A Translational Multi-Hinged Fiber Bragg Grating Accelerometer

Abstract

The present invention provides a translational multi-hinge fiber Bragg grating acceleration sensor, which includes a base, a double-rod four-hinge structure and a sensing optical fiber, wherein the double-rod four-hinge structure includes a mass block that translates relative to the base and at least two connecting rods, wherein one end of the connecting rod is hinged to the base and the other end is hinged to the mass block, and the sensing optical fiber is fixed to the base and the mass block along the direction in which the mass block can translate relative to the base. In the present invention, the base and the mass block are hinged to form a parallelogram mechanism by hingedly connecting the connecting rods and are innovatively applied to the sensor, and the inertial force causes the mass block to translate in a large amplitude and rotate in a small amplitude, which significantly reduces the bending deformation of the fiber Bragg grating and improves the fatigue strength of the fiber Bragg grating, thereby 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 a translational multi-hinge optical fiber grating acceleration sensor. 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. Accelerometers with fiber Bragg grating as sensitive elements have broad prospects in vibration detection applications. The existing fiber Bragg grating accelerometers mainly include hinge type, diaphragm type, and cantilever beam type. Among them, the flexible hinge has the structural characteristics of simple structure, high precision and high reliability, and is widely used in fiber Bragg grating accelerometers.

[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 translational multi-hinge fiber Bragg grating acceleration sensor 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 translational multi-hinge fiber grating acceleration sensor, comprising:

[0007] A base, a double-rod four-hinge structure and a sensing optical fiber, wherein the double-rod four-hinge structure includes a mass block that moves relative to the base and at least two connecting rods, one end of the connecting rod is hinged to the base, and the other end is hinged to the mass block, and the sensing optical fiber is fixed to the base and the mass block along the direction in which the mass block can move relative to the base.

[0008] Optionally, the base includes a bottom plate, one end of the connecting rod away from the mass block is hinged to the bottom plate, the bottom plate extends to form fixed brackets respectively located at both ends of the mass block in the translation direction, and the sensing optical fiber is fixed to the fixed brackets.

[0009] Optionally, a fixing surface for fixing the sensing optical fiber is provided at the upper end of the fixing bracket, and the fixing surface is located at the same height as the mass block in a natural state.

[0010] Optionally, the length direction of the mass block is parallel to the length direction of the base plate, one end of one connecting rod is hinged to the mass block, and the other end of the connecting rod is hinged to the base plate, one end of another connecting rod is hinged to the mass block, and the other end of the connecting rod is hinged to the base plate, and the two connecting rods, the base plate, and the mass block form a parallelogram.

[0011] Optionally, the connecting rod is hinged to the base plate and the mass block via a flexible hinge.

[0012] Optionally, the sensing optical fiber includes a first optical fiber grating and a second optical fiber grating, and the first optical fiber grating and the second optical fiber grating are coaxially arranged in parallel.

[0013] Optionally, one end of the first fiber grating is fixed to the mass block, and the other end of the first fiber grating is fixed to one of the fixed brackets; one end of the second fiber grating is fixed to the mass block, and the other end of the second fiber grating is fixed to another of the fixed brackets.

[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 mass block and the connecting rod 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 base and the mass block are hingedly connected with the connecting rod to form a parallelogram mechanism and innovatively applied to the sensor. The inertial force causes the mass block to undergo a large translation and a small rotation, which significantly reduces the bending deformation of the fiber Bragg grating and improves the fatigue strength of the fiber Bragg grating, thereby increasing the service life of the fiber Bragg 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 three-dimensional structural schematic diagram of the translational multi-hinge fiber Bragg grating acceleration sensor of the present invention;

[0021] Figure 2 The schematic diagram of the principle of the translational multi-hinge fiber Bragg grating acceleration sensor of the present invention is as follows:

[0022] Wherein: 1-base, 11-bottom plate, 12-fixed bracket, 2-double-rod four-hinge structure, 21-mass block, 22-connecting rod, 3-sensing optical fiber, 31-first optical fiber Bragg grating, 32-second optical fiber Bragg grating. 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 translational multi-hinge fiber Bragg grating acceleration sensor, which includes: a base 1, a double-rod four-hinge structure 2 and a sensing optical fiber 3, wherein the double-rod four-hinge structure 2 includes a mass block 21 that translates relative to the base 1 and at least two connecting rods 22, wherein one end of the connecting rod 22 is hinged to the base 1, and the other end is hinged to the mass block 21, and the sensing optical fiber 3 is fixed to the base 1 and the mass block 21 along the direction in which the mass block 21 can translate relative to the base 1.

