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Screw Detection

  1. Jun 5, 2013 #1
    A mechanical design question, just wanted to pick your brains about a project I'm working on.

    I have a fixture that houses a magnet, when an operator loads a part with a screw the magnet jumps and a thru beam on the magnet detects that a screw is present. Without a screw (below) the magnet stays home and the process fails.

    3MEblNp.png


    I have a new part, the screw location is 15mm from the current screw location. My magnet will only accommodate 10mm range so I need to come up with something else. One idea I had was to slot my fixture, install reflective tape, and place a retro reflective sensor near the back of the fixture; if a screw is absent the sensor will detect light.

    My concern with this design is an operator could potentially block the sensor and get a false pass. I'm running out of ideas, what are your thoughts?
     
  2. jcsd
  3. Jun 5, 2013 #2

    berkeman

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    Staff: Mentor

    I'm not tracking your explanation very well. Do you mean that currently when the part with the screw is brought down from above the magnet, the magnet lifts up to contact the screw, and you have some optical detector that can tell when the magnet is lifted up? What is the hole-looking thing in the upper 1/3 of the magnet? Where is the current screw location on the magnet when it makes contact? Where is the new screw location?

    Can you just use inductive sensors to detect the presence of the screw? You could have two inductive sensors, one for each screw position...
     
  4. Jun 5, 2013 #3
    Hi berkeman,

    Sorry for the poor explanation, I put together a real CAD model of my fixture:

    GkTkNIY.png

    You are correct, the magnet sits inside the hole, lifts with a screw present, an optic sensor detects the magnets absence and tells a PLC the part is 'good'. Without a screw the magnet is not attracted enough to lift.

    I'd thought about inductive sensors but the problem is, the material the screw drives in to is ferrous and will give a false pass even without a screw.

    Any other ideas?
     
  5. Jun 5, 2013 #4

    berkeman

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    Can you just use mechanical sensing? When no screw is present, its hole is open, right? Can you just have spring-loaded pins that get pushed down when the screw is present?
     
  6. Jun 5, 2013 #5
  7. Jun 5, 2013 #6

    berkeman

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  8. Jun 7, 2013 #7

    Danger

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    Curse you for making me waste yet another slot in my bookmark folder.

    Fitz, why don't you just aim an optical sensor into the hole?
     
  9. Jun 9, 2013 #8

    rollingstein

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    I had the same idea. The screw will obscure a light beam.
     
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