Comparison of belt stiffnesses July 07, 2015 01:03AM |
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Re: Comparison of belt stiffnesses July 07, 2015 12:06PM |
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Re: Comparison of belt stiffnesses July 07, 2015 02:39PM |
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Re: Comparison of belt stiffnesses July 07, 2015 03:29PM |
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Re: Comparison of belt stiffnesses July 07, 2015 05:55PM |
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Re: Comparison of belt stiffnesses July 08, 2015 12:40PM |
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Re: Comparison of belt stiffnesses July 08, 2015 12:53PM |
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Re: Comparison of belt stiffnesses July 08, 2015 01:19PM |
Registered: 11 years ago Posts: 564 |
Quote
dc42
What formula do you think extruder hysteresis compensation needs to follow? My fork of the Duet firmware allows for a term proportional to extrusion rate to be added to the extrusion amount, but it isn't successful at avoiding over extrusion at corners. I am prepared to try other ways of modifying extrusion, but I would like a mathematical basis to work from.
Re: Comparison of belt stiffnesses July 16, 2015 08:56PM |
Registered: 9 years ago Posts: 344 |
Quote
LoboCNC
Quote
dc42
What formula do you think extruder hysteresis compensation needs to follow? My fork of the Duet firmware allows for a term proportional to extrusion rate to be added to the extrusion amount, but it isn't successful at avoiding over extrusion at corners. I am prepared to try other ways of modifying extrusion, but I would like a mathematical basis to work from.
I'm ecstatic to find someone willing and able to work on the hysteresis issue as this ripples thru the entire printer design. If I understand the existing extruder advance code, it looks like he's got a pretty sophisticated model of the flow rate adjustment, but it looks like he tries to implement the compensation by jamming in extra steps into the extruder step stream. People who have tried using this code mostly report that it just makes the extruder skip steps.
As a first cut, what I would really like to see is a very simple time advance of the extruder motion. In other words, you do all of the normal calculations for coordinating the extruder motion with the the X-Y motions, but you simply start executing the resulting extruder motion profile N millisec before you start the X-Y motion profile. And then, of course, the extruder will also stop moving the same N millisec before the X-Y motion terminates. In practice, it may be easiest to implement this as a delay in spitting out the X-Y step & direction signals. I've been tempted to try this myself in the Marlin code, but I have no clue how the bowels of the step generation interrupt code work.
My guess is that this simple approximation should help quite a bit.
Re: Comparison of belt stiffnesses July 17, 2015 10:45AM |
Registered: 11 years ago Posts: 335 |
Re: Comparison of belt stiffnesses July 17, 2015 11:49AM |
Registered: 11 years ago Posts: 564 |
Quote
691175002
I suspect that the amount of time you need to advance the extrusion commands will vary by print speed, material and temperature.
At some point you have to wonder if just sidestepping the problem entirely by running higher acceleration is the best option. If you don't slow down for corners to begin with, there is no need to adjust the extrusion rate.