KR101498381B1 - System for monitoring three-dimension shape of pipe-structure using fiber bragg grating sensor - Google Patents

Abstract

The present invention relates to a three-dimensional shape monitoring system. The present invention includes: a pipe wherein optical fibers are embedded; fiber Bragg grating sensors formed along a line of the optical fibers inside the pipe at preset intervals; a light transceiver to emit lights into the optical fibers embedded in the pipe, and receiving data of frequency signals reflected from the fiber Bragg grating sensor; and a computer estimating and monitoring the three-dimensional shape and position of the pipe based on the data of the frequency signals received by the light transceiver. According to the present invention, an effect of easily monitoring the three-dimensional shape and strain of the pipe using the fiber Bragg grating sensor is obtained.

Description

TECHNICAL FIELD [0001] The present invention relates to a three-dimensional shape monitoring system for a pipe structure using a fiber Bragg grating sensor,

The present invention relates to a three-dimensional shape monitoring system of a pipe structure, and more particularly, to a three-dimensional shape monitoring system of a pipe structure using an optical fiber Bragg grating sensor.

The stresses of structures such as bridges and buildings are very important for evaluating the condition of structures. Generally, the stresses of structures are measured by strain gauges and then converted into stress by multiplying the elastic modulus.

In order to measure such a strain, an electric resistance type strain gauge has been widely used. However, the electric resistance type sensor has a disadvantage of increasing the noise according to the cable length, and has many disadvantages when measuring a large structure. There is a problem in long-term durability such as corrosion of the sensing part due to the effect. In addition, since cables need to be installed several tens to several hundreds of meters for each sensor, not only a lot of manpower is required but also the quality of acquired signals is not good.

Recently, in order to overcome these shortcomings, FBG (Fiber Bragg Grating) fiber optic sensors are increasingly used for long-term measurement of industrial facilities such as bridges, dams, and buildings.

Fiber Bragg Grating (FBG), which has been actively researched in response to optical fiber sensors, is currently being used for fiber laser, filter, and pulse compression. Advantages of fiber Bragg Grating (FBG) sensors It is possible to measure the amount of physical change at various points by inserting several sensors in a single optical fiber as well as measurement using a single sensor and it is easy to measure the wavelength reflected from the sensor.

The FBG optical fiber sensor generates a Bragg grating that reflects a specific wavelength in the optical cable and changes the wavelength reflected by the tensile-compression or temperature change. Therefore, by converting the change amount of the reflected wavelength at the initial wavelength into tensile- , It is possible to install multiple sensors with different wavelengths on one cable at the same time so that it can be multiplexed and the noise is not generated in the signal even if the cable length is long because the light is a source, It has the advantage of transmitting signals without amplifiers. In addition, it has almost no influence on electromagnetic waves, and it is a sensor which is excellent in long-term durability because it is made of glass and hardly affected by corrosion due to moisture or the like.

A fiber Bragg grating (FBG) sensor generates a periodic refractive index in an optical fiber core. The center wavelength of an optical signal reflected by a fiber Bragg grating (FBG) sensor changes by a physical change due to an external physical change. Therefore, if the wavelength change amount is detected, the physical change amount can be calculated.

Korea Patent No. 10-1082467

SUMMARY OF THE INVENTION It is an object of the present invention to provide a system for easily monitoring the shape of a pipe using an optical fiber Bragg grating sensor.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a fiber Bragg grating sensor including a pipe having an optical fiber therein, a fiber Bragg grating sensor spaced apart from the pipe along a line formed with the optical fiber in the pipe, Dimensional shape and position of the pipe are estimated by using a light source transmission / reception device for inputting a light source to the optical fiber Bragg grating sensor and receiving wavelength signal data reflected from the fiber Bragg grating sensor, and wavelength signal data received by the light source transmission / Includes computers to monitor.

The pipe may include three optical fibers formed in the longitudinal direction at intervals of 120 degrees.

The computer obtains coordinate information of the x-axis, the y-axis, and the z-axis using the wavelength signal data, and estimates the three-dimensional shape of the pipe using the coordinate information.

The computer may obtain x-axis coordinate information from the first optical fiber among the three optical fibers formed in the pipe, obtain y-axis coordinate information from the second optical fiber, and obtain z-axis coordinate information from the third optical fiber. Because three values of r, θ and α are required to be obtained, three optical fiber sensors are used.

(수학식 5)로 나타낼 수 있다.The radius of curvature is r, the curvature angle is θ, and the angle indicating the degree of tilting of the curvature in the pipe section is α, the center of the cross section on which each fiber Bragg grating sensor is located is defined as

(Equation 5).

