Software Development For Fault Diagnosis Of Helicopter Transmission System Gearbox Based On Time-frequency Analysis Method

With the development of helicopter technology, helicopter has been widely applied.In the maritime emergency, fire and rescue, firefighting, medical aid, tourism and otherfields, helicopter teams are growing. However, the occasional occurred accidents that thehelicopter crashed also warn people: the research of helicopter fault diagnosis is urgentgreatly. Helicopter transmission system is as the sole channel of power transmission,once the event of failure occurs, which will be likely to result in significant losses,according to statistics, the failure caused by transmission system gearbox is one of themain fault in the helicopter mechanical failure. The structure of transmission systemgearbox is very complex, and background noise is fully rich, hence, the effective solve offault feature extraction based on the time-frequency distribution under background noiseis the key to the study. Therefore, the design of transmission system gearbox faultdiagnosis software based on the time-frequency analysis has an important engineeringsignificance to the safety and effectiveness of the helicopter.1. The basic structure of helicopter transmission system gearbox is analyzed, thenthe main fault forms and failure mechanism of rolling bearings and gears are discussed.2. The common time-frequency theory is studied, such as the short-time Fouriertransform、Wigner-Ville、Pseudo-Wigner-Ville、Smooth Pseudo-Wigner-Ville、EMD. Asimulated signal is used to analyze the advantage and limitation of those time-frequencyanalysis methods, which provides theoretical basis for the development of softwarealgorithm.3. The basic theory of LCD method are studied, an adaptive waveform matchingcontinuation method is proposed to solve the problem of end effect. The analysis ofsimulation signal shows that the problem of the endpoint effects is well solved by thismethod, through further analysis,when the simulation signal is decomposed by Localcharacteristic-scale decomposition (LCD) method, the appearance of the stagnation pointon low frequency intrinsic scale component (ISC) is discovered. The generated reason ofthese stagnation points on low frequency intrinsic scale component is analyzed and anew method which called eliminate stagnation point-based Local characteristic-scaledecomposition method is presented. Finally, compared with EMD, the results haveshown the obvious advantages of the improved LCD method on eliminating stagnation,which is suitable for real-time analysis of fault. 4. The fault diagnosis software for helicopter transmission system gearbox based ontime-frequency analysis method is designed. The overall design plan、the main function、the main module of fault diagnosis software are studied. A simulated signal is proceededto be time-frequency analysis in the build-essential of Matlab and Labwindows/CVI,which verifies the correctness of the time-frequency analysis algorithm in CVI software.Lastly, the software is applied to fault diagnosis of inner, outer of rolling bearings andbroken, crack of gears in transmission system of the helicopter, which illustrates thepracticability of the software.