A connecting rod deformation detection method based on fiber grating sensors

Abstract

This invention discloses a method for detecting link deformation based on fiber Bragg grating sensors, including steps such as establishing a finite element model of the link, finite element analysis, designing the arrangement scheme of the fiber Bragg grating sensors, calibration of two types of fiber Bragg grating sensors, experimental preparation for the link under test, loading experiment of the link under test, calculation of deformation parameters, reconstruction of each structural unit of the link, reconstruction of the overall structure of the link, and comparison of deformation detection results. Beneficial effects: This invention can utilize fiber Bragg grating sensors to perform overall deformation detection on links involving both thin-walled annular structures and long rod structures; it can output detection results more intuitively and accurately, providing a new and feasible method for accurate detection of link performance and deformation detection of other critical components in marine power equipment.

Description

Technical Field

[0001] This invention relates to a method for detecting engine connecting rod deformation, and more particularly to a method for detecting connecting rod deformation based on a fiber optic grating sensor, belonging to the field of structural component deformation detection technology. Background Technology

[0002] Connecting rods are an important component of engines in automobiles, ships, and other vehicles. Their performance directly affects the overall performance. When connected rods are subjected to force, they will deform, including bending and twisting. These deformations may cause the crankshaft to become obstructed or stuck, and in severe cases, they may even damage the engine block.

[0003] The connecting rod is a transmission device that connects the piston and the crankshaft, transmits the force on the piston to the crankshaft, and converts the reciprocating motion of the piston into the rotational motion of the crankshaft.

[0004] The connecting rod consists of three parts: the part connected to the piston pin is called the small end; the part connected to the crankshaft is called the big end; and the section connecting the small end and the big end is called the connecting rod body. The small end and big end are thin-walled annular structures, while the connecting rod body is a long rod. The deformation of the connecting rod mainly occurs in these three parts; therefore, obtaining an accurate and reliable deformation detection method that can be used in practice is particularly important.

[0005] With the development of high-end equipment and its increasing precision, accurate detection of connecting rod deformation is particularly urgent. It is essential not only to understand the patterns of deformation but also to achieve high-precision measurement. However, because connecting rods operate at high speeds during installation, current technology cannot directly measure their deformation with high precision. Currently, connecting rod deformation detection mainly relies on experimental analysis to infer the deformation of connecting rods from the same batch or those with the same structure.

[0006] The most common methods for detecting deformation during experiments include strain gauge testing, visual inspection, laser scanning testing, and methods using fiber optic grating sensors. While strain gauge testing utilizes small, lightweight strain gauges that easily conform to the object being measured, various interference factors in practical applications can cause measurement instability and lead to deviations in accuracy. Visual inspection, although efficient, does not require contact with the object, and is relatively inexpensive, cannot detect internal deformations in practical applications, and is impossible when vision is limited. Laser scanning testing does not require contact with the object, complex post-processing and calculations, and offers high accuracy; however, it is easily affected by environmental interference in practical applications and is difficult to implement for dynamic measurements.

[0007] The method of using fiber Bragg grating sensors for detection is commonly used to detect the local deformation of various important components. Since the connecting rod assembly involves both thin-walled circular structure and long rod, which is a composite structure, a single fiber Bragg grating sensor cannot complete the overall deformation detection of the connecting rod. Summary of the Invention

[0008] Purpose of the invention: The purpose of this invention is to address the problem in the prior art that it is impossible to accurately detect the deformation of engine connecting rods, and to propose a connecting rod deformation detection method based on a fiber optic grating sensor.

[0009] Technical solution: A method for detecting link deformation based on fiber Bragg grating sensors, comprising the following steps:

[0010] Step 1: Establish the finite element model of the connecting rod. Based on the structural dimensions of the connecting rod to be tested, the elastic modulus of the material, and Poisson's ratio, establish the finite element model of the connecting rod.

[0011] Step 2: Finite element analysis. By applying simulated loads to the finite element model of the connecting rod to be tested established in Step 1, the deformation of the connecting rod is analyzed, and the simulated deformation types and simulated deformation amounts of the small end, big end and body of the connecting rod are obtained respectively.

[0012] Step 3: Design the arrangement scheme of fiber Bragg grating sensors. Based on the simulated deformation type and simulated deformation amount in Step 2, design the distribution of fiber Bragg grating sensors at the small end, large end, and body of the connecting rod.

