Search

It is necessary to determine the degradation path model of products at first when using the method based on degradation path model to evaluate the degradation reliability of products. At present, the degradation path model is mainly determined by scatter plots of degradation data. However, this method has strong subjectivity and is liable to cause the evaluation results to be inconsistent with the actual situation. In this paper, a degradation reliability analysis method based on TOPSIS (technique for order preference by similarity to an ideal solution) model selection is proposed, and its implementation process is given. The optimal degradation path model is selected according to the calculated proximity. With the help of TOPSIS method, various degradation path models can be selected and quantified, and the original degradation path method can be improved to avoid the risk of errors in product reliability evaluation caused by inaccurate subjective hypothesis, so as to ensure the objectivity and accuracy in the process of model determination. The validity and practicability of the proposed method are verified by the degradation analysis of the injector of a certain type of diesel engine.

To effectively extract the fault feature information of rolling bearings and improve the performance of fault diagnosis, a fault diagnosis method based on principal component analysis and support vector machine was presented, and the rolling bearings signals with different fault states were collected. To address the limitation on effectively dealing with the raw vibration signals by the traditional signal processing technology based on Fourier transform, wavelet packet decomposition was employed to extract the features of bearing faults such as outer ring flaking, inner ring flaking, roller flaking and normal condition. Compared with the previous literature on fault diagnosis using principal component analysis (PCA) and support vector machine (SVM), one-to-one and one-to-many algorithms were taken into account. Additionally, the effect of four kernel functions, such as liner kernel function, polynomial kernel function, radial basis function and hyperbolic tangent kernel function, on the performance of SVM classifier was investigated, and the optimal hype-parameters of SVM classifier model were determined by genetic algorithm optimization. PCA was employed for dimension reduction, so as to reduce the computational complexity. The principal components that reached more than 95 % cumulative contribution rate were extracted by PCA and were input into SVM and BP neural network classifiers for identification. Results show that the fault feature dimensionality of the rolling bearing is reduced from 8-dimensions to 5-dimensions, which can still characterize the bearing status effectively, and the computational complexity is reduced as well. Compared with the raw feature set, PCA has a higher fault diagnosis accuracy (more than 97 %), and a shorter diagnosis time relatively. To better verify the superiority of the proposed method, SVM classification results were compared with the results of BP neural network. It is concluded that SVM classifier achieved a better performance than BP neural network classifier in terms of the classification accuracy and time-cost.