Vibration sensor based on fiber bragg grating

Abstract

The utility model provides a fiber bragg grating-based vibration sensor, a base is fixed on a shell, a cantilever beam is a metal sheet with an I-shaped structure as a whole, and comprises a first fixing part and a second fixing part which are connected into a whole and are positioned on two sides, and a deformation part positioned in the middle, the first fixing part and the second fixing part are fixed to the base and the mass block respectively, the bottom of the mass block is attached to the shell, the surface of the cantilever beam is provided with a containing groove penetrating in the direction of the first fixing part, the deformation part and the second fixing part, and the fiber bragg grating is pasted and fixed in the containing groove. A Bragg grating on the fiber bragg grating is positioned in the middle of the deformation part; the mass block drives the cantilever beam to generate displacement in the thickness direction of the cantilever beam, so that the Bragg grating on the cantilever beam is extruded or stretched. The cantilever beam provides structural support for the fiber bragg grating, is suitable for application scenes with low sensitivity and large amplitude vibration, and has excellent anti-seismic and anti-falling performance.

Description

Technical Field

[0001] This utility model relates to the field of fiber Bragg grating sensor technology, and in particular to a vibration sensor based on fiber Bragg grating. Background Technology

[0002] During operation, wind turbine blades are susceptible to vibration due to various factors such as wind force and inertial force. Prolonged abnormal vibration can not only affect the power generation efficiency of the wind turbine but also damage the blade structure and even cause safety accidents. Therefore, monitoring the vibration of wind turbine blades can promptly detect and address blade vibration issues, ensuring the safe and stable operation of the wind turbine. Fiber Bragg grating-based vibration sensors are widely used in monitoring the swaying and flapping vibration of wind turbine blades. For example, patent CN117553899A discloses a vibration sensor measurement system based on fiber Bragg gratings. This system monitors the vibration of wind turbine blades using a fiber Bragg grating (FBG) technology, which offers significant advantages such as being passive, requiring no power supply, possessing strong electromagnetic interference resistance, long lifespan, and high temperature resistance, enabling it to adapt to various complex and harsh environments.

[0003] Vibration sensors based on fiber Bragg gratings mainly consist of a base, fiber Bragg gratings, an elastic element (cantilever beam), and a mass block. The mass block, as the core sensing element, generates a vibration response when external acceleration is applied, driving the elastic element to undergo displacement changes, thereby converting the acceleration signal into a strain signal in the fiber Bragg grating. This strain alters the refractive index modulation period of the Bragg grating on the fiber Bragg grating and the effective refractive index of the fiber core, causing changes in the reflection or transmission center wavelength. By detecting these wavelength changes, information about external acceleration can be accurately obtained, enabling effective monitoring and measurement of acceleration, and thus monitoring external vibration signals. Currently, fiber Bragg gratings in vibration sensors are all suspended, resulting in high sensor sensitivity, but they are not suitable for measuring vibrations with large amplitudes. Furthermore, the mechanical stability of fiber Bragg gratings is poor, easily leading to insufficient shock and impact resistance. When monitoring wind turbine blade vibration, the fiber Bragg grating element is easily damaged, resulting in poor equipment durability. Summary of the Invention

[0004] This invention provides a vibration sensor based on a fiber Bragg grating. In this sensor, the fiber Bragg grating is bonded and fixed to a cantilever beam, and the cantilever beam provides structural support for the fiber Bragg grating. This moderately reduces the sensitivity of the sensor, making it suitable for applications with low sensitivity and large amplitude vibrations. It also has excellent shock and drop resistance.

[0005] To solve the above-mentioned technical problems, the technical solution of this utility model is as follows:

[0006] A vibration sensor based on a fiber Bragg grating includes a housing and a base, a cantilever beam, a mass block, and a fiber Bragg grating installed within the housing. The base is fixed to the housing. The cantilever beam is a thin metal sheet with an overall I-shaped structure, including a first fixed part and a second fixed part connected as a whole on both sides, and a deformation part located in the middle. The first fixed part and the second fixed part are respectively fixed to the base and the mass block. The bottom of the mass block is in contact with the housing. The surface of the cantilever beam is provided with a placement groove that runs through the first fixed part, the deformation part, and the second fixed part. The fiber Bragg grating is pasted and fixed in the placement groove, and the Bragg grating on the fiber Bragg grating is located in the middle position of the deformation part. When there is external vibration, the mass block drives the cantilever beam to displace in its thickness direction, causing the Bragg grating on the cantilever beam to be compressed or stretched.

[0007] Furthermore, the placement slot is a semi-circular slot, and the radius of the semi-circular slot is greater than or equal to the radius of the grating fiber.

[0008] Furthermore, the lead-out end of the fiber Bragg grating is connected to a detection device to detect signal changes caused by compression or stretching of the Bragg grating on the fiber Bragg grating.

[0009] Furthermore, the base, cantilever beam, mass block, and fiber optic grating are all provided in two sets, with the thickness direction of one set of cantilever beams and the thickness direction of the other set of cantilever beams arranged in two different orthogonal directions.

