electronic measurement of distance of a rotating object within 3 meter 2

[earthzap]

I am working on a project that requires for me to measure electronically the distance(cm) of a rotating object. The full range needed is 3 meters maximum.
I was looking into infrared and ultra sonic but this will be effected by objects getting in the way.
Does anyone have a good solution for me?

 

[Higgler]

use doppler or RF maybe, add a sonic or RF generator somewhere on the rotating object, circuit card, small speaker/antenna. If the object is coming at you frequency increases. You could correlate the measured frequency with it's position.

If you could calibrate the item, you could do many rf or acoustic tricks, i.e. hand position the item, measure signals, reposition the item, measure again.

 

[VEBill]

This same sort of 'project' (ahem...) has come up on these forums many times before and many solutions have been proposed. It's almost as common a problem as measuring the depth of a liquid.

In this case, why not a vision system?

 

[earthzap]

say this project uses 6 points that i want to measure the distance between each one. Would the last 2 replys work?

 

[Higgler]

It's hard to predict the future.

Optical sounds good.
One of our programs used a high resolution Sony camera to view points in a moving item and as the points moved, the camera noted which pixel they moved to and did a recalibration based on location. your management can grasp that working easily, hence it's a good concept just based on marketing appeal.

costwise, it's mostly software to do the math on the points.
there's a time delay of course using a camera and doing the processing.
There are software programs out there that can show you the changes in pixels, i.e. subtract one scene from the next. It's used to detect intruders when they enter an area. So you may be able to use that and operate on their subtraction results.

are you adjusting something based on your measurements? Or just gathering data for later analysis?

kch

 

[earthzap]

i think you don't follow me.
The 6 objects are rotating. so light ans ultrasonic can't work.
is it possible to scan 6 different rf transmitters to measure their distance away from each other?

 

[earthzap]

i need to make cm measurements. similar to a gps but distance in cm.

 

[Higgler]

What physical accuracy is needed?

Don't plan on RF working, too much multipath and high cost.

If this is for an internal engine motion, that's way different than a conveyor belt. Hence, you give so little detail, it's like asking for someone to give you a car for an upcoming race and not saying if it's soap box derby or the Indy 500.

Acoustic transducers measure accuracy at 0.1% accuracy

http://www.senscomp.com/specs/X1_Ranging_Module_Pro_Specifications_Rev1.pdf

if that's good enough. But that's a transducer pointing at a reflecting object or wall and telling you the distance in the 0.5 to 20 feet range. If you could, set two on each moving item and make reflectors a certain distance away. If the 0.1% accuracy is ok, you can tell where each sensor is, then with calibration and math find their relative postions. You'd probably need wireless or slip rings to send the data out to a computer to get your results.

As mentioned earlier, everyone asks this question and no one gets a good easy just go buy this inexpensive chip answer. Acoustics are pretty inexpensive though.

kch

 

[biff44]

Sure, there are lots of ways of doing that. I have worked on a system that uses interferometry to measure distances to within a mm or so. About the only concern might be if the object were rotating very quickly and therefore imparting a dopler frequency shift in addition to its phase (position) information.

Rich

http://www.MaguffinMicrowave.com

Microwave and wireless design consulting