Stable running on a kneed biped robot with only hip-joint actuation

Passive dynamic locomotion is well-known for its fabulous advantages in energy efficiency. In this paper we focus on the level passive running problem of a kneed biped. The knee joints of our robot model are elastic with torque springs. So energy dissipation is avoided at landing. Passive gaits have been firstly demonstrated on this kneed biped in this paper, yet they are not stable. Note that there is only one actuation at the hip joint. The robot thus has three degrees of under actuation, which increases the difficulty of control design. We derive an event-based control law to stabilize the system, and add energy shaping part to enlarge the basin of attraction as well as provide additional robustness. The effectiveness of our approach has been verified by numerical simulations.