A layered smart sensing platform for physiologically informed human-exoskeleton interaction

Abstract: Wearable exoskeletons offer transformative potential to assist mobility across diverse user groups with reduced muscle strength or other forms of impaired mobility. Yet, their deployment beyond laboratory settings remains constrained by sensing systems able to fully capture users' physiological and biomechanical states in real time. We introduce a soft, lightweight smart leg sleeve with anatomically inspired layered multimodal sensing, integrating textile-based surface electromyography (sEMG) electrodes, ultrasensitive textile strain sensors, and inertial measurement units (IMUs). Each sensing modality targets a distinct physiological layer: IMUs track joint kinematics at the skeletal level, sEMG monitors muscle activation at the muscular level, and strain sensors detect skin deformation at the cutaneous level. Together, these sensors provide real-time perception to support three core objectives: controlling personalized assistance, optimizing user effort, and safeguarding against injury risks. The system is skin-conformal, mechanically compliant, and seamlessly integrated with a custom exoskeleton (<20 g total sensor and electronics weight). We demonstrate: (1) accurate ankle joint moment estimation (RMSE = 0.13 Nm/kg), (2) real-time classification of metabolic trends (accuracy = 97.1%), and (3) injury risk detection within 100 ms (recall = 0.96), all validated on unseen users using a leave-one-subject-out protocol. This work demonstrates a lightweight, multimodal sensing architecture for next-generation human-exoskeleton interaction in controlled and semi-structured walking scenarios, with potential for scaling to broader exoskeleton applications towards intelligent, responsive, and personalized wearable robotics.