Multi-modal Cooperative Posture Control of Wheel-legged Hybrid Robots

Introduction: Posture control is critical for wheel-legged hybrid robots to improve adaptability and motion stability in unstructured terrains. Recent patents in this field provide important references for this study. Methods: We establish a kinematic model for posture adjustment considering terrain variations. Leveraging the serial-chain structure of the wheel-leg system, we employ an improved Denavit- Hartenberg (D-H) method to develop single-leg and whole-body kinematic models. Wheel-ground contact force data is processed using first-order low-pass filtering, and a variable-damping admittance control algorithm is designed for leg motion. Additionally, a centroid height control algorithm and a wheel control strategy are proposed to assist in constraining leg states. Results: Comparative simulation experiments demonstrate that the proposed control strategy effectively tracks desired body postures, maintains constant wheel-ground contact forces, and stabilizes centroid height. This significantly improves the robot's adaptability and motion stability in unstructured terrains. Discussion: The multi-modal cooperative control strategy integrates posture feedback, force tracking, height stabilization, and wheel-driven assistance, overcoming the limitations of traditional decoupled control methods. The simulation results validate its robustness in complex terrains. Conclusion: The developed multi-modal cooperative control strategy enables precise posture control for wheel-legged robots, thereby enhancing their performance in challenging environments through the integration of kinematic modeling, admittance control, and wheel-leg coordination.