Double-fiber Bragg grating strain sensor based on flexible hinge and test method

Abstract

The invention discloses a double-fiber Bragg grating strain sensor based on a flexible hinge and a test method, and the sensor is installed in a sealing barrel, and comprises a first transverse supporting arm and a second transverse supporting arm which are parallel to each other; the second transverse supporting arm is arranged right above the first transverse supporting arm; the first end part of the second transverse supporting arm is a free end, and the second end part of the second transverse supporting arm is connected with the first end of the first flexible hinge; the second end part of the first flexible hinge is connected with the upper end of the rectangular metal sheet, and the lower end of the rectangular metal sheet is fixed on the support frame; the supporting frame is arranged at the top of the inner side of the sealing barrel; the first end of the first transverse supporting arm is connected with the first end of the second flexible hinge, and the second end of the second flexible hinge is fixed to the supporting frame. The second end of the first transverse supporting arm is connected with the first end of the elastic strain unit, and the second end of the elastic strain unit is connected with the second transverse supporting arm.

Description

Technical Field

[0001] This invention relates to the field of strain sensor design technology, and in particular to a dual-fiber Bragg grating strain sensor based on a flexible hinge and a testing method thereof. Background Technology

[0002] Strain monitoring is widely used in civil engineering structures, mechanical engineering, oil and gas exploration, aerospace and other fields to assess structural health, prevent accidents, and optimize processes. Existing strain monitoring methods mainly utilize electromagnetic strain sensing technology and fiber optic strain sensing technology. However, electromagnetic strain sensors are susceptible to electromagnetic interference and have poor stability, making them unsuitable for multi-point distributed measurement methods. FBG sensors, on the other hand, offer advantages such as small size, good long-term stability, resistance to electromagnetic interference, and ease of networking and reuse, thus gaining increasing attention in the field of strain monitoring.

[0003] Numerous researchers have conducted extensive studies on FBG strain sensors, developing various types. Barbosa C et al. investigated a novel weldable strain sensor based on a fiber grating, which can be directly welded to a metal structure, achieving a strain sensitivity of 1.2 pm / με. Jing Y et al. proposed a long-size FBG strain sensor with enhanced sensitivity, encapsulated by two T-shaped metal blocks. The strain sensitivity can be flexibly adjusted by changing the encapsulation method, achieving a strain sensitivity of 3.2 pm / με. Zhang R et al. ] A flexible hinge strain sensor using an FBG (Flexible Buckling Gear) as the sensing element was proposed. The sensor employs a bridge-type displacement amplification structure to increase the displacement and deformation of the measured object, achieving a strain sensitivity of 1.89 pm / με. Liang L et al. proposed a temperature-self-compensated FBG strain sensor with a strain sensitivity of 3.76 pm / με, virtually eliminating the influence of temperature. These research results have, to some extent, promoted the development of FBG strain sensors. However, the low sensitivity and the existence of temperature cross-sensitivity issues have continued to hinder the development of FBG strain sensors in strain measurement applications. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a strain sensor based on a flexible hinge and a testing method for a dual-fiber Bragg grating. The sensitivity of the strain sensor is theoretically analyzed, and the structural parameters are optimized. SolidWorks and ANSYS software are used to model and simulate the sensor. Based on the simulation results, a physical sensor is developed, and strain and temperature testing systems are built to test the sensor's performance.

[0005] On the one hand, a dual fiber Bragg grating strain sensor based on a flexible hinge is provided and installed inside a sealed barrel, including: a first transverse support arm and a second transverse support arm arranged parallel to each other; the second transverse support arm is located directly above the first transverse support arm.

[0006] The first end of the second transverse support arm is a free end, and the second end of the second transverse support arm is connected to the first end of the first flexible hinge; the second end of the first flexible hinge is connected to the upper end of the rectangular metal sheet, and the lower end of the rectangular metal sheet is fixed on the support frame; the support frame is located at the top of the inner side of the sealed barrel.

[0007] The first end of the first transverse support arm is connected to the first end of the second flexible hinge, and the second end of the second flexible hinge is fixed on the support frame; the second end of the first transverse support arm is connected to the first end of the elastic strain unit, and the second end of the elastic strain unit is connected to the second transverse support arm.

[0008] The lower middle point of the first horizontal support arm is connected to the first end of the third flexible hinge, and the second end of the third flexible hinge is connected to the upper end of the column; the lower end of the column is fixed at the center of the bottom of the sealed barrel.