[0013] Step 4: Calibration of two types of fiber Bragg grating sensors. Design calibration experiments for helical fiber Bragg grating sensors for the small end and large end of the connecting rod, and for fiber Bragg grating sensors for the inclined shaft of the connecting rod. Based on the wavelength offset of the fiber Bragg grating sensor, determine the correspondence between the wavelength offset of the fiber Bragg grating sensor and the displacement and curvature, and complete the calibration of the two types of fiber Bragg grating sensors.

[0014] Step 5: Preparation for the test of the connecting rod. Arrange the fiber optic grating sensor according to the design scheme in Step 3, connect the data acquisition equipment, connect the fiber optic grating sensor to the fiber optic grating sensor demodulator, and connect the fiber optic grating sensor demodulator to the host computer through the data connector. The center wavelength of the fiber optic grating sensor is demodulated by the fiber optic grating sensor demodulator and transmitted to the host computer.

[0015] Step 6: Loading experiment on the connecting rod under test. Simulated load experiments are conducted on the small end, large end and body of the connecting rod respectively. When the connecting rod deforms, the center wavelength of each fiber optic grating sensor changes. The offset of the center wavelength is obtained according to the calibration results in Step 4.

[0016] Step 7: Calculate deformation parameters. The host computer calculates the deformation curvature k and the arc length l after deformation at each measuring point based on the changes obtained in Step 6.

[0017] Step 8: Reconstruct each structural unit of the connecting rod. Based on the deformation reconstruction method, use the deformation information of each structural unit to reconstruct the small end, big end, and body structure of the connecting rod respectively.

[0018] Step 9: Reconstruct the overall structure of the link. Based on the reconstruction algorithm, combine the structural units from Step 8 into a whole to complete the reconstruction of the overall structure of the link.

[0019] Step 10: Comparison of deformation detection results. Compare the results of finite element model simulation analysis with experimental results to determine the true deformation type and amount of the connecting rod under test.

[0020] This invention utilizes finite element analysis (FEM) to determine the deformation types of the small and large ends of the connecting rods under test. These deformations are identified as planar drum-shaped, inclined drum-shaped, and bent, while the rod body undergoes bending deformation. Based on the simulated deformation types and amounts obtained from the FEM analysis, fiber optic grating (FBG) sensor arrangement schemes are designed. For the two deformation modes, spiral and inclined FBG sensor arrangements are used respectively, and calibration experiments are conducted to determine the correspondence between the FBG sensor wavelength offset and displacement and curvature. After obtaining the calibrated correspondence, experimental testing is performed on the connecting rods under test. Data collected during the experiments is used to reconstruct the structural units of the connecting rod and the overall structure of the connecting rod. The results of the FEM simulation analysis are compared with the experimental results to determine the true deformation type and amount of the connecting rod under test. This invention provides a more intuitive and accurate output of test results, offering a new and feasible method for the precise testing of connecting rod performance and the deformation detection of other critical components in marine power equipment.

[0021] In a preferred embodiment, in order to achieve accurate detection of the thin-walled annular structure, the fiber Bragg grating sensors on the small end and large end of the connecting rod in step three are arranged in the same spiral shape, evenly distributed on the inner walls of the small end and large end of the connecting rod. The spiral angle of the fiber Bragg grating sensor on the large end of the connecting rod is α, and the spiral angle of the fiber Bragg grating sensor on the small end of the connecting rod is β.

[0022] In a preferred embodiment, while ensuring detection effectiveness, the fiber Bragg grating sensor arrangement is convenient. The number of fiber Bragg grating sensors on the small and large ends of the connecting rod is at least two, and each fiber Bragg grating sensor has at least two grating points. In the case of a helical fiber Bragg grating sensor arrangement, this invention, through algorithmic reconstruction and data measured from a limited number of grating points, can deduce the overall deformation of the small and large ends of the connecting rod. This facilitates the arrangement of the fiber Bragg grating sensors while reducing the number of grating points in the sensors, thus saving costs.

[0023] In a preferred embodiment, to further improve the rationality and accuracy of the fiber Bragg grating sensor arrangement on the thin-walled annular structure, the helix angle of the fiber Bragg grating sensor on the large end of the connecting rod is determined to be α, and the helix angle of the fiber Bragg grating sensor on the small end of the connecting rod is determined to be β.

