A fiber grating sensor for simultaneous measurement of real-time velocity and displacement

Abstract

The present invention relates to the field of fiber grating sensors, and discloses a fiber grating sensor for simultaneously measuring real-time rate and displacement, comprising a housing, a movable probe is arranged at one end of the housing, a support, rack 1, rack 2, gear 1, gear 2, a probe, a reset device, an optical fiber and a spring 1 are arranged inside the housing; one end of the rack 1 is connected to the probe, and the other end is connected to the spring 1; the gear 1 and the gear 2 are fixedly connected; the gear 1 is meshed with the upper surface of the rack 1, and the gear 2 is meshed with the lower surface of the rack 2; the lower end of the reset device is connected to the probe, and the needle of the probe is located on the wavy surface of the upper surface of the rack 2; the middle part of the optical fiber is adhered to the side of the probe, one end is located in the housing, and the other end is tightened and pasted on the inner surface of the housing and then led out, and the optical fibers located on both sides of the probe are respectively engraved with grating 1 and grating 2. The sensor disclosed by the present invention can detect real-time rate and displacement simultaneously, and has the characteristics of large range, high sensitivity and practicality.

Description

Technical Field

[0001] The invention relates to the field of fiber grating sensors, and in particular to a fiber grating sensor capable of simultaneously measuring real-time velocity and displacement. Background Art

[0002] Natural gas hydrate (chemical formula CH4·6H2O) is a sustainable clean energy with development prospects. It is an ice-like crystalline substance formed by natural gas and water under high pressure and low temperature conditions. Because it looks like ice and can burn when exposed to fire, it is also called "combustible ice". In the process of marine combustible ice mining, potential geological engineering risks have become one of the main uncertainties for safe and efficient development. Creep is one of the main causes of geological engineering risks. Studies on the instability of submarine land slopes based on two-dimensional and three-dimensional seismic reflection data show that creep-induced landslides are widely distributed in submarine slopes. Among them, whether the dissociation of combustible ice will lead to creep slip is a problem worthy of attention.

[0003] The seabed is an extremely complex environment, with the characteristics of extreme depth, low temperature, and high pressure. In addition, methane hydrate is flammable, so the displacement sensor used to detect whether the dissociation of methane hydrate produces lateral creep has very high requirements. Traditional electromagnetic displacement sensors require power supply, are not suitable for flammable and explosive environments, and are susceptible to electromagnetic interference and cannot detect over long distances and for long periods of time, which limits their application in displacement detection in seabed environments.

[0004] Fiber Bragg grating sensing is a new technology that uses light wavelength as a carrier, Bragg grating as a sensitive unit, and optical fiber as a transmission medium. It has the advantages of safety, high precision, fast response speed, low requirements for the working environment, and suitability for long-term and long-distance detection. It can accurately detect physical quantities in harsh environments. It has attracted the attention of scientific researchers and engineers and is widely used in the field of displacement detection.

[0005] In the process of displacement detection, the rate can not only describe the speed of the current displacement, but also accurately predict the displacement to be generated. These two points are of great significance for preventing safety accidents such as landslides. However, the current fiber grating sensors are mainly used to detect strain and temperature, while fiber grating sensors for detecting real-time rate are rare. Fiber grating displacement sensors mainly include cantilever beam structure, spring structure and fixed structure at both ends. The principle of the three structures only uses the axial strain of the optical fiber, so it cannot meet the needs of measuring real-time rate and displacement at the same time. In addition, they have the disadvantages of large volume, and the relationship between range and sensitivity is restricted after the structure is determined. It cannot be simply changed according to the changes in actual needs. Therefore, it is necessary to design a fiber grating sensor that can detect real-time rate and displacement at the same time to meet the measurement of creep during the dissociation of combustible ice. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a fiber grating sensor for simultaneously measuring real-time rate and displacement, so as to achieve the purpose of simultaneously detecting real-time rate and displacement, which has the characteristics of safety, large range, high sensitivity, extremely high flexibility and practicality.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A fiber grating sensor for measuring real-time rate and displacement simultaneously, comprising a shell, a movable probe is arranged at one end of the shell, and a support, rack 1, rack 2, gear 1, gear 2, a probe, a reset device, an optical fiber and a spring 1 are arranged inside the shell; the support is located at the bottom of the shell, the rack 1 passes through the groove on the top of the support, one end of the rack 1 is connected to the probe, and the other end is connected to one end of the spring 1, and the other end of the spring 1 is fixed to the inner wall of the shell; the two ends of the rack 2 are installed in the sliding groove of the inner wall of the shell through a sliding rod; the gear 1 and the gear 2 are fixedly connected and installed on the inner wall of the shell through a coaxial shaft; the radius of the gear 1 is smaller than the radius of the gear 2, the gear 1 is meshed with the upper surface of the rack 1, the gear 2 is meshed with the lower surface of the rack 2, and the upper surface of the rack 2 is wavy;

