Transparency Evaluation for the Kinematic Design of the Harnesses through Human-Exoskeleton Interaction Modeling

Lower Limb Exoskeletons (LLEs) are wearable robotic systems that provide mechanical power to the user. Human-exoskeleton (HE) connections must guarantee the sub- sistence of the user’s natural behavior during the interaction, avoiding the exertion of undesired forces, i.e., the robot must be transparent. Since transparency is an essential feature of exoskeletons’ design, numerous works focus on its maxi- mization, e.g., employing passive joints at the HE interfaces. Given the inherent complications of repeatedly prototyping and experimentally testing a device, modeling the exoskeleton and its physical interaction with the user emerges as an extremely valuable approach for assessing the design effects. This paper proposes a novel method to compare different exoskeleton configurations with a flexible simulation tool. This approach contemplates simulating the dynamics of the device, including its interaction with the wearer, to evaluate multiple connection mechanism designs along with the kinematics and actuation of the LLE. This evaluation is based on the minimization of the interaction wrenches through an optimization process that includes the impedance parameters at the interfaces as optimization variables and the similarity of the LLE’s joint variables trajectories with the motion of the wearer’s articu- lations. Exploratory tests are conducted using the Wearable Walker LLE in different configurations and measuring the interaction forces. Experimental data are then compared to the optimization outcomes, proving that the proposed method pro- vides contact wrench estimations consistent with the collected measurements and previous outcomes from the literature.