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摘要:
为了解决在复杂电磁环境下大位移量的监测问题,实现对大型机械和工程结构健康安全状况的实时监测,设计了一种基于悬臂梁结构的可调量程拉绳式光纤布拉格光栅位移传感器。悬臂梁两侧对称粘贴了两个不同中心波长的光纤光栅,当悬臂梁自由端的位置发生变化时,两个光纤光栅分别受到拉力和压力,因此光栅的中心波长向相反方向漂移。通过对两个中心波长差值与位移量关系的标定,可以排除温度的影响,实现对位移量的测量。传感器采用了拉绳式的位移传递方式,使得传感器的安装位置及测量方式更加灵活;便于拆装的位移转换装置,可以方便地调整传感器的量程,使其具有更广泛的适用性。位移传感实验结果表明,在传感器量程为60 mm时,位移传感器的平均灵敏度为47.7 pm/mm,相关系数达到0.998,重复性误差为2.83% FS,迟滞误差为1.02% FS。该位移传感器具有结构简单、量程可调的特点,可以满足不同环境下的位移测量需求。
Abstract:Abstract: In order to solve the problem of displacement monitoring of health monitoring system in the complex electromagnetic environment, and realize the real-time monitoring of large mechanical and engineering structure health and safety conditions, a novel fiber Bragg grating displacement sensor based on the structure of the cantilever beam is designed. Two fiber gratings with different central wavelengths are symmetrically pasted on the both sides of the cantilever beam. When the free end of the cantilever beam is changed, the two fiber gratings are respectively subjected to tension and pressure, which leads to the drift of the gratings center wavelength to the opposite directions. Through demarcating the relationship between the two center wavelength difference and displacement, it is possible to realize the measurement of the displacement. At the same time, the problem of cross sensitivity between temperature and displacement is solved. The sensor adopts draw-wire type displacement transmission mode, which makes the sensor installation location and measurement method more flexible. In addition, a smart device used to change the measuring range of the sensor is designed and it is also easy to be assembled and disassembled, so the whole sensor can be widely used. The experimental results show that when the range is 60 mm, the average sensitivity of the displacement sensor is 47.7 pm/mm, the correlation coefficient is 0.998, the repeatability error is 2.83% FS and the hysteresis error is 1.02% FS. The displacement sensor is characterized by simple structure and adjustable range, which can meet the demands of displacement measurement under different environments.
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Key words:
- fiber Bragg grating(FBG) /
- cantilever beam /
- displacement sensor /
- adjustable range
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Displacement measurement technology is widely used and it is one of the most basic testing techniques. Inorder to solve the problem of displacement monitoring of health monitoring system in the complex electromagneticenvironment, and realize the real-time monitoring of large mechanical and engineering structure health and safetyconditions, a novel fiber Bragg grating displacement sensor based on the structure of the cantilever beam is designedin this paper. The fiber Bragg grating displacement sensor is mainly composed of cantilever beam, fiber Bragg grating,central transmission shaft, bearing, torsion spring and displacement conversion device. The main body of the sensor isencapsulated inside a box, and a smart displacement conversion device is specially designed outside the box, which isused to adjust the range of the sensor and realize the measurement in wide range. Two fiber gratings with differentcentral wavelengths are symmetrically pasted on the both sides of the cantilever beam. When the free end of the cantilever beam is changed, the two fiber gratings are respectively subjected to tension and pressure, which leads to thedrift of the gratings center wavelength to the opposite directions. Through demarcating the relationship between thetwo center wavelength difference and displacement, it is possible to realize the measurement of the displacement. Atthe same time, the influence of the temperature on the wavelength shift can be eliminated by central wavelength difference of the two gratings, and the problem of cross sensitivity between temperature and displacement is also solved.The sensor adopts draw-wire type displacement transmission mode, which makes the sensor installation location andmeasurement method more flexible. In addition, a smart device used to change the measuring range of the sensor isdesigned and it is also easy to be assembled and disassembled, so the whole sensor can be widely used. The displacement measurement system and temperature measurement system are set up to test the overall performance of the displacement sensor. The experimental results show that when the range is 60 mm, the average sensitivity of the displacement sensor is 47.7 pm/mm, the correlation coefficient is 0.998, the repeatability error is 2.83% FS and the hysteresis error is 1.02% FS. The temperature coefficients of FBG1 and FBG2 are 25.8 pm/ and 28.9 pm/ , as well as the ℃ ℃temperature coefficient of the sensor is -3.1 pm/ . The structure of the ℃ double grating can achieve the effect of temperature compensation, reduce the temperature coefficient of the displacement sensor, and reduce the influence of thechange of the environmental temperature on the displacement measurement. The displacement sensor is characterizedby simple structure and adjustable range, which can meet the demands of displacement measurement under differentenvironments.
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表 1 实际位移量与测量值间的测量误差.
Table 1. The error between actual displacement and the measured value.
位移/mm 测量值/mm 测量误差/mm 0 0.626 0.626 5 5.204 0.204 10 9.836 -0.164 15 14.685 -0.315 20 19.721 -0.279 25 24.657 -0.343 30 29.840 -0.160 表 2 正、反行程平均校准点及偏差值.
Table 2. The average calibration point and deviation value of the positive and reverse stroke.
位移/mm 正行程平均校准点/nm 反行程平均校准点/nm 正、反行程偏差值/nm 0 0.774 0.795 0.021 5 0.977 0.966 0.011 10 1.166 1.170 0.004 15 1.387 1.378 0.009 20 1.625 1.61 3 0.012 25 1.873 1.844 0.029 30 2.105 2.079 0.026 35 2.340 2.337 0.003 40 2.605 2.588 0.017 45 2.844 2.842 0.002 50 3.092 3.086 0.006 55 3.358 3.367 0.009 60 3.615 3.615 0 表 3 相同行程中各位移点的标准偏差.
Table 3. The standard deviation of different displacement points in the same journey.
位移/mm 正行程标准偏差/mm 反行程标准偏差/mm 0 0.0126 0.0188 5 0.0105 0.0089 10 0.0131 0.0204 15 0.0115 0.0215 20 0.0094 0.0079 25 0.0110 0.0094 30 0.0063 0.0099 35 0.0178 0.0188 40 0.0267 0.0194 45 0.0215 0.0110 50 0.0230 0.0068 55 0.0188 0.0047 60 0.0162 0.0162 -
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