Interesting reading - Presure in advance
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Hi,
I have find this web.... Has interested articule, one of this, speak of linear advance, think is the same that pressurein advance.
Linear Advace/Pressure in advance
P. D.: Too speak a new type of infill. Gyroid infill, very promissing
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@peirof said in Interesting reading - Presure in advance:
P. D.: Too speak a new type of infill. Gyroid infill, very promissing
You may be interested to know that gyroid infill will be coming to Cura soon. If you are keen to try it today, install one of my development releases that you can find at
https://www.dropbox.com/sh/s43vqzmi4d2bqe2/AAADdYdSu9iwcKa0Knqgurm4a?dl=0
All feedback is welcome.
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@peirof said in Interesting reading - Presure in advance:
Hi,
I have find this web.... Has interested articule, one of this, speak of linear advance, think is the same that pressurein advance.
Yes, it's the same as the pressure advance that RepRapFirmware has provided since early 2015. We originally called it "extruder elasticity compensation".
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hi,
after some readings... i think the optimal pressure in advance depends primary two factors:
- Distance from extruder to nozzle
- Kind of filament (Pla, Abs, Petg,....)
- Some factor more in take in account?
- There is some test for find the optimal value?
- Can pressure in advance setup in DWC, for filament?
- There is one value for pressure in advance that works well for stardart filaments? (no flexibles, no metal, no ceramic,.....)
thaks
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@peirof said in Interesting reading - Presure in advance:
hi,
after some readings... i think the optimal pressure in advance depends primary two factors:
- Distance from extruder to nozzle
- Kind of filament (Pla, Abs, Petg,....)
- Some factor more in take in account?
- There is some test for find the optimal value?
- Can pressure in advance setup in DWC, for filament?
- There is one value for pressure in advance that works well for stardart filaments? (no flexibles, no metal, no ceramic,.....)
thaks
You could take a look at my blog some time - lots of testing on there. There is also a new post and video coming very soon which will interest you.
Nozzle diameter has a big impact on how pressure builds up. Smaller nozzles suffer more than larger ones. Pressure build up is a function of both print speed and time at that speed. So the best way to test in my opinion, is to do long straight moves at highish speed and observe the thickening at the ends. Increase pressure advance until the lines are even thickness. Pressure build up also takes time to decay. Once I have found the optimum value for a nozzle / filament combination then that value will work for all speeds between 40 and 300mm/sec (but you need multiple melt chambers to be able to print that fast). Filament temperature has negligible effect on pressure (on my machine). I haven't done much work on evaluating different filament types but it's on my list of things to try.
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Still amazes me how long it took Marlin to get a pressure advance function. Sailfish and Marlin come from roughly the same code background and Sailfish had JKN advance back in 2011 or so. There were many GitHub discussions and attempts at it, there just never seemed to be any developers with the right kind of chops to do it. I don’t know if the big refactors over the last few years made it easier, or if it was just about getting the right dev looking at it.
Smoothieware still doesn’t have it, but that’s due to a pretty big, early motion control code architecture decision to slave E to the other axes... makes it really difficult to move E steps around.
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I have no words... Congratulations for your work in the blog/web...
Impressive 3d printer ... and impressive camera with which you have recorded the videos ...
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@peirof said in Interesting reading - Presure in advance:
I have no words... Congratulations for your work in the blog/web...
Impressive 3d printer ... and impressive camera with which you have recorded the videos ...
Thanks. The camera is nothing special - just a hand held Camcorder - Panasonic HC-X900 about 5 years old.
One other thing about pressure advance that I forgot to mention is that acceleration also plays a big part. What happens is that the rate at which extruded filament comes out of the nozzle cannot be accelerated fast. The entire extrusion system acts a bit like a sponge. So when if you accelerate too fast, all you get is a pressure pulse inside the extrusion system and there is a lag before the filament starts to come out faster. Meanwhile, the print head is moving faster so you get under extrusion to start with. This is of course why we need pressure advance to compensate. However, there are limits and if you set acceleration too high for the print head, no amount of pressure advance will compensate. For me, on my machine, the critical acceleration rate is 1000mm/sec^2 and no higher.