(수학식 6)의 수식으로 나타낼 수 있고, 이때

(수학식 7)이다.When the length of the fiber Bragg grating sensor is s and the strain is ε,

(Equation 6), where < RTI ID = 0.0 >

(Equation 7).

(수학식 8)의 수식으로 나타낼 수 있다.When the values of r ₁ , r ₂ , and r ₃ in Equation (7) are applied to Equation (5) and Equation (6) by combining the three optical fiber Bragg grating sensors,

(8). ≪ / RTI >

(수학식 9)의 α에 관한 식으로 표현하거나,

(수학식 10)의 곡률 반경 r에 대한 식으로 표현할 수 있다. _{ε 12 = ε 2 -ε 1,} ε 13 = ε 3 -ε 1, ε 23 = ε 3 and _{-ε 2, σ 1 = 1 +} ε 1, σ 2 = 1 + ε 2, σ 3 = 1 + ε ₃ , equation (8)

(9) ", or "

Can be expressed by the equation for the radius of curvature r of Equation (10).

(수학식 11)로 나타낼 수 있다.If the function f (x, y, z) expressing the coordinate values of x, y and z, which is the sectional position of the pipe in which the fiber Bragg grating sensor is located, is called output and n is the number of position data,

(11). &Quot; (11) "

The light source transceiver may be an FBG interrogator.

The computer can calculate the strain of the pipe and the three-dimensional shape of the pipe based on the strain.

According to the present invention, it is possible to easily monitor the three-dimensional shape and strain of a pipe by using an optical fiber Bragg grating sensor.

Also, in the present invention, it is expected that strain can be measured using a wavelength reflected from an optical fiber Bragg grating sensor, such as a material including a pipe, a structure, and the like, .

1 is a view for explaining a structure and a principle of a general optical fiber Bragg grating sensor.
2 is a diagram showing the operation and waveform of the fiber Bragg grating sensor system.
FIG. 3 and FIG. 4 are views showing a three-dimensional shape monitoring system using an optical fiber Bragg grating sensor according to an embodiment of the present invention.
FIGS. 5 to 7 are views for explaining an algorithm for expressing a three-dimensional shape and position of a pipe using an optical fiber Bragg grating sensor according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted in an ideal or overly formal sense unless expressly defined in the present application Do not.

In the following description of the present invention with reference to the accompanying drawings, the same components are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

FIG. 1 is a view for explaining the structure and principle of a conventional fiber bragg grating sensor (FBG sensor).

Referring to FIG. 1, an optical fiber Bragg grating sensor forms a periodic lattice on a core of an optical fiber, and thereby utilizes a refractive index change of light. That is, when a broadband light is incident on the Bragg grating, the light is reflected at the interface where the refractive index changes. The Bragg wavelength λ _b corresponding to the Bragg condition is reflected without passing through the Bragg grating, The light of the light passes through the Bragg grating. The Bragg condition is expressed by the following equation.

Here, n _e is an effective refractive index of the optical fiber grating, which represents the average refractive index when light propagates through one period of the fiber Bragg grating, and A represents a grating period engraved in the optical fiber core.

That is, the Bragg wavelength corresponding to the Bragg Condition as shown in Equation (1) is reflected without passing through the Bragg grating, and the light of other wavelengths passes through the Bragg Condition.

The Bragg wavelength reflected from the optical fiber Bragg grating represented by Equation (1) is a function of the effective refractive index and the lattice spacing. When an external physical quantity such as a short distance strain is applied to the optical fiber Bragg grating, Bragg wavelength is changed by these values. By precisely measuring the change of the Bragg wavelength, an unknown physical quantity applied to the optical fiber grating can be obtained.

The fiber Bragg grating sensor is easy to measure because the amount of change of the Bragg reflection wavelength is measured, and the line width of the reflection wavelength of the fiber Bragg grating is narrow. In addition, since the optical fibers having different Bragg reflection wavelengths are not influenced by each other, multi-point measurement using one optical fiber is possible.

In the fiber Bragg grating sensor, a plurality of gratings are used for a single optical fiber. In this case, by making all the reflection wavelengths of the gratings different, it is possible to easily distinguish physical quantities experienced by a specific grating from the spectrum of the reflected light source. This method is called wavelength division method.

The Bragg wavelength reflected by the grating is a function of the effective refractive index and the lattice spacing. When an external physical quantity is applied to the optical fiber Bragg grating sensor, the Bragg wavelength is changed. Therefore, if the Bragg wavelength is measured, Can be obtained.

