Generic differential kinematic modeling of articulated mobile robots

This paper presents a generic method to obtain the kinematic model of articulated multi-monocycle mobile robots. It is based on an extension of the reciprocal screw method to asymmetrical and constrained parallel mechanisms. The proposed formulation allows to obtain the input/output velocity equations for such kinematic structures in an analytical form. Its efficiency is illustrated by an application to the RobuRoc6 mobile robot. The complex kinematic structure of this articulated multi-monocycle robot isfirst transformed into a spatial parallel mechanism which encapsulates the differential driving wheel systems. Then, we establish the analytical form of the reciprocal screw system which corresponds to the actively controlled wrenches applied to the controlled body. The model then provides explicit kinematic and static performances. Subsequently, the concept of multi-wheeled traction ellipsoid is introduced to evaluate quantitatively the obstacle clearing capabilities of such systems, even though their configuration and the contact conditions are highly variable.