[0024] The method for determining the helix angle of a fiber Bragg grating sensor is the same, and the specific steps are as follows:

[0025] Step 4.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between axial strain and helix angle can be obtained as follows:

[0026]

[0027] In the formula: ε is the strain of the helical fiber Bragg grating sensor, α is the helix angle, and ε b For axial strain, μ is the Poisson's ratio of the material;

[0028] Step 4.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the helix angle range, and determine the corresponding axial strain using the relational formula;

[0029] Step 4.3 Due to the following relationship between axial strain and transverse strain:

[0030] ε a =-με b

[0031] Where: ε a For transverse strain, ε b For axial strain, μ is the Poisson's ratio of the material;

[0032] Step 4.4 The Poisson's ratio of the material is known. The corresponding axial strain can be determined according to the helix angle range set in the tensile test. From the relationship between axial strain and transverse strain, it can be seen that when the axial strain is the maximum, the absolute value of the transverse strain is the maximum value. Therefore, the angle with the maximum axial strain is selected as the helix angle.

[0033] In a preferred embodiment, in order to achieve accurate detection of the deformation of the connecting rod body, the fiber optic grating sensors on the connecting rod body in step three are arranged such that one fiber optic grating sensor with the same tilt angle is set on each of the two adjacent sides and is centrally symmetrically distributed on the surface of the connecting rod body, wherein the tilt angle is γ.

[0034] Preferably, to improve the accuracy of detecting the deformation of the connecting rod, the fiber Bragg grating sensors on adjacent side surfaces of the connecting rod are tilted in opposite directions, and each fiber Bragg grating sensor has at least two grating points. Arranging the fiber Bragg grating sensors on adjacent side surfaces of the connecting rod with opposite tilt directions facilitates sensor placement and reduces costs while ensuring detection accuracy.

[0035] Preferably, to further improve the accuracy of detecting the deformation of the connecting rod, the tilt angle of the fiber optic grating sensor on the connecting rod is γ. The specific steps for determining the tilt angle are as follows:

[0036] Step 7.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between longitudinal strain and tilt angle can be obtained as follows:

[0037]

[0038] In the formula: ε is the strain of the fiber Bragg grating sensor, γ is the tilt angle, and ε d For longitudinal strain, μ is the Poisson's ratio of the material;

[0039] Step 7.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the tilt angle range, and determine the corresponding longitudinal strain using the relationship formula;

[0040] Step 7.3 Due to the following relationship between longitudinal strain and transverse strain:

[0041] ε c =-με d

[0042] Where: ε c For transverse strain, ε d For longitudinal strain, μ is the Poisson's ratio of the material;

[0043] Step 7.4 The Poisson's ratio of the material is known. The corresponding longitudinal strain can be determined according to the inclination angle range set in the tensile test. From the relationship between longitudinal strain and transverse strain, it can be seen that when the longitudinal strain is the maximum, the absolute value of the transverse strain is the maximum value. Therefore, the angle with the maximum longitudinal strain is selected as the helix angle.

[0044] In a preferred embodiment, to achieve the reconstructed shape of the small end and the large end of the connecting rod after deformation, the deformation curvature k and the arc length l of the small end and the large end of the connecting rod in step seven are...

[0045] The steps for calculating the deformation at the corresponding measuring point are as follows:

[0046] Based on the relationship between the wavelength and strain of the fiber Bragg grating sensor and the sensing principle of the helical fiber Bragg grating sensor under tension, the strain is calculated as follows:

[0047]

[0048]

[0049] In the formula: λ B Δλ is the Bragg wavelength, measured in nm. Bε is the wavelength shift in nm, p is the strain of the helical FBG, and p is the wavelength shift in nm. e α is the photoelastic coefficient, with units of nm / με. T ζ is the thermal expansion coefficient of the grating, α is the photothermal coefficient of the grating, and ε is the helix angle. b For axial strain, μ is the Poisson's ratio of the material;

[0050] The change in axial length due to deformation is calculated based on the relationship between strain and length.

[0051] Δb=ε b *b

[0052] In the formula: Δb is the change in axial length, ε b y is the axial strain, b is the pitch;

[0053] The length l of the busbar containing the j-th grating point of the i-th fiber optic grating sensor is calculated based on the change in axial length. ij (i = 1, 2, 3, 6, 7, 8; j = 1, 2, ...) is:

[0054] l ij =l-Δb ij

[0055] Given the radius r of the inner wall of the connecting rod, then the deflection angle φ between the bending direction and the base coordinates... j and curvature k j for:

[0056]

[0057]

[0058] The data from each fiber Bragg grating sensor is fused to obtain the reconstructed shape of the deformation of the big end and small end of the connecting rod.

[0059] In a preferred embodiment, in order to achieve accurate detection of the deformation of the connecting rod body, the calibration experimental method for the inclined fiber optic grating sensor in step four is to use a standard curvature mold, determine the correspondence between the wavelength offset of the fiber optic grating sensor and the curvature based on the change of the wavelength offset of the fiber optic grating sensor under different curvatures, and complete the calibration of the fiber optic grating sensor.

