Variable Stiffness and Antagonist Actuation for Cable-Driven Manipulators Inspired by the Bird Neck

Abstract This paper discusses stiffness and antagonistic actuation in light-weight cable-driven bio-inspired manipulators suitable for safe interactions. Manipulators under study are built upon arranging in series several tensegrity joints, called “modules.” A comparative study of several modules revealed that the X module, in contrast to modules based on pivots, allows one to increase joint stiffness by increasing antagonistic input forces like during muscle coactivation. For a planar manipulator with N modules, antagonistic actuation schemes with 2N and N + 1 cables are proposed and compared. It is shown that the N + 1 cable actuation scheme allows controlling both the manipulator configuration and joint stiffness satisfactorily. As compared with a manipulator with 2N active cables, one on each side of each module, higher forces are required to achieve the manipulator configuration. However, the N + 1 cable actuation scheme is a reasonable solution that allows reducing the moving masses and cost.