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I found very interesting the fact that acceleration limitation is not mechanical (inertia)... Great blog post!
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@deckingman said in Interesting reading - Presure in advance:
For me, on my machine, the critical acceleration rate is 1000mm/sec^2 and no higher.
1000mm per second per second? So, assuming a brisk print speed of 100mm/sec, you reach full speed in 1/10th of a second from a full stop?
I've seen the videos of your machine and I'm surprised that the mass of your "print head" (with it's diamond hot end, 3-5 extruders and stepper motors) would be able to accelerate that fast.
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@garyd9 said in Interesting reading - Presure in advance:
@deckingman said in Interesting reading - Presure in advance:
For me, on my machine, the critical acceleration rate is 1000mm/sec^2 and no higher.
1000mm per second per second? So, assuming a brisk print speed of 100mm/sec, you reach full speed in 1/10th of a second from a full stop?
I've seen the videos of your machine and I'm surprised that the mass of your "print head" (with it's diamond hot end, 3-5 extruders and stepper motors) would be able to accelerate that fast.
Yes that's exactly right. In fact, doing the maths on the motor specs, and taking one carriage mass of around 2Kgs, I could (and have) run at twice that acceleration). Also, the maths assumes a single motor so because on a CoreXY, each motor contributes to motion when doing pure X or pure Y moves, I could double those accelerations again and likely achieve 4,000 mm/sec^2. However, for 45 degree moves, only a single motor is used. But then again, the geometry of a CoreXY is such that for such moves the belts move around 1.4X the distance that the gantry travels, giving a leverage effect. So the maximum acceleration for that mass, with those motors (Nema 17, 59N.cm) is about 1.4 x 2,000 - say 2,800 mm/sec^2.
I do of course have the extruder mass as well making the total mass moving in the Y direction in tad over 4Kgs but the extruder gantry is a separate XY gantry with it's own motors, so for pure X or pure Y, 4 motors are employed and for 45 degree infill, 2 motors are used.
Once in motion, things get a little better still because instead of starting from a standstill, it starts from the instantaneous speed threshold (jerk) which in my case is set to 20mm/sec.
If you read my latest blog post, you'll see that I was printing at up to 300mm/sec with "jerk" set to 20mm/sec. So a speed change of 280mm/sec at 1,000 mm/sec^2 would take 0.28 seconds during which time the head would travel 39.2mm. Meaning that the acceleration and deceleration distance would be around 78 mm which for a 100mm long move means that the print head would only be at 300mm/sec for 22mm. If acceleration was set to less than 784 mm/sec^2 then it would never reach 3000mm/sec during a 100mm long move.
If you want to see it in action, watch the video that accompanies that blog post from about 9 minutes onwards. Here is a link https://www.youtube.com/watch?v=rUV5IZxfAxU
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then I ... print without problems, at a speed, grab the chair, of ... 50 mm / s or 60 mm / s.
How do you stay? HE ...
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@peirof There is nothing wrong with that. Most people print at 50 to 60mm/sec and usually that's fine. You start the print going, then go away and do something else and come back when it's finished so it doesn't really matter how long it takes.
The advantage of being able to print fast really comes into it's own when you have a big printer and want to print big items. That can often take several days. Personally I would never feel comfortable about leaving the house with the printer running. The same applies to washing machines. I'm comfortable with them running over night as I have smoke and fire alarms etc, but if I had to go out, I'd either turn the washing machine off or wait until it finished. That's not an option with my printer as the heated bed would cool down and the part would likely fall off. So it can come down to a choice between not leaving the house for 3 or 4 days, or print at 5 to 6 times the speed and have the job finished overnight. Or if you make things commercially where the adage "time is money" counts.
But I agree, for the majority of hobbyists, printing fast doesn't really matter. -
It is also nice to be able to print fast when prototyping, making several iterations to tune dimensions. I go up to 120-150mm/s, with 1 perimeter, 10% infill, so small parts take less that 15 minutes to print.
As you, I don't print with nobody at home!
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@fma said in Interesting reading - Presure in advance:
It is also nice to be able to print fast when prototyping, making several iterations to tune dimensions. I go up to 120-150mm/s, with 1 perimeter, 10% infill, so small parts take less that 15 minutes to print.
