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Electronic bent rod compensation

Posted by newbob 
Electronic bent rod compensation
September 13, 2017 05:43PM
I have yet to purchase perfectly straight linear rod and I think - just like we have automatic bed leveling - we could have automatic X and Y compensation. All one would need is a straight edge reference -metal ruler or thin wire - and metal probe (nozzle?). Stretch a wire/ruler along X or Y axis and use script that moves along the axis and looks for contact of probe with the ruler/wire. For example, when calibrating 200mm X axis:

move probe to X=0 then towards ruller/wire, once contacted record Y position,
move Y+10
move X+20
move Y until wire/ruller contacted - record Y position
move Y+10
move X+20
move Y until wire/ruller contacted - record Y position

all results outside of the line between (0, contact point) and (200, contact point) would be a compensation value applied to X axis.


Another way would be to draw a grid with a pen/marker attached to hotend, take a picture of it then have a program process the picture to calculate a compensation grid that would be uploaded to printer's firmware.

EDIT: this feature would be even more useful with carbon fiber rods that cannot be straightened

Edited 1 time(s). Last edit at 09/13/2017 06:30PM by newbob.
Re: Electronic bent rod compensation
October 12, 2017 01:13PM
The original prusa i3 does this, it has magnets embedded in the bed to use as references and can correct for a skewed frame if you put it together wonky, I assume it could also correct for an axis which moves in a curve due to bent rods.

For the record, as long as your rods are bent just in the vertical direction (or you rotate them so the bend is purely vertical), regular bed leveling should account for the fact your nozzle will dip or rise in height at the bend. If you only have one bent rod, or rods that aren't bent to similar extents, you have some issues. If your carriage runs at all, your effector will experience some twist/tilt (since one rail will dip up/down, the other remains at the same height) or may bind up as the distance between the rails changes.

I can't think of any ways to compensate for bent Z rods though.
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