[sendkeys]

i have 1024 encoder 750oz on ballscrews on a benchtopmill

I'm tuning my system now, im able to get it at 0-overstep with (even setting it to jump 4000 steps,1turn)

2000kp 1800kd 0ki

Should i be happy with this? I mean it sounds nice to me but,should i add in ki and keep trying?

When i added some ki i end up getting over step. THe pdf says this is normal but also says with 0 ki overstep is normal.

Does adding ki make the servo's run smoother? better surfance finish or somthing... It zips around the table nice when setting the tuning software to higher pps.

Thank you for the help

[HuFlungDung]

For what it's worth, I would try your Ki at 1 (because you should have a little bit) and knock the Kp back to 200 and work Kp up from there. Your Kd sounds to be in about in the right range.

[unterhaus]

ki improves steady state error at the expense of stability. kd gives you stability at the expense of introducing noise into the system. There are a lot of PI controllers out there that just skip the D. Myself, I'm addicted to D.

If you have errors in the position that don't get corrected then you need ki.

[rutexus]

Gentlemen,

Regarding tuning, I'll ad my 2 cents. This is kind of an art, so different people have preferences.

First, if you are using the Rutex tuning software, you normally want some overshoot. This is because there is no deceleration in the tuning, and you want the servo motor to move quickly to the destination. When you add deceleration, as in a cnc operation, the motor should slide into position perfectly. If you tune for no overshoot, you are probably not driving your motor hard enough.

Vladimir insists on getting some ki in the pid. I have had a few little nema23 motors that would not tolerate any on the bench with no load. He also says 1 is never enough--try to get near 100. We try to get 125 normally, but in some motors I only get ki to 25 or 35.

I always use Kd also. If you are getting the kp up to where it should be (where it produces some overshoot) you will normally need some kd to tame it down.

I hope this helps.

Tom Eldredge
Rutex LLC

[HuFlungDung]

Tom,
Is there any kind of universal standard between controllers, and amps, for whatever the values of KI, KD, and KP represent, or are the values all relative to some unnamed constant? That is would a KI of 1 on system X correspond to a KI of 100 on another manufacturer's system?

I hope that made sense

[unterhaus]

there is no standard. It all depends on how they implement the feedback loop, there are gains that are inherant in every drive that would make it different. Some drives from different manufacturers may end up having very similar values for a given motor, but that would just be by chance.

[sendkeys]

Great just what i needed to know i will get back to turning Thank you all very much

[rutexus]

Sendkeys,

I concur with the advice you have been given. There is no standard. The pid values are multipliers, and every manufacturer selects their own scale. My experience tells me that the pid values are only related to one another within a given product line at best. I am not the final authority on this however. That is just what I have experienced in dealing with several different servo drive manufacturer's products.

Tom Eldredge
Rutex LLC