[0009] The first end of the second transverse support arm is connected to the first end of the first fiber Bragg sensor; the second end of the first fiber Bragg sensor is connected to the first end of the first transverse support arm; and the first end of the second fiber Bragg sensor is connected to the second end of the first flexible hinge.

[0010] On the other hand, a testing method for a dual-fiber Bragg grating strain sensor based on a flexible hinge is provided, including:

[0011] Finite element analysis was performed on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

[0012] Performance testing was conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

[0013] Repeatability tests were conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

[0014] Linear response testing was performed on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

[0015] Temperature tests were conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

[0016] The above technical solution has the following advantages or beneficial effects:

[0017] To address the low sensitivity and temperature cross-sensitivity issues of current fiber Bragg grating (FBG) strain sensors, a dual-FBG strain sensor based on an integrated flexible hinge is proposed. A strain sensor model is developed and theoretical formulas are derived. Structural parameters are optimized using the controlled variable method. SolidWorks and ANSYS are used to model and simulate the sensor. Based on the simulation results, a physical sensor is fabricated, and strain and temperature testing systems are built to test its performance. The results show that the strain sensor has a sensitivity of 5.09 pm / με, approximately 4.2 times that of a bare FBG, with a linearity greater than 99%. It exhibits high sensitivity, good stability, and temperature compensation capabilities. These findings provide a new reference for the development of flexible hinge-based fiber Bragg grating strain sensors. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0019] Figure 1 This is a schematic diagram of the sensor structure in Example 1;

[0020] Figure 2 This is an equivalent force analysis diagram of the sensor in Example 1;

[0021] Figure 3(a) is a three-dimensional model of the straight circular flexible hinge of Embodiment 1;

[0022] Figure 3(b) is a planar model of the straight circular flexible hinge of Embodiment 1;

[0023] Figure 4 This is a planar uniaxial flexible hinge model of Example 1;

[0024] Figure 5(a) shows the effect of the flexible hinge parameter w on the sensitivity enhancement factor k in Example 1;

[0025] Figure 5(b) shows the effect of the flexible hinge parameter r on the sensitivity enhancement factor k in Example 1;

[0026] Figure 5(c) shows the effect of the flexible hinge parameter t on the sensitivity enhancement factor k in Example 1;

[0027] Figure 6 This is a sensor simulation analysis diagram from Example 1;

[0028] Figure 7(a) is a physical image of the sensor in Example 1;

[0029] Figure 7(b) is a sensor packaging diagram of Embodiment 1;

[0030] Figure 7(c) is a schematic diagram of the support frame structure of Embodiment 1;

[0031] Figure 8 The FBG strain sensor testing system of Example 1;

[0032] Figure 9(a) shows the time history curve of Example 1;

[0033] Figure 9(b) shows the effect of force on the center wavelength of the FBG in Example 1;

[0034] Figure 10 The effect of the load on the center wavelength drift of the FBG in Example 1;

[0035] Figure 11 The effect of the load on the center wavelength drift of the FBG in Example 1;

[0036] Figure 12 This is the temperature compensation experimental testing system of Example 1;

[0037] Figure 13 This illustrates the effect of ambient temperature on the center wavelength of the FBG in Example 1.

[0038] Among them, 1. First transverse support arm, 2. Second transverse support arm, 3. Sealed barrel, 4. Support frame, 5. First flexible hinge, 6. Second flexible hinge, 7. Elastic strain unit, 8. Third flexible hinge, 9. Column, 10. First fiber Bragg grating sensor, 11. Second fiber Bragg grating sensor, 12. Rectangular metal sheet. Detailed Implementation

[0039] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] Example 1

[0041] This embodiment provides a dual-fiber Bragg grating strain sensor based on a flexible hinge;

[0042] A dual-fiber Bragg grating strain sensor based on a flexible hinge is installed inside the sealed barrel 3, comprising:

[0043] A first transverse support arm 1 and a second transverse support arm 2 are arranged parallel to each other; the second transverse support arm 2 is located directly above the first transverse support arm 1.

[0044] The first end of the second transverse support arm 2 is a free end, and the second end of the second transverse support arm is connected to the first end of the first flexible hinge 5; the second end of the first flexible hinge 5 is connected to the upper end of the rectangular metal sheet 12, and the lower end of the rectangular metal sheet is fixed on the support frame 4; the support frame 4 is located at the top of the inner side of the sealing barrel 3.

