Sunday, October 21, 2012

Dealing with variation (have I used that title before?)

Back on October 7th I started to talk about the challenge of inspecting objects that vary in appearance. This was in reference to meat (“The intelligent bacon slicer”) but even stamped, cast, molded and machined parts have a habit of changing.

Now the normal, random, short-term variation you should take in to account when the system is first designed. But how about the unexpected shift that takes place when Purchasing switch you to a different coating supplier? Chances are, no one thinks to tell you there’s a change coming; you’re only the machine vision engineer after all. So the first you know is when you get a phone call to tell you all the parts are failing inspection.

First off, your troubleshooting skills are put to the test. This is where some initial setup images are so useful. Pull them out and compare them with the latest images. If you can run your software offline – in emulator mode perhaps – so much the better. That way you should see what’s gone wrong. But what do you do?

Personally, I like to rant at those who made the change – “throwing my toys out the pram,” my co-worker calls it – but then it’s time to make some changes.

Don’t tweak the lens. Once you start altering hardware you’ll never get it back to the original settings. And be careful about changing thresholds because what will you do when Purchasing switch back to the old supplier?

I suggest you create a new configuration – call it “Product 999-dark” and have the original be “Product 999-light”. Then, if you’re really clever, you’ll find some way for the system to determine which of these is in front of the camera and auto-select the right file.

This approach won’t get you out of every hole, but if it did what would I right about next? But I hope it stops from digging yourself in deeper.

As always, your comments are welcomed.

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