1 Topic by IanJohnson

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Topic: Automatic Bed Leveling

Check out this post at the Makergear Google Group -

https://groups.google.com/forum/?fromgr … HU5VEH6YxY

I don't know if his code is in the regular Marlin, there is a command (G29) to probe the bed at 3 spots using an endstop mounted to the extruder.  The endstop on the extruder is wired together with the Z endstop.  It will return coordinates for each endstop hit to the log, and you can see if they are the same, or if a screw needs to be adjusted somewhere.

G32 will check the 3 coordinates, determine bed's orientation with respect to X and Y, then create a transformation matrix that it will use to adjust Z on the fly to compensate for the bed's level.  You could add it to the start code, and never level the bed again, unless it gets so bad that the Z movement starts to slow everything down.

The automatic compensation may not work without Z backlash being eliminated, but the probing by itself would be a great built-in replacement for using a dial gauge to determine level.  The only challenge would be finding a way to extend and retract the endstop, because it would get in the way during a print.

Here is a video of a retractable Z probe on a Mendel - http://www.youtube.com/watch?v=uk29TIPouLk

He uses a magnet to hold it in place, and bumps into a screw from one direction to lever it down, and bumps it from the other direction to lever it back up.

2 Reply by jooshs

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Re: Automatic Bed Leveling

I'm curious if this can actually work well for in print adjustments since the bed is continuously out of level, while the z steps are discontinuous. It seems like it could be great for easy leveling, but I might be suspicious of its capabilities for in print adjustments. Hopefully I will get the azteeg soon and some extra limit switches to try this.

3 Reply by ErroneousBosch

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Re: Automatic Bed Leveling

Ian, I don't suppose you have tried this?

4 Reply by IanJohnson

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Re: Automatic Bed Leveling

Not yet, I'm still trying to get some non printer projects done, so it doesn't seem like I just got a printer to print things for the printer.   I really want to do this one,  at least with the probing.  If you suspect the bed is out of level, it would be a quick check.   

Maybe the limit switch could lay flat, sideways against the bottom ofthe x carriage, and then flip down.

5 Reply by cmetzel

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Re: Automatic Bed Leveling

Thinking out loud here... If you had a little pedestal on the z table you could "park" the limit switch there in a holder.  Another mount to the extruder assy could go pick it up with magnets, sliding it out of a skyhook using gcode movements and probe the bed.  Then return it back under the skyhook and pull straight up to unlock from the magnets.  Again I'm not in front of the machine just going from memory.  Kind of like a CNC machining center grabbing a tool and putting it back.  If nothing else it would certainly look cool and can be done without adding electronics.

6 Reply by cmetzel

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Re: Automatic Bed Leveling

Have you seen this guys videos yet?

http://www.youtube.com/user/MatterHacke … ture=watch

7 Reply by cmetzel

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Re: Automatic Bed Leveling

http://www.3ders.org/articles/20120427- … pment.html

8 Reply by IanJohnson

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Re: Automatic Bed Leveling

I've seen the video, but can't think I a way to lever it like he did.  I like the magnet idea.  It's more complicated than flipping it down with your finger, but much cooler.  The end stop would need to be close to the nozzle so it can reach enough of the bed.  Maybe it can be positioned to the side, in the dump area.  Managing the endstops wire might be a challenge if it isn't mounted full time to the carriage.

9 Reply by cmetzel (edited by cmetzel 2012-11-21 16:14:43)

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Re: Automatic Bed Leveling

IanJohnson wrote:

I've seen the video, but can't think I a way to lever it like he did.  I like the magnet idea.  It's more complicated than flipping it down with your finger, but much cooler.  The end stop would need to be close to the nozzle so it can reach enough of the bed.  Maybe it can be positioned to the side, in the dump area.  Managing the endstops wire might be a challenge if it isn't mounted full time to the carriage.

Use a retractable keychain / ID badge thing  to keep the wire in tension

Do you feel like the z backlash is solved to the point where on the fly code adjustment would work?

You don't really need to cover the entire bed, 3 points determine a plane so you're going to know the limits of the bed no matter where you pick if your readings are accurate.

10 Reply by gvarnadoe (edited by gvarnadoe 2012-11-23 19:58:09)

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Re: Automatic Bed Leveling

Another option might be to place the limit switch on top of the extruder assembly and mount a small rod vertically next to the extruder to actuate it. If the rod and switch could be mounted together the whole assembly could be held in an up position during normal operation by a spring and locked down during probing. Similar to a ball point pen mechanism.

Another option that might be even simpler would be to eliminate the switch itself and just use a spring loaded rod to contact three pre-selected points on the print bed which have had the kapton tap removed, exposing the aluminum. Properly wired the  rod and bed become the switch.

I wonder if the tip of the extruder is consistently clean enough to be used as a contact point.

11 Reply by cephdon

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Re: Automatic Bed Leveling

@gvarnadoe:

I have a CNC Mill that has a probe which works similar to that idea.  The probe is used for 3d scanning of surfaces.  Basically, it has a metal ball tipped rod that contacts a 5 direction switch( vertical, left, right, front, back).

So, if we were to construct something of that nature, you could have the 3d printer perform surface scanning also.  It wouldn't be as fast as laser scanning or using a kinect... but it would be self contained.

12 Reply by Tomek

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Re: Automatic Bed Leveling

This is only semi-on topic. However, to what extent do you think z-leveling on the fly is really necessary? 

In what sort of scenarios can I see it matter? Once I leveled my printing bed I saw immediate improvements, but since then I haven't had to frequently re-level it.  I looked into the printer mounted dial, and I balked a little at the $40-60 dollar cost of a dial. Let alone the electronics upgrade to ramps that would likely be required for a z-bed probe. 


That said, it sounds like you folks see scenarios in which it might be worth it.  I'm trying to learn more about what sort of scenarios it might be useful over the typical paper-test leveling test (which while clearly inferior, is still pretty decent.)

13 Reply by IanJohnson

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Re: Automatic Bed Leveling

The Z bed probe doesn't actually require an electronics upgrade.  It just gets spliced in with the Z endstop so when the probe contacts the bed, the printer just thinks it hit Z home.  When it does, the log shows the Z coordinate it was at when the endstop triggered.  You check the 3 values for the 3 positions, then adjust the screws until they read the same. 

The endstop switches are pretty cheap, and having something attached to the extruder that can measure the bed level is a lot more convenient that mounting a gauge, and more accurate than paper.

14 Reply by poppinfresh

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Re: Automatic Bed Leveling

This thread just .....died....

Did nothing ever become of this?  I sure wish I didn't have to continuously re-level my print bed

15 Reply by carl_m1968

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Re: Automatic Bed Leveling

poppinfresh wrote:

This thread just .....died....

Did nothing ever become of this?  I sure wish I didn't have to continuously re-level my print bed


Unless you are excessively rough removing your parts or the adjusters work loos you should only have to level about once unless you change layer height but then you just adjust your Z.. I have not had to level in two months now and print nearly every day..

Printing since 2009 and still love it!
Anycubic 4MAX best $225 ever invested.
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