[0045] The first end of the first transverse support arm 1 is connected to the first end of the second flexible hinge 6, and the second end of the second flexible hinge 6 is fixed on the support frame 4.

[0046] The second end of the first transverse support arm 1 is connected to the first end of the elastic strain unit 7, and the second end of the elastic strain unit 7 is connected to the second transverse support arm 2.

[0047] The lower middle position of the first horizontal support arm 1 is connected to the first end of the third flexible hinge 8, and the second end of the third flexible hinge 8 is connected to the upper end of the column 9; the lower end of the column 9 is fixed at the center of the bottom of the sealing barrel.

[0048] The first end of the second transverse support arm 2 is connected to the first end of the first fiber Bragg sensor 10; the second end of the first fiber Bragg sensor 10 is connected to the first end of the first transverse support arm 1.

[0049] The first end of the second fiber Bragg sensor 11 is connected to the second end of the first flexible hinge 5.

[0050] Furthermore, the longitudinal central axis of the first flexible hinge, the longitudinal central axis of the second flexible hinge, and the longitudinal central axis of the third flexible hinge are all perpendicular to the transverse central axis of the second transverse support arm.

[0051] Furthermore, the first flexible hinge, the second flexible hinge, and the third flexible hinge are all straight-round flexible hinges.

[0052] The first, second, and third flexible hinges have the same structure, each including a hinge body with symmetrical arc-shaped grooves on both sides of the hinge body.

[0053] The hinge body includes two horizontal posts and one vertical post. The two ends of the vertical post are respectively connected to the center points of the two horizontal posts. The vertical post has symmetrical arc-shaped grooves on both sides.

[0054] Furthermore, the elastic strain unit is an O-type elastic strain unit; the elastic strain unit includes an O-type ring, the top end of the outer surface of the O-type ring is connected to the second transverse support arm through a first metal rod; the bottom end of the outer surface of the O-type ring is connected to the first transverse support arm through a second metal rod.

[0055] There is a predetermined distance between the longitudinal central axis of the elastic strain unit and the longitudinal central axis of the first flexible hinge.

[0056] Furthermore, the support frame is a symmetrical portal frame, which includes two vertical rods and one horizontal rod. The two ends of the horizontal rod are connected to the ends of the two vertical rods respectively. The support frame is used to fix the second end of the second flexible hinge and the lower end of the rectangular metal sheet.

[0057] Strain sensor structural model as follows Figure 1 As shown, the strain sensor includes a dual fiber Bragg grating and an integrated flexible hinge structure. The integrated flexible hinge structure enhances the sensitivity of the strain sensor, while the dual fiber Bragg grating structure effectively avoids the problem of cross-sensitivity between strain and temperature. A plumb bob applies prestress to the optical fiber. The first fiber Bragg grating sensor is attached to different lever arms at both ends, sensitive to both strain and temperature. The second fiber Bragg grating sensor is attached to a fixed support at only one end to measure temperature changes and is unaffected by strain. Complete assembly of the fiber Bragg grating strain sensor requires mounting the sensor on a support frame and then installing it on a column inside a sealed cylinder.

[0058] Assuming the strain sensor only experiences elastic deformation via a flexible hinge within the mechanism, with the deformation remaining within linear limits and the components themselves being rigid, the internal structure of the strain sensor is simplified as a rod model. The specific force analysis of the sensor is as follows: Figure 2 As shown.

[0059] Furthermore, the flexible hinge-based dual-fiber Bragg grating strain sensor includes:

[0060] After being subjected to a uniform force, the base of the sealed barrel transmits the force to the column. The third flexible hinge, due to its stiffness, prevents the column from deforming upward. A force F is generated between the column and the third flexible hinge. Under the action of the force F, the first transverse support arm rotates upward counterclockwise around the second flexible hinge with a rotation angle of θ1.

[0061] According to the torque balance, the first transverse support arm also has an upward force F2 and a reaction force F1 generated by the elastic strain unit; under the action of force F2, the second transverse support arm is raised clockwise around the first flexible hinge with a rotation angle of θ2.

[0062] The strain ε of the strain sensor and the strain Δε of the first fiber Bragg grating sensor are expressed as follows:

[0063]

[0064] Among them, X in and X outThe input and output displacements are integrated into the flexible hinge structure; L is the distance between the two bonding points of the first fiber Bragg grating sensor; l4 is the length of the second lateral support arm; k is the sensor strain amplification factor; k1 = X. out / X in It is the displacement amplification factor generated by the integrated flexible hinge structure, and k2=l4 / L is the amplification factor generated by shortening the bonding distance; the integrated flexible hinge structure includes: a first flexible hinge, a second flexible hinge and a third flexible hinge.

