Study On Method Of Cyclostationary Demodulation And Its Application In Gearbox Fault Diagnosis

As a necessary part of connecting and force transmission in mechanical equipment, gear and gearbox system play a comprehensive role, with the development of modern industry. When the gear system works, periodic impulse impact force will produce owing to the faults of gear abruption or corrosive pitting, etc. So phenomena of modulation produced at this moment and spectrum of the vibration signal has symmetrical modulation side-bands besides the meshing frequency or natural frequency. Extracted modulation information and its strength and modulation frequency order can be analyzed which can be used to judge the fault parts. It is a compressively used in mechanical fault diagnosis.The statistical feature of vibration signal in gearbox shows that the statistical function (such as mean or related function, etc.) is periodic when the faults produced. A method of cyclostationary analysis has been proposed to demodulate this kind of signals and its limitations have also been discussed. The modulation side-bands of amplitude modulation signal are symmetrically distributed besides the carrier-frequency. The cyclostationary analysis method has been applied to the demodulation of two groups of amplitude modulation signal. Each one of the demodulation spectrum of the signal can be achieved by using this method, while the traditional methods can not work. There are also two limitations when using the cyclostationary demodulation method. One is the limitation of demodulating the two-added harmonic signal. The other one is known as the effect of frequency mixing when the sampling frequency is not selected properly. The modulation side-bands of frequency modulation signal (or phase modulation signal) are symmetrically distributed besides the carrier-frequency. However, the quantity of the side-bands components is decided by the modulation rating. The modulation principle of this kind of signal has been deduced theoretically. Two methods have been proposed accordingly to demodulate this kind of signal. One is called time-delay autocorrelation demodulation. In another method, the asymmetrical filter technology is needed while applying the traditional demodulation methods to the signal. The modulation side-bands become asymmetrically distribution besides the carrier-frequency, when the amplitude and frequency modulation are mixed in the signal.