Control consistent speed for feeding machine - aluminium foil

[ilikbeer]

ck:

I work at a can manufacturing plant with the same issues you are probably dealing with. Our Uncoiler is hydraulic driven and then feeds into a Lubricator and then feeds into the Cupper. Before feeding into either of these machines there is "sag" in the material because of the constant speed changes as a result of downstream conditions. We are now achieving daily output of 3.2 million finished cans per day running 24/7. This is how we run our system and it may or may not help you depending our your setup. Our Cupper takes its speed command from how full the conveyance is that supplies the Bodymakers and this constantly changes due to machinery jamming one second and all running in high the next. The Bodymakers are also speed controlled depending our their downstream conditions.
We make steel cans but I do not believe that to make any difference in how you may want to run your loop control. Also the control is done by a TI 545 (can you say real PLC(a little bias there)) using the SFPGM (special function program) so you may have to modify it for your PLC.
The Cupper speed is fed back to the Lubricator through an analog output from the Cupper VFD to the Lubricator/Uncoiler PLC. There are three photo-eyes that detect the loop height between the Cupper and the Lubricator. Depending on the condition of these eyes there are different multipliers times the speed of the Cupper. Note: Because of the constant speed changes a PID LOOP was to erratic and this works very well.
WY213 = Lubricator speed; WX201 = Cupper speed
IF top eye and middle eye are blocked (slight debounce timers in these eyes) then
MATH WY213 := 0.937 * WX201 (This actually results in the Lubricator slightly overfeeding the Cupper)
IF all three eyes blocked then
MATH WY213 := 0.716 * WX201 (This is slightly under feeding the Cupper)
IF all three eyes ever become unblocked then
MATH WY213 := 1.1 * WX201
The Lubricator is ran off of a VFD and min/max are set-up for its gear ratio making for a well behaved loop.
Now to the Uncoiler feeding the Lubricator.
Here again we use a three eye system just like above plus some additional features. One is we use a Hyde Park ultra-sonic sensor to give us coil diameter. This signal is inverted and SCALED into "V1" with a low limit 8.25 and a high limit of 26.25 (radius of coil). Depending on speed of lubricator changes the value of "V3" you may have to figure what works for you. "V100 & V101" represent +900 and -400 depending on the condition of the eyes. The angular velocity of the Uncoiler is equal to the Lubricator speed divided by the radius of the coil(V1.), all multiplied by a constant.
MATH WY214 := WX201 * V3. * (0.03438 * V1 + 0.23683) / V1 + V100 + V101

As I mentioned somewhere clear back in chapter one, I think, our Uncoiler is hydraulic driven so the value of WY214 is only a 0-10VDC signal and the Vickers proportioning valve controlling the Uncoiler speed is 24VDC. To operate this correctly we send the value in WY214 to a Vickers controller that has tunable pots on it for response proportion and time. After all of this we really do end up with a very good loop.

Good luck and I hope this was of some help.

 

[msinclair]

With the caternary (loop) leading into your machine, the actual speed of the unwind (and consistency of it) should really be irrelevant. You basically want to feed enough material so that you have effectively "no tension" going into your machine.

If your caternary gets too big, the weight of the aluminum will create tension feeding into the machine. If the caternary disappears, the unwind will create tension feeding into the machine. Anything in between is probably fine.

So - I think the simplest solution is basically what ilikbeer recommends. In your case, using the analog distance signal in your picture: pick a High and Low threshold (loop depth), and pick three speeds that make sense for your machine. If too "high" (too short a loop), run at the fast speed (maybe 100%), if too "low" (too big a loop), run at the slow speed (maybe stopped?), if between the two, run at "standard" speed.

----------------------

If your machine performance is very sensitive to the weight in the caternary (I'd be surprised based on your drawing), you'll have to set your unwind target speed in a more sophisticated fashion (ie: well matched to your "machine" speed) to maintain a very consistent loop depth (like what Khalil and others have said). In this case, your existing sensor could become more of an alarm than a control device. That said, you could use this loop depth signal to trim the "linear speed" setpoint for the unwind, but you have to scale whatever speed setpoint you have based on diameter to get "spindle speed".

I get UW diameter in one of two ways - either with an ultrasonic sensor (as others have suggested) measuring the spindle diameter directly, OR with an encoder mounted on the unwind spindle (in a similar fashion to what Thomas Sullens and Khalil recommend). Many drives have this diameter calculation built in . . .


Also - if your machine runs "continuously", you'll need to answer some of the questions in other posts. How you splice will be important to define the "best" way.





Marc

 

[MicB]

Hi
You dont say the drive works Electric, Hydraulic etc. If Electric with a Variable speed drive you could try and use the torque setting instead of speed. Rather than vary the speed as the roll decreases. The torque is maintained to keep tension and all slack removed reguardless of diameter. You need to istall max speed limits otherwise if the foil breaks the motor will increase to that max speed trying to get the torque load up. This is how some tissue plants work. This also gets rid of the sensor looking at the diameter.
Cheers

 

[ilikbeer]

MicB,
If ckchew666's application is anything like the rest of what I have seen in my limited experience, he does not want tension. As msinclair stated

With the caternary (loop) leading into your machine, the actual speed of the unwind (and consistency of it) should really be irrelevant. You basically want to feed enough material so that you have effectively "no tension" going into your machine.

This is really not as complicated as my post may have sounded. It all depends how how nice you want your loop to look going into the lubricator and cupper. We try not to have any touch the floor support rails and never want it to got taught, so just a happy medium works great and holding the loop to about 6"-9" of sag variance works and looks very nice.

 

[ControlFreq]

As was stated before....if you want a constant inches per second IPS of feed, why not put a rotary wheel riding on the back side of the roll. Measure the IPS as you would with a tachometer with a wheel. Same process as with an encoder that referenced the surface. For a known daimeter on your encoder/tach, calculate the revolutions per minute times the change in time multiplied by the circumferance. All you want is the surface speed of the product. With an encoder riding on the foil, take the amount of clicks per scan, determine the time lapse of the scan. knowing the clicks per revolution and the size of wheel on the encoder, it's simple math.....now you know the IPS, feed it back to your drive. the drive would have the desired speed as a reference, and would follow that reference using the encoder/tach feedback.

 

[EOS]

Foil Feed

Hi Ilikbeer,
Perhaps this is a bit simplistic, but if you say all that you are after is a minimum sag and a maximum of not touching the floor.
Then loose the analogue input, and just use two sensors to control the foil feed motor.
Drive motor to bottom sensor, stop motor and dont drive again until it sees the minimum sag sensor. OK it may require a slight delay to stop bounce but you can refine it, but its independent of the machine and coil size.
Again you may need a coil low warning, or foil end but this could be a simple mechanical rod microswitch resting on the foil.

Regards, Gene.

 

[ilikbeer]

Hi there Gene,

Yes, I am sure there are a lot of very good ways to achieve this goal. I was only relaying what we do here at the facility where I am employed. This is a very good looking system loop but was not my doing. I wish I could take credit for this program, but it was prior to me and it works. I did make a few changes when we added a second line but that was only due to not being able to match the new with the old and my extreme lack of experience.

That is what I really appreciate about this forum. So many different ideas, suggestions, comments and the knowledge base on here is staggering. For an individual such as myself to be able to contribute any information is a priveledge.