On the Design of Fast-Response Variable-Stiffness Continuum Robot with Electro-permanent Magnet-based Ball Joints

Abstract

Continuum robots offer exceptional adaptability and dexterity for tasks in confined and complex spaces. However, their flexible structures inherently limit payload capacity and structural robustness. To overcome this trade-off, many previous studies have proposed variable stiffness continuum robots, but these robots have slow response times that hinder rapid tasks. In this regard, we propose a novel continuum robot with electro-permanent magnet (EPM)-based ball joints. This robot has two key components: an EPM actuator and a variable stiffness ball joint (VSBJ). The EPM-embedded VSBJ constitutes discrete segments of the robot and dynamically transitions between low- and high-stiffness states by controlling the EPM’s magnetic field. This provides the robot with fastresponse and variable-stiffness capabilities. In experiments, the VSBJ achieved a 205-fold stiffness variation ratio with a response time of 0.019 s, surpassing the performance of many previously studied robots. Leveraging these capabilities, the proposed robot demonstrated single or multiple bending motions by controlling the stiffness of discrete segments. Finally, the potential of the fast-response variable-stiffness continuum robot for real-world applications was confirmed.