A new variable stiffness design: Matching requirements of the next robot generation

TLDR

Conventional rigid robotic joints struggle with unknown environments, safety constraints, and performance, limiting their use in tasks requiring rapid, safe interaction. The authors propose a variable‑stiffness joint (VS‑Joint) to overcome these limitations. The VS‑Joint integrates compact, high‑performance actuation with dynamically adjustable stiffness and mechanically programmable behavior. It adapts easily to diverse tasks, resists impacts, enables faster trajectories, and is well suited for shoulder and elbow joints of anthropomorphic arms.

Abstract

Facing new tasks, the conventional rigid design of robotic joints has come to its limits. Operating in unknown environments current robots are prone to failure when hitting unforeseen rigid obstacles. Moreover, safety constraints are a major aspect for robots interacting with humans. In order to operate safely, existing robotic systems in this field are slow and have a lack of performance. To circumvent these limitations, a new robot joint with a variable stiffness approach (VS-Joint) is presented. It combines a compact and highly integrated design with high performance actuation. The VS- Joint features a highly dynamic stiffness adjustment along with a mechanically programmable system behavior. This allows an easy adaption to a big variety of tasks. A benefit of the joint is its intrinsic robustness against impacts and hard contacts, which permits faster trajectories and handling. Thus, it provides excellent attributes for the use in shoulder and elbow joints of an anthropomorphic robot arm.