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A demodulation method based on improved local mean decomposition and its application in rub-impact fault diagnosis

机译：基于改进局部均值分解的解调方法及其在碰摩故障诊断中的应用

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摘要

Demodulation is an available method for mechanical diagnoses, and a demodulation technique based on improved local mean decomposition (LMD) is proposed in this paper. A method of boundary process and a strategy for determining the step size of moving average are presented to improve the LMD algorithm. Instantaneous amplitude (IA) and instantaneous frequency (IF) of the signal can be computed independently of Hilbert transform using the improved LMD method. A well-constructed description of the derived IA and IF is given in the form of instantaneous time-frequency spectrum (ITFS) which preserves both the time and frequency information simultaneously. Results of three synthetic signals indicate that this proposed method is the best demodulation approach to extracting the all-round carrier and modulated components as well as the accurate IF, compared with Hilbert-Huang transform and stationary wavelet transform. The validity of the technique is then demonstrated on a real rotor system of a gas turbine with rub-impact fault. Due to the opposite friction during operation, the transient fluctuations of the IF of the fundamental harmonic component are successfully identified in the ITFS. In addition, we find that the proposed technique is more effective and sensitive than other methods in detecting sub-harmonics and FM components contained in the rub-impact signals. Thus the present method is powerful in the analysis of modulated signals and is an effective tool for the detection of rub-impact faults.
机译：解调是一种可用于机械诊断的方法，本文提出了一种基于改进局部均值分解（LMD）的解调技术。为了改进LMD算法，提出了边界处理方法和确定移动平均步长的策略。使用改进的LMD方法，可以独立于希尔伯特变换来计算信号的瞬时幅度（IA）和瞬时频率（IF）。以瞬时时间频谱（ITFS）的形式给出了对导出的IA和IF的结构良好的描述，该频谱同时保留了时间和频率信息。三种合成信号的结果表明，与Hilbert-Huang变换和平稳小波变换相比，该方法是提取全方位载波和调制分量以及准确IF的最佳解调方法。然后在具有摩擦冲击故障的燃气轮机的真实转子系统上证明了该技术的有效性。由于在运行过程中存在相反的摩擦，因此在ITFS中成功识别出基本谐波分量的IF的瞬态波动。此外，我们发现，所提出的技术在检测摩擦冲击信号中包含的次谐波和FM分量方面比其他方法更加有效和敏感。因此，本方法在调制信号的分析中是有力的，并且是检测摩擦影响故障的有效工具。

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