Transportation of a thin sheet metal disk using magnetic levitation and tilt control

Abstract

With magnetic levitation, ferromagnetic objects such as sheet metal can be handled without any contact. This has the beneficial properties of no contamination and no direct contact forces to the object, which can be important for sheet metal to keep the surface quality high. Levitation is realized by actively controlling the magnetic field depending on a measured gap between object and levitator, so that the attractive magnetic force balances the gravitational force. For levitating thin sheet metal, magnetic actuators can be placed at the top surface to control the gap, roll, and pitch motions, but the area of the side surface is not large enough to realize active control for horizontal motions. However, these horizontal motions are passive stable as there is a natural restoring force that will keep the object aligned with the levitator. Unfortunately, this passive force is far weaker than the controlled levitation force. This can be a problem for manipulation of the levitated sheet metal as horizontal accelerations have to be restrained in order to prevent loosing the object. This paper discusses a solution using a feed-forward tilt control strategy in which, similar to how a waiter tilts a tray of beverages during motion, both levitator and object are tilted during motion. In theory, significant improvements can be realized and a preliminary experiment verified that the feed-forward tilt control strategy is indeed very effective and that improvements could be realized.