Optimization of Whole-Body Motion for Humanoid Robot Walking Down Stairs with Small Joint Range of Motion

Traversing through stairs stably is a challenging task for humanoid locomotion. Previous researches mostly focus on empowering humanoid robots with the capability of walking up stairs. There are only a few studies about walking down stairs, not to mention the case of humanoid robots walking down stairs with small joint range of motion (RoM). This paper proposes a whole-body motion optimization method for humanoid robots walking down stairs continuously with restricted joint RoM. Motion generation consists of two sequential optimization problems. The first is a segmented parameter optimization of swing foot trajectory considering trajectory smoothness and collision avoidance. The second is a whole-body motion optimization based on the centroidal dynamics and whole-body kinematics model, which takes the optimized swing foot trajectory as hard equality constraints and optimizes physically feasible whole-body trajectory for walking down stairs within small joint RoM. Finally, the effectiveness of the proposed method is validated in simulation with the humanoid robot BHR7P.