Accelerometer and measuring system

Abstract

The embodiment of the invention provides an accelerometer and a measurement system, and relates to the technical field of optical measurement. The accelerometer comprises a mass block, an elastic diaphragm and a fiber bragg grating; the mass block is connected to the elastic diaphragm, the mass block is provided with a first deep hole, and the hole depth direction of the first deep hole is perpendicular to the elastic diaphragm; the fiber bragg grating is arranged on one side, deviating from the mass block, of the elastic diaphragm, and a first end of a fiber core main body of the fiber bragg grating penetrates through the elastic diaphragm and extends and is fixed in the first deep hole. The mass block is used for conducting the vibration signal so that the center wavelength of the fiber bragg grating can change based on the vibration signal. In the invention, the provided accelerometer has relatively high acceleration sensitivity, can detect tiny vibration acceleration signals, and is highly immune to vibration in a non-working direction.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical measurement technology, and in particular to an accelerometer. BACKGROUND

[0002] Vibration measurement is very important in engineering systems, because vibration can reveal the health of the system and can be used for early warning and diagnosis of faults. Generally, most vibrations will cause damage to mechanical components, so it is necessary to develop an accelerometer for measuring and analyzing vibration in the fields of aerospace, rail transportation, petroleum and chemical industry, etc.

[0003] Existing accelerometers can be mainly divided into two categories: piezoelectric device-based accelerometers and optical fiber sensor-based accelerometers. Due to wiring requirements, piezoelectric elements usually have manufacturing and signal attenuation problems, which limits the practical application of piezoelectric device-based accelerometers in long-term and long-distance monitoring. Optical fiber sensors have the characteristics of light weight, anti-electromagnetic interference and flexible multiplexing, but the stability of optical fiber sensor-based accelerometers has great defects. SUMMARY

[0004] The embodiments of the present application provide an accelerometer with good acceleration measurement performance and high stability.

[0005] In a first aspect, the embodiments of the present application provide an accelerometer, comprising a mass block, an elastic diaphragm and an optical fiber Bragg grating;

[0006] The mass block is connected to the elastic diaphragm, and the mass block has a first deep hole with a hole depth direction perpendicular to the elastic diaphragm;

[0007] The optical fiber Bragg grating is arranged on the side of the elastic diaphragm away from the mass block, and a first end of a fiber core body of the optical fiber Bragg grating passes through the elastic diaphragm and is fixedly extended in the first deep hole;

[0008] The mass block is used to conduct a vibration signal, so that the center wavelength of the optical fiber Bragg grating changes based on the vibration signal.

[0009] Optionally, the accelerometer further comprises a housing having a cavity, the housing is formed by splicing a first shell and a second shell, and the elastic diaphragm is fixed at the interface of the first shell and the second shell;

[0010] The second shell has a first through hole opposite to the first deep hole, and a second end of the fiber core body of the optical fiber Bragg grating passes through the first through hole and extends to the outside of the housing.

[0011] Optionally, a grating part of the optical fiber Bragg grating is located in the cavity of the housing.

[0012] Optionally, the elastic diaphragm is a copper alloy metal plate with a plurality of openings.

[0013] Optionally, the elastic diaphragm comprises a cross-shaped beam structure and a frame structure located at the periphery of the cross-shaped beam structure, and the cross-shaped beam structure and the frame structure are connected.

[0014] The mass block is connected at the intersection of the beams of the cross-shaped beam structure.

[0015] Optionally, the ratio of the length of the beam to the width of the beam of the cross-shaped beam structure is greater than or equal to 1.5 and less than or equal to 120.

[0016] Optionally, the thickness of the elastic diaphragm ranges from 0.1mm to 0.3mm.

[0017] Optionally, the fiber core body of the fiber Bragg grating is a single-mode optical fiber.

[0018] Optionally, the accelerometer further comprises a base plate, and the base plate comprises a positioning hole for fixing the accelerometer to the surface of the object to be measured.

[0019] In a second aspect, an embodiment of the present application provides a measurement system, comprising a measurement device and an accelerometer as provided by any embodiment of the present application.

