Sunday, December 2, 2012

Vision system maintenance

Electronic devices are pretty reliable, so once your vision system is installed you can leave it alone until a program change is needed, right?

Now that you’ve finished laughing, let me explain where I got that idea. “The Many Faces of Machine Vision Maintenance”, written by Winn Hardin and posted on the AIA website November 27th, 2012, quotes a number of very knowledge vision experts on the subject of maintenance. Now maybe this is a result of the editing process, I don’t know, but everyone who contributed seems to have overlooked a major maintenance issue.

It’s been my experience that image quality can deteriorate quite quickly – certainly in months and often in weeks. And as you know, if the image changes, the vision tools won’t find features in quite the same locations and the system will give different results.

So why does the image change? Here’s a short checklist:

  • Reduced intensity or contrast in the image
Lights get dirty, output drops off with age (yes even with LED’s,) and lenses gather dust.

  • Noise or clutter in the background
Coatings wear, surfaces gather dust, scratches and marks accumulate over time

  • Position/part presentation variation
Tooling wears

  • Upstream process changes
Cleaning water becomes contaminated leading to staining, coatings change in reflectivity

I could go on, but you’re probably bored already.

So what’s to be done? My advice, besides doing regular cleaning, is to save some master images from when the system was first installed. Make sure you can load these in to some kind of emulator where grayscale values can be extracted. Then, if you find false reject rates are rising, do a quick comparison of a recent image with the old master. I’ll wager my lunch you’ll find the image is different.

Vision system maintenance – you know it makes sense.

1 comment:

Brian Durand said...

As one of the guys quoted in the article, I agree that vision system maintenance makes sense, and is a wise investment.

When I was interviewed by Winn Hardin, I had a particular customer site in mind. We’ve installed 16 systems at one plant for this Fortune 100 manufacturer. We’re in the second year of a maintenance contract with this plant, and are on site one day each month to inspect equipment and provide additional training.

Our site visits are uneventful. In fact, quite boring. What do we see go wrong? Small things. Number one problem? Camera trigger sensors drift out of adjustment.

Why does this company contract mine to have us on site so frequently? Because these systems are critical to their production, and with our help their system utilization stays at about 100%.

Despite the boredom, I love visiting this customer. I often come away with new ideas on how to make our systems even more reliable. Relationships like this are truly good for all involved.