Joint Amplitude and Frequency Demodulation Analysis Based on Variational Mode Decomposition for Multifault Diagnosis of a Multistage Reducer

Feng Li,Zhaojian Yang,Xinyu Pang

doi:10.1155/2018/9869561

Abstract

Multistage reducer vibration signals have complicated spectral structures owing to the amplitude and frequency modulations of gear damage-induced vibrations and the multiplicative amplitude modulation effect caused by time-varying vibration transfer paths (in the case of local gear damage) when the multistage reducer contains both planetary and spur gears. Moreover, the difference between the vibration energies of these gears increases the difficulty of fault feature extraction when multiple failures occur in the reducer. As the meshing frequency of each gear group often varies significantly, variational mode decomposition can be performed to decompose the vibration signal according to frequency, enabling separation of the vibration signals of the spur and planetary gears. The common fault features of these gears can be extracted from the spectrum of the amplitude demodulation envelope. To verify the effectiveness of this method, we first analyzed a simulation signal, and then utilized the experimental signals from a laboratory multistage reducer for verification. In the multistage reducer simulation, we considered the amplitude and frequency modulation of the gear damage and transfer paths. In the experimental verification, we processed local faults (broken teeth) and uniform faults (uniform wear) on the sun gear and the spur gear of the planetary gear separately.

Highlights

Multistage reducers are used extensively as key components in industry because of their compact structures, large transmission ratios, strong carrying capacities, stable operation, and high efficiencies [1, 2]
When many gear faults occur in a multistage reducer, modulation of the gear faults and transmission paths to the vibration signal and the difference between the vibration energies of the gear groups increase the difficulty of diagnosing multiple simultaneous failures
The meshing frequencies of each gear group change significantly because of rotation speed variations. us, the amplitude modulation (AM) and frequency modulation (FM) of the gears at each level occur in different frequency bands. Based on this vibration signal property, this paper proposes a method of frequency and amplitude demodulation with combined variational mode decomposition (VMD) and envelope demodulation. e proposed method is significantly different from the demodulation methods used in the previous studies

Summary

Introduction

Multistage reducers are used extensively as key components in industry because of their compact structures, large transmission ratios, strong carrying capacities, stable operation, and high efficiencies [1, 2]. Because multispeed reducers often contain multiple spur, planetary gears, or a combination thereof, the housing vibration signals of the gearbox are more complex than that of single-stage reducers, especially when planetary gears are involved [3]. A planetary gear usually consists of a sun gear, several planet wheels, a ring gear, and a planet carrier. The ring gear is stationary, the sun gear rotates, and the planet gears revolve with the planet carrier, and spin around their own centers. Because of the complicated internal dynamics and external environmental excitation, the vibration signals of planetary gears exhibit complex time-varying modulation, which leads to fault feature extraction difficulty [1]. To achieve more effective transmission, a planetary gear is often used with a spur gear, which makes the multistage reducer vibration signal more complex. When many gear faults occur in a multistage reducer, modulation of the gear faults and transmission paths to the vibration signal and the difference between the vibration energies of the gear groups increase the difficulty of diagnosing multiple simultaneous failures

Methods

Findings

Discussion

Conclusion