Effects of Spring-like Magnetic Energy from Embedded Permanent Magnets on Elastic Actuation

Abstract

Series elastic actuators (SEAs) are increasingly used in robotic applications where tasks require safe human-robot interaction. Motivated by the growing need to develop SEAs with nonlinear stiffness to tradeoff between force tracking bandwidth and low output impedance, this paper presents an analytical approach to model the magnetic force/torque of a magnetic (Mag) SEA using the distributed current source method to provide a basis to derive the noncontact magnetic compliance; both translational and rotational stiffnesses are considered. The Mag-SEA model, which relaxes several common assumptions in the published literature that treat the magnetic lead screw as an ideal transformer, is numerically illustrated. The findings demonstrate that the simplified (ideal transformer) model fails to characterize the displacement-dependent magnetic force/torque and underestimates the mechanical advantage that can be capitalized from the spring-like magnetic energy of the embedded permanent magnets.