Conveyor belt tension sensing!!!!

Hi all. On conveyor belts tail roller i have put a pick up flag with three points. An inductive sensor picks the pulses. In the l5k program its timed such that if the flag is missed for 3seconds an alarm is triggered for engineers to check. This does not stop the production line. My manager now whats more out of me. He want to check that the conveyor is of the right tension all the time. If the belt slacks alarm is generated. The plant has intralox belts conveying potatoes, which is slightly different. I am struggling to be clear cut on this any help will be appreciated.

Densam said:

Hi all. On conveyor belts tail roller i have put a pick up flag with three points. An inductive sensor picks the pulses. In the l5k program its timed such that if the flag is missed for 3seconds an alarm is triggered for engineers to check. This does not stop the production line. My manager now whats more out of me. He want to check that the conveyor is of the right tension all the time. If the belt slacks alarm is generated. The plant has intralox belts conveying potatoes, which is slightly different. I am struggling to be clear cut on this any help will be appreciated.

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I think you would only be able to detect belt slippage on the return idler, To detect belt tension you would need to be able to detect the belt sag between return rollers.

I can imagine like chelton that you would have to detect the tension on the rollers between pulley and idler at the ends.
One thing is that it will be expensive. Some kind of load cell arrangement.
Another thing is that it will be untrivial.
On the upper rollers, the tension will increase when there is load on the conveyor.
On the lower rollers, the tension will decrease when there is load on the conveyor.
So you would also have to sense the amount of material on the conveyor.
Your manager probably think there is a simple inexpensive switch or something.

The proper solution (IMHO) is to have a maintenance regimen where an experienced person checks the belts at regular intervals. As far as I have seen, belt conveyors are tricky and it is not merely a question of the right tension. Also wear, weld seam breakage, 'straightness' of the belt after welding, change in the stiffness from new to worn, proper centering of the material after each belt transition, deposit on the rollers, deposit on the belt, wear of the rollers, etc...
This is one of the situations where humans are still better than any sensor or automated system.

Thanks Chelton and JesperMP. Thats exactly what i told him, in short it will be expensive. The enviroment is wet potato peel on belts.

The Intralox belts I'm familiar with are driven by toothed sprockets. They would have to be pretty loose before they would 'slip' (jump a tooth).

Maybe you could monitor the slack underneath (the return section) for excessive droop?...



-Eric

Our conveyor belt systems have two ways of detecting a loose belt. One uses an idler mounted on a spring powered slide that stays fully compressed when belt tension is correct but will move a couple of inches if tension is released. The other one uses an air cylinder to do the same job as the spring. A small prox is opened after about .25" of movement.

Both of these are factory built and I'm sure wouldn't be cheap to implement.

Some belts are long they have iddler pulleys on weight for tensioning. Others are short. Can monitor the return loop. Thanks for the ideas i will put up a spread sheet with all the belts we have and sensing parts required for each particular belt. Get the cost sorted see what my manager thinks to that. Or just get to basics as we do our visual inspections every week, identify worn belts and replace. Even if all these sensing are in place we still have mantanance engineers doing ppms and visual inspections when lines are running.

If you are worried about slippage due to tension, you can monitor the speed of an idler roll and compare it to the speed of a driven roll. Expensive though.

I personally like belt tensioners. The kids out there might say "huh?", but many of us remember the good ole car days of pulling hard on the alternator while locking down the bolt to get good belt tension. If you look at how new cars get longer service intervals, I'll guarantee that the belt tensioners have a lot to due with the reduction in water pump and alternator failures. Anyway, with a tensioner, you can use a prox to know when the tensioner is stroked out too far.

....Or if you'd like to score some "Lean Manufacturing Points", install tensioners with some sort of mechanical indicators that show they are within or outside of the proper range - visual factory management. Of course that only works if some one actually looks at it AND doesn't just assume that some one else will take care of it.