Evaluating spatio-temporal consistency in robotic-assisted tasks across varied gravity compensation levels

Robotic devices offer assistance to individuals with upper-limb impairments. Among different control strategies, assistance should specifically account for the weight of both the device and the wearer's arm without introducing any distortion to the kinematic behaviour. This study investigates how varying weight support levels in the Harmony exoskeleton impact hand spatio-temporal features and inter-joint coordination during a pick-and-place task. Eight healthy subjects performed the selected functional movement across five distinct levels of arm support. Results indicated that movement smoothness and planning in the Cartesian space were not influenced by the Harmony exoskeleton. A decreased accuracy was noted only at high levels of weight support for movements against gravity, while movements propelled by gravity suffered an overall drop. Consistent inter-joint coordination was observed across different support levels, except for shoulder intra-extra rotation during movements against gravity. This study shed light on the effect of gravity compensation provided by the Harmony exoskeleton on kinematic performance, providing valuable insights for optimizing assistive devices for individuals with upper-limb impairments.