Balance loss is a significant challenge in lower-limb exoskeleton applications, as it can lead to potential falls, thereby impacting user safety and confidence. We introduce a control framework for omnidirectional recovery step planning by online optimization of step duration and position in response to external forces. We map the step duration and position to a human-like foot trajectory, which is then translated into joint trajectories using inverse kinematics. These trajectories are executed via an impedance controller, promoting cooperation between the exoskeleton and the user. Moreover, our framework is based on the concept of the divergent component of motion, also known as the Extrapolated Center of Mass, which has been established as a consistent dynamic for describing human movement. This real-time online optimization framework enhances the adaptability of exoskeleton users under unforeseen forces thereby improving the overall user stability and safety. To validate the effectiveness of our approach, simulations, and experiments were conducted. Our push recovery experiments employing the exoskeleton in zero-torque mode (without assistance) exhibit an alignment with the exoskeleton's recovery assistance mode, that shows the consistency of the control framework with human intention. To the best of our knowledge, this is the first cooperative push recovery framework for the lower-limb human exoskeleton that relies on the simultaneous adaptation of intra-stride parameters in both frontal and sagittal directions. The proposed control scheme has been validated with human subject experiments.

翻译：平衡丧失是下肢外骨骼应用中的重大挑战，可能导致潜在跌倒风险，影响用户安全与信心。我们提出一种控制框架，通过在线优化跨步持续时间和位置以应对外部推力，实现全方位恢复跨步规划。经过逆运动学将跨步持续时间和位置映射为类人足部轨迹，进而转化为关节轨迹。这些轨迹通过阻抗控制器执行，促进外骨骼与用户之间的协同配合。此外，该框架基于运动发散分量（即外推质心）概念——该概念已被确立为描述人体运动的一致动力学模型。该实时在线优化框架增强了外骨骼用户应对意外推力的适应能力，从而提升整体稳定性与安全性。为验证方法有效性，我们开展了仿真与实验研究。在零力矩模式（无辅助）下使用外骨骼进行的推挤恢复实验显示，其与外骨骼辅助恢复模式具有一致性，表明该控制框架与人类意图相吻合。据我们所知，这是首个基于矢状面与额状面步态参数同步自适应的下肢人机外骨骼协同推挤恢复框架。所提出的控制方案已通过人体实验验证。