Improving auto-calibration.

Qdeathstar · 28 Nov 2016, 19:28

The trigger height should be the same at each location, correct?

Am I measuring the distance between the nozzle and the bed, of the irprobe and bed?

My ir probe is situated 5mm away from my heat block.

Qdeathstar · 28 Nov 2016, 19:29

How can I get the probe to stop at its trigger?

DjDemonD · 28 Nov 2016, 20:01

So the trigger height will be the same distance above the bed at each location but if your effector has tilted the nozzle to bed distance at the trigger height will be different. This difference is what you are measuring relative to the trigger height at bed centre where effector tilt should be zero. Your IR probe according to your config.g is pretty close to your nozzle so these will be small values.

You are measuring the distance between the trigger height and the nozzle hitting the bed. So go to a coordinate, send G30 the head will descend and stop when triggered OR lower the head manually until the LED comes on, on the IR sensor board. Then manually lower until you grip a piece of paper or actually make contact with the bed whichever is easier to measure. Do this at bed centre, and each of the autocalibration probing points.

H = (trigger height measured at the point) - (trigger height at the bed center)

So enter for each of your points in bed.g the H value i.e.

G30 P0 X0.00 Y110.00 Z-99999 H0
G30 P1 X70.71 Y84.26 Z-99999 H0.3
G30 P2 X108.33 Y19.10 Z-99999 H-0.4
G30 P3 X95.26 Y-55.00 Z-99999 H-0.6

See how you get on with that.

kraegar · 29 Nov 2016, 16:28

I too likely need to add H values to my probe points. My main issue is with the variability of the test for when the nozzle is gripping a sheet of paper. There's some subjectivity there.

What increments are you moving when you're calibrating those H values? 0.1mm, or lower?

I'm also a bit confused about how you determine the H value. Do you do a paper test like is outlined for configuring Z0 in the IR Probe setup? (Move to that point, lower the head until it grips a sheet of paper, set that as Z0, move up 5mm, then probe and then subtract the height at the bed center from that new value?

dc42 · 29 Nov 2016, 16:45

@kraegar:

I too likely need to add H values to my probe points. My main issue is with the variability of the test for when the nozzle is gripping a sheet of paper. There's some subjectivity there.

What increments are you moving when you're calibrating those H values? 0.1mm, or lower?

I'm also a bit confused about how you determine the H value. Do you do a paper test like is outlined for configuring Z0 in the IR Probe setup? (Move to that point, lower the head until it grips a sheet of paper, set that as Z0, move up 5mm, then probe and then subtract the height at the bed center from that new value?

I use 0.025mm increments on my delta with 160 steps/mm. If you have 100 or 200 steps/mm then you should use 0.020mm instead. The procedure I use is:

1. Move the head to over the probe point.

2. Lower the head until it just grips a sheet of paper (this is where I use 0.025mm increments near the end).

3. Send G92 Z0.

4. Raise the head 5mm.

5. Send G30 S-1 to lower the probe until it triggers.

6. Read off the Z height in the web interface.

I usually repeat steps 4-6 a few times to make sure the trigger height is consistent. The H parameter for each point is (trigger height at that point) - (trigger height at centre of bed).

HTH David

kraegar · 29 Nov 2016, 17:17

David, that's exactly what I was looking for - thank you!

(You might consider adding those steps to the wiki for clear instructions on setting an H value for each point)

Is there a way to set the web interface to jog at 0.020? I have the "half move rate" checked, which took it down to 0.05mm

StephenRC · 29 Nov 2016, 17:27

You could make a macro with a relative move. Something like this for going down:
G91 ; relative moves
G1 Z-0.020 ; go down a bit
G90 ; absolute moves

dc42 · 29 Nov 2016, 19:10

@StephenRC:

You could make a macro with a relative move. Something like this for going down:
G91 ; relative moves
G1 Z-0.020 ; go down a bit
G90 ; absolute moves

That's exactly what I do, except I use 0.025mm because that is an exact number of microsteps on my printer.

kraegar · 29 Nov 2016, 20:04

Mine's at 80 steps/mm

As an aside, I'm only calibrating down to 0.06 now, so hoping this makes a big improvement

Qdeathstar · 29 Nov 2016, 22:22

When you say, "just gripping a piece of paper, is that until the paper can't move, or until we feel some resistance?

Qdeathstar · 30 Nov 2016, 02:05

One thing i found out while doing this was that my endstops were loosely goosey… i tightened them up and now at least i can get repeatable results

dc42 · 30 Nov 2016, 07:17

@Qdeathstar:

When you say, "just gripping a piece of paper, is that until the paper can't move, or until we feel some resistance?

I lower the nozzle until i can feel a significant resistance. The important thing is to be consistent.

Qdeathstar · 1 Dec 2016, 00:32

What do you guys think about my H-values… most of them are negative... i'd expect for them to be centered around zero, not mainly negative?

Jackal · 1 Dec 2016, 01:10

Qdeathstar, in what way does the auto calibration got worse?
Your H values seems ok to me, I am probing 32 points and my H values add up to 1.6
I don't think the effect of the end effector tilt would simply make them center around 0

Qdeathstar · 1 Dec 2016, 01:16

Sorry, i did not find the real trigger height, i subtracted z-values (which made the h-values the inverse of what they needed to be)… I think i have the issue fixed, im testing now. The z-height overall was a little low on the first go.

Jackal · 1 Dec 2016, 01:30

Glad to hear you got it solved

Qdeathstar · 1 Dec 2016, 04:22

well, i got that part of it solved but now it seems like the area across from the y tower is a little low and the area close to the y tower heading around to the z-tower is low…

i'm wondering if i can make manual adjustments to the H values to dial it in?

dc42 · 1 Dec 2016, 07:48

You should only use H corrections to compensate for actual variations in trigger height, which on a delta printer are usually caused by effector tilt. If you are still getting significant errors close to points that are included in the auto calibration bed probing, either fix the geometrical errors that are causing them, or use the new grid bed compensation in the 1.17dev6 build after auto calibration to compensate for them.

I have it on my list to add a wiki page on delta calibration.

Qdeathstar · 1 Dec 2016, 23:24

Thank you. Geometrical errors in this case are most likely to be a warped bed, correct? Or is there something else i should check?

Also, should the nozzle hit the bed at z=0 for x=0 & y = 0? When i check there i got .25mm off the bed?

Qdeathstar · 2 Dec 2016, 01:40

actually, it turns out when i found out my endstops were loose, i never readjusted z=0….

I redid the h-value test and now it's almost perfect!