Evaluating the interaction between human and paediatric robotic lower-limb exoskeleton: a model-based method

Lower-limb exoskeletons (LLEs) have shown potential in improving motor function in patients for both clinical rehabilitation and daily life. Despite this, the development and control of pediatric exoskeletons remain notably underserved. This study focuses on a unique pediatric robotic lower limb exoskeleton (PRLLE), tailored particularly for children aged 8-12. Each leg of the robot has 5 Degrees of Freedom (DOFs)-three at the hip and one each at the knee and ankle. The interaction between the child user and the PRLLE is intricate, necessitating adherence to essential requirements of comfort, safety, and adaptability. Testing numerous prototype variations against diverse user profiles, particularly for children with neurological disorders where each child differs, is impractical. Model-based methods offer a virtual testbed that is useful in the design stage. This study uses MATLAB (R) to simulate and evaluate the interaction between users and PRLLE after deriving the nonlinear dynamic model of the PRLLE, which is simplified through multiple layers. To verify the accuracy of the derived dynamic model, a Computed Torque Control method is employed. The study provides detailed outcomes for children aged 8, 10, and 12 years, for passive and active users along with variations in PRLLE assistance levels. The study shows significant reductions in human joint torques, up to 56%, alongside substantial actuator powers, reaching up to 98W, for a 10-year-old child user. Furthermore, examining 8 and 12-year-old child users revealed variations in interaction forces, with changes up to 29.5%. Consequently, meticulous consideration of the human user's limitations is crucial during the PRLLE's design and conceptualization phases, particularly for PRLLEs.