Modern technologies, e.g. in the field of high-resolution measurement, high-precision manufacturing processes and super lightweight construction, require effective anti-vibration solutions to achieve maximum performance. This is particularly true for experiments or processes where the typical amplitudes of the ambient vibration and the dimensions of the investigated or manufactured structures fall in the same range, e.g. submicron semiconductor production, interferometry, confocal optical imaging and scanning probe microscopy. Ever since high-precision measurement and manufacturing techniques have reached nanometer resolution, vibrations have become a major problem.

Sources of disturbing vibrations are:
- building and floor vibrations (vertical: 5-30 Hz, horizontal: 0.5-10 Hz)
- acoustic vibrations (>20 Hz)
- motorized equipment and machinery (10-500 Hz).

How is the performance of Passive Vibration Isolation?

Passive damping treatments are commonly used to reduce vibrations. Passive damping treatments consist of an elastic spring and a damping unit. The combination of a mass (given by the weight of the device to be protected against the vibrations) and the spring is known as a mechanical low-pass. The mechanical response of the spring-mass system decreases significantly for frequencies above the eigenfrequency, and the damper reduces the vibration amplitude especially within the resonance range.

Because of the low-pass characteristic, passive damping treatments are designed with very low eigenfrequencies. Since pneumatic springs are characterized by low stiffness and high damping, most anti-vibration mountings available are pneumatic systems. Eigenfrequencies between 2 to 5 Hz are commonly achieved. Due to resonance, pneumatic systems amplify vibrations from approx. 1 to 8 Hz instead of damping them. The solution to this problem is active vibration control (AVC).

How works Active Vibration Isolation?

The signals acquired by extremely sensitive vibration detectors are analyzed by electronic circuitry driving electro-dynamic actuators which instantaneously produce a counter-force to compensate for the vibration. The active vibration isolation damping system has no resonance and no amplification of vibrations in any frequency.

Fig. 1: Comparison of the transmissibility of a passive and an active system. Since the transmissibility of the active isolation unit is the same in the vertical and horizontal directions, just one curve is plotted. The comparison reveals the complete absence of resonance in the active damping treatment. Furthermore, the isolation of the active system is better at all frequencies than the horizontal transmissibility of the passive unit and is inferior to its vertical transmissibility only at high frequencies, where both systems isolate so well that the difference is unlikely to be of any importance.

What can we offer?

Accurion provides sophisticated active vibration isolation and reduction systems based on state-of-the-art engineering methods. Continuous advances in the development of active vibration suppression and close contacts with leading research institutes ensures systematic integration of leading-edge technology. The engineering know-how which goes into the design of these systems is also available for analyzing vibration problems and creating customized solutions.

What means "Transmissibility"?

This function describes the relation between the resulting oscillation amplitude multiplied by two and the incoming oscillation amplitude.

Example:
The incoming oscillation amplitude is 100 µm, the resulting oscillation amplitude is 0.5 µm.

T = (0.5 µm x 2)/(100 µm x 1) = 0.01

There are three regions in every transmissibility vs. frequency diagram:
T > 1 the resulting oscillation is bigger than the incoming one T = 1 the resulting oscillation is the same like the incoming one T < 1 the resulting oscillation is smaller than the incoming one

The transmissibility values change according to the frequency. That is why they are drawn as transmissibility versus frequency diagrams. The range for the transmissibility values is usually very big, therefore often logarithmic scales are use to picture them. Instead of transmissibility values often decibel numbers are used.

To calculate this the following equation is needed:
T (dB) = 20 dB log((resulting osc. x 2)/(incoming osc. x 1))

For the above example:
T (dB) = T (dB) = 20 dB log((0.5 µm x 2)/(100 µm x 1)) = -40dB.

-60 dB = 0.001
-40 dB = 0.01
-20 dB = 0.1
-6 dB = 0.5
0 dB = 1
6 dB = 2
20 dB = 10
40 dB = 100
60 dB = 1000