Design and implementation of knee-ankle exoskeleton for energy harvesting and walking assistance

The increasing requirement of powering portable electronic devices can be potentially met by recycling the biomechanical energy generated during the human joint motion through a knee-ankle exoskeleton. In this paper, a knee-ankle exoskeleton is designed to recycle the negative work from the wearer's knee extension and ankle dorsiflexion. The exoskeleton can convert the mechanical energy into electrical energy for energy harvesting and assist the knee flexion and ankle plantarflexion to reduce the wearer's metabolic cost during walking. It is mainly composed of two torsion springs, two one-way transmission mechanisms, a gear train, and a generator. The torsion springs can store the elastic energy when the wearer's ankle and knee joints do negative work and release it to assist walking when positive work is required. The one-way transmission mechanisms are employed to filter the knee flexion and ankle plantarflexion and to convert the knee extension and ankle dorsiflexion into the one-way rotation of the generator by symmetrically arranging the gear train. Finally, experiments are conducted to evaluate the performance of the developed knee-ankle exoskeleton. The experimental results indicate that the exoskeleton can generate an average electrical power of 0.49 W and a maximum instantaneous electrical power of 1.8 W at a walking speed of 5.5 km h(-1) during a gait cycle, and reductions of 3.48% +/- 0.33%, 9.50% +/- 0.29%, and 4.54% +/- 0.47% of the average muscle activities of the semitendinosus, soleus, and gastrocnemius during a gait cycle are observed, respectively.