As part of a sorting machine, I need to orient a pile of plastic brick-shaped objects (which are all identical in size - about 3cm x 2cm x 1.5cm) so that they always end up with the white side facing up:

enter image description here

These will then be fed into a bowl feeder type of machine for further re-orienting.

How can I accomplish this, preferably without optical sensors? I was thinking about cutting into the bricks and putting magnets inside, but is there a more elegant solution?

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    $\begingroup$ You say "always end up with the white side facing up" but in your drawing they have 5 white sides. Does it matter which white side is upper most? $\endgroup$ Jan 8, 2016 at 17:16
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    $\begingroup$ Side note: try inkscape. You won't regret it. $\endgroup$
    – Shahbaz
    Jan 8, 2016 at 18:13
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    $\begingroup$ I'm voting to close this question because it's an open-ended design question. Even if more clearly defined, all the answers posted here are going to be speculation; there is no "correct" answer. $\endgroup$
    – Chuck
    Jan 8, 2016 at 18:28
  • $\begingroup$ @Matt They are always going to have one of those two sides facing up $\endgroup$ Jan 10, 2016 at 17:59
  • $\begingroup$ Welcome to robotics NullUserException, but you know the drill - edit your question into a practical, answerable question and we can reopen it. $\endgroup$
    – Mark Booth
    Jan 11, 2016 at 15:34

1 Answer 1


Its a bit difficult to give you an exact answer because its quite an open question.

You are sorting the bricks based on an optical characteristics so I can't see any way of doing it other than by using an optical sensor. If you start sorting them by magnetic properties then you aren't sorting them by their colour anymore. So what is the reason you don't want to use an optical sensor?

Using one of the colour detector sensors is probably overkill if you only want black and white.

Since black and white are quite different you should be able to use a system that compared the reflectiveness, unless they are high shine. Could you fire a light beam (laser) off the bricks, would you get different amount amounts of energy absorbed and if you can detect the difference then.

Temperature could be another option, the black side should get hotter faster.

  • $\begingroup$ The optical sensor would require an additional mechanism to flip the bricks, which I believe would slow down the whole thing quite a bit. Ideally I'd want something that allows the bricks to naturally orient themselves the right way. Magnets inside seem to be the best option; otherwise I'd have to deform the bricks somehow. $\endgroup$ Jan 10, 2016 at 18:06
  • $\begingroup$ Without optical sensors and without an actuator is a very different question to just without optical sensors.When you were suggesting a magnet, I was expecting you to use the magnet to sense orientation, not try to turn the brick over with it. $\endgroup$
    – Mark Booth
    Jan 11, 2016 at 14:42

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