IR sensor has suddenly changed

Discussion in 'Calibration, Help, and Troubleshooting' started by Turtle, Nov 13, 2016.

  1. Turtle

    Turtle Member

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    My IR sensor is giving me issues with sensing height.

    One day this week it jumped from being set at -1.7mm~ to now -3.8mm without anything mechanically changing.

    I've reset the sensor height in case something had been hit but it's still sensing at a much greater distance.

    It's also wildly inconsistant at that distance, although its always been a little janky it's never been all over the place like it is now.

    For instance below are five "m48 p20" commands, as you can see I can't rely on it at all. I used to run a G28 and G29 before each print and get fairly consistant results but with the sensor way off the bed leveling just does incredibly stupid corrections so my first layers are unusable. At this point I'm at a loss, I don't know if it's just failed (but it always triggers) or I am missing something. Any help would be greatly appreciated as my printer is unusable at the moment and I've been using with great results for months up until this week.

    Recv: Mean: 3.809000
    Recv: Standard Deviation: 0.147839

    Recv: Mean: 3.786500
    Recv: Standard Deviation: 0.137077

    Recv: Mean: 3.559250
    Recv: Standard Deviation: 0.077991

    Recv: Mean: 3.572500
    Recv: Standard Deviation: 0.096573

    Recv: Mean: 3.581750
    Recv: Standard Deviation: 0.106900
     
  2. Jasons_BigBox

    Jasons_BigBox Well-Known Member

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    Check how level the sensor is too. People have reported issues if it's not square to the bed.

    I found sunlight also confuses it and fitted a 'shade'. Surface on the bed seems to make a difference. I like to keep a small amount of UHU in that region and try to avoid cleaning it off.

    To be honest the most reliable thing I've done is to use Mesh Bed Levelling. That sorts the bed relative to the home position. That means you only really have to sort out the reading at one point.


    Good luck!!

    Jason
     
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  3. biline

    biline Active Member

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    I had this happen to me twice!
    The little black and clear parts that detect the IR level were bent slightly when they snagged on a stray part.
    I had to re-position all three to look at the print-bed better.
    Note the picture below is a little obscured (it was the one I had) I'm sure you get the idea.
    You will still need to re-home and adjust your z-start height but it should be fine until the next time those little buggers move on you!

    T IMG_3881.JPG
     
  4. dc42

    dc42 Well-Known Member

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    If it's triggering at a high value such as 3.8mm then I can think of a couple of possible explanations:

    1. The IR LEDs or the phototransistor have been bent out of position. This can happen if the sensor collides with the print. See the previous post.

    2. If you have strong direct sunlight reflecting off the bed into the sensor then it will saturate. The LED will blink rapidly if this happens, in order to alert you. This can be more of a problem in winter when the sun is low.

    Later versions of the IR sensor use SMD optical components so as to be more robust, and they also have a higher dynamic range.
     

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