Fiber bragg grating tilt angle sensor structure based on mechanical equilibrium principle

Abstract

The utility model relates to the technical field of fiber bragg grating inclination angle measurement, in particular to a fiber bragg grating inclination angle sensor structure based on a mechanical equilibrium principle, which comprises a shell and a fiber bragg grating, on the basis of the mechanics principle, an inclination angle measuring structure based on the mechanics lever principle is provided, a novel inclination sensing mechanism is adopted through movable connection between the lead block and the fixed cross rod, and the inclination angle measuring accuracy is improved. The inclination angle sensor can overcome the problem that the sensor has errors due to friction caused by rigid fixation between the mass block and the cross bar in the existing inclination angle sensor. According to the method, a mechanical lever model is established, structural parameters are optimized, finally, an inclination angle test platform is established, and the sensitivity, the precision, the resolution ratio, the creep resistance, the repeatability error and the like of the sensor are tested, so that the overall practicability is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of fiber grating inclination measurement, in particular to a fiber grating inclination sensor structure based on the principle of mechanical balance. Background Technique

[0002] After searching the Chinese patent document with the existing publication number CN219532040U, a high-precision fiber grating inclination sensor is disclosed, which includes a housing, a lid and a fiber grating; the lid is adaptively connected to the housing; the housing has an installation groove; an inner core body is connected in the installation groove; the inner core body includes a fiber fixing block, a connecting piece and a mass core body; the front end of the fiber fixing block is connected to the front side of the installation groove; the mass core body is connected to the fiber fixing block through the connecting piece and is suspended in the installation groove; one end of a fiber grating passes through the left side of the housing and is connected to the left side of the fiber fixing block and extends to the mass core body; the other end of the fiber grating passes through the right side of the housing and is connected to the right side of the fiber fixing block and extends to the mass core body. The device improves the accuracy of measuring the inclination change of structures such as buildings, with small errors.

[0003] The fiber grating sensor belongs to a kind of fiber sensor. The sensing process based on the fiber grating obtains sensing information through the modulation of the fiber Bragg wavelength by external physical parameters, and it is a wavelength modulation type fiber sensor. The fiber grating inclination sensor based on the principle of mechanical balance is a device that uses a fiber Bragg grating (FBG) as a sensing element and combines mechanical structure design to detect the inclination angle. The existing disadvantages of fiber grating inclination measurement include high manufacturing cost, complex structure, difficult maintenance, and the rigid connection between the heavy object and the crossbar resulting in the influence of friction on the sensor accuracy, leading to poor practicability. Content of the Utility Model

[0004] The technical problem to be solved by the utility model is to overcome the defects of the prior art and provide a fiber grating inclination sensor structure based on the principle of mechanical balance, aiming to solve the technical problems of high manufacturing cost, complex structure, difficult maintenance, and the influence of friction on the sensor accuracy caused by the rigid connection between the heavy object and the crossbar in the prior art.

[0005] To solve the above technical problems, the utility model provides the following technical solutions:

[0006] The structure of a fiber Bragg grating inclination sensor based on the principle of mechanical balance of the present utility model includes a housing and a fiber Bragg grating. An oblong hole is provided in the upper part of one end surface of the housing. A cavity is provided in the middle of the inner side of the housing. A fixing rod is provided on the top surface at the inner part of the housing. A cross bar is provided on the bottom surface of the fixing rod. First fiber Bragg grating elements and towing ropes are respectively provided at both ends of the bottom surface of the cross bar. A counterweight lead block is provided on the bottom surface of the towing rope. A second fiber Bragg grating element is provided at one end of the inner part of the housing close to the oblong hole.

[0007] As a further description of the above technical solution:

[0008] The housing is arranged in a cuboid shape, the cavities inside the housing are all arranged in a cuboid shape, the oblong hole is arranged in a hollowed-out shape, the housing and the fixing rod are fixedly connected, the fixing rod is arranged in a cylinder shape, and the fixing rod and the cross bar are connected and fixed through a spring element.

