1st to apologize if I am doing something wrong, I am a first timer to this site so I don't know no better. I have read some of the posts though and you guys seem pretty knowledgable.

I have a problem with a winding application. I am winding paper on a spindle. The paper is being fed to the spindle from another machine through a series of 'free' spinning rollers. The winding spindle/motor/drive is in "torque mode" where I am asking it for a certain torque or current. The problem comes when the incoming paper speed is increased/accelerating. From what I understand, the winding spindle can only accelerate so fast with a certain amount of torque. When the winding spindle is accelerating, this acceleration is taking some of the torque away from the winding tension, so the winding roll's tension is decreased during an acceleration. If the acceleration is great enough, the winding roll will lose all tension, causing the incoming paper before the spindle to drop or bag and continue to get worse as all torque is now accelerating but not accerlerating as fast as the incoming paper.

When the incoming paper speed does level out the winding roll is moving at such a high speed, by the time it winds the fallen paper back up, and this paper again becomes taught, it 'pops' the paper and if bad enough will break the paper. The loss of tension during acceleration is acceptible unless bagging and subsequent popping occurs. In theory one could increase the torque to account for acceleration and there would be no tension loss. This is a tricky game however as this introduced acceleration torque must be applied exactly in magnitude and timing and removed similarly or this acceleration torque if not applied correctly could allow some bagging only to rapidly accelerate the winding spindle and perhaps create worse of a pop then before, as well if the magnitude is great enough and not removed in time this torque could break the paper as well.

Controlling this loop seems impossible when thinking about delays in detecting the acceleration and delays in calculating/applying the compensation torque. Additionally as one can imagine, the smaller the diameter of the winding spindle the worse the situation gets. Previous designs with larger spindles have not been perfect with our acceleration rates but have been acceptible, it is this new attempt with smaller spindles in which this problem has grown to unacceptible levels. Is there something simple that I am overlooking or any other ideas that I should be trying to resolve or improve this scenerio? Any help or ideas that anyone can offer would be greatly appreciated. Thank you for your time.

 

Your control application could be greatly simplified by adding a dancer arm or a tension measuring roll. Then you could close the loop for dancer position or web tension. Is this an option?

Otherwise, you need a well synchronized drive system. I have used SSD drives for similar applications, they have a pretty nice set of tools to solve these kinds of applications.

Bill

 

You need an acceleration feedforward algorithm thst takes into account the diameter of the winnding roll. This value will be summed with the tension torque value. Modern controls can compute this so rapidly that the physical system will be the source of any limitation. It can be computed from the command values for the winding roll, not the measured values. If you are not fairly well versed in controls, you need to get the vendor or a system integrator involved. I am sure this problem has been solved many times in the paper industry. Do you know any peers doing similar work? If so, give them a call.

Good luck,
Tom Bullock

Thomas B. Bullock,
President Bull's Eye Research, Inc.
N7614 County Hwy. WH Fond du Lac, WI 54935
Tel: 920: 929-6544
Fax: 920: 929-9344
E-mail: [email protected]
www.bullseyenet.com

 

I don't know how your machine is set up as far as a DC or AC drive, but it sounds like you are attempting to do this application wrong. And yes I think there is something simple to fix this.

I would use a drive from www.ssddrives.com Parker/SSD Drive division. They have AC and DC drives that have precanned winder functions in them that are tested and tried. Look at the 890 or 690 for a AC model and the 590 for a DC model. I think one of the issues you have is that you need to give the upstream line speed to your winder drive, this acts a feedforward so you don't have delays in detecting acceleration changes. The way you state it you are relying on the torque loop to do two things, compensate for tension in steady state and compensate for tension because of line speed changes. So you could simplify it by doning a line speed + PID which takes care of the +/- your tension/torque trim. The other nice thing about the SSD Drives product is that it has precanned compensations for intertias, widths, diameters etc... which you mention is one of your issues as well. This type of system helps apply the proper torque when it is needed. Hope that helps. Let me know if you need more info.

Drive.Guy

 

Two loops, a "coarse" tension loop that is active when there is a droop. And your existing torque loop when the droop is corrected to a certain degree.

Regards
cww

 

I work in a printing plant where there is a lot of web control and I would add that even a lot of the very techy big name press and equipment companies buy specialized drives for this. It's sort of an art with considerable knowhow involved. I doubt that its because they don't have servo engineers that can do it, it's most likely that building it in the drive offers technical advantages like additional feedback terms and eliminates some variables. They tend to do this with registration as well, probably due to the speed needed to maintain <mm. registration at 2000 fpm. The non-integrated stuff tends to use 10 loop dancers, etc. to buy time. I'm frankly amazed at how well these servos work.

Regards
cww

 

I would recommend AMK drives. They have these winders/unwinders applications directly from the KU or KE/KW drives, with no PLC needed. I think is a very robust servo drive with good functionalities.

Regards