A fiber grating acceleration sensor with parallel multi-hinge structure

Abstract

The present invention provides a fiber Bragg grating acceleration sensor with a parallel multi-hinge structure, which includes a base, an outer frame, at least two parallel hinge structures, a mass block, a first fiber Bragg grating, and a second fiber Bragg grating. The outer frame is fixed to the base, the mass block is arranged in the outer frame, and two parallel hinge structures are symmetrically arranged on both sides of the mass block. One end of the parallel hinge structure is connected to the mass block, and the other end of the parallel hinge structure is connected to the inner wall of the outer frame. The two ends of the first fiber Bragg grating are respectively fixed to the outer frame and the mass block, and the two ends of the second fiber Bragg grating are respectively fixed to the outer frame and the mass block, and the second fiber Bragg grating is coaxial with the first fiber Bragg grating. In the present invention, the outer frame and the mass block are connected by parallel hinge structures, so that the mass block moves in translation when subjected to force, so that the first fiber Bragg grating and the second fiber Bragg grating will not produce bending deformation, thereby improving the fatigue strength of the fiber Bragg grating and increasing the service life of the fiber Bragg grating acceleration sensor.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, and in particular to an optical fiber grating acceleration sensor with a parallel multi-hinge structure. Background Art

[0002] Acceleration detection is an important technical means for structural health monitoring in aerospace, bridge engineering, subway tunnels, etc. By real-time monitoring of vibration signals, the real-time status of equipment, mechanical structures, engineering, etc. can be timely understood, effectively avoiding the occurrence of safety accidents. Traditional electrical vibration sensors are easily affected by external electromagnetic interference and have cumbersome wiring. They have defects such as zero drift and temperature drift, and cannot meet their application requirements for long-term, long-distance, and real-time monitoring in harsh environments.

[0003] Fiber Bragg grating is widely used in structural health monitoring due to its advantages of anti-electromagnetic interference, small size, and easy networking. Therefore, acceleration sensors using fiber Bragg grating as sensitive elements have broad prospects in vibration detection applications. Fiber Bragg grating acceleration sensors mainly include hinge type, diaphragm type, and cantilever beam type. The hinge type is widely used in fiber Bragg grating acceleration sensors because of its simple structure, high precision, and high reliability.

[0004] However, when the mass block of a traditional hinged accelerometer rotates, tensile stress and shear stress exist simultaneously at the fixed point of the fiber Bragg grating. Under the action of infinitely many alternating loads, this shear stress significantly reduces the fatigue strength of the fiber Bragg grating, thereby reducing the service life of the fiber Bragg grating accelerometer. This defect is particularly obvious in high-frequency accelerometers. Summary of the invention

[0005] In view of this, it is necessary to provide a fiber Bragg grating acceleration sensor with a parallel multi-hinge structure to solve the problem in the prior art that the hinge-type acceleration sensor affects the fatigue strength of the fiber Bragg grating.

[0006] The present invention provides a fiber grating acceleration sensor with a parallel multi-hinge structure, comprising:

[0007] A base, an outer frame, at least two parallel hinge structures, a mass block, a first fiber Bragg grating, and a second fiber Bragg grating. The outer frame is fixed to the base, the mass block is arranged in the outer frame, the two parallel hinge structures are symmetrically arranged on both sides of the mass block, one end of the parallel hinge structure is connected to the mass block, and the other end of the parallel hinge structure is connected to the inner wall of the outer frame, the two ends of the first fiber Bragg grating are respectively fixed to the outer frame and the mass block, the two ends of the second fiber Bragg grating are respectively fixed to the outer frame and the mass block, and the second fiber Bragg grating is coaxial with the first fiber Bragg grating.

[0008] Optionally, the outer frame is vertically fixed to the base, a hollow area is opened in the middle of the outer frame, and the two parallel hinge structures and the mass block are arranged in the hollow area.

[0009] Optionally, the parallel hinge structure includes a first connecting rod, a second connecting rod, a first flexible hinge, a second flexible hinge, a third flexible hinge and a fourth flexible hinge, the first connecting rod and the second connecting rod are arranged in a horizontal direction, the first flexible hinge is connected to the first connecting rod and the mass block, the second flexible hinge is connected to the first connecting rod and the outer frame, the third flexible hinge is connected to the second connecting rod and the mass block, and the fourth flexible hinge is connected to the second connecting rod and the outer frame.

