Material detecting sensor(s) system.

[JJoll]

Hi,
I am working on a project where i need to detect and differentiate between different
types of containers. I am trying to build a system that sorts out different materials types.
To be specefic, I need to sort out glass, metal, plastic and paper. So I need a sensor system that
detects material types. Is this possible? if yes, how can I achieve this?
Some people have told me that this is not possible and I need complex
sensors and spectrometers for this. But I have also heard this might be done
using array of sensors. 1 inductive sensor to detect metal and 1 capacitive sensor to detect non metals and metals and so on.
Any ideas how to implement such a system? how capacitive sensors work? do they output different voltage when they are exposed to certain materials?

I would be grateful if you point me to the right direction.

thanks

 

[Martaine2005]

Hi jjoll, have a look at this video.. It is quite informative.

It will give you an idea how it's done 'large scale'.
Then work out which way you want to begin your project.
Martin.

 

[Gryd3]

Hi,
I am working on a project where i need to detect and differentiate between different
types of containers. I am trying to build a system that sorts out different materials types.
To be specefic, I need to sort out glass, metal, plastic and paper. So I need a sensor system that
detects material types. Is this possible? if yes, how can I achieve this?
Some people have told me that this is not possible and I need complex
sensors and spectrometers for this. But I have also heard this might be done
using array of sensors. 1 inductive sensor to detect metal and 1 capacitive sensor to detect non metals and metals and so on.
Any ideas how to implement such a system? how capacitive sensors work? do they output different voltage when they are exposed to certain materials?

I would be grateful if you point me to the right direction.

thanks

Martaine posted a good starting point.
Here's a bit of a problem though. Think about the types of sensors and the properties of the objects.
Plastic and Paper for example share a lot of traits... both can be opaque or transparent, colours vary, density varies, both can be glossy or matte... So optics is out of the question. Weight was never going to be an option, induction can be used to a limited degree depending on the sensitivity. Using audio to detect material characteristics from an impact is also out of the question unless you control the size and shape of each object.
I think you have to do it the old fashioned way... or invest in some higher end sensors.

 

[Martaine2005]

I think you have to do it the old fashioned way.

Yellow washing up gloves flashed in my mind..

 

[Martaine2005]

Hey jjoll, would I be right in thinking this could be homework?

 

[Arouse1973]

Well metals are easy. Eddy current detection (Metal detector) Plastics are a bit more tricky and as mentioned would require some special sensors. One of the main types of sensors used are NIR (Near field Infrared). All material absorb different amounts of NIR which is dependant on the type of material. The maximum absorption is at material resonance and so a range of NIR wavelengths would be used. The amount of light coming back from the surface can indicate the type of material that is being tested. It does involve some special equipment, but it would be interesting to get a "NIR laser (WARNING! DANGER)" and do some testing.
Adam

 

[poor mystic]

Can you tell us the origin of the materials? Is there to be pre-processing; is is to be in water, or on a conveyor, or or?