AutomationTechBrian
Lifetime Supporting Member
I'm doing my first wind/unwind project, and I need some input from someone with more experience. ...I'm getting my butt kicked trying to control it.
It's a simple wind/unwind laminating machine. One winder, two unwinders. The drives have firmware for the application. I thought that would be the safe bet, since I was updating the machine with the the same brand drives as it had, with the most recent model and the latest application firmware.
It's the unwind drives that are giving me problems. The old drives had a control loop based on torque, so that is what I expected in the new model. There is a load cell on each unwind roll web. You enter the setpoint for the web tension, and the feedback comes from the load cell. The drive also keeps track of the roll dimension to use in calculations. After setting up the application with the manual (and sometimes wanting more detail about the parameters) I was unable to get the control loop to control the negative torque at all to match the tension setpoint. After several frustrating days I got some help from the local distributor and manufacturer. In turn, they got the applications tech desk involved. I went through everything with them and shared my parameter files. They couldn't get it to work, either. The application firmware was just not controlling the torque at all. The application guys admitted they didn't have experience with that particular firmware and said they needed to consult with specialists later in the day/evening.
After a conference call with a wind/unwind application specialist they got back in touch with me and said we needed to change the control mode to "speed", not torque. I knew that was an option, but it didn't seed as solid as torque. We made the parameter changes and the control loop started to work. Then, it was obvious that I needed to focus on the PID, since the tension control trend was ugly.
After a couple of frustrating days working on the gain and integral, I started to see a pattern. When the rolls were full, I had a decent amount of control... not perfect, but promising. But once the rolls got small, and the RPMs high, (line speed is kept constant), the control fell completely apart. Someone mentioned to me that torque was the better control method for wind/unwind, and it got me wondering if I'm headed toward a dead-end trying to get this machine working.
Tomorrow, I'll head back to try again, and I'm thinking about changing my strategy from proving it can be done, to proving it *can't* be done. I just need some thoughts from someone with more experience.
I always like throwing a picture in, so here's a visual for you. You can see the two loops, paper and poly. The tension feedback for each roll is there, along with the setpoint. You can also see the ramp and the speed of the winder in red. Can't remember what the Magenta line was, though. You can see how the control fell apart towards the end.
Any thoughts are appreciated.
It's a simple wind/unwind laminating machine. One winder, two unwinders. The drives have firmware for the application. I thought that would be the safe bet, since I was updating the machine with the the same brand drives as it had, with the most recent model and the latest application firmware.
It's the unwind drives that are giving me problems. The old drives had a control loop based on torque, so that is what I expected in the new model. There is a load cell on each unwind roll web. You enter the setpoint for the web tension, and the feedback comes from the load cell. The drive also keeps track of the roll dimension to use in calculations. After setting up the application with the manual (and sometimes wanting more detail about the parameters) I was unable to get the control loop to control the negative torque at all to match the tension setpoint. After several frustrating days I got some help from the local distributor and manufacturer. In turn, they got the applications tech desk involved. I went through everything with them and shared my parameter files. They couldn't get it to work, either. The application firmware was just not controlling the torque at all. The application guys admitted they didn't have experience with that particular firmware and said they needed to consult with specialists later in the day/evening.
After a conference call with a wind/unwind application specialist they got back in touch with me and said we needed to change the control mode to "speed", not torque. I knew that was an option, but it didn't seed as solid as torque. We made the parameter changes and the control loop started to work. Then, it was obvious that I needed to focus on the PID, since the tension control trend was ugly.
After a couple of frustrating days working on the gain and integral, I started to see a pattern. When the rolls were full, I had a decent amount of control... not perfect, but promising. But once the rolls got small, and the RPMs high, (line speed is kept constant), the control fell completely apart. Someone mentioned to me that torque was the better control method for wind/unwind, and it got me wondering if I'm headed toward a dead-end trying to get this machine working.
Tomorrow, I'll head back to try again, and I'm thinking about changing my strategy from proving it can be done, to proving it *can't* be done. I just need some thoughts from someone with more experience.
I always like throwing a picture in, so here's a visual for you. You can see the two loops, paper and poly. The tension feedback for each roll is there, along with the setpoint. You can also see the ramp and the speed of the winder in red. Can't remember what the Magenta line was, though. You can see how the control fell apart towards the end.
Any thoughts are appreciated.