Hybrid Rigid-Soft and Pneumatic-Electromechanical Exoskeleton for Multi-Joint Lower Limb Assistance

Human augmentation typically employs either rigid exoskeletons or soft exosuits. Rigid exoskeletons enhance stability and weight support through load-bearing frames and direct joint torque. Conversely, soft exosuits, devoid of rigid frames, utilize proximally positioned actuators and tendons to transmit forces to textile parts affixed to limbs, thereby enhancing adaptability and simplifying mechanics. To exploit the benefits of both, this study introduces a multi-joint hybrid-assisted device that combines a soft tendon-driven hip exosuit with a rigid pneumatic knee exoskeleton. The hip joint, featuring three active degrees of freedom, is assisted during the swing by the exosuit to minimize kinematic restrictions, mechanical complexity, and weight. The knee joint, with its single active degree of freedom, receives assistance during the stance from the rigid knee exoskeleton, pneumatically actuated, ensuring inherent knee compliance during load response. The study investigates the hybrid system's impact on metabolic cost, muscle activity, and kinematics in four conditions (unassisted, hip-assisted, knee-assisted, and hybrid-assisted) with seven healthy subjects on an inclined treadmill (15° at 3 km/h). Findings indicate that hybrid assistance yields the greatest significant metabolic reductions, followed by hip assistance and knee-only assistance, with assisted muscles exhibiting significantly reduced activity and minimal impact on kinematics.