[BUG] Rapid changes of acceleration break linear advance when using Junction Deviation #15473
Comments
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How did you arrive at the K Factor value of 2? Did you do a k factor calibration test? http://marlinfw.org/tools/lin_advance/k-factor.html |
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I think every change of acceleration need to be a recalibration of K-factor. Marlin use for lin advance only the single K-factor with speed and length without to check the acceleration. If Marlin use K-factor depending from acceleration, Marlin need massiv more calculations, especially if S-Curve enabled. |
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Cura is attempting to make things work well on a machine that doesn't have independent intelligence to adjust flow and speed and so on. If you like the way Cura tunes things with its internal logic, it would be a good idea to turn off all of Marlin's advanced features. |
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@BarsMonster still having issues? |
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given the lack of activity and that this is more likely to be cura that screws up with marlin by trying to optimize independant of marlin i will close this one we can always reopen |
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@boelle Yes, issue is still there and does not allow me to get perfect prints even with linear advance disabled, and cura acceleration disabled. Even without linear advance and without acceleration changes - issue is still there, though very rare to reproduce, and is less terrible, but it is still there. Here and there you get spots of underextrusion on outer shell and it does not look perfect. It seems that it is some sort of race condition somewhere in the Marlin's core, which causes to skip extruder steps in certain conditions. And changing acceleration makes it more significant. I believe acceleration changes should not cause extruder step skips so massively and consistently, as it generates valid g-code. Enabling acceleration control in Cura is just a convenient way to show this error in reproducible manner. |
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@boelle Can we reopen it? |
While I agree with you from the practical side, behavior of Marlin here is definitely completely broken by valid G-code. Is looks like completely broken math, when E stepping is stopped for some time, and then restarted. Again, due to consistence of under-extruded areas it looks like code error, and not mechanical issue. |
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Ive yet to see a valid k value greater then 0.5 with any filament on any of my 6 printers k2 seem very high and is considered the max k. i would totally slice the model shown if you post the stl for my printer and post my result. |
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The sort of “chattering” under extrusion you show in the first picture is a lot like what I saw on some prints when I had Linear Advance enabled. And I was not using acceleration control or jerk control (PrusaSlicer) and my K was only 0.7. |
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@Vertabreak @ManuelMcLure This is for Bowden, that is the reason for high K value. Anyways, issue is not in K value itself. I am pretty sure that you will be able to print model with your settings - the issue is not that I am unable to print it. If I remove all acceleration control, linear advance, e.t.c. it will print just fine. The issue is that there seems to be some sort of math error in the core of step calculation code in this corner case, that is rarely used (linear advance enabled, bowden = high K value, rapid acceleration changes). Model I was printing is this one: https://www.thingiverse.com/thing:24238 |
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Let's just say it's a "feature, not a bug" that Linear Advance doesn't like frequent changes in acceleration. Cura is naively assuming you're not using such features. |
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Unfortunately, there are still major problems with Linear Advance even if not using acceleration control. |
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@BarsMonster is the issue still the same with all the updates in the last 8 days? |
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btw, who can confirm there is an issue? use the same configs as OP and the same hardware if possible |
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@boelle I've tested with latest Marlin-bugfix-2.0.x and currently it is much worse, "pulsating" extrusion starts from the very first layer, and under-extrusion is so severe that print cannot stick to bed. Not sure whether it is code change or config change. Please see attached latest config files for 2.0.x and latest cleaner gcode. 5mm_acceleration_stress_LA.zip
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just remember i'm not a code guy, i just keep the issue list, making sure issues dont die @thinkyhead is the maintainer that does code arround here :-) |
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I compared behavior on K=0.5 and K=1. On K=0.5 it is not terrible, but far from perfect. At K=1 you can see that it looks like skeleton. At K=2 it is not printable. So currently it looks like linear advance is completely unusable for Bowden setups, and I assume for direct extruders it might still show rare glitches.
