Auto bed leveling using piezo discs
by elenhinan, published
Auto Bed Leveling using piezo electric discs for very high sensitivity.
Mounted between the bed springs and the z-stage, any force down on the bed can be registered and used as a probe signal. Hence one can measure when the hot-end touches the bed surface. No modification to the hot-end or carriage is therefore needed, and the probe is insensitive to temperature.
This is still a work in progress, so although it is working for me in it's current form, it needs constant tuning as the circuit is not yet perfected, and the mechanical mounts have some known issues. A new circuit and new mounts have been designed but not yet tested.
So far, I've tried to only use parts available from sparkfun. I'm guessing a total cost for all parts of less than $20 USD.
Video of version 0.1 doing bed height mapping : https://www.youtube.com/watch?v=Zn9X-WGBuvQ
Discussion at soliforum:
Print the v0.3 back, and two v0.3 fronts, one of the mirrored. Drill the smaller hole out to 3 mm, and the larger one to 4.5mm. Glue the piezo disc underneath using silicone glue. Use an m4 screw to center the lever on the holes in the bed-holder, and drill through the 3mm into the aluminium, so that you can use some m3 screws to fasten the levers to the bed-holder. The rest of the mounting should be self explanatory.
Since the sensors are very sensitive, the acceleration of the z-axis and the intertia of the bed can be enough to trigger the probe. It can therefore be helpful to disable z-jerk and decrease z acceleration. With repetier firmware, there's a seperate travel acceleration setting, so this is the script I use:
G0 Z10; goto 10mm z height to prevent crashing in bed
M202 Z30; set z acceleration
M207 Z0; disable z-jerk
G32 S0; auto level
M207 Z5; restore z-jerk
M202 Z300; restore z acceleration
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