CN114777734A - In-situ optical fiber inclinometer and inclination measuring method based on vertical cantilever beam and double FBGs - Google Patents
In-situ optical fiber inclinometer and inclination measuring method based on vertical cantilever beam and double FBGs Download PDFInfo
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- G—PHYSICS
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- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C9/00—Measuring inclination, e.g. by clinometers, by levels
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C25/00—Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C9/00—Measuring inclination, e.g. by clinometers, by levels
- G01C9/02—Details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35309—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer
- G01D5/35316—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using multiple waves interferometer using a Bragg gratings
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C9/00—Measuring inclination, e.g. by clinometers, by levels
- G01C9/02—Details
- G01C9/06—Electric or photoelectric indication or reading means
- G01C2009/066—Electric or photoelectric indication or reading means optical
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Abstract
The invention provides an in-situ optical fiber inclinometer and an inclinometry method based on a vertical cantilever beam and double FBGs (fiber Bragg gratings), which comprise a computer, an optical fiber grating demodulator and an optical fiber inclinometer module; the optical fiber inclinometer module consists of three optical fiber inclinometer units which are connected in series and have the same structure but different central wavelengths; the optical fiber clinometer unit comprises a shell, a weight and a cantilever beam for hanging the weight, and two optical Fiber Bragg Gratings (FBGs) with similar central wavelengths are attached to the cantilever beam. When the optical fiber clinometer module is inclined, the fiber Bragg gratings attached to the cantilever beam in the optical fiber clinometer unit are stretched and compressed correspondingly, so that the wavelength interval of the double FBGs in the reflection spectrum of the optical fiber clinometer unit is changed. The wavelength interval change of all the optical fiber clinometer units in the optical fiber clinometer module is monitored by using an optical fiber grating demodulator and a computer, so that the change of the inclination angle of each unit on the whole outline of the optical fiber clinometer module can be sensed.
Description
Technical Field
The invention belongs to the technical field of optical fiber inclination sensors, and particularly relates to an in-situ optical fiber inclinometer and an inclinometry method based on a vertical cantilever beam and double FBGs.
Background
The optical fiber inclinometer has the excellent characteristics of electromagnetic interference resistance, corrosion resistance, low cost and the like, so that the optical fiber inclinometer is widely concerned. In practical engineering application, a new requirement is provided for monitoring performance of an optical fiber inclinometer with large-range multi-state and high multiplexing capability, most of the traditional optical fiber inclinometers can only distinguish a single inclination angle direction, and the reusability is poor.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: an in-situ optical fiber inclinometer and an inclinometry method based on a vertical cantilever beam and a double FBG are provided, and the in-situ optical fiber inclinometer and the inclinometry method are used for measuring the displacement of a land section in a large-range reusable manner.
The technical scheme adopted by the invention for solving the technical problems is as follows: an in-situ fiber inclinometer based on a vertical cantilever beam and double FBGs (fiber Bragg gratings) comprises a fiber inclinometer module, a fiber Bragg grating demodulator and an upper computer which are connected in sequence; the optical fiber inclinometer module is used for sensing an inclination angle and comprises a first optical fiber inclinometer unit, a second optical fiber inclinometer unit and a third optical fiber inclinometer unit which are sequentially connected in series through single-mode optical fibers and have unequal central wavelengths; a single-mode fiber in each fiber clinometer unit is respectively provided with a first fiber Bragg grating and a second fiber Bragg grating; the first optical fiber clinometer unit, the second optical fiber clinometer unit and the third optical fiber clinometer unit respectively comprise a cantilever beam and a heavy object; the cantilever beam is used for hanging a heavy object; the first fiber Bragg grating and the second fiber Bragg grating of each fiber clinometer unit are respectively attached to two sides of the cantilever beam and used for monitoring tensile strain and compressive strain on the cantilever beam; the fiber grating demodulator is connected with the fiber clinometer module through a single-mode fiber, and the upper computer is connected with the fiber grating demodulator through a network; the fiber grating demodulator and the upper computer are used for monitoring the output spectrum and analyzing and demodulating the inclination angle information.
According to the scheme, the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit respectively comprise a flexible connecting arm and a shell; threads are arranged above and below the shell and used for connecting the flexible connecting arms; the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit are connected through a flexible connecting arm; the cantilever beam, the weight, the first fiber Bragg grating and the second fiber Bragg grating of each fiber inclinometer unit are fixed in the shell by adopting epoxy resin and a fixing pin; each optical fiber inclinometer unit is also provided with an optical fiber jumper joint which extends out from the upper part of the shell and is used for connecting the single-mode optical fibers between the two optical fiber inclinometer units.
