long range, rugged position transducer

[jabbey]

I have an application that requires accurate, reliable and continuous position feedback, in one dimension, range up to 30 meters. I need the sensor to give me absolute distance from a base point to the target. It's also going to be outdoors and in a high traffic area, so it'll definitely get dirty, oily, bumped, lots of electrical noise etc... Laser seems to be about the only thing I can find that might work to that range, but I doubt I can keep it aligned and clean very long. I'm wondering about gps, or a local position system (I've heard about them for keeping track of items/people in a large plant), but can't seem to find anything off the shelf for that purpose. Anyone have any suggestions?

 

[nbucska]

Please give NUMBERS: What kind of accuracy and measuring speed do you need? How many degrees of freedom of motion ?
<nbucska@pcperipherals.com>

 

[jabbey]

I'm not sure on the numbers yet, I'm still very early in the design process, just trying to figure out if it can be done and how. But for an early guess...
accuracy: probably within an inch
speed: several times a second, maybe ~10? Faster is better, within reason(and cost)
motion: will be mostly on one vertical axis, call it z, but there will likely be some swing in the x and y directions. I only care about z, but the sensor still has to give me that measurement if the target moves slighty in the x and y

 

[nbucska]

Your device will move on the ground or rails (it wont fly )
-- why not measure the wheels rotation and calibrate it
with a position sensor e.g. at home position ? <nbucska@pcperipherals.com>

 

[IRstuff]

A GPS with differential capability will easily meet the requirements. Mostly, they're for surveying work, so you might want to start there. If you couple the DGPS with a small inertial nav, it should be good enough to spit out better that 1 Hz data rates.

TTFN

 

[jabbey]

unfortunately my target is suspended from a pulley system. an encoder or proxsensor solution on one of the pulleys or takeup drum is an option, but because of varying cable stretch and other unknowns an absolute position at any given time will be uncertain. I can't really have anything around the target as it moves up and down, so a home position reading will be hard to get.

 

[nbucska]

If it is suspended I don't think you can get 1&quot; accuracy ! <nbucska@pcperipherals.com>

 

[automatic2]

How about a sonor system. The units I've used were typically close range (~ 12') but they worked excellent in harsh enviroments.

 

[IRstuff]

There are some tracking theodolites available. Given the short range involved, an angular accuracy 2 arcsec of the theodolite will get an error of less than 0.1&quot;

TTFN