Modeling and experimental study of rotor drop dynamics in maglev rotor systems with caged deep-groove ball touchdown bearings

Active magnetic bearings (AMBs) require touchdown bearings (TDBs) to protect the rotor–stator system in the event of failure. To describe the detailed dynamics during rotor drop, a dynamic model of a caged deep-groove ball TDB is developed by explicitly considering the motions of the inner ring, outer ring, cage, and rolling elements. The effects of TDB clearance and initial drop position on ball slip, ball load, and post-drop rotor response are investigated. The results show that smaller clearances reduce ball–raceway slip. In the non-full-rub whirl state, the ball load is minimized at a clearance of -(Formula presented), whereas under full-rub whirl conditions, larger clearances lead to lower ball loads. Both negative clearances and excessively large positive clearances increase the likelihood of full-rub whirl. The initial drop position strongly affects the rotor response at intermediate rotational speeds and may also trigger full-rub whirl. High-speed rotor drop experiments under different TDB clearances, initial drop positions, and rotational speeds are conducted to validate the model and the main findings.