A temperature self-compensating large structure deformation sensing device based on flat ribbon optical cable

Abstract

The application discloses a kind of temperature self-compensation large structure deformation sensing device based on flat ribbon optical cable, mainly by multichannel fiber grating demodulator, host computer, transmission optical fiber and flat ribbon optical cable constitute.The flat ribbon optical cable includes support body and two symmetric fixed sensing fiber grating arrays, and is wrapped with protective material and is encapsulated into ribbon shape by being pasted on both sides of support body in parallel.When structure is deformed, two sensing fiber grating arrays generate tension and compression strain respectively, which causes the reverse drift of grating center wavelength.The demodulator measures the wavelength change and carries out differential processing, which can directly offset the temperature influence and realize temperature self-compensation.The compensated differential signal has linear relationship with structure curvature, and the structure deformation can be reconstructed by inversion of host computer.The application has the advantages of temperature self-compensation, high sensitivity, good stability and suitability for distributed measurement, and is suitable for long-term health monitoring of large structure.

Description

Technical Field

[0001] This invention belongs to the field of fiber optic sensing technology, and specifically relates to a temperature self-compensating deformation sensing device for large structures based on flat strip optical cables. Background Technology

[0002] The safe service and health monitoring of large structures (such as bridges, dams, high-rise buildings, and wind turbine blades) are crucial, as their deformation is a key parameter for assessing structural condition, predicting damage, and enabling preventative maintenance. Traditional deformation monitoring mainly relies on electrical sensors, such as resistance strain gauges, linear variable differential transformers (LVDTs), and inclinometers. While these sensors are technologically mature, they have significant limitations in large-scale structural applications: they are susceptible to electromagnetic interference, have poor long-term stability, limited measurement range, and are difficult to implement distributed multi-point measurements; their reliability decreases in high humidity, corrosive, or vibration fatigue environments; and large-scale deployment leads to complex wiring, severe signal attenuation, high system costs, and difficult maintenance.

[0003] The emergence of fiber Bragg grating (FBG) sensors has provided a new technological path for deformation monitoring. FBGs sense physical quantities such as strain and temperature by detecting Bragg wavelength drift, and have outstanding advantages such as resistance to electromagnetic interference, corrosion resistance, and ease of wavelength division multiplexing and space division multiplexing. However, when applying traditional FBGs directly to the macroscopic, large-scale, high spatial resolution deformation field sensing of large structures, a series of challenges remain: First, the inherent problem of measurement inaccuracies caused by the cross-sensitivity of temperature and strain. In existing technologies, the wavelength drift of a single FBG responds to both strain and temperature changes simultaneously, making it difficult to directly distinguish between the two. This leads to significant errors introduced by temperature disturbances when relying solely on a single FBG for measurement, while using independent temperature sensors for compensation easily complicates the monitoring system and makes it difficult to achieve accurate and integrated temperature self-compensation. Second, there is a contradiction between the location sensitivity of strain measurement and the accuracy of shape inversion. In the monitoring of large structures, FBG sensors are usually deployed at different locations on the surface of the structure in a discrete manner. When a large structure deforms, its surface strain distribution exhibits a gradient, and its relative position to the neutral plane directly determines the sign and magnitude of the strain. Traditional point-based FBG deployment struggles to accurately guarantee the geometric relationship between each measurement point and the structure's neutral plane, resulting in strain values ​​at each point reflecting not only overall deformation but also a strong dependence on their local deployment location. This directly leads to significant model errors when performing overall shape inversion based on these discrete, location-sensitive strain measurements, reducing the accuracy and reliability of deformation field reconstruction. Furthermore, the traditional single-FBG measurement method, relying on absolute wavelength changes, has limited resolution for minute strains; specific deployment locations may further restrict the ability to capture minute deformations. Thirdly, there is a contradiction between encapsulation complexity and long-term maintenance reliability. To protect the fragile bare fiber and achieve strain transfer, multi-layered and complex encapsulation of the FBG (such as metal tube encapsulation and resin curing) is required. However, encapsulation processes are complex and costly, and additional structures may introduce additional errors such as hysteresis and creep. On-site deployment involves cumbersome installation procedures, requires highly skilled operators, and hinders rapid, large-scale deployment and subsequent maintenance and replacement, impacting the efficiency of technology engineering and promotion. In conclusion, developing an FBG deformation sensing device that combines high sensitivity, temperature self-compensation, support for distributed multi-point and multi-dimensional measurement, robust and stable structure, and ease of on-site installation and maintenance is of paramount importance for advancing intelligent monitoring technology for large structures from the laboratory to large-scale engineering applications. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a temperature self-compensating deformation sensing device for large structures based on flat strip optical cables. This device can improve the sensitivity of shape sensing for large structures, achieve temperature self-compensation, and support distributed multi-point multi-dimensional measurement. It has the advantages of high practicality, good stability, and safety and reliability.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A temperature self-compensating deformation sensing device for large structures based on flat ribbon optical cable includes a multi-channel fiber optic demodulator, a host computer, two transmission optical fibers, and a flat ribbon optical cable.