[0009] The reset device is fixed to the top of the inner wall of the shell, and the lower end of the reset device is connected to the probe. In the initial state, the needle tip of the probe is located in the wavy trough of the upper surface of the rack 2; the middle part of the optical fiber is glued to the side of the probe, one end is located in the shell, and the other end is tightened and glued to the inner surface of the shell and then led out, and the optical fibers located on both sides of the probe are engraved with grating one and grating two respectively.

[0010] In the above scheme, the reset device includes a shell and a second spring located in the shell, the second spring is connected to the tail of the probe, four strip grooves are longitudinally opened on the inner wall of the shell, four slides are arranged on the side of the probe, and the slides are located in the strip grooves.

[0011] In the above scheme, the probe is disc-shaped, the back side of which is fixedly connected to the rack, and the edge of which is in contact with the inner wall of the shell and can slide on the inner wall of the shell.

[0012] In the above solution, the probe is cylindrical, one end of which passes through the shell for detecting displacement, and the other end is fixedly connected to the rack.

[0013] In the above solution, one end of the optical fiber located in the housing is in a free state.

[0014] In the above solution, one end of the optical fiber located in the housing is fixed to the inner wall of the housing, and a pre-tension is applied to the other end.

[0015] In the above scheme, the gear one and the gear two are fixed in a plug-in manner, a socket is provided on the gear one, and a plug is provided on the gear two, and the plug is located in the socket.

[0016] Through the above technical solution, the fiber grating sensor for simultaneously measuring real-time velocity and displacement provided by the present invention has the following beneficial effects:

[0017] 1. The present invention first draws a function curve of the change of the reflection center wavelength drift over time, and after performing time-frequency analysis on the function curve by short-time Fourier transform algorithm or wavelet transform, the relationship between the rate of probe movement and the frequency of the above function curve is calibrated to achieve rate detection. At the same time, the number of the maximum value of the reflection center wavelength is multiplied by the peak-to-trough distance on the upper surface of the second rack to obtain displacement information, thereby achieving simultaneous measurement of rate and displacement.

[0018] 2. The present invention uses optical wavelength as information transmission, which has the advantages of safety, high precision, fast response speed, low requirements on the working environment, and suitability for long-term and long-distance detection, and is suitable for more application scenarios.

[0019] 3. The present invention fixes the optical fiber directly to the probe and the housing, and the probe jumping causes the optical fiber to undergo axial deformation. Compared with other displacement sensors with added elastic devices, the present invention has higher sensitivity.

[0020] 4. The present invention can increase the range of the sensor by increasing the length of rack 1 and rack 2, increase the depth of the wave tooth shape of rack 2 to increase the sensitivity of the sensor, reduce the distance between adjacent wave peaks, and increase the magnification of the amplification device composed of gear 1 and gear 2 to improve the resolution of the sensor. In summary, the sensor overcomes the restrictive relationship between the range and sensitivity of the previous fiber grating displacement sensor, and can simultaneously have the ability of large range, high sensitivity, and high resolution measurement.

