Detection and diagnosis of fault roller bearings under variable speed conditions

In the past, the research method of bearing fault diagnosis based on constant speed has a good effect on the steady-state signal measured under stable conditions, but it is not very effective for variable speed mechanical bearing fault. The Computed Order Tracking (COT) method normalizes the frequency by the equal angle sampling method, avoids the frequency ambiguity caused by the change of speed, and has a certain effect on the fault diagnosis of nondestructive detection. At the same time, the starting speed of the bearing moving at variable speed often contains constant speed component, which can be processed by the envelope spectrum method based on Variational Mode Decomposition (VMD), Therefore, this paper proposes a fault diagnosis method for variable speed bearing based on VMD and COT. Several experiments are carried out on the mechanical fault simulator. In the experiment, the rotating shaft with the fault bearing is accelerated by the frequency converter. The time domain signal generated in the process of the fault bearing is collected by the computer, and the non-stationary signal in the time domain is transformed into the stationary signal in the angle domain by COT. VMD is used to decompose the stationary signal in diagonal domain, and the order spectrum and fault information of the decomposed signal are obtained. Compared with the bearing characteristic frequency, the effect of the proposed method is verified. In order to verify the calculation results under the condition of variable speed, the sensor is also used to collect the vibration signal of rolling bearing. In the process of variable speed, the tachometer is used to collect the bearing speed signal, from which a constant speed component is extracted. The envelope spectrum method based on VMD is used to process the short constant velocity component. The experimental results of the latter verify the effectiveness of the proposed method.