Design And Research Of Energy Harvester Based On Vibration-Rotational Motion Conversion Mechanism

The emergence of portable electronics has greatly facilitated people’s work and life,and these electronics currently rely mainly on electrochemical batteries for power supply.The batteries of these electronics need to be frequently charged or to be replaced due to their limited storage capacity,resulting in great inconvenience and high maintenance costs.An ideal solution to this problem is energy harvesting technology.Since human motion contains abundant energy,and portable electronics usually move with the human body,using the vibration energy generated by human motion to power portable electronics is a feasible strategy.However,the irregular and ultra-low frequency nature of vibrations induced by human motion make its effective utilization still a challenge.In order to effectively harvest the ultra-low frequency vibration energy,an innovative flexible mechanical motion rectifier is proposed in this thesis.The rectifier is mainly composed of a strap-driven shaft structure and a plectrum-driven ratchet structure.The strapdriven shaft structure includes an elastic strap,an inelastic strap and a shaft.The plectrumdriven ratchet structure is mainly composed of a plectrum with self-adaptive stiffness and a ratchet.The plectrum is composed of a rigid layer and a flexible layer.Firstly,the flexible mechanical motion rectifier converts the ultra-low frequency vibration or linear motion into the bi-directional rotation of the shaft through the elastic strap and inelastic strap,and then the shaft is used to drive the ratchet to rotate counterclockwise through the plectrum with self-adaptive stiffness.In order to verify the effectivity of harvesting the ultra-low frequency vibrations from the flexible mechanical motion rectifier,a corresponding rotational electromagnetic energy harvester is developed based on the flexible mechanical motion rectifier.In order to harvest the human induced ultra-low frequency vibrations effectively and to power portable electronics,a flexible energy harvesting backpack is designed based on a rotational electromagnetic energy harvester.The energy harvesting backpack can not only effectively harvest energy from the vertical oscillations of the backpack load in the process of human walking and running,but also reduce the pressure of heavy objects on the human body and reduce the damage to the human body.The theoretical model of the dynamic response of the energy harvesting backpack is established and verified by experiments.The rotational electromagnetic energy harvester can produce a frequency-multiplied electrical output under the human walking induced ultra-low frequency excitation through a flexible vibration-rotation motion conversion mechanism.Both the experimental and simulation results show that the open-circuit voltage and output power of the rotational electromagnetic energy harvester increase monotonically with the increase of the walking speed of the human body.The experimental results show that at a running speed of 9 km/h,the energy harvesting backpack(with a payload of 3.6 kg)can achieve an output power of 1.284 W and the power density of the energy harvesting backpack is as high as 0.357 W/kg.The experimental results also show that the energy harvesting backpack can reduce the pressure on the human body by the backpack shoulder straps.Through the theoretical model established in this thesis,the effects of different parameters on the performance of the rotational electromagnetic energy harvester are predicted.In addition,the ability of the rotational electromagnetic energy harvester to charge the capacitor is also studied.The experimental results show that the electricity produced by a single rotational electromagnetic energy harvester can rapidly increase the voltage across the capacitor and is achieved up to the rated voltage of commonly used portable electronics.At different walking speeds,the electrical energy,which a single energy harvester of the energy harvesting backpack(with a payload of 1.7 kg)yields,can supply a variety of typical portable electronics.The rotational electromagnetic energy harvester based on the flexible vibration-rotation motion conversion mechanism is proposed in this thesis.The energy harvester can effectively scavenge the human induced ultra-low frequency vibrations.The experiments of the energy harvester in application have demonstrated its potential to power directly the portable electronics.