Research On Over Modulation And Demodulation Method For Sensorless Fault Diagnosis Of Bearing

Rolling bearing is an important part of industrial equipment.Whether it can work normally affects the operation of the whole equipment.It is particularly important to identify the failure of rolling bearing accurately and replace it in time.The sensorless fault diagnosis method,with its unique advantages,has become a hot spot in the research of bearing fault detection.But,because of the weak component of the mechanical fault in the stator current signal,there is a problem of over modulation frequency confusion.Therefore,it is of great significance to study the over modulation and demodulation method in the fault diagnosis of the sensorless bearings.On the basis of the analysis of the fault induction mechanism of the rolling bearing,the influence of the change of the torque on the stator current is deduced.And analysis the phenomenon of over modulation in the current signal and frequency folding and the problem of frequency confusion caused by the current signal,a modulation single side band signal shift frequency demodulation algorithm has proposed,and it is simulated by computer digital signal.Then,under the Matlab/Simulink environment,established the motor simulation model of the impact torsional vibration excitation of the rolling bearing,collected the motor stator current signals under normal and fault conditions and analyzed by Hilbert transform and frequency shift demodulation.Finally,establish the rolling bearing fault simulation test bench,which drive by a three phase motor,DC generator as the load,through artificial simulation of rolling bearing outer ring fault,collected the vibration and current signals by the acceleration sensor and current transformer,the comparison and analysis of simulation experiments under normal and fault conditions are carried.The simulation and experiment results show that when the fault frequency exceeds the carrier frequency,there will be over modulation phenomenon.Using Hilbert transform method to demodulate analysis will appear confusion frequency in low frequency,and affect the accuracy of fault diagnosis.The modulation single side band signal shift frequency demodulation method in this paper,after two times shift frequency and envelope demodulation analysis,the frequency confusion caused by over modulation can be effectively suppressed,the characteristic frequency of bearing fault can be highlighted,and the accuracy of bearing sensorless fault diagnosis can be improved.