Programming a ''feedback loop'' for a servo?

We have this machine that laser welds a flat piece of metal that can range from 30ft to 50ft long. It is servo driven. If the material is 50ft, then we want it to stop exactly at 50ft. What is the best way to do this? I am new to the company and dont want to make a bad impression. Its all AB stuff, SLC-500 with a ultra3000. thanks..matt

So you are setting your 50 ft tolerance at 50 +/ zero? Little tight if you ask me - can you not spare an extra 5 to 10 thou?

What is tolerance on motor stopping after teh stop command is it always with no variation? If any variation you will have to include that in your specs which wipes out your zero tolerance.

What is environment of welding - I have never seen laser welding how much smoke and particulate? I have seen laser cutting and there was a fantastically low amount of smoke and particulate.

You are going to need a really good sensor to meet your demands.

Dan Bentler

This is a R&D Project. Our company uses laser extensively for everything.Cutting, Welding, Cladding,ect... their is a small fiber optic fiber going inside the joint and the laser has the least amount of heat contamination. Im not exactley sure on how exact they want it...i will find out more soon. I am just trying to get a jump start on this. I just wanted to get a couple of second oppinions on this..thanks matt

The way we did it for valve stem mounting on wheels was to have a photoeye detect the hole as it was coming up to where the insertion point was and then have the servo run to that point. A second PE would bring the servo to a full stop when the wheel rotated into position.

For your flat sheet you could do the same thing, read the end of the sheet say about a foot before where it has to stop. Then slow down your drive and count the number of pulses until the sheet is at its stopping point.

Don't try running the photoeyes through DeviceNet either, it will have you stopping all over the place.

You really want to hardwire your inputs into the drive if you want the best response from your servo.

We have motion control guys hanging out here that can answer your question much better than I can. Hopefully one will show up and take mercy on us.