Realization of flexible motion by musculoskeletal humanoid “Kojiro” with add-on nonlinear spring units

Abstract

We are developing musculoskeletal humanoid robots with humanlike muscles and bones that can perform humanlike flexible motions. For the “muscles”, we use a wire-driven system in which motors wind wires used to flexibly move the joints. This system not only moves the robot itself but also controls the motion stiffness with nonlinear spring units. A musculoskeletal robot with these units distributed throughout its body can change the stiffness of its joints in accordance with the situation, enabling it to adjust to objects flexibly and to reduce external force, as humans do. We have created a humanoid robot called “Kojiro” that uses the wire-driven system for its whole body and four nonlinear spring units in its forearms. These units are used to change the stiffness of the wrists, but it is not enough these units can change the stiffness of the wrists only. In order to add these units to another part of Kojiro's body, we have to redesign this part or at least unstrap its wires. Redesigning some parts or unstrapping wires not only takes some time but also lead to some troubles on occasion. We thus newly developed enhanced add-on type nonlinear spring units that can be added to wires made before without redesigning it or unstrapping the wires. We added these enhanced units to some parts of Kojiro's body, enabling Kojiro to perform more powerful and flexible motions, such as American football motions.