Vibration isolation

In machine dynamics, vibration isolation is the method by which the transmission of vibrations from one body to another can be reduced.

For this purpose, one or more parallel spring / damper elements are arranged between the two bodies; H. the machine to be insulated is mounted on elements with elastic and damping properties. Depending on the application (weight, frequency range, type of excitation ...) different components and materials are used, e.g. B. elastomers .

The insulation behavior is influenced by the damping of the element: the higher the damping, the lower the insulating effect (see the illustration of the amplitude frequency response below).

application

Unwanted vibrations and impacts occur in all technical fields, especially in the machine and electrical industry , traffic , construction and process engineering . Vibration isolation is used in machine and plant construction ,

to protect the environment from vibration emissions or dynamic stress from machines (e.g. from presses , compressors or gearboxes in wind turbines ); this type of vibration isolation is also called source isolation or active isolation;
to protect vibration-sensitive machines ( e.g. measuring machines ) from vibration immissions or dynamic stress from the environment; this type of vibration isolation is also called receiver isolation or passive isolation.

principle

Vibration isolation takes advantage of the fact that the transmission of mechanical vibrations that arise due to external excitations can be reduced by inertial forces . This is also known as mass force compensation . The inertial forces arise from the oscillating movements of the given oscillating system . I.e. the elastically mounted mass (machine, system, etc.) must perform oscillating movements itself; the behavior that is still permissible here is system-specific.

Amplitude frequency response ( amount of the transfer function ) of a single-mass oscillator for various damping values; green = lowest attenuation = greatest insulation, but also strongest resonance at the same time

Only from a frequency ratio of the excitation frequency to the natural frequency of the oscillating system (natural frequency of the body to be isolated on the spring-damper element) do the inertial forces counteract the excitation forces, and vibration isolation occurs. The relatively high frequency ratio corresponds to a low tuning (see following section). ${\ displaystyle \ eta> {\ sqrt {2}}}$

poll

For tasks in the area of vibration isolation, a distinction is made between high and low coordination (design of the bearing according to the respective requirements):

with high tuning, the natural frequency of the bearing is greater than the excitation frequency,
if the tuning is low, the natural frequency of the bearing is lower than the excitation frequency.

A deep coordination should be aimed for, since only then can vibration isolation be achieved. The vibration isolation usually has tuning frequencies, i. H. Natural frequencies of the storage, below 25 Hz .

Magnification function

The magnification function (base point or displacement excitation) on which the vibration isolation is based for a single-mass oscillator with one degree of freedom can be calculated as follows: ${\ displaystyle \ alpha _ {4}}$

{\ displaystyle \ alpha _ {4} = {\ sqrt {\ frac {1 + 4 \ cdot D ^ {2} \ cdot \ eta ^ {2}} {(1- \ eta ^ {2}) ^ {2 } +4 \ cdot D ^ {2} \ cdot \ eta ^ {2}}}}}

With

the damping ${\ displaystyle D}$
the frequency ratio between excitation and natural frequency. ${\ displaystyle \ eta}$

In order to achieve vibration isolation, the elastically mounted machine must be operated above its natural frequency, i.e. in the critical range.

When the machine is started up and also when it is switched off, the resonance is passed through briefly . The resonance peaks can vary in size, depending on the damping of the vibration isolating elements.

Differentiation from other measures

Structure-borne sound insulation

Like vibration isolation, structure-borne sound isolation also serves to reduce the transmission of mechanical vibrations. The actual goal of structure-borne sound insulation, however, is to reduce the secondary air- borne noise caused by the structure-borne sound transmission .

Vibration damping

In contrast to vibration isolation, there is vibration damping, in which an additional mass (a damper ) is installed on the vibrating object . Their storage is adjusted to the resonance frequency of the object.

Individual evidence

↑ Vibration technology. Retrieved November 10, 2016 .

[1] Vibration technology. Retrieved November 10, 2016 .