[0020] The accelerometer is installed on the surface of the object to be measured.

[0021] The accelerometer is used to generate a vibration signal by collecting the acceleration of the object to be measured by the mass block, so that the center wavelength of the fiber Bragg grating changes based on the vibration signal.

[0022] The measurement device is connected to the accelerometer and is used to measure the change in the center wavelength of the fiber Bragg grating and calculate the acceleration of the object to be measured.

[0023] In an embodiment of the present application, the accelerometer comprises a fiber Bragg grating, a mass block and an elastic diaphragm. The center wavelength of the fiber Bragg grating has high sensitivity to axial strain, so that the accelerometer has high sensitivity to the axial acceleration of the fiber Bragg grating, can detect a small vibration acceleration signal, and can realize long-distance transmission of the acceleration signal using the fiber Bragg grating. The elastic diaphragm is a sheet structure with elasticity. If the elastic diaphragm is subjected to a force perpendicular to the elastic diaphragm, the elastic diaphragm will deform. If the elastic diaphragm is subjected to a force parallel to the elastic diaphragm, the elastic diaphragm is difficult to deform. Therefore, the combination of the elastic diaphragm and the mass block enables the accelerometer to resist vibration in a non-working direction.

[0024] It should be understood that the content described in this part is not intended to identify key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent through the following description. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description only some of the embodiments of the present application, and for those skilled in the art, other drawings can be obtained without creative labor based on these drawings.

[0026] Figure 1 is a structural schematic diagram of an accelerometer provided by an embodiment of the present application;

[0027] Figure 2 is a three-dimensional structural schematic diagram of another accelerometer provided by an embodiment of the present application;

[0028] Figure 3 is a three-dimensional structural schematic diagram of another accelerometer provided by an embodiment of the present application;

[0029] Figure 4 is a structural block diagram of an accelerometer test experiment device provided by an embodiment of the present application;

[0030] Figure 5 is a time domain response waveform of the accelerometer provided by an embodiment of the present application under different vibration frequencies when the vibration acceleration is 1g;

[0031] Figure 6 is a frequency response amplitude of the accelerometer provided by an embodiment of the present application when the vibration acceleration is 1g;

[0032] Figure 7 is a time domain response waveform of the accelerometer provided by an embodiment of the present application under different accelerations when the vibration frequency is 100Hz;

[0033] Figure 8 is a wavelength shift response of the accelerometer provided by an embodiment of the present application in the working and non-working directions. DETAILED DESCRIPTION

[0034] In order to make the person in the technical field better understand the present application, the following will combine the drawings in the embodiments of the present application, and the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only some of the embodiments of the present application, but not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0035] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; for example, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It must be noted that as used herein:

[0036] Figure 1 is a structural schematic diagram of an accelerometer provided by an embodiment of the present application, and the present application provides an accelerometer suitable for measuring acceleration of a to-be-measured object. Figure 1 As shown in the figure, the accelerometer comprises a mass block 2, an elastic diaphragm 3 and a fiber Bragg grating 4; the mass block 2 is connected to the elastic diaphragm 3, and the mass block 2 has a first deep hole with a hole depth direction perpendicular to the elastic diaphragm 3; the fiber Bragg grating 4 is arranged on a side of the elastic diaphragm 3 away from the mass block 2, and a first end of a fiber core body of the fiber Bragg grating 4 extends through the elastic diaphragm 3 and is fixed in the first deep hole; the mass block 2 is used for conducting a vibration signal so as to change a central wavelength of the fiber Bragg grating 4 based on the vibration signal.

[0037] Figure 2 is a three-dimensional structural schematic diagram of another accelerometer provided by an embodiment of the present application. Figure 1 As shown in the figures, the elastic diaphragm 3 is located between the mass block 2 and the fiber Bragg grating 4, the fiber Bragg grating 4 is vertically placed with the elastic diaphragm 3, and the mass block 2 is arranged at the center of the elastic diaphragm 3. Figure 2 When the to-be-measured object appears acceleration in a direction perpendicular to the elastic diaphragm 3, due to inertia, the mass block 2 will appear displacement relative to the to-be-measured object, so as to cause elastic deformation of the elastic diaphragm 3, and cause axial strain of the fiber Bragg grating 4, thereby changing the central wavelength of the fiber Bragg grating 4.