[0010] Optionally, there are two parallel hinge structures, and the two parallel hinge structures are symmetrical about the mass block.

[0011] Optionally, the plane where the first connecting rod and the second connecting rod are located is perpendicular to the base.

[0012] Optionally, the axes on which the first fiber grating and the second fiber grating are located are perpendicular to the base.

[0013] Optionally, screw holes for threaded fixation with the structure to be measured are provided at both ends of the base.

[0014] Optionally, the first fiber grating and the second fiber grating are fixed to the fixing bracket and the mass block by epoxy resin glue.

[0015] Optionally, the first fiber grating and the second fiber grating need to be pre-stretched before being fixed.

[0016] Optionally, the base, the outer frame, and the mass block are made of stainless steel and are integrally formed by wire cutting.

[0017] The beneficial effects of the present invention are:

[0018] In the present invention, the outer frame and the mass block are connected by the parallel hinge structure, and the inertial force causes the mass block to move horizontally, so that the first fiber grating and the second fiber grating will not produce bending deformation, thereby improving the fatigue strength of the fiber grating and thus increasing the service life of the fiber grating acceleration sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 It is a schematic diagram of the three-dimensional structure of the fiber Bragg grating acceleration sensor with parallel multi-hinge structure in the present invention;

[0021] Figure 2 for Figure 1 Schematic diagram of the connection of the parallel hinge structure;

[0022] Wherein: 1-base, 2-outer frame, 21-hollow area, 3-parallel hinge structure, 31-first connecting rod, 32-second connecting rod, 33-first flexible hinge, 34-second flexible hinge, 35-third flexible hinge, 36-fourth flexible hinge, 4-mass block, 5-first fiber grating, 6-second fiber grating, 7-epoxy resin glue. DETAILED DESCRIPTION

[0023] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0024] like Figure 1 As shown, an embodiment of the present invention provides a fiber Bragg grating acceleration sensor with a parallel multi-hinge structure, which includes: a base 1, an outer frame 2, at least two parallel hinge structures 3, a mass block 4, a first fiber Bragg grating 5, and a second fiber Bragg grating 6. The outer frame 2 is fixed to the base 1, the mass block 4 is arranged in the outer frame 2, and the two parallel hinge structures 3 are symmetrically arranged on both sides of the mass block 4. One end of the parallel hinge structure 3 is connected to the mass block 4, and the other end of the parallel hinge structure 3 is connected to the inner wall of the outer frame 2. The two ends of the first fiber Bragg grating 5 are respectively fixed to the outer frame 2 and the mass block 4, and the two ends of the second fiber Bragg grating 6 are respectively fixed to the outer frame 2 and the mass block 4, and the second fiber Bragg grating 6 is coaxial with the first fiber Bragg grating 5.

[0025] Specifically, the base 1, the outer frame 2, and the mass block 4 are made of stainless steel and are integrally formed by wire cutting, and the process is simple.

[0026] It should be noted that, when measuring acceleration, the fiber Bragg grating acceleration sensor with a parallel multi-hinge structure of the present invention needs to be fixed on the structure to be measured according to the sensitive direction, and the fixing method includes but is not limited to: coating structural adhesive on the bottom surface of the base 1 of the fiber Bragg grating acceleration sensor and sticking it on the structure to be measured; welding the base 1 of the fiber Bragg grating acceleration sensor to the structure to be measured by laser welding; and fixing it to the structure to be measured by screws by setting screw holes at both ends of the base 1 of the fiber Bragg grating acceleration sensor.

[0027] Specifically, the outer frame 2 is vertically fixed to the base 1 , a hollow area 21 is opened in the middle of the outer frame 2 , and the two parallel hinge structures 3 and the mass block 4 are arranged in the hollow area 21 .

[0028] Specifically, Figure 2 As shown, the parallel hinge structure 3 includes a first connecting rod 31, a second connecting rod 32, a first flexible hinge 33, a second flexible hinge 34, a third flexible hinge 35 and a fourth flexible hinge 36, wherein the first connecting rod 31 and the second connecting rod 32 are arranged in the horizontal direction, the first flexible hinge 33 is connected to the first connecting rod 31 and the mass block 4, the second flexible hinge 34 is connected to the first connecting rod 31 and the outer frame 2, the third flexible hinge 35 is connected to the second connecting rod 32 and the mass block 4, and the fourth flexible hinge 36 is connected to the second connecting rod 32 and the outer frame 2. The two parallel hinge structures 3 in the present invention form a parallelogram structure symmetrical to the two ends of the mass block 4, so that the rotations generated by the mass block 4 when subjected to force movement cancel each other out, so that the mass block 4 only moves in a translational direction in the sensitive direction. In this way, the first fiber grating 5 and the second fiber grating 6 will not produce bending deformation, thereby improving the fatigue strength of the fiber grating, thereby increasing the service life of the fiber grating acceleration sensor.

