result, since the wavelength of the light reflected by the Bragg grating 5 changes due to the change of the Bragg wavelength, by detecting the change in the wavelength peak of the reflected light observed by the optical measuring instrument 9 shown in FIG. The deformation amount of the optical fiber deformation detection sensor can be measured.

  In the intrusion detection system using the optical fiber deformation detection sensor configured as described above, the optical fiber deformation detection sensor 1 installed on the frame 7 when the intruder tries to get over the fence 6 in FIG. When a load is applied, the long structure is deformed downward by the pair of spacers 8, and the presence of an intruder can be detected by detecting the deformation amount with the optical measuring instrument 9. In addition, since the Bragg wavelengths of the plurality of optical fiber deformation detection sensors are different, the deformed optical fiber deformation detection sensor can be specified by the wavelength of the reflected light that changes, and thus the intrusion position can also be detected.

  In FIG. 3, the load 10 applied to the optical fiber deformation detection sensor has been described in the direction of the arrow. However, the direction of the load 10 can be changed by installing the optical fiber deformation detection sensor at an angle. For this reason, even if the deformation amounts at the positions where the respective optical fiber deformation detection sensors are arranged are different, by attaching the long structure to the measurement object at an arbitrary angle, a notch is formed with respect to the deformation amount of the measurement object. The amount of deformation of the part can be adjusted. As a result, even if the deformation range of the measurement object is wide and the deformation amount of each Bragg grating is greatly different, the deformation amount can be accurately measured by the optical fiber deformation detection sensor having the same configuration. Can do.

  FIG. 4 shows a cross-sectional view of a long structure having another shape in the present embodiment. The notch is formed at a substantially central position of the long structure as in FIG. The long structure 2 shown in FIG. 4A has a U-shaped cross section, and the notch is formed by notching a part of the opposing surface of the U-shape. With such a structure, the difference in rigidity between the notch and the other part can be made larger than that of the L-shaped cross section shown in FIG. The long structure 2 shown in FIG. 4B has a circular shape with a cross-sectional shape having an opening, and the notch is formed by expanding the area of the opening. If the cross-sectional shape is L-shaped or U-shaped, there is a corner and there is an unstable rotation angle, but with such a structure, a long structure is used to adjust the amount of deformation of the notch. When rotating the, it can be arranged in a stable state at any rotation angle. A long structure 2 shown in FIG. 4C has a U-shaped cross-section and is formed on the opposite side, and is the same as the long structure shown in FIG. effective.

  When such an optical fiber deformation detection sensor is attached to a fence or the like and used for intruder detection, it is necessary that the optical fiber deformation detection sensor is not damaged even with a load of 100 kg, and the deformation starts when a load of about 15 kg is applied. It is necessary to be a long structure. Furthermore, it is also necessary that the material rigidity is lowered by long-term installation, and a low-rigidity portion such as a notch is not bent by its own weight. Fiber reinforced plastics (Fiber Reinforced Plastics: FRP) are suitable as a material for long structures as a lightweight and highly reliable material that satisfies these required characteristics. For example, as a long structure as shown in FIG. 3, a composite material (Glass Fiber Reinforced) in which L-shaped glass fibers having a width of 75 mm, a height of 35 mm, a thickness of 5 mm, and a length of 180 mm are dispersed is dispersed. A plastic having a notch with a width of 20 mm at the center can be used using Plastics: glass fiber reinforced plastic: GFRP.

  The amount of deformation when using such a long structure made of GFRP will be specifically described. In this embodiment, when a load of 15 kg is applied to the optical fiber deformation detection sensor, the peak wavelength of the reflected light from the Bragg grating shifts by 0.15 nm toward the long wavelength side with respect to the case of no load. This indicates that the optical fiber at the position where the Bragg grating is formed is deformed in the pulling direction. Further, the peak wavelength of the reflected light changes in direct proportion to the load up to 60 kg, and shifts by 0.6 nm to the long wavelength side at the load of 60 kg. Further, in the range of 60 kg to 100 kg, the rate of change is slightly smaller, but the peak wavelength of the reflected light changes in proportion to the load, and the shift amount at the load of 100 kg is 1 nm or less.

