Metal & Non-Metal Sorting

Hey everyone,

I'm currently working on a school project that sorts different nuts. We're limited in our use of purchasable sensors, so i was wondering if this approach of sorting metal and non metal nuts is feasible:

Essentially, the nuts would all pass through a point which has metal contacts on either end. When there is a metal nut the circuit would complete and a pin on the Arduino would read out a HIGH, conversely when its a non-metal (a Nylon nut) no current would be passed and it would read a LOW.

Does this seem feasible?
Do you see any possible problems with this method?

Thanks in advance for any replies.

What about an absence of nut?

If the nuts are steel, you could use a magnet.

Nylon nuts will be much lighter than metal ones. Run them over a very sensitive switch ( eg a microswitch with a long lever ) to detect. Or just a light spring which deflects enough with metal ones to move that nut to a different path .

Nylon is translucent, and would pass/ scatter a small amount of light - metal ones aren't. A photocell?

I'd doubt the reliability of transient contacts - but worth a try with very springy ones

regards

Allan

AWOL:
What about an absence of nut?

Wow, good point. I guess since i'm only trying to sort metals and non-metals i could 'default' to a LOW at all times, only reading a HIGH when the circuit is tripped and completed.

allanhurst:
If the nuts are steel, you could use a magnet.

Nylon nuts will be much lighter than metal ones. Run them over a very sensitive switch ( eg a microswitch with a long lever ) to detect. Or just a light spring which deflects enough with metal ones to move that nut to a different path .

Nylon is translucent, and would pass/ scatter a small amount of light - metal ones aren't. A photocell?

I'd doubt the reliability of transient contacts - but worth a try with very springy ones

regards

Allan

The nuts are steel, brass, and nylon - we're using a hall effect to sort the brass from the steel. Just wondering if the method i proposed could be done with the Arduino

If you pass the nuts, flat, down a path with a narrow light emitter on top and a photocell underneath , you'd see dark, light ( the hole) dark for a metal nut, and dark/dim/light/dim/dark for a nylon one.

The arduino using an analog input and a suitable photodetector could certainly do this.

regards

Allan

edit : a small cheap laser module would be a good light source. And any 'dims' means a nylon part.

Actually this would work for any nut orientation.

The conductive (resistive) method requires good and reliable contact with the nuts, and may fail with greasy/oiled nuts (rust protection) or oxidized surface (copper).

Another solution is a capacitive sensor. A capacitive sensor does not require proper contact, and reacts well on conductive material (metal).

A light barrier can detect the presence of an object.

Throw them in the air and see which ones come down first.

Seriously, run them down a little ramp and set up two buckets underneath.

I think your first idea has most promise.

I'd try setting up a little "slide", with many wires running parallel to the direction the nuts will side down it. As close as possible... without touching. Actually, as I type I can think of a better answer, but that will do for now.

"Number" the wires, left to right.

CONNECT the "odd" number wires.

CONNECT (separately) the even number wires.

Put a voltage across the two sets of wires... I bet if you got angles, dimensions, etc, right, there would be enough partial short circuits as a metal nut slid down the slide to detect it.

===
Construction of the slide: Instead of wires, proceed as follows...

Take a bunch of strips of metal. Say 20cm long, 8cm wide. And a similar number of strips of cardboard, same length, about 3 mm less wide. Make a super sandwich: metal/cardboard/metal/ cardboard....

Turn so long axis is horizontal, width of strips pointing "up".

Tap, to get all the upper edges of metal strips in line, with the cardboard strips not quite as high. (There are easier, better ways to reach the desired result, but this will do to describe it.)

Clamp together. Again... connect "odd" strips. Connect "even" strips. Make circuit.

Suppose the nuts are of various different sizes?

Allan