Lower-limb driven energy harvesting backpack: Design, performance and energetics

A biomechanical energy harvesting backpack that generates electricity during human walking is presented. By recognizing the out-of-phase motion between two limbs, this energy harvesting technology differs from previous designs in a way that it integrates the motion from both of the user´s lower limbs into a single mechanical drive train and generator. A prototype was developed and experimental results demonstrated that the device was able to generate a large amount of electricity (9W) with a efficiency of 72%, which is higher than the existing walking based energy harvesters. To quantify the performance of the harvester we introduced a new performance measure, total cost of harvesting (TCOH), which evaluates a harvesters overall efficiency in generating electricity including the device carrying cost. The new harvester captured the motion from both lower limbs and operated in the generative braking mode to assist the knee flexor muscles in slowing the lower limbs. From testing on 10 participants, under different walking conditions, the harvester achieved an average TCOH of 6.1, which is comparable to the estimated TCOH for a conventional power generation method of 6.2. When generating 5.2W of electricity, the TCOH of the lower limb-driven energy harvester (4.0) is lower than that of conventional power generation methods. These results demonstrated that the lower limb-driven energy harvester is an energetically effective option for generating electricity during daily activities.