Analog DC servo very big response delay

Well, jerk feedforward does help!






I've used values between 2e-06 to 4e-06 for axes. Increasing this further does reduce start undershoot, but increases end overshoot/undershoot.
I think P gain scheduling based on velocity should help too with start undershoot, but that will be another day.
I'm glad that it reduced by some degree almost all overshoots/undershoots, so I definitely think this should be added to PID component.
I attached modified pid.c

Sure, I will check that.

That's interesting, but this paper suggests to use derivative of jerk instead, do you think it's worth to try? Maybe even both can be used, I've seen that in a different paper too,

Did a quick test in servo sim:

Not sure about usability of this one(values are ridiculous). If used alone it will just make two spikes in different directions and in my opinion this will cause more troubles than help. If used with jerk, it will increase starting amplitude, but decrease it's duration. Looks like it is not usable with trapezoidal motion profile.

Have some results on jerk feedforward in work, X axis is a bit too tight and FF3 value used for it was too big. I had to reduce it by half, because machine became too jerky on engraving work. But in overall it did a bit better with one problem on Z axis.
Also I did a check of snap(jounce) feedforward, values for it were 10^-9, but it didn't help in any way, increasing it only did worse.

Hi,
I am going similar path with WF 31 CH. Can you share your setup, please?
Did you get it all sorted?

thanks
Josef

Hi Josef,
This is mostly a mechanical problem with a friction in hard linear slides. You have to overcome sticking which translates into this following error. I firstly though that this can be some issue with analog input filter inside the BOSCH regulator card, so i reduced the time constant of this RC filter, but it didn't help. Adding another feed forward term again doesn't help much, but makes machine more jerkier. With those machines the only viable way to reduce this error is to reduce acceleration. Other possible way is to integrate some low friction polymers into the slide, this was done on our machine on Y axis due to mechanical wear. This did reduce the following error by really small value.
Also you should check the ball screw, those machines are old and very likely you may need to replace the balls and re tighten the ball screw