BL Touch Failsafe?



  • Hey guys,

    I'm using a BL touch with my duet wifi with FW 1.21.

    Sometimes, my BL touch will stick just a bit preventing the pin from coming out and the BL touch will start flashing. The problem is the Duet board doesn't seem to have any knowledge of this and continues driving the Z axis down until it crashes into the bed.

    Is there a setting/parameter I need to set to avoid this?



  • You could try taking the pin out and cleaning it with some 99% isopropyl and fine grit sand paper.

    Also the behaviour of the BLTouch has been improved a bit in later firmware. You could try the newly released 2.01.

    Are you using probe type P5 or P9 which was dedicated for the BLTouch?



  • @phaedrux said in BL Touch Failsafe?:

    You could try taking the pin out and cleaning it with some 99% isopropyl and fine grit sand paper.

    Also the behaviour of the BLTouch has been improved a bit in later firmware. You could try the newly released 2.01.

    Are you using probe type P5 or P9 which was dedicated for the BLTouch?

    I am using P9 in my config.g

    I know I could take apart my BL touch, but really my concern is shouldn't the duet have the ability to sense the BL Touch's alarm condition (Flashing LED) and abort movement?

    I could update to 2.01, but I'm hoping an admin can tell me if this is expected behavior.



  • The flashing alarm LED is only internal to the BLTouch - this signal is not available for the controller.
    Therefore the Duet can only send the control signals, but not read any status from the BLTouch.



  • @resam said in BL Touch Failsafe?:

    The flashing alarm LED is only internal to the BLTouch - this signal is not available for the controller.
    Therefore the Duet can only send the control signals, but not read any status from the BLTouch.

    Ok, well, that's not ideal ๐Ÿ™‚

    Is there no way to prevent the nozzle from crashing into the bed without me standing there finger poised over the emergency stop button?



  • @tsitalon1 yes, use a functioning probe.


  • administrators

    It seems logical that the BLTouch should send the "triggered" signal when it is in an error state.



  • Could you do something with stall detection? Wouldnt prevent the crash but at least it would be less damaging.



  • I always drop the motor currents as the first line of any homing files (because homing moves to be be slow so one can get away with it), then put the current back up at the end of homing. Any switch or probe on any axis could fail so this will help to limit any potential damage in such an eventuality.



  • Revisiting this topic.

    I've recently replaced my bltouch with the new unit with a plastic tip, I can not seem to get consistent behavior. I no longer get the failure which flashes the LED, but sometimes it does quite work correctly.

    My last print attempt, it Z-homed just fine, but during the leveling procedure, the pin stayed deployed as it tried to move the carriage in the x-axis and bent the plastic pin 90ยบ.

    So after 2 BL touches, I'm starting to get a bit frustrated, so I'll ask again, is there any way to implement a failsafe?

    Like maybe a endstop switch in conjunction with the BL touch, in case it moves to close to the bed?

    I'm not 100% committed to using a BLtouch, but I prefer to print on glass so I believe my options are limited right?



  • @tsitalon1 I have personally used 5 genuine BLTouches without a single defective unit. Do you have the genuine thing, or the knockoff? I'm sure you can get the BLTouch to work without faults on your printer.

    I have only gotten the blinking red light (error condition) in two situations: 1) If I messed with the probe (like I pulled the pin down and held it down, or pushed the pin up and held it up when the sensor was expecting the opposite condition. 2) If I turned the printer on with the nozzle touching the bed. In this orientation, The probe tries to run through its startup routine, but it can't fully extend and this triggers the error condition.

    Therefore, it is important to lift the Z axis by hand when first turning the machine on. Also, put the following line at the top of your homeall.g: M280 P0 S160 (Note, if you are not using the DUEX expansion board, you will need to append an I1 to invert the pin: M280 P3 S160 I1) This code releases the error and resets the BLTouch.

    The power of Macros is such that you should be able to come up with a sequence of events that makes sure the BLTouch is retracted and not popping an error before any printing or homing is done. These are the G-code commands for the BLTouch:

    M280 P0 S260 ;reset
    M280 P0 S120 ;self test (Note, this runs when the BLTouch is first powered on)
    M280 P0 S90 ;retract probe
    M280 P0 S10 ;extend probe


 

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