[0021] 5. The sensor of the present invention can meet actual needs by only replacing the amplification device according to actual needs, and has the advantages of extremely high flexibility and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0023] Figure 1 This is a schematic diagram of a fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement disclosed in Example 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of a fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement disclosed in Example 1 of the present invention;

[0025] Figure 3 is a schematic diagram of the inner wall of the shell;

[0026] Figure 4 Schematic diagram of the structure of gear 1;

[0027] Figure 5 It is a schematic diagram of the structure of gear 2;

[0028] Figure 6 It is a schematic diagram of the cross-sectional area of ​​the reset device housing;

[0029] Figure 7 Schematic diagram of the probe structure.

[0030] In the figure, 1, shell; 2, disc-shaped probe; 3, support; 4, rack 1; 5, rack 2; 6, gear 1; 7, gear 2; 8, probe; 9, optical fiber; 10, spring 1; 11, concentric axis; 12, jack; 13, plug; 14, shell; 15, spring 2; 16, strip groove; 17, slide; 18, grating 1; 19, grating 2; 20, cylindrical probe; 21, sliding rod; 22, slide groove; 23, circular groove. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] Example 1

[0033] The present invention provides a fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement, comprising a housing 1, a movable disc-shaped probe 2 is arranged at one end of the housing 1, the back of the probe 2 is fixedly connected to a rack 4, and the edge of the probe 2 contacts the inner wall of the housing 1 and can slide on the inner wall of the housing 1. In this embodiment, the side wall of the left side of the housing 1 connected to the probe can be omitted, and the probe serves as the side wall of the housing 1.

[0034] The housing 1 is provided with a support 3, a rack 1 4, a rack 2 5, a gear 1 6, a gear 2 7, a probe 8, a reset device, an optical fiber 9 and a spring 10. The support 3 is located at the bottom of the housing 1. The support 3 is a trapezoidal structure with a groove on the upper surface. The rack 1 4 passes through the groove on the top of the support 3 and can move back and forth in the groove. One end of the rack 1 4 is connected to the probe, and the other end is connected to one end of the spring 10. The other end of the spring 10 is fixed to the inner wall on the right side of the housing 1. When the rack 1 4 moves to the right, the spring 10 is compressed, which can help the rack 1 4 to reset.

[0035] Gear 1 6 and gear 2 7 are fixedly connected and mounted on the inner wall of housing 1 through concentric shaft 11. Specifically, gear 1 6 and gear 2 7 are plug-in fixed. Figure 4 and Figure 5As shown, four jacks 12 are provided on the gear 1 6 , and four plugs 13 are provided on the gear 2 7 . The plugs 13 are located in the corresponding jacks 12 , so that there is no relative sliding between the gear 1 6 and the gear 2 7 .

[0036] Gear 1 6 and gear 2 7 form an amplification device. The radius of gear 1 6 is smaller than that of gear 2 7. The ratio of the two radii is the amplification factor. The amplification factor can be changed by replacing gears with different radii, thereby changing the sensor measurement parameters. Gear 1 6 meshes with the upper surface of rack 1 4, and gear 2 7 meshes with the lower surface of rack 2 5. The upper surface of rack 2 5 is wavy, with evenly arranged troughs and peaks. The two ends of rack 2 5 are installed in the strip-shaped slide groove 22 of the inner wall of housing 1 through a sliding rod 21, and the sliding rod 21 can slide left and right in the slide groove 22.

[0037] The reset device is fixed to the top of the inner wall of the housing 1, and the lower end of the reset device is connected to the probe 8. In the initial state, the needle of the probe 8 is located in the wavy trough of the upper surface of the rack 5; the reset device includes a housing 14 and a spring 15 located in the housing 14, and the spring 15 is connected to the tail of the probe 8. The spring 15 can help the probe 8 to reset. Figure 6 As shown, the inner wall of the housing 14 is provided with four strip-shaped grooves 16 in the longitudinal direction. Figure 7 As shown, four slides 17 are arranged on the side of the probe 8 , and the slides 17 are located in the strip groove 16 and can slide up and down in the strip groove 16 .

[0038] The middle of the optical fiber 9 is glued to the side of the probe 8, one end is located in the housing 1 and is free; the other end is tightened and glued to the inner surface of the housing 1 and then led out. Grating 1 18 and grating 2 19 are engraved on the optical fiber 9 on both sides of the probe 8. Grating 1 18 is used to measure the temperature and compensate for the temperature of grating 2 19. Driven by the probe 8, grating 2 19 will produce reciprocating stretching and contraction, which is used to measure the speed and displacement.

