CN100559116C - Fiber Optic Inclinometer - Google Patents

Abstract

A fiber optic inclinometer, comprising: a base; one end of the connecting plate is fixedly connected with the base; a rotary end seat connected with the connecting plate by a rotary pair structure; and the at least two fiber Bragg grating components are respectively arranged on the opposite surface sides of the connecting plate, and the two ends of each fiber Bragg grating component are respectively fixed on the base and the rotating end seat. When the rotating end seat and the connecting plate have relative rotation movement, one fiber Bragg grating component generates axial tensile deformation, the other component generates axial compression deformation, and the rotating angle of the rotating end seat relative to the connecting plate can be obtained by respectively measuring and calculating the Bragg wavelength drift amount of the pair of fiber Bragg grating components. The optical fiber inclinometer can measure the inclination degree of a structural body and monitor the change condition of the inclination angle.

Description

Fiber Optic Inclinometer

[technical field]

The invention relates to an optical fiber inclinometer for measuring the skew or deflection angle of a structure.

[Background technique]

An optical fiber is mainly composed of a core and a cladding covering the core. The refractive index of the core is higher than that of the cladding layer. Since the total reflection occurs when the light is transmitted from the optically dense medium (high refractive index region) to the optically sparse medium (low refractive index region), the light can be continuously in the propagate in an optically dense medium.

In 1987, K.O. Hill used an argon ion laser to fabricate a fiber grating (grating) in a germanium-doped fiber core for the first time. In addition to being widely used in optical fiber communication systems, it also has a huge space for use in the sensing field. In 1989, Meltz et al. exposed the photosensitive optical fiber to high-energy ultraviolet laser to change the bonding state of its internal molecules to increase the refractive index, and its refractive index showed periodic changes along the fiber axis. This type of fiber is also called Fiber Bragg Grating (FBG) component.

FIG. 1 is a perspective view of an optical fiber 10 with a fiber Bragg grating. The optical fiber 10 includes a core 13 with a total length L, which is covered by a cladding layer 12 and a protective layer 11 in turn. An incident light 14 enters from the left end of the fiber core 13 and passes out from the right end to form a transmitted light 15 . Because the refractive index changes periodically and regularly along the fiber axis, the incident light 14 with a specific wavelength cannot pass through, and will be reflected back to the original incident end (left end).

FIG. 2( a ) is a wavelength distribution diagram of incident light and reflected light in FIG. 1 . The incident light 14 includes light in a certain wavelength range, and the reflected light 16 is mainly light with a specific wavelength λb1 in this wavelength range. Therefore, the wavelength range of light included in the transmitted light 15 is less light with a wavelength λb1. The wavelength λb1 is called the Bragg wavelength (Bragg wavelength), as shown in Figure 2(b).

When the optical fiber 10 is subjected to temperature or external force to produce axial elongation ΔL, its Bragg wavelength will shift from λb1 to λb2, as shown in FIG. 3 . Or generate a compression amount, so that the Bragg wavelength will be shifted from λb1 to λb3. So the following formula can be obtained:

$\frac{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}$

Among them, ΔT represents the temperature difference; Kt is the temperature sensitivity coefficient; Ke is the strain sensitivity coefficient; ε is the axial strain value, which is equal to ΔL divided by L.

If the axial strain value is 10 ⁻⁶ at a fixed temperature, the Bragg wavelength shift value Δλ=λb2−λb1 is about 0.00115˜0.0012 nanometers (nm). Because the fiber Bragg grating component can be used as an extremely precise gauge for measuring physical quantities such as strain and temperature, it has been widely used in the monitoring of stress and deformation of civil engineering structures. Compared with the traditional resistive strain gauge, which needs to lead out the signal lines of individual measurement points, is susceptible to electromagnetic wave interference, and cannot be used in harsh environments such as humidity and heat, the Fiber Bragg Grating component has low energy consumption, fast transmission speed, wide transmission frequency and resistance Due to the advantages of harsh environment factors, especially the ability to simultaneously measure the strain of multiple points by using a single-wire series optical fiber, it can replace various applications of known resistance strain gauges, such as inclinometers or inclinometers.

[Content of the invention]

The object of the present invention is to provide a fiber optic inclinometer using a fiber Bragg grating component, which can measure the tilt degree of a structure and monitor the change of the tilt angle.

Another object of the present invention is to provide a fiber optic inclinometer with a simple structure, which can be assembled into a compact and compact fiber optic inclinometer with a small number of simple components. The manufacturing cost is low and the price is very competitive.

