Problems with Probing (G38.2 command)?

Home › Forums › TinyG › TinyG Support › Problems with Probing (G38.2 command)?

Tagged: 

Viewing 9 posts - 1 through 9 (of 9 total)
  • Author
    Posts
  • February 19, 2018 at 1:10 pm #10845
    cmcgrath5035
    Moderator

    Read thru this thread, it has some useful user experience

    Z probe moves Z axis up instead of down

    February 26, 2019 at 11:01 am #11319
    kiwigrant
    Member

    I have a switched probe that is that is “NC”.

    G38.2 seems to ignore $ST

    I read in earlier post (2014ish) that during that G38.2 looks for a state change and is therefore not affected by $ST.

    This would be ideal as I intend to use both a touch off plate “NO” as well as my sensor probe “NC”

    So far my G38.2 command is responding as if it is not looking for a state change rather it is behaving as if it only supports transitions from the NO state.

    February 26, 2019 at 1:18 pm #11320
    cmcgrath5035
    Moderator

    What version of tinyG FW are you running?

    I believe 440.20 ignores $st for G38.2 probes but does assume Zmin will be NO.
    It further appears (see: https://github.com/synthetos/TinyG/issues/183) that FW 449.01 introduced some new behavior, but unclear that was ever fully debugged. 449.01 remains Edge.

    Also note that discussions for G2core FW 100.xx and above do not apply as of yet to tinyG

    February 26, 2019 at 3:40 pm #11321
    kiwigrant
    Member

    [fv] firmware version 0.97
    tinyg [mm] ok>
    $fb
    [fb] firmware build 440.20
    tinyg [mm] ok>

    Let me do some reading on the edge versions. Now deciding whether or nto to build a logic inverter attempt the new edge version. If I can roll back to 440.20 without issue Im willing to give it a try.

    Thanks for the assist.

    February 26, 2019 at 3:59 pm #11322
    cmcgrath5035
    Moderator

    You would be able to roll back to 440.20 should you choose to.

    March 2, 2019 at 5:46 pm #11328
    kiwigrant
    Member

    @cmcgrath5035

    I installed..
    [fb] firmware build 449.01
    [fv] firmware version 0.97

    It did not change the behavior of the probing routine to recognize $ST for probing and still assume probes are NO…

    I was hoping it would detect state change in either direction. but only operates going low-> high ie Normally Open behavior

    Time to make a logic inverter… sadly

    March 24, 2019 at 2:26 pm #11344
    steverichab
    Member

    I am using a TinyG V8 with FW build 440.20 ver 0.97
    I have connected both a Z probe(NO) and a Z min limit switch(NC) to the z min input on the tinyG.

    The wiki has this not concerning the probing cycle:
    Note that probing cycles (G38.2) will work regardless of the switch setting. Probing (currently) assumes a normally open switch in the Z minimum position. During the probe cycle switches are set to NO (and ignored). They are restored to their actual $st setting when probing is complete.

    I assumed that the FW would ignore the z min(NC) limit when probing per the note above. Unfortunately if the NC contact is connected when I try the z probe widget in ChiliPeppr it “sees” the z min(NC) and stops the probing process.

    If I disconnect the z min limit it probes just fine. Also I set $zsn=0 for this test.
    Is there a way to have both Z probing(NO) and z min(NC) with $zsn=2 as the note above leads me to beleive?
    Thanks, Steve

    March 24, 2019 at 3:41 pm #11345
    cmcgrath5035
    Moderator

    Is there a way to have both Z probing(NO) and z min(NC) with $zsn=2 as the note above leads me to beleive?

    Homing on the Zaxis is logically hardwired to Zmax.
    I suppose you could have a Zmin Limit switch but it would have to be a NO and not mechanically make contact before the probe switch.
    You should read the wiki item this way: During a probe cycle, the Probe switch is assumed to be a NO, therefore the input port to the controller will be logic high.
    The closure of the NO probe switch will cause a high to low transition and the probe process will initiate completion. tinyG can’t physically change a switch from NC to NO, and during probe cycle assumes it is NO.

    How would you propose to use a limit switch, given that the Probe process is mechanically capable of accommodating various probed values for the Z=0 position?

    March 31, 2019 at 9:15 pm #11356
    kiwigrant
    Member

    If you wire a probe to zmax, it should not be configured as a Z max limit switch. If you do this you will find that if there is any contact bounce during the probing operation. it will detect the first contact as the probe signal and then the 2nd contact as a z limited causing the tinyG to go into limit mode and will need to be reset.

    The G38.2 command does not observe NO/NC action of the zLimit switch sense. It only operates as a NO. I built a transister based inverter circuit that allows me to use a N/C touch probe as well as a NO contact probe if needed.

    I havent drawn this up properly yet but could make a drawing available to anyone who would find this useful in a week or so.

    While this was a temporary set back Im happy with it functionality.

    Grant

    • This reply was modified 5 years, 9 months ago by kiwigrant.
  • Author
    Posts
Viewing 9 posts - 1 through 9 (of 9 total)
  • You must be logged in to reply to this topic.