[0060] In a preferred embodiment, to reconstruct the shape of the connecting rod body after deformation, the method for reconstructing the connecting rod body using deformation information in step eight is as follows:

[0061] The curvature K of the corresponding measuring points on the connecting rod body is obtained according to the calibration method in step four.

[0062] Based on the calibration relationship, the radius R corresponding to the j-th grating point of the fiber Bragg grating sensor can be obtained.ij (i = 4, 5; j = 1, 2, ...) is:

[0063]

[0064] From radius R ij The arc length l of the deformed rod can be obtained from the length d of the connecting rod body. ij for:

[0065]

[0066] The data from each fiber Bragg grating sensor is fused to obtain the reconstructed shape of the connecting rod body deformation.

[0067] Beneficial effects: This invention can use fiber optic grating sensors to perform overall deformation detection on connecting rods that involve both thin-walled annular structures and long rod structures; it can output detection results more intuitively and accurately, providing a new and feasible method for accurate detection of connecting rod performance and deformation detection of other critical components of marine power equipment. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0069] Figure 1 This is a flowchart of the detection method of the present invention;

[0070] Figure 2 This is a schematic diagram of the fiber optic grating sensor of the present invention;

[0071] Figure 3 This is a schematic diagram of the standard curvature mold of the present invention;

[0072] Figure 4 This is a schematic diagram showing the arrangement of the fiber optic grating sensor of the present invention on the connecting rod;

[0073] Figure 5 This is a schematic diagram of the detection system of the present invention;

[0074] Figure 6 This is a schematic diagram of the finite element model of the connecting rod and the path selection of the present invention;

[0075] Figure 7 This is a schematic diagram of the deformation of the thin-walled annular structure of the small end and large end of the connecting rod of the present invention. Detailed Implementation

[0076] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0077] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0078] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0079] like Figure 1 As shown, a method for detecting link deformation based on a fiber Bragg grating sensor includes the following steps:

[0080] Step 1: Establish the finite element model of the connecting rod. Based on the structural dimensions of the connecting rod to be tested, the elastic modulus of the material, and Poisson's ratio, establish the finite element model of the connecting rod.

[0081] Step 2: Finite element analysis. By applying simulated loads to the finite element model of the connecting rod to be tested established in Step 1, the deformation of the connecting rod is analyzed, and the simulated deformation types and simulated deformation amounts of the small end, big end and body of the connecting rod are obtained respectively.

[0082] Step 3: Design the arrangement scheme of fiber Bragg grating sensors. Based on the simulated deformation type and simulated deformation amount in Step 2, design the distribution of fiber Bragg grating sensors at the small end, large end, and body of the connecting rod.

[0083] Step 4: Calibration of two types of fiber Bragg grating sensors. Design calibration experiments for helical fiber Bragg grating sensors for the small end and large end of the connecting rod, and for fiber Bragg grating sensors for the inclined shaft of the connecting rod. Based on the wavelength offset of the fiber Bragg grating sensor, determine the correspondence between the wavelength offset of the fiber Bragg grating sensor and the displacement and curvature, and complete the calibration of the two types of fiber Bragg grating sensors.

[0084] Step 5: Preparation for the test of the connecting rod. Arrange the fiber optic grating sensor according to the design scheme in Step 3, connect the data acquisition equipment, connect the fiber optic grating sensor to the fiber optic grating sensor demodulator, and connect the fiber optic grating sensor demodulator to the host computer through the data connector. The center wavelength of the fiber optic grating sensor is demodulated by the fiber optic grating sensor demodulator and transmitted to the host computer.

[0085] Step 6: Loading experiment on the connecting rod under test. Simulated load experiments are conducted on the small end, large end and body of the connecting rod respectively. When the connecting rod deforms, the center wavelength of each fiber optic grating sensor changes. The offset of the center wavelength is obtained according to the calibration results in Step 4.

[0086] Step 7: Calculate deformation parameters. The host computer calculates the deformation curvature k and the arc length l after deformation at each measuring point based on the changes obtained in Step 6.

[0087] Step 8: Reconstruct each structural unit of the connecting rod. Based on the deformation reconstruction method, use the deformation information of each structural unit to reconstruct the small end, big end, and body structure of the connecting rod respectively.

[0088] Step 9: Reconstruct the overall structure of the link. Based on the reconstruction algorithm, combine the structural units from Step 8 into a whole to complete the reconstruction of the overall structure of the link.

[0089] Step 10: Comparison of deformation detection results. Compare the results of finite element model simulation analysis with experimental results to determine the true deformation type and amount of the connecting rod under test.