In order to achieve the above object, the present invention provides a kind of optical fiber inclinometer, it is characterized in that: it comprises:

a base;

a connecting plate, one end of which is fixedly connected to the base;

A rotating end seat is connected with the connecting plate by a rotating pair structure;

At least two fiber Bragg grating components are respectively arranged on opposite surface sides of the connecting plate, and two ends of each fiber Bragg grating component are respectively fixed on the base and the rotating end seat.

The optical fiber inclinometer is characterized in that: the rotating pair structure includes a cylinder fixed to the end of the connecting plate and a holding portion provided on the rotating end seat, and the holding portion just accommodates the cylinder , and form a rotation fit with the cylinder with the direction of its cylinder axis as the axis.

The optical fiber inclinometer is characterized in that: the rotating end base further includes a V-shaped groove, which is arranged on the surface of the connecting plate and connects with the holding part, and the V-shaped groove restricts the cylinder and the connecting plate The angle of rotation.

The fiber optic inclinometer is characterized in that it further includes at least four fiber extensions, respectively jointed with the fiber Bragg grating assembly, and extending to the outside of the base and the rotating end seat.

The optical fiber inclinometer is characterized in that: a connector is provided at the end of the optical fiber extension.

The optical fiber inclinometer is characterized in that it further includes two rigid pipes respectively sleeved on opposite sides of the base and the rotating end base.

The optical fiber inclinometer is characterized in that: the outer wall of the rigid pipe is provided with several guide pins.

The present invention also provides an optical fiber inclinometer, characterized in that: it comprises:

a base;

a connecting column, one end of which is fixedly connected to the base;

A rotating end seat is connected with the connecting column by a spherical structure;

At least three fiber Bragg grating components are respectively arranged on the outer concentric circle of the connecting column, and the two ends of each fiber Bragg grating component are respectively fixed in the base and the rotating end seat.

The optical fiber inclinometer is characterized in that: the spherical surface structure includes a sphere affixed to the end of the connecting column, and a holding portion provided on the rotating end seat; the holding portion just accommodates the sphere , and form a rotational motion fit with the sphere in a direction perpendicular to the peripheral surface of the connecting post.

The fiber optic inclinometer is characterized in that it further includes at least six fiber extension parts respectively jointed with the fiber Bragg grating assembly, and extending to the outside of the base and the rotating end seat.

The optical fiber inclinometer is characterized in that: a connector is provided at the end of the optical fiber extension.

The optical fiber inclinometer is characterized in that it further includes two rigid pipes respectively sleeved on opposite sides of the base and the rotating end base.

The optical fiber inclinometer is characterized in that: the outer wall of the rigid pipe is provided with several guide pins.

The fiber optic inclinometer is characterized in that: the fiber Bragg grating assembly is arranged at a point that equally divides the circumference of the concentric circle outside the connecting column.

To sum up, the present invention discloses a fiber optic inclinometer, which includes a pair of fiber Bragg grating components, a base, a connecting plate and a rotating end seat. One end of the connecting plate is fixedly connected to the base, and the other end is connected with the rotating end base by a turning pair structure. In addition, the two ends of each fiber Bragg grating component are respectively fixed in the base and the rotating end seat, and the two components are respectively arranged on opposite surface sides of the connecting plate. When there is relative rotational movement between the rotating end seat and the connecting plate, one of the fiber Bragg grating components produces axial tensile deformation, and the other component produces axial compressive deformation. By separately measuring and calculating the Bragg wavelength shift of the pair of fiber Bragg grating components, the rotation angle of the rotating end seat relative to the connecting plate can be obtained.

The invention also provides a fiber optic inclinometer, which includes at least three fiber Bragg grating components, a base, a connecting column and a rotating end seat. One end of the connecting column is fixedly connected to the base, and the other end is connected with the rotating end base in a spherical pair (ball joint) structure. In addition, the two ends of each fiber Bragg grating component are respectively fixed in the base and the rotating end seat, and the components are respectively arranged on equal angular positions of the outer circumference of the connecting column. When there is relative rotational movement between the rotating end seat and the connecting plate, the fiber Bragg grating assembly at some positions produces axial tensile deformation, and the assembly at other positions produces axial compression deformation. The Bragg wavelength offset of the fiber Bragg grating component is measured and calculated respectively, and the difference between the two offsets can be calculated to obtain the two-dimensional rotation angle of the rotating end seat relative to the connecting plate. Since the calculation is based on the difference of the variation of the two fiber Bragg grating components, the effect of the fiber Bragg grating component itself on temperature can be offset, so it can be applied to outdoor temperatures.

