| Reference | Features | Classifier | Defects considered | Classified states | Accuracy (%) |
| [4] | Permutation entropy of intrinsic mode functions (IMFs) decomposed by ensemble empirical mode decomposition (EEMD) | SVM + parameter optimized by intercluster distance (ICD) | N, B (0.18, 0.36, 0.54, and 0.72 mm), IR (0.18, 0.36, 0.54, and 0.72 mm), and OR (0.18, 0.36, and 0.54 mm) | 2, 3, 4, 11 | 97.91–100 |
| [6] | Statistical features from the time and frequency domains, wavelet packet energy, and complex envelope magnitudes | SVM, the -nearest neighbor classifier (-NN), and multilayer perceptron (MLP) | N, B (0.18, 0.54 mm), IR (0.18, 0.54 mm), and OR (0.18, 0.54 mm) | 7 | 98.13–99.97 |
| [7] | Skewness, kurtosis, standard deviation, root mean square (RMS), crest factor, and five entropies | SVM and artificial neural network (ANN) with different attribute filters | N, B (0.18, 0.54 mm), IR (0.18, 0.54 mm), and OR (0.18, 0.54 mm) | 7 | 100 |
| [18] | Features derived from higher order statistics analysis (HOSA) with feature reduction using PCA | SVM + one against all (OAA) | N, B (0.18, 0.36, 0.54, and 0.72 mm), IR (0.18, 0.36, 0.54, and 0.72 mm), and OR (0.18, 0.36, and 0.54 mm) | 4 | 96.98 |
| [19] | Multiscale entropy (MSE), hierarchical entropy (HE) | SVM + parameter optimized by PSO | N, B (0.18, 0.72 mm), IR (0.18, 0.36, 0.54, and 0.72 mm), and OR (0.18, 0.36, and 0.54 mm) | 10 | MSE + SVM: 97.75 HE + SVM: 100 |
| [20] | Statistical features from the time and frequency domains, the energy of empirical mode decomposition (EMD) | Statistical locally linear embedding (S-LLE) + -NN, classification and regression trees (CART), and RBF-SVM | N, B (0.54 mm), IR (0.54 mm), and OR (0.54 mm) | 4 | 97.26 |
| [21] | Features extracted from wavelet kurtogram and quefrency cepstrum | Swarm Rapid Centroid Estimation (SRCE) + Hidden Markov Model (HMM) | N, B (0.54 mm), IR (0.54 mm), and OR (0.54 mm located at three different positions) | Drive end: 5 Fan end: 5 | Drive end: 95.08 Fan end: 100 |
| Present work | Features derived from MFDFA and ASD with feature fusion using KPCA | LSSVM + parameter optimized by PSO | N, B (0.18, 0.54 mm), IR (0.18, 0.54 mm), and OR (0.18, 0.54 mm) | 7 | 98.6 |
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