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The case of the loose line speed
I was at the donut shop when Francisco sat down with his sinkers and joe. After the howdies, he told me his problem.
“KC, I can’t keep my packaging line balanced,” he confided. “We documented the optimum speed settings in the setup SOP. They should be stable but whenever I look the conveyor is running a different speed even though the control is set correctly. It’s making me crazy.”
“Tell you what”, I said. “When we finish here, we’ll go watch your team set up the line”
I hung about while the operators set up. I watched them set the conveyor speed to 65 as the SOP called for. So far, so good.
Then they started the line. After a few minutes, the mechanic decided that the conveyor looked a bit slow so he cranked the speed up. Then, he loosened the knob on the speed control and reset it to show 65 as required by the SOP.
“Fiddlesticks on speed variation!” I told Francisco. “Your team is gaming the system. Single-turn speed controls are imprecise at best. If you are going to use them, you need to add a tachometer to indicate actual conveyor speed and set the control by that. Better yet, use a controller with tachometer feedback.”
My buddy Dan Pollock says that “Conveyors are intelligent bridges between islands of automation.” He’s right. They must be treated with the same respect as every other machine in the line.