Question about PID control of drum RPM using load cell

[Elijah Charles]

Hi all,

I have a brief question concerning a project where I am using the v130 vision controller and a load cell to control the RPM of a drum that makes rolls of paper. I am attempting to do this using PID control where my load cell provides the process value while the drum is running (I have to keep a certain tension (# of lbs) --my set point-- on the paper as it is pulled off of a line and rolled onto the drum). Can I get my PID to speed up or slow down the drum RPM in order to maintain my desired tension? In my attached program my PID function is under the subroutine "PID Control"

much thanks in advance for any help

Paper Roller Inclinometer Project.vlp

[Ausman]

How is the load cell set up?  PID might not be best for this at all.

cheers, Aus

[Elijah Charles]

Ausman,

Thank you for responding. The load cell is attached to/supports a roller that the paper is pulled over as it moves through the line and just before it gets rolled onto the drum. I attached a crude illustration to help with my explanation.

[kratmel]

Why load cell is used?

In typical cases this task looks like a winder.
For its implementation, a dancer is used.
Contact or contactless potentiometers are used to determine its position.
This analog signal about the position of the dancer is used for the PID control. 

[Simon]

I expect the loadcell is used to measure the tension of the web.

I would have some concerns over the V130 PID being fast enough to control this loop.  Happy to have those concerns overturned by the experience of others though 🙂

[Ausman]

I wasn't going to chime in yet, but Simon has triggered me!  Showing my age but in the old days we did it with what was colloquially called a wig-wag, and is still done in a lot of situations.  I think the name came from old style railway crossing signals, and is the same principle.  Pretty much a speed pot linked to an idler arm that was effectively Kratmel's "Dancer".  (The funny names that all appear for the same things!)  It was either sprung, or Gravity based which was the better system as it never breaks or gets turned off.

That is why I was saying is PID really necessary?  Correctly set up, they were stable and consistent.  The KISS principle in action, instead of tech for tech's sake.

cheers, Aus