AutomationTechBrian
Lifetime Supporting Member
I was working at a customer's location yesterday and I came across an intermittent issue on their wind/unwind machine. I'm still trying to figure out what is causing it, but I thought I'd share a graphic for those who have a little experience with this application.
Hardware:
3, ABB ACS 800 drives with wind/unwind firmware... 2 unwind, 1 wind-up
1 Siemens HMI, with PLC program software (step 7)
Profibus Network, HMI to the 3 drives.
Fiber optic connection between the 3 drives.
Load cells, for tension control. Feedback to the 2 unwind drives.
Simple control system:
HMI is used for entering values, including tension set point and roll diameters.
Profibus feeds the values into the drives.
Application is run by the drives.
There is an intermittent issue, that is illustrated by the graph. The second line is the load cell feedback for the paper unwind roll. The other 3 lines are the torque feedback from the drives... 1. Paper, 3. Windup, 4. Poly
I did several studies on the signals using an analog data logger. This particular one captured the intermittent anomaly perfectly. You can see near the beginning, the torque for BOTH the paper and the windup roll increase at the same time the load cell drops. The situation remains unstable for a section of time, then it comes back into control about 3/4 the way through the cycle. You can see a decrease in torque in both rolls at the same time, then "normal" until the end.
I'm suspecting the feedback signal from the load cell is to blame, since the situation doesn't seem to affect the poly torque. I just don't know how to isolate the different aspects of the load cell signal yet to confirm my theory. I wish I could have a second device to confirm whether the tension really drops when the load cell signal drops.
Any thoughts would be appreciated. The customer wants us to update this machine, since the components are soon to be obsolete. I'm working on the learning curve right now as time allows.
Hardware:
3, ABB ACS 800 drives with wind/unwind firmware... 2 unwind, 1 wind-up
1 Siemens HMI, with PLC program software (step 7)
Profibus Network, HMI to the 3 drives.
Fiber optic connection between the 3 drives.
Load cells, for tension control. Feedback to the 2 unwind drives.
Simple control system:
HMI is used for entering values, including tension set point and roll diameters.
Profibus feeds the values into the drives.
Application is run by the drives.
There is an intermittent issue, that is illustrated by the graph. The second line is the load cell feedback for the paper unwind roll. The other 3 lines are the torque feedback from the drives... 1. Paper, 3. Windup, 4. Poly
I did several studies on the signals using an analog data logger. This particular one captured the intermittent anomaly perfectly. You can see near the beginning, the torque for BOTH the paper and the windup roll increase at the same time the load cell drops. The situation remains unstable for a section of time, then it comes back into control about 3/4 the way through the cycle. You can see a decrease in torque in both rolls at the same time, then "normal" until the end.
I'm suspecting the feedback signal from the load cell is to blame, since the situation doesn't seem to affect the poly torque. I just don't know how to isolate the different aspects of the load cell signal yet to confirm my theory. I wish I could have a second device to confirm whether the tension really drops when the load cell signal drops.
Any thoughts would be appreciated. The customer wants us to update this machine, since the components are soon to be obsolete. I'm working on the learning curve right now as time allows.