[0090] This invention utilizes finite element analysis (FEM) to determine the deformation types of the small and large ends of the connecting rods under test. These deformations are identified as planar drum-shaped, inclined drum-shaped, and bent, while the rod body undergoes bending deformation. Based on the simulated deformation types and amounts obtained from the FEM analysis, fiber optic grating (FBG) sensor arrangement schemes are designed. For the two deformation modes, spiral and inclined FBG sensor arrangements are used respectively, and calibration experiments are conducted to determine the correspondence between the FBG sensor wavelength offset and displacement and curvature. After obtaining the calibrated correspondence, experimental testing is performed on the connecting rods under test. Data collected during the experiments is used to reconstruct the structural units of the connecting rod and the overall structure of the connecting rod. The results of the FEM simulation analysis are compared with the experimental results to determine the true deformation type and amount of the connecting rod under test. This invention provides a more intuitive and accurate output of test results, offering a new and feasible method for the precise testing of connecting rod performance and the deformation detection of other critical components in marine power equipment.

[0091] like Figure 4 and 5 As shown, a link deformation detection system based on fiber Bragg grating sensors includes a link under test 1, multiple spirally arranged fiber Bragg grating sensors 2, a demodulator 3, a main unit 4, and a display 5. A schematic diagram is shown below. Figure 4 and 5 As shown, multiple fiber Bragg grating sensors 2 are connected in parallel. A group of three fiber Bragg grating sensors 2 with a helix angle of α is distributed on the inner wall of the large end of the connecting rod, and a group of three fiber Bragg grating sensors 2 with a helix angle of β is distributed on the inner wall of the small end of the connecting rod. The same group of fiber Bragg grating sensors 2 are spaced 120° apart. The wavelength data from the fiber Bragg grating sensors 2 arranged on the connecting rod body of the connecting rod under test are demodulated and output by a demodulator 3. The demodulator 3 is connected to the host computer 4 via a communication interface. The center wavelength of the fiber Bragg grating sensors is demodulated by the demodulator 3 and transmitted to the host computer 4. The data information from each fiber Bragg grating sensor is fused and displayed on the display 5 to reconstruct the structure of the small end, large end, and connecting rod body of the connecting rod. The structural units are then combined into a whole to complete the reconstruction of the overall connecting rod structure. The results of the finite element model simulation analysis are compared with the experimental results to obtain the true deformation type and amount of the connecting rod under test, providing a direct and accurate detection result.

[0092] like Figure 6 and 7As shown, a finite element model of the connecting rod was established based on its structural dimensions, material elastic modulus, and Poisson's ratio. Finite element analysis of its deformation was performed using Ansys. The model material was structural steel with a Poisson's ratio of 0.3 and a density of 7850 kg / m³. Triangular elements were used for meshing, with an element size of 1 mm, resulting in 836,385 elements and 1,176,939 nodes. By applying loads of different magnitudes and directions to the large end of the connecting rod, the deformation of the large end can be categorized into three different cases (e.g., ...). Figure 7 (As shown): planar drum shape, inclined drum shape, and curved shape.

[0093] like Figure 1 and 4 As shown, the fiber Bragg grating sensors on the small and large ends of the connecting rod are arranged in the same spiral shape, evenly distributed on the inner walls of the small and large ends of the connecting rod. The spiral angle of the fiber Bragg grating sensor on the large end of the connecting rod is α, and the spiral angle of the fiber Bragg grating sensor on the small end of the connecting rod is β.

[0094] The number of fiber optic grating sensors on the small and large ends of the connecting rod is three, such as... Figure 2 As shown, each fiber Bragg grating sensor has multiple grating points.

[0095] The helix angle of the fiber optic grating sensor on the large end of the connecting rod is determined to be α, and the helix angle of the fiber optic grating sensor on the small end of the connecting rod is determined to be β.

[0096] The method for determining the helix angle of a fiber Bragg grating sensor is the same, and the specific steps are as follows:

[0097] Step 4.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between axial strain and helix angle can be obtained as follows:

[0098]

[0099] In the formula: ε is the strain of the helical fiber Bragg grating sensor, α is the helix angle, and ε b For axial strain, μ is the Poisson's ratio of the material;

[0100] Step 4.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the helix angle range, and determine the corresponding axial strain using the relational formula;

[0101] Step 4.3 Due to the following relationship between axial strain and transverse strain:

[0102] ε a =-με b

[0103] Where: ε a For transverse strain, ε bFor axial strain, μ is the Poisson's ratio of the material;

[0104] Step 4.4 The Poisson's ratio of the material is known. The corresponding axial strain can be determined according to the helix angle range set in the tensile test. From the relationship between axial strain and transverse strain, it can be seen that when the axial strain is the maximum, the absolute value of the transverse strain is the maximum value. Therefore, the angle with the maximum axial strain is selected as the helix angle.

