RINGING the electromechanical challenge

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walshlg
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Re: RINGING the electromechanical challenge

Postby walshlg » Sun Nov 05, 2017 9:35 pm

JERK- jetguy explained it to me. Jerk is the speed below which acceleration/ deceleration will NOT be applied.

Acceleration - still don't understand it. Units on display are max mm/sec. not mm/sec**2. If not at max, how do you calculate how much acceleration to apply? Does the slicer know jerk and acceleration since they are settings in firmware?

Vice Chief
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Re: RINGING the electromechanical challenge

Postby Vice Chief » Sun Nov 05, 2017 9:49 pm

The gcode doesn't say anything about acceleration that I can see, so I assume it is stored in firmware.

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walshlg
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Re: RINGING the electromechanical challenge

Postby walshlg » Sun Nov 05, 2017 10:02 pm

yes afaik it is in firmware but without knowing the setting the slicer can't really predict print time very well.

Vice Chief
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Re: RINGING the electromechanical challenge

Postby Vice Chief » Tue Nov 14, 2017 3:27 pm

I have an accelerometer setup which can collect vibration data.

I'd like to pursue this further. I could use help with the analysis side. I'm specifically looking for someone with some programming skill in Python, or some experience in signal analysis with Matlab.

Anyone interested in working with me on this?

MDVolle
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Re: RINGING the electromechanical challenge

Postby MDVolle » Thu Nov 16, 2017 7:34 am

All,

I'm SO glad that this is continuing as a conversation - I have been out of town for a bit and missed all of this and was just enjoying catching up.

A few notes - I have noticed that there is some (to a machinist) slop in the fit of the linear bushing/bearing in the head block - a visible play if you rock the head and watch the bushing - at least on my machine - which may also be an odd machine - I have the new "V2" arrangement but the 9 point bed and LED lights only on one side (which I removed anyway).

I have also been experimenting with using spindle oil on the linear rods - I felt that there was a tremendous amount of stiction in mine - which wasn't new when I got it.

The oil seems to be a bit better and smoother - not enough to send everyone looking for a squirt bottle yet - I have a few more things to try (I want to clean everything out and try TCS slideway, like I use on my mill).

I also found it very interesting that the material vs ringing tracks so well - but I suspect not with density - probably with elasticity - the wood filled material has almost no spring and polyFlex is like printing with a spring attached to the end of the nozzle - my guess is that it would also change in magnitude as you adjusted the temperature of the polyflex - essentially "adjusting" the viscosity and spring constant.

I need to watch the excellent 1000FPS video from Vice Chief a little more - If I am seeing correctly, the bounce is in the "idle" axis - so the forward motion of the head stops, the motor stops and that entire axis/motor/belt/bearing is (in theory) parked at that location - so possibly kevlar reinforced timing belt would reduce the total spring? I have also worked with the perforated stainless "belts" that use a sprocket type drive wheel and they seem much stiffer - again, possibly not solving the problem but changing its nature.

Is belt tension a factor? - I don't see how it would be adjusted on our machines but it is on others.

Mark

firesped
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Re: RINGING the electromechanical challenge

Postby firesped » Thu Nov 16, 2017 11:08 am

for the 1.2.2 firmware, this is the configuration of movement on the printer.
/**
* Default Settings
*
* These settings can be reset by M502
*
* Note that if EEPROM is enabled, saved values will override these.
*/

/**
* With this option each E stepper can have its own factors for the
* following movement settings. If fewer factors are given than the
* total number of extruders, the last value applies to the rest.
*/
//#define DISTINCT_E_FACTORS
#ifdef DUAL
#define DISTINCT_E_FACTORS
#endif

#ifdef DUAL
#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 200*16/4, EXT0_STEPE , EXT1_STEPE }
#define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25, 25 }
#define DEFAULT_MAX_ACCELERATION { 9000, 9000, 100, 10000, 10000 }
#else
/**
* Default Axis Steps Per Unit (steps/mm)
* Override with M92
* X, Y, Z, E0 [, E1[, E2[, E3]]]
*/
#define DEFAULT_AXIS_STEPS_PER_UNIT { 80, 80, 200*16/4, EXT0_STEPE }

/**
* Default Max Feed Rate (mm/s)
* Override with M203
* X, Y, Z, E0 [, E1[, E2[, E3]]]
*/
#define DEFAULT_MAX_FEEDRATE { 300, 300, 5, 25 }

/**
* Default Max Acceleration (change/s) change = mm/s
* (Maximum start speed for accelerated moves)
* Override with M201
* X, Y, Z, E0 [, E1[, E2[, E3]]]
*/
#define DEFAULT_MAX_ACCELERATION { 9000, 9000, 100, 10000 }
#endif

/**
* Default Acceleration (change/s) change = mm/s
* Override with M204
*
* M204 P Acceleration
* M204 R Retract Acceleration
* M204 T Travel Acceleration
*/
#define DEFAULT_ACCELERATION 1000 // X, Y, Z and E acceleration for printing moves
#define DEFAULT_RETRACT_ACCELERATION 3000 // E acceleration for retracts
#define DEFAULT_TRAVEL_ACCELERATION 1000 // X, Y, Z acceleration for travel (non printing) moves