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think ill take video of printing the model linked with my machine and posting it. |
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@BarsMonster, can you try your configuration with this branch? It addresses a LA issue which might be related to this. This is currently experimental, and not cleaned up like I would a normal PR. You should completely replace my configuration files with your own. |
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@sjasonsmith I tested EXPERIMENTAL_LA and got identical result for K=1. BTW, just weighted the parts. Cura's simulation shows 4g, with K=0 actual print weight 3.47g, with K=1 weight is 1.15g. So there is severe underextrusion. |
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K1 seems extremely high even on a 2 foot Bowden tube have you run calibration to find valid k value. |
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@Vertabreak Yes, I did calibration and got optimal value around 2. When not using acceleration control - prints look almost ok (corners are square), but there are still rare glitches (pulsating extrusion). Anyways, my understanding is that from math point of view for any K value and regardless of whether acceleration control was used or not - weight of the print should be the same (i.e. same total length of filament pushed though). |
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soon as i sort out cura not starting ill try printing the model and posting results to compare. |
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My config for marlin Configuration.zip |
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have you checked if your nozzle is clean? ie take it out and heat it up with lighter and remove all filament so you can see light through it on e3d nozzles you can use a 2mm drill bit to clean out from the filament side... but use the bit with your fingers and be carefull when you got all filament out use a sewing needle to clean the last bit, |
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A dirty nozzle is not going to violate conservation of mass. If there's really underextrusion you can measure it by putting a mark on the filament according to the total extruded length in the gcode file, and check whether the mark reaches the hole into the extruder when the print finishes. If it doesn't, then either the extruder is slipping or missing steps or the planner is moving the extruder axis less than the gcode tells it to do (logically skipping steps). The latter should be detectable in a simulation run not connected to any actual hardware. |
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As an aside, I just started trying TPU and I've found calibration indicating a need for K>4 at 230 °C, but increasing the temp to 250 let me take it back down to 3.4. Just to confirm, again, that high K values are meaningful. I did not experience this issue even with K=5, but I'd already switched back to classic jerk because of it. |
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@boelle Thanks for the tests, indeed your configs looks correct for reproduction of the issue. |
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mcu: re-arm (you would have known from the configs) Here is the benchy: 3DBenchy_0.2mm_PLA_MK2.5S_1h50m.zip i use prusa slicer and not cura, not sure if that makes any difference |
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How is this "inactive"?! The OP replied just a week ago and there's clearly an issue that OP and others are involved in reporting test results on and debugging. |
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I notice under-extrusion after enabling Junction Deviation in my config. If I go back to traditional jerk, there is no under-extrusion. That is the only change I make when troubleshooting this. I found this thread by searching for my problem. My version of Marlin is a little old now. It is from 09/17/2020 (I'm not sure where the exact version number is). |
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For those with these issues, have you tried the following tips (source):
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Update: After updating to v.2.0.4.4 I've spent the last several days testing @thisiskeithb's comments. I find I still need combing in Cura as well as retraction to keep stringing and blobbing away, but I've been able to tune my machine where there is no underextrusion now. So I am no longer reporting the same problem; just the opposite. |
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I confirm this issue too. MKS Robin nano, PrusaSlicer without any pressure controls. Lin adv with JD take the same under extrusion. Just rollback to classical jerk for good results with lin adv. |
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On MKS Gen-L board I was able to reproduce consistent (same place on 2 prints of the same part) pulsating extrusion without acceleration control, linear advance (K=0) and with junction deviation disabled, just on 1 layer. I.e. these 3 options make this issue much more severe, but issue exist even without JD and without LA, just very rare. This line defect is quite long, under-extrusion is visible for ~70mm length of the perimeter. Also, printing outer perimeters first makes it more visible.
