Sunday, January 23, 2011

When good vision systems go bad

Plant Managers seem to loathe machine vision, and with good cause. They’re supposed to prevent problems but some days it can seem like they’re making things worse rather than better. Instead of finding defects and catching incorrect assemblies all they want to do is reject product that conforms to the standards. Or worse still, and often it takes a customer complaint to point this out, they just quietly go to sleep, allowing everything, both good and bad, to be shipped.

So what’s the answer? Well I know some Plant Managers who’ve thrown out machine vision systems; they’d rather use physical error-proofing and human inspection than rely on lighting, sensors and software, and I can see their point. Wouldn’t it be better though to engineer robustness into the shop floor vision systems, and at the same time, teach people how to carry out effective vision troubleshooting?

Of course it would, and for that reason I will be returning to both those ideas in coming blog posts. But to get the ball rolling, let me refer you to “
Troubleshooting Vision Systems,” written by John Sprovieri and published in the January 2011 edition of Assembly Magazine.

This article, based largely around comments from Mr. Steve Maves of PPT Vision, discusses what should be done when “a system starts missing defects or signaling false positive,” and as such I think it’s a great start point for anyone involved in machine vision maintenance. To give you a little taster, and as encouragement to read the article, some of the ideas covered are:

  • Consider casting shadows as a way of checking feature presence. (While this is more about lighting design than troubleshooting, I think it’s a great idea as it may be possible to get better contrast from a shadow.)
  • Watch out for variation in the parts being inspected.
  • Put the camera in an enclosure.
  • Be aware that light intensity can change over time.

But those are the good points. I’m of the opinion that the article also contains a few less good points

What are they? Well you’ll have to check back for them.

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