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The case of the unseeing eye

I was cogitating on my comfy couch when the phone jangled. Jeff was on the blower with a problem.

“I am using a photoeye to count rejected cartons and sometimes it works, sometimes it doesn’t. I have adjusted sensitivity all over the map and just can’t get it to detect reliably. Help me!”

Not long after, I was on Jeff’s line and he was showing me the problem.

“There are several inspection stations in the cartoner,” he explained. “Any problem cartons are blown into a reject chute with an air blast. A photoeye at the entrance to the chute is supposed to detect them and send a signal to a counter. Sometimes they fly right by the photoeye without triggering it.”

I could see the problem right off. “Fiddlesticks on blind photoeyes,” I told him. “You are using the wrong kind.”

He was using a diffuse sensing photoeye, which bounces a beam off the package. They work well when package is in a fairly repeatable position. Not so well otherwise.

“What is happening here,” I told Jeff, “is that the carton is being blown inconsistently across a gap. Sometimes closer to the eye, sometimes further. Carton orientation is inconsistent too. Change to a retro-reflective photoeye. That way the carton will always break the beam regardless of position.”

“Great idea, KC. That sounds like it will solve the problem.”

I may not be an optician but I always enjoy helping people see more clearly.

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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