IR sensor and glass or different reflectivity

Discussion in 'Calibration, Help, and Troubleshooting' started by Brian Dowling, May 16, 2016.

  1. Brian Dowling

    Brian Dowling Active Member

    Joined:
    Sep 4, 2015
    Messages:
    26
    Likes Received:
    3
    I'm just curious what others have seen with regards to what the IR sensor is actually measuring. I know there was some talk about it reflecting off the heated bed, not the top of the glass, feels like somewhere in between.

    Doing some experiments with mbl I was putting a block under the ir to keep nozzles way off the bed. Doing this, I noticed that Z0 was not touching my block, as it would with the regular bed.

    I also tried with some opaque paper.

    In the end, opaque materials and seeming color/reflectivity matters as well, most were detecting 1.5-2mm before the glass normally does. Glossy opaque can be even further. I also tried a piece of smoked glass I had, 0.6mm further.

    Given the glass is about 3.7mm. Seems inconclusive. So just curious if anyone else looked.

    In the end I'm trying to think how precise this can be for automatic leveling...

    Also been wondering why we don't just borrow from the cnc world and use electrical contact of the nozzle to a control block of known thickness for true precision. ;)
     
    mike01hu likes this.
  2. R Design

    R Design Well-Known Member

    Joined:
    Oct 7, 2015
    Messages:
    918
    Likes Received:
    183
    Interesting experiment.

    It is supposed to be super precise ( 3 micron), the known source of interference being secondary reflections coming from BEHIND the glass, such as might occur if you have an aluminium print bed underneath.

    You're free to implement another solution if you like but the IR should work well.

    btw. if you're still using 4 point automatic bed levelling (which is highly dependent on the IR sensor) then setting up 9-point mesh bed levelling is highly recommended for other reasons (it compensates for any curvature the system) and renders Z sensing a much less exciting topic!

    The key point about the sensor is Repeatablity, and if it always gives the same results on the glass then that would be OK. However your experiments would leave me concerned about the impact of a patch of glue!
     
  3. Rob Heinzonly

    Rob Heinzonly Well-Known Member

    Joined:
    Sep 20, 2015
    Messages:
    362
    Likes Received:
    125
    There is a informative article about this here.
    I quote:
    "Glass (with or without coatings such as hairspray, PVA or Kapton tape): works as-is if placed directly on a PCB bed heater or other surface that does not reflect strongly. If there is an aluminium heat spreader or bed plate underneath the glass, then either paint the aluminium surface matt black (see below), or put a sheet of matt black paper between the glass and the aluminium."
     
  4. Brian Dowling

    Brian Dowling Active Member

    Joined:
    Sep 4, 2015
    Messages:
    26
    Likes Received:
    3
    @R Design I'm interested in seeing the IR be used automatic MBL as a possibility, as I like a machine that can keep itself in check. I want to enable my sons to print whenever they want with less fuss, etc.

    Thanks for the article link Rob, I had read that. I think it left me with questions on accuracy, although repeat-ability here is the key.

    I'll be pulling out the dial indicator and doing some more tests in the near future..
     
  5. R Design

    R Design Well-Known Member

    Joined:
    Oct 7, 2015
    Messages:
    918
    Likes Received:
    183
    Yes you may have noticed (talked about in this forum) there's a guy who says he'll program MBL / IR.

    If you're really keen head over to his page and tell him you're a fan of the idea!

    (I did! )
     

Share This Page