[0007] The flat ribbon optical cable consists of a support material, two sensing fiber grating arrays, and a protective coating. The support material is a rectangular strip with a certain degree of flexibility. The two sensing fiber grating arrays are glued and fixed to both sides of the support material and are parallel to each other. The positions of the gratings on the two sensing fiber grating arrays are one-to-one corresponding in the axial direction. The protective coating covers the support material and the two sensing fiber grating arrays.

[0008] The flat ribbon optical cable is used to be pasted and fixed along the axial direction of the large structure to be tested, serving as the sensing area.

[0009] The two ports of the multi-channel fiber optic demodulator are respectively connected to the two transmission optical fibers, and the other ends of the two transmission optical fibers are respectively connected to the two sensing fiber optic arrays in the flat ribbon optical cable; the multi-channel fiber optic demodulator is used to transmit optical signals and demodulate reflected signals.

[0010] The host computer is electrically connected to the multi-channel fiber Bragg grating demodulator and is used to receive demodulated data and perform data processing, shape inversion and reconstruction.

[0011] This invention also provides a deformation measurement and shape inversion method based on the above-mentioned device. This method utilizes two parallel sensing fiber optic grating arrays in a flat ribbon optical cable to perform differential measurement of the strain signal caused by structural deformation, thereby achieving temperature self-compensation and enhancing strain sensitivity. Finally, the shape change of the structure is reconstructed through a shape inversion algorithm. Specifically, it includes the following steps.

[0012] Step 1: Securely attach the flat ribbon optical cable along the axial direction of the large structure to be tested. After the device is powered on, the multi-channel fiber optic demodulator emits a broadband optical signal, which is injected into the two sensing fiber optic arrays in the flat ribbon optical cable through two transmission optical fibers. The demodulator receives and demodulates the signals reflected back from each fiber optic grating, obtains its initial center wavelength in the undeformed state of the structure, and uploads the data to the host computer for recording and storage.

[0013] Step two: When the large structure deforms, the flat fiber optic cable attached to it bends accordingly. Since the two sensing fiber grating arrays in the flat fiber optic cable are fixed to opposite sides of the flexible support material, one sensing fiber grating is stretched while the other is compressed in the same axial direction. This causes a positive shift in the center wavelength of the stretched sensing fiber grating array and a negative shift in the center wavelength of the compressed sensing fiber grating array. The multi-channel fiber grating demodulator demodulates and acquires the changed center wavelength data of these two sets of sensing fiber grating arrays in real time and uploads it to the host computer.

[0014] Step three: The host computer processes the real-time data. First, it calculates the center wavelength change of each sensing fiber Bragg grating in the flat-band optical cable. Then, it performs a differential operation on the wavelength changes of two fiber Bragg gratings at the same axial position. Since the two sensing fiber Bragg gratings have the same temperature sensitivity, the wavelength changes caused by temperature cancel each other out after differential analysis; however, because they experience equal strain values ​​but opposite signs, the wavelength changes caused by strain are enhanced (added) after differential analysis. This step eliminates the influence of ambient temperature changes on the measurement and achieves a doubling of the strain signal sensitivity.