[0105] When vertical and horizontal loads are applied to the small end and large end of the connecting rod, the center wavelength of each fiber Bragg grating sensor changes as the small end and large end of the connecting rod deform, and fiber Bragg grating sensors 2-1, 2-2, 2-3, 2-6, 2-7 and 2-8 generate corresponding offsets.

[0106] The host 4 calculates the deformation curvature k of each measuring point based on the offset of the center wavelength of the spiral F fiber grating sensors 2-1, 2-2, 2-3, 2-6, 2-7 and 2-8;

[0107] The steps for calculating the deformation at the corresponding measuring point are as follows:

[0108] Based on the relationship between the wavelength and strain of the fiber Bragg grating sensor and the sensing principle of the helical fiber Bragg grating sensor under tension, the strain is calculated as follows:

[0109]

[0110]

[0111] In the formula: λ B Δλ is the Bragg wavelength, measured in nm. B ε is the wavelength shift in nm, p is the strain of the helical FBG, and p is the wavelength shift in nm. e α is the photoelastic coefficient, with units of nm / με. T ζ is the thermal expansion coefficient of the grating, α is the photothermal coefficient of the grating, and ε is the helix angle. b For axial strain, μ is the Poisson's ratio of the material;

[0112] The change in axial length due to deformation is calculated based on the relationship between strain and length.

[0113] Δb=ε b *b

[0114] In the formula: Δb is the change in axial length, ε b y is the axial strain, b is the pitch;

[0115] The length l of the busbar containing the j-th grating point of the i-th fiber optic grating sensor is calculated based on the change in axial length. ij (i = 1, 2, 3, 6, 7, 8; j = 1, 2, ...) is:

[0116] l ij =l-Δb ij

[0117] Given the radius r of the inner wall of the connecting rod, then the deflection angle φ between the bending direction and the base coordinates... j and curvature k j for:

[0118]

[0119]

[0120] The data from each fiber Bragg grating sensor is fused to obtain the reconstructed shape of the deformation of the big end and small end of the connecting rod.

[0121] like Figure 4 As shown, in step three, the fiber optic grating sensors on the connecting rod are arranged such that one fiber optic grating sensor with the same tilt angle is set on each of the two adjacent sides and is centrally symmetrically distributed on the surface of the connecting rod. The tilt angle is γ.

[0122] The fiber Bragg grating sensors on adjacent side surfaces of the connecting rod are tilted in opposite directions, and each fiber Bragg grating sensor has multiple grating points.

[0123] The tilt angle of the fiber optic grating sensor on the connecting rod is γ. The specific steps for determining the tilt angle are as follows:

[0124] Step 7.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between longitudinal strain and tilt angle can be obtained as follows:

[0125]

[0126] In the formula: ε is the strain of the fiber Bragg grating sensor, γ is the tilt angle, and ε d For longitudinal strain, μ is the Poisson's ratio of the material;

[0127] Step 7.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the tilt angle range, and determine the corresponding longitudinal strain using the relationship formula;

[0128] Step 7.3 Due to the following relationship between longitudinal strain and transverse strain:

[0129] ε c =-με d

[0130] Where: ε c For transverse strain, ε d For longitudinal strain, μ is the Poisson's ratio of the material;

[0131] Step 7.4 The Poisson's ratio of the material is known. The corresponding longitudinal strain can be determined according to the inclination angle range set in the tensile test. From the relationship between longitudinal strain and transverse strain, it can be seen that when the longitudinal strain is the maximum, the absolute value of the transverse strain is the maximum value. Therefore, the angle with the maximum longitudinal strain is selected as the helix angle.

[0132] like Figure 3 As shown, the calibration experiment method for the inclined fiber optic grating sensor in step four is to use a standard curvature mold, determine the correspondence between the wavelength offset of the fiber optic grating sensor and the curvature based on the change of the wavelength offset of the fiber optic grating sensor under different curvatures, and complete the calibration of the fiber optic grating sensor.

[0133] The method for reconstructing the connecting rod body in step eight, using deformation information to reconstruct the connecting rod body structure, is as follows:

[0134] The curvature K of the corresponding measuring points on the connecting rod body is obtained according to the calibration method in step four.

[0135] When vertical and horizontal loads are applied to the connecting rod, the center wavelength of the fiber optic grating sensor changes as the rod deforms, and fiber optic grating sensors 2-4 and 2-5 generate corresponding offsets.

