Design of a Noncontact Bending Testing Device Using Magnetic Levitation Mechanism

This article proposes a noncontact bending testing device using magnetic levitation mechanism, which is expected to facilitate material testing in special environments. To stabilize global levitation degrees of freedom (DOFs) while saving hardware, a structure allowing four levitation DOFs to be passively stabilized is designed, in particular, the principle by which a special configuration passively stabilize one of the levitation DOFs is explained using finite element method (FEM) analysis. In addition, since the levitated object will bear a wide range of bending force, which will pose a disturbance on the levitation, a fixed stiffness-damping controller is designed based on proportional derivative (PD) controller to deal with the disturbance. Control simulation results demonstrate that the adopted control method can effectively keep levitation stiffness and levitation damping constant even under the bending force. Moreover, a force control system with a proportional integral (PI) controller is designed to control the loading of the bending force. Finally, two groups of experiments are performed with a high-stiffness material and a low-stiffness material, respectively. Experiment results demonstrate that the special configuration can passively stabilized the levitation DOF, and the fixed stiffness-damping control method allows the device to withstand a bending force up to 50 N while keeping levitation stable. Also, the force control system is proved to be feasible even when specimen deflection is large.