Multidirectional Human-in-the-Loop Balance Robotic System

We present the design and performance of a novel multidirectional balance robotic system. This robot adds mediolateral standing balance control to the functionality of previous systems. To evaluate the performance of the system, we quantified its motion-tracking capability by applying target trajectories related to perturbed and unperturbed quiet standing balance. We observed minimal delays (9.4-13.9 ms) and near-unity gain up to 4 Hz when tracking multi-sine trajectories and small errors when tracking natural balance trajectories (≤0.05mm, corresponding to ≤0.009°), which were all below human perceptual thresholds reported for standing balance (150 ms and 0.17° at 0.06°/s). Next, we evaluated the human-in-the-loop real-time robot performance when participants (N=6) maintained their upright balance in the mediolateral direction while firmly secured to the robot. The results revealed small errors between the predicted and robotic motion (