Estimation of the Mechanism that the Plate Spring Transversely Moves to Follow the Excitation Frequency

Abstract

Vibration energy harvester has gained attention in accordance with the growth of the demand of wireless sensors used for vibration condition monitoring of machinery. Most conventional vibration energy harvesters consist of a linear oscillator. These devices are designed so as to resonate with the mechanical vibration for the purpose of getting large electricity. However, once the frequency of the input vibration changes, the linear oscillator cannot maintain resonance. As the result, the amount of electricity obtained by the vibration energy harvester decreases considerably. In our laboratory, we devised a test equipment of the vibration system in which resonance automatically follows the fluctuated excitation frequency. This equipment is comprised of sector-like shaped bases and a long and narrow plate spring. Under the excitation, the test equipment automatically tunes its natural frequency in such a way as to match the excitation frequency without any controllers. By applying this automatic tuning mechanism of the test equipment to a vibration energy harvester, it will be able to keep high generating efficiency even when the excitation frequency of the mechanical vibration changes. However, the detailed mechanism that the test equipment automatically tunes its natural frequency into excitation frequency has not been explained. In this paper, we conduct excitation experiments on the proposed equipment and detailed observation of the behavior of the plate spring in the automatic tuning phenomenon. As the result, a part of the mechanism of the automatic tuning phenomenon can be experimentally deduced.