Application of a Magnetic Actuator As an External Excitation Source in Fault Detection

Rotating machinery covers a broad range of industrial applications. Consequently, unexpected failures may lead to suddenly manufacturing break-off involving high maintenance costs. The most common faults in such machines introduce anisotropy to the system causing changes in its modal parameters and increasing the response backward component. Modal analysis methods can be used to identify changes in the machine behavior and foresee incipient faults. This paper presents the time domain Multiple Output Backward Autoregression (MOBAR) method and discusses its advantages over frequency domain methods on field tests in industry. For the MOBAR method, a tuned non-synchronous excitation called blocking test is applied to the shaft using a magnetic actuator, and when the excitation is turned off, the decay response is used to estimate natural frequencies of the system and the corresponding modal damping. The changing of these parameters can be used to predict system failures. To demonstrate the usability of electromagnetic actuators to apply this method for fault diagnosis and identification, a case study is presented in which the directional coordinates modal parameters are identified for a rotor supported by journal bearings using the MOBAR technique.