Trigger height compensation

Viald

Hi all.
Something I don't understand about trigger height on delta printer using FSR.
Let's get an exemple.
For sure, I read all the calibration process available here https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer

I measure using piece of paper and others G code stuff the trigger height at X0 Y0, I got the value -0.05, I set it in config.g
G31 P500 X0 Y0 Z-0.05

So it means that the printer knows that at this position, there is an error of -0.05 when triggering using the hothead.

Next I did an autocalibration to recalibrate the homing height.

From this point, I want to check the probe height at X0 Y0, I use this G code command:
G30 P0 X0 Y0 Z-99999 S-1

G32 bed probe heights: 0.03, mean 0.03, deviation from mean 0.000

I expect to have around 0 for the probe height at this position

Then I try this command:
G30 P0 X0 Y0 Z-99999 H0.03 S-1

G32 bed probe heights: 0.005, mean 0.005, deviation from mean 0.000

Does it mean that the G30 command doesn't take into account the trigger height correction specified in config.g file using G31 command ?

Viald

Nobody knows if G30 takes into account the height correction from G31 ?

Phaedrux

G30 should take G31 Z height into account, that's how it sets the known Z position, but I don't know how that relates to the G30 S-1 commands you used.

Viald

Thank you for your reply.

According G30 description, it should
"The optional H parameter is a height correction for that probe point. It allows for the Z probe having a trigger height that varies with XY position. The nominal trigger height of the Z probe (e.g. at bed centre) is declared in the Z parameter of the G31 command in the config.g file. When you probe using G30 and the probe triggers, the firmware will assume that the nozzle is at the nominal trigger height plus the value you have in the H parameter."

So doing a G30 trigger at the same position (X0 Y0) should give a height around 0

May I'm wrong ...

dc42

@viald said in Trigger height compensation:

Nobody knows if G30 takes into account the height correction from G31 ?

Do you mean G30 with no parameters, or G30 S-1, or G30 with XY parameters and Z-999 as used in bed.g?

G30 with no parameters does take the G31 Z value into account. So when the probe triggers and movement is stopped, it sets the Z height to the G31 Z parameter (0.05 in your example).

G30 S-1 is for measuring the trigger height when you have set the Z=0 position manually. So the value it reports (the Z height at which it stops) is not affected by the G31 Z parameter.

HTH David

Viald

Hello.
I mean G30 P0 X0 Y0 Z-99999 S-1, which is use to report the height trigger.

Viald

@dc42 Does it make sense ?

dc42

G30 with S-1 and a P parameter is normally used at the end of a sequence of G30 commands with different P parameters. It displays the mean and standard deviation of the height errors of the points probed. In working out the height error, it does use the trigger height defined by the G31 Z parameter.

Viald

So, if it uses the trigger height defined by the G31 Z parameter, why I have such error (0.03) when probing only the center ?

G31 P500 X0 Y0 Z-0.05

G30 P0 X0 Y0 Z-99999 S-1

G32 bed probe heights: 0.03, mean 0.03, deviation from mean 0.000

dc42

@viald said in Trigger height compensation:

So, if it uses the trigger height defined by the G31 Z parameter, why I have such error (0.03) when probing only the center ?

G31 P500 X0 Y0 Z-0.05

G30 P0 X0 Y0 Z-99999 S-1

G32 bed probe heights: 0.03, mean 0.03, deviation from mean 0.000

It could be because you homed Z at a different probe point, or just variation in the trigger height of the probe.

Viald

I homed and probe Z at the same position X0 Y0. I don't think this a variation in the trigger height, because I checked several times the trigger height at X0 Y0. And when I specified H parameter for G30 like this

G30 P0 X0 Y0 Z-99999 H0.03 S-1

I get this result each time

G32 bed probe heights: 0.005, mean 0.005, deviation from mean 0.000

As soon as my delta will be ready again, I'll do new tests changing Z setting in G31 P500 X0 Y0 Z-0.05 to confirm that this value is taking into account by G30 P0 X0 Y0 Z-99999 S-1 command.

Thanks

dc42

Bear in mind that when you execute G1 X0 Y0 and then G30, it is the nozzle that is at X0 Y0. Whereas when you set up mesh bed probing, or execute G30 P0 X0 Y0 Z-00000 S-1, that command puts the probe at X0 Y0. So if the Z probe is offset from the nozzle, it is not the same position.

Viald

@dc42 You are right, but as my Delta uses 3 FSR sensors, the nozzle and the probe are exactly the same.
This is why I suspect something wrong with G30 P0 X0 Y0 Z-99999 S-1

dc42

@viald said in Trigger height compensation:

G32 bed probe heights: 0.005, mean 0.005, deviation from mean 0.000

0.005mm is probably one microstep on your machine. A variation of 1 microstep is to be expected.

G31 P500 X0 Y0 Z-0.05

Are your FSRs really so sensitive that the nozzle only needs to depress the bed by 0.05mm to trigger then?

Viald

@dc42 I think so
I have checked again probing height at X0 Y0
I have set the FSR board at the max sensitivity level which is 0.95V, by default the level is 0.92V

09:19:32M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.024 mm
09:19:26M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.024 mm
09:19:20M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.024 mm
09:19:15M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.029 mm
09:19:09M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.024 mm
09:18:59M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.024 mm
09:18:40M98 P"0:/macros/Calibration/Z0 Delta"
Stopped at height -0.044 mm

It's even better -0.024

I noticed that each time I did this test, the first measure (-0.044) is always lower than the others. This is why when I probe the bed, I did it several times (M558 P5 X0 Y0 Z0 H1.5 I1 T15000 F50 A5 S0.01)