Static buildup.
Static buildup.
(OP)
I work for a company that is into CMM, and we are having a static build up problem. We have a large measuring head that floats on a ceramic beam via air bearings. It is driven by a small rubber wheel which contacts the surface. Static builds up on the Ceramic beam through some mechanism unknown to me (the drive wheel / support wheel on the other side rubbing?). I have been looking at various static control products, but am having a tough time discerning which product is best suited to either dissipating the static, or possibly preventing it from building up. Any help is appreciated.





RE: Static buildup.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Static buildup.
Also, is there any way to temporarily test this ion blowing method without purchasing a unit?
Also, would one of the static dissipating films be capable of removing static from the beam? Would I have to run it only in a small strip, or would it be necessary to cover the entire surface that is building the charge?
RE: Static buildup.
If you have a small fan that can blow down the beam - try it! You know, like a computer fan or a small room fan. If that's enough you've got a solution. If it helps appreciatively but not quite enough then it's time to try a static augmented fan.
Very dry air can transport static just like the air being used to carry away your static. That said, there is probably no static source in your air to cause it to bring static to your beam. The beam is becoming charged via triboelectric generation from the insulated bar being rubbed by the insulated rubber wheel.
If you could blow moist air across your beam then the static would dissipate in a New York Minute!
Peel some scotch tape off a roll and then hold it next to a surface. You will see the tape attracted via the static charge generated by the unrolling tape.
Do it again, then before holding the tape next to a surface, blow on it, mouth open, like you want to fog your glasses before wiping them. Now hold the tape near a surface. NADA - the charge was shorted and conducted away on your breath and to your fingers.
This would work well on your beam too.
As for static films.. Could work, could not work! There are antistatic soaps that you can spray on things but your app doesn't sound like this would work too well, and would require frequent reapplication.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Static buildup.
The first thing I would try is a static brush like Ion Cord attached to the moving part of the CMM close to the stationary slide that is showing the static. The brush does need to be grounded.
What is the problem that the static is causing?
RE: Static buildup.
I tried using a pair of computer fans on either side of the rubber tensioning wheel, it being the only thing in contact with the surface.
I also checked all of the fittings in the air supply system for any slight charge, in case it *may* be causing the VERY dry air to transport charge, but did not find any. The air is piped in through well grounded pipes to a series of air dryers, which connect to the air bearings via nylon tubing. I checked against the machines chassis ground and the fittings as well as the piping and the fittings, and the piping / chassis ground.
Other than static buildup, is there any reason a spark would jump between the reader head and the beam? It seems like a short would got to one of the grounded screws holding the reader to the head rather than jump across 1/8in of air to an insulated ceramic beam. Is there a specific way I could determine precisely is this was a static buildup problem? Removing the position feedback reader is a last choice due to HIGH calibration costs associated with the unit.
Other cheap solutions I've seen are the copper tinsel that floats above the surface, or like composite pro suggested the static dissipating brushes. Also the inexpensive thin film that is conductive in some manner to dissipate / ground static. Ion knives/curtains/blowers are expensive, and they require expensive power supplies.
RE: Static buildup.
Have you run a field strength meter on this structure? You need something like 20 kV to jump a 1/4-inch gap.
Have you looked to see if there's some sort of carbon-impregnated wheels that you could use as an alternate?
TTFN
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RE: Static buildup.
RE: Static buildup.
RE: Static buildup.
What I believe is that this strip was previously removing the static charge from the beam, but is now insufficient. Is there some way to ensure a VERY good electrical contact between the two copper films, such as some sort of very conductive paste or some such that I can apply between / on top of them?
Right now I am liking the idea of a carbon fiber brush that rides above the surface of the beam. While sprays and cleaners would be easy, we cannot risk putting any sort of film or covering of cleaner on the air bearing surface or the position scale. Ionizing air units are prohibitively expensive.
RE: Static buildup.
http://www.fibraplex.com/IonCord.htm
By the way, aluminum foil over your encoder and wiring will protect it from sparks but it, too, must be grounded as well as the entire conductive structure of your CMM.
RE: Static buildup.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Static buildup.
RE: Static buildup.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Static buildup.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Static buildup.
A CMM always has a set of cables and tubes supplying electricity and air as well as bringing measurement signals back to the computer (you have Zeiss' own touch probes or some other make? Or optical edge sensing?). The cable harness usually has a copper strip bringing ground to the moving parts and also screening power and signal flat cables from each other. Being usually a thin copper or bronze band, this strip sometimes comes loose or breaks near the end or where flexure is at maximum.
It may be that something has happened to this grounding system.
Gunnar Englund
www.gke.org
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RE: Static buildup.
RE: Static buildup.
RE: Static buildup.
That does not indicate an open circuit. It sounds more like the operator has accumulated some charge and that he discharges himself when touching the probe. Do they not get the same shock when they "ground themselves" to the control box? Are you sure that some kind of myth or mistake hasn't been added to actual observations?
Time for a thorough check of the whole installation. Check continuity (when moving through the whole operating volume). And also the environment, floor, operator's dress and shoes, air humidity. Are you on the southern hemisphere? (air is getting dry this time of the year)
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...