Research on planetary gearbox monitoring and diagnosis method based on generalized modulation envelope framework

Planetary gearboxes typically operate under harsh environmental conditions and complex working regimes. Consequently, their vibration signals are often contaminated by strong noise interference and exhibit complex modulation phenomena. Conventional spectral analysis techniques have difficulty in accurately extracting and enhancing fault-related features from such signals, as well as in effectively separating these features from irrelevant signal components. To address these challenges, this article proposes a novel generalized modulation-envelope framework, termed the generalized amplitude modulation enhanced weighted envelope spectrum, and applies it to the condition monitoring and fault diagnosis of planetary gearboxes. First, envelope analysis and modulation characteristics are unified in a generalized manner to construct the generalized amplitude modulation envelope spectrum. Subsequently, a generalized spectrum signal-to-noise ratio, derived from frequency-domain characteristics, is introduced to provide a refined representation of fault features. This metric also serves as the basis for the nonlinear enhancement of multiple fault-related components. Building on the above, we develop an extensible generalized modulation-envelope framework that can be adapted to a variety of diagnostic tasks. The framework is capable of suppressing complex noise interference in vibration signals, enhancing fault signatures, and isolating fault-related spectral lines. Experimental analyses demonstrate that, compared with existing spectral analysis methods, the proposed generalized modulation-envelope framework achieves significant improvements in overall computational efficiency and in quantitative metrics such as the fault characteristic amplitude ratio. It proves effective in extracting and enhancing weak fault features under conditions of strong background noise and low rotational speeds. Moreover, the framework exhibits superior performance in monitoring and diagnosing incipient faults in planetary gearboxes, as well as faults occurring in multistage transmission systems.