Abstract
This work presents a pendulum kinetic energy harvester with a unique mechanical motion rectifier design which uses a string-driven rectifier (SDR) with just a single clutch to convert bidirectional input oscillation of a pendulum to the unidirectional rotation of a DC motor to produce electricity. Unlike typical mechanical rectifiers which use two clutches, this rectification system has no gearing, minimising the complexity and weight of the rectifier for the energy harvester. Through experimentation, the energy harvester was found to have a normalised average power output of 4.39 W/g2 and a normalised average power density of 5.85 W/g2/kg when excitation was applied at the 1.5 Hz resonant frequency with a 0.75 kg pendulum mass. This corresponds to a normalised average voltage production of 55.47 V/g. Time-domain analysis of the transducer showed the successful operation of the SDR. By selectively harvesting kinetic energy during different stages of the pendulum motion, the kinetic energy of the pendulum mass was extracted while the stored potential was preserved and converted to kinetic. This allowed a high pendulum velocity to be maintained, while the rectified input motion generated a single polarity voltage from the DC motor. The construction of this system has advantages over existing designs by reducing the complexity of rectification mechanisms, providing an alternative approach to mechanical motion rectification for pendulum vibration energy harvesters.
Highlights
The applications and demand for low-frequency vibration energy harvesters continue to become ever greater with the increasing prevalence of battery powered portable electronics and the persis tent developments in autonomous vehicles and remote sensors re quiring localised power sources
Small-scale vibration energy harvesting transducers can take many forms, including piezoelectric [1,2,3], triboelectric [4,5,6], and electromagnetic designs [7,8,9], al though there remains a need for the improved viability of devices capable of operating in low frequency environments such as the 0.5–3.5 Hz range found on the ocean surface [10]
This means that the DC motor is no longer driven, which reduces the damping on the system and allows the mass to maintain its stored potential and convert it to kinetic energy during this stage of motion where the pendulum velocity is increasing
Summary
The applications and demand for low-frequency vibration energy harvesters continue to become ever greater with the increasing prevalence of battery powered portable electronics and the persis tent developments in autonomous vehicles and remote sensors re quiring localised power sources. Was presented by Liang et al [24], which used clutches mounted within driven bevel gears to fully rectify the oscillatory motion of a pendulum This system is effective at rectifying the rotation of the pendulum mass; an alternative design by the present au thors [25,26] demonstrated a significantly higher power density, incorporating a mechanical rotation rectifier system comprised of spur gears. Since frictional losses are minimal, by not harvesting during the return swing of the pendulum, the remaining potential energy from the mass can be converted to usable kinetic energy, allowing the pendulum to maintain a high velocity This novel design has the potential to reduce the complexity and weight of vibration energy harvester rectifiers and can be applicable to any such harvester where displacement may be used to create an ex tension of the string
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