[0029] The working principle of the fiber Bragg grating acceleration sensor with a parallel multi-hinge structure of the present invention is: when the structure to be measured is subjected to external excitation, the fiber Bragg grating acceleration sensor vibrates together with the structure to be measured, so that the mass block 4 generates a slight vibration under the action of the inertial force, and the mass block 4 undergoes translational motion due to the interaction between the two symmetrical parallel hinge structures 3, thereby causing the first fiber Bragg grating 5 and the second fiber Bragg grating 6 to undergo axial stretching and axial compression, generating a wavelength change signal.

[0030] It should be noted that, in this embodiment, there are two parallel hinge structures 3 , and the two parallel hinge structures 3 are symmetrical about the mass block 4 .

[0031] In this embodiment, the plane where the first connecting rod 31 and the second connecting rod 32 are located is perpendicular to the base 1 .

[0032] Specifically, the axes of the first fiber grating 5 and the second fiber grating 6 are perpendicular to the base 1. When in use, the mass block 4 moves in translation, so that the first fiber grating 5 and the second fiber grating 6 are axially stretched and compressed. Such axial stretching and compression cause the first fiber grating 5 and the second fiber grating 6 to produce wavelength drifts of equal magnitude and opposite directions. By differentiating the two, the sensitivity of the sensor can be doubled, and temperature compensation can be achieved at the same time.

[0033] It should be noted that the first fiber grating 5 and the second fiber grating 6 need to be pre-tensioned before being fixed, so that negative strain can be effectively sensed. There are many ways to fix the first fiber grating 5 and the second fiber grating 6. In this embodiment, the first fiber grating 5 and the second fiber grating 6 are fixed to the outer frame 2 and the mass block 4 by epoxy resin glue 7.

[0034] In order to better illustrate the advantages of the present invention, a model analysis is now performed on the fiber grating acceleration sensor with a parallel multi-hinge structure provided by the present invention:

[0035] Sensitivity analysis of acceleration sensor:

[0036] Assuming the acceleration of the structure to be measured is a, the following equation can be obtained based on the moment balance:

[0037] mad-2k λ Δlb-8kθ=0;

[0038] Wherein, m is the total mass of the mass block 4; d is the distance between the mass center of the mass block 4 and the center of the first flexible hinge 33; b is the distance between the surface of the mass block 4 to which the optical fiber is attached and the center of the first flexible hinge 33; Δl is the stretching distance of the first fiber grating 5 or the compression distance of the second fiber grating 6; k λ is the elastic coefficient of the optical fiber; k is the rotational stiffness of the hinge; θ is the rotation angle of the hinge. Where d, b, θ satisfy the following formula:

[0039] d = b = 3r + c + e / 2;

[0040]

[0041] Where r is the radius of the straight circular flexible hinge, c is the length of the connecting rod, and e is the width of the mass block 4.

[0042] Assume that the wavelength shift of the first fiber grating 5 is Δλ1, the strain is ε1, and the wavelength shift of the second fiber grating 6 is Δλ2, the strain is ε2. Since the strains of the first fiber grating 5 and the second fiber grating 6 are the same in magnitude but opposite in direction, ε1=-ε2=ε.

[0043] The wavelength variation of fiber Bragg grating is:

[0044] Δλ1=k T ΔT+k ε ε1;

[0045] Δλ2=k T ΔT+k ε ε2;

[0046] Among them, k T is the sensor temperature sensitivity coefficient, k ε is the strain sensitivity coefficient of the sensor, ΔT is the temperature change, and ε1 and ε2 are the axial strains of the fiber Bragg grating.

[0047] After differentiating the wavelength changes of the two fiber gratings, we get:

[0048] Δλ=Δλ1-Δλ2=k ε (ε1-ε2)=2k ε ε;

[0049]

[0050] Where l is the length of the fiber Bragg grating.

