Weak Mechanical Fault Signal Detection Based On Dual-coupling Duffing Vibrator

Due to its sensitivity to initial condition,the chaos theory is introduced to detect weak signals as one of the nonlinear detection methods,is widely used in many fields such as mechanical fault diagnosis,voice processing,biomedical engineering.However,how to detect the weak signal submerged in the background of other strong signals,is one of the key problems in engineering practice,need to be solved in the field of signal processing.Therefore,a new dual-coupling system detection method is proposed in this thesis to reduce the signal-to-noise ratio of detecting weak signals and to improve detection accuracy and sensitivity.The specific research content and results are as follows:(1)The principle of weak signal detection based on Duffing oscillator is introduced by describing the chaos theory and analyzing the motion state discrimination.In order to solve the problem of low detection sensitivity of traditional Duffing oscillator,an improved Duffing oscillator detection model is obtained by replacing the low dimensional nonlinear restoring force term of traditional Duffing oscillator with the high dimensional nonlinear restoring force term.The nonlinear dynamic characteristics of the model was analyzed,and it could be found that it had higher detection sensitivity.(2)The conditions for the existence of periodic orbits of the modified Duffing oscillator are analyzed,and a weak signal detection system for the dual-coupled Duffing oscillator was established.A method was proposed to quickly search for the critical threshold of the dualcoupled Duffing oscillator to detect the system’s critical threshold by using the dichotomy,and the critical threshold for the system to change from a chaotic state to a periodic state was obtain.It is found that the system can detect weak signals well through the results of simulation numerical calculations.(3)This thesis proposes a weak signal detection method combining dual-coupled Duffing oscillator and ensemble empirical mode decomposition(EEMD).At first,this method first uses EEMD to decompose the signal to be measured into multiple intrinsic modal components(IMF)that contain the characteristics of the original signal.Subsequently,each IMF component is input into the dual-coupled Duffing vibrator detection system for detection,thereby realizing the detection of weak signals.It has been verified that this method can avoid modal aliasing in the signal decomposition process and improve the detection accuracy of the system.(4)Aiming at the problem that the frequency difference and phase difference between the periodic driving force of the dual-coupled Duffing vibrator detection system and the signal to be measured affect the evolution of the system phase trajectory.A method of phase diagram segmentation processing is proposed to reduce the frequency difference and phase difference to the influence of the detection system.It was found that when the system frequency difference is less than or equal to 1/4 of the guard bandwidth,the dual-coupled Duffing vibrator detection system can detect weak periodic signals through phase diagram segmentation processing.Through the detection test of the weak signal of the rolling bearing at the fan end,the fault information of the rolling bearing is obtained,which verifies the feasibility of the method.