Roll-Over Shapes of Musculoskeletal Biped Walker

Abstract

Abstract In this paper, we investigate how the roll-over characteristic of a passivity-based walking robot with flat feet is created and affected by its musculoskeletal structure, which is easily modeled by an agonistic and antagonistic pair of muscles. We hypothesize that the curvature radius and the center position of the roll-over shape (ROS), defined as the centers of pressures transformed into a shank coordinate, is strongly related to the stiffness and the equilibrium posture of the ankle joint, which are determined by the tonuses of the agonistic and the antagonistic muscles. We built a new musculoskeletal biped walking robot driven by pneumatic actuators and conducted exhaustive walking experiment with various ankle conditions. The hypothesis is verified experimentally by analyzing the ROSs of the walking robot.