Application Of Pulsed Eddy Current Sensor In The Inspection Of Brake Disc Surface Defects

As an important part of automobile braking system,brake disc often runs in harsh environment.The long-term use will cause defects,such as wear and corrosion,and its quality has an important impact on driving safety.At present,the defect detection method of brake disc workpiece is visual inspection or magnetic particle inspection equipment.The detection rate is low depending on visual inspection method,and the magnetic particle inspection equipment causes great environmental pollution.In view of the limitations and shortcomings of the current detection methods of brake disc defects,the pulsed eddy current sensor is explored to detect the surface defects of the brake disc.Based on electromagnetic theory,a mathematical model of pulsed eddy current testing is established,and the principle of pulsed eddy current defect detection is analyzed combined with eddy current effect.The equivalent model of pulsed eddy current and the characteristics of pulsed excitation signal are discussed,and the standard penetration depth of pulsed eddy current testing is analyzed on the basis of skin effect.On the basis of theoretical research,an experimental platform for pulsed eddy current testing is built,which consists of DG1022U function generator,brake disc,sensor probe,signal processing circuit,USB4711A data acquisition card,transmission mechanism,support structure and computer.The experiment designed a cylindrical coil and a rectangular coil,using SS495A hall sensor to detect changes in the magnetic field.The working principle of signal processing circuit and the specific design process of each functional module are elaborated in detail.The detection signal is further processed by software filtering method.The optimal parameters of wavelet threshold denoising are determined by multiple sets of comparison experiments.It is concluded that the maximum signal-to-noise ratio and minimum root mean square error can be obtained by choosing soft threshold function and using coif4 wavelet basis function under the rigrsure threshold rule.The upper computer program is designed based on VI,and data is managed by Access database.It adopted the control variable method to study the influence of different influencing factors on brake disc surface defects by cylindrical pulsed eddy current sensor from three aspects:the duty cycle of excitation signal,the voltage amplitude and the liftoff height of excitation coil.Combined with COMSOL simulation and experiment,the pulse eddy current response signals of different magnetic sensor installation positions are analyzed when rectangular coil was used to detect the surface defects of brake disc.Moreover,the influence of defect width and depth on pulse eddy current detection signal is discussed by synthesizing the positive peak,negative peak and first derivative of fitting equation.