Layer Shift Detection Not Working  

Re: Layer Shift Detection Not Working

Correct me if I´m wrong, but I think its not in the official Marlin yet so it is also not in the Prusa drivers?
As seen on Tom´s Channel:

Re: Layer Shift Detection Not Working

Crash detection is working on mine, I just tried it.

Go to settings and ensure Crash det. is set to on and Mode is set to Normal (not Stealth).

Re: Layer Shift Detection Not Working

Already done, everything looks to be set correctly in the menus,

What firmware is your's loaded with? Also which version of the new Rambo is your's running?

-Sam

Re: Layer Shift Detection Not Working

When you force the head out of position, what is slipping?

If you are causing the stepper motors to be out of position, I would think firmware should catch it. However, if instead you induce a belt slip or your stepper sheet is slipping in the pulley, you might get layer slip with no firmware detection.

If firmware feature is there and on, check belt tightness and pulley set screw?

Re: Layer Shift Detection Not Working

The belts are tensioned and the steppers themselves are skipping.
I can move x, y or z manualy and the printer does not seem to notice that a stepper did not do what it was supposed to be doing.

In an attempt at helping find a fix I'd like to note that this printer came with the Einsy Rambo that has an extra daughter board for the LCD.

-Sam

Re: Layer Shift Detection Not Working

This is weird, because if it couldn't detect skipped steps it wouldn't have let you past the selftest step of the build, right?

Re: Layer Shift Detection Not Working

I think maybe on has to push "to the right" while x is moving left - Not push in the same direction X is moving. Maybe you "pushed it wrong?":-)

So basically the motor has to stall aka really miss a step.

Re: Layer Shift Detection Not Working

I did try pushing the axis against the direction of travel (as well as with) so I don't think that is the reason for it not working on mine.

Interestingly it homes completely normally so the back emf detection is working. It just seems like there is a firmware bug that keeps mine from actually enabling the feature during printing.

-Sam

Re: Layer Shift Detection Not Working

Here is a video documenting the problem.

-Sam

Re: Layer Shift Detection Not Working

having listened to the video are you sure the stepper motor is actually slipping when you push the carriage? It sounds to me like the cog is slipping on the shaft rather than the motor actually being forced to move. i would check the grub screws for tightness.

Re: Layer Shift Detection Not Working

Everything seems to be tight and not slipping.

See the below video for a close up,

-Sam

Re: Layer Shift Detection Not Working

I should mention that I got in touch with Prusa support today and they did say that there would be a firmware update sometime in the next few days.
With any luck that will fix this issue but I would like to know what version of firmware people who do not have this same issue are running.

-Sam

Re: Layer Shift Detection Not Working

Hello Sam,

I've checked all the videos you posted here and it's really not a proper test to state if the detection is working on your printer or not.
Stahlfabrik already said the point, but let me clear out a bit how the detection works.

Detection is based on StallGuard feature of Trinamic stepper drivers we used on new electronics. Our layer shift detection is programmed to catch situations which can occur during the print, such as crash to the print it self, or some obstacle which can form or fall in the printer (cats sometimes like to do that). This means it's very difficult to simulate, or test, by simply grabbing the axis and move somewhere. The proper way how to test this feature is by blocking the axis, such as holding the smooth rod and let the head actually crash, as we presented on the shows. Also good thing to point out is that this detection is sensitive to belt tension. (But we've figured out a pretty straight forward way how to check belt tension and tell user if it's ok or not based on data in the stepper driver. We're working on it for few days now to guide builders as much as possible to have perfect machine 🙂 )

You can check out the datasheet ( https://www.trinamic.com/fileadmin/assets/Products/ICs_Documents/TMC2130_datasheet.pdf ) of the drivers if you're interested to have more detailed informations.

Keep us informed about your machine, cheers and happy printing!

Re: Layer Shift Detection Not Working

Hi Michal,
Thanks for chiming in.

I am happy to report that I was in fact doing something wrong. When I try to simulate the nozzle running into a bad print by simply pinching the linear rail the printer behaves as intended. I've taken a video and posted it below.

Since the issue appears to be a case of user error I am now interested as to what might have gone wrong with one of my prints.