According to the scheme, the interval of the initial reflection wavelengths of the first fiber Bragg grating and the second fiber Bragg grating is 6 nm; the first fiber Bragg grating and the second fiber Bragg grating are respectively pre-stretched by applying 1000 microstrain and then fixed on two sides of the cantilever beam through epoxy resin glue; the model of the fiber grating demodulator is Micron Optics Si255, and the resolution is 1 pm.
According to the scheme, the flexible connecting arm is made of polyvinyl chloride, the outer diameter is 73mm, the inner diameter is 59mm, and the length is 1000 mm; the shell is cylindrical and made of aluminum alloy, the outer diameter is 63.5mm, the inner diameter is 51.5mm, the length is 300mm, and the length of threads on the upper surface and the lower surface of the shell is 2 cm; the cantilever beam is made of aluminum alloy, and the weight of a weight connected below the cantilever beam is 0.25 kg.
An inclination measurement method of an in-situ optical fiber inclinometer based on a vertical cantilever beam and double FBGs comprises the following steps:
s0: constructing an in-situ optical fiber inclinometer based on a vertical cantilever beam and double FBGs, which comprises an optical fiber inclinometer module, an optical fiber grating demodulator and an upper computer which are connected in sequence; the optical fiber inclinometer module comprises a first optical fiber inclinometer unit, a second optical fiber inclinometer unit and a third optical fiber inclinometer unit which are sequentially connected in series through single-mode optical fibers and have unequal center wavelengths; a single-mode fiber in each fiber clinometer unit is respectively provided with a first fiber Bragg grating and a second fiber Bragg grating; the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit respectively comprise a cantilever beam and a heavy object; the heavy object is hung below the cantilever beam; the first fiber Bragg grating and the second fiber Bragg grating of each fiber clinometer unit are respectively attached to two sides of the cantilever beam; the fiber grating demodulator is connected with the fiber clinometer module through a single-mode fiber, and the upper computer is connected with the fiber grating demodulator through a network;
s1: disconnecting the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit, respectively carrying out zeroing calibration on the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit by using an angle dial, and recording the initial reflection wavelength interval of the first optical fiber Bragg grating and the second optical fiber Bragg grating of each optical fiber inclinometer unit by using an optical fiber grating demodulator and an upper computer; then connecting the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit;
s2: when the optical fiber inclinometer module is inclined, the weight drives the cantilever beam to be strained under the action of gravity, the first fiber Bragg grating and the second fiber Bragg grating attached to the two sides of the cantilever beam are also strained, one fiber Bragg grating is stretched to cause the grating pitch to be lengthened, and the other fiber Bragg grating is correspondingly compressed to cause the grating pitch to be shortened;
s3: the fiber grating demodulator monitors the change of the reflection spectrum of the double fiber Bragg gratings along with the inclination state of the fiber clinometer module, the distance between two peak values of the reflection superposition wavelength of the two fiber Bragg gratings of each fiber clinometer unit changes, the wavelength interval change of all the fiber clinometer units in the fiber clinometer module is monitored through the fiber grating demodulator and the upper computer, the change information of the inclination angle is obtained through demodulation, and therefore the change of the inclination angle of each unit on the whole profile of the fiber clinometer module is sensed.
Further, in step S2, the specific steps include:
let σ be the maximum stress to which the cantilever beam is subjected, E be the Young's modulus of the cantilever beam, m be the mass of the weight, L, b and h be the length, width and thickness of the cantilever beam, and θ be the inclination angle; the maximum strain epsilon experienced by the cantilever beam under the action of gravity when it is tiltedxComprises the following steps:
let Δ λ1Is a change in the reflected wavelength of the first fiber Bragg grating, λ10Is the initial wavelength of the first fiber Bragg grating, Pe is the photoelastic coefficient, ε1The (alpha + xi) delta T is the influence of temperature on the wavelength of the fiber Bragg grating; under the action of stress, the variation of the pitch of the single fiber bragg grating is:
further, in step S3, the specific steps include:
the two fiber Bragg gratings are subjected to the same stress and in opposite directions, and the influence directions of the temperature on the wavelength are the same, so that the reflection wavelength interval of the two fiber Bragg gratings is not influenced; let Δ λ2Is a change in the reflected wavelength of the second fiber Bragg grating, λ20The initial wavelength of the second fiber Bragg grating; when the inclination angle theta is smaller, sin theta is approximate to theta; the change Δ λ in the wavelength interval of the reflection peaks of the two fiber bragg gratings caused by the tilt is:
when the shape of the cantilever beam is determined, the change delta lambda of the wavelength interval of the reflection peaks of the two fiber Bragg gratings is linearly changed along with the change of the inclination angle; the inclination degree of the outside is detected by monitoring the change of the reflection wavelength of the two fiber Bragg gratings.
