Abstract: A double closed-loop control strategy for the wheel-legged mobile platform is proposed to enhance resistance to external disturbances, and it is mainly used to address the difficulty in maintaining platform stability when the body is subjected to strong external perturbations. Firstly, the wheel-end contact force estimator is established by combining the single-leg dynamics model and the recursive least squares method with forgetting factor, dealing with the problem of challenge in obtaining the contact force without ground reaction force sensors. Furthermore, the changes in the additional kinetic energy of the platform's movement in different directions are solved through the motion orbit reference energy method, and based on it, an external disturbance trigger is designed. The linear and angular flexible mass-spring-damping model ideas are used to analyze the mapping relationship between motion parameters such as displacement, velocity, acceleration and equivalent forces and torques in the linear and angular motion of the center of mass of the platform. Considering the influence of the relative position between the wheel end and the center of mass on the virtual force distribution of the legs, the dynamic relationship of the contact force tracking error and the wheel position tracking error is established. Then the double closed-loop control framework of body position closed loop and wheel end force closed loop is built. Finally, simulation and prototype experiment verify the real-time performance and effectiveness of the proposed method.

Key words: wheel-legged mobile platform, external disturbance rejection double closed-loop control, contact force estimation, disturbance detection trigger