Active magnetic bearing-supported rotor with misaligned cageless backup bearings: A dropdown event simulation model

• A dynamic model of cageless backup bearing of an AMB system is proposed.
• A simulation model is used to study the effect of bearing misalignment.
• The model is verified by comparing the simulations to measurements.
• A parametric study of a system with two misaligned cageless backup bearings is done.
• The dropdown is found to be fatal when misalignment is 75% of the air gap.

Active magnetic bearings (AMB) offer considerable benefits compared to regular mechanical bearings. On the other hand, they require backup bearings to avoid damage resulting from a failure in the component itself, or in the power or control system. During a rotor-bearing contact event – when the magnetic field has disappeared and the rotor drops on the backup bearings – the structure of the backup bearings has an impact on the dynamic actions of the rotor. In this paper, the dynamics of an active magnetic bearing-supported rotor during contact with backup bearings is studied with a simulation model. Modeling of the backup bearings is done using a comprehensive cageless ball bearing model. The elasticity of the rotor is described using the finite element method (FEM) and the degrees of freedom (DOF) of the system are reduced using component mode synthesis. Verification of the misaligned cageless backup bearings model is done by comparing the simulation results against the measurement results. The verified model with misaligned cageless backup bearings is found to correspond to the features of a real system.