Dynamic modeling, analysis, and experimental study of ball screw pairs with nut spalling faults in electromechanical actuators

Condition monitoring and fault diagnosis on electromechanical actuators (EMAs) have gradually become a research hotspot in the field of aviation, but few studies have examined the failure mechanism of an EMA by establishing a dynamic model. As such, this paper establishes the two-degree-of-freedom radial dynamic models of ball screw pairs under normal and faulty conditions to analyze the dynamic characteristics that may occur in the vibration responses of normal and faulty ball screw pairs. After analyzing the simulation results of the established models, in this study, it is determined that after a spalling fault occurs in the inner raceway of a ball nut, the amplitude at the third harmonic of the ball passage frequency will increase significantly compared with the first and second harmonics of that frequency in the acceleration spectrum of the nut. This phenomenon can be regarded as a characteristic expression of the nut spalling fault in the acceleration spectrum, and it is verified by experiments on an EMA test rig. The experimental results show that this fault characteristic can also be observed even when the screw shaft rotating speed varies from 60 rpm to 420 rpm. However, under high-speed conditions, additional signal processing and noise reduction methods are required to solve the problem of background noise interference.