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Air Bearings Benefits

AIR BEARINGS
WHY YES
ROLLING BEARINGS
WHY NO
In case of: high dynamics on maintenance free guide systems
A correctly dimensioned Air Bearing guarantees the stability of the air meatus and therefore of the lubrication also at very high speed values, accelerations and frequencies of positioning.

• No wear, absolute reliability and long duration
• No stroke restraints 

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--- HIGH DYNAMICS ON MAINTENANCE FREE GUIDE SYSTEMS ---

BENEFITS OF THE AIR BEARINGS TECHNOLOGY
In the air bearings do not exist the creep and stick-slip phenomena: there is no mechanical contact and consequently no wear among the sliding elements even with high speed, accelerations and positioning frequency.
The guide systems are highly reliable and durable, with limited or no maintenance.
The friction is significantly lower than the friction of sliding and rolling bearings, and it is also much lower than the typical friction of hydraulic couplings, enabling to reduce the power required.
In contrast to the caged rollers systems, the air bearings feature no in-trinsic limit in operating runs.

DISADVANTAGES OF SLIDING / ROLLING BEARINGS
The sliding and rolling bearings suffer from creep and stick-slip. What is creep? The creep is a parasitic effect of the traditional rolling bearings (spheres or rollers). Stick-slip occurs at the beginning of the movement, causing a temporary drag (-> sliding friction) between the rolling element (roller or ball) and the track on which the element slides, before the element starts rolling (-> rolling friction).
Creep becomes more significant as the frequency of motion inversion and acceleration increase, since the loads are higher and the distance travelled by the rolling element in sliding friction condition before rolling, increases.
For accelerations up to 10g, in rolling systems the reduction of damages due to creep depends on lubrication efficiency (with grease or oil), which must be periodically restored. For very high dynamics, the layer of grease or oil breaks down, causing metal on metal contact and sig-nificantly reducing the durability due to premature wear of the parts.

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As the inversion frequencies of motion and of accelerations increase, the behaviour and therefore the life of the rolling bearings is similar to that of NON-lubricated sliding bearings.

• Early wear, compromised reliability
• Significant restraints on useful strokes
In case of: high precision positioning and/or measurement
Air Bearings enable superior levels in terms of measurement precision, positioning control and speed.

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--- HIGH PRECISION POSITIONING AND / OR MEASUREMENT ---

BENEFITS OF THE AIR BEARINGS TECHNOLOGY
Air bearings, thanks to the low viscosity of air, feature very low, constant friction. Movement is very fluid, and actuation CN can achieve accurate positioning without difficulty.

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The air gap can also “corrects” small shape errors, due to waviness and roughness, of the guides on which it slides, either linear or rotary, avoiding microjams and partly compensating the shape errors of the guide systems, increasing its accuracy.

DISADVANTAGES OF SLIDING / ROLLING BEARINGS
Rolling bearings suffer for the presence of creep and stick-slip phenomena.
Due to creep, at motion start (and in opposite direction to the positioning end) a rolling part meets 3 (not only 2) decreasing friction coefficient values: static sliding friction (first detachment friction, known as stick-slip), kinetic sliding friction and rolling friction.
This means that at very low speeds, near zero, the friction force of the rolling guide system changes, making precision positioning quite difficult: it is as if you'd try to stop your car in a specific point with an engine brake which, when the machine is almost still, suddenly increases its power.
Positioning control relies on motors power and on the readiness of the actuators used. Finally, in radial bearings the roller or ball rotation, due to imperceptible unevenness, can lead to microjams, which affect measurements, positioning control and speed.

Using rolling bearings, extremely high precision positioning and accurate speed control is quite difficult.
In case of: need for absence of environmental pollution
Air Bearings DO NOT pollute. They are the priority choice for whiteroom applications.

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--- NEED FOR ABSENCE OF ENVIRONMENTAL POLLUTION ---

BENEFITS OF THE AIR BEARINGS TECHNOLOGY
The lubricant in pneumostatic application is suitably filtered, deoiled, dehumidified air. Such air has no polluting power. Besides, with no wear between parts, no dust is generated.
A further benefit is the pressurization of the environments due to the air supplied to the pads which escapes from the air gaps. This enables air tight environments, protected from dust.

DISADVANTAGES OF SLIDING / ROLLING BEARINGS
The presence of oils or greases is a pollutant: in case of high dynamics there may be significant overheat which in turn may cause the evap-oration of the lubricants. Besides, if lubrication is poor, metal wear on parts may produce dusts. Such pollution may not be acceptable in dif-ferent industries, for several grounds.

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Generally, the guide systems may require optical transducers (photodiodes, lasers, etc.): the deposit of the lubricant vapours on the optic components over time may alter their performance, up to complete malfunction.
In case of hydraulic systems or hydrostatic systems, leaks of water or oil cannot be avoided, and it is necessary to set up a system to recover and recycle the fluids.

Systems based on rolling technology may significantly pollute particular working environments.
In case of: low noise and absence of vibrations
Air Bearings are very quiet and their vibrations are limited and indipendent by the dynamic system.

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--- LOW NOISE AND ABSENCE OF VIBRATIONS ---

BENEFITS OF THE AIR BEARINGS TECHNOLOGY
The air gap avoids the contact between rigid parts: the noise is limited to the hiss of air escaping from air gaps. The air has as well a damping effect, which absorbs the vibrations in a specific range of frequencies.

DISADVANTAGES OF SLIDING / ROLLING BEARINGS
The creep and the stick-slip effects generate noise and vibrations, due to the high rigidity of the contact combined with the difficulty to control the movement: at high frequencies, this may become a quite important design parameter. Due to the recirculation effect, the continuous change of the number of the elements (spheres or rollers) on contact on the rail, creates itself drive vibrations.

Systems based on rolling technology may feature unacceptable noise and vibrations depending on the dynamic system.
In case of: high temperatures and / or radioactivity
Air Bearings are reliable even with high temperatures and radioactive sources.

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--- HIGH TEMPERATURES AND / OR RADIOACTIVITY ---

BENEFITS OF THE AIR BEARINGS TECHNOLOGY
Air viscosity virtually does not change as the temperature changes, and is not sensitive to radioactivity: the pneumostatic systems ensure maximum reliability even in difficult environmental conditions.

DISADVANTAGES OF SLIDING / ROLLING
The durability of the parts in the rolling guide system decreases significantly when the operating temperature increases, because there is a decay of the mechanical characteristics of the metals (surface strength, stress resistance) and of the lubrication effectiveness of lubrication oils and greases. The latter are quite sensible also to radioactivity.

The durability of systems based on rolling technology with high temperatures and radioactive sources may be limited.

 

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