[0065] When the first fiber Bragg sensor is subjected to only strain Δε, the relationship between the center wavelength and the strain is expressed as:

[0066]

[0067] It should be understood that the flexible hinge structure is the most critical part in a strain sensor. Taking a straight circular flexible hinge as an example, the dimensional parameters include the hinge radius r, thickness w, and narrowest width t, as shown in Figure 3(a). In order to better simulate the deformation of the flexible hinge, two conditions are usually assumed: (1) the deformation of the flexible hinge is limited to the hinge length, and the deformation of the outer parts at both ends is not considered; (2) the deformation of the flexible hinge is a small deformation, and the various deformations do not affect each other.

[0068] Furthermore, the working processes of the first flexible hinge, the second flexible hinge, and the third flexible hinge include:

[0069] The flexible hinge is analyzed by projecting it onto a two-dimensional plane using the method of infinitesimal elements.

[0070] The hinge width t varies with x, as shown in Figure 3(b).

[0071] The width t(x) and cross-sectional area A(x) of the infinitesimal element at the hinge are expressed as:

[0072]

[0073] like Figure 4 As shown, a planar uniaxial flexible hinge is modeled, with one end fixed and the other end stretched. Therefore, only its three degrees of freedom in the plane need to be considered: the tensile displacement u along the x-axis. x Displacement u along the y-axis y And the rotation angle θ around the z-axis z .

[0074] F x F y M z Acting on the right free end respectively, where u x Due to axial force F xGenerate, u y Force F in the vertical direction y Generate, θ z By M z and F y Generate. According to mechanics of materials, u x and u y Represented as

[0075]

[0076] In formula (4), E1 is the elastic modulus of the flexible hinge, E2 is the elastic modulus of the FBG, A(x) is the cross-sectional area at the micro-element, and d is the diameter of the first fiber grating Bragg sensor.

[0077] Combining equations (1) and (4), we obtain:

[0078]

[0079] As can be deduced above, the strain amplification factor k of the sensor is affected by the dimensional parameters of the flexible hinge and the integrated flexible hinge structure.

[0080] Furthermore, the relative wavelength drift of the first fiber Bragg grating sensor under the combined effects of temperature and strain is as follows:

[0081]

[0082] Where Δλ1 is the wavelength drift of the first fiber Bragg grating sensor, λ1 is the Bragg wavelength of the first fiber Bragg grating sensor, and P e ε is the effective optical elastic coefficient of the optical fiber, ε is the strain of the first fiber Bragg grating sensor, and ζ is the effective optical elastic coefficient of the optical fiber. f It is the thermo-optic coefficient of the optical fiber, α f It is the coefficient of thermal expansion of optical fiber, α s ΔT is the coefficient of thermal expansion of the lever arm material and ΔT is the temperature change of the optical fiber.

[0083] Furthermore, the relative wavelength drift of the second fiber Bragg sensor, under the influence of temperature alone, is as follows:

[0084]

[0085] In formula (7), Δλ2 is the wavelength drift of the second fiber grating Bragg sensor, and λ2 is the Bragg wavelength of the second fiber grating Bragg sensor. Two coefficients are set to simplify the equation:

[0086]

[0087] Combining equations (6) and (7), we get:

[0088]

[0089] According to equation (9), the design of the dual fiber grating Bragg sensor can effectively suppress the influence of temperature on strain measurement and reduce the cross-sensitivity problem between strain and temperature.

[0090] Furthermore, the radius of the first flexible hinge, the second flexible hinge, and the third flexible hinge ranges from 1.90 to 2.10 mm, the thickness ranges from 0.90 to 1.10 mm, and the narrowest width ranges from 0.90 to 1.10 mm; the length of the second lateral support arm is 25.5 mm.

[0091] For example, the radius r, thickness w, and narrowest width t of the flexible hinge are key parameters affecting the sensor's sensitivity enhancement factor k. Using the controlled variable method, with a given parameter, modeling and simulation were performed using SolidWorks and ANSYS software respectively. The sensor structure design considered the maximum stress the flexible hinge could withstand; excessive stress could lead to fiber grating breakage. Also considering the sensor's practical application, the sensor should be as miniaturized as possible while avoiding complex structural design. Therefore, parameters l4 = 25.5 mm, w range from 0.90 to 1.10 mm, r range from 1.90 to 2.10 mm, and t range from 0.90 to 1.10 mm were selected, resulting in fitting curves as shown in Figures 5(a), 5(b), and 5(c).

