Dynamic modeling of tip-over stability of mobile manipulators considering the friction effects

This paper extends the models developed previously by the authors for simulating tip-over stability of mobile manipulators, to include the friction of the contact between the base and the ground. Thus, the present model takes into account the detailed dynamics of the base that can rock back and forth during the movement of the manipulator, the combined vehicle suspension and ground-tire compliance and, the friction between the wheels and the ground. 'LuGre' tire friction model is employed, which along with the novel method of virtual links transforms the system into a fixed base manipulator with single degree of freedom at each joint. The model is then used to simulate planar movements of a 215B Caterpillar excavator-based log-loader machine. The results are also compared to those obtained by the simplified model, which was developed previously based on the assumption that the friction between the base and the ground is high enough to prevent the base from skidding forward or backward. The results clearly show that the friction properties between the wheels and the ground affect machine stability. Thus, one has to include the frictional effect in order to accurately predict the tip-over behavior of mobile manipulators.