Modeling, design and experimental validation of a small-sized magnetic gear

A magnetostatic analytical model is created to analyze and design a small-sized magnetic gear for a robotic application. Through a parameter variation study, it is found that the inner rotor magnet height is highly influential to the torque, and based on which, the design is performed. Several magnetic gears with different rotor pole pair combinations are designed to suffice the required gear ratio, taking into account manufacturing constraints of such a small device. A design is chosen to be manufactured considering the following criteria: material cost, cogging torque level and rotational stiffness. Measurement and 3D FEM simulation results indicate that discrepancies between the expected and measured torque as well as efficiency arise due to axial flux leakage, which becomes severe in the presence of bearings. Meanwhile, a frequency response measurement result shows that the first resonant mode in the magnetic gear, which has implications on control, can be well estimated given the simulated values of rotational stiffness, damping, and rotor inertia and thus could actually be anticipated early in the design phase.