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Horizontal banding on UM2


Dim3nsioneer

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Posted · Horizontal banding on UM2

I actually also found that the temperature in bang-bang mode is surprisingly stable

 

Of the bed or the nozzle? I'm not surprised at all about the bed. But my theory is that the nozzle temp changes significantly when the bed comes on versus off.

 

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    Posted · Horizontal banding on UM2

    Of the bed or the nozzle? I'm not surprised at all about the bed. But my theory is that the nozzle temp changes significantly when the bed comes on versus off.

     

    You mean there is cross-talk somewhere?

     

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    Posted · Horizontal banding on UM2

    Looking at the three cases in the last picture, I see a huge difference between the first two cases, but I'm not convinced I see any meaningful differences caused by the new nut. I mean, I do see some differences, but nothing that doesn't look minor and random as between any two prints.

     

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    Posted · Horizontal banding on UM2

    p.s. I'm surprised that turning the heaters on gently is more of an EMF problem than turning it 100% off to 100% on.

     

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    Posted · Horizontal banding on UM2

    Absolutely true. But in reality the difference is a bit better visible. I would say the improvement from the first to the second print is 95% and from the second to the third 5%.

     

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    Posted · Horizontal banding on UM2

    p.s. I'm surprised that turning the heaters on gently is more of an EMF problem than turning it 100% off to 100% on.

     

    I'm not. In bang-bang mode you have a quasi-steady current while in PID mode you have an AC. It's all about frequency.

     

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    Posted · Horizontal banding on UM2

    You mean there is cross-talk somewhere?

     

    I'm thinking something much lower frequency.

    I can always come up with 10 theories but the simplest one for now is that when the heat bed is on it draws so much power that the voltage going to the nozzle heater drops significantly maybe from 24V to 19V e.g. The problem could be the brick itself or the traces are too thin somewhere along the heater path or other resistance (connectros, FET). Then what happens is when the heat comes on the bed the PID controller for the nozzle thinks it has the perfect PWM for nozzle heat but it doesn't realize the voltage dropped a lot so the head cools. After a few layers the head gets back to normal temp (goal temp) and then the bed heater shuts off and the voltage goes up. Then suddenly the PID doesn't realize this change and the nozzle gets too hot for a few layers. Eventually the PID controller gets the nozzle back to goal temp only to have the problem repeat every minute or two.

    This is just one possible theory but it explains everything. I have already come up with a few other theories that seem less likely and more difficult to investigate. This one should be investigated first.

     

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    Posted · Horizontal banding on UM2

    By the way the easiest fix for above (if the voltage change is consistent across printers) is to measure the two voltages when bed is on and off and it's very easy to compensate in the PID algorithm if you know the change in voltage and knowing if the bed is on or off at the current moment.

     

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    Posted · Horizontal banding on UM2

    @gr5: If this theory is correct then I see a lot more troubles coming for the UM2 dual extruder... :eek:

    I would have expected the heater electronics is current-controlled...

     

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    Posted · Horizontal banding on UM2

    Both heaters are controlled with a switch. In PID mode they typically switch 10 to 20 times per second. You can see the LEDs flashing when the heated bed gets within 10 degrees below goal. This is because the 24V is changing enough for the LED's to dim when it's on.

    So this is basically current control. But the voltage is not measured and accounted for. power is proportional to voltage squared so a 2X change in voltage is a 4X change in power. The PID controller can handle the wrong voltage just fine but it takes a minute to adjust. If the voltage keeps changing, the temp is often wrong.

    However this should not be a problem on a well designed board and power brick. The brick should be able to put out 24V +/- .5V with bed on and off. Anyway this is all still just an untested theory.

     

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    Posted · Horizontal banding on UM2

    So when did this change from PID to bang/bang happen? And is there still a build switch defined in the source code?

    [Edit] Actually, belay those questions: it's all in the other thread.

     

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    Posted · Horizontal banding on UM2

    Hi there,

    I'm a complete newb so go easy on me :smile:. I'm not sure if this is the best thread for the following but figured it's as good a place to start as any.

