appropriate servo tuning.... help?

[howling60]

background:
cincinatti 10hc horizontal mill (approx weight 40 thou pounds)
SEM 221 in/lb servos
z-axis: 3rev-inch ballscrews (moving approx 10 thou pounds front/back)
1000-line encoders
Galil DMC 1860 controller

So, after spending several months trying to tune-out velocity-mode amps, using torque-mode methods... i finally realized why nothing was working out right!... swapped over to torque mode on the amps.. now everything is going MUCH better...

my problem however is this. I've been using galil wsdk software to tune these, and was running a 1000 line pulse for step response moves. had things tuned out, or so i thought.. 15 cnts following error and decent steady-state holding. then, went to a 100 cnt pulse, and realized my steady-state error was wandering +- 5 counts.

i've tried to damp this out more, but just end up with a servo that REALLY wants to sing on short moves. introduced some pretty hefty pole filter to cut down on that, but still don't feel i'm where i should be.

current settings kP: 275 kD: 2000: kI:havne't decided yet how much to drop in

i'm looking for any ideas/assistance that people might be able to offer. getting SOO close to having this machine up & running where i can be happy, and now i feel like i'm chasing my tail.. argh....

thanks in advance all!

-nate

[Jason Ross]

Your I value controls your steady state response. I believe your Kp is too low and your Kd too high. Disable your filters, Lower Kd and raise Kp until you have about 3% overshoot. Raise Kd until to square off response and then raise Ki to as high as stable. If you have resonance then look at adding filters. Filters limit the range of gain.

[howling60]

so, i re-tuned, again.. found "new" info hiding on the galil website, and in their command reference manual, which i dind't have before.. no wonder i couldn't figure out how to do things!

in any case, i now have motors that are very happy, you were right, my damping was WAAAYYY too high. by retuning, i was able to lower the damping, lower the proportional, and introduce some pretty significant integral.

I also found some info regarding the feedforward options available with the galil controller. Feedforward accellerations saved my tush ALOT.. let me drop my proportional to get my overshoot back down to something reasonable, without having to crank the derivative to compensate.

motion is still a very slight be grainy @ low speeds.. but i am very certain i can get even that out now that i feel like i know what i'm doing!

-nate

[Karl_T]

My next job is tuning some small DC servos on my Hardinge CHNC lathe X and Z axis... I'm using a galil 1840 card.

I haven't yet purcahsed the WSDK software. Is it needed? Did you like it? Worth the money? Etc.

Karl

[howling60]

IMHO, the wsdk software is WELL worth the $$

if only for the fact that you can communicate directly with the galil card, and not rely on the interface through camsoft.

Also, there are several auto-tune methods available within the wsdk software, although if you are setting up a velocity-mode system, you cannot use the auto-tunes, and must use the manual tune.

if you haven't been to the galil website, go and check out their support forum (on their site), if you dig through alot of the old posts in the tuning part, you will find alot of handy/helpful hints to using the more advanced features of their software/hardware.

soo.. you don't necessarily NEED the wsdk software if you are running through say the camsoft interface.. HOWEVER, i feel that it makes life alot easier, and will help alleviate some headaches...

if i can offer any other assistance when you start the tuning & such.. please, feel free to get ahold of me.

[Al_The_Man]

I would recommend anyone that uses the Galil products, especially as part of packaged systems like Camsoft etc, to first get aquainted with the Galil through the DMC terminal interfaces, and experiment with tuning, motion and controls etc, This helps alot to get a feel of what you are dealing and helps understand some of the more powerfull features of the card.
The Tuning video by Jacob Tal from the Galil site is a good starter.
Al.

[howling60]

what he ^ said

when i initially started this retro, it was my (and my co-workers) understanding that this would be very much a plug & play style install/tuning. but, that's literally just not possible from within the interface software of camsoft that we were using. once i realized the power of the galil card itself, i was already incredibly frustrated. after using galil's software, and after downloading their command manual, i was MUCH happier, and the process has only improved since then!

-nate