[Description of drawings]

Fig. 1 is a schematic perspective view of an optical fiber with a fiber Bragg grating;

Fig. 2 (a) is the wavelength distribution figure of Fig. 1 incident light and reflected light;

Fig. 2 (b) is the wavelength distribution diagram of Fig. 1 penetrating light;

Fig. 3 is a schematic diagram of Bragg wavelength shift;

Fig. 4 is the three-dimensional schematic view of the optical fiber inclinometer of the present invention;

Fig. 5 is an enlarged schematic diagram of a rotating pair structure;

Fig. 6 is the schematic diagram that the optical fiber inclinometer of the present invention measures the inclination angle in the soil burrow;

Fig. 7 is a perspective view of another optical fiber inclinometer of the present invention;

Fig. 8 is a perspective view of another optical fiber inclinometer of the present invention.

Explanation of component symbols in the attached drawings:

10 fibers 11 layers of protection 12 cladding layers 13 fiber core

14 incident light 15, 15' penetrating light 16 reflected light 40, 70, 80 fiber optic inclinometer 41, 71, 81 base 42 connecting board 421 cylinder 43 rotating end seat 431, 731, 831 grip 432 V-groove 44, 74, 84 fiber Bragg grating components 45, 75, 85 fiber extension 46, 76, 86 connectors 47 rotating pairs of structures 61 rigid tubing 62 guide pins 63 inclined tube 72, 82 connecting columns 721, 821 spheres 73, 83 rotating end seat 77, 87 spherical face structure

[Detailed ways]

FIG. 4 is a schematic perspective view of an optical fiber inclinometer 40 of the present invention. The fiber optic inclinometer 40 includes a pair of fiber Bragg grating components 44 , a base 41 , a connecting plate 42 and a rotating end base 43 . One end of the connecting plate 42 is fixedly connected to the base 41 , and the other end is connected to the rotating end base 43 by a rotating pair structure 47 . One degree of freedom is retained between the rotating end base 43 and the connecting plate 42 for relative rotational movement, that is, a relative angular displacement is generated along the direction (X axis) perpendicular to the side of the connecting plate 42 .

In addition, two ends of each Fiber Bragg Grating assembly 44 are respectively fixed in the base 41 and the rotating end seat 43 , and the Fiber Bragg Grating assemblies 44 are respectively disposed on different surface sides of the connecting plate 42 . The fiber extension part 45 extends from both ends of the fiber Bragg grating assembly 44 and is respectively exposed on the surface of the base 41 and the rotating end seat 43 , and each end surface has a connector 46 for serial connection.

In order to make the fiber Bragg grating assembly 44 remain in a tight state when measuring the inclination angle, it is necessary to give appropriate pre-tensile stress (pre-tensile-stress) when the two ends of the fiber Bragg grating assembly 44 are fixed, so as to Prevent the fiber Bragg grating assembly 44 on one side from being squeezed and loosened. That is, when there is relative rotational movement between the rotating end seat 43 and the connecting plate 42 , one of the fiber Bragg grating components 44 produces axial tensile deformation, while the other relative component produces axial compressive deformation. By measuring and calculating the difference of the Bragg wavelength offset Δλ of the pair of fiber Bragg grating assemblies 44 respectively, the rotation angle of the rotating end seat 43 relative to the connecting plate 42 can be obtained. In addition, because the pair of fiber Bragg grating assemblies 44 are located in a symmetrical position, the stress changes caused by temperature changes will balance each other.

FIG. 5 is an enlarged schematic view of the rotating pair structure 47 . The rotating pair structure 47 includes a cylinder 421 disposed on the end surface of the connecting plate 42 , a V-shaped groove 432 disposed on the surface of the rotating end base 43 , and a gripping portion 431 . The holding portion 431 can just accommodate the volume of the cylinder 421 and allow the cylinder 421 and the connecting plate 42 to rotate along a direction perpendicular to the drawing. The opening angle of the V-shaped groove 432 will limit the maximum relative angular displacement θmax of the connecting plate 42 , and generally the maximum relative angular displacement θmax is less than about 2 degrees.