[0092] As shown in Figures 5(a), 5(b), and 5(c), k increases with increasing w and decreases with increasing r. With increasing t, k first increases and then decreases, reaching its maximum value at t ≈ 1.027 mm. In the sensor design, the main dimensions of the flexible hinge are selected as w = 1 mm, r = 2 mm, and t = 1 mm.

[0093] Example 2

[0094] The testing method for a dual-fiber Bragg grating strain sensor based on a flexible hinge includes:

[0095] S201: Perform finite element analysis on the dual-fiber Bragg grating strain sensor based on flexible hinge described in Example 1;

[0096] S202: Performance testing of the dual fiber Bragg grating strain sensor based on flexible hinge described in Example 1;

[0097] S203: Perform repeatability tests on the dual fiber Bragg grating strain sensor based on flexible hinges described in Example 1;

[0098] S204: Perform linear response testing on the dual fiber Bragg grating strain sensor based on flexible hinge described in Example 1;

[0099] S205: Conduct a temperature test on the dual fiber Bragg grating strain sensor based on a flexible hinge as described in Example 1.

[0100] Furthermore, the finite element analysis specifically includes:

[0101] Based on the determined sensor parameter values, a 3D model was created using SolidWorks software and imported into ANSYS software for finite element analysis. The sensor material properties were set to 304 stainless steel, with an elastic modulus of 200 GPa and a Poisson's ratio of 0.3, and the model was meshed. Constraints were applied to the bottom surfaces at both ends of the sensor, while the middle end, which is in contact with the column, was a free end with an upward vertical force F. y Given 20N, the total deformation contour map of the sensor in the Y direction is obtained, as shown below. Figure 6 As shown.

[0102] Depend on Figure 6 It can be seen that the strain of the sensor is concentrated on the flexible hinge and the lever arm. The fixed end provides sufficient stiffness support to ensure the normal operation of the sensor. After the applied force is applied to the integrated flexible hinge structure, the output end of the lever arm bears the maximum strain on the sensor, with a maximum deformation of 0.20518 mm, which is within the normal strain range of the fiber optic grating.

[0103] Furthermore, the performance test specifically includes:

[0104] A two-point bonding method is used to bond the optical fiber, thus avoiding chirping caused by uneven strain in the FBG grating region. First, one end of the optical fiber is bonded with UV adhesive and simultaneously irradiated with a UV lamp for 60 seconds to fix it. After resting for five minutes, the integrated flexible hinge structure is placed vertically, and a 20g weight is used to pull the optical fiber, applying a prestress. The optical fiber is then fixed using the same UV adhesive and UV lamp operation. Under the applied prestress, the two ends of the first fiber grating Bragg sensor are bonded to different lever arms using UV adhesive. Simultaneously, one end of the second fiber grating Bragg sensor is bonded to the fixed support, and the assembled strain sensor is installed on the internal column.

[0105] Based on the structural optimization and simulation analysis results, the physical prototypes of the FBG strain sensor were developed, as shown in Figures 7(a), 7(b), and 7(c).

[0106] The fiber optic strain sensor testing system mainly consists of a universal testing machine, an FBG demodulator, and a computer.

[0107] The universal testing machine has a maximum force of 5kN, an effective force measurement range of 0.4% to 100% (0.5 grade), and a resolution of 1 / 300,000 of the maximum load. It is suitable for testing metallic and non-metallic materials.

[0108] The FBG demodulator has a sampling frequency of up to 1kHz and a built-in laser light source. The emitted light waves are transmitted to the strain sensor through optical fiber, and spectral analysis and data acquisition can be completed internally. Finally, the acquired data is analyzed.

[0109] The entire testing system consists of two computers: one controls the operation of the universal testing machine, and the other collects data acquired by the FBG demodulator. Using this equipment, a strain sensor testing system was built to study the linear response characteristics and repeatability of the FBG strain sensor, such as… Figure 8 As shown.

[0110] Furthermore, the repeatability test includes:

[0111] The strain sensor was fixed in a tensile testing machine, and after prestressing was applied to both ends of the reference FBG, it was adhered to the inner wall of the cylinder. The tensile load of the tensile testing machine was increased from 0N to 2000N in increments of 200N. After each loading process, the load was paused for 10 seconds to allow the center wavelength to stabilize before recording the experimental data. Then, the tensile testing machine was unloaded in the same increments, gradually decreasing to 0N. This process constituted one experimental cycle. The experimental cycle was repeated three times to test the stability of the sensor's output response.

