Decoupled 2-DOF Magnetic Levitation Actuator for Single-Body High-Throughput Pick-and-Place Module

This article presents the design, control methods, and experiments of a novel two degree-of-freedom (DOF) magnetic levitation actuator, which is capable of decoupling the levitational- and lateral-direction control in a compact single-body configuration. Our single-body 2-DOF actuator is composed of an U-shaped iron-core with its legs wrapped by two actuating coils and an internal permanent magnet (PM) inserted to the core, levitating a target of 1-inch steel ball at a nominal airgap of 10 mm. We present the decoupled 2-DOF stabilization control method using a combination of common and differential current excitation modes on top of the biased flux generated from the internal PM, with the target position feedback measured by dual fiber optic sensors. For the rapid target lifting, we use a hybrid method of open- and closed-loop controls to have a robust and long-range lifting operation up to the sensing limit of -18 mm below the nominal levitation position, also achieving more than 30 % faster operation compared to a common method of lifting by a predetermined trajectory. Our decoupled lateral-position control also significantly improves both the stiffness and damping in that direction, thereby achieving approximately 82 % reduction of the lateral deviation and 99 % reduction of the target settling time during high-acceleration transportation.