Development Of Rail Straightness Measuring Instrument Based On Eddy Current Principle

With the development of high-speed rail transportation and semiconductor microelectronics industry in modern life,the use of sensors is becoming more and more popular,and the measurement requirements for physical quantities in various environments are becoming more and more diverse.The straightness of the rail surface directly affects the speed and safety of rail traffic,so the measurement of the rail straightness becomes very meaningful.Capacitive sensors have high resolution,but the measurement is easily affected by various pollutants in the environment,and the stability of the results is limited by many factors.Eddy current sensor is a kind of non-contact sensor widely used in various industrial environments and research experiments.It has the characteristics of wide bandwidth,high sensitivity and reliability.This paper takes the eddy current displacement sensor applied to measure the surface flatness of the rail as the research core,aiming to achieve ±2mm measurement range,0.05 mm accuracy,linearity better than 4%,and measurement speed higher than two points per second.Focusing on the two major components of the eddy current sensor used in the measurement of rail flatness: the probe coil and the impedance change detection circuit.The main work and research results are as follows:1.Based on the eddy current effect,the overall design scheme of the rail flatness measuring instrument and the index requirements of the sensor are proposed.The hardware platform includes the main control board and the acquisition board.The STM32 microcontroller is used as the control core,and the MCU and peripheral circuits are placed in the On the main control board,the sensor system and ADC and other devices are placed on the acquisition board,and the algorithm design and functional requirements for the software are proposed based on the hardware platform.2.The design method of the probe coil of the eddy current displacement sensor has been analyzed,and the parameters of the probe coil have been simulated and analyzed by the COMSOL finite element simulation software.Combined with the specific design indicators of the rail flatness measuring instrument,the parameter design of the coil has been completed.3.The impedance change measurement circuit of the probe coil of the eddy current displacement sensor has been analyzed.Based on the phase method and the PWM pulse width modulation principle,two circuit structures were proposed to achieve the goal of converting the probe displacement into a variable DC voltage.In order to reduce the influence of the coil resistance on the measurement results,a circuit and specific parameters that can improve the range of the phase difference between the output voltage and the input voltage are designed.At the same time,the correctness of the scheme was verified by using MATLAB software to analysis data and Multisim software to simulate the circuit,the final scheme has applied for relevant patents.4.The hardware of the measuring instrument except the sensor was designed,the device selection was completed,the schematic diagram and PCB were drawn,and the welding and debugging were carried out,a prototype of the measuring instrument was built,and the flat surface of the I-beam was completed.degree measurement.At the same time,the experimental results are summarized and analyzed,which verifies the feasibility of the eddy current sensor and the measurement prototype designed in this paper.