Trajectory adaptation of biomimetic equilibrium point for stable locomotion of a large-size hexapod robot

This paper proposes a control scheme inspired by the biological equilibrium point hypothesis (EPH) to enhance the motion stability of large-size legged robots. To achieve stable walking performances of a large-size hexapod robot on different outdoor terrains, we established a compliant-leg model and developed an approach for adapting the trajectory of the equilibrium point via contact force optimization. The compliant-leg model represents well the physical property between motion state of the robot legs and the contact forces. The adaptation approach modifies the trajectory of the equilibrium point from the force equilibrium of the system, and deformation counteraction. Several real field experiments of a large-size hexapod robot walking on different terrains were carried out to validate the effectiveness and feasibility of the control scheme, which demonstrated that the biologically inspired EPH can be applied to design a simple linear controller for a large-size, heavy-duty hexapod robot to improve the stability and adaptability of the motion in unknown outdoor environments.