Real-Time Motion Generation and Control Systems for High Wheel-Legged Robot Mobility

A wheel-legged mobile robot (WLMR) has both leg and wheel structures. WLMRs have adaptability advantages because they can change locomotion methods depending on the terrain. However, the location of a WLMR's center of gravity (CoG) is very high; thus, almost all existing WLMRs move statically. In this paper, whole body motion generation and various control systems are studied to facilitate higher WLMR mobility. To this end, a zero moment point (ZMP) is introduced as a stability index. In addition, WLMRs are modeled as single point mass linear inverted pendulums. Subsequently, online CoG pattern generation methods are proposed; one is a preview control approach, and a second is an approach that realizes the desired ZMP pattern using a zero-phase low-pass filter. It is then possible to generate the desired CoG patterns more easily and faster than with a preview control approach. The CoG patterns based on the single point model are constructed via the resolved-momentum-control approach. Finally, the effectiveness of the whole body motion pattern generated by the proposed methods is validated by simulations and experiments.