[0025] In the present invention, the base 1 and the mass block 21 are hingedly connected with the connecting rod 22 to form a parallelogram mechanism and innovatively applied to the sensor. The inertial force causes the mass block 21 to undergo a large-scale translation and a small-scale rotation, which significantly reduces the bending deformation of the fiber Bragg grating and improves the fatigue strength of the fiber Bragg grating, thereby increasing the service life of the fiber Bragg grating acceleration sensor.

[0026] Specifically, the base 1, the mass block 21 and the connecting rod 22 are made of stainless steel and are integrally formed by wire cutting, and the process is simple.

[0027] It should be noted that, when measuring acceleration, the translational multi-hinge fiber Bragg grating acceleration sensor 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 setting screw holes at both ends of the base 1 of the fiber Bragg grating acceleration sensor to fix it to the structure to be measured with screws.

[0028] Specifically, the base 1 includes a bottom plate 11, and one end of the connecting rod 22 away from the mass block 21 is hinged to the bottom plate 11. The bottom plate 11 extends to form fixed brackets 12 respectively located at both ends of the mass block 21 in the translation direction, and the sensing optical fiber 3 is fixed to the fixed brackets 12.

[0029] Furthermore, a fixing surface for fixing the sensing optical fiber 3 is disposed at the upper end of the fixing bracket 12 , and the fixing surface is located at the same height as the mass block 21 in the natural state.

[0030] Specifically, the length direction of the mass block 21 is parallel to the length direction of the base plate 11, one end of one of the connecting rods 22 is hinged to the mass block 21, and the other end is hinged to the base plate 11; one end of the other connecting rod 22 is hinged to the mass block 21, and the other end is hinged to the base plate 11, and the two connecting rods 22, the mass block 21, and the base plate 11 form a parallelogram structure. The working principle of a translational multi-hinge fiber Bragg grating acceleration sensor of the present invention is: under the external excitation of the measured structure, the fiber Bragg grating acceleration sensor vibrates with the measured structure, so that the mass block 21 generates a slight vibration under the action of the inertial force, and the parallelogram mechanism composed of two connecting rods and four flexible hinges causes the mass block 21 to translate, so that the pre-stretched fiber Bragg grating is axially stretched and axially compressed to generate a signal.

[0031] It should be noted that the connection between the connecting rod 22 and the bottom plate 11 and the mass block 21 is realized by a flexible hinge. In this embodiment, there are four flexible hinges, which are respectively arranged at the two ends of the two connecting rods 22.

[0032] Specifically, the sensing optical fiber 3 includes a first fiber grating 31 and a second fiber grating 32, and the first fiber grating 31 and the second fiber grating 32 are coaxially arranged in parallel. When in use, the mass block 21 moves in translation, so that the pre-stretched fiber grating undergoes axial stretching and axial compression, and such axial stretching and compression cause the first fiber grating 31 and the second fiber grating 32 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] Furthermore, one end of the first fiber grating 31 is fixed to the mass block 21, and the other end of the first fiber grating 31 is fixed to one of the fixed brackets 12; one end of the second fiber grating 32 is fixed to the mass block 21, and the other end of the second fiber grating 32 is fixed to another of the fixed brackets 12.

[0034] It should be noted that the first fiber grating 31 and the second fiber grating 32 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 31 and the second fiber grating 32. In this embodiment, the first fiber grating 31 and the second fiber grating 32 are fixed to the fixing bracket 12 and the mass block 21 by epoxy resin glue.

[0035] In order to better illustrate the advantages of the present invention, a model analysis is now performed on the translational multi-hinge fiber Bragg grating acceleration sensor provided by the present invention:

[0036] like Figure 2 As shown, the base 1 and the mass block 21 form a parallelogram mechanism by hingedly connecting the connecting rod 22. Under the action of the inertial force F, the parallelogram mechanism undergoes a small rotation θ, and the mass block 21 undergoes a large translation and a small rotation. Assume that the center distance between the two flexible hinges in the same plane is L, the translation displacement of the mass block 21 is x, and the rotation displacement is y. From the geometric relationship, we can get:

[0037] x 2 +(Ly) 2 =L 2

[0038] x 2 ≈2Ly

[0039] When the center distance between the two flexible hinges is L = 50 mm and the translation displacement of the mass block 21 is x = 10 μm, the rotation displacement y of the mass block 21 is only 1×10 -3 μm.

[0040] Analysis of the sensitivity of the acceleration sensor:

[0041] When the acceleration a generated by the measured structure acts in the sensitive direction of the sensor, the system reaches a moment balance under the inertial force of the mass block 21, the tension of the optical fiber and the force of the hinge, and the balance equation is obtained:

[0042] mad-2k f Δl f e-4kθ=0

[0043] Wherein, m is the total mass of the mass block 21; d is the distance between the center of mass of the mass block 21 and the center of the hinge connected to the bottom plate 11; e is the distance between the surface of the mass block 21 to which the optical fiber is attached and the center of the hinge connected to the bottom plate 11; Δl f k is the fiber Bragg grating stretching distance or compression distance; f is the elastic coefficient of the optical fiber; k is the rotational stiffness of the hinge; θ is the rotation angle of the hinge.

