Balancing strategy using the principle of energy conservation for a hopping humanoid robot

Even though many humanoid robots have been developed and they have locomotion ability, their balancing ability is not sufficient. In the future, humanoid robots will work and act within the human environment. At that time, the humanoid robot will be exposed to various disturbances. This paper proposes a balancing strategy for hopping humanoid robots against various magnitude of disturbance. The proposed balancing strategy for a hopping humanoid robot consists of two controllers, the posture balance controller and the landing position controller. The posture balance controller is used for small disturbances, and its role is to maintain stability by controlling the ankle torque of the robot. On the other hand, if disturbance is large, the landing position controller, which changes the landing position of the swing foot, works with the posture balance controller simultaneously. In this way, the landing position controller reduces large disturbances, and the posture balance controller controls the remaining disturbances. The landing position controller is derived by the principle of energy conservation. An experiment conducted with a real humanoid robot, HUBO2, verifies the proposed method. HUBO2 made a stable and continuous hopping action with the proposed balancing strategy overcoming various disturbances placed in the way of the robot.