[0015] Step four involves establishing a linear relationship between the difference in wavelength variation between the two sensing fiber gratings in the flat ribbon optical cable and the curvature variation of the large structure through experimental calibration. The conversion coefficient between the curvature variation and the wavelength variation difference is proportional to the width of the supporting material. Since the width of the supporting material is fixed, this coefficient is constant. This relationship allows the difference in wavelength variation to be directly converted into the curvature distribution of the large structure along the sensing path.

[0016] Step 5: Using the curve integral reconstruction algorithm, a series of discrete curvature changes measured along the length of the flat fiber optic cable are inverted into the deformed shape of the structure.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) Temperature self-compensation and sensitivity multiplication: This invention employs two sensing fiber optic grating arrays with one-to-one correspondence in the flat strip optical cable. By performing differential calculations on the wavelength changes of the two arrays, it cleverly utilizes the characteristic that the strain signs on both sides are opposite when the structure is bent. The differential operation not only completely cancels the common-mode error caused by changes in ambient temperature and achieves high-precision temperature self-compensation, but also doubles the signal amplitude caused by strain, significantly improving the detection sensitivity to minute deformations.

[0019] (2) Simple structure, easy to deploy and maintain: The flat strip optical cable adopts an integrated flat structure design, which integrates sensing optical fiber, support material and protective coating together, making the structure robust and flexible. This design simplifies the packaging process, reduces costs, and is easy to directly stick to the surface of large structures like tape, which greatly simplifies the difficulty of on-site construction and is suitable for large-scale distributed deployment.

[0020] (3) High scalability: This device supports multi-channel expansion. One multi-channel fiber optic demodulator can connect to multiple flat-band optical cables to realize synchronous monitoring of multiple large structures or different locations of the same structure, which has extremely high engineering application value. Attached Figure Description

[0021] Figure 1 This is a connection diagram of a large structure shape sensing device based on a flat strip optical cable with temperature self-compensation according to the present invention.

[0022] Figure 2 This is a schematic diagram of the internal cross-sectional structure of a flat ribbon optical cable according to the present invention. Detailed Implementation

[0023] The present invention will now be further described with reference to the accompanying drawings.

[0024] like Figure 1 As shown, a temperature self-compensating shape sensing device for large structures based on flat ribbon optical cable includes a multi-channel fiber optic demodulator 1, a host computer 2, a transmission optical fiber 3, a transmission optical fiber 4, and a flat ribbon optical cable 5.

[0025] The multi-channel fiber Bragg grating demodulator 1 is electrically connected to the host computer 2. Port 1-01 of the multi-channel fiber Bragg grating demodulator 1 is optically connected to the transmission fiber 3, and port 1-02 of the multi-channel fiber Bragg grating demodulator 1 is optically connected to the transmission fiber 4. The transmission fiber 3 is optically connected to the sensing fiber Bragg grating array 9-01 in the flat ribbon optical cable 5, and the transmission fiber 4 is optically connected to the sensing fiber Bragg grating array 9-02 in the flat ribbon optical cable 5. The flat ribbon optical cable 5 is attached to the large structure 6, and the flat ribbon optical cable 5 is aligned with the axial center of the large structure 6. The host computer is electrically connected to the multi-channel fiber Bragg grating demodulator.

[0026] like Figure 2 As shown, the above-mentioned flat ribbon optical cable 5 includes a support material 7, a protective coating 8, a sensing fiber optic grating array 9-01, and a sensing fiber optic grating array 9-02.

[0027] Two sensing fiber Bragg grating arrays 9-01 and 9-02 of the flat ribbon optical cable 5 are respectively attached to both sides of the supporting material 7, and are parallel to each other. The grating points on the two sensing fiber Bragg grating arrays correspond strictly one-to-one in the axial direction. The protective coating 8 covers the supporting material 7 and the two sensing fiber Bragg grating arrays 8 9-01 and 9-02, and plays a role in moisture protection, corrosion protection and mechanical protection.