Embodiment 2. FIG.
In the second embodiment, an example of an optical fiber deformation detection sensor using a long structure having a pipe-like structure will be described. FIG. 5A is a schematic diagram showing the shape of the optical fiber deformation detection sensor in the present embodiment. In Fig.5 (a), the elongate structure 2 is a pipe shape with a circular cross section, and has a circular cavity part in a longitudinal direction. The cutout portion 3 is configured by removing the upper portion while leaving the bottom surface at the substantially central portion of the long structure 2. The optical fiber deformation detection sensor 1 is configured by fixing the optical fiber 4 to the bottom surface so that the portion where the Bragg grating 5 is formed is disposed at the position of the notch 3 of the long structure 2. .

  Since the optical fiber deformation detection sensor configured in this way has a circular cross section, when the long structure is rotated in order to adjust the deformation amount of the notch, the rotation state is stable at any rotation angle. Can be arranged. In addition, since the optical fiber is protected by the pipe-like long structure except for the notch, the optical fiber is not subject to cutting or unnecessary deformation due to external force, and is highly reliable.

  In this embodiment, the pipe-like long structure has a circular cross section. However, as shown in FIG. 5B, a pipe having a rectangular cross section may be used. it can.

  Moreover, as shown to Fig.6 (a) and (b), the notch part 3 may be comprised by removing the two places which the pipe-shaped elongate structure 2 opposes. With such a configuration, the effect of protecting the optical fiber with the pipe-like long structure increases, and the reliability is further improved.

  Furthermore, in the present embodiment, the description has been made using a long structure having a circular or rectangular cross section, but the cross section is triangular, pentagonal, or more polyhedral (hexagonal, octagonal, dodecagonal, etc.). There may be.

Embodiment 3 FIG.
In the present embodiment, a case where the optical fiber deformation detection sensor shown in the second embodiment is used in an intrusion detection system will be described. FIG. 7 is a schematic diagram of an intrusion detection system in the present embodiment. An optical fiber deformation detection sensor 1 is installed at a substantially central height position of the fence 6, and each optical fiber detection sensor 1 is connected by a single optical fiber 4. A Bragg grating is formed on the optical fiber 4 fixed at the position of the notch of each optical fiber detection sensor 1. An optical measuring instrument 9 is connected to the end of the optical fiber 4.

  FIG. 8 is a schematic diagram showing a cross section of the optical fiber deformation detection sensor installed on the fence in the present embodiment. In FIG. 8, when an intruder tries to get over the fence 6, an external force 11 acts on the fence 6 from the lateral direction. 8A, when the notch 3 of the optical fiber deformation detection sensor 1 is disposed in close contact with the fence 6, in FIG. 8B, the optical fiber deformation detection sensor 1 is shown in FIG. FIG. 8C shows a case where the optical fiber deformation detection sensor 1 is rotated 180 ° clockwise with respect to FIG. 8A when arranged clockwise by 90 °. When arranged in this way, even if an external force 11 having the same force is applied to the fence 6, the deformation amount of the notch 3 varies depending on the positional relationship between the notch 3 and the fence 6 of the optical fiber deformation detection sensor 1. become. As a result, the deformation amount of the optical fiber 4 disposed in close contact with the notch 3 is also different in FIGS. 8A, 8B, and 8C.

