when auto homing IR sensor does not see the bed

Discussion in 'Calibration, Help, and Troubleshooting' started by KNM3D, Apr 16, 2016.

  1. KNM3D

    KNM3D Well-Known Member

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    axi all home great,
    except the IR sensor does not see the bed.
    so the tips love to go all the way to the glass.
    and the IR sensor is even lower then the nozzels a hair just to make sure it wouldn't bury the nozzles into the bed,
    but obviously im having that problem. lol

    any ideas?

    thank you for any help.
     
  2. wfredette

    wfredette Well-Known Member

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    Do you see the LEDs in the sensor light up at any point as the bed approaches the nozzles?
     
  3. Spoon Unit

    Spoon Unit Well-Known Member

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    I've had this when the IR sensor was too high. It was only a fraction (after I first fitted volcanos). I put a bit of tape in the right place and the sensor saw that, which let me carry on at the time.
     
  4. KNM3D

    KNM3D Well-Known Member

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    yeah the lights are on as it approaches.
     
  5. KNM3D

    KNM3D Well-Known Member

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    anyone else view this as a solution?
     
  6. KNM3D

    KNM3D Well-Known Member

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    ok now no LEDs are NOT turning on.
    im confused.
     
    #6 KNM3D, Apr 17, 2016
    Last edited: Apr 17, 2016
  7. KNM3D

    KNM3D Well-Known Member

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    got the IR sensor to stop the z axis by putting blue painters tape down,
    but the head doesn't end up in the middle of the print bend when done auto homing.

    whats up with that?
     
    #7 KNM3D, Apr 17, 2016
    Last edited: Apr 17, 2016
  8. R Design

    R Design Well-Known Member

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    - autohome doesn't go to the middle of the bed, but a bit towards the front left corner

    - the IR reflects off the PCB and not the glass: make sure the PCB is flat against the back of the glass;

    - sometimes Marlin can take the IR sensor to a place where it is not even over glass/pcb at all: watch out for that because it will obviously crash!
     
  9. Alex9779

    Alex9779 Moderator
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    I have been thinking about this, @LiviLammister posted a related statement in another post but I am not sure about this.
    If you just have look at the specs and the actual numbers you can see that this cannot be:
    "The trigger height is checked before shipment to be between 2.5 and 3.5mm, measured between the bottom edge of the board and a target of 3mm glass on top of a dark surface." (taken from here)
    We set the distance to the surface of the glass with the GT2 belt which has roughly 1.5mm.
    So 2.5 - 1.5 = 1 and 3.5 - 1.5 = 2. The glass is ~3.8mm thick...

    I am not saying the PCB has no influence on this as it seems to matter what color is under the glass but I think the distance is measure to the top of the glass...
     
  10. Springfield-Jack

    Springfield-Jack Well-Known Member

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    The LEDs can be knocked out of alignment and then bounces more off the underside of the glass.They can be gently tweaked as shown in the link in Alex9779's post.
     
  11. Alex9779

    Alex9779 Moderator
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    Ya but it says just "a little" no actual number. So what is "a little" concerning the small numbers we are already having?
    And I think all that discussion is not helping to solve @KNM3D problem...

    Did you check the polarity of the connector? What does the IR LEDs do when you power up your machine?
     
  12. Old_Tafr

    Old_Tafr Well-Known Member

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    If all fails try resetting the Rumba to "factory settings" (Actually called "Restore failsafe" in the menu) and re-do the commissioning or at least part of it. Also take care with the commissioning instructions as the home settings for the "Pro & Lite" and the "Dual" are different and it is easy to mix up the two when scrolling down through the instructions.

    Pro and Lite

    After homing has completed the Printhead will stop in the middle of the build space.

    Dual

    Using the knob navigate to the Prepare menu.
    Rotate the knob to select Auto home.
    Check the printer is clear of potential hazards.

    Push the knob.

    The head(s) should move to (roughly) the origin i.e. X= 0.0 and Y = 0.0 and the bed should move up with the nozzles a short distance from the glass plate and then stop.
     
  13. R Design

    R Design Well-Known Member

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  14. Alex9779

    Alex9779 Moderator
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    That is the post I was talking about and which I linked some posts before...
     
  15. Alex9779

    Alex9779 Moderator
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    Oh here it is, right at the top in the description:
    "Unlike capacitive and inductive sensors, the sensor measures the height to the top surface of a glass bed, not the distance to a backing plate."
    :D
     
  16. R Design

    R Design Well-Known Member

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    ha @Alex9779 ! you are very right.

    I was confused about this because had been reliably told reliability improved if you painted the BACK of the glass. And I leapt to conclude that was to give something for the IR to bounce off.

    Now I see that that was to prevent INTERFERENCE from some secondary reflections coming from the back of the glass confusing the interpretation of the signal from the top surface.

    I think @LiviLammister 's latest theory is that the white lines on the black PCB can set up secondary reflections that distract the sensor.

    I'm now going to try putting some little squares of black paper in the sensor areas to see if that improves levelling!
     
  17. Springfield-Jack

    Springfield-Jack Well-Known Member

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    I had the problem that anything I tried (including mirrors) would trigger the sensor but the pcb and glass wouldn't, at the suggestion of the designer I placed black paper under the glass.This worked until a print failure jammed under the sensor.I gently twisted(the adjustment was very small) the led with long-nosed pliers as described in the post and the sensor now works as it did originaly without the black paper. I believe this is the solution to the original problem of the sensor not seeing the bed.
     
  18. Alex9779

    Alex9779 Moderator
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    Ya that's what I think too and what I read from the post of the creator.
    You actually measure the top but If you have a very reflective surface under the glass then the sensor has problems. So you should have an IR unreflective surface under the glass.
    @LiviLammister also told she has problem with the black build tack but the author says it works, maybe depending on environment conditions it may work but a black mate surface is maybe absorbing too much IR...
     
  19. KNM3D

    KNM3D Well-Known Member

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    got it thank you.
     
  20. Rajasundar

    Rajasundar Member

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    What is the strategy for ABL on the BB Pro when using the blue masking tape or adhesive tapes. For me the IR sensor detects the surface too early(triggers z limit) when using the masking tape making it impossible to have the nozzle touch the bed. Any advice please ?
     

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