Research And Design Of Stress Sensor Based On Micro Capacitance Measurement

With the increase of mining depth,the probability of geodynamic disasters,such as water burst,earthquake,impact pressure,and roof collapse,is increasing.The occurrence of these power disasters is c losely related to the stress imbalance of surrounding rock near the disaster source.The ground stress data can be obtained by theoretical calculation,regression inversion and field measurement.Practice shows that the stress information of deep surrounding rock obtained by theoretical calculation and regression inversion may have some difference from the actual situation.It is very important to measure the stress of surrounding rock in deep coal mining by using high precision stress sensor.There are two problems in the existing methods of rock stress detection: 1)the stress of surrounding rock can only be measured in one direction;2)Low accuracy of stress detection.Based on the design of the stress sensor,the measurement method and the accuracy of the measurement results,this paper studies and designs a kind of surrounding rock stress sensor with capacitance structure.It can make up for these two defects in the common stress measurement method.In the design of sensor structure,parallel plate capacito rs for measuring positive stress and coaxial cylinder capacitors for measuring shear stress are designed respectively.And the parallel plate capacitors and coaxial cylinder capacitors are described in detail from four aspects: structure description,volume calculation,strain relation and detection model.In this paper,a micro-capacitance detection system based on digital capacitance conversion(CDC)is established to detect pF capacitance.By analyzing the measurement requirements,FDC1004 chip is selected as the capacitance acquisition chip of the double capacitance measuring circuit.The hardware circuit of the micro capacitance detection system consists of three parts: the micro capacitance detection circuit,the single chip control circuit and the seria l communication circuit.The software is composed of two modules: capacitance measurement and transformation,data processing and display.The stress-capacitance relationship is investigated through physical experiments.The data is stored,calculated and displayed by using MySQL database and WPF technology,and the stress detection accuracy can reach two decimal places.Simulation of the positive stress of parallel plate capacitors and shear stress of coaxial cylinder capacitors using Comsol Multiphysics mult iphysical field simulation software.Firstly,the reliability of the surrounding rock stress sensor based on micro capacitance detection is verified from the angle of the stress-capacitance change trend.Then,from the angle of the numerical relation of strain-capacitance,the measurement error of the sensor is accurately analyzed.When parallel plate capacitors produce the same strain at the distance of the plate,the maximum difference between capacitance simulation and experimental value is 0.22 pF;When the outer radius strain of the coaxial cylinder capacitor is the same,the maximum difference between capacitance simulation and experimental value is 0.09 pF.The accuracy and reliability of the micro capacitance measurement system in measuring the stress of surrounding rock are verified by the small difference between the capacitance simulation and the experimental measurements.