Hierarchical Optimization-Based Whole-Body Control With Terrain Adaptation for a General Nonholonomic Wheeled Mobile Robot

This paper proposes a novel dynamic model and a locomotion framework based on it for nonholonomic wheeled mobile robots (NWMR) with a general configuration. The general configuration is established on a nonholonomically constrained wheeled mobile platform driven by two motors, into which a 3-DoFs waist-leg mechanism, a torso, and a 7-DoFs dual-arm system are integrated. Based on this configuration, a novel terrain-adaptive NWMR dynamics model (TAND) is formulated to operate on arbitrary inclined planes, which unifies the dynamic equations of NWMRs with those of conventional 6-DoFs floating-base robots. Consequently, traditional 3-DoFs floating-base NWMR dynamic models are encompassed as specific cases within the proposed TAND. Furthermore, by incorporating hierarchical optimization-based whole-body control (HOWBC) with TAND, a terrain-adaptive HOWBC (TAHC) is introduced, enabling the achievement of motion tracking, posture maintenance, and manipulability optimization (MTO) across varied terrains. For the MTO sub-task, a new whole-body manipulability index specifically designed for NWMR is proposed, and gradient optimization methods at the acceleration level are applied to enhance it. The proposed TAND, MTO, and TAHC are validated through comprehensive simulations, demonstrating their effectiveness in enabling coordinated locomotion across different terrains.