Re: Constant tension winder control

Ok, so what your really saying is that my hydro bill will remain constant for the winder, correct.

Paul,

There are a couple of different ways you can implement the controls.

I have seen Eurotherm drives on extruders that essentially counted the number of revs, assumed a nominal product thickness and then calculated the roll diameter. This application was a little different because the machine did have a dancer roller but needed to know where to start the drive after a product break or EStop.

If you are using an AC inverter then I'll assume that you are doing something more than just frequency control - something like vector voltage or vector current. If this is the case then the motor will need an encoder. Now all you need to do is install an encoder on the dancer roller and the ratio of the two speeds gives you roll radius. You will need a drive that can be programmed or set up in some way. Lenze and SEW are two options that I know of. AFAIK, both have winder applications that are pre-written, you just set a couple of options and parameters (roll core size and one or two other things).

You can use load cells. The issue is how much you are prepared to modify your winders. Encoders can be fitted by simply boring the correct diameter hole in the shaft. Load cells generally replace one or more of the bearing supports - which is more work, you decide.

Regards Steve B.

Paul,

Actually this does all make sense. If your motor runs at constant power, tension * linear speed = torque * RPM = volts * amps = power (All in consistent units, of course.) Controlling at constant power means that if the linear speed is higher, then the tension must go down. this will tend to self correct. A VFD may even have a constant power option. If not, it may have a 4-20 mA output proportional to actual power that you send to a controller.

Walter.

I definately cannot go with your suggestion as we wind several different gage products and each winds differently so doing roll diameter calculations will not work each wind would need a different calculation constant, I definately want to stay away from dancers and do not want to slave the winder to another drive like the extruder drive or final puller.I must stress that I cannot have the operators programming drives for specific applications, sometimes we will run 4-5 different parts in 24 hours and as many may predict, the operators are not that skilled. In an extruded sheet application your setups would work well but not in an application such as I have described. If you read back a few posts you will see that the load cell will be the tension feedback devise, this tension feedback would be run through a conditioner to convert it to a useable signal, 0-5VDC, 4-20Ma. Now I have a signal which is directly proportional to tension, this signal I would then feed into a process controller (temperature controller) and we would tune the signal through a PID loop for the process, this would make the signal more usable, then send the signal to a standard AC inverter(nothing special, no tach). As far as the load cell goes, I was thinking now (after some feedback from this group) that the whole winder head could be mounted on rubber mounts over a base frame, these rubber mounts can be pretty solid, then I would sandwich the load cell so that the cell takes load between the base frame and the rubber mounted winder head when there is tension.Since the load cell does not require a large deflection I think this would be sufficient.

"Stephen Bettesworth" wrote in message news: snipped-for-privacy@win.co.nz...

Don't get me wrong here I am not trying to put anyone down or their ideasI am just trying to come up with an idea that is simple and straight forward. I have seen too often control system which have been vastly over engineered, costly, problematic and eventually are tossed due to their complexity. My brother and myself have owned and operated a few companies and our theory is keep it simple. I have seen process controls do things in the past which have impressed me not because of the job they do but how simple they are. I am presently working with SEW on a drive application which I am dealing with two engineers and what started out as a simple drive setup is now a complex over engineered (in my mind) setup. I sit back and wonder why it got so complicated and the only answers I have is that the company is doing this to cover their asses, they know that the drive setup will work however at a price of 4-5 thousand too much. Our simple idea which my engineers and myself think will work they will not stand behind, so if we go with it we are on our own. Our winders are at present simple DC drives running on a simple pot, open loop, they work, we have used them for over ten years but I want to improve on them, make them more consistant, shooting ideas back and forth is always my first step to implementing a trial control system.

calculations

Won't work. You are sharing the load between the rubber mounts and the cell. I don't know how wide the winder rolls are but the point the 'tension' is applied will move from side to side trying to skew the whole winder making the proportion applied to the cell even less predictable.

On top of that as the roll size increases the leverage the 'tension' applies to the frame increases or decreases (depending on if you are under or over winding).

Just a step back for a quick reality check are you certain you even want constant tension? Are you trying to get good wind quality or is it something in the manufacturing process where constant tension on the product helps?

I ask because in many winder applications tension is deliberately reduced as the roll size increases. Systems with dancer controlled tension go to the trouble of measuring roll diameter and reducing the dancer force in proportion. Constant tension winding results in ever increasing crushing forces on the material already wound and increased leverage from the increasing roll size tends to make roll wind up internally possibly deforming it and scuffing and damaging the product.

