Innovative servo gap-retainer design by applying electromagnetic attraction force

A TDOF (Two Degrees of Freedom) Servo Gap-Retained Mechanism (SGRM) is proposed and verified by experiments in this work. It mainly consists of a flywheel and an Intelligent Posture Tracking System (IPTS). The flywheel, driven by an induction motor for spinning, is regarded as the tracking objective of the IPTS. The IPTS is mainly composed by an intelligent disc and the Hybrid Magnetic Actuators (HMAs). The posture of the intelligent disc is controlled by the magnetic forces induced by the HMAs to retain a constant gap with respect to the eccentric flywheel which spins, tilts and wobbles. Since the HMA is highly nonlinear, a Feedback-Linearized Sliding Mode Control (FLSMC) is synthesized to account for system parameter nonlinearities or unmodeled dynamics. The dynamics of the flywheel and the IPTS are theoretically investigated and analyzed. In fact, the proposed SGRM is a part of an entire flywheel cell. That is, once the MGU (Motor/Generator Unit) in flywheel cell operates at idle mode, the shaft of flywheel will be separated apart from MGU in order to avoid the energy loss of the flywheel by the back EMF induced by the magnetic field of MGU. On the other hand, the shaft of flywheel and MGU still need to maintain synchronous power transmission even at idle mode so that a non-contact clutch is equipped. Generally speaking, the role of SGRM in a flywheel cell is to ensure the centerline of the flywheel properly aligned with the non-contact clutch. At last, intensive computer and experimental simulations are undertaken to verify the feasibility of the proposed SGRM and FLSMC. It is evidently showed that the proposed SGRM under FLSMC exhibits superior transient response and servo capability upon constant gap retained. The steady-state tracking errors are about 5% with respect to the amplitudes of the reference trajectories in two radial directions (i.e., X-axis and Y-axis).