which sensor should i use?

Thread Starter

a1604

Joined Apr 9, 2014
4
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.
 

Thread Starter

a1604

Joined Apr 9, 2014
4
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
 

tshuck

Joined Oct 18, 2012
3,535
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.
 

wayneh

Joined Sep 9, 2010
16,114
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.
 

MaxHeadRoom

Joined Jul 18, 2013
19,162
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.
 

Alec_t

Joined Sep 17, 2013
10,432
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?
 

mcgyvr

Joined Oct 15, 2009
5,394
How will a disembodied human eye detect coins? Perhaps one from one of the Pirates of the Caribbean?
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
 

Thread Starter

a1604

Joined Apr 9, 2014
4
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.
 

MaxHeadRoom

Joined Jul 18, 2013
19,162
Conveyor is belt type about 6 inches wide
Passing one at a time is possible
Speed of conveyor motor is in range 30-40 rpm. It is not to be stopped anywhere.
Did you explore the prox sensor under the belt?
RPM means nothing, it is the IPM travel that would be more meaningful.
Max.
 

Thread Starter

a1604

Joined Apr 9, 2014
4
Did you explore the prox sensor under the belt?
RPM means nothing, it is the IPM travel that would be more meaningful.
Max.
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.
 

strantor

Joined Oct 3, 2010
5,158
Hello A1604

Take a look at this link.
http://www.best-microcontroller-projects.com/coin-detector-and-counter.html
is probable that something might be useful.
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.
 

tshuck

Joined Oct 18, 2012
3,535
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.
 

alfacliff

Joined Dec 13, 2013
2,458
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?
 

wayneh

Joined Sep 9, 2010
16,114
There are other things too apart from coins but they have sufficient thickness so not a problem.
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.
 

DC_Kid

Joined Feb 25, 2008
794
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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