Physical interaction between individuals plays an important role in human motor learning and performance during shared tasks. Using robotic devices, researchers have studied the effects of dyadic haptic interaction mostly focusing on the upper-limb. Developing infrastructure that enables physical interactions between multiple individuals' lower limbs can extend the previous work and facilitate investigation of new dyadic lower-limb rehabilitation schemes. We designed a system to render haptic interactions between two users while they walk in multi-joint lower-limb exoskeletons. Specifically, we developed an infrastructure where desired interaction torques are commanded to the individual lower-limb exoskeletons based on the users' kinematics and the properties of the virtual coupling. In this pilot study, we demonstrated the capacity of the platform to render different haptic properties (e.g., soft and hard), different haptic connection types (e.g., bidirectional and unidirectional), and connections expressed in joint space and in task space. With haptic connection, dyads generated synchronized movement, and the difference between joint angles decreased as the virtual stiffness increased. This is the first study where multi-joint dyadic haptic interactions are created between lower-limb exoskeletons. This platform will be used to investigate effects of haptic interaction on motor learning and task performance during walking, a complex and meaningful task for gait rehabilitation.

翻译：个体间的物理交互在共享任务中对人类运动学习和表现具有重要作用。利用机器人设备，研究者已研究过双人触觉交互的影响，但主要集中于上肢。建立支持多人下肢间物理交互的基础设施，可扩展先前工作并促进新型双人下肢康复方案的研究。我们设计了一套系统，在使用多关节下肢外骨骼行走时，可渲染两名用户间的触觉交互。具体而言，我们开发了一种基础设施，基于用户运动学与虚拟耦合特性，将期望的交互力矩指令发送至个体下肢外骨骼。在此项初步研究中，我们验证了该平台在呈现不同触觉特性（如软、硬）、不同触觉连接类型（如双向与单向）以及关节空间与任务空间表达连接方面的能力。触觉连接使双人产生同步运动，且随虚拟刚度增加，关节角度差异减小。这是首个在多关节下肢外骨骼间建立双人触觉交互的研究。该平台将用于探究行走过程中（一项复杂且对步态康复具有意义的任务）触觉交互对运动学习与任务表现的影响。