IR Z Probe offsets and multiple extruders



  • I've been searching through the forum and the documents for probing here: https://duet3d.com/wiki/Setting_up_automatic_probing_of_the_print_bed

    I'm putting one of DC42's IR probes on the fan mount of a chimera today. This leads me to questions that I can't find the answer for.

    • Do I need to do something about the fact that there's a +/-9mm offset around center for each of my hot ends? If so, what?
    • There are X and Y offsets for the probe in the config file. Do I just put the offset of the probe from the centerline of my effector here?

    Basically the procedures for using the z-probing are well defined except I can't figure out what, if anything, I need to do to handle the offset of my tool or my sensor.

    Am I being dumb and not seeing obvious documentation or is this a hole in the instructions?

    Thanks!


  • administrators



  • @dc42

    The first link takes me to tool configuration which I've already done as part of my setup but doesn't seem to have anything regarding z-probing.

    The second link only mentions this about offsets:

    "The G31 command also has also optional X and Y parameters to define the horizontal offset of the Z probe from the nozzle. On a delta printer these should be left at zero, because the calibration routine needs to know where the nozzle has been placed, not where the probe is."

    Sadly, I'm still confused.

    • Do I need to worry about tool offset during z-probing?
    • The second link implies that I should not use a probe offset for a delta but the logic doesn't make sense to me. Wouldn't the system want to actually measure the point in question and not some point near the point in question?

    I'm presuming that I'm just being paranoid. For a reasonably flat surface, the error of the probe position will largely be irrelevant.

    Right now, I believe I should do the following:

    1. Zero out probe offsets in my config.
    2. Ignore that the tool offset exists and run z-probing.


  • administrators

    @LeonMF:

    @dc42
    Right now, I believe I should do the following:

    1. Zero out probe offsets in my config.
    2. Ignore that the tool offset exists and run z-probing.

    For a delta, that is correct. Bed probing does auto calibration. The algorithm assumes the bed is flat, and it needs to know the nozzle position, not the probe position. The assumption that the bed is flat means that the nozzle offset shouldn't affect the height reading (although in practice it will if there is varying effector tilt - but that isn't really predictable anyway).

    You may need to ensure that no tool is selected when probing, by sending T-1 just before you start, to ensure that it is the centre of the effector that is over the specified probe points and not one of the nozzles. Let me know if you find this is the case, in which case in a future release I'll have it not add on the tool offset when probing even if a tool is selected.



  • Rather than start a new thread with similar title…

    dc42 - I didn't find this info on your site or this forum:
    What are the XZ offset dimensions (in mm, relative to upper surface of and in PCB coordinates) to the IR z probe's notional 'sense axis'?
    Dimensions either WRT the PCB bottom left corner or possibly better yet, relative to the IR z probe PCB LH mounting hole would be appreciated.

    My own rough estimate: X=12 from LH PCB edge | 9.3 from LH mounting hole center, Z=4 mm from PCB upper surface. N.B. To prevent confusion I'll delete my estimate after you reply.

    I see the following from Appendix: Board dimensions and mounting holes for version 1.1 and 1.2 boards on your website, but no positional data for the probe's 'sense-axis' location.

    If the bottom left corner of the board is position (0, 0) then other points on the board are at the following (X, Y) coordinates, in mm:

    Top right corner (24.0, 17.62)
    Mounting hole centres (2.70, 14.92) and (21.11, 14.92)
    Mounting hole diameter 2.8

    Last updated 2017-05-10.


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