The optical fiber inclinometer 40 of the present invention can be further applied to monitor the stability of the inner wall during deep excavation of tunnels, buildings and dams, or as an instrument for long-term monitoring of landslides, debris flows and slope formation displacements. FIG. 6 is a schematic diagram of the fiber optic inclinometer 40 measuring the inclination angle in a borehole in the soil. In FIG. 6 , an inclined tube 63 is embedded in the borehole for the optical fiber inclinometer 40 and its related structures to slide along the inner wall or guide groove of the inclined tube 63 to the depth of the ground. There is a rigid pipe 61 on the opposite side of the base 41 and the rotating end seat 43 to protect it, and the connector 46 of the adjacent optical fiber inclinometer 40 can be connected in the rigid pipe 61, so dozens of optical fiber inclinometers 40 can be combined Dozens of rigid pipes 61 simultaneously measure the continuous variation of the inclination angle from the surface to the deep underground. In addition, the rigid pipe 61 is provided with several guide pins 62 (holding pins or guiding pins) or pulleys. Since the guide pins 62 around are closely attached to the inner wall or guide groove of the inclined pipe 63, the optical fiber inclinometer 40 and this part of the inclined pipe can be secured. 63 remains parallel, however, rotating the end seat 43 can produce an angular displacement -θ to reflect the inclination angle of the inclined tube 63 .

FIG. 7 is a schematic perspective view of another fiber optic inclinometer 70 of the present invention. The fiber optic inclinometer 70 includes four fiber Bragg grating components 74 , a base 71 , a connecting post 72 and a rotating end seat 73 . One end of the connecting column 72 is fixedly connected to the base 71 , and the other end is connected to the rotating end base 73 via a spherical surface structure 77 . Therefore, the relative rotational movement of two degrees of freedom is maintained between the rotating end seat 73 and the connecting column 72 , that is, a relative angular displacement along the X-axis and the Z-axis is generated.

In addition, two ends of each fiber Bragg grating component 74 are respectively fixed in the base 71 and the rotating end seat 73 , and the fiber Bragg grating component 74 is respectively disposed on the opposite surface side of the connecting post 72 . The fiber extension part 75 extends from both ends of the fiber Bragg grating assembly 74 , respectively exposed on the surface of the base 71 and the rotating end seat 73 , and each end surface has a connector 76 for serial connection.

In order to keep the fiber Bragg grating assembly 74 in a tight state when measuring the inclination angle, it is necessary to give appropriate pre-tensioning stress when fixing the two ends of the fiber Bragg grating assembly 74, so as to avoid the fiber Bragg grating on one side. The grating assembly 74 is compressed to relax. That is, when there is relative rotational movement between the rotating end seat 73 and the connecting post 72, some fiber Bragg grating components 74 will produce axial tensile deformation, while other components will produce axial compressive deformation. By separately measuring and calculating the Bragg wavelength shift Δλ of the fiber Bragg grating assembly 74 , the rotation angle of the rotating end seat 73 relative to the connecting post 72 can be obtained.

The spherical pair structure 77 includes a spherical body 721 disposed on the end surface of the connecting column 72 , and a gripping portion 731 disposed on the rotating end seat 73 . The holding portion 731 can just accommodate the volume of the ball 721 and allow the ball 721 and the connecting post 72 to rotate along the Z-axis and the X-axis. The optical fiber inclinometer 40 or 70 of the present invention has many advantages compared with the traditional electronic inclinometer probe (Inclinometer Probe; IP), for example: it can be placed in the casing in the soil for a long time to monitor the inclination change, the sensitivity is extremely high, and it is free from electromagnetic interference , It can also be used in water, no power supply is required at the construction site, convenient and fast connection and installation, multi-point and remote measurement at the same time, easy sensing data acquisition, simple operation and automatic recording of measurement results.

FIG. 8 is a perspective view of another fiber optic inclinometer 80 of the present invention. The fiber optic inclinometer 80 includes three fiber Bragg grating components 84 , a base 81 , a connecting post 82 and a rotating end base 83 . Compared with FIG. 7 , this embodiment can obtain the rotation angle of the rotating end seat 83 in the two-dimensional direction with the minimum number of fiber Bragg grating components 84 , so it has a more advantageous cost competitiveness. One end of the connecting column 82 is fixedly connected to the base 81 , and the other end is connected to the rotating end base 83 via a spherical surface structure 87 . In this way, the relative rotational movement of two degrees of freedom is maintained between the rotating end seat 83 and the connecting column 82 , that is, a relative angular displacement along the X-axis and the Z-axis is generated.

