Olin Lathrop wrote:

>Vasile Surducan wrote:
>
>
>>The problem which requires to be solved its a small distance
>>measurement at high speed (about 15cm/second) in a high EM radiation
>>environement (near a few KW generated from 300KHz inductors). The
>>medium distance to be measured is about 2mm, between a a metal
>>surface which have inflexions (it's not a plane surface) and a moving
>>tool. The metal surface is painted, dirty and gruffly, where the
>>paint+dirt have a variable thickness.
>>The generators can't be shutted off while the measurement is
>>performed.
>>I will be glad to hear any possible ideea from specialists (or just
>>thinkers) from these lists.
>>
>>
>
>How about shining a thin light beam at an angle and using parallax from
>another sensor to measure distance?
>
>
>

At Edmund Scientific (somewhat expensive, but they have a bit of
everything) they have laser beams and special heads that split the light
spot into a line. You can put a camera in front of the tool, and the
laser at, say, 45 degrees, but with the light line aligned along the
tool. The image is going to be a vertical line while the laser is on the
tool and a diagonal line when the laser shines on the surface of the
metal. The pixel of this line that is aligned to the first segment (from
the tool) is right beneath the tool, so the distance can be calibrated
and then measured.

According to the camera lenses, this measurement can be made through a
relatively long distance, trying to avoid all that EM fields, or at
least you can build an enclosure for the camera.

The camera resolution and the thickness of the laser line will give you
the accuracy of the system. You will need fast electronic shutter,
though, and a good quality frame grabber

Hope this helps
Francisco

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