Using both the Z-limit-switch and Z-probe as endstops?



  • I have installed the IR-probe and it works perfect, actually better than expeceted. The mesh compensation,.. perfect.

    -- Duet 2 wifi, reprap 2.x. IR-probe, simple Z-switch --

    Ok, what is the issue, I would like to use the original Z-limit switch on the printer as a backup in case the Z-probe can't find the bed (removable bed).
    This is needed when I would inadvertedly hit autohome without placing the print bed back; the head would crash down and possibly damage.

    I need the printer to respond to either signal that is triggered first, the Z endtop switch or the probe.

    I have now used:

    ; emergency endstop Z trigger
    M581 Z1 S1 T0 ; invoke Trigger 0 (emergency stop as if M112) when a rising edge is detected on the Z1 endstop.

    This works as a safety but resets the machine. (not optimal)

    I have also used a trigger.g with (T2) with a simple code to lift Z 10mm after the Z-limit switch is activated

    However, while the emergency endstop trigger (T0) works whenever the limit switch is activated.
    The trigger file (T2) only loads after the Z-probe finds a surface first.

    Is there a way to get the trigger register (T2) whenever it hits the Z-limit switch? (Before or After the IR-probe registers?)


  • Moderator

    Emergency stop is doing exactly what it's supposed to. Inconvenient as that may be. There is no way to interrupt the G30 probing move as far as I'm aware.

    Another thing you can do to decrease the risk of damage in case of a probe fault is reduce the motor current during homing moves to the minimum needed for reliable motion and then return it to normal afterwards.



  • @Phaedrux Thank you for the information!
    In our mechanism, the Z spindle nut has a safety feature; when the down movement is blocked (for whatever reason) the Spindle nut dislodges from the carriage and starts spinning free, so we cant have the motor on it's lowes power setting... This is to save the spindelnut and spindle from any damage.
    Unfortunately in such event, the tip of the extruder still crashes into the printer (or what ever is in the way)...
    And it's a bit of a hasslo to get the nut back into the carriage...
    I was hoping on a win win to combine the two sensors for extra safety.

    RRF3.1 has the same condition?

    Is there maybe a way to interrupt the probe signal by routing it trough the switch as a secondary falesafe?
    Basically have the switch somewhere between the board and the 3.3v wire to the probe?

    Thanks!
    y.


  • Moderator

    I'll move this to the firmware wishlist forum for consideration by @dc42



  • @Phaedrux ha, that would be great, but then the first option; just regular wiring. Then a software update would work automatically.


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