An Unpowered Flexible Lower-Limb Exoskeleton: Walking Assisting and Energy Harvesting

Powered exoskeletons are used to assist human walking, but it is inconvenient for a user to carry a bulky energy-supply system. During walking, human lower limbs accelerate and decelerate alternatively, during which period the human body does positive and negative work, respectively. Therefore, if the negative work performed during deceleration can be harnessed using some assisting device to then assist the acceleration movement of the lower limb, the total metabolic cost of the human body during walking can be reduced. In this work, an unpowered flexible lower limb exoskeleton is proposed; it is worn in parallel to the lower limbs to assist human walking without consuming external electrical power. The flexible exoskeleton imitates the physiological structure of a human lower limb, consisting of elastic and damping components. When worn on the lower limb, the exoskeleton can partly replace the function of the lower limb muscles, which can scavenge kinetic energy during lower limb deceleration to assist the acceleration movement, so that the biomechanical power consumption can be reduced during walking. In addition to the walking assistance, the generator in the exoskeleton, serving as a damping component, can harvest kinetic energy to produce electricity for powering wearable electronics. A prototype of the flexible exoskeleton was developed, and experiments were conducted to validate the effectiveness. The experiments showed that the lower limb exoskeleton could reduce the metabolic cost by 3.12% at the walking speed of 4.5 km/h, and a maximum electrical power of 6.47 W was generated at the walking speed of 5.1 km/h.