Gear Fault Detection Using Angle Domain Average and Hilbert-Huang Transform Phase Map

Abstract

Varying speed machinery fault diagnosis is more difficult due to non-stationary machine dynamics and vibration. A new approach to fault diagnosis of bearing under running up based on angle domain average and Hilbert-Huang transform (HHT) phase map is presented. The non-stationary vibration signals are transformed from the time domain transient signal to angle domain stationary one using order tracking. Empirical mode decomposition (EMD) can adaptively decompose the vibration signal into a series of zero mean Intrinsic Mode Functions (IMFs). Hilbert transform can track the instantaneous amplitude and instantaneous frequency of the intrinsic mode functions at any instant. The experimental results show that average domain average and Hilbert-Huang transform phase map can effectively diagnosis the faults of the gear crack. Vibration signal analysis has been widely used in the fault diagnosis of rotating machinery. At present, for the fault diagnosis of the rotating machinery, many researches have been focused on the stationary process. However, little research has been carried out for the run-up and run-down process. Non- stationary vibration signals are difficult to investigate with classical Fourier Transform analysis. Nevertheless, non- stationary vibrations signals from varying speed machinery, especially during run-up and run-down process of gears drive, may include more abundant information about its condition. The operation condition of rotating machinery varies with time during run-up and run-down. During run-up, the speed of rotating is increased until the machine reaches its steady operation speed. While in the transient region, all excitation force changes both in amplitude and frequency. Therefore, some phenomena, which are usually not obvious at constant speed operation, may become more apparent under varying speed conditions. Therefore in the last decade vibration analysis and condition monitoring techniques for varying speed machinery have attracted a lot of attention of scientists and engineers. Some progress has been made in the theoretical analysis, the signal processing methodology, measurements and practical applications of varying speed machinery monitoring (1-4). In this work, the angle domain average technique and Hilbert-Huang transform (HHT) phase map are introduced and applied specifically to gearbox fault diagnosis during run-up. This method is based on the resample technique and Hilbert- Huang transform of the resampling signal which is a function of the angle of the input shaft of the gearbox. This resampling signal can be obtained by resampling of the vibration signal which has been previous sampled in the time domain. The angle average technique provides such a capability for the monitoring of gears by presenting the vibration information as a function of the angle of rotation of the gear, enabling a comparison of the vibration produced by those teeth which are presumed healthy and those that are damaged. Then the amplitude and phase maps of the Hilbert-Huang transform are used to assess gear damage. The Hilbert-Huang Transform phase maps both exhibit a characteristic signature in the presence of a cracked tooth.