[0112] The three repeatability experiments are shown in Figure 9(a) and Figure 9(b). In the repeatability experiments, the center wavelength of the strain sensor FBG drifts significantly with the change of external pressure.

[0113] As shown in Figure 9(a), the changes in the center wavelength of the first fiber grating Bragg sensor were basically the same in the three experiments. Figure 9(b) shows the linear relationship between the force and the drift of the FBG center wavelength. As shown in the figure, the sensor has good stability.

[0114] The repeatability error of a sensor is represented by the relative standard deviation (RSD), expressed as follows:

[0115]

[0116] Where SD is the standard deviation. This represents the corresponding average value.

[0117] The calculation of the experimental data using the formula shows that the repeatability error of the strain sensor in three experiments is 0.9%, indicating that the designed sensor has a small repeatability error and good stability.

[0118] Furthermore, the linear response test includes:

[0119] To obtain the linearity and sensitivity parameters of the strain sensor, the working load range of the tensile tester was increased from 0N to 2000N in 200N increments. After the center wavelength stabilized, the experimental data were recorded. After the load was increased to the maximum, the load was also unloaded in 200N increments, and the data was recorded.

[0120] The above process constitutes one cycle. The experiment was repeated three times to obtain the effect of different loads on the center wavelength drift of the FBG, such as... Figure 10 As shown in the figure, the linear fitting curves of the strain sensor and the reference FBG show that the sensitivity enhancement factor k of the strain sensor compared to the reference FBG is approximately 4.47.

[0121] The relationship between the center wavelength drift of the sensor and strain is as follows: Figure 11 As shown in the figure, the sensitivity of the strain sensor is 5.09 pm / με, and the average linear correlation coefficient R is... 2 =0.999, the sensitivity of the strain sensor is about 4.2 times that of the theoretical sensitivity of bare FBG 1.21pm / με, which is basically consistent with the experimental value of 4.47, but there is still a certain deviation, which may be related to the processing accuracy of the sensor and the loosening of the clamps of the universal testing machine during the tensile process.

[0122] Furthermore, the temperature test includes:

[0123] The temperature experimental system consists of an FBG demodulator, a temperature control chamber, and a computer, such as... Figure 12 As shown.

[0124] The temperature control chamber can measure temperatures between -70°C and 170°C with an accuracy of ±0.01°C, a fluctuation of no more than ±0.5°C, and a deviation of no more than ±2.0°C, fully meeting the high-precision temperature control requirements of this experiment. The FBG strain sensor was placed inside the temperature control chamber, and the temperature was adjusted every 20 minutes. The temperature setting range was -20°C to 40°C, with a step size of 10°C. Data was recorded and linear fitting analysis was performed. The experimental results are as follows: Figure 13 As shown.

[0125] Depend on Figure 13 It can be seen that the center wavelength of the two fiber Bragg sensors drifts at different temperatures. The temperature sensitivity coefficients of the first and second fiber Bragg sensors are 21.03 pm / ℃ and 10.23 pm / ℃, respectively, and the fitted linear correlation coefficient R0 is [missing value]. 2All are 0.999. After obtaining the temperature sensitivity of the two fiber Bragg sensors, according to formula (9), the accurate temperature measured by the second fiber Bragg sensor can be used for strain calculation, avoiding the influence of temperature on strain measurement. The maximum change in the temperature range of -20 to 40℃ is 23.3 pm, which can realize the self-compensation function for changes in ambient temperature.

[0126] Table 1 Comparison of Sensor Performance

[0127]

[0128] Table 1 compares the performance of the FBG strain sensor proposed in this invention with that of strain sensors in other papers. As can be seen from Table 1, the FBG strain sensor proposed in this invention has high sensitivity and good performance, and also features temperature compensation, which can reduce the impact of temperature on the FBG strain sensor.

