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The combined library of wavelet library (Symmlet-8 wavelet) and Heaviside library is selected as the library structure of atomic decomposition, and Kp=2log(p)/2. Figure 3 shows the two analog pulse signals after noise reduction. Compared with the rush signal, the noise reduction effect is quite good. This is particularly advantageous for mechanical fault diagnosis, because when the mechanical system fails, the vibration signal of the machine often appears as a pulse shock, and this pulse shock is often overwhelmed by strong background noise.
Gear Fault Diagnosis The gearbox is used as the transmission part of mechanical equipment and is responsible for the transmission of power. It is widely used in industrial production.
The test was carried out on an LC5T81-type automotive transmission with five forward gears and one reverse gear for medium-duty trucks. Under the three-speed load condition, the gearbox is subjected to fatigue test. The test is carried out in 5 cycles. The test time of each cycle is 15h. A set of data is measured at regular intervals, and the fifth data is taken. The third gear is broken during the cycle. The data used in this paper was taken just before the third gear was broken, and the sampling frequency was 2 kHz.
Strong background noise, it is difficult to see the periodic pulse signal; (b) is the power spectrum of the signal, the maximum energy at 500Hz, which is the meshing frequency of the third gear. There is also a higher energy distribution between 230 Hz and 300 Hz; there is also a higher energy at the high frequency of 640 Hz.
The merged library of the wavelet library and the Heaviside library is still selected as the library structure of the atomic decomposition, and Kp=62log(p). (a) For the time-domain waveform after the noise reduction, the pulse signal appearing periodically can be clearly seen, and the occurrence period is 54 ms. Therefore, by de-noising the base tracking of the vibration signal of the transmission case, it can be determined that the third gear of the transmission has a broken tooth failure. (b) For the power spectrum of the noise-reduced signal, it can be seen that the 500 Hz meshing frequency component and the 640 Hz high-frequency component are removed, while the frequency component of 230 Hz to 300 Hz is retained. This shows that the base tracking noise reduction method can effectively suppress the strong gear meshing noise and high frequency noise interference, while retaining the broken tooth fault pulse signal, which provides a new means for gear broken tooth fault diagnosis. At the same time, it is also shown that the characteristic frequency band of the gearbox gear breaking fault is 230-300 Hz. For different gear faults, different combined libraries can be selected, and the corresponding gear fault characteristic information can be extracted through base tracking noise reduction to achieve the purpose of fault diagnosis. This method is also suitable for fault diagnosis of other mechanical equipment with strong noise interference.
Conclusion According to the characteristics of pulse shock in the vibration signal generated by mechanical equipment, this paper proposes a method of extracting fault pulse signal submerged in noise by using base tracking noise reduction method. A new method for fault diagnosis of gears is provided. This method is also suitable for fault diagnosis of other mechanical equipment with strong noise interference by selecting different combined libraries.