This print was sliced at "draft" quality and I think that a miss tensioned extruder is why the part exhibits such a bad surface finish. That said I am more interested in the layer shift evident in the part.

Image:
https://drive.google.com/file/d/12kF4SR2StLnOofyFp5uTJVudP6Gtfx1Z/view?usp=sharing

I thought that the skipped step detection would keep this from happening. So far I have seen such a layer shift in this part (printed in normal mode with crash detection turned on) as well as a print attempt of the benchy on the SD card (printed in silent mode so no crash detection).

I think that the higher speeds that the slicer is using for this printer may be to blame. I have had limited success by turning down the speed multiplier at the start of prints (to 60%) but I think that some of these shift issues are occurring during fast traverse moves. I do not know if these are affected by the on screen speed multiplier value.

Of course in Slic3r it is possible to set up some new profiles with slower speed settings and I do plan to perform this step. I would like to know if you would be willing to add a setting to Prusa Control for the same layer height settings but slower movement, this would allow for better quality prints (less ringing) as well as lower chances of skipped steps.

Thanks again for letting me know what I was doing wrong,
-Sam

Re: Layer Shift Detection Not Working

I had layer shift on the included Nefertiti file found on the SD card.

If that layer shift detection fix is coming (and different from the crash detection), then I am very excited to be getting that 😀

Re: Layer Shift Detection Not Working

The crash detection won't stop all kinds of layer shifts, for example if the model comes loose off the build plate, or if a support fails.

Here's hoping Prusa geniuses can come up with some kind of optical sensor for detecting more kinds of print failures for the MK4. 😀

Re: Layer Shift Detection Not Working

The crash detection won't stop all kinds of layer shifts, for example if the model comes loose off the build plate, or if a support fails.

Here's hoping Prusa geniuses can come up with some kind of optical sensor for detecting more kinds of print failures for the MK4. 😀

true - though none of that happened on mine. it just shifted about a centimeter to the side and kept printing.

Then again, I was on silent mode, so crash detection wasn't on anyway, but I'd thought layer shift detection and crash detection were different

Re: Layer Shift Detection Not Working

So I had a really weird layer shift on my print. Both top and bottom sections of a fidget cube.

Actually, I guess you could say the top and bottom layers are where they should be... but the middle layers are severely shifted.

Hard to say what happened exactly, but could it be the case that:
- It failed to detect/recover from the first layer shift
- somehow smacked into the print again toward the end of the print, then homed and recovered?

The shift happened on the Y-axis.

[attachment=0]20171214_093025[2].jpg[/attachment]

Re: Layer Shift Detection Not Working

The crash detection won't stop all kinds of layer shifts, for example if the model comes loose off the build plate, or if a support fails.

Here's hoping Prusa geniuses can come up with some kind of optical sensor for detecting more kinds of print failures for the MK4. 😀

true - though none of that happened on mine. it just shifted about a centimeter to the side and kept printing.

Then again, I was on silent mode, so crash detection wasn't on anyway, but I'd thought layer shift detection and crash detection were different

When the print comes loose and flies away from bed, then you cannot detect anything, but if the print breaks, or detaches from the bed, and stuck under the bed, it'll trigger the crash detection. According to this, you can monitor how many triggers were there in for example last 5 minutes and if you consider them large enough you can wait and ask user to check if you want to continue. This is being implemented at the moment and it's possible to detect significant percentage of very common failed prints and wasted filament. At the moment, the crash detection is able to recover layer shift caused by obstacles formed during print (and by foreign objects), as I wrote before, and of course detect detached print getting smashed by the print head, but it'll try to fix it anyways 🙂 .

By the way, similar algorithm is implemented for the power failure detection. If the power goes off for short time, the print will recover automatically, but the outage is longer, machine requests user confirmation to continue. Longer or shorter time is derived from temperature drop of the heat-bed. If the bed temperature is lower than target, before power went off, by at least 5 °C, because there is high probability of print being detached from the bed by chemical properties of PEI which increases adhesion with temperature, and also by different thermal expansion of the plastic being printed and structure of the surface, which basically copies the spring steel.