Effect of Terrain Traction, Suspension Stiffness and Grasp Posture on the Tip-Over Stability of Wheeled Robots with Multiple Arms

In this paper, dynamics, postural stability and control of suspended wheeled mobile manipulators for cooperative heavy object manipulation are elaborated considering the effect of grasping posture. The presented model considers a system equipped with multiple manipulators with flexible suspension, which also contains an accurate nonlinear behavior of the tires. Moreover, it includes the vibratory response of the tires as unsprung masses. Therefore, this is one of the most complete models that have been presented for wheeled mobile manipulators to date. First, based on the Newton-Euler formulation for a chain of rigid bodies, the dynamics model of such complicated systems in three-dimensional maneuvers is developed without considering a nonlinear frictional model of tires, which was verified using the ADAMS multibody simulator. Then, a proper nonlinear friction model is added to the developed dynamics to provide a more complete one. Considering pneumatic tires, the Dugoff tire friction model is adopted to describe the longitudinal and lateral forces produced at the contact patch of the wheels. Using the obtained dynamics along with the moment-height stability measure the effect of frictional effects as well as suspension attributes on the postural stability of such systems are accurately investigated for maneuvers over flat and rough terrains. Finally, the effect of grasping posture and relevant configuration of the robot on the stability of the system is examined during a heavy object manipulation task. (C) Koninklijke Brill NV, Leiden and The Robotics Society of Japan, 2012