TWrist: An agile compliant 3-DoF tensegrity joint

Tensegrity structures, with their unique physical characteristics, hold substantial potential in the field of robotics. However, the very structures that will give tensegrity robots potential advantages over traditional robots also hold long term challenges. Due to the inherent high redundancy of tensegrity structures and the employment of tension elements, tensegrity robots exhibit excellent stability, compliance, and flexibility, although this also results in lower structural deformation efficiency. Existing research has endeavoured to enhance the motion performance of tensegrity robots, exploring diverse approaches such as actuation schemes, structure design, aligned with control algorithms. However, the physical constraints of the elements in such structures and the absence of suitable controllers impede further advancements in the usefulness of tensegrity robots. This paper presents a novel design based on an under constrained transition region design and a tailored control approach based on inverse kinematics, improving the motion performance of the proposed novel tensegrity joint. Through this approach, the tensegrity joint, while preserving the advantages of compliance and flexibility expected from tensegrity structures, offers three degrees of rotational freedom, mirroring the controllability of conventional rigid-body joints. The results demonstrate the capability of tensegrity- based robotic joints to provide flexible actuation under situations demanding high compliance. The integration of structure design with a tailored control approach offers a pioneering model for future development of tensegrity robots, underscoring the practical viability of tensegrity structures in the realm of robotics.