Analysis and Testing of a Four Coil Magnetic Levitation Configuration

Magnetic levitation in general is relevant to applications which require fine control of motion, vibration, force and torque. One common method for magnetic levitation is to use four iron core coils connected in pairs, two Hall effect sensors, and an outer ring of permanent magnets to levitate disk magnets from below. This method uses only two feedback control loops to stabilize rotation and translation of the magnet together in both horizontal directions, where vertical translation is passively stable and its vertical axis yaw rotation is left uncontrolled to rotate freely. The advantageous features of this levitation configuration is that only two sensors and actuators are needed to levitate a magnet above an array of coils.To investigate the characteristics of this magnetic levitation method, we have modeled the forces and torques produced on the levitated magnet from the fixed magnets and induced magnetization of the coil cores according to its position and orientation. This model will enable modification of the system design parameters to optimize performance in terms of levitated weight, height, stability or any other desired criteria of the levitation system. Our control implementation demonstrates that simple proportional-derivative (PD) control of the two feedback loops is sufficient to stabilize the motion of the levitated magnet.