Research On Instantaneous Frequency Of Non-stationary Signals

With the development of science and technology,the analysis and processing method of stationary signal has matured,but the engineering signal has the non-stationary characteristics because of the external factor interference.Transient component is the important performance of the non-stationary signal,it contains a lot of useful information.Instantaneous frequency can well reflect the characteristics of signal transient component,it can be used to determine the moment and type of failure of the mechanical equipment.Many researchers at home and abroad have carried out in-depth exploration,and achievements were made in this field.However,there are still some problems in the instantaneous frequency analysis of non-stationary signal.In this paper,several common methods for calculating the instantaneous frequency of non-stationary signal are compared and analyzed.Aiming at the Hilbert-Huang transformation method,the cause of endpoint effect in the process of empirical mode decomposition is analyzed,the method of reducing the endpoint effect is proposed—the Gauss fitting method.Extending the original data by the Gauss fitting,we can see that the method is effective in suppressing the endpoint effect in the decomposition process.In the calculation of instantaneous frequency,the method based on the Second Ordinary Differential Equations in polar coordinates is more simple,can quickly track the instantaneous frequency of a signal.Based on this,a new method for calculating instantaneous frequency is proposed—the threshold segmentation method,this method is mainly aimed at the characteristics of non-stationary signal.Use the change of the area around the signal and the x axis to determine the amplitude mutation point of each signal component signal.Segment the signal at the point of magnitude mutation,and find out the instantaneous frequency of each segment.Then synthetic instantaneous frequency in chronological order,obtain the complete instantaneous frequency on each single component signal time domain.The experiment verifies that this method is not only simple in calculation but also can reduce the effect of abrupt change of non-stationary signal amplitude to instantaneous frequency calculation.In order to verify the practicability of the threshold segmentation method for calculating the instantaneous frequency of non-stationary signal,this method is applied to fault diagnosis of rolling bearings,the vibration signal of rolling bearing under three kinds of different conditions are analyzed,and the instantaneous frequency of the signal is obtained by the threshold segmentation method,and then the Hilbert marginal spectra is derived.By comparing with the Hilbert marginal spectrum obtained by the traditional Hilbert-Huang transform method,we can see that the method can effectively eliminate the interference,judge the fault type of the rolling bearing,and make the fault information ability stronger.