Large Range Fiber Bragg Grating Displacement Sensor Based On Cantilever Stucture

Diplacement is an important parameter in the safety monitoring of geotechnical engineering. It provides a reliable information to understand the geotechnical where the cracks, landslides, sliding and overturning as well as the surrounding rock stress with mechanical parameters of the inversion.At present, the displacement measurements were powered by the power class displacement sensor, multi-point displacement monitoring technology and digital phontgraphy. But the traditional electric displacement sensor measurement accuracy is low, poor waterproof seal and is not suitable for the geotechnical monitoring; the multi-point displacement sensor has been used in the geomechanical test widely, but it is vulnerable to electromagnetic interference, poor waterproof seal and the installation is relatively complex; the digital camera is a new type of displacement measurement technique, but because the jitter of the camera itself,the measurement accuracy is lower. Compared with the conventional displacement measurement technology, the fiber Bragg grating displacement sensor has small size, high precision, anti-electromagnetic interference ability, waterproof performance,easy networking and other features. It was subject to widespread concern in the domestic and foreign experts and engineering personnel.This subject is based on this demand to design a cantilever structure, large number of range fiber Bragg grating displacement sensor.The linearity is0.57%, the sensitivity is1.096pm/mm, the hysteresis is1.49%, the repeatability rate is2.01%. This article involving machinery,information, materials and many other subjects. My major work are as follows:(1) Discribed the types of the displacement sensors based on fiber Bragg grating, compared the various sensor principles, advantages and disadvantages;(2) Formulated the basic structure and transmission theory of the fiber Bragg grating, and the rationship between temperature and stress, which affect the measurement accuracy.(3) Analysed the mechanical properties of the sensitive components of the displacement sensor—cantilever in theoretical,including cantilever beam of rectangular,trapezoidal cantilever,isosceles triangle cantilever. This paper used isosceles triangle cantilever as the sensing element. Established the sensor model of the cantilever fiber Bragg grating displacement sensor. When the measuring rod move, it will lead the spiral spring to produce a deformation, so that the free end of the strength of the cantilever deflection change,eventually leading the fiver Bragg grating pasted on the surface of the cantilever to shift.(4) Designed the mechanical structure of the cantilever fiber Bragg grating displacement sensor. Calculated the specific dimensions of the various components of the sensor based on the range and properties of the matericals.(5) According to the chart and working environment of the various parts of the sensor,selecting the material, processing,selecting the adhesives based on the theoretical calculations.Pasted the fiber Bragg grating on the surface of the sensitive component.At last, assembly each precessed component. Creatively used the torque wrench to installate the cantilever and acquired good results.(6) Desinged the fixture and experimental programs to calibrate the sensor. Acquired the actual performance of the wide range cantilever fiber Bragg grating displacement sensor based on the loading and unloading experiments.According to the experimental data, the performance of the sensor has been acquired.