RESEARCH ON HIGH-EFFICIENCY LOW-FREQUENCY ENERGY HARVESTING OF LOWER LIMB JOINTS BASED ON BIDIRECTIONAL EJECTION MECHANISM

Human lower-limb motion generates work relying on large muscle groups and contains abundant bio-mechanical energy. Efficient conversion of such energy into electrical energy is an effective technical approach to solving the problem of sustainable energy supply for wearable devices. However, the low frequency and unsteady oscillatory characteristics of lower-limb motion severely restrict the conversion efficiency from mechanical energy to electrical energy. Therefore, how to efficiently convert joint swing into unidirectional high-speed rotation of electromagnetic energy harvester (EMH) has become a key technology for improving the collection efficiency of lower-limb bio-mechanical energy. Inspired by the finger marble ejection game, this study proposes a cable-driven EMH integrated with a bidirectional ejection (BE) unit on a ratchet mechanism. The energy harvester employs the cam to drive steel balls, which stretch the elastic cables connected to the pawls for elastic potential energy storage, and achieves bidirectional instantaneous ejection through the preset slideway notches. Without an additional gear set frequency-up-conversion mechanism, it can realize the integrated function of bidirectional energy storage and ejection frequency-up throughout the full cycle. Experimental results show that within the typical lower-limb motion frequency range of 0.5 ~ 2 Hz, the output voltage and power ranges of the EMH with the BE unit are 3.31 ~ 5.15 V and 287 ~ 697 mW, respectively. Compared with the EMH without the BE unit, its output power is increased to 4.7 ~ 57 times, and the lower the frequency, the more significant the power increase multiple. The BE mechanism proposed in this study not only simplifies the up-frequency structure of the EMH and reduces the volume and weight of the device, but also realizes the conversion from low-frequency lower-limb motion to high-frequency rotational power generation of the EMH, improves the collection efficiency of bio-mechanical energy, and provides an efficient, portable and sustainable energy supply solution for wearable electronic devices.