Precise Distance Sensor - Arduino?

[John Saunders]

I am trying to build a system to measure the height of various objects.  The objects will be on a rotating platform (e.g. lazy susan).   The heights will range from 0.5" to 3" so ideally it would be a non-physical way to measure their height - e.g. mount a distance sensor over the platform that measures the height as each object is passed under.   

The problem I'm running into is precision.  It would need to be accurate to ideally +/- 15 thousands of an inch (~1/64th). I may be able to make something less accurate work by using multiple sensors.    The problem thus far is the various ping/sonar/distance sensors I've seen on adafruit, sparkfun, trossen, etc are all far less precise; they seem to only measure to about 3/8" of an inch.

Any ideas or recommendations? 

[Ted Hayes | Limina.Studio]

Do you know for sure what kind of material(s) the object(s) will consist of?  Sounds like you're going to need a laser-based system.

—t3db0t

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[Luke Schantz]

Maxbotixs has 1mm resolution ....... but that is not the thousands of an inch you are looking for.  http://www.maxbotix.com/Ultrasonic_Sensors.htm

[jpbar...@aol.com]

I would think you could achieve some reasonable resolution with a Sharp LED triangulation sensor (~$15.00).

They come in various ranges and I recall a model having a range of about 0.5" to 4".  The lower the range the better the resolution you should get.  I think they have a non-linear (inverse distance function) analog output you could linearize with a micro.

There are some high end laser triangulation sensors on the market, ie Keyence, but they could be a few hundred $.

If you have a good amount of time to put into the project I can envision a fun endeavor of employing a rotating prism or mirror to scan a laser beam from the top to bottom range of the object and using timing of the beam blockage or reflection synchronous to the mirror rotation.  Maybe you can repurpose the guts of a laser printer.

[Tikka308]

Material will be metal - probably brass. 

The maxbotix.com sensors with 1mm are interesting except the minimum distance to the object of 30cm (~12") isn't ideal.  If it were half that, maybe.

The Keyence look VERY interesting - thanks for throwing that name out there.  I see there's a youtube video of one being used on an Arduino, so I'll dig in.

Price isn't a huge concern - if it does what I want, I wouldn't have a problem with it costing $200.

[Paul Strohmeier]

Can you control the lighting?

Is the material and surface of the items you are measuring constant?
If it is you could possibly use this guy: https://www.sparkfun.com/products/8959

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