Running with lower-body robot that mimics joint stiffness of humans

Human running motion can be modeled using a spring-loaded inverted pendulum (SLIP), where the linear-spring-like motion of the standing leg is produced by the joint stiffness of the knee and ankle. To use running speed control in the SLIP model, we should only decide the landing placement of the leg. However, for using running speed control with a multi-joint leg, we should also decide the joint angle and joint stiffness of the standing leg because these affect the direction of the ground reaction force. In this study, we develop a running control method for a human-like multi-joint leg. To achieve a running motion, we developed a running control method including pelvis oscillation control for attaining jumping power with the joint stiffness of the leg and running speed control by changing the landing placement of the leg. For using running speed control, we estimated the ground reaction force using the equation of motion and detected the joint angles of the leg for directing the ground reaction force toward the center of mass. To evaluate the proposed control methods, we compared the estimated ground reaction force with the force measured by the real robot. Moreover, we performed a running experiment with the developed running robot. By using ground reaction force estimation, this robot could accomplish the running motion with pelvic oscillation for attaining jumping power and running speed control.