[0028] In the above device, the multi-channel fiber Bragg grating demodulator 1 is the optical signal transmitting and demodulation device, the flat ribbon optical cable 5 is the shape sensing area, and the host computer 2 is the data processing and shape inversion algorithm execution area, which is used to receive the demodulated data of the multi-channel fiber Bragg grating demodulator 1 and perform data processing, shape inversion and reconstruction.

[0029] The working principle and process of this invention are as follows:

[0030] The light emitted by the multi-channel fiber Bragg grating demodulator 1 passes through port 1-01 and is transmitted through transmission fiber 3 to the sensing fiber Bragg grating array 9-01 of the flat-strip optical cable 5. The light passing through port 1-02 is transmitted through transmission fiber 4 to the sensing fiber Bragg grating array 9-02 of the flat-strip optical cable 5. At this time, the light waves satisfying the Bragg condition of the sensing fiber Bragg grating array 9-01 in the flat-strip optical cable 5 are reflected back and propagated in the reverse direction along transmission fiber 3, and are received by the multi-channel fiber Bragg grating demodulator 1 through port 1-01. Similarly, the light waves satisfying the Bragg condition of the sensing fiber Bragg grating array 9-02 in the flat-strip optical cable 5 are reflected back and propagated in the reverse direction along transmission fiber 4, and are received by the multi-channel fiber Bragg grating demodulator 1 through port 1-02. The multi-channel fiber Bragg grating demodulator 1 transmits the received data to the host computer 2.

[0031] The flat ribbon optical cable 5 is glued to the large structure 6, with the axial centers of the flat ribbon optical cable 5 and the large structure 6 aligned. After complete fixation, the host computer 2 records the wavelength information of the two sensing fiber optic grating arrays 9-01 and 9-02 in the flat ribbon optical cable 5 in the initial state, that is, the center wavelength value in the no-load or reference state. and .

[0032] When the large structure 6 undergoes a shape change, the flat ribbon optical cable 5 attached to its surface bends accordingly. The two sensing fiber Bragg grating arrays 9-01 and 9-02 within the flat ribbon optical cable 5, located at the same axial position, are subjected to tensile and compressive strains, respectively. Assuming 9-01 is under tension and 9-02 is under compression, the center wavelength of the stretched fiber Bragg grating in 9-01 increases. The center wavelength of the compressed fiber grating 9-02 is reduced. .

[0033] The center wavelengths of the two sensing fiber optic arrays 9-01 and 9-02 in the flat strip optical cable 5 are obtained by signal demodulation using a multi-channel fiber optic demodulator 1. After the data is transmitted to the host computer 2, the center wavelengths of the two sensing fiber optic arrays 9-01 and 9-02 in the flat strip optical cable 5 are also obtained. and Center wavelength of the initial state recorded and The wavelength change is obtained by performing a difference. and Then, the difference in the center wavelength changes of the two sensing fiber optic arrays 9-01 and 9-02 in the flat strip optical cable 5 is used to obtain the difference value of the wavelength change. This reduces the impact of temperature on the two sensing fiber optic arrays 9-01 and 9-02 in the flat strip optical cable 5, achieving temperature compensation. This is solely due to the strain acting on the flat strip optical cable 5. Furthermore, The linear relationship between curvature change and the curvature change of structure 6 is established, and the shape inversion algorithm is used to obtain the shape change of the large structure 6 from the curvature. The specific analysis is as follows.

[0034] The expression for the response characteristics of the center wavelength (Brag wavelength) of the fiber optic grating to temperature and strain is as follows:

[0035] (1)

[0036] (2)

[0037] As shown in equation (1), The center wavelength of the fiber grating. The effective refractive index of the fiber grating. Let be the grating period. In equation (2) The effective photoelastic coefficient is determined by the photoelastic coefficient and Poisson's ratio of the fiber material and the effective refractive index of the grating. Equation (2) shows that the relative offset of the center wavelength of the fiber grating is a linear superposition of the strain and temperature terms, where... This represents the change in the center wavelength of the fiber optic grating.

