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#1 2020-04-09 09:23:25

Screen0
Member
Registered: 2018-08-11
Posts: 5

Reversing Z axis direction during printing

Hello,
after a month long pause I turned on my 3D printer (RPi 3 MSLA 5.5" machine - www.oliver3d.com) and started printing. The print failed and I quickly found the issue. Despite a proper calibration (driving the platform down, manually calibrating using a sheet of paper and clicking on a "Measure" button on the Tibus interface to drive the platform up and measure the length of the Z axis), the platform didn't come all the way down and there was about 2 mm high gap between the LCD and the aluminium platform. I was perplexed and restarted the printer and tried to calibrate it again. However, I accidently clicked on the "Calibrate" button instead and weird things started to happen.

The platform moved to Z-max position and then the NanoDLP interface showed 0 mm level. When I started the print without FlexVAT just to see what will happen, the printer started printing at the top of the Z axis! One would have thought it's just a matter of reversing the Z axis direction, but the problem is that during a manual operation, the direction is correct and if I try to swap the Z-min and Z-max endstops, the printer just crashes into them.

Now as you can see, I have no idea if there's any "proper way" to calibrate and set up a MSLA machine with NanoDLP. I hacked the firmware together in summer using trial and error method and it has worked ever since until now. Therefore I would be glad if someone could, apart from solving my problem, actually explain to me the difference between "Measure" and "Calibrate" and generally explain to me how to implement more robust calibration settings in NanoDLP. So far only 1/3 of all prints on my printer have been succesfull and I'm sure 4 out of 5 failed due to firmware issues.

Thanks in advance for any help. I greatly appreciate it.

Best,
Adam

Last edited by Screen0 (2020-04-09 09:24:50)

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#2 2020-04-09 11:17:20

bigfilsing
Member
Registered: 2016-11-20
Posts: 206

Re: Reversing Z axis direction during printing

Hi Adam
To the best of my knowledge which can, at the best of times be limited. I consider calibration the setting up of a an actual machine rather than setting it up to specs. Example :- a lead screw has a fixed pitch , lets say 4mm . So for every rotation the lead nut should travel 4mm....in theory.   so based on that you should be able to set your stepper driver to "X" amount of steps per mm. However due to manufacturing inaccuracy in both lead screw and lead nut as well as backlash compensators etc you will usally see the nut move slightly more ( or less) that the expected distance.  Measuring the actual travel then compensating the "steps per mm" i consider calibration.

" i hacked the firmware together" sounds a bit sketchy but heh if it worked then fine
Whenever it comes to any stepper motor direction / reversal issue the first place id look would be the DIR signal to the stepper driver. All the stepper drivers ive seen need 3 signals - Enable, DIR & STEP . If the DIR signal is low it will step in one direction and logically if the DIR signal is high it will step in the opposite direction
Good luck

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#3 2020-04-10 09:10:25

Screen0
Member
Registered: 2018-08-11
Posts: 5

Re: Reversing Z axis direction during printing

Hello,
thanks for your explanation. The problem still persists, though. I have posted a video on YouTube, so that you can get a better understanding of my issue: https://youtu.be/PEzrpIC9bIA

0:02 - the platform is moving in a proper direction
1:28 - the Tibus interface shows current position at -22 mm; I click on "Measure" to calibrate the printer.
3:09 - the platform is at the top, but the display shows position of 0 mm (which should be shown at the bottom, not at the top)
3:40 - I start a test print and the platform stays at the top (it should go to the bottom)

I tried absolute/relative positioning, but that did not change anything. I have no idea how to solve this. Could you please help me?

Last edited by Screen0 (2020-04-10 09:10:59)

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#4 2020-04-11 06:44:06

bigfilsing
Member
Registered: 2016-11-20
Posts: 206

Re: Reversing Z axis direction during printing

Ah just noticed that it uses a RASPI with an adapter board
So here's what i think
The z axis is rotating in the wrong direction You can swap the plug 180 deg and the motor will turn the other way.    NEVER connect or disconnect a stepper motor with power ON !!!!  Thats an easy way to destroy a stepper driver
Before you power back on set the Z axis about half way up its travel Manually
Then power on
( while doing this i would recommend removing the print head )
On the screen to the right side there is a grey button with "FLOOR" on it Can you press that ?? if not then press the red down arrow untill the head is all the way down.
Now press calibrate Hopefully that will set it to zero

As per your video its showing -22.0968 as "current"when its in the home position It should of course read 0 (zero). 
That would also explain why it moves away from the screen when printing . It wants to compensate for the -22.0968
Good luck
PS Have you read the manual

Last edited by bigfilsing (2020-04-11 06:50:50)

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