Machine gluer on a roll.

HI there,

It has been a while i've program a AB Motion control.
I have a servo that is coupled to a roll 1:1 that has "A" horizontal heat bar. The roll circumference is about 36".

When my material flow through this roll, it will heat up the plastic and cut it at 36".

I would like to have two functions which i would like to get an opinion on:

1. I want to allow the user to be able to "fast-forward, or retard" during this process, so that they can get the position aligned during running in. What method would i use to advance/retard the roll momentarily while they are holding a button?

2. If they would want to cut at 18", would changing gear ratio do this? is there any other method that someone can think off?

It has been a while I have done motion in AB.
Any sample software, pointers, screen shot would be appreciate.
I don't even know how i can change the gear ratio pro-grammatically.

After thinking more about the application, since this is plastic bags.
I think it is not as simple as just by changing gear ratio of the rolls to match cutoff will do the work.
If the knife were to cut the material at different speed than the plastic speed, then the plastic might get stretched or torn i think.

Does anybody have any application sample that they can share ?

Thanks! AT

this looks like a classic flying shear application to me.
keep in mind when the knifes come together to cut they must be traveling at the same line speed as the material they are cutting.
they must speed up and slow down to account for the material travel
do a google search there are a lot of examples