Full-Dynamics Analytical Modeling of Normal Forces for Skid-Steering Mobile Heavy-Duty Manipulators with Actively Articulated Suspension

Abstract

This paper presents a geometric approach to calculating the ground reaction normal forces of a four-wheel heavy-duty parallel-serial mobile manipulator in an analytical manner. Such a skid-steering mobile platform is endowed with an actively articulated suspension, thus becoming a rigid multibody system itself. Our solution exploits the wheel’s dynamics decomposition to project the wheels’ internal dynamics and friction forces, preserving all their mechanical effects without hard assumptions. Developing a closed-kinematic chain dynamical analysis, our approach embraces the parallel-serial manipulator and the articulated suspension in a unique screw-theory formulation. Additionally, with respect to previous approaches, our normal forces solutions account for all nonlinear dynamics and accelerations in both the articulated suspension and the wheels. This results in an accuracy enhancement, as demonstrated by a reduction of the average error in normal forces computation by half while traversing uneven terrains when simulating a 7-DoF mobile manipulator with a 2-DoF suspension. We include a losing-contacts robust formulation.