Robotic Ankle Mechanism Capable of Kicking While Jumping and Running and Adaptable to Change in Running Speed

Abstract

When humanoid robots perform dynamic operations such as jumping and running, large outputs are required at each joint. It is known that humans save energy by using muscles and tendons effectively during dynamic motion. Therefore, we consider that energy saving and dynamic motion can be realized in robots by adding elements that replace such muscles and tendons. Based on this, we previously developed a robot with elasticity in the leg joints. However, its ankle joint mechanism did not have sufficient power to kick like a human while running. In addition, although the joint quasi-stiffness of the human leg changed according to the running speed, it could not handle high speeds nor simulate the required stiffness at low speeds. Therefore, we developed an ankle mechanism that is capable of kicking while jumping and running and adaptable to changes in running speed. By placing leaf springs in series, the mechanism achieved a joint stiffness of 250 to 350 Nm/rad, which is the ankle joint quasi-stiffness required for running at speeds of 2.0 to 5.0 m/s. By using a double motor, moreover, the mechanism succeeded at active kicking with a load torque of 110 Nm, equivalent to the value of active kicking while jumping.