Dynamic interaction of energy-harvesting backpack and the human body to improve walking comfort

Vibration energy harvesting from backpacks has the potential to generate electrical power while leading to no significant user metabolic cost increase. Many researchers have invented different energy-harvesting backpacks, but the dynamics between the human body and the backpack have not been studied thoroughly in the literature. The goal of this paper is to investigate the dynamic interaction between the human body and the energy-harvesting backpacks to improve human comfort. The amplitude and phase of the force transmitted from the backpack to the human body are characterized and the ground reaction forces (GRF) after wearing the backpack are studied in detail. It is found that tuning the backpack parameters can reduce the GRF in the push-off phase (when the muscle injects energy into the human body) and potentially improve human comfort. System performance is optimized based on energy harvesting and human walking comfort criteria. Three backpacks, i.e., fixed, SDOF, 2DOF-linear, and 2DOF-with-MMR backpacks are analyzed and compared. The tradeoff between energy-harvesting performance and human walking comfort is analyzed, and guidelines for energy-harvesting backpack design are summarized. The mechanical-motion-rectifier-based system can reduce the peak GRF in the push-off phase by 16% and is experimentally verified.