Human motion energy harvesting backpack using quasi-zero stiffness mechanism

In this study, a quasi-zero stiffness energy harvesting backpack (QZS-EHB) is proposed. The bistable quasi-zero stiffness mechanism is constructed by paralleling a pair of positive stiffness springs and a pair of negative stiffness springs to make the vibration system more easily excited by low-frequency human motion and generate snap-through action. The bidirectional vibration is mechanically modulated into unidirectional higher speed rotation, thus improving the electromechanical conversion efficiency. The theoretical model of the bistable system is established by using the Lagrange functional method to verify the bistable mechanism. A prototype is manufactured to validate the advantages of the design. The effects of spring stiffness, load weight, and motion speed on the performance of the harvester are investigated through a series of experiments. The results show that the peak voltage is 5.11 V and the peak power is 2.37 W, and the average power of the harvester is 0.77 W, with the load of 5 kg and the speed of 10 km/h. The QZS-EHB can light up a combination of LED lamps with a total power of 6 W, charge the cell phone, and enable self-powered localization and wireless information transmission, when people are jogging with the load of 2 kg. These tests verify that the proposed design can be used for emergency power consumption of people's outdoor activities.