    I bought an Ultimaker 2 at the beginning of December and had extremely good results straight out of the box for the first couple of weeks. I only used the spool of Ultimaker Blue PLA that came with the machine and everything seemed to be working perfectly until around Christmas-time when I began to experience issues with what I believed to be under-extrusion caused by spool binding as the UM Blue PLA was getting low. If you take a look at IMG_1716.JPG in the following link, you can see the results I started to get.

    https://www.dropbox.com/s/70fjp4k6igym0c8/IMG_1716.JPG?dl=0

    All of my prints have been within normal parameters with PLA: nozzle temperatures ranging from 190 - 240 as I looked to trouble shoot the problem. Generally I have printed with a nozzle temp of 210 and a bed temp of 55 with a speed of 30 mm/s at a layer height of .1 mm.

    In an attempt to combat the spool binding I have tried placing the spool on the floor below the machine, which did very little to improve the print quality. I then tried straightening a length of spool by hand and this seemed to improve the overall quality to about 85% of what I had been achieving beforehand, rather than the current quality which I'd put at around 50%. (Sorry for the terrible metrics) As a result of seeing improvement from hand straightening, I thought that the issue was mostly related to spool binding as the PLA became wrapped more tightly near the end of the spool, so I ordered some new PLA from ColorFabb, with the hopes that this would alleviate my issues.

    Unfortunately, even with a new spool of good filament I am still having problems with pronounced horizontal banding, where initially I was getting amazing, smooth prints. I am currently using the ColorFabb PLA/PHA Blue Grey off of a brand new spool and have had the results seen in this image:

    https://www.dropbox.com/s/4uqawuyrzo6wey4/IMG_1715.JPG?dl=0

    What you are looking at in the image is the horizontal band test produced one of the forum members. I have looked through many threads trying to resolve the issue and tried a number of fixes. In IMG_1715 you can see from left to right: a print with Cura 14.12.1, a print with Cura 14.03, and a print with Cura 14.12.1 and a freshly greased Z-screw. All prints were done with a nozzle temp of 200, bed temp 55, speed 30 mm/s at a layer height of 0.1 mm. The reason why I attempted a print with Cura 14.03 was because I read in one thread that someone had discovered that the old PID control of the bed was causing temp fluctuations in the print head, however this didn't resolve anything as you can see by the middle print. So going back to Cura 14.12.1 I tried greasing the Z-screw as it did seem a little bare near the top, however this didn't have any effect.

    I have noticed a change in the noise made when the bed and print head move into place at the very beginning of the print, during the move that follows the initial release of filament during the "priming". Initially the sound it made seemed to be comparable to the other types of noise the machine gives off, but about three weeks after getting the printer, the noise it made seemed to become louder and more like gears grinding. Here is a link to a video with audio of the noise, which actually seems to have become somewhat quieter and less obvious as of late. I'm not sure the audio will be of much help but figure it can't hurt.

    https://www.dropbox.com/s/lmul8swqrfah8eq/221.MOV?dl=0

    Among the various fixes I've tried were the atomic nozzle cleaning, however the ColorFabb prints in the image link above seem to have pretty regular banding that I have been assuming was not based on some type of clogging. I've never used anything other than PLA and now PLA/PHA

    If you could please take a look at the attached files and try to decipher what I have been attempting to describe, I would be very appreciative. I am a newbie to 3D printing and was over the moon for the first few weeks. Unfortunately, since then I've become more and more confused and concerned that I am not going to be able to resolve this issue.

    Thanks in advance!

     

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    Posted · Horizontal banding on UM2

    Hi 3Devos,

    Welcome to the forum!

    When you say you have tried with other Cura versions did you install the firmware as well? If you just used the software without installing the firmware on the printer it wont make a change at all since the heated bed control is firmware based.

    Like you mentioned, that type of banding did not occur for you at first so it seems like the power fluctuations could be made worst after some time of use. I have no real proof of that but I can see from my first print to the more recent ones that banding changed over time

    IMG 2835

    IMG 20141014 195656

     

    Can you try printing a section of the banding test with the heated bed off? Start your print at your normal bed temp and then stop it for a cm or two. As you may have read in this thread the heated bed bang bang mode seems to be the cause of change of flow on the nozzle.