[0009] As a further description of the above technical solution:

[0010] The cross bar is fixedly connected with both the first fiber Bragg grating element and the towing rope. The towing rope and the counterweight lead block are arranged in a sphere shape. The housing and the second fiber Bragg grating element are fixedly connected. Corresponding slot holes for the first fiber Bragg grating element and the second fiber Bragg grating element are provided on the bottom surface of the housing.

[0011] The present utility model has the following beneficial effects:

[0012] In the present utility model, based on the mechanical principle, an inclination measurement structure based on the principle of mechanical lever is proposed. By adopting a new type of tilt sensing mechanism with a movable connection between the lead block and the fixed cross bar, the friction caused by the rigid fixation between the mass block and the cross bar in the existing inclination sensor can be overcome, thus solving the problem of errors in the sensor. A mechanical lever model is established and the structural parameters are optimized. Finally, an inclination test platform is built to test the performance of the sensor, such as sensitivity, accuracy, resolution, anti-creep performance, repeatability error, etc., so as to improve the overall practicability. Description of the Drawings

[0013] The drawings are used to provide a further understanding of the present utility model, and constitute a part of the specification. They are used together with the embodiments of the present utility model to explain the present utility model, but do not constitute a limitation to the present utility model. In the drawings:

[0014] Figure 1 is the overall structural schematic diagram of the present utility model;

[0015] Figure 2 is the schematic diagram of the internal structure of the housing of the present utility model;

[0016] Figure 3It is a schematic diagram of linear fitting of the angle and wavelength offset of the present utility model;

[0017] In the figure: 1. Outer shell; 2. Square hole; 3. Cavity; 4. Fixed rod; 5. Cross bar; 6. First fiber grating component; 7. Traction rope; 8. Counterweight lead block; 9. Second fiber grating component. Specific implementation mode

[0018] The preferred embodiments of the present utility model will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present utility model and are not used to limit the present utility model.

[0019] Among them, the same reference numerals in the drawings all refer to the same components.

[0020] Embodiment 1

[0021] Referring to Figures 1-3 , an embodiment provided by the present utility model: A fiber grating inclination sensor structure based on the principle of mechanical balance, including an outer shell 1 and a fiber grating. On the upper part of one end surface of the outer shell 1, there is a square hole 2. In the middle of the inner side of the outer shell 1, there is a cavity 3. On the top surface of the inner part of the outer shell 1, there is a fixed rod 4. On the bottom surface of the fixed rod 4, there is a cross bar 5. At both ends of the bottom surface of the cross bar 5, there are respectively a first fiber grating component 6 and a traction rope 7. On the bottom surface of the traction rope 7, there is a counterweight lead block 8. Near one end of the inner part of the outer shell 1 where the square hole 2 is located, there is a second fiber grating component 9.

[0022] The outer shell 1 is arranged in a cuboid shape, and the cavity 3 inside the outer shell 1 is also arranged in a cuboid shape. The square hole 2 is arranged in a hollow shape. The outer shell 1 and the fixed rod 4 are fixedly connected, and the fixed rod 4 is arranged in a cylinder shape. The fixed rod 4 and the cross bar 5 are connected and fixed through a spring component.

[0023] The cross bar 5 is fixedly connected to both the first fiber grating component 6 and the traction rope 7. The traction rope 7 and the counterweight lead block 8 are arranged in a sphere shape. The outer shell 1 and the second fiber grating component 9 are fixedly connected, and on the bottom surface of the outer shell 1, there are corresponding slot holes for the first fiber grating component 6 and the second fiber grating component 9.

