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的人类运动学习与表现中起着重要作用。借助机器人设备，研究人员主要针对上肢研究了双人触觉交互的影响。构建能够实现多人下肢间物理交互的基础设施，可拓展先前研究，并促进对新型双人下肢康复方案的探索。我们设计了一个系统，使两名使用多关节下肢外骨骼的步行者之间能够实现触觉交互。具体而言，我们开发了一套基础设施，根据用户的运动学数据和虚拟耦合特性，向下肢外骨骼个体发出期望的交互力矩指令。在本初步研究中，我们验证了该平台能够呈现不同触觉特性（如软硬程度）、不同触觉连接类型（如双向与单向），以及关节空间和任务空间中的连接表达。通过触觉连接，双人组产生了同步运动，且随着虚拟刚度的增加，关节角度差异逐渐减小。这是首次在下肢外骨骼之间实现多关节双人触觉交互的研究。该平台将用于探究步行过程中触觉交互对运动学习与任务表现的影响——步行是步态康复中一项复杂且具有重要意义的任务。