The case of the drifty dots

By KC Boxbottom in Coding on July 24, 2011

I was chilling with a hot cup of coffee when the call came: “KC, my dots are not matrixing! They’re all over the place and the inkjet code is a mess. Get over here pronto.”

My first reaction was to have them reset the system or call the vendor but that only works when the problem is consistent and theirs wasn’t. Mostly it was fine but would then go haywire for a bit.

Intermittent problems are hardest because they never seem to happen when you’re looking. They look random but seldom are. It requires some serious cogitation to figure out what’s going on.

When I got eyeballs on the system it was printing a nice legible code. First appearances can be deceiving and I knew that if I watched long enough I would see something interesting.

Sure enough, after about 20 minutes, we got a series of about 50 bottles in a row with illegible printing. After that, normal.

“Fiddlesticks on printer problems,” I told the superintendent. “The printer is fine but it’s next to the warehouse door. Each time the door opens, the air curtain blows on the printhead. As the ink droplets cross the gap between printhead and bottle, the air knocks them silly. When the curtain stops, the droplets fly normally. This may be a hard problem to troubleshoot but an easy one to fix. A baffle around the printhead will prevent the air from blowing on it.”

Now, back to that coffee…


KC Boxbottom, packaging detective, is on the case to solve tough packaging puzzles. He is the alter-ego of John Henry, CPP. Known as the Changeover Wizard, Henry is the owner of, a consulting firm that helps companies find and fix the causes of inefficiencies in their packaging operations. He produces a free monthly newsletter called Lean Changeover, which contains articles and tips on changeover and related issues. Reach him at [email protected].


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Here is a similar event you should know about. We put a vision system into a plant to read barcodes on packages and direct them to a loading dock based on the code. The system worked flawless for about 9 months when we received a call stating the system does not work from 2 PM to about 3:15PM. We thought about it and said hey do you have a skylight nearby? Sure enough well how about a light blocking baffle?
A hidden mystery solved: I had a sticky banner in one of my 8 feet wide Roland printers every time the production hits about 2 hours running. It was a mess. Printer’s head problem? a $3000 US per head fixed, Plate’s heat problem? a $2500 US labor and material. Finally I fixed this problem with $4.00 US. The friction of the PVC banner material between heads and heat plate was creating static after 2 hours of continued production. I went to my local grocery store and I bought a $4.00 box of anti-static papers, the same one your wife uses in your wash and dry machine every weekend. I cleaned the hit plate several times and the static was gone. I had to repeat this operation twice a day, but I’ve saved a lot of money doing it. It was my wife’s solution and it worked.
I met a phone repairman once who’d had to troubleshoot a phone that would ring mysteriously at 3AM. Turned out that was when the furnace came on and would warm up an abraded phone wire in the basement just enough for it to elongate, sag, and short out against a plumbing pipe. (Exactly how a short produced a ring I don’t know.)
Thanks for the comments. It is nice to see that KC is not alone out there. Sometimes we think problems are unique and then we find that they are not. Always good to know. John Henry A/K/A KC Boxbottom
Yup, that shuold defo do the trick!