[0051] The sensor sensitivity S is the ratio of the change in the central wavelength of the fiber Bragg grating Δλ to the acceleration a, that is:

[0052]

[0053] Elastic modulus k of optical fiber λ for:

[0054]

[0055] In the formula, A λ is the cross-sectional area of ​​the optical fiber; E λ is the elastic modulus of the optical fiber.

[0056] The hinge stiffness k is:

[0057]

[0058]

[0059] Where E is the elastic modulus of the material; w is the thickness of the hinge.

[0060]

[0061] Where r is the hinge radius and t is the minimum thickness between hinges.

[0062] Accelerometer resonant frequency analysis:

[0063] Assuming the moment of inertia of mass block 4 rotating around the hinge center is J, the dynamic equation of the system can be obtained as follows:

[0064]

[0065] Then the resonant frequency of the accelerometer is:

[0066]

[0067] The moment of inertia obtained from material mechanics is:

[0068]

[0069] Wherein h is the height of mass block 4.

[0070] The beneficial effects of the present invention are:

[0071] 1. The present invention innovatively applies a parallel multi-hinge structure consisting of two connecting rods and four flexible hinges to an acceleration sensor. When in use, the inertial force causes the mass block to move horizontally, so that the fiber Bragg grating will not produce bending deformation, thereby improving the fatigue strength of the fiber Bragg grating, thereby increasing the service life of the fiber Bragg grating acceleration sensor.

[0072] 2. The present invention establishes a mathematical model of a parallel multi-hinge structure fiber Bragg grating acceleration sensor, which can optimize the design of the hinge size, mass block mass and other structural parameters of the sensor to meet the requirements of sensor sensitivity and resonant frequency in different applications. The sensor has good application prospects.

[0073] 3. The acceleration sensor of the present invention symmetrically arranges the same fiber gratings on both sides of the mass block. The central wavelength drifts of the two fiber gratings are equal in magnitude and opposite in direction. Differentiating the two can eliminate the influence of temperature changes and improve the sensitivity of the sensor.

[0074] The above are only preferred specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A fiber Bragg grating acceleration sensor with a parallel multi-hinge structure, characterized in that: include: A base, an outer frame, at least two parallel hinge structures, a mass block, a first fiber Bragg grating, and a second fiber Bragg grating, wherein the outer frame is fixed to the base, the mass block is arranged in the outer frame, the two parallel hinge structures are symmetrically arranged on both sides of the mass block, one end of the parallel hinge structure is connected to the mass block, and the other end of the parallel hinge structure is connected to the inner wall of the outer frame, the two ends of the first fiber Bragg grating are respectively fixed to the outer frame and the mass block, the two ends of the second fiber Bragg grating are respectively fixed to the outer frame and the mass block, and the second fiber Bragg grating is coaxial with the first fiber Bragg grating, wherein The parallel hinge structure includes a first connecting rod, a second connecting rod, a first flexible hinge, a second flexible hinge, a third flexible hinge and a fourth flexible hinge. The first connecting rod and the second connecting rod are arranged in a horizontal direction. The first flexible hinge is connected to the first connecting rod and the mass block. The second flexible hinge is connected to the first connecting rod and the outer frame. The third flexible hinge is connected to the second connecting rod and the mass block. The fourth flexible hinge is connected to the second connecting rod and the outer frame. There are two parallel hinge structures, and the two parallel hinge structures are symmetrical about the mass block.

2. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The outer frame is vertically fixed to the base, a hollow area is provided in the middle of the outer frame, and the two parallel hinge structures and the mass block are arranged in the hollow area.

3. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The planes where the first connecting rod and the second connecting rod are located are perpendicular to the base.

4. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The axes where the first fiber grating and the second fiber grating are located are perpendicular to the base.

5. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The two ends of the base are provided with screw holes for threaded fixing with the structure to be measured.

6. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The first fiber Bragg grating and the second fiber Bragg grating are fixed to the outer frame and the mass block by epoxy resin glue.

7. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1 or 4, characterized in that: The first fiber Bragg grating and the second fiber Bragg grating need to be pre-tensioned before being fixed.

8. The fiber Bragg grating acceleration sensor with parallel multi-hinge structure as claimed in claim 1, characterized in that: The base, the outer frame and the mass block are made of stainless steel and are integrally formed by wire cutting.

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