One of the biggest applications of fiber Bragg grating sensors is to diagnose the condition of the structure. For example, a fiber optic sensor is installed in a concrete in the manufacture of bridges, dams, buildings, etc., and the safety state of the structure can be diagnosed by sensing the tensile distribution or bending degree inside the structure.

2 is a diagram showing the operation and waveform of the fiber Bragg grating sensor system.

Referring to FIG. 2, when broadband light is input to the optical fiber 230, the light is reflected at the interface where the refractive index is changed, and the Bragg wavelength? _B corresponding to the Bragg condition The light is reflected without passing through the Bragg grating, and the other light is transmitted through the Bragg grating.

The photodetector 220 serves to detect the reflected light without passing through the Bragg grating.

In Fig. 2, the input spectrum waveform (a), the signal waveform (b) transmitted through the Bragg grating, and the reflected signal waveform (c) are shown.

Equation 1 is expressed by the effective refractive index and the period of the grating, which is a function of the temperature and the strain, and when the disturbance such as temperature or strain is applied to the fiber Bragg grating, the Bragg wavelength? _B changes.

FIG. 3 and FIG. 4 are views showing a three-dimensional shape monitoring system using an optical fiber Bragg grating sensor according to an embodiment of the present invention.

3 and 4, a three-dimensional shape monitoring system using an optical fiber Bragg grating sensor of the present invention includes a pipe 100, a light source transceiver 200, and a computer 300.

In Figs. 3 and 4, A is an enlarged cross-section of the pipe 100. Fig.

The pipe 100 includes three optical fibers 110 formed in the longitudinal direction at intervals of 120 degrees.

In the present invention, the computer 300 requires three pieces of information of the x-axis, the y-axis, and the z-axis of the pipe 100, so that three optical fibers are formed in the pipe 100.

In the present invention, the shape of the pipe point where the optical fiber sensor is located is estimated by using the strain measured using the three optical fiber sensors formed on the pipe 100.

The fiber Bragg grating sensors FBG are formed at predetermined intervals along a line formed with the optical fibers 110 in the pipe.

The light source transceiver 200 receives a light source from the optical fiber 110 built in the pipe 100 and receives wavelength signal data reflected from the optical fiber Bragg grating sensor.

In an embodiment of the present invention, the light source transceiver 200 may be an FBG interrogator.

The computer 300 estimates the three-dimensional shape and position of the pipe 100 using the wavelength signal data received by the light source transmission / reception device 200. In addition, the computer 300 can calculate the strain of the pipe 100 while estimating the three-dimensional shape and position of the pipe 100. [

In the present invention, the computer 300 can acquire coordinate information of the x-axis, y-axis, and z-axis using the wavelength signal data, and estimate the three-dimensional shape of the pipe 100 using the coordinate information. For example, the computer 300 acquires x-axis coordinate information from the first optical fiber among the three optical fibers formed in the pipe 100, acquires y-axis coordinate information from the second optical fiber, Information can be obtained.

The principle of measuring the strain of the pipe 100 using the fiber Bragg grating sensor (FBG) will now be described.

Referring to FIG. 1 and FIG. 2, when the pipe 100 is deformed due to an external force or changes in temperature, a wavelength reflected from the optical fiber Bragg grating sensor changes. The relationship is as follows.

In Equation (2),? Is the expansion coefficient according to the temperature of the optical fiber, and? Is the thermal optical coefficient according to the temperature of the optical fiber. ? _e is the photoelastic coefficient, and has the following relationship (3).

Typically, ρ _e has a value of 0.22.

Assuming that the temperature change is 0, i.e., DELTA T = 0, Equation (2) can be simply expressed by Equation (4).

In the present invention, the strain generated in the fiber Bragg grating sensor can be calculated using Equation (4).

As a result, in the present invention, it is possible to measure the strain of a material, a structure, and the like including a pipe by using a wavelength reflected from an optical fiber Bragg grating sensor, and thereby it can be utilized for studying structural health monitoring, shape estimation, and the like.

FIGS. 5 to 7 are views for explaining an algorithm for expressing a three-dimensional shape and position of a pipe using an optical fiber Bragg grating sensor according to an embodiment of the present invention.

5 to 7, an algorithm for expressing the shape and position of a pipe using three lines of fiber Bragg grating sensors will be described.

As shown in FIG. 5, coordinates of x, y, and z are required to represent the shape of the pipe. For this purpose, the coordinate points are calculated and parameters necessary for calculating them are obtained using the strain value of the fiber Bragg grating sensor.

