Vibration Control Devices Utilized in Various Ways

When it comes to research on vibration control devices, many people, especially Japanese, think of earthquake countermeasures.

Of course, that is an important subject, but vibrations and shaking are actually everyday phenomena that are present all around us. We are making efforts to utilize and suppress them to make our lives more convenient.

For example, health equipment and the silent mode of mobile phones make good use of vibration. Conversely, cars and trains improve ride comfort by reducing shaking, and washing machines enhance usability and prevent damage to floors and walls by controlling vibrations.

Closer to home, the rubber used in shoe soles absorbs the impact vibrations when walking, reducing strain on our feet and bodies. Air in bicycle tires suppresses vibrations. These accumulated technologies are also applied to earthquake countermeasures.

Our Machine Dynamics Laboratory focuses on the study of vibration, especially dampers.

Regarding the definition of the word “damper” in dictionaries, its literal meaning may indicate something that moistens or dampens, but in the engineering field, it specifically refers to a device that weakens or attenuates vibrations.

One of the basic structures of a damper can be easily understood by imagining it as a bamboo tube-shaped water gun, that is, something like a large syringe.

When the piston is pushed or pulled, air in the cylinder flows in and out through a valve at the end of the cylinder. Closing this valve makes it harder to push the piston. It is just like a bicycle tire. In addition, the valve can be adjusted to control the airflow in and out to absorb different pushing forces.

Types of dampers vary widely, from cylinders filled with oil as well as air, and from hand-held tubes to huge devices. Dampers are developed and designed according to their specific applications, such as in vehicles and buildings, to ensure the right damper for the right purpose.

Therefore, in our laboratory, we are dedicated to evolving dampers through innovative ideas.

Development of Dampers Utilizing Deep Reinforcement Learning and Forces of Inertia

One of the research themes we are currently working on is the development of a device that uses computer-based deep reinforcement learning to control dampers and effectively suppress vibration.

For example, dampers used in cars, as road conditions vary, would provide better ride comfort if they could exert optimal damping force according to the vibrations at the time. Similarly, with earthquakes, there are different types of shaking, such as vertical and horizontal, with different characteristics of strong and sudden forces and weak and continuous forces.

Therefore, we aim to achieve optimum damping force according to vibration characteristics, for example, by computer-controlling the adjustment of the valve at the end of the damper tube mentioned earlier.

Of course, computers are already being used in the development of dampers. However, we believe that by incorporating deep reinforcement learning, we can obtain more optimal solutions that are adaptable to various situations.

Furthermore, this research is also connected to our other research: the study of dampers that change inertia mass. This started with the idea that inertia forces could be used to suppress vibration.

The term “inertia force” might not be familiar to many people, but I believe that everyone has experienced this phenomenon.

For example, while riding a train, if the train accelerates, the body leans in the opposite direction of travel. On the other hand, when the train brakes, the body leans in the direction of travel.

At such times, people feel as if they are experiencing a force in the opposite direction of the train’s acceleration or deceleration. However, it’s important to note that there is no physical object pushing them. In other words, people feel a fictitious force in response to the acceleration or deceleration of the train. This is what we refer to as inertia force.

And this fictitious force is also referred to as fictitious weight.

For example, consider a pot filled with water. When the water surface is flat, meaning the water is at rest, it doesn’t require much force to rotate the pot. However, if the water is spinning rapidly, creating a raised surface near the rim of the pot, it becomes significantly heavier and requires more force to rotate.

The actual amount of water inside the pot has not changed. This means that the actual weight of the pot has not changed, yet the fictitious weight has increased owing to the rapid rotation of the water.

The difficulty in rotating the pot is referred to as the moment of inertia. In short, fictitious inertia forces are at work here as well, adding fictitious weight to the pot.

We are considering whether we can utilize this fictitious weight for the vibration control.

For example, when shaking is subjected, the way it is transmitted differs between heavy and light objects. Therefore, even though lighter objects may be more convenient under normal circumstances, the idea is to make them instantly become heavier when shaking comes, thereby altering the transmission of the shaking or absorbing it.

And we are considering utilizing a computer trained with deep reinforcement learning for this instantaneous control of weight.

Further Improvement of Wisdom and Technology for Coexisting with Earthquakes.

Previously, we successfully experimented with using a magneto-rheological fluid as a material to instantly alter the fictitious weight.

A magneto-rheological fluid is, in essence, a liquid containing iron particle that responds to magnetic forces.

In the experiment, we generated a magnetic field to apply to the outside of the container filled with the magneto-rheological fluid using an electromagnet, and the flat surface instantly moved and adhered to the peripheral edge part of the container. A moment of inertia was created in the container. We found that the apparent weight of the container changed. Moreover, this phenomenon can be generated instantaneously by turning the electromagnet on and off.

The success of this experiment is just the first step, and it does not immediately lead to the development of a new damper.

Indeed, the phenomena of inertia force and moment of inertia are known and understood, but there has been very little research on utilizing them for vibration control purposes. I myself, currently working on this research, am not sure if this can be effectively applied to dampers or not.

However, the accumulation of pioneering ideas and exploration in uncharted territories has led to the development of excellent dampers that are in use today.

In fact, Japan’s technology for reducing shaking is highly regarded by researchers and experts worldwide, to the extent that it can be considered the best in the world.

This is because Japan, being one of the most earthquake-prone countries in the world, has accumulated wisdom for coexistence with earthquakes since ancient times. Currently, seismic regulations for buildings in Japan exceed global standards, and buildings that meet these standards are being constructed.

Our university has also contributed to the accumulation of such knowledge and wisdom.

For example, the Vibration Analysis Facility at the Ikuta Campus has a large vibration table that can simulate earthquakes and other vibrations. It is a large scale experimental facility, which is rare in universities. As a result, we are often asked to conduct tests by companies involved in the development of seismic equipment and related technologies.

The predecessors at our university have conducted research based on such facilities, aiming to foster a society that coexists with earthquakes. Our research laboratory also aims to contribute to the development of superior dampers through innovative ideas based on such a historical background.

While the development of Japanese technology for coexisting with earthquakes is making further progress, we hope that ordinary people will also accumulate correct knowledge about earthquakes.

Nowadays, we can easily obtain various knowledge and information through mobile phones and computers, but on the other hand, the abundance of information available is a mixed bag of valuable and unreliable sources. Acquiring essential and accurate knowledge enables individuals to independently discern and make choices among them.

Even without researcher-level knowledge, 0.1 is better than zero, and 0.5 is better than 0.1, you will no longer be misled by incorrect information.

By raising the level of knowledge of all people, not just researchers, the overall level of society in coexisting with earthquakes will rise. I believe this will lead to our society becoming more prosperous.

Information noted in the articles and videos, such as positions and affiliations, are current at the time of production.