Design and modeling of a torsion spring-based actuator (TSA) with valid straight-arm length adjustable for stiffness regulation

This paper presents the design and modeling of a novel torsion spring-based actuator (TSA) with variable stiffness. The mechanical structure of stiffness regulation contains two opposite-handed torsion springs and two cam bearing followers (CFs). The operational principle is by changing the contact point of the torsion spring and the CF to regulate the stiffness. The proposed design allows for the improvement of an actuator with a wide range of stiffness and a low friction of transmission mechanism. Wire-rope drive is used to avoid the backlash in a rack and pinion transmission system and low-response in a ball screw drive system. Only one contact point for each CF to torsion spring exists to replace the sliding friction while moving in a sliding groove with the rolling friction. Small size, compact structure and modular design are considered preferentially for the application on multi-dof (degree of freedom) robotic system. Simulation experiment results are presented to demonstrate the wide range of stiffness, the fast response and the excellent tracking performance achieved by the proposed TSA.