Measuring Method Of Torsional Vibration Based On Hilbert Transformation And Its Application In Gear Fault Diagnosis

Torsional vibration is one of the common vibration forms of shaft. When the torque acting on the shaft changes, the shaft will produce torsional vibration .Various kinds of large-scale rotary machinery shaft will make torque change or vibrate transiently or lasting because of any unstable course of electric or machinery, power or loading, so it can arise free or force vibration of shaft. This kind of torsional vibration will cause the fatigue accumulation of the shaft material, and finally it will make shaft damaged. So it is very important to measure the torsional vibration.In this paper we use the high-accuracy photoelectric encoder to pick up the torsional vibration signal, replacing expensive, complex and low-performance torsional vibration sensors. When torsional vibration happens, the pulse signal that the encoder outputs will produce the density change, because the torsional vibration signal does frequency modulate to pulse signal. With Hilbert transformation the signal can be demodulated, and can get the torsional vibration signal..In this paper we analyze the system response under the function of external stimulation by researching the dynamics simplified model to the experimental system. By analyzing it, we can know the amplitude depends on physical feature (quality, rigidity, damp) , frequency and amplitude of stimulation, and has nothing to do with the way (initial condition) of the system entering the movement. The frequency of torsional vibration should be the same with the frequency of the stimulation.In specially designed experimental equipment of torsional vibration measuring, the output pulse of the encoder reflects the respond of the external stimulation in this section, the external stimulation can be examined by the pressure sensor. The torsional vibration response of system can be got from the demodulation theory of mentioned above. The relation of the torsional vibration signal and stimulation matches to the theory analysis.In the end we attempt to identify the gear fault by utilizing this measuring method of torsional vibration. It shows that this signal is sensitive to fault, and signal-to-noise ratio is high. So it is suited to gear early fault diagnosis.