[0010] Furthermore, the two sets of bases are fixedly connected as a single structure.

[0011] Furthermore, the thickness of the cantilever beam is 0.2-0.3 mm.

[0012] Furthermore, the mass block weighs 25 grams.

[0013] Furthermore, the mass block is made of platinum, tungsten, copper, or iron.

[0014] Furthermore, the base is made of stainless steel.

[0015] Furthermore, the base and the outer shell, as well as the cantilever beam and the base and mass block, are fixed by bolts, screws or set screws.

[0016] Compared with the prior art, the beneficial effects of this utility model are: (1) The vibration sensor based on fiber optic grating provided by this utility model drives the cantilever beam to generate displacement in its thickness direction through the mass block, thereby causing the Bragg grating on it to be squeezed or stretched, thereby generating wavelength change and realizing vibration information monitoring. It is suitable for the working scenario of wind turbine blade vibration monitoring with low sensitivity, large amplitude vibration and excellent shock resistance and drop resistance. Moreover, the sensor has a simple structure and simple manufacturing process.

[0017] (2) In this utility model, the fiber grating is bonded and fixed to the cantilever beam, and the cantilever beam provides structural support for the fiber grating. This moderately reduces the sensitivity of the sensor, making it more suitable for measuring vibrations with larger amplitudes. In addition, it improves the mechanical stability of the sensor, effectively solving the problem of insufficient shock and drop resistance caused by large swing amplitude during transportation and use of traditional fiber grating sensors, and enhancing the durability of the sensor.

[0018] (3) The vibration sensor based on fiber optic grating provided by this utility model can adopt a dual-axis structure design, which can simultaneously monitor vibrations in two different orthogonal directions. It is suitable for monitoring the vibrations in two directions, namely flapping and oscillating, on the wind turbine blades, providing comprehensive monitoring of the wind turbine blade status. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of the vibration sensor based on fiber Bragg grating provided in Example 1;

[0020] Figure 2 This is a schematic diagram of the structure of the fiber Bragg grating-based vibration sensor provided in Example 2;

[0021] In the figure, 1-base, 2-cantilever beam, 21-first fixing part, 22-second fixing part, 23-deformation part, 3-mass block, 4-fiber grating, 41-Bracket grating, 5-placement slot. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] The structure of the fiber Bragg grating-based vibration sensor provided in this embodiment is as follows: Figure 1 As shown, the sensor includes a housing (not shown in the figure) and a base 1, a cantilever beam 2, a mass block 3, and a fiber optic grating 4 installed inside the housing. The base is fixed to the housing and is made of stainless steel, providing a stable support structure for the entire sensor.

[0025] The cantilever beam is a thin metal sheet with an overall I-shaped structure, including a first fixing part 21 and a second fixing part 22 connected as one piece on both sides, and a deformation part 23 located in the middle. The first fixing part and the second fixing part are fixed to the base and the mass block, respectively, and the bottom of the mass block is in contact with the housing. When installing the sensor, it is necessary to ensure that the bottom of the mass block is in contact with the housing of the sensor mounting surface, so as to ensure that when the object under test vibrates, the vibration energy is transmitted through the housing to the mass block and then to the cantilever beam. Specifically, the base and the housing, and the cantilever beam and the base and the mass block are fixed with bolts, screws or set screws. As an important component of the sensor, the mass block's main function is to enhance the detection sensitivity by amplifying the inertial force. When the sensor is subjected to an external force, the mass block can amplify the small inertial force, causing the cantilever beam to vibrate with a controllable amplitude, thereby improving the measurement accuracy and expanding the effective measurement range. Preferably, the mass block is made of materials such as platinum, tungsten, copper or iron, and the mass block weighs 25 grams.

[0026] In this embodiment, the upper surface of the cantilever beam is provided with a placement groove 5 that extends through the first fixed part, the deformable part, and the second fixed part. The fiber optic grating is adhered and fixed in the placement groove, and the Bragg grating 41 on the fiber optic grating is located at the middle position of the deformable part. Specifically, the placement groove is a semi-circular groove, and the radius of the semi-circular groove is greater than or equal to the radius of the fiber optic grating. Further, the fiber optic grating is placed in the placement groove after being coated with adhesive, thereby adhering and fixing it to the placement groove.

[0027] In this embodiment, the fiber Bragg grating is bonded to the placement slot on the cantilever beam. The thickness of the cantilever beam is crucial. If the cantilever beam is too thick, it will weaken the vibration transmission efficiency, reduce the sensor sensitivity, and affect the measurement accuracy. If the cantilever beam is too thin, it cannot provide sufficient structural support, and the fiber Bragg grating will still be easily damaged under large vibration conditions. Therefore, this embodiment optimizes the thickness of the cantilever beam to between 0.2 and 0.3 mm, which ensures structural stability and achieves ideal vibration response characteristics, while avoiding unnecessary sensitivity enhancement. By flexibly adjusting the I-beam dimensions, thickness, and weight of the mass block of the cantilever beam, the sensitivity and natural frequency of the sensor can be precisely adjusted to adapt to different monitoring needs.