[0038] (3)

[0039] (4)

[0040] (5)

[0041] As shown in equations (3) and (4), and The change in the center wavelength of the two sensing fiber optic arrays 9-01 and 9-02 in the flat strip optical cable 5 is where is The strain sensitivity of the two sensing fiber optic arrays 9-01 and 9-02 in the flat ribbon optical cable 5 It refers to the temperature sensitivity of the two sensing fiber optic arrays 3 and 4 in the flat strip optical cable 5. In equation (5) It represents the difference in the center wavelength variation of the two sensing fiber grating arrays 3 and 4 in the flat strip optical cable 5.

[0042] The two sensing fiber Bragg grating arrays 9-01 and 9-02 in the flat ribbon optical cable 5 are made of the same material and are in the same environment, exhibiting the same strain sensitivity and temperature sensitivity. When the axial neutral plane of the flat ribbon optical cable 5 and the large structure 6 under test are aligned, as the shape of the large structure 6 changes, the two sensing fiber Bragg grating arrays 9-01 and 9-02 of the flat ribbon optical cable 5 are compressed and stretched, respectively. The values ​​are equal, but the signs are opposite.

[0043] The host computer 2 performs differential calculations on the two signals from the multi-channel fiber optic demodulator 1 to obtain the differential value of the wavelength change. :

[0044] (6)

[0045] As can be seen from equation (6), the temperature term The strain term is completely canceled out, achieving temperature self-compensation; while the strain term becomes The sensitivity is doubled.

[0046] Furthermore, strain The curvature change of structure 6 There is a linear relationship between them:

[0047] (7)

[0048] In equation (7), d is the distance between the two sensing fiber optic arrays 9-01 and 9-02 in the flat ribbon optical cable 5 (i.e., the width of the supporting material 7). Substituting into equation (6), we get:

[0049] (8)

[0050] because Both and d are constants, therefore the wavelength difference value With curvature change It exhibits a strictly linear relationship. Even if the flat strip optical cable 5 is not perfectly aligned with the neutral plane of the structure during installation, as long as d is fixed, this proportionality coefficient remains constant, ensuring the stability of the measurement. Therefore, by measuring the difference in the center wavelength changes of the two sensing fiber optic grating arrays 9-01 and 9-02 in the flat strip optical cable 5... This allows for the measurement of the curvature change of the large structure 6. The obtained curvature change can then be converted into the shape change of the large structure 6 using a shape inversion algorithm, thereby achieving highly sensitive shape monitoring of the large structure 6.

[0051] (9)

[0052] (10)

[0053] (11)

[0054] Equation (9) is the formula for calculating the tangent angle in the plane curve reconstruction algorithm based on curve integrals. It involves integrating the curvature change obtained after the above process based on the initial position (arc length) of the fiber grating and adding the initial angle to determine the tangent direction at that point, where s is the arc length of the sensing fiber grating array. Let be the initial tangential angle. For a large structure with a flat initial state, this value is 0. Equations (10) and (11) express that after obtaining the tangential angle at this location, the cosine and sine values ​​of this direction are calculated using the tangential angle, and then a second integration is performed. The integration result, plus the initial coordinate position, yields the shape coordinate values ​​after the shape change. and These are the initial position coordinates of the fiber optic grating.

[0055] The key technologies enabling this device to realize a temperature-self-compensated shape sensing device for large structures based on flat strip optical cables include:

[0056] 1. Because fiber optic gratings are subjected to tensile and compressive forces resulting from the shape changes of large structures, the flat ribbon optical cables used need to be made of support materials with appropriate rigidity and toughness to ensure that the optical fibers do not break when subjected to tensile and compressive stresses and can effectively transmit strain.

[0057] 2. The flat ribbon optical cable proposed in this invention uses two sensing fiber grating arrays that are respectively attached to both sides of a support material with a fixed width, so that the spacing between the two sensing fiber grating arrays is kept consistent, ensuring that the conversion coefficient between strain and curvature is fixed and can be adjusted by changing the width of the support material.

[0058] 3. This invention achieves temperature self-compensation and strain sensitivity multiplication by differentially measuring the wavelength changes of two sensing fiber optic grating arrays in a flat strip optical cable, thereby significantly improving the signal-to-noise ratio and measurement accuracy.

