Acceleration self-compensation type multi-point temperature sensor for measuring surface temperature field of rotating shaft

Abstract

The invention discloses an acceleration self-compensation type multi-point temperature sensor for measuring a surface temperature field of a rotating shaft, and belongs to the field of optical fiber sensing. The device comprises a multi-core photonic crystal fiber, a high thermo-optical coefficient liquid, a fiber bragg grating, a flexible metal capillary tube, a polyimide composite material coating and an elastomer material damping layer. The flexible metal capillary tube, the polyimide composite material coating and the elastomer material damping layer are sequentially arranged from inside to outside to form a hollow cavity. The multi-core photonic crystal fiber is arranged in the cavity, and one end of the multi-core photonic crystal fiber is fixed. And the fiber bragg gratings are written into each fiber core of the multi-core photonic crystal fiber in an array form. The multi-core photonic crystal fiber has at least five cores and comprises a central fiber core and four side fiber cores, wherein at least six large-size air holes are distributed in the periphery of the central fiber core, and the side fiber cores surround in a square shape. The central wavelength of the central fiber core FBG is different from the central wavelength of the side fiber core FBG. The large-size air holes are filled with high-thermal-optical-coefficient liquid and sealed through ultraviolet glue. The flexible capillary metal tube is a cylindrical tube with two unsealed ends.

Description

Technical Field

[0001] This invention relates to an acceleration-compensated multi-point temperature sensor for measuring the surface temperature field of a rotating shaft, belonging to the field of fiber optic sensing. Background Technology

[0002] As a critical transmission component, the surface temperature distribution of a rotating shaft is a key parameter for judging the lubrication status, thermal deformation, and structural health of bearings, directly reflecting the operating status of the equipment. Abnormal temperature increases may indicate bearing wear, lubrication failure, or overload, making accurate temperature monitoring of the rotating shaft surface crucial. However, rotating shafts often experience interference from high-speed rotation, strong electromagnetic fields, and severe vibrations during operation. Current methods for measuring rotating shaft temperature commonly use thermocouples or fiber optic sensors. While thermocouples offer high accuracy, their size and wiring limitations make them unsuitable for installation in confined spaces and pose challenges in disassembly after a failure. Fiber Bragg grating temperature sensors suffer from stress interference caused by the acceleration generated by the high-speed rotation of the shaft, introducing measurement errors. Existing technologies often only compensate for the temperature itself, with some additional electronic accelerometers or mechanical decoupling systems, which are bulky, have complex wiring, and poor surface adaptability. Furthermore, installation stress may introduce additional errors.

[0003] Overall, current fiber optic temperature sensors used for measuring the surface temperature field of rotating shafts lack a self-compensation mechanism for acceleration interference, leading to a further decrease in the accuracy of multi-point temperature data under rotational conditions. Therefore, developing a fiber optic temperature sensor with acceleration self-compensation that can accurately measure the temperature field of curved surfaces under high-speed rotation, filling a gap in existing patents, is of great significance for promoting the development and application of fiber optic temperature sensor technology. Summary of the Invention

[0004] To address the problem of inaccurate measurement of the surface temperature field of high-speed rotating shafts, this invention aims to provide an acceleration-self-compensated multi-point temperature sensor for measuring the surface temperature field of rotating shafts. When the rotating shaft generates centrifugal acceleration, the symmetrical side fiber core will experience axial strains of opposite signs, namely tension and compression, due to the constraint differences in the inertial soft region. Since the temperature has a consistent effect on the symmetrical side fiber core, the sensor performs differential calculations on the wavelength drift of the symmetrical side fiber core FBG to cancel out the temperature term, retaining only the strain signal induced by acceleration, thus achieving acceleration self-compensation. At the same time, the optical signal can be distinguished by the different center wavelengths of the FBG at each location, which can meet the temperature measurement needs at different locations on the rotating shaft surface, thereby realizing temperature field monitoring.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] The present invention discloses an acceleration self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft, comprising a multi-core photonic crystal fiber, a liquid with a high thermo-optic coefficient, a fiber Bragg grating, a flexible metal capillary, a polyimide composite material coating, and an elastomer material damping layer.

