Design of a Noncontact Bending Testing Device Using Magnetic Levitation Mechanism

Abstract

This article proposes a non-contact 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 was designed, in particular, the principle by which a special configuration passively stabilize one of the levitation DOFs was explained using 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 was designed based on PD-controller to deal with the disturbance. Control simulation results demonstrated 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 PI-controller was designed to control the loading of the bending force. Finally, two groups of experiments were performed with a high-stiffness material and a low-stiffness material respectively. Experiment results demonstrated that the special configuration can passively stabilized the levitation DOF, and the fixed stiffness-damping control method allow the device to withstand a bending force up to 50N while keeping levitation stable. Also, the force control system was proved to be feasible even when specimen deflection was large.