Passive Vibration Isolation

As it relates to vibration isolation table, platform and bench top systems developed by Minus K Technology

Vibrations can be isolated from equipment using active or passive technology. With active methods, equal but opposite forces are created electronically using sensors and actuators to cancel out the unwanted vibrations. With passive methods, isolation is achieved by limiting the ability of vibrations to be coupled to the item to be isolated. This is done using a mechanical connection which dissipates or redirects the energy of vibration before it gets to the item to be isolated. Passive methods sometimes involve electromechanical controls for adjusting the system, but the isolation mechanism itself is passive. Passive systems may use elastomers, springs, fluids, or negative-stiffness components. Passive systems generally cost less than active systems and their relative simplicity makes them more reliable and safe.

One of the most basic passive isolators is a spring placed between the surface transmitting shock or vibration and the item to be isolated. The spring opposes the impulse on it and absorbs some energy as it deforms. A fluid or elastomeric element is added to the spring element for damping. A simple example is the shock absorber in a car. In this case, mechanical energy from the shock or vibration does work on the fluid and is converted to thermal energy in the fluid, reducing the amount of energy transmitted to the body of the car.

Elastomers are rubber-like materials which absorb mechanical energy by deforming. Examples of elastomeric isolators are shock and vibration mounts for automobile engines, aircraft components, industrial machinery, and building foundations. Because rubber does not have the same characteristics in all directions, isolation may be much better in one axis than the others.

The most sophisticated passive isolators use air or negative-stiffness technology. In advanced technology applications, such as interferometry, microscopy (including SPM, SEM, etc.), nano-fabrication and micro-hardness testing, the best passive vibration isolation devices allow the instruments to perform at their highest possible level.

Pneumatic systems support a heavy table or platform on compressed air pistons, which provide the decoupling link between the ground and the table, i.e. the table floats on the air. The most sophisticated air tables do a good job of isolating floor vibrations at small amplitudes, but can be quite expensive. While they isolate in a passive manner, they require an air supply, a leveling system, and associated maintenance and controls. The less sophisticated air systems do not isolate well in all directions or at the low frequencies which are handled so well by negative-stiffness systems. The air supply system for pneumatic isolators can create problematic ambient vibration. The use of electrical methods of leveling the table and controlling air cylinder pressure adds complexity and the potential for failure.

Negative-stiffness isolators provide a simple, reliable, and highly effective isolation solution for sensitive instrumentation at the low frequencies and amplitudes of floor and building vibrations. They are relatively small, light weight, stable, and cost-effective. Minus K negative-stiffness isolators are completely mechanical; for special applications, an optional electronic auto-adjust system is available. Isolation is achieved using an arrangement of springs and negative-stiffness mechanisms. These systems provide isolation in 6 degrees of freedom with resonant frequencies as low as 0.5 Hz or lower. For a 0.5-Hz system, isolation begins around 1 Hz and is 50-100 times better than most high-performance air tables in the 5-10 Hz range which is so important in buildings. Multiple isolators can be used together while still acting as one with respect to vibration, which allows great versatility in designing for a range of applications. Minus K's negative-stiffness technology has been successfully implemented for sensitive instrumentation loads from a few pounds to many tons. The isolators are easy to use and adjust. They can be more economical than air systems, take up less space, provide better isolation at very low vibration amplitudes, and require no maintenance.

Negative-stiffness systems are typically not designed to handle large angular changes and shock loads such as occur in vehicle or aircraft applications. However, the Minus K devices can be used selectively to greatly enhance the performance of sensitive instruments during operations in vehicles or aircraft. Both pneumatic and negative-stiffness systems can be sensitive to temperature change but can be adjusted to compensate. Negative-stiffness systems can easily be used in a vacuum chamber or clean room, while air systems are prone to difficulties in this environment.

In addition to the standard products, Minus K designs custom systems for special applications.