A computer storage medium having stored therein a computer program executable by a computer processor, the computer program performing a method of inclinometer for an in situ fiber optic inclinometer based on a vertical cantilever beam and dual FBGs.
The invention has the beneficial effects that:
1. according to the in-situ optical fiber inclinometer and the inclination measuring method based on the vertical cantilever beam and the double FBGs, three optical fiber inclinometer units respectively comprising two optical fiber Bragg gratings are connected in series with a flexible connecting arm to form a sensing structure, the optical fiber Bragg gratings are attached to the cantilever beam, when inclination occurs, the reflection wavelengths of the two optical fiber Bragg gratings are changed, and the function of measuring the land section displacement in a large-range and reusable manner is realized by distinguishing and monitoring the reflection spectrums of the optical fiber Bragg gratings.
2. The cantilever beam is used as the support beam, so that the maximum degree of freedom and robustness are provided for the inclinometer, and inclination sensing in different states is realized; the fiber bragg grating demodulator and the computer are utilized to monitor the wavelength interval change of all fiber inclinometer units in the fiber inclinometer module, the change of the inclination angle of each unit on the overall profile of the fiber inclinometer module is sensed, and the fiber bragg grating module has the characteristic of large-range measurement.
3. The invention uses two fiber Bragg gratings to increase the measurement sensitivity, and also reduces the interference of factors such as external temperature fluctuation, and the like, and the whole device has good measurement repeatability and is insensitive to temperature disturbance.
Drawings
FIG. 1 is a schematic diagram of an embodiment of the present invention.
Fig. 2 is a schematic structural view of the optical fiber inclinometer unit according to the embodiment of the present invention.
In the figure: 1. a computer; 2. a fiber grating demodulator; 3. a fiber optic inclinometer module; 4. a first fiber inclinometer unit; 5. a second fiber inclinometer unit; 6. a third fiber optic inclinometer unit; 7. a cylindrical housing; 8. a weight; 9. a cantilever beam; 10. a first fiber Bragg grating; 11. a second fiber Bragg grating.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Referring to fig. 1, the embodiment of the present invention includes a computer 1, a fiber grating demodulator 2, and a fiber tilt meter module 3, which are connected in sequence.
The fibre-optic inclinometer module 3 comprises three series connected fibre-optic inclinometer units for inclination sensing. The first optical fiber inclinometer unit 4, the second optical fiber inclinometer unit 5 and the third optical fiber inclinometer unit 6 are identical in structure but different in central wavelength, and each inclinometer unit internally comprises two serially connected optical fiber Bragg gratings. As shown in fig. 2, each of the first optical fiber inclinometer unit 4, the second optical fiber inclinometer unit 5, and the third optical fiber inclinometer unit 6 includes a flexible connecting arm, a cylindrical housing 7, a weight 8, a cantilever beam 9 for suspending the weight, and two optical Fiber Bragg Gratings (FBGs) with similar but different central wavelengths attached to two sides of the cantilever beam 9, i.e., a first optical fiber bragg grating 10 and a second optical fiber bragg grating 11. When the entire fiber tiltmeter module 3 is tilted, the fiber bragg gratings attached to the cantilever beam within the fiber tiltmeter unit are stretched one and compressed the other accordingly, whereby the wavelength separation of the dual FBGs in the fiber tiltmeter unit's reflection spectrum changes.
Threads are arranged above and below the cylindrical shell 7 of each optical fiber inclinometer unit, and the optical fiber inclinometer units are conveniently connected with the flexible connecting arms. The inner cantilever beam 9, the weight 8, the first fiber Bragg grating 10 and the second fiber Bragg grating 11 are fixed inside the cylindrical shell 7 by epoxy resin and a fixing pin, and the optical fiber jumper joint extends out from the upper part of the cylindrical shell 7 and is used for connecting other optical fiber inclinometer units.