/**
* Default Jerk (mm/s)
* Override with M205 X Y Z E
*
* "Jerk" specifies the minimum speed change that requires acceleration.
* When changing speed and direction, if the difference is less than the
* value set here, it may happen instantaneously.
*/
#define DEFAULT_XJERK 12.0
#define DEFAULT_YJERK 12.0
#define DEFAULT_ZJERK 0.4
#define DEFAULT_EJERK 5.0


EXT0_STEPE and EXT1_STEPE are set earlier in the configuration file for easier use by the end user. Everything they need to change is set at the beginning.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
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zemlin
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Re: RINGING the electromechanical challenge

Postby zemlin » Fri Nov 17, 2017 12:44 pm

My thought is that on the N2/N2+ the cross-rods supporting the extruder head are probably the biggest springs in the system. I'm swamped right now, but if nobody beats me too it, I will test that theory.
If I'm right, magnitude of the ringing in either axis will be dependent on the placement in the build volume. The center should be more prone to XY ringing than the edges - and a build in the center of one axis and at the outer limit of the other should demonstrate differences in magnitude of the ringing in each direction accordingly. A build in the center of the Y axis and the left edge of the X axis should show more ringing in X than in Y.

Another factor I've seen impact ringing and build quality are the dynamics settings (acceleration and jerk) on the extruder drive. I've done a bit of testing of this on my Makergear printer, which is also a direct extruder, Marlin-based, gantry printer. The table slides for the Y axis on this machine.

Setting extruder accel and jerk to very low settings slows the build time and impacts ringing and build quality. FWIW, I am currently running both printers with extruder accel set to 5000, and extruder jerk also set to 5000. I haven't done careful a/b comparisons with this setting, but my impression is that ringing is reduced compared to lower settings on the extruder jerk.

MDVolle
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Re: RINGING the electromechanical challenge

Postby MDVolle » Wed Nov 22, 2017 9:45 pm

Just sticking my nose into the discussion again - feel free to trim it off or refute it completely - that's the beauty of discussion.

Reading our collective posts, a few things started to gel together - NOT a solution but some things that might be related?

I have noticed that for some strange reason, my prints that are done at higher speeds (as much as 60mm/sec with NylonX) seem to have smoother finishes and more uniform corners (yes, a little ringing but still better looking)

It also seems from my glance at the code posted (I'm not really a software guy) that the term "Jerk" isn't actually anything to do with the actual Jerk rate (which is the derivative of acceleration) but a threshold below which we won't worry about the jerk because the momentum of the stepper and the system will tolerate the change in speed as an instantaneous change (technically an acceleration approaches infinity scenario).

Having done some work with steppers, I sure get the advantage of dumping the extra code and calculation - just change the speed and be done with it (I have one piece of equipment that has NO ramps at all, but for the specific case, its very infrequent and works)

What if the threshold was set as low as possible, so that only frequency changes less that 2 were excluded from ramping?

It wasn't clear to me if the function was a "speed below which we won't ramp" or an "amount of change below which we won't ramp".

I also don't know if the system allows for the ramp to be scaled to a constant jerk rate or just scaled or how the ramp is shaped - so I have a LOT I don't understand about the system (yet).

Has anyone else experienced the smoother/faster scenario?

As for "damping" the steppers - there are several commercially available products - all variations on "visco-elastic" absorption - some are a plate that goes between the motor and the final mounting surface, others are a coupling or in some cases, what looks like a flywheel on the back end of the motor -

All of the effective ones I have seen or tried were specific to a motor or series of motors and were usually used with systems where the drive chain didn't include any elastic components - we have belts - OR they were employed to reduce noise or transmitted vibration to an absolute minimum - the N2 is actually fairly quiet (after you mod out the blower on the motion control board).

My specific experience is with vibration issues and damping and used in conjunction with a bellows type shaft coupler but its so different from the printer that it doesn't seem to apply much (astronomy and astrophotography mounts).

Apart from bad filament, bad nozzles or really bad settings, I continue to be amazed at how well the N2+ works. When it really screws up, its usually because "I told it to" somewhere in my design or settings - and there have been a few.

I also have had really decent luck with the extruder drive - no real problems unless the heat tube blocks and that could happen with any extruder
BUT It is clearly a part that could have some "weight management" applied to try and reduce the total moving mass - especially the left motor, which is quite a distance from the CG of the head and the bearings.

Mark

Tinkerer
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Re: RINGING the electromechanical challenge

Postby Tinkerer » Sat Dec 02, 2017 10:47 pm

Regarding weight /acceleration / printing speed:

https://www.youtube.com/watch?v=AKTvykTPjQw
...there's nothing like the smell of fresh ABS in the morning...

firesped
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Re: RINGING the electromechanical challenge

Postby firesped » Sun Dec 03, 2017 5:55 pm

so they are saying that the over all weight of the print head, rods, and everything effects how fast you can go.

what are the dimensions of our rods and would replacing them with Carbon Fiber rods be of benefit?