[0136] The host 4 calculates the arc length l of each measuring point after deformation based on the offset of the center wavelength of fiber optic grating sensors 2-4 and 2-5;

[0137] Based on the calibration relationship, the radius R corresponding to the j-th grating point of the fiber Bragg grating sensor can be obtained. ij (i = 4, 5; j = 1, 2, ...) is:

[0138]

[0139] From radius R ij The arc length l of the deformed rod can be obtained from the length d of the connecting rod body. ij for:

[0140]

[0141] The data from each fiber Bragg grating sensor is fused to obtain the reconstructed shape of the connecting rod body deformation.

[0142] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0143] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for detecting link deformation based on a fiber Bragg grating sensor, characterized in that, Includes the following steps: Step 1: Establish the finite element model of the connecting rod. Based on the structural dimensions of the connecting rod to be tested, the elastic modulus of the material, and Poisson's ratio, establish the finite element model of the connecting rod. Step 2: Finite element analysis. By applying simulated loads to the finite element model of the connecting rod to be tested established in Step 1, the deformation of the connecting rod is analyzed, and the simulated deformation types and simulated deformation amounts of the small end, big end and body of the connecting rod are obtained respectively. Step 3: Design the arrangement scheme of fiber Bragg grating sensors. Based on the simulated deformation type and simulated deformation amount in Step 2, design the distribution of fiber Bragg grating sensors at the small end, large end, and body of the connecting rod. Step 4: Calibration of two types of fiber Bragg grating sensors. Design calibration experiments for helical fiber Bragg grating sensors for the small end and large end of the connecting rod, and for fiber Bragg grating sensors for the inclined shaft of the connecting rod. Based on the wavelength offset of the fiber Bragg grating sensor, determine the correspondence between the wavelength offset of the fiber Bragg grating sensor and the displacement and curvature, and complete the calibration of the two types of fiber Bragg grating sensors. Step 5: Preparation for the test of the connecting rod. Arrange the fiber optic grating sensor according to the design scheme in Step 3, connect the data acquisition equipment, connect the fiber optic grating sensor to the fiber optic grating sensor demodulator, and connect the fiber optic grating sensor demodulator to the host computer through the data connector. The center wavelength of the fiber optic grating sensor is demodulated by the fiber optic grating sensor demodulator and transmitted to the host computer. Step 6: Loading experiment on the connecting rod under test. Simulated load experiments are conducted on the small end, large end and body of the connecting rod respectively. When the connecting rod deforms, the center wavelength of each fiber optic grating sensor changes. The offset of the center wavelength is obtained according to the calibration results in Step 4. Step 7: Calculate deformation parameters. The host computer calculates the deformation curvature k and the arc length l after deformation at each measuring point based on the changes obtained in Step 6. Step 8: Reconstruct each structural unit of the connecting rod. Based on the deformation reconstruction method, use the deformation information of each structural unit to reconstruct the small end, big end, and body structure of the connecting rod respectively. Step 9: Reconstruct the overall structure of the link. Based on the reconstruction algorithm, combine the structural units from Step 8 into a whole to complete the reconstruction of the overall structure of the link. Step 10: Comparison of deformation detection results. Compare the results of finite element model simulation analysis with experimental results to determine the true deformation type and amount of the connecting rod under test. In step three, the fiber optic grating sensors on both the small and large ends of the connecting rod are arranged in the same spiral pattern, evenly distributed on the inner walls of both ends. The spiral angle of the fiber optic grating sensor on the large end is... The helix angle of the fiber optic grating sensor on the small end of the connecting rod is... ; The helix angle of the fiber optic grating sensor on the big end of the connecting rod is determined as follows: The helix angle of the fiber optic grating sensor on the small end of the connecting rod is... ; The method for determining the helix angle of a fiber Bragg grating sensor is the same, and the specific steps are as follows: Step 4.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between axial strain and helix angle can be obtained as follows: ; In the formula: For strain in a helical fiber Bragg grating sensor The helix angle, For axial strain, Poisson's ratio of the material; Step 4.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the helix angle range, and determine the corresponding axial strain using the relational formula; Step 4.3 Due to the following relationship between axial strain and transverse strain: ; In the formula: For lateral strain, For axial strain, Poisson's ratio of the material; Step 4.4 The Poisson's ratio of the material is known. Based on the helix angle range set in the tensile test, the corresponding axial strain can be determined. From the relationship between axial strain and transverse strain, it can be seen that when the axial strain is at its maximum, the absolute value of the transverse strain is at its maximum. Therefore, the angle with the maximum axial strain is selected as the helix angle.

