Just curious: auto-levelling

[rhoogenboom 3]

I only occasionally read through posts on the board here and saw a big discussion on auto-levelling which made my curious on what auto-levelling actually does.

 

Does auto-levelling actually adjust any setting/layer height or print condition or is it only a safety check to see if the build plate isn't complete mounted sideways?

 

Just curious to know the inner workings,..

[johnse 31]

To my understanding there are a couple kinds of auto leveling. They both allow the printer to adjust the z-axis dynamically to maintain an accurate layer height for the first layer. After that, I think they gradually adjust so the layers are level to the xy plane of head movement.

 

They do this by measuring the actual height of certain points on the bed. Simplest is a 3-point sampling like is used on the UM3. Three points define the plane of the bed in 3-space...assuming the bed is actually flat. Others (I think the UM S5 does this) sample multiple points in a grid pattern. This defines a mesh that can model curvature of the plate that might occur, for example, from uneven heating.

 

Of course, the better the mechanical leveling and the flatter the plate, the less needs to be corrected by the algorithms.

[rhoogenboom 3]

Hi Johnse,

 

Thank you for the answer, I assumed a similar thing that it does some Z-axis adjustment, but what specifically wonders me how it would deal with the 3 point measurement. 

 

On my UM3 you do the manual levelling mid point, right front, left front and the dual nozzle midpoint by adjusting the screws underneath. This should put the build plate level.

 

Assuming I messed this up and right forward is way too low. How would my UM3 auto-levelling deal with that? It cannot adjust the right forward screw to make the plate level, so the only thing it can do is figure out mid point is 0, right forward is too low and left forward is at 0 too. Would it then constantly adjust the Z-axis during printing while the printhead moves from right forward towards left behind? It would have to be otherwise taking all those measurements doesn't make sense. If it only adjusts the initial layer height, taking a measurement mid-point would have been sufficient. 

 

Which is why I'm thinking the auto-levelling sequence is just a double check if you have levelled the bed not completely tilted and bails out of the print if you have and otherwise starts because it's 'within acceptable bounds'.

 

Anyway, maybe one of the UM people can give some insight is what it does or try to figure out during that process.

 

Cheers,

 

Richard

  

 

 

 

[tinkergnome 927]

Hi Richard,

 

once upon a time... as the UM3 was launched... a lot about the bed level compensation was explained by the developer(s) itself:

 

 

[rhoogenboom 3]

Hi, 

 

Now that was what I was looking for! Thanks for pointing it out! 🙂

 

Cheers,

 

Richard

 

[rhoogenboom 3]

And I switched active levelling back on 🙂