Transformed magnetic force model of zero power permanent electromagnetic suspension system by using Hall effect based distance sensor

The dream of levitating an object with ultra-low power consumption has been a long-standing one. The rapid advancement of rare-earth magnetic materials in recent years has made the permanent-electromagnetic suspension (PEMS) technology a viable option for achieving zero-power levitation. This work presents a quantitative analysis of the zero-power PEMS system through theoretical modelling, numerical simulation, and experimental investigation. Traditionally, the magnetic force of the PEMS system is characterised with respect to the coil current and the absolute floating distance, leading to a highly nonlinear critical proportional (P) gain and significant uncertainty for the distance controller. This work proposes a transformed magnetic force model for the zero-power PEMS system, where the floating distance is measured by the Hall-effect-based distance sensor based on the magnetic flux density induced by the floating magnet. This approach ensures that the critical P gain becomes approximately constant over a wide range of the payload, allowing for a fixed P gain to maintain a sufficient stability margin. Nevertheless, the zero-power PEMS experiment confirms the effectiveness of the transformed model, demonstrating the loading capacity from 245 to 1205 g with an unchanged P gain.