[0024] Specifically, its structure is formed by a housing 1, a square hole 2, a cavity 3, a fixing rod 4, a cross bar 5, a first fiber grating component 6, a traction rope 7, a weight lead block 8 and a second fiber grating component 9 to form a fiber grating inclinometer structure based on the principle of mechanical balance. The fiber grating inclinometer structure based on the principle of mechanical balance is usually used in application scenarios that require high-precision monitoring of structural inclination, such as the safety monitoring of structures such as bridges, buildings, and dams. Ferdinand et al. proposed a temperature-insensitive fiber grating type inclinometer. This sensor has a fiber Bragg grating pasted on each of the upper and lower surfaces of a cantilever beam, and these two fiber Bragg gratings are symmetrically distributed based on the cantilever beam. When the sensor tilts, the strains of the sensor are opposite, and the central wavelengths shift in opposite directions. Since the two fiber gratings are in the same temperature field and are consistent in terms of the influence of temperature, this sensor has a temperature self-adaptive function, and the tilt angle and the change in wavelength show a linear relationship. The housing 1 and the cavity 3 are used to protect the internal components, provide mechanical support, achieve environmental isolation, facilitate installation, and have strong durability. The cavity 3 provides a solid housing 1 that can protect the sensitive internal fiber gratings from external environmental factors such as humidity, temperature changes, physical impacts, etc.; the cavity 3 provides the necessary mechanical support for the sensor to ensure that the sensor can maintain the correct alignment during use and can withstand a certain amount of external force without affecting its normal operation; the cavity 3 can also help isolate the sensor from the external environment and reduce the influence of non-target factors (such as temperature changes or electromagnetic interference) on the measurement results; a good cavity 3 design can make the sensor easier to be installed in various different application environments, whether it is fixed installation or portable application. For applications with long-term deployment, the material selection and design of the cavity 3 are directly related to the overall durability of the sensor, especially for sensors working in harsh environments. The square hole 2 serves as a fiber access point. The sensor needs to be connected to a bare fiber grating, and the square hole 2 can be used as the access point for the fiber, facilitating wiring while maintaining the structural integrity. The fixing rod 4 provides a stable installation foundation, enabling the sensor to be firmly fixed in the specified position, avoiding measurement errors caused by loosening or displacement, and can precisely control the installation direction of the sensor to ensure that the sensor can accurately capture the required tilt angle changes for direction positioning. The design of the fixing rod 4 usually takes into account the possibilities of various installation methods, such as pasting or other methods to be installed on different surfaces to construct a lever structure. The cross bar 5, as part of the lever, can convert a small angle change into a large displacement change. This is because when one end is subjected to an external force or an angle change, a larger displacement will occur at the other end. This characteristic improves the sensitivity of the sensor to the tilt angle, enabling even very subtle changes to be accurately detected and magnifying the torque; the cross bar 5 connects different parts of the sensor to ensure that the entire system works as a whole.It connects the fiber Bragg grating (FBG) and other mechanical components to form an effective force transmission path; the design of the crossbar 5 can help determine the installation position and direction of the sensor, ensuring that the sensor can accurately capture the required tilt angle changes. In addition, it can also serve as a guiding device to ensure that the sensor moves in the expected manner during tilting; in the lever structure, it ensures that under the action of external forces, the stress can be evenly distributed to avoid structural failure caused by local overload; the reasonable length and material selection of the crossbar 5 can increase the stability of the entire system and reduce false measurements caused by external vibrations or other interferences; by adjusting the length of the crossbar 5, the sensitivity of the sensor can be adjusted. A longer crossbar 5 can provide higher sensitivity but may sacrifice some resolution; on the contrary, a shorter crossbar 5 can improve the resolution to a certain extent; the presence of the crossbar 5 also facilitates the daily maintenance and regular calibration of the sensor, making the sensor easier to disassemble and reassemble. The first fiber Bragg grating component 6 is directly connected to the lever structure. When the sensor experiences tilting, the lever structure will deform or displace, thereby causing the stretching or compression of the fiber Bragg grating. This physical change will cause a change in the refractive index of the fiber Bragg grating, thus changing its Bragg wavelength; since the Bragg wavelength of the fiber Bragg grating is related to its stress state, the first fiber Bragg grating component 6 can convert the physical angle change into a measurable optical signal change. By monitoring the change in the Bragg wavelength, the tilt angle information can be indirectly obtained; the fiber Bragg grating is very sensitive to minute strains, so even a slight angle change can be captured by the first fiber Bragg grating and converted into an obvious spectral change, thereby achieving high-precision angle measurement. The displacement or stress generated by the lever structure during tilting is transmitted to the fiber Bragg grating through the towing rope 7. When the sensor tilts, one end of the lever will move up or down, and this movement is converted into the stretching or compression of the fiber Bragg grating through the towing rope 7; through appropriate mechanical design, the towing rope 7 can help linearize the output signal of the sensor. That is to say, when the tilt angle of the sensor changes, the towing rope 7 can ensure that the strain change of the fiber Bragg grating maintains a consistent proportional relationship with the tilt angle. The counterweight lead block 8 can help maintain the balance state of the sensor under static conditions. By adjusting the position and mass of the counterweight lead block 8, it can be ensured that the sensor is in the zero position, i.e., the horizontal state, when there is no external force. This is very important for initializing the sensor and subsequent calibration; in a dynamic or vibrating environment, the counterweight lead block 8 can play a stabilizing role and reduce the influence of external vibrations on the sensor output. A reasonable counterweight design can reduce unnecessary interferences and make the sensor more focused on measuring real tilt changes; during installation and calibration, the counterweight lead block 8 can help quickly find the zero position of the sensor.By adjusting the counterweight lead block 8, the sensor can be easily restored to its initial horizontal state, simplifying the debugging process; the use of the counterweight lead block 8 can ensure that the sensor returns to the same initial position after each tilt, thereby improving the repeatability and consistency of measurement. The Bragg wavelength of the fiber grating of the second fiber grating component 9 is affected not only by mechanical strain but also changes with temperature. The second fiber grating is usually placed in a position not affected by mechanical stress changes but exposed to the same temperature conditions. By monitoring the difference in wavelength changes of these two fiber gratings, the temperature effect can be separated, thus achieving compensation for temperature changes.