Paul,

Let me throw another spanner in the works. If we take SEW (or Lenze - the only two I know well enough) then you get some really nifty features for not much more than you would spend on a VFD. For starters you will need a motor, if you are switching from DC to AC then you will need at least a new motor. If you match inverter to motor you will get really tight integration, the vendor knows their motors better than anyone else, so they know their motor models better than anyone else. If you run the drive in torque control mode, it will control the torque very precisely. To do this it needs an encoder - supplied with the motor (I am assuming vector control).

Now the drive can tell precisely where the rotor is so that it can feed just the correct amount of current or voltage to give you the torque you asked for and its essentially closed loop. An added bonus is that the encoder will also give you speed, again very accurately.

If you add another encoder on the film then you can do two things:

1. Accurately determine roll diameter - ratio of speeds.
2. More easily start and thread the machine. You can match the roll speed to the film or sheet until the drive makes a certain torque value and then switch to torque control. If the film should break, you can limit the speed of the drive; the roll should never be running faster than the sheet if you are in torque control mode.

I don't quite see how you will do all of the above with a single loop controller.

Regards Steve B.

PS: If you are considering using load cells then check out BLH. They have some very good application notes on CD-ROM that they give away free. They have special loadcells for web tension application. Check out

I am wondering, could there be a drive manufacturer that has an AC inverter with a torque taper function such as my DC drive I am using on one of my winders. It is basically open loop and has a circuit board with two trim pots, one for current limit and one for taper. It works by tapering the speed to torque thus as the speed decreases the torque increases and does not a bad job. I would just love to have this function in an ac drive. SEW says they can do it but they want to program a drive for it and says it will only work for one product then you would have to switch to another program, I can just see this winder with ten thousand dollars worth of drive and PLC, not!

I can't resist any longer ... here's my hat in the ring ...

Some of the better AC drives have this very function or a variant of it. Wind/unwind applications are a standard part of the armoury of drives engineers.

I hesitate to recommend particular hardware, but here goes, these guys (from my UK perspective) can definitely give you something that might work to your requirement (in no particular ranking order):

Lenze

Control Techniques

ABB, especially the ACS600 or ACS800 range

Siemens, and in this particular application the Micromaster 440 would be a good bet.

Rockwell (Allen Bradley), probably a PowerFlex 70 or 700, perhaps even a

700S if what you want is *really* clever.

Hi guys! I'm back!.. I think. (I'll see how long my ISP's news server holds up this time.. :-( )

I would like to put my support behind everything Dave has said (below):

You will need some sort of vector drive (either a VVVF or sensorless vector). The ABB ACS600 has an option module available that can do this sort of thing off-the-shelf and if you want fancier features, the AB PowerFlex drives coupled with a ControlLogix PLC make a powerful combination. I have used both for automated cranes (aircraft parts) and for sheet metal press feeder control (making roof purlins).

I too would recommend leaving load cells on the suppliers' shelf and rely on rotary encoders and distance measurement to get the feedback you need.

Talk to your local ABB Drives rep.

Cameron:-)

Paul,

If the motor/winder assembly is allowed to move freely over a very small range with the axis of motion parallel to the incoming string, a single load cell at the 'push' end of travel will give an accurate tension reading. If this parallel motion cannot be achieved, three load cells in a triangle against which the carriage can push will give the correct reading when averaged out. These averaging arrangements are very common. That is how one weighs a vessel.

There is no 'load sharing' with the rubber mounts. Force is transmitted from the carriage to the cell to the rubber bumper and to the fixed end stop.

end stop | rubber bumper () load cell []

Paul:

I worked for a firm in which I designed a number of lines just as you are talking about. In a similar application I used a Eurotherm model

605C AC Drive. This drive is called a "smart" drive. This means that you have quite a bit of programmable functionality in the drive itself.

To make the unit work as you say, you can set the drive to run in a forward direction and hook a trim pot into the analog input to the drive. You can then link this analog input to a current control function block in which you will adjust the torque of the drive to a constant tension.

First you will start the winder and adjust the torque input to the desired operational level. This will maintain a constant tension on the cable. You then start your production line or whatever payoff method you are using. The takeup or winder will then begin operation and wind the product at a constant tension. Note that there is no dancer feedback in this type of system. 300 feet per minute is easily achievable in this type of system (I have ran this type of product in this type of application at around 450ft. per minute).

