Axis jerk, servo tuning and capturing data

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GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Thu Jul 08, 2021 11:56 pm

Hi Tom.

I still have some jerk motion in my g-codes.

Before I had some play in the X axis, but solved it with a preload in the ballscrew.
I still find some jerk in the axis movement and can't find the source of the problem.

I captured some motion with the CaptureXYZPosDestToFile example, but don't know what to do with the data.

Do you have a tutorial or can give me a help to solve this ?
Also, how can I generate the path with the data from the capture?

I can supply you with all the data you need, just request it please.

There are 3 example with different g-codes in the KFLOPdata files attached.

Thanks Tom!
Attachments
KFLOPdata.txt
(898.44 KiB) Downloaded 9 times
KFLOPdata - Copy.txt
(898.44 KiB) Downloaded 5 times
KFLOPdata - Copy (2).txt
(898.44 KiB) Downloaded 4 times

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TomKerekes
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Re: Axis jerk, servo tuning and capturing data

Post by TomKerekes » Fri Jul 09, 2021 4:39 pm

Hi Gabriel,

Do you know Microsoft Excel?

Attached is an Excel Spreadsheet to import the data.

Here is a plot of the XY Path

XY.png


Here is the X Velocity of the Trajectory vs time:

VelX.png

Here is the Following Error vs time:

Following Error X.png
Attachments
PlotPosDestXYZ.xlsx
(2.58 MiB) Downloaded 4 times
Regards,

Tom Kerekes
Dynomotion, Inc.

GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Re: Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Sat Jul 10, 2021 12:16 am

Hi Tom.

That was exactly what I needed.

I tried but wasn't reaching that final result.

It seems that the profile and the following error are good, do you agree?
For woodworking at least.
30~ counts following error, 17000 counts / inch, total: 0.0017" or 0.05mm

So it must be coming from mechanical backslash?

Attached some photos of the "steps" in the final parts.
Theses steps are a little bit small, there are some other that I run with double speed that are concerning big. i think around 0.2mm.
The ones on the photos may be 0.1mm.

The data collected was at a high speed, around 8000mm/min.
The cutting that you see in the photos was done around 2000mm/min
The ones that had big steps were done at 4000mm/min

Thanks!
Attachments
IMG_20210709_211140.jpg
IMG_20210709_211103.jpg
IMG_20210709_211040.jpg

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TomKerekes
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Re: Axis jerk, servo tuning and capturing data

Post by TomKerekes » Sat Jul 10, 2021 2:24 am

Hi Gabriel,

Sort of hard to say. The following errors are +/-0.05mm. Then you say the errors in the part are 0.1mm. But then you say those are at a lower speed?
Regards,

Tom Kerekes
Dynomotion, Inc.

GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Re: Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Sat Jul 10, 2021 2:21 pm

Hi tom.

Will cut another piece with fast speed and take some photos.

Also will capture data with the same data for us to compare.

Thanks

GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Re: Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Wed Jul 14, 2021 11:50 pm

Hi Tom.

Can you take a look at these captured motions ?

I analyzed them and found just the acceleration looks strange. It looks like accelerate and decelerate very fast.

They give a lot of jerk when the helix end and the radial motion starts.

the 3 data captured are from the same g-code, but with increasing speed and then increasing acceleration.

KFLOPdata7000 is captured with 7000mm/min and so on.

Thanks
Attachments
MGA.txt
(12.99 KiB) Downloaded 5 times
KFLOPdata14000acel60.txt
(898.44 KiB) Downloaded 4 times
KFLOPdata14000.txt
(898.44 KiB) Downloaded 4 times
KFLOPdata7000.txt
(898.44 KiB) Downloaded 4 times

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TomKerekes
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Re: Axis jerk, servo tuning and capturing data

Post by TomKerekes » Fri Jul 16, 2021 10:46 pm

Hi Gabriel,

The acceleration goes to ~53 inches/s^2 which is under 60 inches/s^2 so I believe that is correct.

RapidThenArc.png
Regards,

Tom Kerekes
Dynomotion, Inc.

GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Re: Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Mon Jul 19, 2021 7:15 pm

Hi Tom.

The jerk seems to be where the helix end and the radial motion starts. (flat, not with Z movement).

Raising the Tau from 0.01 to 0.02 seems to do a lot better.

Now the machine is simple stopping in random places in linear one axis movement. (G1)

Without outputing a console error. photo attached.

Thanks.
Attachments
tp.PNG
strange.PNG

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TomKerekes
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Re: Axis jerk, servo tuning and capturing data

Post by TomKerekes » Mon Jul 19, 2021 7:29 pm

Hi Gabriel,

It seems something is disabling the Axes. You might have checked the Axis Screen to verify.

Do you have any code running that disables axes?
Regards,

Tom Kerekes
Dynomotion, Inc.

GabrielR922
Posts: 74
Joined: Thu Aug 13, 2020 10:07 pm

Re: Axis jerk, servo tuning and capturing data

Post by GabrielR922 » Mon Aug 02, 2021 9:09 pm

Hi Tom. I have a code that disable axis all axis if one axis is disabled due to following error.

I had the Y axis following error set to 10.000, lowering it to 100 solved the problem. (my system is tuned for around 50 counts).

The Y axis seems to be doing very fine, but the X axis, at ~4000mm/min gives some marks on the finish, if you hold your hand in the axis, you can feel that it runs with some bumps. (even without load)

At 6000mm/min this can't be seem.

I'm starting to tune X axis again. Can you give me a help with filters?

Check the attached photo. i need to lower the Gain to raise D. what can i use? is ok to use for example a low-pass filter of 300 ?

Thanks.
Attachments
Capture.PNG

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