Walking control for compass-like biped robot with underactuated ankle

The paper aims at solving the walking control problem of a compass-like biped robot with underactuated ankle on the level ground or even uphill environment. The compass-like biped robot is equipped with a constraint mechanism to lock the hip angle when the swing leg retracts to a desired angle. For this system, an angular momentum based control is presented in order to make the biped robot walk on little downhill slope or even uphill. Existence conditions of limit cycle under angular momentum based control are presented. They can be used to determine whether there exists a gait on the slope or not. Furthermore, we apply the method of Poincare return map to analyze the stability property of the gait with angular momentum based control. Finally, an event-based control is adopted to make the walking gait of compass-like biped robot asymptotically stable.