In
the ideal world I’d use a linescan camera to inspect a beer can or
jar of pickles. That way there’d be no distortion in my high-res
image. The problem with this approach though is that it means
rotating said can or jar. It’s a problem easily solved with money,
but that’s always in short supply.
The
approach many integrators take is to use a number of matrix cameras
to image the cylindrical surface. Usually, as in this
system
developed by UK integrator Adbro
Controls,
that number is four.
To
my way of thinking, that means a lot of distortion out on the
periphery of the image. And that problem becomes worse when a short
focal length lens is used, as is the case here.
Had
I developed the system you’d have seen at least five cameras
viewing the OD, each with a long working distance and long focal
length lens. Of course, that would make the inspection system much
bigger, unless you could come up with a clever way of folding the
lightpath, but I have my ways.
In
addition to reducing distortion, this would have solved the problem
of each light shining directly into the camera opposite. Now in the
story, (which I lifted from the most excellent Vision Systems Design
magazine,) we’re told each camera is “equipped with a polarizing
filter to ensure that light emanating from white light LEDs will not
saturate the imager in the camera directly opposite it.”
Say
what?
Now
if the light is polarized there might be some benefit in using a
polarizing filter, but if all they’re trying to do is reduce
intensity there are other ways of achieving that result. Like a
neutral density filter.
Or
am I missing something? Please let me know.
2 comments:
Use direction of polarization to filter out unwanted light?
No idea how well it works, but in theory..
I'd assume they put filters after the LEDs in one orientation and rotated by 90 degrees in front of the camera. Then direct light is completely filtered, but reflected light is not.
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