sound level from air bearings?

[edoardo777]

dear all,

we are in need to develop an ultra quiet test setup for an equipment, meaning maximum isolation from any source of mechanical disturbance.
We were thinking about deploying air bearings as supports, but we were also wondering about the eventual sound level generated by the airstream flowing into the bearing, and it's eventual spectrum distribution.

Anybody has information in this sense?

Thanks a lot in advance,
Edo

 

[IRstuff]

The typical optical table isolator is not an air bearing, it's an air damper. That means that there should be no air flow under steady-state conditions. Only when the table gets unleveled will there be air flow to re-level.

TTFN

FAQ731-376

 

[edoardo777]

Probably I did not described properly our needs.

The point is that we need to microvibrate our equipment along a given direction, within a few micrometer resolution. We need to avoid any additional movement component.
Air dampers would anyhow "shake" the test rig, introducing lateral or rotational undesired movements

therefore we need something really stiff as linear guide, avoiding to have side effects (e.g. linear guides based on rolling bearings would introduce the ball bumps, teflon guides would anyhow introduce static friction induced vibrations, and so on). that's why we were reasoning on air bearings.

Any information on the sound level produced by air bearings?

thanks a lot,

Edo

 

[IRstuff]

How are you controlling this motion? Without active gyro stabilization, air bearings will allow more degrees of freedom than what you appear to want.

Ballbearing systems are successfully used in higher performance designs. There are gimbals with better than 10 urad rms jitter stabilization using precision spherical bearings.



TTFN

FAQ731-376

 

[edoardo777]

we were thinking of having large surface air bearings on the vertical direction (meaning, acting horizontally), setting the air gap to a few micrometers, and having an actuator placed in order to push on the gig baricentre.

the vibration ranging up to 1000 Hz. The control based on spectral amplitude.

We experienced with rolling bearings microvibrations generated by the spheres and slight lateral pushs. but maybe we could have some more accurate rolling bearings?`

thanks for your suggestions,
Edo

 

[IRstuff]

For something that precise, if you do not actively control the vertical motion and horizontal rocking, the system will rock, as it is almost impossible to maintain perfectly horizontal stimulus through the center of mass. Any displacement of the force vector from the center of mass will induce a rotation.

TTFN

FAQ731-376

 

[edoardo777]

this is why we were thinking about having as vertical guides air bearings with tight tolerance (1 um), in order to have high lateral stiffness, low clearance and low friction coefficients.

And as you mentioned, trying to have all the push/pull force centered in the baricentre.

you still think this is stupid?

Do you know commercial vibration controllers that are able to control your inertia movement up to 1000 Hz with tight accuracy?

Thanks,
Edo

 

[edoardo777]

we were thinking of having large surface air bearings on the vertical direction (meaning, acting horizontally), setting the air gap to a few micrometers, and having an actuator placed in order to push on the gig baricentre.

the vibration ranging up to 1000 Hz. The control based on spectral amplitude.

We experienced with rolling bearings microvibrations generated by the spheres and slight lateral pushs. but maybe we could have some more accurate rolling bearings?`

thanks for your suggestions,
Edo

 

[GregLocock]

In the absence of any better suggestion I'd say the spectrum will be broadband white noise, with a corner frequency related to the gap, and with an overall sound power that is 1% of the cushion pressure*flow rate.

I realise that is not much help but might form the basis of an experiment.




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[edoardo777]

Hallo Greg,

thanks for this tip, this is really giving at least a starting point to assess my point of view

merci,
Edo