VSA-II: a Novel Prototype of Variable Stiffness Actuator for Safe and Performing Robots Interacting with Humans

TLDR

VSA‑II is an improved variable‑stiffness actuator built on a prior co‑design principle, addressing torque, life‑cycle, and implementability limitations of the first version. The study presents the design, performance, and stiffness behavior of VSA‑II for robots that physically interact with humans. A simple PD controller independently regulates joint stiffness and position in a 1‑link arm. VSA‑II delivers higher torque capacity, greater robustness, longer life, superior stiffness characteristics, and demonstrates safer operation in impact tests.

Abstract

This paper presents design and performance of a novel joint based actuator for a robot run by variable stiffness actuation, meant for systems physically interacting with humans. This new actuator prototype (VSA-II) is developed as an improvement over our previously developed one reported in [9], where an optimal mechanical-control co-design principle established in [7] is followed as well. While the first version was built in a way to demonstrate effectiveness of variable impedance actuation (VIA), it had limitations in torque capacities, life cycle and implementability in a real robot. VSA-II overcomes the problem of implementability with higher capacities and robustness in design for longer life. The paper discusses design and stiffness behaviour of VSA-II in theory and experiments. A comparison of stiffness characteristics between the two actuator is discussed, highlighting the advantages of the new design. A simple, but effective PD scheme is employed to independently control joint-stiffness and joint-position of a 1-link arm. Finally, results from performed impact tests of 1- link arm are reported, showing the effectiveness of stiffness variation in controlling value of a safety metric.