[0129] This invention proposes a dual-FBG strain sensor based on a flexible hinge structure. The design employs an integrated flexible hinge structure, using two FBGs respectively bonded between two lever arms and to a fixed support. Through a research method combining simulation analysis and experimental verification, the designed sensor was optimized and its performance tested. Results show that the sensor's strain measurement sensitivity is 5.09 pm / με, approximately 4.2 times that of a bare FBG, with a linearity greater than 99% and a repeatability relative standard deviation of 0.9%. Compared to other FBG strain sensors, this sensor has advantages such as high sensitivity, small size, high linearity, and temperature compensation, and can be used for stable strain measurement.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-fiber Bragg grating strain sensor based on a flexible hinge, characterized in that, Installed inside the sealed barrel, it includes: a first transverse support arm and a second transverse support arm arranged parallel to each other; the second transverse support arm is located directly above the first transverse support arm; The first end of the second transverse support arm is a free end, and the second end of the second transverse support arm is connected to the first end of the first flexible hinge; the second end of the first flexible hinge is connected to the upper end of the rectangular metal sheet, and the lower end of the rectangular metal sheet is fixed on the support frame; the support frame is located at the top of the inner side of the sealed barrel. The first end of the first transverse support arm is connected to the first end of the second flexible hinge, and the second end of the second flexible hinge is fixed on the support frame; the second end of the first transverse support arm is connected to the first end of the elastic strain unit, and the second end of the elastic strain unit is connected to the second transverse support arm. The lower middle point of the first horizontal support arm is connected to the first end of the third flexible hinge, and the second end of the third flexible hinge is connected to the upper end of the column; the lower end of the column is fixed at the center of the bottom of the sealed barrel. The first end of the second transverse support arm is connected to the first end of the first fiber Bragg sensor; the second end of the first fiber Bragg sensor is connected to the first end of the first transverse support arm; and the first end of the second fiber Bragg sensor is connected to the second end of the first flexible hinge.

2. The dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 1, characterized in that, The longitudinal central axis of the first flexible hinge, the longitudinal central axis of the second flexible hinge, and the longitudinal central axis of the third flexible hinge are all perpendicular to the transverse central axis of the second transverse support arm; the first flexible hinge, the second flexible hinge, and the third flexible hinge are all straight-round flexible hinges; the first flexible hinge, the second flexible hinge, and the third flexible hinge have the same structure, each including a hinge body, with symmetrical arc-shaped grooves on both sides of the hinge body.

3. The dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 1, characterized in that, The elastic strain unit is an O-type elastic strain unit; the elastic strain unit includes an O-type ring, the top end of the outer surface of the O-type ring is connected to the second transverse support arm through a first metal rod; the bottom end of the outer surface of the O-type ring is connected to the first transverse support arm through a second metal rod; the support frame is a left-right symmetrical portal frame, the support frame includes two vertical rods and one horizontal rod, the two ends of the horizontal rod are respectively connected to the ends of the two vertical rods, and the support frame is used to fix the second end of the second flexible hinge and the lower end of the rectangular metal sheet.

4. The dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 1, characterized in that, The flexible hinge-based dual-fiber Bragg grating strain sensor includes: After being subjected to a uniform force, the base of the sealed barrel transmits the force to the column. The third flexible hinge, due to its stiffness, prevents the column from deforming upward. A force F is generated between the column and the third flexible hinge. Under the action of the force F, the first transverse support arm rotates upward counterclockwise around the second flexible hinge with a rotation angle of θ1. According to the torque balance, the first transverse support arm also has an upward force F2 and a reaction force F1 generated by the elastic strain unit; under the action of force F2, the second transverse support arm is raised clockwise around the first flexible hinge with a rotation angle of θ2. The strain ε of the strain sensor and the strain Δε of the first fiber Bragg grating sensor are expressed as follows: Among them, X in and X out The input and output displacements are integrated into the flexible hinge structure; L is the distance between the two bonding points of the first fiber Bragg grating sensor; l4 is the length of the second lateral support arm; k is the sensor strain amplification factor; k1 = X. out / X in It is the displacement amplification factor generated by the integrated flexible hinge structure, and k2=l4 / L is the amplification factor generated by shortening the bonding distance; the integrated flexible hinge structure includes: a first flexible hinge, a second flexible hinge and a third flexible hinge.

5. The dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 1, characterized in that, The working processes of the first flexible hinge, the second flexible hinge, and the third flexible hinge include: The flexible hinge is analyzed using the infinitesimal element method by projecting it onto a two-dimensional plane; the hinge width t varies with x; the infinitesimal element width t(x) and cross-sectional area A(x) at the hinge are expressed as: Modeling a planar uniaxial flexible hinge, where one end is fixed and the other is stretched, we only need to consider its three degrees of freedom in the plane: the tensile displacement u along the x-axis. x Displacement u along the y-axis y And the rotation angle θ around the z-axis z ; F x F y M z Acting on the right free end respectively, where u x Due to axial force F x Generate, u y Force F in the vertical direction y Generate, θ z By M z and F y Generate; according to mechanics of materials, u x and u y Represented as: In formula (4), E1 is the elastic modulus of the flexible hinge, E2 is the elastic modulus of the FBG, A(x) is the cross-sectional area at the micro-element, and d is the diameter of the first fiber grating Bragg sensor. Combining equations (1) and (4), we obtain: As can be deduced above, the strain amplification factor k of the sensor is affected by the dimensional parameters of the flexible hinge and the integrated flexible hinge structure.

