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Auto-levelling efforts

Posted by neildarlow 
Re: Auto-levelling efforts
May 24, 2014 08:16PM
If I were to implement this I would also use magnets in a similar way and then when the print finishes and the head re-homes a small lever on the central support could push the probe back down ready for the next print.

No manual intervention required.

It would be great if we could collectively implement this for stock nophead M90's....
Re: Auto-levelling efforts
May 24, 2014 08:19PM
Doing this a few times ... out by 0.02 - 0.05mm each time

I mostly print at 0.3mm layers so this margin of error would be fine with me....
Re: Auto-levelling efforts
May 25, 2014 04:21AM
I don't find the manual intervention a problem because at the end of a print I have to manually remove the parts, the skirt, the start blob and any ooze from the nozzle and swill the bed with acetone. I then pull the probe down so the next start can be completely unattended.

Re: Auto-levelling efforts
May 25, 2014 12:28PM
Manual intervention is another thing to forget :p

I'm waiting for they day when I can just go from a model to 'print' and it rotates itself, decides on support, layer height, whether it needs a brim or other features, starts the printer, prints it, auto ejects it (into limoene if it has supports) and texts me to say it's done. All I have to do is keep the filament full...

Auto z-height calibration will be a standard feature for all printers soon, having it standard in the Mendel90 now can only improve sales....
Re: Auto-levelling efforts
May 25, 2014 01:11PM

I had my Mendel90 for nearly a year and I'm very happy with it, but I must say that an auto-level feature would be quite interesting.

In my case, I have to recalibrate it when I move it on some other place even thought the surface seems flat and sturdy.
Well, normally it's not supposed to be moved often…
The other advantage might be to compensate for approximate manual calibration and make it more forgiving.

At any rate, it's truly an ingenious system you made here Chris, and like you said, I also don't see the problem having a manual system since we must go to the printer after a print anyway.

It would be great to have it implemented…

Mendel90 from Nophead + E3D v5
Smartrap from Smartfriendz
Re: Auto-levelling efforts
June 02, 2014 07:03AM
I'm wondering why the Z-home-pos is changed in firmware rather than eeprom.
Re: Auto-levelling efforts
June 02, 2014 07:44AM
You can enable the EEPROM and change it there (you might need a later Marlin version such as Neil Darlow's) but I personally prefer to change source code than send random G-codes. Also I disable the EEPROM by default as it can be very confusing because it overrides what you have in the source code unless you reset it, then you risk losing settings as the firmware then overrides the EEPROM. It seems much better to me to keep just one version of the settings in a human readable form stored on a host. In my case an RPI attached to the machine. If you swap hosts or just run the machine from an LCD then you need to keep everything in the EEPROM.

For auto levelling with a probe it it would need to be stored in EEPROM unless you do it every build. That is what I do with my own firmware / host and it has the advantage of probing at the extents of where the object is, rather than fixed places. If the bed is not completely flat that is more accurate as it models the part of the bed you are actually using and ignores the rest.

I am not sure why people find the Z height changes when they move their machine. I have taken mine to shows and not had to change it. Basically if the machine is on a flat plane the height and levelling should not vary even if it is slightly inclined. On the other hand if it is not a flat plane it will cause the Y bars to not be exactly parallel vertically, in which case the Y carriage will roll around the Y axis as it moves backwards and forwards. That shows up as only being able to level three corners. The three point levelling I implemented on Hydraraptor will not compensate for that, neither will the implementation in Marlin. It would need four sample points and a non-affine transformation I think.

Edited 1 time(s). Last edit at 06/02/2014 07:45AM by nophead.

Re: Auto-levelling efforts
June 05, 2014 01:00PM
Maybe I missed something but a optical sensor could fit :

Placed somewhere in the probe height, when the probe is going up between the 2 teethes the signal is switching.

Or a hall sensor :
But if you have magnet around maybe it can have unwanted signals switch.
open | download - image.jpg (2.4 KB)
Re: Auto-levelling efforts
June 05, 2014 01:05PM
Both are analogue electronic devices where the exact switch point will vary with stray fields, temperature and supply voltage. With two gold contacts I think the only variation is thermal expansion of the plastic part.

Re: Auto-levelling efforts
June 06, 2014 04:45AM
Ok i am agree for the hall but the optical is not analog (or I didn't understand what u mean), one side is a ir led which produce enough strength with big vcc variation and other side is a transistor either open collector so z-signal will be vcc or satured to ground.

Anyway was just a idea if the micro switch can work in all conditions it's the better choice.
Re: Auto-levelling efforts
June 06, 2014 05:08AM
Optos are analogue devices. They have a slot with a finite size, 0.5mm in this case. As the tab moves to cover it the amount of IR light reaching the photo transistor gradually reduces. That causes the transistor to come out of saturation and the voltage on the collector to gradually increase. When it reaches the switching threshold of the Atmega input it will be sensed. Any variation in background IR (sun, halogen bulbs, etc), temperature of the semiconductors, etc, will change the trip point slightly.

I don't know a lot about hall effect limit switches but they are sensing a magnetic field, which is inherently an analogue value that must be compared with a threshold to obtain a digit signal. The same applies to force sensors.

Edited 1 time(s). Last edit at 06/06/2014 05:09AM by nophead.

Re: Auto-levelling efforts
June 06, 2014 07:30AM
ok I get it now smiling smiley
Re: Auto-levelling efforts
June 14, 2014 12:10PM
What about this approach?

Sadly I couldn't find any further information.
Re: Auto-levelling efforts
June 14, 2014 12:15PM
What about this approach?

Intriguing - looks like something equivalent to the mechanical depth gauge in that it appears to be a method of getting the bed level rather than providing any sort of auto levelling.

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