[0025] Working principle: During the process of leading out the pigtail of the force-bearing fiber grating from the upper cover plate of the protective housing 1, first, use sandpaper to clean the aluminum chips at the punched hole of the upper cover plate of the housing 1, then wash the punched hole with alcohol, wait for the alcohol to volatilize, apply a certain prestress to the fiber grating, then drop a small amount of 502 glue at the punched hole, and after the pasting position is fixed, apply a certain amount of epoxy resin 353ND glue all over the punched hole, and use a heating lamp to irradiate at a high temperature for more than half an hour until the epoxy resin 353ND glue is completely cured. At the surface l of the cross bar 5, after using sandpaper to polish the stainless steel cross bar 5 evenly. Paste the other end of the force-bearing fiber grating vertically and naturally on the surface of the cross bar 5, and a small amount of 502 glue can be dropped at the joint. After the position is fixed, evenly apply epoxy resin 353ND and irradiate at a high temperature until it is cured. In this way, the goal of the relative level of the position of the cross bar 5 and the perpendicular connection between the fiber grating and the cross bar 5 can be achieved. When in use, fix the sensor in the area to be measured, record the initial wavelength after standing for a period of time, and according to the wavelength method and the angular linear fitting relationship, the angular movement value can be obtained based on the wavelength.

[0026] Preparation method of the fiber grating inclinometer sensor structure based on the principle of mechanical equilibrium:

[0027] The mechanical model of the fiber grating inclinometer sensor includes:

[0028]

[0029] Among them, Δλ is the wavelength drift of the first fiber grating, θ is the tilt angle, pe is the effective elasto-optic coefficient of the fiber grating, λ is the initial wavelength of the fiber grating, m is the mass of the lead block, g is the acceleration due to gravity, E is the elastic modulus of the fiber grating, and r is the cross-sectional radius of the fiber grating.

