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Optical - servo alignment or "registration"

For a number of purposes (eg. registration of printing) it's useful to be able to servo a X-Y-theta platform to center multiple markings of some kind in an couple of arbitrary areas viewed by a digital camera or cameras-- in the printing case, we'd want to align a substrate (perhaps with previous impressions already having been made) with the printing screen, stencil or plates.

What's available off the shelf for that sort of thing? I must not be using the correct search terms- I'm not finding much. This should be a fairly standard building block for motion control systems.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany
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The only time I ran into that problem was for the Cambridge Instruments electron beam microfabricator, where we had to image the semiconductor surface to find and locate reference marks (usually evaporated gold crosses) to sub-micron accuracy before we could start writing the next layer of lithography.

The programmer responsible for that job didn't find it too difficult - as far as I known they didn't bother talkig to the image analysis programmers who looked after the Cambridge Instruments image analysis products (which came from Metals Research who had taken over Cambridge Instruments some ten years earlier before going bust a few years later).

-- Bill Sloman, Nijmegen

Reply to
bill.sloman

Growing up in the digital age, I always assumed that real world systems did this kind of thing by connecting a 2d camera to a computer, and then "thinking" about the picture.

Then I learned that so many inherit from older ideas - often 1d sensors, setups designed to give basically binary contrast (or peak searches to do that), triangular masks over photocells, position sensitive devices, etc...

What I'm trying to say is that there's the fancy "imaging processing" solution, and then there are the simple ones that find a single mark and calculate a deviation and go from there. Similarly, there are software solutions to the noise problem and there are use a really bright light and lots of flat non-reflective shields type ones.

Probably comes down to which is more fun / cost effective - building physical apparatus or writing software.

Reply to
cs_posting

There was a project yet to be completed, using a imaging system which also included depth. It did focus on points. Software was written for this. The part not completed was the 6 axis servo system moving a persons body to keep a PET scan in line.......

greg

Reply to
GregS

This company should be able to help since they have built small positioner tables almost since I was a kid:

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Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

Perhaps the word you're looking for is "fiducial".

Cheers, John

Reply to
John KD5YI

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