Resetting home position



  • Is there a way for the printer to 'forget' its current home position?

    Currently, when I home twice, (when the printer already knows it's home position) it makes itself crash into the back of the corexy machine that I have.

    Any ideas?

    Many thanks in advance.



  • Are you asking if it can happen on its own, or if its possible to make it forget?

    I suppose "yes" in either case. Loosing steps, or loose belts/pulleys will shift the physical home position with respect to what the Duet think is 0,0

    G92 will allow you to set a new 0,0 location.



  • @bearer When I home then home again I get an unexpected result. The printer goes to near the back (its a corexy) and crashes into the back because of this.

    I assumed it would be due to my positioning method, but I'm currently in relative positioning when I home, is that right?

    Or do you have any other ideas?

    Thank you very much in advance!



  • @danwillm said in Resetting home position:

    but I'm currently in relative positioning when I home, is that right?

    Maybe, you still need to send the g-code to make the printer move in the direction of your limit switch regardless of absolute or relative movement.

    If you add your config file and the homing file I'm sure someone can shed some light on what the issue is. And where is your limit swithces physically located, to confirm with the config?



  • @danwillm said in Resetting home position:

    I assumed it would be due to my positioning method, but I'm currently in relative positioning when I home, is that right?

    It should not matter. BECAUSE, your /sys/homeall.g should have absolute and relative position commands prior to move commands, as appropriate. So the prior state of the machine is irrelevant.

    For example, mine (for a delta, this is actually homedelta.g) is shown below. Realize that deltas "home to the top".

    ; homedelta.g
    ; called to home all towers on a delta printer
    ;
    ; generated by RepRapFirmware Configuration Tool on Fri Jan 12 2018 20:07:04 GMT-0600 (Central Standard Time)
    G91                        ; relative positioning
    G1 S1 X955 Y955 Z955 F1800 ; move all towers to the high end stopping at the endstops (first pass)
    G1 X-10 Y-10 Z-10 F1800 S2    ; go down a few mm
    G1 S1 X15 Y15 Z15 F360     ; move all towers up once more (second pass)
    G1 Z-20 F6000               ; move down a few mm so that the nozzle can be centred
    G90                        ; absolute positioning
    G1 X0 Y0 F6000             ; move X+Y to the centre
    

    Notice it uses BOTH relative and absolute, at different points in the script.





  • @Danal

    @Phaedrux

    That is currently what I have at the moment, with G91 at the top of the script. Sending the G28 command to home twice causes the printer to crash into the back. Do you know of anything that could cause this?

    Thanks in advance.



  • @bearer said in Resetting home position:

    @danwillm said in Resetting home position:

    but I'm currently in relative positioning when I home, is that right?

    Maybe, you still need to send the g-code to make the printer move in the direction of your limit switch regardless of absolute or relative movement.

    If you add your config file and the homing file I'm sure someone can shed some light on what the issue is. And where is your limit swithces physically located, to confirm with the config?



  • There's nothing special or magic about homing, in terms of the firmware. Homing is just a set of G commands, contained in a file.

    There IS something special or magic about homing, in terms of that script. At the start of that script, the machine could be ANYWHERE. Miles from the limit switches, or a hairsbreadth, or even already pressing the limit switches.

    Therefore, the sequence of G commands has to "handle" any initial position of the machine. The sample files that are generated have worked for many machine configurations... yet there could be some unique setups that need something different.

    So...

    Please post your homeall.g. And your config.g. And your config_override.g (if you use it).

    Please post a photo of the printer, and a close up of the area of the limit switches, and a close up of the machine post-crash.


 

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