[0007] A flexible metal capillary, a polyimide composite coating, and an elastomer damping layer are arranged sequentially from the inside out to form a hollow cavity. A multi-core photonic crystal fiber is placed in the cavity and fixed at one end.

[0008] The fiber Bragg grating is written in an array into each core of the multi-core photonic crystal fiber.

[0009] The multi-core photonic crystal fiber has at least 5 cores, including 1 central core and at least 4 side cores arranged in a square pattern; at least 6 large-sized air holes are distributed around the central core; the center wavelengths of the central core FBG and the side core FBG are different.

[0010] The large-sized air hole is filled with a liquid with a high thermo-optic coefficient and sealed with UV adhesive.

[0011] The edge fiber core consists of two sets of symmetrical edge fiber cores, with a row of triangular lattice air holes missing along the axial direction on the outer side, forming an inertial soft region.

[0012] The flexible capillary metal tube is a cylindrical tube with open ends, which serves to isolate static strain.

[0013] The polyimide composite coating has good thermal conductivity, and is resistant to high temperatures and has good insulation properties.

[0014] The aforementioned elastomeric material damping layer is an elastomeric material with a honeycomb structure filled with highly thermally conductive filler.

[0015] The length of the inertial soft region is consistent with the length of the filling section of the large-sized air hole. When the rotating shaft generates centrifugal acceleration, the symmetrical side fiber core will generate axial strains of opposite signs of tension and compression due to the constraint difference of the inertial soft region. The effect of temperature on the symmetrical side fiber core is consistent. By performing differential calculation on the wavelength drift of the symmetrical side fiber core FBG, the temperature term can be completely canceled, and only the strain signal caused by acceleration can be retained, thereby realizing acceleration self-compensation.

[0016] The FBG array has the same FBG grating length and distinguishes optical signals by different center wavelengths, which can meet the temperature measurement needs at different positions on the rotating shaft surface and provide a data foundation for building temperature field monitoring.

[0017] Beneficial effects:

[0018] 1. The acceleration self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft disclosed in this invention uses a high thermo-optic coefficient liquid filled in a large-sized air hole to improve the temperature sensitivity of the central fiber core without reacting with the optical fiber and adhesive, thus meeting the requirements for high-precision temperature measurement.

[0019] 2. The acceleration-compensated multi-point temperature sensor for measuring the surface temperature field of a rotating shaft disclosed in this invention comprises a flexible metal capillary, a polyimide composite material coating, and an elastomer material damping layer arranged sequentially from the inside out to form a hollow cavity. A multi-core photonic crystal fiber is placed in the cavity and fixed at one end. Fiber Bragg gratings are inscribed in an array into each core of the multi-core photonic crystal fiber. This invention features an all-fiber structure, is resistant to electromagnetic interference, has good environmental adaptability, can operate stably in complex environments such as aerospace, and has strong bending resistance, meeting the requirements for long-term temperature monitoring.

[0020] 3. The acceleration self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft disclosed in this invention has the following characteristics: the length of its inertial soft region is consistent with the length of the filling section of the large-size air hole, and the two sets of side fiber cores generate differential strain responses to accelerations in two mutually perpendicular directions, which can provide a signal basis for acceleration self-compensation. Therefore, the sensor has multi-point temperature monitoring and acceleration self-compensation functions, can measure the surface temperature field of a high-speed rotating shaft, and can also measure the temperature field of curved components under other possible high-speed rotation conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the acceleration self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft according to the present invention.

[0022] Figure 2 This is a structural diagram of section A of the self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft according to the present invention.

[0023] Figure 3 This is a structural diagram of section B of the self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft according to the present invention.

[0024] Figure 4 This is a schematic diagram showing the installation layout of the self-compensating multi-point temperature sensor for measuring the surface temperature field of a rotating shaft according to the present invention.

