Cartesian space feedback for real time tracking of a supernumerary robotic limb: A pilot study

We present a system to provide the user with real time proprioceptive feedback regarding the state of a supernumerary robotic limb (SRL). The system converted the robot kinematics into a vibration amplitude-frequency value, using a custom electronic board. Four eccentric-motors placed on the leg delivered the vibrotactile pattern to subjects. We measured the accuracy in real-time tracking of the robot end-effector position and the delay from the robot movement onset. We tested four subjects in a preliminary study, and we found an average Position Error and a Delay of 0.084 ± 0.010 m and 1.169 ± 0.408 s respectively, which validated the feasibility of the presented setup. Increasing the learning phase duration should further improve subject performance. Additionally, the present platform could easily be employed to test the efficacy of different feedbacks (such as joint angles and torques) for real time tracking of SRL.