What Is a Vibration Isolator?
A vibration isolator is a device used to reduce vibrations transmitted from the ground, foundation, floor, or other surrounding areas so that they are not transmitted to the equipment.
Vibration isolation, also known as vibration insulation, is the practice of preventing vibrations generated by the surrounding environment from being transmitted to the equipment being tested. Likewise, “vibration isolation” can refer to stopping vibrations generated by a source from spreading to the surrounding area. The term “vibration control” encompasses both preventing the transmission of existing vibrations and stopping the source of vibrations from transmitting them.
Vibration control is also known as “vibration damping.” Vibration control is the damping of vibrations by direct action on the object to be controlled. There are two types of vibration isolators: passive isolators, which suppress and prevent vibrations from the surrounding environment, and active isolators, which use sensors and actuators to perform vibration-damping movements.
Applications of Vibration Isolation Benches
Vibration isolators are used in precision processing equipment and as the base of electron microscopes. Minimizing the effects of vibration is essential for micron-order processing and measurement in precision measuring instruments, semiconductor and liquid crystal manufacturing inspection equipment, as well as ultra-precision processing machines.
Vibration suppression is also important for observation under high magnification with electron microscopes.
Principle of Vibration Isolation Table
There are two types of vibration isolators: passive and active. It is important to select the most appropriate method depending on the purpose of use, ambient environment, and natural frequency of vibration.
1. Passive Type
Passive vibration isolators combine elasticity, such as springs, and viscosity, which acts as a damper. Elasticity, of which springs are a typical example, temporarily stores vibration energy by deforming itself and reduces vibration through temporary energy accumulation.
Viscous uses the viscosity of air or fluid to absorb vibration energy by converting it into heat. Vibration is absorbed by the damper converting the vibration energy stored by the spring into heat.
Another key to the principle of vibration isolation is how fast the spring and damper move. If the pendulum is moved slowly and widely, it will swing widely, but if it is moved quickly and finely, it will hardly move at all.
2. Active Type
In an active vibration isolator, a sensor fixed to the floor or other surface constantly senses external vibrations, and through an actuator generates vibrations that have a frequency opposite to that of the sensor. This allows the device to remain stationary as the external vibration and the vibration generated by the table cancel each other out.
Active vibration isolators can be divided into two control methods: feedback control, in which the vibration of the equipment or vibration isolator is sensed by a sensor, and feedforward control, in which the vibration of the floor or ground is sensed.
Other Information on Vibration Isolation Table
What Are Vibration Transmission Characteristics That Indicate Vibration-Isolation Performance?
A graph of vibration transmission characteristics shows the performance of a vibration isolator. The vertical axis is the vibration transmission coefficient (db) and the horizontal axis is the vibration frequency (Hz). Generally, the vibration transmission characteristics rise to a peak at a certain frequency, touching the vertical axis at 0, and then decrease with increasing frequency in a gentle arc like the ridgeline of Mt. Fuji. Zero on the vertical axis indicates that the vibration transmission coefficient is 0db, or synchronous. The object moves as if it were one with the vibration source. In other words, the vibration is transmitted as it is.
The peak part of the vibration transmission characteristics is a condition called “resonance”. It means that the object vibrates very loudly in response to the generated vibration, and in some cases, the machine may be destroyed. Resonance is a point to be avoided in machinery. The area where the frequency increases from resonance and the vibration transmission coefficient becomes negative, which is less than zero, is the vibration-isolation area.
When selecting a vibration isolator, the frequency of vibration in the installation environment can be used to determine the degree to which vibration can be suppressed based on the magnitude of the vibration transmission coefficient.