[0039] Example 2

[0040] like Figure 2As shown, the difference between this embodiment and embodiment 1 is that, firstly, a disc is no longer used as a probe for detecting displacement, but a cylindrical probe 20 is used, one end of which passes through the housing 1 for detecting displacement, and the other end is fixedly connected to the rack 1 4. Secondly, the optical fiber 9 in embodiment 2 is obliquely pasted on the inner surface of the two ends of the housing 1, and the middle is pasted and fixed on the side wall of the probe 8, wherein the grating 18 can be tightened, while the grating 2 19 needs to apply a certain pre-tension, so that when the probe 8 slides upward, the grating 1 18 is stretched, the reflection center wavelength is red-shifted, and the grating 2 19 is contracted, and the reflection center wavelength is blue-shifted. When the probe 8 slides downward, the grating 1 18 is contracted, the reflection center wavelength is blue-shifted, and the grating 2 19 is stretched, and the reflection center wavelength is red-shifted. The difference in the strain response of the two gratings is used to improve the sensitivity of the sensor. At the same time, since the gratings are both sensitive to temperature, the difference between the two also eliminates the influence of temperature.

[0041] Finally, the optical fiber 9 led out from the tail in Examples 1 and 2 receives the reflected light signal through a spectrometer, which is manifested as the left and right drift of the center reflection wavelength of the spectrum. A curve of the reflection center wavelength changing with time is drawn. After filtering and removing noise, the frequency information within a period of time is obtained by the signal processing algorithm. The rate measurement can be achieved by calibrating the relationship between frequency and rate. In addition, the number of times the maximum value of the reflection center wavelength is transformed, the distance between adjacent wave peaks on the upper surface of the rack 5, and the magnification are multiplied to obtain the external displacement, and finally the simultaneous measurement of rate and displacement is achieved.

[0042] like Figure 3 As shown, in the present embodiments 1 and 2, the inner wall of the housing 1 needs to be made with a circular groove 23 and a sliding groove 22 for the coaxial shaft 11 of the fixed gear 1 6 and the gear 2 7 and the sliding rod 21 supporting the rack 2 5, respectively.

[0043] In the present embodiments 1 and 2, the probe and the housing are tightly matched to prevent sand from entering the interior and affecting measurement and resetting.

[0044] In the present embodiments 1 and 2, the end of the sliding rod 21 is placed in a sliding groove 22 of the same height as the side wall of the housing 1 .

[0045] In the present embodiments 1 and 2, grating 18 and grating 2 19 are relatively close to each other, so as to prevent the gratings in the sensor from being in different temperature gradients.

[0046] The probe can be recorded as the zero point at any position within the measuring range. When subjected to force, it moves to the right to produce displacement. When not subjected to force, it moves to the left under the action of spring 10, thus realizing automatic resetting of displacement and round-trip measurement.

[0047] The working principle of the present invention is as follows:

[0048] (1) The principle of gears for displacement amplification. Assume that the radii of gear 1 6 and gear 2 7 are r1 and r2 respectively. When the two concentric circles are fixed and no relative sliding occurs, the two gears have the same angular velocity ω during rotation. According to the relationship between the linear velocity V, the angular velocity ω and the radius R:

[0049] V=R×ω

[0050] In the same time Δt, the displacement of gear 1 6 and gear 2 7 is:

[0051] D1=r1×ω×Δt

[0052] D2=r2×ω×Δt

[0053] Since the angular velocity ω and the time Δt are the same, the magnification K is the ratio of the two displacements:

[0054] K=D2 / D1=r2 / r1

[0055] The ratio of the gear radii is the magnification factor.

[0056] (2) Principle of rate measurement: The optical signal is demodulated to obtain a time-varying function curve of the drift of the reflection center wavelength. After denoising, a short-time Fourier transform or wavelet transform algorithm is used to perform time-frequency analysis to obtain the relationship between the frequency of the curve and time. The probe movement rate and the curve frequency are then calibrated to obtain a linear relationship between the rate and the curve frequency, thus achieving real-time rate detection.

