Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: Overloaded on August 18, 2008, 07:30:05 PM
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:)
Anyone here have any experience with Capacitive encoders ?
Thanks for any input,
RC
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Can's see why they would not work well, provided they can take the abuse and have sturdy construction. Where or who is making them?
Kristin
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RC,
Never heard of them. I wonder what frequency is being used and the amount of RF generated. Also the units sensitivty to interference from other devices. What kind of enviroment and what applications are they recomended for?
Just some gut reaction's to a new device. Bottom line question is ....what are the short comings if any?
RICH
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Thanks Guys for the responses.
Here is a clip from the tutorial found here:
http://dkc1.digikey.com/us/en/tod/CUI/AMTEncoders_NoAudio/AMTEncoders_NoAudio.html
It clearly says for DC motors and I can only assume that they are quadrature. No mention of an index, not necessary for what I need anyway.
Look it over and tell me what you think.
I might order 2 tomorrow. $30 ea. and $7 for a cable with matching plug....Worth a try...
Check out the dip switch for selecting the resolution....pretty neat.
Thanks again,
RC
And here is one interesting note pertaining to steppers, so it does mention an index.
RC
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A capacitive position encoder which provides a digital output indication of the relative position between two plates. One of the plates includes first and second conductive input areas which are separated by a gap having the shape corresponding to a square wave. The second plate includes a number of rectangular output pads whose length is equal to one-half of the wavelength of the square wave. The pads are separated from one another by an integral fraction of the wavelength. Periodic input signals which are the inverse of one another are applied to the input areas and are capacitively coupled to the output pads. When the degree of overlap between an output pad and the input areas is equal, a null signal will be generated. Each pad will provide a null signal corresponding to a different position of the plates.
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Very interesting....GOOD stuff.
It's easy to see this working in a linear scale....like the digital caliper.
Thanks Ed,
RC
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One potential downfall that comes to mind (since were comparing them to calipers) is the ability to function at high speed. Now obviously, this is not a problem on calipers, and one would/should assume a motor encoder would have definitely addressed this. I would at least look into it before making a purchase, though.
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The data sheet lists the number of ppr and rpm as :
Max RPM Resolutions
7500 RPM 2048, 1000, 800, 384 (plus res. from 15k and 30k RPM)
15000RPM 1024, 500, 400, 192 (plus res. from 30k RPM)
30000RPM 512, 250, 200, 96; 256,125, 100, 48
Although I have to wonder how those plastic hubs stand up to 30000 RPM.
Kristin
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RC
The idea of selectable resolution is kind of neat. Seems like easy installation. I am still a little concerned on operabilty from an RF / electrical field standpoint. Located any where near a a device which generates white noise, ie; like a motor or variable speed drive. But you don't know until you try it out. Wise man once said......one @30 to try is better than two in the drawer .........
:) RICH
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Sam, That was one of my suspitions as well. I saw the data sheet too, thanks KD.
Rich, the cables ARE sheilded, hope that takes care of it.
We'll soon see, I have one on the way.
Thanks again All,
RC
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OKEE DOKEE,
Got one all mounted up and ready to go.
Waiting for the Gecko and power supply.
These little suckers are very nifty. It comes as a kit to fit almost any shaft dia. and 2 different mounting plates to match many bolt patterns.
Anxious to see how they perform.
Will post back when running....Wish me luck. New technology, I may be the first sacrificial SUCKER !
RC
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The thing I didn't like about them was the 30,000rpm limit. That would lower my travel speeds to slightly below the sound barrier. I'm just not ready to take a performance hit like that. If all you potentially loose is $37, then your more of a small lollipop than a sucker. I hope they work flawlessly!
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Sam,
I plan to keep it at or below 28K...so I should be OK. :D
RC 8)
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Hey Overloaded,
Never did say what you were going to try it on. So what's the scoop so far?
RICH
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RICH,
Here is what I am/was planning: http://www.machsupport.com/forum/index.php/topic,8101.0.html
I have hit a stump however. (Or it hit me)
May have to get out of this for a while.
Thanks,
rc
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whats the problem RC?
Hood
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Hood,
I may need to change employment. Would probably destroy my time at home.
RC
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Well I'm servo illiterate so can't help you there. Now stumps, well they don't call us "stump jumpers" for nothing back n the
coal region, we just jump over them. :)
I was hoping that you would get a chance to check out the resolution settings and also see how prone to interference they are.
RICH
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All is not lost...yet.
Also have a PA22-160 to recover. :P
Really eating up my spare time.
Some stumps we couldn't jump......Got out the ol' "Improvised Munitions Handbook" and wallah...(had to replace some of my neighbors windows, and a few of mine as well) ::)
RC
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RC, that sucks. Hope you get it sorted quick.
Brett
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RC
MUNITIONS ? I can help you out there. ;)
Ed
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Sorry to hear that RC, hope you get things sorted soon.
Hood