For constant wind torque as the reel fills up you can utilize an ultrasonic sensor that senses the level of the wind as it fills up. You can utilize this as another analog input into the Eurotherm drive and trim the torque as the reel fills (however, based on my experience, this may not be needed.)

THe Eurotherm drive costs about $1000 and will have all of the logic you will need to program the system, and it will work. I can also look through my files to see if I have a sample program that I can email to you.

Jeff snipped-for-privacy@ix.netcom.com

Paul:

I worked for a firm in which I designed a number of lines just as you are talking about. In a similar application I used a Eurotherm model

605C AC Drive. This drive is called a "smart" drive. This means that you have quite a bit of programmable functionality in the drive itself.

To make the unit work as you say, you can set the drive to run in a forward direction and hook a trim pot into the analog input to the drive. You can then link this analog input to a current control function block in which you will adjust the torque of the drive to a constant tension.

First you will start the winder and adjust the torque input to the desired operational level. This will maintain a constant tension on the cable. You then start your production line or whatever payoff method you are using. The takeup or winder will then begin operation and wind the product at a constant tension. Note that there is no dancer feedback in this type of system. 300 feet per minute is easily achievable in this type of system (I have ran this type of product in this type of application at around 450ft. per minute).

For constant wind torque as the reel fills up you can utilize an ultrasonic sensor that senses the level of the wind as it fills up. You can utilize this as another analog input into the Eurotherm drive and trim the torque as the reel fills (however, based on my experience, this may not be needed.)

THe Eurotherm drive costs about $1000 and will have all of the logic you will need to program the system, and it will work. I can also look through my files to see if I have a sample program that I can email to you.

Jeff snipped-for-privacy@ix.netcom.com

n Wed, 09 Jul 2003 08:19:19 +1200, Stephen Bettesworth wrote:

Someone is missing the point. The question was how to get a method of tension cotnrol WITHOUT pots.

The challenge is to maintain constant tension, NOT torque. Is it necessry to explain that they are not the same?

The reel does not fill evenly.

Life would be a lot simpler if we mesured tension and controlled the motor accordingly. That is the parameter of interest. All other variables are indirect and require compensations that add complexity without adding accurcy or reliability. If the objective is to maintain constant tension then we measure tension, not torque, not RPM, not reel diameter, not motor power, not anything else.

Walter.

Yes, the trim pot is just for setting the level of the torque (or current) in the drive. The drive itself will maintain a set torque throughout the wind process. When you access the Euortherm site, download the free copy of the CElite programing software. In the software there are several Macro templates you can use as a starting point. Within the software you will find a function block called "Motor Current" This is normall set to a percentage of max, but you have the option of connection of a link to set the max current. You could then use another "Value" function to scale your input Analog signal and then link this scaled input to the current block. You would then just program the drive to run at a set speed (100% of max) and start the drive. Adjust the trim pot so that the drive will start and "stall" when you have no cable comming into the winder. The trim pot can be adjusted to set the tension you are looking to maintain.

Regarding the taper function, I have tried working with this type of function and have found that the best way to maintain constant wind torque as the reel fills is to use an ultrasonic sensor to measure the cable as it is filling up. You could then run this ultrasonic input (0-10volts or 5-20mA) as a second analog signal into a math function in the Eurotherm and gradually increase the torque as the reel fills up.

i.e. (Analog_1 x scaling factor) + (Analog_2 x calibration factor) = Motor current in %of max

Scaling factor is just that, the calibration factor is to normalize the ultrasonic sensor at an empty reel.

The speed of the drive should be the max speed you will expect to run, remember that the speed will actually be controlled by the tension input and not the set speed.

Remember keep it simple. Email me if you have any questions. I will check my file and see if I have a sample of an old torque control drive program.

snipped-for-privacy@ix.netcom.com

Jeff

Number 1: Well, if you do not want a trim pot, use the HMI function and put the input as a value. In my experience, I have not found a good quality trim pot that failed in this type of application.

Number 2: The point is to maintain constant wind torque as the reel fills. If you read the earlier comment, adjust the current to the drive and run at max speed. The dirve will "stall" when the torque on the cable is reached as set by the trim pot. To maintain the torque on the cable throughout the wind, add a calibrated input value from an ultrasonic sensor.

PS, I have done this with everything from optical fiber to armored building wire.

jeff