Design and Treadmill Test of a Broadband Energy Harvesting Backpack With a Mechanical Motion Rectifier

The energy harvesting backpack that converts the kinetic energy produced by the vertical oscillatory motion of suspended loads to electricity during normal walking is a promising solution to fulfill the ever-rising need of electrical power for the use of electronic devices in civilians and military. An energy harvesting backpack that is based on mechanical motion rectification (MMR) is developed in this paper. Unlike the conventional rack-pinion mechanism used in the conventional energy harvesting backpacks, the rack-pinion mechanism used in the MMR backpack has two pinions that are mounted on a generator shaft via two one-way bearings in a way that the bidirectional oscillatory motion of the suspended load is converted into unidirectional rotation of the generator. Due to engagement and disengagement between the pinions and the generator shaft, the MMR backpack has broader bandwidths than the conventional energy harvesting backpacks; thus, the electrical power generated is less sensitive to change in walking speed. Two male subjects were recruited to test the MMR backpack and its non-MMR counterpart at three different walking speeds. For both subjects, the MMR backpack for most of the time generated more power than the non-MMR counterpart. When compared with literature, the MMR backpack had nearly sixfold improvement in bandwidth. Finally, the MMR backpack generated nearly 3.3 W of electrical power with a 13.6 kg load and showed nearly two- to tenfold increases in specific power when compared with a conventional energy harvesting backpack.