Bio-Inspired Spherical Joints for a Soft Articulated Artificial Hand

The introduction of soft robotics technologies represents a promising direction to enhance system robustness and natural interaction. However, the inherent flexibility in joint designs can pose challenges in achieving both precise and repeatable gripping. This work introduces a soft artificial hand design with constrained ball joints, inspired by the anatomical structure of bones and tendons in the human hand. The key innovation lies in the integration of selectable stiffness levels in the spherical joints, enabling distinct stiffness characteristics to achieve both power and precision grasps. Through a set of contact simulations, this study characterize different behaviors in the finger model according to the stiffness level of its joints. The final hand design encompasses 15 degrees of freedom (DoF) actuated by a unique tendon and a single motor, and a passive proximal thumb joint. The developed prototype was preliminarily tested to assess its manipulation taxonomy and demonstrated the ability to grasp everyday objects in different configurations. Results show the potential of the proposed joint design in achieving a trade-off between precision and adaptability in grasping.