[0025] Among them, 1-multi-core photonic crystal fiber, 2-high thermo-optic coefficient liquid, 3-fiber Bragg grating (FBG), 4-flexible metal capillary, 5-polyimide composite material coating, 6-elastic material damping layer, 7-central fiber core, 8-side fiber core, 9-large size air hole, 10-inertial soft zone. Detailed Implementation

[0026] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0027] Example 1:

[0028] As attached Figure 1 As shown, the acceleration-compensated multi-point temperature sensor for measuring the surface temperature field of a rotating shaft disclosed in this embodiment includes a multi-core photonic crystal fiber 1 and multiple fiber Bragg gratings 3 etched on the fiber 1 using a femtosecond laser. The grating length of the fiber Bragg gratings 3 is 5 mm. One end of the fiber 1 is rigidly connected to a flexible metal capillary 4 via adhesive, and the other end of the fiber 1 does not exceed the flexible metal capillary 4. The fiber 1 can freely deform within the flexible metal capillary 4, which is a cylindrical tube with open ends. The inner diameter of the flexible metal capillary 4 is as small as possible while allowing the photonic crystal fiber to pass through. The outer layer of the flexible metal capillary 4 is coated with a polyimide composite material coating 5 by spraying, with a coating thickness of less than 100 μm. An elastomeric material damping layer 6 is wrapped around the polyimide composite material coating with adhesive. The elastomeric material damping layer 6 is a boron nitride-filled silicone rubber honeycomb structure. Figure 2 As shown, fiber 1 is a 5-core fiber, including a central core 7 with 6 large-sized air holes 9 distributed around its perimeter and 4 side cores 8 arranged in a square. The large-sized air holes 9 are filled with ionic liquid with high thermo-optic coefficient and sealed with UV adhesive. The side cores are 2 sets of symmetrical side cores, with a row of triangular lattice air holes missing along the axial direction on the outside, forming an inertial soft region 10.

[0029] Appendix Figure 4 This is a schematic diagram of the installation layout of the fiber optic temperature sensor. A single fiber optic temperature sensor can be used to perform multi-point temperature measurement and acceleration self-compensation to achieve temperature field measurement on curved surfaces.

[0030] When the fiber optic temperature sensor in this embodiment is mounted on the surface of the rotating shaft, the sensor bends. The stress caused by bending is reduced by the protection of the capillary metal tube and the elastomeric material damping layer, thus improving the measurement accuracy and stability after mounting on the curved surface. When subjected to temperature changes, thermal expansion and contraction, and acceleration caused by high-speed rotation, the grating period and refractive index change, leading to a shift in the reflected wavelength. The center wavelength corresponding to the FBG on the central fiber core changes as shown in formula (1).

[0031] Δλ B =λ0·[(α+ξ)ΔT+(1-P e )ε acc (1)

[0032] Δλ B: The center wavelength shift (pm) of the FBG on the central fiber core;

[0033] λ0: Initial center wavelength (nm) of the FBG on the central fiber core;

[0034] α: Coefficient of thermal expansion of optical fiber ( / ℃);

[0035] ξ: Thermo-optic coefficient of optical fiber ( / ℃);

[0036] ΔT: Temperature change (°C);

[0037] P e : Effective elastic-optic coefficient of optical fiber;

[0038] ε acc : Axial strain caused by acceleration.

[0039] Due to the constraint differences in the inertial soft region, the edge cores will generate axial strains with opposite signs of tension and compression, as shown in formulas (2) and (3). Temperature has a consistent effect on the symmetrical edge cores. By performing a differential operation on the wavelength drift of the symmetrical edge core FBG, as shown in formula (4), the temperature term can be completely canceled out, leaving only the strain signal induced by acceleration, as shown in formula (5). For example, a set of symmetrical edge cores 1 and 2...

[0040] Δλ B1 =λ0·[(α+ξ)ΔT+(1-P e )ε acc (2)

[0041] Δλ B2 =λ0·[(α+ξ)ΔT-(1-P e )ε acc (3)

[0042] Δλ B1 -Δλ B2 =2λ0·(1-P e )ε acc (4)

[0043] λ0·(1-P e )ε acc＝ (Δλ B1 -Δλ B2 ) / 2 (5)

[0044] Δλ B1 : Center wavelength shift (pm) of FBG on edge fiber core 1;

[0045] Δλ B2 : The center wavelength shift (pm) of the FBG on the side fiber core 2.

[0046] By using the wavelength changes caused by the perpendicular acceleration measured by two sets of symmetrical edge cores, the wavelength changes in the central fiber core caused by acceleration are compensated for, thereby achieving acceleration self-compensation.