The flexible connecting arm is made of polyvinyl chloride, and has an outer diameter of 73mm, an inner diameter of 59mm and a length of 1000 mm;
the cylindrical casing 7 was made of aluminum alloy, and had an outer diameter of 63.5mm, an inner diameter of 51.5mm, a length of 300mm, and a thread length of 2cm on the upper and lower surfaces.
The cantilever beam 9 is made of aluminum alloy, and the weight 8 connected below the cantilever beam has the mass of 0.25 kg.
The initial reflection wavelength interval of the first fiber bragg grating 10 and the second fiber bragg grating 11 is about 6nm, and the double FBGs are fixed on two sides of the cantilever beam 9 through epoxy resin glue after being subjected to about 1000 microstrain, so that the FBGs can monitor the tensile strain and the compressive strain on the cantilever beam 9.
The type of the fiber grating demodulator 2 is Micron Optics Si255, the resolution is 1pm, and the fiber grating demodulator 2 and the computer 1 are used for monitoring an output spectrum and analyzing and demodulating inclination angle information; the first optical fiber clinometer unit 4, the second optical fiber clinometer unit 5 and the third optical fiber clinometer unit 6 are connected through flexible connecting arms, and the fiber bragg grating demodulator 2 is connected with the optical fiber clinometer unit in the fiber clinometer module 3 through single-mode optical fibers; the fiber grating demodulator 2 is connected with the computer 1 through an Ethernet cable.
The invention discloses an in-situ optical fiber inclination angle measuring method based on a vertical cantilever beam and double FBGs (fiber Bragg gratings), which comprises the following steps of:
first, the angle dial is used to perform zeroing calibration on each inclinometer unit, and the fiber bragg grating demodulator 2 and the computer 1 are used to record the initial reflection wavelength interval of the first fiber bragg grating 10 and the second fiber bragg grating 11. The first fibre inclinometer unit 4, the second fibre inclinometer unit 5 and the third fibre inclinometer unit 6 are then connected.
The signal light sequentially reaches the first optical fiber clinometer unit 4, the second optical fiber clinometer unit 5 and the third optical fiber clinometer unit 6 through the single-mode optical fiber, when the optical fiber clinometer module 3 is inclined, the weight 8 drives the cantilever beam 9 to be strained under the action of gravity, the first optical fiber Bragg grating 10 and the second optical fiber Bragg grating 11 attached to two sides of the cantilever beam are also strained, one optical fiber Bragg grating is stretched, the grating pitch is lengthened, the optical fiber Bragg grating on the other side is correspondingly compressed, and the grating pitch is shortened.
The fiber bragg grating demodulator 2 is used for monitoring the reflection spectrum of the bragg grating, the distance between two peak values of the reflection superposition wavelength of the two fiber bragg gratings of each group of fiber inclinometer units changes along with the change of the inclination state, namely the inclination angle, the fiber bragg grating demodulator 2 and the computer 1 are used for monitoring the wavelength interval change of all the fiber inclinometer units in the fiber inclinometer module 3, the change information of the inclination angle is obtained through demodulation, and therefore the change of the inclination angle of each unit on the whole profile of the fiber inclinometer module 3 is sensed.
In this embodiment, the gravity and the inclination can be converted into the change of the stress by attaching the fiber bragg gratings on both surfaces of the cantilever beam 9 and connecting the weight 8 below the cantilever beam 9, and then the inclination is converted into the change of the wavelength by the fiber bragg gratings. For the cantilever beam 9, the maximum strain epsilon it is subjected to under the influence of gravity when tiltedxIs determined by its shape and the mass of the suspended weight 8:
σ is the maximum stress experienced by the cantilever beam 9, E is the Young's modulus of the cantilever beam 9, m is the mass of the weight 8, L, b and h are the length, width and thickness of the cantilever beam 9, and θ is the angle of inclination.
