Group: DynoMotion	Message: 10665	From: cnc_machines	Date: 12/12/2014
Subject: CL Stepper Dithering

Greetings,

I am using the KStep, using encoders in CL mode. I read the suggestions on how to set this up and added a very small amount to the integrator value (.01). When I do this it causes the axis to vibrate horribly. I have tried to reduce it to an even lower level but it has the same issue.

Really all I want is gradual correction if any steps are lost. Does anyone have any tuning suggestions that would make the axis more stable?

Thanks,

Scott

Group: DynoMotion	Message: 10666	From: TK	Date: 12/12/2014
Subject: Re: CL Stepper Dithering

Hi Scott,

Do the red and blue plots follow each other well in open loop mode?

What are your Filter settings?

There should be some value small enough to be stable. How small have you tried?

Regards
TK

On Dec 12, 2014, at 7:09 AM, cnc_machines@... [DynoMotion] <DynoMotion@yahoogroups.com> wrote:

Greetings,

I am using the KStep, using encoders in CL mode. I read the suggestions on how to set this up and added a very small amount to the integrator value (.01). When I do this it causes the axis to vibrate horribly. I have tried to reduce it to an even lower level but it has the same issue.

Really all I want is gradual correction if any steps are lost. Does anyone have any tuning suggestions that would make the axis more stable?

Thanks,

Scott

Group: DynoMotion	Message: 10667	From: cnc_machines	Date: 12/12/2014
Subject: Re: CL Stepper Dithering

Tom,

I will have to check, I didnt set any filter settings. This is probably my issue.

Thanks,

Scott

Group: DynoMotion	Message: 10673	From: cnc_machines	Date: 12/15/2014
Subject: Re: CL Stepper Dithering

Tom,

I checked and it appears that I had the default values for the low pass 2nd filter active (Feq 100 and q = 1.4).

When I run open loop (all PID set to 0) I get a max position error of 25 (this seems to be good?). When I change the Integrator value to 0.01 the following error drops down to 10. The problem is the axis begins to vibrate horribly.

I have tried reducing the integrator value all the way down to .00003. The axis continues to move a few steps up and down, however it does it very slowly. With a higher value it appears to be doing the same thing, just a lot faster. I have played with the Q and frequency settings, but I dont really know what they do and it doesnt seem to help.

Do you think this could be error in my pulley ratio or something? Any suggestions to get it to hold position would be excellent. Would it be best to just run open loop and use the encoder as a fault device?

Thanks,

Scott

Group: DynoMotion	Message: 10675	From: cnc_machines	Date: 12/15/2014
Subject: Re: CL Stepper Dithering

I think I may have solved this using the dead band parameters. I put a range of 2 and a gain of 0 and it seems to stop vibrating, even when I have a higher "I" value.

If I missed a better way to fix this please let me know.

Thanks,

Scott