Coupling Rigid Pneumatic Knee Exoskeleton with Soft Tendon-Driven Hip Exosuit: First Insights

In exoskeleton research, humans are augmented using either rigid exoskeletons or soft exosuits. Soft exosuits exhibit superior adaptability for human coordination, while rigid exoskeletons provide crucial support to weight-bearing joints. This study explores a coupled rigid-soft system on multiple lower limb joints to leverage the benefits of both. Specifically, hip joint with higher degrees of freedom (DoF) is fitted with an exosuit to reduce weight and mechanical complexity, and a rigid exoskeleton is used on the knee joint with a single active DoF that is crucial for supporting body weight. Additionally, as the knee is compliant during load response, the rigid knee exoskeleton is pneumatically actuated. This work serves as a preliminary study where three healthy subjects participated in inclined walking trials (15° at 3 km/h) under four conditions: unassisted, hip-assisted, knee-assisted, and hybrid assistance. The first results show consistent patterns in metabolic cost, with hybrid assistance leading to the highest reductions, followed by hip assistance and knee-only assistance. Assisted muscles exhibit reduced activity with minimal impact on kinematics.