Shaw130

New user! Semi green programmer

6 posts in this topic

Hello, I was hoping by joining this site that I could get the chance to talk to a couple of much smarter more experienced individuals. Currently I am trying to figure out a way to track a spool of material as it unwinds, I’d have it display a warning when it gets low , and stop further processes when empty. This would be easy if the spool would be a consistent size, but that’s where I’m having issues. I was initially thinking of using a laser sensor but I’m not sure that would work since of the differences in size. If you have any tips or ideas I’d love to hear them thank you!

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There are thread detection or presence limit switches with microswitches on the market.  Set up so that the lever makes the switch true or on.  When the thread is gone, then trigger a stop.

Look at Cherry Limit switches by ZF, probably roller lever arm style

Edited by pcmccartney1
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Thank you I will look into this!

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Spool of material, different diameter spools, but the spool mandrel should be same/similar?  If that is the case, no matter what spool diameter is run, the stop point will be the same.

If stop the process before the spool runs out, will this create scrap?  How quick must the spool detection system react?  Some processes want to utilize as much materials as possible, so triggering to stop with material left on the spool is not acceptable.

If you use a non-contact sensor, such as a laser sensor, keep in mind the vision sensor may behave differently for different materials.  

How should the system be stopped for low/empty spool?  Some processes cannot be emergency-stopped - a graceful shutdown command may be needed.

Once you know the proper shutdown method (E-stop or graceful stop), pull out the machine system electrical drawings and get an understanding of what is the new "spool low/empty" stop command to do?  Drop out the E-stop circuit (to issue an immediate stop such as depressing an E-STOP button) or trigger a graceful stop (such as pressing the red STOP button).

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Where I've used this in the past was for unwinding and rewinding from spool to spool.  In my case the microswitch served two purposes.  It was a "thread break detection" and served to initiate a controlled stop.  Servo driven on both ends and I had an external encoder that coordinated both servos along with a dancer to coordinate the speed of each servo.  The switch was located about a meter downstream and the thread was routed through a series of ceramic rollers so the position of the thread was always known.  I didn't need to know diameter of either the unwind or rewind spools.  The external encoder gave me length of product and when I reached the "order" amount and did a controlled stop.  That being said, I also knew how fast the machine was running in feet per min and was able to calculate a dynamic value for necessary decel for each servo when the machine needed to slow or stop quickly upon thread break detection.

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Our roll winder process uses a mathematical formula called the Pulley Calculation to measure the diameter of our rolls. If you know the speed and diameter of another roller, and the speed at which your spool is turning, you can calculate the diameter of the spool on the fly. We use it to trigger an alarm if the roll gets too big for our machine to handle and it works really well for that. I've also seen this same calculation in the code on our raw material unwinder which sounds like it works exactly like your spool but this was originally intended to be used for an auto-splice mechanism that never really worked so that chunk of code isn't really used for anything.

Here's a link that explains the formula

And a calculator that might help visualize the concept.

The LR-T series all-purpose laser sensors manufactured by Keyence can also be used to measure roll diameter according to our local sales rep but I can't really vouch for that since we couldn't see a way to justify the cost instead of sticking with our existing method. 

Edited by kcox1980
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