  FIG. 9 is a characteristic diagram showing the relationship between the rotation angle of the optical fiber deformation detection sensor and the shift amount of the wavelength peak of the reflected light observed by the optical measuring instrument when the optical fiber deformation detection sensor is attached to the fence. is there. In FIG. 9, the angle of 0 ° is when the notch 3 is disposed in close contact with the fence 6 as shown in FIG. The long structure of the optical fiber deformation detection sensor has a pipe shape with an outer diameter of φ6 mm, an inner diameter of φ3.5 mm, and a length of 1800 mm, and a notch with a width of 15 mm is formed at the center. An optical fiber is fixed to the notch so that the Bragg grating is located. Reflected light observed by the optical measuring instrument when the optical fiber deformation detection sensor configured in this way is fixed to the center of a metal fence having a length of 1900 mm and a width of 1900 mm and a load of 15 kg is applied from the lateral direction. The relationship between the shift amount of the wavelength peak and the rotation angle of the optical fiber deformation detection sensor is shown. In the optical fiber deformation detection sensor, the notch portion of the long structure is less rigid than the other portions. Therefore, when the notch portion is in closest contact with the fence as shown in FIG. The rotation angle at 9 is almost the same as the deformation amount of the fence, and the Bragg grating formed on the optical fiber is deformed in the extending direction. Is the largest. When the optical fiber deformation detection sensor is rotated and the notch is in contact with the fence as shown in FIG. 8B (the rotation angle in FIG. 9 is 90 °), the notch is deformed against the deformation of the fence. Is deformed in the horizontal direction, and the optical fiber fixed in the notch is deformed in the horizontal direction, but the distance between the diffraction grating stripes of the Bragg grating is almost changed, so that the wavelength shift amount is almost zero. Furthermore, as shown in FIG. 8 (c), when the notch is farthest from the fence (the rotation angle is 180 ° in FIG. 9), the notch is deformed in the opposite direction to that in FIG. 8 (a). Therefore, since the Bragg grating formed in the optical fiber is deformed in the contracting direction, the distance between the diffraction grating fringes is deformed in the narrowing direction, and the wavelength shift amount takes the negative value and becomes the largest.

  As described above, a notch part having a lower rigidity than the other part is provided in a part in the longitudinal direction excluding both ends of the long structure having a uniform cross-sectional shape, and a Bragg grating forming part is provided in this notch part. The optical fiber placed in close contact is attached to the measurement object for deformation detection by arbitrarily rotating the long structure around the longitudinal direction as the center of rotation, so depending on the amount of deformation at the position where the Bragg grating is placed Further, the deformation of the measurement object can be detected by transforming the notched portion into a change in the interval between the diffraction grating stripes of the Bragg grating.

  In addition, even if the amount of deformation at the position where each Bragg grating is arranged differs greatly, by attaching the long structure to the measurement object at an arbitrary angle, the notch portion of the measurement object is deformed. Since the amount of deformation can be adjusted, the amount of deformation of the notch can be adjusted so as to be within an allowable range of the amount of change in the spacing between the diffraction grating stripes of the Bragg grating.

It is a schematic diagram of the optical fiber deformation | transformation detection sensor by Embodiment 1 of this invention. It is a schematic diagram of the intrusion detection system by Embodiment 1 of this invention. It is a perspective view of the optical fiber deformation | transformation detection sensor by Embodiment 1 of this invention. It is a perspective view of the elongate structure body by Embodiment 1 of this invention. It is a perspective view of the optical fiber deformation | transformation detection sensor by Embodiment 2 of this invention. It is a perspective view of the optical fiber deformation | transformation detection sensor by Embodiment 2 of this invention. It is a schematic diagram of the intrusion detection system by Embodiment 3 of this invention. It is a schematic diagram which shows the cross section of the optical fiber deformation | transformation detection sensor installed in the fence by Embodiment 3 of this invention. It is a characteristic view of the optical fiber deformation | transformation detection sensor by Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber deformation | transformation detection sensor 2 Long structure 3 Notch 4 Optical fiber 5 Bragg grating 6 Fence 7 Frame 8 Spacer 9 Optical measuring instrument 10 Load 11 External force

Claims (4)

Has a uniform cross-sectional shape with a rotation axis in the longitudinal direction,
Attached to the measuring object at an arbitrary angle around the longitudinal rotation axis,
A plurality of long structures in which notches that are lower in rigidity than other parts are formed in a part other than both ends,
An optical fiber disposed in the longitudinal direction of the plurality of long structures , the Bragg grating forming portion is disposed in close contact with the notch of the long structure ,
Connected to an end of the optical fiber, the optical fiber deformation detecting sensor, characterized in that an optical measuring instrument having the function of measuring the wavelength distribution of the reflected light from the Bragg grating. 2. The optical fiber deformation detection sensor according to claim 1, wherein the long structure is made of fiber reinforced plastic. The optical fiber deformation detection sensor according to claim 1, wherein the long structure has a cylindrical shape. The optical fiber deformation detection sensor according to claim 1, wherein the uniform cross-sectional shape is a rotationally symmetric shape with respect to the rotation center.

Images