which sensor should i use?

Discussion in 'The Projects Forum' started by a1604, Apr 9, 2014.

  1. a1604

    Thread Starter New Member

    Apr 9, 2014
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    I have to detect coins as they pass by on a conveyor. Which type of sensor will give me best results??
    I tried IR but it doesn't work for thin objects.
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    How do you define 'best'?
    Does the sensor have to be a non-contact type?
    What are the coins made of?
     
  3. a1604

    Thread Starter New Member

    Apr 9, 2014
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    yes non contact preferably. I was thinking limit switches but I'm not sure if they pass through exact same position because feeding isn't controlled.
    Coins are metallic both ferrous and non-ferrous
    best = accurate
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    You have given much too little information for anyone to even suggest a decent answer.

    Are there different type of coins? Are they all the same size? Are they guaranteed to go by in a single file? Are they guaranteed to not touch? What speed are they going by?

    There is no "best" solution in engineering. There are ones that meets the requirements and those that another engineer suggests to accomplish the task on time while you're off finding the "best" solution.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    To add another question: Are there things other than coins going by, or are you only trying to detect an object, and you know it's a coin?

    Obviously, detecting coins - the signal - mixed in with counterfeits - the noise - is a whole different challenge.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    A human eye?
     
  7. joeyd999

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    Jun 6, 2011
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    How will a disembodied human eye detect coins? Perhaps one from one of the Pirates of the Caribbean?
     
  8. ScottWang

    Moderator

    Aug 23, 2012
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    Using some stuff to narrowing the IR transmitter light to the IR receiver.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is it a belt conveyor? Is it possible to place a non-ferrous metal detector on the underside, or if coins are single items, can a N.F. prox be placed above?
    A load cell when they come off the end?
    Max.
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Do you have to distinguish between different types/values/sizes of coins?
    Can you modify the coin conveying so that one-at-a-time pass the sensor?
     
  11. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I never said "disembodied"..
    As the question was presented a "human eye" would be the best sensor to detect coins going by on a conveyor..
    No details were provided that would rule out human interaction at all in this system..

    Best sensor to detect ferrous and non-ferrous coins on conveyor via non-contact methods.. No mention of what happens after these coins are detected or anything..

    My output is at the same level as the input..foolish :D
     
  12. a1604

    Thread Starter New Member

    Apr 9, 2014
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    Sorry if my ques wasn't clear
    Some more info -
    coins are of different sizes from about 10-30 mm dia
    Conveyor is belt type about 6 inches wide
    Passing one at a time is possible
    There are other things too apart from coins but they have sufficient thickness so not a problem.
    Speed of conveyor motor is in range 30-40 rpm. It is not to be stopped anywhere.
     
  13. MrCarlos

    Active Member

    Jan 2, 2010
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  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Did you explore the prox sensor under the belt?
    RPM means nothing, it is the IPM travel that would be more meaningful.
    Max.
     
  15. a1604

    Thread Starter New Member

    Apr 9, 2014
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    How do I place a sensor under the belt? The belt is made of PVC plus there's no guarantee the coins will pass through the same point.
     
  16. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Yes something like this is what I see having the best chance of success. Too many variables with coins laying flat on a conveyor 6" wide: coins could be stacked on top of each other, things other than coins could be present, etc. To really be accurate with the coins flat on 6" conveyor, you would need a vision sensor, so it would probably be cheaper to pick up a human from the unemployment office or the homeless shelter, as long as they don't walk off with the coins.
     
  17. tshuck

    Well-Known Member

    Oct 18, 2012
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    Now that some more details have been garnished, I lean toward an automated computer vision setup.

    OpenCV is a widespread computer vision library that is up to the task. You would need to train it to know what to recognize and count/analyze/discriminate against, which, when done properly, would probably give you better results that many other options.
     
  18. alfacliff

    Well-Known Member

    Dec 13, 2013
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    coin operated vending machines and games use a farly sophisticated coin mechanism to determine size, whether the edge is milled (the little lines), conductivity, magnetic charistics, thickness and such, woldnt one of those be ok to use?
     
  19. wayneh

    Expert

    Sep 9, 2010
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    Cool. Use a slot to separate those out and run everything else through a commercially available coin sorter (something using the technologies just given by alfacliff). No need to reinvent a wheel.
     
  20. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    i can perhaps lend my 2cents.

    many ways, but probably just a handful of methods that will meet the requirements. from what i read:

    1) an optical camera with correct software, unfortunately this does not detect if the coin is real or not
    2) some sort of Rf and you detect a "coin" by the return signature as the Rf bounces off the object.
    3) backscatter technology, similar to #2 but this usually involves "dangerous" Rf

    does the belt have coins only? can a coin fall on top of another coin on the belt? can the coins be collected and dropped into a coin machine like alfacliff mentioned?
     
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