Auto-levelling efforts

Re: Auto-levelling efforts

Alzibiff — Sat, 14 Jun 2014 12:15:15 -0400

Quote
sguzzel
What about this approach?

Intriguing - looks like something equivalent to the mechanical depth gauge in that it appears to be a method of getting the bed level rather than providing any sort of auto levelling.

Alan

Re: Auto-levelling efforts

sguzzel — Sat, 14 Jun 2014 12:10:09 -0400

What about this approach?
[www.youtube.com]

Sadly I couldn't find any further information.

Re: Auto-levelling efforts

The_ccm — Fri, 06 Jun 2014 07:30:31 -0400

ok I get it now :)

Re: Auto-levelling efforts

nophead — Fri, 06 Jun 2014 05:08:11 -0400

Optos are analogue devices. They have a slot with a finite size, 0.5mm in this case. As the tab moves to cover it the amount of IR light reaching the photo transistor gradually reduces. That causes the transistor to come out of saturation and the voltage on the collector to gradually increase. When it reaches the switching threshold of the Atmega input it will be sensed. Any variation in background IR (sun, halogen bulbs, etc), temperature of the semiconductors, etc, will change the trip point slightly.

I don't know a lot about hall effect limit switches but they are sensing a magnetic field, which is inherently an analogue value that must be compared with a threshold to obtain a digit signal. The same applies to force sensors.

Re: Auto-levelling efforts

The_ccm — Fri, 06 Jun 2014 04:45:35 -0400

Ok i am agree for the hall but the optical is not analog (or I didn't understand what u mean), one side is a ir led which produce enough strength with big vcc variation and other side is a transistor either open collector so z-signal will be vcc or satured to ground.

Anyway was just a idea if the micro switch can work in all conditions it's the better choice.

Re: Auto-levelling efforts

nophead — Thu, 05 Jun 2014 13:05:36 -0400

Both are analogue electronic devices where the exact switch point will vary with stray fields, temperature and supply voltage. With two gold contacts I think the only variation is thermal expansion of the plastic part.

Re: Auto-levelling efforts

The_ccm — Thu, 05 Jun 2014 13:00:13 -0400

Maybe I missed something but a optical sensor could fit :
[www.tme.eu]

Placed somewhere in the probe height, when the probe is going up between the 2 teethes the signal is switching.

Or a hall sensor :
[www.tme.eu]
But if you have magnet around maybe it can have unwanted signals switch.

Re: Auto-levelling efforts

nophead — Mon, 02 Jun 2014 07:44:34 -0400

You can enable the EEPROM and change it there (you might need a later Marlin version such as Neil Darlow's) but I personally prefer to change source code than send random G-codes. Also I disable the EEPROM by default as it can be very confusing because it overrides what you have in the source code unless you reset it, then you risk losing settings as the firmware then overrides the EEPROM. It seems much better to me to keep just one version of the settings in a human readable form stored on a host. In my case an RPI attached to the machine. If you swap hosts or just run the machine from an LCD then you need to keep everything in the EEPROM.

For auto levelling with a probe it it would need to be stored in EEPROM unless you do it every build. That is what I do with my own firmware / host and it has the advantage of probing at the extents of where the object is, rather than fixed places. If the bed is not completely flat that is more accurate as it models the part of the bed you are actually using and ignores the rest.

I am not sure why people find the Z height changes when they move their machine. I have taken mine to shows and not had to change it. Basically if the machine is on a flat plane the height and levelling should not vary even if it is slightly inclined. On the other hand if it is not a flat plane it will cause the Y bars to not be exactly parallel vertically, in which case the Y carriage will roll around the Y axis as it moves backwards and forwards. That shows up as only being able to level three corners. The three point levelling I implemented on Hydraraptor will not compensate for that, neither will the implementation in Marlin. It would need four sample points and a non-affine transformation I think.

