  In this paper, we present a whole-body control framework for Wheeled Inverted
Pendulum (WIP) Humanoids. WIP Humanoids are redundant manipulators dynamically
balancing themselves on wheels. Characterized by several degrees of freedom,
they have the ability to perform several tasks simultaneously, such as
balancing, maintaining a body pose, controlling the gaze, lifting a load or
maintaining end-effector configuration in operation space. The problem of
whole-body control is to enable simultaneous performance of these tasks with
optimal participation of all degrees of freedom at specified priorities for
each objective. The control also has to obey constraint of angle and torque
limits on each joint. The proposed approach is hierarchical with a low level
controller for body joints manipulation and a high-level controller that
defines center of mass (CoM) targets for the low-level controller to control
zero dynamics of the system driving the wheels. The low-level controller plans
for shorter horizons while considering more complete dynamics of the system,
while the high-level controller plans for longer horizon based on an
approximate model of the robot for computational efficiency.