[0038] The fiber Bragg grating 4 is a grating, and has a Bragg grating capable of periodically distributing spatial refractive index inside a fiber core of the fiber Bragg grating 4, and a region where the Bragg grating inside the fiber core is located is a grating region.

[0039] When a light beam is coupled into the fiber Bragg grating 4 and transmitted through the grating region, light with a wavelength equal to a central wavelength of the fiber Bragg grating 4 will be reflected, and the central wavelength of the fiber Bragg grating 4 can be expressed as: B = 2n effΛ;

[0040] wherein λ B is the center wavelength of the fiber Bragg grating 4, n eff is the effective refractive index of the grating region of the fiber Bragg grating 4, and Λ is the grating period. When the conditions of the fiber Bragg grating 4 change, such as the fiber Bragg grating 4 is strained or the temperature of the fiber Bragg grating 4 changes, the grating period or the effective refractive index of the grating region of the fiber Bragg grating 4 will change, and thus the center wavelength λ B of the fiber Bragg grating 4 will change accordingly. Since the fiber Bragg grating 4 is only sensitive to axial strain and temperature change, complex physical quantities, such as acceleration, displacement or stress, can be indirectly measured by converting them into the axial strain of the fiber Bragg grating 4 through the accelerometer structure provided by the embodiments of the present application.

[0041] Optionally, the accelerometer further comprises a housing having a cavity, the housing is formed by splicing the first shell 1 and the second shell 5, and the elastic diaphragm 3 is fixed at the interface of the first shell 1 and the second shell 5; the second shell 5 has a first through hole opposite to the first deep hole, and the second end of the fiber core body of the fiber Bragg grating 4 extends to the outside of the housing through the first through hole.

[0042] Figure 3 is a three-dimensional structural schematic diagram of still another accelerometer provided by the embodiments of the present application, referring to Figure 3 , the first shell 1 and the second shell 5 are fixed by screws, and the mass block 2, the elastic diaphragm 3 and the fiber Bragg grating 4 (referring to Figure 1 ) are encapsulated inside, and the elastic diaphragm 3 is fixed at the interface of the first shell 1 and the second shell 5 by means of screws. When the motion state of the object to be measured changes, the housing fixed on the surface of the object to be measured will keep consistent with the speed of the object to be measured, and the mass block 2 will appear displacement relative to the housing due to inertia, and the elastic diaphragm 3 will be elastically deformed under the action of the mass block 2 and the housing, so as to make the fiber Bragg grating 4 fixed on the mass block 2 be axially strained. In addition, the closed housing can make the accelerometer not be affected by the external environment, and increase the measurement accuracy of the accelerometer.

[0043] The relationship between the shift amount of the center wavelength of the fiber Bragg grating 4 and the axial strain and the temperature change can be expressed as:

[0044]

[0045] wherein Δλ B is the shift amount of the center wavelength of the fiber Bragg grating 4, Δε is the axial strain, and ΔT is the temperature change amount, and ρ eThe elastic optical coefficient of the fiber Bragg grating 4 is α, and the thermal optical coefficient and the thermal expansion coefficient of the fiber Bragg grating 4 are ξ and α respectively.

[0046] When measuring the acceleration of an object to be measured, an accelerometer is fixed on the surface of the object to be measured, and the vibration displacement of the object to be measured can be expressed as:

[0047] X(t) = x0cosωt.