Re: Auto-levelling efforts

Ralph.Hilton — Mon, 02 Jun 2014 07:03:39 -0400

I'm wondering why the Z-home-pos is changed in firmware rather than eeprom.

Re: Auto-levelling efforts

Mytch — Sun, 25 May 2014 13:11:56 -0400

Hi!

I had my Mendel90 for nearly a year and I'm very happy with it, but I must say that an auto-level feature would be quite interesting.

In my case, I have to recalibrate it when I move it on some other place even thought the surface seems flat and sturdy.
Well, normally it's not supposed to be moved often…
The other advantage might be to compensate for approximate manual calibration and make it more forgiving.

At any rate, it's truly an ingenious system you made here Chris, and like you said, I also don't see the problem having a manual system since we must go to the printer after a print anyway.

It would be great to have it implemented…

Re: Auto-levelling efforts

Traveltrousers — Sun, 25 May 2014 12:28:27 -0400

Manual intervention is another thing to forget :p

I'm waiting for they day when I can just go from a model to 'print' and it rotates itself, decides on support, layer height, whether it needs a brim or other features, starts the printer, prints it, auto ejects it (into limoene if it has supports) and texts me to say it's done. All I have to do is keep the filament full...

Auto z-height calibration will be a standard feature for all printers soon, having it standard in the Mendel90 now can only improve sales....

Re: Auto-levelling efforts

nophead — Sun, 25 May 2014 04:21:05 -0400

I don't find the manual intervention a problem because at the end of a print I have to manually remove the parts, the skirt, the start blob and any ooze from the nozzle and swill the bed with acetone. I then pull the probe down so the next start can be completely unattended.

Re: Auto-levelling efforts

Traveltrousers — Sat, 24 May 2014 20:19:11 -0400

Quote
ElectroWomble
Doing this a few times ... out by 0.02 - 0.05mm each time

I mostly print at 0.3mm layers so this margin of error would be fine with me....

Re: Auto-levelling efforts

Traveltrousers — Sat, 24 May 2014 20:16:39 -0400

If I were to implement this I would also use magnets in a similar way and then when the print finishes and the head re-homes a small lever on the central support could push the probe back down ready for the next print.

No manual intervention required.

It would be great if we could collectively implement this for stock nophead M90's....

Re: Auto-levelling efforts

chris33 — Sat, 24 May 2014 13:35:27 -0400

i run a I3 but i think if someone gets a 5v solenoid to run on ramps i know you can run one from the arduino with some added circuitry, use the solenoid to push the probe down to operate the probe, im going experiment later with a laser pen and a micro camera that be best way forward be able to use the laser to read the distance based on webcam range finder just be hard to find some code to implement in in my firmware as i know no programming knowledge but ill have to learn sometime or another lol

Re: Auto-levelling efforts

neildarlow — Fri, 23 May 2014 08:45:50 -0400

I am not sure that a shared signal is a safe thing to do for two reasons:

If bed levelling is not performed, operation should be normal Mendel90 behaviour.
The failure of the levelling mechanism, in any manner, should not impact normal Z-limit switch operation.

Regards,
Neil Darlow

Re: Auto-levelling efforts

nophead — Fri, 23 May 2014 06:20:17 -0400

The state of the probe is open when retracted, closed when deployed and open when deployed and activated.

Re: Auto-levelling efforts

svanteg — Fri, 23 May 2014 06:13:06 -0400

Just following up the possibility of sharing the Z endstop signal with the probe... Unless I am missing something an OR gate would work?

Z endstop	Z probe	out	Z endstop state				Z probe state				Comment
closed		closed	closed	connected; not triggered		connected; retracted			either all ok or short circuited
closed		open	open	connected; not triggered		not known if connected; deployed	
open		closed	open	not known if connected; triggered	connected; retracted	
open		open	open	not known if connected; triggered	not known if connected; deployed

Re: Auto-levelling efforts

svanteg — Fri, 23 May 2014 05:59:57 -0400

[removed due to technical posting error...]

