Smart effector and trigger height (and a few new grey hairs)

janjoh

Sooo, I am not getting to terms with trigger height of my smart effector.

Here is what's going on when I am working from https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe

Board: Duet 2 WiFi (2WiFi)
Firmware: RepRapFirmware for Duet 2 WiFi/Ethernet 3.1.1 (2020-05-19b2)
Duet WiFi Server Version: 1.23

My print bed is a PEI-sheet, so yes I suppose there is a bit of flex in it. If that matters.

Power up machine (doh)
Home machine
M561
Jog head to barely touch bed. (But I used a feeler gauge 0.20mm, so in my case "barely touch feeler gauge)
Issue G92 Z0.2, because I know I am now at 0.2mm, right?
Move head up 10mm
Issue G30 S-1, Head descends, touches bed, and my readout is Z -0.21
Move head up and repeat a "few"(*) times. I consistently get -0.21 (I'd say >80% of my runs), -0,22 (probably 15%) , and a very rare -0,23.
So, great, my trigger height is -0.21. Excellent. I put that in my config.g

G31 P500 X0 Y0 Z-0.21 ; set Z probe trigger value, offset and trigger height

I check that there is no G31 in config override.
I reboot my machine, home, and run a G30 S-1. effector descends, hits bed, stops, and i read Z 0.26. And head is litterary Touching bed.
I decide to find out how much I must jog up to get a feeler in.
At Z0.54 i can get a 0.10mm feeler under the nozzle.

What's going on here? What am I doing wrong?

(*)When I did it the first time, I did it 3 times. But as the end result confused me, I re-did it and tried probably 50 times, as I assumed that I had made some misstake.

BoA

I belive You need to set Z probe offset to 0.21, not -0.21

janjoh

Readin (7) and (9) here in the linked article, it says to use the reported height. It also says that the smart effector should have a negative ofset. So..

You may be correct, but in that case the documentation is highly unclear.

BoA

I will describe a certain picture.
Assumption - nozzle has to be pushed a little to trigger Z

And imagine what is going on when probing. Nozzle touches bed, but not triggered yet, goes to -0.21mm and then it is triggered.

Which means nozzle is at -0.21 when Z trigger, and in other words, Z triggers 0.21 above the nozzle tip.
So, Z probe offset should be above the nozzle level (+0.21mm).

OR

You can assume Z trigger is at 0.00, and set tool offset in Z to -0.21

Hope this short description helps to understand what and why is going on

fcwilt

For the smart effector a negative value is correct.

What does your M558 command look like?

In step 10 you use G30 S-0. I can find no documentation for an S-0 parameter. Did you try just G30?

Frederick

janjoh

@BoA That, however, goes against both the linked article, AND what is stated in the commissioning guide for the smart effector https://duet3d.dozuki.com/Wiki/Smart_effector_and_carriage_adapters_for_delta_printer

Just a quick check, do you actually use the Smart Effector with a positive offset on your machine?

janjoh

@fcwilt I meant S-1, same as in step 6. Good catch. Edited.

M558 P5 R0.4 C"zprobe.in+zprobe.mod" H5 F1200 T6000

fcwilt

@janjoh said in Smart effector and trigger height (and a few new grey hairs):

@fcwilt I meant S-1, same as in step 6. Good catch. Edited.

M558 P5 R0.4 C"zprobe.in+zprobe.mod" H5 F1200 T6000

G30 S-1 reports the trigger height.

In Step 5 you correctly set Z to a known height.

In Step 10 you home which likely sets Z to an incorrect height.

Remove the S-1 and just have G30. See if that doesn't fix things.

Frederick

janjoh

@fcwilt Noooooooooooo... (or rather yes)....

Yeah, that's spot on... at Z0.32 I can now get a 0.30 feeler in. At Z0.28 I can not.

So, that was flipping silly of me..... Especially as this means that my start script was correct, but my manual testing was (really) flawed... Sigh.

Nothing to see here... move on...

Thank you.

BoA

@janjoh So is the offset negative or positive after all ?

fcwilt

@BoA said in Smart effector and trigger height (and a few new grey hairs):

@janjoh So is the offset negative or positive after all ?

Negative.

When the nozzle is just touching the bed that is Z=0.

For the smart effector a bit more movement is needed to trigger the sensor.

At the point Z will be negative.

Frederick

janjoh

@BoA Negative, as per the documentation.

BoA

OK. When Im thinking about it now, You are right, as G31 takes not the offset, but trigger height (which is effectively offset * -1). My bad.

NexxCat

From someone who bashed their head into a wall about this before. Make sure you perform the Z-probe offset and all probing with the bed and hotend heated. I use 60C on the bed and 130C on the nozzle.

A Former User

@BoA said in Smart effector and trigger height (and a few new grey hairs):

I will describe a certain picture.
Assumption - nozzle has to be pushed a little to trigger Z

And imagine what is going on when probing. Nozzle touches bed, but not triggered yet, goes to -0.21mm and then it is triggered.

Which means nozzle is at -0.21 when Z trigger, and in other words, Z triggers 0.21 above the nozzle tip.
So, Z probe offset should be above the nozzle level (+0.21mm).

OR

You can assume Z trigger is at 0.00, and set tool offset in Z to -0.21

Hope this short description helps to understand what and why is going on

I'm sorry but (your logic) Is 100% flawed

BoA

@CaLviNx What do You mean ?

A Former User

@BoA said in Smart effector and trigger height (and a few new grey hairs):

@CaLviNx What do You mean ?

Really?

BoA

@CaLviNx Yes. I would say the only mistake is caused by Z offset beeing not the same as Z trigger height, and G31 takes trigger height, which in this case is offset * -1

Phaedrux

@BoA said in Smart effector and trigger height (and a few new grey hairs):

Z offset beeing not the same as Z trigger height,

Z offset = z trigger height

BoA

@Phaedrux OK. I stand corrected