[0048] The relative displacement of the mass 2 is Y(t), and the motion equation of the system is expressed as:

[0049]

[0050] Wherein, m is the mass of the mass 2, k is the elastic coefficient of the spring system, and c is the damping coefficient. The steady-state solution of the above formula is:

[0051] Y(t) = y0cos(ωt-θ);

[0052] Wherein, the amplitude y0and the initial phase θ are:

[0053]

[0054] Wherein, ξ is the damping ratio, ω n is the resonance angular frequency of the system. From the above analysis, it can be seen that the steady-state response is highly nonlinear in the entire vibration frequency range. When the vibration frequency ω is lower than 0.2ω n , it can be considered that the vibration frequency ω is much smaller than the resonance frequency ω n , that is, the size of is much smaller than 1 and is approximately 0, so and in the denominator of the amplitude y0can be approximated to 0, and and in the initial phase θ can be approximated to 0, so the initial phase θ is approximately 0, and the amplitude y0can be expressed as:

[0055]

[0056] Then the particular solution of the steady-state solution can be expressed as:

[0057]

[0058] It can be easily seen that the relative displacement of the mass 2 is proportional to the acceleration of the excitation signal X(t) , and has Then the center wavelength shift Δλ B of the fiber Bragg grating 4 is proportional to the acceleration of the excitation signal X(t) The relationship is:

[0059]

[0060] Through the above analysis, we can know the resonant frequency ω of the accelerometer n The resonant frequency determines the accelerometer's measurement range and sensitivity, while the resonant frequency is related to the mass m and elastic modulus k of mass 2. Therefore, the resonant frequency needs to be adjusted by adjusting the values ​​of m and k to maximize the accelerometer's measurement range and sensitivity. Finite element analysis determined the optimal Young's modulus of elastic diaphragm 3 to be 133 GPa, and the optimal weight of mass 2 to be 7.1 g.

[0061] Optionally, the grating portion of the fiber Bragg grating 4 is located within the cavity of the housing. This more enclosed environment reduces the impact of ambient noise on the fiber Bragg grating 4, allowing the acceleration of the object to be measured to be more accurately reflected in the changes in the central wavelength of the fiber Bragg grating 4, thereby improving the accuracy of the accelerometer.

[0062] Optionally, the elastic diaphragm 3 is a copper alloy metal plate with a plurality of openings. Copper alloy QBe2 has excellent strength, wear resistance and elasticity, and its Young's modulus is 133 GPa, making it a preferred material for making the elastic diaphragm 3.

[0063] refer to Figure 2 Optionally, the elastic diaphragm 3 includes a cross-shaped beam structure and a frame structure located outside the cross-shaped beam structure. The cross-shaped beam structure and the frame structure are connected, and the mass block is connected to the intersection of the cross-shaped beam structure. The cross-shaped beam structure can provide stable support for the mass block and the fiber Bragg grating. When the object to be measured experiences acceleration in a non-operating direction, that is, acceleration in a direction parallel to the elastic diaphragm, the cross-shaped beam structure can support the mass block and the fiber Bragg grating without displacement, making the accelerometer highly immune to vibrations in the non-operating direction.

[0064] Optionally, a ratio of the beam length to the beam width of the cross-shaped beam structure is greater than or equal to 1.5 and less than or equal to 120. Optionally, the elastic diaphragm has a thickness ranging from 0.1 mm to 0.3 mm.

[0065] The cross-beam structure's structural parameters within the aforementioned ranges ensure both the elastic diaphragm's sensitivity to acceleration in the operating direction and its high immunity to acceleration in the non-operating direction. Finite element analysis was used to numerically study the accelerometer's structure, revealing an optimal thickness of 0.3 mm for the diaphragm 3, 2 mm for the cross-beam structure, and 6 mm for its length.

[0066] Optionally, the fiber core of the fiber Bragg grating 4 is a single-mode fiber. The single-mode fiber has small transmission loss and small transmission dispersion, which makes the signal transmitted in the fiber farther, and the acceleration signal measured by the accelerometer can be transmitted farther.

[0067] Optionally, the accelerometer further comprises a base plate 6, the base plate 6 comprises positioning holes for fixing the accelerometer on the surface of the object to be measured. Figure 1 And Figure 3 The base plate 6 is flush with the outer surface of the shell, and the accelerometer can be fixed on the surface of the object to be measured by screwing through the positioning holes.

