Rotor frequency response self-identification using an active tilting-pad bearing

The identification of the rotor-bearing frequency response function (FRF) in a rotating machine is useful to check the actual dynamic parameters of the system (e.g. stiffness, damping, additional mass) during operation. For that, one conventionally adopts some sort of excitation device connected to the rotor to excite the system in the frequency range and measure the consequent rotor vibration response. Active bearings are designed not only to support the rotor but also to attenuate and control rotor vibrations during the machine’s operation. The presence of an actuation system in the active bearing brings an additional capability to these systems: the excitation capacity. This work presents the successful identification of the rotor-bearing FRF using a tilting-pad journal bearing with active pads. The pads of this active bearing are subjected to electromagnetic forces, which affect the angular position of the pads. Consequently, they change the lubrication behaviour of the lubricant film, thus affecting the behaviour of the rotor. Experimental results show the feasibility of identifying the rotor-bearing FRF during operation with acceptable precision. This represents an advantage in comparison with the conventional identification procedure because there is no need to mount additional actuation devices in the system as in the conventional identification approach (the bearing itself is capable of performing the system’s identification).