In need of solution

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Aleman...yes it is variable tension o volts web spool spins freely 24V it is locked (synchronized with 1st spool). There are 2 spools that a a plastic film (stretch wrap((web)) is stretched between.
A motor directly drives spool 1 and the 2nd spool is connected with gears and the clutch I am talking about. so the 2nd spool sees the stretch wrap from the expendable roll and pulls it off the roll while the 1st spool pulls it off the 2nd roll and stretches it. How much it is stretched is dependant on the voltage (current) to the clutch.

one thing is for sure you cant have current without voltage and voltage without current. Meaning I don't know if its the voltage or current that is actually varied all i know is that at 24V it pulls .5A and 0V=0A If you had a power supply that could supply 2000000000000A at 24V I would think it would still draw .5A at 24V so to me its voltage controlled and current follows by ohms law. Of course you could look at it the other way and pose the same argument either way its all related through power. If I supply .5A @ 1V i don't know what it would do but my guess is it wouldn't be locked or fully engauged?

Power to me is most meaningful as long as you have one of the other components... maybe there is someone who has a simple example as to the difference of the way it can be controlled?
 
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151223-2204 EST

boptrop:

I will respond a little later. If your existing power supply can handle the clutch current, then it is usable. If this is manually controlled, then is it necessary to control the clutch thru the PLC?

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No I can use a POT or voltage divider....or what ever need not be through the PLC but needs to be accessible to operator.. PS can handle it.
 
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That part I posted would do the job. You need to deliver a higher current that is proportional to the 4-20, and that's pretty much what this part will do. The only
problem with it is the valve connector, but it could be jury rigged. The best thing about it is you can set the range. Look around, there should be other
parts out there that will do that job for you and maybe in a better package.
 
151223-2343 EST

boptrop:

Your very simplest solution is a potentiometer.

http://www.ohmite.com/cat/controls_rheostats.pdf
Page 189 Rheostats (potentiometers) 25 W 100 ohm. The current rating of a 25 W 100 ohm potentiometer is 0.5 A. A potentiometer is current limited rather than power. Wire temperature is the criteria.

To your load this will not produce a linear current change with knob rotation, but this may not be a problem. At a 50% position the equivalent circuit of the pot from 24 V is 12 V source with an internal resistance of 25 ohms. Thus, load current would be 12/73 = 0.16 A instead of a desired 0.25 A. At 75% rotation the current is 18/(18.75+48) = 0.27 A instead of 0.38 A.

The next simplest approach is a reversed biased diode across the clutch, and a bipolar power transistor operated as an emitter follower. Mosty a power transistor plus a higher resistance potentiometer than in the potentiometer only approach. Possibly a 5 k pot. The current will be more linear with pot rotation.

The more complex approach uses a LM 317 T adjustable voltage voltage regulator. Details can be provided if you don't like either of the above two methods.

Check my math on the potentiometer method.

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boptrop said:
A motor directly drives spool 1 and the 2nd spool is connected with gears and the clutch I am talking about. so the 2nd spool sees the stretch wrap from the expendable roll and pulls it off the roll while the 1st spool pulls it off the 2nd roll and stretches it. How much it is stretched is dependant on the voltage (current) to the clutch.
Click to expand...

My perceived operation of stretch wrappers with prestretch is different than yours. The prestretch is a constant percentage of the payout speed. The clutches on the machines I have worked on operate on full voltage. The web tension after the prestretch is monitored by what is in effect a dancing idler, and the payout motor drive is controlled by the dancing idler tension. On the machines I work with the payout motor is the item that needs the control. However this may not be how your machine functions.
 
151224-0927 EST

boptrop:

If you use a 100 ohm pot plus your 48 ohm clutch the maximum power supply load is (24^2/100) + (24^2/48) = 5.76 + 12 = 17.76 W.

Change the pot to 50 ohms at 25 W and the angular position linearity improves at the cost of an additional 5.76 W in the pot. Now the pot presents a continuous load of 11.52 W. So maximum power supply load is 11,52 + 12 = 23.52 W.

One of the Warner controls suggested by sii will probably work.

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Question: Presuming you are trouble shooting a tear out problem on your wrapper. Does it tear out inbeween your prestretch rolls or after? If it tears out after the prestretch area and then backwraps around the clutch driven roll then your payout motor is not operating correctly. If it tears out first in the prestretch area then you have a prestretch problem.


boptrop said:
can get a small one (din rail mount preferred).
Click to expand...


Here is a couple of din rail mounted controllers, if you have a prestretch problem.

http://www.wago.us/products/compone...ty-modules/proportional-valve-control-module/

http://www.pwmcontrols.com/dinrail.html
 
-Aleman, thanks for the reply, I will look for a part similar to your link, it does look like it will do what I want, If I cant find that I will Just use a
simple potentiometer as gar suggested.

I need to get this thing out of the door and am running out of time to do so. The co I worked for milled around with the rebuild for 3-4 months, guess they checked the price on a new one and pulled the trigger on the rebuild. Now they want it done yesterday. Typical lucky charm crap (it magically appears).