[0068] Based on the same inventive concept, the embodiments of the present application also provide a measurement system, comprising a measurement device and an accelerometer provided by any of the embodiments of the present application; the accelerometer is installed on the surface of the object to be measured, the accelerometer is used to collect the acceleration of the object to be measured by the mass 2 to generate a vibration signal, the center wavelength of the fiber Bragg grating 4 is changed based on the vibration signal, the measurement device is connected to the accelerometer, and is used to measure the change of the center wavelength of the fiber Bragg grating, and calculate the acceleration of the object to be measured.

[0069] Figure 4 is the structure block diagram of the accelerometer measurement system provided by the embodiments of the present application. Referring to Figure 4 The accelerometer measurement system is composed of a broadband light source 7, an accelerometer 8, a photodiode 9, a data collector 10 and a processor. The vibration table 12 can realize one-dimensional vibration of different frequencies and different sizes of acceleration, which is used to simulate the vibration condition of the object to be measured. The broadband light source 7 is composed of an amplified spontaneous emission broadband light source, the photodiode 9, the data collector 10 and the processor 11 constitute a measurement device. The light beam emitted by the broadband light source 7 is input into the accelerometer 8 through the fiber Bragg grating 4, because the vibration table 12 drives the accelerometer 8 to vibrate, the center wavelength of the fiber Bragg grating 4 fluctuates, the light beam reflected by the fiber Bragg grating 4 is received by the photodiode 9, the data collector 10 collects the wavelength information of the reflected light beam, and then transmits the wavelength information of the reflected light beam to the processor 11, and the processor 11 calculates the acceleration of the vibration table 12.

[0070] In the test, when the vibration acceleration of the vibration table 12 on which the accelerometer 8 is placed is set to 1g (1g = 9.8m / s 2 ), the vibration frequency of the vibration table 12 is controlled to be 10Hz to 500Hz. Figure 5 is the time domain response waveform of the accelerometer provided by the embodiments of the present application under different vibration frequencies when the vibration acceleration is 1g. Figure 6 is the frequency response amplitude of the accelerometer provided by the embodiments of the present application when the vibration acceleration is 1g. Referring to Figure 5 And Figure 6The results show that the frequency range of the flat response region of the time domain response waveform of the accelerometer 8 is 10 Hz to 200 Hz, that is, the preferred working vibration frequency range of the accelerometer 8 is 10 Hz to 200 Hz. It can also be found that the wavelength displacement increases with the increase of the vibration frequency, and when the frequency approaches 500 Hz, the wavelength displacement reaches the maximum value, which indicates that the frequency is close to the resonance frequency of the sensor.

[0071] Similarly, using the accelerometer measurement system shown in Figure 4 , the sine excitation signal output by the vibration table 12 is changed to a sine excitation of 100 Hz, the vibration acceleration of the vibration table 12 is set to increase from 0.6g to 6g with a step of 0.6g, and the central wavelength displacement of the fiber Bragg grating 4 under different accelerations is recorded. Figure 7 is the time domain response waveform of the accelerometer provided by the embodiment of the application under different accelerations when the vibration frequency is 100 Hz. It can be seen that the time domain response of the accelerometer 8 increases with the increase of the vibration acceleration of the vibration table 12.

[0072] Similarly, using the accelerometer measurement system shown in Figure 4 , the excitation frequency of the vibration table 12 is kept at 100 Hz, and the excitation accelerations are 1.2g, 2.4g, 3.6g, 4.8g and 6g respectively, to obtain the time domain responses in the working direction and the non-working direction. Figure 8 is the wavelength displacement response of the accelerometer provided by the embodiment of the application in the working direction and the non-working direction, wherein the working direction is the direction perpendicular to the elastic diaphragm 3. Referring to Figure 8 , the results show that when the vibration occurs in the non-working direction of the sensor, the wavelength displacement is relatively small and the waveform is flat, and when the vibration occurs in the working direction, a larger wavelength displacement is induced. The maximum cross-error is less than 3.26%, indicating that the accelerometer provided by the embodiment of the application has high immunity to vibration in the non-working direction.