Re: Auto-levelling efforts

ElectroWomble — Fri, 23 May 2014 05:15:27 -0400

You wouldn't. I was hoping eventually to have several extruders with different nozzle size and be able to swap them (change a value in firmware to represent the calibrated offset of the nozzle) and be able to swap them back without having to do any manual calibration (ie just dial in the per extruder offset again.) Not a problem i currently have though.

Re: Auto-levelling efforts

nophead — Thu, 22 May 2014 19:21:55 -0400

Why would you ever take it off though unless replacing the hot end or swapping it for another one?

Normal micro switches need a lot of force. That is why I used a special low force one on my original design.

Re: Auto-levelling efforts

ElectroWomble — Thu, 22 May 2014 18:55:54 -0400

Some (not particularly scientific) results:

The spring in micro switches is sufficiently strong to bend the bed by 0.08 - 0.1mm in the middle and 0.06mm in the corners. I attached a dial gauge to the X carriage and pushed down on the bed (2mm glass) just next to it with a small micro switch (the kind of thing everybody uses for end stops with the leaver arm removed) until I could hear the click and then read the gauge.

I then increased Z by 10cm unscrewed the dial gauge took it off and then screwed it back on again (to simulate taking off the extruder). Dropped Z by 10 again and looked at the reading on the guage. Doing this a few times ... out by 0.02 - 0.05mm each time. So you can nearly get away with taking off and reattaching the extruder but not quite.

Would be interested if others get the same results.

Re: Auto-levelling efforts

nophead — Thu, 22 May 2014 13:02:45 -0400

Yes it varies a bit depending on the tightness of the wingnuts. It also seems to take some time for a new J-head to stabilise in length as they seem to stretch a bit, or maybe the Wades block does.

I always check the first layer height if I remove the extruder, although I do that very rarely, I can't remember the last time.

Re: Auto-levelling efforts

ElectroWomble — Thu, 22 May 2014 12:34:55 -0400

I cant work out which would be most convenient... having the probe attached to the wades block V having it attached to the carriage? It would be nice to keep the symmetrical air flow from the fan duct.

How repeatable is the Z hight when you take off and reinstall the extruder? ie dose that muck up your Z hight calibration anyway... I would have thought it would depend on how tight you screw on the wing nuts (or there low profile replacement).

When I get a moment I may try to get some crude measurements.

Re: Auto-levelling efforts

nophead — Thu, 22 May 2014 11:43:10 -0400

>you deploy your probe by hand (I vaguely sense a risk of being misunderstood here) and you use a programmed move to retract it, yes?

Yes I pull the probe down before I start the machine and it refuses to start if it is not down. After probing it just moves the nozzle closer to the bed and as soon as the magnet gets past half way it snaps to the top.

I don't think it can be wired to the Z limit as that is normally closed for safety. The probe is also normally closed when deployed, opening when triggered but is permanently open when retracted.

Re: Auto-levelling efforts

svanteg — Thu, 22 May 2014 11:26:52 -0400

@neildarlow: the way Marlin does a g29 it resets the Z-offset using the probe data - the at-the-top homed Z is discarded. As long as top-Z-referenced "-1" is physically below the plate and you start the probe above the plate you're good. The GitHub snapshot from your repository did not work out of the box though - I don't remember if the fix was mechanical or via code fix but it only tried to probe for up to 20mm before calling a hit regardless if that was in mid air.

@nophead: to be sure I am not missing anything in your new design - you deploy your probe by hand (I vaguely sense a risk of being misunderstood here) and you use a programmed move to retract it, yes? That is what I understood from your blog on the original design, just want to make sure I am not missing anything magical... Otherwise very neat and inspiring for a v2 of my design. This week I had a demo at another location where I had to move the printer. Sticking it in the trunk I snapped the lifter thread for the probe rod so I am thinking about another arrangement for the top end that protects the rod in the retracted position using a magnet to keep it still.

