Novel electromagnetic repeated launch locking/unlocking device (RLLUD) based on self-locking for magnetic bearing flywheel

Although magnetic bearings seem capable of holding the rotor during launch by electromagnetic forces, most available magnetic bearing flywheels are equipped with an additional launch locking/unlocking device (LLUD). As the ground environmental test and transport, flywheel systems need multiple locking/unlocking. Therefore, to remedy the limitation of one-off LLUD which cannot repeat locking/unlocking, a novel electromagnetic repeated launch locking/unlocking device (RLLUD) based on self-locking to keep locking and springs to carry out unlocking is presented in this paper. Its composition, operating principle and functional performance requirements are introduced. First, the self-locking condition and spring parameters are designed. Subsequently, by comparatively analyzing four electromagnetic forces corresponding to four steps including carrying out locking/unlocking and keeping locking/unlocking, the internal permanent magnet is adopted as actuator of RLLUD. Second, based on equivalent magnetic circuit method, the mechanics models of electromagnet under four steps are established, and two high-sensitivity parameters including magnetic ring length and permanent magnet magnetization length are obtained. Upon this, by taking into account spring elastic forces, the four electromagnetic forces are calculated and designed in detail by using finite element method (FEM). It ensures the repeated locking/unlocking of RLLUD. The prototype RLLUD is manufactured and verified by environmental mechanics tests. The results show that no resonant vibration occurs and the maximum vibration displacement between stator and rotor is 40 μm, far less than the protection gap of 200 μm. It indicates the novel RLLUD can effectively carry out the protection function for magnetic bearing flywheel.