[0059] The above embodiments are merely preferred embodiments of the present invention. It should be understood that any changes and improvements made to the sensing structure, light source type, demodulation method, etc., within the core principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A temperature self-compensating deformation sensing device for large structures based on flat strip optical cables, characterized in that, include: Multichannel fiber Bragg grating demodulator; The host computer is electrically connected to the multi-channel fiber Bragg grating demodulator; Two transmission optical fibers are respectively optically connected to two ports of the multi-channel fiber Bragg grating demodulator; A flat ribbon optical cable contains two parallel sensing fiber grating arrays, and the other ends of the two transmission optical fibers are respectively optically connected to the two sensing fiber grating arrays. The flat ribbon optical cable is used to be pasted and fixed along the axial direction of the large structure to be tested, serving as a sensing area; the multi-channel fiber optic demodulator is used to transmit optical signals and demodulate reflected signals; and the host computer is used to receive demodulated data and perform data processing, shape inversion, and reconstruction.

2. The temperature self-compensating deformation sensing device for large structures based on flat strip optical cable according to claim 1, characterized in that, The structure of the flat strip optical cable includes: The supporting material is a rectangular strip with a certain degree of flexibility; Two sensing fiber grating arrays are glued and fixed to both sides of the support material, and are parallel to each other. The positions of the gratings on the two sensing fiber grating arrays are one-to-one corresponding in the axial direction. A protective coating covers the supporting material and the two sensing fiber optic grating arrays.

3. The temperature self-compensating deformation sensing device for large structures based on flat strip optical cable according to claim 2, characterized in that, The width of the support material is fixed, which keeps the distance between the two sensing fiber grating arrays constant, thereby ensuring the stability of the conversion coefficient between strain and curvature change.

4. The temperature self-compensating deformation sensing device for large structures based on flat strip optical cables according to any one of claims 1 to 3, characterized in that, The multi-channel fiber optic demodulator can connect to multiple flat-band optical cables to achieve distributed synchronous monitoring of multiple large structures or different locations of the same structure.

5. A method for deformation measurement and shape inversion based on the device according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: The flat ribbon optical cable is pasted and fixed along the axis of the large structure to be tested. After the device is powered on, the multi-channel fiber optic demodulator emits a broadband optical signal, which is injected into the two sensing fiber optic arrays in the flat ribbon optical cable through the transmission fiber to record the center wavelength in the initial state. Step 2: When the large structure deforms, the flat fiber optic cable bends accordingly, causing the two sensing fiber optic grating arrays at the same axial position to be stretched and compressed respectively, and their center wavelengths drift in opposite directions; the multi-channel fiber optic grating demodulator demodulates and acquires the changed center wavelength data in real time, and uploads it to the host computer. Step 3: The host computer calculates the change in the center wavelength of each sensing fiber optic grating array and performs differential calculations on the two wavelength changes corresponding to the same axial position to eliminate the influence of temperature and enhance the strain signal. Step 4: Using a pre-calibrated linear relationship, convert the difference in wavelength variation into the curvature variation of the large structure along the sensing path; Step 5: Using the curve integral reconstruction algorithm, the discrete curvature change is inverted into the three-dimensional shape coordinates of the deformed large structure.

6. The method according to claim 5, characterized in that, Since the two sensing fiber Bragg grating arrays have the same temperature sensitivity, the wavelength changes caused by temperature cancel each other out after differential operation; since the strain values ​​of the two sensing fiber Bragg grating arrays are equal but opposite in sign, the wavelength changes caused by strain are added together after differential operation, thus achieving a multiplication of strain sensitivity.

7. The method according to claim 5, characterized in that, The conversion coefficient between the difference between the curvature change and the wavelength change is proportional to the width of the support material. Since the width of the support material is fixed, this coefficient is a constant.

8. The method according to claim 5, characterized in that, The curve integral reconstruction algorithm specifically includes: The tangential angle at each point is obtained by integrating the curvature change and the initial arc length. By performing a double integral on the cosine and sine values ​​of the tangential angle and combining them with the initial coordinate position, the shape coordinate values ​​after deformation are calculated.

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