Wearable up-frequency energy harvester based on a novel unidirectional excitation mechanism

A novel unidirectional excitation mechanism (UEM) operating under harmonic excitation is proposed in this paper, which has two advantages, one is the long effective working time, and the other is to overcome the deceleration process of harmonic motion. The UEM mainly consists of a belt drive and a lead screw nut drive. Thus, this paper adopts the coupling method of the gear drive and the belt drive to realize frequency increase, which actualizes the up-frequency conversion from the slow swing to the high-speed rotation. Based on different movements of the UEM-based energy harvester (UEMEH) under the excitation of the human arm swing, the dynamic piecewise model is established and makes the calculation results more accurate. To investigate the effect of the wearable energy harvester on the human body, the reaction torque of the harvester driving by the upper arm swing is calculated. Since the reaction torque is far less than the output torque of the upper arm swing, the results show that the UEMEH is much more suitable for human motion, even strenuous motion. Comparing the output characteristics of the UEMEH with the None-UEM frequency-up energy harvester (NUEH), it is proved that the UEMEH has better power generation performance under harmonic excitation. Finally, the power generation efficiency of the UEMEH is tested under human walking and running. When the subjects are in a running state, the average output power of UEMEH could reach 20.52 mW, and the maximum energy conversion efficiency is as high as 70.88%.