Feature request/idea: Bed leveling via force control

General Discussion
1

I have installed the TMC2209 motor driver and do not use any limit switches on the printer but the virtual endstop function. And then I thought to myself if it wouldn’t be possible to level the bed with it as well. Are there already approaches or is the idea not possible at all. I would be happy about a lively discussion

2

It is generally not recommended:

  • X / Y is not too critical in terms of accuracy
  • Z is highly critical
  • Depending on the bed setup the flex / bending can be too high
  • With a lead-screw the forces will be too high and may damage your head
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3

Ok, I understand. Thanks for the reply. It was an idea but you are right and I don’t like things like BL-Touch. So I will see what I can find for this routine.

4

I have implemented bed leveling based on forces in a sense, but you will need a proper force sensor for this :slight_smile: The sensor is a load cell which needs to be mounted “in between” the hotend and its support, so upwards going forces on the nozzle can be measured. I have created a pull request for this, for which I have received already some comments:

If you want, you can give it a try. I can help you and guide you a bit, but of course it will involve some rather substantial hardware work. (In my printer model this was build in from the beginning…)

5

@mhier Thank you for your offer. But my IDEX Cubix is just build new, so I must first a Design for the force sensor. Do you have a link or picture from the sensor.
Greetings

6

Here is a (partial) rendering from a CAD model of my printer:

The two bars with the green arrow on the front are the load cells (type TAL220B). They are mounted on the X carriage of the guild rail. At the other end of the load cells, there is a metal sheet traverse, at which the hotend is suspended. Electrically, the two load cells are connected in parallel to e.g. a HX711.

You can find a full 3D model (FreeCAD) of my printer here:

You can probably also chose smaller load cells, if space is limited. Just make sure they can take the extrusion forces and do not bend too much (otherwise print quality will suffer).

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