Actively Controlled Magnetic Bearing System Using Compliant Mechanism

Abstract

Rotors with speeds more than 20000 rpm, like Flywheel Energy Storage System (FESS), are fully or partially evacuated to reduce drag but have to be geometrically constrained except in the rotation axis. Magnetic bearings are preferred over a rolling element or journal bearings. The high-speed rotor is supported on active magnetic bearings. Though magnetic bearings with multi-axis support are possible, we look at building the support using desired passive compliance along five DOFs and one contactless support using a magnetic field with high stiffness at the set gap. A single DOF active magnetic bearing system is designed to precisely position a shaft along the longitudinal direction. The shaft is supported on a pair of compliant ortho-planar mechanisms at the two ends. The compliant structure is designed to provide bearing support along the radial directions. The position of the shaft along the longitudinal direction is actively controlled using the magnetic bearing system. A two-unit system based on magnetic attraction, one at either end, is designed. A candidate compliant ortho-planar mechanism is designed to support the shaft and fabricated using rapid prototyping. Stresses and bearing stiffness along different axes are calculated and analyzed using FEM. The 3D printed part was used for visualization and tested for compliance in the active magnetic bearing direction. The active magnetic bearing system is modeled. The controller will be optimized for disturbance rejection and minimize excursion around a desired axial location. The developed setup can be used to study and develop multi-axis AMB for high-speed rotating applications.