Robust balance shift control with posture optimization

Abstract

In this paper we present a control framework which creates robust and natural balance shifting behaviours during standing. Given high-level features such as the position of the center of mass projection and the foot configurations, a kinematic posture satisfying these features is synthesized using online optimization. The physics-based control framework of the system calculates internal joint torques that enable tracking the optimized posture together with balance and pelvis control. Our system results in a very stable pose regardless of the position of the COM projection within the foot support polygon. This is achieved using an online knee bending and hip joint position optimization scheme. Moreover, we improve the robustness of the character under external perturbations by an arm control strategy that regulates the body's angular momentum. The capabilities of the system are demonstrated under different scenarios. The proposed framework doesn't include equations of motions or inverse dynamics. The simulations run in real-time on a standard modern PC without needing any preprocessing like offline parameter optimization. As a result, our system is suitable for commercial real-time graphics applications such as games.