As you, I don't print with nobody at home!
Yes I do that a lot too. That's why I print on removable glass and why I have 3 sheets of it - so that I can slide one out when a print finishes, slide a new one in and be printing again, in less than 2 minutes.
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The irony here is that I checked my direct drive delta kit's printer settings and found my accel and "jerk" are also 1000mm/s^2 and 20mm/s:
M201 X1000 Y1000 Z1000 E8000 ; /sec, not /min
M566 X1200 Y1200 Z1200 E1600 ; /min, not /secI never realized that they were this high, but I never had problems so never tinkered with them. On the other hand, I've never even tried a print speed of 300mm/s. (I've done 120mm/s successfully, but prefer to stay around 80mm/s max print.)
So, I owe you a "thank you" for making me look at my configuration and realizing something I hadn't paid attention to.
(I wouldn't even dream of running my duet converted FFCP at these speeds. For that printer, I start to see quality losses at 50mm/sec.)
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@garyd9 Spooky how you happen to have the same values.
Actually, in the grand scheme of things, 1,000 mm/sec^2 is nothing much. Acceleration due to gravity is 9.81metres/sec^2 so we are are only talking 1/10th G.
In a previous life I did a lot of stuff with internal combustion engines. You probably know that a typical road car engine can do 6,000 rpm plus. For the sake of keeping the maths simple, the stroke might be 100 mm, and every piston has to start at the top, travel 100mm, reverse direction and travel back up to the top. So have you considered that at 6,000 rpm, it does that 100 times per second. Or 5ms for a complete up-down-up cycle or 2.5ms to go from rest, travel 100mm and slow down to a stop, before reversing direction and repeating. And that's nothing special either. F1 engines are now limited to (I think) 12,000 rpm but 18,000 rpm has been rumoured to be true in the days of 1.5 litre turbo engines. That's 2 to 3 times faster still. So in the world I used to inhabit, 1,000 mm/sec^2 is bu**er all.
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@deckingman ahh, but how much acceleration does your printer actually see during a corner jerk? Hmm
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@rcarlyle said in Interesting reading - Presure in advance:
@deckingman ahh, but how much acceleration does your printer actually see during a corner jerk? Hmm
Nobody likes a smart are*e
All jesting apart, I have mulled this over from time to time. It won't be infinitely high acceleration - that's impossible. All else being equal, I guess it depends on what "gives" (and something must). When a ball is struck by a foot or a club, the ball itself deforms at the moment of impact, then it accelerates until the force is no longer applied.
As an aside but interesting none the less, is that my (now deceased) father-in-law used to make arrows for traditional long bows. He was somewhat of an expert in his field and wrote a book on it. What is interesting is that, when an arrow is "loosed", it bends as it accelerates forwards. The optimum "bend rate" for accurate shooting is such that the arrow does 1 1/2 deflections before it leaves the bow. I won't go into the details but it's called "the archers paradox". The stiffness of the arrow is called the "spine" and a matched set of arrows will all not only have the same weight, thickness, taper and length, but also have the same "spine", and that "spine" will be matched to the draw weight of the bow. Surprising how much science there is in a simple thing like an arrow.....
So maybe the optimum "jerk" (I hate that term) for a 3D printer is one that matches the printer equivalent of an arrows "spine".
Another thing I wondered about (and you will know the answer to this better than I) is does motor rotor inertia play a part? I'm just thinking along the lines that the motors (on a CoreXY) will be spinning in one direction, then when there is a corner jerk, they will have to reverse direction, which can't happen instantly because of the inertia of the rotor. My gut feel is that the rotor inertia would be insignificant in comparison to the inertia of all the other moving mass but do you know differently?
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@deckingman said in Interesting reading - Presure in advance:
My gut feel is that the rotor inertia would be insignificant in comparison to the inertia of all the other moving mass but do you know differently?
If I remember correctly, the resulting torque is moment of inertia (kg·m²) x angular acceleration (rad.s⁻²).
Moment of inertia of the rotor is: mass (kg) x radius² (m²), where radius is taken at center of gravity of the section of the half rotor (R/2 for a plain cylinder).
Correct me if I'm wrong...
