The case of the crazy case

By KC Boxbottom in Coding on December 20, 2011

“KC,” she exclaimed, “my codes are wandering all over my case.”

I wrestled myself out of my comfy chair, pulled on my seven league boots and was on my way.

When I got there, Sue showed me the problem. She was using an inkjet to print bar codes and other information on the side of a shipper case and the printing wandered forward and backwards. The operators kept fiddling with the trigger photoeye trying to compensate. As usual, this only made the problem worse.

As soon as I got my eye on the problem, I saw that their eye was the problem.

“Fiddlesticks on adjusting the photoeye,” I told her. “You have the wrong one. Change it any your problems will disappear.

“Your photoeye is retroreflective bouncing a beam of light back and forth across the conveyor. These are fine for many applications but not this one. If the case is not perfectly straight on the conveyor, or if the case itself is not perfectly square, the far corner will break the beam. When this happens, the printer will start printing early and your code will be out of position.

“A proximity sensing convergent beam photoeye is what you need. It can be set to trigger off the near corner of the case regardless of what the back corner is doing.”

I do a bit of wandering myself but your codes never should. You need to make them stay in their place.


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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Boom shakalaka boom boom, polrbem solved.
Or instead of aligning the photoeye and receptor perpendicular to the case, set it up at a slight angle so that the proper case corner is the first thing to break the beam. Then a slight misalignment on the conveyor or off-square box won’t be as big of a problem. No new sensor needed.