[0057] (3) Principle of displacement measurement: When the probe senses an external displacement S, it pushes rack 14 to move rightward by the same displacement S. Since gear 16 meshes with the upper surface of rack 14, gear 16 rotates counterclockwise and drives gear 27 to rotate counterclockwise. The radius ratio of gear 27 to gear 16 is K. Gear 27 meshes with the lower surface of rack 25, driving rack 25 to slide to the left. The sliding distance is L = K × S. The upper surface of rack 25 is wavy. Let B be the distance between two adjacent wave peaks, A be the amplitude of the waveform, and D be the length of grating 219. The needle of probe 8 rises and falls with the wavy teeth on the upper surface of rack 25, causing grating 219 to stretch and contract repeatedly, resulting in a blue shift and a red shift of the reflection center wavelength. Let N be the number of times the maximum reflection center wavelength appears, and the maximum wavelength difference is Δλ. max , Δλ max It is related to the amplitude A and the length D of the grating 19. According to the above parameters, the displacement S, sensitivity R and resolution M of the sensor can be obtained as follows:

[0058]

[0059]

[0060]

[0061] It can be seen from the above formula that when the distance between adjacent wave crests of the wave tooth shape is determined, the range of the sensor is related to the number of times the probe 8 passes through the wave crest, while the sensitivity is mainly related to the maximum value Δλ of the reflection center wavelength. max The above parameters are all related to the magnification K, so the parameters of the sensor can be changed by changing only the amplification device, which successfully solves the restrictive relationship between the range and sensitivity, and the resolution can be artificially controlled.

[0062] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement, characterized in that: It comprises a shell, a movable probe is arranged at one end of the shell, and a support, rack 1, rack 2, gear 1, gear 2, a probe, a reset device, an optical fiber and a spring 1 are arranged inside the shell; the support is located at the bottom of the shell, the rack 1 passes through the groove at the top of the support, one end of the rack 1 is connected to the probe, and the other end is connected to one end of the spring 1, and the other end of the spring 1 is fixed to the inner wall of the shell; the two ends of the rack 2 are installed in the slide groove of the inner wall of the shell through a sliding rod; the gear 1 and the gear 2 are fixedly connected and installed on the inner wall of the shell through a coaxial shaft; the radius of the gear 1 is smaller than the radius of the gear 2, the gear 1 is meshed with the upper surface of the rack 1, the gear 2 is meshed with the lower surface of the rack 2, and the upper surface of the rack 2 is wavy; The reset device is fixed to the top of the inner wall of the shell, and the lower end of the reset device is connected to the probe. In the initial state, the needle tip of the probe is located in the wavy trough of the upper surface of the rack 2; the middle part of the optical fiber is glued to the side of the probe, one end is located in the shell, and the other end is tightened and glued to the inner surface of the shell and then led out, and the optical fibers located on both sides of the probe are engraved with grating one and grating two respectively.

2. A fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: The reset device comprises a shell and a second spring located in the shell, wherein the second spring is connected to the tail of the probe, four strip grooves are longitudinally provided on the inner wall of the shell, and four slides are arranged on the side of the probe, wherein the slides are located in the strip grooves.

3. The fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: The probe is in the shape of a disk, the back side of which is fixedly connected to a rack, and the edge of which is in contact with the inner wall of the shell and can slide on the inner wall of the shell.

4. The fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: The probe is cylindrical, one end of which passes through the shell for detecting displacement, and the other end is fixedly connected to the rack.

5. The fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: One end of the optical fiber located in the housing is in a free state.

6. The fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: One end of the optical fiber located in the housing is fixed on the inner wall of the housing, and a pre-tension is applied to the other end.

7. The fiber Bragg grating sensor for simultaneously measuring real-time velocity and displacement according to claim 1, characterized in that: The gear one and the gear two are fixed in a plug-in manner, a socket is provided on the gear one, a plug is provided on the gear two, and the plug is located in the socket.

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