Research On Fault Diagnosis Method Of Planetary Gearbox Based On Motor Current

Planetary gearbox is a transmission system in which many planetary gears revolve around the sun wheel in mechanical equipment.It can reduce the speed and increase the torque at the same time.It is suitable for high-speed,high-power and low-speed,high-torque mechanical transmission.In operation,planetary gearboxes often bear complex dynamic heavy loads and are prone to failure.Whether the planetary gearbox can work properly not only affects the operation status of the whole mechanical transmission system,but also closely relates to the personal safety of workers.Therefore,the fault diagnosis of planetary gearbox is very significant for the actual industrial production.Vibration analysis method is the most significant fault diagnosis method with complete theoretical basis and early development.It has been applied to fault diagnosis in various industrial fields maturely.However,as planetary gearbox contains many rotating parts,the vibration signals collected are superimposed,the components are complex and the mechanical resonance interference is serious.At the same time,it is difficult to collect vibration signals for mechanical equipment in special environment such as coal mine and wind farm.Therefore,it is of practical significance to apply the motor current signature analysis(MCSA)to the fault diagnosis of planetary gearbox.?In this paper,motor current signal is used as fault information source,planetary gear box integrated fault simulation test rig is used to simulate planetary and solar wheel faults.Current signals of planetary and solar wheel cracks,broken teeth and missing teeth in single fault state and planetary gear-solar wheel compound fault state are collected respectively,and current signals are extracted.By analyzing the change of time domain factor(kurtosis value,kurtosis index,etc.)and frequency domain amplitude characteristic of current signal,the existence of fault is preliminarily determined.In order to further accurately extract fault features,empirical mode decomposition(Empirical Mode Decomposition,EMD)method is used.EMD can decompose the original current signal into a series of modal components(Intrinsic Mode Function,IMF)from high frequency to low frequency.By observing the time-domain characteristics of the components,meaningful modal components can be found,and the spectrum of the components can be obtained by Fourier transform.By analyzing the spectral line components in the spectrum and comparing with the current signals in the non-fault state,the characteristic frequencies of the local faults of planetary gear and solar gear are found.The faults of missing teeth and broken teeth of planetary gear and solar gear of planetary gear box are effectively diagnosed,but the diagnosis effect is not remarkable for the crack faults and the compound fault of planetary gear andsolar gear.At the same time,in the process of EMD decomposition of current signal,there are two shortcomings: uncontrollable number of mode decomposition and simple mode aliasing.To overcome the shortcomings of EMD method,a feature extraction method based on current signal variational mode decomposition(VMD)is proposed.This method combines the theory of cross-correlation and kurtosis,which can effectively avoid mode aliasing and preset the number of mode decomposition.The collected current signal is decomposed by VMD,and the effective component is selected by cross-correlation and kurtosis theory,and the envelope spectrum of the effective component is drawn.By analyzing the spectral line components in the envelope spectrum,the diagnosis and recognition of planetary gear box,solar gear fault and planetary gear-solar wheel compound fault are realized.The experimental results indicate that the VMD decomposition can decompose the current signal more carefully.It can decompose the current power frequency and fault characteristic frequency into different modal components,effectively reduce the interference of current power frequency on fault characteristic frequency,and provide a new reference for the application of current analysis method in planetary gear box fault diagnosis.