Effect of Slippage on Knee Exoskeleton Comfort

Researchers have paid less attention to comfort while wearing exoskeleton robots. The slippage of the exoskeleton on the patient’s body can significantly contribute to discomfort. This leads to energy wastage and exacerbates the misalignment between the robot and the human body. This misalignment increases undesired forces on the patient’s body, resulting in user discomfort. To address this, some researchers considered adjusting the exoskeleton’s instantaneous center of rotation (ICR) with that of the user. However, despite the variability in the ICR among different individuals, movements, and the softness of the body tissues, slippage of the robot on the body still can occur. In this paper, the placement location of the thigh, knee, and tibial interfaces of the FUM-NEXA II knee exoskeleton and the type of padding material used under each interface are optimized to minimize robot slippage on the body. The Taguchi method was used for optimization, and experiments related to this method were simulated in Adams software. The soft tissues and padding under the interfaces were modeled with linear spring-dampers to make the simulations more accurate. Data was obtained from a volunteer’s leg and sample pads. Finally, the slippage of the optimized FUM-NEXA II robot, equipped with a polycentric knee joint, was compared with a simplified two-link model of the knee exoskeleton robot equipped with only a hinge at the knee joint. The comparison showed that the FUM-NEXA II robot with polycentric knee joint significantly reduced robot slippage by about 2.3 times.