Force Distribution Characteristics of Actively Reconfigurable Wheeled Vehicle Systems

Abstract This paper addresses the force distribution issues associated with redundantly actuated wheeled vehicles that are suited for operation on uneven terrain. Basic results relating to the partitioning of motion and force variables in these mechanisms are developed. The redundant actuation scheme allows for the control of force distribution in the system, in addition to motion control. The unique kinematic characteristics of wheeled systems, that makes these vehicles ‘singular’ on even terrain, and ‘near-singular’ on uneven terrain; and the presence of ‘kinematic slipping’ when these vehicles move on uneven terrain make their force distribution mathematics distinct from other systems considered in the literature. In a singular configuration, it is shown here that these active wheeled vehicles possess only a partial control over their internal force distribution. A procedure to partition the ‘force space’ into controllable and uncontrollable spaces is provided based on a geometric approach. Closed-form force space results are included for an actively articulated multi-module system (a generalization of a passive, articulated mobile robot that has been studied extensively in literature). The force distribution in actively reconfigurable wheeled vehicles is closely related to their rate kinematics. Rate kinematics of these vehicles has been studied in a companion paper [SN96].