[0044] The above formula d, e, θ can be expressed as

[0045] d=3r+l+b / 2

[0046] e=3r+l+b

[0047]

[0048] In the above formula, l is the length of the connecting rod 22, b is the height of the mass block 21, and r is the radius of the flexible hinge.

[0049] The strains generated by the first fiber grating 31 and the second fiber grating 32 are equal in magnitude and opposite in direction, that is, ε=ε 1 =-ε 2 , and under the same temperature field, the wavelength changes of the two fiber gratings are differentiated to obtain

[0050] Δλ=Δλ 1 -Δλ 2 =k ε (ε 1 -ε 2 )=2k ε ε

[0051] Where k ε is the gauge factor of the fiber Bragg grating. When the central wavelength of the fiber Bragg grating is in the 1500nm band, k ε =1.2pm / με.

[0052] The sensitivity S of the sensor is the ratio of the change in the central wavelength of the fiber Bragg grating Δλ to the acceleration a, that is,

[0053]

[0054] Elastic modulus k of optical fiberf for

[0055]

[0056] In the formula, A f is the cross-sectional area of ​​the optical fiber; E f is the elastic modulus of the optical fiber.

[0057] The hinge stiffness k is

[0058]

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

[0060]

[0061] Where t is the minimum thickness between hinges.

[0062] Analysis of the resonant frequency of the accelerometer:

[0063] The resonant frequency is another important parameter of the acceleration sensor. The higher the resonant frequency, the wider the working frequency band of the acceleration sensor. Assuming the moment of inertia of the mass block 21 rotating around the hinge center is J, the dynamic equation of the whole system is:

[0064]

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

[0066]

[0067] The moment of inertia J is:

[0068]

[0069] Wherein, c is the length of the mass block 21.

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

[0071] 1. In the present invention, the base 1 and the mass block 21 are connected by a hinged connecting rod 22 to form a parallelogram mechanism. The inertial force causes the mass block to undergo a large translation and a small rotation, which significantly reduces the bending deformation of the fiber Bragg grating and improves 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 translational multi-hinge fiber Bragg grating acceleration sensor, which can optimize the design of structural parameters such as hinge size and mass block 21 weight 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 two fiber gratings at both ends of the mass block 21. The center 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 translational multi-hinge fiber Bragg grating acceleration sensor, characterized in that: include: A base, a double-rod four-hinge structure and a sensing optical fiber, wherein the double-rod four-hinge structure comprises a mass block that moves relative to the base and at least two connecting rods, one end of the connecting rod is hinged to the base, and the other end is hinged to the mass block, the sensing optical fiber is fixed to the base and the mass block along the direction in which the mass block can move relative to the base, the base comprises a bottom plate, one end of the connecting rod away from the mass block is hinged to the bottom plate, the bottom plate extends to form fixed brackets respectively located at both ends of the mass block in the translation direction, the sensing optical fiber It is fixed to the fixed bracket, the length direction of the mass block is parallel to the length direction of the base plate, one end of one connecting rod is hinged to the mass block, and the other end of the connecting rod is hinged to the base plate, one end of another connecting rod is hinged to the mass block, and the other end of the connecting rod is hinged to the base plate, the two connecting rods, the base plate and the mass block form a parallelogram, and a fixing surface for fixing the sensing optical fiber is provided at the upper end of the fixed bracket, and the fixing surface is at the same height as the mass block in the natural state.

2. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 1, characterized in that: The connecting rod is hinged to the bottom plate and the mass block via a flexible hinge.

3. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 1, characterized in that: The sensing optical fiber includes a first optical fiber grating and a second optical fiber grating, and the first optical fiber grating and the second optical fiber grating are coaxially arranged in parallel.

4. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 3, characterized in that: One end of the first fiber grating is fixed to the mass block, and the other end of the first fiber grating is fixed to one of the fixing brackets; one end of the second fiber grating is fixed to the mass block, and the other end of the second fiber grating is fixed to another of the fixing brackets.

5. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 4, characterized in that: The first fiber Bragg grating and the second fiber Bragg grating are fixed to the fixing bracket and the mass block by epoxy resin glue.

6. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 3, characterized in that: The first fiber Bragg grating and the second fiber Bragg grating need to be pre-tensioned before being fixed.

7. The translational multi-hinge fiber Bragg grating acceleration sensor according to claim 1, characterized in that: The base, the mass block and the connecting rod are made of stainless steel and are integrally formed by wire cutting.

Images