Wireless or Non-Contact Motion Control Help?

I sure do hope somebody has some good ideas on this one...
We are working on a prototype one-off setup for a customer that will
transport a 2,000 lb. load across a concrete floor and then return to its original position. The transport is in a straight line from point A to point B.
During workup we built the carriage, which is hydraulically wheel driven and includes a steering axle mechanism, and it works well. Our guidance was planned through a recessed floor railing but the customer now says that is unacceptable (dirty work area).
I'm considering a couple of options including laser guidance to target and floor embedded radio. I'm wondering if anyone has other ideas or knows vendors that might have employed similar solutions.
The envisioned system would work by pressing a "Send" button or command and travel about 25 feet in a straight line at low speed. Once unloaded, a operator would press a "Return" button to send the carriage back to its original position. Guidance must not employ devices overhead, raised from the floor, or recessed in a manner that will collect dirt and grime. Accuracy of +- 6 inches to either side of the travel line is desired.
Any ideas or help would be appreciated!
Thanks,
Jake
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Jake wrote:

What about a metal strip in the floor and a pair of induction coils for detecting the metal? Sense the difference between the induction coils & there you are.
Alas I work in itty bitty clean things, since you're working on a great big dirty thing I can't help you with vendors.
--

Tim Wescott
Wescott Design Services
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Can you use the flow through the hydraulic motor as a measure of distance or flow rate as a measure of velocity ?
Dan
Tim Wescott wrote:

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Dan Mckenna wrote:

It's bad practice to rely on wheels not slipping and seals not leaking for long-term measurements. "Dead reckoning" can give useful estimates for short distances, but (to continue the navigation metaphor) periodic fixes are important. An intermittent magnetic stripe parallel to the continuous guide stripe can provide those fixes and also provide information to correct the dead-reckoning estimators as they age over time.
Jerry
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Engineering is the art of making what you want from things you can get.

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Jake wrote:

What is the composition of the floor? If it's essentially non-magnetic and embedding a piece of iron so that it's flush with the surface is acceptable, you could take that route. I am leery of laser guidance or any other use of light where dirt or dust could interfere.
A pair of sensors on the carriage positioned on opposite sides of the buried rail and operated differentially can provide proportion control.
Jerry
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Well Guys, Thanks for the quick responses but....
The app. is in a foundry..... ferrous metal all over the place. I'm not so sure the magnetic sense would be a good way to go...
Thanks,
Jake
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Jake wrote:

That kinda rules out your embedded radio in the floor, too, unfortunately.
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Tim Wescott
Wescott Design Services
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wrote:

It doesn't have to be radio. How about a long coil excited at an audio frequency? Perhaps you could use two frequencies - one on the left and the other on the right. Then when the amplitude of the two frequencies is in balance, you are right in the middle. This is sort of the way an airport localizer approach works. -Robert Scott Ypsilanti, Michigan (Reply through this forum, not by direct e-mail to me, as automatic reply address is fake.)
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Robert Scott wrote:

Robert,
Hmm, reminds me of a tracking job we scoped a while back... You can try using RFID chips and readers in reverse. Put the reader on the carriage and the RFID tags at known locations. The right tag/reader combo will tell you distance to reader. A touch of triangulation and you are on your way. IIRC the frequency is in MHz, which puts it out of the range for most of the interference you are likely to come across.
Have Fun, Steve B.
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Steve,
I've researched the RFID idea quite a bit this afternoon... seems like it may be an option, but I was wondering whether anyone had actually seen a White Paper where the "Reverse Triangulation" system had been applied successfully? Sure seems like I could use four RFID tags (one in each corner of the 'corridor' of travel) and make this work over the short distances required, but I do wonder about accuracy.
I saw where SICK has this really nifty product called the NAV 200 specifically designed for AVG's (Automated Guided Vehicles) but I'm afraid the cost would be prohibitive as the device is really designed to do a lot more than what I'm looking for here.
I'm not an RF engineer, but the comments on aviation parallels are also interesting... perhaps narrow navigation 'beacons' located at either end of the travel 'corridor'?
Thanks for the great ideas,
Jake
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Hrm.. Exactly how dirty is it? We talking piles of graphite everywhere...or something less than that? Might consider a cognex camera..but the dust may preclude that...dunno...
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Anthony

You can't 'idiot proof' anything....every time you try, they just make
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Jake, SICK have a vast range of all kinds of goodies designed specifically for AVGs - not just the radio stuff.
The older model DMEs (laser rangefinders) and optical scanners would do exactly what you want but at less cost than the newer, sophisticated gadgetry - but you'll have to talk to a sales rep to find out what they can offer in your price range.. and it is extremely high-quality and robust gear.
Tell them what you are trying to do and they'll tell you what you need to do it...
I hope this helps, Cameron:-)
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Thanks, Cameron...
I'll find a local rep or call them directly.
Jake

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Jake wrote:

I would propose to use a relatively simple system of acoustic navigation (using ultrasonic pulses), that should work properly in such condition, but probably must be developed (I do not think, that somebody offers it in a ready made form).
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Wieslaw Bicz

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