“…However, once the envelope was obtained for each vibration signal, it was necessary to devise a method to determine automatically from that vibration spectral signal if the bearing is defective and its defect type. In the literature, different approaches in the frequency domain have been proposed (Su and Lin, 1992;Su and Sheen, 1993;Tse et al, 2001;Altmann and Mathew, 2001;Gelman and Braun, 2001;Del Castillo et al, 2002;Artes and Del Castillo, 2003;Sheen, 2004;Rivas et al, 2009). In recent years, several researchers have proposed new methods based on artificial intelligent techniques, as an alternative diagnosis technique (Korbicz et al, 2004;Andrew et al, 2006).…”