As for input pins there is the option to use the existing z-stop as the probe signal since the Mendel90 design cannot physically home and probe at the same time. This _should_ also work with Marlin since homing and probing commands start by deploying the probe. It also assumes open-when-untriggered switches and a pull up on the input which I think is the case. I might give it a try for v2.

@ElectroWomble: I went with the "very long probe" approach using a 2mm drill rod (d.o. piano wire is cheaper and would work just as well) and drilled out the printed pilot hole to 2.1mm making it pretty stable and located in the x-y plane. The top "paddle" tends to rattle slightly against a locating reference "bump" though - although that has no bearing on the function. An advantage (IMHO) with this approach is that the probe stays calibrated relative the extruder tip when you remove the extruder assy. Also, nohead is right about the heat expansion - if you want the last bit of precision you want to stick the "set Z offset" command in the slicer startup code so you can tune it differently for e.g. PLA and ABS. If you haven't already you can take a look over here for my current design.

@demetris: your right about things causing the extruder-tip-to-probe-distance to "move"...however this is not so much of a problem since it "just" needs to stay within about +/- 2-3 hundreds of a mm. Which it basically will if you have a descent switch and probe under controlled conditions - i.e. at the same point in the startup code with things at a stable and same temperature. And since the auto levelling removes the plate slant causing differences between right, left, upper, lower part of a test print it is actually pretty easy to get inside the +/- 1 hundreds window if your plate is flat enough.

The switch is a key part of the precision and it is not a given that a micro switch is precise enough - the only one I found that repeats consistently better than 0.01 mm is the one I use. An optical "fork" is also sensitive since it depends on clean power to the led and keeping stray light away. Even nopheads approach with gold pins - good and simple as it is - requires having a handle on the contact bounce.

Re: Auto-levelling efforts

nophead — Tue, 20 May 2014 13:37:55 -0400

Yes a dual row 0.1" SMT header.

Re: Auto-levelling efforts

ElectroWomble — Tue, 20 May 2014 13:31:58 -0400

I suspect thats true. When I have the dial gauge on the bed I only have to look at the bed a bit funny to make it move by quite a long way.

So gold contacts = pins from a pin header?

Re: Auto-levelling efforts

nophead — Tue, 20 May 2014 12:38:53 -0400

The probe force needs to be small because the bed easily flexes with a dial gauge for example. The machines that I have probes on have 6mm aluminium under the glass rather than a PCB. Low force micro switches are expensive and big so I switched to just a pair of contacts. It should be more accurate as you can't get more digital than that and should have close to zero hysteresis.

I think three magnets would give too much force. One magnet and two steel items seems about right.

Re: Auto-levelling efforts

ElectroWomble — Tue, 20 May 2014 12:10:29 -0400

I was thinking of trying to create something like the Z probe you documented on your blog [hydraraptor.blogspot.co.uk]. I was still thinking of using a micro switch.

My plan was to try to make it smaller by using 3 magnets all lined up in a row and use the magnetic field (not just gravity) to provide the pull against the micro switch. The central magnet would be attached to the probe/plunger (think of it being hidden in the plastic disc of your original Z-probe). If the probe is lower the central magnet is pulled down by attraction to the lower magnet (hopefully) with sufficient force to operate the micro switch. If the probe is pushed up a small amount (in normal probing) it would open/close the switch. When you wont to retract the probe you just push it up past the 1/2 way point where it would then be attracted to the upper magnet and hopefully held out of the way while the machine prints. [Hope that description is vaguely comprehensible].

I got stuck on how to mount it on the carriage... I wast starting to think of putting it on top of the wades block and having a very long probe through a hole in the wades block next to the filament path. It would have to magically go through the fan duct if installed. I also thought it would be too long and wobbly. Yours looks much smaller and neater than anything I could come up with.