roll centering

I would like to keep my paper centered as it is pulled off the parent roll for use. Parent roll runs front to back of the machine. Line runs left to right of the machine. Because of this setup we need to make adjustments to keep paper from coming off bars at times.

I would like to know if anyone has experience or can offer advice for using a linear type devive that would move in and out based on the output of a type of sensor telling it to do so depending on the paper placement. It would not have to move very fast at all, as the paper drifts slowly.

I may have to repeat this several times so budget is of concern.

Thanks again

Web centering

I've done this a couple of ways. A company called Fife makes a web guide system that I've recently used. It works pretty well, but it was for a higher end system so budget wasn't one of the concern items.

I've also done this with a lower budget system several years ago. We had some photoeyes on one edge of the rolls - say three, one for centered, one for too far left and one for too far right. A roller at this point in the process could be shifted left or right from straight line (slightly) by a couple of solenoids and an air cylinder.

When the PLC sensed the web at the right edge we shift the roll to move it back towards the center. When we cross the center edge we straighten the roll. When we sense the web at the left edge we move the web in the other direction. The web was lycra, and the system worked pretty well. We were, however, moving at a fairly low speed (about 100 fpm) and didn't need that precise of centering control.

Ken Schunk

Unless:

A) You already have a plc and available I/O
and
B) There is no money value to your time

I would stick with the web guide manufacturers. Fife was already mentioned. Accuweb, Erhardt+Leimer and BST Promark are just a few others. These systems come pre-engineered with all the parts you need. They do look expensive until you add up all the components you would need to buy and then add in your engineering time.

Take a look here for some ideas:
http://www.fife.com/fife_webguiding.asp

If your guiding precision isn't important and all you need to do is keep the material on your rollers Ken's idea looks pretty good. But be VERY careful if your web sensors are a long way from your guide actuator. Take a look at this thread:
http://www.plctalk.net/qanda/showthread.php?t=27396&page=1&pp=15
It's a little specific to that application but some good things are discussed.

Keith