Tham khảo tài liệu 'gear noise and vibration episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 160 Chapter 9 The selected lines are removed by putting their amplitude to zero. The resulting remaining frequency components are subjected to the inverse Fourier routine iffi which resynthesises the original time sequence signal with all the normal vibration removed. The residual signal will show up minor faults much more effectively than the original signal. Fig. shows an example of a simple apparently regular time signal which has had the regular signal of 1 tooth and harmonics subtracted. The difference signal shows very clearly that there was a phase delay or pitch error on one tooth in the original signal. The method is especially useful when there are irregularities in small harmonics which cannot be seen due to large components at 1 tooth and similar frequencies. A typical Matlab program to eliminate the large lines for a once per revolution averaged file obtained in a test is as follows loads pinion vibration averaged file pvbN for viewing and line elimination clear N inputfNumber of test file averaged file 405 points long eval load pvb int2str N figure plot Y original file called Y w fft Y wabs abs w 1 202 figure plot wabs looks at sizes of lines smalls abs w ones size w logic check for small lines less than 1 resw smalls. w resvib iffi resw hor 1 405 realres real resvib imgres imag resvib checks imag negligible figure plot hor realres hor imgres title Residual 1 pinion vibration for test int2str N xlabelfOne pinion revolution ylabelf Acceleration in g end knocks out lines greater than 1 regenerates time series of residuals X axis for plot one rev. This approach may also be useful if there is a small hidden component such as a ghost frequency in the signal due to a faulty gear cutting machine though any regular signal will usually show up sufficiently clearly in the frequency analysis. There is much current interest in using wavelet analysis techniques instead of frequency analysis 1 . Wavelets are very useful in visual pattern recognition for .
