In the present study, four pinion wheels whose details are as
mentioned in Table 2 were used. One was a new wheel and was assumed
to be free from defects. In the other three pinion wheels, defects
were created using EDM in order to keep the size of the defect
under control. The details of the various defects are depicted in Table
3 and its views are shown in Fig. 4.
The size of the defects is a little bigger than one can encounter
in the practical situation; however, it is in-line with work reported
in literature (Gadd & Mitchell, 1984). The vibration signal from the
piezoelectric pickup mounted on the test bearing was taken, after
allowing initial running of the bearing for sometime.
The sampling frequency was 12,000 Hz and sample length was
8192 for all speeds and all conditions. The sample length was chosen
arbitrarily; however, the following points were considered.
Statistical measures are more meaningful, when the number of
samples is more. On the other hand, as the number of samples increases
the computation time increases. To strike a balance, sample
length of around 10,000 was chosen. In some feature extraction
techniques, which will be used with the same data, the number
of samples is to be 2n. The nearest 2n to 10,000 is 8192 and hence,
it was taken as sample length. Many trials were taken at the set
speed and vibration signal was stored in the data. The raw vibration
signals acquired for various experimental conditions form
the gear box using FFT are shown in Fig. 5.