Hi all, I have to program a machine with an unwinder and a winder. Currently I have 3 VFD Powerflex 527. I need your experience about this topic. Currently I am having trouble with the unwinder because I do not have a sensor to read the diameter of the roll so I do not know how can I program the close loop to increase the speed in accordance to the diameter of the roll. As you know when the material's roll is full the unwinder goes slow and when the roll becomes to a core measure the speed becomes faster. The linear speed to feed the material has to be constant in meter per minute. Do someone has an idea about how can I fixed? Best Regards
Unwinder
- Thread starter ELGC
- Start date
Hello ELGC.
First question: Is there a PLC controlling this? If so, what IO/fieldbuses do you have?
If you really want to "Close the loop", you would need a sensor to accurately tell the diameter of the remaining spool. Another thing you can do is to try and use either a formula over time/# of rotations, or make a lookup table of diameter-vs-desired speed-vs-time, and do a linear interpolation of this every time you need to do a speed adjustment(this can be done every few seconds or something like that, or even faster for lower RPMs).
I'm going to try and derive a formula for this, it's been some time since I've done this, but maybe, just maybe, I wouldn't need to call my PhD student friends or google it
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drbitboy
Lifetime Supporting Member
As PreLC asked, what measurements do you have? And at what resolution? And to what accuracy?
Specifically, do you have an accumulating length measurement, or a line speed measurement that could be used to model an accumulation? And do you have an encoder on the unwinder, even one pulse per revolution might be enough? If you have both, then you can have the PLC model both diameter and material thickness on the fly; if you have only one or the other, then you may have to assume a constant thickness, perhaps entered via operator recipe.
What is the ultimate goal? That is, what parameter are you trying to ultimately control (e.g. linear speed or tension of a web), and what can you directly control (e.g. speed or torque of the motor(s?) driven by the 527s)? What is outside your control?
Specifically, do you have an accumulating length measurement, or a line speed measurement that could be used to model an accumulation? And do you have an encoder on the unwinder, even one pulse per revolution might be enough? If you have both, then you can have the PLC model both diameter and material thickness on the fly; if you have only one or the other, then you may have to assume a constant thickness, perhaps entered via operator recipe.
What is the ultimate goal? That is, what parameter are you trying to ultimately control (e.g. linear speed or tension of a web), and what can you directly control (e.g. speed or torque of the motor(s?) driven by the 527s)? What is outside your control?
Steve Bailey
Lifetime Supporting Member + Moderator
Instead of a diameter sensor, if you know the line speed, you can calculate diameter by tracking the time for on one rotation of the unwinder or rewinder chuck. It is probably easier to install a proximity or photoelectric sensor to give you a pulse each rotation. Line speed divided by rotation time equals roll circumference. Divide that by PI for diameter.
Answer to PreLC
Hi PreLC,
I am using an AB PLC it is the L33ERMS and I only have 2 I/O card one for inputs one for outputs both digital. I have 3 VFD, one for the unwinder, 1 for a slitter and the last one is used in the winder. Currently with the powerflex 527 you can program it with motion comands.
Today I'm going to try to develop a table diameter vs desired speed vs time.
If you have another idea please tell me.
Best regards
Hi PreLC,
I am using an AB PLC it is the L33ERMS and I only have 2 I/O card one for inputs one for outputs both digital. I have 3 VFD, one for the unwinder, 1 for a slitter and the last one is used in the winder. Currently with the powerflex 527 you can program it with motion comands.
Today I'm going to try to develop a table diameter vs desired speed vs time.
If you have another idea please tell me.
Best regards
Hello ELGC.
First question: Is there a PLC controlling this? If so, what IO/fieldbuses do you have?
If you really want to "Close the loop", you would need a sensor to accurately tell the diameter of the remaining spool. Another thing you can do is to try and use either a formula over time/# of rotations, or make a lookup table of diameter-vs-desired speed-vs-time, and do a linear interpolation of this every time you need to do a speed adjustment(this can be done every few seconds or something like that, or even faster for lower RPMs).
I'm going to try and derive a formula for this, it's been some time since I've done this, but maybe, just maybe, I wouldn't need to call my PhD student friends or google it
Answer to Drbitboy
Hello Drbitboy,
Answering to your questions, I have the diameter of the core and the diameter of the initial roll (full and empty). I have the line speed.
