Low Speed for 3d Printing application

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05 Dec 2019 20:22 #152097 by Muz94

PCW wrote:

Muz94 wrote:

PCW wrote: One way to avoid the entire TP issue is to use velocity based extrusion.
For optimal operation, this probably requires delaying the motion in hal
before its feed to the joints so the extruder response over time can be
modelled and compensated

I believe that Machine kit has implemented a delay component that could
be used for delaying motion. If simple lookahead is not good enough, a
FIR filter could be used to process the velocity signal. All of this is pretty
slow so a servo thread loop time resolution should be fine.


How would this work? Do you need to make changes in the gcode to have velocity data or it can be done with the information already present in a normal slicer gcode?
Do you have any advice on where to start?


In the very simplest case you would take motion.current-vel, scale it and feed it to the extruder stepgen velocity

Next would be to delay all motion joints with a delay component and feed the non-delayed velocity to the stepgen

Fancier would be to feed the non-delayed velocity to a filter that compensates for the time domain response
of the extruder


The problem is that there are also moves withous extrusion, how can you deal with those? I fear it would take some additional effort

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05 Dec 2019 20:24 #152098 by Muz94

andypugh wrote: Hopefully in the pipeline.

“The good news is, I have a branch that supersedes it, and does a slightly more complex blend (using two tangential arcs), and can also blend in ABC as well.”

What is this?

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05 Dec 2019 20:39 #152102 by andypugh

What is this?


Potentially good news from an email.

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05 Dec 2019 20:42 #152105 by andypugh

Muz94 wrote: The problem is that there are also moves withous extrusion, how can you deal with those?


hackaday.com/2014/05/10/blobless-printin...-velocity-extrusion/

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05 Dec 2019 20:46 #152106 by Muz94

andypugh wrote:

What is this?


Potentially good news from an email.


:0 is there a way to access that branch?

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05 Dec 2019 20:47 #152107 by Muz94

andypugh wrote:

Muz94 wrote: The problem is that there are also moves withous extrusion, how can you deal with those?


hackaday.com/2014/05/10/blobless-printin...-velocity-extrusion/


I was reading exactly that (and this, where there is a detailed explaination basdebruijn.com/2014/09/velocity-extruding-revisited/ )
Very cool and interesting, but also a very hard work to replicate, i will have to find a different solution if possible.

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06 Dec 2019 09:34 #152135 by andypugh

Muz94 wrote: Very cool and interesting, but also a very hard work to replicate, i will have to find a different solution if possible.


The basic idea is much simpler than it sounds from that write-up.

Though I don't think it is trivial to work-in filament retraction.

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06 Dec 2019 12:36 #152151 by Muz94
Yes, it's absolutely feasible, but I just don't have the time for a project like that. Tonight I'll try to turn my config. Into a simulator and swap U and Z axis.

Do you think there might be a way to delay the u axis without driving it in velocity mode?

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06 Dec 2019 14:45 - 06 Dec 2019 14:46 #152158 by PCW

andypugh wrote:

Muz94 wrote: Very cool and interesting, but also a very hard work to replicate, i will have to find a different solution if possible.


The basic idea is much simpler than it sounds from that write-up.

Though I don't think it is trivial to work-in filament retraction.


I would think that this could be handled with acceleration factored in
(perhaps with some accel/deccel assymetry)
Last edit: 06 Dec 2019 14:46 by PCW.

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06 Dec 2019 18:23 #152167 by Muz94

Muz94 wrote: While looking around for an idea i came across to this configuration :
github.com/dabit20/rpi_cnc

and guess what? he runs the machine with swapped A - Z axes.
I'll try to ask him if he did that to fix this exact problem


The author of this config. confirmed that this solved his issues, so i have a question: would it be hard to change the setup in the TP so that the blending happens between XYU instead of XYZ? This would be much more elegant than working with a machine with swapped axes. Is it just a matter of changing a few lines of code and recompiling or what?

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