Wheeled motion kinematics and control of a hybrid mobility CENTAURO robot

Abstract Legged-wheeled robots combine the advantages of efficient wheeled mobility with the capability of adapting to real-world terrains through the legged locomotion. Thanks to their hybrid mobility skill, they can excel in many application scenarios where other mobile platforms are not suitable for. However, the improved versatility of their mobility increases the number of constraints in their motion control, where both the properties of legged and wheeled functionalities need to be considered. Relevant schemes for legged-wheeled motion control so far have attempted to address the problem by exploiting separate motion control of the wheeled and legged functionalities. The contribution of this paper is the introduction of derivation of the legged-wheeled motion kinematics without constraining the camber angles of the wheels. To this end, the wheel geometry is approximated by torus that more precisely represents a real wheel geometry than a standard sphere/cylinder. On the basis of the derived legged-wheeled motion kinematics, a first-order inverse kinematics (IK) scheme that resolves the legged-wheeled robot whole-body motion respecting the wheel rolling constraint is described. Furthermore, a higher-level method to resolve wheel steering to comply with a non-holonomic constraint is designed. A damping scheme is proposed to handle a structural singularity when a system non-holonomy deteriorates. Finally, the work adopts a floating base model that allows to easily incorporate the legged motion into the proposed scheme. The developed control scheme is tested in experiments on a legged-wheeled centaur-like robot — CENTAURO.