Session: 07-01-05: General Dynamics, Vibration, and Control

Paper Number: 119959

119959 - Performance of Vibration Isolators Using Two-Layered Foldable Structure Made of Sheet Material 

The objective of this study is to fabricate a vibration isolator using a bistable foldable structure by folding a sheet material such as origami, confirm quasi-zero-stiffness characteristics of the isolator, and evaluate its vibration isolation performance through tensile-compression tests and single-axis excitation tests.

Origami engineering is the application of traditional Japanese origami techniques in an engineering context, exploring various properties of origami such as high rigidity and designability to achieve complex spatial shapes from planer sheets. The vibration isolator utilizing foldable structures is well known as a new prospect of this field. As the foldable structure shows bistable spring characteristics during the expansion and contraction, it theoretically possesses zero-spring stiffness by adding a linear spring on it so that the structure with a linear spring works as a vibration isolator, which decreases vibration response at wide frequencies when it is used around the equilibrium position at which the spring stiffness is zero. Excitation experiments in the previous studies revealed that the prototyped vibration isolators using the zero-spring-stiffness foldable structures could reasonably mitigate vibration. However, the vibration isolator had a geometrical constraint that the isolator simultaneously got twisted when it was extended and contracted, which caused an extra rotational motion of a mass applied on the isolator. Additionally, the construction of the isolator was considerably complex as it was composed of numerous mechanical components and the manufacturing process was challenging.

In this study, we addressed these issues and involved a simpler foldable structure by folding a single sheet of polypropylene, much like origami, and adding a single coil spring. The use of a sheet material for the vibration isolator resulted in a remarkably simple mechanical structure, making it cost-effective and easy to manufacture. Also, the vibration isolator was constructed by stacking the two alternating foldable structures in a mirror-symmetric manner; i.e., a two-layered foldable structure utilizing two coil springs. Owing to this construction, the twisting motion was effectively resolved and the vibration isolator was expected to behave as a two-degree-of-freedom vibration system with two resonance frequencies.

Tension-compression tests revealed that the vibration isolator made of polypropylene sheet and coil springs exhibited nonlinear quasi-zero-stiffness-spring characteristics as required. In single-axis excitation tests, a small resonance occurred at the first resonance frequency, because the stiffness of the vibration isolator was quasi-zero or not exactly zero. However, the first resonance frequency of the vibration isolator was sufficiently lowered so that the vibration isolator maintained a transmissibility below 1 at wide frequencies as well as the single-layered vibration isolators in the previous study. As for the second resonance, it was not clearly observed due to high damping effect owing to the plastic material and mechanical friction between the coil springs and their supporting components. Apparently, this result indicates that the two-layered vibration isolator behaved as a one-degree-of-freedom vibration system. However, a unique characteristic of the two-layered vibration isolator was found at the joint position of the two folding structures, where the lower layer could vibrate larger than the upper layer at high frequencies so that the transmissibility of the lower layer approached and even exceeded that of the upper layer. This behavior shows that the two-layered vibration isolator can be referred to as a two-degree-of-freedom vibration system.

Presenting Author: Yuto Sakamoto Meiji University

Presenting Author Biography: Yuto Sakamoto (M.Eng., Dynamics of Machinery)BEng., Mechanical Engineering, 2022, Meiji University, is from Kanagawa Japan. Yuto's past research has focused on Vibration isolator made of Sheet Material. His research is a study that applies origami, a traditional Japanese recreational activity, to engineering. His passion lies in leveraging play for research and contemplating its practical benefits for the world.

Authors:

Yuto Sakamoto Meiji University
Sachiko Ishida Meiji University