I do not have an accumulating length measurement but I know the line speed. I do not have an encoder but I have a sensor in the winder pulley so I can calculate the line speed.
About the thickness of the material it is constant.
I am trying to control the linear speed of the unwinder. Currently to control the VFD 527 you can use motion commands.
Best regards
ELGC
Hello Drbitboy,
Answering to your questions, I have the diameter of the core and the diameter of the initial roll (full and empty). I have the line speed.
I do not have an accumulating length measurement but I know the line speed. I do not have an encoder but I have a sensor in the winder pulley so I can calculate the line speed.
About the thickness of the material it is constant.
I am trying to control the linear speed of the unwinder. Currently to control the VFD 527 you can use motion commands.
Best regards
ELGC
This could be accomplished in a lot of ways. It entirely depends on how your system is set up to run mechanically.
If this uncoiler has a loop of material that droops towards the floor before going into a straightener, then you could bypass any need to account for how thick the roll is and just go off of how high or low the drooping material is after the uncoiler.
we've accomplished this either by using photo sensors, ultrasonic sensors, and even mechanically with "dancer arms" on potentiometers directly connected to VFD inputs for speed variation and just allowed the system to run at X speed based on how much material needed to be fed out. This required a bit of fine tuning initially due to line speeds varying and uncoiler mechanics limiting how fast you can accel and decel. but once tuned, it never mattered how much material was left, the uncoiler would start and stop more often with lots of material as it didn't need to feed as much. and as it got lower and had to spin more, it would just tend to not stop as much and speed up as the coil got tighter feeding in.
you could attempt to try to match the speed perfectly, but it almost seems not worth the effort when most places i've seen just go off of these types of systems when it's not critical to have a precise amount of material coming off the uncoilers.
If this uncoiler has a loop of material that droops towards the floor before going into a straightener, then you could bypass any need to account for how thick the roll is and just go off of how high or low the drooping material is after the uncoiler.
we've accomplished this either by using photo sensors, ultrasonic sensors, and even mechanically with "dancer arms" on potentiometers directly connected to VFD inputs for speed variation and just allowed the system to run at X speed based on how much material needed to be fed out. This required a bit of fine tuning initially due to line speeds varying and uncoiler mechanics limiting how fast you can accel and decel. but once tuned, it never mattered how much material was left, the uncoiler would start and stop more often with lots of material as it didn't need to feed as much. and as it got lower and had to spin more, it would just tend to not stop as much and speed up as the coil got tighter feeding in.
you could attempt to try to match the speed perfectly, but it almost seems not worth the effort when most places i've seen just go off of these types of systems when it's not critical to have a precise amount of material coming off the uncoilers.
Hi Ian,
Currently I do not have a "dancer arm" in my system.
How can i fixed with a photo sensor? Currently I do not have space to add an analog input card to add a sensor to measure the diameter.
What to you recommend to me to fix it?
Best regards
ELGC
Currently I do not have a "dancer arm" in my system.
How can i fixed with a photo sensor? Currently I do not have space to add an analog input card to add a sensor to measure the diameter.
What to you recommend to me to fix it?
Best regards
ELGC
you're going to need to figure out first what you have available to use, what you can get to use. In addition to that, you'll need to know how the system needs to operate (does it need to keep the uncoiling material tight, or does it form a loop, etc).
you don't necessarily need to have an analog card added if all you are doing is sending a scaled 0-10v signal to a drive input, you just won't have as much control because it won't be going through any other logic.
a lot of variables seem unanswered here.
There are a lot of sensors to choose from that you can set the min/max distance to give you a scaled 0-10v or 4-20ma signal out depending on the position of the coil. and those can be wired directly to a drive, or a hydraulic servo valve, etc. That's the simplest of operations, but that depends on how much control you need in your system
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Hi,
The machine is like this.... I have an spindle on the left that is the one to unwind material, the next step is a slitter (blades) to cut material and the 3rd step is the winder to wind the material that was cutted before in independent rolls. At the begging I have a cylinder of the material with a width of 2 meters and the goal is to have different rolls with a with of 15 to 20 centimeters.
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