In addition, the two ends of each fiber Bragg grating assembly 84 are respectively fixed in the base 81 and the rotating end seat 83, and the fiber Bragg grating assembly 84 is respectively arranged on the outer concentric circle of the connecting column 82. It is more suitable to be at a point that equally divides the angular position or the circumference of the circle. In the figure, the fiber Bragg grating assembly 84 is set at the position that equally divides the angular position. The fiber extension part 85 extends from both ends of the fiber Bragg grating assembly 84, respectively exposed on the surface of the base 81 and the rotating end seat 83, and each end surface has a connector 86 for serial connection. In order to keep the fiber Bragg grating assembly 84 in a tight state when measuring the inclination angle, it is necessary to give appropriate pre-tensioning stress when fixing the two ends of the fiber Bragg grating assembly 84, so as to avoid the fiber Bragg grating on one side. The grating assembly 84 is compressed to relax. That is, when there is relative rotational movement between the rotating end seat 83 and the connecting post 82 , some angular fiber Bragg grating components 84 will produce axial tensile deformation, while other angular components will produce axial compressive deformation. By separately measuring and calculating the Bragg wavelength shift Δλ of the fiber Bragg grating assembly 84 , the rotation angle of the rotating end seat 83 relative to the connecting post 82 can be obtained.

The rotating pair structure 87 includes a ball 821 disposed on the end surface of the connecting column 82 , and a gripping portion 831 disposed on the rotating end base 83 . The holding portion 831 can just accommodate the volume of the ball 821 and allow the ball 821 and the connecting post 82 to rotate along the Z-axis and the X-axis.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various substitutions and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the contents disclosed in the embodiments, but should include various replacements and modifications without departing from the present invention.

Claims (14)

1. A fiber optic inclinometer, characterized in that: it comprises: a base; a connecting plate, one end of which is fixedly connected to the base; A rotating end seat is connected with the connecting plate by a rotating pair structure; At least two fiber Bragg grating components are respectively arranged on opposite surface sides of the connecting plate, and two ends of each fiber Bragg grating component are respectively fixed on the base and the rotating end seat. 2. The optical fiber inclinometer according to claim 1, wherein the rotating pair structure includes a cylinder fixed to the end of the connecting plate and a gripping portion provided on the rotating end seat, the gripping The part just accommodates the cylinder, and forms a rotation fit with the cylinder around the direction of the axis of the cylinder. 3. The optical fiber inclinometer according to claim 2, characterized in that: the rotating end base further includes a V-shaped groove, which is arranged on the surface of the connecting plate and connects with the holding part, and the V-shaped groove restricts the The angle by which the cylinder is rotated with respect to this web. 4 . The fiber optic inclinometer according to claim 1 , further comprising at least four fiber extensions, respectively jointed with the fiber Bragg grating assembly, and extending to the outside of the base and the rotating end base. 5. The fiber optic inclinometer according to claim 4, wherein a connector is provided at the end of the fiber extension. 6 . The fiber optic inclinometer according to claim 1 , further comprising two rigid tubes respectively sleeved on opposite sides of the base and the rotating end base. 7 . 7. The fiber optic inclinometer according to claim 6, wherein a plurality of guide pins are provided on the outer wall of the rigid pipe. 8. An optical fiber inclinometer, characterized in that: it comprises: a base; a connecting column, one end of which is fixedly connected to the base; A rotating end seat is connected with the connecting column by a spherical structure; At least three fiber Bragg grating components are respectively arranged on the outer concentric circle of the connecting column, and the two ends of each fiber Bragg grating component are respectively fixed in the base and the rotating end seat. 9. The optical fiber inclinometer according to claim 8, wherein the spherical pair structure includes a sphere fixed at the end of the connecting column, and a gripping portion provided at the rotating end seat; the gripping portion The holding part just accommodates the sphere, and forms a rotational motion fit with the sphere along a direction perpendicular to the peripheral surface of the connecting post. 10 . The fiber optic inclinometer according to claim 9 , further comprising at least six fiber extensions respectively jointed with the fiber Bragg grating assembly and extending to the outside of the base and the rotating end base. 11 . 11. The fiber optic inclinometer according to claim 10, wherein a connector is provided at the end of the fiber extension. 12 . The fiber optic inclinometer according to claim 8 , further comprising two rigid tubes respectively sleeved on opposite sides of the base and the rotating end base. 13 . 13. The fiber optic inclinometer according to claim 12, wherein a plurality of guide pins are provided on the outer wall of the rigid pipe. 14 . The fiber optic inclinometer according to claim 8 , wherein the fiber Bragg grating assembly is arranged at a point that equally divides the circumference of the concentric circle outside the connecting column. 14 .

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