Vibration monitoring for detecting rotor eccentricity in brushless motors

In this paper the possibility to detect rotor eccentricity in brushless motors by means of the monitoring of current and vibration is investigated. The problem is analysed by taking into account the researches in literature concerning the effects of rotor eccentricity in various kinds of electrical machines (induction, synchronous and brushless), in order to evaluate appropriate fault detection indicators. The current and vibration spectra obtained as results of several experimental tests on two motors, one of which modified on purpose with dynamic eccentricity, have been analysed in order to highlight characteristic frequencies that are more evident in case of eccentricity. The vibration has been measured along two radial directions (horizontal and vertical) by means of two accelerometers and the experimental tests have been carried out at different values of rotor speed.