[0073] The accelerometer provided by the embodiment of the application comprises a fiber Bragg grating, a mass block and an elastic diaphragm, the central wavelength of the fiber Bragg grating is very sensitive to axial strain, so that the accelerometer has high sensitivity to the acceleration of the fiber Bragg grating in the axial direction and can detect a tiny vibration acceleration signal; the elastic diaphragm is a sheet structure with elasticity, if the elastic diaphragm is subjected to a force in a direction perpendicular to the elastic diaphragm, the elastic diaphragm will be deformed, if the elastic diaphragm is subjected to a force in a direction parallel to the elastic diaphragm, the elastic diaphragm is difficult to be deformed, so that the combination of the elastic diaphragm and the mass block enables the accelerometer to resist vibration in a non-working direction. The material of the elastic diaphragm is preferably high-performance copper alloy QBe2, so that the elastic diaphragm has high strength, hardness, elasticity, wear resistance, fatigue limit and heat resistance. The structure of the elastic diaphragm is preferably a cross-shaped diaphragm structure, and the structure parameters of the cross-shaped beam structure can be in the above range to balance the sensitivity of the elastic diaphragm to acceleration in the working direction and the high immunity to acceleration in the non-working direction, so that the performance of the elastic diaphragm is greatly improved.

[0074] The above detailed description does not constitute a limitation on the protection scope. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An accelerometer, characterized in that include: Mass block, elastic diaphragm and fiber Bragg grating; The mass block is connected to the elastic diaphragm, and the mass block has a first deep hole, and the hole depth direction of the first deep hole is perpendicular to the elastic diaphragm; The fiber Bragg grating is arranged on a side of the elastic diaphragm away from the mass block, and the first end of the core body of the fiber Bragg grating passes through the elastic diaphragm and extends to be fixed in the first deep hole; The mass block is used to conduct a vibration signal so that the central wavelength of the fiber Bragg grating changes based on the vibration signal.

2. The accelerometer according to claim 1, wherein Also includes: A housing having a cavity, the housing being formed by splicing a first shell and a second shell, the elastic diaphragm being fixed at an interface between the first shell and the second shell; The second shell has a first through hole opposite to the first deep hole, and the second end of the core body of the fiber Bragg grating passes through the first through hole and extends to the outside of the shell.

3. The accelerometer according to claim 2, wherein: The grating portion of the fiber Bragg grating is located in the cavity of the housing.

4. The accelerometer according to claim 1, wherein: The elastic diaphragm is a copper alloy metal plate with a plurality of openings.

5. The accelerometer according to claim 1, wherein: The elastic diaphragm includes a cross-shaped beam structure and a frame structure located outside the cross-shaped beam structure, and the cross-shaped beam structure and the frame structure are connected; The mass blocks are connected at the intersections of the cross beams of the cross beam structure.

6. The accelerometer according to claim 5, characterized in that The ratio of the beam length to the beam width of the cross-shaped beam structure is greater than or equal to 1.5 and less than or equal to 120.

7. The accelerometer according to claim 1, wherein: The thickness of the elastic membrane ranges from 0.1 mm to 0.3 mm.

8. The accelerometer according to claim 1, wherein: The core body of the fiber Bragg grating is a single-mode optical fiber.

9. The accelerometer according to claim 1, wherein: Also included is a bottom plate, the bottom plate including positioning holes; The positioning hole is used to fix the accelerometer on the surface of the object to be measured.

10. A measurement system, characterized in that: comprising a measuring device and an accelerometer according to any one of claims 1 to 9; The accelerometer is installed on the surface of the object to be measured; The accelerometer is used to collect the acceleration of the object to be measured through the mass block to generate a vibration signal, so that the central wavelength of the fiber Bragg grating changes based on the vibration signal; The measuring device is connected to the accelerometer and is used to measure the change in the central wavelength of the fiber Bragg grating and calculate the acceleration of the object to be measured.

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