Novel Pendulum Vibration Energy Harvesters for Unmanned Surface Vehicles

Abstract

Unmanned Surface Vehicles (USVs) are typically used for data gathering operations such as remote exploration and surveillance, though their practicality for these applications is limited by the finite capacity of existing energy storage mechanisms. Through the design, simulation, fabrication and testing of four novel energy harvester concepts, this work delivers solutions that improve the viability of energy harvesting technologies for USV applications, thereby providing the potential to increase the operational time of these vessels. By critically analysing existing vibration energy harvester designs, key areas for improvement were identified in the literature review to allow for the further development of these technologies. To address the need for greater efficiency and power output capabilities of electromagnetic vibration energy harvesters, a pendulum-based transducer with an original mechanical rotation rectifier (MRR) has been presented. This demonstrated a higher average normalised power density than existing works with a value of 12.32 W/g2/kg, and an efficiency of 43.5% at a 1Hz resonance. This design was also shown to be highly scalable, and the use of offset spur gears and sprag clutches in the MRR assembly allows the device to handle large amounts of torque. Taking this a step further, a counterweight system was proposed, which was proven to be capable of tuning the resonant frequency of a pendulum energy harvester without increasing its arm length. This allowed the device to operate at ultra-low frequencies in the 0.5-1.0 Hz range, thus increasing the power output at 0.75 Hz by a factor of 5.95x compared to the same device without the counterweight. The third device presented herein provides an improved mechanical energy storage regulator, which was shown to produce the same voltage smoothing effects as a flywheel while simultaneously improving start-up performance and reducing the torque which critical components were subjected to. Finally, a simplified mechanical rectifier was proposed, which was shown to be capable of converting bidirectional input rotation to unidirectional rotation of a DC motor while using just a single clutch and no gearing, thus providing a method for reducing the complexity of electromagnetic vibration energy harvesters of this kind. Overall, each of these four transducers addresses fundamental challenges with existing vibration energy harvesters, providing mechanisms through which the viability of this technology for USV applications is significantly improved.