Enhancing Motor Synchrony in Rhythmic Dyadic Tasks Through Portable Elbow Exoskeletons

Synchrony is a cornerstone for the successful physical interaction between humans while cooperating or competing towards a goal and is achieved by correct and smooth information exchange between subjects. Recently, Human-Robot-Human (HRH) interaction arose as an emerging paradigm for improving motor control in collaborative and dyadic motor tasks. Among the robotic solutions explored for agent coupling, exoskeletons are powerful tools for exerting torque and force feedback at the joint level. In this work, two identical torque-controlled elbow exoskeletons were used in dyadic interaction, to provide haptic feedback and improve synchrony between two individuals performing a tapping task. Each exoskeleton is lightweight and compact, weighing 0.8 kg on the arm. Bench tests to verify the performance of closed-loop torque control showed a residual torque below 0.2 Nm when the reference torque was set to zero, and a bandwidth higher than 6 Hz, thus achieving adequate performance for applications in HRH scenarios. In human subjects' experiments, the root-mean-squared error between the two users' joint trajectories was 50% lower when users received haptic feedback compared to the condition without feedback; the relative phase error was lower than 60%. The results of this study suggest that exoskeletons can enhance synchrony in HRH interactions, being potentially useful in rehabilitation training, collaborative industrial tasks or sport and music learning.