[0028] The working principle of the fiber Bragg grating-based vibration sensor provided in this embodiment is as follows: When external vibration occurs, a mass block drives a cantilever beam to displace in its thickness direction, thereby causing the Bragg grating on it to be compressed or stretched, resulting in a wavelength change. Furthermore, the lead-out end of the fiber Bragg grating is connected to a detection device, which detects the signal change caused by the compression or stretching of the Bragg grating on the fiber Bragg grating, thus achieving accurate capture of the vibration signal. The wavelength change of the Bragg grating (FBG) on the fiber Bragg grating is obtained through the detection device, and the wavelength change can be expressed by the Bragg condition: λ B =2nΛ; where λB λ is the Bragg wavelength, n is the effective refractive index of the grating region, and Λ is the grating period. When external vibration occurs (i.e., acceleration is applied), the mass block drives the cantilever beam to displace, which in turn causes the FBG to be compressed or stretched, resulting in changes in the grating period Λ and / or the effective refractive index n, thereby affecting the Bragg wavelength λ. B The relationship between acceleration and FBG wavelength change is typically modeled using elasticity and material properties. Assuming the deformation caused by acceleration can be expressed as ΔL, then the wavelength change of the FBG is Δλ. B It can be approximated as: in The sensitivity coefficient, representing the wavelength variation with length, depends on the specific design of the FBG and the properties of the materials used, while ΔL is related to the applied acceleration a and can be determined by the system's mechanical response function, i.e., ΔL = f(a). Therefore, by adjusting the wavelength variation Δλ... B By monitoring the system and combining it with known system parameters and response functions, the applied acceleration 'a' can be deduced, thus achieving accurate measurement of acceleration.

[0029] Example 2

[0030] The fiber Bragg grating-based vibration sensor provided in this embodiment adopts a biaxial structure design, enabling the sensor to accurately capture vibration information from two orthogonal directions. Specifically, two sets of bases, cantilever beams, mass blocks, and fiber Bragg gratings are provided. The structural design and installation of the two sets of bases, cantilever beams, mass blocks, and fiber Bragg gratings are the same, the difference being that the thickness direction of one set of cantilever beams and the thickness direction of the other set of cantilever beams are arranged along two different orthogonal directions, thereby monitoring vibration information in two orthogonal directions. Specifically, the two sets of bases are fixedly connected as a single structure.

[0031] When this vibration sensor is applied to wind turbine blade vibration monitoring, one set of cantilever beams is arranged with its thickness direction along the blade flapping direction (i.e., the Y-axis direction), and the other set of cantilever beams is arranged with its thickness direction along the blade oscillation direction (i.e., the Z-axis direction). Figure 2 As shown, this improves the accuracy and reliability of wind turbine blade condition monitoring.

Claims

1. A fiber grating based vibration sensor comprising a housing and a base, a cantilever beam, a mass and a fiber grating mounted within the housing, characterized in that: The base is fixed on the shell, and the cantilever beam is a metal sheet in an I-shaped structure as a whole, including a first fixed part, a second fixed part and a deformation part located in the middle and connected as a whole, the first fixed part and the second fixed part are fixed with the base and the mass block respectively, the bottom of the mass block is in abutment with the shell, the surface of the cantilever beam is provided with a placing groove penetrating in the direction of the first fixed part, the deformation part and the second fixed part, the fiber Bragg grating is fixedly attached in the placing groove, and the Bragg grating on the fiber Bragg grating is located at the middle position of the deformation part; when external vibration occurs, the mass block drives the cantilever beam to produce displacement in the thickness direction, so that the Bragg grating on the cantilever beam is subjected to extrusion or stretching.

2. The fiber grating based vibration sensor of claim 1, wherein: The placing groove is a semicircular groove, and the radius of the semicircular groove is greater than or equal to the radius of the grating fiber.

3. The fiber grating based vibration sensor of claim 1, wherein: The leading end of the fiber Bragg grating is connected with a detection device, and the signal change of the Bragg grating on the fiber Bragg grating due to extrusion or stretching is detected.

4. The fiber grating based vibration sensor of claim 1, wherein: The base, the cantilever beam, the mass block and the fiber Bragg grating are provided with two groups, and the thickness direction of the cantilever beam of one group and the thickness direction of the cantilever beam of the other group are arranged along two different orthogonal directions respectively.

5. A fibre optic grating based vibration sensor according to claim 4, characterised in that: The two groups of bases are fixedly connected as an integral structure.

6. The fiber grating based vibration sensor of claim 1, wherein: The thickness of the cantilever beam is 0.2-0.3 mm.

7. The fiber grating based vibration sensor of claim 1, wherein: The mass block weighs 25 grams.

8. The fiber grating based vibration sensor of claim 1, wherein: The mass block is made of platinum, tungsten, copper or iron.

9. The fiber grating based vibration sensor of claim 1, wherein: The base is made of stainless steel.

10. The fiber grating based vibration sensor of claim 1, wherein: The base and the shell, the cantilever beam and the base and the mass block are fixed by bolts, screws or jacks.

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