The center of the cross section where the fiber Bragg grating sensor of the pipe is located can be expressed by the following equation (5).

To obtain the coordinate values of x, y and z, we obtain the value of the curvature radius r, the curvature angle θ, and the angle α indicating the degree of tilting of the curvature in the pipe section.

As shown in FIG. 6, the θ value can be obtained by the strain value, which can be expressed by the following equation.

Here, the value of strain ε is known as the strain value of the optical fiber Bragg grating sensor. That is, the length s and the strain ε of the fiber Bragg grating sensor are known, and the values of r ₁ , r ₂ , and r ₃ are obtained, thereby obtaining the θ value.

Referring to FIG. 7, it is possible to derive an expression for obtaining the values of r ₁ , r ₂ , and r ₃ . This is shown in Equation (7).

When the values of r ₁ , r ₂ , and r ₃ are applied to Equation (5) and Equation (6) in Equation (7), equations relating to r and? Can be obtained as Equation (8).

Here, 120 ° is an angle formed by the three fiber Bragg grating sensors.

_{ε 12 = ε 2 -ε 1,} ε 13 = ε 3 -ε 1, ε 23 = ε 3 and _{-ε 2, σ 1 = 1 +} ε 1, σ 2 = 1 + ε 2, σ 3 = 1 + ε ₃ , equation (8) can be expressed by the following equation (9) which is an equation for?.

Equation (8) can also be expressed as Equation (10), which is an equation for the radius of curvature r.

As described above, the r value,? Value and? Value can be obtained by using the formula. Also, the coordinate values of x, y, and z, which are the cross-sectional positions of the pipe where the fiber Bragg grating sensor is located, can be finally obtained using the obtained values.

Here, the output is a function for f (x, y, z) position and n is the number of position data.

In the present invention, the cross-sectional position of the pipe in which the optical fiber Bragg grating sensor is located can be obtained, and then the overall shape of the pipe can be estimated using the information between the positions of the optical fiber Bragg grating sensors.

While the present invention has been described with reference to several preferred embodiments, these embodiments are illustrative and not restrictive. It will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

100 Pipe 200 Light source transceiver
300 computer 110 optical fiber

Claims (11)

Pipes with fiber optics;
A fiber Bragg grating sensor formed at predetermined intervals along a line formed with an optical fiber in the pipe;
A light source transceiver for inputting a light source to an optical fiber built in the pipe and receiving wavelength signal data reflected from the optical fiber Bragg grating sensor; And
And a computer for estimating and monitoring the three-dimensional shape and position of the pipe using the wavelength signal data received by the light source transmitting / receiving device,
The pipe includes three optical fibers formed in the longitudinal direction at intervals of 120 degrees,
The computer obtains coordinate information of the x-axis, the y-axis, and the z-axis using the wavelength signal data, estimates the three-dimensional shape of the pipe using the coordinate information,
The computer acquires x-axis coordinate information from the first optical fiber among the three optical fibers formed in the pipe, obtains y-axis coordinate information from the second optical fiber, obtains z-axis coordinate information from the third optical fiber,
The radius of curvature is r, the curvature angle is θ, and the angle indicating the degree of tilting of the curvature in the pipe section is α, the center of the cross section on which each fiber Bragg grating sensor is located is defined as

(5)
Lt; / RTI >
When the length of the fiber Bragg grating sensor is s and the strain is ε,

(6)
Can be represented by the following equation,

(7), < / RTI >
When the values of r ₁ , r ₂ , and r ₃ in Equation (7) are applied to Equation (5) and Equation (6) by combining the three optical fiber Bragg grating sensors,

(8)
Can be represented by the following equation,
_{ε 12 = ε 2 -ε 1,} ε 13 = ε 3 -ε 1, ε 23 = ε 3 and _{-ε 2, σ 1 = 1 +} ε 1, σ 2 = 1 + ε 2, σ 3 = 1 + ε ₃ , equation (8)

(9) ", or "

Can be expressed in terms of a curvature radius r of Equation (10)
If the function f (x, y, z) expressing the coordinate values of x, y and z, which is the sectional position of the pipe in which the fiber Bragg grating sensor is located, is called output and n is the number of position data,

(11)
Dimensional shape monitoring system of the pipe structure.
delete delete delete delete delete delete delete delete The method according to claim 1,
Wherein the light source transmission / reception device is an FBG interrogator.
The method according to claim 1,
Wherein the computer calculates a strain of the pipe and calculates a three-dimensional shape of the pipe based on the calculated strain.

Images