Probabilistic movement primitive based motion learning for a lower limb exoskeleton with black-box optimization

Abstract

As a wearable robot, an exoskeleton provides a direct transfer of mechanical power to assist or augment the wearer’s movement with an anthropomorphic configuration. When an exoskeleton is used to facilitate the wearer’s movement, a motion generation process often plays an important role in high-level control. One of the main challenges in this area is to generate in real time a reference trajectory that is parallel with human intention and can adapt to different situations. In this paper, we first describe a novel motion modeling method based on probabilistic movement primitive (ProMP) for a lower limb exoskeleton, which is a new and powerful representative tool for generating motion trajectories. To adapt the trajectory to different situations when the exoskeleton is used by different wearers, we propose a novel motion learning scheme based on black-box optimization (BBO) PI^BB combined with ProMP. The motion model is first learned by ProMP offline, which can generate reference trajectories for use by exoskeleton controllers online. PI^BB is adopted to learn and update the model for online trajectory generation, which provides the capability of adaptation of the system and eliminates the effects of uncertainties. Simulations and experiments involving six subjects using the lower limb exoskeleton HEXO demonstrate the effectiveness of the proposed methods.

摘要

外骨骼作为一种可穿戴的机器人，通过拟人化的构型直接传递机械动力来辅助或增强穿戴者运动。当外骨骼用于促进穿戴者的运动时，运动生成过程通常在高层控制中发挥重要作用。该领域的主要挑战之一是实时生成符合人类意图且可以适应不同情况的参考轨迹。在本文中，我们首先提出了一种基于概率运动基元（ProMP）的下肢外骨骼运动建模方法，它是一种用于生成运动轨迹的新型且强大的代表性工具。为了在不同穿戴者使用外骨骼时使轨迹适应不同情况，我们接着提出了一种基于黑盒优化PIBB结合ProMP的新型运动学习方案。运动模型首先由ProMP离线学习，它可以生成参考轨迹供外骨骼控制器在线使用，再采用PIBB在线学习和更新模型，提供了系统的自适应能力，消除了不确定性的影响。使用下肢外骨骼HEXO对六名受试者进行的模拟和实验证明了所提出方法的有效性。