What can be done to reduce the weight of the print head carriage block itself? different material? making it not solid by creating openings in the sides while still keeping it structurally sound?

It does actually make a little bit of since because everything that is weight on the moving parts would cause vibration in the printer.

he does state that reducing acceleration may reduce ghosting with heavier weight but you will lose quality elsewhere. printing slower is more likely to increase quality.

Thank you for sharing this video as this was an issue I was beating my brains out about like 4 to 6 monthes ago when I was trying to get a job done with my upgraded trinus.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
Monoprice Maker Select v2

zemlin
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Re: RINGING the electromechanical challenge

Postby zemlin » Tue Dec 05, 2017 3:42 pm

I'm wondering how well carbon fiber rod would work with the ball bushings on the gantry. I'm thinking that it wouldn't be a good match. There are polymer linear bushings that would probably swap out, but I'd expect to lose a little precision going that route.

firesped
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Re: RINGING the electromechanical challenge

Postby firesped » Tue Dec 05, 2017 6:30 pm

actually I had emailed Jetguy asking
would there be any benefit to switching out the rods on the N2 to
carbon fiber rods to decrease weight?


His reply was
No,
#1 it's wear surface. Either the linear ball bearings in the center cross will destroy the surface leaving tracks or the outer ring of sliding bushings will stick slip and bind.
#2 About all you could do is gun drilled hollow case hardened tubes.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
Monoprice Maker Select v2

Tinkerer
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Re: RINGING the electromechanical challenge

Postby Tinkerer » Tue Dec 05, 2017 8:54 pm

I believe the major mass of that system in our N-series printers is the extrusion-head.
I would not care too much about the rods as of now.

By the way, I have a Bondtech Dual-Extruder-Kit in my N2 which is approx. half the weight of the
original extruder - and still experience ringing.
...there's nothing like the smell of fresh ABS in the morning...

MDVolle
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Location: Fullerton CA

Re: RINGING the electromechanical challenge

Postby MDVolle » Tue Dec 05, 2017 11:26 pm

Tinkerer has answered one of the most frustrating questions - does a lighter weight head reduce ringing - maybe - but even at half the weight, using the Bondtech extruders, the problem should still exist but the frequency of the oscillation should go up - lighter weight, faster vibration for the same input and with the lighter weight, it probably settles out a little faster?

There are glides that would work on CF rods, but it wouldn't be the type of bearings we have currently.

There are also ceramic coated AL and CF guide rails available but choices are limited in the small diameter this series uses.

Does anyone have info on the software question about jerk rate? I really like the simplicity of just using the ideaMaker software - I know some other programs would offer more detailed control but I've found workarounds for most of the things I had issues with.

zemlin
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Re: RINGING the electromechanical challenge

Postby zemlin » Wed Dec 06, 2017 1:36 pm

Jerk and acceleration are easy to alter in the start script.

I currently run

M201 X1600 Y1600 E5000 ; acceleration
M205 X16 Z1.0 E5000 ; jerk

Tinkerer
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Re: RINGING the electromechanical challenge

Postby Tinkerer » Wed Dec 06, 2017 2:10 pm

MDVolle wrote:Tinkerer has answered one of the most frustrating questions - does a lighter weight head reduce ringing - maybe - but even at half the weight, using the Bondtech extruders, the problem should still exist but the frequency of the oscillation should go up - lighter weight, faster vibration for the same input and with the lighter weight, it probably settles out a little faster?


To be precise:
The bondtech extruder does weight roughly half of the original Raise3D-Extruder on the N2, yes.
I do not know the weight of the whole thing (extruder, housing, hotends etc.) but I guess the extruder maybe is 50% of the whole thing regarding weight? After all the stepper motors are quite heavy, aren't they?
...there's nothing like the smell of fresh ABS in the morning...

zemlin
Posts: 362
Joined: Sat Oct 21, 2017 2:02 pm

Re: RINGING the electromechanical challenge

Postby zemlin » Wed Dec 06, 2017 5:57 pm

Thinking through this, swapping out the shafts for something lighter weight might be counter-productive if, as I believe, the shafts are a significant spring component of the gantry system. There are aluminum shafts with ceramic coating, for example, but the elasticity of aluminum is 1/3 that of steel for the same cross section - so while reducing the mass of the moving shafts, the dynamic response of the gantry could get worse due to the increased elasticity of the aluminum shafts.

I have also installed the Bondtech extruder. Drilling/milling out the gantry block to reduce mass would probably yield the best results, although I have not studied that block to see how much opportunity there might be for weight reduction.

firesped
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Re: RINGING the electromechanical challenge

Postby firesped » Wed Dec 06, 2017 9:02 pm

My next question is, which firmware are you guys using as well?

That may also have a major impact on it. there could be changes in the newer firmware I did based on marlin 1.1.0 that effect things.
RL name: Michael Nolen
printers:
raise3D N2 kickstarter Early Bird
Trinus Deluxe (running smoothieware on Azteeg X5 GT board)
Monoprice Maker Select v2


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