Since the reflection wavelength of the fiber bragg grating is determined by the pitch, the fiber bragg grating is pre-stretched when the fiber inclinometer module 3 is installed, so that the pitch of the grating will be widened or narrowed under the action of stress, and for a single fiber bragg grating, the change is as follows:
Δλ1for variations in the reflection wavelength, λ, of the fibre Bragg grating 110Where Pe is the initial wavelength of the first fiber bragg grating 10, the photoelastic coefficient and (α + ξ) Δ T is the effect of temperature on the fiber bragg grating wavelength. Because the two Bragg gratings are respectively attached to the two surfaces of the cantilever beam, the stress applied to the two Bragg gratings is the same in magnitude and opposite in direction, the influence direction of the temperature on the wavelength is the same, and the reflection wavelength interval of the two fiber Bragg gratings is not influenced due to the fact that the two fiber Bragg gratings are not influencedThe change Δ λ of the wavelength interval of the reflection peaks of the two fiber Bragg gratings caused by the tilt is:
λ20the initial wavelength of the second fiber bragg grating 11 is Pe, the photoelastic coefficient, and θ, which is an approximation of sin θ at a smaller angle. It can be seen that when the shape of the cantilever beam 9 is determined, the wavelength interval between the two fiber bragg gratings changes linearly with the change of the inclination angle. The external inclination can be detected by monitoring the change of the reflection wavelength of the two fiber Bragg gratings.
The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.
Claims (8)
1. The utility model provides an in situ fiber clinometer based on perpendicular cantilever beam and two FBGs which characterized in that: the optical fiber inclinometer comprises an optical fiber inclinometer module, an optical fiber grating demodulator and an upper computer which are connected in sequence;
the optical fiber inclinometer module is used for sensing an inclination angle and comprises a first optical fiber inclinometer unit, a second optical fiber inclinometer unit and a third optical fiber inclinometer unit which are sequentially connected in series through single-mode optical fibers and have unequal central wavelengths; a single-mode fiber in each fiber clinometer unit is respectively provided with a first fiber Bragg grating and a second fiber Bragg grating;
the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit respectively comprise a cantilever beam and a heavy object; the cantilever beam is used for hanging a heavy object; the first fiber Bragg grating and the second fiber Bragg grating of each fiber inclinometer unit are respectively attached to two sides of the cantilever beam and used for monitoring tensile strain and compressive strain on the cantilever beam;
the fiber bragg grating demodulator is connected with the fiber optic inclinometer module through a single mode fiber, and the upper computer is connected with the fiber bragg grating demodulator through a network; the fiber grating demodulator and the upper computer are used for monitoring the output spectrum and analyzing and demodulating the inclination angle information.
2. An in-situ fiber optic inclinometer based on a vertical cantilever beam and dual FBGs as claimed in claim 1, characterized in that:
the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit respectively comprise a flexible connecting arm and a shell; threads are arranged above and below the shell and are used for connecting the flexible connecting arms; the first optical fiber inclinometer unit, the second optical fiber inclinometer unit and the third optical fiber inclinometer unit are connected through flexible connecting arms;
the cantilever beam, the weight, the first fiber Bragg grating and the second fiber Bragg grating of each fiber clinometer unit are fixed in the shell by adopting epoxy resin and a fixing pin;
each optical fiber inclinometer unit is also provided with an optical fiber jumper joint which extends out from the upper part of the shell and is used for connecting the single-mode optical fibers between the two optical fiber inclinometer units.
3. An in-situ fiber optic inclinometer based on vertical cantilever beams and dual FBGs as claimed in claim 1, characterized in that:
the interval of the initial reflection wavelengths of the first fiber Bragg grating and the second fiber Bragg grating is 6 nm;
the first fiber Bragg grating and the second fiber Bragg grating are respectively prestretched by applying 1000 microstrain and then are fixed on the two sides of the cantilever beam through epoxy resin glue;
the model of the fiber grating demodulator is Micron Optics Si255, and the resolution is 1 pm.
4. An in-situ fiber optic inclinometer based on vertical cantilever beams and dual FBGs as claimed in claim 1, characterized in that:
the flexible connecting arm is made of polyvinyl chloride, and has an outer diameter of 73mm, an inner diameter of 59mm and a length of 1000 mm;
the shell is cylindrical and made of aluminum alloy, the outer diameter is 63.5mm, the inner diameter is 51.5mm, the length is 300mm, and the length of threads on the upper surface and the lower surface of the shell is 2 cm;
the cantilever beam is made of aluminum alloy, and the weight of a weight connected below the cantilever beam is 0.25 kg.
