FlyingCutoff

[DLTimmons]

Has any one out there set up a flying cut using a PLC? Looking for logic as this is a slow system.

[Controls Guy]

Yeah, but it's been a long time!

First question's going to be: Will the product tow the shear, is the shear head self-propelled, or a hybrid of both?

Next:  What's the line speed and desired cut-to-length tolerance?

[DLTimmons]

Its currently driven by the main line motor by engaging a clutch that powers the shear head to match speed with the material with no adjustment once you fire the clutch. Basically we trigger the clutch a the right point to have the shear at the correct point to cut when it hits a limit switch.Line speed has a big effect on the point we have to fire the clutch. Line speed is about 120 to 150 FPM and slows down just before the cut starts.  We currently working off a -1/16 to +1/8 tolerance . Looking at adding a servo to drive the shear and getting to +/- 1/16 or better tolerance. The current PLC is a D450 that will get a Do-more upgrade.

[Controls Guy]

Ok, if you're doing self-propelled, and with a Do-More and a servo, I remember a thread on here about master-follower you could do off an encoder on the main drive, with offsets to make phase adjustments as you're following before you start the cut.   I'll see if I can find it and link.

[Controls Guy]

Ok here it is.  Didn't go back and re-read the thread to check relevance, but the topic seems worthwhile.

https://forum.hosteng.com/index.php?topic=2709.0

[DLTimmons]

Thanks.

About the time you think found all the things the Brx can do yo find something like this. Once I get my dull mind wrapped around this, I see a 405 rack up grade coming!

[Controls Guy]

Another option would be to keep the clutch and have a servo just do compensation for the variation in clutch lockup.  Have the shear head slightly adjustable relative to the assembly driven by the clutch maybe 1/2" to 1" total adjustment travel.  Smaller servo, smaller drive, and potentially less mechanical mods.

[DLTimmons]

I see what you are thinking. Not sure if that would be any easier than pulling every thing and connect direct to the pinion shaft.

[DLTimmons]

Been studying this and have a few questions to start with it will drive the other questions. Would I have to wait till the cut point passed the shear to start the following or can I start following before the cut gets to the shear without it trying to run the shear backwards?

It is currently run on A D450 now and we reset the counter on every cut and a air cylinder returns the shear to home and waits till the next trigger fires the clutch and cut when the shear hits a limit switch. the trigger point is calculated based on speed of the material speed

[Controls Guy]

I haven't used the BRX AXx instructions yet,, but it sounds as if some of them are velocity gearing instructions, so you could accelerate your servo to synch speed (lock your clutch) then make an offset or differential move to get the position perfect, then cut.

[BobO]

AXGEAR is essentially a velocity gear with a variable ratio, although the underlying implementation is position...meaning it shouldn't have any position creep for a given gear ratio. AXFOLLOW and AXCAM are both position-centric.