Are you using Siemens' Winder and Tension library as part of your system?

https://support.industry.siemens.com/cs/document/58565043

You might want to do a search of these forums for that same library to see what Product Conference seems to find the best answers for situations closest to your own.  It might be the SINAMICS general conference would be better - if you are using Siemens SINAMICS drives.

AutoGen_5045471

I am running a Tension control application on my machine. The machine has an unwinder a winder an LTC and a leading axis. The web goes from unwind axis to an LTC axis then the leading axis and then the winder.

In one mode the web needs to be synchronized with the web of another machine. I am doing this by:

1. I have an external encoder that provides encoder signals from the lead axis of the other machine
2. I have gear locked this external encoder to the leading axis of my machine. 
   

When I run tension control in the gear locked mode, I see a lot of vibration on the web. But without the gear-locked mode, the Tension Control unit seems to be ok.

I checked the variable gasWinderDiag.sActLineAxisMotionVector.r64LineSpeed and in gear-lock mode this value seems to be oscillating and my assumption is that this oscillation is causing the vibrations, so my question i:

1. Do I need to do some smoothening in the external encoder values?
   
2. Is my approach correct. or gear-lock mode should I directly define my external encoder as a leading axis and my current lead axis as another LTC axis?
   

Depending on the type of encoder, how much backlash and mechanical "slop" between encoder and physical load (gearing / linkages / motor shaft / gearbox and so on), you may need or want a variety of filtering capability.

If the tension control application / library has an "auto-tuning" option, I recommend using that for each operational mode, saving each operational mode to a unique instance-DB (along with appropriate logic - and maybe even a "transition" instance DB for each type of transition) to help make bump-less transitions between modes).

If there is no auto-tune capability, are you savvy enough (with available people and online information) to create and integrate that capability yourself?

All that said, you may be able to simply insert a simple filter in between the encoder signal and whatever uses the encoder feedback, and adjust the tuning until the vibration is gone while in Tension control (with that encoder).

Siemens has a library, LGF, Library of General Functions, which has filter blocks available.

If the vibration is detectable via PLC software from an existing external device (like small current, speed, torque, tension, accelerometer, etc), you may be able to make an "adaptive" filter.

If so, it could work something like this:

1. If starting up, retrieve saved filter setting closest to current control configuration settings.  If no settings are available, start with a small but non-zero filter time - maybe T#0.1 for S7-1200, or T#0.01 for S7-1500.
2. Small filter input adjustment is made (Save adjustment amount)
3. System waits - for as long it takes until the overall system is stable (you can probably hard-code this value from experience at this point)
4. Evaluates vibration signal.
   1. If vibration increased, make (-2 x Last Adjustment) to go other direction.  Go to 2.0
   2. If vibration decreased but not enough, make (Last Adjustment amount again).  Go to 2.0
   3. If vibration decreased to within tolerance, save current filter setting and current configuration settings that affect filtering requirements. Go to 2.0

Hopefully that gives you an idea on how to go about manually and/or adaptively tuning.  Of course for adaptive tuning, you need some max and min values for filtering to prevent instability or to let people know something is physically wrong - before something breaks.

Adding a 30 second filter for example masks the problem to the point where things can run-away without anything slowing it down fast enough.

If you are very control theory savvy, ignore most of everything I've said and post what you really do!   

AutoGen_5045471

I am running a Tension control application on my machine. The machine has an unwinder a winder an LTC and a leading axis. The web goes from unwind axis to an LTC axis then the leading axis and then the winder.

In one mode the web needs to be synchronized with the web of another machine. I am doing this by:

1. I have an external encoder that provides encoder signals from the lead axis of the other machine
2. I have gear locked this external encoder to the leading axis of my machine. 
   

When I run tension control in the gear locked mode, I see a lot of vibration on the web. But without the gear-locked mode, the Tension Control unit seems to be ok.

I checked the variable gasWinderDiag.sActLineAxisMotionVector.r64LineSpeed and in gear-lock mode this value seems to be oscillating and my assumption is that this oscillation is causing the vibrations, so my question i:

1. Do I need to do some smoothening in the external encoder values?
   
2. Is my approach correct. or gear-lock mode should I directly define my external encoder as a leading axis and my current lead axis as another LTC axis?