A Model Predictive Capture Point Control Framework for Robust Humanoid Balancing via Ankle, Hip, and Stepping Strategies

The robust balancing capability of humanoids is essential for mobility in real environments. Many studies focus on implementing human-inspired ankle, hip, and stepping strategies to achieve human-level balance. In this article, a robust balance control framework for humanoids is proposed. First, a model predictive control (MPC) framework is proposed for capture point (CP) tracking control, enabling the integration of ankle, hip, and stepping strategies within a single framework. In addition, a variable weighting method is introduced that adjusts the weighting parameters of the centroidal angular momentum damping control. Second, a hierarchical structure of the MPC and a stepping controller was proposed, allowing for the step time optimization. The robust balancing performance of the proposed method is validated through simulations and real robot experiments. Furthermore, a superior balancing performance is demonstrated compared to a state-of-the-art quadratic programming-based CP controller that employs the ankle, hip, and stepping strategies.