I'm in the making of constructing a conveyor belt for transporting wood logs into cutting/processing machinery (no commercial purpose). In order to not get any nails or other harmful metal objects into the cutting machinery(and avoid expensive repairs), my thought is to have some sort of tunnel (about 1 meter in diameter) for the log to pass through before and detect any metal objects lodged in the wood. Further on, it would be nice if this could be controlled/monitored by an Arduino Uno, since this is the board that I have to control other stuff already.
What I need is your help with to get some ideas on how to approach this kind of project, so not to start at the wrong end. I'm not asking for complete codes or blueprints, just help and guidance to get started since my electronics knowledge is at an amateur level to be honest.
My idea so far is to make something like a big a** coil like those on a regular metal detector. Though my knowledge about and experience with coils and magnetic fields is almost next to null, so I'm not sure about what implications that come to play when constructing such a large coil. But since there are metal detecting "tunnels" at every airport there are some solution to all this too.
Another concern is that the conveyor belt is made solely by metal, so how would such a metal detecting device be shielded not to detect surrounding metal objects? Also, is it possible at an amateur level to have such an accuracy so it can detect objects as small as an 2" long nail?
Or is a coil simply not a good approach at all?
Many questions and thoughts, hope you can make sense of it!
hello i think you are going to be able to pull it off, even without much experience.
however i am not sure if you should let the log go through a coil, or rather should send it through a field of it, like metal detectors detect metals under the floor.
anyhow, i think you might get some form of inspiration of the following, it is pretty nice explained and illustrated.
One word of warning. If you have a large, strong magnetic field you must clearly display this information so that those of us with pacemakers or defibrillators can keep a safe distance away.
Hi, I don't think lots of power is required, a transmitting coil above the belt and a receiving coil below the belt.
Google this subject would be Boggling with responses.
@nickn4: my thought was that the field inside the coil would be disturbed by the metal if ot went through it all, but i see now from your link that the receiver coil could be a problem to place with that kind of design?
@henry_best: thank you, thats exactly the kind of thing i would not have thought of, with regards to my comment about implications earlier...
@fulliautomatix: i have, sure. but i had no idea where to get one for starters, and my thought where that it would be kind of expensive to buy one, expecially if i screwed it up but the simple idea with the buzzer circuit was not bad at all... i shall look around!
@tomgeorge: it sure did boggle!(especially with some well thought of search words)
i'm looking around as we speak and already have found a couple of sites that look promising, and also provide some simple enough schematics for inspiration.
But i'm still thankful for every idea or thought about this kind of project, as not all knowledge and ideas has yet been put up on the web, but instead come through in forums like this. at least in my experience.
You could just set up an oscillator with a large coil as the inductor in it and see how the frequency changes with different things passing through. It is roughly how metal detectors work but you would get a change with anything passing through but a different one for metal or wood.
Another concern is that the conveyor belt is made solely by metal, so how would such a metal detecting device be shielded not to detect surrounding metal objects?
That makes the whole project a non goer if the metal is in any way magnetic, that rules out any steel or iron, nickel, or cobalt. Although certain grades of stainless steel are non magnetic.
I used to design such systems in the 60s. The fields you are using are so very small that they will not affect pacemakers.
You need three coils, one excitation, and two pickup. Each coil should have one turn only. The excitation can be driven with 12v at 40KHz, and the two pick up coils are manipulated so that there is a balance and the two signals cancel to as greater extent as you can manage. Then a metal object causes a miss balance and thus an output signal. Feed the coils into an instrumental differential amplifier.
However you WILL need a non magnetic conveyor and you will only pick up magnetic metals.
but the simple idea with the buzzer circuit was not bad at all... i shall look around!