Preliminary evaluation of gait assistance during treadmill walking with a light-weight bionic knee exoskeleton

In this paper, we present the preliminary evaluation of gait assistance during treadmill walking with a powered bionic knee exoskeleton (BioKEX) which is intended for gait rehabilitation of patients with knee joint movement disorder. The BioKEX is a unilateral and light-weight wearable exoskeleton. The anthropomorphic joint design is that the tibia rolls on the femur during knee flexion/extention implemented by gear meshing mechanisms. We applied a finite-state machine based impedance control approach for exoskeleton control. The desired joint torque for the locomotion mode is controlled by finite-state machines, which modulate the joint impedance according to the phase of gait. In the experiments, we firstly verified the effect of assistance performance through the torque given by the exoskeleton during the gait cycle. Then, we performed energetics experiments and found human wearing BioKEX under assistance mode had a lower metabolic cost than wearing same weight load (an average reduction is approximately 6.21% (p < 0.05). It implies that the assistance torque provide by the knee exoskeleton can compensate the energy consumption caused by exoskeleton intrinsic weight generating load for proximal joint. Therefore, the BioKEX system provides knee joint assistance for gait requirement, but not increases metabolic cost in spite of an extra weight (exoskeleton weight) on human.