Ultimaker 2+ Connect severe Pause and Resume bug!!

[kupfeli 9]

Hi all,

 

I have noticed a severe bug in the Ultimaker 2+ Connect Pause and Resume functionality.

Pausing works (question: when is a pause actually performed in the gcode? What does the Engine wait for before it finally pauses the print after pressing the touchscreen??), but when I perform a resume, all of a sudden instead of printing circles (I was printing a Cylinder) of the outside, the printer is "stitching" a pattern, so it makes circles in a stuttering motion which results in a terrible outer surface. So basically instead of doing a smooth circle, it makes a stuttering movement in a circular pattern.

I assume that after resume, the printer did not restore all settings stored when pausing the print.

 

This makes it completely impossible for pausing and resuming a print.

 

Help solving this problem (maybe I am doing something wrong?) is much appreciated!!

Edited December 29, 2022 by kupfeli

[dfrez 21]

I believe this is due to what’s known as “buffer overrun” I’ve seen it on my own UM2+C as well as my UM2+ when printing over USB via OctoPrint. After a pause on my UM2+C, if the printer starts on an arc or circle, it begins to stutter, which you described as “stitching”. This is because arcs and circles are made up a bunch of linear moves and the printer runs out of buffer basically and results in the slow performance. This is also common when printing over USB because the serial connection has limited bandwidth. There's a Cura plugin designed to solve this called "ArcWelder" which combines these many linear moves into a single arc move which reduces the likelihood of a buffer overrun. But I'm not sure if this would be compatible with newer Ultimakers since they use a different flavor of g-code. The UM2+C also may not recognize the arc command, I know it recognizes a limited number of Marlin commands, hence why you have your workaround for pausing a print, since it doesn't recognize an M0

command. 
 

What’s interesting is the latest version of FW for the Connect was supposed to address the buffering issue but my up to date machine still exhibits the “stuttering” after a pause. 
 

Firmware Release Notes

Edited March 14, 2023 by dfrez

[kupfeli 9]

Thanks for your detailed reply! I hope that Ultimaker will solve this problem.