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Old May 4th, 2014, 10:26 PM   #16
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OkiePC is offline
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I think using good winder control at the drive level is the way to go for you, but you should get a good handle on what is going on at the drive level and how it works, all the parameters involved, so you could in the future, use a generic drive and move more of the control to the PLC.

I have done winder control with a PLC for a line that had frequent stops and starts. The pure PID approach is not the best until your line speed is stable, and a PID is reactive, so I prefer to use line speed as the main source of the signal, and have some math to allow the calculated winder ratio to get the dancer under control when it is outside a deadband, and only let the PID have a small influence over the correction of the diameter calculation.

The dancer needs to have the most influence over drive speed when it is at the extremes, so it does not "top out" or "bottom out" after a stoppage and restart. At all times the inches per second of the winder is within known limits so just let the math make corrections to this magic ratio and multiple it by your line speed from the nip roller.

The main factor is the line speed, so when the line starts and stops, your dancer does not have to move to cause a PID to react and then cause motion, the winder will pick up where it left off with the known ratio.

The ratio is clamped between the known core size and max diameter, and allowed to "find" the actual diameter by adjusting the calculation to get the dancer error within a small deadband and letting the PID drive it slowly from there. Be sure to stop the PID when you stop the line too. This allows you to start a partial roll, for example, or use a larger core and still have good control until the math quickly catches up and the dancer moves right toward the target with very little overshoot.

You want the line speed as accurate as possible. In most really good slitters and winders, this is a quadrature pulse or a frequency connected from the nip or slitter drive to the winder drive and the drives have the smarts to make it a simple matter of entering parameters. This is the course you took, letting the drives do it, and the better performing machines I worked on were all done like that.
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Old May 5th, 2014, 07:31 AM   #17
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Some other thoughts..

An external ultrasonic diameter sensor can be helpful when starting a new roll to provide the initial starting diameter to the diameter calculator - especially if the starting roll diameters vary. Once the roll starts turning and the diameter calculator can kick in, the calculated diameter is the way to go and there is no purpose for the sensor.

As you have seen from other replies, there is a lot to consider when building the diameter calculator. Steady state is always the easiest. Making things work for the dynamic situations takes a lot of time, effort, and learning - but that's where the fun is.

Lastly, if this is a turret, you will want to consider that the effective "line speed" or "speed reference" for the winder changes while the turret is rotating (because the entire winding spindle is moving toward or away from the line). I have seen code that just turrets very slowly, freezes the diameter calculator, increases the trim limits, and lets the dancer control the winder speed, but that's really sloppy. For proper control, you should calculate the web speed created by the turret and add/subtract it from the line speed reference. (Quoting OkiePC - you want your line speed to be as accurate as possible)
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Old May 5th, 2014, 04:38 PM   #18
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I really appreciate all the helpful insight into the workings of how I can go about working on this project. I work for a relatively small company that likes to make our small engineer core do all sorts of projects. They do not like to sub out much of the work and that is why I have been tasked with writing the ladder logic and panelview programs for this double turret winder.

I have a feeling that this will be the start of many more projects on my plate since almost all of our equipment is AB based and we like to always expand on the capabilities of our equipment. So you guys have definitely given me some good things to think about as I move forward with this learning curve of understanding everything that goes into programming PLC's.

Thank you for the assistance
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Old June 10th, 2021, 07:15 PM   #19
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I just found this thread and am happy I did. I am new to programming and am working on a tension control project. We wrap tape around wire using a vfd and motor to basket and payoff the tape from inside holding torque to the tape web. Right outside the head the wire with the wrapped tape goes over a load cell.

Our issue we have is we used to start the machines very slowly and stop them the same. Now lean management control wants less scrap/ waste. So machines were increased for startup and accelerated shutdowns. Causing web breaks.

I understand the comment of monitoring linespeed and stopping and starting PID control. That's is what I need to figure out.

Right now we just look at the loadcell and determine if we are less than or greater than setpoint and adjust voltage going to the clutch by a very small step.

So really always chasing the setpoint... ah.

The want is to control the web tension on all steps of the process. Startup, steady state, and shutdown.

We were able to now bring in a pad diameter to the plc via a analog laser which will be helpful to diameter reading of web. Now its figuring all the other parts.

Thanks for posting. I am now going in a better direction. Still lost but hopefully can concur.
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