Biomechanical modeling and experiments of energy harvesting backpacks

Abstract

The energy harvesting backpack is a promising solution for powering wearable electronic devices by converting biomechanical energy from human motion into electricity. However, the majority of current energy harvesting backpack models primarily focus on harvester dynamics while neglecting the crucial role of humans as an energy source in the system. Some studies have utilized inverted pendulum models through active control torque and optimization-based methods to investigate human factors in bioenergy harvesting systems, but this is complex for the practical application of biomechanical models. To overcome these issues, a new biomechanical model of the energy harvesting backpack is proposed in this paper. The contribution of this study is not only modeling the cooperative dynamics between backpacks and humans which is easily solvable and comprehensible but also defining multi-indicators for model verification and backpack evaluation. The biomechanical model without load is established based on the D' Alembert principle and empirical gait phase division of 3:1 when it is assumed that the gait parameters remain constant regardless of the load being carried. Four sets of data from two distinct databases are utilized to analyze the dynamics of the bipedal walking model in both vertical and horizontal directions. The biomechanical model with energy harvesting backpacks is proposed to define four single direct indicators and two global indirect indicators for demonstrating the proposed model’s ability to predict the characteristics of backpacks. Finally, the foot-reaction force, the vibration of the center of mass, and the output power of three subjects are acquired in five experiments (i) with no backpack under variable walking speed; (ii) an ordinary backpack under variable walking speed; (iii) an ordinary backpack under variable loads; (iv) an energy harvesting backpack under variable walking speed; and (v) an energy harvesting backpack under variable loads. The comparison between the proposed model and experimental results demonstrates that the proposed model is easy to solve and comprehend, and can effectively capture the characteristics of both human and energy harvesting backpacks.