[0030] Sensitivity analysis, resolution analysis:

[0031] (1) The tilt response test starts from the zero value state. The tilt platform rotates to 0°, increases step by step by 1° to 10°, and then decreases from 10° by 1° each time to 0° to complete a cycle test. Read the wavelength change through the host computer, and keep each test point for 5 minutes to stabilize the sensor reading;

[0032] (2) Repeat the experiment in (1) three more times to form four cycle tilt response tests;

[0033] (3) During the cycle test, plot the real-time response curve of the wavelength drift of the first fiber Bragg grating and the measurement output result of the change value of the first fiber Bragg grating;

[0034] (4) Process the response curve to obtain eight curves of tilt and wavelength drift in the forward and reverse processes during the four cycle tests. Perform linear fitting on the arithmetic mean of the eight curves to obtain a fitting function, and then obtain the tilt measurement sensitivity and tilt measurement resolution of the sensor. Hold for more than 30 minutes and then return to the zero value. The demodulator collects the wavelength data of the first fiber Bragg grating of the sensor in real time. When the tilt angle of the sensor is 10°, judge whether the wavelength fluctuation range is within the set range. If so, it means that the stability of the fiber Bragg grating tilt sensor meets the requirements; otherwise, it means that it does not meet the requirements.

[0035] Precision analysis specifically includes: The mathematical expression of linearity is:

[0036]

[0037] Among them, ΔLmax is the absolute value of the maximum deviation between the average value of the output of the cycle experiment and the fitting curve, yFS = ymax - ymin is the full-scale output value, where ymax is the average value of the output of the forward and reverse strokes at the maximum range;

[0038] Use the least squares method to perform linear fitting on the average value of the experimental data of the three cycle tilt response tests. Substitute the tilt angle into the fitting curve to obtain the fitting value, calculate the absolute value of the deviation, and substitute the absolute value of the deviation into formula (11) to obtain the linearity of the fiber Bragg grating tilt sensor;

[0039] The mathematical expression of hysteresis is:

[0040]

[0041] Process the experimental data of the forward and reverse strokes in the four cycle experiments to obtain the maximum difference between the forward and reverse stroke outputs of 30 pm and the full-scale output value of 2720 pm. Substitute into formula (12) to calculate the hysteresis of the sensor;

[0042] Precision expression:

[0043]

[0044] Among them, γL is the linearity error, γH is the hysteresis error, and γR is the repeatability error;

[0045] Substitute the linearity and hysteresis values into formula (13) to obtain the accuracy of the fiber grating inclination sensor based on the cantilever pendulum bearing structure.

[0046] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A fiber Bragg grating inclination sensor structure based on the principle of mechanical balance, comprising a housing (1) and a fiber Bragg grating, characterized in that: A square hole (2) is provided at the upper portion of one end surface of the shell (1), a cavity (3) is provided at the middle portion of the inner side of the shell (1), a fixing rod (4) is provided at the top end surface of the inner side of the shell (1), a cross rod (5) is provided at the bottom end surface of the fixing rod (4), a first optical fiber grating component (6) and a traction rope (7) are provided at both ends of the bottom end surface of the cross rod (5), a counterweight lead block (8) is provided at the bottom end surface of the traction rope (7), and a second optical fiber grating component (9) is provided at one end of the inner side of the shell (1) close to the square hole (2).

2. The fiber Bragg grating inclination sensor structure based on the mechanical balance principle according to claim 1, characterized in that: The outer shell (1) is in the shape of a rectangular parallelepiped, the inner cavity (3) of the outer shell (1) is in the shape of a rectangular parallelepiped, the square hole (2) is in the shape of a hollow, the outer shell (1) and the fixing rod (4) are fixedly connected, the fixing rod (4) is in the shape of a cylinder, and the fixing rod (4) and the cross rod (5) are connected and fixed by a spring member.

3. The fiber Bragg grating inclination sensor structure based on the mechanical balance principle according to claim 1, characterized in that: The cross bar (5) is fixedly connected to the first fiber optic grating component (6) and the traction rope (7); the traction rope (7) and the counterweight lead block (8) are spherical; the outer shell (1) is fixedly connected to the second fiber optic grating component (9); and the bottom surface of the outer shell (1) is provided with corresponding slots for the first fiber optic grating component (6) and the second fiber optic grating component (9).

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