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
- Position/part presentation variation
- Upstream process changes
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.
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1 comment:
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.
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