Gravity Compensation and Full-Body Balancing for Humanoid Robots

This paper proposes gravity compensation and contact force control for multi-DOF humanoid robots and demonstrates various balancing experiments. Gravity compensation is derived in the context of controlling contact force. It makes the robot passive with respect to the external force, hence plays a very important role for physical interaction. A desired applied force from the robot to the environment, such as anti-gravitational force, is optimally distributed to the contact forces at arbitrary contact points, then transformed to the whole-body joint torques directly. Different from previous methods, the proposed method does not require contact force measurement, inverse kinematics/dynamics, nor to specify the weight that determines which joint should compensate for external forces. The experimental results show the robot could actually keep self-balance under unknown disturbances, track to some desired task-space trajectories, and interact with the environment at any contact points. It is the first time that gravity compensation and force-based balancing/interaction have been realized by a full-sized biped humanoid robot