Recently I performed a drive audit on a line. I found that the slitting tension zone had a load cell tension regulator tuned for a Bandwidth (BW) of 0.5 radians/second. That is a time constant of 2 seconds. A tension disturbance will be settled out in 8 seconds.
Right next to the slitting zone (on the same line) was a calendering zone with a load cell tension regulator. This was tuned with a BW of 0.001 radians/second. This regulator would calm down a tension disturbance in 4000 SECONDS (66 minutes). In that time, this line produces 50 rolls.
Something is wrong and we don’t know what. Is the calender tuned correctly and the slitting section wildly over-tuned? Is the slitter tuned correctly and the calender far too slow? Are both sections far too slow?
Years ago, a major paper slitter/winder vendor scolded me, indicating the drive supplier I worked for was always “far too aggressive” in tuning their precious equipment.
Many times I have been chided by operators because the slow tension regulator was giving “bad starts”.
Note that most drive suppliers and many equipment suppliers have internal specifications for tuning drives for specific applications. They may tune all sections the same as the slowest section, all as fast as they can be, duplicate a previous contract or use some other guidance.
In order to bring some sanity to this situation, we need metrics. It is difficult to get these metrics because the tuning parameters are proprietary. It may be no one has measured the values. It may just be that no one knows.
I have been on my knees begging you readers that tuning information on some real-world lines be made available. I promised to collate the information and present it through AIMCAL and other web handling forums. No response.
Tuning theory is in every textbook, in drive setup manuals and all over the web. Just because you don’t know how your lines are tuned, doesn’t make that information proprietary.