Adjustable spring mechanisms inspired by human musculoskeletal structure

Adjustable springs have been employed in robotic applications including physical interaction with humans or the environment. In this paper, planar multi-degree-of-freedom spring mechanisms with adjustable springs are investigated from a viewpoint of stiffness. We propose multi-degree-of-freedom biomimetic spring mechanisms inspired by the musculoskeletal structure of the human upper-extremity, which possesses highly nonlinear kinematic coupling among redundant muscles within its structure. The stiffness characteristics in the operational space of the proposed and conventional mechanisms with torsional springs are analyzed. The stiffness solution of springs for a certain workspace is given and the applicability of these mechanisms is verified through simulation.