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After I migrated to SKR PRO 1.1, I was unable to reproduce the issue with migrated config. So the issue could be more reproducible on slower CPUs. |
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This is worth a read for anyone using 2208 and 2209… #11825 (comment) |
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@BarsMonster: That does not sound like an accurate representation of the findings. Acceleration control has nothing to do with the segment sizes Cura produces. That's a function of the mesh resolution and deviation settings. |
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@richfelker You are correct. I've retested it just now, not sure why I believed that. I've deleted comment with incorrect information. |
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@BarsMonster |
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Hi. For PLA, with a correct direct drive extruder and short path between gears and nozzle, usual values are within the range [0. ; 0.2] Second thing : when printing your K factor calibration pattern, you should also change your firmware printer settings (jerk, acceleration...) to the desired values as firmware value are generally quite different to the slicer ones. I already saw people saying that any K factor value provide the same result, except that their built-in jerk and accel value prevent linear advance to even start to change anything... Linear advance is meant to be tune with a "constant" set of move parameters. If you change your acceleration dynamically, there is no point in using Linear Advance: don't. As you may now FDM printing is ruled by viscoelastoplastic fluid dynamics, so NO, there not any single reason at high extrusion speeds and accelerations that the amount of "asked" filament will eventually extrudes depending on your configuration... You seem to know what you are doing , but I would also check whether your extruder is flowing nicely or not. I would be more convinced you have an issue if posting a proper Kfactor calibration patern... |
My calibrated K for PETG with a bowden is 1.4. K=2 is high but not "insanely out of the range".
This is false. LA slows down the entire print speed if jerk and accel settings prevent keeping up with the necessary extruder pressure adjustments at the requested speed.
Everything reported here was reproduced with acceleration and jerk control in the slicer completely turned off (i.e. using a fixed setting from the default or from custom start gcode).
Unless the extruder gear skips or the extruder motor misses steps, the total extrusion volume (and the total integrated E-axis move) should be exactly the nominal amount, regardless of LA. This is completely testable.
If it were a clog the extruder would grind and the effect would not go away with different LA/JD/jerk settings.
This is really hard to do since the canonical pattern generator produces something with ooze/stringing all over the place that's destroyed when you remove it from the bed, and hard to photograph on the bed when your filament is black and bed is black. I actually use a one-wall skew-cylinder test instead, with Cura overhang angle settings tuned to switch speeds for about 1/4 of the circumference. It's easy to eyeball the appproximate K needed to get a consistent wall at the switchover using the Tune menu, then fine-tune it with a caliper. |
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Won't go in a quote war. There is - in this whole thread - no reproductible method providing details to reproduce the problem or explain it on a standard setup. If you can't even make a "nice" canonical pattern to assess your K-factor value is good and not the result of a "not bad but not perfect" hardware, there is no point discussing further. To me this looks like people with a Traban trying to go fast like a Ferrari and ending up in the wall. Go direct drive, fine tune your printer and don't ask the firmware to make your "standard hardware" printing faster than what is physically achievable, especially with a bowden setup, constant feedrate changes, and an elastic material. |
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This issue is stale because it has been open 30 days with no activity. Remove stale label / comment or this will be closed in 5 days. |
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This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs. |
Description
When objects sliced by Cura with acceleration control enabled - Cura generate g-code with lots of speed changes, which is not invalid. When this g-code is printed with linear advance and junction deviation enabled (M900 K2) - sometimes extruder is missing alot of steps, and this breaks everything. This is not hardware related, as position of defects is consistent on every print, and also alot of hardware tweaks did not solved the issue. Example g-code is attached.
It seems geared extruder show less of an issue (i.e. looks like fixed number of steps are missing). So with Esteps 415 issue is much less, with Esteps 93 it is much more significant.
Lots of hardware tricks tried - with no luck:
Different drivers: A4988, TMC2209 (spreadcycle). Microstepping 1/16 and 1/8 (to reduce step rate). EMI supressors on E-motor, series diodes (for A4988). Different marlins: 1.1.9 and latest 2.0 x. With different extruders (stock one with Esteps 93 and geared BMG with Esteps 415, with different spring tension. This is definitely not filament slipping). Also tried different oversized power supply to ensure there is no power sag.
Steps to Reproduce
5mm_acceleration_stress_LA.zip - cleaner example, with no timelapse code
Expected behavior:
Everything is smooth and extruded uniformly.
Actual behavior:
Steps are severely missing on extruder, which makes printing not feasible for K=1 and higher.
Additional Information
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