Probing speed with analog piezo sensor



  • I have a D-Bot corexy printer with Duet2 Wifi/Duex2 and currently running RRF3beta12.

    I have just upgraded my Precision Piezo Universal PCB to the latest V2.85 which has both a digital and analog output. The digital output works as before and I can probe at 6mm/s with these settings

    M558 P8 C"!zprobe.in" R0.5 H3 F360 T9000 A5 S0.03   
    G31 X0 Y0 Z-0.1 P100  
    

    When I switch to the analog output I change the settings to

    M558 P1 C"^!zprobe.in" R0.5 H5 F360 T9000 A5 S0.03 
    G31 X0 Y0 Z-0.1 P540  
    

    (The DWC z probe reads 529 most of the time)

    It works but the 6mm/s requested results in an actual 2mm/s which is painfully slow.
    I have read in other posts that the probing speed is reduced to 1/3 for analog probes but this isn't appropriate for piezo probes. I have tried increasing the probing speed x3 but I then have to increase the z max speed to 18mm/s which is too high for the z axis. I get a 6mm/s probe followed by an 18mm/s bed down movement.
    Increasing the G31 P540 to P590 seems to disable the 1/3 speed reduction for some reason but then the probe doesn't always trigger causing bed crashes.
    It would be good if there was a way of permanently disabling the 1/3 speed reduction.
    Has anyone else experienced this with the PP 2.85 board?


  • administrators

    @tekkydave said in Probing speed with analog piezo sensor:

    It works but the 6mm/s requested results in an actual 2mm/s which is painfully slow.

    That's because with analog probes, RRF slows down probing to 1/3 speed when the reading gets close to the threshold, exactly as you said. What's the reason for not using it in digital mode?



  • Only the convenience of having the trigger level adjustment in the Duet rather than the fiddly pots on the pcb.



  • Is the 1/3 slowdown something specific of RRF3? I can't say I'm experiencing it on RRF2 but could be wrong



  • @matt3o said in Probing speed with analog piezo sensor:

    Is the 1/3 slowdown something specific of RRF3? I can't say I'm experiencing it on RRF2 but could be wrong

    It's been around for an awfully long time - at least 2 years.



  • I can see the sense in the slowdown for other analog sensors but not for piezos. The analog output is constant until the nozzle makes contact with the bed.
    Can I suggest 2 possible solutions:

    1. A way of specifying the amount of slowdown for analog sensors in M558
    2. A separate M558 probe type for piezo probes with no slowdown applied.


  • I'm guessing there has been no movement on this issue. I just ordered a new universal piezo since I wore out the pots on my older version and I was excited to see that the pots could be avoided. However, if the probe speed is locked with this 1/3 speed modifier it seems like this feature of the new universal piezo is pretty useless. They even mention that this feature is compatible with Duet hardware in the documentation.


  • administrators

    Have you tried increasing the trigger threshold in the G31 command? The slowdown only occurs when the output is close to the threshold.



  • @dc42 I've tried that but it then moves the threshold above what the probe actually generates. Then it doesn't trigger at all and crashes the bed.
    The analogue piezo probe has no concept of how far away from the bed it is unlike a traditional analogue sensor. I hope it can be catered for at some point but I realise on the scale of current developments it will be low priority.


  • administrators

    @tekkydave, it's likely that in a future version of RRF3 I will remove the automatic slowdown and replace it with 2 configurable feedrates in the M558 command: a fast feedrate for initial probing, and a slower feedrate for the second and subsequent probes, for those types of sensor that benefit from slow probing.



  • @dc42 That would be a good solution. Cheers 🙂


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