Trigger height compensation



  • 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 ?



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



  • 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.



  • 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 ...


  • administrators

    @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



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



  • @dc42 Does it make sense ?


  • administrators

    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.



  • 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


  • administrators

    @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.



  • 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


  • administrators

    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.


 

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