Incipient Fault Diagnosis of Cylindrical Roller Bearings Using Dynamic Response Analysis
Detecting faults early on is important in order to maintain the health of rotating machinery. Incipient faults in rolling-element bearings lead to the generation of micro-defects which create weak transient impact signals. However, these are often buried within the background vibration of the machine and structural transmission effects. Indicators based on traditional time-domain methods possess sensitivity to impulsive damage, but when the signal exhibits non-stationarity or a noisy trend. The current study compares time-domain statistical parameters and FFT spectral analysis for progressive inner race damage in an NJ307 cylindrical roller bearing. A wire electrical-discharge-machining technique produces artificial inner-race defects with sizes of 0.25 mm, 0.50 mm, 0.75 mm and 1.00 mm, while a healthy bearing serves as the reference condition. Vibration is measured with a single-axis accelerometer connected to an eight-channel Dewesoft data- acquisition system with a sampling frequency of 20 kHz; the shaft speed is 800 rpm by use of a variable-frequency drive. The RMS, standard deviation, peak value, crest factor, kurtosis, and form factor are taken into account during the analysis. FFT spectra are observed at the calculated inner-race fault frequency and its harmonics. The findings reveal that at the earliest damage stage, there is only a gradual change in both RMS and standard deviation. In contrast, changes in peak value, crest factor, kurtosis, and amplitudes of the BPFI-related FFT are more robust indicators of progressive damage. The FFT provides statistically interpretable frequency information, which scalar time-domain features cannot. As suggested by the findings, the proposition is for a combined diagnostic procedure in which the time-domain features provide a rapid screening while the FFT confirms the bearing-fault frequency. Keywords: cylindrical roller bearing; incipient fault; dynamic response; condition monitoring