2. The link deformation detection method based on fiber optic grating sensor according to claim 1, characterized in that: The number of fiber Bragg grating sensors on the small end and large end of the connecting rod is at least two, and each fiber Bragg grating sensor has at least two grating points.

3. The link deformation detection method based on fiber optic grating sensor according to claim 1, characterized in that: In step three, the fiber optic grating sensors on the connecting rod are arranged such that one fiber optic grating sensor with the same inclination angle is installed on each of two adjacent sides, and they are centrally symmetrically distributed on the surface of the connecting rod. The inclination angle is... .

4. The link deformation detection method based on a fiber optic grating sensor according to claim 3, characterized in that: The fiber optic grating sensors on adjacent side surfaces of the connecting rod are tilted in opposite directions, and each fiber optic grating sensor has at least two grating points.

5. The method for detecting link deformation based on a fiber optic grating sensor according to claim 4, characterized in that, The tilt angle of the fiber optic grating sensor on the connecting rod is: The specific steps to determine the tilt angle are as follows: Step 7.1 Based on the principle of tension in fiber Bragg grating sensors, the relationship between longitudinal strain and tilt angle can be obtained as follows: ; In the formula: For the strain of the fiber Bragg grating sensor The angle of inclination. For longitudinal strain, Poisson's ratio of the material; Step 7.2 Determine the strain range of the fiber optic grating sensor through tensile experiments using finite element simulation, set the tilt angle range, and determine the corresponding longitudinal strain using the relationship formula; Step 7.3 Due to the following relationship between longitudinal strain and transverse strain: ; In the formula: For lateral strain, For longitudinal strain, Poisson's ratio of the material; Step 7.4 The Poisson's ratio of the material is known. Based on the inclination angle range set in the tensile test, the corresponding longitudinal strain can be determined. From the relationship between longitudinal strain and transverse strain, it can be seen that when the longitudinal strain is the maximum, the absolute value of the transverse strain is the maximum value. Therefore, the angle with the maximum longitudinal strain is selected as the helix angle.

6. The method for detecting link deformation based on a fiber Bragg grating sensor according to claim 1, characterized in that, In step seven, the curvature k of the small end and the arc length l of the connecting rod after deformation are... The steps for calculating the deformation at the corresponding measuring point are as follows: Based on the relationship between the wavelength and strain of the fiber Bragg grating sensor and the sensing principle of the helical fiber Bragg grating sensor under tension, the strain is calculated as follows: ; ; In the formula: The wavelength is the Bragg wavelength, measured in nm. This is the wavelength offset, in nm. For the strain of the helical FBG, The elastic coefficient is expressed in units of 1000 ppm. , is the coefficient of thermal expansion of the grating. The photothermal coefficient of the grating, The helix angle, For axial strain, Poisson's ratio of the material; The change in axial length due to deformation is calculated based on the relationship between strain and length. ; In the formula: For axial length variation, y is the axial strain, b is the pitch; The length l of the busbar containing the j-th grating point of the i-th fiber optic grating sensor is calculated based on the change in axial length. ij (i=1, 2, 3, 6, 7, 8; j=1, 2, ...) is: ; Given the radius r of the inner wall of the connecting rod, then the deflection angle φ between the bending direction and the base coordinates... j and curvature k j for: ; ; The data from each fiber Bragg grating sensor is fused to obtain the reconstructed shape of the deformation of the big end and small end of the connecting rod.

7. The method for detecting link deformation based on a fiber Bragg grating sensor according to claim 5, characterized in that: The calibration experiment method for the inclined fiber Bragg grating sensor in step four is to use a standard curvature mold, determine the correspondence between the wavelength offset of the fiber Bragg grating sensor and the curvature based on the change of the wavelength offset of the fiber Bragg grating sensor under different curvatures, and complete the calibration of the fiber Bragg grating sensor.

8. The method for detecting link deformation based on a fiber optic grating sensor according to claim 7, characterized in that, The method for reconstructing the connecting rod body in step eight, using deformation information to reconstruct the connecting rod body structure, is as follows: The curvature K of the corresponding measuring points on the connecting rod body is obtained according to the calibration method in step four. Based on the calibration relationship, the radius R corresponding to the j-th grating point of the fiber Bragg grating sensor can be obtained. ij (i=4, 5; j=1, 2, ...) is: ; From radius R ij The arc length l of the deformed rod can be obtained from the length d of the connecting rod body. ij for: ; The data from each fiber grating sensor is fused to obtain the reconstructed shape of the connecting rod body deformation.

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