Laying the Groundwork for Intra-Robotic-Natural Limb Coordination: Is Fully Manual Control Viable?

Supernumerary Robotic Limbs (SRLs) have been successfully applied in bracing and as an assistive technology for people with disabilities. These tasks only require perception internal to the SRL-human system. However, SRLs show promise in applications requiring external perception such as opening a door when one’s hands are full. One path toward developing SRLs that accomplish these tasks is to use human-in-the-loop control, thus leveraging the human’s superior perception system to help the SRLs. However, the effects on the user of controlling additional limbs are unclear. This article presents an experimental study where humans, wearing two single degree of freedom SRLs, were instructed to minimize the position error between the subject’s natural and robotic limbs and the corresponding targets, one for each limb. First, subjects performed worse with their natural limbs when asked to perform the task with two natural and two robotic limbs as opposed to with just their natural limbs, suggesting that shared control could help. Second, subjects moved their natural limbs together followed by moving their SRLs together. This informs both the choice of control scheme for the SRLs and the division of labor within a task. Third, subjects showed significant concurrent use of the natural and robotic limbs.