Model Decoupling and Control of the Wheeled Humanoid Robot Moving in Sagittal Plane

The wheeled humanoid robot is such a new type of robot that combines both the humanoid structure and the Wheeled Inverted Pendulum (WIP) base. They are able to move rapidly on flat ground as well as stand still on the slope, which has been well demonstrated on the WLR-II robot in this paper. In order to achieve it, a novel but simplified control framework is designed, which comprises of two main modules, the wheel balance controller and the centroidal adjustment controller. The former controller helps to maintain balance of the robotic system by rotating the wheel to move forward or backward, while the latter controller works by moving the Center of Mass (CoM) of the robot at a distance from the equilibrium point, which will result in a specified acceleration used to drive the first wheel balance controller. In order to design such these two controllers, the dynamic model of the robot in sagittal plane is decoupled into two relatively simplified model. In particular, the coupled dynamics between each other is significantly considered and alleviated. Experiments conducted on the WLR-II robot show that the proposed control framework can make the robot both accurately track the velocity tajectory and steadily stand on the slope.