     

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    Posted · Horizontal banding on UM2

    Hi PM!

    Thanks for the suggestions. I'm away from the printer until this evening but will implement your ideas when I get a chance tonight. In response to your questions:

    >> When you say you have tried with other Cura versions did you install the firmware as well?

    - No I did not... seems obvious but didn't cross my mind at the time. I will give this a go following the test you mentioned in your other suggestion. (see below) In regards to installing the firmware, do I just run the older version of Cura and install it from there?

    >> Can you try printing a section of the banding test with the heated bed off? Start your print at your normal bed temp and then stop it for a cm or two.

    - I will run this test first before trying to revert to the version of Cura that uses PID and post the results

    Thanks again for the quick response. I have a ticket submitted as well with Support but I get the sense from various comments on the forum that they may be a little overwhelmed.

     

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    Posted · Horizontal banding on UM2

    From Cura you can push the firmware version to the printer via USB. Each version of cura include the corresponding version of firmware.

    I'm still running with 14.07 and some had issues with 14.12 recently. Note that firmware versions prior to 14.07 do have inconsistent build plate level from print to print.

     

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    Posted · Horizontal banding on UM2

    Hi there,

    I ran a test print with the latest Cura where I used the heated bed at 55 C for the first 1 cm of the print and then turned the bed off after that. The print ultimately broke loose from the bed, however it printed long enough to run through the section that should have had the bed heat turned off. The horizontal banding appears as usual and is exactly the same through both sections, when the bed is on and when the bed is off. Below is a link to a pic of the test results:

    https://www.dropbox.com/s/871jjwkf6eryo80/IMG_1721.JPG?dl=0

    I'm currently running a test with Cura 14.03 (firmware installed on printer as well) to see if there is any difference when printing with PID enabled...

     

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    Posted · Horizontal banding on UM2

    Ok so I started another test print of the banding column, this time on Cura 14.03. I could see the same results so aborted the print mid-way. When I looked at the print more closely I could see the banding was very regular... I'm guessing it may be over extrusion due to some error in the Z-step? Below is a pic of the bands, which show what may be over extrusion when looking at the profile edges?

    https://www.dropbox.com/s/8u97hu6f7wqr90x/IMG_1722.JPG?dl=0

     

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    Posted · Horizontal banding on UM2

    These prints with the banding - it's incredibly regular. It looks like it might be making a band on every layer? Is that possible? Is your layer height still .1mm or did you change it? Is it .1mm in the picture in the previous post above this post?

    Are those bands .1mm apart or farther apart?

     

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    Posted · Horizontal banding on UM2

    Hi gr5 - all of the prints in these posts were printed at a layer height of .1mm.

    I'm not sure if it is making a band on every layer... I'm guessing not as it looks like there are roughly 5 bands per mm in the alternating over/under-extruded pattern. My guess is that it's not precisely .2mm per band, but I'm not sure how to accurately measure that.

    I guess if it's over extruding one layer then under extruding the next, the layer height would be alternately compressed then stretched if the Z step is off?

     

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    Posted · Horizontal banding on UM2

    What is the initial layer height?

     

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    Posted · Horizontal banding on UM2

    The initial layer height on all of the test prints was .3mm

     

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    Posted · Horizontal banding on UM2

    Are the bands equal on the entire layer or are they shifting from one layer to the other? I'm asking because the bed could be moving sideways on z step.

     

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    Posted · Horizontal banding on UM2

    I don't have the prints in front of me right now but I am pretty sure they are accurately laid down in both X and Y with no noticeable variance in either of those axes. I don't think there is any actual lateral movement in X or Y occurring. I will double check later this evening to confirm.

    I noticed when I switched to Cura 14.03 that the cylinder had a slight hourglass curvature inwards for the first half a centimetre but this corrected itself. On all of my prints with Cura 14.12.1 the cylinder is perfect straight in the vertical, minus the banding issue. Since using 14.03 didn't have any real positive effect on my test prints I'm just going to disregard that issue as something not worth pursuing.

     

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