Do-More CPU, H2-CTRIO2 closed loop control?

[ERokc]

I definitely have a low bandwidth application.  That should work to my advantage using this method.

In an attempt to understand the CTAXTRAP instruction in Designer I discovered the yellow Instruction Help window has the description for CTAXLIMT instead.  I'm guessing it was copied and pasted but not edited for the differences.

b_carlton, I don't understand how to apply your modified "distance left to travel".  Is that applied using the CTAXTRAP instruction?  I'm interested because I expect my control problems are going to be in hitting the target.  My limitation is I can't reverse the machine and maintain correct material alignment.  Material on the conveyor will always travel in one direction (except for un-jamming).  I want maximum acceleration but hitting the target is a must. I can't know how hard that will be until I put the drive together and run it. I'm a few weeks away for that. If I have the option for a different slope on deceleration that's good.

OK, I had a thought, CTAXCFG might let me set acceleration, yes it does.  Can I use variables or constants, YES.  The green/red dots (GO/NO-GO) great feature in Designer.  I'm liking Do-More, More and More.

I ran across the article that turned me on to CTRIO2. Automation NOTEBOOK issue 24, Tech Brief by Jason Horine.  Jason says "When a servo is too much and a stepper is not enough, simple closed loop control might do the trick."That caught my attention but Jason didn't suggest what to use for driving the load.  I think an AC induction motor and VFD might just work.  I intend to find out.

[b_carlton]

I was using a counter card for position but then an analog output as a speed command to the VFD. I've even send the speed reference using relatively higher speed communication connection and achieved good results.

Get current position, subtract from destination, derive absolute value.
Take square root of the result.
Multiply by empirically determined constant.
Out to analog card (or communication instructions).

When within final 'good enough' window then stop. Our positioning mechanical system had enough friction and a high ratio worm gear that 'holding' was not necessary.

[BobO]

In an attempt to understand the CTAXTRAP instruction in Designer I discovered the yellow Instruction Help window has the description for CTAXLIMT instead.  I'm guessing it was copied and pasted but not edited for the differences.

Yes, likely a cut and paste bug. Thanks for reporting it.

b_carlton, I don't understand how to apply your modified "distance left to travel".  Is that applied using the CTAXTRAP instruction?  I'm interested because I expect my control problems are going to be in hitting the target.  My limitation is I can't reverse the machine and maintain correct material alignment.  Material on the conveyor will always travel in one direction (except for un-jamming).  I want maximum acceleration but hitting the target is a must. I can't know how hard that will be until I put the drive together and run it. I'm a few weeks away for that. If I have the option for a different slope on deceleration that's good.

You wouldn't use his concept with the CTRIO's pulse output. He is describing an alternative method of controlling the motor that is used in lieu of the the CTRIO's output. I would suggest that you start with the CTRIO's output, and then only get into rolling it yourself if it doesn't give you the desired result.

[franji1]

In an attempt to understand the CTAXTRAP instruction in Designer I discovered the yellow Instruction Help window has the description for CTAXLIMT instead.  I'm guessing it was copied and pasted but not edited for the differences.

Fixed.  This will show up in the next maintenance release of Designer.

[DLTimmons]

Actually, positioning using induction motors is very common in lower bandwidth high-hp applications like automated warehousing or automated rigid cranes and so on.  When done properly, you'd never know looking at one of these applications except for the bandwidth that you're not looking at a servo app.

Now, "done properly" tends to mean vector grade drives running in torque mode with encoder feedback and not chintzing out on motor hp, but it does work and it works very well.

I've actually taken a motor elevating a load, and just let it hang there stalled without the brake engaged to see how it would do and it would hold position withing an encoder count or so for hours.

Do you have a example of how you did this?

[Controls Guy]

Do you have a example of how you did this?

Did what?  Servoish motor control or one count accuracy?

If you mean that application in general, one example would be a Control Logix with motion control cards receiving the encoder signal and controlling AB 1336-FORCE drives in either torque or velocity mode (and with no direct encoder feedback).  We had 5hp horizontal axes moving approx 2,000 lbs at 300-400ft/min and stopping smoothly +/- 1/4".   Don't remember the hoist axis hp or speed, probably also about 5hp and say 100ft/min.  You could do the same with any appropriate VFD and a standalone motion controller if the PLC you want to use doesn't have a motion controller card that will work for your app.

As far as the one-count goes, that was part good design / commissioning and part luck / random chance.  It was well tuned, but even so it was a little better behaved than other supposedly identical axes.  I actually just left it there for hours with the brake off just to see how long it could do that.  So, while it's not literally representative, my point in saying that was to show that positioning with induction motors is very practical.

[DLTimmons]

Do you have a example of how you did this?

Did what?  Servoish motor control or one count accuracy?

If you mean that application in general, one example would be a Control Logix with motion control cards receiving the encoder signal and controlling AB 1336-FORCE drives in either torque or velocity mode (and with no direct encoder feedback).  We had 5hp horizontal axes moving approx 2,000 lbs at 300-400ft/min and stopping smoothly +/- 1/4".   Don't remember the hoist axis hp or speed, probably also about 5hp and say 100ft/min.  You could do the same with any appropriate VFD and a standalone motion controller if the PLC you want to use doesn't have a motion controller card that will work for your app.

As far as the one-count goes, that was part good design / commissioning and part luck / random chance.  It was well tuned, but even so it was a little better behaved than other supposedly identical axes.  I actually just left it there for hours with the brake off just to see how long it could do that.  So, while it's not literally representative, my point in saying that was to show that positioning with induction motors is very practical.

I'm looking at an elevator appilication that uses induction motors that I need to hold position till the brake can set. I looking at using a Do-More, CTRIO-2 and a GS3 drive with encoder feed back. it the hold till the brake can set and realse that I not quite sure of.

[Controls Guy]

I hear the word "elevator" and it makes me nervous! 

You're not elevating people, are you?  Or elevating stuff over space where people could be?  If so, beware of liability.  For the VFD companies for which I know one way or the other, they have special drives with special firmware for crane apps (and that's not even for elevating people).  ABB ACS-800's (the generic ones, though I don't doubt the crane ones have it too) have a torque proving feature so you can guarantee you have torque before releasing the brake.

[DLTimmons]

I hear the word "elevator" and it makes me nervous! 

You're not elevating people, are you?  Or elevating stuff over space where people could be?  If so, beware of liability.  For the VFD companies for which I know one way or the other, they have special drives with special firmware for crane apps (and that's not even for elevating people).  ABB ACS-800's (the generic ones, though I don't doubt the crane ones have it too) have a torque proving feature so you can guarantee you have torque before releasing the brake.

Its a material lift that is part of a convoyor system so using lift may be a better way of talking about it. Hitachi SJ300 and a Siemen Micromater 440 have that featrure.