MaintDude

Need Help - Change sensor to accurately detect box jams

6 posts in this topic

Hi guys....first post here. It's been about 6 years since I worked heavily with PLC's and automation, but I'm getting back into it. I was hoping you might be able to help me with an issue I've noticed at work. 


Problem: 

The sensor we use just reads if there's something there, or not. A make or break if you will. When boxes are pushed together and there is no gap between them it thinks there's a jam (after 6 seconds) even when the boxes are moving past (as they should).  A jam stops the conveyor belt requiring someone to physically move the boxes to clear the sensor and restart the equipment.  

I'm trying to find a sensor that will see the distance changes from box to box (mounted on the side of the conveyor). Only when there is a true jam and the distance isn't changing will it send a jam signal. 


I've tried researching sensors and have been overwhelmed by the endless possibilities and combinations (not all of which I understand). 

We are currently using an Allen-Bradley 42EF-P2RJB-A2H

It would be ideal to have a similar style plug, but it isn't a deal breaker. 


Here's an idea of what I'm dealing with. (The actual conveyor the jams are occurring on is a decline belt, not a roller accumulator.) There are varying box sixes, but they are all packed together. Creating a gap between boxes or using metering belt is not an option here.

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Thank you for any help/guidance you can offer!

-Steve

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Are the roller conveyors powered? If so, you can flip the rubber bands around so the rollers role backwards, creating a mini gap. Then mount your sensor right at that gap.

 

We have used vision before to detect different box sizes and thus know if the box doesn't change in a certain period of time.

 

We have also used a spring loaded brush to create a gap. 

 

I think you need to figure out a way to create a gap, or use multiple sensors. Saying if a box passed this sensor, but the next sensor downstream isn't on, then there is a jam.

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You must create a gap or put in a sensor that will detect a gap (very unlikely) or use a smart sensor.  A gap separator may be the easiest and most robust solution, but will eat into your available conveyor space.

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Is the belt a motorized belt?
Does it stop moving when there is a real jam or continues sliding under the boxes?
Maybe you can monitor the belt's speed to help you decide when you have a real jam.

Another idea (in case you must create a gap): Every next belt should move faster than its predecessor.
 

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Creating a gap between the boxes is the best option, but if you want to try a distance sensor, we've used these in the past:

873M-D18AI800-D4 (ultrasonic, we've used the discrete version since we're just detecting the presence/absence of an object)

45BPD-8LTB1-D5 (visible laser, several options in this series for min/max range)

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If you move to a distance sensor, you will have to have an analog input to read it in.  You could use a few non-contact optical limits set at different distances to detect if things are moving, but if you should happen to get multiple boxes riding one side of the conveyor, you may get a false jam signal.  If you want a single sensor that can do either, look into the IFM O1D laser sensors, they can be used as a discrete programmable distance sensor, or you can use the analog signal to get actual distance from the sensor face.

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