The vibration signal of a rotor bearing system is usually nonlinear and non-stationary. Fourier transform is hard to
analyze these signals. A new method based upon empirical mode decomposition (EMD) and Hilbert spectrum is
proposed for fault diagnosis of roller bearings. We get vibration signals from 6205-type ball bearings with inner-race
faults and with outer-race faults, then analyzing its local Hilbert spectrum and local Hilbert marginal spectrum.
Comparing the results with theory value, we can diagnose the fault of rotary machinery fault. In this study, we find that
local Hilbert spectrum and local Hilbert marginal spectrum are very useful. Hilbert Transformation is introduced to
confirm the HHT method is fit to process nonlinear and non-stationary signals.