[LarsSweden]

Hi everybody

I¨m currently in the process of converting a OKK mcv-300 with a new control.

I¨m at the state of tuning the axis servos. I have read up on tons of threads on howto go about tuning with no luck.
I´m running with Cncdrive¨s DGS16035 servo driver.
There is no autotune program to run, So i have started with turning up the gain, Ap, until the motor starts to occilate. Then added some damping, Ad. I can get a pretty good curve when not adding any I. That value is a zero. I¨m tuning with 100 steps. The strange thing is that when i try to go for 5000 steps it overshoots alot in both dirrections and finally end up at zero line. Is that normal? Is that because i cannot set acceleration in this tuning software?

Fanuc DC ser. 5 servos.

Any tips or tricks?

/Lars

[Tkamsker]

Hi i did similar with Granite devices it took me more than 10 weeks to get it done ,..


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[LarsSweden]

Hi

Any tips or tricks for tuning? A problem i think a have is that i cannot change acceleration or velocity while pid tuning i the servoconf by cncdrive. As soon as i for ex make a 5000 steps analyse i get a totaly different grapf. It overshoots like hell, back and forth until it steadys out at zero. It does not occilate. I get no error between commanded steps and machine steps.

Should i just tune at say 100 steps and then try with the motion controlbord to set acc and velocity?

/Lars

[bhurts]

You are not making a large enough move while tuning. That prevents your motor from having time to accelerate to a reasonable speed before reversing. Try tuning one of your motors using a step value equal to 25-100mm. When you have it running good run plots at 100 and 500mm and compare performance between the step sizes. It's really hard to say for sure what will work best without tuning at different step sizes. Also what is the resolution of your encoders, screw pitch and do you use any gearing between tour motor and screw. Lastly is the motor connected to the axis or are you tuning on a bench.

Ben

[LarsSweden]

Hi Ben.

Ok, I have been running only 100 and axis is barely moving. I will have to check pitch and gearing. Encoder is at 2500 p/rev.

When i have tested 5000 steps it moved perhaps 20-30 mm.

/Lars

[bhurts]

Try tuning a axis using that 5000 step move and then report your following error once you have gotten to a good stable tuning for that move.

[LarsSweden]

Ok, will do that later today. And yes, the motor is mounted on the machine.

Thank you for your help!

/Lars

[LarsSweden]

How to upload pictures? Taken some screenshots of the tuning program.

Got it

[LarsSweden]

Still some way to go. Should I wait to try to increase I last?
Overshoots pretty mutch still. It sometimes occilate for a sec when reaching zero line. Pitch of ballscrew is 5mm, geared 2:1.
1000 steps/mm.

[bhurts]

Yes. Start at all zeros for p,I and d. Increase P until the motor goes unstable and then back off 30%. Then increase d until the motor goes unstable and then back off 30%. Then go back to p and increase until the motor goes unstable then back off 30%. Then back to d and same. Keep going back and forth until your error starts to increase instead of decrease or the motor will no longer allow increases without going unstable. Then last increase I until you go unstable and back off 50%. I should be a small value.

Ben

[mike_Kilroy]

Still some way to go. Should I wait to try to increase I last?
Overshoots pretty mutch still.......

u r not doing it totally right. I shud be 0 until last yes.

but P should NEVER be adjusted to give ANY overshoot. Period. I brings responce up; P should be as hi as you can make it WITHOUT any overshoot.

I would not screw with D until very end.

adjust P to hi as poss without any overshoot, then add I until you get it to about 5-10% overshoot. that is correct setting for velo loop gain. D is in my opinion a last resort if you cannot tun properly with P then I. I generally never use it. some cheap drives I suppose will need it; I dont work with cheap drives.