[BUG]Filament change in sequential print - collision with earlier print

[MechanicalCat]

Apologies if this is a duplicate - I searched all issues open/closed for "sequential" in title and only found a handful, none related. Did I do my search wrong?

If filament runs out during a "print objects sequentially" print-run, then the head moves to X=max and the bed moves to Y=0, ready for new filament to be inserted. Z doesn't appear to be significantly changed during this move.

This means the head collides with any earlier-printed object which is in the way and which happens to be higher than the current layer.

[Prusa-Support]

Hello! Sorry for the issue. Was this with FW 3.11.0 and Prusa Slicer 2.4.2? Can you please send me an example GCode and 3mf file of one of the models where there was the error? We'll look into this!

Alessandro Pantaleo
Prusa Research

[Prusa-Support]

Hello @MechanicalCat! Following up on this thread, I found more information about this.

At this moment the firmware on the MK2.5/S and MK3/S/+ stop procedure is:
SD card print
Z is lifted by 10 mm of current position
This would mean if the previous print is higher than 10mm it may crash into it.
Moves to cancel position with is X=50 and Y=150 both axis moving at the same time.

Host/Octoprint print
    If Octoprint is configured correctly then it behaves the same as it sends M603 Gcode command to the printer and does 
    the same as with SD card print
        Octoprint Settings -> GCODE Scripts
            After print job is cancelled ==> M603
            After print job is paused ==> M601
            Before print job is resumed ==> M602
    If Octoprint doesn't have the configuration above
        It probably just stops above the print.

Example where it would likely fail:
1st print is at X=50 Y=190 and is 20mm tall
2nd print is at X=100 Y=140 also 20mm tall
3rd print is at X=150 Y=90 also 20mm tall

A workaround could be to arrange the prints differently.
1st print as close as possible to x=250 and y=0
2nd print clearance distance behind and left
and so on.

Still, feel free to send me the 3mf file (https://help.prusa3d.com/article/saving-projects-as-3mf_1773), let me know if we were in the SD card or Octoprint case and if rearranging the objects would solve the issues!

Alessandro Pantaleo
Prusa Research

[github-actions]

This issue has been flagged as stale because it has been open for 60 days with no activity. The issue will be closed in 7 days unless someone removes the "stale" label or adds a comment.

[ulab]

This is still something that should be looked at. :)

[MechanicalCat]

If the above statement that "Z is lifted 10mm from current position [and then the head moves to (250,0) ]" is correct, then... if (say) the filament runs out when the head is at 0.5mm on the second or later object, then the head will sweep a line across the deck and only about 10.5mm high. Which means the head (or the lower X-rod) is likely to collide with something almost irrespective of the order the items are arranged on the bed. Seems like Z should move to an absolute position which is calculated to be higher than any position reached during the current print-run (so far). Or (even simpler) just don't move the X/Y position at all.

[Prusa-Support]

PrusaSlicer wants all objects to be below the extruder clearance height except for the last object, which can be as tall as the printer's max Z.
[...]
The collision detection logic is pretty basic and will sometimes prevent you from Exporting printable G-code. It's up to you to take responsibility and increase the height tolerance.

https://help.prusa3d.com/article/sequential-printing_124589

In other words, all objects should be within extruder clearance height - except the last one.
The extruder clearance height should normally be set as the Z distance between the nozzle and the lower smooth rod.

I didn't reproduce all print scenarios myself but, theoretically, if

• the objects are within extruder clearance height (except the last one),
• don't overlap in extruder clearance radius,
• don't share the same X or Y coordinate,
• are distributed diagonally from front-left to rear-right,

there won't be a collision - not even if the filament runs out after the first object is completed because the nozzle will move in the other (supposedly free) direction and the lower rod will move above any (necessarily small) printed object.

The stock clearance values in our pre-sets are probably intentionally tighter than necessary but that's for safety reasons.
If there are that are uncovered print scenarios, please share a 3mf/gcode and a videos of them for us to review.
This should probably be discussed in Prusa Slicer's repository though.

If you modify our pre-set clearance height or radius, please do it at your risk and do your best to avoid print interruptions.

If your suggestion is about changing the Z height during a filament change then please check/follow other more specific issues and pull requests about this (e.g. #2875, #3532, #4115, #4344).

Can this issue be closed?

Michele Moramarco
Prusa Research

[ulab]

"don't share the same X or Y coordinate" and "the objects are within extruder clearance height" reduce the size of objects quite a bit to a point where sequential printing doesn't make much sense anymore.

Filament runout is also not the only case where this can become an issue. See #3623 for example.

It looks like @3d-gussner has assigned this to himself and is working on it? I am not sure why you want to close it now?

[3d-gussner]

@ulab

It looks like @3d-gussner has assigned this to himself and is working on it? I am not sure why you want to close it now?

I like the idea that is why I assigned myself to this issue. Not sure if and how fast we can implement it.

[3d-gussner]

With an improved Pause G-code in FW 3.14.0 we can now set the Z lift/raise height during a print.

Please follow the guide how to place the sequential parts and their order from above.

1. Most important rule: Order of sequential part needs to be from front to back.
   a. As we have the wire loom in the back anything behind the x axis is a "no-drop-zone"
2. Ideally place the parts small to high also from front to back to avoid unnecessary high pause raise between the parts.

• Add to Printers Tab -> Custom G-code -> After layer change G-Code {if (complete_objects) && (max_layer_z>20)}M125 Z[max_layer_z] S1; set pause height{endif}
  • This will set after each layer change, that is higher than 20mm and seqential printing is selected, a new Z raise height.
• Change in the Print Settings tab -> Output options -> Sequential printing -> Extruder clearance -> Height to 210mm or max height of your parts.
  • Otherwise PrusaSlicer will not allow sequential objects parts to be sliced, where the height is higher than 20mm (default).

Example:
Not optimized sequential print of two objects, where the first has 100 mm height and the second is only 20 mm (with a pause at 5mm).
Still following the Rule 1 object print order front to back

During the first 100mm high object print PrusaSlicer will add after at each layer above 20mm a M125 Z<value> S1 G-code line.

When the second object is printing and the pause at 5 mm is reached the printer will

• Raise Z by 100mm, which has been set in the previous higher print.
• Move to X Y pause position.
• Pause the print.

An optimized sequential print following Rule 1 and 2 will never have the extra high Z lifts and so save some time.

The default radius in PrusaSlicer is set to 45mm which is quite a bit. My measurements show ~35mm radius from the nozzle to the 45° part cooling fan on a MK3S.

When you follow the two rules and reduce the radius (please double check if that is the case on your printer, especially when you have a modified extruder, even the MK2.5 and MK3 will have a different radius than the MK2.5S and MK3S/+) you can place more parts on the bed.
If the highest part doesn't exceed the 20mm you can keep the default height clearance.
Please don't use the auto arrange in PrusaSlicer as it will not optimize the placement for sequential prints.

[3d-gussner]

@ulab

"don't share the same X or Y coordinate" and "the objects are within extruder clearance height" reduce the size of objects quite a bit to a point where sequential printing doesn't make much sense anymore.

You can place 7x6 28.2x28.2x = 42 cylinders on the bed

Now you want to print these sequential, this will only work if you have the clearance around the nozzle and all parts around it, and that is the Z distance from nozzle to PINDA ~0.1mm
With the Extruder clearance of 35mm radius and 25mm height you still can output 14 of these cylinders.

[3d-gussner]

Removed myself form this issue as there is a workaround for that.