5. A method for inclinometer based on the in-situ fiber clinometer based on vertical cantilever beam and double FBGs as claimed in any one of claims 1 to 4, characterized in that: the method comprises the following steps:
s0: constructing an in-situ optical fiber inclinometer based on a vertical cantilever beam and double FBGs (fiber Bragg gratings), which comprises an optical fiber inclinometer module, an optical fiber grating demodulator and an upper computer which are connected in sequence; the optical fiber inclinometer module comprises a first optical fiber inclinometer unit, a second optical fiber inclinometer unit and a third optical fiber inclinometer unit which are sequentially connected in series through single-mode optical fibers and have unequal center wavelengths; a single-mode fiber in each fiber inclinometer unit is respectively provided with a first fiber Bragg grating and a second fiber Bragg grating; the first optical fiber clinometer unit, the second optical fiber clinometer unit and the third optical fiber clinometer unit respectively comprise a cantilever beam and a heavy object; the heavy object is hung below the cantilever beam; the first fiber Bragg grating and the second fiber Bragg grating of each fiber clinometer unit are respectively attached to two sides of the cantilever beam; the fiber grating demodulator is connected with the fiber clinometer module through a single-mode fiber, and the upper computer is connected with the fiber grating demodulator through a network;
s1: disconnecting the first optical fiber clinometer unit, the second optical fiber clinometer unit and the third optical fiber clinometer unit, respectively carrying out zeroing calibration on the first optical fiber clinometer unit, the second optical fiber clinometer unit and the third optical fiber clinometer unit by using an angle dial, and recording the initial reflection wavelength interval of the first optical fiber Bragg grating and the second optical fiber Bragg grating of each optical fiber clinometer unit by using an optical fiber grating demodulator and an upper computer; then connecting the first optical fiber clinometer unit, the second optical fiber clinometer unit and the third optical fiber clinometer unit;
s2: when the optical fiber clinometer module is inclined, the heavy object drives the cantilever beam to generate strain under the action of gravity, the first fiber Bragg grating and the second fiber Bragg grating attached to two sides of the cantilever beam also generate strain, one fiber Bragg grating is stretched to prolong the grating pitch, and the other fiber Bragg grating is correspondingly compressed to shorten the grating pitch;
s3: the fiber bragg grating demodulator monitors the change of the reflection spectrum of the double fiber bragg gratings along with the inclination state of the fiber inclinometer module, the distance between two peak values of the reflection superposition wavelength of the two fiber bragg gratings of each fiber inclinometer unit is changed, the wavelength interval change of all the fiber inclinometer units in the fiber inclinometer module is monitored through the fiber bragg grating demodulator and the upper computer, the change information of the inclination angle is obtained through demodulation, and therefore the change of the inclination angle of each unit on the whole profile of the fiber inclinometer module is sensed.
6. The method of claim 5, wherein: in the step S2, the specific steps are:
let σ be the maximum stress to which the cantilever beam is subjected, E be the Young's modulus of the cantilever beam, m be the mass of the weight, L, b and h be the length, width and thickness of the cantilever beam, and θ be the inclination angle; the maximum strain epsilon experienced by the cantilever beam under the action of gravity when it is tiltedxComprises the following steps:
let Δ λ1Is a change in the reflected wavelength of the first fiber Bragg grating, λ10Is the initial wavelength of the first fiber Bragg grating, Pe is the photoelastic coefficient, ε1The (alpha + xi) delta T is the influence of temperature on the wavelength of the fiber Bragg grating, and is the strain quantity of the first fiber Bragg grating; under stress, a single lightThe variation of the pitch of the fiber bragg grating is as follows:
7. the method of inclinometry of claim 6, wherein: in the step S3, the specific steps are as follows:
the two fiber Bragg gratings are subjected to the same stress and opposite directions, and the influence direction of the temperature on the wavelength is the same, so that the reflection wavelength interval of the two fiber Bragg gratings is not influenced; let Δ λ2Is a change in the reflected wavelength of the second fiber Bragg grating, λ20Is the initial wavelength of the second fiber Bragg grating; when the inclination angle theta is smaller, sin theta is approximate to theta; the change Δ λ in the wavelength interval of the reflection peaks of the two fiber bragg gratings caused by the tilt is:
when the shape of the cantilever beam is determined, the change delta lambda of the wavelength interval of the reflection peaks of the two fiber Bragg gratings is changed linearly along with the change of the inclination angle; the inclination degree of the outside is detected by monitoring the change of the reflection wavelength of the two fiber Bragg gratings.
8. A computer storage medium, characterized in that: stored therein is a computer program executable by a computer processor, the computer program performing the method of any one of claims 5 to 7.
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