Vibration isolation
A few of these applications are for industrial equipment such as pumps, motors, HVAC systems, or washing machines; isolation of civil engineering structures from earthquakes (base isolation),[2] sensitive laboratory equipment, valuable statuary, and high-end audio.
The curve below shows the typical performance of a passive, negative-stiffness isolation system with a natural frequency of 0.5 Hz.
Damping dissipates energy in the system, which reduces the vibration level which is transmitted at the natural frequency.
The fluid in automotive shock absorbers is a kind of damper, as is the inherent damping in elastomeric (rubber) engine mounts.
Large machines such as washers, pumps, and generators, which would cause vibrations in the building or room, are often isolated from the floor.
To solve this, the solution is a double elastic suspension where the engine and alternator are mounted with vibration dampers on a common frame.
"Snap-through" or "over-center" NSM devices are used to reduce the stiffness of elastic suspensions and create compact six-degree-of-freedom systems with low natural frequencies.
These isolation systems enable vibration-sensitive instruments such as scanning probe microscopes, micro-hardness testers and scanning electron microscopes to operate in severe vibration environments sometimes encountered, for example, on upper floors of buildings and in clean rooms.
[citation needed] Similarly, they enable vibration-sensitive instruments to produce better images and data than those achievable with pneumatic isolators.
It uses a conventional spring connected to an NSM consisting of two bars hinged at the center, supported at their outer ends on pivots, and loaded in compression by forces P. The spring is compressed by weight W to the operating position of the isolator, as shown in Figure 1.
Using a suitably designed vibration-isolator (absorber), vibration isolation of the supporting joint is realized.
This is defined as a device that reflects and absorbs waves of oscillatory energy, extending from a piece of working machinery or electrical equipment, and with the desired effect being vibration insulation.
The illustration shows a vibration isolator from the series «ВИ» (~"VI" in Roman characters), as used in shipbuilding in Russia, for example the submarine "St.Petersburg" (Lada).
Under action of weight loading of the machine, the rubber envelope deforms, and the spring is compressed or stretched.
The amount of elastic deformation of the rubber largely dictates the magnitude of vibration absorption that can be attained; the entire device (including the spring itself) must be designed with this in mind.
Lastly, the vibration isolator must also be designed for long-term durability as well as convenient integration into the environment in which it is to be used.
Sleeves and flanges are typically employed in order to enable the vibration isolator to be securely fastened to the equipment and the supporting foundation.
Semiactive vibration isolators have received attention because they consume less power than active devices and controllability over passive systems.
Active vibration isolation systems contain, along with the spring, a feedback circuit which consists of a sensor (for example a piezoelectric accelerometer or a geophone), a controller, and an actuator.
As a result of such a feedback system, a considerably stronger suppression of vibrations is achieved compared to ordinary damping.
A couple of companies produce active isolation products as OEM for research, metrology, lithography and medical systems.
In the microchip production, the smallest structures today are below 20 nm, so the machines which produce and check them have to oscillate much less.
