Precision vibration isolation technology
Technology used to prevent vibrations in the floor to be transmitted to precision machinery, including semiconductors and liquid crystal manufacturing and testing equipment, ultra-precision machines, etc.
About Vibration Isolation
"Vibration isolation" is a process to prevent vibrations created by floors from being transmitted to the equipment on the floor.
Principles of Vibration Isolation
(Fig. 1) Air spring vibration isolation frame
Vibration isolation using air springs
- ・When it is not desired to transmit the vibrations in the floor to precision equipment, it is necessary to use vibration isolation frames..
- ・In general, vibration isolation frames use air springs to support equipment. (Fig. 1)
- ・The vibration isolation frame is supported by 3 air springs or more.
- ・The sizes of air springs are determined by the load applied to the vibration isolation frame.
- ・The softer the air springs (lower the resonance frequency), the higher the performance of the air springs will be. The vibration isolation area expands.
Transmissibility of vibration
- ・The ratio between the vibrations on the vibration isolation frame and in the floor is called the transmissibility of vibration. (Fig. 2 and 3)
- ・If the transmissibility of vibration is greater than 0 dB, vibrations will be amplified in the resonance zone.
- ・If the transmissibility of vibration is smaller than 0 dB, vibrations will be reduced in the vibration isolation zone.
- ・The frequency at which the transmissibility of vibration peaks is called the natural frequency.
(Fig. 2) Vibration isolation model
(Fig. 3) Formula for transmissibility of vibration
Vibration isolation in the horizontal direction
- ・Including in the vertical directions, vibrations occur in 6 different directions, such as horizontal and rotational directions.
- ・In the case of general diaphragm type air springs, natural frequencies in the horizontal direction are in multiples of those in the vertical directions and tend to influence the equipment.
- ・It is important to lower the natural frequencies not only in the horizontal direction but also in the vertical direction of the vibration isolation frame.
Passive Specific Technology
A gimbal piston is assembled in the diaphragm air spring piston for stable vibration isolation frames.
- ・Compact structure
- ・A soft spring property in the horizontal direction can be achieved. A vibration effect equivalent to that in the vertical direction can be achieved.
Dome gimbal piston
The dome gimbal piston is a product which has a spherical rotor on the load disc of the gimbal piston. This achieves a spring property which is much lower than that of gimbal pistons.
Gimbal piston 1.2 Hz
Dome gimbal piston 0.8 Hz
- ・This is more reasonable than the dual structure and its performance is excellent.
*Please contact us when using the dome gimbal piston for equipment which has a higher center of gravity. This piston may not be suitable for such equipment.
Active Specific Technology
Control of active vibration isolation frame
Vibration isolation performance
The vibration isolation is categorized into two control systems: The feed back control which detects the vibrations of equipment or a leveling block with an acceleration sensor and then controls them, and the feed forward control which detects the vibrations of floor and controls them. Kurashiki Kako is capable of using both controls as standard systems.
Vibration damping performance
The vibration damping is also roughly categorized into the feed back and feed forward controls. The feed back system controls displacements using a displacement sensor. The feed forward system is further categorized into two controls: FFKEAP control which is effective for repeated disturbance, and MFF (Motion Feed Forward) control which is effective in the random disturbances. The feed forward control is optional.
This is a type of control in which input signals from a sensor are distributed to four legs efficiently and effectively.
Vibration isolation performance
The above figure shows an example of performance measured under the circumstance of micro-oscillations in the floor.
By combining an active control with the excellent vibration isolation performance of air spring, resonance is eliminated, and thus vibration isolation is possible at all frequency ranges.
- ・When not controlled (passive)
Air spring only
- ・When controlled (active)
Feed back control + feed forward control
Vibration damping for the random movement of stage
MFF (Motion Feed Forward) is a control system used to start controlling before vibration isolation frames or equipment starts its movement, when the movement of a stage is random, by estimating the vibrations based on the preliminarily input stage movement information.