new idea for auto bed leveling?

[bvandiepenbos]

I am working on auto bed leveling.
Thinking about a different way to sense build surafce.
looking at this sensor www.mpja.com/Vibration-Switch-Sensor-Module/productinfo/31580%20MP/

do you think it would be able to "hear" the nozzle tap the glass build plate?


I have seen auto leveling done using varoius other sensors/switches (each has it's own strengths/weakness)
-micro switch probe (clunky, prone to breakage and out of adjust)
-Force sensing resistors under build plate (can't stand heated buld plate temps, also seems very finicky to get just right pressure)
-micro switch on the hot end mount (looks to work well, but would be hard to manufature into design easy and reliable)
-printrbot uses some kind of non-contact prox sensor, but don't know why delta printers don't (looks to work good)
  ... probably has a steel build plate to sense?


does glass reflect IR, like from this one?
www.mpja.com/Proximity-Detector-I_R-Reflective-Raspberry-Pi-Arduino-Compatible-Sensor/productinfo/30312%20HD

what about using a steel instead of aluminum "heat spreader" plate under the glass? so this one can sense surface...
www.mpja.com/Proximity-Sensor-Inductive-PNP-NO-Output-LJ12A3-4-Z_BY/productinfo/30306%20HD

[BeeAmaker]

Glass don't reflect IR, Steel don't spread the heat like Alum would, plus it would rust over time and you can't use Stainless Steel as it's not magnetic. I think you are over thinking it. I see nothing wrong with a switch probe on the hotend.

but if you really want to be extravagant, mount an Ir eye on each tower exactly at the bed height. If each eye can't see the other two then the bed is not level - red light.

This is'nt something that has to be a permanent fixture it is? how often will you need to level the bed? you could also use a thin sheet of tin connected to a to capacitive touch sensor (there are a few up at the hive). Lay it on your bed and place a stylus pen point on the hot end tip.

But I think something like this www.getlofi.com/storeImages/momentary_button_switch.jpg mounted to the side of your hotend platform would work just as good. Take your hotend off (so switch point will touch bed)- level the bed - put you hotend back on re-adjust the z and good to go. no moving parts.

[bvandiepenbos]

yes, ideally this would be permanent on machine and not something user has to add/remove or fiddle with.

I don't think IR eyes would give the right data. The auto level routine probes bed at many locations. With that input it adjusts tower trims, Z height AND the delta radius value. So machine travel is flat & level with print surface and perfect Z0 height.

I am going to try one of these ...
store.linksprite.com/piezo-vibration-sensor-small-vertical/

[jimustanguitar]

Have you seen the "JohnSL FSR" setup?

forum.seemecnc.com/viewtopic.php?f=42&t=6539#p50497 (about 3/4 down the page)

I don't remember why the force sensing resistors aren't a viable option... Was it the bed heat?

[sgraber]

Yep the heated bed.

Why not a hall effect sensor?

[sgraber]

Weeeeeeeeeeeeeee: Cerberus Pup: Auto bed leveling:

[jimustanguitar]

Nice!

How does the machine tell when it's touching the bed, what kind of a sensor does it have?

[sgraber]

It's using a standard microswitch mounted on the effector to sense the build platform surface. The hotend is mounted in a pivoting holder and the holder has a tab extending out from it. When slight pressure is applied to the hotend, the holder is slightly deflected, and the tab on the hotend holder then actuates the microswitch, which "senses" the platform. If you listen really closely, you might be able to hear a slight "click," which is the microswitch actuating.

It's using Rich Cattell's fork of Marlin (github.com/RichCattell/Marlin), which supports auto-calibration and auto-leveling. I spent an hour or two last night adjusting the firmware for my particular setup: RAMBo v1.3, RRD Full Graphical Controller, and my old Makerbot Cupcake steppers (0.4A). I'll push the changes to my git tonight in case others wait to look at it or use it.

BTW the auto-calibration routine ROCKS.  I connect via Repetier and issue "M502" (load default settings), "M500" (save default settings to EEPROM), then "G30 A" which starts the auto-cailbration routine.  "G30 A" adjusts the endstops, arm lengths, etc, to minimize variation across the build platform to a pre-determined precision.  I can literally issue the G30 A command and walk away from the machine and it will calibrate everything.  

[sgraber]

Brian:

Have you tried an Inductive Sensor?

forums.reprap.org/read.php?1,429296

www.google.com/search?q=inductive+sensor&oq=inductive+sensor&aqs=chrome..69i57&sourceid=chrome&es_sm=122&ie=UTF-8#q=inductive+sensor+reprap

Some people are experimenting with them for autocalibration.

----------------------------------------

As an aside: Not sure if you guys are aware of it or not, but Marlin now has Thermal Runaway protection (not enabled by default):

github.com/ErikZalm/Marlin/commit/43c298a7a9674bade1395a75fe54667cdb22fce4#diff-2518586b18177db2030f90768e459dc1

What this does is protects you from a failed thermistor, which would cause your printer to think it's not up to temperature so it would keep sending signals to heat your hotend resistor even more. I backported that commit into Rich Cattell's Marlin to protect my Pup and it works.

[BeeAmaker]

This works great

[jimustanguitar]

What is the arrow supposed to mean?

[BeeAmaker]

Dec 8, 2014 14:12:52 GMT -5 jimustanguitar said:

What is the arrow supposed to mean?

You point that towards the high spot before you swing.

[bvandiepenbos]

Thanks for the info Shane

[BeeAmaker]

Dose the nozzle actually have to touch the bed?

[sgraber]

Dec 11, 2014 11:11:46 GMT -5 BeeAmaker said:

Dose the nozzle actually have to touch the bed?

Yep.