Need help for an idea for auto bed leveling...

This is about auto bed leveling: I'll need some help from someone familiar with electronic components. I know the theory (somewhat) but I lack real life experience.

There are some auto bed leveling solutions out there, one with an RC servo, one with a weird movement of the extruder, both trying to extract and retract an endstop switch. I just hate mechanics at that point as it introduces yet more error (failure, precision,...).

The idea I have is to mount a laser (diode or pointer) on the front size of the extruder, and some photo diod/transistor such that when you move the extruder down, you'll ge a reading when the laser light is reflected and points to the photo diod.

There are several issues with this, I admit.
- precision depends on the photo cell, however, we only need reproducible results, not exact readings, so as long as the laser or the photo cell don't move, that should be ok.
- What to do with a taped bed? Is there enough reflection? (No idea, I'd think no, comments welcome).
- Maybe ultrasound would be better, but I didn't find any electronic components for that.

Comments welcome

 

I don't think thiw will work.
Lasers need a reflector and without that you get an unpredictable signal (strenght) so this won't be accurate.

Unltrasound modules are avaiable, but those which are accurate enough are very expensive.

It would be cheaper to use a capacitive sensor. But I'm not shure if they are accurate enough. They need to give the signal in a less than 0,1mm interval.

 

I have seen some printers use hall sensors (magnetic) for sensing bed level, this could be done without using "mechanics"

an example could be to use: http://www.marcoantonini.eu/doku.php?id=reprap:rostock:bed_level

without the plunger-assembly, and then tape/glue/secure neodymium magnets to the build plate (http://reprap.org/wiki/Hall-Θ)

the hall sensor would have to be at the same height(z) as the nozzle end or/and add an offset to the "trigger" height

 

Any news ?

 

Too much other stuff going on right now. I guess I'll follow up on this after the summer...