6. The dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 1, characterized in that, The relative wavelength drift of the first fiber Bragg grating sensor under the combined effects of temperature and strain is: Where Δλ1 is the wavelength drift of the first fiber Bragg grating sensor, λ1 is the Bragg wavelength of the first fiber Bragg grating sensor, and P e ε is the effective optical elastic coefficient of the optical fiber, ε is the strain of the first fiber Bragg grating sensor, and ζ is the effective optical elastic coefficient of the optical fiber. f It is the thermo-optic coefficient of the optical fiber, α f It is the coefficient of thermal expansion of optical fiber, α s The coefficient of thermal expansion of the lever arm material and ΔT represent the temperature change of the optical fiber. The second fiber Bragg sensor exhibits the following relative wavelength drift under temperature influence only: In formula (7), Δλ2 is the wavelength drift of the second fiber grating Bragg sensor, and λ2 is the Bragg wavelength of the second fiber grating Bragg sensor; two coefficients are set to simplify the equation: Combining equations (6) and (7), we get: According to equation (9), the design of the dual fiber grating Bragg sensor suppresses the influence of temperature on strain measurement and reduces the cross-sensitivity problem between strain and temperature.

7. A testing method for a dual-fiber Bragg grating strain sensor based on a flexible hinge, characterized in that... include: Finite element analysis was performed on a dual-fiber Bragg grating strain sensor based on a flexible hinge. Performance testing was conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge. Repeatability tests were conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge. Linear response testing was performed on a dual-fiber Bragg grating strain sensor based on a flexible hinge. Temperature tests were conducted on a dual-fiber Bragg grating strain sensor based on a flexible hinge.

8. The testing method for the dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 7, characterized in that, The finite element analysis specifically includes: Based on the determined sensor parameter values, a 3D model was created using SolidWorks software and imported into ANSYS software for finite element analysis. The sensor material properties were set to 304 stainless steel, with an elastic modulus of 200 GPa and a Poisson's ratio of 0.3, and the model was meshed. Constraints were applied to the bottom surfaces at both ends of the sensor, while the middle end, which is in contact with the column, was a free end with an upward vertical force F. y With a value of 20N, the total deformation contour map of the sensor in the Y direction is obtained.

9. The testing method for the dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 7, characterized in that, The performance test specifically includes: using a two-point bonding method to bond the optical fiber. First, one end of the optical fiber is bonded with UV adhesive and simultaneously irradiated with a UV lamp for 60 seconds to fix it. After resting for five minutes, the integrated flexible hinge structure is placed vertically, and a 20g weight is used to pull the optical fiber to apply a prestress. Then, the optical fiber is fixed with UV adhesive and UV lamp in the same way. Under the applied prestress, the two ends of the first fiber grating Bragg sensor are bonded to different lever arms using UV adhesive. At the same time, one end of the second fiber grating Bragg sensor is bonded to the fixed support, and the assembled strain sensor is installed on the inner column of the cylinder.

10. The testing method for the dual-fiber Bragg grating strain sensor based on a flexible hinge as described in claim 7, characterized in that, The repeatability test includes: fixing the strain sensor in a tensile testing machine, applying prestress to both ends of the reference FBG and then attaching it to the inner side of the cylinder wall; increasing the tensile load of the tensile testing machine from 0N to 2000N in increments of 200N, pausing for 10 seconds after each loading process, waiting for the center wavelength to stabilize, and then recording the experimental data; then unloading the tensile testing machine in the same increments, gradually reducing it to 0N, and this process constitutes one experimental cycle; repeating the experimental cycle three times to test the stability of the sensor output response; the linear response test includes: in order to obtain the linearity and sensitivity parameters of the strain sensor, setting the working load range of the tensile testing machine from 0N to 2000N in increments of 200N, waiting for the center wavelength to stabilize, recording the experimental data, and then unloading the load in increments of 200N after it reaches its maximum and recording the data.

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