Ultimaker 3 - Weird retraction behaivor while timelapse

[abetub 0]

Hello everyone,

 

I'm currently using Cura's timelapse feature (extensions > post-processing > modify g-code) to capture one camera image per layer. Since stringing occurs when the print head moves into the corner, I have set a retraction of 3mm within the timelapse function. Now, unfortunately, a strange behavior occurs during printing with no discernible pattern. After the print head moves back to the original position (after the photo is taken) the printer starts pulling the filament half way back to the feeder, only to move it back to the print head and continue printing. Sometimes this happens several layers in a row, sometimes not at all.

 

In addition to higher completion times, the print head sometimes loses contact with the filament in the process because it does not push the filament back far enough, which means the print has to be aborted. I tested this on 2 UM3s - the problem occurs on both. Deleting the retraction in the timelapse function solves the issue, but it results in heavy stringing again, when the print head moves to the parking position.

 

So I think the problem is either with the cura timelapse function (which I think is unlikely, since the problem does not occur with every layer) or the reason is some kind of exception handling of the printer, but I dont unterstand why ...

 

BTW: The function insert this into the G-Code after every layer (I removed the command for triggering the internal camera, because i am using an external one): 

 

M83 ;Extrude Relative

G1 F3000 E-3 ;Retract filament

M82 ;Extrude Absolute

M400 ;Wait for moves to finish

G1 F3000 Z1.47 ;Z-Hop

;TimeLapse Begin

G1 F9000 X0 Y190 ;Park print head

M400 ;Wait for moves to finish

 ;Snap Photo

G4 P700 ;Wait for camera

G0 X91.72 Y82.72 Z0.47; Restore position

M400 ;Wait for moves to finish

M83 ;Extrude Relative

G1 F3000 E3 ;Retract filament

M82 ;Extrude Absolute

 

Do you guys have any ideas why this happens? Do you have different solutions for retracting the filament?  I am open to any idea. 

 

Best regards

Edited November 18, 2022 by abetub

[abetub 0]

Please tell me if more information is needed as I am relatively new to the topic

Edited November 18, 2022 by abetub

[abetub 0]

It seems that I have found the problem. Maybe the following solution will help someone else who also encounters this problem:

 

Ultimaker does not use pure Marlin as firmware in the UM3, but a slightly adapted version of it (Griffin). This one does not support the commands used by the extension M82/M83 (Relative vs. Absolute Extrusion) - at least not without errors. You can read this in the community post of a former software developer of Ultimaker about the release of the UM3.

 

Quote

Other absent codes are the M82/M83, relative E mode. I don't know if there is a slicer that depends on this. Due to some archtectual things in the code, these commands are difficult to support right now. (Note, I think they do something, but they might stop working in the future, or we will fix the bugs related to them)

https://community.ultimaker.com/topic/15555-inside-the-ultimaker-3-day-1-gcode/

 

Sometimes the code was executed correctly, sometimes not. When it didn't, the command was implemented with the E3 extrusion absolute and not relative, so as the layer count increased, the filament was retracted further and further, only to be fully retracted again with the next extrusion command. I modified the Cura PlugIn so that the retraction commands are inserted absolutely in the code.