[0047] In practical applications, based on the above principles, the temperature operating curves of each temperature measuring point of the fiber optic temperature sensor are first calibrated. This calibration is performed under static conditions (i.e., ε...). acc (If the value is 0), the center wavelength of each grating in the fiber core is obtained by the acquisition processor. Then, by establishing the relationship between the output center wavelength value of each fiber Bragg grating at each calibration temperature point under static conditions and the calibration temperature point, the temperature working curve of each temperature measurement point can be obtained.

[0048] During the measurement process, the measured central fiber core wavelength value λ B Subtracting the wavelength changes Δλ1 and Δλ2 of the two sets of side cores caused by mutually perpendicular acceleration, and then substituting the obtained wavelengths into the calibrated working curve of the known temperature-wavelength relationship, the fiber optic sensor can measure the temperature at various points on the surface of the rotating shaft and establish the temperature field on the rotating shaft surface. For example, the calibration working curve of one of the central core gratings installed on a rotating shaft with a diameter of 4 cm and a rotation speed of 1000 rpm is as follows:

[0049] ΔT=-7.396222723λ 2 +22853.399975218λ-17653157.6533249

[0050] Where λ=λ B -(Δλ1+Δλ2), the measured grating wavelength of the central fiber core is 1538.54252nm, and the wavelengths of the two sets of symmetrical side cores are 1539.6463nm, 1539.39359nm, 1537.32971nm, and 1537.14586nm, respectively. That is, λ=1538.54252-[(1539.6463-1539.39359) / 2+(1537.32971-1537.14586) / 2]=1538.32424nm. That is, without acceleration self-compensation, the measured temperature of the grating is 74.3℃, and after compensation, it is 53.3℃. Therefore, it shows that using a sensor with acceleration self-compensation significantly improves the accuracy of temperature measurement.

[0051] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An acceleration-self-compensated multi-point temperature sensor for measuring the temperature field on the surface of a rotating shaft, characterized in that: Including multi-core photonic crystal fiber, high thermo-optic coefficient liquid, fiber Bragg grating, flexible metal capillary, polyimide composite coating, and elastomeric material damping layer; A flexible metal capillary, a polyimide composite coating, and an elastomer material damping layer are arranged sequentially from the inside to the outside to form a hollow cavity; a multi-core photonic crystal fiber is placed in the cavity and kept fixed at one end; The fiber Bragg grating is written in an array into each core of the multi-core photonic crystal fiber; The multi-core photonic crystal fiber has at least 5 cores, including 1 central core and at least 4 side cores arranged in a square pattern; at least 6 large-sized air holes are distributed around the central core; the center wavelengths of the central core FBG and the side core FBG are different. The large-sized air hole is filled with a liquid with a high thermo-optic coefficient and sealed with UV adhesive. The FBG consists of two sets of symmetrical FBGs, with a row of triangular lattice air holes missing along the axial direction on the outer side, forming an inertial soft region.

2. The sensor as described in claim 1, characterized in that: The flexible capillary metal tube is a cylindrical tube with open ends, which serves to isolate static strain.

3. The sensor as described in claim 1, characterized in that: The polyimide composite coating has thermal conductivity, high temperature resistance, and insulation properties.

4. The sensor as described in claim 1, characterized in that: The aforementioned elastomeric material damping layer is an elastomeric material with a honeycomb structure filled with highly thermally conductive filler.

5. The sensor as described in claim 1, characterized in that: The length of the inertial soft region is consistent with the length of the filling section of the large-size air hole. When the rotating shaft generates centrifugal acceleration, the symmetrical side fiber core will generate axial strains with opposite signs of tension and compression due to the constraint difference of the inertial soft region. The effect of temperature on the symmetrical side fiber core is consistent. By performing differential calculation on the wavelength drift of the symmetrical side fiber core FBG, the temperature term is canceled out, and only the strain signal caused by acceleration is retained, thereby realizing acceleration self-compensation.

6. The sensor as described in claim 1, characterized in that: The FBG array has the same FBG grid length, and the optical signals are distinguished by different center wavelengths, which meets the temperature measurement requirements at different positions on the rotating shaft surface.

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