Vibration isolation system Micro-g

Depending on the location and surrounding environment of a room in which a work area is situated, vertical and horizontal floor vibration may occur. This vibration is between 2 and 50 Hz and has amplitudes in the micrometer range. Typical sources of this interference are vibrations in buildings and randomly occurring interference, such as impact sound waves caused by people walking down a corridor and traffic noise. This vibration negatively affects work conditions and results to a considerable degree. To prevent most of this vibration from being transferred to a work surface, a vibration isolation system must be used. The Micro-g vibration isolation system ensures reliable protection against vertical and horizontal floor vibration, even in highly sensitive applications.

A criterion for assessing the quality of a damping system is its resonant frequency. This frequency depends on the load of a system and on the amplitude of the vibration or oscillation causing resonance. Vibration is only absorbed at frequencies that are 1.4 times higher than the resonant frequency. As a result, the resonant frequency must be kept as low as possible.

This is exactly where the patented Micro-g system stands out from other vibration isolation systems. The Micro-g features extremely low resonant frequency even in the critical range of very low amplitudes.

At excitation amplitudes of 0.1 mm, the resonant frequency is 1.5 Hz in the vertical and 1.7 Hz in the horizontal direction. For amplitudes of 1 mm, this frequency is 1.0 Hz in the vertical and 1.2 Hz in the horizontal direction. At an excitation frequency of just 5 Hz, the Micro-g’s isolation efficiency is 95% in the vertical and 80% in the horizontal direction. An integrated level controller ensures automatic return to the original position as the load applied to a work surface changes. This repositioning accuracy is ±1 mm and can be increased to ±0.1 mm by using precision valves.

The Micro-g isolation system works using air only. Since it does not require any hydraulic damping or absorption media, it is ideal for use in clean rooms, ensuring maintenance-free operation with consistent technical specifications over many years.

Vibrational isolation is provided by a gimbal-piston assembly, free to move in an upper air chamber, or compression chamber, sealed by a 0.5 mm thick, Dacron-reinforced, bellows that excludes ambient air. A supporting rod welded onto the underside of the unit's mounting plate is bolted to the piston's flexible baseplate. The compression chamber is pneumatically interconnected to a second chamber, a so-called "damping" chamber, via a calibrated orifice. When these units are used, table tops are supported on air cushions constituting extremely "weak" springs of a spring-mass system.

These types of table systems have extremely low resonant frequencies, due to the low restoring forces of their supports and the high weights of their tops. The bellows used for sealing add no stiffness to support units, since they are rather thin, and thus highly flexible.

If a table top supported on these units is vertically displaced, the resulting motions of their pistons will alter the volumes of their compression chambers, thereby altering chamber pressures. This is what provides the desired cushioning effect. Since air may enter or exit compression chambers through calibrated orifices in the walls separating them from damping chambers, air will flow back and forth through these orifices as compression chamber volumes vary, damping the motions of the mounting plates on which the table top rests.

Horizontal displacements of table tops are transmitted via supporting rods, producing lateral motions of flexible piston baseplates. This causes pistons to execute vertical tilting motions about points lying roughly in the planes of their sealing bellows. The lengths of pistons and supporting rods have been chosen to optimize the resonant frequencies of these motions. Horizontal displacements of table tops thus also cause air to flow back and forth between compression and damping chambers, thereby damping any lateral motions of table tops.

The lowest resonant frequencies achievable with these vibration isolators range from 1.5 Hz to 1.7 Hz in both vertical and horizontal planes, and vary with the loads supported. The following graphs present typical vibration-transmission and transmissibility curves for our Micro-g vibration-isolators.

Micro-g systems effectively damp vibrational motions in both vertical and horizontal planes over the entire critical range, which extends from 2 Hz to 50 Hz.

This superior performance makes these systems suitable for supporting experimental setups, such as those used in interferometry and holography, that are highly sensitive to vibrations.