- sii, milldrone the dancer control is most likely is what was integrated into the OEM circuit board...of course that is gone now and I am trying to rebuilding from scratch. The operation of what that device does is most likely how this rotating platform wrapper use to work, it had a load cell connected to the final spool ect...however I don't have the time now to integrate that device so I am trying to keep it simple and get it out the door. The company I work for doesn't care about how much wrap they expend per palette so.... Thanks for that input. If I had more time I would definitely take a hard look at using it.

-milldrone, you may be correct in the operation of the wrapper that I have. I can only say what I observe and the operation of the machine described by their tec. support (which they are usually reluctant to talk about). They don't publish documentation of the operation so I cant refer to definitions so I may not be correct in words... Sometimes definitions get crossed unintentionally and i don't have a lot of experience with web machines. So you may be 100% correct. The unrolling process I described is what I observed and there is a load cell on the final "free" roller that certainly incorporates feed back to the OEM board for speed control of the un-roller motor, i suppose for different size loads on the pallet, corners of the load..ect. Support did say that the clutch is varied in voltage to vary the stretch of the web...the drawings state 0-250% clutch and the users manual says stretch of the film up to 250% so I believe it is a variable clutch and not fully locked all the time.
I am not sure that I even need to worry about it at all but am trying to make it some what of what it was.

The wrapper was 100% automatic in its OEM state now it will be more manual control. If I had the time I could make it fully automatic but Its not necessary.

This company has a wrapper that they built from a turntable with a tower and a simple film holder with a adjustable brake built in that is pulled up and down by a car winch & pulleys from Lowes or wherever, its medieval at best but it works. They use a foot pedal to run the turntable and a pendant to run the winch motor....so what what they will have with this rebuild will be much better than that!

FYI the reason the OEM board burned up is because the upper limit stop of the carriage tower was moved beyond it's range and the carriage ran up (carriage is driven by gear box and motor) to the point it jammed with the gearbox and wound up and stalled. Burned up the board & the carriage motor. Had the Mfg. integrated proper OL protection of the motor on the circuit board this post would probably not exist.

-gar, thanks for all your insightful input.

merry x-mas all
 
-milldrone

I haven't got to put the wrapper rebuild in service yet, Just got final parts for turntable rollers yesterday and didn't have time to install. Will do so Monday...so I don't know what it's going to do until then, only been able to test the program so far with out material on the turntable (turntable is not on machine).

The facility this machine came from tore it to pieces and the shipment to me created even more damage due to carelessness. Everything I have taken apart on this machine has been into by it's home plant maintenance and I have had to replace over $3K in damaged parts plus the rebuild of controls. I don't know what kind of maintenance people are at this other facility but in my opinion they are hacks at best.

Many of the components mechanical components were jury rigged together so it's not been the best of rebuilds for me.

Ill run it Monday and see how it does, and post how it behaves. I am going to run it with the clutch free wheeling..and try to dial it in what what I have.
 
Thanks,
for all the replies and input, put machine in service today with a potentiometer as suggested, pre-stretched film as needed. Everything worked out well. Should I have had enough time I would have integrated one of the other suggestions into the control setup. Running things with out the pot, Seemed to work just as well, could stretch film using film payout motor...heck I could stretch the film to 50% of it's original with w/o pot (guess the POT/clutch combo may save the drive motor).

Sometimes I wonder if all the technology is worth the hassle, for other than to say "look what I can do and how complicated I can make it" and then design a machine to measure it's performance. Put it on the market, invite others to beat it and mark it up to some ridiculous price. After all "Its the best in the world" for what it does.

Which isn't much :)

Thanks all, glad to know there are people on here other than NEC vultures!
 
There are no PLC analog voltage outputs that will give you 1/2 an amp anyway - mostly you will find they can supply no more than 20 or 30 mAmps.

0-24VDC is not a common analog voltage.

However, if you were to call your local hydraulic valve guy, he can probably get you an amplifier that can be tweaked to work the way you want with enough current to operate.

As long as the pot works I would not get real worried about it. A lot of these machines include features that are not used in every application because it is more cost effective to include them in all the machines made rather than trying to take it out where it might not be needed.

ETA: The warner electric units look like a closer fit though.
 
boptrop,

The only reason I can think of for having a prestretch is when you have light weight product that needs to be stretch wrapped. If you are wrapping rolls of building insulation you need it. If you are wrapping a pallet of 50 lb boxes of nails you don't need it. Light weight items tend to pull off the pallet when you apply enough tension to get good stretch.
 
mildrone---and that is the reason I needed a solution -needed a solutuion, the co I work for is a EPS company, raw bead, to out the door expanded product, building materials packing materials, ect.

What wrapping machines do you deal with?
 
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boptrop said:
What wrapping machines do you deal with?
Click to expand...

Antique lantech units, wrapping building insulation rolls. You mentioned up and down travel so I'm presuming you have 12" to 24" tall rolls of stretch film. This should help your dilemma. The stretch film we use is 60" tall, If we did not do prestretch it would pull the product over (no pallets).

I have also had some experience with a unit that used a brake only, no prestretch. If my presumption is right, I would think that a brake only approach would work for you.
 
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