Generic differential kinematic modeling of articulated multi-monocycle mobile robots

This paper presents a generic kinematic modeling approach for articulated multi-monocycle mobile robots. The formulation proposed to deduce the input/output velocity equations for such kinematic structures is an extension of the reciprocal screw based method of asymmetrical and constrained parallel mechanisms. The efficiency of this methodology for setting up the differential kinematic model is illustrated through application: the RobuRoc mobile robot. Its complex kinematic structure is first transformed into a spatial parallel mechanism which encapsulates the differential driving wheels system. Then, the analytical form of the reciprocal screw system which corresponds to the actively controlled wrenches applied on the controlled body is established. Reciprocally, it describes the way the wheel velocities are transferred to the output body. It also provides a geometrical information for an exhaustive singularity analysis and traction distribution optimization during the evolution of the system on highly irregular surfaces. From the differential kinematic model, the concept of traction ellipsoid is introduced for evaluating quantitatively the obstacle clearance capabilities when the configuration of the system and the contact conditions are highly variable