Opto vs Mech

Which has the best repeatability for keeping the Z zero point steady?

(Also any bad reson not to just run a wire to the nozzle and a piece of copper tape on the bed/zero points , and just let the nozzle find home/zero by touching off?)

You know, that's a good question. I know that I have heard some talk about self homing print nozzle but I'm not sure what the consensus was (or if there ever was one). One problem I could see is that if your nozzle is not completely clean you are not going to get an electrical connection. I think you might run into some repeat ability issues with this and if the nozzle doesn't make a clean contact with the copper tape your nozzle will keep trying to go through your print bed potentially ruining both.

I know the community has moved to either mechanical or hall effect endstops. I have heard that for sheer finite control and repeat ability, hall endstops are the way to go. My understanding is that the opto endstops can be "confused" depending on the lighting in the room (in particular flourescent lights). I know there are still a few people out there that use opto but it seems to have fallen out of favor.

... for high accuracy referencing I'm using inductive sensors - common ones with around 10 microns accuracy, some highres types from Omron with submicron resolution ...

Inductive difference-sensors with three congruent coils and micron accuracy could be DIY, but as long cheap mechanical or optical switches are around and 0.05mm referencing accuracy is sufficient for common use, this won't be adressed seriously

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Viktor,

Those are some pretty expensive sensors!

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

i don't know about all the above, but from my experience always mechanical is most reliable, you can here it when it works with the click click action so you know it should be working, it has a lower resistance than optical so less line noise, and it has the best isolation of any other sensor type.


I am for nozzle direct sensing if it is with a mechanical switch that is protected behind some heat shield.

first off direct circuit contact off of exposed copper to high temp is probably not going to happen,as the oxygen will oxidize the surface at an accelerated rate right under the nozzle and probably within 10 seconds so you would have an insulator that becomes unreliable as a contact, and imagine if you have filament on you nozzle and no contact is made to close the circuit at all. your nozzle will settle in the bed, and probably not stop without the z axis popping apart. work on some of the issues and it might work.

edit: for z axis i do not use the lever switch, i use a mechanical switch pull off the lever, and have anchored the homing switch holder with a zip tie below it on the smooth rod because the flag will bend out of position otherwise. also homing is done with firmware g28 homing not just going down to z as far as i can.

Edited 2 time(s). Last edit at 01/18/2013 11:16AM by jamesdanielv.

I have issues with Mech stops on my z. I feel they are fine for X/Y, but Z needs something accurate.

I think a better mechanical endstop with a more solid mount is needed on my z, if not I may try optical or proximity based like viktor uses (yes those are as much as 100$ each...)

There is also a possibility of getting my hands on some of these used laser sensors, I doubt those will have issues with any stray light, I've never seen any of the type have any issues.

you can also remove the lever from mechanical switches.

jamesdanielv Wrote:
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> you can also remove the lever from mechanical
> switches.

At the risk of your z banging into it really hard. May need to adjust z homing speed in firmware even slower for that... I'm already slow enough on my z homing. :-)

perhaps your z homing mount has to much flex in it?

Edited 1 time(s). Last edit at 01/18/2013 11:16AM by jamesdanielv.

Absolutely. My z endstop situation is a mess. And I do need a better mount.

I will find a more suitable mount or make one, just haven't had time this week as work laid off more people and guess who gets to pick up even more slack...

Anyone using hall effect sensors?
I'm considering using one for Z. For X and Y I'll make do with the mechanical switches I have, but for Z I think it should be a good option. I guess unipolar or omnipolar should work (I'm a hall noob).

I use mechanical switches on my printers I found them more reliable that optical switches.
My mill uses Hall effect sensors for it's home switches and they seem to work fine.

Great stuff people!
(though still a little confused to wich way I will go) I'm used to closed loop systems over this open loop version. But open is a LOT cheaper and easier to code.

X&Y aren't nearly as critical. Maybe I'll design a RF touchoff system, not unlike the systems I work on now. (time permitting)

I once saw some extremely accurate mechanical switches made from 4 balls. The forth ball was spring loaded against the other three balls sitting in a triangle. Wires were connected to two of the three balls. The fourth ball makes contact with the other three completing the circuit. The switch plunger passes through the center of the three balls and pushes against the fourth ball. The switch is normally closed, and extremely repeatable on opening. Claimed resolution was 0.000025" Very simple, could be very robust too.

anode505 Wrote:
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> Great stuff people!
> (though still a little confused to wich way I will
> go) I'm used to closed loop systems over this
> open loop version. But open is a LOT cheaper and
> easier to code.
>
> X&Y aren't nearly as critical. Maybe I'll design
> a RF touchoff system, not unlike the systems I
> work on now. (time permitting)

I use mechanical switches. Don't get the ones with the lever, just use the button.
And, get the snap action ones - very quick, so less flyback spark - so the contacts don't get messed up and they hold their position.

just use two small bolts that touch each other, now moving parts and they are very accurate